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Covering Best Practices for the Industry

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IN THIS ISSUE > > > > Covid-19 recovery amid a commodities price rally

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Absorption-irrigation systems

Glencore Nickel replaces sulfuric acid drying tower in record time

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Clean Technologies

Making everyday life better, safer, cleaner For 100 years, we have partnered sulfuric acid producers with innovative technology and expert trouble-shooting technical support. And our tradition of designing advanced solutions to solve site-specific challenges continues – so we can together deliver cleaner air productively, efficiently and reliably.

Learn more on www.cleantechnologies.dupont.com

MECS® Sulphuric acid & environmental technologies Copyright © 2019 DuPont. The DuPont Oval Logo, DuPont™, is registered trademarks or trademarks of E.I. du Pont de Nemours and Company or its affiliates. All rights reserved.

Sulfuric Acid

Covering Best PraCtiCes for the industry

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Vol. 27 No. 1

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FROM THE PUBLISHER

On the Cover …

7 Abu Zaabal Fertilizers & Chemical Industries Co. in Egypt embarked on a major revamp of their sulfuric acid Unit 6.

Departments 4 Industry Insights News items about the sulfuric acid and related industries 16 Lessons Learned

Case histories from the sulfuric acid industry

Dear Friends, Welcome to the Spring/Summer 2021 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.

As we entered 2021 there was still significant focus on the COVID-19 pandemic, but the outlook was growing increasingly positive on the development of vaccinations. While the recovery process is ongoing and vaccination distribution needs to be more widespread, many commodity prices began to rally driven by the prospect of a better-performing economy compared with 2020. Please see Acuity Commodities’ informative article ‘COVID-19 recovery amid a commodities price rally’ on page 10 for further details.

COVID-19 has also affected many industry conferences and meetings slated for 2021. The organizers for the AICHE Clearwater Florida Conference have recently decided to cancel their June 2021 event and will host again in 2022. The Chilean Sulfuric Acid Roundtable in Temuco, Chile has been rescheduled to October 2022. Additionally, due to on-going restricted international travel associated with COVID-19, we have rescheduled both of our sulfuric acid events.

Our North American Sulfuric Acid Roundtable will take place April 4-7, 2022 in The Woodlands, Texas and the Australasia Sulfuric Acid Workshop has been rescheduled to September 13-16, 2022 in Brisbane, Queensland, Australia.

In this issue, we have several informative articles regarding state-of-the-art technology and projects.

EDITOR April Kabbash EDITOR April Smith

Sincerely, Kathy Hayward

FEATURES & GUEST COLUMNS

PUBLISHED BY Keystone Publishing L.L.C. PUBLISHER Kathy Hayward

Our cover story, on page 7, focuses on Abu Zaabal Fertilizers & Chemical Industries Co. (AZFC). After three decades of service, AZFC’s sulfuric acid unit 6 embarked on a major revamp. Weir Minerals incorporated Lewis® vertical externally mounted (form E) sulfuric acid pumps to replace the incumbent horizontal pumps for a smelter in South America (page 14), Glencore replaced a sulfuric acid drying tower with DuPont Clean Technologies’ design in record time (page 24), and NORAM Engineering & Constructor’s client replaced their cold reheat exchanger with a new cold exchanger with NORAM’s proprietary hot sweep feature (page 30).

I would like to welcome our new and returning Sulfuric Acid Today advertisers and contributors, including: Acid Piping Technology Inc., Acuity Commodities, Alphatherm Inc., Beltran Technologies, Breen Energy Solutions, Central Maintenance & Welding, Chemetics Inc., Clark Solutions, DuPont MECS, EXP, HUGO PETERSEN, Integrated Turbomachinery, Koch Knight LLC, Mercad Equipment 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 2021 issue. If you have any suggestions for articles or other information you would like included, please feel free to contact me via email at kathy@h2so4today.com. I look forward to hearing from you.

10

Covid-19 recovery amid a commodities price rally

12 Acid Piping Technology celebrates 30 years of service

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14 Lewis® vertical sulfuric acid pumps save South American smelter $100K & 200 hours

Marketing ASSISTANT Tim Bowers

18

Understanding spray technology to optimize sulfur burning

DESIGN & LAYOUT

20

Training designed for success

24

22 Absorption-irrigation systems 281-545-8053 Mailing Address: P.O. Box 3502 Covington, LA 70434 Phone: (985) 807-3868 E-Mail: kathy@h2so4today.com www.h2so4today.com SUBSCRIPTIONS U.S. Plant Personnel —‑Complimentary U.S. Subscription —‑ $39 per year (2 issues) Internat’l Subscription —‑$59 per year (2 issues) Subscribe Online: www.h2so4today.com

24 Glencore Nickel replaces sulfuric acid drying tower in record time 26 EXP’s sulfuric acid team delivers reliable, client-focused solutions 28

Sulfuric acid gas & mist cleaning: wet electrostatic precipitators for superior performance

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NORAM’s hot sweep cold exchanger does the trick

32

Special alloys changing how sulfuric acid plants are built and operated

30

Department

Industry Insights International private equity consortium to buy DuPont Clean Technologies

WILMINGTON, Del.—An international private equity consortium consisting of BroadPeak Global LP, Asia Green Fund, and The Saudi Arabian Industrial Investments Company announced recently that they have signed a definitive agreement whereby they will purchase the Clean Technologies business of DuPont de Nemours, Inc. for $510 million in cash. As part of the transaction, Tensile Capital Management LP is providing preferred equity financing. The transaction is expected to close in the second quarter of 2021 subject to customary closing conditions and regulatory approvals.

Since first producing sulfuric acid catalyst in 1925, DuPont Clean Technologies has become the global leader in advanced catalyst and process technologies to produce and regenerate sulfuric acid, hydroprocessing technology to desulfurize motor fuels, alkylation technology to produce clean gasoline, and advanced air pollution control systems for refineries and chemical facilities.

DuPont Clean Technologies also offers a comprehensive suite of aftermarket services and solutions. The consortium and DuPont are working together to execute a seamless transition plan that will serve Clean Technologies and its global customer

base both reliably and safely.

For more information, please visit www. dupont.com.

PQ Group Holdings sells performance chemicals, acquires catalyst activation business

MALVERN, Pa—PQ Group Holdings Inc., a leading integrated and innovative global provider of specialty catalysts, chemicals, and services, announced recently that it has entered into a definitive agreement to sell its Performance Chemicals business to a partnership established by Cerberus Capital Management, L.P. and Koch Minerals & Trading LLC for a purchase price of $1.1 billion.

Upon the anticipated close in 2021 and finalization of net cash proceeds, PQ plans to return capital to shareholders through a special dividend of $2.50 to $3.25 per share (subject to Board approval and declaration), which is expected to result in a debt reduction of $450 million to $550 million.

In addition, PQ also signed an agreement to acquire Chem32, LLC from its founders for a purchase price of $44 million to complement its Refining Services business, Eco Services Operations Corp.

Chem32 is a leading supplier of catalyst preactivation services used in the production of traditional and renewable fuels. This addition, with its patented technology and

For the past 30 years VIP International has led the industry in innovative equipment and procedures in maintaining sulfuric acid plants. As the industry demands longer run times between catalyst screening, VIP’s patented catalyst handling system ensures the longest run time with lowest pressure drops to ensure maximum performance of your converter. Contact VIP International to learn how to reduce your downtime and increase your production and on stream factor.

225-753-8575 6638 Pecue Lane, Baton Rouge, LA 70817-4400 | www.vipinc.com PAGE 4

services, is expected to grow rapidly and generate strong margins.

For more information, please visit pqcorp.com.

would be 155,000 TPA from the Indore manufacturing facility.

For more information, please visit www. ramaphosphates.com.

Egypt’s Sprea Misr awards sulfuric acid plant contract to Nuberg

DuPont Clean Technologies awarded Lithuanian refinery upgrade contract

RAMADAN CITY, Egypt—Sprea Misr has awarded the engineering, procurement, construction, and project management of its new 500 TPD sulfuric acid plant contract to Nuberg EPC. Nuberg EPC will be the single-point solution company responsible from concept to commissioning of the project. The 500 TPD sulfuric acid plant project will be based on the latest Double Contact Double Absorption (DCDA) process technology.

The double contact process is used for the production of sulfuric acid in high concentrations which is required for industrial purposes. The project also incorporates a 5MW turbine with a steam-based power generation plant with a complete bypass arrangement.

This is the first time that Nuberg EPC is building a turbine unit for electricity production. Sulfuric acid produced in the plants will be provided to the agriculture industry for the production of urea and other fertilizers.

In the Middle East, Nuberg EPC has successfully delivered over fifteen turnkey projects in countries like Oman, Qatar, Saudi Arabia, Turkey, and the UAE. This has positioned Nuberg EPC as one of the top EPC companies in the region.

On being awarded the project, AK Tyagi, MD, Nuberg Engineering said: “We are thankful to Sprea Misr for entrusting our turnkey project engineering capabilities and our EPC services and solutions with its sulfuric acid plant.”

Nuberg EPC’s scope of services for this project includes process design and technology including product and technology development, process knowhow and licensing, basic engineering, front end engineering design, construction management, operation & maintenance, detailed engineering, project management, commissioning, EPC and LSTK solutions, heavy fabrication, and start-up of the plant.

For more information, please visit www.nubergepc.com.

Rama Phosphates Ltd commences commercial production of sulfuric acid and derivatives from new unit

MUMBAI, India—Rama Phosphates has commenced commercial production of sulfuric acid and its derivatives from the new manufacturing facility (Unit 2) at its existing factory. Unit 2 can produce up to 55,000MT/ year of sulfuric acid, as well as liquid SO3 and oleum.

With this capacity addition of 55,000 TPA from Unit-2, the company’s overall annual production capacity of Sulphuric Acid

WILMINGTON, Del.—DuPont Clean Technologies has been awarded the contract to supply Orlen Lietuva with licensing, engineering, and technical services for a Stratco alkylation unit and a MECS spent acid regeneration (SAR) unit at the Mažeikiai refinery in Mažeikiai, Lithuania.

The Mažeikiai refinery processes an average of 8 million tons of crude per year with capacity of up to 10 million tons of crude per year. In order to increase refinery complexity and flexibility of the Mažeikiai refinery, Orlen commissioned DuPont for a Stratco alkylation unit with 240,000 metric tons per year alkylate capacity. The alkylation unit will utilize LPG in the conversion to alkylate, and therefore upgrade refinery profitability. The 75 mt/d MECS SAR unit, also under license from DuPont, will provide the refinery with a consistent supply of sulfuric acid, which is utilized as the catalyst for the alkylation unit, while ensuring compliance with the region’s stringent emission regulations.

The Stratco alkylation unit will enable Orlen to generate low-sulfur, high-octane, low-Rvp alkylate with zero olefins that meets the criteria of the EURO VI standard. Startup for both units is targeted for 2025.

For more information, please visit www. dupont.com.

Metso Outotec to modernize Norilsk Nickel’s smelting line

HELSINKI, Finland—Metso Outotec has been awarded a landmark contract by PJSC MMC Norilsk Nickel to modernize one of the company’s two existing smelting lines at their Nadezhda Metallurgical Plant in Norilsk, Russia.

The contract value is nearly $108 million. Metso Outotec’s contract includes engineering and delivery of a nickel flash smelting furnace and a heat recovery boiler with related automation and advanced digital products. Replacing the existing smelting line with the latest process technology and furnace structures will significantly increase the line’s capacity and availability, reduce metal losses and ease maintenance. The new line will also allow for the easy connection and efficient operation with potential future sulfuric acid production and neutralization projects. The delivery of the equipment will take place during the first quarter of 2022.

For more information, please visit www. mogroup.com.

Dürr Megtec introduces “next generation” Wet ESP

DE PERE, Wis—Dürr Megtec recently released its “next generation” wet electrostatic precipitator (WESP)—an air pollution control system that efficiently Sulfuric Acid Today • Spring/Summer 2021

cleans industrial gases of fine particulate matter, acid mists, and aerosols to meet global environmental regulations and protect downstream equipment. Key improvements of Dürr Megtec’s advanced WESP system include decreased maintenance, enhanced performance, standardization, and faster installation times.

Dürr Megtec designed the new WESP with both the environment and its customers’ operations and maintenance teams in mind.

As a result, a strong focus was placed on the system’s high-intensity, offline automatic cleaning features, which reduce maintenance efforts, eliminate carryover of entrained matter during washing and provide better operational performance during cleaning.

System components are also now easily accessible for maintenance inspections.

In order to enhance the performance of its WESP, Dürr Megtec aimed at achieving a more efficient contaminant capture. This was achieved through increased operating voltage that requires less collecting surface area.

Additionally, the gas distribution system was completely reimagined to optimize flow through the system, and various tube shapes and electrodes were tested to improve overall performance.

Time is always of the essence, so the “next generation” WESP allows for faster installation times. Modules with tube bundles are pre-assembled in Dürr’s production facility for shipment to the customer. All electrodes are pre-loaded and pre-aligned, thus avoiding this lengthy and tedious task on the construction site. When compared to other commercially available WESP designs, the manufacturing and installation timeline of the advanced Dürr product is dramatically lower.

“After talking to our customers, our product development departments generated innovative, patent pending ideas in the area of particulate removal efficiency, and tube and electrode cleaning – all with a keen eye towards reduced maintenance and increased reliability,” says Rodney Schwartz, Dürr Megtec Vice President, Sales.

For more information, please visit www. durr-megtec.com.

ABB awarded contract to supply complete electrical and automation system for China’s Northern Copper Industry

BEIJING, China—Northern Copper Industry Co., Ltd—part of the largest producer of raw material copper stock in North China—has selected ABB to supply and install a complete electrical and automation system for its new cold rolling mill, which is scheduled for startup in 2021.

Based on ABB Ability™ System 800xA distributed control system (DCS) with highperformance AC 800PEC master controller, the package integrates ABB Metals Roll@ xA Optimize cold rolling control solution and ABB’s Collaborative Production Management for Metals (CPM4Metals) system for the copper production process.

Sulfuric Acid Today • Spring/Summer 2021

On completion, the mill will become a first-class high-performance rolled copper strip and foil production line with an annual output of 50,000 tons. As new material produced with state-of-the-art technology the products will be widely used in aerospace, 5G communications, new energy industries, smart manufacturing and other high-tech application fields.

ABB’s Roll@xA Optimize solution incorporates alloy measurement and advanced thickness control functions, ensuring rolled products, including a hard alloy-bronze that contains tin elements, fulfill stringent requirements. It also ensures strict synchronization between the roller surface and the copper strip foil to eliminate surface scratches caused by non-synchronized rotating of deflection rollers, and enables the customer to meet specific surface quality requirements. This is achieved through a range of proprietary drive control functions including static friction compensation, online controller parameter adaptation, dynamic compensation for acceleration and deceleration for deflection rollers.

“The 20-high finishing mill project is part of an important strategic vision of Northern Copper Industry to build a centurylong copper enterprise,” said Zhenhua Zhang, ABB Metals Lead, North Asia and China.

“We will provide ABB Metals well-proven expertise to ensure the new mill meets expectations for producing high-precision and high-quality copper strip and foil.”

“We have built strong bonds with our NCI counterparts, demonstrating technical competence and stable product quality. This electrical and automation system will provide a foundation for growth and development in several high-tech material application fields.”

ABB’s latest drive system model ACS880, AXR engineering high-pressure cast-iron motor, AMI high voltage modular motor, ABB’s dedicated instrumentation Millmate Tensiometer System, and measuring instrumentation and sensors will also be installed.

The quality of cold rolled flat products is a decisive factor for the metals industry. The ABB process and power system, designed for cold rolling mills, offers advanced solutions for quality supervision and analysis to meet the needs of cold rolling steel in terms of thickness tolerances, flatness and surface characteristics.

Northern Copper Industry Co., Ltd. with headquarters in Yuncheng, China, was established in 2002 and operates in the mining, mineral processing, and smelting sector for copper. The main products are raw material copper stock produced through cathode electrolysis, sulfuric acid, etc. It has an annual mining production capacity of 9 million tons, 200,000 tons of cathode copper, and 570,000 tons of sulfuric acid.

With parent company ZhongTiaoShan Non-ferrous Metals Group Co. it is the largest raw material copper stock producer in North China.

For more information, please visit www. abb.com. q

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PAGE 5

Department

Industry Insights

30 Year

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Cover Story

Abu Zaabal revives its 30-year-old workhorse Lifting into place of new tower during acid plant revamp

By: April Smith, Editor, Sulfuric Acid Today

A

fter squeezing over three decades of service from a vital sulfuric acid unit, managers at Abu Zaabal Fertilizers & Chemical Industries Co. (AZFC) knew something had to give. They were patching unit 6 with increasing regularity and they knew that continuing to rely on it for regular output meant investment in a longterm solution.

Unit 6 is responsible for about 30 percent of the sulfuric acid used as feedstock for AZFC’s downstream phosphoric acid and SSP plants. From its start in 1984, it produced more than six million tons of sulfuric acid that were used to produce 18 million tons of single superphosphate to fertilize more than 36 million acres of ground. It also generated over 600 million KW of clean electricity, allowing AZFC to cut CO2 emissions by 11 million kg.

But sulfate build-up and gas leaks were forcing daily downtime. And by 2015, facing multiple shutdowns and significant losses in production time, the company embarked on a major revamp.

Sulfuric Acid Today • Spring/Summer 2021

About AZFC

Established in Egypt in 1947, AZFC is one of the oldest and largest phosphate fertilizer producers in Africa and the Middle East. Located just west of Cairo’s city center, it was privatized and purchased by the Polyserve Fertilizers and Chemicals Group in 2002. AZFC currently serves international markets in Africa, Asia, Europe, and Latin America, primarily Brazil.

The company runs two sulfuric acid units producing concentrated 98.2 percent sulfuric acid as raw material for phosphate fertilizer manufacturing. Products include single and triple superphosphates, 80 percent agricultural phosphoric acid, and NPK. AZFC is currently working on the development and improvement of products with micro-nutrients Zn, Mn, Cu, and B. A further improvement includes phosphoric acid to be manufactured with less Fe, F, and SO4 for DCP and MCP production.

Sulfuric acid unit 6 is the older of the two units and

AZFC’s sulfuric acid unit 6 after its overhaul.

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Cover Story

by 2015 deteriorating equipment was causing an exponential rise in sudden unit shutdowns. Company managers decided that overhauling the facility would not only allow AZFC to resolve productivity issues, but also meet Egypt’s new emissions regulations, which limited SO2 emission to 450 mg/m3 for new plants and to 800 mg/m3 for existing plants.

Known issues

It was clear the original brick-lined drying and absorption towers were in very poor shape with acid leaking from the bottom of the vessels and at the outlet nozzles of the acid tower, causing sulfate build up and severe corrosion.

The tube sheet of the IPAT’s mist eliminators was clogged with sulfate and build up on the pump suction was causing corrosion and damage to the pump shaft.

Corrosion also affected the acid distributor, which had already undergone past repairs. “The original cast iron acid distributor had at one point been updated with material fabricated on the local market,” explains Ayman Abd El Hafeiz, manager of AZFC’s sulfuric acid plant.

“This was replaced with 316 stainless steel, which began corroding on the headers, distributor arms, and holes after just a short operating time, forcing us to replace all these elements every one to one-and-a-half years, or at every shutdown.”

The brick linings were also deteriorating. Sections were regularly coming loose and falling into the acid cooler, leading to further leakage from cooler pipes. In the sulfur furnace, some of the refractory bricks had fallen out, exposing the steel which subsequently deformed. The furnace baffles had fallen over, suggesting that the gas was not mixing sufficiently, and that sulfur was entering downstream equipment and causing corrosion.

Much of the cast iron piping was severely corroded.

The elbow of the IPAT had a number of holes. Repairing these was difficult because the pipes were very heavy and difficult to access.

Sometimes, the plant was shut down three to four times per day to attend to all of these problems. And finding spare parts was becoming more of a challenge, which in turn extended downtime.

Adding still more to the list of challenges was a significant plume from the stack, gas leaks from the shell of the cold heat exchanger, missing refractories in the waste heat boiler, and acid carryover from the IPAT leading to accumulating sulfates, corrosion, and increased emissions.

Temporary repairs to cast iron piping carried out in 2013.

PAGE 8

Operating the old plant had clearly become extremely difficult, costly, and unsafe.

Planning the revamp

Tackling an extensive overhaul would take careful planning. “We had three main challenges we had to address,” Abd El Hafeiz said, “the major one being time.”

Because unit 6 was so integral to downstream production, the project had to be executed as efficiently as possible to get the unit back online. The team set a target of 12 months.

The second challenge was to assess the condition of the remaining equipment by completing a thorough inspection of every part in the plant.

The third challenge was to protect equipment identified for re-use from damage during the dismantling of the old acid towers.

To meet these goals, AZFC chose contractors who were best suited for the job, including DuPont Clean Technologies (DuPont) for its world leading MECS® sulfuric acid technology, as well as big engineering companies ABB, STEULER-KCH, ASF–EL Sewedy Industries Group, and I.E.M.S.A. Construction.

DuPont had established a relationship with AZFC over the past several years supplying MECS® catalyst and Brink® mist eliminators for the company’s new unit 7 plant, as well as helping to resolve various operational and mechanical issues.

Over the course of the revamp, DuPont fulfilled multiple roles. “They not only provided the process design and engineering for the acid towers,” Abd El Hafeiz said, “but also supported the revamp in an advisory role, helped with quality control inspections during the fabrication of the acid towers at ASF–EL Sewedy Industries Group, and assisted us with the start-up of the plant.”

ducted by DuPont identified leaks in the heat exchanger, which had been re-tubed just two to three years earlier.

PeGASyS™ also identified opportunities to optimize converter operations.”

Project specifics & execution

The new acid towers were designed to reduce overall SO2 emissions as well as improve converter performance.

The aim was to guarantee a production rate of 615 MTPD, achieve SO2 emission targets of less than 800 mg/Nm3, as well as SO3 absorption and SO3/acid vapor emission control levels of less than 35 mg/Nm3. To this end, the design specs included MECS® Brink® mist eliminators and modern UniFlo® acid distributors made with corrosion-resistant MECS® ZeCor®-Z alloy.

Abd El Hafeiz regards the new equipment as key features of the design. “Replacing the old cast iron pipe distributors and metal mesh pads in the final tower with Brink® fiber bed mist eliminators and erecting new MECS® UniFlo® acid distributors for three acid towers greatly improved the towers’ efficiency and clearly reduced acid mist emissions,” he said.

The design also included MECS® GEAR® catalyst, which enabled AZFC to use the same style converter to achieve target production rates and SO2 emissions.

The revamp began in late 2015 with dismantling of the old acid towers and repairing the foundations. The new carbon steel tower vessels were fabricated off-site by local engineering company ASF–EL Sewedy Industries Group, and then transferred to Abu Zaabal in three sections and

Taking stock

The full scope of the revamp became clear after AZFC completed a thorough assessment with MECS® technology specialists. Besides the known replacements necessary in the strong acid area – towers, pumps, mist eliminators, and acid distributors – internal inspection of the stationary equipment revealed the poor condition of the converter.

DuPont project lead Jurgens Hanekom determined that quite a number of internal parts needed replacing—“mainly cast-iron grid supports and columns that were damaged or in a poor condition,” Hanekom explained. “MECS® PeGASyS™ gas sampling and diagnostic analysis con-

AZFC’s unit 6 before the revamp–the drying and absorption towers were in very bad shape.

Acid was leaking from the bottom of the acid tower, causing corrosion issues.

Cold heat exchanger gas leak.

Sulfuric Acid Today • Spring/Summer 2021

Cover Story

erected on site. The towers were brick lined under the supervision of STEULER-KCH. DuPont carried out an acid levelling test and regulated the acid levels in all the troughs of the acid distributors.

MECS® ZeCor®-Z alloy was used for pipes, all elbows, bends, fittings, spool pieces with field work carried out by local engineering company I.E.M.S.A. Construction, whose welders DuPont had qualified to ensure they could weld the MECS® ZeCor® alloy correctly and provide future maintenance support if needed.

During the revamp, most of the first pass converter cast iron internals such as support grids and columns were also replaced, and new woven wire screens installed for all passes. When the brick lining had been restored, the converter was then loaded with new catalyst.

The revamp further specified the repair of the main blower and almost all rotating equipment, seven new gas valves, a new gas duct for the IPAT, re-tubing of the cold inter-pass heat exchanger, a pristine demineralized water plant, plus a new modern DCS control room.

Notably, there were no real challenges during project execution because “most problems were anticipated,” Ayman Abd El Hafeiz explains, “and there was also clear communication between AZFC’s leadership and the project team, among AZFC team members, and between AZFC and DuPont/MECS® technical staff.”

Hanekom agrees, adding that regular visits to the build site as well as local fabricator shops were very valuable.

There was also not a single incident or accident. “We made safety our high priority during project execution, following all safety procedures,” Abd El Hafeiz said.

“Replacing instrumentation and the old control system with a new ABB DCS helped a lot in controlling the plant safely.”

Starting up & looking back

A revitalized unit 6 started up successfully in midNovember 2016 after a shorter than anticipated shutdown period. Since startup, the plant has operated to performance guarantees, producing up to 640 MTPD acid.

The project concluded on budget as well, at 10 to 20 percent of the cost of a new plant, but with the same life expectancy. “Making use of local fabricators and labor reduced the costs and duration of the project,” said Hanekom. “That and the AZFC team’s quality control during the fabrication stage made using local labor very effective.”

Abd El Hafeiz is proud of what they were able to achieve, crediting the project team and its strong communication protocols. “A small and dedicated team, with support from AZFC’s leadership, was able to succeed and execute the project safely because the communication between the project team was so clear and specific.”

After a few years running, plant managers have gathered impressive statistics. The downtime average is now 3.9 days per year, compared to 138 days per year before the revamp. After the revamp, the plant ran for more than 3 years before its first cold shutdown, compared to a shutdown every 4-6 months before.

“And we have a clear stack now,” Abd El Hafeiz said, “without the visible plume we had back in 2016.”

As a symbol of the plant’s greener footprint, actual greens in the form of roses were planted throughout the grounds. As Abd El Hafeiz explains: “We had a vision to fill the site with roses to illustrate the clean nature of the plant and demonstrate the creation of environmentally friendly conditions where both the plant and the roses are able to grow.” q

Since start-up, unit 6 has operated to performance guarantees, producing up to 640 MTPD acid.

Sulfuric Acid Today • Spring/Summer 2021

The Unit 6 revamp was managed by Ayman Abd el Hafeiz (right) and Mr Hassan Hussein, AZFC coordinating manager (center), supported by Jurgens Hanekom of DuPont (left).

MECS® Brink® mist eliminators in the new acid tower.

Installing new MECS® ZeCor®-Z alloy piping.

PAGE 9

Feature

market outlook

Covid-19 recovery amid a commodities price rally

Fiona Boyd, Acuity Commodities

Freda Gordon, Acuity Commodities

By: Fiona Boyd and Freda Gordon, Directors of Acuity Commodities

As we entered 2021, there was still significant focus

on the Covid-19 pandemic, but the outlook was growing

increasingly positive on the development of vaccinations.

While the recovery process is ongoing and vaccination

distribution needs to be more widespread, many commodity prices began to rally driven by the prospect of a better performing economy compared with 2020.

In this article we will discuss what are still the most

relevant impacts of the Covid-19 pandemic on the sulfur

and sulfuric acid markets. We will then discuss the commodity price boom and its impacts on the relevant markets.

One of the more notable impacts of the Covid-

19 pandemic remains reduced sulfur production which has also impacted the sulfuric acid market due to tight

availability of the raw material. Lower sulfur output is

a reflection of refineries slowing throughput as demand for refined products, namely gasoline and jet fuel, was

significantly hampered by the impacts of Covid-19 as lockdowns were put in place to help slow the spread of the virus. Overall global refinery utilization for 2020 has

been reported to be about 72% on average, although it is expected to rebound to 75-80% later this year.

In addition to the lower utilization, which reduced

by-product sulfur production accordingly, permanent refinery closures and conversions to renewable fuels

were seen, namely in the U.S. and Europe. And while we

do expect long-planned new refining capacity to come online globally, it could impact refinery throughput in other regions. This year, we expect notable new refining capacity to come online throughout Asia, including West

Asia (Middle East) where the bulk of refining investments have been made in recent years. WoodMac reported that over 1m bbl/day of refining capacity will be completed this year in the region. We also expect some of these

new refineries to be notable in terms of sulfur production as they are generally higher complexity, allowing them

to accommodate a variety of crude types. The refining

capacity additions could also result in refiners continuing to shed unprofitable refineries and focusing on upgrades of better positioned assets.

Finally, the long-term effect of shifting to lower

carbon emissions in some countries could increase pro-

duction of renewable fuels, thereby reducing traditional refining accordingly. In addition, this may result in unin-

tended consequences such as more demand for base metals to support the electric vehicle (EV) evolution, which

would be bullish for the sulfur and sulfuric acid markets in terms of pricing. This is because many raw materials

to support battery and car production use sulfuric acid to support their production plans. And with the benefits

created by power cogeneration by sulfur burning, some are hoping to build sulfur-based plants to cover their

downstream consumption which would provide further PAGE 10

support in terms of sulfur demand.

In terms of the impact on sulfur production on lower refinery throughput, last year we estimate that throughout Europe, around 700,000t of sulfur production was lost due to lower utilization and some refineries being idled or closed. We do not expect a notable rebound this year.

For the US, data reveals around 800,000t of production was lost in 2020 compared with 2019. In 2019, we saw production decline by around 900,000t from 2018 mainly due to a lighter crude slate, resulting in an accumulated loss of 1.7m t in the two-year period. This represents a combined permanent loss of supply of 2.4m t between Europe and the US. Meanwhile, we estimate combined growth of around 3.6m t, mainly throughout Asia. While this growth of will counterbalance the permanent losses, additional permanent closures because of the issues described above will impact the sulfur balance and trade flows accordingly.

Amid the tighter sulfur availability, demand for sulfuric acid has been stable, and in some regions higher.

The stable demand for sulfuric acid highlights its use as a key chemical for many applications including fertilizer production, water treatment, and for production of some pulp and paper products. Some weaker demand was seen from some related sectors, such as automotive, but it was not enough to have a notable market impact with the strength seen from others and the sulfur supply tightness.

With availability of sulfur reduced, it made opportunistic sales of sulfur-based material more challenging while at the same time, it created more demand for smelter acid.

At the time of our last article, we had yet to see the trend of firmer sulfuric acid pricing emerge. However, as the loss of sulfur production became pronounced and sustained, it continued to support sulfuric acid purchasing, including from atypical buyers as way to augment their own sulfur-based production. At the same time, commodity prices began to boom.

The driver of the sustained commodity price rebound is stimulus spending by governments across the world in efforts to recover from the impacts of the Covid-19 pandemic. A lot of the commodity price growth can be attributed to China. This year its recovery from the pandemic is driving expectations of firmer economic growth. In 2020, China’s industrial activities were impacted which reduced its sulfur imports accordingly while its domestic sulfur

production grew. As an indication, its sulfur imports last year were around 8.5m t, down a notable 3.2m t from its 2019 import volume of just over 11.7m t. Meanwhile on the sulfuric acid side, its exports dropped around 450,000t due to less smelting of base metals as well as reduced sulfur availability to run sulfur-based burners which supply the merchant market. The price graph below reflects the upward price trajectory seen since late 2020.

The following price graph for copper is an illustration of prices rebounding which has provided support for sulfuric acid purchases and at higher prices. In February 2021, copper pricing hit a 10-year high which continues to inject confidence into the market. Again, China can be credited with supporting some of this growth due to the economic growth expected there this year. As such, we expect firmer demand in Chile to support copper leaching this year after seeing some slower consumption last year amid the pandemic. At the same time, new acid-consuming copper projects in Peru, its primary source of supply, are ramping up, which will reduce availability for Chile accordingly.

In terms of the agricultural sector, the largest sulfur consumer, firm crop prices are supporting demand for phosphate fertilizer products. This in turn is driving up sulfur consumption levels which contributes to the sulfuric acid market in terms of reduced availability and opportunistic purchasing.

As the year progresses, we will be closely watching commodity price growth amid chatter of an emerging supercycle which will present interesting market dynamics due to the inelasticity of sulfur and smelter acid pricing. Neither firmer nor weaker demand for these products dictates how much by-product materializes. Amid high demand for both products, as we are currently seeing, there appears to be little downside potential for either of the markets.

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 as well as bespoke consulting work. Please visit www.acuitycommodities.com for detailed information. q Sulfuric Acid Today • Spring/Summer 2021

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Feature

Acid Piping Technology celebrates 30 years of service By: April Kabbash, Editor, Sulfuric Acid Today

When Ed Knoll started Acid Piping Technology (APT) in 1991, it was truly from the ground up—he even enlisted his sons, Alex and Fritz, to help pour concrete for the building during that summer. From those humble beginnings in Arnold, Missouri, Acid Piping Technology has grown to be a premier supplier of sulfuric acid piping, fittings, and tower internals around the globe.

With excellent customer service and an unparalleled knowledge base, APT is known not only as a supplier of MONDI™ piping and equipment, but as a team of sought after experts in the field of acid piping. And what started as a family business has stayed that way – Alex is a member of APT’s sales team, while Fritz serves as Production Manager. As the company celebrates 30 years in the sulfuric acid industry, they took a moment to reflect on changes they’ve seen in the business, and what sets the company and its offerings apart.

Acid Piping Technology has focused on piping for the sulfuric acid industry for 30 years. What piping options are there for these facilities?

The choices of acid piping material in today’s sulfuric acid plants typically include MONDI™ high silicon ductile iron and high silicon stainless steel. There are other materials—such as Alloy 20, SS316, SS310, and Teflon®-lined piping—which can have specific uses within an acid facility and are not the best options for the contact areas of the plant. Those materials are better suited for smaller piping sizes, less than 3 inches (80 mm), such as sample lines and effluent drains. For hot, concentrated sulfuric acid in the drying and absorbing tower sections of the process, MONDI™ and high silicon stainless steel are the more appropriate choices.

What made Acid Piping Technology decide to focus on MONDI™ piping?

MONDI™ and alloy high silicon stainless steel products both work well when the plant is running within the recommended operating parameters. However, the true test of the real value of a sulfuric acid pip-

Two generations of the Knoll family work together to meet the needs of Acid Piping Technology’s customers. From left are Ed, Fritz and Alex Knoll.

PAGE 12

Fritz Knoll at age 15. Today, he serves as APT’s Production Manager.

Fritz Knoll, left, and the late Jon Quarles, right, discuss the progress on APT’s headquarters in 1991 with one of the many craftsmen involved in the project.

ing system is how well it performs when the operating conditions go awry.

Over the expected service life of a typical sulfuric acid plant, it is not a matter of if, but when, a weak acid excursion will occur. MONDI™ is the only type of sulfuric acid piping system that can tolerate a weak acid excursion without suffering catastrophic damage.

First developed in 1983, MONDI™ is a proprietary material available from Acid Piping Technology and a registered trademark of Monsanto Enviro-Chem. The material evolved as the industry moved away from cast iron into ductile iron. While at the time the newer ductile iron was an improvement over brittle cast iron in some respects, the thinner-walled ductile iron piping corroded at a faster rate than cast iron. Though MONDI™ is in the ductile iron family, its metallurgy is an alloyed ductile iron with an increase in silicon and other alloying elements and thus an improvement over the previously used standard ductile iron materials. MONDI™ quickly became a preferred choice having over 800 plant systems worldwide. Today, at least 92 percent of the acid plants in North America use MONDI™ piping materials. Avoiding the problems of the thinner-walled materials available in the standard ductile iron industry, MONDI™ piping and fittings are produced with much heavier-walled sections providing a generous corrosion allowance.

Advantages

While MONDI™ requires additional joints due to flanged connections and re-

quires operating velocities no greater than 5 to 10 ft/sec depending on pipe size and conditions, MONDI™ has many advantages including: • Provides approximately four times the corrosion resistance of standard ductile iron. Of the choices available today, it is the only material able to handle the corrosive qualities of chloride and fluoride.

• Suitable into the oleum ranges.

• Has excellent ability to withstand weak acid excursions as compared to other choices.

• Pipe walls are heavy, providing a generous corrosion allowance and long life.

• Most fittings are designed with wall thicknesses heavier than 250 psi ductile iron patterns.

• MONDI™ utilizes simple bolt together flanged connections.

• Much less expensive than high silicon stainless steel by 1/3 to 1/4 the cost.

• MONDI™ doesn’t require chaplets in fittings or pipe.

How reliable is MONDI™ piping in a strong acid environment?

It is in the best interest of sulfuric acid plant owners and operators to have the piping supplier provide the “available corrosion allowance” for the piping material that you choose. Generally speaking, the available corrosion allowance for MONDI™ piping is approximately one half of the original wall thickness.

As an example, a 24” MONDI™ Flanged Short Radius 90 Degree Elbow has an initial wall thickness of 1.16”, so one half of this thickness would be 0.58” of available corrosion allowance before the item should be considered for replacement.

The yearly corrosion rate of MON-

MONDI™ piping is a valuable option for sulfuric acid plants.

APT has MONDI™ tees and crosses in a range of sizes.

APT can provide specialty items, like this large-diameter S02/SO3 damper valve, to fill any need.

DI™ is approximately 5-8 mils (0.0050.008”)—so if you have 0.58” of available corrosion allowance, and you use less than 0.01” of wall thickness per year, you can see how long this MONDI™ elbow will last in sulfuric acid service.

By comparison, the available corrosion allowance for alloy high silicon stainless steel is approximately 1/32” (0.03125”). This miniscule available corrosion allowance leaves you very little margin for error.

The corrosion resistance of high silicon stainless steel varies depending on acid strength. Corrosion rates increase dramatically as the acid concentration decreases, and rates below 90% can result in catastrophic failure, since you only have 1/32” of available corrosion allowance to work with. Higher corrosion rates in the 60-90% concentration range are likely attributable to insufficient oxygen available to passivate the alloys.

Can you tell us a little bit about your service and customer satisfaction initiatives?

At APT, we do everything we can to make the purchase and installation process easy for our customers. MONDI™ arrives from several large U.S. inventories prefabricated as a flanged system ready to install with basic hand tools. Field fabrication or modification can be done by most machine shops. Custom-fabricated MONDI™ spools and the mating fittings can be shipped the same day if required.

Both the chemical composition and manufacturing techniques used to cast MONDI™ have evolved to the point where APT can now provide a virtual lifetime warranty on MONDI™ strong acid piping.

The 30-year warranty applies to all MONDI™ fittings 6” and larger. It provides nocharge replacement for the first 15 years and pro rata for the balance; and it applies to new grass roots plant construction with temperatures and velocities in accordance with published guidelines.

As Acid Piping Technology heads into its fourth decade serving the sulfuric acid industry, the company will continue to bring the highest-caliber service and products to its growing list of satisfied customers.

For more information, please visit www.acidpiping.com. q Sulfuric Acid Today • Spring/Summer 2021

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Department

Lewis® vertical sulfuric acid pumps save South American smelter $100K & 200 hours By: Martha Villasenor, Senior Sales Engineer, Weir Minerals

Leaks and failures

A smelter in South America was experiencing pump leakage and failure due to the extremely corrosive, high temperature acid in its sulfuric acid plant. The incumbent horizontal pumps leaked at the shaft seal and volute, causing excessive wear in the pumps’ components. This led to constant disruptions in the process, with failures occurring at least once a week.

Additionally, the leaks caused damage to the floor and hazardous working conditions for operators. The facility needed a reliable solution to keep their workers and the environment safe, and to increase uptime, since the plant was operating at only 50-70% of capacity due to the pump failures.

New pump design

The Weir Minerals team completed a full analysis of the sulfuric acid process and proposed a new layout incorporating Lewis® vertical externally mounted (form E) sulfuric acid pumps to replace the incumbent horizontal pumps.

By selecting a Lewis® externally mounted vertical pump design configuration, the

Lewis® vertical sulfuric acid pump

facility would not need to build a separate pump tank, which would save on cost and space. Compared to a horizontal pump design, harsh acids do not touch the shaft sealing and won’t compromise the sealing elements in the vertical design of a Lewis® pump, eliminating the risk of acid leaks or spills on operators.

Additionally, Lewis® pumps are made from robust construction materials to combat the effects of a corrosive acid environment.

Lewmet® nickel-chrome alloy is used for critical wearing parts to provide maximum corrosion resistance.

Saving maintenance time and money

Now the pumps at the plant are no longer leaking or restricting plant capacity. Af-

Leaks in the seal of the incumbent pumps.

ter the layout changes were completed and the Lewis® pumps were installed, the pumps operated for more than 12 months without leaking or needing maintenance. Operators were extremely pleased by how long the pumps lasted and stopped for preventative maintenance after 12 months. Once restarting, the Lewis® pumps continued to operate for another 18 months without downtime.

Compared to the incumbent horizontal pumps that lasted only one week, the operation saw a decrease in maintenance time by more than 200 hours per annum.

In addition to more reliable and safer operations, the plant no longer needed to

Lewis® vertical pump in operation.

make regular short-term replacements of the pumps’ impellers, volute, and seals, which resulted in a significant cost savings of more than $100,000 per annum.

For more information, please visit

www.global.weir. q

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PAGE 14

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Sulfuric Acid Today • Spring/Summer 2021

Department

lessons learned: Case histories from the sulfuric acid industry

The risks of overlooking the support of the catalyst

By: Walter Weiss, Process Engineer, DuPont Clean Technologies, owner of MECS® sulfuric acid technology

In sulfuric acid production, over the years there has been much effort placed on improving catalyst performance in the oxidation of SO2. This effort has resulted in new formulations, new shapes and sizes, lower light off temperatures, and improved dirt handling capability. This effort has also seen modification in converter flow arrangements. In fact, there are a few basic items that have remained relatively unchanged, except for the support of the catalyst. Overlooked and taken for granted maybe, a refresher may be in order.

When overlooked long enough, problems may result.

Catalyst is loaded into a multipass converter vessel with interbed cooling. A flow of gas bearing SO2 is directed through the bed, normally in a downward direction. In the design of the converter vessel, using stainless steel or carbon steel/cast iron, there is a support network that keeps the catalyst in its intended location. If this support network is compromised or fails, catalyst can move from its intended location to other locations within or even outside the converter. Needless to say, catalyst not in the location necessary to properly contact the gas flow is not effective in the conversion of SO2 to SO3.

In current designs, the converter fabrication often utilizes a welded grid of stainless steel members supported by posts or by direct attachment to vessel or core walls. Older designs utilized a piecemeal arrangement of triangular cast iron grids supported by cast iron posts. On top of either system was a screen and the bed was loaded on the screen.

A typical catalyst bed loading is depicted in Fig. 1, with the catalyst layered between two 50 mm (2 inch) courses of ceramic such as support balls or special river rock. The upper level of ceramics serves to stabilize the top of the bed against the horizontal movement from gas flow as well as provide some preliminary distribution of dust and ash entering the bed with the gas.

The lower level of ceramic support separates the catalyst from the screen. It is important to completely cover the screen with ceramics as contact between the catalyst and stainless steel material may cause damage to both. During catalyst screening, the support material is also removed from the bed to allow inspection and cleaning of the screen.

The ceramics are replaced upon completion, but some loss of material is common. More screenings result in more material loss. There is rarely an effort made to replace this missing material and the thickness of the ceramic bed declines over time. This allows contact between the catalyst and the screen. In addition to increased screen corrosion, catalyst rings may fall through the damaged screen.

Screen material recommended for the higher operating temperatures of passes one and two is 321 stainless steel. The other passes operating at lower temperatures can utilize 304 stainless steel. Although some owners prefer to use 321 stainless screen material throughout to Fig. 1: Typical catalyst bed loading elevation. simplify inventory.

Screen diameter is normally 3.76 mm (0.148 inch) with centerline spacing of 13 mm (0.51 inch). This should give an open area of 50 percent or more. This is sufficient to support the 19 or 25 mm PAGE 16

(0.75 or 1 inch) ceramic material.

The converter diameter and all the internals expand with heat. A large converter can grow several inches radially from cold to operating temperature. The installation of the screen needs to accommodate this growth. Note that the screen may not grow directionally with the converter but may deflect some of its growth downward into the open area of the steel supports below. Pressure drop likewise tends to deflect the screen into these openings and not expand fully with the shell. Hence, screen sections are not installed with joints edge to edge. An overlap of about 80 mm (3 inches) is suggested.

The overlapped screen is tied with wire roughly 3.43 mm (1/8 inch) diameter made of the same material as the screen.

Screen is trimmed to the shell diameter (cold) and the edges rest on a 90 mm (3.5 inch) wide retainer ring, which is part of the converter shell. Some utilize the practice of a slight roll of this screen edge up the shell wall. Posts in the converter must pass through the screen and catalyst bed. The screen needs to be cut to fit around these posts. A retainer ring inside radius is 5 mm larger than the post and is installed to slide down the post and cover the screen. Retainer ring annulus is 70 mm (2.75 inch) wide radially. It is then wired into place using the same wire as the screen joints. See Fig. 2.

The life of pass one screen and wire is typically eight to

Fig. 2: Retainer rings help seal space around converter posts.

ten years when operated at 600°C (1100°F) or more. Screens in the other beds last longer–often much longer–and are not changed out for many years.

The screen should be inspected and cleaned whenever the catalyst bed is screened. Many owners change this material out proactively based on time or visual appearance. Even without screening, the condition of the screen may be observed from the vestibule below. Sometimes, the screen is left in service too long and failure results, as shown in Fig. 3.

Failed screen material allows the support media and then the catalyst rings to pass through and fall to the divi-

Fig. 3: Failed converter screen section.

Fig. 4: Thinning catalyst bed section due to failed support.

sion plate or converter floor below. This leaves a thin spot in the catalyst bed. See Fig. 4.

Thin spots allow a low resistance path for gas circumventing the catalyst bed with a reduction in overall bed pressure drop, temperature rise, and conversion. The catalyst may remain directly below the opening in the support screen but may be carried downstream and into the outlet duct and heat exchangers.

There is no on-line repair solution for the operator. There is no good short shutdown solution either. If loss of throughput or high stack emissions resulting from the support failure make further operation intolerable, then the plant needs to be shut down, the converter needs to be cooled, and the bed contents removed to access the screen.

About DuPont Clean Technologies The Clean Technologies division of DuPont is a global leader in process technology licensing & engineering, with an unwavering commitment to customer support. We provide extensive global expertise across our portfolio of offerings in key applications - MECS® sulfuric acid production, STRATCO® alkylation, BELCO® wet scrubbing and IsoTherming® hydroprocessing. Offering critical process equipment, products, technology and services, we enable an array of industrial markets, including phosphate fertilizer, non-ferrous metals, oil refining, petrochemicals and chemicals, to minimize their environmental impact and optimize productivity. We are dedicated to helping our customers produce high-quality products used in everyday life in the safest, most environmentally-sound way possible, with a vision to make the world a better place by creating clean alternatives to traditional industrial processes. We make everyday life better, safer, cleaner. For more information, please visit www.cleantechnologies.dupont.com About DuPont

DuPont (NYSE: DD) is a global innovation leader with technology-based materials, ingredients and solutions that help transform industries and everyday life. Our employees apply diverse science and expertise to help customers advance their best ideas and deliver essential innovations in key markets including electronics, transportation, construction, water, health and wellness, food and worker safety.

More information about the company, its businesses and solutions can be found at http://www.dupont.com. Investors can access information included on the Investor Relations section of the website at investors.dupont.com.

DuPont™, the DuPont Oval Logo, and all trademarks and service marks denoted with ™, SM or ® are owned by affiliates of DuPont de Nemours, Inc. unless otherwise noted. q Sulfuric Acid Today • Spring/Summer 2021

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Feature

Understanding spray technology to optimize sulfur burning By: Chuck Munro, Regional Spray Specialist, Spraying Systems Co.

Furnace optimization and efficiency are directly related to the spray nozzle used to inject sulfur. Spray nozzles provide a specific volume of fluid at a specified pressure drop.

Spray nozzles also convert the sulfur into a predictable drop-size spectrum with a specific spray coverage. The ability to compare and understand spray performance attributes is important when deciding which spray nozzle to use.

Spray nozzles are designed to produce a specific spray pattern, typically full cone, hollow cone, and flat spray. These names reference the shape of the resultant spray, and each has distinct differences. For instance, a full cone spray pattern typically has a wider drop size spectrum (the difference between the smallest and largest droplet size formed), has the largest droplet size in general, and has a comparably smaller maximum free passage.

The flat spray has a more compressed pattern, resembling a cat’s eye or oval. Hollow cone has a comparably tighter drop size spectrum, smaller droplets in general, and a larger maximum free passage.

Of the three, hollow cone sprays are widely used in sulfur burning due to their spray droplet distribution. The hollow cone spray pattern is formed by injecting a stream of fluid tangentially into a swirling chamber.

The swirling action allows a uniform film of liquid to discharge from the nozzle forming a ring of fluid, hence the “hollow cone” designation. Hollow cone spray nozzles produce smaller droplets and a tighter spectrum of droplets than full cone or flat spray nozzles.

This means the droplets are relatively uniform in size throughout the spray. Having uniform droplet size means that during the combustion process (inside the furnace) there is a defined combustion zone and defined distance for full evaporation and combustion. This ensures the molten sulfur is fully combusted and converted to SO2 at the outlet of the furnace. Hollow cone spray nozzles have a large free passage, so the risk of clogging is minimal.

Accurate droplet size information is an important factor in optimizing spray nozzle performance. In addition to spray pattern, other factors such as liquid properties, nozzle capacity, spraying pressure, and spray angle affect droplet size. Lower spraying pressures provide larger droplets. Conversely, higher spraying pressures yield smaller droplet sizes.

For sulfur burning, 50 psi (3.4 bar) minimum spraying pressure is recommended, both for practical and performance reasons. The hollow cone spray nozzle can form a spray pattern below 50 psi (3.4 bar); however, droplet integrity tends to diminish below that. When considering a change to spray nozzle capacity, note that smaller capacities produce smaller droplets and larger capacities produce larger droplets at the same spraying pressure.

Accounting for this change is important when PAGE 18

3/8” BA WhirlJet® Hydraulic Nozzle @ 100 psi (7 bar) - Flow Rate: 5 gpm (19 lpm) Fig. 2: Hollow cone spray pattern

Fig.1: Computational Fluid Dynamics (CFD) illustrates the swirling action inside CBA WhirlJet® hollow cone nozzles that produces a uniform spray in a ring-like pattern.

Conventional sulfur guns protrude slightly from the steam jacket. CBA sulfur gun is recessed into the steam jacket to ensure temperature uniformity and eliminate or dramatically reduce the chance the sulfur will solidify and plug the gun.

looking to increase capacity of the furnace.

Fig. 3 provides an excellent example of how much the performance changes with operating pressure and flow rate. The larger droplets are clearly seen when we reduce the operating pressure from 100 psig (7 bar) to 20 psig (1.5 bar). These larger droplets will then take longer to evaporate and combust.

Drop size terminology is often a major source of discrepancy and confusion in understanding spray droplet size. To accurately compare droplet size from one nozzle to another, the same identifying characteristics must be used. Droplet size is usually expressed in microns (micrometers). Following are the most common characteristic diameters and their definitions.

Volume median diameter, Dv0.5, droplet size, when measured in terms of the volume, is a value where 50% of the total volume of liquid sprayed is made up of drops with diameters larger than the median value and 50% with smaller diameters. Similarly, Dv0.9 is a value where 90% of the total volume of liquid sprayed is made up of drops with diameters smaller or equal to this value. This measurement is a key variable to consider, because the dwell time required inside the furnace for complete combustion will be based on the largest droplets in the spray.

Sauter mean diameter, D32, describes the diameter of a droplet having the same volume-

to-surface area ratio as the total volume of all the droplets to the total surface area of the droplets. Sauter mean diameter is important to consider for sulfur burning because it provides the best measure to understand the fineness of the spray. It’s a measurement used in studying mass transfer and rates of reaction for applications such as evaporation and combustion.

A brand-new spray nozzle has a predictable flow rate, spray pattern, and spray droplet distribution. In a sulfur burning application, over time, a layer of sulfur may form inside the nozzle leading to spray nozzle orifice plugging. As the sulfur builds up inside the nozzle, the original swirl chamber and uniform film of liquid that discharges the orifice changes. This results in a complete shift in performance. The most common identifiers that a producer will notice is a reduction in flow rate and the spray ring potentially having streaks of heavy spray. If either of these are observed, it is also certain that spray droplet distribution has changed.

A preventive maintenance schedule should be established to monitor spray nozzle flow rate and spray visual. After removing a sulfur gun, do a visual inspection of the spray nozzle orifice and look for any buildup of sulfur. This can be difficult to detect visually, so a bench test while spraying water can often be a better determinant. Spray water through the nozzle for a defined period while capturing the water. Note the spray pressure and compare the flow rate versus pressure to a performance chart of the spray nozzle. If there is any buildup, a decrease in liquid sprayed

3/8” BA WhirlJet® Hydraulic Nozzle @ 20 psi (1.5 bar) - Flow Rate: 2 gpm (8 lpm) Fig. 3: Optimal spray pattern (top). Visible droplets (bottom) appear with reduced pressure and flow rate.

at similar pressures will be noticeable. “Fig. 4 compares a new spray nozzle (black line) to a used spray nozzle (red dots) that has sulfur buildup on the spray nozzle internals.

Please note that a spray orifice should never be cleaned with a wire brush or any other tool that could damage the orifice. This can also result in a negative change in performance. If the spray nozzle is clogged by foreign debris, different acceptable methods for cleaning include soaking in a solvent, flushing with running water, or using compressed air with an air hose.

Understanding spray nozzle performance and how that performance affects overall production efficiencies can help in selecting the best equipment for a facility.

Reliability and maintenance are linked to the spray nozzle performance and should be considered as well.

Chuck Munro has more than 20 years of experience in spray technology with Spraying Systems Co. He is a specialist in the petrochemical sulfur industries and is active in several industry committees. For more information, visit www.spray.com. q

Fig. 4: Effect of sulfur buildup on spray nozzle (red dots) versus clean nozzle (black line).

Sulfuric Acid Today • Spring/Summer 2021

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New CBA sulfur gun reduces the risk of pluggage and maximizes production time.

The nozzle is recessed in the steam jacketed gun to ensure the sulfur remains at the optimal temperature even when flow rate is reduced. CBA sulfur nozzles provide the same performance as our BA WhirlJet® nozzles – the industry standard – small droplet size and narrow droplet spectrum.

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FloMax® sulfur guns use air atomizing nozzles to produce smaller droplets than conventional hydraulic nozzles.

The result is enhanced evaporation and combustion. The atomizing air flow provides a secondary benefit of purging the guns of potential build-up and ensuring uninterrupted operation.

Ideal for use in spent acid plants.

Maximize sulfur gun performance and minimize the chance for problems such as sulfur impingement on walls with our modeling services. Using Computational Fluid Dynamics, we can determine the best gun placement in the furnace, ideal drop size for complete vaporization and more to ensure maximum production and minimal maintenance.

Feature

Training designed for success

By: Tony Constantino, Safety Coordinator, VIP International Inc.

We should ask ourselves, what is our goal in developing a training process?

Should we consider a proactive approach to effective developmental skills such as communication, decision making, and time management? The environment in which we work today has evolved through improved training techniques along with a dedication to overall safety. The establishment of the Occupational Safety and Health Administration (OSHA) provides a great number of positive changes that are adopted by many industries. Companies have strived to develop and advance training in order to increase safety and quality of work. While OSHA has set the minimum standard requirements for training, it is up to the organization to exceed the expectations. As a whole, companies worldwide have seen a decrease in accidents, injuries, and death due in part to effective training.

With the development of a strategic program, we allow employees an opportunity to utilize hard skills, as well as soft skills, to reach their full potential.

Thinking back on past training design, it is clear that the point of interest was always “how to do the job.” Hard skills are technical and developed in many cases through on-the-job experience. It is easy

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to identify the importance of hard skills in that they are the foundation of the work ethic. During hard skill training, employees undergo the necessary training to accomplish job tasks in the field. This provides a hands-on advantage and can be performed and reinforced while on the job.

It allows the employee to be productive while learning new skills. On the other hand, some training is best suited to a classroom with an instructor or computerbased application. Companies must take into consideration the training needs best suited for each employee and their learning styles. The most common types of learning styles include visual, auditory, and physical. In order to effectively provide training, the company may choose a multipurpose training module created to provide a hands-on approach with group projects, lectures, and videos.

Although these fundamentals are necessary, companies have learned they are not enough. Organizations have discovered that it is beneficial to look at a more holistic (comprehensive) approach to learning.

One way of doing this is by implementing soft skill training where the focus is on the development of the employee’s interpersonal skills. Companies may perform a training needs analysis to identify opportunities of improvement. For example, the focus for success can be communication, decision making, and time management.

After additional training modules have been identified, the training should be developed based on the needs and evaluated on the effectiveness of that training.

Communication is one of the most important tools in our box. It is crucial to have employees in the field who are

proficient in hard skills while being able to successfully communicate. Effective communication includes the ability to listen, collaborate with others, present ideas, and communicate with team members—all highly valued skills in a healthy workplace. Along with communication, it is important that employees understand a strategic process for decision making. This will enable them to define the problems more efficiently, thus enhancing their work performance. Time management has proven again and again an important ingredient to reaching personal and professional goals. When employees and managers are aware of the goals, it puts everyone on the same page and working toward the same outcome. Employees will then begin to use their action items to complete tasks throughout the workday.

These soft skills are directly transferrable to any job, organization, or industry.

“ The goal is to never

stop improving…

The more companies empower their employees, the more they will naturally develop tools to succeed.

” The development of the employee is continuous with a holistic approach. Soft skills are equally as important as hard skills.

The hard skills serve as the foundation, but the soft skills obtained will transform employees to greater levels of leadership, teamwork, and job performance. The goal is to never stop improving. The more companies empower their employees, the more they will naturally develop tools to succeed.

If the employee is successful, then the company is as well. Invest in the employee and they will invest in themselves.

For more information, please visit www.vipinc.com. q

Sulfuric Acid Today • Spring/Summer 2021

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Absorption-irrigation systems

Drying and absorption towers are usually packed irrigated columns where the gas is fed in counter-current to the acid.

There are other designs on the market, especially as pre- or hot absorbers, where venturies are in use.

Brick-lined towers

The classical design of the absorption tower is a mild steel shell with acid-resistant brick lining. The most common design includes a foil-protected steel surface and bricks laid in mortar against the foil. The foil itself is not resistant against the strong sulfuric acid, but is carbonized forming a dense layer of carbon. This carbon layer increases in volume and prevents acid from contacting the steel surface.

If the brickwork is executed in a professional way these towers are very robust and long-lasting equipment. With skilled preventive maintenance the towers last more than 40 years, as some examples show.

The bricks to be used are preferably low in Al2O3, Fe2O3, CaO, and MgO and are laid in potassium silicate cement. The red acid proof bricks available in some areas of the world are less resistant and have reduced lifetime, as they are more vulnerable to variations in acid concentration.

There are two different kinds of grid designs on the market, supported grids and self-supported grids.

vantages resulting from the fact that the bricks between the arches were not in compression. Any acid leaking to the carbon steel shell would corrode the shell forming iron sulfate which would cause the bricks in the floor to heave upwards. Modern designs use a dished bottom so that the brick lining is always in compression.

Self-supporting grid

The standard in self-supporting domes is the Steuler-KCH Domed Self-Supporting Grid (Fig. 2). This grid was invented in the 1970s and patented in 1975. The dome can be designed to span over 10,000 mm.

It eliminates the need for the brick arch walls which greatly reduces the weight of the entire tower. The elimination of the supporting arch walls opens up the possibility to use any shape for a tower bottom the designer wishes. Domes also allow the installation of multiple packed sections in one tower without the need for additional supports. Hundreds of such domes have been installed already.

Supported grid designs

The traditional grid type involves beams lying on a brick ring at the circumference of the shell and on columns or arches in the center (Figs. 1). This design is still in use today. This type of packing support can be used for the smallest of towers and has virtually no upper limit in terms of the diameter of the tower since more arches are simply added to the design.

Former tower designs were made of flat bottoms on which the arches on columns rested. The weight of the arches, packing support, and packing all were transmitted down to the flat floor and onto structural steel beams located below the tower. The flat bottom has several disad-

Fig 1: Finished grid with grid blocks on top.

PAGE 22

Fig 2: Self-supporting grid.

Stainless steel towers

Stainless steel towers have been in operation since the end of the 1980s with good performance. They are made entirely of austenitic steels, mostly of Si alloy. In some instances they are formed with conventional austenitic steel, like AISI 310, especially when the risk of oleum formation is high. Today all designated major sulfuric acid plant designs have stainless steel towers in their portfolio.

A cost comparison between mild steel brick-lined towers and stainless steel towers would result in nearly equal costs, but in some cases, as with a revamp, it would be cheaper to install stainless steel towers.

Generally the local conditions and access to materials determine costs.

The advantage of stainless-steeltowers: • ease of repair of the tower.

• light construction, especially for revamp.

Their main disadvantage is their sensitivity to halogens like Cl and F.

In conclusion, assuming quality construction, the brick lined tower is the most reliable tower design, but stainless steel towers are an attractive alternative. The correct choice depends on the specific application.

Compactness

Compared to the system of the 1960s, the volume capacities have been substantially reduced. Some equipment has only half of the volume; this is especially true for sulfur furnaces, converters, and absorption towers. In addition, modern plate heat exchangers are a third the size of a tube bundle heat exchanger. The gas residence time in the process equipment of a sulfur combustion plant has decreased from 90 seconds in 1960 to below 50 seconds today.

Nowadays old ideas are reborn. The use of oxygen instead of air as a combustion medium in sulfur furnaces, metallurgical converters, and furnaces will lead to much higher SO2 concentrations. While normal atmospheric acid plants at maximum can operate with SO2-concentrations of up to 11.5 Vol.%, oxygen-enriched designs process SO2 concentrations up to 30% or higher.

Sizes of plants are considerably smaller and the plot sizes could be downsized to the half of today’s existing plants. This requires even more and more effective irrigation systems.

Fig 3: Pipe distributor.

Deflection plate distributor

A modification of the pipe distributor is the deflection plate distributor, where the acid leaves at the upper part of the tubes and sprays against a deflector plate. Obviously, this creates a lot of spills as the distributor has to be installed above the packing.

Irrigation distributors

Irrigation distributers were originally made from cast-iron in a trough design (open channel). In the 1980s, the first high-corrosion resistant austenitic steels appeared, significantly influencing distributor design. Pipe distributors developed and became widely used for their precision distribution and performance.

However, there were significant disadvantages to the pipe distributors and other distributors in the market. This inspired the development of today’s high-performance absorption towers.

The following compares some wellknown distributor systems.

Pipe distributor

In a high-performance pipe distributor system, acid is fed by a header and the acid flows out under pressure. The system can be designed in a flat design saving some tower height, but that is mostly not achievable as the height between packing and mist elimination is defined by human accessibility. An advantage is that the distributor can be covered with additional packing to reduce spillage.

Fig. 4: Deflection plate distributor.

Trough distributor

A well-known design is the trough design reminiscent of the cast-iron age.

With new stainless steel materials like SX, or other silicon-containing austenites, the design could be made with greater precision allowing for a very homogeneous distribution. The principle is that the acid is free-flowing in channels and flows out by down–comers into the packing. Designs

Fig. 5: Trough distributor.

Sulfuric Acid Today • Spring/Summer 2021

Remarks

Results

Distribution

equal irrigation along irrigation arm by liquid chamber – transverse distribution ~ 300 to 500 mm

✔

Acid Inlet Velocity

lowest velocity of all known systems due to force by gravity

✔

Creation of Droplets

also small droplets are avoided

✔

Free Gas Flow Area

65 – 80% depending on irrigation rate

✔

Risk of Blockages

no risk because smallest gap is:

✔

•

more than 50 % larger than open screen size and

•

max 50% of width of outlet-triangle and flushes out of larger particles

Table 1: Advantages of HP Fall-Film distributor

can be configured with more than 40

opening of the distributor will create some

down-comers per square meter, but this is

problems due to blockages of the slots at the

expensive and requires high maintenance.

out-flow in the packing.

Film distributor

HUGO PETERSEN Fall-Film

tributor, as it is adapted to high-gas-veloc-

An up-to-date design is the film dis-

ity towers. The acid is homogeneously distributed inside the distributor over a slotted tube and out-going acid flows along a guiding plate into the packing.

The system needs a relatively low pres-

sure drop to achieve a good distribution, no spillages, and homogeneous distribution along the irrigation channels. The narrow

distributor

The HUGO PETERSEN Fall-Film

distributor (pat. pending) improves on many of the previous designs. The basis is a film distributor with internal distribution of the acid in a channel via slotted plates into a lower channel with triangular out-

Type of System

Distribution

Acid Inlet Velocity

Avoidance Creation of Droplets

NON-Risk of Blockages

Free Gas Flow Area

Rank

Fall-Film Distributor

++

++

++

++

++

1

Film Distributor

++

++

++

-

++

2

Trough System

++

++

++

-

-

3

Pipe Distributor

+

O

O

-

++

4

Deflection Plate System

++

o

--

-

--

5

Table 2: Distributor comparison.

LEGEND: ++ excellent + good O satisfactory - poor -- very poor

The spillage- and blockage-free

tor by avoiding blockages from particles.

design, in combination with a homoge-

Table 2 compares the distribution systems

neous distribution, is an innovation in liq-

previously discussed.

uid distribution. The distributor is specially

made for today’s generation of drying and

strate again the first class design of HUGO

absorption towers.

PETERSEN’s Technology.

The following table lists the achieve-

The before mentioned facts demon-

The patent pending Fall-Film distribu-

ments reached with the new design.

tor is a development of HUGO PETERSEN

ing plate forcing the acid to flow along the

Finally, the Fall-Film distributor

GmbH Wiesbaden, Germany. For more infor-

plate into the packing.

includes the advantages of a film distribu-

mation, please visit www.hugo-petersen.de. q

lets, where the acid flows towards a guid-

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www.hugo-petersen.de Sulfuric Acid Today • Spring/Summer 2021

PAGE 23

Feature

Features

Feature

Glencore Nickel replaces sulfuric acid drying tower in record time A world-leading producer and marketer of nickel, Glencore Nickel operates assets in Australia, Canada, and Europe. The company mines nickel in Ontario, Quebec, western Australia, and New Caledonia, and operates a nickel refinery at Kristiansand in Norway.

The Norway site, Glencore Nikkelverk, can produce around 92,000 mt of nickel, 39,000 mt of copper, 5,000 mt of cobalt, and 115,000 mt of sulfuric acid a year.

When the brick-lined sulfuric acid drying tower began to leak back in 2016, the company realized it had to be replaced as it could not be repaired. Time was of the essence. Glencore wanted to limit shutdown for dismantling and installation to a maximum of seven days. The company commissioned DuPont Clean Technologies with the design and fabrication of a new 3,000 mm MECS® ZeCor® drying tower with the aim of achieving a fast turnaround through a “plug and play” installation. The tower size was based on advanced DuPont Clean Technologies design standards to allow for maximum drying efficiency and low pressure drop. This case study traces the journey of the replacement tower development and installation.

brick-lined towers which are irreparable when sulfate starts to leak into the space between the bricks and the outer shell.

In addition to the ZeCor® drying tower, DuPont also supplied all the tower internals including ceramic packing, a UniFlo® acid distributor and Brink® CS mist eliminators to achieve maximum drying efficiency and low pressure drop. Low pressure drop translates into energy savings at the start of the production cycle and allows sulfuric acid plant operators to maximize throughput over time.

To speed the project along, Glencore managed on-site work itself and local contractors in Kristiansand were hired to dismantle the old tower and fit the new tower internals. To prepare for the construction and installation of the new tower, a 3D model was produced by Glencore based on DuPont Clean Technologies’ drawings and assets. This proved to be extremely useful to secure correct positions for the new tower structure, acid piping, and the connections and gas ducts between the old and new equipment.

Project constraints

Safe removal, installation, and operation of any equipment is key to ensuring timely start-up. “DuPont has long focused on safety as one of our four core values, not only to safeguard the wellbeing of all site personnel, but also because it is regarded as a major contributor to operational performance,” Lepeu explained.

“Safety is therefore routinely integrated into all stages of any DuPont project development and execution. In this case, that not only includes the tower design, but also its construction, installation, operation, and maintenance. Before and during installation every shift held safety and coordination meetings, making certain that everyone was aligned and aware of what was happening.”

Planning was also considered to be a crucial element to making sure there would be no incidents in the run-up to commissioning. Nikkelverk and DuPont therefore took the time to calculate the weight of the old tower to determine the required crane size and to organize each step of the dismantling process. The technical 3D model of the plant with the new tower helped with accurate piping and platform positioning. All connections were prefabricated, with final adjustments made during installation.

The leaking brick-lined drying tower at the Kristiansand Nikkelverk site had originally been installed in 1987. By 2016, several leaks in the bottom section near the gas inlet and the manhole were presenting the operating team with a day-to-day issue. It was clear that patching and repairs were not going to last, and the ongoing maintenance was beginning to cost valuable production time. To ensure production could continue smoothly, the plant needed a new tower.

However, time was of the essence. “We wanted to limit shutdown for dismantling and installation to a maximum of seven days,” Øyvind Ommundsen, roaster and acid plant manager, Glencore Nikkelverk AS, explained. “After looking at several options, we decided on a MECS® ZeCor® alloy tower from DuPont Clean Technologies to reduce down time and ensure fast delivery and installation.”

Nicolas Lepeu, key account manager EMEA, DuPont Clean Technologies, was not fazed. “While construction of drying towers can take time, it is possible to safely install a new tower in a shut-down window of seven days given good planning and collaboration between the plant operator and engineering/design suppliers,” he said.

After initial technical discussions in August 2016, DuPont Clean Technologies was awarded the design and fabrication of the new MECS® ZeCor® drying tower in November of that year. One of the benefits of ZeCor® alloy towers compared to bricklined towers is that they are easy to reweld if a leak occurs. That is not the case for PAGE 24

Good planning is key to a safe and timely execution

Model of Nikkelverk acid plant with new tower.

required safety performance records. All suppliers also receive the necessary training to work safely with the different hazards existing in and around an acid plant.”

All projects furthermore had their own risk assessment prior to execution. This project needed careful planning of all crane lifting activities as the old tower was much heavier than the new ZeCor® tower and both needed to be lifted over other existing equipment. The weight of the old tower was estimated at 50 tons including packing and bricks while the new tower with internals weighed 26 tons. To be able to lift the old tower the required distance safely, a 500-ton crane was hired.

Both the old equipment to be removed and the new equipment to be installed needed to be lifted over and across other critical equipment. Any damage during these activities could easily delay production start-up.

Special focus was put on the use of PPE during removal of old equipment containing sulfuric acid. Other high-risk safety issues that needed daily attention and planning were working at height, working in confined space areas, the risk of hydrogen formation

from corroded material in the old tower, and acid spills, among others.

Achieving fast installation

In order to keep shut-down time to a minimum, fabrication of the tower took place in a workshop with which DuPont Clean Technologies has a close, longstanding partnership. This allowed for very accurate quality control during all critical phases of the manufacturing process, while at the same time achieving the logistical agility to provide Glencore with a high level of responsiveness and on-time delivery.

All the tower internals were preassembled near the nickel production plant and were installed by a local contractor. In this way, final installation could be limited to the removal of the old tower and the “plug and play” of the new tower.

ZeCor® is an extremely light, highly corrosion-resistant alloy that has proven its worth in a variety of sulfuric acid concentrations, temperatures, and applications. Its low weight meant that there was no need to modify existing civil works. The tower could simply be lifted into place in the exact same location as

Safety considerations during dismantling and installation

As Ommundsen explained, “Nikkelverk works with prequalified subcontractors who have the right qualifications and documented

Pre-assembly of internals.

Sulfuric Acid Today • Spring/Summer 2021

minimize their environmental impact and optimize productivity. We are dedicated to helping our customers produce highquality products used in everyday life in the safest, most environmentally-sound way possible, with a vision to make the world a better place by creating clean alternatives to traditional industrial processes. We make everyday life better, safer, cleaner.

For more information, please visit www. cleantechnologies.dupont.com.

MECS® ZeCor® drying tower being lifted into place at Nikkelverk Norway, in May 2017.

Conclusion

the quality specified with zero safety or environmental incidents.

While construction of drying towers for SO2 gases before they enter the sulfuric acid plant can take time, this case study demonstrates that it is possible to safely install a new tower in a shut-down window of seven days given good planning and collaboration between the plant operator and engineering/design suppliers. As a result of this approach, the project was executed safely, quickly, on time, and to

About DuPont Clean Technologies The Clean Technologies division of DuPont is a global leader in process technology licensing & engineering, with an unwavering commitment to customer support. We provide extensive global expertise across our portfolio of

offerings in key applications - MECS® sulfuric acid production, STRATCO® alkylation, BELCO® wet scrubbing and IsoTherming® hydroprocessing. Offering critical process equipment, products, technology and services, we enable an array of industrial markets, including phosphate fertilizer, non-ferrous metals, oil refining, petrochemicals and chemicals, to

About DuPont DuPont is a global innovation leader with technology-based materials, ingredients and solutions that help transform industries and everyday life.

Our employees apply diverse science and expertise to help customers advance their best ideas and deliver essential innovations in key markets including electronics, transportation, construction, water, health and wellness, food and worker safety. For more information, please visit www.dupont. com. Investors can access information included on the Investor Relations section of the website at investors.dupont.com.

DuPont™, the DuPont Oval Logo, and all trademarks and service marks denoted with ™, SM or ® are owned by affiliates of DuPont de Nemours, Inc. unless otherwise noted. q

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PAGE 25

Feature

the old tower by standard cranes. New ducting and piping were pre-assembled and required minimal work for final tie in. This made it possible to substitute the tower in a normal turnaround window, so that no production time was lost because of the replacement.

The final tower inspection at the workshop took place in March 2017. It was delivered to the site and pre-assembled mid-April 2017 and started up within a single day in May 2017. Since installation, it has performed beyond performance guarantees, even achieving a lower pressure drop than specified. The new drying tower, with its UniFlo® acid distributor and Brink® CS mist eliminators, has now been in operation for three-and-a-half years, delivering reliable drying and a much lower mean differential pressure than the old tower.

Feature

EXP’s sulfuric acid team delivers reliable, client-focused solutions

By: April Kabbash, Editor, Sulfuric Acid Today

With a mission to understand, innovate, partner, and deliver, EXP provides engineering, architecture, design, and consulting services to the world’s built and natural environments. As a leader in the fertilizers and chemicals sector, EXP’s experts have provided solutions for sulfuric acid plants around the globe. The company’s committed team of professionals apply their knowledge to deliver integrated, innovative solutions across industries. With a commitment to clients’ bottom lines and operational needs, EXP’s sulfuric acid team brings proven solutions to help meet each customer’s goal, whether that is plant expansion, heat and energy utilization and recovery, plant optimization or reliability, or safety services.

Headquartered in Brampton, Ontario, Canada, EXP employs more than 3,500 creative professionals across North America who provide the passion and experience needed to deliver successful projects around the globe.

Consistently ranked one of Canada’s top design and engineering firms, EXP is also the winner of countless engineering excellence awards. This team of experts is dedicated to providing innovative solutions across markets and geographies to solve clients’ most complex challenges. Those solutions, along with everything the company does, are firmly rooted in EXP’s core values: Integrity, Passion, Accountability, Transparency, Diversity,

and Community + Sustainability. These pillars consistently guide team members, no matter the size or scope of the job. As with most things in the sulfuric acid industry, finding the right people for the job makes all the difference to the outcome.

Sulfuric Acid Today sat down with EXP sulfuric acid experts Vulcan Mutler, Trevor Van Daele, Douglas Louie, Wayne Boyd, Brennan Afelskie, and Yi Zhou to get their insights on EXP’s role in the sector.

EXP serves a wide range of industries.

What sets your sulfuric acid team apart?

Vulcan Mutler, Senior Vice President of the Oil, Gas + Chemicals market: EXP experts have decades of experience across the complete range of acid plants, from sulfur burning through spent acid to metallurgical gas. To address the market’s dynamic needs of expected outcomes with tailored execution strategies that consider sustainability and unique client-specific requirements, EXP assembled the sulfuric acid team with recognized leaders in the industry, each bringing their unique experience to further enhance our ability to meet clients’ objectives. Furthermore, a significant portion of the sulfuric acid team is based in Houston, the center of the OG+C business, where there is a higher concentration of sul-

mental impacts, improving plant reliability, and increasing the capacity of operations. We are proud to deliver projects on time and on capacity that meet stringent process specifications and emissions requirements.

What strengths do you as a group bring to a project?

3D rendering of plant during design process.

furic acid plants than anywhere else.

What types of projects have you worked on in the sulfuric acid sector? Can you give us some details on your role in those projects and what EXP is most proud of?

Trevor Van Daele, Director of Engineering, Oil, Gas + Chemicals in Canada: EXP experts have been engaged in nearly every type of sulfuric acid project, from the replacement of plant equipment, to capacity upgrades, to greenfield projects. EXP experts have contributed to noteworthy and sizeable projects around the world. Our role for each project, whether metallurgical, sulfur burning, or spent acid plants using single absorption, DCDA, advanced heat recovery, and scrubber systems is to provide engineering and process solutions to each plant, as well as support our clients in reducing environ-

Wayne Boyd, Process Engineer: EXP’s strengths relate to the wealth of experience in process knowledge and breadth of execution models. Our team offers clients flexibility in the marketplace, accompanied by professionals who possess the experience to meet owner’s requirements, including completing a project on time, within budget, and meeting technical expectations. In addition, EXP brings clients the comfort of established relationships with technology providers and key suppliers to streamline project success. This includes over 50 years of working in varying geographic areas from arctic zones to deserts, as well as high seismic zones. In addition, the team’s experience ranges from the smallest to largest capacity (3x5050 MTPD) plants and the ability to scale the scope of a project to the client’s needs with extensive experience designing the balance of plant facilities, including power plants, tank farms, loading and unloading facilities, water treatment plants, and other utilities.

416.444.4880 admin@mercad.com ● www.mercad.com

PAGE 26

Sulfuric Acid Today • Spring/Summer 2021

Brennan Afelskie, Process Engineer: EXP is a client-focused organization and we are committed to working with clients on various contract models to result in reliable outcomes. We are confident in our ability to execute projects including on a lump-sum turnkey basis whereas other engineering companies may no longer execute under this model. The difference is that EXP has the expertise to execute and the ability to mitigate risk.

What’s the benefit to customers of EXP’s multi-faceted engineering and design teams?

Yi Zhou, Mechanical Engineer: EXP serves clients as a one-stop solution and trusted advisor. EXP provides clients with a full range of services, contract models, and

scope definition. We’re nimble and flexible to ensure requirements and specifications are met, from early project definition through commissioning and start-up. EXP can assist clients with their sulfuric acid plant with the following services:

• Conceptual design • Risk assessment • Environmental and permitting • Regulatory and compliance • FEL 1, 2, 3 studies • EPC – LS project management • Detail engineering • Global procurement • Construction management • Revamping and turnaround • 3D laser scanning • 3D modelling • PSV verification audits • HAZOP/HAZID, PSR, PSSR reviews • FEA/CFD analysis • Modular/containerized concepts • Commissioning & start-up • Operational readiness • Power studies What are the most common hurdles you face when beginning a new sulfuric acid sector project? What steps do you take to mitigate them?

Douglas Louie, Process Engineer: With our transparent approach and close working relationship with our clients, any hurdles are quickly removed. With any

Converter segments undergoing shop fabrication.

large project across complex industries, particularly the oil, gas, and chemicals industry, our teams are focused on satisfying owner expectations, while respecting budget and schedule constraints. With this understanding, our designs also consider environmental regulations, gaseous emissions, and more stringent standards. We have experience in incorporating innovative processes to accommodate revised emission regulations and our experienced team has been able to adopt and adapt accordingly. Our team walks through the scope of the work with the client to fully understand their core drivers and restrictions, so that we are fully aligned.

How does your Integrated Project Delivery option benefit customers?

Wayne Boyd: Whether EXP is serving as an EPC Contractor or through standalone Engineering and FEED services, our integrated project delivery approach remains consistent—utilizing the right experts to deliver expected outcomes to meet the cost, schedule, and safety standards of our clients.

What are the company’s future plans for the sulfuric acid industry?

Trevor Van Daele: EXP established the sulfuric acid group as an integral part of the company’s strategy. With the combined expertise of EXP’s experienced engineers and designers, we look forward to providing sul-

furic acid plants around the globe with reliable and effective solutions.

How do you apply the company’s Core Values (Integrity, Passion, Accountability, Transparency, Diversity, Community + Sustainability) to work in the Sulfuric Acid sector?

Vulcan Mutler: EXP’s core values reflect our commitment to exploring the possibilities with our employees, clients, and communities. Working in tandem with EXP’s mission and vision, we stay diligent in our efforts to enhance our workforce and the built and natural environment. Understanding we are in a dynamic and challenging sector, we utilize our values to propel our clients forward. The focus of each core value, from transparency in keeping our clients informed, to diversity, where we foster an environment where employees can grow and bring forth innovative ideas, yields results and reliability for our clients. At EXP, we are committed to upholding these values to result in more efficient sulfuric acid plants, as they are a crucial part of environmental emissions reduction. Through our role as a trusted advisor, we bring our decades of experience to provide proven results for our clients – and this all stems from who we are at EXP and what we do.

For more information, please visit www. exp.com or emailing Walter.Mutler@exp.com or Trevor.VanDaele@exp.com. q

40+

#13

years of experience across the energy industry

Chemical Plants, Top Design Firms in Manufacturing, ENR, 2020

With more than 40 years of sulfuric acid experience in North America and internationally, the EXP team delivers end-to-end services for our clients taking projects from conceptual study through to EPC LSTK. Our team of experts has demonstrated experience from the smallest to the largest sulfuric acid plants including advanced heat recovery systems, power generation, and oleum production within the metallurgical, sulfur burning and spent acid recovery markets.

Whether as an EPC project or through stand-alone engineering and FEED services, our focus is consistent - delivering expected outcomes through tailored execution, compliance, cost, schedule, quality and safety.

OIL + GAS | CHEMICALS | RENEWABLES | MIDSTREAM | OFFSITES | UTILITIES | INFRASTRUCTURE

exp com EXP_SAT_Ad.indd 4

Sulfuric Acid Today • Spring/Summer 2021

OG+C Head Office | Houston, TX | +1.713.439.3670

2/11/2021 8:45:38 AM

PAGE 27

Feature

Do you offer turnkey solutions, in addition to smaller-scope project oversight?

Feature

Sulfuric acid gas & mist cleaning: wet electrostatic precipitators for superior performance

By Gary Siegel, Marketing Director, Beltran Technologies Inc.

Industries that generate sulfur oxides and sulfuric acid include metallurgical smelters and refineries, petroleum refineries, natural gas processing facilities, electric generating units, spent acid regeneration plants, and municipal waste incinerators. In many cases, a common and cost-effective solution for capturing and utilizing sulfur oxides and corrosive sulfuric acid emissions is to have a downstream sulfuric acid manufacturing plant.

Operators of these facilities can take advantage of the high industrial market value of purified sulfuric acid, a primary industrial chemical used in fertilizer manufacturing; mineral processing; petroleum refining; wastewater processing; the manufacture of paints, dyes, detergents, lead batteries, and explosives; and the synthesis of other chemicals, as in the alkylation of gasoline additives.

An efficient sulfuric acid manufacturing process strictly requires the removal of contaminants from the input gas streams, especially fine particulates and acid mists such as those emitted from metal ore roasters and smelters, petroleum refineries, and coal-fired industrial boilers. This is necessary for protecting downstream components such as catalyst beds from corrosion, fouling, and plugging, as well as for preventing the formation of a “black” or contaminated acid end-product. Proper gas cleaning also results in lower maintenance and operating costs for affected industries.

For removing fine particulates, acid mists, and other contaminants from the gas stream, the one technology that is almost universally specified for this application is the wet electrostatic precipitator (WESP).

Primarily targeted at capturing submicron-scale particulate matter, saturated sulfuric or other acid aerosols, and condensable organic chemicals, the advance designed Beltran WESP system is often specified to be incorporated after the gas scrubbers, and can achieve collection efficiencies including submicron particulate matter of greater than 99.9%—far superior to other equipment.

However, it is important for engineers to recognize that there are key differences in features and benefits offered by the various precipitator systems. Although they may share the similar operating principles and basic structures, WESPs can vary greatly in design, materials, gas flow rate, durability—as well as collection efficiency.

A basic WESP is comprised of an array of ionizing electrodes such that negatively charged discharge rods generate a PAGE 28

Mopani Copper Mines currently has nine Beltran WESPs for sulfuric acid gas cleaning at their copper smelter plants in Zambia, Mufulira, and Kitwe.

strong electric field and corona. These are surrounded by or interfaced with positively charged or grounded collection surfaces, which attract and hold the charged particles. In operation, the source gas is passed through the electrode array, which induces a negative charge in even the most minute, submicron-size particles, propelling them toward the grounded collection surfaces, where they adhere as the cleaned gas passes through. The captured particles

are cleansed from the plates by recirculating water sprays; residues, including aqueous sulfuric acid, are extracted for further use or disposal. The cleaned gas is ducted to downstream equipment or to the stack, depending on the application.

A traditional problem has been with high-resistivity contaminants, such as lowsulfur coal ash. However, Beltran WESP configurations and designs can overcome this challenge. The system is engineered

At the Hindustan Zinc Acid Plant in India, Beltran WESPs virtually eliminate particulate re-entrainment acheving 99.9% collection efficiency and faster throughput.

with multistage ionizing rods, star-shaped discharge points, and space-saving hexagonal tube designs. This unique geometry generates a corona field 4-5 times more intense than other ESPs, achieving superior collection efficiency on resistant materials.

These features also allow higher velocity gas streams, resulting in faster throughput. WESPs impose a significantly lower pressure drop compared to scrubbers, and also contribute to increased production speeds. Furthermore, these gains in efficiency enable the use of smaller-scale, less-expensive equipment for a given set of operating parameters.

Another challenge for traditional precipitator designs was the re-entrainment back into the gas stream of particles from the collection surfaces. Dry-operating ESPs, especially those using mechanical or acoustical vibrating rapper machinery, are particularly susceptible to this phenomenon. Precipitators based on wet operation, however, minimize re-entrainment, as the aqueous flushing is continuously effective.

The elimination of mechanical rapping also reduces the higher cost and energy drain imposed by that equipment.

Other critical features to look for in WESP equipment are the more advanced electronic controls, which can optimize operating parameters such as gas flow, saturation, temperature, and corona intensity to achieve maximum efficiency.

Superior technology for wide applications

Because it operates at cooler temperatures—usually at the process gas saturation temperature between 100-170° F—the WESP is uniquely adept at capturing condensable organic materials and acid mists, making this technology an invaluable component for sulfuric acid production plants.

Since sulfur is a common element found in the earth, sulfuric acid and other sulfurbased pollutants are most associated with industrial processes that deal with materials originating underground. These industries include: • Metals and metallurgical plants (mining and extraction; smelting and refining; finishing and metallurgical processing such as steelmaking, alloys, etc.)

• Fossil fuels (petroleum refineries/processing or fossil fuel-fired power generating units) For more information, contact Beltran Technologies, Inc. at info@beltrantechnologies. com or visit www.beltrantechnologies.com. q Sulfuric Acid Today • Spring/Summer 2021

THE ART OF ACID PROOFING

S O U TH WEST REFRACTORY DELIVERS THE HIGHEST Q U ALITY ACID PROOFING, REFRACTORY, INDUSTRIA L MASONRY AND FIREPROOFING WORK.

With in-depth engineering support, meticulous craftsmanship and extensive planning down to the finest details, we’re turning industry into artistry.

VIEW OUR GALLERY OF ACID PROOFING AND OTHE R REFRACTORY PROJECTS AT SWRREFRACTORY.CO M . ( 2 8 1) 8 2 4 9 3 42

IN FO @S WR - U S . C O M

Feature

NORAM’s hot sweep cold exchanger does the trick

By: Guy Cooper*, Andres Mahecha-Botero, Werner Vorster, NORAM Engineering and Constructors Ltd., Vancouver, Canada.

Increasing acid production using split flow heat exchangers

In early 2017, NORAM completed a capacity increase study for a client’s two sulfur burning acid plants. A key finding was that the cold reheat exchanger in both plants contributed significantly to plant pressure drop due to cold end fouling and design. Because of mechanical integrity concerns with one of the exchangers, the client decided to replace it and selected a NORAM cold exchanger with NORAM’s proprietary hot sweep feature.

Cold and cold interpass conventional exchangers

In a cold interpass exchanger, the cooled SO3 gas leaves the gas exchanger en route to an economizer before entering the interpass tower. The counter-current gas in a cold interpass exchanger in a sulfur burning plant is the cold SO2 gas from the interpass tower. For a cold exchanger in a smelter or acid regeneration plant, the cold SO2 gas can also be from the drying tower. In both cases metal temperatures at, or below, the gas dewpoint are likely. Condensation

37th

can occur and weak acid is formed which reacts with the metal to form iron sulphate.

In a carbon steel gas exchanger the sulfate formation can be considerable, resulting in short exchanger lifespans. Standard stainless-steel exchangers have significantly less sulfate corrosion but, over time, fouling and plugging will occur.

NORAM’s hot sweep feature

To address the cold end condensation problem found in cold and cold interpass gas exchangers, NORAM developed and patented a split flow exchanger with a hot sweep feature. This exchanger takes a slipstream of the hot SO3 shell gas and introduces it to the cold end of the exchanger adjacent to the entry of the cold SO2 gas.

This hot gas warms up the top of the bottom tube sheet of the gas exchanger and flows co-currently with the SO2 gas for a short distance. This SO3 gas then co-mingles with the counter-current SO3 gas and exits the exchanger. The result is the bottom of the exchanger is significantly warmed up well above the sulfuric acid dewpoint, greatly reducing the chance of condensation and corrosion. A schematic is shown in Fig. 1.

NORAM has been supplying this popular style of gas exchanger for over 21 years now

Oil | Gas | Fertilizers | Metallurgy | Industrial

Sulphur + Sulphuric Acid 2021 1-3 November 2021

CALL FOR PAPERS

DEADLINE 14 MAY 2021 CRU Sulphur + Sulphuric Acid 2021 is the global gathering for the sulphur and acid industries to meet, learn, and do business.

Why submit an abstract?

The conference is an ideal platform to demonstrate thought-leadership and operational experience, or showcase your product or service to a large global audience of technical experts.

What subjects are we looking for?

We welcome operational case studies, and/or new technology, process, materials or equipment developments, that offer the potential of improved reliability, safety, environmental or production efficiencies.

Where can I go for more information?

Visit the website www.sulphurconference.com or contact amanda.whicher@crugroup.com

PAGE 30

NORAM engineer inspects fabrication of cold exchanger.

Transporting large NORAM gas exchanger.

Fig. 1: Flow arrangement for NORAM’s Cold InterPass Gas Exchanger with Hot Sweep.

with the original unit, installed in 2000, still in service.

Exchanger design aspects

When NORAM designs replacement sulfuric acid equipment, key considerations are to provide equipment with improved performance compared to the existing while matching the gas ducting. For this replacement exchanger, NORAM’s design accommodated the higher duty required for the planned capacity increase with 2/3 of the pressure drop of the existing exchanger, and minimal ducting changes. On top of those benefits, NORAM’s improved design had ¾ of the tube surface area compared to the existing old-style exchanger. All of these features, coupled with the benefit of a hot sweep to minimize condensation, ensures excellent long-term performance at a very competitive price.

Fabrication

For large sulfuric acid equipment, shipping can often present challenges. For a gas exchanger, it is preferred to shop fabricate and ship the unit in one piece to the site. For this project, the client provided the names of local fabricators. NORAM inspected and qualified a fabricator in close shipping proximity to the plant site and retained a local quality inspector to assist NORAM engineers, who visited the fabricator and site frequently to ensure the highest-quality final product was delivered.

Delivery and start-up

Fabrication was uneventful, which is always good, and the exchanger was delivered on time. The client installed the exchanger; NORAM provided installation and start-up assistance. NORAM and the client were both pleased with the performance.

Installing NORAM Cold IP Gas Exchanger with Hot Sweep.

Next unit

Fast forward two years after the installation of the first unit. At the first turnaround, the client inspected the now two-year-old NORAM gas exchanger and was satisfied to see a clean exchanger compared to the sulfate fouling of the previous unit. This demonstrated performance made it easy for the client to award NORAM a second cold exchanger with hot sweep for the other acid plant in the same site. This second hot sweep exchanger is currently under fabrication and will have half the pressure drop, significantly less area, and greater capacity compared to the existing fouled exchanger.

The new exchanger will be shipped to site in the second quarter 2021.

NORAM Engineering and Constructors Limited designs and supplies sulfuric acid equipment. They have designed and supplied over 120 radial flow gas exchangers. For more information, email acid@noram-eng. com or visit www.noram-eng.com. *Corresponding Author: C. Guy Cooper., P.Eng. gcooper@noram-eng. com, phone (604) 724-8219 q Sulfuric Acid Today • