Pulp & Paper Canada October/November 2009

October/November 2009

www.pulpandpapercanada.com

BURNING BIOMASS Wood fuel WATER TREATMENT Get the scoop on dredging

replaces fossil fuel in boiler rebuild

Process control for mechanical pulping

JOURNAL OF RECORD, PULP AND PAPER TECHNICAL ASSOCIATION OF CANADA WEBSDALE: Upgrading a lime kiln to improve thermal efficiency

The Chemistry of Paper and Water You can’t make paper without water and at Kemira, we know both. Built on our expertise in water and fiber chemistry management, we offer a complete product portfolio designed to provide value for our customers. Our solutions not only help enhance your paper processes, but also help you make better use of scarce resources like water, energy, and fibers.

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February 2009

www.pulpandpapercanada.com

OCT/NOV 2009 Vol. 110, No. 8 A Business Information Group Publication ISSN 0316-4004

FEATURES

11 13

Mechanical Pulping: Energy Savings via Process Control Mechanical pulping is so energy-intensive that BC Hydro is lending a hand to improve process control at the province’s 10 TMP mills.

BURNING BIOMASS

16

DREDGING LAGOONS

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Dredging up the dirt Expert advice on cleaning your waste water treatment lagoon.

16 B urning Biomass — Wood Fuel Replaces Fossil Fuel in Boiler

Rebuild Converting a boiler to burn more biomass and less natural gas has a twofold benefit for AbitibiBowater Thunder Bay

TECHNICAL PAPERS

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PAPTAC Abstracts A brief introduction to some of the technical papers available from the Pulp and Paper Technical Association of Canada at www.paptac.ca

20 U sing Optical Brightening Agents (OBA) for Improving the Optical Properties of HYP-Containing Paper Sheets The brightness loss due to the HYP substitution can be recovered.

By H. Zhang, Z. He, Y. Ni, H. Hu, and Y. Zhou

IN EVERY ISSUE

25 A Comparison of Options to Improve Brightness Stability of Chemical Pulp A combination of ozone and peroxide yields the best brightness.

By D. Davies, T. Dietz, and H.U. Suess

33 B leachability of Pulps Produced From Different Kraft Pulping Methods: A Laboratory Study The results show that the ITC pulp had the highest bleachability.

By P. Fatehi, R.O. Malinen, and Y. Ni

39 U pgrading a Lime Kiln Chain Section to Reduce Dust Loading and Improve Thermal Efficiency Excessive dust recycle in the kiln hindered kiln production.

By O. Websdale, B. Downing, and H. Tran

45 D etecting Aliasing Between Cross and Machine Direction

4 Editorial 6 News 38 Calendar 50 T echnology News 52 Advertiser Index 52 Classified Ads 54 Photo File

MISSION STATEMENT:

Variations by Variable Sampling Rate Aliasing effects are particularly troublesome when MD fluctuations have a strong component close to the scanning frequency of the sensor.

By S. Aslani, M.S. Davies, G.A. Dumont, and G.E. Stewart

To promote the pulp and paper industry in Canada by publishing news of the people and their innovations in research, technology, management and financing, as well as forecasts of future trends.

Authorized to publish papers of the Pulp and Paper Technical Association of Canada, which are identified by the symbol Serving the industry since 1903.

pulpandpapercanada.com

October/November 2009 PULP & PAPER CANADA

3

EDITORIAL

Are we ready to play in energy markets?

T

he pursuit of biofuels business takes pulp and paper companies into a new industry sector: energy. There they will compete with the established big oil interests, new alternative energy resources such as wind, solar and tidal, and renewable energy sources, such as corn ethanol.

An article in the September issue of Air Water Land magazine introduced a new concept to me, that of EROEI (energy returned on energy invested, pronounced e-roy).

In the energy industry, it’s a measure of the efficiency of harnessing a particular energy source, a ratio of how much energy input is required to achieve a certain output.

Quoted in “Quest for a Better Biofuel” (Sept. 2009, Air Water Land), energy analyst Peter Tertzakian notes that the EROEI of oil has been dropping steadily, to the point where it now averages about 22:1 for conventional oil in North America. Extraction and conversion from oilsands has a much less desirable EROEI of only 3:1.

In comparison, Tertzakian says the EROEI of wind is an impressive 18:1. Corn ethanol is 1:1, and biodiesel only slightly better at 2:1.

The article does not specify the EROEI of biofuel from wood, but it’s a measure that our industry will need to consider if it hopes to make inroads into selling biomass as an energy source. We need to evaluate the energy expended to harvest, transport, and convert wood to fuel or electricity. Keep in mind that the concept of EROEI is distinct from the economics of energy production.

We also need to create a distinction — in the minds of consumers, legislators, investors — between biofuels from crops such as corn, and biofuels produced from woody biomass. The economics are not the same, nor are the conversion technologies or the business model.

David Layzell, in this same Air Water Land article, says Canada will need to create an economically viable biofuels sector if it wants to strengthen its position as an energy leader. Layzell is executive director of the Institute for Sustainable Energy, Environment and Economy.

He says straw and wood have much higher energy content per hectare than grain. In addition, wood and straw can be converted into a liquid fuel or synCindy Macdonald thetic natural gas, using technologies Editor that are based on thermochemical conversion, rather than fermentation, as is news releases: media@ the case for grain ethanol. pulpandpapercanada.com Thermal and chemical processes are letters to the editor: something this industry understands. cindy@ Energy markets, not so much. On this pulpandpapercanada.com point, I agree with the cadre of biorefinery researchers who suggest that it would be wise for pulp and paper firms to partner with someone who is already a player in the energy field.

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PULP & PAPER CANADA October/November 2009

EDITORIAL Editor CINDY MACDONALD 416-510-6755 cindy@pulpandpapercanada.com Contributing Editors HEATHER LYNCH

Sustaining member, Pulp and Paper Technical Association of Canada; Member, Canadian Business Press and Audit Bureau of Circulation.

ADVISORY BOARD Richard Foucault Greg Hay Dr. Richard Kerekes Barbara van Lierop Dr. David McDonald Dennis McNinch Dr. Yonghao Ni Bryant Prosser Dr. Paul Stuart Ross Williams

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INDUSTRY NEWS Prince Rupert claims pulp mill for non-payment of taxes

PRINCE RUPERT, B.C. — The City of Prince Rupert in British Columbia is the new owner of a pulp mill on Watson Island and the majority of land on the island. The town claimed the mill after Sun Wave Forest Products failed to pay the more than $6.4 million owed in back taxes by the tax sale deadline, according to a report on Northernview.com on Sept. 29.

The pulp mill was most recently operated by Skeena Cellulose, but had been shut down by the time is was sold to Sun Wave in 2006.

“For the first time in 12 or 13 years we are in charge of our destiny with that property. Whether that is the sale of the property or leasing the property has to be determined by council,” said acting mayor Kathy Bedard.

“The ultimate [result] would be an operating mill, but I think the community gave up on that some time ago.”

According to the report on northernview.com, Sun Wave purchased the pulp mill on June 15, 2006, and was offered relief from property taxes and the taxes owed to the city provided the mill was operational by the end of 2007. However, the mill was never restarted and taxes never paid, leaving a total tax bill of $6.4 million owed to the City of Prince Rupert.

A story in the Vancouver Sun on Sept.

21 said the mill is in a state of poor repair.

John Helin, Chief Counsellor with the Lax Kw’alaams band that considers Watson Island its territory, said the site “has been essentially abandoned with many of the old pulp mill buildings either flooded, overgrown with vegetation, or infested with various kinds of wildlife.”

Boise explores potential to sequester paper mill emissions underground

WALLULA, WASH. — Battelle and Boise Inc. will conduct a feasibility study of carbon capture and storage technology that could be of interest to the pulp, paper, and paperboard industry.

This project will focus on capture technology developed by Fluor Corporation and will take place at Boise’s pulp and paper mill near Wallula, Washington.

Van Lierop joins industry Hall of Fame for work in bleaching MONTREAL — Canadian scientist Barbara van Lierop has been inducted into the Paper Industry International Hall of Fame. Van Lierop is honoured for her contributions to the industry, particularly in the area of bleaching technology.

At the time of her retirement in 2007, Barbara van Lierop was principal scientist in the chemical pulping program at the Pulp and Paper Research Institute of Canada (now FPInnovations – Paprican).

She has made significant contributions to bleaching research during her 33-year career with the research organization.

These developments at Paprican included the application of oxidative extraction in pulp bleaching and the use of oxygen, peroxide, and ozone in both TCF and ECF bleaching. She was also part of a research team that is developing technologies to improve chlorine dioxide bleaching efficiency.

Van Lierop has played an important role in the transfer of these research technologies to mills, either directly or indirectly, through her participation in committee work with both the Pulp and Paper Technical Association of Cana-

da (PAPTAC) and the Technical Association of the Pulp and Paper Industry (TAPPI).

She served as chair of PAPTAC’s Bleaching Committee from 1981-83. van Lierop She later served as PAPTAC councilor from 1994-96 and then chair from 1996-98. She received honorary life membership in 2004.

And in 2007, van Lierop was awarded the distinguished John S. Bates Memorial Gold Medal in recognition of long-term contributions to the science and technology of the paper industry. She has also been named a TAPPI fellow, an honor bestowed on less than 1% of the organization’s membership.

The Paper Industry International Hall of Fame (www.paperhall.org) is located at the Paper Discovery Center (www. paperdiscoverycenter.org), a hands-on museum of papermaking housed in a former Kimberly-Clark paper mill in Appleton, Wis.

“This study provides us an opportunity to assess the feasibility of safely and permanently storing CO2 in deep underground basalt formations for a commercial-scale operation,” said Pete McGrail, Laboratory Fellow at Pacific Northwest National Laboratory (PNNL) and chief scientist for the project.

Coupling the capture system with permanent geologic sequestration of the CO2 represents an opportunity for Boise — and the pulp and paper industry in general — to seek a potentially new revenue source from carbon credits.

Dr. Chen has invented a new chemical additive that increases the wet-web strength of paper while preserving recyclability and using less water than is typical in the paper making industry. It provides a potential solution to address the critical issue of wet-web paper breakage.

Dr. Chen studied how linear polyvinylamine derivatized with phenylboronic acid improved the instantaneous wet adhesion between cellulose surfaces.

Earlier research concluded that polyvinylamine microgels are better paper strength-enhancing polymers than linear polymer. He developed a microgel production method that makes them more uniform and demonstrates that they provide exceptionally strong adhesion.

This invention could have major implications for recycling. Much less energy would be required to recycle paper products made with boronic acid-based additives compared to products made with traditional additives.

New wet-web additive research receives NSERC Innovation Award

HAMILTON, ONT. — Wei Chen, a researcher and recent PhD graduate of the Department of Chemical Engineering at McMaster University, was awarded a $5,000 second place prize in the NSERC Innovation Challenge Awards on October 19 at a gala ceremony in Ottawa.

SAWMILL SLOWDOWN TRANSLATES TO HIGHER FIBRE COSTS…U.S. COATED PAPER INDUSTRY FILES UNFAIR TRADE CASES…FRASER PAPERS RECEIVE s s s

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PULP & PAPER CANADA October/November 2009

pulpandpapercanada.com

INDUSTRY NEWS

Domtar gets largest share of $1-billion Green Transformation allocations OTTAWA — The federal government announced the allocation of credits to pulp producers under its Pulp and Paper Green Transformation Program on Oct. 9. Twenty-four companies, representing 38 pulp and paper mills across Canada, have qualified for credits.

Eligible companies will now have access to funding under the $1-billion program to invest in capital projects that improve their environmental performance. Credits were awarded based on an allocation of $0.16/litre of black liquor produced.

To determine their eligibility for black liquor credits, companies were asked to register with the program and report on their black liquor production by September 18, 2009. At the close of this registration period, the government verified production reports prepared by companies and calculated the amount of credits to be allocated to eligible companies.

It is expected that firms will begin to receive funding for projects in late 2009 or early 2010. Eligible firms can invest their credits in any of their pulp and paper facilities across Canada.

Qualified companies must now submit project proposals for their facilities.

Each project will be subject to a federal environmental assessment. In addition,

Catalyst appeals tax decision

RICHMOND, B.C. — Catalyst Paper is continuing its court battles against four British Columbia municipalities over property tax rates. The British Columbia Supreme Court ruled in October that property taxes Catalyst has to pay are valid. The decision used Catalyst’s dispute with North Cowichan as a test case.

In mid-November, the company appealed the decision, according to the Vancouver Sun. Catalyst refused to pay its municipal taxes in the four communities in which it has mills, and filed suit against the municipalities. Several other companies have taken similar action. (See the Sept.

2009 issue of Pulp & Paper Canada at www.pulpandpapercanada.com for more details on the tax battle.)

contribution agreements will be negotiated for projects under the program.

More details about the program and

its eligibility requirements are available at http://cfs.nrcan.gc.ca/subsite/pulp-papergreen-transformation.

Green Transformation Program credits AbitibiBowater AlPac Forest Products Inc. AV Group Canfor Pulp LP Cascades Inc. Catalyst Paper Inc. Daishowa-Marubeni Inc. (including Cariboo Pulp and Paper joint-venture with West Fraser Mills) Domtar Inc. West Fraser Mills Ltd. (including Cariboo Pulp and Paper joint-venture with Daishowa-Marubeni) Fraser Papers Inc. Howe Sound Pulp & Paper Irving Pulp & Paper Kruger Inc. Meadow Lake Mercer Celgar Nanaimo Forest Products Neucel Specialty Cellulose Ltd. Northern Pulp Nova Scotia Corp.

SFK Pulp Smurfit-Stone Container Corp.

Tembec Inc. Terrace Bay Pulp Inc. Tolko Industries Ltd. Weyerhaeuser Canada Inc.

$ million $33.2 $62.9 $36.4 $122.2 $6.1 $18.0 $59.1 $143.5 $88.4 $33.1 $45.5 $33.4 $6.9 $2.6 $57.8 $26.9 $6.5 $28.1 $20.9 $29.6 $24.2 $19.2 $13.4 $32.4

CN’s wood pellet traffic growing at double-digit rates MONTREAL — CN is on track to haul more than 800,000 tons of wood pellets this year and sees more opportunities in the future for this “green” source of heating energy.

“Since 2005, we have experienced a 16% compounded annual growth in our wood pellet traffic, and we see growing potential for this business in domestic and international markets,” says James Foote, executive vice-president, sales and marketing, for the rail company.

“Wood pellets are a renewable resource, right in our backyard,” Foote adds. “Our network has direct access to wood pellet production areas and reaches key consumption markets in

eastern Canada and the northeastern U.S., as well as key export terminals on the Pacific, Atlantic and Gulf coasts.”

According to CN, global wood pellet production in 2008 was almost 11 million tons, and some analysts believe worldwide production could double by 2014. North American consumption is expected to exceed 3.3 million tons in 2010.

CN reports that Canada’s 29 wood pellet plants have a combined production capacity of approximately 2.2 million tons. Most producers are located in British Columbia, with some in Alberta and a few in Quebec. The first major Ontario producers are expected to start production in 2010.

ES FURTHER EXTENSION OF CCAA PROTECTION…STRATHCONA PAPER RECEIVES FSC CHAIN OF CUSTODY CERTIFICATION…QUEBEC INVESTS $5.8 MI s s s pulpandpapercanada.com

October/November 2009 PULP & PAPER CANADA

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INDUSTRY NEWS

Cascades unveils eco-sensitive tissue plant expansion

LACHUTE, QUE. — Cascades has unveiled a visually stunning expansion to its tissue mill in Lachute, Que. The 6800 m2 addition has an exposed wood frame, stained glass windows, and 37 skylights, and meets the LEED specification for new construction. The LEED certification recognizes buildings that are of high environmental quality and that meet stringent performance standards, notably in terms of energy, water

PAPERCLIPS

consumption, and the use of local materials.

According to Cascades, this is the first North American paper manufacturing facility to qualify for such a certification.

The expansion houses a new converting line from Fabio Perini which will increase the facility’s capacity by 50%, to 3.3 million cases of hand towels and toilet tissue per year.

Most of the materials used for construction of the new expansion come from ecologically-sound sources or are recovered materials. Three stained-glass windows and a bell from the former Saint-Julien church located in Lachute were harmoniously integrated into the building. (See Pulp and Paper Canada’s December issue for more details.)

ON THE MOVE

Catalyst Paper has appointed Brian Baarda as vice-president, finance and chief financial officer. Baarda brings 20 years of industry experience to the post, most recently as vice-president, operations responsible for recycled paper production and facilities. He began his career with Fletcher Challenge at the Mackenzie pulp mill in northern British Columbia.

The members of the Alberta Forest Products Association have selected Roger Loberg as the chairman of the AFPA’s Board of Directors. Loberg has a 35-year history in the forest industry, in manufacturing, wood handling, and wood procurement. Since 2001, he has served as timberlands manager at Weyerhaeuser’s Grande Prairie location.

Domtar Corporation has appointed Mark Ushpol senior vice-president of distribution, effective January 4, 2010.

Ushpol will be responsible for the Domtar Distribution Group, Domtar’s merchant business. He will be based in Covington, Kentucky.

Lift off! Space-faring plants provide insight about tree growth The first Canadian botanical experiment destined for the International Space Station took flight on Nov. 16. The APEX-Cambium experiment will use 24 willow saplings to help determine the role gravity plays in the formation of wood. The knowledge gained from the space-faring saplings will help improve understanding of the fundamental biological processes in trees, which the Canadian Space Agency says “is expected to benefit the lumber and pulp and paper industries in achieving more uniform and higher quality products.”

Rodney Savidge, a University of New Brunswick tree physiologist, is principal investigator for the project. He says that relatively little of forestry research focuses on the basic physiology of trees.

Canadian astronaut Bob Thirsk will tend the trees during the 30-day experiment, after which the well-travelled specimens will return to Earth. A group of saplings will be grown in similar conditions on Earth, so that the only variable between the two groups is the weight produced by gravity.

Well, that and the cachet of being Canada’s only extraterrestrial trees.

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PULP & PAPER CANADA October/November 2009

The space shuttle Atlantis with a payload of 24 trees and six astronauts lifts off from NASA’s Kennedy Space Center in Florida on Nov. 16.

Photo credit: Jim Grossman

pulpandpapercanada.com

GET YOUR ENERGY-HUNGRY SYSTEMS ON A MONEY-SAVING DIET. It goes without saying that big industrial systems can have big appetites for energy. Our job at Power Smart is to prove that the hungrier your equipment, the bigger your opportunities to save. The truth is, if your pumps, compressors, fans and other systems are gobbling up more than they truly need, you may be paying for more than just wasted power. That’s because the excess energy doesn’t just vanish—it leads to excess heat, vibration, and loads that can wear down your equipment faster, causing pricey failures.

We can help you find the savings squirreled away inside your systems.

For a limited time, we’re offering 100 percent funding for you to hire your own dedicated, on-site energy manager.

That’s 100 percent of your energy manager’s salary plus generous training allowances, for up to two years—but only if you apply by November 30, 2009.

Our Mechanical Pulping Initiative is about bringing together a whole array of experts, resources, and funding opportunities that are especially relevant to our mechanical pulping customers.

Of course, saving energy isn’t just a clever way to save money. It’s a way to protect yourself from volatility in the market. A way to get the best possible performance from your facilities. And it’s a way to stand out as a leader in our province’s bright, sustainable energy future.

Have an appetite for all that? Then go ahead and get in touch with us today.

Email us at industrial@bchydro.com for more information or visit bchydro.com/industrial

A09-552

INDUSTRY NEWS STOPS, STARTS, CHANGES

West Fraser Timber Co. Ltd. will permanently close its Eurocan integrated pulp and paper mill in Kitimat, B.C. as of January 31, 2010, putting more than 500 people out of work. The company says the 40-year-old mill, which produces linerboard and kraft paper, has historically struggled with high costs and negative returns. A contributing factor to the mill’s problems in recent years has been sawmill curtailments in the region, which have reduced the supply of lower-cost residual wood chips to Eurocan and increased the mill’s reliance on more expensive whole log chips.

“We deeply regret the impact the mill closure will have on our 535 employees, their families and the community, and we will ensure those who are affected are treated with fairness and respect,” said Hank Ketcham, West Fraser’s chairman, president and CEO. The Eurocan site operates a kraft pulp mill, chemi-mechanical pulp mill, and two paper machines.

Fraser Papers Inc. has been granted a further extension of creditor protection under the Companies’ Creditors Arrangement Act (Canada) through to December 4, 2009.

Kruger has reversed its decision to shut down all coated paper production at its Trois-Rivières mill, announcing in early October that it will keep one of the two production lines in operation.

After announcing last July that it would halt all coated

paper production on October 30, Kruger now says one production line will remain in operation as long as market conditions are favourable, therefore preserving 120 jobs. The company says it was able to implement a more efficient production method and credits efforts made by the mill’s employees to reduce production costs.

Annual coated paper production will be reduced from 130,000 tonnes to 75,000 tonnes. The other production line, as well as the debarking and groundwood pulp plants, were shut down indefinitely on October 13. Approximately 280 employees were to be laid off gradually in order to facilitate the shut down.

AbitibiBowater indefinitely idled paper machines at several Canadian and U.S. mills as part of its restructuring efforts and to adjust to falling demand for newsprint and printing papers, effective Oct. 31.

The company has shut down operations at its Beaupre, Que., mill which produces digital printing paper. The move leaves 340 workers unemployed.

AbitibiBowater also idled paper machine 4 at the Clermont, Que., mill, and cut newsprint production by half at the Bowater Mersey mill in Brooklyn, N.S. PM 4 is one of two newsprint machines at the Clermont facility. Its shutdown put 120 employees out of work.

In Fort Frances, Ont., a paper machine producing commercial printing paper was shut down, putting 75 workers out of work. The Fort Frances facility also produces NBSK pulp.

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PULP & PAPER CANADA October/November 2009

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MECHANICAL PULPING

ENERGY

SAVINGS

via process control

Mechanical pulping is so energy-intensive that BC Hydro is lending a hand to improve process control at the province’s 10 TMP mills.

B

ritish Columbia has more than 4 million residents and 24,000 businesses, but a large portion of the province’s electricity is consumed by one easily identifiable group: its 10 mechanical pulp mills. These 10 facilities consume 11% of the province’s connected load.

They use, on average, 5,500 GWh/yr.

As such, BC Hydro is in the midst of a long-term Mechanical Pulping Initiative aimed at reducing the electrical energy consumption of these mills. To address the electricity consumption of mechanical pulp mills, BC Hydro has had to delve much further into the process than simply monitoring plant-wide energy use. The utility has concluded it must help TMP mills with measurement and control of the refining process before the industry can fully capitalize on energy saving opportunities.

“One of our biggest issues right now is how to measure and verify the energy savings,” says Norm Wild, program manager, industrial programs, with BC Hydro — Power Smart.

BC Hydro’s engineers believe they can pulpandpapercanada.com

shave 20% off the energy requirements of each mill with state-of-the-art processes, equipment, and heat recovery. But they can’t do that without a reliable monitoring and quality control system in place to measure their progress and ensure consistent product quality.

Wild notes, however, that the impetus to invest in energy efficiency is not strong right now, given B.C.’s traditionally low electricity costs and the industry’s current woes. His hook line for the program is this: “We will achieve our energy savings targets by helping you build a better process.”

The utility is looking at a suite of projects which could include operational changes, chip conditioning improvements, low energy refiner plates, process simplification, and pumping and screening optimization. “We are hoping to get as much as 1,000 GWh/yr in energy savings,” says Wild.

But BC Hydro has identified a need for advanced process monitoring and control for pulp manufacturing because it needs reliable, consistent data to establish

plant KPIs and determine the refining energy vs. pulp quality profile unique to each pulp and paper grade produced at each mill.

“The most significant energy efficiency projects that we can do all affect the refining-energy-topulp-quality curve,” says Wild.

Therefore, to measure the suc success of these energy-efficiency projects, the mill must be able to monitor pulp quality and relate that to refining energy.

Craig Thomson, energy and environmental supervi supervisor at Canfor Taylor Pulp, agrees with the need for greater process control. pro“Automating the pro cess control around the elecrefiners will enable potentially huge elec trical energy savings that will benefit both BC Hydro and the mill,” he says.

One approach BC Hydro has adopted as part of its Mechanical Pulping Initiative is to promote the development of a “tool box” of new technologies that, once proven established, will help mills to monitor and control pulp quality. BC Hydro is offering to bring in its expertise, suppliers, and consultants to test these new technologies in a mill environment.

“Mills are very reluctant to spend money right now. They’re short-staffed, money is tight, there is a lot of uncertainty, and it’s difficult to engage them in new technology,” notes Wild. “We ask them if they’d like to participate in site-appropriate demonstration projects in which BC Hydro shares the financial risk and helps with the testing.”

Continuous pulp quality monitoring is promising

In the past, pulp properties were measured manually in a lab using samples drawn from the production floor — results were reported typically the next day. In recent years there’s been an introduction of automated testing, which is quicker and less labour-intensive, typically returning results in about an hour. But the target, in BC Hydro’s eyes, is inline, continuous

October/November 2009 PULP & PAPER CANADA

11

MECHANICAL PULPING and control devices,” Wild explains. mills to produce optimal pulp quality for pulp quality monitoring.

To this end, the utility has already par- “Once you’ve got the power metering and minimal input — minimal energy, miniticipated in two demonstrations of a near instrumentation in place you can deter- mal water, and minimal chemicals. real-time fibre analyzer called InovoCell. mine what the plant is physically doing.

“Mills will get a much more tightly This device uses image analysis of the However, this is only half the story — you controlled process out of this,” says Wild. pulp fibres to determine morphological need continuous pulp quality monitoring “With less variability in the pulp, mills data, and then estimates the physical and a standardized way to operate to con- can lower their quality set-points and still properties of the pulp using proprietary sistently make one pulp grade, one way. make a comparable product. Then the “With this level of process monitoring industry can move to optimize the contrisoftware.

BC Hydro’s demonstration projects and control in place we will be able to bution of each unit process in their mills consisted of taking pulp samples and establish much better energy consump- and investigate energy saving technologies such as low-energy refining plates comparing the results from the fibre tion baselines than we currently do.”

Managing electricity demand is a pri- and targeted refining by means of more analyzer with the results from an indeority for the provincial utility, so large effective fibre fractionation.” pendent lab.

For Thomson, the quality control iniForty samples were taken throughout modernization or expansion projects at the process from the secondary refiner pulp mills could be eligible for financial tiative ties in to competitiveness. “In discharge through the mainline screening assistance. The potential for energy sav- order for mechanical pulp mills in Canada and rejects refining systems and finally ings at mechanical pulp mills is so great to remain competitive, the need to conthe disc filter discharge, at two mills. that the utility “can put quite a bit of tinually improve and to reduce our depenThe participating mills were Canfor’s money towards a project and still pass all dency on electrical energy and fossil fuels Taylor mill and Catalyst Paper’s Port the financial criteria that we have to meet is paramount. There is no magic bullet; to go forward with it,” says Wild.

Alberni site. hence the sustainable approach, based on Thomson says the trial at Taylor Pulp structured continual improvement.” emphasized the need for inline monitor- Benefits will be felt And, as all manufacturers know, ing to optimize the use of the refiner in the long term measurement is the first step toward quality control system. “The demo raised BC Hydro is laying the groundwork for improvement.

PPC the awareness of all parties at the mill to push for capital to install the InovoCell analyzer for both quality BC Hydro’s tool box for Goodness of fit between standard testing and InovoCell and energy optimization. pulp mills analyzer testing: Canfor Taylor Pulp results summary “The lack of a feedback signal BC Hydro is financially supportIndex of to give timely pulp property feeding research and testing of a Physical property determination R2 back, such as that provided by portfolio of devices and equipFreeness ml 0.96 the InovoCell inline analyzer, is ment that can help mechanical Plumac 6-cut shives % 0.88 pulp mills to measure and conthe current drawback to the QC Bauer Mc.Net fractions trol the refining and screening system we have in place. There’s processes. One device that has still much room for improvement R14 % 0.90 shown promise is the InovoCell through automation in both the R14/R28 % 0.87 fibre analyzer. refining area as well as bleach plant R28/R48 % 0.92 The device measures imporoptimization,” he concludes.

R48/R200 % 0.95 tant fibre morphological characteristics inline using high-resR200 % 0.98 Utility works to help plants olution image analysis.

SophisP200 % 0.98 reduce demand ticated software uses this data It’s a tough climate right now to Bulk cm3/g 0.92 to compute some of the physiintroduce process changes, but the Burst index kPa.m2/g 0.96 cal properties of pulp, without provincial utility is doing all it can Tensile index Nm/g 0.98 the need for sheet-making and to help mechanical pulping facilitesting procedures. It has provStretch % 0.93 ties boost their energy efficiency en quite accurate in its predicTensile energy absorption J/m2 0.92 as part of its efforts to reduce the tions, when compared with lab Tear index nM.m2/g 0.98 province’s energy needs through results (See table at right). demand-side management.

“I was very impressed with The process control approach the correlation between the independent lab results and InovoCell, as well as the that BC Hydro is proposing for speed at which the samples from InovoCell were obtained,” remarks Craig Thomson, mechanical pulp “would require, energy and environmental supervisor, Canfor Taylor Pulp. as a start, metering of all the big Other equipment suppliers offer inline pulp measurement that can be linked to process-related drives in the plant, refiner control and BC Hydro is currently looking for mills to demonstrate these comadequate inline instrumentation parable technologies as well. together with flow measurement 12

PULP & PAPER CANADA October/November 2009

pulpandpapercanada.com

WATER TREATMENT

Dredging up the dirt Waste water treatment lagoons should be periodically cleared to maintain their efficiency. A good service provider will dewater on site, returning as much water as possible to the lagoon before safely disposing of the solids.

By Wayne Clark and Luc Robinson, Newalta Corporation

P

ulp and paper companies generate waste from their operations that is typically comprised of a mixture of liquid and solid materials. This sludge is pumped into onsite water treatment lagoons in order to allow for the separation of water and solids.

Such water treatment has a low initial capital cost but requires ongoing maintenance to remove and dewater the precipitated solids. Over time, solids build up and reduce the space available in lagoons and the efficiency of the water treatment operation. Therefore, lagoons require periodic maintenance to remove and dewater the solids. The dewatered

solids can then be properly disposed of and the water returned to the lagoon for reuse.

Go it alone or hire an experienced partner?

The maintenance of these lagoons requires a number of considerations, the first of which is whether a company wants to manage each step of the process on its own or outsource the work to a qualified service provider. Not only do many pulp and paper mills not have the capital and human resources to execute this maintenance internally, they often prefer not to take on the considerable risk involved.

Effective dewatering minimizes disposal

One of the most cost-effective and efficient maintenance options for pulp and paper lagoons involves dredging the lagoon to remove the sludge and then dewatering the sludge prior to disposal.

The goal through each step is to ensure optimal dewatering results to maximize the water content recovered and returned to the lagoon, and to minimize the volume of solids required for disposal.

This is where employing an experienced service provider can be invaluable, by reducing costs associated with transport and disposal of waste.

A manned dredge on the lagoon at West Fraser’s Hinton pulp mill. pulpandpapercanada.com

October/November 2009

PULP & PAPER CANADA

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WATER TREATMENT The key elements involved in a typical project are sludge analysis, dredging, dewatering, disposal.

Sludge analysis dictates best way to separate solids

To ensure optimal results, extensive analytical testing of sludge samples prior to beginning a project is key to determining the right polymer chemical mixture to separate the solids from the liquids. Also, sample testing helps determine the type and size of centrifuge required and the anticipated outcomes.

“This upfront analysis allows us to determine, with a high degree of accuracy, the amount and type of polymer required, and the concentration or dryness, quantity, and characteristic make-up of the resulting solids,” says Ron Keenan, regional manager of onsite services for Newalta in Quebec. “This means no surprises for the customer – they know ahead of time exactly how long the service provider will be on site, how the solids will be managed and how much the project will cost.”

Dredging – manned or unmanned?

In some cases lagoons can be temporarily removed from service so that water can

be pumped off and sludge exposed to the elements to dewater naturally over time.

However, most lagoons are critical to a pulp and paper mill’s operation so dredging is typically the preferred method to remove solids that build up. In this case, the lagoon stays online and the company can continue to operate without interruption.

A dredge is essentially a floating pump that transfers the in-situ sludge to onshore dewatering processing equipment. There are two types of dredges: manned and unmanned. Unmanned dredges are typically used in hazardous environments where hydrogen sulfide (H2S) or other hazards exist. While safer, unmanned dredges tend to have reduced pump capacity and therefore are less efficient.

Manned dredges are more complex, have a larger pumping capacity, and require skilled onboard operators to manage the dredging process.

“Manned or unmanned, skilled dredge operators are key to ensuring safe, efficient dredge operation with no risk to lagoon aeration systems,” says Keenan.

The sludge is removed from the lagoon or pond and chemicals are added to the sludge before the mixture is separated.

Centrifuge-based dewatering most efficient

There are a number of ways to dewater sludge, including beach drying, the use of “geo-tubes,” filter presses, and centrifugation. Centrifugation is the most costeffective and efficient method. Centrifuges use centrifugal force to separate the solids from the liquids prior to disposal.

To increase efficiency, polymer chemicals are added to the sludge prior to being centrifuged.

“Polymers work to bind the suspended particles in the sludge which facilitates and enhances the separation of solids and water,” says Mark McMillan, regional manager of onsite services for Newalta in Western Canada. “Choosing the right polymer is essential. Every lagoon or pond is different and in order to achieve the driest solids, which is what we’re after, you have to have get the mixture just right.”

Polymers are added in such low concentrations that they do not affect or change the characteristic make-up of the resulting solids after centrifugation.

Therefore, the solids require no additional processing or treatment prior to disposal to manage the addition of polymers.

This is a typical decanter centrifuge operating at a customer’s site.

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October/November 2009

pulpandpapercanada.com

WATER TREATMENT There are many different types of decanter centrifuges that can be employed to complete the task of separating liquids from solids. The size and type of decanter centrifuge must be matched to the pumping capacity of the dredge and the nature of the solids involved. Easyto-separate solids are processed through a large bowl with little retention time (the amount of time the material spends in the centrifuge), whereas hard-to-separate solids with smaller particles require bowl designs with increased retention time to optimize separation.

It is critical in the planning stages to profile the solids to ensure the appropriate centrifuge design is applied to the dewatering process with a supporting chemical program to enhance separation.

Many providers of dewatering services have only one centrifuge and employ a one-size-fits-all approach, which can result in inefficiencies. When choosing a service provider, pulp and paper companies should take into account not only the experience, depth and breadth of the operating personnel, but also the equipment being used to ensure the most effective solution possible.

Liquids and solids go their separate ways

After going through the dewatering process, the solids are transported by a series of conveyors and either stored on site or loaded directly onto sealed transportation units for shipment to an appropriate disposal facility in accordance with all regulatory requirements. The treated liquids are usually returned to the lagoon and ultimately reused in the mill’s process operations.

Projects are generally priced in one of two ways: using a per-day rate or based on the total volume of material disposed per “bone dry tonne” (BDT). BDT is the measure of how dry the solids are — the weight of the dewatered solids minus measured moisture content. Mobilization and demobilization of the process equipment are billed in addition to the BDT cost. With day-rate pricing, the customer pays a fixed amount for the equipment and manpower.

Safety considerations

In addition to finding a partner with the pulpandpapercanada.com

Another example of on site dewatering.

operational expertise and the right equipment to get the job done, the environmental, health, and safety aspects of the project are an important consideration.

“A safe, environmentally secure work site is our number one priority on every job,” says Keenan. “Our priority is to ensure the safety of our people and those around the project site, while also preserving the integrity and cleanliness of the customer’s site and eliminating any risk of soil contamination.”

Experience counts

“While the process involved in dredging and dewatering these lagoons sounds fairly straightforward, every project is unique, involving varying specifications of sludge,” says McMillan. “The importance of skilled operators of both dredges and centrifuges cannot be underestimated. This experience enables us to adapt quickly to changing circumstances throughout a project to ensure the job is

completed in a timely and cost-effective manner with as little impact as possible for the customer.”

Partnering with an experienced service provider involves additional costs, but significantly lessens risk for the pulp and paper company and allows it to focus on its primary business. Reputable waste management and environmental service companies providing lagoon processing services should have strong environment, health and safety credentials, extensive experience with these types of projects, a range of required equipment, and should be able to complete the task without affecting ongoing operations.

PPC Wayne Clark is corporate accounts manager, Western Canada, and Luc Robinson is regional accounts manager, Quebec, for Newalta Corporation. Newalta is a national industrial waste management and environmental services company with extensive experience in the pulp and paper industry.

Every project is unique: Hinton and Espanola The highly effective process Newalta employs at customer sites to service water treatment lagoons has been refined over many years.

Newalta has partnered with a number of companies in Quebec and northern Ontario on dredging and dewatering projects. In March 2009, the company completed a job with the Domtar Espanola mill in Ontario. Newalta used a large manned dredge and two large bowl decanters to remove 2,875 BDT from 35,000 cubic metres of sludge. Nearly 80% of the water was returned to the lagoon.

These results allowed the Espanola mill to reduce the environmental impact of this work by reducing the amount of transport required to dispose of the solids.

Newalta has also successfully completed several projects in western Canada, including one in July and August 2009 for West Fraser Timber’s Hinton, Alta., pulp mill. The project involved manned dredging on a lagoon containing both aerobic biological waste generated from the plant’s operations, as well as the town’s municipal effluent. West Fraser has an agreement to accept the town’s effluent into its lagoon and this additional waste needed to be properly analyzed and treated. Newalta successfully processed and removed 6,000 BDT of sludge and returned the water to West Fraser’s lagoon for reuse.

October/November 2009 PULP & PAPER CANADA

15

BIOMASS

Boiler rebuild BOOSTS biomass combustion Converting a boiler to burn more biomass and less natural gas has a two-fold benefit for AbitibiBowater Thunder Bay: lower energy costs and lower greenhouse gas emissions.

By Heather Lynch

I

production on biomass; and to introduce the capability of swinging boiler steam production while on biomass only, in order to meet the demands of the mill’s 850 lb. steam header.

t’s a simple formula: A reduction of You can get the amount of natural gas you burn plus an increase in the amount of significant biomass you burn equals a reduction in Biomass feeders increases greenhouse gas emissions (GHG). custom designed Studies undertaken by FPInnovations “The design-build team assessed the in boiler steam researchers confirm a mill can slash its capability of the boiler furnace, combusproduction, with fuel costs by $1.25-$8 million per year, tion air and induced draft fans, fuel feed depending on the size of its boiler and system and the ash system, with regards little or no capital the cost of natural gas or oil, simply by to the increased biomass firing to deterexpenditure, optimizing biomass combustion in its mine whether the performance criteria wood/natural gas fueled boiler. could be met and what would have to be by identifying This is exactly what AbitibiBowater modified to meet the performance taroperating in Thunder Bay did with a recent gets,” explains Dave Knutson, president rebuild of a power boiler. The company of Cook Engineering. Alstom Canada problems and enlisted the help of EKT General Condesigned the mechanical modifications remedying them. tractors, Alstom Power Canada, Cook to the boiler and upgrade of the air sysEngineering, and Automation Applicatem and fuel delivery, as well as the tions for the project. upgraded burner management system.

When AbitibiBowater undertook to upgrade its No. 6 Cook Engineering provided design for the new biomass delivpower boiler, three goals were set: to improve the boiler’s abil- ery system, back-end dry ash systems, and integration of the ity to burn biomass and process sludge; to increase MCR steam boiler automation work.

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PULP & PAPER CANADA October/November 2009

pulpandpapercanada.com

BIOMASS

If a mill has the potential for biomass-fired power generation and available wood fuel, these modifications would allow for increased green power generation.

Five areas were addressed by the project: boiler pressure part modifications, new bark and sludge handling equipment, new biomass fuel combustion system, advanced combustion controls including predictive header pressure, and a new burner management system.

The process involved a combination of both new and existing technologies.

“To reduce cost and provide some redundancy, the existing conveyor and in-feed system were incorporated into the new system to minimize the impact on fuel firing during the construction period,” Knutson outlined. The biomass fuel feeders were custom-designed to provide control of fuel metering, which is critical to being able to control the mill’s process steam header pressure on the biomass fuel.

The power boiler was originally built as a fixed-bottom boiler and required daily ash raking, and the biomass handling and delivery system was not constructed to provide typical steam requirements on a continuous basis. The mill’s normal operational procedure was to burn bio-fuel with natural gas as the responsive auxiliary fuel, with a bio-fuel burning capability of roughly 240,000 lb. of steam per hour.

The furnace bottom was replaced with a modern, dry mechanical conveying design, while the bio-fuel delivery system was upgraded with an apron feeder, reclaim drag chain conveyor, a vibrating taper slot screen and hog. Tapered volume fuel metering screw feeders were also installed at the boiler, allowing for final element control of fuel feed to the boiler. Bio-fuel was transferred to the distribution conveyor, which supplies three of the four bins in consecutive order, and finally discharges into the last bin. Belt weightometers were installed on the No.1 bark supply belt and on the sludge feed conveyor to determine the ratio of sludge to hog fuel in the fuel mixture feed to the boiler, and upgrades to the air system were made to ensure properly distributed air was supplied to the furnace and to the undergrate for proper combustion.

Conditioning the ash was a challenge

As Knutson notes, operational challenges are inherent to any capital improvement of this magnitude. However, several glitches particular to this project led the design team back to the drawing board on occasion.

“We needed to install piling and the foundation for the new grate underneath the boiler. This was difficult and only possible because of the style of grate originally installed,” Knutson says.

“The second issue was how to condition the dry ash. This is historically difficult to do on a consistent basis.” The project team borrowed technology from another industry to install a precise conditioning device that measured the weight of ash, added the correct proportion of water, and then mixed the material to create a consistency of damp earth. This quenched the ash and reduced dusting during handling, but required the design, fabrication, and installation of a custom metering bin. pulpandpapercanada.com

Wood fuel replaced fossil fuel

Several objectives were achieved with this project. Most notably, the mill minimized fossil fuel purchases and associated costs by displacing it with wood fuel – a material that has a much lower GHG emission rate. Upon completion of the project, the boiler was able to meet its steam demand on biomass alone. Savings from this ability, resulting from the reduction in natural gas consumption, paid for the capital costs of the project in one year. Further, in the first year of operation, CO2 emissions were reduced by close to 20%.

The bigger picture

Federal funding programs such as the Short Term Competitiveness program, and the Pulp and Paper Green Transformation Program are helping to make capital improvement projects with an environmental edge a worthwhile undertaking for many Canadian operations. As Vic Uloth, principal research engineer and leader of boiler optimization and emissions control for FPInnovations, points out, many mills could easily benefit from having their power boiler operations similarly evaluated.

“FPInnovations member company mills can get this done for free under the Short Term Competitiveness program funded by NRCan,” he says. Uloth’s estimate, based on the research institute’s experience of looking at more than 40 power boilers, is that only one third of them run well.

“You can get minor increases in the thermal efficiency and hog steaming rates but these boilers are generally operating close to their limits. Another third runs poorly due to control problems, poor hog distribution on the boiler grate, or poor combustion air distribution. You can get significant increases in boiler steam production, with little or no capital expenditure, by identifying these operating problems and remedying them.”

The final third run poorly due to design problems, Uloth confirms. “Significant capital expenditures are required to upgrade their air, hog delivery systems, or emission control systems. While the upgrade on the power boiler at the Thunder Bay mill included significant capital expenditures for rebuilding the lower furnace, the combustion air system, the hog feed system, and the ash handling system, the payback was less than one year due to the very significant increases in biomass-generated steam.”

As Knutson of Cook Engineering highlights, any mill currently firing biomass fuels conventionally (on a grate-fired unit with a combustion air system using technology from the 1970s or earlier) is likely considering an upgrade similar to that in Thunder Bay. “Many mills may have some components in place already so that each location would have to assess their needs on a case-by-case basis. If a mill has the potential for biomass-fired power generation and available wood fuel, these modifications PPC would allow for increased green power generation.”

October/November 2009 PULP & PAPER CANADA

17

PAPTAC ABSTRACTS

A Multivariate Analysis of Recovery Boiler Fouling

By P. Verseeg (University of Toronto), H. Tran (University of Toronto), V. De Leo (Domtar Industries)

Une analyse multidimensionnelle de l’encrassement des chaudières de récupération

Abstract: Operating data from two recovery boilers was analyzed using Principal Component Analysis (PCA) and Partial Least Squares Analysis (PLS). PCA allowed visual and operational comparisons between periods of high fouling and low fouling in both boilers. PLS extracted the correlation structures between variables and provided a better understanding of overall boiler operation and a focus on which variables might be adjusted to improve boiler performance. Together these two techniques can help identify the main operating variables that cause fouling in recovery boilers.

Paper presented at the 2007 International Chemical Recovery Conference in Quebec, Que., May 29 - June 1, 2007.

Keywords: RECOVERY BOILER, FOULING, PLUGGING, MULTIVARIATE ANALYSIS, BOILER OPERATION

Full manuscript available at www.paptac.ca.

(Full peer-reviewed manuscripts available at www.paptac.ca)

Electrochemical Bleaching of Kraft Pulp Employing Polyoxometalates

By M.R. Martins, J.A.F. Gamelas, D.V. Evtuguin, H.M. Carapuça (University of Aveiro, Portugal)

Blanchiment électrochimique de la pâte kraft utilisant des polyoxométallates

Abstract: The a-Keggin heteropolyanion [SiW11V VO40]5- was employed as electrochemically reversible catalyst in the delignification of eucalypt kraft pulp. Pulp was treated at 85ºC in the conventional batch reactor integrated with electrochemical cell providing the continuous catalyst regeneration. This approach allowed the highly selective pulp delignification, which was limited, however, to 45% under the applied conditions. The electrochemical pre-bleaching stage was considered to be economically feasible tool to decrease the ECF bleaching costs without deterioration of pulp strength properties.

Paper presented at the 2008 International Pulp Bleaching Conference in Quebec City, Que., June 2-5, 2008.

Keywords: ECF BLEACHING, ELECTROCHEMICAL OXIDA-

TION, EUCALYPTUS GLOBULUS, OXIDATIVE DELIGNIFICATION, POLYOXOMETALATE, KRAFT PULP.

