Covering Best Practices for the Industry
Sulfuric Acid T
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Bestgrand Chemical successfully starts up worldâ€™s largest wet-gas sulfuric acid plant in China Page 7
IN THIS ISSUE > > > > Sulfur and sulfuric acid: what 2017 taught us page 10
Kalium Mining chooses SAFEHR ÂŽ for its new sulfuric acid plant page 20
Impala Platinum smelter facility off-gas processing Page 24
Sulfuric Acid T
Vol. 24 No. 1
Covering Best Practices for the Industry
FROM THE PUBLISHER On the Cover … 7 Haldor Topsoe reaches milestone with largest WSA plant at Bestgrand Chemical in China. Departments 4 Industry Insights News items about the sulfuric acid and related industries 16 Product News News items about sulfuric acid products and services 30 Lessons Learned Case histories from the sulfuric acid industry 37 Faces & Places Covering sulfuric acid industry events 38 Calendar of Events
Dear Friends, Welcome to the Spring/Summer 2018 issue of Sulfuric Acid Today magazine. We have dedicated ourselves to covering the latest products and technology for those in the industry, and hope you find this issue both helpful and informative. In this edition you will find several articles regarding various processes for emissions reduction. Our cover story delved into Haldor Topsoe’s Wet Gas Sulfuric Acid (WSA) technology which converts sulfurous gases to commercialgrade sulfuric acid without drying the gas, with high energy efficiency, and very low emissions. The largest WSA plant recently came online at Bestgrand Chemical Group in China (page 7). NORAM Engineering & Constructors’ plant design shares many of the characteristics of a single absorption sulfuric acid plant. However, there are a number of important differences: no catalytic converter is required, process equipment is operated under higher pressure, and multiple blowers are operated to achieve the required process performance (page 12). Mosaic’s Louisiana facility chose the Cansolv SO2 Scrubbing System, which uses a regenerable amine-based solvent to selectively capture SO2 from flue gas or tail gas streams, versus converting to double absorption (page 18). Lastly, MECS-DuPont Clean Technologies’ engineering and state-of-the-art equipment was integrated into Impala Platinum’s South Africa facility, which consisted of expanding and upgrading some of the existing gas treatment infrastructure to handle the
Sincerely, Kathy Hayward
FEATURES & GUEST COLUMNS
PUBLISHED BY Keystone Publishing L.L.C. PUBLISHER Kathy Hayward
increased off-gas volumes. In addition, several new operations were added to improve desulfurization efficiency and reduce atmospheric emissions of SO2 and acid mist (page 24). Other informative articles in this issue of Sulfuric Acid Today include: “Sulfur and sulfuric acid: what 2017 taught us” (page 10), “Sulfur gun advancements” (page 14), “Kalium Mineração chooses SAFEHR® for its new 150 MTPD sulfuric acid plant” (page 20), “Wet electrostatic precipitators for optimal sulfuric acid gas cleaning” (page 22) “Cleaning of the sulfur recovery unit is essential to efficiency” (page 28), “Looking out: a quick guide to establishing an effective jobsite safety review program” (page 32), and “Dirty sulfur pumps: how to overcome challenges for a smooth operation” (page 34). I would like to welcome our new and returning Sulfuric Acid Today advertisers, including: Acid Piping Technology Inc., Alphatherm Inc., Beltran Technologies, Central Maintenance & Welding, Chemetics Inc., Clark Solutions, Conco Services Corp., FLEXIM, Haldor Topsoe A/S, Koch Knight LLC, MECS Inc., NORAM Engineering & Constructors, Optimus, Southwest Refractory of Texas, Spraying Systems Co., VIP International, and Weir Minerals Lewis Pumps. We are currently compiling information for our Fall/Winter 2018 issue. If you have any suggestions for articles or other information you would like included, please feel free to contact me via e-mail at email@example.com. I look forward to hearing from you.
EDITOR April Smith
High pressure 300 MTPD SO2 plant in North America
Sulfur gun advancements
Five years later: Comparing single absorption plant using Cansolv vs.
Marketing ASSISTANT Tim Bowers DESIGN & LAYOUT
Sulfur and sulfuric acid: what 2017 taught us
double absorption 20
Kalium Mineração chooses SAFEHR® for its new 150 MTPD sulfuric acid plant
Wet electrostatic precipitators for optimal sulfuric acid gas cleaning
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Impala Platinum smelter facility off-gas processing
Cleaning of the sulfur recovery unit is essential to efficiency
Looking out: a quick guide to establishing an effective jobsite safety
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4 People on the Move
EDITOR April Kabbash
review program 34
Dirty sulfur pumps: how to overcome challenges for a smooth operation
Info sharing at CRU’s conference, Sulphur 2017
Industry Insights Outotec to deliver modular sulfuric acid resources in the Democratic Republic of Congo
ESPOO, Finland—Outotec has been awarded a contract by Shalina Resources Limited for the delivery of advanced sulfuric acid plant technology to the Mutoshi project near Kolwezi in the Democratic Republic of Congo. The order value, approximately EUR 33 million, is booked in Outotec’s 2018 first quarter order intake. Outotec’s scope includes the delivery of three skid-mounted, modular sulfuric acid plants that will produce the acid and SO2 gas required in the process of the new Mutoshi copper-cobalt plant. The innovative plant concept, based on Outotec’s technology and expertise gained
from 650 plants delivered globally, ensures the many benefits of modular prefabricated plant delivery, such as low investment, installation and operation cost, increased availability and maintainability, as well as environmentally sound and safe operation. The order complements the copper and cobalt processing technology delivery to the Mutoshi project Outotec announced in December 2017. “We really look forward to working with Shalina Resources in the Mutoshi project, and are extremely pleased that we can complete our diverse technology package for the copper and cobalt processing now with sulfuric acid plants. These modular plants represent our latest technology, and remarkably improve the environmental performance of the plant,” says Kalle Härkki, head of Outotec’s Metals, Energy & Water business. For more information please visit www.outotec.com.
people on the move Jim Dougherty brings quarter century of expertise to MECS-DuPont Clean Technologies
years, having presented over a dozen Jim Dougherty is joining MECS– conference papers and authored several DuPont Clean Technologies after articles as well as serving as co-chairworking 25 years in sulfuric acid man of the AIChE Clearwater Conferplant operations and engineering with ence Sulfuric Acid Workshop, industry the legacy companies of Mosaic. At chairman of the HRS User’s Group, MECS, Dougherty will serve as a sales and a member of the inmanager for metallurgidustry’s Hydrogen Safety cal and spent acid regenCommittee. eration customers in the MECS, Inc. is the Gulf Coast, Western U.S., world leader in sulfuric and Canada for sulfuric acid plant and environacid plant equipment such mental technologies, as catalyst and Brink® providing engineering mist eliminators, as well design, services and highas plant engineering and performance products technical services. for the phosphate fertil Dougherty held poizer, oil and gas, chemisitions as an assistant production superinten- Jim Dougherty, sales cal and non-ferrous metmanager, MECS-DuPont als industries. Specific to dent for two 2,500 TPD ® the oil and gas industry, MECS offers HRS plants and as a production engisolutions for treating sour off gas from neer supporting eight MECS-designed amine treaters and sour water strippers sulfuric acid plants during the first 10 to achieve ultra-low emissions specifiyears of his career. Over the next 15 cations. MECS is a wholly owned subyears, Dougherty worked as a process sidiary of DuPont. engineer responsible for developing The DuPont Clean Technologies and executing capital projects includportfolio includes technology for proing: debottlenecking five MECS sulduction of clean, high-octane gasoline; furic acid plants from 2,500 TPD to desulfurization of motor fuels; acid 3,100 TDP; retrofitting BFW pre-heat production and regeneration; air quality exchange equipment and 32 MW of control systems for FCC flue gas scrubco-generation; retrofitting two HRS® bing, other refinery scrubbing applicasystems and 30 MW of co-generation; tions and marine exhaust gas scrubbing; designing, constructing, and startingsulfur recovery and tail gas-treating; and up the world’s largest sulfur melter (165 a comprehensive suite of aftermarket TPD), which included an MECS Dyservice and solutions offerings. naWave® Scrubber. For more information, visit www. Dougherty has also been active cleantechnologies.dupont.com. q in the sulfuric acid industry over the
Port Pirie Redevelopment allows increased operating flexibility
ZURICH—Located on the eastern shore of the Upper Spencer Gulf in South Australia, approximately 230 km north of Adelaide, the Port Pirie smelter has been in constant operation for over 127 years. There is an adjacent dedicated port facility where concentrates are received, with final products dispatched by road and rail. The Port Pirie Redevelopment project involves the conversion of the Port Pirie operations into an advanced metal recovery and refining facility, enabling the facility to process a wider range of high margin feed materials, including internal zinc smelter residues and concentrates. Once fully ramped-up, the facility will allow Nyrstar to capture a greater proportion of the value contained within the feed material consumed by its global network of smelters as well as third party residues. The increased operating flexibility of the smelter following the project’s completion is expected to create a fundamentally different operating and business model. The key aspects of the Port Pirie Redevelopment include the replacement of the existing sinter plant with an oxygen enriched bath smelting furnace and replacement of the existing sulfuric acid plant with a new plant with greater capacity and upgraded technology. Additionally, investment in proven state-of-the-art technology will also deliver step change reductions in airborne metal, dust, and sulfur dioxide emissions resulting in significant reductions in community blood lead levels. In parallel, Nyrstar and the South Australian Government have agreed to further improve community health through the establishment of a Targeted Lead Abatement Program (TLAP). In early 2017, following the arrival of its new CEO, Nyrstar undertook a detailed review of the Port Pirie Redevelopment project to ensure that the scope, flow sheet, and commissioning would provide Port Pirie with industry leading performance. Also as part of the review, a number of technical engineering improvements have been identified to unlock additional value. Port Pirie is at a stage where the identified improvements can still be implemented efficiently and effectively ahead of the hot commissioning milestone. Following the review in early 2017, the TSL furnace hot commissioning was postponed by six months to September 2017. In H1 2017, the Port Pirie Redevelopment project focused on completing the rework of modules and enhancing the slag tapping arrangements on the TSL furnace while completing the modular construction and progressing the commissioning of the new infrastructure and related control systems. In addition, training of Nyrstar personnel commenced at the Kazzinc lead smelting operations in Kazakhstan. The lime plant commissioning and the piling for the relocation of the slag
caster was completed during Q2 2017. The furnace is enclosed ensuring all metal fumes and off-gas are recovered. Blended feed materials and flux is fed through the roof of the furnace. Core to this technology is the lance that injects air and oxygen at a high rate into a high lead slag bath. This ensures that oxygen is so well mixed with the slag and blended feed material, that the required reactions occur at a high rate and high temperature and means they are operated very close to equilibrium. These aspects enable using a wide variety of feed materials, making it one of the most flexible pyro metallurgical furnace operations available. The Port Pirie Top Submerged Lance (TSL) process will produce lead bullion and a high lead slag suitable for further treatment in the Blast Furnace. The lead bullion settles to the bottom of the furnace which is batch tapped from a water cooled tap-hole, while the slag will continuously overflow via a weir. The acid plant will take the off gas from the Outotec Ausmelt TSL Furnace after being cleaned and conditioned, and will convert the sulfur dioxide contained in the gas to concentrated sulfuric acid which will be sold to the market. For more information, please visit www.nyrstar.com.
Mosaic completes acquisition of Vale Fertilizantes
PLYMOUTH, Minn.—Mosaic recently announced that the Vale Fertilizantes acquisition is now complete, marking the largest acquisition in the company’s history. In addition to transforming Mosaic’s business in Brazil, the acquisition doubles the size of its global workforce. Integrating assets and 7,300 talented employees from Vale Fertilizantes–including five phosphate mines, one potash mine, and four chemical and fertilizer production facilities–greatly enhances Mosaic’s global growth strategy and expands market access. With the additional 4.5 million tonnes of phosphate fertilizer production capacity, Mosaic’s global phosphate fertilizer production capacity is now 16.8 million tonnes. The acquisition also included Vale’s 40 percent economic interest in the Miski Mayo phosphate mine in Peru. As the operating partner, Mosaic’s interest in the joint venture is now 75 percent. Mosaic expects that its U.S. phosphate production facilities will continue to operate at high rates in order to meet strong and growing global demand. The company’s premium MicroEssentials® products are also expected to continue to be produced exclusively in the United States, and Brazil is expected to remain a key market for MicroEssentials. The Mosaic Company is one of the world’s leading producers and marketers of concentrated phosphate and potash crop nutrients. Mosaic is a single-source Sulfuric Acid Today • Spring/Summer 2018
provider of phosphate and potash fertilizers and feed ingredients for the global agriculture industry. For more information, visit www.mosaicco.com.
Umm Wu’al begins production
IRVING, Texas—The Ma’aden Wa’ad Al-Shamal Phosphate Company’s (MWSPC) Umm Wu’al Phosphate Project in Saudi Arabia has started production of ammonia, merchant-grade acid and fertilizer. Fluor is providing overall program management services for this $8 billion megaproject, in addition to engineering, procurement and operations and readiness services for various scopes. “As part of Saudi Arabia’s Vision 2030, this world-class project will have a long-lasting impact on the region, as it diversifies the country’s economy and creates local job opportunities for citizens,” said Tony Morgan, president of Fluor’s Mining and Metals business. “After less than four years from the start of the execution phase, we are proud to have partnered with Ma’aden to bring this facility to production. We look forward to continuing our partnership with Ma’aden in developing their next phase of mining projects in Saudi Arabia through our recently signed memorandum of understanding.” Production has begun on diammonium phosphate fertilizer, merchant-grade acid, and ammonia. Phosphate serves as a key element in fertilizer for agricultural crops. As one of the largest integrated phosphate fertilizer plants in the world, the facility will help meet global food supply needs by delivering 3 million metric tons per annum of diammonium phosphate and nitrogen, phosphorous and potash fertilizers. With a peak site workforce of 28,000 from more than 50 nationalities, Fluor implemented its world-class safety programs, including its Life CriticalSM program, to support the project. As a result of these programs, the project has achieved more than 46 million consecutive work hours without a lost-time incident. MWSPC is a joint venture between The Saudi Arabian Mining Company (Ma’aden), The Mosaic Company and Saudi Arabia Basic Industries Corporation (SABIC). For more information, please visit www.fluor.com.
New projects boost Iran’s copper sector TEHRAN, Iran–Thirteen expansion projects of Kerman Province’s National Iranian Copper Industries Company (NICICO) were inaugurated recently by President Hassan Rouhani and Minister
of Industries, Mining and Trade, Mohammad Shariatmadari. The total value of the projects exceeded 35 trillion rials ($760.8 million), the Iranian Mines and Mining Industries Development and Renovation Organization announced. NICICO is the leading copper producer in the Middle East and North Africa region, as the mines it operates hold close to 14 percent share of Asia’s copper deposits and about 3 percent of global reserves. Iran holds about 4 billion tons of estimated copper reserves, according to Geological Survey of Iran. The new production projects include: a flash smelter with a capacity of 282,000 tons of copper anode per year alongside the purchase of casting wheels and anode furnaces with an investment of 2.4 trillion rials ($51.6 million) in addition to €182 million; Khatunabad Copper Smelter with an annual capacity of 200,000 tons of copper cathode and an investment of 640 billion rials ($13.7 million) in addition to €143 million; Sarcheshmeh copper plant’s new convertor furnaces’ gas discharge system with 1.54 trillion rials ($33 million) in addition to the investment of €19 million; Sarcheshmeh cathode washing system with 1 trillion rials ($21 million) of investment; Sarcheshmeh’s explosive material production plant with a capacity of 12,000 tons of gelatin dynamites per year with 120 billion rials ($2.5 million) of investment; and expansion of Sarcheshmeh’s sulfuric acid plant capacity to 300,000 tons per year with 580 billion rials of investment in addition to €3 million. The new infrastructure projects included: the second line of the 80-kilometer Sarcheshmeh-Shahr-eBabak Road with an 800-billion-rial ($17 million) investment; the first and second phase of Sirjan’s 500-megawatt combined cycle power plant with an investment of 700 billion rials ($15 million) in addition to €285 million; Khatunabad’s new copper concentrate storage with a 60,000-ton capacity and a molybdenum dewatering, drying and drum-filling plant, with a combined investment of 790 billion rials ($17 million); increasing the capacity of quicklime storage by 1,250 tons with an investment of 110 billion rials ($2.3 million); MeymandShahr-e-Babak electricity substation with 50 billion rials ($1 million), in addition to an investment of €15 million; and nine electricity substations to feed flash smelters, acid sulfuric and molybdenum plants with 480 billion rials ($10 million) of investment, according to NIOC’s website. The company, however, stopped short of saying whether the projects’ “inauguration” meant that they have become operational or simply that work has just begun on them. For more information, please visit www.en.nicico.com. q
Sulfuric Acid Today • Spring/Summer 2018
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Wet-gas tech asserts standing with largest plant in China
By: April Smith, Editor, Sulfuric Acid Today
aining ever wider acclaim in the area of capturing and treating sulfurous waste gases, wet-gas sulfuric acid (WSA) technology recently passed a milestone. The largest WSA plant, a 300,000 ton per year sulfuric acid facility, came online this year in Huizhou, China. A process that captures sulfur in large enough quantities to ensure environmental compliance with room to spare, WSA draws equal attention for a key side benefit: the generation of commercial grade sulfuric acid.
Sulfuric Acid Today • Spring/Summer 2018
Other features contributing to WSA’s popularity include the system’s overall efficiency when compared to the traditional alternative, a Claus plant. Unlike the Claus process, in which sulfurous waste is converted to elemental sulfur, WSA recovers more heat and the sulfuric acid produced is easier to transport and often more valuable than elemental sulfur. Plus, a WSA plant can be configured simply and with a small footprint, has low consumption of utilities, generates no waste products or wastewater, and offers a wide turndown capability. WSA was developed and patented by Haldor Topsoe A/S in the mid-1970s, and the first plant started up in 1980. The process began as a spin-off from the company’s activities as a catalyst producer for the sulfuric
acid industry. Catalyst for the production of sulfuric acid was the first catalyst Topsoe produced, and the company has been supplying it since 1944. Currently, Topsoe supplies its VK-WSA catalyst to the over 130 WSA plants it has licensed worldwide. The oil refining industry remains the predominant application of the technology, accounting for roughly half of today’s WSA plants. In oil refining, off-gas treatment facilities such as a WSA plant are needed to capture the hydrogen sulfide (H2S) gas that is generated as a consequence of removing sulfur from petroleum products, such as gasoline, diesel, and other fuel oils. The sulfur is removed to reduce sulfur dioxide emissions when those fuels are ultimately used in cars, trucks, jets, etc. PAGE 7
Though oil refining is the largest market for WSA, the tech can be applied to other industries, including coal gasification, natural gas sweetening, coking, viscose, and metallurgical industries. In addition to capturing H2S gas from refinery operations, WSA plants also handle sour water stripper (SWS) gases and spent sulfuric acid regeneration from alkylation.
SO2 Converter WSA Condenser
Steam Drum Selective Catalytic Reduction (SCR) Reactor
WSA goes big in China
Since 2000, Topsoe has sold 68 WSA plants in China, with 54 of them already on stream. The most recent and largest WSA plant to come online was sold to Bestgrand Chemical Group, and treats off-gases from the neighboring petrochemical complex, known as “Nanhai” in Huishou, Guangdong province. The new WSA plant has the capacity to treat 131,000 tons per year of acid gas and produce 300,000 tons per year of sulfuric acid. The Nanhai complex is operated by CSPC, a joint venture between China National Offshore Oil Corporation (CNOOC) and Shell Petrochemicals Co. Ltd. CNOOC is the largest offshore oil and gas producer in China. The Nanhai refinery has an ethylene production capacity of 950,000 metric tons per year which it converts to 2.7 million metric tons per year of derivative products. CSPC supplies these products to the Chinese domestic market, which uses them as raw materials in household goods, electric appliances, automobiles, medicine, agriculture, and other products. As CSPC sought ways to capture hydrogen sulfide emissions from its refining process, the company looked to Bestgrand Chemical Group to build a neighboring facility to handle over-the-fence waste gas from the refinery. Bestgrand then contracted with Haldor Topsoe to license the new WSA plant. Bestgrand Chemical Group is the chemical arm of Bestgrand Holdings Co. Ltd., an enterprise with diverse businesses including commercial real estate development and venture capital investment. When the Chinese government began developing the Nanhai complex, Bestgrand entered the chemical industry collaborating with CSPC on the refinery’s construction. Bestgrand also coordinates with CSPC as a distribution partner for styrene and a supplier of benzene, liquid caustic soda, and potassium hydroxide for the refinery.
As Bestgrand considered the options for off-gas abatement, it was attracted to the efficient and economical manner in which a WSA plant converts waste gas to sulfuric acid. “The WSA technology from Topsoe produces commercial-grade sulfuric acid directly from acid gas,” said Gu
Morten Lykke Poulsen, Licensing Director for WSA
Combustor / Waste Heat Boiler (WHB) Configuration of 300,000 TPY WSA plant includes Topsoe’s proprietary condenser. The system’s waste heat boiler ensures high heat recovery to produce valuable steam and the optional selective catalytic reduction reactor captures NOx from tail gas.
Hongkuan, Standing Vice Manager at Bestgrand, “so we eliminate the intermediate step of producing elemental sulfur as in the traditional Claus process.” Bestgrand also weighed the cost savings from the energy that the WSA system delivers to CSPC’s refining operation. “The WSA plant supplies a huge amount of highpressure steam to CSPC, saving its operation four million dollars in steam costs every year,” Hongkuan said. As for the environment, nearly complete sulfur capture is another chief driver. “WSA recovers up to 99.99 percent of sulfur in waste gases or liquids, even without tail gas treatment,” said Morten Lykke Poulsen, Licensing Director for WSA. Bestgrand predicts the plant will also reduce carbon dioxide emissions by at least 260,000 tons per year and SO2 emissions to a level 50 percent lower than what is required of the sulfuric acid industry. And then there’s the acid. “WSA produces commercial grade, concentrated sulfuric acid (above 98 percent) from waste gases or liquids,” Poulsen said. The sulfuric acid then provides licensees with a cost offset because the acid can be re-used in production or sold as a commercial product.
Bestgrand Chemical Group’s WSA plant came online in February 2018. The plant is predicted to reduce carbon dioxide emissions by at least 260,000 tons per year and SO2 emissions to a level 50 percent lower than what is required of the sulfuric acid industry.
Construction on the plant began in January of 2016. Topsoe provided the licensing tech as well as tech services, engineering design, hardware, and performance catalysts. The plant came online in February 2018.
The process technology
The WSA system condenses wet process gas into concentrated sulfuric acid. Because the WSA design relies on wet feed gas, there is no pre-treatment drying step and hence generation of waste water and loss of sulfur are avoided. During the first step of the process, feed gases such as hydrogen sulfide and other sulfurous compounds are combusted to produce an SO2 gas at the operating temperature of the oxidation catalyst in the SO2 converter. The excess heat from this operation is recovered as steam. Next, catalytic conversion of SO2 to SO3 takes place: SO2 + ½ O2 -> SO3 + 99 kJ/Mol Conversion is achieved in catalyst beds using Topsoe’s VK-WSA catalyst, which has been specially developed for this purpose. The number of beds depends on the SO2
Bestgrand Chemical Group has successfully started the world’s largest WSA plant.
Sulfuric Acid Today • Spring/Summer 2018
concentration and the degree of conversion required. In a multi-bed arrangement, inter-bed cooling can be achieved in different ways depending on the heat balance of the plant and the requirement to recover energy from the process. Reaction heat is recovered between the catalyst beds to generate high pressure steam. At the converter’s exit, the gas is cooled allowing the SO3 to react with water vapor to form gas-phase sulfuric acid: SO3 (g) + H2O (g) -> H2SO4 (g) + 101 kJ/Mol The cooled sulfuric acid gas enters Topsoe’s proprietary WSA condenser, which condenses the sulfuric acid gas to form the liquid product. The WSA condenser is a vertical shell and tube falling film condenser/concentrator with tubes made of boronsilicate acid and shock resistant glass. The process gas flows up the tubes and is cooled by ambient air circulating on the outside of the tubes. Sulfuric acid condenses in the tubes and flows downward counter-current to the rising hot process gas. This contact with the hot process gas concentrates the acid to the desired concentration. Clean gas exits the top of the WSA condenser and the sulfuric acid collects in the brick-lined bottom section where it is pumped out, then cooled and stored. Hot air generated in the WSA condenser can be used as preheated combustion air to ensure optimal energy efficiency. The process is easily adapted to handle gases containing impurities such as NOx. A selective catalytic reduction (SCR) reactor can be positioned before the SO2 converter and ammonia is introduced into the gas stream before the SCR reactor in a stoichiometric amount to the NOx in the gas. The NOx is converted to nitrogen and water: NO + NH3 + ¼ O2 -> N2 + 3/2 H2O + 410 kJ/Mol
sulfur without costly tail gas treatment. The WSA-DC technology utilizes the high conversion efficiency of the double contact principle. At the same time only a modest change in the design is required to include the intermediate WSA condenser.
Evolving the system
As clients seek economical options to manage ever stronger environmental standards, Topsoe has been enhancing the technology. A recent introduction is the double-condensation (DC) WSA that removes up to 99.99 percent of
Stack for clean gas after the WSA condenser.
Sulfuric Acid Today • Spring/Summer 2018
Typical WSA plant cleaning H2S and sour water stripper gases.
Although the predominant market for WSA tech has been in oil refining, with roughly half the world’s WSA acid generated from refineries of all sizes, licensing continues to be strong across other industries. Another large segment is coal gasification for production of ammonia, methanol, or substitute natural gas (SNG). Bestgrand also sees a larger role for WSA. “With the mutual benefits we have seen from our new WSA plant,” said Hongkuan, “Bestgrand will definitely propose similar sulfur management solutions for other large refinery operations in China.” Poulsen expects the technology to expand into new markets as well. “Because of its versatility, we are still able to introduce WSA into new applications and industries.” Poulsen has the paper & pulp industry on his radar screen. For all its versatility and effectiveness, it’s the system’s economic sense that cinches the deal. “Before anything else,” Poulsen said, “customers look at total cost of ownership, and in most situations WSA offers an unrivalled business case compared to competing technologies, first and foremost Claus technology. The simplicity, reliability, and long lifetime of WSA offer manufacturers in a multitude of industries a cost-efficient way to comply with and even turn a profit from waste.” Haldor Topsoe provides sulfuric acid producers and refineries with several technologies beyond WSA. Haldor Topsoe is a world leader in catalysis and surface science, committed to helping customers achieve optimal performance, using the least possible energy and resources, in the most responsible way. Headquartered in Denmark, the company has project development, R&D, engineering, production plants, and sales and service across the globe. For more information, visit www.topsoe.com. q
WSA condenser principles.
The Nanhai complex is operated by CSPC, a joint venture between China National Offshore Oil Corporation (CNOOC) and Shell Petrochemicals Co. Ltd. CNOOC is the largest offshore oil and gas producer in China.
Sulfur and sulfuric acid: what 2017 taught us
By: Fiona Boyd and Freda Gordon, Directors, Acuity Commodities
2017 was an interesting year for the sulfur and sulfuric acid markets. Demand for sulfur slowly outstripped supply as the year progressed, and by year end trader speculation fueled an unexpected pricing bubble, which will have repercussions on the market this year. Sulfuric acid prices were relatively low going into 2017 but picked up later due to unplanned issues on both the supply and demand side. The upward pricing attracted attention from more traders, creating interesting dynamics for this year. In this article, we identify the key trends from last year that will shape the sulfur and sulfuric acid markets in 2018.
In 2017, supply was constrained when several anticipated new projects failed to materialize, including the 400,000-800,000 t/yr Barzan project in Qatar and the 1.1m t/yr Kashagan project in Kazakhstan. Availability was further squeezed by unexpected issues, such as Hurricane Harvey in the United States and limitations on navigation near Kavkaz in Russia; as well as planned events, such as increased domestic consumption by Ma’aden Wa’ad Al Shamal Phosphate Company in Saudi Arabia and the closure of the 410,000 t/yr Shuaiba refinery in Kuwait. By the second half of 2017, constrained supply amid healthy consumption began to affect sulfur pricing. Demand for sulfur from phosphate fertilizer producers was strong as the cost of ammonia was relatively low and sale prices of fertilizers higher compared with the year before. The price of sulfur began to move upward from the third quarter and, with Chinese speculative traders’ participation by October, a pricing bubble was created. Long-delayed new sulfur production finally materializes This year, one highly anticipated project finally began to export sulfur, with Kashagan selling at least three trial export cargoes since December 2017. The project had been producing sulfur throughout 2017, but export activity was hindered by unsteady prilling rates and logistical challenges. Although its nameplate production capacity will not be reached this year, we expect around 150,000 t to be available for export in quarter one and the quantities to grow as the prilling operation ramps up. The Reliance gasification project in India has been delayed for years and is now expected to start up late in the first quarter or early in quarter two. This expansion program includes four sulfur recovery units (SRU) with a designed capacity of 5,400 t/day of sulfur combined. The Barzan project is heard to still face technical issues and the general consensus is it will not alter market fundamentals this year, although there remains talk of a potential start up in the second half of 2018. The timing and actual export quantities from new production projects will be key in shifting market supply this year. As it stands now, Acuity expects Kashagan and Reliance to have a more prominent impact on fundamentals only in the the second half of 2018. Volatility makes a comeback Following the unprecedented volatility brought on by the global financial crisis during 2008-09, the sulfur market returned to a period of relative price stability due to more direct business dealings between producers and consumers under long term contract. In the first half of 2017, sulfur was traded at a narrow range of around $25/t in China. But later in the year, tight supply and healthy demand threw everything off balance. The spot price surged from around $100/t cost-in-freight (CFR) in China in June to as high as PAGE 10
$215/t CFR in mid November. Market fundamentals lent support to spot pricing, but the bubble was fueled by speculation. Many speculative traders located in China jumped at the opportunity to make a profit and started taking position in early October, artificially keeping demand firm. For fertilizer producers, the growth in sulfur price was faster than the growth in fertilizer prices. They therefore decided to buy as much, and as forward, as possible despite having to pay the high price to ensure there were enough stocks for the domestic fertilizer season. This was followed by the prompt exit of end-users, which caused the price decline to around $160/t CFR in China at the end of the year. There are already signs that volatility will stay in 2018. By late January, prices dropped to the $130s/t CFR in China. But, at the time of writing, the market bottomed out and was heating up. This was down to traders’ strategy to place as much to non-China markets as possible between December and January, despite some at a loss because of the misalignment of freight-on-board (FOB) and CFR levels. This reduced availability in March amid a firm phosphates market, a recipe for further pricing volatility.
ducing availability for offshore spot business and keeping the northwest European spot export price firm. Better copper economics also led to firmer acid demand for copper leaching in Chile. Operations from small to medium sized leaching projects have continued to recover. In 2017 Chile imported 2.18 m t of acid, a 27 percent increase from 2016, according to customs data. This trend has continued into January and February this year, right after the settlements of annual contracts in late 2017, and drawing more long haul and sulfur-based acid towards Mejillones. It should be noted that Chile’s strong appetite for acid at the start of the year was also led by local smelter supply issues. For example, Enami’s 22,000 t/month Paipote smelter was down on strike action in December and January, while Codelco’s 45,000 t/month Potrerillos smelter had less volume than expected in January due to unscheduled operational issues.
The sulfuric acid market has remained firm since the second quarter of 2017, largely supported by firm demand from related markets. Supply was also interrupted for most of 2017 due to unplanned and scheduled maintenance work at smelters globally. To fill in the gap, sulfur-based acid from China, South Korea, Italy, Spain, and also the United States was shipped to long-haul destinations. For instance, China set a record in 2017 with close to 700,000 t exported. In 2018, we are expecting a finely balanced market. The number of scheduled turnarounds this year will be fewer than in 2017, but firm demand and an expected reduction of sulfur-based acid being circulated in the acid trading market should keep it in balance for most of 2018. Upbeat outlook on global economy strengthens demand A more upbeat outlook on the global economy and the commodities market will continue to drive the sulfuric acid market this year. Europe is an example of sulfuric acid supply being tight as a result of a more positive economy, which increases demand for industrial applications. The eurozone has made strong recovery from years of financial crisis, currently recording an annual growth rate of 2.5 percent in 2017, the highest since 2007, according to Eurostat. A European Commission poll shows that confidence levels remain close to the 17-year high recorded in December last year, therefore the growth looks set to stay in 2018. Strong demand from multiple small-volume buyers has kept smelter acid producers’ focus on the domestic market, further re-
Price recovery draws more trader participation The market situation last year led to a steady recovery of spot prices and created opportunities for traders to step in, as they reached out to global sulfur burners to fill in the gaps left by smelters. This encouraged more traders to get involved in acid trading. This was an unexpected development following some market consolidation on the trading side in the past two years, including the acquisition of Chemtrade Aglobis by Mitsui and solvadis by Sojitz. The low-priced environment in 2015-16 encouraged producers to reduce contracted volume with traders. At the end of 2017, we observed strong competition among traders to secure long-term contracts with smelters. As a result, trader participation in the acid market is high and the implication for 2018 is pricing direction will be more dependent on trader position than we have seen in the last two years. Acuity Commodities provides insight into the sulfur and sulfuric acid markets through price assessments, data, and supporting analysis. Offerings include weekly reports on the global sulfur and sulfuric acid markets and a bi-weekly report focusing on North America. Please visit www.acuitycommodities.com for detailed information. q Sulfuric Acid Today • Spring/Summer 2018
High pressure 300 MTPD SO2 plant in North America
By: Kim Nikolaisen, Kang Lee, Hongtao Lu, JP Sandhu, Pablo Carbajal, Brad Morrison, Tony Mah, Tony Walsh, Andrés Mahecha-Botero, C. Guy Cooper, and co-author John Orlando, NORAM Engineering and Constructors Ltd.
When a Vancouver-based mining company approached NORAM several years ago with a request for a plant to produce large quantities of sulfur dioxide (SO2) gas, NORAM was glad to pitch in. Three hundred tons per day of SO2 was required for a new metals leach process to be located in North America. The plant would be one of the largest SO2 plants ever built.
Making SO2 is relatively easy. Just burn sulfur in air and voila: SO2. But wait, there’s more! You need to look at the optimum SO2 strength, the pressure, temperature, and impurities. From a simple sulfur furnace one can operate as high as about 17 percent SO2 before approaching practical oxygen furnace temperature limits. NORAM evaluated options to produce a high strength SO2 gas using either oxygen enrichment or amine scrubbing and found that simpler was better. The high strength gas would reduce the volume and size of the equipment but capital and operating costs were considerably higher. Also, the client had found from bench scale testing that 17 percent SO2 would work fine for the leaching reaction, and for that reason NORAM designed a high-pressure air-based system.
So with the SO2 strength set at 17 percent, NORAM had to figure out a way to get the SO2 gas pressure high enough to overcome the head of the leach tanks. The design features are summarized below: • Feedstock: Liquid sulfur with a delivery system similar to that of a conventional acid plant. • Process gas product: SO2 gas at the following conditions: o Capacity: 300 MTPD (330 STPD) of SO2. For reference, this is enough SO2 gas to produce 459 MTPD (505 STPD) of sulfuric acid (as 100 percent w/w). o Concentration: The system is designed to produce SO2 gas of up to 17 percent (vol/vol). In comparison, acid plants typically operate with a concentration of 12 percent (vol/vol). o Pressure: The plant delivers the product gas at about 2 bar(g) (or 30 psi(g)), which is about four Fig. 1: Plant 3-D model.
times higher than the 0.5 bar(g) (or 7 psi(g)) of a conventional sulfuric acid plant. The gas is fed into the bottom of a tank filled with mineral slurry of 11.5 m height (38 ft). For this reason, the plant gas delivery system operates at high pressure. • Steam product: The plant is designed to maximize heat recovery and produce superheated steam as follows: o Steam specification: 62 bar(a) (900 psi) at 480°C (896 °F). o Steam production rate: 450 MTPD (496 STPD). • Turndown rate: The plant is designed to allow for rapid production rate changes from 25-100 percent capacity. The plant also has the ability to feed SO2 gas to a number of different consumers in a controlled manner. The plant design shares many of the characteristics of a single absorption sulfuric acid plant. However, there are a number of important differences: no catalytic converter is required, process equipment is operated under higher pressure, and multiple blowers are operated to achieve the required process performance. A 3-D model of the plant is shown in Fig. 1.
The plant uses NORAM’s proprietary, shop-fabricated equipment, which includes: • A dry tower system to remove water vapor: dry tower, acid pump, and acid cooler. • A refractory-lined sulfur furnace system for combustion of sulfur: sulfur furnace, sulfur delivery system, gas bypass, and recycle system. • A steam system for removal of heat: deaerator, boiler Shop fabrication of NORAM equipment, clockwise starting top left: acid cooler fabrication and inspection; sulfur furnace ready to ship; acid tower fabrication; expansion joints; and acid tower ready to ship. Installation of equipment internals, clockwise from top left: NORAM Smart™ acid distributor; tower bricking and dome; installation of candle de-misters; installation of mesh pads; and installation of packing and partition rings.
Installation of major process equipment on site.
feed water pumps, economizer, boiler, superheater, and blowdown system. • An acid tower for removal of traces of SO3: acid tower, acid pump, and acid cooler. The plant delivers concentrated, pressurized SO2 gas that is essentially free of H2O and SO3.
Startup and final results
A team of NORAM and client engineers commissioned and started up the plant.
Successfully operating plant.
The plant has been in operation since late 2015, working under a variable rate dictated by the requirements of SO2 consumption. NORAM Engineering and Constructors Limited performs engineering studies, conducts training, and supplies equipment at attractive prices for sulfuric acid plants. For more information, email Andrés Mahecha-Botero at firstname.lastname@example.org, email email@example.com, or call (604) 681 2030. q Sulfuric Acid Today • Spring/Summer 2018
World-class Technology for Worldwide Markets We deliver a wide range of products and services, from engineering studies through to full EPC projects for the Sulphuric Acid Industry
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Chemetics Inc., a Jacobs company
Sulfur gun advancements
By: Chuck Munro, Refinery Application Specialist, Spraying Systems Co.
In the production of sulfuric acid from molten sulfur, it is critical the sulfur is atomized into droplets so combustion occurs efficiently. The spray nozzle converts bulk sulfur into a predictable droplet size distribution, spray angle, and coverage. The most widely used nozzle in sulfuric acid production today is the BA WhirlJet® nozzle. These nozzles provide superior performance during normal operation, but when flow is decreased or turned off, the nozzles may plug because the nozzles protrude beyond the steam jacket of the sulfur gun. Without the cooling provided by the steam jacket, the sulfur flowing inside the nozzle heats up beyond the normal working temperature. This causes the sulfur viscosity to increase and plugging may occur. Operators have been compensating for this by purging the nozzles or removing the guns at the end of operation. However, if one of these actions doesn’t occur quickly, pluggage is likely. Flexibility in production rates is required to optimize sulfuric acid production. Sulfur guns are either turned on and off or flow rate is increased or decreased. To meet this requirement and minimize pluggage, a new sulfur nozzle and gun have been introduced. The CBA SulfurJet™ nozzle has the same superior performance as the BA WhirlJet nozzle. The CBA SulfurJet gun features a steam jacket that fully protects the nozzle to minimize or eliminate plugging. As sulfur passes through the CBA SulfurJet nozzle, sulfur temperature is maintained in the optimal range as production rates change.
CBA SulfurJet nozzle and CBA SulfurJet gun validation research
Computational Fluid Dynamics (CFD) was used to model heat transfer in a sulfur gun equipped with BA WhirlJet nozzles and one equipped with CBA SulfurJet nozzles. A full flow rate condition of 9,410 kg/hr (20,745 lbs/hr) sulfur at 150 psig ΔP (10 bar) was compared to a reduced flow condition of 1,745 kg/hr (3,847 lbs/hr) sulfur at 5 psig ΔP (0.35 bar). The sulfur temperature was set at 290° F (143° C) and steam in the steam jacket pipe was at 300° F (149° C) and PAGE 14
60 psig (4.1 bar). At full flow conditions for both spray nozzles, the sulfur temperature was maintained until it exited the spray nozzles. The temperature change in the BA WhirlJet nozzle was validated when the reduced flow conditions were used. Fig. 1 shows the BA WhirlJet nozzle at the reduced flow conditions. The sulfur polymerizes inside the nozzle as the temperature rises above 303.5° F (151° C) and starts to form a skin. Over time, the skin grows thicker and reaches the point where the sulfur can no longer pass through the nozzle. The CBA SulfurJet nozzle is shown in Fig. 2. At the same reduced flow condition, the sulfur temperature remains at 286° F (141° C) as it passes through the nozzle. Polymerization does not occur. As the pressure to the gun is decreased to reduce the flow rate, the velocity in the spray nozzle is also decreased. Velocity for both nozzles at the exit is reduced from approximately 15 m/sec (49.2 ft/sec) at full flow rate to approximately 5 m/sec (16.4 ft/sec) at reduced flow rate. This velocity decrease increases the heat transfer through the BA WhirlJet® nozzle, which causes the sulfur temperature to rise and eventually solidify inside the nozzle. The velocity decrease in the CBA Sulfur®Jet nozzle does not significantly impact temperature and pluggage is avoided.
Fig. 1: BA WhirlJet® nozzle at the reduced flow conditions.
The new CBA SulfurJet nozzle and CBA SulfurJet gun deliver the flexible performance required by producers. The new nozzle provides superior atomization of bulk sulfur so producers can achieve the same or better performance than the BA WhirlJet spray nozzles currently in use. In addition, the new gun design allows production rates to be adjusted with reduced risk of pluggage. Producers will be able to maximize production time, reduce maintenance time, and extend gun life. Chuck Munro has more than 20 years of experience in spray technology with Spraying Systems Co. He is a specialist in the petrochemical and chemical industries and is active in several industry committees. For more information, visit www.spray.com. q
Fig. 2: CBA SulfurJet™ nozzle.
Sulfuric Acid Today • Spring/Summer 2018
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Product News Howden expands turbo technologies portfolio
GLASGOW—Howden’s turbomachinery arm, Howden Turbo Technologies, recently boosted its portfolio with the acquisition of Siemens Turbomachinery Equipment businesses in Europe and China along with a Siemens Energy business in America. The October 2017 acquisition gives Howden a comprehensive range of compressors, blowers, fans, and now steam turbines. Established brands that have been newly acquired include Turblex® in the U.S., as well as HV-TURBO® and Kuhnle, Kopp & Kausch® in Europe. These brands have been added to Howden’s Turbo Technologies, which also includes brands like Roots®, Donkin®, and Exvel®. As a result of the acquisition new manufacturing, engineering, and service sites have been added to provide customers with more personal support locally as well as broader global service for international locations. New business sites are planned for Springfield, Missouri; Frankenthal, Germany; Helsingoer, Denmark; Mornago, Italy; and Beijing, China. Howden is a worldwide engineering company providing high quality air and gas handling products and services to the power, oil and gas, mining, and petrochemical industries. The company is undergoing a period of significant business growth with
6,000 employees in 27 countries. Howden’s global headquarters is based near Glasgow. For more information, please visit www.howden.com.
Sinochem Group’s SRU gets new DuPont™ MECS® DynaWave® scrubber
BEIJING—The Sinochem Group has successfully started up a new MECS® DynaWave® wet gas scrubbing unit installed as a Claus tail gas treatment process to reduce emissions at one of Sinochem’s refineries in China. DuPont Clean Technologies (DuPont) supplied the technology license, engineering, and proprietary equipment for the scrubbing system in 2017 to ensure the refinery would comply with stricter emission regulations on sulfur dioxide. Typically, for sulfur recovery unit (SRU) tailgas applications, the incoming gas to the scrubber can exhibit two distinct conditions: normal Claus operation and SRU bypass operation. Prior to the upgrade, SO2 emission levels during normal operation of this 165 TPD capacity SRU were at levels that are no longer permitted in the area. During bypass conditions, the SO2 even reached peaks well above the emissions measured during normal operations. Since starting the DynaWave® scrubber, Sinochem significantly reduced airborne
coatings, adhesives, sealants, and caulks, developed 23 new product formulations in 2017 to serve a variety of industries, including chemical processing. Pelseal created the formulations to refine the properties of its existing products for better VOC, higher solids content, process viscosity, or adhesion. The new formulations can be brushed, sprayed, or caulked into seams or cracks where O-rings, gaskets, and other seals cannot adequately prevent gaps or leaks. Among the new products is Pelseal® A1104, an AFLAS® fluoroelastomer caulk designed to resist alkalis, aminos, and other high pH chemicals. It also has excellent oil and fuel resistance and can withstand temperatures beyond 400 degrees F (205 degrees C). Fluoroelastomers feature extreme chemical resistance, flexibility, high abrasion resistance, and broad temperature capability. Pelseal products also bond to a variety of substrates, including most metals, concrete, glass, ceramics, other elastomers, and some plastics. In chemical processing applications, Pelseal fluoroelastomer coatings and sealants protect various substrates against acid corrosion. Common uses include concrete crack repair, expansion joint sealant, coating for metal supports and housings, and sealant for tank lids and pipe penetrations. For more information on the company’s products, visit www.Pelseal.com. q
emissions from this refinery in all operating modes. The SO2 emissions are now guaranteed to stay below 50 mg/DNm3 (corrected to 3 percent O2), even during Claus bypass conditions. Licensed by DuPont Clean Technologies, MECS® DynaWave® scrubbers work with a variety of reagents and handle multiple functions in one vessel. As such, the process makes it possible to quench the incinerated gas and remove potential particulates while absorbing the remaining acids from the Claus tail gas units. The technology also offers the flexibility of bypassing the SRU or the SRU tail gas system during maintenance and repairs, so operations can continue without interruption. Over the last 40 years, MECS® DynaWave® technology has been successfully installed at more than 400 sites around the world. DuPont Clean Technologies is a business unit of DowDuPont Specialty Products Division. For more information, visit www.cleantechnologies.dupont.com.
Pelseal Technologies introduces new liquid fluoroelastomer formulations
BENSALEM, Pa.—Pelseal Technologies, LLC, a manufacturer of more than 800 high-performance liquid fluoroelastomer
Radial Flow Gas-Gas Heat Exchangers Experience: • Introduced in 1977 • Originally developed and patented by Chemetics • Industry standard best-in-class design • More than 300 in service worldwide Features and Benefits: • Radial flow design – Minimises differential thermal stress – Eliminates dead flow zones to yield reduced fouling and corrosion – High efficiency and lower pressure drop for energy savings • Typically 20+ years leak free life with minimal maintenance • Flexible configuration allows retrofit into any plant • Advanced design options to suit demanding services
Innovative solutions for your Sulphuric Acid Plant needs Chemetics Inc.
Chemetics Inc., a Jacobs company
(headquarters) Vancouver, British Columbia, Canada Tel: +1.604.734.1200 Fax: +1.604.734.0340 email: firstname.lastname@example.org
(fabrication facility) Pickering, Ontario, Canada Tel: +1.905.619.5200 Fax: +1.905.619.5345 email: email@example.com
Sulfuric Acid Today • Spring/Summer 2018
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Five years later: Comparing single absorption plant using Cansolv vs. double absorption By: Paolo Olis, Mosaic, and Nicolas Edkins, Shell Cansolv
The production of sulfuric acid has seen numerous changes since its original deployment. In addition to increased production demands, lower emission regulations have driven changes in design of single absorption contact process sulfuric acid plants. These changes include increased equipment sizes, additional catalyst, and tail gas scrubbers. Some of these improvements, however, are not sufficient to upgrade existing facilities to new design conditions. In order to reduce sulfur dioxide emissions and ensure that acid production is as steady as possible, several additions to new or existing acid plants in the form of tail gas treatment technologies can be considered with each solution including its own set of inputs and outputs. In 1968, the Mosaic Uncle Sam, LA, facility was constructed with three sulfuric acid plants named A-, B-, and C-Trains. These plants produced sulfuric acid for use in adjacent phosphoric acid plants. The technology at the time was single absorption and of the three trains, only A-Train remains in operation today.
Modifications to A-Train were needed in 2009 in order to meet a new emissions specification. Mosaic considered several options in modifying A-Train. In addition to Cansolv, these options included: • conversion to double absorption • soda ash/caustic scrubbing • ammonia scrubbing Adding a second acid absorption tower would have reduced emissions but not to the level of the other solutions. It was also desired to install a best-available control technology (BACT). The caustic and ammonia scrubbers had a lower capital investment but much higher operating costs. These centered-on reagent costs, disposal of waste streams or byproducts, and effects on plant water balance. The prices of soda ash, caustic, ammonia, and Cansolv amine were considered in the operating costs of each option. Outlets for byproducts and waste streams were analyzed for risk and market value. The effect on water balance for the facility was also considered for its effect on the production process. After analyzing the costs and risks associated with each option, Mosaic decided to pursue the Cansolv solution. Since start-up of the plant in 2011, the unit has shown very high availability, greater then 98%. The plant has proven to be very reliable and in most cases is only shut-down because of planned turn-around work. In addition to high availability, the plant is quick and easy to start-up and shut-down when required. Minimal time is needed to get the system running and up to temperature; 1-3 hours is typical. This is a benefit for operators and allows for better emissions control during acid plant start-up.
Shell Cansolv SO2 Scrubbing System
The Cansolv SO2 Scrubbing System uses a regenerable amine-based solvent to selectively capture SO2 from flue gas or tail gas streams. Low-pressure or saturated steam is used to strip the targeted chemical compounds from solution and the solvent is returned to the absorption column for re-use. Fig. 1 shows the basic configuration. A pure water-saturated stream of SO2 exits the system and can then be used as feedstock for other industrial processes. The Amine Purification Unit (APU) is used to maintain the amine solvent quality to minimize the amount of make-up. PAGE 18
Fig. 1: Simplified Cansolv process diagram.
The system operates on the same principles as refinery amine units, of which there are hundreds, with the main difference being the low absorption process pressure and the presence of O2. Being that amine systems are familiar to the refining community, it is not surprising to see that the Cansolv SO2 Scrubbing System is being used in the industry to treat a range of refinery off-gases. In addition to refinery operations, the system has been deployed to treat metallurgical furnace off-gases as well as acid plant tail gas for the past 15 years. When looking specifically at acid plant tail gas processing, the nature of the gas to be treated makes this the easiest of applications for such a regenerable tail gas scrubbing system. The gas is generally free of contaminants and has a very low water saturation temperature favoring amine system absorption performances. Combining these conditions with the need for very little additional pressure drop, adding a Cansolv system is not only simple but also enables users to: • Decrease emissions of SO2 to levels as low as 10 ppmv, if required. • De-couple the emissions from the plant operations and catalyst aging. • Recycle the SO2 from the emissions back to the process. • Reset operational parameters to achieve desired emissions control. The following sections compare data from two sulfur burning plants. One is a single absorption acid plant using a Cansolv system as tail gas treatment (A-Train) and the other is a sulfur burning double absorption acid plant (D-Train).
stripping steam. After the SO2 is absorbed into the amine, the amine must be regenerated by stripping the SO2. This is done by increasing the temperature of the amine through countercurrent contact with steam generated in a reboiler. Increasing the steam flow to the stripper reboiler gives a more complete regeneration, improving lean loading of the amine. This makes SO2 emissions a function of the quantity of stripping steam and SO2 partial pressure in the amine (lean loading). Using this steam in the Cansolv unit decreases the available steam for other uses, such as evaporation or cogeneration. The steam used in the reboiler is the main cost in operating Cansolv. Achieving lower SO2 emissions from the Cansolv SO2 absorber tower can be as simple as increasing the specific steam consumption. The operation of Cansolv then becomes an optimization between the operating costs of the unit, changing production demands, and emissions limits. The optimum solvent concentration is a balance between the capital cost for the size of the towers and the operating cost of the unit. The optimum steam consumption is a balance between the energy cost of the stripping steam and emission limitations on plant production rate.
Emissions during normal operation
Fig. 2 shows the emissions from a single absorption acid plant equipped with a Cansolv SO2 scrubbing system. Each point represents monthly averaged emissions over a period of 5 years in units of pounds of SO2 emitted per short ton of sulfuric acid produced (lb SO2/ton acid). The design of this unit is for 1.0 lb/ton emissions. SO2 emissions from the system are so low in comparison to the environmental target that, after the third year of operation, the site decided to modify operating parameters to relax SO2 absorption. The lean amine strength is decreased in order to reduce operating costs with makeup of fresh amine solution. The effect of this change is shown in Fig. 3. Amine flow is decreased as well to reduce the amount of steam used for stripping. This steam is instead used in other areas of the plant for evaporation. Over the 5-year period, the average monthly SO2 emissions never exceed 0.65 lb/ton, continually achieving emissions below the environmental requirement of 1 lb/ton.
Cansolv operation and considerations
In a sulfur burning plant, emissions can be a rate restriction to production. This can occur when a plant is pushed beyond design rates, such as when another unit is down for repairs or turnaround. Increasing rate with the same amount of catalyst decreases the liters/ton and increases the amount of SO2 that is not converted into SO3. Using a Cansolv SO2 Scrubbing System to treat the acid plant tail gas changes the limitations in operating an acid plant thus providing maximum flexibility for operators. It may become possible to increase throughput beyond design rates without exceeding emissions. Operational set points within the Cansolv unit can be adjusted based on rate to maintain emission targets. The two main variables are the lean amine flow to the absorber tower and the steam flow to the stripper reboiler. The design of the absorber tower depends on the gas mass flux, liquid mass flux, and the ratio between the two. Increasing the liquid flow increases the slope of the operating line and increases the driving force for mass transfer. Typically, as emissions drift higher, the amine flowrate to the SO2 absorber tower is increased in order to control it. The other key variable set point within Cansolv is the
Fig. 2: Cansolv SO2 Scrubbing System emissions.
Fig. 3: Lean amine strength vs. emissions. Sulfuric Acid Today • Spring/Summer 2018
mance from a Cansolv unit versus those of a double absorption sulfuric acid plant. Again, the depicted data represents monthly averaged emissions over a period of 5 years in units of lb SO2 emitted per short ton of sulfuric acid produced. Since start-up, the Shell Cansolv unit has successfully met the design and environmental SO2 emissions targets. The day-to-day operating averages are well below emissions
Fig. 4: Double absorption emissions
targets. Fig. 6 presents the monthly averages of the SO2 concentration at the inlet and outlet of the CANSOLV SO2 unit in ppmv. The Cansolv SO2 process displays a robust ability to handle changes in SO2 inlet concentration while maintaining the desired emissions.
During a cold start-up of a sulfur burning acid plant, the converter catalyst is gradually heated up to normal operating temperatures. Before the catalyst beds are all at normal operating temperatures, the emissions in a start-up may be higher than when the plant is running stable. With a tail gas SO2 recovery system such as the Cansolv SO2 Scrubbing system, these peaks in SO2 emissions can be captured and returned to the front-end of the acid plant. This results in lower emissions overall, especially during a cold startup, and compliance to emissions regulations almost instantaneously. Fig. 7 shows several start-ups for A-Train. The depicted data for the Cansolv acid plant configuration shows inlet and outlet SO2 emissions in ppmv on a minute-by-minute basis. The unit has normal steady-state emissions in some cases after only one hour. In contrast, the SO2 emissions from the D-Train can remain above normal operating emissions and requires more care in starting up.
Fig. 4 shows the emissions from a double absorption (3:1 configuration) acid plant at the same site. Similarly, the depicted data represents monthly averaged emissions over a period of 5 years in units of lb SO2 emitted per short ton of sulfuric acid produced. As can be seen on the graph, the target emission is higher than the previous target with the Cansolv. Fig. 5 compares the emissions perfor-
Faced with a need to maintain SO2 emissions with increasingly strict environmental standards and public scrutiny, sulfuric acid plant operators have to consider several options when looking at improving performance. Several options are readily available but the use of a regenerable tail gas treatment unit such as the Shell Cansolv SO2 Scrubbing System has proven to be competitive not only in terms of SO2 emission figures but also on a project life cycle cost basis compared to alternative solutions. The added emission control flexibility can also be considered an attractive feature for regions anticipating future reduction in environmental limits. Adjustments to absorbent circulation and regeneration heat can suffice in meeting the most stringent of SO2 emission standards in the world. The absorption capability can also help operators keep emissions low when starting up a unit. In the case of Mosaic Uncle Sam, Cansolv has proven to be a good fit for the operation. Cansolv has advantages of being a regenerable system and having a much smaller effluent than other options. This reduces the interaction with other process units and provides smooth reliable operation. The operators are able to adjust parameters within Cansolv to maintain an efficient operation with changing plant rates. The ease of startup compared to a double absorption plant is a major benefit as well. q
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Fig. 7: Cansolv SO2 emission performance upon acid plant start-up.
Sulfuric Acid Today • Spring/Summer 2018
SAT 1/4 V NitroLance 2017.indd 1
1/30/17 5:26 PM
Kalium Mineração chooses SAFEHR ® for its new 150 MTPD sulfuric acid plant Kalium Mining is a Brazilian mining company based in Dores do Indaiá, in the mineral rich state of Minas Gerais. Kalium operations are currently aimed at extraction of glauconite to produce potassium and magnesium sulfate, as well as iron and aluminum oxides of high purity. After careful evaluation of the requirements of the company’s 150 MTPD 98 percent sulfuric acid plant operating at low-pressure, 8 bar steam, it was concluded that on-site acid manufacture was advantageous. Clark Solutions proposed a modular (skid mounted), sulfur burning, single absorption acid plant with hydrogen peroxide tail gas scrubbing and maximum steam generation through Clark Solutions’ SAFEHR® heat recovery technology.
Given logistics and road access limitations, the chosen configuration was modular, built on metal skids, and transported to the site. The modular plant occupies a small area of less than 8,000 square feet. The processes are divided among seven modules and eleven skids, each about the size of a standard 40foot container. One of these modules enhances the steam generation via Clark Solutions SAFEHR® technology. This technology offers safety and efficiency improvements.
Energy recovery plays an important role in sulfuric acid plants with standard heat recovery occurring in the furnace and catalytic bed steps, using wastewater reboiler, superheater, and economizers. Sulfuric acid plants, however, are long known to generate a substantial amount of heat during the SO3 absorption process. While the technologies for recovering SO3 absorption energy have evolved, the corrosion, shut-down, and explosion conPAGE 20
Figure 1: Skided plant.
cerns are still issues that limit the industry from implementing these technologies as standard. Clark Solutions SAFEHR® heat recovery technology addresses these issues, making heat recovery safer than conventional operations. In a conventional absorption tower, heat recovery relies on absorbing the SO3 into highly concentrated acid (99.0 percent) at temperatures above 180° C to produce a hot acid stream. This hot acid stream could be cooled by a boiler, generating saturated 8- to 10-bar steam instead of rejecting heat to the cooling tower. Some solutions for recovering downstream energy were proposed through the years seeking efficiency and safety. Compared to previous methods, SAFEHR® technology offers distinct advantages: it’s safer, since water and acid are never in contact, it produces more high-pressure steam, and it reduces downtime costs. SAFEHR® offers safety using a family of proprietary fluids, CS Fluids, which are non-corrosive, non-toxic, nonflammable, and non-oxidant. They also have low vapor pressures and are odorless, inert, and immiscible to acid and water, having a density between the two liquids and high boiling points (between 200-300° C). CS Fluids are used inside a closed loop as an intermediate between acid and boiler feed water streams, where the fluids cool the acid and heat the water. The CS Fluid stream oper-
ates with pressure below the adjacent ones. This way, in the event of a leak, acid or water streams flow to the closed loop where they will not mix, due to CS Fluids’ properties. In a leakage scenario, the phase separation occurs in a liquid-liquid coalescer. Even in a case where water and acid leak at the same time, separation of the three phases is possible. Controlling this process with appropriate instrumentation can
detect the leak quickly. This configuration gives the plant operators more time, allowing for a planned maintenance period, rather than having to perform an emergency shutdown and incurring the downtime costs, as with conventional heat recovery systems. A substantial advantage of SAFEHR® with regard to heat recovery is the certainty of no contamination in the water side of the system. This allows the hot water generated in the boiler side to be transformed into high pressure steam in the plant’s main boiler. Since there is no hot acid contamination risk in the system, both low pressure and high pressure boilers can be constructed using less expensive materials. At Kalium’s sulfuric acid plant, SAFEHR® technology will recover energy from the absorption tower. The 99 percent sulfuric acid goes from the tower bottom to
a fully welded heat exchanger built in 310SS that prevents corrosion on the process side. The CS Fluid stream cools the acid, which passes through a liquidliquid coalescer before finally recovering energy with boiler water in a 316L heat exchanger. The cooled acid returns to the absorption tower to be distributed over the lower packed bed promoting contact with the SO3, leading to a highly exothermic reaction heating the acid stream again. The gas continues to the tower top section where carried mist originated due to the absorption reaction. High acid vapor pressure is condensed in the tower upper packed bed using circulating acid that is collected in a collector tray. Meanwhile, the hot absorption acid accumulates in the bottom, pumped to the SAFEHR® intermediate circuit. At the water side of the intermediate circuit, CS Fluids enter the heat exchanger, generating heat for Kalium’s 8 bar steam, which is directed to the mining processes. In an acid leakage scenario, acid and CS fluid will flow to the coalescer ensuring proper phase separation. Once collected, leaked acid is drained. In the coalescer bottom, instrumentation can detect the leakage quickly. Pressure and level sensors detect water leakage.
Figure 2: Steam system schematics
Figure 3: SAFEHR® intermediate circuit schematics.
SAFEHR® is a new approach to acid production with higher energy output and lower cooling water requirements than conventional acid plants. While adding process safety and reducing corrosion risk, SAFEHR® reduces substantial energy losses. Depending on the configuration, the system can also improve the plant’s highpressure steam formation, a particularly interesting advantage for plants generating electrical energy. For more information, please visit www.clarksolutions. com.br. q Sulfuric Acid Today • Spring/Summer 2018
Wet electrostatic precipitators for optimal sulfuric acid gas cleaning
By: Gary Siegel, Marketing Director, Beltran Technologies, Inc.
The versatile mineral sulfuric acid is both the world’s most highly used chemical and the one with the highest production volume. Its use as a primary and intermediate raw material spans hundreds of industrial production processes. Agricultural fertilizer manufacturing, just one of the end uses of sulfuric acid, consumes 70 percent of H2S04 production. The growth of the fertilizer industry alone has continued to drive the demand for the purest form of sulfuric acid. The sulfuric acid plant is designed to capture and commercialize industrial quality sulfuric acid from off-gasses produced by mining/metallurgical roasting, smelting, and refining plant operations. Before entering an acid plant’s drying tower, smelter and refinery off-gasses must be cleaned of impurities, such as sulfuric acid mists, particulate, submicron particulate, condensable organic compounds, etc. These impurities must be removed partly to prevent corrosion, fouling, and plugging in downstream compressors, catalyst beds, and other sensitive equipment, but most important to be sure the sulfuric acid end product is pure and free of black contaminated acid. To achieve pure sulfuric acid, plant engineers specify that WESP (Wet Electrostatic Precipitator) systems be employed for their advanced technology and ability to remove up to 99.9 percent of submicron particulates and to clean flue gases and acid mist in the gas stream. Aside from the WESP’s collection efficiency, other advantages include: • Cleaning greater volumes of specified source gases with faster through speeds with minimal impedance and a low pressure drop. • Achieving the greatest reductions in costs related to capital investment, operating costs, energy consumption, system maintenance, and long-term equipment replacement.
Beltran WESP installation at Mopani Copper Mines cleans large volumes of source gases.
The Beltran Wet Electrostatic Precipitator
After considerable research and development, Beltran Technologies, Inc. designs, engineers, and builds a unique wet electrostatic precipitator with a tubular design component. The Beltran WESP is designed using a vertical flow upward through the precipitator with continuous aqueous flushing. The system is usually designed with two sets of spray headers. The first set continually cools and saturates the flue gases. The second set, positioned at the top and directly below the collector, wash the collector and electrodes, operating on a periodic and as needed basis. The continuous flushing greatly minimizes the problem of re-entrainment of particles from the collection surfaces back into the gas streams that traditional dry-operating electrostatic precipitators have to deal with due to the use of mechanical or acoustical rapping units. The Beltran WESP design eliminates the need for rappers. Beltran advanced WESPs are designed around a multistage system of ionizing rods with proprietary PAGE 22
star-shaped discharge points enclosed within square or
hexagonal tubes. Unlike the common round type, the
square or hexagonal tubes are much more space efficient
and produce a greater collection efficiency in a given volume. The tubes are lined with grounded collection surfaces. This unique electrode geometry generates a corona field 4-5 times stronger than ordinary wet or
dry electrostatic precipitators. The multistage charging
configuration also avoids corona quenching due to high particulate densities, and assures maximum corona field strength with a minimum energy load. As flue gas travels through the tubular array, the corona fields induce a negative charge propelling particulates and submicron particulates plus acid mists toward the collection surfaces where they adhere as cleaned gas is passed through. The surfaces are cleaned of residues by the recirculating water sprays. A heated purge-air stream should be used to keep the high-voltage insulators dry, reducing maintenance costs. Since fine and submicron particulate have very little significant mass, they pass through scrubbers but are captured with remarkable efficiency by advanced WESP systems. Beltran Technologies, Inc. has supplied two Beltran tubular WESPs to Mopani Copper Mines, Kitwe, Zambia, for its copper smelter acid plant. The gas cleaning plant was engineered, supplied, and erected by MDEEL (a subsidiary of MECS), of Mumbai, India. The two 10 ft by 8 ft WESP modules are operating in parallel and designed to reduce smelter emissions by 99.55 percent before the gas enters the sulfuric acid plant. The WESPs are handling a smelter gas flow rate of 39,000 Nm3/hr and 25 degrees C. The housings of the WESPs are FRP, with conductive graphite composite collectors and C-276 internals. Beltran Technologies, Inc., has more than 1,000 installations and has installed WESP systems at major sulfuric acid plants worldwide. For more information visit www.beltrantechnologies.com, call 718-338-3311, or email email@example.com. q Sulfuric Acid Today • Spring/Summer 2018
Non-intrusive flow and concentration of Sulfuric Acid and mass flow of Molten Sulfur
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Impala Platinum smelter facility off-gas processing
By: J.I. Ramsay, Lesedi Nuclear Services Ltd., and F. Jennes, DuPont Clean Technologies
Impala Platinum Holdings Limited, the world’s second largest platinum producer, operates a large integrated mining, concentrating, and smelting complex in the Rustenburg area of South Africa. Owing to the operation’s large scale, efficient capture and treatment of off-gas from the furnaces and converters poses a significant environmental challenge. A few years ago, the company increased its smelter capacity by almost 50 percent to 2.65 million ounces of platinum per year. The expansion significantly raised off-gas, which had to be captured and treated. The off-gas treatment section of the project was awarded to Powertech IST Industrial (now Lesedi Nuclear Services) in collaboration with MECS, Inc., a wholly owned subsidiary of DuPont Clean Technologies. The scope involved expanding and upgrading some of the existing gas treatment infrastructure to handle the increased off-gas volumes. In addition, several new operations were added to improve desulfurization efficiency and reduce atmospheric emissions of SO2 and acid mist. A new fugitive gas capture and treatment system was also added. The project, commissioned in 2009, spanned 2½ years.
Ore is mined near the smelting operation and transported via rail to two concentrator plants for milling. The milled ore is introduced to flotation banks where concentrate containing precious metals is separated from the non-valuable tails, which are deposited onto a tailing dam. The concentrate is pumped as slurry to the smelter, where it is dried to less than 1 percent moisture, smelted in the furnaces to remove gangue materials (predominantly silica) in the slag, and the matte converted in Peirce-Smith converters to remove sulfur and iron. Two primary off-gas streams are generated within the smelter: furnace off-gas and converter off-gas. The furnace off-gas, from the two six-in-line electric smelting furnaces,
Fig. 1: Impala Platinum simplified flow diagram.
Fig. 2: Abatement equipment before expansion. PAGE 24
Furnace off-gases Converter off-gases
Flow rate (Nm³/h)
SO2 conc. (percent v/v)
SO2 mass (kg/h)
SO2 captured (kg/h) 900 (Sulfacid® plant) 4 840 (acid plant) 9 400 (acid plant)
SO2 emitted to atmosphere (kg/h) 200 100 400
Table 1: SO2 emitted by Sulfacid® and sulfuric acid plants, and SO2 captured, before expansion project.
has a relatively low SO2 concentration (0.9 percent) and high dust load (65 g/Nm³). The gases are ducted to three dry electrostatic precipitators (ESPs) for dust capture and recovery and then cooled and saturated in a quench tower. Following quenching, the gases are treated in a Sulfacid® plant, where most of the SO2 is captured and converted into weak sulfuric acid (10–15 wt percent). The tail-gas is then discharged from the Sulfacid® plant stack. The converter off-gas, from the six Peirce-Smith converters, has a relatively high SO2 concentration (4–8 percent) and low dust load (2 g/Nm³). The gases are ducted to a radial flow scrubber, where they are quench-cooled and the majority of the dust is captured. Further cooling and condensation takes place in a star cooler. Dust and acid mist are further reduced by two primary and one secondary wet electrostatic precipitators (WESPs) in series. The gas then passes into a sulfuric acid plant where the majority of the SO2 is captured and converted into 98.5 wt percent sulfuric acid. The tail-gases are then discharged from the acid plant stack. In addition, fugitive gas is released from both processes. Table 1 provides data on the SO2 emissions from the furnace and converter operations prior to the upgrade. The majority of the SO2 emissions occurred via the sulfuric acid plant stack. Impala operates a ‘single-contact’ sulfuric acid
plant, which limits SO2 conversion to around 96–98 percent, depending on the gas strength. Because of this, the concentration of unconverted SO2 discharged from the stack was high and variable, typically ranging from 1,000 to 3,000 ppm by volume (0.1–0.3percent v/v). Unconverted SO2 from the Sulfacid® plant was emitted from the plant’s stack. The design of the plant limited conversion of SO2 to around 82 percent, resulting in discharged tail-gas concentration of about 900 ppm (0.09 percent v/v). To comply with the requirements of the new Air Quality Act, the SO2 concentration in the stack gases had to be reduced to < 100 ppm (0.01 percent v/v). Acid mist emissions from the sulfuric acid plant stack were not uncommon. These emissions resulted in a persistent blue plume that was visible from a distance and adversely affected public perception of the smelter complex. The cyclical nature of the converter operation caused rapidly fluctuating gas strengths, which made stable operation of the acid plant difficult. In addition, prolonged periods of heavy emissions occurred whenever the plant started up. To solve the problem, Impala required a system that could capture acid mist and limit future emissions to < 24.5 mg/Nm3. At this level, stack discharge opacity due to acid mist would be negligible. Dust emissions to the atmosphere via the sulfuric acid and Sulfacid® plant stacks were already very low and well within the environmental limits. However, the large quantity of dust in the furnace off-gases contains significant value: unsmelted concentrate on top of the molten bath. The existing dust capture system consisted of three relatively inefficient ESPs, which limited dust recovery and contributed to fouling of the downstream Sulfacid® plant catalyst beds. Impala required a more efficient dust collection and recycle system that would limit dust emissions to < 30 mg/Nm3. In order to minimize the smelter’s total SO2 emissions and improve air quality in the converter aisle, fugitive gases from the furnace matte-tapping stations and the converters needed to be captured and treated. To achieve this, a new fugitive extraction and treatment system for SO2 and dust was required.
Fig. 3: Abatement equipment after the expansion. Sulfuric Acid Today • Spring/Summer 2018
Greater smelter capacity increased off-gas volumes, which were handled by: • Increasing drying capacity and dried concentrate storage capacity. • Converting the cold standby furnace into a continuously operable furnace (i.e. converting from a two-furnace to a three-furnace operation). • Completely upgrading the furnace off-gas train (including the ESP and Sulfacid® plant). • Adding a Peirce-Smith converter. • Completely upgrading the converter off-gas train and increasing sulfuric acid plant capacity. • Adding tail-gas scrubbing at the Sulfacid® and sulfuric acid plants. • Capturing and treating fugitive gas. Existing off-gas infrastructure had to be upgraded and expanded to accommodate 50 percent and 25 percent increases in furnace and converter off-gas flows respectively. Also, additional unit operations were employed to improve desulfurization efficiency and reduce emissions of SO2 and acid mist. A new fugitive gas capture and treatment process was also installed. In the expanded off-gas treatment process, each of the gas streams is treated separately. The gases are then combined and treated for final SO2 removal. Originally, fugitive gases from furnace and converter operations were combined and treated for SO2 and dust removal. However, fugitive gas capture from the furnace was decommissioned to maximize collection of fugitive gas from the converter. The original post-expansion process flow is illustrated in Fig. 3. Furnace off-gas treatment Furnace off-gas treatment is depicted in the upper portion of Fig. 3. Furnace gases are ducted to a hot ESP for dust removal and recovery. The de-dusted gases are then cooled and saturated in a quench tower before treatment in an expanded Sulfacid® plant for SO2 removal. To accommodate the increased gas flow and achieve the required collection efficiency, a new single ESP was installed to replace three older units. The new ESP is a 4-field unit designed to reduce the dust load in the off-gases from 54 g/ Nm3 to less than 30 mg/Nm3 under conditions where only three of the four fields are energized. The effective collection efficiency is 99.95 percent. The de-dusted gas stream exits the ESP at a temperature of 300–350°C, passes through the furnace ID fan, and is ducted to a venturi-type quench tower that cools and saturates the gas stream prior to the Sulfacid® plant. Cooling is achieved by continuous circulation and spraying of weak sulfuric acid into the hot gas stream. Water is evaporated, the gas is cooled and saturated, and the weak acid from the Sulfacid® process is concentrated. Quench-cooling of the hot furnace gases also desublimates some volatilized metals and creates acid mist. The weak acid is supplied to an adjacent fertilizer plant or, when necessary, neutralized prior to disposal. The original Sulfacid® plant, built in 2002, was developed to recover SO2 from weak gas streams to produce dilute sulfuric acid (10–15 wt percent). The plant comprised eight 12.7 m long, 4.5 m diameter cylindrical FRP reactor pods filled with activated carbon. To accommodate the increased gas throughput, an additional four reactors were installed as part of the upgrade. The Sulfacid® process allows SO2, H2O, and O2 in process gases to react in the presence of an activated carbon catalyst to produce weak sulfuric acid. For effective operation, the feed gas is saturated with water vapor ranging from 30 to 80°C. The quenched gases are diluted with air prior to entering the reactor pods to ensure that the SO2 concentration is always below the maximum of 0.5percent. Sulfuric Acid Today • Spring/Summer 2018
Combined gas to tail-gas scrubber
Flow rate (Nm³/h)
SO2 conc. (percent v/v)
SO2 mass (kg/h)
SO2 captured (kg/h)
SO2 emitted to atmosphere (kg/h)
166 400 (max.)
Table 2: SO2 emitted by DynaWave® tail-gas scrubber, and SO2 captured (design basis).
Converter off-gas treatment Converter gas treatment is illustrated in the lower portion of Fig. 3. The addition of a new, large converter increased the maximum primary off-gas flow by 25 percent, to 54,000 Nm3/h (dry). The SO2 concentration in the gases, although highly variable (4–8 percent v/v), is high enough for the production of sulfuric acid. The dust load (2 g/Nm3) is significantly lower than in the furnace off-gases. Since converter gases are used for the production of sulfuric acid, it is vital that any impurities that can lead to either contamination of the acid or fouling of the converter catalyst beds be removed. Furthermore, since the plant produces a concentrated acid (98.5 wt percent), the gas must be cooled to a certain temperature to balance the water content, depending on the SO2 concentration. The Impala gas cooling and cleaning plant comprises several unit operations: gas quenching and scrubbing in a radial flow scrubber (RFS), indirect gas cooling in two star coolers arranged in series, and dust and acid mist removal in primary and secondary WESPs. Converter off-gases up to 400°C are quench-cooled in an RFS. In the RFS, a co-current spray of recirculated weak acid saturates and cools the gases to about 45–50°C. The scrubber also reduces the incoming dust load from around 2 g/Nm3 to less than 200 mg/Nm3. To maintain constant scrubbing performance under variable flow conditions, the pressure drop across the scrubber is automatically controlled at approximately 8 kPa by an adjustable plunger in the scrubber throat. Process gases from the RFS exit through a 2-stage chevron droplet eliminator before passing through the RFS ID fan and into the star coolers. The star cooler arrangement at Impala consists of two identical units in series, each with two stacked shell-and-tube bundles in series. Gas cooling is achieved by a combination of plant cooling water and chilled water. By using chilled water in the final bundle, it is possible to produce 98.5 percent acid at low converter gas concentrations even during hot and humid days. Potable water is continuously added to the sump of the secondary cooler to account for purge and evaporation losses across the whole gas cooling system. The cool saturated process gases from the outlet of the secondary cooler are ducted to primary and secondary WESPs, which reduce the dust loading and acid mist concentration in the gas to very low levels. The WESP arrangement at Impala comprises two parallel primary WESPs in series with two parallel secondary WESPs. The WESPs are of the proven compact bundle design. The inlet gas is routed through the precipitator tubes, with discharge electrodes suspended centrally, down the vertical axis of each tube. Applying a high voltage produces an electric field that charges the acid mist and dust particles, causing them to migrate to the collection electrodes. This system was designed to reduce acid mist loading from 5,900 mg/Nm3 to < 6 mg/Nm3 (99.9 percent removal), and dust loading from a maximum of 600 mg/Nm3 to < 2 mg/Nm3 (99.7 percent removal). The sulfuric acid plant at Impala is a single-contact plant with four catalyst beds. Gas dehydration is carried out in a packed tower in which the gas rises countercurrent to a descending flow of strong sulfuric acid. The ‘drying’ acid absorbs the water vapor remaining in the gas after it leaves the gas cleaning and cooling section of the plant and so prevents corrosion by wet SO2 before converter, and by sulfuric acid after the converter. Drying the gas also helps maintain a clear discharge stack by minimizing acid mist formation. In the
drying process, the water vapor content of the gas is typically reduced to about 50 mg/Nm3. H2O(g) + H2SO4(l) [strong acid] —> H2SO4(l) [slightly diluted acid] + H2O(l) Oxidation or conversion of SO2 to SO3 is handled in a converter where the SO2 and O2 in the gas react in the presence of a molten vanadium-based catalyst to form SO3, according to the following, highly exothermic, reversible reaction: SO2(g) + ½ O2(g) <—> SO3(g) + Heat Catalyst The SO3-rich gas produced in the converter passes through a packed absorption tower in which it rises countercurrent to a descending flow of 98.5 percent sulfuric acid. The SO3 is absorbed into the acid by reaction with the water contained in the strong acid. Dilution water is continuously added to maintain the acid strength at 98.5 wt percent. SO3(g) + H2O(l) + H2SO4(l) —> H2SO4(l) 98.5 percent acid —> 98.5 percent acid The purpose of the new quench-mist eliminator is to prevent any acid mist or unabsorbed SO3 from the acid plant from passing through the tail-gas scrubber and venting to the atmosphere. The gases leaving the absorption tower of the sulfuric acid plant are quenched by a recirculating stream of weak acid to hydrolyze any unabsorbed SO3 to sulfuric acid mist. The hydrolyzed SO3, as well as any acid mist carried over from the absorption column, is then captured and removed in fiber-bed mist eliminator elements. The quench section is based on the MECS® DynaWave® reverse-jet scrubbing technology. Continued on page 26
Quench-mist eliminator vessel. PAGE 25
Furnace and converter primary off-gases Total SO2 mass (kg/h)
SO2 captured Sulfacid® plant (kg/h)
SO2 captured acid plant (kg/h)
SO2 captured tail-gas scrubber (kg/h)
Total SO2 captured (kg/h)
Overall SO2 capture efficiency (percent)
11 00 (max.)
14 000 (max.)
Table 3: SO2 captured before and after the expansion project. Continued from page 25
Combined tail-gas treatment The furnace off-gases from the Sulfacid® plant and the converter off-gases exiting the mist eliminator vessel are combined upstream of the new tail-gas scrubber. The tail-gas scrubber is the final SO2 removal stage in the gas path and is required to reduce SO2 concentration to < 100 ppm (v/v) before discharge. It uses a wet-lime forced oxidation (WLFO) scrubbing process, which produces calcium sulfate di-hydrate (gypsum) as a reaction product. In the WLFO process, the SO2 dissolved in the recirculated slurry reacts with dissolved lime to form calcium sulfite hemihydrate (CaSO3.½H2O) according to the following reaction: SO2 + Ca(OH)2 —> CaSO3.½H2O + ½H2O Oxidation air is bubbled through the slurry to convert CaSO3.½H2O to gypsum (CaSO4.2H2O) according to the following reaction: CaSO3.½H2O + ½ O2 + 1½H2O —> CaSO4.2H2O The gypsum produced from WLFO systems is more stable than calcium sulfite and can therefore be disposed of in landfills. It is also, in many cases, suitable for use as a cement additive or in wallboard production.
DynaWave® tail-gas scrubber (5.5m diameter). PAGE 26
The WLFO system installed at Impala is based on the MECS® DynaWave® reversejet scrubbing technology. The heart of this system is the reverse-jet gas-slurry contactor, which creates a zone of intense mixing (froth zone). Incoming gas enters through the top of a vertical duct (inlet barrel) and encounters the circulation liquor, which is injected vertically upwards through three large-bore injectors (reverse-jet nozzles). A standing wave is created at the point where the liquid is reversed by the gas. In this zone, a very high rate of liquid surface renewal occurs, creating a highly efficient environment for simultaneous gas quenching, particulate scrubbing, and SO2 absorption (Table 2). Purging of slurry from the scrubber to the dewatering plant is controlled to maintain the scrubber solids concentration in the correct range. The Impala tail-gas and fugitive scrubbers use lime as the alkaline absorbent for SO2 removal. Fugitive gases To minimize the smelter’s total SO2 emissions and improve air quality in the converter aisle, fugitive gases from the furnace matte-tapping stations and the converters needed to be captured and treated. Extraction hoods were installed at the matte tapping platforms of all three furnaces to capture both launder off-gases and ladle off-gases. These were later decommissioned to maximize suction for the secondary converter off-gases. The converter fugitive capture system was limited to a new secondary hood on the new large converter. Fugitive gas from the furnaces and converters are extracted in separate ducts before being combined into a common duct upstream of the ID extraction fans. The gases are then discharged from the fans into a 2-stage fugitive gas scrubber for removal of SO2 and dust, and then released via a stack mounted on top of the scrubber. The fugitive gas scrubber was designed for the removal of both SO2 and dust. The system is a WLFO process producing byproduct gypsum, again based on the MECS® DynaWave® reverse-jet technology. The requirements of SO2 and dust emissions were < 100 ppm (v/v) and < 50 mg/Nm3 respectively. The design of the fugitive gas scrubber differed from the tail-gas scrubber in that two stages of reverse-jet scrubbing were employed. The tail-gas scrubber treats an essentially ‘dust-free’ gas so a single contact stage is sufficient. The fugitive scrubber, how-
ever, requires a second stage to achieve high removal efficiencies of the very fine dust. The operation and control of the fugitive gas scrubber is similar to the tail-gas scrubber. Lime slurry is automatically added to the system to maintain the pH of the slurry in the optimum range. Purging of slurry from the scrubber to the dewatering plant is controlled to maintain the scrubber solids concentration in the correct range. Makeup water is automatically added to replace evaporation and other losses. Both sets of droplet eliminators are periodically washed with potable water to minimize solids buildup.
DynaWave® fugitive gas scrubber.
Under conditions of maximum converter gas strength and prior to the expansion project, overall SO2 capture from furnace and converter primary off-gases was approximately 94.6 percent. Following the expansion project and the installation of the tail-gas scrubber, SO2 capture was increased to 99.7 percent (Table 3). Despite an increase in off-gas volumes, SO2 emission to atmosphere decreased from approximately 595 kg/h to 44 kg/h. Current emissions are now around 8 percent of what they were prior to the expansion project. Under conditions of maximum converter gas strength, the consumption of lime (CaO) is approximately 730 kg/h and the mass of gypsum produced is 2015 kg/h (dry basis). The purity of the product gypsum is approximately 96 percent (dry basis). The installation of the quench-mist eliminator has been very effective in reducing stack emission opacity caused by acid mist. Furthermore, the heavy emissions that contributed to poor public perception of the smelter have been eliminated. During times of unstable acid plant operation, a cloud of acid mist is visible through the upstream viewing ports. However, after quenching and passage through the mist eliminator elements, the gas viewed through the downstream ports is optically clear. The off-gas abatement system has been in operation for nine years with almost no downtime and emissions well below target. Initially there was a blockage in the slaking tank every two months. This was resolved by installing a dust filter. No scaling has occurred inside the scrubbers, although the pH occasionally rose to 9. Only one of the reverse-jet nozzles has been replaced to date (due to a ceramic tile falling on it). No signs of wear have been detected on other nozzles and no blockages have occurred.
350 mm reverse-jet nozzle.
The upgrade of the Impala smelter facility was executed successfully, without any major safety incidents. The off-gas abatement system has been in operation for nine years and was able to handle challenging conditions. The upgraded off-gas abatement system has kept SO2 concentrations at the stack below the new future air quality act requirements (<100 ppm v/v). q ACKNOWLEDGEMENTS
The authors thank Impala Platinum
Ltd, Lesedi Nuclear Services Ltd for permission to publish this article. REFERENCES 1.
Graham, F. and de Bruin, N. (Not dated). Impala Platinum Rustenburg Smelter
quality while increasing capacity. 2.
Jones, R.T. (2012). Platinum smelting in South Africa. http://www.mintek. co.za/Pyromet/Platinum/Platinum.htm
3. Impala (2009). Report
Development upgrade air
reports/2009/sd/smelter.htm 4. Westcott G, Tacke M, Schoeman N, Morgan N: Impala Platinum Smelter, Rustenburg – an integrated smelter off-gas
SAIMM, vol 107, May 2007.
Sulfuric Acid Today • Spring/Summer 2018
Cleaning of the sulfur recovery unit is essential to efficiency By: Tim Meyer, general manager industrial division, Conco Services Corp.
The Sulfur Recovery Unit (SRU) is an extremely important component in many industrial settings including oil refining and gas processing plants. Hydrogen sulfide (H2S) is a by-product of high-sulfur crude oil and natural gas processing, and is a very toxic gas at high concentrations. Because hydrogen sulfide is defined as both an environmental and industrial pollutant, plants are required to recover between 95 and 99.9 percent of total sulfur that arrives at the SRU. The SRU converts hydrogen sulfide to nontoxic elemental sulfur. Without the SRU, the toxicological and environmental consequences of H2S would be harsh and severe, including acid rain and ground level sulfur dioxide contamination. Because the stakes are so high for refineries and other plants that must manage H2S, the SRU must be well maintained, reliable, and able to meet the required recovery efficiency for the long term. The proper performance of SRUs within a process can affect the cost of the final product, or even the production rate. Unfortunately, SRUs are prone to fouling. The nature of the fouling depends on the fluids flowing within and over the tubes;
and the reduction in heat transfer that results almost invariably has an impact on product cost. To reduce this impact, SRU performance should be intelligently monitored and the SRU cleaned at intervals based on optimal economic criteria.
Sulfur Recovery Unit fouling and its effects
Just as heat exchangers and condensers are prone to fouling, so, too, are Sulfur Recovery Units. In most cases, it is unlikely that fouling is exclusively due to a single mechanism, but in many situations, one mechanism will be dominant. Fouling tends to increase over time, with the trajectory being very site specific. Fouling has an economic impact, and determining when to clean often requires striking a balance between maximizing the quantity of finished product from the process and its cost. The sulfur buildup that accumulates in the tubes of SRUs can be hard and chalky, and it is not uncommon for tubes to be wholly obstructed. SRUs are a part of a process and when fouling occurs, the temperature of the heat-
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ing fluid must rise if the same amount of heat is to be transferred through the tubes. This temperature rise must be associated either with an increase in the total energy input to the process or a reduction in production rate, both of which represent a cost incurred due to fouling. Clearly, in order to make intelligent economic decisions, these costs must be quantified at a series of points in time and, preferably, in relation to the fouling resistance as well.
Methods for cleaning the Sulfur Recovery Unit
Options for cleaning SRUs include: • TruFit® tube cleaners • Liquid nitrogen • HydroDrill™ Improving the performance of fouled SRUs requires that the tubes be cleaned periodically. Each time the tube deposits are removed, the tube surfaces are returned almost to bare metal, providing the tube itself a new life cycle.
TruFit® mechanical tube cleaning
The most frequently chosen and fastest method to address light to moderate SRU fouling is TruFit mechanical tube cleaning. The TruFit system is an offline method in which the mechanical tube cleaner is propelled through the tube with low-pressure water, flushing the debris out of the tube, leaving the tube free and clear of fouling. Fig. 1 shows a mechanical tube cleaner in action. For off-line mechanical cleaning, it is essential to select the appropriate cleaner. The TruFit cleaner manufactured by Conco
Fig. 1: TruFit® mechanical tube cleaner.
has proven to be the most effective.
Sulfur Recovery Units with more moderate to heavy fouling have been successfully cleaned with the Conco HydroDrill system. The HydroDrill uses a brush or drill bit mounted to the tip of a rotating
Fig. 2: HydroDrill™ cleaning with rotating brush or drill bit. PAGE 28
extension or Kelly Rod, and as the rod rotates, the unit pumps water through the rod to the weep holes, flushing away hardened deposits as they are loosened. Fig. 2 illustrates the action of the HydroDrill. HydroDrill cleaning is safe for all tube materials. Drill bits are sized to be 0.005 inches below the minimum tube I.D., and they feature long shanks to ensure that the axis of the bit and the axis of the tube are in complete alignment. The bits are designed with carbide tips on the leading edge only and with rounded corners to ensure that no sharp edges directly impact the tube wall. The small onsite footprint of the cleaning system (50 to 100 sq. ft.) makes it an attractive and workable solution.
Nitrolance™ liquid nitrogen cleaning
When SRU fouling is heavy to severe, and tubes are filled and obstructed with deposition, Nitrolance liquid nitrogen cleaning can be used to restore flow. Using the power of liquid nitrogen, a super-cooled cryogenic jet emerges from the Nitrolance nozzle, filling and expanding the cracks and crevices of the deposit, and causing rapid breakup of all debris within the tube. Fig. 3 demonstrates the mechanics of the Nitrolance nozzle.
Fig. 3: Nitrolance™ liquid nitrogen cleaning.
Liquid nitrogen cleaning is safe and ideally suited for the most challenging fouling scenarios, yielding quicker turnarounds for critical path components. And because liquid nitrogen readily dissipates, only the removed deposit is left behind, saving the plant thousands of dollars in cleanup costs. The residual sulfur deposition can be vacuumed away, leaving the SRU in as-new condition.
Maintenance for life
There has never been a better time to consider maintenance options for the Sulfur Recovery Unit. These units are prone to fouling, but with routine assessments and periodic cleaning interventions, the SRU can maintain its reliability and efficiency for the long-term. There is a cleaning protocol for every fouling scenario, and all are safe and effective. For more information, visit www.conco.net or contact Tim Meyer at tmeyer@ conco.net. q Sulfuric Acid Today • Spring/Summer 2018
lessons learned: Case histories from the sulfuric acid industry Don’t forget the sulfur pump
Recently, several sulfur burning plants experienced the same problem when their plant shut down. The sulfur pump was not shut off and in a couple of cases, the interlocks failed. One case had a foot of sulfur pooled at the bottom of the sulfur burner. If you are unaware, this can sublime the sulfur and cause sulfur vapor to condense as a solid on mist eliminators and in the packing. This can, in extreme cases, require candle replacement and vacuuming and removing of packing. Lesson Learned: Periodically check the interlocks and have the field operators make sure the sulfur pump is turned off when the plant is shut down.
Acid pipeline precautions
A newly installed sulfuric acid pipeline is a few miles long. A hazard review revealed the potential for an acid spill on the ground if the pipe leaks. To minimize the spill, the engineer installed block valves in the line for isolation. The engineer changed the valves to a smaller size to reduce costs, not realizing the size and lack of vents in the line prohibited the pipe from filling with acid. The pipeline leaked after having been in service only a short time. Lesson Learned: Smaller valves work as reducers, so air entrapment between them causes excessive erosion corrosion.
Over-insulating a sulfur furnace is not cool
A 25-year-old sulfur furnace was scheduled for re-insulation. Thinking more is better, the 1-inch of “Temp-
Mat” was replaced with three inches of calcium silicate insulation and aluminum jacketing. However, the failing insulation had allowed moisture to reach the furnace shell, causing thinning. Over insulation caused a dramatic rise in temperature and the shell ripped open. Lesson Learned: Thorough understanding of the total condition with a proper engineering study of a project is imperative before beginning a job. Proper front-end loading could have prevented this incident.
Acid strength control
During an oil fire following a turnaround, the fresh acid transferred to the plant was set up to come into the final absorption tower system and exported from the final tank to the drying system. The acid in the interpass system became weak due to moisture from the combustion process. In the months following, the IPA piping experienced more leaks than usual. Lesson Learned: Develop standard operating procedures for acid strength control during plant start-up. Include transfer of acid between plants. Conduct training sessions on strength control for all shifts.
Analyze your instruments
During a turnaround start-up, a plant had a visible stack. A common problem, it cleared up and later returned with no obvious indication of operating parameters outside the established limits. The dilution water flow meter indicated a flow and both the IPA and FAT concentration analyzers indicated acid strengths returning to normal. An investigation found the acid to be strong–it had increased
to 100 percent and continued to increase. Lesson Learned: Concentration analyzers indicate decreasing strength as the actual strength increases above 100 percent since conductivity reverses direction at 100 percent. Also, instruments may not be functioning properly after a major shutdown.
Heat exchanger tube failure
A heat exchanger in 99 percent sulfuric acid service had a major tube (waterside) failure. Removing the exchanger and performing NDT analysis determined that an erosion corrosion mechanism had eroded the outside of certain tubes near the water inlet. The wear pattern was most severe at the trailing edges of the cooling water supply deflector plate. Lesson Learned: To prevent further problems with this and similar exchangers, drill several ½-inch holes in the plates to diffuse the flow and lower the velocity around the edges.
The weld between the tubesheet and the shell failed along an arc at the top of the tubesheet. This allowed water to enter the gas side of the plant. It was determined the weld cracking was due to the presence of a vapor space in the top of the boiler. The boiler riser nozzles extended into the boiler and this created the vapor space. The failure was accompanied with loss in thickness of the tubesheet in this zone. Lesson Learned: Ensure that riser nozzles are coped and fitted flush with the I.D. of the boiler shell. q
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Looking out: a quick guide to establishing an effective jobsite safety review program By: Patrick Ferguson, Safety Coordinator, VIP International
There are many tools in the arsenal that improve safety performance during maintenance operations. The hierarchy of controls (elimination, substitution, engineering, administrative, and PPE) can be a great tool used to approach safety during job tasks. When used properly, it can effectively reduce or completely eliminate the hazards faced in the workplace. One aspect of administrative controls that can be easily overlooked is supervision. When one thinks of supervision, they may characteristically think of a person standing over a coworkers’s shoulder or telling someone how to perform a task. In reality, supervision is not a title dedicated to any one particular individual when it comes to safety. Today, every person should be empowered to be a supervisor on the job when it concerns safety. That empowerment can come easily by performing jobsite safety reviews. Jobsite safety reviews are known by many official labels in industry: EHS audit, safety observation card, safety visit, EHS walkthrough, etc. The list of terms could go on forever and is not important in the grand scheme of things. More important is the quality of the action itself. Jobsite safety re-
views can be as informal as a worker simply taking notes around an active jobsite, or as official as a team stopping the work to interview all workers and extensively document all findings. Since the intentions are to improve the existing environment, neither is necessarily better or worse as long as the
“ It is important when empowering every
person with the opportunity to conduct jobsite safety reviews that each has a framework to follow, a path to move forward, and achievable goals.
quality is present and there is a positive outcome as it relates to safety. It is important when empowering every person with the opportunity to conduct jobsite safety reviews that each has a
Sulfuric Acid A s s o c i a t e s
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framework to follow, a path to move forward, and achievable goals. The quality of the jobsite safety review will be severely diminished if any of these are lacking or absent. Tailored checklists, guided cards, and other developed forms can assist in the process of establishing a needs-based
framework. Encouraging self-participation, scheduling formal reviews, or performing unannounced visits are methods of ensuring that the program has variation and continues to move forward. Any results or participating expectations should be within reason, particularly when initially putting jobsite safety reviews into practice. Baseline results and the evolution of program needs will dictate achievable goals. Scheduling formal training for reviewers is one option that can ensure uniformity in data collection and control over interactions. Casual programs where less experienced reviewers shadow more experienced reviewers may allow for interactions on a more personal level and enable some data collection that may have otherwise been overlooked. Both the least and most experienced of the industry can bring vital insight to the table with the right formula. The term ‘fresh eyes’ is used a lot in industry when describing people who perform a jobsite safety review on a task which they may never have seen or had knowledge. Those ‘fresh eyes’ can make just as much, if not more, of a difference than a seasoned veteran. There are many different actions that occur during a jobsite safety review. The reviewer is going to observe the jobsite— observations can be made on the condition of the area despite a lack of actual work being performed. There may be conditions that need to be improved or adjusted immediately but there may also be questions that are noted for later interactions with workers. If work is taking place when the review is performed, there will undoubtedly be interactions with the workers. It is important that reviewers identify themselves immediately and attempt to establish an open dialogue. If the reviewer is
the worker completing a guided card in the workplace, they should be given ample time to make their observations and any other support they may require to complete a quality review. If any opportunities for improvement are present, the reviewer should communicate them to the responsible parties so they may be addressed immediately. Certain situations will require additional review and decision making as to whether a certain action or task should continue. Reviewers should always recognize the more positive aspects of the work taking place as the review progresses, and emphasis should also be placed on ending reviews on a positive note. As review data is compiled, it should be categorized and analyzed for trends. During maintenance operations, running totals in certain categories can be communicated with transparency to all parties involved. Depending on the needs of the end user(s), trends should highlight where opportunities for additional improvements can be made. This will allow work groups to determine where additional emphasis should be placed or if they need to make immediate changes in operations. Longterm goals will most likely be determined and modified as the data pool gets larger. A jobsite safety review program should always be evaluated. The effectiveness of a review program may be compromised if the structure of the reviews does not align with the actual work taking place. Additional feedback should be collected from unbiased sources to ensure that the program is not suffering from a one-dimensional approach or obstacles of any type. When executed appropriately, a program should grow over time and become integrated into the overall culture of the end users. Additional funding can allow for enhancements such as incentives and awards for workers and reviewers. End users of jobsite safety review programs should, however, take care to ensure that the program does not become too large and convoluted for its own good. A simple program may be all that is required to achieve the same goals set by the end user. It is easy to overlook the supervisory aspect of safety with all of the other controls that are present in the workplace today. Jobsite safety reviews will continue to be a critical part of empowering every worker with the opportunity to observe, identify, and eliminate hazards. Establishing a program may seem like a daunting task at first but the end results will be well worth the effort. Looking out pays dividends when it comes to safety in the workplace. For more information, please visit www.vipinc.com. q Sulfuric Acid Today • Spring/Summer 2018
Dirty sulfur pumps: how to overcome challenges for a smooth operation By: Martha Villaseñor, Weir Minerals Lewis Pumps, and Jan Hermans, Sulphurnet-Liquid Sulphur Processing
Pumping molten sulfur is not an easy task because it is very dense, almost twice the specific gravity of water. It also solidifies below 120 degrees Celsius (250 degrees F). If your plant is burning sulfur you already know about the added challenges of supply, and the inevitable impurities that can be present. To maintain sulfur in its molten state, a pump with a rugged mechanical design that can manage fluid with a high specific gravity of 1.8 with a steam jacketed shaft column and discharge pipe is required. Additionally, the pump must be designed to deal with a range of foreign solids. This is why we refer to these applications as “dirty sulfur.” The root cause of pump problems in a dirty sulfur application can stem from: • poor pump design and materials • clogged filters • poor sulfur processing • inadequate maintenance In this article, we offer some considerations and best practices our teams have developed based on decades of material development, engineering design, manufacturing, and field experience in the sulfur processing industry.
Pump design and materials are crucial
“Clean sulfur” processes require a robust vertical jacketed pump with a one-piece, large diameter shaft for increased power and radial load requirements. While the bearings are immersed in and lubricated by the sulfur, the pump shaft sealing arrangement does not come in contact with the molten sulfur by nature of the pump design. In dirty sulfur applications, a vertical pump’s critical high-wear parts should be made from hardened steel. Some replicators make these parts out of alternate materials such as stainless steel. However, regular stainless steel doesn’t have nearly the hardness of the hardened steel used in Lewis® pump parts (~120 versus ~500 Brinell). Replicated parts may also lack the close tolerance fit and abrasion resistance of original equipment manufacturer (OEM) parts. As a matter of good practice in dirty sulfur applications, pumps that have closed or semi-open impellers should be designed so a maintenance engineer can renew the tolerances between the impeller, suction wear plate, and suction head by adjusting the pump shaft—a distinguishing feature of Lewis® pumps.
Fig. 1: A dirty sulfur cantilever Lewis® pump with semi-open impeller and suction wear plate. Tight tolerances can be maintained to ensure high efficiency throughout the life of the pump.
Unlike in clean sulfur applications, the bearings of a dirty sulfur pump are not submerged in sulfur. Instead, they have lower and upper ball bearings to handle the radial PAGE 34
loads. In theory, this should be enough to guarantee troublefree performance. However, reality can present some conflicting scenarios.
The dirt in dirty sulfur can still cause problems
Unfortunately, it is fairly common for pumps in dirty sulfur filter feed applications to break down. For example, during a recent plant visit, the maintenance engineer told us the pump shaft had failed three times in a six-month period. And even when it was working, the pump failed to deliver its designed flow rate at times. What was really going on? Well, as a pump manufacturer, our first response was to get our flow meters out and determine where the pump is operating along the flow curve. In dirty sulfur applications, foreign matter often clogs the suction head filter, which leads to pump starvation. Occasionally, these solids can get caught in the pump’s wetted parts. When using pumps in dirty sulfur, the total dynamic head can vary greatly: from almost no system resistance when the filter is clean, to excessive losses when the filter is dirty. At start-up, when system resistance is low, the pump can run out of the flow curve, pumping such a large volume of sulfur that it’s cavitating. As the filter gets dirty, the total dynamic head through the filter exceeds what the pump was designed for and flow rate declines. Neither extreme is good for the pump, nor the product. Keeping a steady flow of sulfur through the filter is crucial and affects cake quality and consistency.
Poor processing design or procedures can create solids that overwhelm the pump
Powdered lime needs to remain powdery To control acidity of sulfur, manufacturers add lime, Ca(OH)2. The lime reacts with the acid present in the sulfur, forming gypsum, CaSO4. It’s crucial that when the lime is added, it’s in a powdery form and it doesn’t create large gypsum lumps. Otherwise, the acid won’t be adequately neutralized and the lumps could get caught inside the pump impeller and casing. The melting plant and pump tank should keep solids suspended The sulfur melting plant can include a melting tank, a melting tank with overflow tank, an underground melting tank, and/or a pump pit. Depending on the design, the following problems can affect pump operation: • Inadequate tank agitation: This can allow solids to accumulate at the pump inlet. It is important that the pump pit has agitation, preventing the solids from settling. • Solids overflowing from the melting tank into the pump pit: Lumps and heavier solids should settle in the melting tank and be removed through a bottom drain. When agitation speed is high, a strainer can be installed in the overflow to prevent lumps from entering the pump pit. Your liquid sulfur filter draining process and procedure matter When the sulfur process team drains the liquid sulfur filter, it’s crucial to follow the correct procedure, otherwise an excessive amount of solids can build up in the pump pit.
Martha Villaseñor, Weir Minerals
Jan Hermans, Sulphurnet
Two common shortcuts that cause pump problems are: • The drain’s flow rate is too high: This can cause filter cake erosion (see Fig. 2), and the return of an excessive volume of solids to the pump pit. • Incorrect draining sequence: To prevent a long down-time, the sulfur process team may leave the filter drain open, thereby driving a large percentage of the solids into it. Instead, it would be better to drain the filter through the filtrate outlet as long as possible (using air pressure). This approach would mean far fewer solids (only about one-third of the tank’s volume) would be returned to the pump pit.
Fig. 2: A liquid sulfur filter.
Talk with the OEM about installation and modifications
Any number of seemingly sensible, site-specific modifications can render a powerful, robust pump in dirty sulfur weak and problematic. Here are a few considerations to keep in mind when installing a pump: Installing suction extensions and strainers As an example, a Lewis® vertical cantilever pump is available in lengths up to 84 inches. If you needed a longer length, you could add a suction extension. Would it work, based on NPSHA (net positive suction head available) calculations? There are other factors to be mindful of. It is imperative to consider the geographical location of a pump; sea level versus high elevation makes a significant difference in NPSHA. A two-meter extension may be feasible for a pump operating at sea level, but completely infeasible for the same pump at 3,000 meters (10,000 feet) elevation. Another important consideration is that during startup, it is important to comply with minimal submergence requirements so that the pump is primed. Once the pump is primed it can lift sulfur through the suction extension without any problems. If the pump isn’t primed, entrained air can get into the pump head, forming air pockets. With lesser amounts of entrained air, the pump capacity can be weakened. However, if air is present the pump can become air bound, stopping flow through the pump completely. A similar note of caution applies to suction strainers. Be sure to ask your manufacturer for tolerances. While suction strainers are considered by some to be a “must” for dirty sulfur pump applications, the strainer can cause blinding (screen blockage). Starved for flow, the pump would be better off without a strainer and focus instead on better lime dosing and filter draining procedures (see previous discussion). Sulfuric Acid Today • Spring/Summer 2018
the manufacturer’s recommendation. Using anything else can cause damaging pump vibrations, because regular commercial bearings are not designed for the high radial loading vertical sulfur pumps endure. In addition, the upper and lower bearings both need to be serviced at the same time. (Unfortunately, we’ve found it is common for maintenance teams to overlook the lower ball bearings.)
control than throttle control valves. To send a constant flow of sulfur at a lower head, the pump needs to operate at a decreased speed. In Fig. 4, for example, the speed was brought down from 1,750 RPM (60 HZ) to 1,450 RPM (50 HZ) to maintain 25 cubic meters per hour at 30 meters of head.
Decrease downtime by following recommended maintenance practices
Suction wear plate impeller clearance Even though pumps manufactured for dirty sulfur applications are made with hardened iron to resist the abrasion caused by small solids, with time, the design clearances are lost. A key component of the dirty sulfur pump is the suction wear plate. To lengthen the service life of the impeller, the wear plate needs to be adjusted periodically to maintain a proper clearance from the impeller blades. (See Fig. 5.) In sum, pumping molten sulfur through filters is a dirty
Bearings Cantilever pumps don’t have submerged ball bearings. Instead, they use upper and lower bearings. It’s critical to use high-capacity replacement ball bearings according to
Fig. 5: Abrasion-worn semi-open impeller of a Lewis® cantilever pump in dirty sulfur application.
Fig. 3: Lewis 2CLS vertical cantilever pump curve. ®
business! We hope the best practices and considerations we’ve outlined here can help your plant’s operation be ever more cost-effective and successful. For more information, please visit www.minerals.weir orsulphurnet.com. q
Fig. 4: Lewis® 2CLS vertical cantilever pump curves at different speeds.
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Using a variable frequency drive to ramp flow up and down Pumps in dirty sulfur applications are chosen based on the desired flow rate and the highest head possible. In other words, the pump is sized to meet the most demanding requirements. However, at filter start-up, there are basically no restrictions. As the filter begins to fill, resistance grows, the head increases, and flow rate is cut back. With barely any restrictions at start-up, the pump is operating almost out of the flow curve (see Fig. 3). For this reason it is highly recommended to operate these pumps with a variable frequency drive (VFD), which is much less expensive in the long run and offers much finer
Info sharing at CRU’s conference, Sulphur 2017 Sulphur 2017, last year’s edition of an annual sulfur conference hosted by industry analyst CRU, took place November 6-9 in Atlanta, Ga. The annual meeting gathers sulfur and sulfuric acid professionals to meet, learn, and network. Held at the Hilton Atlanta, this 33rd iteration of the conference offered over 400 participants from 37 countries in-depth programming and numerous networking opportunities. Attendees included sulfur and sulfuric acid producers, operators, and engineering and technology suppliers. Two concurrent programs were offered, one for sulfur and one for sulfuric acid. The event also included a large scale exhibition in which over 70 presenters demonstrated the latest technologies and engineering services. A pre-conference workshop for sulfuric acid included a workshop on HAZOPs in sulfuric acid plants, which was moderated by Rick Davis of Davis and Associates Consulting. Panelists for the workshop included Jim Dougherty of Mosaic Co., Herbert Lee of Chemetics, and Leonard Friedman of Acid Engineering & Consulting. The workshop focused on various aspects of process safety management and the
A pre-conference workshop for sulfuric acid included a session on HAZOPs in sulfuric acid plants, which was moderated by Rick Davis of Davis Associates Consulting, second from right, and included panelist Jim Dougherty of Mosaic Co., left, Leonard Friedman of Acid Engineering & Consulting, second from left, and Herbert Lee of Chemetics, right.
HAZOP protocol as it applies to sulfuric acid procedures and production. The workshop included methodology and regulatory obligations and delved into several sulfuric acid incidents. It also explored the reasons why the HAZOP process did not produce the desired results. On the conference’s official opening day, CRU staff offered informative presen-
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We are delighted to invite all organisations to submit an abstract for consideration for the 2018 programme. Subject areas include: Desulphurization of fossil fuels SRU operations and troubleshooting Environmental compliance and emissions management Sulphuric acid operations and troubleshooting Sulphuric acid plant design, catalysts and equipment Logistics, handling & forming
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Paolo Olis of Mosaic Co. presented an informative update on his facility’s successful operation of a single absorption acid plant using Cansolv vs. double absorption five years later.
Steve Puricelli of Sulphuric Solutions moderated an interactive sulfuric acid troubleshooting clinic during the conference.
tations that included market outlooks, strategic challenges, and opportunities for the oil and gas industry, as well as the sulfur and sulfuric acid industries. The second and third days delved into separate concurrent programming aimed at specific industry interests. Sulfuric acid industry programming consisted of the following sessions:
Improving efficiency and reducing OPEX with novel plant designs: • “Industrie 4.0–Complementing or leading the way?” Stefan Braeuner, Outotec • “CORE™–A new approach to acid plant design,” Rene Dijkstra, Chemetics • “The next generation of sulfuric acid technology,” Garrett Palmquist, MECS-DuPont Clean Technologies Achieving cost savings and productivity increases through new catalyst developments and revamping strategies: • “Cost-effective boost of plant performance with new LEAP5 catalyst for SO2 oxidation,” Mårten Granroth of Haldor Topsoe • “New developments in BASF sulfuric acid catalysts,” Christopher Rausch, BASF • “Sulfur melter hygiene is Ob(li)vious,” Steve Puricelli, MECS-DuPont Clean Technologies Effectively managing SO2 emissions: • “Five years later: Comparing operation of single absorption acid plant using Cansolv vs. double absorption,” Nicolas Edkins, Cansolv Technologies Inc (Shell), and Paolo Olis, The Mosaic Co. • “The case for cleaner plants,” Brian Lamb, MECS-DuPont Clean Technologies • “Gas emission reduction strategies,”
Andres Mehecha-Botero, NORAM Engineering & Constructors “What do blast furnace coke and modern sulfuric acid plants have in common?” Dr. Zion Guetta, Thyssenkrupp Industrial Solutions
Utilizing equipment and materials to ensure reliable, effective operations: • “Improving the overall equipment effectiveness (OEE) in your sulphuric acid plant,” Geert Jamaer, H2SO4.pm • “Innovative acid resistant lining construction and materials,” James Daley, Magneco/Metrel, Inc. • “Comparison of wet and dry ESP technology,” Buzz Reynolds, Hamon Research-Cottrell Measurement, monitoring, and repair technology: • “Advances in process gas dew point measurement technology for sulfuric acid manufacturing processes,” Daniel Menniti, Breen Energy Solutions • “Monitoring sulfuric acid and oleum strength with only one measuring device,” Alexandra Graf, SensoTech GmbH • “In-service repair welding with pressure for the leakage of the converter,” Wang Xiao Mian, Wylton New for 2017 was an interactive sulfuric acid troubleshooting clinic. Moderated by Steve Puricelli of Sulphuric Solutions LLC, the clinic was designed to allow participants an open forum to discuss operational problems, share experience, and develop solutions. Themes explored included drip acid, opacity, converter issues, acid cooler leaks, blower surging, blocked mist eliminators, and sulfur sublimations. CRU’s Sulphur 2018 will take place November 5-8, 2018 at Gothia Towers in Gothenburg, Sweden. For more information, please visit www.events.crugroup. com/sulphur/home. q Sulfuric Acid Today • Spring/Summer 2018
Faces & Places
2017 Sulphur Conference November 6-9, 2017 • Atlanta, Georgia MECS-DuPont Clean Technologies hosted a dinner for their customers in conjunction with the Sulphur Conference. Pictured, from left, are Jeff Bolebruch of Blasch Precision Ceramics, Paolo Olis of Mosaic Co., John Horne of MECS-DuPont, Kathy Hayward of Sulfuric Acid Today, Kirk Schall of MECS-DuPont, Brian Lamb of MECS-DuPont, Richard Mason of Cornerstone Chemical Co., Lori Gicewicz of Blasch Precision Ceramics, Carlos Cavalca, Jeff Watson of Lucite International, Garrett Palmquist of MECS-DuPont, Steve Puricelli of Sulphuric Solutions, Cristina Kulczycki of MECS-DuPont, Ernesto Castaneda of MECS-DuPont, Jim Dougherty of Mosaic Co., Matt Thayer of Koch Knight, and Hugo Amaral of MECS-DuPont.
Michael Beltran of Beltran Technologies shared his company’s vast knowledge of the features and benefits of wet electrostatic precipitators at the Sulphur Conference.
Graeme Cousland of Begg Cousland Envirotec visits with participants in his exhibition stand during the Sulphur Conference.
Visiting in the exhibition area of the Sulphur Conference, from left, are Greg Zahayko of Border Chemical Co., Marwan Karaki of Weir Minerals Lewis Pumps, Randy Stanfill of Weir Minerals Lewis Pumps, and Stephen Hillis of Panamerican Consulting International. Michael Cole of Chemtrade Logistics, left, Kirk Schall of MECSDuPont, center, and Jacque Shultz of Howden network during a hospitality function at the Sulphur Conference.
John Horne of MECS-DuPont, right, enjoyed the view of downtown Atlanta with Sumeet Karna of Hindustan Zinc, left, during an evening dinner hosted by MECS-DuPont at the Sulphur Conference
Enjoying the hospitality function hosted by Outoec at the Sulphur Conference are, from left, Stefan Bräuner of Outotec, Cristian Roempler of Noracid, Hannes Storch of Outotec, and Collin Bartlett of Outotec.
NORAM Engineering & Constructors hosted a dinner in conjunction with the Sulphur Conference. Pictured, from left side, are Cristian Roempler of Noracid, Guy Cooper of NORAM, Jeff Watson of Lucite International, John Orlando of NORAM, Joanne Orlando, Andrés Mahecha-Botero of NORAM, Rob Young of Simplot, Werner Watznauer of Noracid, Nelson Clark of Clark Solutions, and Richard Mason of Cornerstone Chemical Co.
Marten Granroth of Haldor Topsoe explained the benefits of his company’s new LEAP5 catalyst to participants during the sulfuric acid session of the Sulphur Conference.
Matt Thayer of Koch Knight, left, visits with Mansour Al-Gahtani of Ma’aden Phosphate Co., center, and Osama Al-Ghamdi of Ma’aden Phosphate Co. during an evening dinner hosted by MECS-DuPont at the Sulphur Conference.
Rene Dijkstra of Chemetics explained his company’s pseudo-isothermal converter technology, CORE™, during the sulfuric acid session of the Sulphur Conference.
Jamal Bouarsa of OCP, left, and Brahim Nait Telhak of OCP enjoyed a dinner hosted by MECS-DuPont Clean Technologies at the Sulphur Conference.
calendar of events AIChE Central Florida Section Conference
June 8-9, 2018 Clearwater, Florida LAKELAND, Fla.—Each year, members of the AIChE Central Florida Section and colleagues from all over the world gather at Clearwater Beach to share ideas concerning chemical process technology, specifically the production of phosphoric acid, phosphate fertilizers, and sulfuric acid. The Sheraton Sand Key Resort in Clearwater will once again be the site for this anticipated event, scheduled for June 8-9, 2018. This year’s Sulfuric Acid Workshop will take place on Friday, June 8, 2018 and will focus on various aspects of engineering, specification, fabrication, operation, and maintenance of heat recovery steam systems utilized in sulfuric plants including waste heat boilers, superheaters, and economizers. The Workshop will include a review of specifications, fabrication, quality control, steam purity, steam quality, water treatment, and maintenance. As always, the convention also provides a relaxing getaway with friends and family, good food, and a lot of fun. Social and networking events are planned during the event, with a little something for everyone. For more information, please visit www.aiche-cf.org.
12th Chilean Sulfuric Acid Roundtable October 21-25, 2018 Puerto Varas, Chile SAN FELIPE, Chile—Holtec Ltd. is pleased to announce the 12th Roundtable for Sulfuric Acid Plants (Mesa Redon-
da de Plantas de Acido Sulfúrico) to be held October 21-25, 2018 in Chile. This year the conference will take place in the beautiful town of Puerto Varas, located 1,000 km south of Santiago. Operators and maintenance experts, technology providers, plant owners, consultants, and engineering firms specializing in sulfuric acid technology will discuss the latest developments in technology, projects, operations, and sulfuric acid markets. As usual, organizers will welcome delegates from almost all sulfuric acid plants of the Spanish speaking countries in Central and South America to present their projects and operational and maintenance topics during the three days of the sessions. At the same time, technology providers will have a chance to chat with their customers and present their new developments and products. Simultaneous translation in English/Spanish will be provided. For information on hotel, deadlines of presentations and papers, travel details, and other relevant information, please visit www.mesaredondachile.com or email info@ holtec.cl.
November 5-8, 2018 Gothenburg, Sweden LONDON—Sulphur 2018, a premier industry event for the sulfur and sulfuric acid markets, will take place at the Gothia Towers in Gothenburg, Sweden November 5-8. Attracting over 450 industry professionals from around the globe, the conference offers industry leaders the opportunity to meet, learn, and network. Each year, the extensive program covers key market trends, project updates,
and supply and demand forecasts in the commercial sessions, with presentations from respected industry figures and high level analysis from CRU’s Sulphur Team. The two-day split stream technical program showcases the latest technological developments to improve efficiency and compliance, and provides a high-level forum for engineers from the sulfur and sulfuric acid industries to share experience and develop solutions to common operational problems. For more information, please visit www.crugroup.com/ events/sulphur.
2019 Sulfuric Acid Roundtable
March 25-28, 2019 ChampionsGate (Orlando), Florida COVINGTON, La.—Plans are underway for Sulfuric Acid Today magazine’s bi-annual Sulfuric Acid Roundtable. The event will take place March 25-26, 2019 at the Omni in ChampionsGate in Orlando, Fla. The 2017 Sulfuric Acid Roundtable attracted more than 180 participants from around the world, and 2019 is shaping up to be an even bigger event. As in years past, sulfuric acid insiders will gather to attend presentations given by event co-sponsors on a variety of topics relevant to the industry. Panel discussions and co-sponsor booths will provide more opportunities for information sharing, while social events will ensure that participants get to enjoy the beautiful area while building relationships that promote beneficial business exchanges in the future. For more information, please email Kathy Hayward at firstname.lastname@example.org, or visit the event’s website: www. acidroundtable.com. q
Save the Date! 2019
R O U N D T A B L E
March 25-28, 2019 Omni ChampionsGate Orlando, Florida
The Sulfur 2019 Roundic Acid table will
offer : — Keyno te Addre ss Globa l Sulfuric on the Acid Mark — Produ cin et Discus g Plant Panel sions & Presenta — New T tions ech — Safety nology Develop ments Issues & Incident Reviews
Sulfuric Acid T
Industry’s Premier Event for Networking & Sharing Best Practices™ PAGE 38
Sulfuric Acid Today • Spring/Summer 2018
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