Pulp & Paper Canada July/August 2009

July/August 2009

www.pulpandpapercanada.com

Tweaking paper properties at the

nano level WILL BLACK LIQUOR pull companies out of the red?

LUBRICATION: Automatic doesn’t mean unattended JOURNAL OF RECORD, PULP AND PAPER TECHNICAL ASSOCIATION OF CANADA DING: Effects of some wood chip properties on pulp qualities

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JULY/AUG 2009 Vol. 110, No. 6 A Business Information Group Publication ISSN 0316-4004 PACWEST

11

PAPERMAKING

14

WOOD CHIP PROPERTIES

20

FEATURES

7 11 13 14 17

Black Liquor Subsidies: Out of the Red and Into the Black?

The federal government’s Green Transformation Program will boost investment, but some say it has too many strings attached.

PacWest Offers Real-life Solutions A strong technical program anchored the 2009 PacWest conference.

The Biggest Lube Problem?

One expert says the biggest problem with lubrication is a lack of knowledge.

Papermaking on a Nano Scale You don’t need expensive equipment upgrades to boost machine speed — just some very, very small additives.

Workplace Safety — Empower the Employees Every single employee on every shift should be involved in hazard management.

TECHNICAL PAPERS

20 Effects of Some Wood Chip Properties on Pulp Quality

On-line chip measurement systems can be used to predict some pulp qualities.

By F. Ding (CRIQ), M. Benaoudia, P. Bédard (SEREX), and R. Lanouette (UQTR)

24 Effect of White Water Consistencies on Hydrosulfite Bleaching

of DIP and TMP Pulps at AbitibiBowater Gatineau Optimal brightness was achieved when clarified white water combined with floated fines was reused prior to bleaching.

By G. Rangamannar (Rohm and Haas), R. Bellemare (Rohm and Haas), Y. Dionne, J. Najim, and R. Amyotte continued on page 4

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July/August 2009 PULP & PAPER CANADA

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CONTENTS

continued from page 3

28 Effect of Separate Refining and Co-refining of BCTMP/KP

on Paper Properties BCTMP/KP co-refining produced handsheets with improved surface smoothness.

By Y. Gao (UNB), F. Huang (UNB), V. Rajbhandari (UNB), K. Li (UNB), and Y. Zhou (Tembec)

34 Ageing of Flexographic Printed Model Cellulose Surfaces and Determination of the Mechanisms Behind Ageing Elevated temperatures, UV light, and longer storage time have a negative effect on ink detachment.

By J. Andersson and L. Wågberg (Royal Institute of Technology)

TECHNOLOGY NEWS

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39 A New Technique for Measuring Periodic Patterns

Within a Paper Sheet The Fourier-based technique detects small- and medium-scale patterns.

By J. Bernié (Ondimage), and R. Trépanier (OpTest Equipment)

43 Internal Interconnections Impact on Process Operability

A model structure for a TMP line, including internal interconnecctions, has been developed.

By K. Eriksson (Chalmers University of Technology), and A. Karlström (Chalmers Industrial Technology Foundation)

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INDUSTRY NEWS BLACK LIQUOR

Canada’s black liquor response: $1 billion for environmental and energy projects

OTTAWA — The Canadian government revealed in June its $1-billion response to the U.S. black liquor tax credit. The Green Transformation Program intends to provide Canadian pulp and paper companies funding of $0.16 per litre of black liquor produced during 2009, to be used for capital expenditures that make improvements to energy efficiency or environmental performance of any mill in Canada.

For further information and analysis, see “Out of the Red and Into the Black with Black Liquor Subsidies?”, page 7.

AWARD

Aboriginal entrepreneur wins FPAC/AFN business award

CALGARY — The Forest Products Association of Canada (FPAC) and the Assembly of First Nations (AFN) have selected Grace Esquega, president of Niigaani Enterprises, as the first winner of the FPAC/AFN Aboriginal Forest Products Business Leadership Award.

The award honours First Nations entrepreneurs for their success in a forest products business that exemplifies business leadership, exceptional environmen-

The Aboriginal Forest Products Business Leadership award was presented during the Assembly of First Nations annual meeting in Calgary.

Shown above are (from left to right): Roger Augustine, AFN Regional Chief for NB-PEI; Avrim Lazar, president and CEO, FPAC; Grace Esquega, president of Niigaani Enterprises; Luke Drapeau, general manager wood products NW Ontario, AbitibiBowater.

PROTEST

Several B.C. companies take stand against high property taxes

TORONTO — A deadline for payment of municipal property taxes has passed in British Columbia, with mixed reactions. Catalyst Paper, protesting its tax rate, paid only $1.5 million each to four B.C. municipalities. Likewise, Mercer International reportedly did not pay its taxes to Castlegar, while TimberWest did not pay its bill to Campbell River in full. West Fraser is reported to have paid its bill to Kitimat for the Eurocan pulp mill, but all four companies, independently, are challenging various municipalities in court, protesting the high tax rate.

In early June, Catalyst Paper petitioned to the Supreme Court of British Columbia for judicial review of recently set property tax rates in North Cowichan, Port Alberni, Campbell River, and Powell River. These are the four municipalities where its B.C. paper mills are located. It seeks declarations, under Section 262 of the Local Government Act, that the tax rates are unreasonable and therefore beyond the municipalities’ jurisdiction.

Catalyst Paper owed $23 million in property taxes to the four municipalities.

Mercer, TimberWest, and West Fraser have initiated similar actions.

Quoted in the Vancouver Sun, Ken McRae, mayor of Port Alberni, called Catalyst’s tax revolt unacceptable. “I was really hoping they wouldn’t break the law,” he said.

McRae told the Vancouver Sun the tax shortfall — $3.3 million in his community — means the town will have to draw down on its reserves, money it hoped to use to lever federal and provincial stimulus funds for shovel-ready projects. tal and safety performance, and the delivery of high-quality products and services.

“This award means a great deal to me and to my staff,” says Ms. Esquega.

“It signifies the successful culmination of a long journey for my family and the many workers who were part of a dream — a dream that my husband had in 1983 when he started Niigaani Enterprises. He envisioned a logging operation, owned and operated by native people, which would provide our community with meaningful employment for a long time. I look around and see many families that benefit from this company and feel a sense of security.”

Niigaani has been delivering fibre to Thunder Bay area sawmills and pulp and paper mills for more than 25 years.

CONFERENCE

PAPTAC issues call for papers for EXFOR & Annual Meeting 2010

MONTREAL — The Pulp and Paper Technical Association of Canada is actively planning the program for EXFOR & Annual Meeting 2010, which will take place at the Fairmont Queen Elizabeth Hotel in Montreal on February 2-3, 2010.

Anyone who wishes to submit an

abstract for presentation should submit directly to Greg Hay, ghay@paptac.ca.

Submissions are welcome in English and French.

The deadline for abstract submissions is September 10, 2009. For further information, please visit www.paptac.ca.

BANKRUPTCY

Fraser Papers files for creditor protection

TORONTO — Fraser Papers Inc., together with its subsidiaries, has initiated a court-supervised restructuring under the Companies’ Creditors Arrangement Act in the Ontario Superior Court of Justice and will be seeking similar relief in U.S. bankruptcy court.

Fraser Papers has been working with employees, suppliers, customers, and governments over many months in an effort to reduce costs, improve fibre access, and optimize operations in a challenging environment.

“Unlike many restructurings, the court filing was not the result of excessive leverage,” says Peter Gordon, CEO. “Our paper business remains profitable, particularly the specialty packaging and printing segments where there

VISIT WWW.PULPANDPAPERCANADA.COM FOR DETAILS: XPEDX ACQUIRES VANCOUVER-BASED GOULD PAPER (CANADA)… s s s pulpandpapercanada.com

July/August 2009 PULP & PAPER CANADA

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INDUSTRY NEWS are opportunities to grow in a number of key segments. However, weak pulp and lumber markets have drained our limited resources, more than offsetting the progress in our paper business.”

Fraser Papers has operations in New Brunswick, Maine, New Hampshire, and Quebec.

ACQUISITION

Cascades to acquire Atlantic Packaging’s tissue business

KINGSEY FALLS, QUE. — Cascades Inc. has reached an agreement

with Atlantic Packaging Products Ltd. to acquire its tissue business for approximately $60 million.

Once completed, this transaction will enable Cascades Tissue Group to increase its annual capacity of recycled tissue by 55,000 tonnes, while augmenting converting capacity by close to 70,000 tonnes.

These assets are located in or close to Toronto, increasing the number of Cascades employees in Ontario by 175.

Commenting on the transaction, Alain Lemaire, president and CEO, states: “The tissue sector has prov-

STARTS, STOPS, CHANGES

Kruger Inc. will cease the production of coated paper at its Trois-Rivières, Que., mill for an indefinite period, effective October 30, 2009. The company cites as reasons to the decreasing demand for coated paper, which dropped 35% in North America in 2009 over the previous year, as well as falling prices, and the appreciation of the Canadian dollar.

Three paper machines and two coaters will be shut down, as well as the woodroom and groundwood plants, resulting in approximately 400 layoffs. The TroisRivières mill will, however, continue to produce newsprint and supercalendered paper, maintaining 550 jobs at the site. The company will maintain coated paper production at its Wayagamack mill.

Tembec announced a three-week extension to the previously announced curtailment of the Pine Falls, Manitoba Newsprint Operations. The original curtailment, which began on June 16, was estimated to be for three weeks.

“The market for newsprint continues to be challenging. This extended curtailment is a result of unacceptably low prices offered in some markets due to supply and demand imbalances and the black liquor tax credits available to some newsprint mills in the southern U.S.,” states Chris Black, executive vicepresident and president of the Paper Group.

Kruger has laid off 130 employees at its Corner Brook Pulp and Paper newsprint mill. The company had shut down the No. 4 paper machine earlier this year, and has now decided it will remain down indefinitely, until the market for newsprint improves.

Two other paper machines at the mill will remain active.

Tembec has announced a temporary curtailment of its newsprint and sawmill operations in Kapuskasing, Ont. The shutdown will run from July 24 to August 10, and is directly related to the ongoing challenging market conditions for newsprint and lumber. Approximately 510 employees at all levels of the newsprint, sawmill, and forestry operations will be affected.

Howe Sound Pulp and Paper (HSPP) will indefinitely curtail one-third of its newsprint production at its Port Mellon, B.C., mill. The company attributes the closure to “unsustainable low pricing in certain regions of the U.S. [which] are a direct result of the black liquor tax rebate.” The production curtailments will be accomplished through a combination of paper machine shut downs and reduced operating rates.

en itself to be recession resistant, showing steady growth through the economic cycles and we believe business perspectives for this sector will continue to be advantageous for us going forward, particularly in the area of recycled products where Atlantic brings us added expertise.”

This transaction is subject to the usual conditions, including the approval of the Competition Bureau.

ON THE MOVE

As part of its restructuring, AbitibiBowater has reviewed and streamlined the organization of executive responsibilities. According to the company, the new, leaner structure will provide for enhanced efficiency and reduced costs.

A functional approach was taken in designing the new executive team, which will be comprised of five executives reporting to David J. Paterson: — Alain Grandmont, executive vicepresident, human resources and supply chain, — William G. Harvey, executive vicepresident and chief financial officer, — Yves Laflamme, senior vice-president, wood products, — Pierre Rougeau, executive vicepresident, operations and sales, — Jacques P. Vachon, senior vicepresident, corporate affairs and chief legal officer.

Also, as previously announced, Bruce K. Robertson will serve as chief restructuring officer.

Stephen Frasher has been appointed president and CEO of Western Forest Products Inc. Dominic Gammiero, who has served in this position for the last six months while a recruitment process was underway, will continue in his role as chairman of the board.

Frasher has spent most of his career in the transportation industry, most recently as president and CEO of Washington Marine Group in Vancouver. His experience at WMG has provided him with an understanding of the political, labour, and First Nations environment in B.C.

VISIT WWW.PULPANDPAPERCANADA.COM FOR DETAILS: CASCADES SUPPORTS QUEBEC UNIVERSITY’S ENVIRONMENTAL EFFORTS… s s s

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PULP & PAPER CANADA July/August 2009

pulpandpapercanada.com

ANALYSIS

Out of the RED and into the BLACK with black liquor subsidies?

By Heather Lynch

T

he recently announced federal aid package for Canada’s forest products sector comes with a hefty mandate: “to help ensure Canada’s pulp and paper sector is both commercially and environmentally sustainable for years to come.” In an industry as volatile as forestry, certainty about the sustainability of anything is difficult to come by. But the $1-billion Pulp and Paper Green Transformation Program prompted a major shift in gears for at least one company, as Tembec forwent plans to idle its Skookumchuck pulp mill in light of the committed capital.

Several producers have used the promise of funding to move ahead with improvement projects, but the federal government’s Green Transformation program still has its detractors. become more energy- and cost-efficient while making them more competitive and better able to keep pulp and paper jobs in Canada,” says Avrim Lazar, president and CEO of the Forest Products Association of Canada, indicating his organization’s profound approval of the package. “We are very supportive of (this) announcement.”

With an emphasis on environmental sustainability, the package provides a $0.16 per litre credit for black liquor produced by Canadian mills between January 1, 2009, and December 31, 2009.

The funds are capped; meaning total

The Canadian program comes with many strings attached, whereas the U.S. program doesn’t.

Kevin Mason, Equity Research

While the inherent potential of the package to assist pulp and paper mills and return them to profitability remains hotly contested, as Tembec’s decision demonstrates, it has already acted as a stimulus. Mercer has also announced it will rework its Green Energy Project for its Castlegar, B.C., mill, in light of promised funding from the program.

“Not only does this [program] demonstrate a commitment to the future of the industry through its support of capital improvements, but it will help mills pulpandpapercanada.com

payouts to Canadian mills will not run over the $1 billion mark. Possible projects that could be eligible for funding include energy efficiency improvements for recovery boilers and pulp and paper machinery, cogeneration unit upgrades, and machinery that converts forest biomass to ethanol.

The program has several critical stipulations however: the funds must be spent over a three-year period on capital expenditures that improve energy efficiency and environmental performance,

and funding is tied to the production of black liquor, an element considered problematic by some.

“While a response to the American black liquor subsidy (see Black liquor subsidies, pg. 10) is welcome news for the Canadian pulp industry, in my opinion, this is not an appropriate response for a number of reasons,” laments Arnie Bercov, president of Pulp, Paper and Woodworkers of Canada Local 8 in Nanaimo, B.C. “[This package] targets only chemical pulp while leaving out the mechanical pulp mills, and it is specific as to what the Canadian mills can do with the money, while the American mills are free to decide how they will spend [theirs].”

Natural Resources Canada estimates 27 mills in Canada will be eligible for the funding.

Analyst Kevin Mason agrees with Bercov’s assessment, saying that while the package will be helpful to producers, it is not on par with the U.S. program, a factor sure to penalize Canadian mills.

“It is unfortunate that the Canadian program optically tries to match the U.S. program, but falls short on its application. The Canadian program comes with many strings attached, whereas the U.S. program doesn’t.”

Mason, who is managing director of forest products for Equity Research, July/August 2009 PULP & PAPER CANADA

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ANALYSIS

BLACK LIQUOR SUBSIDIES: A cross-border comparison acknowledges however, that industry is not prepared to turn up its nose at any bones tossed its way. “No producer is about to look a gift horse in the mouth,” he notes.

Also at issue is the pivotal matter of timing. A recent report by the Globe and Mail noted industry may have to wait until late fall or early 2010 for funds to start moving. The package, partially created to mitigate the negative effects of the US$6- to US$8-billion black liquor subsidies to U.S. pulp producers, will be, according to some, too late in its response.

“It [the package] does not provide any immediate relief to Canadian companies to meet immediate cash flow problems,” Bercov says. “To become environmentally sustainable over the long haul requires the

Coles also pointed out that Catalyst Paper and Fraser Paper expressed their disdain for the package, chalking it up to, “too little, too late.” Both companies own kraft pulp mills.

While the inner workings of economics ensure the package, on a fundamental level, will prove effective in achieving its goal of helping mills improve their operating conditions, an economist consulted for this story who requested anonymity, says the forestry industry is somewhat of a special case. “Economically, this cannot be construed as a bad decision. Economics is all about making the best allocations from a fixed quantity of resources.

Nevertheless, it is the prerogative of our industrial leaders to develop strategies that do not solely draw from Canada’s

Instead of meaningful action, we get empty promises of financial aid, such as the $1-billion Pulp and Paper Green Transformation Program.

Dave Coles, Communications, Energy and Paperworkers’ Union

ability to survive over the short haul.”

The current economic crisis is squeezing the resources and operating conditions of already cash-starved mills, an environment not conducive to the reception of this particular aid package, he adds. “At almost any other time, the goals of the black liquor rebate program would be extremely laudable but under the unprecedented economic crisis, mills, communities, and workers are facing, a lot of mills may not survive to invest in green technology.”

The news of Fraser Paper’s bankruptcy declaration, the day after the funding announcement, further illustrates the futility of the package, says the Communications, Energy and Paperworkers’ Union, which has been alternatively calling for loan guarantees, job protection, and pension protection measures.

“We have been pleading with the government for months,” CEP president Dave Coles says. “Instead of meaningful action, we get empty promises of financial aid, such as the $1-billion Pulp and Paper Green Transformation Program.”

10

natural resources, but by shifting to longterm sustainability with an emphasis on economic viability.”

FPAC’s Avrim Lazar argues the program is already doing this, saying it craftily combines commercial and environmental change. “This is smart policy and smart spending,” he notes. “The industry has long recognized and acted on the fact that its future lies in being the greenest supplier of product to the global marketplace. However, continued environmental improvements require large capital investment — something that is not readily available during these difficult economic times. The government’s new Green Transformation Fund provides the industry with the capital it requires today to make the environmental upgrades needed to prepare for the return of markets.”

A lack of capital investment has oft been cited as one of the most significant contributors to the industry’s downfall.

Linking access to grants and subsidies with investment is indisputably a tool with which to encourage and secure capital spending. However, as Pricewater-

PULP & PAPER CANADA July/August 2009

T

o qualify for a biofuel tax credit, U.S. mills started adding diesel to the black liquor they produced. Critics argue that this provides American facilities with a veritable and unfair leg up on Canadian producers struggling to survive in a cutthroat economic climate. The U.S. subsidy program will expire at the end of 2009.

The impact of the U.S. program was made clear by Domtar’s ability to reopen its pulp mill in Baileyville, Maine in June.

The facility had been shut down for close to four months, and Domtar directly cited the refundable tax credits as a major driver behind the decision. At the same time as the Baileyville closure, Domtar temporarily idled a pulp mill in Dryden, Ont., which remained closed until the announcement of the Canadian $1-billion aid package, at which point the company confirmed employees would return to work by the end of July.

While the U.S. subsidy has upset the world pulp market, several Canadian companies charge that the black liquor subsidies have also allowed integrated producers in the U.S. to lower their prices for newsprint.

Equity Research analyst Kevin Mason describes the discrepancy between the two packages as “Darwinian in design” in that, “the stronger firms will benefit while the weaker ones won’t be helped and will still fail. That’s not necessarily a bad policy, but it is distinctly different that the U.S. program that provides a huge amount of funds to any mill producing black liquor, and the U.S. monies come with no strings attached.

The Canadian pulp and paper industry was destined to shrink going forward, and this program won’t change that trend. It will just slow it a bit.”

houseCoopers aptly notes, “sharp rises in material, oil and gas, fibre and operating expenses are hamstringing the sector’s ability to both compete and to innovate.”

As a result, “for the Canadian forestry industry, financial returns continue to be below the cost of capital.” In short, while the $1-billion Pulp and Paper Green Transformation program may very well prompt investment, there are no guarantees that once the balance sheets are tallied, profits will outweigh costs. PPC pulpandpapercanada.com

CONFERENCE REPORT

PacWest: real life solutions A strong technical program leaning toward solving operational problems anchored the PacWest 2009 event.

T

he industry’s financial constraints may have diminished the attendance at PacWest, but the conference remained a valuable gathering for networking and professional development. The final count was 150 attendees, enjoying the June sunshine in the mountains at Sun Peaks Resort, near Kamloops, B.C. PacWest is hosted each year by the Pacific Coast and Western branches of the Pulp and Paper Technical Association of Canada (PAPTAC).

PacWest’s opening forum touched on the subject of carbon markets and bioenergy. Experts from various fields made it clear that global policy decisions are creating opportunities for forest products companies in these emerging markets, although much of the legislative framework is not yet set.

Michael Weedon, executive director of the BC Bioenergy Network, noted: “There’s an enormous interest but this industry is really in its nascent stage.”

Dong Singbeil of FPInnovationsPaprican elaborated on some of the challenges the industry faces in its efforts to create a bioenergy or biochemicals

By Cindy Macdonald, editor market in Canada. He noted that there is an opportunity to take lignin out and make new products with it, but in doing so, we may compromise other uses of forest biomass. “Our processes are designed to optimize the properties of cellulose.

Optimizing for lignin might be detrimental to that.”

Already, small scale modifications to existing infrastructure are underway, he commented. He predicted that new partnerships will be formed, recognizing the interdependence between sawmills, pulp and paper companies, and energy companies.

higher tensile index than other pulps.

Maurice Douek and Wayne Bichard of FPInnovations conclude that, in general, softwood pulps produced in Canada exhibit superior fibre and handsheet properties compared with pulps from other countries. Canadian pulps had the lowest coarseness, highest tensile strength, highest light scattering coefficient, and lowest bulk.

“This should translate into superior papermaking potential, in terms of better formation, increased sheet bonding, higher smoothness and opacity, but lower stiffness,” they report.

Canadian kraft pulp is the best

Tackling tall oil issues

PacWest attendees had the pleasure of hearing that Canada’s kraft pulp is superior in many ways to pulps from other nations. Research comparing Canada’s kraft market pulp with those produced elsewhere in the world arrived at some conclusions that Canadian pulp producers will be happy to hear. In 2008, FPInnovations-Paprican conducted a program to benchmark the quality of bleached kraft market pulps to provide a database of physical, optical, and chemical properties. The program included 49 pulps from Eastern and Western Canada, the southeastern U.S., Scandinavia, southern Europe, South America, Asia-Australasia, and South Africa.

Among the softwood pulps, the average fibre coarseness of Canadian species was found to be 25% lower than that of other species. Also, at 400 CSF, Canadian pulp generally exhibited an 18% George Weyerhaeuser Jr. (centre) was the feature speaker at PacWest.

He gave attendees an insider’s view of international policy development as it relates to the pulp and paper sector.

He is joined by conference co-chair Alan Humber (left) and conference chair Carlo Dal Monte.

pulpandpapercanada.com

Research at FPInnovations-Paprican has shown that tall oil production at mills pulping grey stage mountain pine beetle attacked wood has dropped substantially due to higher soap solubility in black liquor, a reduced tendency for the soap to “float” off in storage vessels and skimmers, and lower soap quality (acid number).

Two experimental approaches to address this problem were discussed at PacWest. First, Vic Uloth and Erin Guy of FPInnovations-Paprican assessed the effect of higher air injection rates on skimmer performance when pulping mountain pine beetle infested wood.

They determined the higher air injection rates provided little benefit, and concluded that this procedure is not recommended.

Later, in a paper entitled “Waste Fatty Acid Addition to Black Liquor to Decrease Tall Oil Soap Solubility and Increase Skimming Efficiency in Kraft Mills Pulping Mountain Pine Beetle Infected Wood”, Uloth and Guy discussed a mill trial which confirmed that waste fatty acid addition decreased tall oil soap solubility, increased tall oil soap skimming effiJuly/August 2009 PULP & PAPER CANADA

11

CONFERENCE REPORT Speakers at the conference forum addressed ways the industry could profit from its green potential.

From left: Douglas Singbeil, FPInnovations-Paprican; Michael Weedon, BC Bioenergy Network; Ron Ezekiel, Fasken Martineau; Paul Lansbergen, Forest Products Association of Canada.

ciency and produced a higher quality soap that was readily processed in the mill’s tall oil plant.

This submission was coauthored by Dale Shewchuk of Cariboo Pulp and Paper and Ron van Heek, now with with Aker Kvaerner, Vancouver.

Best practices for capital projects

Terry Good and Cal Green discussed a pulp machine capacity upgrade undertaken at Canfor’s Intercontinental mill in Prince George, B.C. Good is with Allnorth Consultants Ltd., while Green works at the Intercontinental mill.

As a result of numerous runnability improvements and upgrades over the years, the pulp machine had become the bottleneck of the Intercontinental mill.

Phase 1 of the plan to increase the capacity and reliability of the pulp mach­ ine was designed to achieve a capacity increase of 20 ADMT/day. It included top felting the first and third presses, increasing the capacity of the dry end repulper, and significant improvements to the layboy. The project team determined that the most economical method for increasing the capacity of the machine was to increase the consistency of the pulp sheet entering the dryer. Top felting of the third press provides the biggest contribution to increased consistency.

GL&V was selected as the vendor for

Around this table, everybody helps each other

One unique benefit of the PacWest meeting is the peer-to-peer roundtable meetings, such as the Pulp Machine Superintendent Round Table. Dwayne Sklapsky, who organizes the group, describes it as Participants in the 2009 Pulp face-to-face discussions among people Machine Superintendent Round Table who do the same job. Sklapsky is machine (from left): Rob Gardner, room superintendent at Zellstoff Celgar Sandwel Engineering (moderator); Ltd., Castlegar, B.C. Jay Van Dee, Alabama River Pulp; “Even though we can be a diverse Colin Hansen, Weyerhaeuser; Greg group, the problems can be very similar. Seebach, Domtar; Lindsay Dickinson, Carter, Holt, Harvey Pulp and Paper; We discuss some operational issues, but Dwayne Sklapsky, Zellstoff Celgar.

90% of what we have in common is people issues,” says Sklapsky. “It’s very reassuring, like a support group.”

The group is a loose collection of individuals in similar positions at pulp mills across the country, with a few participants from the U.S. and one from New Zealand. A few months prior to the meeting, Sklapsky sends an invitation and solicits questions for discussion. Anyone not able to attend can still benefit from the group’s expertise by reading the detailed minutes circulated after the meeting.

The Pulp Machine Superintendent Round Table usually has about 8 to eleven participants. They convene for two all-day meetings during PacWest. Participation in the group is free, but those wishing to attend the round table must be a registered attendee of PacWest.

“We’re not an organized association,” remarks Sklapsky, “just a network of peers. We have discussions that are very open, very frank.”

Plus, he says, if you’ve met someone at the round table, it gives you confidence to call them and get their input on problems at a later date.

One attendee of past meetings comments: “The ideas generated through exposure to the experiences of other mills have a positive spin on increasing equipment reliability and machine runnability.”

For further information about the group, contact Sklapsky at 250-365-4120 or dwaynes@celgar.com.

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PULP & PAPER CANADA July/August 2009

the top felting portion of the project. The top felting equipment was able to operate at rated capacity immediately after startup, and achieved an average consistency increase of 2.52%.

Robert Matchett of Cook Engineering presented a case study of a power boiler upgrade at AbitibiBowater Thunder Bay, which allowed the mill to reduce its greenhouse gas emissions and burn more biomass.

The paper, “Greenhouse Gases and Multifueled Boilers: A Case Study in Efficiency Improvements on Renewable Fuel Usage”, was authored by Trent Woolsey of AbitibiBowater, Dave Burton of Alstom Power Canada, Robert Matchett, Cook Engineering, and Randall W. Morrison, Automation Applications Inc. The project included improvements to the biomass handling equipment, boiler bottom configuration modifications, new combustion air control strategies, and a new ash removal system, all controlled by an Invensys DCS with the application of advanced control strategies developed by AAI. The project met its goal of reduced natural gas consumption and reduced the mill’s CO2 emission by nearly 20% in the first year of project operation (20062007). With the boiler able to meet its steam demand using biomass only, the project’s capital costs were recovered in one year through savings in natural gas consumption.

Rounding out the PacWest program were a panel discussion of trends in product certification and an insightful panel on energy management led by Alex Adams of BC Hydro. Speakers on the energy management panel generally agreed that the pumping system is a good early target for energy conservation projects, as are compressed air systems and blowers.

Armed with ideas and examples from other mills, PacWest attendees headed home invigorated, knowing they aren’t alone in the challenges they face day to day.

PPC pulpandpapercanada.com

MAINTENANCE

The biggest lube problem:

lack of knowledge Automatic systems can solve many of the issues related to

By Bill Roebuck, editor, Machinery & Equipment MRO manual lubrication methods.

T

he biggest problems regarding industrial lubrication were identified in a recent interview with Mike Deckert, vice-president at Flo Components Ltd., Mississauga, Ont., an automatic greasing systems specialist and a supplier of lubrication solutions to major manufacturers in Ontario.

Deckert, a member of the Society of Tribologists and Lubrication Engineers (STLE) who has taught part-time at the Lubrication School at Mohawk College in Hamilton, ON, for the past 15 years, has witnessed an increase in the number of ‘lubricators’ employed by forward-thinking companies, from steel mills to food plants to large aggregates firms. Despite this, he says, many companies don’t give lubrication the respect it deserves.

According to Deckert, lack of knowledge about lubrication, lack of knowledge about lubricants, and a lack of concern among companies about the importance of lubrication issues are the top three problems with industrial lubrication today.

“In North America, lubrication is like a necessary evil,” he says. For example, in Europe, automatic lubrication systems are much more accepted than here. Deckert estimates 85% of lubrication systems in use in North America are still manual.

He hears about concerns that automatic systems will put people out of work, but says that isn’t the case. “It doesn’t replace somebody, it just replaces the grease gun.” Automatic systems solve the problem with manual methods, for example, of using too much grease in bearings, and the uneven and irregular application of the correct amount of grease. This can result in early bearing failures.

“With manual methods, you get peaks and valleys of lubricant in a bearing.

Manual lubrication can mean feast or pulpandpapercanada.com

famine conditions, especially when lubrication is done only ‘when there’s time.’ As soon as there’s a void, heat builds up and problems start.

“Automatic systems put in smaller, measured amounts of lubricant at frequent intervals while the equipment is operating, maintaining the correct amount of grease in bearings at all times. As well, contamination is constantly being moved out.”

However, there is a disadvantage to an automatic system, Deckert points out.

“People think that it looks after itself. But no, it’s just another tool. Somebody still has to check the lines and look for leaks.

It’s not a total solution. Someone needs to take ownership of the system.”

The lack of knowledge about lubricant products, and oil and grease compatibility in particular, is another major problem Deckert sees. “If incompatible lubricants are used, you can get plugged lines, sticking metering valves, and so on. These problems can shut down a whole series system. And in a parallel setup, the system will work around the problem until it’s too late.”

Lubrication is an afterthought in many companies, Deckert has noted. “They don’t recognize the significance lubrication plays. Even in some schools, it doesn’t get the attention it deserves. For example, a millwright training program

might only discuss lubrication for one day, and that generally is about using a grease gun and grease fittings. Lubrication typically isn’t given relevance.”

Suppliers can help companies justify the cost of automatic systems by showing the return on investment, through reduced downtime and energy savings, he notes.

Deckert cites a study that showed improper lubrication accounted for 53% of all bearing failures for a major component manufacturer. The majority of failures were determined to be caused by contamination of bushings by dust, dirt, and moisture, inadequate amounts of lubricant applied to bearings, or overlubrication of key pivot points.

Direct costs from inadequate lubrication include replacement bearings, labour to repair or replace bearings, and unscheduled downtime. Indirect costs include work safety and housekeeping issues, wasted lube, environmental issues, and higher labour costs related to inefficient manual lubrication practices.

“An automatic lubrication system helps eliminate these unplanned and unnecessary expenses,” says Deckert. PPC Reprinted from Industrial Lubrication, a supplement of Machinery & Equipment MRO.

July/August 2009 PULP & PAPER CANADA

13

COVER STORY

Papermaking

on a nano scale Papermakers don’t need equipment upgrades to boost machine speed and product uniformity — just some very, very small additives.

By Martin Koepenick, Innova

We are always looking for better ways to control the physical and optical properties of coated paper, and nanomaterials might make this possible.

W

hat if fibre content in paper could be replaced with significantly less costly minerals, and quality went up? What if this substitution saved energy, as well? What if paper could win out over not-in-kind materials, because of innovative changes in formulations that produce a “greener”, more dynamic sheet? For Canadian papermakers, these what-ifs are not as far-fetched as some might think.

“There are some nano applications in papermaking that have been around for a long time, such as retention/dewatering aids and some coating formulations. We are also seeing new concepts in coating pigments, binders, and starch which look promising,” notes Dean Benjamin, director of research for NewPage Corporation.

“Nano is the buzzword these days, even for materials we would have looked at anyway, but nonetheless, it’s important on a practical basis.”

Professor Art Ragaustus, of the School of Chemistry and Biochemistry — Institute of Paper Science and Technology at Georgia Institute of Technology, believes now is the right time for paper scientists to re-invent paper, employing knowledge on a nano level to achieve big results.

“Composite materials are the way of the future,” he states. “This includes nano-composites — composed of fibre, minerals, silica sols, starches, resins, and more — designed to achieve desired results in a more efficient way. Some innovations will require radical change, and others will require modest adjust14

Dean Benjamin, NewPage Corp.

ments for very big results. So what are we waiting for?”

According to Tony Lyons, director of research, Imerys Pigments for Paper Business Group, “Nano-engineering is becoming as important as, or maybe even more important than, the use of nano-materials. Structuring paper on the nano-scale to optimize its properties, at as low a cost as possible, without new capital investments, is the way to go in today’s new world.”

Downstream benefits are numerous

Benjamin confirms that many NewPage mills have employed silica and bentonite nanoparticle or microparticle systems for retention, drainage, and formation of the sheet for more than fifteen years. He says that the efficiencies achieved would not have been possible with standard polymers.

“Some of the mechanics and chemistry of forming a paper web happen on a very small scale approaching the nanometer dimension. So, naturally we need materials that can function in that size range.

PULP & PAPER CANADA July/August 2009

“Anything that enhances formation will improve the uniformity of the sheet,” he continues. “For example, our printers will see better-looking prints because the sheet is more uniform in appearance. Strength is also more uniform, which leads to better runnability on our paper machines and in our customer’s pressroom. Better uniformity also allows lighter basis weights of paper, which create savings in postage costs for our customers.”

On the papermaking side, “better drainage leads to a higher solids web, which translates to energy savings because of a reduction of the drying energy demand.”

Retention breakthrough: fourth generation silica sols

Mark Zempel characterizes Eka Chemicals’ fourth generation structured silica nanoparticle technology as the first major breakthrough in retention/drainage systems since the early 1990s. Zempel is market manager-retention for Eka Chemicals in North America.

“Dramatic efficiency and performance gains have been regularly achieved at lower active nanoparticle dosage rates.

These results have been achieved in commercial applications while maintaining and often improving fines and filler retention levels,” he explains.

Zempel notes that the first pioneering U.S. customer using this technology, called Eka NP 2180, has documented an 8% average machine speed increase, pulpandpapercanada.com

COVER STORY

Photo: NewPage Corp.

which, along with improved additive efficiencies, has resulted in considerable cost benefits.

According to Zempel, the basis for these efficiency and performance improvements is the nano-scale engineering of the colloidal silica particles themselves. “Manufacturing and formulation innovations have allowed careful control of particle size, degree and type of aggregation, and surface modification. The resulting improvements in these important product dimensions have lead to the ability to provide paper and board makers with more dewatering and retention than were previously possible.”

Joakim Carlén, Eka’s paper chemistry research and development manager, who led this initiative, puts it in perspective.

“This advance in particle design represents a step change from any previous nanoparticle design.”

Carlén says the new nanoparticles are even more like a strand of pearls than before, with particles only 2.5 nanometers in size. “Just as the most desirable pulpandpapercanada.com

sea pearls have perfection in size and shape, it’s the same for our nanoparticles.

Smaller particles in extended structure with perfect roundness are better.”

Give printers an edge

A wide range of white top liner producers have employed advanced micro and nanoparticle systems for years, gaining smoothness of the sheet for better printability. Smurfit Kappa Facture in France, Eurocan of Spain, Kemiart of Finland, and Simpson Tacoma are notable examples of producers adding value for their customers through dynamic graphics on packaged goods.

According to Zempel, as the knowledge continues to grow about the application of retention and drainage chemistries, the additional value delivered by nanoparticle technologies increasingly impacts the properties of the final paper and board. “We hear about even better results at the printers and converters, on fast modern printing presses and other machinery.”

Embracing nature’s nanoparticles

Nanoparticles have applications in other areas of papermaking as well. Nanoclays are emerging in the coatings field, with nano innovations in binders on the horizon as well.

NewPage’s Benjamin explains that nano-sized, in reference to clays, primarily refers to the thinness of clay platelets.

This equates to many more plates for a given volume or mass of clay.

What makes nano-sized clay particles even more interesting, as Benjamin sees it, is how they open doors to other nanosized additives. “Now, we can look at latex and starch binders, which are smaller and smaller. The end result will be thinner coats of equal or higher effectiveness, adding new dimensions to coating with less raw material content.”

He continues: “Anytime you can be just as effective, or better, but use less raw material you are ahead. We are always looking for better ways to control the physical and optical properties of coated July/August 2009 PULP & PAPER CANADA

15

COVER STORY

Structuring paper on the nano-scale to optimize its properties, at as low a cost as possible, without new capital investments, is the way to go in today’s new world.

Photo: NewPage Corp.

Tony Lyons, Imerys Piments

paper, and nanomaterials might make this possible.”

Imerys’ Lyons adds, “Nano-thin and large aspect ratio clay products are already revolutionizing the way in which coatings are being formulated. This new dimension opens up new avenues of creativity to meet the needs of the end user.”

Lyons is particularly enthusiastic about nanomaterials found in nature. “What is especially motivating is naturally occurring materials like oyster shells, made of stabilized calcium carbonates plates of nano-dimension in their thickness that can achieve incredible stiffness and optical properties. You win for the mill, your print customers, and for the environment.

What nature has been able to design, by building up the right sized binder and pigment morphology, is impressive, compared with man’s best efforts. The ability to mimic natural systems is of great interest.”

Translating knowledge of nanomaterials to papermaking presents opportunities for unique optical properties and strength, says Lyons. “Stiffness is very important for paper if you are reducing weight. Nano options offer incredible stiffness, brightness, colour, opacity, and unique optical properties. Opacity gains could be very valuable.”

With research continuing at both the industrial and academic level, papermakers, converters, and printers are sure to feel the effects of these very small particles in a big way.

PPC Martin Koepenick of Innova has written about the paper industry and innovations in technology for more than 25 years. He can be reached at mkoepen@earthlink.net.

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PULP & PAPER CANADA July/August 2009

ArboraNano receives funding to pursue nanomaterials research A network of Canadian researchers will be focusing on how nanomaterials derived from forest products can be used in a variety of industries.

FPInnovations announced in February that ArboraNano — the Canadian Forest NanoProducts Network has been selected as one of four new Business-led Networks of Centres of Excellence funded by the Government of Canada. ArboraNano is receiving $8.9 million over four years.

ArboraNano is a research and development network bringing together nanotechnology and forest sector expertise. It will strive to create a suite of highlyengineered, carbon-neutral products containing nanomaterials, using wood and wood fibre from Canada’s forests.

Dave McDonald, vice-president, pulp and paper, FPInnovations, says many of the new products will be based on a plant-derived nanomaterial: nanocrystalline cellulose (NCC), while others will use other nanomaterials in the development of new forest products. “NCC is a nanomaterial that has yet to establish a presence in the marketplace but that holds great promise. Research by FPInnovations scientists has shown that NCC has many remarkable properties, some of which are unique and others that are comparable to those of other well-known nanomaterials.”

NCC can be economically extracted from trees. The properties of NCC and the many forms in which it can be made means that it has the potential to be used in many different ways, namely advanced building products, recyclable structural and interior components for the transportation industry, innovative coatings and fillers for papermaking, novel bioplastics, fibre-reinforced composites, switchable optical films, bio-composites for bone repair, additives for paints/pigments/inks and for cosmetic products, iridescent or magnetic films, electrically-conductive membranes, printed paper electronic devices, encapsulated quantum semiconductor crystal dots, and advanced or “intelligent” packaging materials. FPInnovations researchers have also shown the advantage of using nanomaterials other than NCC to significantly enhance the performance of forest products such as building materials, paper, board, packaging.

“Nanotechnology bridges a broad spectrum of scientific disciplines and cuts across many industrial sectors. The growing interest in nanotechnology is a consequence of the promise this science holds to create new materials for a wide variety of manufactured goods,” states Pierre Lapointe, president and CEO, FPInnovations. “Nanotechnology is expected to represent a dominant force in economic growth over the next few decades and has been identified as a strategic platform for development. ArboraNano will build on this strategic platform and apply Canada’s forest resource to create new unique opportunities for Canadian manufacturing industries.” pulpandpapercanada.com

OPINION

The next step in workplace safety:

empower the employees Every single employee on every shift should be involved in hazard management. We should be concentrating on continuous bottom-up action and feedback to reduce risk exposure.

By John E. Little

O

verall workplace safety performance around the globe has improved over the last 60 years, but for the last 10 years it has stalled.

After 30 years in the safety management business, I believe that to get past the current level of stagnation in industrial safety performance, employers should shift the focus of their safety strategy to an employee-managed approach that will not only generate new gains in safety performance but facilitate much improved cost benefit analysis and control for safety initiatives.

There are two problems that need to be addressed. One, despite dramatic reductions in overall work related accident/illness rates (total medical cases),

global safety progress as measured by fatalities and severe injury/illness rates is stalled, and has been for at least 10 to20 years. Studies in recent years indicate that fatalities and high-severity/low frequency injuries have different causal factors than less severe but more frequent incidents.

Two, for the most part, current safety metrics can demonstrate empirically, or through correlation, the improvements or lack of improvements in outcomes following safety interventions but they do not demonstrate exactly why or how these interventions succeeded or failed.

Moving beyond the status quo

So how do we get to the next level in safety performance if the current approaches,

good as they me be, have stalled? The challenge is to develop tools and strategies to achieve the following: 1. Substantial reductions in fatality and high-severity injury/illness rates.

2. Continued reductions in the total accident rate (Total Medical Case Rate or Total Recordable Incident rate).

3. Lower total cost of safety to the enterprise which is composed of both prevention and failure costs.

Suggested strategies are: Safety metrics: Improve the methods and techniques of measuring the effectiveness of safety initiatives by using continuous hazard feedback from all workers, (not just management, staff and safety specialists).

Residual hazard management: The conventional safety management systems need complementary support by workers, especially to manage residual hazards at the workface.

Values-based empowerment: The application of the above initiatives is best achieved by first explaining the approach to all employees and involving them in developing the process from the beginning, starting with the alignment of safety with other enterprise values such as production, quality, and cost.

Cost and managerial fiscal reality: Better safety metrics will allow enterprise financial managers to establish the real financial benefits of proposed safety initiatives to the enterprise. This leads to better overall safety performance at lower cost to the enterprise through managerial fiscal reality or the ability to allocate scarce resources more efficiently.

The missing piece in the puzzle The old methods of workplace safety management have stalled, argues John Little.

The way forward lies in involving all employees in hazard management. pulpandpapercanada.com

The single common denominator in the aforementioned disappointing conJuly/August 2009  PULP & PAPER CANADA 

17

OPINION clusions is safety metrics. That is, the inability to link cause and effect. In other words, we are able to measure the outcomes (rates of losses, failures) of our collective safety interventions but we are unable to explain which ones are truly effective and why. Until we can do exactly that, we will make no progress.

Improvements in all of the other above

items are dependent on resolving this single major obstacle. An old Chinese proverb states “Only when you know why you have hit the target can you truly say you have learnt archery.”

My suggestion is that no safety initiative should be considered unless a method for measuring its performance is established and applied.

Optimizing safety management: a deployment strategy Most pulp and paper mills have basic safety management systems in place. However, achieving any incremental progress in safety performance starts with all managers, supervisors, and workers understanding and agreeing to how all employees can integrate safety into every task, every shift, during every working day. So, rather than focusing on compliance, we should be concentrating on safety fundamentals and on continuous bottom-up action and feedback to reduce risk exposures with the full support of all levels of management.

Foresight is the key ingredient.

Before starting this exercise, all employees must understand that risk lies where we are going, not where we have been. The emphasis should be on a forwardlooking, dynamic strategy of identifying new and/or residual hazards that lie ahead in any work activity and dealing with them as opposed to the “rear view mirror” approach of relying solely on past incident data and rigid safety rules to prevent future incidents. Better to take the rear view mirror and hang it out in front to see the dangers that lie around the corner.

Step 1: Define the proactive work methodologies that facilitate task-based hazard management and exposure control by all employees.

Productivity is like the seat on a four-legged stool; the four legs being production, quality, safety, and cost. Cut or shorten any one leg and we have a productivity problem. Weak performance by any of the four legs decreases enterprise profitability. The first step is to define what a safe and productive worker is and how he/she performs her work.

Step 2: Train all employees in these proactive work methodologies.

This consists of instruction and/or training in simple, practical task-based pretask planning and risk assessment skills as well as rudimentary project planning skills. In addition, they are trained and shown how to provide essential system performance feedback to superiors by reporting the failures of upstream filters to remove hazards that they observe on every shift.

Feedback is necessary for management, operations, engineering, purchasing, maintenance, training, supervision, and safety/health personnel to improve engineering design safety and upstream safety system hazard filters.

Step 3: Measure that employees are indeed applying these proactive work methodologies.

Immediate supervisors are the best placed to consistently observe and coach subordinates in the application of these proactive work methods.

Step 4: Reward employees for their accomplishments of these proactive work methods.

Every superior should demonstrate some form of positive recognition to subordinates for their application of these desired work methods and the proper utilization of the methodologies.

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PULP & PAPER CANADA July/August 2009

Promising developments

Looking ahead, the picture is not all one of doom and gloom. There are some promising developments on the horizon.

Thinking outside the box: Safety professionals are questioning everything about workplace safety: the way we define it, measure it, achieve it, what it costs, and even their own ability to contribute to safety improvement and business goals, and whether they have a future in this business.

For example, in a 2004 article in Professional Safety, Packer Engineering consultants Curry, Quinn, Atkins, & Carlson explained why experienced workers were still having serious injuries and concluded that “the only truly viable long-term strategy for increasing workplace safety lies in combining normal safe design, guarding, and warning strategies with the fostering of an increased understanding among workers of the actual risk involved in their activities.” This sentiment is echoed by Hatscan, a reputable safety training company in Alberta. In a due diligence training course, Hatscan states, “The single most frequent cause of accidents is failing to take the time to think through the work, identify the hazards, and deal with them.” New strategies suggest achieving risk reduction by focusing on hazard identification and exposure reduction rather than through hazard elimination as being more realistic and less costly.

The business case for safety: In the April 2009 issue of Professional Safety, a group closely associated with the Liberty Mutual Research Institute for Safety (LMRIS) in the U.S. authored a very revealing article titled Financial Decision Makers’ Views on Safety. It was part of a larger study performed in 2007. More than 200 corporate financial decision makers in medium- to large-size companies (100 employees or more) were surveyed. The focus was to explore their perceptions of the leading safety priorities, concerns, and losses. The top priorities cited as the leading causes of workers’ compensation losses, causes of concern, and targets for future resource allocation were: • overexertion, • repetitive motion • bodily reaction injuries.

Fatalities were not mentioned.

Although this group favoured pulpandpapercanada.com

OPINION more/better safety-focused training as the best safety intervention, they did not elaborate as to why they believed this, nor did they appear to understand the importance of other safety interventions. In conclusion, they said that the top benefits of an effective workplace safety program were predominantly financial in nature (e.g. increased productivity, reduced costs), claiming an average ROI for safety initiatives of US$4.41 per $1 spent on safety.

Yet there appears to be a lack of understanding on the part of financial decision makers as to exactly what safety interventions are effective and why. Nonetheless, it is reassuring to note that these financial managers essentially believe in the business case for safety, that it has a positive impact on productivity and cost reduction, and that they are receptive to what they believe will be cost-effective safety initiatives.

What is safety really all about? What is the ultimate fundamental activity that leads to incident-free performance on the job? It is the removal of the cause or causes that lead to undesired workplace incidents and losses. Safety management is defined by the Health and Safety Executive, a form of national safety council in the U.K., as simply a process that converts uncontrolled hazards into controlled hazards. Success or failure in achieving workplace safety boils down to how well we identify uncontrolled hazards and then control them, where control involves either hazard elimination (preferable) or exposure avoidance. More specifically, this is done through hazard management.

A 2005 American Society of Safety Engineers (ASSE) survey of more than 5000 safety professionals revealed that the two most important elements for them (or anyone else) to effectively manage workplace safety were: • understand the hazards present and the risks associated with them, and • be able to convince the workforce to act in a safe manner.

Good hazard management is the key to a safe workplace. How do we do this?

For many years Occupational Health and Safety Management Systems (OHSMS) have been the method of preference at trying to either avoid the creation of hazards at the source in the first place or, failing that, providing management-driven pulpandpapercanada.com

New strategies suggest achieving risk reduction by focusing on hazard identification and exposure reduction rather than through hazard elimination as being more realistic and less costly. safety rules, regulations, and strict work procedures and practices to avoid them.

They are fairly effective but experience has shown that they are far from perfect at eliminating the hazard burden at the point-of-risk or worker/workplace interface. They appear to have reached their optimal performance point only where properly implemented.

In reality, most OHS management systems do not operate at peak performance as they are not fully implemented and/or do not have the proper feedback to measure and improve performance.

So how do we complement or improve on hazard management by the OHSMS? We need a solution to manage residual and new hazards/risks at the point-of-risk as well as providing continuous, real-time feedback to management on the failings of the OHSMS at filtering out hazards upstream of the point-of-risk That solution is the knowledgeable worker!

Every single employee should be involved in hazard management (during every shift and every work day), not just the safety specialists, supervisors, engineers, and managers. The more eyes the better.

The current problem with high-severity injuries and fatalities requires new, innovative solutions as the causes are different from the typical high-frequency, low-severity injuries on which much of the past prevention theory and systems are based. The causes of these highseverity injuries are linked to sudden changes to routine operating conditions or to non-routine work conditions and tasks that introduce new hazards at the point-of-risk. Due to the dynamic nature of these hazards and risks, the worker is required to adapt and adjust quickly to

the changes on the fly.

The worker is best placed to provide feedback to management on the hazards that are not being filtered out by the OHSMS upstream hazard detection/ control activities. Management can then correct and improve these safety management systems.

Ownership and empowerment: The caveat here is that every employee needs to be part of the entire project from the beginning, with the opportunity to participate in establishing core enterprise safety values and to provide input on safety content, planning, implementation, and maintenance.

Above all, it must be simple!

Involve everyone in hazard management

The most profound yet simple indicator of a safe operation I ever heard of came from an Australian bank study of three different companies regarding their compliance to Australia-New Zealand’s AS/NZS 4801 occupational safety and health management system standard. The company that had the least documented system and the least level of compliance with the AS/NZS 4801 standard had the best safety performance.

All managers and employees of this company were clearly able to articulate the system and apply the key preventative activity - hazard management - as part of their everyday work activities.

The system developed and used by the company focused attention at a high level on three major elements: hazard management, leadership, and performance measurement.

The company had created a work environment where employees at all levels of the organization were actively participating in the decisions and processes that affected health and safety.

It clearly demonstrated the achievement of superior health and safety performance based on the elimination of risks to health and safety, and the creation of a workplace culture where safety was considered to be a critical feature that involved everyone at the workplace on an ongoing basis.

PPC John Little is a risk management consultant and can be reached at jelittle@videotron.ca July/August 2009 PULP & PAPER CANADA

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PULP QUALITY

Effects of Some Wood Chip Properties on Pulp Quality

By F. Ding, M. Benaoudia, P. Bédard, R. Lanouette Abstract: As the raw material, wood chips influence pulp and paper quality. On-line detection and evaluation of the intrinsic properties of wood chips are therefore a basis for quality control. Following CMS measurement of some properties of the chips, a series of TMP experiments were performed at the CIPP pilot plant. A PLS analysis demonstrated that CMS measurements can be used to predict some pulp properties.

W

ood chips being the raw material in pulp and paper making, their properties, such as wood species, freshness, moisture content, and size, are the most important factors affecting pulp quality [1, 2]. Variations in the wood raw material and its fibres may give rise to 30-40% variations in pulp properties [3]. Continuous variations in wood basic density and moisture content occurring in the chip flow tend to cause variations in refining consistency, which, in turn, affect pulp uniformity and energy consumption [4]. Homogeneous chip size distribution and low fines content produce good pulp strength while knots and bark content decrease pulp strength and brightness [5]. Unfortunately, the industry does not have an efficient method to predict pulp quality from wood chip properties due to the lack of on-line measurement technology.

In this research we used CRIQ’s CMS (chip management system) to measure some chip quality parameters before the chips entered the thermomechanical pulping (TMP) process. The CMS has been implemented in several mills for on-line monitoring of chip unloading and TMP pulping.

Chip brightness (or luminance) has been considered a synthetic function of chip properties [6, 7]; and we also found that it could be used to reduce bleaching agent consumption [6]; this was not enough, however, to estimate pulp quality. For this reason, CRIQ developed two new soft sensors (a virtual screen and a virtual bark content detector) and added them to the CMS. With the new soft sensors, CMS measurements became more powerful and included more important chip properties such as aging, wood species ratio, chip size distribution, bark content, etc. By applying a principal component analysis (PCA) method, we were able to find an inherent relationship between wood chip properties and CMS measurements, which gave us a better interpretation of some chip properties.

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A series of TMP experiments were performed at CIPP’s TMP pilot plant, and some pulp properties were measured. By comparing chip and pulp properties, and using projections to latent structures (PLS) analysis, we were able to demonstrate that on-line CMS measurements can be used to predict some pulp properties.

It should be pointed out that the focus of this paper is to show how CMS measurements can be used to predict some pulp properties. This prediction will suggest ways to control chip quality so as to ensure pulp quality. We tried to explain some important chip properties included in the measurements, but did not try to model them.

EXPERIMENTAL

F. DING, Centre de Recherche Industrielle du Québec (CRIQ) Sainte-Foy, Que.

M. BENAOUDIA, Formerly with Centre de Recherche Industrielle du Québec (CRIQ) Sainte-Foy, Que.

Materials For basic raw materials, we selected a mixture of balsam fir and black spruce in varying proportions, and then added jack pine and yellow birch.

The ten-chip sample protocol involved these four pure species and six mixtures of these species in different proportions. Chip aging is one of the important parameters involved in TMP. In order to evaluate aging impact, initial testing involved chips of a known age, and the test was repeated fives times with chips of up to six months of age.

The chips were stored outside under ambient air conditions, thus aging occurred naturally.

P. BÉDARD, SEREX Amqui, Que. Formerly with Centre de Recherche Industrielle du Québec (CRIQ) Sainte-Foy, Que.

Chip Measurement Before entering the refiner, the wood chips were measured by the CMS and its new soft sensors.

The CMS is a multi-sensor system that includes principal and auxiliary sensors [6]. The former, e.g., artificial vision sensor and near infrared sensor, measure chip optical properties and moisture content. The latter, e.g., distance sensor and air conditions sensor (air temperature, velocity and relative humidity), etc., provide information to extend measurements by the principal sensor, and stabilize

R. LANOUETTE, Centre intégré en pâtes et papiers (CIPP), Université du Québec à Trois-Rivières (UQTR) Trois-Rivières, Que pulpandpapercanada.com

PULP QUALITY

FIG. 1. Chip aging component overview.

FIG. 2. Score scatter plot of chip aging process.

FIG. 3. Chip species component overview.

FIG. 4. Score scatter plot of chip species.

the system. CMS measurements provide extensive information on chip properties that we can use to evaluate chip quality.

Pulping Chip measurement and pulping were performed at CIPP’s TMP pilot plant. The first phase of refining was performed under steam pressure (128°C) and the second under atmospheric pressure. During the test, four samples based on freeness/refining energy indices were prepared and evaluated. The pulp properties were measured by different sensors, such as: FQA (fibre quality analyzer), to measure fibre length distribution; and Pulmac, to measure shives content, etc.

RESULTS AND DISCUSSION

Chip Aging State Chip freshness is a very important parameter for the TMP process because fresh wood chips are brighter than older chips.

Chip aging is a very complex phenomenon that depends on the wood species, log and pulpandpapercanada.com

chip storage, ambient air conditions, etc.

It would be very difficult and unnecessary to estimate chip age from their aging state.

As mentioned in the Experimental section, ten samples were measured five times (tests A, B, C, D and E) by the CMS during natural aging (about six months).

Although chip brightness can provide an indication of chip aging, this is only useful when the wood species distribution does not vary. For an uncertain proportion of wood species, we need more information.

On the basis of laboratory and mill tests, we chose nine CMS measurement parameters, i.e.: moisture content, darkness, six optical parameters, and standard deviation of luminance.

Using PCA (principal component analysis), which involves a mathematical procedure that transforms a number of possibly correlated variables into a smaller number of uncorrelated variables called principal components, to analyze the CMS measurements, we developed an inherent relationship for chips at different aging

states. As shown in Fig. 1, the variations are well explained and predicted by two components [Comp(1) and Comp(2)], where X are variables, R2X(cum) is the cumulative sum of the squares of all the X values explained by all extracted components, and Q2(cum) is the cumulative Q2 value for the extracted components.

In the PCA, the R2 is the goodness of fit, that is the fraction of the sum of squares of all the X values explained by the current component and the Q2 value is the goodness of prediction, that is the fraction of the total variation of the X values that can be predicted by a component.

Figure 2 shows the plot obtained when plotting the scores of the two first principal components. From the first component, we divided the tests into 3 groups.

Group 1 was formed of test A; Group 2 was formed of test B, and tests C, D and E were superimposed to form Group 3.

From the second component, we were barely able to separate test E from tests C, D and B. July/August 2009 PULP & PAPER CANADA

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PULP QUALITY Taking the test conditions into account, we found that tests C and D had been performed in the winter of 2001; the chips were frozen, thus aging had almost stopped. Test E was performed in the spring of 2002; the measured results had changed only slightly, indicating that chip aging tended to stabilize. It is clear that the chip aging state information was reflected in the CMS measurements.

Wood Species Information Wood chip species is another important variable for the TMP process. Optical test methods [8, 9] and chemical vapour analysis [10] have been applied in the laboratory or for on-line monitoring of single wood species. But these sensors cannot be used to evaluate a mixture of more than two species.

Using PCA to analyze the CMS measurements, we obtained a good explanation and prediction of variations from two components as shown in Fig. 3.

Figure 4 shows a scatter plot of t1 vs. t2. The four wood species, i.e. spruce, balsam fir, jack pine, and birch scattered in different positions. If a mixture is close to a point corresponding to a pure species, one can conclude that the mixture contains a higher proportion of this particular species. The distances from the mixture point to different pure species points represent the proportions of these species in the mixture.

Although the chip aging state did not influence this conclusion, it did affect the different species’ positions in the t1-t2 plane (see Fig. 2). Therefore, the chip aging state is an auxiliary parameter for recognizing wood species. We concluded that the wood species information implicated in the CMS measurements. It should be noted that this analysis was based on four known wood species; we did not try to model species identification. For future modeling, we think that much additional testing and research will be required because of the variability of chip properties.

Chip Size Distribution and Bark Content Indices There are about 12 different types of chip classifiers available for off-line laboratory testing, and a few on-line discontinuous measurement systems [11]. Size measurements are based on only one portion of the wood chips, which is not really representative.

The identification of bark in wood chips is a manual operation conducted in the laboratory. In order to perform on-line chip size and bark content measurements, we developed two soft sensors: a virtual screen and a virtual bark content detector, both based of the CMS system. The virtual screen is a granulometry tool based on mathematical morphology; it simulates chip sifting through screens of increasing mesh sizes, which is what is done to compute size distribution in real tests. The virtual screen calculates the percentage of pixels for chips of a certain size (such as width, length, diagonal and area)) in relation to total pixels in an image.

This is different from the Williams classifier, which calculates the percentage by weight of the different chip sizes in relation to total chip weight. The two methods cannot be compared directly, but a relationship can be established with PLS modeling. The PLS is a regression extension of PCA; instead of finding the hyperplanes of minimum variance, it finds a linear model describing some predicted variables in terms of other observable variables. Validation test results (width) for the four wood species are plotted in Fig. 5.

The virtual bark detector was based on a colour classifier that 22

PULP & PAPER CANADA July/August 2009

FIG. 5. Virtual screen vs. Williams classifier.

FIG. 6. Pulp fibre predictive variable overview.

FIG. 7. Pulp fibre length prediction.

identifies zones in the image having the color of bark. As there are no basic colours for bark, the classifier had to be trained to identify bark despite variations in colour, luminance and shadows.

In the laboratory tests on the four pure wood species chips, detection accuracy for sound chips was about 95%; for the bark, it was about 80%. The test samples included 50% fresh chips and 50% old wood chips. The percentages represent the number of pixels of sound chips or bark in relation to total pixels in the images.