Peracetic Acid Bleaching of Kraft Pulps: Present Status, Development and Mill Experiences

By H. Hämäläinen, V.M. Vuorenpalo, M. Nyman (Kemira Pulp&Paper, Finland), R. Anderson (Kemira Chemicals Inc., Canada)

Blanchiment de la pâte kraft avec acide peracétique: mise à jour, développement et expériences en usine

Abstract: The interest in TCF bleaching in the early 1990s sparked a renewal in the development of peracetic acid as a bleaching agent. Although the market for TCF pulp did not develop as anticipated, many mills that incorporated the use of peracetic acid to provide the flexibility for TCF pulp production have further realized the potential for benefits with ECF pulp bleaching and paper production. This paper reviews the present status of peracetic acid for treatment of kraft pulps, summarizing the latest developments and mill experience.

Paper presented at the 2008 International Pulp Bleaching Conference in Quebec City, Que., June 2-5, 2008.

Keywords: PERACETIC ACID, PULP, BLEACHING, PAPER Full manuscript available at www.paptac.ca.

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PULP & PAPER CANADA

October/November 2009

Full manuscript available at www.paptac.ca.

Winder Vibration Related to Set Throw-outs

By J. Zwart (Spectrum Technologies), W. Tarnowsky (NorskeCanada)

Vibration de la Bobineuse Reliée aux Rebuts

Abstract: Throwing a set out of a 2-drum winder has been a problem since winders became shaftless, and worsens with increasing winder speed. This paper presents a case study of solving a roll throw out problem through modeling and vibration testing. The vibration occurred predominately at set rotational frequency, with the vibration at this frequency greatly increasing when the set reached 718 mm diameter. Included in this study are the significant factors that put this winder at risk for throw outs. A computer model was developed to show how sinusoidal caliper variation in the paper imparts eccentricity into a roll while being wound. The model shows there is no roll eccentricity until the wavelength of the variation is equal to the set circumference, at which point there is a step change in eccentricity. This model explains some of the effects seen in the case study.

Paper presented at the 89th Annual Meeting in Montreal, Que., January 28-30, 2003.

Keywords: WINDER, ROLL THROW OUTS, VIBRATION,

WINDING MODEL, SHAFTLESS WINDING, ECCENTRICITY

Full manuscript available at www.paptac.ca.

pulpandpapercanada.com

PAPTAC ABSTRACTS

Paper Machine Heat Recovery Revisited – A New Era

By P. Cherry (Johnson Controls Inc.)

Récupération de la chaleur des machines à papier (révision) – une nouvelle ère

Abstract: Conventional approaches to paper machine dryer exhaust heat recovery achieve marginal efficiencies. New technology and approaches are capable of not only improving the heat recovery efficiency but the utilization percentage of this energy within the mill to achieve significant cost avoidance and higher return on investment.

Paper presented at the 92nd PAPTAC Annual Meeting in Montreal, Que., February 6-10, 2006.

Keywords: COST, DRYER, HEAT, RECOVERY, THERMAL Full manuscript available at www.paptac.ca

Use of Magnesium Hydroxide For the Bleaching Of Mechanical Pulps (Softwood and Hardwood) and Deinked PulpEfficiency and Environmental Impact

By C. Leduc, J. Martel, and C. Daneault (Université du Québec à Trois-Rivières, Centre Intégré en Pâtes et Papiers)

L’utilisation de l’hydroxyde de magnésium pour le blanchiment de la pàte méchanique et de la pàte de fibre désencrées

Abstract: In this research project, we evaluated magnesium hydroxide as a substitute for sodium hydroxide during peroxide bleaching of two commercial mechanical pulps [(TMP) and (CTMP)]. Magnesium alkali concentration was reduced during bleaching compared to the sodium alkali concentration. After bleaching of both pulps, for a similar level of brightness, carboxylic acids concentration was decreased with magnesium alkali.

Electron Spectroscopy for Chemical Analysis (ESCA) was conducted to better understand the oxidation mechanism. The use of magnesium alkali improved bleaching effluent quality by decreasing BOD5 and COD. Paper presented at the 2008 International Pulp Bleaching Conference in Quebec City, Que., June 2-5, 2008.

Keywords: MAGNESIUM HYDROXIDE, PEROXIDE, BLEACHING, MECHANICAL PULPS, ESCA, ENVIRONMENTAL PARAMETERS

Full manuscript available at www.paptac.ca

pulpandpapercanada.com

(Full peer-reviewed manuscripts available at www.paptac.ca)

Dynamic Control of Coating Consolidation

By C. Alexander, R. Machattie, D. Watson (Honeywell International)

Contrôle dynamique de la consolidation du couchage

Abstract: Uniform coating is an on-going quest for all manufacturers of coated paper products. It is a complex goal, as the coating process is affected by a large number of interrelated variables, ranging from the recipe, rheology and application solids, to base sheet porosity and the unique characteristics of the coater. One key element for end coating homogeneity is control of the coating consolidation process. The ability to control the rate of evaporation requires continuous control of both air dryers and infrared (IR) dryers, providing the papermaker with a valuable tool to significantly enhance their product quality.

This paper examines a measurement & control system that uses derived measurements of water weight change to control the coater drying elements. The calculations are based on a set of surface reflectivity measurements, distributed in the machine direction. A robust, linear relationship between the resultant measurements and effective mass & energy transport is demonstrated. Results from several trials at Dow Chemical’s North American pilot coater are presented.

Paper presented at the 89th PAPTAC Annual Meeting in Montreal, Que., January 28-30, 2003.

Keywords: COATING, CONSOLIDATION, MEASUREMENT, CONTROL, DRYING

Full manuscript available at www.paptac.ca

Numerical Prediction of Flame Length in Lime Kilns

By A. Aloqaily, D.C. S. Kuhn, P. Sullivan and H. Tran (Pulp and Paper Center, University of Toronto)

Projection numérique de la longueur de flamme dans les fours à chaux

Abstract: The variation of flame length in lime kilns was numerically investigated using the standard k-e model. The results are consistent with experimental measurements, showing that the Craya-Curtet number (Ct) and excess air are the dominant parameters affecting the flame length. The results also show that increasing Ct increases the flame length, while increasing excess air decreases it. The flame length can be controlled using Ct and excess air, which in turn can be adjusted by primary air and ID fan speed.

Paper presented at the 2007 International Chemical Recovery Conference in Quebec, Que., May 29 - June 1, 2007.

Keywords: LIME KILN, FLAME LENGTH, NUMERICAL SIMULATION, CRAYA-CURTET NUMBER, BURNER CONTROL, KILN CONTROL

Full manuscript available at www.paptac.ca October/November 2009

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T137 OPTICAL BRIGHTENING AGENTS

Using Optical Brightening Agents (OBA) for Improving the Optical Properties of HYP-Containing Paper Sheets By: H. Zhang, Z. He, Y. Ni, H. Hu, and Y. Zhou Abstract: High yield pulps (HYP) with different brightness levels were used to replace hardwood bleached kraft pulp to determine the influence of HYP substitution on the optical properties of paper products. The effects of OBA, PCC filler, and dyestuff on paper brightness, whiteness, and colour shade were investigated under various HYP substitution rates. The HYP substitution decreases the brightness and CIE whiteness of paper sheets, particularly at a high HYP substitution rate (e.g. 30%). The brightness loss due to the HYP substitution can be recovered by the addition of OBA and/or PCC.

H

igh-yield pulps (HYP), also known as bleached chemi-thermomechanical pulps (BCTMP), can be used to replace bleached hardwood chemical pulp in the manufacturing of highquality paper products, including printing and writing paper, due to their unique properties and lower cost [1-5]. Mechanical pulps have superior bulk and opacity compared with bleached chemical pulp, properties which are desirable for the production of printing and writing paper.

Brightness is one of the most important quality criteria for mechanical pulps. Aspen HYP pulp can be bleached to 85% ISO or even higher brightness, but it is relatively expensive to do so.

The production cost of HYP increases exponentially with brightness levels. In the pulp and paper industry, optical brightening agents (OBAs) or fluorescent whitening agents (FWA) are commonly used to improve the brightness of paper products [6-11]. Essentially all of this literature refers to bleached chemical pulps. Very few references are available which refer to application of OBAs on mechanical pulps.

Since the substitution rate of HYP for hardwood chemical pulp in fine paper grades is usually at about 20% or lower, it was proposed that HYP with a brightness of a few units lower than 85% ISO might not affect the optical properties of final products if fillers, such as PCC, and optical brightening agents (OBA) are used. The production cost of HYP would decrease significantly if the brightness of HYP pulp can be lowered from 85% ISO to about 83% ISO without any sacrifice in the quality of final paper products.

The objective of this research project included: i) to investigate the influence of adding OBA on the brightness of HYP-containing paper sheets, and ii) to determine the feasibility of using a 20

lower-brightness HYP (e.g. 83% ISO) instead of a high-brightness HYP (e.g. 85% ISO) for the production of printing and writing paper.

EXPERIMENTAL

A softwood (mainly spruce) bleached kraft pulp (SWBKP), and a hardwood (eucalyptus) bleached kraft pulp (HWBKP) were refined in a PFI mill to 470 and 490 ml CSF freeness, respectively.

Three grades of commercial aspen high-yield pulp (325/85, 325/83, 250/80) were obtained from Tembec Inc., without further refining treatment.

The properties of the pulp samples are listed in Table I.

H. ZHANG Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and Technology, China

Z. HE Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, N.B.

Y. NI Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, N.B.

Y. ZHOU Tembec Inc.

PULP & PAPER CANADA October/November 2009

H. HU Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and Technology, China pulpandpapercanada.com

PEER REVIEWED T138 TABLE I. Characteristics of the pulp samples used for the experiments.

CSF (ml) Brightness (%) CIE Whiteness (%) SWBKP HWBKP HYP(325/85) HYP(325/83) HYP(250/80)

470 490 510 540 450

87.2 88.4 85.5 83.7 81.2

73.6 76.2 66.7 61.7 55.0

L*

a*

b*

97.2 97.4 97.2 96.9 96.6

-0.72 -0.60 -1.43 -1.55 -1.48

4.28 3.84 5.77 6.73 7.97

TABLE II. Effect of HYP substitutions on the optical properties of handsheets Furnish composition (%) HYP *

HWBKP SWBKP

0% PCC 0% OBA

Brightness (%ISO) CIE Whiteness (%) Scattering Coefficient (m2/g)

Brightness (%ISO) 0% PCC CIE Whiteness 0.2% OBA (%) Scattering Coefficient (m2/g) Brightness (%ISO) 30% PCC** CIE Whiteness 0% OBA (%) Scattering Coefficient (m2/g) Brightness (%ISO) 30% PCC** CIE Whiteness 0.2% OBA (%) Scattering Coefficient (m2/g)

0 70 30

10 60 30

15 55 30

20 50 30

25 45 30

30 40 30

87.4

86.2

85.9

85.5

85.4

85.3

74.3

71.7

70.6

69.1

68.7

68.3

27.8

29.2

29.7

30.7

30.9

31.5

92.2

90.9

90.6

90.0

89.5

88.9

90.3

87.2

85.8

84.0

82.3

81.0

27.1

28.6

29.7

30.4

31.1

31.0

90.3

89.4

89.2

88.8

88.6

88.3

81.8

79.3

78.9

78.1

77.4

76.7

60.8

62.9

64.1

64.2

64.9

65.3

94.3

93.0

92.6

92.3

91.7

91.5

94.1

90.9

89.9

88.8

87.4

86.9

62.5

63.9

64.5

65.3

66.3

67.2

* Grade 325/83 HYP. **PCC filler retention was about 85% in all cases.

A precipitated calcium carbonate filler (Albcar HO) was obtained from Specialty Minerals, one di-sulfonic and one tetrasulfonic optical brightening agent from Ciba, a cationic polyacrylamide (CPAM, Percol 292) from Hydrocol, and a basic blue dye from Tri Tex Quebec.

Unless specified, the tetra-sulfonic OBA was used for all the experiments in this study, and its dosage was based on the liquid product (about 25% solid content). Weighed pulp samples (SWBKP, HWBKP, and HYP), were disintegrated for 15,000 revolutions in a standard disintegrator at 1.5% pulp consistency, and then diluted to 1% suspension. The pulp suspension was transferred to a 500 ml beaker, and a CaCl2 solution was added to reach a Ca2+ concentration of 100 ppm (as CaO). The pH of the mixture was pulpandpapercanada.com

adjusted to about 7.0 followed by the OBA addition. Stirring was provided for 20 minutes under the room temperature.

When needed, PCC (dispersed into a suspension) was then added, followed by the addition of CPAM (0.05%, on pulp).

In some cases, a blue dye was added after the OBA addition and mixed for 10 minutes. The content of the beaker was then transferred to the cylinder of a handsheet machine which was pre-filled with 3 L deionized water that contained 100 ppm Ca2+ (as CaO), and a handsheet was prepared and tested according to the TAPPI methods.

RESULTS AND DISCUSSION

Effect of HYP Substitution Rate We first investigated the effect of the substitution rate of HYP for hardwood

bleached kraft pulp (HWBKP) on the optical properties of paper sheets. In Table II, the percentage of HYP (grade 325/83) in the furnish composition was varied, from 0% to 30%, with softwood bleached kraft pulp (SWBKP) fixed at 30%. The HWBKP percentage changed accordingly from 70% to 40%. The results in Table II show that both the brightness and CIE whiteness decreased with the increase of HYP substitution rate, while the light scattering coefficient increased. The addition of OBA was very effective in recovering the loss of brightness and whiteness due to HYP substitution. With 0.2% OBA, the brightness and CIE whiteness of furnish which contained 30% HYP (88.9% ISO and 81.0%, respectively) were actually higher than those of the control furnish containing 100% bleached chemical pulps without OBA (87.4% and 74.3%, respectively). The PCC fillers were also effective in reducing the negative effects of the HYP substitution on brightness and CIE whiteness. When 0.2% OBA was used together with 30% PCC, at 20% HYP substitution rate, the brightness and CIE whiteness reached 92.3% ISO and 88.8%, respectively, which were compared to 87.4% ISO and 74.3% of the control.

However, it should be noted that OBA is more effective with the bleached chemical pulp. As shown in Table II, if the same amount of OBA and PCC filler was applied to the control stock, higher brightness and whiteness were obtained (94.3% and 94.1%, respectively).

Table II further shows that the effectiveness of OBA decreases when more HYP is present in the furnish. For example, in the case of 0% PCC and 0% HYP, with 0.2% OBA the brightness increased from 87.4% to 92.2% ISO, an increase of 4.8 units. However, in the case of 30% HYP substitution, an increase of 3.6 units (from 85.3 to 88.9% ISO) was observed under otherwise the same conditions.

Effect of HYP Brightness The brightness of the three grades of HYP used in this study varied from 80 to 85% ISO. In Fig. 1, the effect of HYP brightness on the final sheet brightness was compared under the same HYP substitution rate (20%). The results show that the brightness of final sheets is sensitive to the brightness level of HYP. The brightness difference in final sheets between Grades

October/November 2009 PULP & PAPER CANADA

21

T139 OPTICAL BRIGHTENING AGENTS

Fig. 1. Effect of HYP brightness on handsheet brightness.

(HYP substitution rate was 20%, and the OBA dosage was 0.2%; PCC filler retention rate was about 85%).

Fig. 2. Comparison of the brightness profiles of different furnishes at various OBA charges. (The PCC charge was 30%, and its retention was about 85%).

Fig. 3. Fluorescent composition of handsheets at various OBA dosages. (The PCC charge was 30%, and its retention was about 85%).

Fig. 4. Effect of PCC filler on the effectiveness of OBA at various OBA charges. (The furnish composition was 30% SWBKP, 50% HWBKP and 20% HYP (Grade 325/83)).

325/85 and 325/83 was about 0.5 units. A slightly higher OBA dosage may be able to eliminate the difference, which may represent a more economical way to produce similar-brightness paper with HYP, since it is very costly in a HYP manufacturing process to increase the brightness of HYP from 83% to 85% ISO. Effect of OBA Charge As discussed above, the brightness and CIE whiteness of final sheets are sensitive to the brightness levels of HYP and its substitution rate. A question arises as to whether the brightness and whiteness loss due to using a lower-brightness HYP can be recovered by increasing OBA dosages.

In Table III, the OBA dosage was varied from 0 to 0.6%, the HYP substitution rate was fixed at 10%, and no filler was added in this series of experiments. In all the four cases (the control furnish and furnishes 22

containing different grades of HYP), both brightness and CIE whiteness increased significantly with the increase of OBA dosages, while b* decreased dramatically.

Table III further shows that the brightness increment was smaller for furnishes with lower-brightness HYP. These results support the conclusion that HYP decreases the effectiveness of OBA, with the effect more pronounced when the HYP brightness is lower.

The effectiveness of OBA decreased when its charge exceeded 0.2%, regardless of the furnish composition. Nevertheless, the results in Table III clearly show that the brightness deficiency of the HYP containing furnishes can be compensated for by increasing the OBA charge. For example, for a given brightness target of 90% ISO, the OBA charge was 0.05-0.1% for the control furnish, and 0.1-0.2%, 0.2% and 0.4% respectively, for the three HYP-

PULP & PAPER CANADA October/November 2009

containing furnishes. Moreover, the yellow colour shade of HYP can be eliminated by OBA addition, as indicated by the significant decrease of b*.

Similar results were obtained when 30% PCC was applied, although the baselines of brightness and CIE whiteness were at much higher levels. As shown in Fig. 2, a brightness of 94% ISO was achieved for the control furnish with 0.1-0.2% OBA. To reach the same brightness target, the OBA charge had to be increased to 0.30.4%, 0.4-0.5% and 0.6-0.7% respectively for the three HYP-containing furnishes.

Figure 3 shows the fluorescent composition as a function of OBA charge for different grades of HYP. At a given OBA charge, the brightness increase was higher for the control furnish than for the HYPcontaining furnish. Also, the brightness of HYP affected the effectiveness of OBA. The lower the brightness of HYP, the pulpandpapercanada.com

PEER REVIEWED T140 TABLE III. Effect of OBA charge on brightness and CIE whiteness (without filler) OBA dosage (%) 0% HYP, 0% PCC 0 0.05 0.1 0.2 0.4 0.6 10% HYP(325/85), 0 0.05 0.1 0.2 0.4 0.6 10% HYP(325/83), 0 0.05 0.1 0.2 0.4 0.6 10% HYP(250/80), 0 0.05 0.1 0.2 0.4 0.6

L*

97.2 97.0 97.2 97.2 97.3 97.2 0% PCC 96.9 96.8 96.9 96.9 96.9 96.9 0% PCC 97.1 96.8 96.8 96.9 96.9 96.9 0% PCC 96.6 96.5 96.5 96.5 96.5 96.6

a*

b*

CIE Whiteness Brightness Fl. Comp. (%) (%ISO) (%ISO)

-0.45 0.29 0.58 0.92 1.26 1.43

3.90 2.09 1.47 0.63 -0.30 -0.74

75.2 82.9 86.2 90.2 94.4 96.3

87.6 89.6 90.9 92.4 94.0 94.8

0 2.43 3.52 4.93 6.51 7.43

-0.54 0.12 0.36 0.73 1.14 1.28

4.22 2.63 1.97 1.11 0.12 -0.36

73.1 80.1 83.2 87.1 91.6 93.8

86.8 88.7 89.7 91.0 92.6 93.5

0 2.27 3.37 4.73 6.38 7.22

-0.51 0.11 0.40 0.71 1.06 1.23

4.26 2.82 2.13 1.20 0.31 -0.19

73.5 79.2 82.3 86.6 90.9 93.1

86.7 88.3 89.2 90.6 92.3 93.2

0 2.08 3.16 4.45 6.10 6.94

-0.68 -0.08 0.22 0.52 0.94 1.12

4.74 3.32 2.68 1.83 0.80 0.21

69.8 76.0 78.9 82.9 87.7 90.4

85.2 86.8 87.6 89.0 90.7 91.8

0 2.02 3.05 4.35 6.00 6.85

TABLE IV. Effect of OBA types on the optical properties of handsheets OBA dosage (%)

L*

a*

b*

CIE Whiteness Brightness Fl. Comp. (%) (%ISO) (%ISO)

Tetra-sulfonic OBA; 20% HYP(325/83) 0 96.6 -0.71 0.2 96.5 0.48 0.6 96.6 1.06 1.2 96.6 1.20

4.60 1.75 0.35 -0.19

70.5 83.3 89.8 92.2

85.4 89.2 91.5 92.6

0 4.14 6.54 7.78

Di-sulfonic OBA; 20% HYP(325/83) 0 96.6 -0.71 0.2 96.5 0.55 0.6 96.6 1.02 1.2 96.6 1.22

4.60 1.58 0.17 -0.42

70.5 84.0 90.6 93.2

85.4 89.3 91.9 93.1

0 4.38 6.87 8.25

Tetra-sulfonic OBA; 50% HYP(325/83) 0 96.6 -1.06 0.2 96.6 -0.17 0.6 96.7 0.40 1.2 96.7 0.63

5.66 3.46 2.01 1.39

65.7 75.7 82.5 85.4

84.2 87.1 89.5 90.7

0 3.17 5.51 6.78

Di-sulfonic OBA; 50% HYP(325/83) 0 96.6 -1.06 5.66 65.7 0.2 96.6 0.00 3.16 77.2 0.6 96.7 0.51 1.75 83.6 1.2 96.7 0.70 1.12 86.5 Note: OBA dosage was based on the liquid products.

84.2 87.7 89.9 91.2

0 3.67 6.00 7.33

lower the brightness gains from OBA. These results again confirm that HYP decreases the effectiveness of OBA, and the effect is more pronounced when the pulpandpapercanada.com

brightness of HYP is lower.

Effect of OBA Types Some OBAs were claimed to be more

effective in increasing the brightness of mechanical pulps. In Table IV, the effectiveness of two types of OBA was compared under identical conditions. The results support the notion that di-sulfonic OBA is slightly better than tetra-sulfonic OBA. Di-sulfonic OBA probably had higher retention on mechanical pulp fibers than tetra-sulfonic OBA. Effect of PCC Fillers PCC fillers have much higher specific surface area and light reflectance than cellulose fibers, and therefore they can improve the paper optical properties. As shown in Fig. 1, the brightness of the paper sheets improved significantly in all cases when 20-30% PCC was added.

However, the presence of PCC decreased the brightening efficiency of OBA. In Fig. 4, the fluorescent composition of filled and un-filled sheets was compared at various OBA dosages. The fluorescent composition of the filled samples was significantly lower than that of the un-filled samples at the same OBA dosage, indicating that the effectiveness of OBA decreased in the presence of PCC fillers.

Effect of Dyestuff on CIE Whiteness on the Optical Properties of Paper Sheets It is well recognized that the CIE whiteness represents the visual appearance better than brightness. A recent trend in the pulp and paper industry is to use both optical brightening agents and dyes simultaneously, in order to improve whiteness more efficiently [10,11]. Blue dyes, such as anionic direct dyes and basic dyes can give an extra boost to the CIE whiteness [12].

In Table V, a basic blue dye was used together with OBA to improve the CIE whiteness of the HYP-containing furnish.

The CIE whiteness increased dramatically with the addition of the blue dye, while the change in brightness was small. At 4.43 ppm blue dye dosage, the CIE whiteness reached 94.6% and 100.9%, at 0.2% and 0.6% OBA charges, respectively. The change in brightness was negligible. The addition of blue dye also changed the values of L*, a* and b* mainly from yellow hue to blue hue. The total reflectance of light decreased with the addition of the blue dye as indicated by the drop of L*.

CONCLUSIONS

A low HYP substitution for hardwood

October/November 2009 PULP & PAPER CANADA

23

T141 OPTICAL BRIGHTENING AGENTS bleached kraft pulp (10 - 20%) in the production of printing and writing paper grades resulted in a small decrease in brightness. However, the brightness and whiteness loss due to the HYP substitution can be recovered by increasing the OBA charge and the addition of PCC filler.

The blue dye is very effective in improving the CIE whiteness when combined with OBA. Technically it is feasible to use a 83% ISO grade HYP to replace a 85% ISO grade without affecting the optical properties of final paper sheets, provided that OBA charge is increased accordingly. At a 20% substitution for HWBKP, the brightness difference in final sheets when using 83% ISO HYP, instead of 85% ISO HYP was about 0.5 units, such a small difference can be compensated for by using a small amount of additional OBA in the paper making process.

LITERATURE

1. CANNELL, E., COCKRAM, R., The Future of BCTMP, Pulp and Paper, 74 (5): 61-76 (2000).

2. REIS, R., The Increased use of Hardwood High Yield Pulps for Functional Advantages in Papermaking, Proceedings of the 2001 Papermakers Conference, Cincinnati, 2001.

3. XU, E.C., P-RC Alkaline Peroxide Mechanical Pulping of Hardwood, Part 1: Aspen, Beech, Birch, Cottonwood and Maple, Pulp and Paper Canada, 102 (2): 44-47 (2001).

4. ZHOU, Y., Overview of High Yield Pulps (HYP) in Paper and Board, PAPTAC 90th Annual Meeting, Montreal, Canada, 2004.

5. HU, K., NI, Y., ZOU, X., Substitution of Aspen High-Yield Pulp for Hardwood-kraft pulp in Fine Papers and Its Effect on AKD Sizing, Tappi J., 3 (8): 13-16 (2004).

6. CROUSE, B.W., SNOW, G.H., Fluorescent whitening agent in the paper industry: their chemistry and measurement, Tappi J., 64 (7): 87-89 (1981).

7. BOURGOING, S., LECLERC, E., MARTIN, P., ROBERT, S., Use of fluorescent whitening agents to inhibit light-induced colour reversion of unbleached mechanical pulp, Journal of Pulp and Paper Science, 27 (7): 240-244 (2001).

8. ROLTSCH, C.C., LIOYD, T.A., Efficient Use of Fluorescent Whitening Agents in the Paper Industry, Papermakers Conference, Proceedings of the Technical Association of the Pulp and Paper Industry, 1987.

9. BARNARD, J.D., Role of OBAs and Cross Linking Agents, Paper Technology and Industry, 33 (9): 24-30 (1992).

10. AKSOY, B., JOYCE, M.K., FLEMING, P.D., Com-

parative Study of Brightness/Whiteness using Various Analytical Methods on Coated Papers Containing Colorants, Proceedings of TAPPI Spring Technical Conference and Exhibit, Chicago, IL, 2003.

11. OHLSSON, L., FEDERER, R., Efficient use of fluorescent whitening agents and shading colorants in the production of white paper and board, Preprints, 2002 African Pulp and Paper Week, Durban, 2002.

12. NEIMO, L., Papermaking Chemistry, Book 4. In Gullichsen, J., Paulapuro, H., ed., Papermaking Science and Technology. Helsinki: Finnish Paper Engineers’ Association and Tappi, 1999.

TABLE V. Effect of blue dye on L*, a* and b* (20% HYP) Blue dye dosage (ppm) 0

0.89

2.66

4.43

6.20

7.97

13.29

0.2% OBA

89.44 86.38 96.0 0.44 0.81

89.43 91.02 95.2 0.74 -0.63

89.33 94.55 94.5 0.99 -1.76

89.21 97.47 93.9 1.33 -2.68

89.16 99.51 93.4 1.59 -3.59

88.68 106.47 92.1 2.15 -5.46

Brightness % ISO CIE whiteness % L* a* b*

Brightness % ISO

CIE whiteness % 0.6% L* OBA a*

b* Note: The furnish composition

89.44 82.69 96.8 0.33 2.04 91.7 89.61 96.7 0.89 0.47 was 30%

91.78 91.8 91.64 91.53 91.4 91.17 92.63 97.43 100.86 104.01 106.67 113.63 96.2 95.3 94.6 94.0 93.4 92.1 1.02 1.32 1.60 1.87 2.19 2.83 -0.49 -2.00 -3.09 -4.08 -4.19 -7.00 SWBKP, 50% HWBKP and 20% HYP (Grade 325/83).

Résumé: Des pâtes à haut rendement de divers degrés de blancheur ont été utilisées pour remplacer la pâte kraft blanchie de feuillus afin d’évaluer l’influence de ce remplacement sur les propriétés optiques des produits du papier. Les effets des ABO, de la charge de PCC et des colorants sur la blancheur, la brillance et la teinte du papier ont été étudiés en fonction de divers taux de remplacement. La PHR utilisée en remplacement diminue la brillance et la blancheur CIE du papier, surtout lorsque le taux de remplacement est élevé (e.g. 30 %). La perte de brillance attribuable à ce remplacement peut être compensée par l’ajout d’un ABO et/ou de PCC. Reference: ZHOU, Y., ZHANG, H., HU, H., NI, Y., HE, Z., Using Optical Brightening Agents

(OBA) for Improving the Optical Properties of HYP-Containing Paper Sheets. Pulp & Paper Canada 110 (8): T137-T141 (October/November 2009). Paper presented at the 94th Annual Meeting in Montreal, February 5-7, 2008. Not to be reproduced without permission of PAPTAC. Manuscript received December 18, 2007. Revised manuscript approved for publication by the Review Panel January 13, 2009.

Keywords: HIGH-YIELD PULP, HYP, FINE PAPER, OPTICAL BRIGHTENING AGENT, OBA, PCC, BRIGHTNESS, WHITENESS

letters editor TO THE

cindy@pulpandpapercanada.com 24

PULP & PAPER CANADA October/November 2009

pulpandpapercanada.com

BRIGHTNESS STABILITY T142

A Comparison of Options to Improve Brightness Stability of Chemical Pulp

By D. Davies, T. Dietz, and H.U. Suess Abstract: Chromophores remaining in pulp after bleaching or generated in aging have been identified previously. The dominant structure of these chromophores is a resonance stabilized hydroxy quinone moiety.

Such quinones are destroyed in bleaching, though not very easily. The highest benefit is achieved with a combination of stages. Brightness and brightness stability become better in this order for these combinations: Paa/P < D/P < Z/P.

O

ne of the important pulp properties that still needs to be better understood and further developed is brightness stability. Recently, some of the chromophores have been identified and the sources for their generation in aging processes have become clearer [1]. For some decades, the typical message was, “Pulp stability improves with more bleaching, the higher the brightness, the more likely this higher brightness will also be more stable.” Experience showed a final P stage to be more favorable than a final D stage. The first scientific evidence for this effect was the detection of quinones in D2 bleached pulp and the absence of such structures after a final P stage [2]. Alkaline peroxide cleaves quinones and the oxidation products are removed by extraction.

The identified remaining chromophores in fully bleached and aged pulp have a common structural element, hydroxy and dihydroxy quinones.

These compounds are resonance stabilized and have a peculiar reactivity – because they can form a di-anion under alkaline conditions, they cannot be cleaved with alkaline hydrogen peroxide. It is possible to oxidize such compounds with electrophiles, however, the chlorine dioxide reaction generates chlorinated compounds. Under neutral or acidic conditions, the phenolic hydrogen equally belongs to both neighboring oxygen atoms. Oxidation with electrophiles is possible. With chlorine dioxide, this can result in halogenation.

It is the target of this analysis to compare the potential of “typical” bleaching chemicals, not only to increase brightness but also to stabilize brightness. Standard methods for measuring brightness stability – dry aging at 105°C for 4 hours (UM200, Tappi) and humid aging for one hour at 100°C and 100% humidity (E.4P, Paptac) – were applied.

Both methods are rather simple standards. They can be easily conducted in any laboratory. Dry aging just needs an oven. Humid aging is perpulpandpapercanada.com

formed in a simple device over boiling water, thus no complicated treatment is required to reach a certain humidity level.

Materials and methods

All bleaching trials were done with industrial pulp samples taken after oxygen delignification. D and P stages were run in plastic bags in water baths.

Ozone was added to well-fluffed pulp in a fluidized bed reactor; Eop stages were conducted in a pressurized high-shear mixer. All trials were done at 10% consistency with the exception of ozonation, which was conducted at >30% consistency in a fluidized bed reactor. Brightness was measured with ISO 2470. Reversion testing used hand sheets prepared at pH 6 on a Buchner funnel with a weight of 280 g/m².

Final stage chlorine dioxide

The conventional ECF process has four to five stages and is best described by the abbreviations D0EopD1D2 or D0EopD1ED2, following the historical development. Initially chlorine dioxide was added to a CEH bleaching sequence as a final brightness boosting step, changing the process to CEHD. In comparison to hypochlorite, chlorine dioxide bleaching yields brilliant results. It improves brightness without negatively affecting fiber quality. In hypochlorite bleaching, an oxidation of the cellulose chains is hardly avoidable. As we know now, this is the main reason for the poor brightness stability of hypochlorite treated pulp [2]. In contrast, chlorine dioxide generates much better brightness stability. Therefore, it was only consequent to phase out hypochlorite and operate D stages.

The information available on the impact of D stage conditions on brightness stability is moderate. The simple message is “chlorine dioxide provides pulp of high brightness and low brightness reversion” [3]. Lab tests show very little impact October/November 2009

D. DAVIES Evonik Degussa Canada

T. DIETZ Evonik Degussa Germany

H.U. SUESS Evonik Degussa Germany PULP & PAPER CANADA

25

T143 BRIGHTNESS STABILITY PC# (E.4P)

0,7

brightness

0,4 87 0,3 0,2

86

brightness (%ISO)

0,5

post color # (E.4P)

brightness (%ISO)

88

PC #: 75°C Br: 75°C

89

0,6

PC #: 85°C Br: 85°C

0.6 0.5

post color # (E.4P)

89

0.4 0.3

88

0.2 0.1

0,1 85

0 D1

5

7,5

10

87

12,5

5

7.5

act- Cl in D2 (kg/t)

10 act. Cl (kg/t)

12.5

0

Fig. 1: Effect of bleaching softwood kraft with of bleaching softwood kraft pulp with the sequence D0EopD . D1 and D2 the at 75°C, 2h, 10 % cons. Reversion with 1nD2pulp Fig. 2: Impact of higher temperature in the D2 stage on C, 100 % humidity). sequence D0EopD1nD2. D1 and D2 at 75°C, 2h, 10 % cons.

Fig.brightness 2: Impact ofand higher temperature in the D2see stage on brightness and stability (condi stability (conditions Fig. 1) Reversion with E.4P (1h, 100°C, 100 % humidity).

PC#

89

92

0,7

brightness

91

0,5 0,4

87 0,3 0,2

86

90

0,1 85

0 D1

0,5

1

1,5

2

time in D2 (h)

brightness (%ISO)

88

post color # (E.4P)

brightness (%ISO)

0,6

89

bleached

88

after UM200 after E.4P

87 86 85 84 D2

P

Fig. time in Dactive at 85°C withon5 brightness kg/t active chloFig. Brightness stability of eucalyptus kraft pulp final with chlorine di mpact of time in 3: D2Impact at 85°Cof with 5 kg/t chlorine development and post color number (PC#)of eucalyptus Fig. 4:4:Brightness stability kraft pulp final bleached 2 humid aging. rine on brightness development and post color number bleached with chlorine dioxide or peroxide, sequence stage at 70°C, 2h, or P stage at 75°C, 1.5h.

(PC#) following humid aging.

D0EopD1, D2 stage at 70°C, 2h, or P stage at 75°C, 1.5h.

of pH and consistency on reversion. However, as early as 1955, a positive impact of temperature on brightness stability was described [4]. Typically, chlorine dioxide bleaching is conducted at about 70°C; depending on mill conditions, it might be difficult to operate at a higher level. Typically, chlorine dioxide solution is stored at low temperature (~5°C). Thus, with the application of a large amount of chlorine dioxide comes the addition of a lot of cold water. Steam demand for heating the pulp at medium consistency can become high, so steam mixing is a potential temperature bottleneck in a D stage.

Figures 1 to 3 show the effects of amount of ClO2, temperature, and time in chlorine dioxide bleaching on brightness and post colour number (PC#). An oxygen delignified softwood kraft pulp (Kappa 10.4) was bleached with the sequence D0EopD1nD2.

The stages D0Eop, with an active chlorine multiple of 0.25 and 3 kg/t of hydrogen peroxide in Eop, resulted in a brightness of 74% ISO and lowered the Kappa number to 2. The application of 12.5 kg/t active chlorine in D1 at 75°C gave a brightness of 86% ISO. The D2 stage, again at 75°C, produced a further increase in brightness. It becomes obvious from the flat shape of the curve in Fig. 1, the use of much more than 5 kg/t of active chlorine in D2 is not really effective. The brightness ceiling is reached at 88% ISO. Brightness stability in humid aging improves with washing between D1 and D2. In comparison, the effect of more chemical 26

PULP & PAPER CANADA October/November 2009

in D2 is moderate.

A higher temperature in the D2 stage has a positive impact on brightness, as shown in Figure 2. More bleaching chemical has no impact at 75°C. This changes with higher temperature: at 85°C, the increase of the chlorine dioxide charge (from 5 kg/t to 12.5 kg/t) generates an additional brightness point. The impact on brightness stability is dependent on the temperature level, and independent of the change in chemical charge between 5 and 12.5 kg/t active chlorine. As mentioned earlier [5], higher temperature very likely triggers the decomposition of reaction products of lignin with chlorine dioxide, such as quinone intermediates. Quinones are oxidizers themselves, and higher temperature facilitates their reaction. A clue for the existence of such reactions is the strong temperature impact on the removal of AOX and OX. In comparison, a hot D0 stage yields a lower amount of halogenated compounds compared to a hot acid hydrolysis followed with chlorine dioxide addition (hotD0 compared to hotA+D0 without intermediate washing). Even in fully bleached pulp, traces of halogenated quinones are still present [2].

There is a noticeable impact of the reaction time on brightness stability (Fig. 3). An increase of the reaction time of 5 kg/t active chlorine with the pulp from 30 minutes to 2 hours at 85°C gives a gain of one full additional brightness point. In the light of the low residual of just 1.2 kg/t active chlorine after 30 minutes, pulpandpapercanada.com

PEER REVIEWED T144 91 89

bleached

brightness (%ISO)

after E.4P after UM200

brightness (%ISO)

88

87

86

90

89

88 D1

D2

P

87

85

0

2,5

5

7,5

10

12,5

15

17,5

20

active chlorine (kg/t)

84

Fig.6:6:Brightness Brightness development inbleaching D1D2 bleaching with the Fig. development in D1D2 with the active chlorine charge a D0 at 50°C, factor 0.2; Eop at 75°C, 4 kg/t of H2O2; D1D2 at 70°C, 2h; active chlorine charge and impact the substitution of DP2at 75°C, 2h, p Fig. 5: 5: Comparison of brightness stability after D2after stages different a finalfactor P stage in Eop bleaching of 4 kg/t H2O2; D1D2 with P.orD0with at 50°C, 0.2; at 75°C, Fig. Comparison of brightness stability D2 at stages at temperature softwood kraft pulp. at 70°C, 2h; P at 75°C, 2h, peroxide charge constant at 2.5 different temperature or with a final P stage in bleaching of D2 (75°C)

D2 (85°C)

P

kg/t.

softwood kraft pulp.

0,6

0,6 75°C

85°C

0,4 0,3 0,2 0,1

75°C

0,5

95°C

PC # (E.4P)

PC # (UM200)

0,5

85°C

95°C

0,4 0,3 0,2 0,1

0 Eop

D1

30

60

120

time in P (min)

0 Eop

D1

30

60

120

time in P (min.)

7: Dry aging 105°C, 4h)pulp of eucalyptus 7: Dry agingFig. (UM200, 105°C, 4h)(UM200, of eucalyptus kraft bleached withkraft the sequence hotD0EopD1P. Stability expressed 8: Humid of eucalyptus pulp (E.4P, 100°C, pulp bleached with the sequence hotD0EopD1P. Stability ost color number.

Fig.Fig. 8: Humid agingaging of eucalyptus kraft pulpkraft (E.4P, 100°C, 100% humidity, 1h). expressed as post color number.

the brightness gain can hardly be attributed to a more complete consumption of chlorine dioxide. There has to be a considerable amount of reaction of partially oxidized compounds. In addition, the longer the pulp is kept at the very high temperature, the more intense is the degradation of compounds responsible for brightness reversion. The bars for the PC# value decrease significantly with time.

These results allow an addition to the knowledge presented in the text books: • Chlorine dioxide bleaching gives better brightness stability at very high temperature (>80°C).

• Chlorine dioxide bleaching yields higher brightness with extended reaction time (2 h).

• Low temperature and short retention time should be avoided in a final D stage.

As mentioned above, it might be difficult to raise the temperature in chlorine dioxide bleaching because of the need to use cooled ClO2-solution and because of limitations in steam mixing.

Another problem is the construction material for chlorine dioxide towers – tiled towers – cannot be operated above a certain temperature level, as the tiles might fall off too easily. However, these pulpandpapercanada.com

100% humidity, 1h).

data allow the recommendation to go to the limits and to apply the highest feasible temperature. This guarantees the best effects chlorine dioxide can offer.

Final stage hydrogen peroxide

As mentioned above, Vuorinen and coworkers detected traces of quinone compounds in pulp bleached with a final D stage, however, no such products in pulp bleached with a final peroxide stage [2] were found. The destruction of quinoid structures is one of the main reactions of alkaline hydrogen peroxide in bleaching processes [6]. The positive impact of a final hydrogen peroxide stage becomes very visible in humid reversion [7]. Obviously, many reactions resulting in chromophore formation require the presence of water, as dry reversion at >100°C gives less pronounced differences. A conventional 70°C D2 stage gives a good brightness, however, it does not yield very good stability. Figure 4 compares a final D2 stage with a P stage in eucalyptus pulp bleaching. Chemical addition was stoichiometric (5 kg/t active chlorine or 2.5 kg/t H2O2). Effects are similar for softwood pulp (Fig. 5).

The replacement of chlorine dioxide with hydrogen peroxide can be better than stoichiometric. This is valid in pulp mills with October/November 2009 PULP & PAPER CANADA

27

T145 BRIGHTNESS STABILITY 90

0,5

PC# (UM200)

90

0,4

89

0,3

88

PC #

brightness (%ISO)

89 0,7 88

0,6 0,5

87

0,2

87

0,4

0,1

86 85

post color #

PC #(E.4P)

91

0,9

E.4P

0,8

0,6

brightness

brightness (%ISO)

92

brightness

86

0,3 untreated

0

50°C

65°C

80°C

Paa/P(80°C)

Fig. 10: Post treatment of a TCF pre-bleached 10: Post treatment of a TCF pre-bleached softwood kraft pulp softwood with distilled peracetic acid pulp with distilledstability peracetic acid (constant kg/t). Time at 10% con temperature onkraft brightness and brightness after humid reversion5(E.4P).

Impact ofNaOH) temperature on brightness and brightness stabilh and alkalization (5 kg/t after 0.5 h. g. 9: Impact of high input in aperoxide final P stage.

Softwood kraftPpulp bleached both humid at 85°C,reversion 2h in D and(E.4P).

1.5 Fig. 9: peroxide Impact of high input in a final stage.

Soft- with D1P; ity after Time at 10% cons. 3h, with n P. wood kraft pulp bleached with D P; both at 85°C, 2h in D D(12.5) P(2.5)

P(5)

P(7.5) D(17.5) P(2.5)

P(5)

P(7.5) Fig.

amounts of active Cl or H2O2 (kg/t)

90,5

0,3

brightness E.4P

40°C

PC#

PC#

0,4

post color #

0,2 91 0,1

brightness (%ISO)

90

92

brightness (%ISO)

60°C

0,3

89,5 0,2 89 0,1

88,5

90

88 89

0 D

1 kg/t paa

5 kg/t paa

post color (E.4P)

93

Paa/P 0.5 h + 2.5 h and alkalization (5 kg/t NaOH) after 0.5 h.

1

and 1.5 h in P.

0 D

2.5 kg/t H2O2

1

2

time (h)

3

4

5

Fig. 12: Impact Fig. of high storage postdensity bleaching with 2 post kg/t distilled peracetic 12:density Impact of high storage bleaching with acid, pulp p 1: Alternatives post bleaching: in final Paableaching: or final P stage; all trials at 80°C, 1 h, 10% cons .

Fig.in11: Alternatives post final Paa or stage. final P 2 kg/t distilled peracetic acid, pulp pre bleached with a

stage; all trials at 80°C, 1 h, 10% cons.

an overload in the bleach plant and poor washing. Under such circumstances brightness increases only with a very high input of chlorine dioxide in D2. With the replacement of the second D stage, savings in chemical input are higher than the chemical equivalent (Fig. 6). The arrows indicate bleaching to >90.4% ISO with either 15 kg/t active chlorine in D1D2 or 5 kg/t active chlorine plus 2.5 kg/t H2O2 in D1P. Time and temperature in the final P stage affect stability, though differences are not very large. Figures 7 and 8 show the impact of P stage conditions on the stability in dry and humid aging, respectively. The advantage of high temperature is more pronounced in dry reversion. Time can be used to compensate for low temperature. However, as differences are moderate and the application of very high temperature becomes disadvantageous as it lowers viscosity and increases COD, the use of a temperature around 80°C and a retention time of 1 hour are recommended.

Brightness increase in final bleaching with hydrogen peroxide is not limited to the application of just small amounts of H2O2.

An example in bleaching softwood pulp with D0EopD2P is shown in Fig. 9. The additional brightness gain with an increase from 2.5 kg/t to 7.5 kg/t H2O2 is dependent upon the pre-bleaching 28

PULP & PAPER CANADA October/November 2009

final D stage.

conditions. The graph illustrates the impact on brightness and the drop of the post color numbers for dry and humid aging. The advantages regarding brightness stabilization develop with even moderate peroxide input. From a practical point of view, the use of high peroxide input is of limited relevance, as mill operators typically focus their bleach plant control strategy on an “early” brightness development. However, in principle it is possible to compensate for too low D1 brightness with peroxide.

There have been multiple attempts to use even higher amounts of peroxide. The target mostly focused on a decrease of the chlorine dioxide consumption in ECF “light” bleaching [8].

Typically, very high amounts of hydrogen peroxide are simply not consumed, therefore very high temperature is recommended to accelerate peroxide consumption. However, higher temperature, possibly combined with pressurized conditions for a level above 100°C, initiate thermal decomposition of H2O2 into radicals and such hydroxyl radicals may oxidize the cellulose chain. This becomes visible in a viscosity drop and even more so in a sharp increase in the COD load. As an increase of the COD is equivalent to dissolved pulp, it also indicates a yield loss [9,10]. Consequently, the temperature in a final P stage should not become pulpandpapercanada.com

PEER REVIEWED T146 brightness

91

0,6

UM200

0,3 0,2

89

0,1 88

0 D1

1 ozone (kg/t)

brightness (%ISO)

90

post color #

0,4

E.4P

1,2

UM200

1

90

0,5

91

brightness

0,8

89

0,6 88

0,4

87

0,2

86

0 R

2

post color #

92

brightness (%ISO)

0,7

E.4P

0,1

0,25

0,5

1

ozone (kg/t)

Fig. 14: Ozonation of Ozonation softwood kraft pulp, ECF "light" bleached 87 %ISO. Ozonation at g. 13: ImpactFig. of an post of treatment on brightness and brightness stability.

Eucalyptus pulp, sequence D0EpD1, 13:ozone Impact an ozone post treatment on brightness Fig.kraft 14: of softwood kraft pulp, ECF to “light” temperature. bleached to 87 %ISO. Ozonation at pH <5, cons. >30%, <5. and brightness stability. Eucalyptus kraft pulp, sequence

D0EpD1, pH <5.

ambient temperature.

91

bleached

92,0

brightness

E.4P

0,8

aged

90,0 89,0 88,0 87,0

90

0,6

89 0,4 88 0,2

87 86

0 D

86,0 0

0,1

0,25

0,5

1

post color #

brightness (%ISO)

brightness (%ISO)

91,0

P

D

60°C

70°C

P

D

P

80°C in D1

Fig. 16: Impact of Dtemperature stage temperature on final brightness Fig. 16: Impact of D1 stage on final brightness and brightness stability in D 1 pulp. and Initialbrightness Kappa number 13.4, in D0Dwith factor 0.23 at 50°C, with 4 kg/t H2O2 a stability EopD P bleaching of Eop softwood 0 1 chlorine, P with 2.5 after kg/t H2O2 at 80°C,13.4, all stages at 10% cons.0.23 at 5: Ozonation and15: aging: Post bleaching of softwood pulp with small amountsactive of ozone and brightness humid kraft pulp.

Initial Kappa number D0 with Fig. Ozonation and aging: Post kraft bleaching of softwood factor (E.4P), ozone addition pH<5, cons.amounts >30%, ambient temperature. kraft pulpatwith small of ozone and brightness 50°C, Eop with 4 kg/t H O at 75°C, 0.3 MPa O , D with 15 ozone (kg/t)

after humid aging (E.4P), ozone addition at pH<5, cons. >30%, ambient temperature.

extreme and peroxide amounts requiring such conditions should not be applied.

Final stage peracetic acid

Bleaching with peracetic acid is more academic because of its limited availability. It is typically distilled under vacuum from the equilibrium mixture of acetic acid, peracetic acid, hydrogen peroxide and water. The distillate is diluted with water to about 35%. It has to be stored at very low temperature to avoid the regeneration of the equilibrium. With current production found only in Finland, peracetic acid is consequently only applied in Finland and neighbouring Sweden. Within a bleaching sequence, peracetic acid can be seen as the “chlorine-free” alternative for an activation of residual lignin between peroxide and oxygen stages. Under this aspect, peracetic acid bleaching is a kind of a fossil remaining from the high times of TCF bleaching. On the other hand, peracetic acid under high density storage conditions has the advantage of being easily applied, as it fits into the pH profile and can give a final boost of brightness. In contrast to high density bleaching with hydrogen peroxide, there is no need to correct the pH from the normal slightly acidic regime to alkaline – an advantage for pulpandpapercanada.com

2

2

2

1

kg/t active chlorine, P with 2.5 kg/t H2O2 at 80°C, all stages at 10% cons.

peracetic acid.

Reactions of peracetic acid with lignin are oxidation and electrophile substitution. A likely reaction is hydroxylation of aromatic rings systems. Elevated temperature is required (>60°C).

As its dilution with water triggers the reformation of the starting materials, (hydrolysis into acetic acid and hydrogen peroxide), an extended reaction time does not yield an advantage. Figure 10 shows the impact of temperature. In these trials after 3 hours at 80°C, only traces of peracetic acid are remaining, while more than 1 kg/t of H2O2 could be measured as residual. Higher temperature favors the development of more brightness. However, the brighter pulp is – at least in the trials at lower temperature – the more sensitive it is to losses in reversion. As hydroxylation potentially generates quinones, these might be the cause for the lower stability. Conditions removing quinones, namely an alkalization after 30 minutes resulting in a Paa/P combination, not only improve brightness, they also result in better stability.

Effects are similar following a final D stage in ECF bleaching.

A softwood pulp with brightness 89.5% ISO and a post color number of 0.262 (humid aging) is bleached to 90.7 and 91.5% ISO with 1 kg/t and 5 kg/t peracetic acid, respectively. The treatOctober/November 2009 PULP & PAPER CANADA

29

T147 BRIGHTNESS STABILITY aged (Z)

92,0

aged (Z/P)

E.4P

91

0,2

90

0,1 89

brightness (%ISO)

91,0

post color #

brightness (%ISO)

92

bleached

0,3

brightness

90,0 89,0 88,0 87,0 86,0 0

0,1

0,25

0,5

1

0,1+P

0,25+P

0,5+P

1+P

ozone (kg/t)

88

0 D

DP

DPaa

DPaaP

18: the postoftreatment of softwood kraft pulpsmall amount Fig. 18: Fig. Effect of Effect the postoftreatment softwood kraft pulp (see Fig. 15) with peroxide(see treatment on brightness increase and stability.

Fig. 15) with small amounts of ozone followed by an

peroxide g. 17: Impact Paa/P bleaching afterbleaching a D stage.after Paa and stagesPaa at 80°C, peracetic acid, pHtreatment ~4; H2O2 on brightness increase and Fig.of17: Impact of Paa/P a DPstage. and 2 kg/talkaline stability. mount at 2 kg/t, alkali to reach pH 10.5.

P stages at 80°C, 2 kg/t peracetic acid, pH ~4; H O amount at 2 kg/t, alkali to reach pH 10.5.

2

2

ment also improves brightness stability.

Low temperature post bleaching – for example, in high density storage – dominantly gives an improved reversion, both in humid and dry aging. Figure 12 shows an example for post bleaching at lower temperature with extended retention time. In comparison to the application of alkaline peroxide, peracetic acid definitively has an advantage, as it can be conducted without the need to change the “normal” pH in storage. The most serious drawback should be the limited availability of distilled peracetic acid.

Final stage ozone

A final treatment of pulp with ozone had been recommended about a decade ago [11]. The post treatment with moderate amounts of ozone results in a steep brightness increase. Unfortunately, this brightenss is not very stable. Bleaching with 1 kg/t ozone lifts brightness by 3 points, but in humid reversion brightness decreases by 5 points. Thus, the gain in brightness is more than lost in reversion. Figure 13 has an example showing the reversion losses as post color numbers.

The negative impact of ozone on brightness stability is even visible following an application of rather tiny amounts of ozone.

Figures 14 and 15 have examples for post bleaching with ozone charges between 0.01% and 0.1% O3, corresponding to 100 g/t to 1 kg/t. The ECF “light” bleached softwood pulp’s brightness increases only slightly at the lowest input. On the other hand, the destabilization of the brightness in dry and humid aging is quite visible. Consequently, ozone should not be the concluding treatment in pulp bleaching. The answer to the reversion problem is an additional stage that removes the color forming compounds generated in ozonation. The destabilization becomes even more obvious in a direct comparison of brightness gained in bleaching and brightness lost in aging. Figure 15 shows these data. The brightness increase achieved with the ozone addition is more than lost in humid reversion, at levels higher than 0.25% ozone.

Combination of electrophiles and nucleophiles

As seen in the examples above, chromophores and their precursors are removed best under conditions that initially oxidize impurities gently enough to avoid cellulose chain oxidation. Complementing such a treatment, the concluding step should be an extraction combined with an oxidation. This is nothing more than the 30

PULP & PAPER CANADA October/November 2009

normal procedure of ECF bleaching. Consequently, the “best” way to the brightest and most stable pulp is the combination of electrophile chemicals with nucleophile chemicals.

Chlorine dioxide and peroxide (D1P)

The best conditions in chlorine dioxide bleaching and hydrogen peroxide bleaching have already been described: the combination of the D1 stage with a final P stage yields very good stability. It is improved further once the D1 stage temperature is as high as possible. This guarantees very effective oxidation and decomposition of chromophores and potential chromophores (precursors), and some of the halogenated intermediates are decomposed. The good selectivity of chlorine dioxide avoids cellulose oxidation, thus in contrast to oxidizers that are more aggressive, the low oxidation potential of ClO2 is an advantage.

The final peroxide stage cleans up what is left as impurities.

It oxidizes remaining quinones and extracts remaining carboxylic acids. In a conventional ECF bleaching process, the conclusion with the stages D-P offers high brightness with very good stability. Figure 16 shows an example.

Peracetic acid and peroxide (Paa/P)

A very logical combination of chemicals is peracetic acid and hydrogen peroxide. Peracetic acid is generated from hydrogen peroxide and acetic acid, and applied as distilled material or as an equilibrium mixture. In bleaching, it hydrolyzes rather rapidly during the reaction, due to the effects of dilution and temperature, into hydrogen peroxide and acetic acid. Therefore, any Paa stage has a residual of unreacted hydrogen peroxide. In cases where equilibrium peracetic acid was used, such a residual can be high and consequently can be used for alkaline peroxide bleaching [12].

As seen in the experiments with peracetic acid as a final stage, peracetic acid has a bleaching effect but does not necessarily improve the pulp’s brightness stability. Most likely, its reaction – hydroxylation, besides oxidation – generates quinones, which cause chromophore formation. The logical method for the destruction of these quinones is the application of alkaline hydrogen peroxide. This improves brightness stability, as Fig. 17 demonstrates. Following a D stage, an alkaline P stage increases brightness and improves stability. The final treatment with peracetic generates just half of the brightness increase compared to the P stage and just a minor decrease of the post color number pulpandpapercanada.com

PEER REVIEWED T148

brightness (%ISO)

E.4P(Z)

E.4P(Z/P)

UM200 (Z)

UM200 (Z/P)

0,7

92,0

0,6

91,0

0,5

90,0

0,4

89,0

0,3

88,0

0,2

87,0

0,1

86,0

post color #

bleached

93,0

0 0

0,1

0,25

0,5

1

0,1+P

0,25+P

0,5+P

1+P

ozone (kg/t)

• In high density storage bleaching, the application of distilled peracetic acid can be a good “second best” solution for a brightness increase not requiring an adjustment of pH. • A final P stage is a very effective way to improve and stabilize brightness.

• High temperature in D1 and a final P stage are a strongly recommended solution.

• The “best” option is definitely the combination of a small amount of ozone with a subsequent peroxide treatment. It yields top brightness and extremely low reversion.

19: Comparison of brightness ozonation Fig. 19:Fig. Comparison of brightness stability afterstability ozonationafter and following Z/P. Softwood kraft pulp bleached to 89% ISO, post treatment ozone (see Fig.Softwood 15) and peroxide kg/t,bleached 4 kg/t NaOH, 75°C, 1h, 10% cons.). Humid aging according to E4.P. andwith following Z/P. kraft (2 pulp to 89% LITERATURE 1. T. ROSENAU, A. POTTHAST, P. KOSMA; H. U. SUESS, N. NIMMERFROH. ISO, post treatment with ozone (see Fig. 15) and peroxide Chromophores in Aged Hardwood Pulp – Their Structure and Degradation (2 kg/t, 4 kg/t NaOH, 75°C, 1h, 10% cons.). Humid aging Potential, ISWFPC Durban, 2007, Proceedings; First Isolation and Identification according to E4.P. of Residual Chromophores From Aged Bleached Pulp Samples; Holzforschung,

- however, it does not require alkaline conditions. Alkalization after the peracetic acid treatment lifts brightness a bit further and results in the lowest post color number. Thus, the combination of Paa with peroxide is an option but not an attractive one.

Ozone and peroxide (Z/P or Zp/Ep)

Ozone was found to be very effective in the destruction of compounds surviving the bleaching process or formed in brightness reversion. In tests with the model compound 2.5-dihydroxy quinone, destruction was complete. However, it resulted in other intermediates, which formed highly colored chromophores in aging. It was necessary to follow ozonation with alkaline hydrogen peroxide to remove all potential chromophores. The combination of ozonation with peroxide bleaching resulted in extreme brightness and excellent brightness stability [13]. The post treatment with ozone and peroxide was also found to be very effective in pushing the brightness of a so called “poorly bleachable” hemlock softwood pulp [14]. Obviously, the sensitive intermediates generated by ozonation are easily destroyed by the nucleophile peroxo hydroxyl anion, HOO-. Figures 18 and 19 demonstrate the positive impact of a subsequent peroxide stage on brightness stability.

Figure 18 shows the brightness before and after humid reversion.

Figure 19 shows the post color numbers of both humid and dry reversion. With the concluding peroxide treatment, stability improves in both dry and humid aging.

Ozonation of double bonds yields an ozonide, a five member ring, with three oxygen atoms. These ozonides hydrolyze into a carbonic acid and an aldehyde or a ketone. The aldehyde structure can be oxidized further into another carbonic acid. This oxidation requires an additional oxidant, for example hydrogen peroxide.

Therefore, in a preferred application, hydrogen peroxide is added prior to ozone mixing and, directly after the ozone addition, alkali is added to complete the oxidation process [15].

Conclusions

Depending on the possibilities within a bleaching sequence, various options exist for the generation of improved brightness stability. However, the options are mill dependent, as not all chemicals are available everywhere. Distilled peracetic acid and ozone may not be an available solution in all mills. Other options in ECF bleaching are: • In D stages, brightness stability improves by using the highest available temperature. It can be as high as 85°C. pulpandpapercanada.com

61, 656-661, (2007).

2. A.-S. JÄÄSKELÄINEN, A.-M. SAARIAHO, P. MATOUSEK, A. PARKER, M. TOWRIE, T. VUORINEN. Characterization of Residual Lignin Structures by UV Raman Spectroscopy and the Possibilities of Raman Spectroscopy in the Visible Region with Kerr-Gated Fluorescence Rejection; 2003 ISWPC, Madison, WI, proceedings, 139 – 142.

3. C. W. DENCE, D. W. REEVE. Pulp Bleaching - Principles and Practice, Tappi Press, ISBN 0-89852-063-0, (1996), 393.

4. W. D. HARRISON, C. R. CALKINS. A Study of Variables Affecting Chlorine Dioxide Bleaching of Semibleached Sulphate Pulp, Tappi J. 38(11):641 - 648 (1955).

5. H. U. SUESS, C. LEPORINI FILHO. Progress in Bleaching to Top Brightness with Low Reversion, ABTCP 37th Annual Conference, São Paulo, 2004, proceedings.

6. J. GIERER. The Chemistry of Delignification, Holzforschung 36(2):55-64 (1982).

7. H. U. SUESS, C. LEPORINI FILHO. How to Improve Brightness Stability of Eucalyptus Kraft Pulp, ABTCP, 36 Congresso Internacional de Celulose e Papel, São Paulo, 2003, proceedings.

8. M. RAGNAR. Alkaline Extraction and a Control Strategy for the Chlorine Dioxide Charge to the Final Stage in DED Bleaching, Nordic P&P, 18(2):162-167 (2003).

9. H. U. SUESS, N. NIMMERFROH, J. D. KRONIS. The Naked Truth on Hot Peroxide Bleaching, Pulp & Paper Canada 99(4):T122 - T125 (1998).

10. H. U. SUESS, D. DAVIES. ECF Bleaching of Softwood Kraft Pulp: Understanding the Potential of Extraction, 92nd PAPTAC Conference, Montreal, Canada, Feb. 2006, proceedings.

11. Ch. CHIRAT, D. LACHENAL. Other Ways to Use Ozone in a Bleaching Sequence, Tappi J. 80(9):209-214 (1997).

12. P. WICKSTRÖM. Improved Brightness by Adding a Peracetic Acid Stage, 2005 International Pulp Bleaching Conf., Stockholm, proceedings.

13. T. ROSENAU, A. POTTHAST, P. KOSMA, H. U. SUESS, N. NIMMERFROH. Chromophores in Aged Hardwood Pulp – Their Structure and Degradation Potential, ISWFPC, Durban, 2007, proceedings.

14. H. U. SUESS, D. DAVIES, T. DIETZ. Pushing the Brightness Ceiling of “Difficult” Softwood Kraft Pulps, PAPTAC 94th Annual Meeting, Montreal, Feb. 2008, proceedings.

15. C. LEPORINI FILHO, H. U. SUESS, M. RODRIGUES DA SILVA, M. A. LOPES PEIXOTO. Addition of Hydrogen Peroxide to Ozonation for Improved Bleaching Results, ABTCP, 36 Congresso Internacional de Celulose e Papel, São Paulo, 2003, proceedings.

Résumé: Les chromophores qui restent dans la pâte après le blanchiment ou qui sont produits lors du vieillissement ont déjà fait l’objet de déterminations. La structure dominante de ces chromophores est une fraction d’hydroxyquinone stabilisée par résonance. Ces quinones sont détruites lors du blanchiment, quoique pas très facilement. On obtient le plus grand avantage en combinant des étapes. Le degré de blancheur et la stabilité de la blancheur s’améliorent, dans l’ordre, pour ces combinaisons : Paa/P < D/P < Z/P. Reference: D. DAVIES, T. DIETZ, H.U. SUESS. A Comparison of

Options to Improve Brightness Stability of Chemical Pulp, Pulp & Paper Canada 110(8):T142-T148 (October/November 2009). Paper presented at the 2008 International Pulp Bleaching Conference in Quebec City, Que., June 2-5, 2008. Not to be reproduced without permission of PAPTAC. Revised manuscript approved for publication by the Review Panel October 30, 2008.

Keywords: KRAFT, BLEACH, BRIGHTNESS, STABILITY, FINAL, PEROXIDE, CHLORINE DIOXIDE, OZONE, PERACETIC

October/November 2009 PULP & PAPER CANADA

31

BLEACHING COMPARISON T149

Bleachability of Pulps Produced From Different Kraft Pulping Methods: A Laboratory Study

By P. Fatehi, R.O. Malinen, and Y. Ni Abstract: In this work, the difference in the bleachability of Eucalyptus pulps produced in a mill from the SuperBatch (SB) and isothermal cooking (ITC) techniques and in a laboratory from a conventional batch process was evaluated. Two bleaching sequences were studied: D0EpD1 and ZEpD1. The results showed that, under similar conditions, the ITC pulp had the highest bleachability in both sequences. However, the SB pulp had the lowest bleachability in the D0EpD1 sequence, and higher bleachability than the lab-made pulps in the ZEpD1 sequence.

N

owadays, the kraft process is the dominant chemical pulping method in the world. It is generally performed in either batch or continuous systems.

These pulping methods have been continuously modified to enhance the pulping efficiency and to reduce operational cost. Two of the modified pulping technologies are SuperBatch (SB) and isothermal cooking (ITC). Each has its own advantages, e.g., the SB technology is flexible for different types of wood species, whereas the ITC process has a lower operational cost [1].

The cooking methodologies of ITC, SB, and laboratory systems are different [1-3]. The impregnation time is longer in the SB digester than in the ITC digester. All white liquor is added prior to the heating-up stage of cooking in the SB digester, while the white liquor is injected at different spots in the ITC digester. The cooking chemicals flow through the fixed bed of chips in the SB digester. On the contrary, the chips and cooking chemicals flow co-currently in the ITC digester until the outlet of black liquor. Then, the chips and washing liquor flow counter-currently to the bottom of the ITC digester. Furthermore, the cooking temperature in the SB digester is normally higher than in the ITC digester [1-3]. Different from the mill practice, in a laboratory set-up, the chips are preheated with black liquor or steam, and all of the cooking chemicals are usually added at the start of a cooking experiment.

The pulp reactivity towards bleaching chemicals in a bleaching sequence, i.e., the bleachability, is defined as the consumption of bleaching chemicals to obtain a target brightness [4,5]. It is mainly affected by the residual lignin structures, hexenuronic acid (HexA) content, and lignin-carbohydrate complex (LCC) of pulp [6-8]. Pulping technologies and process conditions are different pulpandpapercanada.com

for the ITC, SB and laboratory systems, which can cause changes in delignification kinetics and carbohydrate degradations, yielding pulps with different compositions and characteristics. They will, in turn, affect the subsequent bleaching performance.

There are many studies in the literature regarding the bleachability of lab-made pulps treated under different conditions [4,5,9], and commercial pulps produced from different modified technologies [10,11]. To compare the bleachability of lab- and mill-made pulps, the wood chips from the same source have to be cooked by mill and laboratory digesters to the same kappa number.

Then, a similar bleaching sequence should be applied to obtain a target brightness. Also, it is interesting to investigate the influences of cooking time and temperature on the bleachability of pulps at a constant H-factor [5,9,12].

In this work, two commercial pulp samples produced from the ITC and SB technologies and two lab-made pulp samples from different temperatures, but at the same H-factor, were studied. All of the four samples had similar kappa numbers. They were oxygen-delignified under similar conditions and bleached in the D0EpD1 and ZEpD1 sequences. Finally, the bleachability of the pulps was evaluated based on the formulas available in the literature.

P. FATEHI Dept. of Chemical Engineering & Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, N.B.

R.O. MALINEN Department of Pulp and Paper Technology, Asian Institute of Technology, Pathum thani, Thailand

EXPERIMENTAL

Materials Eucalyptus Camaldulensis chips were received from Advance Agro Company, Thailand. Also, unbleached pulps were collected from the brownstock washers of the ITC and SB digesters of the same company, and washed thoroughly.

Pulping The equivalent of 400g o.d. chips was cooked

Y. NI, Dept. of Chemical Engineering & Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, N.B.

October/November 2009 PULP & PAPER CANADA

33

T150 BLEACHING COMPARISON in a laboratory set-up consisting of 2.5 litre 6-autoclave air-heated digesters to the target kappa numbers of 15-16. The sulfidity and effective alkali were 30% and 22%, respectively. The liquid-to-wood ratio was 4:1. The autoclaves were heated from an ambient temperature to 80˚C in 12 minutes, and then to 165˚C or 155˚C in 70 minutes. The cooking step was conducted at 165˚C or 155˚C for 90 minutes or 225 minutes (H-factor 1018), respectively. The cooked pulps were thoroughly washed with tap water. Pulps were then disintegrated and screened. The screened pulps were centrifuged for 15 minutes and homogenized for 20 minutes. The labmade pulps at 165˚C or 155˚C were denoted as Lab1 or Lab2 samples, respectively.

Oxygen Delignification Oxygen delignification was carried out for all lab- and mill-made pulps in an electrically-heated CSR reactor, where oxygen was pressurized at 8 bars and mixed continuously in the presence of 2% NaOH and 0.4% MgSO4. The pulp consistency was 10%. Pulp washing, centrifuging, and homogenizing processes followed afterwards.

Bleaching Oxygen-delignified pulps were then subjected to the D0EpD1 and ZEpD1 bleaching sequences. Chlorine dioxide (D0 and D1), and extraction (Ep) treatments were all performed in sealed plastic bags in a thermostatically controlled water bath.

Ozone gas (Z) was applied at 0.5% on o.d. pulps from a Trailigaz OZC 1001 ozone generator. Ozone was introduced into the pressurized reactor by employing the solid piston compression method [13].

The ozone concentration in the feed and residual ozone was measured based on the iodometric method [13]. The charge of chlorine dioxide in the D0 stage was a kappa factor of 0.2, whereas it was 1.25% based on o.d. pulp in the D1 stage.

Also, the alkali and H2O2 charges were 1.2% and 0.8% on o.d. pulps in the Ep stage. The pH of each stage was adjusted by introducing an appropriate amount of NaOH or H2SO4, and was obtained by conducting the trial and error of initial pH. The consistency for the D0, D1, and Ep stages was 10%, whereas it was 8% in the ozone bleaching stage. Other conditions are listed in Table I. 34

HexA Analysis The hexenuronic (HexA) content of pulps was measured based on the HUT method [13]. HexA kappa was calculated (11.6 meq/kg HexA responded to one unit of kappa number) in accordance with the method proposed by Li and Gellestedt [14]. Based on the assumption that the total kappa number of unbleached Eucalyptus pulps is from HexA and residual lignin content [15], we calculated the lignin kappa by subtracting the HexA kappa from the total kappa number of pulps. Other required parameters were determined by following the relevant ISO and SCAN standard methods.

Bleachability Analysis One method of investigating the bleachability of pulps is to evaluate the brightness development of pulps versus the consumption of bleaching chemicals as the sum of oxidation equivalents (OXE) divided by the incoming lignin kappa for each stage in the sequences [5,16].

D0EpD1 sequence: OXE/lignin kappa= (1) OXE(D0)+OXE(P) + OXE(D1) Lignin kappa (Ep) Lignin kapa(O2)

ZEpD1sequence: OXE/lignin kappa= (2) OXE(Z) + OXE(P) + OXE(D1) Lignin kapa(O2) Lignin kappa (D0) Lignin kappa (Ep)

Another method is to investigate the brightness development of pulps against the chlorine dioxide consumption per total kappa number of oxygen delignified pulps.

This method is suitable for a sequence having chlorine dioxide bleaching stages.

Chlorine dioxide charge/total kappa= consumption(D0) + consumption (D1) Total Kappa (O2)

RESULTS AND DISCUSSION

(3)

Characteristics of Brownstock Pulp The characteristics of brownstock pulps are listed in Table II. The total kappa numbers of all pulps were fairly close.

Since the lignin content of pulp is roughly 0.15 of its kappa number [17], these results imply similar lignin content of pulps. This similarity permitted us to compare their bleachability. It is evident in Table II that the HexA contents differed remarkably. To illustrate the reason for such differences, the preceding cook-

PULP & PAPER CANADA October/November 2009

ing procedure of each pulp should be considered. It was reported that the dosage of cooking chemicals and the cooking time affect the HexA formation and its removal during the cooking process [5,18]. In fact, the higher the initial EA concentration, the faster the HexA formation in the initial phase, but the greater the HexA loss happens in the later stage of the cooking process [18]. Since all the fresh cooking chemicals are added at once to the digester in the SB technology, such a process leads to the formation of HexA at the early stage of the cooking, and the degradation of HexA at the later stages, resulting in a low HexA content in the SB pulp (Table II) [19-21]. Buchert et al. also reported a low HexA content during SB pulping [21,22].

For the ITC technology, the EA is added to the digester at different spots in the way that the minimum requirement of fresh EA is always met for pulping [2,3]. As such, the limited presence of the EA during pulping leads to the gradual formation of HexA, causing the ITC pulp with a high HexA content (Table II). The lower HexA content of Lab1 vs. Lab2 pulps is ascribed to their higher temperature during cooking. As reported in the literature, the higher the cooking temperature, the faster the HexA formation at the early stage of cooking, hence the faster degradation of HexA at the later stage of cooking, resulting in a lower HexA content [22].

The influence of cooking chemicals and pulping conditions on the pulp characteristics was reported in the literature [16,23]. For the SB technology, the addition of all chemicals at the beginning of cooking caused perhaps severe carbohydrate degradation, particularly during the initial phase, leading to a very low viscosity in the SB pulp (Table II). The ITC pulp, however, showed the highest pulp viscosity. The higher viscosity of ITC compared to conventional-made Eucalyptus pulp was reported in the literature [1]. Also, the viscosity and HexA content of Lab1 pulp were lower than those of the Lab2 pulp. The lower viscosity of Lab1 pulp is most likely attributed to more serious carbohydrate degradation at a higher cooking temperature (165˚C) in comparison with a cooking temperature of 155 ˚C for Lab2 pulp. The influence of cooking temperature on carbohydrate degradation pulpandpapercanada.com

PEER REVIEWED T151

Fig. 1: Brightness development in the D1 stage of the D0EpD1 sequence.

has been reported in the literature [24].

Characteristics of Oxygen Delignified Pulps The characteristics of oxygen delignified pulps are listed in Table III. The kappa number of the ITC pulp was the highest among all, which is due to its highest HexA content. Oxygen delignification is not favorable for HexA removal, as shown in Table III. This is in agreement with the literature results [8,25]. Additionally, the lab-made pulps are much easier to delignify, probably due to less lignin condensation in the pulping process, which results in a higher lignin reactivity during oxygen delignification. Furthermore, less than 10% HexA and viscosity reductions occurred during oxygen delignification (see Table III). These results are consistent with earlier findings about the influencing factors on the bleachability of Eucalyptus pulp, and the HexA impact on the optical properties of pulp under different laboratory cooking and oxygen delignifying conditions [26,27].

Bleachability in D0EpD1 Sequence Figure 1 shows the brightness increase of pulpandpapercanada.com

Fig. 2: HexA and viscosity reductions of pulps versus brightness development in the D0EpD1 bleaching sequence.

pulps in the D1 stage of the D0EpD1 sequence, calculated in accordance with equations 1 and 3. It is inferred that the ITC pulp had the least bleaching chemical requirement (as OXE/lignin kappa and chlorine dioxide consumption/total kappa) to obtain 89% ISO brightness, whereas the SB pulp had the highest consumption.

Therefore, the bleachability of the ITC pulp was much higher than that of laband SB-made pulps. Since oxygen delignification was conducted under similar conditions for all pulps, the difference in the bleachability of pulps would be attributed to the difference in their pulping processes.

The highest bleachability of the ITC pulp based on both formulas (Fig. 1) implies that its residual chromopheric structures were relatively more reactive than those of other pulps. The higher bleachability of Eucalyptus pulp having higher HexA content was reported in the literature for ECF bleaching systems [6,13]. In these systems, the HexA content was claimed to be an influencing factor for the bleachability. The lowest reactivity of the residual lignin structures of the SB pulp can be attributed to the presence of lignin-carbohydrate compounds (LCC) and condensed

structures. In the literature, SB pulp was known to contain more condensed lignin structures, resulting in the lower reactivity of residual lignin structure towards alkaline hydrogen peroxide bleaching [19,20].

One can also find from Fig. 1 that the two lab-made pulp samples had similar bleachability in the D1 stage of the D0EpD1 sequence, indicating that increasing the maximum cooking temperature from 155째C to 165째C, while maintaining the same H-factor, had a negligible effect on the subsequent bleaching processes.

Similar results were obtained in the literature that the cooking temperature had a limited influence on the bleachability of Eucalyptus pulp at different H-factors in the D0E1D1E2D2 sequence [4].

Figure 2 shows the viscosity and HexA reductions in the D0EpD1 bleaching sequence. One can find that the viscosity and HexA content of pulps were reduced as the brightness increased. The highest viscosity of the ITC pulp was maintained in the subsequent D0EpD1 bleaching sequence (Fig. 2). In contrast, the SB pulp had the lowest viscosity of the fully bleached pulp after the D0EpD1 bleaching sequence (Fig. 2).

October/November 2009 PULP & PAPER CANADA

35

T152 BLEACHING COMPARISON Table I: Conditions of Oxygen Delignification and Subsequent Bleaching Stages Parameters/stages O

D0

Z

Temperature, ˚C Time, min End pH

60 60 2-3

50 90 10 90 2-3 10.5-11.5

95 60 10.5-11.5

Ep

D1 70 180 3-5

Table II: Characteristics of Brownstock Pulps Parameter

SB

ITC

Lab1

Lab2

Total kappa Lignin kappa HexA kappa HexA content, meq/kg Viscosity ml/g Yield

13.4 10.2 3.2 37.1 627 N/A*

15.4 10 5.4 63.2 930 N/A*

15.7 11.8 3.9 45.8 661 46.8

16.4 11.9 4.5 53.1 769 46.3

Fig. 3: Brightness development of pulps versus their chemical consumption in the D1 stage of the ZEpD1 sequence.

*Not Available

Table III: Characteristics of Oxygen-Delignified Pulps Parameter

SB

ITC

Lab1

Lab2

Kappa number Lignin kappa HexA kappa HexA content, meq/kg Viscosity, ml/g Yield, % lignin kappa reduction,% HexA kappa reduction,% Viscosity reduction,%

8.4 5.5 2.9 34.1 562 97.6 46 9.3 10.3

11.2 6 5.2 59.9 830 98.6 40 3.7 10.7

8.6 5 3.6 42.2 613 97.8 57 7.7 7.2

9.3 5 4.3 50.1 712 98.3 58 4.4 7.4

Table IV Brightness (%ISO) of Brownstock, Oxygen-Delignified and Fully Bleached Pulps in the D0EpD1 and ZEpD1 Sequences

Brownstock Oxygen delignified D0EpD1 ZEpD1

SB

ITC

Lab1

Lab2

35.3 50.2 87.5 88.0

37.2 52.5 89.5 88.5

31.5 52.5 88.0 85.5

31.3 51.8 88.0 86.0

Based on the results in Figs. 1 and 2, we concluded that the ITC pulp had the highest reactivity, and also the most carbohydrate degradation and HexA removal in the D0EpD1 bleaching sequence. In contrast, the brightness development, viscosity, and HexA drops were the least for the SB pulp, compared to those of other pulps in this sequence.

The lower reactivity of the SB pulp was ascribed to the presence of condensed structures [19,20]. Also, the formation of LCC was reported to affect the 36

Fig. 4: HexA and viscosity reductions of pulps versus brightness development in the ZEpD1 bleaching sequence

bleachability of pulp in an ECF bleaching sequence [8].

Bleachability in ZEpD1 Sequence Figure 3 shows the brightness increase in the D1 stage of the ZEpD1 sequence versus the bleaching chemical consumptions, calculated in accordance with equation 2.

It is inferred from the figure that the ITC pulp had the highest bleachability among all pulps to obtain the target brightness (89% ISO). Also, the SB pulp had higher bleachability than the lab-made pulps.

PULP & PAPER CANADA October/November 2009

Two factors seem to influence the bleachability of pulps in the ZEpD1 sequence: i) the reactivity of residual lignin structure and ii) the ratio of HexA to lignin.

For the ITC pulp, one might expect that it had the most reactive residual lignin structures towards this bleaching sequence so that the highest bleachability was obtained. It was reported that ozone reacts preferentially with HexA [28]. As shown in Table III, the SB pulp had the lowest HexA content after oxygen delignification. As a result, more ozone would pulpandpapercanada.com

PEER REVIEWED T153 be available for the residual lignin of the SB pulp, increasing its bleachability. Such a phenomenon might be responsible for the higher bleachability of the SB pulp versus the lab-made pulps.

Figure 4 shows the HexA drop and viscosity reductions of pulps against the brightness developments in the ZEpD1 sequence. Similar to the D0EpD1 sequence, the ITC pulp had the highest HexA and viscosity drop in this bleaching sequence, in contrast to those of the SB pulps.

The results presented above indicated that the pulp bleachability is different in the two sequences studied, D0EpD1 and ZEpD1. This is partially due to the fact that chlorine dioxide preferentially reacts with lignin, while ozone is more reactive with HexA [13,29]. Also, it is known that ozone is capable of degrading both phenolic and non-phenolic lignin structures [30,31], whereas chlorine dioxide mainly degrades phenolic lignin structures [17,32].

The viscosity drops for pulps bleached in the D0EpD1 sequence were less pronounced than those of pulps bleached in the ZEpD1 sequence. This is because chlorine dioxide is more selective than ozone, and the carbohydrate degradation is more serious in ozone bleaching than in chlorine dioxide bleaching [11,17,28].

Relation between Brightness of Unbleached and Fully Bleached Pulps The brightness of brownstock, oxygendelignified, and fully-bleached pulps in both sequences is listed in Table IV. The brightness of mill-made brownstock pulps (ITC and SB) was somewhat higher than those of the lab-made brownstock pulps.

However, all pulps had approximately similar brightness after the oxygen delignification process. By consuming similar bleaching chemicals (700 OXE/lignin kappa) in both bleaching sequences, pulps tended to have different final brightness.

The final brightness of pulps bleached in the ZEpD1 sequences correlated well to the unbleached pulp brightness despite their similar brightness after the oxygen delignification stage. On the other hand, there was no correlation between the brightness of brownstock and fully bleached pulps in the D0EpD1 sequence.

In the literature, no correlation was found between the brightness of brownstock pulpandpapercanada.com

and fully bleached pulps from the ECF and TCF bleaching sequences [4,9].

CONCLUSIONS

The different pulping methods affected the pulp composition and characteristics significantly. ITC-, SB-, and lab-made pulps with similar kappa numbers possessed remarkably different viscosities and HexA contents. The ITC pulp responded to the oxygen delignification the least among all pulps studied. However, it had the highest bleachability in the D0EpD1 and ZEpD1 sequences. On the contrary, the SB pulp had the lowest bleachability in the D0EpD1 sequence, while possessing a higher bleachability than the lab-made pulps in the ZEpD1 sequence. The ITC pulp had the highest decreases in viscosity and HexA content in both sequences, while the SB pulp had the least. The viscosity drops in the D0EpD1 sequence were less than those in the ZEpD1 sequence.

Additionally, the results of lab-made pulps revealed that the temperature of cooking process at a constant H-factor affected the HexA content and viscosity of brownstock pulps. However, it had a negligible effect on bleachability during the subsequent D0EpD1 and ZEpD1 bleaching sequences.

The final brightness of pulps bleached in the ZEpD1 sequence was closely correlated to the brightness of unbleached pulps.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the Finnish government for partially financing this research. The other portion of this work was gratefully supported by the AIT fellowship. Also, Advance Agro Co. is thanked for providing the pulps, chips, and bleaching chemicals for this project.

LITERATURE

1. GULLICHSEN, J., PAULAPURO, H. Chemical Pulping, Papermaking Science and Technology, B6A, 1st Edition, Finland, Fapet Oy, A493-A570 (1999).

2. NATERCIA, C.P., FERNANDES, J., CASTRO, A.A.M. Steady-State Simulation of a Continuous Moving Bed Reactor in the Pulp and Paper Industry, Chem. Eng. Sci., 55 (18): 3729-3738 (1999).

3. TRAN, A.V. Characterization of a Conventional Kamyr Continuous Digester Producing Hardwood Kraft Pulp, Appita J., 58 (1): 22-27 (2005).

4. NETO P.C., EVTUGUIN, D.V., FUTADO, F.P., SOUSA, A.P.M. Effect of Pulping Conditions on the ECF Bleachability of Eucalyptus Globulus Kraft Pulps, Ind. Eng. Chem. Res., 41: 6200-6206 (2002).

5. GUSTAVSSON, C., SJÖSTRÖM, K., AL-DAJANI, W. The Influence of Cooking Conditions on the Bleachability and Chemical Structure of Kraft Pulps, Nordic Pulp Pap. Res. J., 14 (1): 71-81 (1999).

6. COSTA, M.M., COLODETTE, J.L. The Impact of Kappa Number Composition on Eucalyptus Kraft Pulp Bleachability, Brazilian J. Chem. Eng., 24 (1): 61-71 (2007).

7. NETO, C.P.; DANIEL A.I.D., EVTUGUIN, D., SILVESTRE, A.J. Influence of Kappa Number of Unbleached Pulp on ECF Bleachability of Eucalyptus Globulus Kraft Pulps, Proc. 2000 International Pulp Bleaching Conference, PAPTAC, Halifax, Canada, 2000.

8. JIANG,Z.H., VAN LIEROP, B., NOLIN A., BERRY, R. A New Insight into the Bleachability of Kraft Pulps, J. Pulp Pap. Sci., 29 (2): 54-58 (2003).

9. AL-DAJANI, W., GELLERSTEDT, G. The Effect of Polysulphide Pre-treatment and Cooking Parameters on the Chemical Properties and TCF Bleachability of Alkaline Pulps, Pulp Pap. Canada, 102 (8): 44-48 (2001).

10. FUTADO, F.P., EVTUGUIN, D.V. GOMES, T.M. Effect of the Acid Stage in ECF Bleaching on Eucalyptus Globulus Kraft Pulp Bleachability and Strength, Pulp Pap. Canada, 102 (12): 89-92 (2001).

11. DA SILVA, M.R., PEOXOTO, M.A.L. Mill Experience Using a Hot Acid Stage for Eucalyptus Kraft Pulp Bleaching, Proc. 2002 TAPPI International Pulp Bleaching Conference, San Diego, USA, 287-297, 2002.

12. VUORINEN, T., FAGERSTRÖM, P., BUCHERT J., TENKANEN, M.,TELEMAN, A. Selective Hydrolysis of Hexenuronic Acid Groups and its Application in ECF and TCF Bleaching of Kraft Pulps, J. Pulp Pap. Sci., 25 (5): 155-162 (1999).

13. KARIM, M.R., MALINEN, R.O. Suitability of the Combined Use of Chlorine Dioxide and Ozone in Prebleaching of Eucalyptus Camaldulensis Kraft Pulp, Appita J., 60 (3): 228-234 (2007).

14. LI, J., GELLERSTEDT, G. The Contribution to Kappa Number from Hexenuronic Acid Groups in Pulp Xylan, Carbohydrate Res., 302: 213-218 (1997).

15. COSTA, M.M., COLODETTE, J.L. The Effect of Kraft Pulp Composition on its Bleachability, Proc.

2002 International Pulp Bleaching Conference, Portland, USA, 195-213, 2002.

16. SJÖSTRÖM, K. Kraft Cooking with Varying Alkali Concentration-Influence on TCF Bleachability, Nordic Pulp Pap Res., 13 (1): 57-63 (1998).

17. TOVEN K., GELLERSTEDT, G, KLEPPE, P.,

Résumé: Nous avons comparé l’aptitude au blanchiment de pâtes d’eucalyptus produites selon les procédés de cuisson SuperBatchMD (SB) et ITCMD (cuisson isothermique), et aussi en laboratoire à l’aide d’une méthode classique en discontinue. Nous avons étudié deux séquences de blanchiment : D0EpD1 et ZEpD1. Les résultats indiquent que, dans des circonstances similaires, la pâte ITC possédait la meilleure aptitude au blanchiment selon les deux séquences. Toutefois, la pâte SB présentait la plus faible aptitude au blanchiment dans la séquence D0EpD1 et une plus grande aptitude au blanchiment que les pâtes fabriquées en laboratoire selon la séquence ZEpD1.

Reference: FATEHI P., MALINEN, R., NI, Y. Bleachability of Pulps Produced from Different Kraft Cooking Methods: A Laboratory Study. Pulp & Paper Canada 110 (8) T149-T154 (October/ November 2009). Paper presented at the 2008 International Pulp Bleaching Conference in Quebec City, Que., June 2-5, 2008. Not to be reproduced without permission of PAPTAC. Manuscript received May 05, 2008. Revised manuscript approved for publication by the Review Panel April 8, 2009.

Keywords: ISOTHERMAL COOKING, SUPERBATCH, HEXENURONIC ACID, BLEACHABILITY, BLEACHING COMPARISON, PULPING PARAMETERS, LABORATORY COOKING.

October/November 2009 PULP & PAPER CANADA

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T154 BLEACHING COMPARISON MOE, S. Use of Chlorine Dioxide and Ozone in Combination in Prebleaching, J. Pulp Pap. Sci., 28 (9): 305-310 (2002).

18. CHAI, X.S., LOU, Q., YOON, S.H., ZHU, J.Y. The Fate of Hexenuronic Acid Groups during Kraft Pulping of Hardwoods, J. Pulp Pap. Sci., 27 (12): 403-406 (2001).

19. WIDSTEN, P., HORTLING, B., POPPIUS-LEVIN, K. Reactions of Conventional and SuperBatch Pulp Residual Lignins with Peroxyformic Acid, J. Wood Chem. Tech., 23 (3): 305-323 (2003).

20. WIDSTEN, P., HORTLING, B., POPPIUS-LEVIN, K. Treatment of Conventional Kraft and SB Pulp Residual Lignins with Alkaline Hydrogen Peroxide, J. Pulp Pap. Sci., 30 (7): 191-196 (2004).

21. BUCHERT, J., LAINE, J., TENKANEN, M., VUORINEN, T., VIILAI, L. Characterization of Uronic Acids during Kraft and SuperBatch Pulping, Proc.

1997 International Symposium on Wood Pulping Chemistry, ISWPC, V1, Montreal, Canada, 1997.

22. BUCHERT, J., TENKANEN, M., TAMMINEN, T.

Characterization of Carboxylic Acids during Kraft and SuperBatch Pulping, Tappi J., 84 (4): 70-78 (2001).

23. GULLICHSEN, J., PAULAPURO, H. Forest Product Chemistry, Papermaking Science and Technology, B3, 1st edition, Finland, Fapet Oy, 59-106 (1999).

24. COLODETTE, J.L. Influence of Pulping Conditions on Hardwood Pulp Yield, Quality and Bleachability, Proc. 2000 International Pulp Bleaching Conference, PAPTAC, Halifax, Canada, 2000.

25. SHIN, S.J., SCHROEDER, L.R., LAI, Y.Z. Understanding Factors Contributing to Low Oxygen Delignification of Hardwood Kraft Pulps, J. Wood chem.

Tech., 26: 5-20 (2006).

26. MALINEN, R.O., ZHAO, H.P. Evaluation of the Bleachability of Eucalyptus Camaldulensis Kraft Pulp, Proc. 2005 International Pulp Bleaching Conference, Stockholm, Sweden, 2005.

27. MALINEN, R.O., NHAN, T.T. Control of Hexenuronic Acid Content in Bleached Pulp and its Effects in Optical Properties of Pulp, Proc. 60th Appita Annual Conference, Melbourne, Australia, 2006.

28. RAGNAR, M. On the Importance of the Structural Composition of Pulp for the Selectivity of Ozone and Chlorine Dioxide Bleaching, Nordic Pulp Pap. Res. J., 16 (1): 72-79 (2001).

29. FATEHI, P., MALINEN, R. O., NI, Y. Removal of Hexenuronic Acid from Eucalyptus Kraft Pulps during Chlorine Dioxide- and Ozone based ECF Bleaching Sequence, Appita J, 62 (3): 212-218 (2009).

30. ZHANG, Y., KANG, G., NI, Y., VAN HEININGEN, A.R. P. Degradation of Carbohydrate Model Compounds during Ozone Treatment, J. Pulp Paper Science, 23 (1), J23-27 (1997).

