World Fertilizer - May/June 2021

MAGAZINE | MAY/JUNE 2021

CONTENTS 03 05 10

Comment World News Tacking Into The Wind

25

Gordon Cope, Contributing Editor, addresses how North American producers are reacting to the gale forces of the marketplace.

31

Gordon Cope, Contributing Editor, addresses how North American producers are reacting to the gale forces of the marketplace.

TACKING INTO THE

WIND

Venturing Outside The Comfort Zone Patrik Kolmodin, Sulzer, Sweden, explains how agitators for use in the chemical industry can be optimised during the design process by going beyond specifications.

T

he global fertilizer industry has been experiencing massive challenges over the last year as COVID-19 and its ensuing consequences have upended virtually every segment of business, including agriculture. Fortunately, the sector has responded well in guaranteeing supplies and support to farmers and, as the year advances, prospects in North America are encouraging.

Nitrogen In North America, projections for nitrogen look promising.

During the COVID-induced doldrums in mid-2020, urea prices for NOLA FOB were under US$180/t. Starting in 2021, however, both industrial and fertilizer demand firmed up.

With stocks in short supply, urea prices have risen significantly to over US$350/t in early 2021.

In its 2020 financial report, Nutrien noted that it experienced strong nitrogen fertilizer sales in late 2020 due to various factors. “For our nitrogen business, we saw excellent sales volumes, both for the quarter and the year,” said the then CEO and President of Nutrien, Chuck Magro, during a recent investors conference call. “We increased our nitrogen sales volumes by 700 000 t in 2020 due to strong North American operating rates and benefits from our de-bottlenecks and optimisation projects and good agricultural demand.”

Ammonia input prices in North America are expected to rise over the coming year, but still remain competitive when compared to other jurisdictions. During 2020, the US Energy Information Administration (EIA) noted that the Henry Hub price averaged US$2/1 million Btu, primarily due to demand destruction related to COVID. Domestic production has decreased by 2%, however, and is expected to average 95.9 billion ft3/d through 2021. As consumption recovers, demand pressures are expected to push the price up over US$3/1 million Btu, but will still be significantly less than that experienced by European and Asian producers.

Gulf Coast Ammonia (GCA) is building what is being touted as the world’s largest single stream anhydrous ammonia plant, in Texas City, Texas, US. Completion of the

1.3 million tpy plant and adjacent deepwater port is expected by mid-2023. Air Products is investing approximately US$500 million to build a steam methane reformer, generators and hydrogen pipelines to service the project.

In late 2020, Koch Fertilizer announced a US$90 million investment at its Beatrice nitrogen plant in Nebraska, US. The money will improve environmental and safety performance, as well as increase urea and ammonium nitrate (UAN) capacity by 75 000 tpy. “We are committed to serving our customers, and we continue to see greater UAN demand locally,” said Scott McGinn, Executive Vice President of Koch Fertilizer. “This investment will improve the efficiency and reliability of our operations and add greater production flexibility at Beatrice to meet the demand of both our ammonia and UAN customers.” The upgrades are expected to be completed by late 2021.

In the first part of a two part article, Brandon Forbes and D.J. Cipriano, AMETEK/Controls Southeast Inc., USA, highlight the challenges that arise from the storage of sulfur and show how a well-designed and installed thermal management system can counter these problems.

37

Phosphate Over the last several years, the phosphate market has been depressed due to a combination of low demand and increased competition from producers in the Middle East, Russia and Africa. In order to rebalance the market and meet environmental goals, China has been reducing its phosphate production capacity. Mosaic has also reduced production capacity in Florida. In late 2020, Nutrien wrote down US$760 million in the value of its US phosphate plants at Aurora, North Carolina, and White Springs, Florida.

It cited the market as being “fundamentally oversupplied”, and expects the supply bulge to limit price appreciation for the next several years.

Internationally, other phosphate producers continue to expand. Morocco’s OCP is building three, 1 million tpy granular phosphate units at Jorf Lasfa. Ma’aden is ramping up production at the Wa’ad Al Shamal complex in Saudi Arabia with 3 million tpy of diammonium phosphate (DAP)/monoammonium phosphate (MAP) granulation capacity. PhosAgro has plans to increase production at its Balakovo and Volkov facilities in Russia by 30% by 2025.

Sulfur Storage Tank Challenges: Part One

Following The Trends Barbara Cucchiella and Wilfried Dirkx, Stamicarbon, the Netherlands, discuss trends in finishing technologies, including larger capacities, lower costs and higher efficiencies.

40

Earning Its Stripes Gelmer Bouwman and Geoffrey Havermans, Kreber, the Netherlands, investigate how computer-aided design has become a key tool in the design and optimisation of prilling facilities.

10

15

Gelmer Bouwman and Geoffrey Havermans, Kreber, the Netherlands, investigate how computer-aided design has become a key tool in the design and optimisation of prilling facilities.

Grabbing Gains Carolina Vargas and Peter Simons, TOMRA Mining, Germany, explain how methodical testing can show phosphate producers how much silica can be removed from their feed materials to improve yields and lower production costs.

19

EARNING ITS STRIPES I

n 1918, the physicist and Nobel Laureate Hendrik Antoon Lorentz started the calculations needed to build the Enclosure Dam in the north of the Netherlands. Eight years later, in 1926, his full recommendations containing complex mathematical calculations regarding tides, river flow, wind power and storm predictions – all made without calculators – were published (Figure 1).1

We have come a long way since then.

Nowadays, the computational power of computers is readily available even to the non-physicist, enabling highly complex situations to be analysed in a fraction of the time. Computer-aided engineering (CAE) is also playing an indispensable role in the design of prilling towers. This article will highlight the four application areas where CAE is taking a leading role.

Diving Deep Through Reverse Engineering Werner Barnard, Hydro, Inc., USA, demonstrates the importance and value of reverse engineering critical pumps as part of a contingency planning strategy.

40

45

Fertilizer With A Double Twist Thomas Lansdorf, Eirich, Germany, provides a number of practical examples to showcase how the range of applications for which fertilizer granules are being manufactured is steadily growing.

MAGAZINE | MAY/JUNE 2021

ON THE COVER

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NICHOLAS WOODROOF, DEPUTY EDITOR

R

enewable or ‘green’ ammonia – produced via hydrogen created from electrolysis of water that is powered by renewable sources of energy – is continuing to set the agenda in the fertilizer industry. Earlier this month, Yara and ENGIE announced plans to build a renewable hydrogen plant in Australia’s Pilbara region, backed by AUS$42.5 million of government grants. Once complete in 2023, the plant will produce up to 625 tpy of green ammonia that will be used for, amongst other things, decarbonised fertilizer production.

Elsewhere, Casale, Nutrien, Nel Hydrogen, Shell and GE are part of a group working towards a green ammonia pilot plant in Minnesota, US, that will deploy water electrolysis, ammonia synthesis and ammonia cracking technologies. That this project also has state support – in the form of US$10 million from the US Department of Energy’s Advanced Research Projects Agency-Energy – is a reassuring indicator that governments are realising such schemes urgently require their contribution if they are to be commercially viable and achieve their crucial aim of reducing carbon emissions.

And, as featured in our previous issue’s World Review, the Helios green fuels project in Saudi Arabia’s planned NEOM megacity will aim to produce 1.2 million tpy of green ammonia using technology from Haldor Topsoe. Initial project work is now underway, with start-up planned for 2025.1 I’m therefore delighted to say that on 15 September World Fertilizer will be hosting ‘Ammonia 2021’, an online conference dedicated to showcasing cutting-edge developments in ammonia production technology. We already have some excellent speakers confirmed, with experts from Nel Hydrogen, ICIS and Peddie Engineering set to discuss large scale renewable electrolysis to enable decarbonisation of ammonia production, the short to medium-term outlook for the ammonia market and recent challenges for the ammonium nitrate market.

Complementing these presentations will be a range of interactive features, including live Q&A sessions with each speaker following their presentation. There will also be a virtual exhibition running in parallel, where attendees will have the chance to interact with company representatives and find out more about their products and services. Finally, networking will also be possible (and encouraged!) through live chat and video conferencing. To register to attend, you can go to www.worldfertilizer.com/ammonia2021/ and reserve your free space.

Don’t worry if 15 September is already booked up in your diary – registering will mean that you will automatically receive a recording of the entire conference once it has finished, so you can view all of the proceedings at your convenience. I look forward to seeing you on 15 September.

While on the subject of new digital content, make sure to watch World Fertilizer’s first-ever Spotlight interview on our website if you haven’t already. This discussion with Juan A. González-Léon and Lucas Moore from Arkema-ArrMaz reflected on their article on fertilizer substrates and deliquescence that was published in our November/December 2020 issue – well worth a watch: www.worldfertilizer.com/special-reports/10052021/worldfertilizer-spotlight-with-arkema-arrmaz/ Finally, I hope you enjoy this latest issue of World Fertilizer.

Reference 1.

‘Saudi Arabia moves on $5bn hydrogen project’, https://www.meed.com/saudi-arabia-moves-on-5bnhydrogen-project (8 April 2021).

MAY/JUNE 2021 | WORLD FERTILIZER | 3

Daily Fertilizer Price Assessments

Nitrogen

Ammonia

Phosphates

Sulphur

• Prilled: - China fob

• East Asia cfr

• Granular: - Egypt fob - Brazil cfr - Nola (US Gulf) fob $/st

• Middle East fob

• • • • •

• China cfr granular $/t • China domestic (ex works) Yn/t

(excluding Taiwan)

Read more »

Read more »

DAP fob China DAP cfr India MAP cfr Brazil DAP barges fob Nola MAP barges fob Nola

Read more »

Read more »

Work smarter with groundbreaking daily fertilizer price assessments from Argus Argus daily price assessments provide you with unique benefits, including $

Greater certainty

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Fertilizer illuminating the markets

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Over the highlighted 4 week period (7 Jan to 4 Feb 2021) the price of DAP fob China grew from $397.50/t to $492.50/t, an increase of 24%.

The blue line on the graph, marked by the 5 weekly prices over this period (orange) clearly highlights this price growth. However, the 21 daily prices over this same period (grey line) provide greater detail on how this price growth was achieved.

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Market Reporting Consulting Events

WORLD NEWS USA Casale to participate in green ammonia pilot project

C

asale, as a member of a team that comprises RTI International, the University of Minnesota, Nutrien, GE, Shell, Nel Hydrogen, Xcel Energy, Great River Energy, Ottertail Power, Chemtonergy, Texas Tech University, Pacifica and Agricultural Utilization Research Institute (AURI), will participate in a project that is working towards realising a 1 tpd green ammonia pilot plant, using water electrolysis, ammonia synthesis and ammonia separation and utilisation technologies.

RTI International will lead the consortium and the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) will provide US$10 million in funding.

The project will integrate the most promising breakthrough technologies developed in ARPA-E’s Renewable Energy to Fuels Through Utilization of Energy-Dense Liquids (REFUEL) programme into a modular demonstration facility capable of producing 1 tpd of low- and zero-carbon ammonia.

The technologies include Casale and RTI’s low-temperature,

low-pressure synthesis along with flexible process control strategies that can vary ammonia production to meet available intermittent electricity, and the University of Minnesota’s (UMN) elevated temperature ammonia separation.

The demonstration facility will be located at the UMN West Central Research and Outreach Center (WCROC), Morris, Minnesota, and will leverage the site’s existing hybrid wind and solar generation in the fully integrated process.

The technology integration will also demonstrate several downstream ammonia utilisation technologies, including ammonia cracking to produce hydrogen and power generation to amplify the ability to use ammonia as an energy carrier.

Successful deployment of the technology will reduce the energy intensity and carbon emissions of ammonia production, maximise renewable energy usage by capturing generation fluctuations and matching demand and enable distributed production closer to end users.

THE NETHERLANDS Stamicarbon launches green ammonia technology

S

tamicarbon has announced the launch of Stami Green Ammonia Technology, which relies on renewable resources – instead of fossil fuels – to eliminate carbon from the production process, paving the way for sustainable and green fertilizer production. Ammonia acts as a building block for nitrogen fertilizers and plays an important role in providing optimal plant nutrition, but is responsible for 1% of the world’s greenhouse gas emissions.

The company has signed an exclusive cooperation agreement with Argentinian-based company Raybite S.R.L. for the commercialisation of their small-scale ammonia technology package. The cooperation agreement means that Stamicarbon has become an ammonia licensor for small-scale ammonia plants.

The technology can also be applied in existing plants as part of a hybrid technology solution to make existing fertilizer production more sustainable.

Stamicarbon will provide its green ammonia technology as part of the development of a renewable power-to-fertilizer plant in Kenya.

MET Development, a subsidiary of the Maire Tecnimont Group with Stamicarbon, has signed an agreement with Oserian Development Co. for the development of the plant at the Oserian Two Lakes Industrial Park, located on the southern

banks of Lake Naivasha 100 km north of Nairobi.

The plant will be located near the country’s largest geothermal energy basin and will be partly powered by solar energy sources produced on-site – displacing the need for fossil fuels – and eliminating carbon from the production.

The facility will reduce carbon emission by approximately 100 000 tpy of CO2, compared to a gas-based fertilizer plant. The project will also reduce dependency on imported nitrogen fertilizers.

The project is targeting production of 550 tpd of calcium ammonium nitrate (CAN) and/or NPK fertilizers to meet the demand of local agricultural requirements. MET Development is currently engaging with local and international partners to set up the development consortium.

The project has started preliminary engineering works and NextChem, also a Maire Tecnimont subsidiary, is aiming to start the front-end engineering design (FEED) by the end of 2021. Commercial operation of the plant is currently scheduled to begin in 2025, which will be dedicated to local Kenyan agri-business.

The project will utilise approximately 70 MW of renewable power, will create the starting point for locally produced Kenyan fertilizer and is expected to directly generate over 100 jobs in the region.

MAY/JUNE 2021 | WORLD FERTILIZER | 5

WORLD NEWS NEWS HIGHLIGHTS

IN BRIEF

World Fertilizer Spotlight with Arkema-ArrMaz Haldor Topsoe digital solution operational at Fatima ammonia plant Acron developing calcium nitrate unit in Veliky Novgorod OCI publishes 1Q21 results Nutrien releases 1Q21 results Koch Fertilizer building ammonium thiosulfate terminal at Fort Dodge facility Salt Lake Potash receives environmental permit for Lake Way project

Visit our website for more news:

www.worldfertilizer.com

AUSTRALIA Agrimin signs offtake agreement with

Sinochem Fertilizer Macao

A

grimin Ltd. has signed a binding offtake agreement with Sinochem Fertilizer Macao Ltd. for the supply of 150 000 tpy of sulfate of potash (SOP) produced from the Mackay potash project in Western Australia for sale and distribution in China.

The duration of the contract is 10 years from the commencement of commercial production.

Sinochem Fertilizer Macao is a wholly-owned subsidiary of Sinofert Holdings Ltd., whose controlling shareholder is China National Chemical Corp. Ltd.

SPAIN Highfield Resources delivers positive

environmental report

H

ighfield Resources has delivered a positive report from the environmental department of Aragón to the mining authorities of Madrid, Aragón and Navarra, the last report required in respect of the last section of the Mining Concession documentation submitted for the Muga potash project in northern Spain.

The company has been advised that if no further clarification is

required by the authorities, the next step is to send the text of the Mining Concession document to the Central Government’s lawyer for its legal review prior to the Mining Concession award being issued.

The company has said the engineering and design work for the project is ready and that it is currently progressing the last stage of the Mining Concession.

AUSTRALIA Perdaman and Incitec Pivot sign urea

offtake agreement

I

ncitec Pivot Ltd.’s wholly-owned subsidiary, Incitec Fertilizers Pty Ltd. (IPF) has entered into a 20-year offtake agreement with Perdaman Chemicals and Fertilisers Pty Ltd., with a commitment to take up to 2.3 million tpy of granular urea fertilizer from Perdaman’s proposed urea plant at Karratha in Western Australia.

6 | WORLD FERTILIZER | MAY/JUNE 2021

Agrimin has also awarded Primero Group, a subsidiary of NRW Holdings Ltd., the front-end engineering design (FEED) contract for the project’s process plant and associated non-process infrastructure.

Primero was initially appointed in July 2019 on an early contractor involvement basis to complete the definitive feasibility study engineering design for the process plant.

At the completion of the FEED works, Primero will deliver to Agrimin an engineering, procurement and construction contract to support a final investment decision.

The AUS$4.3 billion plant is scheduled to start production in 4Q25, with construction due to begin in 1Q22. It will be Australia’s first world-scale urea plant.

The offtake agreement remains conditional upon Perdaman finalising its project finance for construction of the plant.

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WORLD NEWS DIARY DATES GPCA Supply Chain Conference 26 – 27 May 2021 Online gpcasupplychain.com

65th Annual Safety in Ammonia Plants and Related Facilities Symposium 29 August – 02 September 2021 San Diego, California, US aiche.org/conferences/annualsafety-ammonia-plants-andrelated-facilities-symposium/2021

Ammonia 2021 15 September 2021 Online worldfertilizer.com/ammonia2021/

Sulphur + Sulphuric Acid 2021 01 – 03 November 2021 Online events.crugroup.com/sulphur/ home

15th Annual GPCA Forum 07 – 09 December 2021 Dubai, UAE

CANADA Government of Saskatchewan backs SOP expansion

project

T

he Government of Saskatchewan has said it supports Saskatchewan Mining and Minerals Inc.’s (SMMI) decision to upgrade its sodium sulfate plant in Chaplin.

SMMI’s CAN$220 million sulfate of potash (SOP) fertilizer production upgrade, once complete, is expected to result in a 50% increase in jobs at the Chaplin facility and more than 360 construction jobs. The upgraded facility is expected to produce 150 000 metric tpy of SOP, which will be sold to North American and international markets as a fertilizer and plant nutrition product.

Further expansion is planned to increase SOP tonnes and utilise reserves at Ingebrigt Lake.

The project has been conditionally approved for the government’s new Sodium Sulphate Incentive, which provides a 10% credit for capital projects that diversify products or improve operating efficiency.

In addition, the provincial government has reduced the royalty rate for sodium sulfate

production from 4% to 3%.

The upgrade has also received conditional approval under the province’s Saskatchewan Chemical Fertilizer Incentive (SCFI). The SCFI is a non-refundable, non-transferable 15% tax credit on capital expenditures valued at CAN$10 million or more for newly constructed or expanded eligible chemical fertilizer production facilities in Saskatchewan.

The Saskatchewan Ministry of Environment has determined that the expansion is not a development and therefore will not require further environmental approvals.

Construction is scheduled to begin by late 2021. The upgraded facility is expected to be complete by the end of 2023.

SMMI has been producing sodium sulfate at Chaplin for over 70 years. The current site is situated on the TransCanada Highway and the Canadian Pacific main east-west line.

gpca.org.ae/events/15th-annualgpca-forum-2/

AUSTRALIA Yara Pilbara and ENGIE to build renewable

Turbomachinery & Pump Symposia 2021 14 – 16 December 2021 Houston, Texas, US

Y

tps.tamu.edu/

To stay informed about the status of industry events and any potential postponements or cancellations of events due to COVID-19, visit World Fertilizer’s events page: www.worldfertilizer.com/events

hydrogen plant for renewable ammonia production ara Pilbara and ENGIE are to build a renewable hydrogen plant to produce renewable ammonia.

As part of the ARENA Renewable Hydrogen Deployment Funding Round, the Australian government is supporting the project with a AUS$42.5 million grant.

Scheduled for completion in 2023, the facility will be one of the world’s first industrial-scale renewable hydrogen production operations.

The project, which builds on the Pilbara’s renewable energy potential, comprises the development, construction and operation of a renewable hydrogen plant within the existing Yara Pilbara ammonia plant to deliver green ammonia to customers

8 | WORLD FERTILIZER | MAY/JUNE 2021

for decarbonising emissions from power generation, shipping, fertilizer or mining explosives.

The key elements of the project are a 10 MW electrolyser; an on-site facility of photovoltaic panels; and a battery storage system that will allow the plant to operate without being connected to the main electrical grid.

Scheduled to commence production in 2023, the first concrete phase of the project will produce up to 625 tpy of renewable hydrogen and 3700 tpy of renewable ammonia. This initial first phase is key to enabling the facility to become the ‘Pilbara Hydrogen Hub’, building on the existing export infrastructure.

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High production output and uniform product quality

Gordon Cope, Contributing Editor, addresses how North American producers are reacting to the gale forces of the marketplace.

TACKING INTO THE

WIND

10

T

he global fertilizer industry has been experiencing massive challenges over the last year as COVID-19 and its ensuing consequences have upended virtually every segment of business, including agriculture. Fortunately, the sector has responded well in guaranteeing supplies and support to farmers and, as the year advances, prospects in North America are encouraging.

Nitrogen In North America, projections for nitrogen look promising.

During the COVID-induced doldrums in mid-2020, urea prices for NOLA FOB were under US$180/t. Starting in 2021, however, both industrial and fertilizer demand firmed up.

With stocks in short supply, urea prices have risen significantly to over US$350/t in early 2021.

In its 2020 financial report, Nutrien noted that it experienced strong nitrogen fertilizer sales in late 2020 due to various factors. “For our nitrogen business, we saw excellent sales volumes, both for the quarter and the year,” said the then CEO and President of Nutrien, Chuck Magro, during a recent investors conference call. “We increased our nitrogen sales volumes by 700 000 t in 2020 due to strong North American operating rates and benefits from our de-bottlenecks and optimisation projects and good agricultural demand.”

Ammonia input prices in North America are expected to rise over the coming year, but still remain competitive when compared to other jurisdictions. During 2020, the US Energy Information Administration (EIA) noted that the Henry Hub price averaged US$2/1 million Btu, primarily due to demand destruction related to COVID. Domestic production has decreased by 2%, however, and is expected to average 95.9 billion ft3/d through 2021. As consumption recovers, demand pressures are expected to push the price up over US$3/1 million Btu, but will still be significantly less than that experienced by European and Asian producers.

Gulf Coast Ammonia (GCA) is building what is being touted as the world’s largest single stream anhydrous ammonia plant, in Texas City, Texas, US. Completion of the

1.3 million tpy plant and adjacent deepwater port is expected by mid-2023. Air Products is investing approximately US$500 million to build a steam methane reformer, generators and hydrogen pipelines to service the project.

In late 2020, Koch Fertilizer announced a US$90 million investment at its Beatrice nitrogen plant in Nebraska, US. The money will improve environmental and safety performance, as well as increase urea and ammonium nitrate (UAN) capacity by 75 000 tpy. “We are committed to serving our customers, and we continue to see greater UAN demand locally,” said Scott McGinn, Executive Vice President of Koch Fertilizer. “This investment will improve the efficiency and reliability of our operations and add greater production flexibility at Beatrice to meet the demand of both our ammonia and UAN customers.” The upgrades are expected to be completed by late 2021.

Phosphate Over the last several years, the phosphate market has been depressed due to a combination of low demand and increased competition from producers in the Middle East, Russia and Africa. In order to rebalance the market and meet environmental goals, China has been reducing its phosphate production capacity. Mosaic has also reduced production capacity in Florida. In late 2020, Nutrien wrote down US$760 million in the value of its US phosphate plants at Aurora, North Carolina, and White Springs, Florida.

It cited the market as being “fundamentally oversupplied”, and expects the supply bulge to limit price appreciation for the next several years.

Internationally, other phosphate producers continue to expand. Morocco’s OCP is building three, 1 million tpy granular phosphate units at Jorf Lasfa. Ma’aden is ramping up production at the Wa’ad Al Shamal complex in Saudi Arabia with 3 million tpy of diammonium phosphate (DAP)/monoammonium phosphate (MAP) granulation capacity. PhosAgro has plans to increase production at its Balakovo and Volkov facilities in Russia by 30% by 2025.

11

Phosphate prices have recently skyrocketed, however. At the beginning of 2020, NOLA DAP prices were under US$300/short t. By May 2021, futures were above US$570.

The main reason is due to American trade duties. In 2019, the US imported 3.2 million short t of phosphate, mainly from Morocco and Russia. Domestic producers, including Mosaic – which supplies approximately half of the US market – claimed that OCP and some Russian suppliers were benefitting from government aid in the form of low licensing fees and cheap natural gas. Mosaic petitioned the US Commerce Department to investigate. In November 2020, the federal agency responded with preliminary duties of 16.88% on Moroccan imports and up to 72.5% on Russian imports.

The American Farm Bureau Federation says that the move has pushed up prices too far. “We think this is really unfortunate,” said a Federation official. “We’re concerned about its impact on American farmers, who have told us clearly that they want and rely on diverse supplies and we’re happy to be a part of that. US farmers have seen a significant rise in their costs – in prices of fertilizers – because of a lack of inputs from OCP. The last thing that farmers should have to worry about is a diminished fertilizer supply.”

“We’re not opposed to competing,” responded Mosaic Senior VP, Benn Pratt. “We compete everywhere in the world we do business, but we need to compete on a level playing field in our home market.” In March 2021, the US International Trade Commission ruled in favour of upholding the Department of Commerce’s moves. The countervailing duties are 9% for PhosAgro, 20% for OCP and 47% for EuroChem.

Potash In late January 2021, Belarusian Potash Co. (BPC) surprised the international market when it signed a contract with India’s Indian Potash Ltd. (IPL) to supply 800 000 t of potash fertilizer at US$247/t, up US$17 from the US$230/t contract in 2020.

Nutrien and other potash suppliers expressed disappointment, saying the low price does not reflect international market conditions. “The US has seen the strongest price rise so far, but Brazilian prices are now transacting at US$300/t,” said Magro. “We continue to fill our order book at higher price levels, and we are fully committed on domestic and international sales through April without positioning or selling volume to India or China. Our 2021 sales volume guidance is for 12.5 million to 13 million t and we expect to match strengthening market conditions.” In April 2021, BPC subsequently renegotiated the contract to US$280/t.

Mosaic noted that favourable grower economics have led to strong demand globally, which is expected to continue through 2021. The company expects to realise a US$20 – US$25/t improvement in average realised prices in 1Q21 over 4Q20, and benefit throughout 2021 from improving pricing globally.

Organics Commercial organic fertilizers are primarily derived from plants (alfalfa meal, compost, corn meal, cottonseed meal, soybean meal and kelp), and animal sources (manure, bird guano, blood meal, bone meal and fish products). Their advantages over conventional fertilizers include environmental benefits of production, as well as improved soil structure and secondary nutrients such as calcium and magnesium.

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A strong consumer demand for organic foods is underpinning rapid growth. The worldwide commercial market for organic fertilizers is approaching US$7 billion annually, and is expected to exceed US$15 billion by 2025. In North America, sales exceeded US$1 billion in 2018, and they are expected to surpass US$2.4 billion by 2027. Key players include AgroCare Canada, ScottsMiracle-Gro and Anuvia Plant Nutrients, which recently launched its new organic fertilizer technology. The Florida-based company takes animal manure, food waste and agricultural by-products to create a crop treatment that delivers nutrients in timely fashion while storing carbon in the soil. The company has a 1.2 million tpy facility, and is raising capital to expand; its yield-improving product is already in use on over 1200 farms and it is aiming to treat 20 million acres by 2025.

Challenges When the full impact of COVID began to emerge in 2020, the US Congress passed a US$2 trillion emergency aid package. The bill expanded the spending authority for the US Department of Agriculture’s Commodity Credit Corp. (CCC) by US$9.5 billion (the CCC is the primary federal vehicle for delivering aid to farmers). The legislation also included US$9.5 billion to aid livestock operations. In Canada, Prime Minister Justin Trudeau also announced the government would extend CAN$5 billion in new lending capacity through Farm Credit Canada to maintain farm cash flows.

Fertilizer companies in both North America and abroad were able to work with retailers and farmers to maintain the movement of product from plant to farms and, at the same time, maintain safety for all participants through digital marketplaces, social distancing and other practices. While disruptions to all sectors of the economy are anticipated to continue through 2021, the introduction of vaccine programmes is expected to alleviate many of the lockdowns and other restrictions that have had an impact on demand.

Trade conflicts between China and the US are expected to continue through 2021 under the new administration of President Joe Biden. The Phase One trade deal struck between the US and China in January 2020 included an agreement by the latter to purchase US$200 billion more of US goods and services, including US$32 billion in additional agricultural products over the next two years. Specifically, China would ensure an additional US$12.5 billion in 2020 over the baseline of US$24 billion in 2017 (for a total of US$36.5 billion), and US$19.5 billion in 2021 (for a total of US$43.5 billion). In 2020, China imported US$23.5 billion of covered agricultural products, one-third short of the target.

Environment The manufacture of ammonia produces approximately 500 million tpy of greenhouse gas (GHG) emissions. The majority is converted into nitrogen fertilizers; producers are thus working continuously to reduce both intensity and overall amounts. A long-term solution to GHG emissions involves the production of ‘green ammonia’, which refers to ammonia produced through a carbon-free process, and blue ammonia, which relates to ammonia produced by conventional processes but with carbon dioxide removed through carbon capture and sequestration (CCS) and other certified carbon abatement projects.

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Analysts predict that hydrogen could meet approximately 20% of the world’s energy needs by 2050, up from less than 1% today. Ammonia, which is composed primarily of hydrogen, is a highly efficient transport and storage mechanism for hydrogen as well as a fuel in its own right.

In late 2020, CF Industries announced that it would build a 20 000 tpy green ammonia unit at its Donaldsonville Nitrogen Complex in Louisiana, US. An electrolysis system powered by renewable electricity will strip hydrogen from water to produce the green ammonia. The company is also working with thyssenkrupp, Haldor Topsoe and other high-technology companies to explore CCS and other carbon abatement projects. The eventual goal is to produce up to 3.5 million tpy of low-carbon ammonia, approximately one-third of its current capacity. In addition to making green fertilizer, the company is exploring ammonia fuel uses with utilities and maritime transportation providers. “The world needs clean energy and hydrogen is a key to meeting this need,” said Tony Will, President and CEO of CF Industries. “Low-carbon ammonia is the critical enabler for storage and transport of hydrogen and thus has a major role to play.”

CVR Partners is generating new carbon offset credits through nitrogen dioxide (NO2) abatement at its nitrogen fertilizer plant in Coffeyville, Kansas, US. In partnership with ClimeCo, the company installed a tertiary system to abate 94% of all NO2 in its nitric acid plant, approximately 450 000 tpy of carbon dioxide equivalent (CO2e). When added to its current NO2 abatement at its East Dubuque facilities, CVR expects CO2e reduction of over 1 million tpy. The projects are

registered with Climate Action Reserve, a North American carbon offset registry that uses an independent third-party verification process.

Conclusion Several factors are causing prices for major North American cereal commodities to strengthen. Soybean prices rose from under US$8.50 per bushel in mid-2020 to above US$16 in May 2021; dry conditions in Brazil and Argentina hampered yields, and China went on a buying binge. In early 2021, wheat consistently traded above US$6.50 (reaching US$7.80 in early May) after languishing under US$5 for much of 2020; the rise is due to drought conditions in Russia and Argentina.

Corn prices have risen from under US$3.50 per bushel in May 2020 to over US$7.50 in May 2021 due to a temporary export cap in Argentina, lower expected output in Russia and rising demand in China. “We believe that China will need to rely more heavily on crop imports going forward as they transition their hog industry to professionally manage large-scale operations utilising feed rations as they rebuild their herds following the devastation caused by African swine fever,” said Magro. “We also see the potential for increased demand for crops in the future for use in biofuels to meet climate change objectives set by many countries around the world.”

In conclusion, food producers in North America are looking forward to a good year with strong commodity prices. Fertilizer suppliers are optimistic that farmers seeking to replenish their soils and cash in with higher yields will create strong demand for nitrogen, potash and phosphates throughout the year.

Carolina Vargas and Peter Simons, TOMRA Mining, Germany, explain how methodical testing can show phosphate producers how much silica can be removed from their feed materials to improve yields and lower production costs.

GRABBING GAINS hen producing phosphates for fertilizers, one of the greatest challenges is to reduce the silica content of the mined materials.

Though there are several technical solutions, the most efficient and environmentally friendly is sensor-based sorting. Today’s X-ray transmission (XRT) sorting technology is capable of removing 95% or more of

unwanted high-siliceous particles, such as chert and flintstone, from feed materials.

This benefits the downstream process by reducing the need for water and chemicals and decreasing maintenance costs. In addition, phosphate recovery rates with single-step sorting are more than 92%, and with double-step sorting recovery rates as high as 99% are reachable.

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Feed materials can vary significantly from one deposit to another, and phosphate producers naturally prefer to see first-hand exactly what can be achieved with their own materials before investing in any sorting machinery. For these reasons, TOMRA works with phosphate producers to demonstrate what is possible through a series of methodical tests.

First steps towards proving results

Figure 1. Example of phosphate (left) and high-siliceous particles (right). The sizing is 25 – 75 mm.

Figure 2. Test work steps.

In the first step, the phosphate producer is requested to answer a few questions covering working conditions, challenges and operational objectives. This information is used by TOMRA’s application department to determine the most suitable testing procedure.

Before the first inspection, the application engineers will already have a good idea which sorting technologies are likely to work best. At this stage, the phosphate producer is required to provide reference sample sets. These typically include a reference sample of product, middlings (neither clean mineral product nor reject/tailings) and waste with 10 – 30 rocks each.

These samples are tested with different sorting technologies to establish which is most appropriate for a larger test. Figure 1 shows a ‘product’ and ‘waste’ reference sample for a phosphate application.

If the results of the first inspection are positive, a large-scale test – known as a performance test – is recommended as the next step. This simulates a real process flow and determines sorter performance and throughput. The performance test is conducted at one of TOMRA’s four test and demonstration centres solely focused on mining, each of which provides different testing possibilities. There are test centres in Germany, Australia, South Africa and Russia.

During this test, a large mass of sample – typically about 3000 kg of each material type and size fraction – is fed into a full-scale sorter at defined capacity. This is an opportunity to test different sorting parameters, such as throughputs and sorting algorithms, with realistic and representative quantities of materials.

After the performance test, the sorted samples are chemically assayed by an independent laboratory. When assessing a phosphate application there is usually also hand-sorting analysis at the laboratory, which gives direct key performance indicators such as removal efficiency of high-siliceous particles and phosphate recovery. With the laboratory results, the next steps are mapped out in a flowsheet that takes into account the producer’s working practices and budget (Figure 2).

In some exceptional cases, the phosphate producer might ask for the performance test to be followed up by another, larger-scale test with something like 100 – 120 t of infeed material. This tends to be requested on those occasions when the producer would like the test data affirmed with even larger quantities of feed materials, and/or needs to further test downstream processes such as crushing, grinding and flotation.

Seeing is believing

Figure 3. Sorting and detection principle of TOMRA X-ray technology in phosphate application.

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The XRT technology enables the removal of high-siliceous particles, and consequently the reduction of silica in phosphates, by seeing differences in the atomic density of each single particle on the processing line (Figure 3). Phosphate ore has a higher atomic density than high-siliceous particles because of its significantly higher concentration of calcium oxide (up to 55%,

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atomic number 20) and lower concentration of silicon dioxide (below 1%, atomic number 14). In fact, silicon dioxide is almost the only component of high-siliceous particles.

These differences are revealed to the sorting machine in the images of the material stream that it captures and instantly classifies. Figure 4 shows how phosphate ore and high-siliceous particles look different in X-ray and classified images. XRT scans such as these are used during tests and plant optimisation to fine-tune sorting algorithms. These algorithms are also tested and, if necessary, further refined in accordance with the producer’s feedback.

Using the company’s XRT technology, unsorted material is evenly fed via a screen feeder or vibration feeder over a transition chute onto a conveyor belt. An X-ray tube creates broad-band radiation that penetrates the material and provides spectral absorption information. The transmitted radiation is measured by a highly sensitive X-ray camera with DUOLINE® sensor technology, using two independent sensor lines with different spectral sensitivities. The data supplied by this camera is analysed using a proprietary high-speed X-ray processing unit.

Each single particle is classified as having high or low atomic density, regardless of the material thickness or dust and dirt on the surface.

To see theory put into practice, one of the most important steps in the entire testing and evaluation process is the phosphate producer’s visit to the test centre for the performance test. Here, setting up the sorter to achieve an optimum test result is an interactive process involving both TOMRA and the producer (Figure 5).

Figure 4. X-ray and processed images showing phosphates versus high-siliceous particles.

Figure 5. Sorter optimisation tailored to customers’ needs.

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During the tests, thousands of single particles are scanned individually, evaluated and precisely ejected by air jets within just milliseconds. This is different from traditional dense media sorting (DMS), as it examines each individual particle and detects even very small differences in atomic density. After observing the tests, the producers realise XRT technology is much more high-tech. This provides phosphate producers with significant scope to alter software parameters in order to optimise sorter setup. The technology can also remove more than 95% of high-siliceous particles in the phosphate ore and provides stable sorting performance even at high throughputs.

Live demonstrations during the pandemic For customers who are unable to visit a test centre because of travel restrictions arising from the COVID-19 pandemic, TOMRA organises live online demonstrations of the tests. These are run the same way they would be if the customer were on the premises to witness the test-run in person. Live pictures from the test are streamed from two or three cameras and the machine’s control screen, and viewers are encouraged to direct one of the cameras to look at the aspects of the test they are particularly interested in seeing in more detail. The engineers explain every action and control input they are taking, while the viewers can ask questions. Because the streamed images are recorded, the customer can later share them with other stakeholders in the decision-making process.

Real-world results A good example of how tests translate into real-world results has been seen at the Wa’ad Al Shamal plant in Saudi Arabia, a joint venture where the leading partner is the Ma’aden Wa’ad Al Shamal Phosphate Co. (MWSPC). A representative sample of 120 t was transported from this plant to Germany in order to conduct performance tests in a particle size range between 9 and 150 mm. Afterwards, the sorted fractions were sent to an independent laboratory for chemical assaying and further test work (e.g. flotation tests). The XRT sorting results were impressive, and the investors decided on having nine TOMRA XRT sorters for material between 9 and 100 mm, which are removing high-siliceous particles at a throughput of about 1800 tph.

The economic and environmental benefits being achieved at this plant are significant. On average, silica content is reduced from 20% to less than 2%, which in turn reduces the costs of crushing by about 75%. Milling costs are also reduced by about 45%. This has the additional advantage of serious reduction of maintenance requirements and downtime in the downstream process.

Effective removal of high-siliceous particles also made it possible from the very beginning to reduce the size of the flotation plant at Wa’ad Al Shamal by 40%, saving millions of dollars in construction costs and about US$10 million a year for flotation reagents. Additionally, the consumption of water – in a region where this natural resource is scarce – has been reduced by 45%.

Achieving these valuable improvements at Wa’ad Al Shamal, as well at other plants, would not have been possible without first conducting thorough preliminary tests. What starts with a small grab sample of material can lead to great economic and environmental gains in the processing of phosphates for fertilizers.

COVER STORY

DIVING DEEP THROUGH

REVERSE ENGINEERING Werner Barnard, Hydro, Inc., USA, demonstrates the importance and value of reverse engineering critical pumps as part of a contingency planning strategy.

S

urprise equipment failures are, by their very nature, unexpected. Even with strong predictive or proactive maintenance strategies, sudden system upsets or other external factors can cause an unforeseen catastrophic event. In many cases, these failures leave plants scrambling to return a pump to service quickly to minimise downtime or reduced capacity. The critical path to repair completion is often determined not by labour hours, but by parts lead times.

While unexpected events cannot be anticipated, it is possible to take steps to be prepared for when they occur. Reverse engineering of critical pumps is a key part of this contingency planning strategy. By proactively

reverse engineering critical equipment, parts supply can be expedited without needing to invest in a large physical inventory.

A US fertilizer plant realised the cost savings potential of using reverse engineering by creating a virtual inventory for the high-pressure (HP) carbamate pumps installed in their urea synthesis plant. When a severe system-driven failure occurred, they were able to use the reverse engineered model to have parts manufactured on an expedited basis. This preparation, in addition to partnering with a responsive repair facility that had experience in complex multistage pumps, shortened the turnaround time for the refurbishment.

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Anticipating future needs: the road to reverse engineering

Figure 1. High-pressure carbamate pump.

Figure 2. Severe damage to stage casting.

Figure 3. Fully dimensional solid 3D model.

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As a result of recurring system problems, the urea plant’s HP carbamate pump was experiencing shortened life and, at times, online failure events. The design of the pump is a multistage, opposed impeller segmental ring, or BB4, pump.

While the original equipment manufacturer (OEM) for the installed pump has a service network in North America for their submersible pump installed base, they did not have the capability to service complex, high-energy multistage pumps.

Without local OEM support for the HP carbamate pump design, engineering information was difficult to obtain and communication was cumbersome and drawn-out. Because the OEM did not have an experienced facility to repair the pump in the US, the site had to find another supplier familiar with this complex design to provide engineering and repair support. Most problematic for the plant was the fact that many critical parts were sourced outside of the US and lead times could be several months.

Having experienced several failures with protracted repair and parts lead times, plant engineering decided to pursue reverse engineering the complete pump assembly.

Fortunately, they had a spare unit that would allow the reverse engineering process to be completed independently of a pump being taken out of service.

The plant’s engineering team approached Hydro’s Houston facility to reverse engineer their spare pump. Based on prior experience working with the company on other high-energy applications, plant engineering had confidence in their overall engineering experience and history with this design. Hydro was also able to show the plant an extensive written process for their reverse engineering department; this process is shared across all service locations and ensures conformity to rigorous standards.

Several years after completing the reverse engineering of the HP carbamate pump, the plant experienced another failure. They sent the pump to Hydro for inspection and refurbishment because the company had created and verified an accurate digital model. In this instance the pump had failed catastrophically, with several components seized and difficult to disassemble. The rotor was in poor condition with extensive heat damage and wear. The stage pieces had also experienced damage as wear components fractured, became dislocated and travelled through the pump. It was clear that the disassembly alone would be a time-consuming process.

As the pump was disassembled and inspected, the service centre identified which parts would be unsalvageable. Under normal circumstances it would have taken time to scan these components, confirm the dimensions and provide an engineering review; however, these steps had already been completed up front.

With the verification steps already completed,

the reverse engineered model could be used to immediately begin the manufacturing process for replacement parts on an expedited schedule. Because of the forward-thinking actions of the plant, the reverse engineered model allowed parts supply to be completed in weeks instead of months.

The anatomy of a robust reverse engineering process While many companies are dipping Figure 4. Casting drawing. their toes into the reverse engineering market, not all reverse engineering efforts are created equal. Any company with a can lead to incorrect final geometry or failure of the part coordinate measuring machine (CMM) can perform a simple when placed in service. laser scan of a component, but that is only the initial part of Additionally, the 3D laser scan cannot determine the the process. A newly fabricated pump component is only as tolerances for the wear ring fit, impeller bore, keyways and, in successful as the expert engineering behind it. some cases, the underfile geometry under the outer diameter Advancing technologies can help significantly in the (OD) of the impeller. In situations where the parts being process of reverse engineering critical parts and components, reverse engineered are worn or had been previously repaired, but relying on these technologies alone is not enough to experience is necessary to judge how use, wear, welding and ensure proper design and manufacture. Geometry, metallurgy, machining have changed the dimensions of the as-found part hardness, tolerances and coatings must all be taken into from the originally supplied component. Creating a robust account and add to the complexity of the reverse engineering process that includes an engineering review and equivalency process. Simple replication without reviewing the hydraulic, analysis is essential for ensuring that the final part functions mechanical and material characteristics of the component as intended.

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An eight step process to quality cast parts in less time The first step in the reverse engineering process is data collection. This is usually achieved using CMM technology coupled with advanced software. The CMM has non-contact (laser) probes that can provide a high rate of data capture, allowing accurate scanning of the component in a short amount of time.

Next, the laser scan is transformed into a fully dimensioned solid 3D model. For complex components, manual measurements may be used to augment the laser

Figure 5. Solidification analysis.

Figure 6. 3D sand printing of mould package.

Figure 7. Casting validation.

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scanning and confirm that critical dimensions have been captured correctly.

The next step in reverse engineering the component is the engineering review and analysis. This is where the ‘engineering’ portion of reverse engineering comes into play. The dimensions captured are evaluated to determine original dimensions for worn parts. The engineering team will also look at the component design to determine if there are any failure modes that are affecting performance and life. Computer-aided design (CAD) and finite element analysis (FEA) software are used to determine if upgrades can be made to reduce wear and improve reliability. For hydraulic components, an analysis can be provided to improve the hydraulic characteristics.

Once the critical design parameters are verified, the 3D model is finalised. When performing reverse engineering proactively, this final model provides the assurance that parts can be manufactured quickly and accurately. An added benefit to having a verified virtual model of the pump is that strategic component upgrades or hydraulic changes can be designed without needing to take a pump out of service. These changes can be reviewed by the plant’s engineering team and budgeted for a scheduled outage. Prior to the upgrade, updated drawings can be created and new parts numbers assigned to facilitate the transition to the new design. The necessary parts for these upgrades can easily be manufactured ahead of time so that they are available for the next planned refurbishment.

With a verified 3D model completed, the manufacturing phase can be entered at any time. When the need for a cast part arises, a casting model is created. The casting model and drawing provides allowance for machining stock. It also allows an evaluation of the casting, rigging and layout.

The casting model is subjected to a solidification analysis, which enables an optimal mould package to be designed. Once the geometry is defined, performing material solidification simulation of the casting is critical. The solidification software is designed around computational fluid dynamics, which allows engineers to simulate the velocities and temperature gradients of the metal throughout the pour cycle. This is critical for pump parts, because most vane passage and volute areas have variable section thicknesses that can result in variable shrinkage.

With the casting model complete, the mould package can be created via computer-aided machining or 3D sand printing. This method is faster to produce than the traditional wooden pattern and provides greater control over the finished product. 3D printing of the sand mould significantly improves the vane spacing of hydraulic components over manual pattern creation. With the casting ready to

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be poured, the component is produced at a ‘metal specific’ and ‘size specific’ foundry to allow rapid production.

Before the machining process can begin, the cast part must pass a casting validation. The component is laser-scanned using the CMM and this model is overlaid on the first model developed from the original component. A heat map is created to analyse the degree of coincidence between the two parts.

Rigorous acceptance criteria are applied and discrepancies are analysed by the engineering team and addressed. The casting validation step ensures that the cooled component conforms to the expected dimensions.

Best practices include scanning of the hydraulic sections of the casting as well as comparison to the design for dimensional deviation. After validation, final machining, drilling, surface finishing and dressing can be completed.

Going one step further Because of Hydro’s history in the nuclear power industry, their reverse engineering design control procedure requires a technical equivalency evaluation for every reverse engineered part. During this evaluation, the failure modes and critical characteristics are evaluated as a part of the equivalency evaluation, ensuring that the critical characteristics are addressed during the reverse engineering and design process.

This analysis of the finished component ensures that the form, fit and function of the finished component is identical to the original component.

Achieving reliability in supply and operation

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In the case of the HP carbamate pump, the plant had carried out their due diligence to ensure reliable parts supply in the case of an emergency. Because of the extent of the damage incurred by the pump, the expected time frame to repair this pump would normally have been significant. The foresight of plant engineering significantly cut that repair time, providing them with a fully operational spare and greatly reducing the risk of downtime in what was clearly a problematic system.

Having performed an engineering review of the pump design during the reverse engineering process, Hydro was able to analyse the design for weaknesses and improve component tolerances. Because they understand the intricacies of high-energy pumps, the engineers took the steps necessary to ensure centreline compatibility of all critical components, reduce vibration and increase stiffness and damping. Through dimensional analysis and improved assembly processes, they reduced susceptibility to hydraulic instability and, in doing so, also reduced the probability of axial thrust fluctuations.

With ageing systems, the global nature of supply and decreasing availability of knowledge and experience, risk assessment is more important than ever for safe and reliable plant operation. In this case, the plant managed an unstable system by ensuring reliable parts supply. By choosing a reverse engineering and repair partner that could help them analyse pump weaknesses and suggest improvements, they were also able to achieve a more rugged design without sacrificing lead time. A well-rounded solution was achieved by combining a forward-thinking strategy and new technologies with a foundation of engineering knowledge and history.

VENTURING OUTSIDE THE

COMFORT ZONE Patrik Kolmodin, Sulzer, Sweden, explains how agitators for use in the chemical industry can be optimised during the design process by going beyond specifications.

S

ulfuric acid is the key chemical used in the production process of wet phosphoric acid (WPA). Consequently, the production of sulfuric acid close to the phosphoric acid plant (PAP) has many advantages. Not only does this arrangement reduce transport costs, but the nearby production of sulfuric acid – which is an exothermal process – allows the residual thermal energy to be used for the manufacture of concentrated phosphoric acid. Steam is generated to feed the heat exchanger located within the concentration unit of the phosphoric plant.

In this article Sulzer will illustrate how to save money and optimise agitators. The article also describes a case concerning the melting of elementary sulfur intended for use in phosphoric acid production.

25

Agitators in the chemical industry In capital-intensive industries with a high focus on productivity and uptime it is easy to stick to old truths.

But that does not mean that something that has worked

for many years is the best design for now, or for the future. A common approach to agitators within the chemical industry is the ‘It is working now so do not touch it’ principle. This is caused by the fear of malfunctioning processes, and is often a result of poor knowledge and the belief that the current process equipment always comes with the lowest risk. However, there are great opportunities to save both operational and capital costs and even increase the reliability without jeopardising the process performance.

Agitators need to be flexible in their design to suit various tank sizes and shapes. It is also important to adapt the agitation intensity to the process needs. Unlike pumps, it is not possible to select an agitator towards a flow and head, but instead the agitation must be quantified in other ways to manage the process. This often leads to misunderstandings, oversizing and costly investments. When designing an agitator, the most common mistakes are: Not getting the right agitation intensity.

Replicating existing agitator design.

Poor input data.

Poor evaluation of the energy costs.

Mechanical design – heavy-duty or light-duty design?

Quantifying agitation – a cup of tea?

Most people have some intuitive idea of mixing and blending processes. For example, the infusion from tea leaves will remain near the bottom of a cup of hot water until it is stirred. Just a small amount of stirring will blend the mixture and achieve a suitable mix; continued stirring will not improve the blend.

There are many processes in the chemical industries that require agitators. Contrary to the way in which tea is blended, many agitators mix too much and at too high intensity, without getting a better result.

Sulzer uses methods such as degree of agitation, Figure 1. A cup of tea (unmixed). which is based on the liquid velocity at the surface in the tank. This is a powerful design method for many types of processes, different rheologies and different tank shapes. It also takes more efficient hydraulics into account. Another dimensioning tool is power per volume, using W/m3. This is a poor dimensioning principle, however, that is neither good for scaling nor takes more efficient hydraulics into account.

Another method is to use the impeller pumping capacity.

Figure 2. A higher degree of agitation will require much more power.

26 | WORLD FERTILIZER | MAY/JUNE 2021

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This method can be difficult as well, because suppliers have different measuring methods and (not least) it greatly depends on the impeller diameter and rotational speed. A large slow-running impeller will generate a higher pumping capacity at the impeller than a smaller impeller running at a higher speed, while the overall agitation level may still be the same. In addition, impeller pumping capacity does not consider the pumping direction.

When targeting a certain agitation level, it is important to understand that a small increase in the agitation level may result in a much higher power consumption, because the power need increases exponentially with the degree of agitation. An increase of the degree of agitation from 8 up to 10 may double the power, but the agitation intensity only increases by 25%.

Too strong agitation – does it really matter?

Mixing a cup of tea intensively for 10 minutes will not do much harm; it will still be a properly blended cup of tea, albeit a bit colder. In an industrial process, the implications of over-mixing are worse. First of all, the power consumption will be higher than needed and will unnecessarily increase the overall energy bill. A higher motor power will also result in a heavier agitator design.

This will increase the investment cost, not only from the agitator itself, but a higher weight will also require a more robust tank support. Furthermore, the greater the agitation intensity there is in the tank the more vibrations there might be, as well as more load on the blades, shaft, bearings, drive unit and motor. For suspensions in particular there will be more wear, causing shorter equipment lifetime. All in all, these issues may result in a short lifetime or even in costly, unplanned shutdowns.

To dare In a demanding industry where uptime and reliability are key factors the easy choice is to continue with existing and proven technology. This is not the best way to utilise technology development such as efficient hydraulics, new design tools and higher reliability. In the fertilizer industry, Sulzer frequently receives agitator enquiries specifying identical copies of old existing designs with too high power, poor hydraulics and oversized equipment. If an efficient design with a lower power consumption and therefore a lower installed weight is offered instead, not only can the operating cost be reduced but a longer lifetime and greater reliability can also be achieved.

It may indeed be scary to venture outside the comfort zone, but daring to do so will result in longer-term benefits from lower energy costs and greater reliability.

Three rules Figure 3. Power savings can be achieved with a Scaba hydrofoil high-efficiency impeller (top) versus a pitch blade turbine (bottom).

Figure 4. Computational fluid dynamics studies of agitator performance.

28 | WORLD FERTILIZER | MAY/JUNE 2021

A challenge in designing agitators is determining how much agitation is needed for the process; what is ‘good enough’ for one person may be different for another. There are essentially three things that must be known to make a good agitator design: The tank shape. This also includes the agitator mounting height.

The process. What is the application or how much intensity is needed?

The media. For example, for mineral suspensions it is important to specify parameters of the solids, such as the particle density and the size distribution, the liquid properties and a process description.

These three simple rules will allow good selections, even though they may not necessarily accord to the original expectations.

Adapt to the actual conditions Agitators are used for multiple industrial processes, including blending liquids, keeping solids in suspension, heat transfer, leaching, dispersion, emulsifying and dissolving. Agitators are, therefore, used for purposes other than just mixing. How to design the agitation for a certain application may be clear but may also require process descriptions. In the fertilizer industry it is important to adapt not only the agitation intensity, but also to adapt the mechanical design of the agitator to the process. Parameters such as reliability and criticality of the process must be considered, as well as the local site conditions.

For lighter applications, agitators can be of a leaner design. This can, for example, mean a drive unit with a gearbox only, lighter shafts and propellers and the use of a bottom bearing, which may require regular service. A heavy-duty design can include a separate agitator bearing, a high gearbox service factor, a stronger mechanical construction and free-hanging shafts where the agitator runs safely outside the critical speed interval. Heavy-duty designs are needed in critical applications, tanks with violent agitation, rock slurries, erosive and/or aggressive media and when running the lowest impeller through the liquid level. Lighter applications can be applied to the storage of clean liquids, slurries with small particles at a low solids content and light-weight chemicals.

A more expensive agitator with a heavy-duty design can help avoid costly shutdowns and reduce the maintenance cost. It must be remembered that a lighter design is sufficient for many applications however; it is still capable of achieving long lifetime but with a lower construction weight.

Agitators are machines that usually operate at a low rotational speed. A correctly designed agitator will have a longer lifetime and need fewer spare parts than, for example, a pump. Therefore, the application and criticality must be considered when selecting the agitator.

Additional mechanical margins are sometimes needed, sometimes not.

High margins will lead to a higher investment cost.

Case study The manufacture of sulfuric acid from solid sulfur starts with producing molten sulfur. The granules are melted in specifically designed equipment. The molten sulfur is then filtrated and conveyed to the sulfur burner. It is highly important to work with reliable equipment from the very beginning of the process. Any issue at the very first step of the process may have dramatic consequences on the whole fertilizer complex. Furthermore, how could sulfur be properly melted without well-performing agitating equipment?

A client had an expansion project that included two sulfur melters. The heat transfer through heating coils was extremely important to managing the process. In addition, cold winters and hot summers caused

During the engineering phase, two cases were evaluated: 132 kW and 200 kW. The velocities inside the tank and locally at the heating coils were examined in a computational fluid dynamics (CFD) study. The average flow velocity in the tank would increase by 11% with 200 kW, while the local velocity at the heating coils would be only 4% higher versus the 132 kW. This illustrates how much more motor capacity is needed to achieve a higher velocity.

Two agitators of type Scaba 240FVPT-Sff with hydrofoil SHP impellers were supplied to the customer. The agitators are equipped with variable frequency drives for a lower operating cost and are running at the rate of 132 kW or lower, while the actual installed motor is 200 kW, only as capacity reserve for extremely cold days. The power saving resulted in annual energy savings of approximately €20 000.

These agitators are of a heavy-duty design due to the critical application and the demanding site conditions. The ambient temperature spans from -47 to +40˚C, which required special precautions for the drive unit and the motor. The agitator is equipped with an industrial gearbox with both heaters and coolers. The wetted parts are made of standard stainless steel, 316L or duplex stainless steel for critical parts where a higher strength is required. The gas phase inside the tank can be aggressive, and the parts exposed to gas are made in 904L with additional rubber lining on top for extra security.

Figure 5. A heavy-duty Scaba 240FVPT-Sff.

Conclusion challenging ambient conditions. It was specified that the agitator should have a 200 kW motor to drive pitch blade turbines.

Rather than just following the specification, Sulzer wanted to fully understand the process and the conditions in order to propose the best technical solution. The Scaba SHP hydrofoil propeller was calculated to provide more agitation than a pitch blade turbine and thereby generate higher velocities and better heat transfer. The company concluded that a 132 kW motor was enough, due to the highly efficient hydrofoil impellers.

This project summarises some important points when designing an agitator for the chemical industry: The agitator should be designed with the correct agitation level: not too much, nor too little.

It should not only be engineered to fulfil the expectations of a customer’s enquiry, but to be better.

Substantial energy savings should be taken into account during the evaluation.

The agitator is a critical application and the conditions in which it operates are severe; it must therefore have a heavy-duty design.

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SULFUR STORAGE TANK CHALLENGES: PART ONE In the first part of a two part article, Brandon Forbes and D.J. Cipriano, AMETEK/Controls Southeast Inc., USA, highlight the challenges that arise from the storage of sulfur and show how a well-designed and installed thermal management system can counter these problems.

T

here are several unique challenges associated with storing sulfur in field-erected tanks. The most significant challenges are those related to safety and those related to maintenance. Over the last decade, sulfur tank safety concerns have become more widely considered, with more publications describing the concerns. The primary safety concerns are as follows:

Accumulation of hydrogen sulfide in the tank vapour space – explosion and exposure Sulfur produced via the modified Claus process will contain high levels (up to 500 ppmw) of dissolved and chemically integrated hydrogen sulfide (H2S). Unless the sulfur goes through an additional degassing process, it will slowly release the H2S into the vapour space as a gas. The lower explosion limit (LEL) of H2S gas mixed with air is roughly 4 vol% (though it changes with temperature and other factors). Additionally, H2S in air is lethal at concentrations as low at 500 ppm. It is therefore critical that the accumulation of H2S gas in the tank vapour space be addressed.

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Providing the tank with an inert vapour space (e.g. a nitrogen blanket) is one method of addressing the LEL concern. However, this method still allows a significant build-up of H2S gas to accumulate. This build-up could present an explosion hazard if oxygen (air) were to be inadvertently introduced; it could also present a health hazard if the vapour were to be inadvertently released. For these reasons, and other reasons described later, a continuous sweep of ambient air is the preferred method of handling the tank vapour space.

Figure 1. Iron sulfide ignition mechanism.

The required rate of sweep air is calculated based on the sulfur turnover rate in the tank, the maximum resulting H2S release rate and the vapour turnover rate required to stay below the 4 vol% LEL. Excessively high sweep rates should generally be avoided as they place a significant heat load on the tank, which can lead to sulfur freezing and blocking nozzles/vents as well as corrosion – both of which can result in additional safety hazards.

This sweep air arrangement can be implemented in one of two forms: a ‘forced sweep’ uses an ejector or blower to move air through the tank and deliver it to a safe location for release or processing. A ‘free convection sweep’ uses strategically located vents to induce a draft that pulls air through the tank and releases it from a vent in the roof. Free convection sweep is typically preferred where the sulfur is expected to have minimal H2S content. Forced sweep is typically used where the sulfur is expected to have high H2S content and the exhaust vapour must be treated for health, safety and environmental (HSE) reasons.

A final point regarding H2S accumulation is the need to avoid ignition sources. Sulfur has a relatively low electrical conductivity and can therefore build up a static charge – especially if it is allowed to freefall. The use of a dip-tube is recommended where sulfur is supplied from a roof nozzle. A second common ignition source is various forms of pyrophoric iron sulfides.

Accumulation of pyrophoric material – fire and explosion

Figure 2. Example of sulfur tank shell corrosion.

Figure 3. Example of sulfur tank structure corrosion.

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When combined, sulfur, steel and water react together to form various iron sulfides. These sulfides are pyrophoric – when exposed to oxygen, a rapid exothermic oxidisation reaction occurs. With a sufficient mass of accumulated sulfides, the temperature resulting from the oxidation reaction can be high enough to ignite H2S in the vapour space or ignite the sulfur itself. To avoid this scenario, either the accumulation of sulfides or the oxidation of sulfides must be prevented.

One method of preventing the formation of iron sulfides is to maintain all carbon steel surfaces above 100˚C (212˚F) to prevent the accumulation of liquid water. The presence of sulfur can frustrate efforts to this end, as solid sulfur that builds up on the interior surface insulates the wall and drives down the temperature. Water vapour can penetrate the porous sulfur, condense at the wall and form iron sulfide.

Worse still, iron sulfide formed in this manner can accumulate in large masses that are only exposed to oxygen when chunks of sulfur fall away from the wall. These large masses of sulfides reach very high temperatures when they suddenly oxidise together.

A better approach is to maintain all carbon steel surfaces above 120˚C (247˚F) to prevent sulfur from freezing. This prevents the formation of iron sulfides. Even if some small cold spots exist, without large sections of solid sulfur accumulation it is unlikely that large masses of iron sulfide will form. Small masses of iron sulfide not buried under frozen sulfur are typically not a problem. They tend to oxidise as they form and never reach the critical mass needed to achieve dangerously high temperatures.

One might attempt to stop the iron sulfide formation by removing water from the system. Unfortunately, this

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approach is not likely to succeed, as there are numerous potential water sources, including: Leaking internal steam coils.

Inadequate vent caps.

A damaged tank roof or nozzles.

Humidity in ambient air.

Oxidation of H2S where: H2S + O2 → H2O + SO2 Rust-catalysed breakdown of H2S where: H2S + O2 → S8 + H2O + SO2 (note this is highly simplified as there are several reaction steps with several intermediate iron oxide [FeOX] and iron sulfide [FeSX] molecules).

Use of snuffing steam.

Use of an inert vapour space (e.g. a nitrogen blanket) will prevent the ignition of iron sulfides. However, this is generally considered to carry significant risk, as without oxygen any sulfides that do form will accumulate over time. When the nitrogen blanket is removed (intentionally or unintentionally) and oxygen enters the tank vapour space, there may be a very large mass of accumulated sulfides available; these will likely burn at a very high temperature, increasing the risk of a tank fire. Using an ambient air sweep will tend to oxidise the sulfides as they form, via the mechanism described above, and is generally considered the safer approach.

Safety summary While each sulfur tank application should receive a specific review, the following high-level recommendations should be considered for any sulfur tank application: Sweeping the vapour space with ambient air is generally preferred over an inert blanket.

The sweep rate must be high enough to prevent the concentration of H2S from reaching the LEL. The sweep vapour must be handled in a way that does not present an HSE concern.

The tank should be heated in such a way that the formation of iron sulfides is prevented or severely limited.

The sweep air system (including tank nozzles) should be heated in such a way that prevents plugging.

Tank corrosion Figure 4. Example of tank roof heating.

Figure 5. Example of tank shell heating.

34 | WORLD FERTILIZER | MAY/JUNE 2021

The primary challenges to sulfur tank maintenance are corrosion and plugging. Problems with plugging are immediately evident and can be addressed with adequate heating. Problems with corrosion can progress undetected, however, and result in extensive damage as well as potentially hazardous material release events. There are several different corrosion mechanisms that can contribute: Internal corrosion can occur due to the iron sulfide reaction described above. This generally occurs in the vapour space and can occur rapidly.

Internal corrosion can also occur in the more conventional manner due to the presence of water.

Common sources of water are as discussed earlier.

External corrosion can occur due to ambient water exposure. This mechanism is not unique to sulfur storage.

Water that penetrates the insulation may sit against the external tank surface for an extended period, as evaporation from under the insulation will be slow.

Field-erected storage tanks are also subject to water intrusion into the space between the tank bottom and the concrete pad (or ring-wall). Again, evaporation from this area will be slow and significant corrosion can result.

External corrosion can occur due to spilled sulfur. There are several mechanisms by which spilled sulfur can accelerate the corrosion of steel surfaces. Mixing sulfur and water can generate small amounts of sulfuric acid that eat through the steel. Together, sulfur, water and steel can react to decompose the steel and form iron sulfides, as described earlier. Finally, thiobacilli bacteria can also produce sulfuric acid as they digest the sulfur. Sulfur tends to accumulate around the tank vents and on the ground at the base of the tank; these are the areas that tend to be most susceptible to this form of corrosion.

Sulfur tank heating Controls Southeast Inc. (CSI) has developed a tank heating technology utilising ControTrace engineered bolt-on jacketing. The system uses a distributed heating arrangement that provides uniform heating to the entirety of the tank shell and roof surfaces. Nozzle and instrument heating can also be provided. The goal of the design is to resolve multiple safety and reliability concerns by addressing the various root causes: Prevent H2S accumulation in the vapour space by heating of the vent nozzles. This prevents sulfur solidification in the nozzles that could restrict or block the vapour flow.

Prevent iron sulfide formation by maintaining the shell and roof above 120˚C (247˚F) at all locations. This prevents sulfur solidification and water condensation, which in turn prevents iron sulfide formation.

Prevent plugging of nozzles by providing direct heating.

Prevent corrosion by maintaining the tank wall and roof temperature. Preventing water and sulfur condensation on the tank surfaces effectively blocks the corrosion mechanisms described previously.

Additionally, the ControTrace external heating system provides heat directly to the liquid sulfur in the tank. This removes the need for internal coils, subsequently eliminating costly coil maintenance and potential water intrusion into the tank.

The heating system is comprised of multiple heating panels, each made up of multiple individual heating elements. The heating elements are spaced at a specified distance that maintains the tank wall temperature above the target temperature (typically 125˚C) at all locations.

Additionally, the panels themselves are shaped to fit closely together and to wrap closely around nozzles and other tank protrusions. In this way, all locations on the tank shell and roof are maintained above the target temperature.

Maintaining the liquid sulfur temperature typically requires additional heat input to offset the heat loss into the ground. The heating panels located near the bottom of the tank typically use more dense heating elements to provide this additional heat. This is especially critical when the liquid level is low and the liquid contact area with the heated tank wall is reduced.

CSI determines the heating system design and predicts the tank temperatures by utilising a proprietary finite-difference model. The model accounts for all relevant heat paths to determine both the liquid and the vapour temperature in the tank. In addition, the model calculates the tank shell and roof temperature profile based on a given ControTrace element spacing.

In this way, not only is the sulfur temperature maintained, but a uniform shell and roof surface temperature is as well.

The company’s thermal model was developed using computational fluid dynamics (CFD) modelling to verify uniform sulfur temperature distribution within the vessel. The model has been validated with detailed field temperature measurements including infrared imaging.

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With each panel custom-fabricated for the application, the ControTrace heating system has several advantages: The element spacing and panel locations are fixed, meaning the wall temperature is assured at all locations.

Each panel is an independent unit attached to a predetermined location on the tank, thus removing any guesswork and minimising the labour required to install the system.

Panels are arranged in columns with a single steam circuit per column, thus minimising the number of circuits and required steam infrastructure.

Conclusion Figure 6. Tank model macro-level heat transfer accounting.

As discussed, the storage of sulfur creates a number of challenges for any facility. The accumulation of H2S and pyrophoric material (e.g. iron sulfides) can lead to serious consequences if not properly mitigated through tank design and temperature control. A few best practices for these were discussed.

Part two of this article will show how a team at a working facility in the Gulf Coast, US, successfully met these very challenges. Previous sulfur tanks in the facility experienced significant corrosion. A tank commissioned in 2006 incorporated the best practices discussed above. A recent detailed inspection revealed the strengths and weaknesses of the new design approach. Their findings and lessons learned will be presented.

Bibliography 1.

Figure 7. Thermal image of ControTrace-heated sulfur tank interior.

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2.

CLARK, P.D., HORNBAKER, D.R., and WILLINGHAM, T.C., ‘Preventing Corrosion in Sulfur Storage Tanks’. Paper presented at Brimstone Sulfur Symposium 2008, Vail, Colorado, US, and British Sulphur 2008, Montreal, Canada.

AFPM, ‘Process Safety Bulletin – Flammability Hazards of Hydrogen Sulfide Accumulation in Sulfur Tanks’, June 2018.

Barbara Cucchiella and Wilfried Dirkx, Stamicarbon, the Netherlands, discuss trends in finishing technologies, including larger capacities, lower costs and higher efficiencies.

FOLLOWING THE TRENDS A

s urea melt plants grow in capacity, so does the need for finishing technologies with higher capacities. Although new technology developments have taken place more in granulation than in prilling, the latter is certainly still relevant but will not be discussed in this article.

Stamicarbon, the innovation and licensing company of the Maire Tecnimont Group, has practical experience with both finishing technologies, which serve different markets.

The decision to go for granulated product instead of prilled product is mainly driven by the interest in export production.

Granules offer a higher strength and better handling and shipping capabilities compared to prilled product, so the construction of urea granulation plants can be found

in countries with low feedstock cost areas and options to export the granulated urea product.

Initial granulation design After the initial development activities in granulation technology conducted in the 1970s, the first test facility was contracted in 1998 in Belarus, where a small granulation unit of 280 tpd was completely converted to the Stamicarbon LAUNCHTM FINISH Granulation Design.

Further scaling up took place in Canada, where two existing granulation lines of 625 tpd were converted to the company’s design. The first grassroot plant with a capacity of 2000 tpd was started up in June 2006 in Egypt.

From then on, almost 20 plants with different capacities have been licensed, designed and put into operation.

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Compared to other fluidised bed granulation processes, the Stamicarbon design shows considerable OPEX savings due to a reduced formaldehyde content in the final product and a low dust formation, which results in a granulation plant that can be operated for 2 – 3 months without any interruption for cleaning.

Larger capacity experience The company’s largest granulation plant with its standard design is the Pardis III plant in Assaluyeh, Iran, contracted in 2011 and started up in August 2018. The name plate capacity is 3250 tpd with a capability to operate at 110% capacity and a turndown ratio of 60% of the name plant capacity. Despite the large scale, an on-stream time of more than two months was achieved during the summer period. The plant meets the expectations of the client and operates in difficult ambient conditions.

Improved granulation design

Figure 1. Process flow diagram of the company’s Optimized Granulation Design.

In 2008, Stamicarbon introduced its Optimized Granulation Design (Figure 1). The design is characterised by a minimal number of equipment items and a reduction of CAPEX and OPEX costs, while keeping its original performance and high on-stream times.

The cost saving in power consumption is approximately 20% and is mainly due to the omission of three major fluidisation fans. The fluid bed granulator cooler was omitted by increasing the length of the cooling zone in the original granulator, and the fluid bed product cooler was replaced by a solids flow cooler. In addition, the respective granulator cooler scrubber with all necessary pumps and fan were omitted as well. The produced granules are cooled down further in the fourth compartment of the granulator, so only a small crusher feed cooler (fluidised bed cooler) for cooling down the coarse product is foreseen as a separate fluid bed cooler.

Process description

Figure 2. Acron’s granulation plant in Russia.

Figure 3. Stamicarbon’s urea granulation design timeline.

38 | WORLD FERTILIZER | MAY/JUNE 2021

The urea melt is still fed to the granulator as per the standard Stamicarbon design.

However, it differs from the previous design in the last compartment, where the granulated product is cooled down to a lower temperature. After passing the lump screen, the product is directly lifted with a bucket elevator to the classification equipment. The complete solid product flows via gravity flow through the main screens. The coarse product is fed to the crusher after cooling to a temperature of 70˚C. The crushed product and the fine recycle flow are combined and recycled into the first compartment of the granulator as so-called seeds. The on-specification end-product in the outlet of the main screens is cooled to storage temperature in a solid flow cooler that makes use of cooling water instead of cooling air. The dust-loaded air

Relax, from the granulator, coarse cooler and all the de-dusting points is collected and fed to a single granulator scrubber.

Furthermore, to reduce the amount of fluidisation cooling air, a water injection system is provided in the discharge of the fluidisation air fan. This feature is only operated on exceptionally hot days, in order to increase the relative humidity and to reduce the total air consumption as well.

The reduction of equipment items resulted in a significant reduction of the granulation plant footprint and the overall capital cost of the plant. The total CAPEX cost reduction is not only achieved by eliminating equipment, but there are also savings in transportation (shipping) costs, cost of insurance, effect of reduced footprint and construction. Less operational equipment will also result in a reduction in maintenance costs and OPEX savings.

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Operational experience The first granulation plant with this new design was a 1760 tpd plant for Shahjalal in Bangladesh, commissioned in 2015. It started up smoothly and the plant still operates reliably, with minimal operator attention required. The power consumption meets expectations and is 20% lower than in the conventional design, while the maintenance costs have been reduced significantly.

The product exceeds the standard commercial quality, even at formaldehyde levels lower than 0.3% in very humid ambient conditions.

Additional practical experience with this optimised granulation design has been gained with five other plants in operation, varying in capacity from 1000 – 2676 tpd, while there are six other plants under construction. The latest granulation plant that went into operation, in 2020, is a plant operated by Acron in Russia, with a capacity of 2000 tpd (Figure 2).

We understand your processes.

Scaling up capacity Over the last decade, the company has seen a rapid increase in the design capacity for granulation plants (Figure 3). All operational granulation plants – although with different product requirements, different ambient conditions, different emissions and with different configurations – have met the set performance guarantees.

Recent practical experiences with Stamicarbon granulation plants with capacities above 3000 tpd are positive, meeting the overall and on-stream factor expectations of clients. The next milestone will be the new plant of EuroChem Northwest in Kingisepp, Russia, with a single line capacity of 4000 tpd, which the company is currently designing and is expected to become operational in 2023. This granulation plant will also be equipped with the MicroMistTM Venturi scrubber, meeting the lowest applicable emission standards.

Conclusion The company’s investigations into the possibility of further scaling up the granulation design over 5000 tpd concluded that there are no actual impediments, provided that a few additional measures are implemented to anticipate the risks of scaling up. Furthermore, a single line of 5000 tpd is estimated to have 30% less CAPEX (on total investment costs) than two lines with a rate of 2500 tpd each.

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Gelmer Bouwman and Geoffrey Havermans, Kreber, the Netherlands, investigate how computer-aided design has become a key tool in the design and optimisation of prilling facilities.

40

EARNING ITS STRIPES I

n 1918, the physicist and Nobel Laureate Hendrik Antoon Lorentz started the calculations needed to build the Enclosure Dam in the north of the Netherlands. Eight years later, in 1926, his full recommendations containing complex mathematical calculations regarding tides, river flow, wind power and storm predictions – all made without calculators – were published (Figure 1).1

We have come a long way since then.

Nowadays, the computational power of computers is readily available even to the non-physicist, enabling highly complex situations to be analysed in a fraction of the time. Computer-aided engineering (CAE) is also playing an indispensable role in the design of prilling towers. This article will highlight the four application areas where CAE is taking a leading role.

41

Industrial research from the desk Firstly, computational modelling provides comprehensive sets of data that are not easily obtained from experimental tests. Experimental testing can be demanding owing to the development of a test set-up and the purchase of instrumentation. In some cases it

Figure 1. Layout of the northern part of the Netherlands, where the water is divided into sections for the purpose of calculating flow from one section to the other.1

might be difficult or even impossible to find suitable instrumentation to collect the desired data. In Kreber’s experience, computational modelling reduces the demand for complex experiments. Two research problems, for which the company uses CAE, will be discussed more elaborately.

The first example of such a problem, where computational modelling provides a solution, can be seen in company research into rotary prillers, which are at the heart of the prilling process. Hot melt is fed into the rotary prillers, which consist of perforated buckets.

By rotating the bucket, the liquid melt forms a vortex and, due to centrifugal forces, the liquid melt leaves the bucket and forms molten droplets. This process of vortex formation, jet break-up and consequent droplet formation is difficult to analyse within an operational tower, as it is difficult to record data on the prilling bucket. The prilling bucket is a fast-rotating piece of heavy machinery with little space for sensors.

Furthermore, modifying the prilling bucket to allow mounting of sensors is not desirable, because the experimental conditions should ideally replicate those experienced within the industry and by the end user.

Computational fluid dynamics (CFD) simulations can be performed to gain a better understanding of the internal dynamics of these rotary prillers. The findings of these simulations (Figure 2) are used to validate an exact mathematical model and can be applied to any newly developed priller to investigate internal flow behaviour.

The use of CFD helps to greatly limit the number of iterations from concept to functional product.

The second problem is the jet break-up, which is hard to research up close. CFD provides a solution, and the results of a simulation are shown in Figure 3. Most experiments for jet break-up can be performed on a laboratory scale, where a vertical jet is analysed and possibly perturbed. In rotary prilling buckets the jet is curved, and the jet shape affects the way droplets are formed. It is possible to produce a spinning device where hot melt leaves a nozzle and analyse the droplet formation, but this direction is labour-intensive and difficult.

CFD can also be applied in this situation. It is possible to investigate any type of melt-based fluid characteristics, which are typically the viscosity and surface tension. Both are a function of temperature, and it can be observed that rapid fluctuations in temperature swing could lead to an improved jet break-up: an interesting phenomenon, even though this cannot be utilised at an industrial scale. The company currently uses pressure fluctuations to improve jet break-up. CFD shows that there is a discrepancy between the optimal frequency as calculated with standard formulas and the modelled values. This is a key insight that Kreber are keen to investigate on an industrial level. Industrial trials are scheduled for later this year.

At the push of a button Figure 2. CFD simulation on vortex formation inside rotary priller.

42 | WORLD FERTILIZER | MAY/JUNE 2021

Secondly, employing CAE results in a reduction of engineering time. Recurrent calculations, as highlighted in the work by Lorentz, can be time-consuming.

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Modelling is most valuable when carrying out repetitive calculations.

The basic designing of a prilling tower is highly repetitive. Based on the physical material properties, the desired prill size and production capacity, it is possible to give a first estimate of the prilling tower. The values of the parameters change for each design, but the calculations remain the same. Since the company have employed a computational model for the tower, a new design can be made with the push of a button. Previously, such design calculations took multiple weeks; nowadays it takes half an hour. Kreber have performed numerous tower design calculations over the past decades, saving a considerable amount of time.

Digital twin Thirdly, CAE has the predictive power to find optimal operational setpoints. In operation, stringent production targets are in place, which makes it hard to experiment with setpoints. As changing setpoints often results in

changes in flow behaviour and possibly lower production, trying to find optimal settings is expensive. Using a digital model of a process allows for optimisation of the process without loss of production capacity.

In prilling towers, the prill outflow as a function of time is an interesting case to highlight. The case discussed here concerns the prill outflow fluctuations from a prilling tower that has a rotating prilling bucket, scraper and conveyor belt. The flow rate depends on the bucket type and its rotational velocity, the scraper design and its velocity and the conveyor belt speed. A resulting image of this modelling can be seen in Figure 4.

The possibility to experiment with setpoints and train operators is often referred to as the digital twin and is a good example of the value of CAE.

Reducing uncertainty in new designs

Finally, CAE provides data for new designs when experimental data is unavailable. Validating a new design can be an expensive affair, especially in the iterative design phase when a large number of resources are required. CAE can reduce uncertainties and limit the number of design iterations prior to the production of valuable equipment.

Kreber has experienced the capabilities of CAE when designing a closed-loop prilling facility. In a closed-loop configuration, the cooling air is recycled by Figure 3. Jet formation and subsequent droplet formation of a spiralling jet. closing the loop and adding a heat exchanger. The cooling gas is forced through the heat exchanger and into the tower by employing a fan. A ring duct design is required to create an even distribution of air flow in the tower.

The uniform air flow distribution results in efficient operation of the prilling process, which means the ring duct design is important.

The design of such a ring duct might seem trivial on paper, but several design iterations and CFD simulations were needed before a satisfying design was reached, resulting in an well-distributed air flow (Figure 5).

Figure 4. Graph indicating the weight distribution of prills at the bottom of a prilling tower. This graph is the result of prills trajectory calculations.

Figure 5. Visualisation of flow inside closed-loop ring duct for one of the iterations during the design phase.

44 | WORLD FERTILIZER | MAY/JUNE 2021

The thrill of the perfect prill CAE has more than earned its stripes in the prilling industry and it will be a vital instrument in the journey to achieve the perfect prill. The continuous development in computational power, improved accessibility and research endeavours will continue to provide a valuable contribution to the development of prilling technology and services.

Reference 1.

Lorentz, H, A.,Verslag van de Staatscommissie Zuiderzee (1926).

FERTILIZER WITH A Thomas Lansdorf, Eirich, Germany, provides a number of practical examples to showcase how the range of applications for which fertilizer granules are being manufactured is steadily growing.

double twist

T

he advanced civilisation of the Egyptians is still astounding today. As well as being masters of mathematics and astronomy, they were particularly skilled in the art of architecture and building. But in addition to this, they also worshipped a tiny beetle – Scarabaeus, also known as the sacred scarab beetle, which symbolised resurrection and represented the circular path of the sun in the sky. This is quite a leap of imagination for a tiny beetle otherwise renowned for its ability to roll dung into round balls. But, of course, these balls are incredibly important as they are used as a food source or as breeding chambers for the larvae of the beetle. And in the process, the dung balls are a typical example of an agglomeration granulate that is comparable to fertilizer granulate, as the basic principle behind their production is very similar. The rolling movement in itself is enough to ensure that a round and stable granulate is formed.

Of course, fertilizer granules are much smaller, but they are produced in surprisingly large quantities.

45

All about the rolling action Just like the efforts of the scarab beetle, with this type of granulate the correct rolling action is key. What the insect manages with skill and endurance, an EIRICH SmartMixer will deliver consistently as well. The secret is in the double-rotation action. The movement of the pan protects the materials, while the rotor delivers the necessary shear forces. The result is a uniform granulate – in the end, it is all just a matter of the correct speed (Figure 1).

The system can be used to granulate almost any kind of powdery substance. With skilled management of the process, the required granulate can be quickly produced. The key requirement is a large surface area, so it is important that the input materials are finely ground. This will ensure that

sufficient adhesion forces for granulation can be generated.

Water is commonly used as the wetting fluid, but additional binding agents can also be used if required.

From single machines to a complete line By using the mixer, raw materials can be mixed, granulated and coated, while chemical reactions can be carried out quickly and completely as required. In many applications, individual processes are combined with each other – for example to produce a homogeneous mixture from filter cake, dusts and slurries. Provided the moisture level is correctly adjusted, the desired granules will form within the space of just a few minutes. Larger pellets are often produced using a disk pelletiser or a rolling drum.

Combining individual processes in this way produces a complete fertilizer production plant capable of running around the clock and continuously manufacturing fertilizer to consistently high standards.

Of dolomite, lime and gypsum

Figure 1. The SmartMixer fully automates mixing and granulation in a single system.

Many carbonates and sulfates are compounds that are difficult to dissolve. These sedimentary rocks can be found in large quantities all around the world. Their poor solubility is an advantage as it guarantees a slow and continuous release of nutrients. For granulation, the raw materials are broken up, ground down and then granulated. Binding agents and additives are added in the mixer and moistened to produce a homogeneous microgranulate. In a disk pelletiser, these microgranules are then grown into the required pellets (Figure 2). Usually between 5 – 10 mm in size, these pellets are round and highly uniform. After drying they can be packaged and stored. When they come into contact with moisture again in the ground, the granules decompose and release the nutrients in the process. They are normally produced in amounts of 10 to 40 tph. The granules can be stored for many years and are perfect for spreading. All around the world, Eirich production lines have been built for precisely this purpose. For example, one large manufacturer in Poland manufactures a fertilizer granulate from dolomite (Figure 3).

Sulfuric acid – the solution for insoluble minerals While humans and animals consume organic food, plants love minerals. Some minerals are completely insoluble in water, putting their nutrients beyond the reach of plants. This is why a dissolution stage with acid is required first, which can be achieved quickly and efficiently by adding sulfuric acid in the mixer. In this way, phosphate ore can be dissolved through the addition of sulfuric acid. Another example is the use of the mineral serpentinite as a fertilizer. Serpentinite is a magnesium silicate that contains many nutrients. The rock is broken up, ground down and then dissolved with sulfuric acid in the mixer. The moist reaction product is formed into granules directly in a disk pelletiser. The minerals can be dissolved in the soil, where they enable maize and grain to grow faster. A RV19 (1500 l) Eirich mixer and a TR36 disk pelletiser have been installed at a modern plant in Paraguay.

Too much of a good thing is bad for you Figure 2. SmartMixer combined with disk pelletisers.

Production of dolomite pellets.

46 | WORLD FERTILIZER | MAY/JUNE 2021

Of course, materials that are completely insoluble are of no value at all to plants. But conversely, if they are too readily

soluble then this is also bad for the plant. For example, incorrect use of urea will often lead to eutrophication.

Solubility can be reduced very easily with the aid of a semi-permeable coating. This can be achieved using polymers, hardly soluble salts or sulfur. In many cases, the coating process needs to be carried out at higher temperatures. Many examples of this type of fully-automated coating process have already been successfully realised. For example, mixers of type RV24 (3000 l) are being used in North America to manufacture a long-term fertilizer from prilled urea.

environment full of people and noise always puts us under more pressure. Some people may reach for a bar of chocolate to calm their nerves. Plants have to cope with these stress factors as well. Heat, drought, cold, lack of light and replanting are just some of the typical stress situations for plants. But there are also a number of natural protection strategies to help ward off these pressures. For example, substances can be used to stimulate their metabolism. Plants become more resistant and the regeneration phase is shortened so that, at the end,

Granulation of easily soluble salts Many salts are important components in fertilizer mixtures.

Typical salts include potassium chloride (MOP) or potassium sulfate (SOP). Polyhalite, a mineral comprising several sulfates, is also among the individual salts used. The goal is to produce uniform and round granules preferably ranging in size from 2 – 4 mm. Applications in which these salts are to be granulated usually have high throughput rates.

This is why mixers of type R28 (5000 l) or R33 (7000 l) are often used. Eirich has developed various methods for doing this so that the granulating process can be kept cost-effective (Figure 4).

Ammonium sulfate is also an important fertilizer salt. It is produced in large quantities during the production of Nylon 6 and in flue gas desulfurisation. A fertilizer factory in Eastern Europe has been producing granules from ammonium sulfate for many years with the aid of mixers manufactured by the company.

Figure 3. A production plant in Poland showing the mixing and pelletising of limestone fertilizer.

Only the best is good enough for football and golf professionals Football (soccer) and golf are played on some of the lushest grass surfaces in the world. These areas require special care to cope with the challenging demands they are subjected to. As a result, it is vital that the supply of nutrients is optimised to ensure healthy growth. These multi-component fertilizers contain the full range of nutrients in every single granule. In production, the nutrient salts are ground in an Eirich Turbo Grinder, before being weighed, homogenised in a mixer, moistened and granulated. At the end, the granules are dried and coated. One such plant for the production of fertilizer for golf courses is located in Switzerland, while another is located in Krefeld, Germany (Figure 5).

Figure 4. The SmartMixer R28 (5000 l) is a big and robust mixer for large throughputs, used for mixing and granulating of mineral salts.

Above all else, good soil is healthy Every farmer knows that it is not enough to just keep fertilizing the soil. As well as minerals, healthy soil also needs humic acids. These are found abundantly in humus, peat and lignite. A granulate made of humic acids is a valuable supplement for soil treatment. Soils that are compacted, display high salinity or are sandy can be significantly improved with this. Leonardite, a by-product of lignite mining, can be used for this purpose. With the aid of Eirich mixers it is moistened and then granulated. Such a plant operates in Grevenbroich in Germany, where a valuable soil improver is manufactured for reactivating infertile soils.

Plants can suffer stress as well Anyone who has ever worked in a large, open-floor office knows what stress is all about. The hustle and bustle of an

Figure 5. A production plant in Krefeld, Germany, showing the mixing and granulating of NPK fertilizer.

MAY/JUNE 2021 | WORLD FERTILIZER | 47

yield and quality can be demonstrably improved. Since the active ingredients are applied in small quantities, it makes sense to deliver them with the aid of carrier materials. Eirich is currently constructing a state-of-the-art granulation plant for the production of biostimulants in Sweden. The active ingredient is a derivative of an amino acid, which is granulated together with a mineral carrier material.

Organic fertilizer The use of natural fertilizer is one of the oldest methods of fertilization. Residues from the digestion of foodstuffs by animals contain many compounds that can be absorbed by plants. These include fermentation residues, nut shells, bone and feather meal, chicken dung, horn shavings and plant fibres. After mixing, the granules are shaped – usually on a disk pelletiser or in granulating drums. Here, larger fibres are entangled and form an agglomerate. After drying, this then produces stable pellets. An Eirich mixer has been installed at a plant in Modena in Italy for this purpose, where an RV19 (1500 l capacity) is used to combine organic residues with mineral substances. Afterwards, the mixture is formed into agglomerates in a drum.

Turning ash into something valuable Ash is usually all that is left over from combustion processes.

One example is in Scandinavia, where large quantities are produced during the burning of wood. Of course, this ash is a valuable fertilizer; potash is rich in potassium carbonate and other minerals. In Sweden, the ash is spread as fertilizer in the forests, but this can be a very dusty business. It is much better

to use it to produce pellets, which are far easier to handle.

Mixers and disk pelletisers from Eirich are used here to manufacture spreadable granules.

All sources are finite – recycling is the top priority Secondary raw materials are becoming increasingly popular as more and more efforts are made to ensure that production is as environmentally friendly as possible and natural resources are used sparingly. Many of these fertilizer raw materials are present as filter cakes, slurries or dusts. As a result, suitable processes need to be employed to break down the process residues and mix them with powders or slurries. An RV23 is used for this in Duisburg in Germany to mix a range of different secondary raw materials. Afterwards, the moistened microgranulate is pelletised in an Eirich disk pelletiser of type TR36. The manufactured granules are used in farming.

A cornucopia of possibilities Our world is in a process of constant change. The prices of raw materials, climate change and the impact of modern living are changing the world every single day. The requirements for fertilizers are also subject to constant change, and it is important that the industry is able to react flexibly to these challenges. Additive granulation offers almost unlimited options for doing this. Many process steps such as mixing, granulating and coating can be combined to streamline processes, and this is rounded off by controlling the temperature, reaction time and amount of liquid to suit the specific requirements.

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