With these two new soft sensors, the CMS can therefore provide additional information on chip size distribution and bark content.

Fibre Length Prediction As previously discussed, the CMS measurements were now able to provide much more implicit information about wood chip properties. Our purpose was not to develop a tool for estimating these pulpandpapercanada.com

PULP QUALITY properties, but to use these measurements to evaluate some pulp properties. If this challenge can be met, TMP model predictive control can be achieved. In order to study the effects of CMS-measured parameters on the TMP process, we tried to find a relationship between CMS measurements and some pulp properties. The pulp properties that can be measured on-line are: freeness, shives content, and fibre length distribution, including: long fibre content, fines content, and mean fibre length (arithmetic, length weighted or weight weighted), etc. In this research, we considered freeness, specific energy, and CMS measurements as inputs; and shives content and fibre length distribution as outputs of the TMP. Outputs were measured by the Pulmac and FQA methods respectively.

Using the test results from the CIPP pilot plant, we developed a PLS model. Figure 6 shows a plot of cumulative R2Y and Q2 values for individual responses, where R2Y (cum) was the cumulative sum of squares of all Y values explained by all extracted components, R2Y was the fraction of the sum of squares of all the Y values explained by the current component, and Y represented predicted variables. Obviously, the explained and predicted variations of the model were very good.

An example of the predictions of the model for fibre length (lw) is shown in Fig. 7. It is clear that the prediction is excellent.

cies. An Optical Technique for Identification and Separation of Wood Species, Wood Sci. Technol., (25): 405413 (1991).

9. LAWRENCE, A. H. Rapid Characterization of Wood Species by Ion Mobility Spectrometry, Journal of Pulp and Paper Science, 15 (5): J196-J199 (1989).

10. FUHR, B. J. On-line Wood Species Sensor, Paper Age, Sept.-Oct., 26-29 (2001).

11. BERGMAN, T. On-line Chip Analysis: New Technology for an Improved Pulping Process, Pulp & Paper Canada, (12) 150-151 (1999).

Résumé: Les caractéristiques de la matière première, les copeaux, influencent la qualité de la pâte et du papier; la détection et l’évaluation en continu des caractéristiques intrinsèques des copeaux représentent donc une base pour le contrôle de la qualité. Après avoir mesuré les caractéristiques des copeaux avec le CMS, nous avons effectué divers essais de PTM à l’usine pilote du CIPP. L’analyse de PLS démontre que les mesures du CMS peuvent être employées pour prédire certaines caractéristiques des pâtes.

Reference: DING, F., BENAOUDIA, M., BÉDARD, P., LANOUETTE, R., Effects of Some Wood Chip Properties on Pulp Qualities, Pulp & Paper Canada 110(6):T91-T94 (July/August 2009). Paper presented at the 89th Annual Meeting of PAPTAC in Montreal, Que., January 28-30, 2003. Not to be reproduced without permission of PAPTAC. Manuscript received March 22, 2004. Revised manuscript approved for publication by the Review Panel Mar. 10, 2009.

Keywords: CHIP QUALITY, ONLINE DETECTION, QUALITY CONTROL, PULP QUALITY PREDICTION, PLS

CONCLUSIONS

The CMS is an excellent on-line chip measurement sensor.

With the assistance of PCA analysis, it allows for interpretation of some implicit chip properties such as chip aging state, species ratio, and moisture content. By integrating two new soft sensors into the CMS, we were also able to evaluate chip size distribution and bark content. Using PLS modeling, we demonstrated that the CMS measurements can provide enough information to predict some pulp properties. In future studies, we will use CMS measurements to define chip quality and refining parameters according to the pulp quality desired.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial support received for this investigation from QMNR (Quebec Ministry of Natural Resources) through the Centre of excellence for wood chip valorization, and Precarn Canada. Thanks are also given to pulp and paper industry staff, especially from our direct partners: AbitibiBowater – Division Belgo Shawinigan, Kruger Inc. Trois-Rivières, and AbitibiBowater Inc. Gatineau.

LITERATURE

1. SMOOK, G. A. Handbook for Pulp & Paper Technologies, Joint Textbook Committee of the Paper Industry, 54 (1982).

2. WOOD, J. R. Chip Quality Effects in Mechanical Pulping – a Selected Review, 1996 TAPPI Pulping Conference, Proceedings, 491-497 (1996).

3. LUNDQWIST, S. O., et al. Wood Fiber Simulation – A Model Based Tool for Optimized Wood and Fiber Utilization, Control System 2002, Proceedings, June 3-5, Stockholm, Sweden, 164-169 (2002).

4. TYRVÄINEN, J. The Influence of Wood Properties on the Quality of TMP Made From Norway Spruce (Picea abies) – Wood From Old Growth Forests, First Thinnings, and Sawmill Chips, International Mechanical Pulping Conference, Proceedings, 23-34 (1995).

5. BRILL, J. W. Effects of Wood and Chip Quality on the TMP Properties, International Mechanical Pulping Conference, Proceedings, Stockholm, 153-161 (1985).

6. DING, F., BÉDARD, P., BENAOUDIA, M. Economizing the Bleaching Agent Consumption by Controlling Wood Chip Brightness, Control System 2002, Proceedings, June 3-5, Stockholm, Sweden, 205-209 (2002).

7. DESHAIES, S. Le classeur de copeaux: Un nouvel outil pour le contrôle de la fraîcheur des copeaux, Les papetières du Québec, juin: 25-27, (2000).

8. SUM, S. T., et al. Laser-excited Fluorescence Spectra of Eastern SPF Wood Spe-

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BLEACHING

Effect of White Water Consistencies on Hydrosulfite Bleaching of DIP and TMP Pulps at AbitibiBowater Gatineau

By G. Rangamannar, R. Bellemare, Y. Dionne, J. Najim, and R. Amyotte Abstract: The purpose of this study was to assess the impact of the consistency of white water on hydrosulfite bleaching of both TMP and DIP pulps. Combinations of laboratory- and mill-scale trials were conducted. A pilot clarifier was used to clarify white water and separate the fines. The separated fines were floated in a laboratory cell. Optimal brightness results were achieved when clarified white water combined with floated fines was reused prior to hydrosulfite bleaching. The results showed that the bleach response and final brightness increased with decreasing white water consistencies.

A

bitibiBowater’s Gatineau mill uses deinked pulp (DIP) in combination with virgin thermomechanical pulp (TMP) for the production of newsprint. The paper machine white water circuit is centralized and the common white water is used for pulp dilution for both DIP and TMP plants.

The two main components of white water are suspended solids and dissolved solids. Total suspended solids can range from 0.1%-0.8% and the dissolved solids range from 0.13%-0.18% measured from headbox to press of a paper machine [1].

Suspended solids consist of fibres, fines, and coating or filler clays, wood extractives, polymers, and other organics adsorbed on the fines. Dissolved solids are organic materials such as fatty and resin acids and lignin derivatives [1]. White water studies carried out by Paprican [2, 3] concluded that to bleach DIP to high brightness, either fines have to be removed or a process to detach and remove ink from fines has to be added. Earlier work by Rohm and Haas (now Dow Chemical) at the AbitibiBowater Gatineau mill supported Paprican’s conclusion and showed an ink removal step either before and/or after hydrosulfite bleaching of DIP pulp can provide significant brightness gains [4].

This study focuses on two process scenarios to decrease the relative amount of ink in the white water system and thereby improve the hydrosulfite bleach response of TMP and DIP pulps. First, a simple clarification of the white water; paper machine white water clarification by a dissolved air flotation (DAF) technique for reuse in pulp mills has been suggested in literature for improving the efficiency of bleaching [5]. Second, the clarification and reuse of floated fibres prior to bleaching.

Recently an attempt was made to remove dissolved and suspended solids, and colour using a combination of DAF process and several additives for reuse in pulp and paper mills [6].

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GATINEAU MILL PROCESS OVERVIEW

A block diagram of the deinking process of the AbitibiBowater mill is shown in Fig. 1. The DIP furnish consists of 75% old newsprint and 25% old magazine. The furnish is defibred in two batch pulpers using chemicals to detach the ink particles. The pulp is processed through a detrasher, high-density cleaners, and a coarse screen to remove coarse contaminants. The pulp from the coarse screen is then passed through flotation cells for ink removal. The pulp brightness before flotation is between 47-49% ISO and after flotation is 59-60% ISO. The flotation accepts are subjected to light- and heavy-weight cleaning and fine screening operations for the removal of stickies and ink particles.

The pulp from the fine screen is thickened from 0.7% to 25% consistency (cy) through a disk filter (0.7% to 10% cy) and a twin wire press (8% to 25% cy). The filtrate from these unit operations is sent to a clarifier for water reuse in the process.

The pulp from the twin wire press is stored at 10% consistency in a tower and diluted to 4% consistency at the bottom of the tower. The pH of the pulp is adjusted to 5.5 using sulfur dioxide water.

G. RANGAMANNAR Rohm and Haas, North Andover, Mass.

R. BELLEMARE Rohm and Haas Canada Inc., Brossard, Que.

Y. DIONNE Formerly with AbitibiBowater Inc., Gatineau, Que.

J. NAJIM Formerly with Rohm and Haas

R. AMYOTTE Formerly with Rohm and Haas

pulpandpapercanada.com

BLEACHING

FIG. 2. White water reuse prior to hydrosulfite bleaching.

FIG. 1. AbitibiBowater Gatineau DIP process

FIG. 3. White water clarification and reuse.

After the high-density (HD) storage tower the pulp is subjected to hydrosulfite bleaching. The amount of bleach chemicals used is varied from 0.3 to 3 kg/t as needed. The bleaching is performed at 45-50°C. Typical unbleached brightness varies from 59% ISO to 60% ISO. The bleached brightness varies from 61% ISO to 62% ISO. In the stock preparation area, 55% TMP is mixed with 45% DIP and sent to the paper machine for making newsprint.

Metals composition and ink content are important considerations when evaluating hydrosulfite bleach response. Table I outlines the metal composition of Gatineau’s DIP process flow.

White water from the central white water chest is introduced in the deinking plant before and after the press. Table I shows the increase in metal levels between the disk filter and HD storage.

Metal content increased by 41% to 52% for Al, Fe and Mn. This is due to the addition of the paper machines’ white water. Hydrosulfite bleach response is also influenced by the amount of ink present in the white water used for pulp dilution. The effective residual ink concentration (ERIC) value of deinked pulp after white water dilution is increased by 30-60 ppm.

Figure 2 shows a general overview of the white water loop. The excess white water from the paper machines is taken to a central location and reused in the DIP for pulp dilution prior to bleaching.

EXPERIMENTAL

Hydrosulfite Bleaching Based on 4% consistency, individual charges of oven dried (OD) pulp were placed in heavy gauge polyethylene bags. The bags were sealed under nitrogen, shaken vigorously to disperse the pulp fibre, and preheated in a constant temperature bath at 50°C for 30 minutes.

Sodium hydrosulfite solution was generated from Borol™ pulpandpapercanada.com

FIG.4. Effect of white water consistency on bleaching of DIP pulp (Process Scenario 1).

solution caustic, and sulfur dioxide. The solution was analyzed for hydrosulfite by titration with a standard iodine solution. The precalculated volume of hydrosulfite was added by pipette below the surface of the pulp. Each bag was resealed, shaken thoroughly to mix, and placed in the constant temperature bath for 60 minutes.

At the end of the bleaching period the pulp was diluted to 1% consistency using deionized water and the slurry was adjusted to pH 5.5 prior to filtration on a Büchner funnel. One brightness pad was made from each run. The brightness levels were measured on a Technibrite TB-1C unit and are reported as the average of five readings from each handsheet.

RESULTS

Two process scenarios were evaluated. To assess the impact of clarification and flotation of white water, a pilot clarifier and a laboratory flotation cell were used.

Process Scenario 1: White water clarification and reuse A modified process with a DAF clarifier in the white water circuit was introduced with the goal of removing some of the contaminants present in this water. Figure 3 shows the schematic of this process.

In the mill, a pilot DAF unit was used to clarify the central white water. The white water was split into fines and clarified water streams. The metal analysis (Table II) shows most of the metals are adsorbed to fines. Hence any reduction in fines content of white water should help to reduce metal and improve bleach efficiency.

In order to simulate the effect of different degrees of white water clarification on bleaching, it was decided to study the bleach July/August 2009 PULP & PAPER CANADA

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BLEACHING TABLE I. DIP plant pulp’s metal analysis (ppm).

Process Newsprint Magazine Retention Tower Disk Filter Press HD Storage

Al

Ca

Fe

Mn

Cu

890 22262 11742 10247 10927 15500

4948 22040 13139 7638 6758 6700

225 512 315 236 244 333

33.5 12.9 19.5 21.0 20.7 32.0

11.8 23.5 26.6 6.50 6.80 8.00

FIG. 5. White water clarification and fines flotation.

TABLE II. Metal analysis of clarified water and clarified fines (ppm).

Process Clarified Fines Clarified water

Al

Ca

Fe

Mn

Cu

14,667 2

4927 109

383 1.2

39 0.2

8.4 0.1

FIG. 6. Hydrosulfite responses of DIP pulp with white water containing floated fines (Process Scenario 2).

FIG. 7. Comparison of bleach performance.

response of DIP pulps diluted with white waters at different consistencies. This was accomplished by mixing the clarified water with different amounts of clarified fines. White water ranging from 0.0% to 0.5% cy was generated and mixed with DIP pulp prior to hydrosulfite bleaching. These pulps were subjected to laboratory hydrosulfite bleaching and their bleach responses are shown in Fig. 4. The results show that low white water consistencies give improved hydrosulfite response. This is due to fact that at low white water consistencies less contaminant is recycled which in turn gives improved bleach efficiency.

Process Scenario 2: White water clarification and fines flotation In the first process scenario, the separated fines were not utilized.

This will have a significant impact on process yield. In order to maintain high yield, a laboratory flotation study was performed on the clarified fines. The goal was to separate the inks from the fines and reuse the deinked fines and clarified water (Fig. 5). The central white water (55.4% ISO, ERIC value: 199 ppm) was sub26

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FIG. 8. Effect of white water consistency on bleaching of TMP pulp.

jected to both dissolved and dispersed air flotation processes and the clarified water was reused prior to bleaching. A pilot DAF clarifier was used for the separation of fines from white water.

The flotation process improved the central white water fines brightness by 4 points and removed 47% of ERIC. The floated fines (59.4% ISO, ERIC value: 106 ppm) and clarified white waters were recombined to generate white water ranging from 0.0% to 0.5% consistencies and their influence on hydrosulfite bleaching of DIP and TMP was studied.

As can be seen from Fig. 6, the bleach response increased at lower fines consistency. The flotation process was able to remove contaminant such as extractives, metals, inks and fillers from the fines, and therefore achieved initial higher brightness. Also, the hydrosulfite bleach response improved. pulpandpapercanada.com

BLEACHING Bleach responses by various processes Figure 7 compares the bleach response of the current process to the modified processes examined in this study. The results show that the use of a clarifier to clarify the white water for dilution in the bleach plant improved the bleach performance of recycled pulp. This study also showed that an ink removal process from the fines in the white water circuit enhances the bleach response of the recycled pulp without significantly affecting the process yield.

Influence of white water consistencies on bleach response of TMP pulp Influence of white water consistency on the bleach response of TMP was studied by diluting the pulp with clarified white water generated from the pilot clarifier.

The response was similar to the recycled pulps. Decreased white water consistencies gave improved bleach response. Figure 8 shows about 1.5 points gain in brightness by reducing central white water consistency from 0.5 to 0.1%.

SUMMARY

The application and consistency of centralized white water, from a paper machine producing newsprint using a furnish of TMP and DIP pulps, for bleach plant dilution influences bleach plant performance. An ink removal step in the white water circuit is an important factor to consider for achieving high brightness values. Contaminants such as metals, inks, and suspended solids (fines) present in the

white water decrease brightness, however, the reuse of clarified white water prior to the bleaching stage can minimize their impact. Results from Process Scenario 2 suggest clarification of the white water with a separate flotation of the separated fines can improve hydrosulfite performance when added to the process prior to hydrosulfite bleaching. The consistency of white water used for dilution of pulp prior to bleaching is an important factor to control. White water at lower consistencies (<0.1% cy) provides optimum bleach response for both DIP and TMP pulps for mills producing newsprint from virgin and recycled pulps.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the assistance of EKA Chemicals Inc. for conducting the lab flotation studies and

Poseïdon Inc. for running the pilot clarifier for this work.

LITERATURE

1. GARVER, M.T., XIE, T., BOEGH, H.K. Variation of white water composition in a TMP and DIP newsprint paper machine, TAPPI Journal, pp.163-172, August (1997).

2. LAPIERRE, L., PITRE, D., BOUCHARD, J.,Fines from deinked pulp: Effect of contaminants on their bleachability and on the pulp final brightness, Pulp & Paper Canada, 104(8):36-39 (2003).

3. LAPIERRE, L., PITRE, D., BOUCHARD, J. Bleaching of deinked recycled pulp: benefits of the fibre fractionation, 5th Res. Forum on Recycling, PAPTAC, pp. 57-63 (1999).

4. RANGAMANNAR, G., DIONNE, Y., BELLEMARE, R. Investigation of residual ink effect on hydrosulfite bleaching for Bowater Gatineau, Pulp & Paper Canada, 104(5):55-57 (2003).

5. GEHR, V., SCHWARZ, M., HEISE, O. Water loop and bleaching process design to recycle recovered paper into printing and writing grades, Pulp & Paper Canada, 99(12):141-145 (1998).

6. METHA, A., SAIN, M., NI, Y., MORNEAUD, D. Chemical additive optimization program: Short–cycle clarification of deinked mill alkaline-water loop, Pulp & Paper Canada, 105(3):43-46 (2004).

Résumé: Le but de cette étude était d’évaluer l’impact de la consistance de l’eau blanche sur le blanchiment à l’hydrosulfite sur les pâtes thermo-mécanique et désencrée. Des combinaisons d’essais en usine et en laboratoire ont été effectuées. Une unité pilote de clarification a été utilisée en usine pour clarifier l’eau blanche en séparant les fines. Les fines provenant de cette clarification ont été flottées dans une cellule de flottation de laboratoire. Les résultats indiquent une blancheur maximale lorsqu’une combinaison d’eau blanche clarifiée et de fines flottées a été utilisée pour diluer la pâte avant le blanchiment à l’hydrosulfite. Les résultats démontrent également que la réponse de blanchiment et la blancheur finale augmentent avec une diminution de la consistance de l’eau blanche.

Reference: RANGAMANNAR, G., NAJIM, J., BELLEMARE, R., AMYOTTE, R., DIONNE, P.Y.

Effect of White Water Consistencies on Hydrosulfite Bleaching of DIP and TMP Pulps at AbitibiBowater Gatineau. Pulp & Paper Canada. 110(6):T95-T98 (July/August 2009). Paper presented at PAPTAC Recycling Conference 2004 in Quebec, Que., September 27-29, 2004. Not to be reproduced without permission of PAPTAC. Revised manuscript approved for publication by the Review Panel Dec. 2008.

Keywords: HYDROSULFITE BLEACHING, BRIGHTNESS, WHITE WATER, CLARIFICATION, FLOTATION, CONSISTENCY, FINES.

letters editor TO THE

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PAPER PROPERTIES

Effect of Separate Refining and Co-refining of BCTMP/KP on Paper Properties

By Y. Gao, F. Huang, V. Rajbhandari, K. Li, Y. Zhou Abstract: The effect of PFI separate refining and co-refining on paper properties was investigated for aspen bleached CTMP (BCTMP) and eucalyptus kraft pulp (EKP). The results showed that for a given freeness, separate BCTMP/EKP PFI refining required more energy than BCTMP/EKP co-refining; compared with BCTMP/EKP separate refining, BCTMP/EKP co-refining produced handsheets with improved surface smoothness and physical strength, while there was no significant difference in opacity and light scattering between these two refining processes. The results indicate that, in paper mill practice, it is possible to choose an appropriate addition level of BCTMP in KP and an appropriate refining process to maintain acceptable paper bulk and paper smoothness.

D

uring the last decades, bleached chemi-thermomechanical pulp (BCTMP), also called high-yield pulp (HYP), has attracted an increasing amount of interest among papermakers in order to reduce costs and improve the quality of woodfree printing and writing paper [1, 2]. In the HYP process, pulps are produced mainly through a mild chemical treatment and the action of mechanical forces, with a yield of 80-90% and retention of most of the lignin in the wood [3]. Compared with chemical pulps, e.g. kraft pulp (KP), HYP contains a higher content of fines. HYP fibres are rigid, coarse, and cannot easily collapse. These differences between HYP and KP can result in different paper properties. Paper from HYP normally has higher bulk, bending stiffness, and dimensionally stability. The light scattering power, opacity, and printability obtained from HYP are also superior to those from chemical pulps mainly because of the higher amount of fines in HYP. Due to these specific attributes, HYP has been used in a variety of paper grades to reduce production cost and improve paper quality [4].

The high bulk of HYP can be used to reduce the basis weight at a given caliper in wood-free printing and writing papers. Higher bulk also increases paper stiffness at a given basis weight, high fines of content and the HYP may also improve sheet formation. In addition, the higher opacity of HYP provides optical benefits, particularly in lightweight specialty grades, such as lightweight coated (LWC) paper.

In recent years, the focus on HYP production and product development has been moving towards optimizing the process to tailor-make HYP with some specific pulp properties for a specific end-use in paper and board, particularly in 28â&#x20AC;&#x192;

PULP & PAPER CANADAâ&#x20AC;&#x192; July/August 2009

the production of wood-free papers. In wood-free papers, such as LWC and printing and writing paper grades, HYP is used to replace hardwood kraft pulp and gives the final sheets higher bulk and opacity. The typical substitution rate of HYP in KP is 5 to 15% for coated and 10 to 25% for uncoated paper grades.

Although the bulk and opacity improvement can be achieved by the addition of HYP, the paper surface smoothness may be affected. Previous studies [5, 6, 7] indicated that thick-walled and

Y. GAO, Department of Chemical Engineering, University of New Brunswick, Fredericton, N.B.

F. HUANG, Department of Chemical Engineering, University of New Brunswick, Fredericton, N.B.

V. RAJBHANDARI, Department of Chemical Engineering, University of New Brunswick, Fredericton, N.B.

K. LI, Department of Chemical Engineering, University of New Brunswick, Fredericton, N.B.

Y. ZHOU Tembec Inc., Temiscaming, Que.

pulpandpapercanada.com

Bulk, cm3/g

PPS Roughness, µm

PAPER PROPERTIES T100

FIG. 1. Bulk versus freeness.

FIG. 2. Roughness versus freeness.

TABLE I. Sample identification.

Sample ID

Description

Se-Re 10%BCTMP/90%EKP Se-Re 20%BCTMP/80%EKP Co-Re 10%BCTMP/90%EKP Co-Re 20%BCTMP/80%EKP

Pulp Pulp Pulp Pulp

furnish furnish furnish furnish

coarse HYP fibres may not only deteriorate paper surface smoothness but may also cause surface roughening upon rewetting in the printing process. To compensate the surface smoothness loss caused by the addition of HYP and to improve paper printability, HYP should be fine-tuned to tailor-make final product qualities. In mill practice, further refining of HYP is quite often employed to reduce the fibre coarseness in the mixed furnish. In some mills, hardwood KP is refined to about 400 mL CSF, and HYP is mixed in hardwood KP without refining, which is referred to separate refining as in this paper. In other paper mills, HYP is co-refined with hardwood KP. The issue of separate or co-refining a mixed furnish of kraft pulps has drawn considerable attention amongst researchers and papermakers [8, 9, 10, 11], since the fibre characteristics of each type of pulp are quite often significantly different. It is difficult to conclude whether separate refining or co-refining provides better quality of the finished product. The method of refining a mixed furnish to achieve an optimal product quality is largely dependent upon the individual components of the furnish, e.g. HYP and kraft pulp, the furnish composition, e.g. percentage of HYP and kraft pulp in the furnish, and the pulp species, e.g. aspen KP or eucalyptus KP. In addition, some investigations revealed that for a given tensile strength, the energy efficiency pulpandpapercanada.com

TABLE II. Pulp properties of eucalyptus KP (EKP) and aspen BCTMP.

(10% (20% (10% (20%

BCTMP BCTMP BCTMP BCTMP

and and and and

90% 80% 90% 80%

EKP) EKP) EKP) EKP)

in in in in

separate refining separate refining co-refining co-refining

and equipment investment between separate refining and co-refining were significantly different [12, 13].

Most published works on the comparison of separate refining and co-refining were based on hardwood and softwood kraft pulps. There is little published data in the literature on separate refining and co-refining of HYP and KP. In this study, the effect of separate refining and corefining of aspen BCTMP and eucalyptus KP is investigated. The influence of the BCTMP substitution ratio on paper physical strength and surface smoothness are discussed.

EXPERIMENTAL

Materials Aspen BCTMP 325/85 from a Canadian pulp mill and a bleached eucalyptus kraft pulp (EKP) from a French pulp mill were used in this investigation.

Refining For separate refining, EKP was refined with a PFI mill to 480, 450, 400 and 350 ml CSF, and then mixed with 10% and 20% aspen BCTMP, respectively. For co-refining, EKP was mixed with 10% and 20% aspen BCTMP, and then refined with a PFI mill to CSF of 480, 450, 400 and 350 ml, respectively. For convenience, a short form ID was given to each pulp sample and different refining process, as listed in Table I.

CSF freeness, ml Fibre length, mm Fines, % Coarseness, g/m Tensile index, N.m/g Opacity, % ISO Bulk, cm3/g PPS roughness, µm Brightness, ISO %

Eucalyptus Aspen kraft pulp BCTMP (EKP) 680 0.95 10.0 0.095 28.06 75.8 1.83 5.67 89.5

570 0.64 23.1 0.174 17.88 80.5 2.48 7.02 84.4

Handsheet making and paper property measurement Handsheets of a basis weight of 60±2 g/m2 (o.d.) were prepared according to TAPPI standard (T205 sp-02). The thickness of the handsheets was measured with an L&W micrometer, and paper bulk was calculated based on the weight of handsheet. The tensile strength of the handsheets were tested with a tensile strength tester by L&W. Opacity, brightness, and light scattering were measured with a TechniBrite Micro-1c tester. Roughness was measured with a Parker surf tester, and internal bond was tested by a TMI station (Model 80-01-03). All the measurements were conducted according to the relevant TAPPI standard methods.

SEM analysis of paper surface characteristics A Jeol JSM-6400 scanning electronic microscope (SEM) was used to study the fibre morphology characteristics of the paper surfaces and cross-sections; the handsheets were coated with carbon and gold before the surface observation. The cross-section was obtained as per the fol-

July/August 2009 PULP & PAPER CANADA

29

Internal bond, J/m2

Tensile index, N.m/g

T101 PAPER PROPERTIES

Fig. 3. Tensile index versus freeness.

lowing: the sample sheet was first cut by a sharp blade, and then it was vertically installed between two metal plates to expose the cross-section, it was then coated with carbon and gold as done in surface observation.

RESULTS AND DISCUISSION

Basic properties of EKP and BCTMP The basic properties of eucalyptus KP (EKP) and aspen BCTMP are summarized in Table II. Aspen BCTMP pulp has higher opacity (80.5%) than EKP (75.8%), which is mainly due to the higher fines content in the pulp (23.1% vs. 10.0%).

The coarseness of aspen BCTMP (0.174 g/m) is almost twice as high as that of EKP (0.095 g/m). Coarser fibres render aspen BCTMP pulp higher in bulk (2.48 cm3/g) than the EKP (1.83 cm3/g), which is the reason for BCTMP to be a partial substitute for KP to improve paper bulk.

However, the higher coarseness of BCTMP pulp results in higher sheet roughness than the EKP pulp (7.02 µm vs. 5.67 µm).

The physical strength is also different between BCTMP pulp and EKP pulp.

Compared with EKP pulp, BCTMP has lower tensile index (17.88 N.m/g vs. 28.06 N.m/g) which is mainly attributed to its coarser, shorter and stiffer fibres [14].

The above comparisons indicate that EKP and BCTMP pulps have significant differences in physical and optical properties. Therefore, it is reasonable to achieve desired paper properties such as higher bulk and better opacity by way of mixing a certain quantity BCTMP with KP [15].

Paper physical properties Bulk and roughness Paper bulk is dependent, to some extent, on the fibre components in the network, 30

Fig. 4. Internal bond versus freeness.

and coarser fibres render higher bulk [16, 17]. For a given bulk, the fibre consumption is lower when using coarser fibres, as a result, the production cost is reduced.

Figure 1 shows how the handsheet bulk properties developed for different pulp furnishes. In comparison with the EKP pulp, the bulk in a blend furnish of BCTMP/ EKP was improved in either separate refining or co-refining, which was mainly due to the coarser and stiffer BCTMP fibres in the furnish. A higher substitution ratio (20%) of BCTMP results in higher bulk. For the same substitution ratio, separate refining and co-refining bring about different results. With separate refining, the average bulk gain (20%) of 20%BCTMP/80%EKP was almost two times higher than that of co-refining (7%).

In the separate refining process, BCTMP was mixed with EKP without refining, therefore, the intact BCTMP fibres contribute more to bulk than when refined with EKP. Figure 2 shows that the influence of BCTMP on paper surface roughness depends on its addition levels, especially in the case of separate refining. In comparison with EKP, the blend furnish produced sheets with higher roughness in either separate refining or co-refining. As mentioned above, the BCTMP fibres are coarser and stiffer, which not only contribute to the bulk gain but also negatively affect paper smoothness. In addition, in both refining processes, higher addition (20%) of BCTMP gives the sheet higher roughness.

Interestingly, compared with the EKP, the roughness increase of corefining BCTMP/EKP was not significant, especially in the case of Co-Re 10%BCTMP/90%EKP. A possible explanation is that in the case of co-refining,

PULP & PAPER CANADA July/August 2009

BCTMP fibres were modified by the refining process, which gives the sheet lower roughness. This indicates that with a substitution ratio of 10 to 20%, co-refining of BCTMP/KP can achieve similar roughness as 100% KP furnish.

Physical strength At a given freeness, although separate refining of BCTMP/EKP had a positive effect on paper bulk and produced acceptable roughness, the physical strength of the sheets was lower, as shown in Figs.

3 and 4. In Fig. 3, for the blends of 10% BCTMP/90%EKP, the average loss of tensile strength was 6% in the separate refining, while it was 4% for co-refining.

Additional blends (moving from 10% to 20%) had significant effects on the tensile loss: 14% for both separate refining and co-refining.

It should be noted that these findings are contradictory with the previous studies: adding a certain HYP (10 to 15%) in KP did not necessarily weaken the paper’s physical strength in disk refining [1]. The possible explanations might include the differences in the refining effects on pulp fibres between the lab PFI mill and disk refiner. In a comparative study between PFI mill and commercial refiners in refining energy, refining intensity, and other factors governing action on pulp, Kerekes and others [18, 19] indicated that the PFI mill is a high energy, low intensity refining device which produces a refining effect that differs significantly from a disk refiner in paper mills. As a result, the pulp fibres refined in a PFI mill revealed higher internal fibrillation, lower external fibrillation, and fibre shortening, which are mainly due to the fact that the PFI mill imposes a greater proportion of compressive to shear pulpandpapercanada.com

Opacity, % ISO

Light scattering coefficient, m2/kg

PAPER PROPERTIES T102

FIG. 5. Opacity and freeness.

FIG. 6. Light scattering coefficient and freeness.

FIG. 7. SEM image: top view of paper surface (Se-Re 20%BCTMP/80%EKP).

FIG. 8. SEM image: top view of paper surface (Co-Re 20%BCTMP/80%EKP).

forces than an industrial refiner. Therefore, for a given freeness, the sheet physical strength produced in PFI mill may be inferior to those in disk refiner.

Similar trends can be observed in the relation of freeness to internal bond, as shown in Fig. 4. The decrease of the internal bond in co-refined BCTMP/EKP was less important than in the case of separate refining. In co-refining, BCTMP fibres were modified by splitting, delaminating, and unraveling actions of mechanical refining, which were favourable for the bonding potential of fibres. Compared with the un-treated BCTMP fibres in separate refining, the refined BCTMP in co-refining contributes more to the paper’s physical strength, i.e internal bond.

In addition, to get the same internal bond from different pulp furnishes indicated a different required freeness.

For example, to achieve 300 J/m2, EKP, Co-Re 10%BCTMP/90%EKP, and CoRe 20%BCTMP/80%EKP were intended to refine to 400, 350, 370 mL CSF, respectively. This may suggest that mixing BCTMP in EKP furnish needs more pulpandpapercanada.com

refining energy to get the same physical strength as that of the individual EKP refining. With a higher percentage of KP being mixed in a BCTMP furnish, more energy is consumed.

The above analysis indicates that replacing KP with BCTMP would deteriorate the physical strength of final product, especially in the case of separate refining of BCTMP/ KP. In mill practice, this disadvantage could be compensated for by process modification and development. For instance, with advancement and modernization in the design of paper machines, the web tolerance on paper’s physical strength would be largely improved. In addition, some new products which are less exigent on physical strength could be developed to fulfill different customer requirements.

Optical properties As indicated in Table II, BCTMP contains a higher fraction of fines (23.1%) than EKP (10%). Compared with chemical pulp fibres, mechanical pulp fines have greater specific surface area owing to the abundant content of fibril-like and flake-

like particles in the fines [20]. Fines have strong effects on the structures and properties of fibre networks, particularly rendering a high opacity and light scattering coefficient [21], which are favourable for printing and writing papers [22].

As expected, adding BCTMP to KP improved optical properties, such as opacity (Fig. 5) and light scattering coefficient (Fig. 6) compared with the EKP. Interestingly, for both opacity and light scattering, there was no significant difference between separate refining and co-refining processes. This finding suggests that the gain in the optical properties is dependent more on the nature (or grade) of the BCTMP, and less on their addition ratio, as reported in [1].

SEM analysis Figures 7 and 8 show the surface characteristics of separate and co-refining of the same blend furnish: 20%BCTMP/80%EKP with the same freeness level (350 ml).

These SEM images indicate that there is no significant difference between the top views of the surfaces. The relatively smooth EKP fibres and fibrillated BCTJuly/August 2009 PULP & PAPER CANADA

31

T103 PAPER PROPERTIES

MP fibres were evenly distributed on the sheet surfaces.

Although there is no evident fibre difference from the topview surfaces between the separate refining and co-refining (Figs. 7 and 8), the SEM cross-sectioned view images (Figs.

9 and 10) revealed an apparent difference in surface roughness between these two refining processes. In separate refining, the sheet surface was uneven and some tube-like uncollapsed fibres were loosely combined together, which renders higher sheet bulk. In co-refining, the sheet surface showed relatively smooth and collapsed fibres which were tightly compacted, and resulted in lower paper bulk. This observation can explain the reason that the separate refining produced handsheets with higher bulk and roughness, but lower physical strength when compared with those of co-refining.

Refining energy In this study, the PFI revolutions were used to evaluate pulp energy consumption in refining. Figure 11 shows the freeness development at different PFI mill revolutions. The initial freeness before refining was 680 ml for EKP and 570 ml for aspen BCTMP (Table II). After refining, the freeness-revolution curves (trends) were different among the different pulp furnishes. For a given freeness, higher energy consumption was found for BCTMP/EKP in a separate refining process than that of BCTMP/ EKP in a co-refining process and EKP individual refining.

In BCTMP/EKP separate refining, the freeness reduction was completely attributed to the EKP refining alone since the BCTMP was directly added into the EKP, after EKP refining, and suffered no subsequent refining action in the blend furnish.

Therefore, for a given refining freeness, BCTMP/EKP separate refining consumes more energy than the EKP individual refining and BCTMP/EKP co-refining. Furthermore, in separate refining, a higher percentage of EKP replacement (20%) required more PFI revolutions to obtain the same freeness level than a lower percentage of replacement (10%).

It should be pointed out that for the BCTMP/EKP co-refining, although a different proportion (10% and 20%) of BCTMP was mixed in EKP, they had similar freeness/revolution trends as the EKP. This suggests that adding up to 20% of the aspen BCTMP to the EKP had no significant effect on the freeness development, compared with the EKP alone. This means that for 32â&#x20AC;&#x192;

PULP & PAPER CANADAâ&#x20AC;&#x192; July/August 2009

FIG. 10. Paper cross-section SEM image (Co-Re 20%BCTMP/80%EKP).

Freeness, mL

FIG. 9. Paper cross-section SEM image (Se-Re 20%BCTMP/80%EKP)

FIG. 11. Freeness and PFI revolutions.

a paper mill, replacing up to 20% of eucalyptus bleached KP with aspen BCTMP may not require a significant increase in energy consumption in the refining operation.

CONCLUSIONS

Partial substitution (10 to 20%) EKP with BCTMP would improve paper bulk, sheet opacity, and light scattering coefficient, however, physical strength would be reduced.

For a given freeness, compared with BCTMP/EKP separate refining, BCTMP/EKP co-refined produced handsheets with improved surface smoothness and physical strength, while there were no significant differences in opacity and light scattering between these two refining processes.

A higher percentage of BCTMP in EKP resulted in higher bulk and higher roughness, but weakened physical strength.

It is possible to choose an appropriate addition level of BCTMP in EKP and a refining process to maintain acceptable paper bulk and paper smoothness.

For a given freeness, BCTMP/EKP PFI separate refining required more energy than BCTMP/EKP co-refining.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the financial support of Natural Science and Engineering Research Council of Canada (NSERC) and the Atlantic Innovation Fund of Canada (AIF). pulpandpapercanada.com

PAPER PROPERTIES T104 LITERATURE

1. XU, E.C., ZHOU, Y.J. Synergistic Effects between P-RC APMP and Bleached Kraft Pulps from Canadian Aspen, Appita J. 58(6): 481-483 (2005).

2. HU, K., NI., Y, ZHOU, Y., Substitution of Hardwood Kraft with Aspen High-Yield Pulp in Lightweight Coated Wood-free Papers: Part I. Impact on Basestock Properties, PAPTAC 90th Annual Meeting, Montreal, Canada: C95-C101 (2004).

3. ZHOU, Y., CANNELL, E. Bleached High Yield Pulp: Process, Installations, and End Uses, PAPTAC 91st Annual Meeting, Montreal, Canada: B231-B239 (2005).

4. ZHOU, Y., ZOU, X. Achieving Desired End-use Performance by Using HYP in Wood-free Coated Papers, International Mechanical Pulping Conferences, Quebec, Canada:15-19 (2003).

5. REME, P.A., HELLE, T., JOHNSON, P.O. Fibre Characteristics of Some Mechanical Pulp Grades, Nordic Pulp & Paper Res. J. 13(4): 263-268 (1998).

6. DANBY, R. SC Print Quality Influenced by Fibre Length, Fabric Structures, and Machine Drainage Characteristics, Tappi J. 1(9): 3-9 (2002).

7. NESBAKK, T., HELLE, T., The Influence of the Pulp Fibre Properties on Supercalendered Mechanical Pulp Handsheets, J. Pulp Paper Sci. 28 (12): 406-409 (2002).

8. PECKHAM, J.R., MAY, M.N. Refining of Softwood and Hardwood Kraft Pulps Separately and As Mixtures, Tappi J. 42(7): 556 (1959).

9. BAKER, C. Optimization of Paper-mill Refining Systems, Proceeding of 3rd International Refining Conference, Atlanta, USA: 20(1995).

10. LUMIAINEN, J.J. Separate or Mixed Refining?, Tappi Papermakers Conference, Philadelphia, USA: 175 (1996).

11. BAKER, C. Advances in Different Refining Methods Particularly Refining of Mixtures, Proceeding of 6th International Refining Conference, Toronto, Canada (2001).

12. SAMPSON, W.M., WILDE, R. An Investigation into the Pilot Scale Refining of Blending Papermaking Furnishes, Appita, J., 54(6): 547-551 (2001).

13. GHOSH, A.K., RAE, C., MOORHOUSE, B. Determination of the Optimal Refining Strategy - Separate Refining or Co-refining - Using a 16” Double Disc Pilot Refiner, Appita J., Vol, (4): 301-307 (2003).

14. BIERMANN, C. Handbook of Pulping and Papermaking, Academic Press, USA (1996).

15. ZHOU, Y. Overview of HYP in Paper and Board, PAPTAC 90th Annual Meeting, Montreal, Canada: B143-B148 (2004).

16. NORMAN, B. The Formation of Paper Sheets, in Bristow, J.A., and Kolseth, P (ed.) Paper Structure and Properties, Marcel Dekker, New York (1986).

17. DODSON, C.T.J., OBA, Y., SAMPSON, W.W. On

the Distributions of Mass, Thickness and Density in Paper, Appita J. 54 (4): 385-389 (2001).

18. KEREKES R. Characterizing Refining Action in PFI Mills, 6th Pira International Refining Conference, Toronto, Canada: 12 (2001).

19. STEVENS, R.V. Refining, Pulp and Paper Manufacture, Vol.6, Stock Preparation, TAPPI-CPPA Joint Textbook Committee, Atlanta, USA (1992).

20. SIRVIO, J., NURMINEN, I. System Changes of Paper Properties Caused by Fines, Pulp & Paper Can. 105(8): 39-42 (2004).

21. XU, E.C., TEUBNER, D. Comparison of Chemical and Chemimechanical Pulps from Hardwoods, Appita J., 57(1): 43-45 (2004).

22. SCOTT, W.E., ABBOTT, J.C. Properties of Paper, Tappi Press, Atlanta, USA (1995).

Résumé: Nous avons analysé les effets sur les propriétés du papier de la séparation du co-raffinage et du raffinage sur PFI d’une pâte chimico-thermomécanique blanchie (PCTMB) de tremble et d’une pâte kraft d’eucalyptus (PKE). Les résultats indiquent que, pour un degré d’égouttage donné, le raffinage séparé de la PCTMB et de la PKE exige davantage d’énergie que le co-raffinage de ces deux pâtes. Comparativement au raffinage séparé, le co-raffinage a produit des formettes dont le lissé de la surface et la résistance physique étaient améliorés, tandis qu’il n’y avait pas de différence notable entre les deux procédés de raffinage en ce qui a trait à l’opacité et à la diffusion de la lumière. Les résultats indiquent que, en usine, il est possible d’ajouter une quantité appropriée de PCTMB dans la pâte kraft et de sélectionner un procédé de raffinage permettant de maintenir un papier doté d’un bouffant et d’un lissé acceptables.

Reference: GAO, Y., HUANG, F., RAJBHANDARI, V., LI, K., ZHOU, Y. Effect of Separate Refin-

ing and Co-refining of BCTMP/KP on Paper Properties. Pulp & Paper Canada 110 (6): T99-T104 (July/August 2009). Paper presented at the PAPTAC 94th Annual Meeting in Montreal, February 5-7, 2008. Not to be reproduced without permission of PAPTAC. Manuscript received December 13, 2007. Revised manuscript approved for publication by the Review Panel Dec. 2008.

Keywords: BCTMP, CHEMI-THERMOMECHANICAL PULP, KRAFT PULP, KP, SEPARATE REFINING, CO-REFINING, PAPER PROPERTIES, HIGH-YIELD PULP.

XIVth Fundamental Research Symposium Sept. 13-18 Oxford, UK www.frc14oxford2009.org.uk

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T105 DEINKING

Ageing of Flexographic Printed Model Cellulose Surfaces and Determination of the Mechanisms Behind Ageing By: J. Andersson and L. Wågberg Abstract: The influence of storage conditions on the ink detachment efficiency of water-based flexographic ink printed onto model cellulose surfaces and handsheets was investigated. It was shown that UV light, elevated temperatures, longer storage time, increasing surface roughness, and increasing surface hydrophobicity all had a negative effect on ink detachment. It was also shown that the ink’s chemical and structural characteristics changed when stored at elevated temperatures. No chemical or structural changes could be observed for the ink when stored under UV light.

D

einked fibres are an important raw material in different paper products, primarily newsprint and tissue, but also in printing and writing papers of higher quality. There are two conventional deinking methods currently in use. The flotation method works well in cases where offset printed papers are being recycled, however this method is not suitable for flexographic printed papers. Flexographic ink particles are too small and hydrophilic which means that they will not attach to the collectors in the flotation process.

Current recycling processes therefore incorporate aggressive washing stages to successfully remove flexographic inks. The yield losses associated with such washing stages are often economically unacceptable. Deinking processes and the fundamentals behind their mode of operation have recently been reviewed elsewhere and will not be given here [1-5].

Ink characteristics and paper surface properties are two important factors to consider when studying deinking. Ink properties such as pigment size and solvent type will strongly influence deinkability [6, 7]. Paper and fibre surface properties are also important since they affect the ease of ink detachment. Inks printed on coated paper surfaces detach more easily than inks printed directly onto uncoated paper surfaces [8]. Surface energy is also of importance. Andreasson and Wågberg [9] showed that sizing a model cellulose surface decreases the ink detachment efficiency of offset ink. Printing conditions also affect the deinking efficiency [8, 10, 11]. It is important to study, in detail, each part of the deinking process separately.

Rao and Kuys [12] investigated the detachment of offset news ink from printed model papers after natural and artificial ageing. The artificial ageing of offset printed papers, by a sunlamp, causes a large decrease in deinkability. This poor 34

PULP & PAPER CANADA July/August 2009

deinkability of aged offset ink and paper has been described as an oxidative process by which the chemical interaction between the ink and paper is increased, negatively affecting the deinkability [12-14]. Aspler [15] suggested that chemical interactions between newsprint ink and the substrate are of limited importance. Aspler explained the oil-paper and water-paper interactions using a traditional approach in which paper is considered a porous substrate and the ink setting is described by the Lucas-Washburn equation. The ink chemistry and the penetration depth of the ink then determine the final interaction between the paper and the ink. Borchardt et al. [16] described a model system based on 1H-NMR imaging where the ink detachment is followed in situ. It was stated that this method provides a rapid screening tool for predicting the effectiveness of deinking surfactants. However, NMR imaging equipment is expensive and still rather complicated to use effectively.

Andreasson and Wågberg [9] studied ink detachment from model cellulose surfaces using an impinging jet technique. They showed that the washing process in fact removes flexographic ink whereas removal of offset ink requires a certain hydrodynamic shear in combination with swelling of the model cellulose surface. Forsström and Wågberg [17] also used the impinging jet technique to study the influence of different storage conditions on deinking efficiency of flexographic ink. They showed that ink detachment becomes increasingly difficult if the printed surface has been stored under UV light and high temperatures.

Sain and Daneault [18] have also investigated the ageing of flexographic ink. They claimed that the presence of univalent metal ions in a sulphopolyester-based flexographic ink inhibits ageing (cross-linking) of acrylic binders. The annealing effect of acrylic latex has previously been studied

J. ANDERSSON Formerly with Fibre Science and Communication Network, Mid Sweden University, Sundsvall, Sweden

L. WÅGBERG Department of Fibre and Polymer Technology, Royal Institute of Technology, Stockholm, Sweden. pulpandpapercanada.com

DEINKING T106

Fig. 1. Deinking efficiency of model cellulose surfaces printed with flexographic water based ink as an effect of UV light, storage temperature and time. Surfaces stored at different temperatures were stored as dark as possible to minimize the effect of UV light. The lines are merely a guideline to the eye.

by several research groups [19-21]. According to these studies, elevated temperatures cause a film formation of the initially distinct latex particles.

The purpose of the present study was to further investigate the reasons behind the difficulties when deinking flexographic ink printed cellulose surfaces stored under different conditions. The influence of surface properties such as topography and surface energy on deinking efficiency was also investigated. Atomic force microscopy and Fourier transform infrared spectroscopy was used to study chemical and structural changes in ink and cellulose.

METHODS AND MATERIALS

Model surfaces. Model cellulose surfaces were prepared by coating a transparent glass slide with a solution of dissolved cellulose according to the method outlined in [17, 22]. The surfaces were stored in a desiccator before use.

To obtain surfaces with different surface energy, the model cellulose surface was coated with propyltrichlorosilane (98%, CAS# 141-57-1, Aldrich). The cellulose surface was placed in a desiccator above a small petri dish filled with propyltrichlorosilane. The propyltrichlorosilane then diffused onto the cellulose surface. The contact angle increased from 25° to 90° as determined with a Dynamic Absorption Tester, Fibro DAT 1121/1122, Stockholm, Sweden.

Sheet preparation. Sheets, with a grammage of 60 g/m2, were prepared from dissolving pulp (dissolving pulp, Domsjö Fabriker AB, Sweden) according to ISO 5269-2:1998.

Ink. The flexographic ink used in this study was 82 Aquajet black ink (~15 wt% pigment (CI PB 07), ~25 wt% acrylate (Joncryl 90), ~2 wt% defoamer, ~1.5 wt% polyethylene wax) from A/S Torda Fabrikker, Lierstranda Norway. The corresponding ink varnish for 82 Aquajet black ink (pigment-free ink) was also used.

Printing technique. Flexographic ink (rastered pattern covering approximately 35% of the model surface) was printed both onto the model cellulose surfaces and the handsheets using an IGT Printability Tester F1, IGT, Amsterdam, Netherlands (anilox force 75 N, printing force 125 N, speed 0.30 m/s).

Storage procedure. Printed cellulose surfaces and ink varnish were stored under UV light, elevated temperatures, and increased storage time. Storage time was 1, 4 or 10 days with temperatures ranging from 15°C up to 105°C. Surfaces stored under UV light pulpandpapercanada.com

Fig. 2. The effect of surface roughness and surface hydrophobicity on deinking efficiency from model cellulose surfaces.

were all stored at 25°C and surfaces not stored under UV light were all stored in black plastic bags for different times and with different temperatures. Ink varnish and spin coated cellulose stored at 25°C under dark conditions for 24 hours were used as reference samples.

Ink detachment from cellulose surfaces. The printed cellulose surfaces were mounted in a liquid-filled impinging jet cell and impinged with an alkaline water solution (pH 10) at room temperature. The detachment was performed and the deinking efficiency was analysed according to the procedure outlined in [17], 100% deinking efficiency defines detachment of all ink whereas 0% deinking efficiency means that no ink was detached.

Ink detachment from sheets. Five grams of the printed sheets made from dissolving pulp were re-slushed in 250 ml alkaline water solution (pH 10). The pulp was then washed/deinked in a Britt Dynamic Drainage Jar equipped with a 35 µm screen (stirrer speed 1000 rpm) according to the outline described in [17].

The brightness value was measured according to the SCAN CM 11:95 and the SCAN P3:93 methods. Non-printed sheets were stored under the same storage conditions as the printed model cellulose surfaces and handsheets. No difference in brightness could be detected, hence sheets stored under completely dark conditions, in air, at 25°C for 1 day were used as reference sheet.

FTIR (Fourier transform infrared) spectroscopy. Ink varnish and spin coated cellulose were exposed to the same storage conditions as previously described and then analysed using ATR-FTIR in order to detect any chemical changes. The IR measurements were performed with the aid of a Perkin Elmer Spectrum 2000 FTIR equipped with a single reflection Attenuated Total Reflection (ATR) accessory from Specac Ltd. (Kent, England).

Atomic force microscopy (AFM). Silicon wafers were used as the base substrate for the ink varnish investigations. The silicon wafers were washed with ethanol and deionised water after which they were cleaned in a plasma cleaner (Harrick Plasma Cleaner, model PDC 002, Harrick Scientific Corporation, New York).

Ink varnish was then spin-coated onto the silica wafer. Model cellulose surfaces and spin coated ink varnish were then stored according to the conditions previously described and analysed using AFM in order to detect any structural changes. The measurements were performed with the aid of a Pico Force SPM (Veeco Inc. USA) and all measurements were performed in tapping mode. The surface roughness of the model cellulose surfaces was measured from the height image and it was defined as RMS over a 1µm2 area.

July/August 2009 PULP & PAPER CANADA

35

T107 DEINKING

Fig. 3. The effect of storage time, UV light and temperature on brightness value of deinked printed sheets. Sheets stored at different temperatures were stored as dark as possible to minimize the effect of UV light.

RESULTS

Deinking efficiency of model cellulose surfaces The effect of different storage conditions on ink detachment from model cellulose surfaces is shown in Fig. 1. It can be seen that increasing the storage time decreased the deinking efficiency.

It can also be seen that storing the surfaces under UV light or at elevated temperatures under dark conditions decreased the deinking efficiency for a given storage time. After two weeks of storage all surfaces were almost impossible to deink regardless of the storage conditions.

The influence of surface roughness and surface energy was also investigated. From Fig. 2, it can be seen that increasing the surface roughness clearly decreases the deinking efficiency.

It can also be seen that increasing the hydrophobicity of the model cellulose surface decreases the ink detachment efficiency.

Flexographic ink was also printed on freshly cleaved mica (a high surface energy substrate) and then ink removal efficiency was 100%. The results are in accordance with earlier results shown by [9] although water based flexographic ink was used in the present investigation instead of offset ink.

Deinking efficiency of sheets Deinking efficiency of reslushed and deinked sheets is shown in Fig. 3.

Increasing the storage time decreased the brightness for sheets stored above 55°C. For surfaces stored at lower temperatures, the increased storage time had no effect. Storage under elevated temperatures or UV light decreased the sheet brightness. Storing the sheets at a temperature of 105°C for 4 days decreased the brightness by as much as 38%. It should be mentioned that UV light had no effect on non-printed pulp. Hence the differences detected in brightness are only due to the amount of ink remaining on the sheet after washing.

Cellulose and ink characteristics

It has previously been suggested that an oxidative polymerization of the ink resin causes ageing of offset ink, thereby decreasing the deinkability [13-15]. It has also been proposed that the difficulties in removing ink from aged paper are due to oxidation of hydroxylgroups of carboxylic acids present both in the fibres and in the ink [13]. It was therefore considered important to investigate if the detected changes in ink removal efficiency for the flexographic printed surfaces could be traced back to any chemical or structural 36

PULP & PAPER CANADA July/August 2009

Fig. 4. ATR-FTIR spectra of UV-treated (top spectrum) and temperature treated (bottom spectrum) ink varnish.

Fig. 5. Tapping Mode, phase images (1x1 µm) of non-treated (left image) and heat treated (right image) ink varnish spin coated onto silicon wafers.

changes in the cellulose and the ink.

It has previously been shown that storing model cellulose surfaces at elevated temperatures causes structural changes that result in a decrease in surface roughness [23]. In this study, spin coated cellulose stored under UV light or at elevated temperatures was studied using ATR-FTIR and no noticeable chemical changes were detected in the cellulose.

Ink varnish was also subjected to heat treatment and UV light.

The results are shown in Figs. 4 and 5.

As can be seen in Fig. 4 (top spectrum), no noticeable changes in chemical shift were observed between non-treated ink varnish and UV-treated ink varnish. Upon heat treatment, a peak at approximately 1710 cm-1 occurred as can be seen in the bottom spectrum. This might indicate that an oxidative reaction is taking place upon heat treating the ink varnish, since this area in the spectrum corresponds to carboxyl groups.

In Fig. 5, left image, a phase image of non-treated ink varnish is presented. Spherical structures can be observed that are most likely latex particles present in the ink. In Fig. 5, right image, it can be seen that upon heat treating the ink at 105°C, the spherical structures disappeared, most likely due to an annealing effect of the latex and consequently a film formation of the binder. pulpandpapercanada.com

DEINKING T108 DISCUSSION

The effect of surface energy on deinking efficiency has previously been investigated [9]. These studies showed that by increasing the hydrophobicity of a model cellulose surface, the deinking efficiency decreases.

The poor deinkability was explained to be due to either a delayed swelling of the surface or due to molecular similarities between ink and the hydrophobizing agent. However water based flexographic ink was used in this study and the washing of flexographic ink is almost independent of swelling. A plausible explanation to the observed deinking difficulties could be that the ink penetrates through the pro­pyltrichlorosilane layer down to the cellulose thereby decreasing the deinking efficiency. The influence of surface roughness was also investigated and it was shown that increasing the roughness decreased the deinking efficiency. Flexographic ink was also printed on freshly cleaved mica, which is an extremely smooth surface with high surface energy. The deinking efficiency from mica was always 100% regardless of storage conditions. An increased surface roughness might facilitate ink penetration into nanometer-sized roughness of the cellulose surface thereby decreasing the deinking efficiency via physical interlocking. When printing on mica no penetration at all was possible and even though mica has high surface energy, all ink was detached.

Different storage conditions were also investigated in this study. It was shown that storage under UV light and high temperatures affected the ink detachment of water based flexographic ink from different cellulose surfaces in a negative way.

The effect of different storage conditions on deinking efficiency has previously been shown for offset ink [12] and flexographic ink [9, 17]. The chemical structure of the ink is believed to change when exposed to different storage conditions. It is also believed that the ink-cellulose interaction changes as covalent bonds between carboxylic group present in the ink and the fibre become possible. These chemical changes in ink and cellulose are believed to be the reason for the difficulties in ink detachment for offset inks. ATR-FTIR and AFM results showed that the changes occurring in ink and ink-cellulose interaction upon storage under different conditions were different depending on whether pulpandpapercanada.com

the surfaces were stored at elevated temperatures or under UV light. After storage at elevated temperatures, chemical changes could be detected in the varnish. An extra peak at 1710 cm-1 in the ATR-FTIR spectra indicated that an oxidative reaction had taken place. The AFM results also showed structural changes in the varnish after storage at elevated temperatures. This indicates that annealing had taken place.

The annealing effect of latex particles has also previously been shown by [19-21].

The annealing and oxidative reaction that takes place upon storage at elevated temperatures can clearly be the reason behind the difficulties in deinking surfaces stored at higher temperatures. Even though the results show no evidence of chemical reactions between cellulose and varnish it should be pointed out that since both the ink and the cellulose have high functionality only a relatively few chemical binding sites are required to create strong bonding between ink and cellulose, making the ink difficult to detach. Hence it is possible that an oxidative polymerization reaction in the varnish-cellulose interface could have taken place when the surface was stored under UV light but that the ATR-FTIR was not sensitive enough to be able to detect them. The results also show that UV light and storage temperature affected the ink detachment negatively for both spin coated cellulose surfaces and handsheets, although the effect was slightly different. Ink detachment was hardly possible for printed model cellulose surfaces, stored in air under UV light or at a storage temperature of 55°C, even after only 1 day of storage. For printed handsheets, UV light and temperature decreased the ink detachment efficiency although it did not reach zero. This indicates that there is a difference in the ink detachment process between these surfaces even though the trends are very similar.

This difference can naturally be traced back to the different physical structure of the surfaces but the differences in ink removal processes should also be kept in mind. The model cellulose surfaces are deinked using the impinging jet cell where the printed cellulose film is exposed to a stream of alkaline water at almost no shear.

Furthermore, the stream hits the surface at the same place at the same impact angle all of the time. The handsheets are reslushed and hyper washed which means that each

fibre is exposed to a high shear and the alkaline water hits the fibre from numerous angles. The exposed surface is much larger for the fibre than for the cellulose film thus enabling a higher deinking efficiency for the fibres.

CONCLUSIONS

The present work has shown that increased hydrophobicity or increased surface roughness decreased deinking efficiency from model cellulose surfaces. It was also shown that storing model cellulose surfaces and sheets under UV light, in elevated temperature, and for a long storage time affected the deinking efficiency in a negative way for both spin coated cellulose surfaces and sheets made from dissolving pulp. ATRFTIR and AFM studies showed that ink varnish changed both chemically and structurally when stored at elevated temperatures. Upon storage under UV light, no changes could be observed.

ACKNOWLEDGEMENT

SCA AB and the Fibre Science and Communication Network (FSCN) at Mid Sweden University are thanked for financial support. Dr. Shannon Notley is thanked for linguistic revision of the manuscript.

LITERATURE

1. BARASSI, J., WELSFORD, J. Latest developments in deinking technology, Appita 45(5):308 (1992).

2. HEINDEL, T. J. Fundamentals of flotation deinking, Tappi J. 82(3):115 (1999).

3. KEMPER, M. State-of-the-art and new technologies in flotation deinking, Int. J. Mineral Proc. 56(1-4):317 (1999).

4. FERGUSON, L.D. Deinking chemistry. Part 1, Tappi J. 75(7):75 (1992a).

5. FERGUSON, L.D. Deinking chemistry. Part 2, Tappi J. 75(8):49 (1992b).

6. RANGAMANNAR, G., GRUBE, G., KARNETH, A.M. Behaviour of water-based flexographic inks in newsprint deinking, Tappi Pulping Conference, Boston, 933 (1992).

7. WASILEWSKI, O. Composition and chemistry of novel inkl used in the newspaper industry and deinking, Tappi Pulping Conference, Washington, 25 (1987).

8. SJOESTROM, L., CALMELL, A. Detachment of printing ink from different types of fibers. [Erratum to document cited in CA126:132808]”, J. Pulp Paper Sci. 23(5):J205 (1997).

9. ANDREASSON, U., WÅGBERG, L. Ink release from printed surfaces - New methodology and initial insights to the true mechanism behind ink detachment, The Science of Papermaking, in 12th Fundamental Research Symposium, Oxford, 339 (2001).

10. SHRINATH, A., SZEWCZAK, J.T., BOWEN, I. J. A review of ink-removal techniques in current deinking technology, Tappi J. 74(7):85 (1991).

11. MILLER, J.D., XIANSHENG, N. The effect of ink types and printing processes on flotation deinking, Recycling Symposium, Tappi proceeding, 131 (1997).

12. RAO, R., KUYS, K. Deinkability of aged paper, Appita 601 (1995).

13. CASTRO, C., DANEAULT, C., DORRIS, G.M. Analysis of the accelerated thermal aging of oil ink vehicles using isothermal thermogravimetry, J. Pulp

July/August 2009 PULP & PAPER CANADA

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T109 DEINKING Paper Sci. 22(10):J365 (1996).

14. ROSINSKI, J. Aging and deinking of soy printed newsprint, Prog. Pap. Recycling, 55 (1995).

15. ASPLER, J.S. Interactions of ink and water with the paper surface in printing, Nordic Pulp Paper Res. J. 8(1):68 (1993).

16. BORCHARDT, J.K., TUTUNJIAN, P., PRIETO, N.E. Novel Methods for laboratory evaluation of deinking surfactants, Tappi J. 76(7):104 (1993).

17. FORSSTROM, J., WAGBERG, L. Influence of different storage conditions on deinking efficiency of waterbased flexographic ink from model cellulose surfaces and sheets, Nordic Pulp Paper Res. J. 19(2):250 (2004).

18. SAIN, M.M., DANEAULT, C. Thermo-oxidative behaviour of water-borne ink binders in the presence of monovalent metal ion, Polymer Deg. Stab. 51(1):67 (1996).

19. GOH, M.C., JUHUE, D., LEUNG, O.M., WANG, Y.C., WINNIK, M.A. Annealing effects on the surfacestructure of latex films studied by atomic force microscopy, Langmuir. 9(5):1319 (1993).

20. WANG, X., MALONEY, T.C., PAULAPURO, H. Internal fibrillation in never-dried and once-dried chemical pulps, Appita 56(6):455 (2003).

21. GOUDY, A., GEE, M.L., BIGGS, S., UNDERWOOD, S. Atomic-force microscopy study of polystyrene latex film morphology - effects of aging and

annealing, Langmuir 11(11):4454 (1995).

22. GUNNARS, S., WAGBERG, L., COHEN STUART, M.A. Model films of cellulose: I. Method development

and initial results, Cellulose 9(3/4):239 (2002).

23. NOTLEY, S. Unpublished data. (2004).

Résumé: Nous avons étudié l’influence des conditions de stockage sur l’efficacité du détachement de l’encre flexographique aqueuse imprimée sur des formettes et des surfaces de cellulose modèles. Nous avons trouvé que la lumière UV, une température élevée, un temps de stockage plus long, une surface plus rugueuse, et une hydrophobicité accrue de la surface avaient tous un effet négatif sur le détachement de l’encre. Nous avons aussi trouvé que les caractéristiques chimiques et structurelles de l’encre changeaient lors du stockage à température élevée. L’encre n’a subi aucune modification chimique ou structurelle lorsque les produits étaient stockés dans un milieu sous lumière UV. Reference: ANDERSSON, J., WÅGBERG, L. Ageing of Flexographic Printed Model Cel-

lulose Surfaces and Determination of the Mechanisms Behind Ageing. Pulp & Paper Canada 110(6):T105-T109 (July/August 2009). Paper presented at the Recycling Conference 2004 in Quebec, Que., September 27-29, 2004. Not to be reproduced without permission of PAPTAC. Manuscript received May 18, 2004. Revised manuscript approved for publication by the Review Panel December 5, 2008.

Keywords: STORAGE CONDITION, FLEXOGRAPHIC INK, MODEL CELLULOSE SURFACE, HANDSHEETS, CHEMICAL CHANGES, STRUCTURAL CHANGES, DEINKING.

TECHNOLOGY NEWS Air-assisted blade holder improves vacuum efficiency 25%

Kadant Web Systems has launched the air-assisted Airset blade holder, which incorporates integrated cavities for targeted delivery of air that boosts the cleaning action of the doctor blade. Air can be targeted behind the blade for dewatering drilled rolls or ahead of the blade for cleaning grooved rolls or belts.

The natural vacuum found in doctoring applications is amplified with the introduction of air. This in turn allows the Airset blade holder to efficiently remove water from the roll surface. More specifically, the patent-pending shape of the holder creates an entrainment zone suspending the removed water from the surface of the roll for removal by a second doctor blade or pan. In-house testing has shown improvements in vacuum efficiency to be more than 25%, and in some cases up to 50%, compared to installations not using the air-assist feature.

For ease of installation, the Airset blade holder can be mounted to the doctor utilizing Kadant’s patented UniTrak™ blade holder installation and removal tool.

Kadant Web Systems Inc. 514-213-6040, www.kadant.com

Eurotherm adopts EtherNet/IP protocol for graphic recorder

Eurotherm has adopted EtherNet/IP as the communications protocol for its 6000 series paperless graphic recorders, allowing its recorders to seamlessly communicate with a large installed base of EtherNet/ IP enabled PLCs and other I/O and control devices in many industrial applications. The implementation is the most robust in any paperless chart recorder, supporting up to 200 I/O ports with simultaneous support for Modbus TCP. The move to EtherNet/IP compatibility means ease of installation in connecting to programmable logic controllers, simple system configuration, better process oversight, and increased flexibility. The use of standard Ethernet networking equipment means no unique hardware or software is needed to connect to most major controllers and configuration is made simple with setup wizards and built-in diagnostic tools.

Eurotherm 703-443-0000, http://tr.im/eurotherm

GL&V announces global alliance with CoorsTek

GL&V Pulp & Paper Group has signed an agreement with CoorsTek, Inc. to sell and service CoorsTek ceramic components for the global pulp and paper industry. Paper mills presently using CoorsTek ceramics may now contact GL&V directly for replacement components, repair, and regrind services.

The agreement includes paper machine wet-end and press section ceramic elements, and ceramic cleaner cones for stock preparation.

“Formalizing our relationship with CoorsTek completes our product offering – if it is on a paper machine and made with ceramic, we can supply it and we can service it,” says Paul Henzell, global business manager for GL&V’s Dewatering Technologies Group.

GL&V Pulp & Paper 819-371-8282, www.glv.com

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PULP & PAPER CANADA July/August 2009

pulpandpapercanada.com

SHEET FORMATION T110

A New Technique for Measuring Periodic Patterns Within a Paper Sheet

By J. Bernié and R. Trépanier Abstract: A new technique, based on Fourier analysis, has been developed to detect and measure periodic patterns within the sheet formation. This technique detects patterns from small scale (e.g. forming fabric marks) to medium scale (streaks with wavelength up to 10 mm) and determines their orientation, period and intensity. These patterns can be caused by felt marking, roll marking, headbox rheology, etc., and are specific to each paper machine. Their characterization provides a useful tool for quality and process control.

I

n the papermaking process it is common for a sheet of paper to have periodic or pseudo-periodic patterns within its structure. For example, fabrics and felts may generate small scale patterns.

Other phenomena, such as headbox rheology or roll marking, may generate larger scale periodic marks.

A periodic mark that is too strong compromises the quality and the value of the product. It also often indicates some problem on the machine (a felt in need of change, a roll problem, etc.). Thus there is an incentive to detect and quantify these periodic marks for quality control and process control.

To that purpose methods based on fast Fourier transform (FFT) spectrum analysis have been used during the last 20 years [1-3]. However these techniques have serious limitations, as discussed below.

EXPERIMENTAL

This paper introduces a new method based on a modified Fourier analysis that characterizes periodic and pseudo-periodic marks, which vary in size from about 0.4 mm to 10 mm. The method determines their size, orientation, and intensity.

The results of this method are compared to that of a standard FFT method.

The analysis uses light transmission images of paper sheets acquired by the Paper PerFect formation analyzer (PPF). These 480 x 480 pixel images cover a 69 x 69 mm sheet area and have a 8-bit pixel depth (256 grey levels).

Figure 1 presents an image of a newsprint sample with a complex series of patterns: large, almost vertical streaks at 85 degrees, smaller oblique streaks at 43 and 53 degrees, and almost horizontal streaks at 4 degrees that are strongest at the lower left corner of the image. The directions of these patterns are summarized in Fig. 2. There are also two small forming fabric marks, almost vertical, that cannot be seen on Fig. 1.

Figure 3 shows the resulting power spectrum pulpandpapercanada.com

for Fig. 1 obtained using a standard FFT method.

The usual characteristics (and usual limitations) of a standard power spectrum appear.

• Poor resolution at low frequencies (centre of the spectrum): at frequencies lower than about 20, corresponding to a wavelength of about 3.5 mm, the spectrum becomes a cloud from which it becomes difficult to identify peaks, unless they are very strong. For frequencies below 10, this becomes almost impossible. This spectrum noise which increases at low frequencies is due to the presence in the signal of low and very low frequency patterns which are not complete, thus creating difficulties for the FFT as it tries to “match” them with sinusoidal waves. This problem is common in FFT analysis and, when present, reduces its field of application to medium and high frequencies.

• Parasitic peaks: Another, less obvious difficulty is the presence of “parasitic” peaks in the spectrum at medium and high frequencies. This question was discussed by I’Anson [1,2]. A periodic mark in the sheet usually generates several peaks on the spectrum, along a line or along several parallel lines (I’Anson describes them as “self-consistent” series of peaks). This multiplication of results makes automatic detection of patterns delicate.

We developed an enhanced FFT-based method that significantly diminishes the impact of these two problems. This is carried out by filtering from the formation image the low and ultra-low frequency components that might result in the cloudy spectrum centre mentioned above, and by increasing the resolution of the discrete spectrum to better isolate the specific peaks from the signal, thereby decreasing the parasitic peaks. The resulting spectrum is shown on Fig. 4.

The enhanced spectrum presents significant improvements from the standard one as the peaks are much clearer. The enhanced FFT significantly reduces the noise created by the ultra-low frequency, thus the signal-to-noise ratio (obtained by divid-

J. BERNIÉ Ondimage Inc., Montreal, Que.

R. TRÉPANIER OpTest Equipment Inc., Hawkesbury, Ont.

July/August 2009 PULP & PAPER CANADA

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T111 SHEET FORMATION

FIG. 1: Image of newsprint (size: 69 mm x 69 mm).

FIG. 2: Direction of periodic marks in Fig. 1 newsprint.

FIG. 3: Standard FFT spectrum of Fig. 1 newsprint.

FIG. 4: Enhanced FFT spectrum of Fig. 1 newsprint.

ing the intensity of the peak by the average intensity of the same frequency) is higher, allowing easier detection. This is especially striking at low frequencies: the peak related to the large, almost vertical streaks of Fig. 1 has a signal-to-noise ratio of 1.17 on the standard spectrum (meaning that the peak is only 17% stronger than the spectrum noise), and of 5.8 on the modified spectrum (meaning that the peak is almost six times stronger than the spectrum noise). Thus with the standard FFT the peaks of the large streaks are almost undetectable, while they are very clear on the enhanced FFT. Furthermore, on the enhanced FFT spectrum the parasitic peaks are either non-existent or weak enough not be confused with the “real” one. Thus a simple threshold can be used to automatically detect the pattern-related peaks.

40

Table I summarizes the periodic patterns detected on Fig. 1 with the enhanced FFT method, with their period, orientation (angle from horizontal, counterclockwise) and relative intensity (signal to noise ratio, as defined above). Figures 5 and 6 show the two largest patterns of Fig. 1 sample, of respective periods 10 mm and 1 mm, as recreated from the FFT spectrum results of Table I.

A NEW APPROACH: THE CARTESIAN SPECTRUM

Standard FFT spectra in polar coordinates such as that shown on Figs. 3 and 4 are difficult to read for non-specialists as the human brain is not adapted to such coordinates. An easier way to carry out the information is to transform such polar spectra into Cartesian ones, where the

PULP & PAPER CANADA July/August 2009

abscissa represents the angle, from 1 to 180 degrees, and the ordinate the frequency.

Fig. 7 represents the enhanced FFT spectrum from Fig. 4 in Cartesian coordinates.

(The standard FFT spectrum could also be represented in Cartesian coordinates but due to its poor angular resolution at medium and low frequencies this would present little interest). Thus a peak at coordinates (x,y) represents a pattern at angle x and with a frequency y.

The Cartesian spectrum is very convenient to provide a quick overview of the patterns that are in the sheet, or to compare the patterns of different samples.

ANOTHER EXAMPLE: TISSUE PAPER

Depending on the papermaking process, sheets may have very different formation pulpandpapercanada.com

SHEET FORMATION T112

FIG. 5. 10 mm, 85 degrees pattern of Fig. 1 newsprint.

FIG. 7. Cartesian spectrum of Fig. 1 newsprint.

FIG. 6. 1 mm, 53 degrees pattern of Fig. 1 newsprint.

FIG. 8. Image of tissue (size: 69 mm x 69 mm).

TABLE I: Patterns of Fig. 1 newsprint sample.

Period (mm) Large patterns 10 Medium patterns 1 0.8 0.7 Small patterns 0.6 0.4

Angle

Intensity (S/N)

85

5.8

53 43 4

6.4 4.6 5.2

99 81

2.6 7.4

and very different patterns. Fig. 8 shows an image of tissue, with two clear oblique patterns. They appear on the Cartesian spectrum, Fig. 9. Thus each papermaking process and each paper machine will present a different spectrum fingerprint.

APPLICATIONS AND FUTURE WORK FIG. 9. Cartesian spectrum of tissue. pulpandpapercanada.com

As the periodic patterns within a sheet can come from various sources, their analysis can provide useful information on the several steps of the papermaking process. Small scale patterns July/August 2009â&#x20AC;&#x192; PULP & PAPER CANADAâ&#x20AC;&#x192;

41

T113 SHEET FORMATION can be used for monitoring felt aging, while medium and larger scale streaks may indicate a roll marking or a headbox rheology problem. The precise determination of the frequency of a specific pattern can be helpful to identify the underlying cause in the papermaking process (e.g. a vibration). Also, the set of patterns in a sheet is specific to the paper machine that has produced the sheet and is the fingerprint of this machine. This can be used, for example in benchmarking, as an additional tool to identify the origin of a sample.

Finally, the analysis of the changes in the size of the forming fabric marks across the CD profile provide information on the non-uniformity of shrinkage, thus on non-uniformity on drying, which can later cause problems of curl, etc.

SUMMARY AND CONCLUSION

This new method for detecting periodic patterns within the sheet formation constitutes a considerable improvement over

previous techniques that relied on standard FFT power spectrum analysis. The precise identification and quantification of these patterns provides a helpful tool to the papermaker for determining their origin. As such patterns usually must be kept below some threshold to ensure good product quality, this new method can be used for product quality control and in a process control loop.

1. I’ANSON, S. Identification of Periodic Marks in Paper and Board by Image Analysis Using TwoDimensional Fast Fourier Transforms - Part 1: The Basics, Tappi J., 78 (3): 113-119 (1995) 2. I’ANSON, S. Identification of Periodic Marks in Paper and Board by Image Analysis Using TwoDimensional Fast Fourier Transforms - Part 2: Forming and Press Section Mark, Tappi J., 78 (7): 97-106 (1995) 3. I’ANSON, S., KROPHOLLER, H. Enhancing Visibility of Wire Mark by Image Analysis, Jour. Pulp & Paper Sci., 17(1): J22-J26 (1991)

Résumé: Nous avons développé une nouvelle technique de mesure des marques périodiques dans la formation de la feuille, qu’elles soient à petite échelle (marques de toile, de feutre) ou de plus grande taille (marques de rouleau, bandes dues à la floculation dans la caisse de tête).

L’orientation, la taille et l’intensité de la marque sont déterminées. Ces marques sont spécifiques à chaque machine. Leur détermination permet un suivi de la qualité du produit ainsi que le contrôle de l’opération de la machine.

Reference:

J. BERNIÉ, R. TRÉPANIER. A New Technique for Measuring Periodic Patterns Within a Paper Sheet. Pulp & Paper Canada 110 (6): T110-T113 (July/August 2009). Paper presented at the 93rd Annual Meeting of PAPTAC in Montreal, Que., February 5-9, 2007. Not to be reproduced without permission of PAPTAC. Manuscript received November 16, 2006. Revised manuscript approved for publication by the Review Panel December 8, 2008.

Keywords: SHEET FORMATION, PERIODIC PATTERNS, FOURIER ANALYSIS, FELT MARKS, FABRIC MARKS, QUALITY CONTROL

TECHNOLOGY NEWS

SKF integrates all lubricant systems and services under its banner

In 2004, the SKF Group acquired Willy Vogel AG, an innovative player in the world of lubrication technology. The company has announced that all lubrication systems, engineered solutions, and services will now be offered under the SKF brand only, instead of the former dual branded SKF VOGEL. This is expected to provide efficient service, from the initial consultation to the final delivery.

Customers now have access to standard lubrication systems, customized units, and complete solutions integrating bearings, lubrication and sealing.

SKF Lubrication Solutions 800-207-5823, www.skf.ca

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REFERENCES

PULP & PAPER CANADA July/August 2009

Machinery condition monitoring now integrated with process control data

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PROCESS CONTROL T114

Internal Interconnections Impact on Process Operability By: K. Eriksson and A. Karlström Abstract: A model structure for a TMP production line, including all the internal interconnections, has been derived. Simulation results show that the model structure reflects the characteristics of the interconnected process and that the nature of the disturbance pattern arises from the fact that so many internal interconnections are present. The model can deliver insight into how modifications of the plant design would affect the production performance. Besides performance, the internal interconnections also influence the process operability, which demonstrates the importance of considering control aspects at the process design stage.

I

nternal interconnections are common in the process industry as a result of the chosen process design. In separation and reaction processes, material recycling is often introduced with the aim to increase process yield. This positive effect can be achieved in some processes, but the complexity of the interconnected process increases the demands on the control system. In pressurized processes, like thermomechanical pulp (TMP) production lines, the auxiliary equipment around the machines is designed to facilitate steam clearance between the different process units. This arrangement sometimes causes internal interconnections built into the process, which have the disadvantage of behaving like a closed-loop system which cannot be broken. As a result, the specific dynamics of the open-loop system cannot be isolated and estimating its dynamics using standard identification techniques from sampled input-output data is not straightforward [1].

The general input-output process description can be extended to incorporate the internal interconnections in an appropriate way. In this work, an extended process description of this kind is presented for a production line consisting of two serially linked twin-disc refiners. The main characteristic of the twin-disc refiner is that it has two refining zones, in which the mechanical treatment of wood, or pulp, material is simultaneously conducted. This allows for a higher production level in the same machine, compared with the single-disc refiners which have one refining zone. However, the twin-disc refiner configuration also increases the complexity of the process, as the treatment in the two refining zones cannot be individually controlled using current technology. The refining process is known as a multi input multi output (MIMO) system with complex dynamics pulpandpapercanada.com

and an intricate disturbance pattern, which may sometimes completely overshadow the intended responses to input changes.

The fact that process interconnections can give rise to complex dynamics, which impose heavy demands on the control system, has been recognized in the literature. A classification of interconnections and a description of their effects on plant dynamics are presented by Morud and Skogestad [2]. Also included in their work is a literature survey of the area, where the systems concerned are referred to as integrated plants.

Closely related to this is the work by Jacobsen [3] on changes in plant dynamics imposed by material recycle. An interconnected heating system is analyzed by Trierweiler et al. [4] and the results show that the risk of the system becoming unstable was eliminated if a bypass for water flow was closed.

Another example is found in the work by Femat et al. [5], where it is shown that interconnecting a biological reactor with recycle streams through a heat exchanger introduces temperature oscillations, which would not be present if the process units were not interconnected. This indicates the need to focus on an approach which integrates both instrumentation and process design and takes account of these integration aspects early in the design procedure [6].

In this paper, a model for a TMP production line, consisting of two serially linked refiners and auxiliary equipment, is derived. The TMP production line includes several internal interconnections which have a significant impact on the process operability and must therefore be considered in the modeling procedure.

MODELING APPROACH

The characteristics of the twin-disc refiner and the TMP refiner production line have been described

K. ERIKSSON Department of Signals and Systems, Chalmers University of Technology, Göteborg, Sweden

A. KARLSTRÖM Chalmers Industrial Technology Foundation, Göteborg, Sweden

July/August 2009 PULP & PAPER CANADA

43

T115 PROCESS CONTROL

Fig. 2: Dilution water control system on the primary refiner and its contribution, ybp(i), to the outlet pressure, y3(i). The objects within the dotted square represent the inside of the refining zone for these variables

Fig. 1: Internal interconnections in a TMP production line.

The objects within the dotted square represent the design of the complete production line. The primary and secondary refiners are labeled G(1) and G(2). The transfer functions of the internal interconnections are labeled for gvk k=1,2,3,4

by Eriksson [7]. In a traditional system configuration the inputs to the primary refiner (indicated by a superscript (1)) are the wood chip feed rate, u1(1), the hydraulic pressures applied to the two stators, u2(1), and the dilution water flow rate to each refining zone, u3(1). The assumed inputs to the secondary refiner (indicated by a superscript (2)) are the pulp feed rate, u1(2), the hydraulic pressures, u2(2), and the dilution water flow rates, u3(2). Substantial disturbances also affect the process performance and measuring the flow of dry pulp to each refiner is not straightforward. As outputs from the refiner, the temperature vectors (y1(1),y1(2)), the consistencies (y2(1),y2(2)), and the blow line pressures (y3(1),y3(2)), are possible candidates. It is assumed that a linear model will be sufficient when describing the internal interconnections and in order to focus on the impact of these interconnections, simple linear transfer function matrices will be used also when describing the conditions inside the refiners. The transfer function matrices are labeled G(1) for the primary refiner and G(2) for the secondary refiner.

Internal interconnection in the refiner system must be described when designing a suitable control strategy. This introduces the need to extend the traditional system modeling approach. In addition to the internal interconnection in the primary refiner, as described by Rosenqvist et al. [8], the introduction of the secondary refiner in the modeling approach is necessary as internal interconnections exist also between the refiners according to Eriksson et al. [9].

The representation given in Fig. 1 illustrates the high level of interconnection in the present process configuration. The interconnections generate feedback in the system and this can impose rigorous demands on the control system. At present, the control system is designed to comply with specified reference values for dilution water flow rates and blow line pressures. The control system treats these objectives separately in that it does not explicitly account for the phenomena which arise from the internal interconnections.

Control of a MIMO system like this can be significantly simplified if it is possible to decouple the inputs and outputs. Among 44

PULP & PAPER CANADA July/August 2009

Fig. 3: The pressure control systems for the two refiners.

The interconnections between the two control loops have now been condensed into the transfer functions (i)

the output candidates are refining zone temperatures if such measurements are available. Taking the decoupling possibilities into account, Berg and Karlström [10] showed that a good candidate is the temperature measurement near the pressure peak. The decoupling possibilities were also examined by Eriksson [7] using the tool of Relative Gain Array and it was shown that the choice of process outputs is essential if a decentralized control strategy is considered. Analysis of refining zone temperature measurements have shown that the responses to a change in any of the inputs are related to location [7, 10]. The temperature vector provides therefore a range of signals which are interesting to consider as outputs in future control strategies for refining processes.

PRESENT CONTROL SYSTEM

The model structure presented in Fig. 1 was derived by Eriksson [7]. It includes the major internal interconnections present in a TMP production line. It reflects only the process design and not the control system.

To study the effects of the internal interconnections observed under continuous process operation, the model structure in Fig. 1 is extended to include the present control loop configuration for dilution water and pressure valves. These valves control the amounts of water and steam in the machines and cannot, for safety reasons, be disconnected when conducting experiments.

This introduces, in each refiner, two loops at the refiner inlet from a dilution water reference to the resulting flows fed into the two refining zones, as well as one loop on the refiner outlet controlling the pressure in that area. Transfer functions for dilution water and pressure valves in a primary refiner have been estimated by Berg [1], where relevant control structures for these loops were presented. These transfer functions were used in the work by Rosenpulpandpapercanada.com

PROCESS CONTROL T116

Fig. 4: Normalized data from step-response experiments.

The left column shows primary refiner data and the right column secondary refiner data. Both columns are arranged as follows, top: inputs; middle: maximum temperature; bottom: blow line pressure

qvist et al. [8]. For the primary refiner, the transfer functions in this case are labeled as follows; H1(1) and H2(1), for dilution water valves; F1(1) and F2(1), for dilution water valve controllers; H3(1) and F3(1), for valve and controller in the pressure loop respectively. For the secondary refiner, the superscript (2) is used.

Fig. 2 shows the dilution water feed system to a twin-disc refiner and how the dilution water flows (i.e. U3FS(i) and U3DS(i)), via elements in the refiner transfer function matrix, produce a contribution to the outlet pressure y3(i), labeled ybp(i) [8]. The signal rd(i) represents the reference value for the dilution water flows.

The dilution water flow rates are influenced by the internal interconnections of the system. This means that, for the primary refiner, a disturbance is gv1 y3(1) added to u3FS(1) and u3DS(1). In the case of the secondary refiner, the corresponding disturbance signal is gv3 y3(1), see Fig. 1.

When control loops are introduced into the model, as presented in Fig. 1, the structure becomes even more complex. In order to focus on the pressure-dilution water interaction, which includes most interconnections, a modified representation can be used. Let, for i=1,2, g33FS(i) g33DS(i) L(i) = ————— + ————— 1 + F1(i) H1(i) 1 + F2(i) H2(i)

and

(1)

M (1) N (1) = —–———

1 – gv1L(1)

(4)

H3(1) Gp(1) = —–——— 1 – gv1L(1)

(5)

(2) = gv3L(2)

(6)

N (2) = M(2) Gp(2) = H3(2)

(7) (8)

In Fig. 3, the system is presented from setpoints in pressure, rp(i), and dilution water flow, rd(i), to the output pressures, y3(i).

Using this approach the interactions between the two refiners become clearly visible, i.e. through the transfer functions (i), which describe how the outlet pressure in one refiner influences the outlet pressure in the other one. Transfer functions from the dilution water setpoints, N (i), are also introduced. In Fig. 3 it is shown how the impact from these setpoints enters as process disturbances to the pressure control loops. The controller transfer functions of the pressure loops remain as before in this representation, but the process transfer functions (i.e. previously just the pressure valves) are modified into Gp(i).

If the pressure loop in the primary refiner is taken into account, the output pressure can be expressed as y3(1) = Gp(1)up(1) + N (1)rd(1) + (i)y3(2)

(9)

The representation given in Fig. 3 is suitable when analyzing the ability of the system to compensate for disturbances which depends on the nature of the subsystems involved. The analysis of transfer functions is facilitated if the linear model is scaled with respect to the largest expected change in disturbance, the largest permitted input change and the largest permitted control error [12]. The fact that the disturbances considered here are measurable makes it possible to determine such scaling factors. In terms of scaled variables requirements like |Gp(1)|>|(1)|–1 at frequencies where |(1)|>1 (10) can be analyzed. If this condition is fulfilled, |rp(1) – y3(1)|<1 is assured and this can be an acceptable performance considering the complex disturbance pattern present in the system. Similar requirements can also be formulated for the impact of the dilution water flow and, in addition, corresponding expressions can be formulated for the analysis of the pressure control loop in the secondary refiner blow line.

A SIMULATION MODEL

F H g F H g M (i) = —————— + —————— (2) 1+F H 1+F H (i) 1

(i) (i) 1 33FS (i) (i) 1 1

(i) 2

(i) (i) 2 33DS (i) (i) 2 2

where g33FS(i) and g33DS(i) are elements in the transfer function matrix G(i). Define the transfer functions 1 (1) = —–——— g 1 – gv1L(1) v2

pulpandpapercanada.com

(3)

The features of the derived model structure can be analyzed in a simulation model. It is assumed that parametric models obtained from data, like the time series presented in Fig. 4, can be used to obtain estimates of the elements in that are sufficient to produce a model reflecting the characteristic behavior of the interconnected system. To focus on the phenomena introduced by the interconnections, parametric model structures of lowest possible orders are used. The transfer functions of the internal interconnections are modeled using first-order systems with time delays when July/August 2009 PULP & PAPER CANADA

45

T117 PROCESS CONTROL necessary. Parameters suitable for use in the simulations can be estimated using knowledge of the process design and behavior.

To create a reliable simulation model, a combination of the structures presented in Fig. 1 and Fig. 3 is required. In other words, it includes all the internal interconnections identified in the production line, see Fig. 1, plus the present control configuration, as described in Fig. 3. The simulation model is constructed using SIMULINK [13].

With the model, simulations can be carried out using process inputs measured from step-response experiments. The outputs delivered by the simulation model can then be compared with measured outputs and validated to some extent. In Fig. 5, simulated outputs are shown, together with temperature measurements from sensors near the temperature profiles maxima and measured motor loads for both a primary and a secondary refiner.

The validation results as presented in these figures show that fairly good agreement can be obtained even from simple models like the one used in these simulations. There is a potential for improvement (which can be quantified using residuals between simulated and measured output), by introducing some appropriate time constants in the transfer functions inside the refiner blocks in the simulation model, for example.

The interaction between blow line pressure and dilution water flows is central. These signals are sometimes found to oscillate with a phase shift of about 180° [8, 9]. A study of the experimental data considered here revealed that this kind of oscillation was also present in this case, see upper plot of Fig. 6. Simulations using the interconnected model reveals that this behavior is reflected by the model, see lower plot of Fig. 6.

Comparing the data presented in the two plots of Fig. 6, reveals that the simulation model produces signals which, in this specific frequency region, have the same amplitude as the variations observed in measured process data. The variables studied in these figures can be characterized as internal states when considering the simulation model. As such, and also considering the simplicity of the transfer functions of the different blocks in the interconnected model, direct comparisons between simulated and measured data are not possible. Instead, the validity of the model can be discussed in this context from signal frequency content and the ability to reproduce the characteristic behavior observed in the actual process and associated with the internal interconnections.

Fig. 5: Validation of the simulation model using data from step response experiments. Upper plot: primary refiner; lower plot: secondary refiner. Both plots show normalized data, solid: simulated output; dotted: maximum temperature of refining zone temperature profile; dashed: motor load

PLANT MODIFICATIONS

Using the simulation model, the consequences of plant modifications can be studied. As the process dynamics are so clearly affected by the internal interconnections, it is interesting to study how the plant is likely to behave if one or several of these interconnections are modified. If the internal interconnection in the primary refiner is broken, i.e. gv1 is set at zero, the simulation model produces the result presented in Fig. 7, where it can be seen that the fluctuations in dilution water flow rate are significantly lower compared with the fluctuations shown in Fig. 6. However, the oscillatory behavior of the pressure appears to be unaffected. An examination of the different pressure contributions accounted for in the simulation model reveals that the main dynamic behavior in this time frame arises from the poorly tuned pressure control loop located in the refiner blow line.

When the interconnection between the primary refiner outlet 46â&#x20AC;&#x192;

PULP & PAPER CANADAâ&#x20AC;&#x192; July/August 2009

Fig. 6: Upper plot: Normalized process data from a primary refiner. Lower plot: Normalized, simulated primary refiner data. In both plots, the solid line is the blow line pressure and the dotted lines are the two dilution water flow rates pulpandpapercanada.com

PROCESS CONTROL T118

Fig. 7: Normalized, simulated process data when the primary refiner internal interconnection is broken, i.e. gv1 = 0.

Black and solid: blow-line pressure; dotted lines: dilution water flow rates

and inlet is eliminated, the other outputs, in addition to the blow line pressure, are also affected. This is illustrated using Fig. 8, where measured and simulated data from the primary refiner consistency are shown. It can be seen that the disturbances affecting the primary refiner consistency are reduced when the process is modified.

In the secondary refiner, as in the primary refiner, the internal interconnections of the plant have a significant impact on the dilution water flow rates. The effect of a weaker interconnection between the two refiners in the production line can be simulated by setting gv3 = 0, see Fig. 9. It is not possible completely to eliminate this interconnection, but the results indicate what can be achieved by a combination of improved process design and control.

A comparison of the changes in the simulated dilution water flow rate in Fig. 9 reveals that the time constant for fluctuations is lowered as a result of the plant modification. Variations in the dilution water flow rate cause variations in the refining zone conditions, which can be registered by temperature sensors, for example. The increased time constants for variations creates the opportunity to control the refining zone temperature, possibly to a specified shape and level of the temperature profile, by changes in hydraulic pressure or dilution water flow rate, for example.

CONCLUSIONS

A complex model structure for a complete TMP production line, including all the internal interconnections in the system, is derived. This model is linear, as it is believed that the aspects of the internal interconnections can be modeled using linear blocks even though the refiner model itself is strongly nonlinear. The behavior of the internally interconnected model has been verified using process data in combination with simulations. The model structure reflects the characteristics of the interconnected process and it is found that the nature of the disturbance pattern arises from the fact that so many internal interconnections are present.

A model description appropriate for studying the ability of the present process design to handle this intricate disturbance pattern is therefore derived.

The system described here, i.e. the TMP production line, has several distinct internal interconnections which influence the production performance, as well as system controllability. The results that have been obtained therefore demonstrate the importance of pulpandpapercanada.com

Fig. 8: Normalized consistency data from the primary refiner. Dotted: measured consistency; dashed: simulated consistency using the original model; solid: modified, simulated consistency when gv1 = 0

Fig. 9: Normalized, simulated dilution water flow to one of the refining zones in the secondary refiner. Dotted: dilution water flow using the original model; solid: dilution water flow when gv3 = 0

considering control aspects at the process design stage.

The internally interconnected model structure serves as a framework which enhances the ability to model the complex process behavior. The simple transfer function matrices, representing the two refiners in this work, can be replaced by more detailed models, such as the entropy-based first-principles model derived

by Eriksson [7].

The extensive model derived can be used for several purposes.

Firstly, it can, by simulations, give directions on how the process design should be modified, i.e. how the process should be rebuilt, in order to reduce the problems that are brought about by the internal interconnections. Secondly, from the supplier’s perspective, the model can be used to demonstrate to the customer how the production line should not be built. This is important since with the purpose of cost reduction, piping must often stand aside.

In the case of the TMP process, and as shown in this paper, this can result in severe problems related to operability.

LITERATURE

1. KARLSTRÖM, A., KOEBE, M. Modelling of wood-chip refining processes. Nordic Pulp and Paper Research Journals, (4):384-388 (1993).

2. MORUD, J., SKOGESTAD, S. Dynamic behaviour of integrated plants. J. of Process Control 6(2/3):145-156 (1996).

3. JACOBSEN, E. W. On the dynamics of integrated plants — non-minimum phase behaviour. J. of Process Control 9(5):384-388 (1999).

4. TRIERWEILER, J. O., SCUTTLE, B., EGNELL, S. Dynamics and control of a process with recycle streams. J. of Process Control 8(5-6):507-515 (1998).

5. FEMAT, R., MÈNDEZ-ACOSTA, H., STEYER, J., GONZÀLEZ-ALVAREZ, V. Temperature oscillations in a biological reactor with recycle. Chaos, Solitons and Fractals 19(4):875-889 (2004).

6. KARLSTRÖM, A., BREITHOLTZ, C., JOVIK, I., LAGERBERG, A. Control

July/August 2009 PULP & PAPER CANADA

47

T119 PROCESS CONTROL system design in distillation processes and its dependence of the original process design. 1st IFAC Workshop on Interactions between Process Design and Process Control, London, UK (1992).

7. ERIKSSON, K. An entropy-based modeling approach to internally interconnected TMP refining processes, Licentiate thesis, R003/2005, Department of Signals and Systems, Chalmers University of Technology, Göteborg, Sweden (2005).

8. ROSENQVIST, F., BERG, D., KARLSTRÖM, A., ERIKSSON, K., BREITHOLTZ C. Internal interconnections in TMP refining. IEEE Conference on Control Applications, Glasgow, UK (2002).

9. ERIKSSON, K., KARLSTRÖM, A., ROSENQVIST, F., BERG, D. The impact of different input variables in a twin-disc refiner line. Control Systems 2002,

Stockholm, Sweden, 229-233 (2002).

10. BERG, D., KARLSTRÖM, A. Approach to 3x3 decoupling and control of thermomechanical pulp refiners. Advanced Process Control Applications for Industry Workshop, Vancouver, Canada (2004).

11. BERG, D. Stability analysis in thermomechanical pulp refiners. Master’s thesis, EX007/2002. Department of Signals and Systems, Chalmers University of Technology, Göteborg, Sweden. (2002).

12. SKOGESTAD, S., POSTLETHWAITE, I. Multivariable Feedback Control, Analysis and Design. John Wiley and Sons, Chichester, England (1996).

13. Mathworks. Simulink (Dynamic System Simulations for MATLAB) version 5.0 (R13). The Mathworks, Inc. (2002).

Résumé : Nous avons élaboré un modèle de structure de chaîne de production de PTM, y compris toutes les interconnexions internes. Les résultats de la simulation indiquent que ce modèle reflète les caractéristiques du procédé, et que le type de perturbation est attribuable au fait qu’un grand nombre d’interconnexions internes soient présentes. Ce modèle donne une meilleure idée des effets des modifications apportées à la conception de l’usine sur le rendement. En plus du rendement, les interconnexions internes ont aussi une influence sur l’exploitabilité du procédé, ce qui démontre l’importance de tenir compte du contrôle à l’étape de conception du procédé.

Reference: ERIKSSON, K., KARLSTRÖM, A. Internal Interconnections Impact on Process

Operability. Pulp & Paper Canada 110(6):T114-T119 (July/August 2009). Paper presented at the 2005 International Mechanical Pulping Conference in Oslo, Norway, June 7-10, 2005. Not to be reproduced without permission of PAPTAC. Manuscript received August 31, 2007. Revised manuscript approved for publication by the Review Panel Dec. 2008.

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PHOTO FILE

PacWest Conference 2009 The PacWest event is an effective combination of professional development and networking opportunities. About 150 people attended the conference, held from June 10-13 at Sun Peaks Resort, near Kamloops, B.C.

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PULP & PAPER CANADAâ&#x20AC;&#x192; July/August 2009

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WORD FROM THE DIRECTOR Dear Members, It is a pleasure to take this opportunity and give you an update on some of your Association’s activities and direction.

Earlier this year, PAPTAC launched a Webinar Program in order to provide its technical and professional development courses in a new accessible and flexible format. The experience was a great success. The Mechanical Pulping Webinars, distributed in two-hour modules over two weeks, allowed for mill personnel from across the country to sit-in on the segments of their choice, thus creating plenty of discussion and interaction. With PAPTAC’s Technical Committees working on hosting presentations and meetings on the Web as well, there are plenty of opportunities ahead for PAPTAC members to develop their network and knowledge in an environment adapted to their schedule.

We look forward to bringing you these exciting opportunities throughout the coming months!

Greg Hay Executive Director

PRE-PRINTS & CDs 7th International Paper & Coating Chemistry Symposium June 10-12, 2009 Hamilton, ON

Paper Modelling Symposium 2008 August 27-29, 2008 Trois-Rivières (QC)

Purchase your copies at www.paptac.org/store

CALL FOR PAPERS – EXFOR & ANNUAL MEETING 2010 PAPTAC is currently planning the technical and business programs for EXFOR & Annual Meeting 2010, which will take place February 2-3 at the Queen Elizabeth Hotel in Montreal.

The new format introduced in February 2009 at the Queen Elizabeth Hotel proved successful and conducive to networking and exchange.

Abstract submissions are actively sought and we encourage all mill personnel, researchers and suppliers to submit their latest work.

New for 2010 is a joint effort between PAPTAC and its Quebec branches to organize a francophone technical track whereby some of the best papers channeled through branch activities will be presented in French.

All abstracts (English & French) are to be submitted by September 10, 2009 to Greg Hay at ghay@paptac.ca.

Based on the level of submissions, the following committees are planning to sponsor sessions at the Annual Meeting: ¾ Bleaching ¾ Energy Cost Saving ¾ Non-Wood Fibres ¾ Paper Machine Technology ¾ Process Control ¾ Research ¾ Engineering & Maintenance ¾ Environment ¾ Fine & Coated Papers ¾ Mechanical Pulping ¾ Paperboard Packaging ¾ Recycling ¾ Biorefining ¾ Supplier Showcase (10-min presentations)

EXFOR 2010

¾ Revised floor plan ¾ Maximum traffic flow ¾ No increase in rates ¾ Guest passes ¾ Supplier Showcase session ¾ Social activities on tradeshow floor

www.paptac.ca

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Š2008 Buckman Laboratiories