31. KANG, G., ZHANG, Y., NI, Y., and VAN HEININGEN, A.R. P. Influence of Lignins on the Degradation of Cellulose during Ozone Bleaching, J. Wood Chem Technol., 15 (4), 413-430 (1995) 32. NI, Y., SHEN, X., VAN HEININGEN, A.R. P. Studies on the Reaction of Phenolic and Non-Phenolic Lignin Model Compounds with Chlorine Dioxide, J. Wood Chem. Technol., 14 (2), 243-262 (1994).

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PULP & PAPER CANADA October/November 2009

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LIME KILN T155

Upgrading a Lime Kiln Chain Section to Reduce Dust Loading and Improve Thermal Efficiency

By O. Websdale, B. Downing, and H. Tran Abstract: Due to a 50% increase in pulp production at DMI PRPD, purchased quick lime was used to supplement the mill’s lime requirements. Excessive dust recycle in the kiln hindered kiln production and was the main cause for poor kiln thermal efficiency. The inefficient, high maintenance kiln chain system was replaced by a high efficiency kiln chain system. This greatly decreased kiln natural gas consumption and allowed sustainable kiln production at high rates, thus reducing quick lime purchases.

D

aishowa Marubeni International (DMI) Peace River Pulp Division (PRPD) in Peace River, Alberta, is a single-line kraft mill originally designed to produce 1100 air dried metric tons/ day (admt/d) bleached hardwood (aspen) pulp.

Pulp production has increased steadily since the mill startup in mid-1990, and reached 1510 admt/d by mid-2002. In late 2002, the digester was converted to a downflow low-solids unit, allowing a further increase in pulp production.

The mill is currently producing 1650 admt/d, a 50% increase over the design capacity.

PRPD’s lime kiln was orginially designed to produce 270 metric tons/d of lime (CaO). By the time the downflow low-solids project was streamlined in late 2003, the kiln production rate required to support the mill maximum sustainable rate (MSR) reached 358 mt/d of lime. The kiln could not support such high mill production rates, and its reburned lime production had to be supplemented with purchased quick lime, representing a significant operating cost to the mill. In order to support the current mill MSR of 1650 admt/d, the kiln must produce 384 mt/d of lime, 42% above its design capacity.

Excessive dust recycle in the kiln was the main factor limiting kiln production. In late 2003, the dust loading on the lime kiln was greater than 50% of the total dry lime mud fed to the kiln.

This high dust loading frequently overwhelmed the dust handling systems, necessitating purging of dust from the system. Dust purging introduced an undesirable kiln operational “swing” that limited throughput on the kiln, negatively impacted lime quality, increased landfill costs, and presented a health hazard and housekeeping nuisance.

In 2003, poor heat transfer in the kiln resulted in excessive natural gas consumption and in high pulpandpapercanada.com

kiln feed end gas temperatures; this had to be controlled via the addition of water to prevent thermal damage to the dust handling systems.

Investigation into both of these issues revealed that the primary obstacle to reducing dust loading and to improving kiln thermal efficiency was a poorly designed kiln chain system. In June 2004, a new, high efficiency chain system was installed to replace the old, inefficient, high maintenance chain system. The upgrade greatly reduced dust loading and increased kiln thermal efficiency.

This paper describes lime production at PRPD, the problems encountered with the old chain system, the installation of the new chain system to overcome the problem, and improvements in kiln operation as a result of the chain section upgrade.

O. WEBSDALE Peace River Pulp Division, Daishowa Marubeni International Ltd., Peace River, Alta.

LIME PRODUCTION AT PRPD

Lime Kiln The lime kiln at PRPD is a 1990 F.L. Schmidt unit, 3.5 m ID x 101.5 m in length, designed to produce 270 mt/d lime. The kiln was originally equipped with nine product coolers, two product dams (one in the product discharge zone and one in the burning zone), four continuous rows of product lifters in the intermediate zone, 3.5 m of feed spirals, and a Fuller round-link curtain type chain system which extended over a 14 m section of the kiln at the feed end. The product dam in the burning zone and all of the lifters were removed in September 1997.

In June 2003, due to the recurrent formation of rings in the kiln, two rows of Powershot nozzles were installed over a 54 m section along the kiln axis in the middle of the kiln. Powershot nozzles allow pressurized carbon dioxide charges to be inserted through the kiln shell into a ring; the carbon dioxide charges are then detonated remotely to remove the ring.

B. DOWNING Peace River Pulp Division, Daishowa Marubeni International Ltd., Peace River, Alta.

H. TRAN Pulp & Paper Centre, University of Toronto, Toronto

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T156 LIME KILN

Fig. 2. High gas velocity and solids accumulation at the ringing location

Fig. 1. Ring formation in the PRPD lime kiln

Kiln Feed Lime mud slurry from the causticizing plant is fed into a lime mud precoat filter where the lime mud is washed and dewatered to 75 to 80% solids before it enters the lime kiln. Purchased lime rock is also used as make-up for process losses and on occasions when maintenance work is required on the lime mud precoat filter and/or associated equipment.

Kiln Dust Handling An electrostatic precipitator is used to remove entrained fine dust particles from the gas stream exiting the kiln, and a vacuum dust handling system recycles the dust collected by the precipitator to the feed end of the kiln. A second dust handling system, which is pressurized, is sometimes used when maintenance work is required on the primary dust handling system. The vacuum dust handling system is designed to move a maximum dust load of 288 mt/d, while the back-up pressurized dust handling system has a maximum capacity of 144 mt/d. Both systems can be operated simultaneously, although when so operated their capacities are not entirely cumulative.

Kiln Fuel Natural gas is the primary fuel for the kiln and is burned via an Andritz burner. Concentrated non-condensable gases (CNCG) from the digester and stripper off-gasses (SOG) have historically been burned in the kiln. Since 2005, CNCG has been burned in the power boiler, but SOG is still burned in the kiln.

Product Lime The residual carbonate content of the product lime is targeted at 3 wt%. The inert content is typically around 7 wt%, giving the product lime a customary availability of 90%.

KILN ISSUES

Dust Loading In late 2002, operational difficulties with the kiln dust recycle system became paramount. At a lime production rate of 337 mt/d, the dust recycle loading on the kiln was measured in excess of 328 mt/d. This exceptionally high dust recycle in the kiln equated to 40

PULP & PAPER CANADA October/November 2009

Fig. 3. Thinned and warped round-link chain

roughly 55% of the total lime mud feed to the kiln and caused frequent plugging of both dust handling systems. To prevent kiln downtime resulting from plugged dust handling systems, it was necessary to purge dust from the dust recycle system. This was accomplished by temporarily shutting down the dust handling system(s) and diverting the dust collected by the precipitator to a dust bunker.

Recycled dust is an integral part of normal kiln load. Dust purging lowered a portion of the normal kiln load and thus resulted in variable kiln load (solids bed depth) along the kiln length.

This made it difficult to judge how much heat was required at any one time to adequately calcine the lime mud feed, and resulted in undesirable kiln thermal cycles. Kiln thermal cycles exacerbated ring buildup downstream of the chain section (Fig. 1). Ring formation accelerated local gas velocities and allowed more solids to accumulate behind the ring, as schematically shown in Fig. 2. Some of the accumulated solids were then entrained in the high velocity gas stream as dust. Thus a cycle of dust purging → thermal cycle → ring formation → accelerated gas velocities → entrained dust → dust purging continued to perpetuate itself.

Heat Transfer Efficiency Increased lime production necessitated burning additional natural gas. The original round-link chain was unable to withstand the extra heat and began to thin and burn-out more rapidly (Fig. 3).

Hangers began to fail and entire lengths of chain appeared in the product lump crusher. The resulting decrease in heat transfer surface area in the chain section increased natural gas consumption and caused feed end gas temperatures to exceed 300°C. High exit gas temperatures, in turn, thermally damaged the baghouse pulpandpapercanada.com

PEER REVIEWED T157

Fig. 4. Trickle valve installed on outlet of baghouse Fig. 5. “Dust scoops” formed by round-link chain

Fig. 7. Mud feed screw shroud (right) and feed spirals (left and bottom)

Fig. 6. (A) Jammbco’s diamond-link heat exchange chain metal, and (B) Econoliner as an insulation medium and an attachment point for diamond-link heat exchange chain.

socks of the dust handling systems, thereby exacerbating the dust handling issues.

In order to reduce the feed end gas temperature to an acceptable level, the solids content of the lime mud from the precoat filter was lowered to 70-72%, and a water addition control loop was installed on the mud feed in late 2003. Both actions reduced the thermal efficiency and increased the natural gas consumption of the kiln.

LIME KILN UPGRADES

Vacuum Dust Handling System Upgrade Two problems with the vacuum dust handling system were identified in mid-2003.

First, although the system was rated for 288 mt/d, investigation of individual equipment capacities revealed that most of the equipment possessed capacity in excess of the rated amount, with the exception of one rotary feeder.

Second, tramp air pulled into the baghouse of the vacuum dust handling system fluidized the dust in the baghouse. The pulpandpapercanada.com

dust collected in the baghouse until it eventually collapsed into the mud feed screw in large spurts. Due to lack of time available to moisten the large amounts of dust being periodically dumped into the mud feed screw, the dust was immediately entrained in the gas stream upon entering the kiln.

To combat the first problem, the rotary feeder limiting the capacity of the vacuum dust handling system was sped up a number of times, until a capacity compatible with the remainder of the system was achieved. To address the second problem, a trickle valve (Fig. 4) was installed on the outlet of the baghouse; this valve effectively prevented tramp air from entering the baghouse and evened out the flow of dust into the lime mud feed screw.

Chain Section Upgrade Prior to June 2004, the chain section consisted of 14 m of roundlink curtain chain suspended from tombstone-style hangers.

Castable refractory was utilized to minimize heat loss through the kiln shell in the chain section. There were two main concerns with the chain section: • Frequent burn-out and thinning of the chain had reduced the chain density in the kiln to 112 kg/mt lime, which was significantly lower than the recommended chain density of 150 kg/ mt lime for modern lime kilns.

• Inherent in the design of round-link chain was the formation of small “dust scoops” by link connections (Fig. 5). The mud colOctober/November 2009 PULP & PAPER CANADA

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T158 LIME KILN

Fig. 8. Amount of lime dust and lime mud landfilled since 2003.

lected by these “dust scoops” was carried out of the solids bed and released into the gas steam as the kiln rotated, thereby increasing dust entrainment.

In June 2004, the kiln cold end internals were completely removed, and an entirely new chain system was installed. The new chain system consisted of: a shroud over the lime mud feed screw; 3.5 m of 813 mm tall, angled feed spirals; 5.6 m of carbonsteel round-link chain in the drying zone; 9.2 m of stainless-steel diamond-link heat exchange chain in the preheating zone (Fig. 6A); and metal econoliner plates with replaceable link hangar caps and bases (Fig. 6B). The complete new chain system was supplied by Jammbco of Barrie, Ont. The new chain system aimed to reduce dust entrainment in the gas stream via the following design specifics: 1. The shroud over the lime mud feed screw (Fig. 7) prevented dust being recycled into the kiln from immediately entraining in the exiting gas.

2. The high angle feed spirals (Fig. 7) promoted mixing and turnover of solids in the feed end, preventing the top layer of mud from drying out prematurely, and thereby getting entrained in the gas steam.

3. The relatively sharp edge diamond-link heat exchange chain (Fig. 6A) was designed to cut through the lime mud layer rather than scooping it up, as it is the case for the round-link chain (Fig. 5). Furthermore, the number of link connections was halved as a result of the larger surface area inherent to the diamond-link chain style. The weight and metallurgy of the diamond-link chain also made it more resistant to thinning and burn-out.

4. The metal econoliners (Fig. 6B) replaced castable refractory as the insulating medium in the chain section. The econoliners did not reduce the inside diameter of the kiln in the chain section as much as castable refractory; this reduced gas velocities, thereby reducing dust entrainment in the chain section.

The original proposal for the chain system upgrade recommended a final chain density of 150 kg/mt lime. However, results of a CFD modeling study of the proposed chain upgrade indicated the feed end gas temperature would be reduced too much.

Exit gas temperatures lower than 180°C for extended periods of time were a concern because of the potential for dewpoint corrosion in the precipitator. Therefore, some of the diamond-link heat exchange chain was not installed and the chain density after 42

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Fig. 9. Kiln production duration curves

Fig. 10. Amount of purchased quick lime since 2003

the chain system upgrade was 124 kg/mt lime.

Installation of Additional Heat Exchange Chain Two years of subsequent operation showed that the chain system upgrade would not result in excessively low exit gas temperatures.

In June 2006, five more rings of diamond-link heat exchange chain were added at the hot end of the chain section. This increased the chain density to 146 kg/mt lime.

RESULTS OF KILN UPGRADES

Effect on Dust Loading The modifications to the vacuum dust handling system implemented in late 2003 increased its capacity to the point where the extreme amounts of lime dust being generated in the kiln could be managed. These simple solutions successfully reduced the frequency of lime dust purging, as can be seen by the decrease in the amount of lime dust landfilled in Fig. 8. However, while the dust handling system upgrade made it possible to reduce the incidences of dust purging, it did little to reduce the actual dust loading in the kiln The chain section upgrade reduced the kiln dust loading by about 50% of that before the chain system upgrade. This estimate is based on the fact that it is now possible to operate with the pressure dust handling system, which has a maximum capacity of 144 mt/d, alone for up to 4 hours without plugging it. This allows maintenance work to be completed on the vacuum dust handling system, while continuing to operate the lime kiln. pulpandpapercanada.com

PEER REVIEWED T159

Fig. 11. Kiln feed end temperature duration curves.

Effect on Kiln Production The impact of dust handling system modifications and chain system upgrade on kiln production was evaluated using load duration curves. A load duration curve is a plot of an operating parameter (e.g. lime production rate) as a percentage of time. In this paper, the conventional method of using the 90th percentile of the lime production duration curve as the maximum sustainable rate (MSR) of the kiln is followed.

Figure 9 shows three duration curves for kiln production rate.

The kiln production increased substantially as a result of the dust handling system upgrade; the difference between the pre-dust handling system upgrade curve and the pre-chain system upgrade curve represents 8,720 mt/yr lime. It is also worth noting that the 90th percentiles on the pre chain system upgrade curve and the post-chain system upgrade curve are both in the neighborhood of 380 mt/d lime, indicating that the dust handling system upgrade alone improved the kiln MSR sufficiently to provide the 380 mt/d of lime required to support the current mill production.

Figure 9 also shows that the pre-chain system upgrade curve drops off sharply at around 68th percentile. This indicates that the large dust loading still present in the kiln following the dust handling system upgrade was counterproductive to stable kiln operation, and that high production rates were not sustainable for long periods of time. The amount of lime mud that still had to be landfilled before chain system upgrade is also indicative of unstable kiln operation.

The chain system upgrade resolved the kiln dust loading issue.

The difference between the pre-chain system upgrade curve and the post-chain system upgrade curve represents 2,300 mt/yr lime.

Figure 10 shows that the chain system upgrade substantially reduced quick lime purchases.

Effect on Kiln Thermal Efficiency Figure 11 presents four duration curves for the feed end gas temperature. The curves show a significant reduction in feed end gas temperature as a result of upgrading the chain system. The feed end gas temperature exceeded 300째C 34% of the time before the dust handling system was upgraded and only 4% of the time after the new chain system was installed. It is important to remember that between November 2003 and May 2004 (concurrent with the dust handling system upgrade), the kiln feed end gas temperature was controlled by decreasing lime mud solids to 70-72% and pulpandpapercanada.com

Fig. 12. Kiln natural gas consumption duration curves.

adding water to the lime mud feed. This measure resulted in low feed end gas temperatures for this period of time. Both of these measures were discontinued after the chain system was upgraded.

Comparison of the natural gas consumption before and after the chain system upgrade is complicated by two factors.

First, the burner tip and primary air damper were both upgraded in June 2004 (concurrent with the chain system upgrade). The existing tip and damper were not sufficient to meet projected fuel requirements, and thus, had to be replaced. The impact of this change of equipment on natural gas usage is not well defined.

Second, in 2003, because of increased natural gas usage to meet increased lime demand, the refractory in the burning zone of the kiln began to degrade rapidly. This refractory was upgraded to a basic type of brick, which had a better chemical and thermal resistance. Unfortunately, the thermal expansion coefficient of the basic brick was considerably higher than that of the underlying insulating refractory. To prevent the basic brick from crushing the insulating brick during a thermal swing on the kiln and causing an unplanned kiln outage, the insulating brick was removed from beneath the basic brick in June 2004 (concurrent with the chain system upgrade). This increased heat losses through the kiln shell in the burning zone, and increased natural gas usage.

Despite these complications, the chain section upgrade proved to be beneficial in reducing natural gas usage. Figure 12 presents four duration curves for kiln natural gas consumption. The reduction in dust purging as a result of the dust handling system upgrade positively impacted natural gas consumption; however, the concurrent reduction in the lime mud solids and the addition of water to the lime mud feed to control the feed end gas temperature reduced the kiln thermal efficiencies. These conflicting conditions can be seen in the erratic nature of the pre-chain system upgrade duration curve.

Figure 12 shows that before the dust system upgrade, kiln natural gas consumption was less than 7 GJ/mt lime 52% of the time, whereas after the chain system upgrade, kiln natural gas consumption was less than 7 GJ/mt lime 72% of the time. This improvement includes heat losses introduced by removing the insulating brick in the burning zone. After additional chains were added in June 2006, kiln natural gas consumption was less than 7 GJ/mt lime 82% of the time.

The 50th percentile of a duration curve represents a median parameter value (e.g. natural gas consumption) in that 50% of the October/November 2009 PULP & PAPER CANADA

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T160 LIME KILN

Fig. 13. Thermography scan of kiln hot end shell showing ring formation downstream of chain section and powershot nozzles

time, the parameter in question exceeds the 50th percentile and 50% of the time the parameter in question falls below the 50th percentile. Using the 50th percentiles of the natural gas consumption duration curves and a required kiln production rate of 380 mt/d lime, the improvement in heat transfer resulting from the chain section upgrade represents a natural gas savings of 13,100 GJ/yr, while the further improvement in heat transfer efficiency resulting from the chain addition represents a natural gas savings of 16,900 GJ/yr.

Effect on Ring Formation Prior to the chain system upgrade, ring formation downstream of the chain section near the middle of the kiln was a common occurrence (Figures 1 and 13). The build-up was generally difficult to eradicate, and had to be periodically physically removed using the Powershot nozzles. Since the chain system upgrade, the formation of mid-kiln rings is less frequent. The rings seem to be softer and Powershot operation is not required, compared to before the upgrade.

In the chain section, mud rings form occasionally (Fig. 14).

They are soft and can usually be removed by introducing a deliberate thermal cycle into the kiln. However, there have been occasions since the chain system upgrade when the build-up in the chain section has limited lime production to the point where purchased quick lime has been used to maintain the mill production rate.

Effect on Chain Maintenance The chain section upgrade and the removal of the insulating brick significantly changed the temperature profiles of the gas stream and the solids bed in the kiln. No measurable thinning has occurred on the diamond-link heat exchange chain and no hanger caps have failed to date. The high efficiency chain system has required no maintenance since its installation in June 2004.

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Fig. 14. Thermography scan of the kiln shell in the chain section showing ring in the chain section

CONCLUSION

The dust handling system upgrade significantly increased the maximum capacity of the kiln, but failed to address dust loading within the kiln, making high kiln production rates unsustainable. Furthermore, the dust handling system upgrade did little to reduce the feed end gas temperature and the natural gas consumption.

The chain system upgrade significantly reduced dust loading and permitted sustained kiln operation at higher production rates.

It also reduced the kiln feed end temperature and natural gas consumption, despite the removal of insulating brick in the burning zone. Subsequent addition of more chain further reduced the kiln feed end gas temperature and the natural gas consumption.

The formation of mid-kiln rings also has occurred less frequently since the upgrade.

Résumé: La production de pâte ayant augmenté de 50 % à DMI PRPD, on a utilisé de la chaux vive pour combler les besoins en chaux de l’usine. Un recyclage excessif de la poussière dans le four a nui à la production et a été la principale cause du manque d’efficacité thermique du four. Le système inefficace du four exigeait beaucoup d’entretien et il a été remplacé par un meilleur système, ce qui a permis de réduire la consommation de gaz naturel du four et d’obtenir un très bon rendement, et de réduire ainsi la quantité de chaux vive achetée.

Reference: WEBSDALE, O., DOWNING, W., TRAN, H. Upgrading a

Lime Kiln Chain Section to Reduce Dust Loading and Improve Thermal Efficiency. Pulp & Paper Canada, 110 (8): T155-T160 (October/ November 2009). Paper presented at the 2007 International Chemical Recovery Conference in Quebec, Que., May 29 - June 1, 2007. Not to be reproduced without permission of PAPTAC. Manuscript received March 14, 2007. Revised manuscript approved for publication by the Review Panel November 24, 2008.

Keywords: LIME KILN, DUSTING, DUST RECYCLE, THERMAL EFFICIENCY, CHAIN SYSTEM, RING FORMATION

pulpandpapercanada.com

CD CONTROL T161

Detecting Aliasing Between Cross and Machine Direction Variations

by Variable Sampling Rate

By S. Aslani, M.S. Davies, G.A. Dumont, and G.E. Stewart Abstract: It is well known that use of scanning sensors in the presence of high frequency machine direction process variations gives rise to aliasing effects that cannot be avoided when designing algorithms that seek to separate cross machine (CD) variations from those in machine direction (MD). These effects are particularly troublesome when machine direction fluctuations have a strong component close to the scanning frequency of the sensor and then often lead to machine direction variations being perceived as cross machine profile effects. It is also possible for a changing profile to be misinterpreted as a periodic MD variation. The method presented here assists in determining whether such observed variations are in MD or CD. The method makes use of variable rate scanning to distinguish between artifacts related to the scanning rate and true process fluctuations.

A

scanning sensor moves slowly back and forth across a rapidly-moving sheet of paper, with the sensor continuously gathering data on one or more paper properties. Typically the sensor takes about 20 seconds to traverse the 10 m sheet, while the sheet may be moving past at up to 120 km/hr. Sensors for sheet basis weight (mass per unit area), moisture content, and thickness are commonly mounted on the sensor. In this paper we consider moisture variations; the methods can be applied equally to the other sheet properties.

The data gathered by the sensor is a combination of the machine direction (MD) process variations, which are assumed uniform across the sheet and changing rapidly, and the cross direction (CD) profile, which is assumed to change relatively slowly. As indicated in Fig. 1, the resulting sampled measurements would follow a set of diagonal paths on the sheet if it were stationary, with irregular but periodic samples being made of the MD direction variations, and essentially continuous measurement along each scan furnishing data that is a combination of CD and MD variations.

It is important to separate sheet property variations into MD and CD components since completely different control mechanisms are used to minimize the two classes of variations. It is useful to identify MD variations accurately but their control is normally only possible through a slow acting loop that involves processes upstream of the paper machine. CD control is possible on the paper machine itself, using a variety of different mechanisms, so that the process delay and dynamics between actuator and measurement pulpandpapercanada.com

become significant in determining the bandwidth that can be controlled.

S. ASLANI Electrical and Computer Engineering, University of British Columbia, Vancouver, B.C.

Distribution of MD frequencies

Table I shows distribution of the MD variations [1]. Only 15% of the MD variations are slow enough to be detected properly by the scanner, using the MD averaging method. The next slowest variations are the 20% around the scan rate, which is the main problem area, and causes most of the aliasing effect in the measurements.

Above this range, about 35% of the total variation is very fast considering the scan time.

These variations are usually discarded as noise, by the filter, since they cannot be controlled. Using the exponential filter, the MD signal is averaged over one scan, which is about 10-20 seconds.

Therefore all the high frequency variations have been eliminated and MD control only deals with the very slow remaining variations.

Filtering methods

Although the problem of MD/CD filtering has been studied by several groups in recent decades, industrial practice still consists of running a simple exponential filter in the MD direction at each CD location. This approach takes no notice of the irregular sampling that results from the scanning pattern. Skelton [5] has developed non-causal filters for rigorous reconstruction in this situation. Other approaches, Wang [8] for example, have also attempted to take the sampling pattern into account, but have resulted in algorithms too complex for reliable industrial use.

More recently, a recursive wavelet filter has been investigated by Aslani [3]

M.S. DAVIES Electrical and Computer Engineering, University of British Columbia, Vancouver, B.C.

G.A. DUMONT Electrical and Computer Engineering, University of British Columbia, Vancouver, B.C.

G.E. STEWART Honeywell Industrial Control, North Vancouver, B.C.

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T162 CD CONTROL

Fig. 1. Scanning sensor path on paper sheet.

No phase shift

Fig. 2. MD profile represented in two dimensions

90 Degree phase shift

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MOTIVATION From industrial data

In order to illustrate the issue addressed here, a test was performed on moisture profile data from a paper machine. After trimming, raw data taken from the scanner is filtered and separated into MD and CD, using the recursive method of wavelet denoising [3,5,6]. After filtering, the CD profiles seemed normal, but if the estimated MD signal is represented in two-dimensional form, (just as is usual for the CD profile), periodic effects at the scan frequency become evident in this two-dimensional MD profile around a few data boxes. This effect is shown in Fig. 2, and gives rise to the idea that this localized frequency actually belonged to the CD profile rather than MD, and as a result of filtering had been leaked in to the MD profile. The method presented here may be used in such cases.

Effect of phase change

MD variation at the scan frequency or close to it can distort the estimated CD profiles unpredictably. For example, the 46

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effect depends dramatically on the phase of the disturbance as well as its frequency.

Figure 3 shows the effect of phase change in the scanned profile. The MD variation is a simple sine wave at the scan frequency. The CD is taken as a flat zero profile. The only difference between the right and left figures is a 90 degree phase shift of the MD wave. This simulation has been run on 40 scans with 100 measurement points in cross-direction. The scan time is 20 seconds, so the Nyquist rate associated with that is 0.025 Hz. The phase change in the MD variation results in a totally different representation of the data, with this difference in the sampled data being due to the fact that the sampling is exactly at the Nyquist rate.

Note that a delay between successive scans, due to sensor calibration or other effects, can lead to such phase changes.

Detecting aliasing by different sampling rates

It is not always possible to control the bandwidth of a signal to ensure sampling above the Nyquist rate. For example,

October/November 2009

most signals include noise components and so are not strictly band-limited. Paper machine measurements are not different in this regard. Even after filtering the scanning mechanism means that the signal will involve aliasing. Here, a method is presented to detect the presence of aliasing by evaluating the apparent spectral content at two or more sampling frequencies. The approach is most useful where the signal spectrum is dominated by a small number of well-defined oscillating modes.

If a frequency component, f1, is evident in the spectrum of a sampled signal, and it is unclear whether this represents a true component of the original continuous signal or is an aliased component, the difference will be manifest if the signal is sampled at a different rate, and the two spectra are compared. If the f1 frequency of f remains in the sampled signal spectrum, 1 it must have been originally present in the continuous-time signal. If the frequency f1 component shifts, it is to be expected that it is artifact of aliasing.

In the following example we have sampled a signal: pulpandpapercanada.com

PEER REVIEWED T163 Frequency content Fs=100 100 50 0

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x(t) = sin(2 f1t) + 2sin(2 f2t), where f1 = 5 Hz and f2 = 25 Hz at the different frequencies fs = 100,40,30 and 20 Hz. At fs = 100 Hz, there is no aliasing. The Nyquist rate is fn = 50 Hz, and so the signal can be fully reconstructed. In the other frequencies fs = ,40,30,20 Hz aliasing is present.

Figure 4 shows the sampled signal at different rates in the time domain. The corresponding discrete Fourier transforms (DFT) [2] are given in Fig. 5, to show the frequency contents of the sampled signals.

Note that the data after half the sampling rate will be redundant and the figures will just repeat. This rate is f=50 Hz, for the first figure (fs =100Hz), and f=20, 25, 10 Hz respectively for the rest. Except the first figure that has already eliminated redundant data, for the rest, the frequency content after fs has not been shown, and is set to zero.

At fs =100 100 Hz, there are two fre-

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Fig. 6. True MD and CD profiles for the simulation.

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quencies f=5 and 20 Hz shown in the DFT of the signal, these being the frequencies present in the original signal.

At fs = 40 Hz which is below the Nyquist rate, frequency content of f=25 is mirrored and aliased at f=15. Running the test at fs =30, and fs =20, again f=5 is present but f=25 is mirrored on f=5 in both cases, and so shows up as a frequency content of f=5 with a triple magnitude.

PROPOSED METHOD AND RESULTS

The average MD sampling rate of the scanner, regardless of the CD position, is equal to the scan time T. The differing CD positions correspond to periodic nonuniform sampling [4]. The maximum MD frequency that is detectable is therefore, 1 /2T, the Nyquist rate.

Two tests were performed on a simulated set of paper machine data for one

paper machine to investigate the interaction between CD and MD estimates at different sampling rates. The scan time has been changed on the reverse scan so that the scanner moves forward across the sheet over the scan time of Ts, and returns over a scan time of 2Ts. Figure 6 shows the typical inputs used for simulations. Simulation is assumed to be on a machine with a scan time of Ts=20 seconds, with 100 measurement boxes across the sheet. It is assumed that MD variations are a pure sine wave at the Nyquist frequency (f=0.025 Hz for this case) for Figs. 7 and 8. For the second set, Figs. 9 and 10 the sine wave has the frequency of f=0.03875 Hz, above the Nyquist rate.

It is evident that the change in scan rates results in a significantly changed perception of MD and CD variations. In cases where there is uncertainty about the

October/November 2009

PULP & PAPER CANADA

47

T164 CD CONTROL variable rate scan

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The aliasing effects of high frequency machine direction disturbances can cause significant errors in estimated CD profiles, especially when these variations are close the scan frequency. Variable rate scanning has been proposed as a method to address these issues.

A significant portion of the MD variations are out of the achievable bandwidth as a result of the scan rate. When variations near this frequency are present they often

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reliability CD or MD data, the scanner rate can be adjusted to address this uncertainty. The simplest change would be to run the scanner at a different, but constant, rate on its way back across the sheet. Alternative patterns would make it possible to refine this approach.

If a particular frequency component belongs to MD, it will appear to change in the MD profile as a result of the different sample rate. This assumes that the CD profile does not have any fast variations.

Figures 7 and 8 demonstrate CD and MD profile after filtering for a scan rate equal to the Nyquist rate. A comparison is made between the estimates for normal fixed rate sampling and for variable rate sampling.

Figure 9 and 10 show filtered CD and MD profiles for a test when the MD variations were slightly above the Nyquist rate.

In Fig. 9 the difference between the CD profiles using the variable sampling rate and the normal rate is significant. It is therefore likely that the CD profiles obtained using the normal scan rate are erroneous and that a strong MD frequency component near the scan rate is present.

PULP & PAPER CANADA

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CONCLUSION

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Table I. Distribution of MD frequencies.

Category 1 2 3 4 5

Frequency (Hz)

Range (s)

25-250 2.5-25 0.25-2.5 0.006-0.25 0.0016-0.006

0.004-0.04 0.04-0.4 0.4-4.0 4.0-167 167-600

become evident in CD profiles. One way to detect these MD variations would be to use a variable scan rate. This gives the possibility of determining whether the suspicious variation actually belong to MD. It is evident that further analysis is needed to determine an organized approach for exploiting the additional information available from variable rate sampling.

LITERATURE

1. CUTSHALL, K. The nature of paper variations, TAPPI Journal, June 1990.

2. OPPENHEIM, A.V., SCHAFER, R.W. Discrete-Time Signal Processing, Prentice Hall, 1989

Percent of total variance 15% 40% 10% 20% 15%

3. ASLANI, S., DAVIES, M.S., DUMONT, G.A., STEWART G.E. Estimation of Cross and Machine Direction Variations Using Recursive Wavelet Filtering, Proc. of IEEE IAS Advanced Process Control Workshop, Vancouver, 2004.

4. MARKS, R.J. II. Advanced Topics in Shannon Sampling and Interpolation Theory, Springer-Verlag, 1992.

5. SKELTON, J.C., WELLSTEAD, P.E., DUNCAN, S.R. Distortion of Web Profiles by Scanned Measurements, Pulp & Paper Canada, Dec. 2003, pp. 81-84.

6. PAPOULIS, A. Generalized Sampling Expansion, IEEE Transaction on Circuits and Systems, 24 (11):652654 (Nov. 1977).

7. NESIC, Z., DAVIES, M.S., DUMONT, G.A. Paper Machine Data Analysis and Compression Using Wavelets, TAPPI Journal, 80(10):191-204 (October 1997).

8. WANG, X.G., DUMONT, G.A., DAVIES, M.S. Estimation in Paper Machine Control, IEEE/ACS Control Systems Magazine, 13(4):34-43 (August 1993).

Résumé: Il est reconnu que l’utilisation de capteurs à balayage en présence de variations de procédé haute fréquence dans le sens machine entraîne des effets de crénelage impossibles à éviter lors de la conception d’algorithmes qui visent à séparer les variations sens travers (ST) des variations sens machine (SM). Ces effets représentent une source particulière de complications lorsque les fluctuations dans le sens machine possèdent un élément rapproché de la fréquence de balayage de ce capteur, ce qui entraîne souvent des variations dans le sens machine perçues comme des effets de profil dans le sens travers. Il est aussi possible qu’un profil qui varie soit mal interprété comme une variation périodique SM. La présente méthode aide à déterminer si les variations observées sont SM ou CD. Cette méthode utilise le balayage à vitesse variable pour faire la différence entre les artéfacts liés à la vitesse du balayage et les fluctuations réelles du procédé.

Reference: ASLANI, S., DAVIES, M.S., DUMONT, G.A., STEWART, G.E. Detecting Aliasing

Between Cross and Machine Direction Variations by Variable Sampling Rate. Pulp & Paper Canada 110(8):T161-T164 (October/November 2009). Paper presented at Control Systems 2004 in Quebec, Que., June 14-17, 2004. Not to be reproduced without permission of PAPTAC. Manuscript received February 18, 2004. Revised manuscript approved for publication by the Review Panel Jan. 7, 2009.

Keywords: SCANNING SENSORS, CD/MD SEPARATION, CD CONTROL, SHEET PROPERTIES, FREQUENCY ALIASING DETECTION.

October/November 2009

pulpandpapercanada.com

TECHNOLOGY NEWS

A safer way to handle bale wire

Western Pulp, a manufacturer of molded fibre products, is now handling hightensile bale wire scrap more safely and efficiently by recycling it at its point of generation with heavy-duty Sweed scrap choppers.

“The primary driver for us was safety, to reduce the risk of pokes and cuts posed from loose, tangled bale wire,” says Terry Glasgow, maintenance supervisor at Western Pulp’s Corvallis, OR plant. “We didn’t want anyone poked in the eye.

Because the Sweed chopper will help to eliminate poke, cut or trip incidents due to loose bale wire in the production area, it should simplify meeting OSHA requirements.”

Glasgow likes a number of the safety features in the heavy-duty bale wire chopper, such as a large opening for smooth feeding of the wire, along with an anti-kickback funnel infeed. He feels its

“safety face” makes an easy target should a user need to stop the machine quickly.

“Since the operator can hit the entire front of the machine with a shoulder, elbow, or body part, it’s a failsafe emergency stop that enhances safety.”

By handling the bale wire once, instead of multiple times, after it’s cut from incoming bales of paper, the company is saving a significant amount of labour.

“We’ve cut bale wire related-labour tremendously,” says Glasgow.

Glasgow acknowledges another economical, ecological plus: “Instead of paying to haul unmanageable bale wire to a landfill, a scrap dealer is now paying us for the chopped, more easily processed bale wire.”

Sweed is an Oregan-based manufacturer of linear material reduction equipment.

The company has designed its bale wire chopper specifically for the rigors of hightensile steel, which is more demanding

Robust paper roll hardness tester

Proceq’s PaperSchmidt is the first rebound hammer designed specifically for paper roll hardness testing. Extensive field tests carried out at major manufacturers and converters in the U.S. and Europe have consistently shown that it provides previously unachievable roll-profiling accuracy and repeatability, according to Proceq.

The instrument is fully compliant with the TAPPI T834 om-07 standard used in North America to regulate roll hardness testing and it delivers instantly all of the key parameters required for assessing the quality of paper rolls.

The PaperSchmidt has three unique features. It has a high compliance plunger and a innovative measurement principle that is independent of the angle of impact. This gives the PaperSchmidt best-in-class roll profiling performance.

In addition, the paper roll profile can be viewed directly on the integrated display. The instrument provides an automatic calculation of the average paper roll hardness, the range and standard deviation.

Finally, robust construction, a sealing system, and specially treated impact plungers greatly extend the lifetime of the instrument.

Proceq, paperschmidt.com, proceq.com.

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PULP & PAPER CANADA

October/November 2009

than steel banding or plastic.

Sweed Machinery Inc. 866-507-3667, sweed.com

Two-drum winder can reduce roll vibration

Matik, Inc. announces the availability of the new Goebel optiwind, a two-drum winder for the paper and cardboard converting industry, capable of handling the high speeds of today’s paper machines.

Optiwind is suitable for converting paper and cardboard — such as offset newsprint, copy paper, NCR base paper, corrugated medium, kraft and liner board. The winder is able to handle materials of up to 7000 mm at a speed of 3000 m/min.

A special feature is its variable drum roller geometry which offers the paper and board converting industry a distinctive advantage. Paper which tends to build up vibrations can cause oscillation during production. The vibrations thus affect the machine operating characteristics and the finished roll quality.

The variable drum arrangement counteracts these negative effects by enabling the rollers in the respective winding stages to change their position one to another automatically, thus reducing the vibrations and improving the finished roll quality.

Another advantage of the optiwind is the arrangement of the slitting section. Optiwind uses individual slitters applied in tangential slitting between unwinding and winding.

Matik Inc. 860-232-2323, matik.com.

pulpandpapercanada.com

TECHNOLOGY NEWS Corporate energy management application monitors energy use

A new application from Invensys Operations Management provides new visibility to help manufacturing and industrial automation customers achieve energy efficiency.

The Wonderware Corporate Energy Management Application allows users to monitor energy and detect and notify personnel of energy inefficiencies.

It connects directly to meters on a network, through industrial controllers, and accepts manual entry. The application is layered on top of the Wonderware System Platform, enabling integration with a wide range of applications, networks and I/O data sources. Application functionality includes recording consumption and demand at main and sub-meters for a wide range of energy types, including power, water, chill, gas, air, and steam. The application also associates production output to energy usage, providing the key performance indicators used in many sustainability programs. It can be quickly installed in a matter of days, and pre-built reports give managers, supervisors and workers new visibility and information on how energy is used within the operation.

Invensys Operations Management’s offerings are delivered under several prominent industry brands, including Action Instruments, ArchestrA, Avantis, Barber-Colman, Chessell, Continental, Eurotherm, Foxboro, IMServ, InFusion, SimSciEsscor, Triconex and Wonderware.

Invensys Operations Management, iom.invensys.com.

High energy recovery boiler will replace three older units

Andritz has received an order from Packaging Corporation of America (PCA) to deliver a high energy recovery boiler (HERB), including a chloride and potassium removal system, to PCA’s Valdosta mill in Georgia. Start-up of the new recovery boiler is scheduled for October 2011.

The energy-efficient HERB technology allows a modern mill to produce more steam, and therefore more electrical energy, to support mill operations. For the Valdosta mill, the boiler is designed to operate at 1,500 psig (103 bar) pressure and a temperature of 920°F (493°C). The new unit will replace three existing boilers installed in the 1950s and 1970s.

Upon completion of the project, the Valdosta mill will use only internally generated wood waste and black liquor in its boilers, which will allow it to self-generate 100% of its electricity requirements. The new recovery boiler technology will also significantly reduce the mill’s air emissions compared to the older installed units.

Andritz 514-631-7700, andritz.com

Two-layer ValFormer concept for lightweight containerboard

Metso has developed a new, cost-efficient two-layer ValFormer forming concept, which makes it possible to produce lightweight containerboard with only one hybrid forming unit. It tackles the boardmakers’ challenges of combining lower basis weights, faster speeds, and higher ash contents brought by the increased use of recycled fiber.

The benefits of the new forming concept include pure layer coverage, considerably lower residual variation in basis weight, as well as excellent formation with no streaks or tiger stripes. Sheet uniformity maximizes the use of the raw material strength potential, enabling the use of more cost-effective raw materials and less starch in surface sizing.

This patented forming concept combines a new ValFlo Pro two-layer headbox and a new VacuBalance vacuumassisted forming board with the well-proven ValFormer shoe blade hybrid former.

The ValFlo Pro produces an excellent two-layer headbox slice jet quality, which generates a fully homogenized, disturbance-free flow onto the forming section. The VacuBalance vacuum-assisted forming board efficiently absorbs jet impact energy and eliminates stock jump on the forming board. The combination of these two units ensures that board layers will not mix together.

The proven ValFormer shoe and blade hybrid former, in turn, facilitates lower inlet consistencies combined with fast, non-pulsating drainage. The concept enables high speeds up to 1,400 m/min, which are impossible to reach with conventional Fourdrinier or hybrid forming solutions.

The new forming technology is especially suitable for rebuilds since it enables production of two-ply testliner with an existing Fourdrinier. One machine can produce both testliner and lightweight corrugating medium, making the concept a viable alternative to gap forming technology. Another application is a three-ply sheet concept with two existing Fourdriniers.

Metso Pulp & Paper 514-380-2418, metso.com

Advanced process control for chemical pulp mills In collaboration with pulp mill engineering and operations personnel, Metso’s process, machinery, and automation expertise has been combined to provide Metso Advanced Process Control (mAPC). mAPC is able to intelligently manage multivariable processes, and brings improved performance to all pulp mill processes. Using predictive controls, shift-to-shift variations are eliminated in all departments from the wood yard to pulp dryer. mAPC enables production and quality targets to be met more quickly while optimizing energy, chemical, and raw material usage for additional savings and environmentally pulpandpapercanada.com

clean operation.

The new mAPC for chemical pulping has been developed from experience with optimization controls installed in more than 200 pulp mill processes around the world. These solutions, based mainly on predictive process models, have achieved a high level of performance in both fibre and recovery line processes. Controls are enhanced in many cases by Metso’s Kajaani process analyzers, which measure process conditions, chemical reaction rates, and product quality.

Metso Pulp & Paper 514-380-2418, metso.com October/November 2009

PULP & PAPER CANADA

51

TECHNOLOGY NEWS Cartridge seal reduces costs and improves reliability

Flowserve Corporation has launched the Innovative Standard Cartridge seal series, ISC2 . According to the company, facilities that standardize with the ISC2 Series will benefit from less inventory, greater flexibility, rapid availability, less downtime, and longer seal life .

“The Flowserve ISC2 seals are designed to fit hundreds of pump models from global manufacturers so customers in virtually all industries and applications will benefit,” said Andrew J . Beall, president, Flowserve Flow Solutions Division .

Flowserve ISC2 seals feature patentpending thermal management technology, which tolerates short-term dry run events without overheating, thereby increasing reliability and preventing a common cause of leakage .

Dual seals enjoy enhanced barrier fluid circulation for the highest flow rate and coolest running when compared to other standard cartridge seals in the industry . Single seals have a sizeable throttle bushing to help protect against leaks .

Flowserve Corp., flowserve.com.

Good things come in small packages.

To inquire about advertising in Pulp & Paper Canada contact

Jim Bussiere 800-268-7742, ext 3606 or 416-442-5600, ext 3606 Fax: 416-510-5140

Advertiser Index

BC Hydro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .BCHydro .com/industrial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Best Glove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .bestglove .ca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Buckman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .buckman .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Cook Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . www .cookeng .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Freeman Staffing Inc . . . . . . . . . . . . . . . . . . . . . . . . . www .freemanstaffing .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Gamajet Cleaning Systems Inc . . . . . . . . . . . . . . . www .gamajet .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Indeck Power Equipment Co . . . . . . . . . . . . . . . . . www .indeck .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Jeffrey Rader Corporation . . . . . . . . . . . . . . . . . . . www .jeffreyrader .com/ppc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Kemira Chemicals Inc . . . . . . . . . . . . . . . . . . . . . . . . www .kemira .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Metso . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .metso .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 PacWest Conference . . . . . . . . . . . . . . . . . . . . . . . . www .pacwestcon .net . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 PAPTAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .paptac .ca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Phoenix Process Equipment Co . . . . . . . . . . . . . . www .dewater .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Poyry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .poyry .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Sandwell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . www .sandwell .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Spraying Systems Co . . . . . . . . . . . . . . . . . . . . . . . . . www .spray .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Wabash Power Equipment . . . . . . . . . . . . . . . . . . www .wabashpower .com . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Equipment

PRODUCT SHOWCASE BEST GLOVES BEST GLOVES research and development has led to a full line of work gloves featuring the latest in glove technology. Each is covered in a specific coating designed with the appropriate protective requirements necessary to service a wide variety of industrial and work applications. Fully integrated – from knitting to sewing and dipping the company takes pride in the quality of its extensive product line.

BEST GLOVE MANUFACTURING LIMITED 253 Michaud Street Coaticook, QC, J1A 1A9 Customer Service 1-800-565-BEST

52

PULP & PAPER CANADA

October/November 2009

pulpandpapercanada.com

Professional Connections Careers

Equipment

PulP & PaPer Jobs Freeman Staffing, Inc. specializes in the placement of engineers (all disciplines), production type supervisors, managers, mill and/or plant managers and corporate executives in the pulp & paper industry, North America-wide. For specific current job searches call us or contact our web site. All resumes are treated with complete confidentiality.

Freeman Staffing, Inc.

(800) 221-9629 or FAX (360) 653-8271 email: markp@freemanstaffing.com

web site: www.freemanstaffing.com

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Engineering services for the pulp and paper industry

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53

PHOTO FILE

PAPTAC Improving Paper Machine Efficiency & Productivity Seminar Paper machine production managers gathered in at FPInnovations – Paprican in October to hear expert opinions on how to boost paper machine productivity. The two-day event was sponsored by PAPTAC’s Paper Machine Technology Committee.

The program included presentations on each section of the paper machine, as well as a discussion of the continuous improvement program at one paper company.

Send us your photos!

We welcome submissions of photos from readers. Send us pics of industryrelated meetings, golf tournaments, conferences, or social events. Include a few lines about the event, and send to cindy@pulpandpapercanada.com

54

PULP & PAPER CANADA October/November 2009

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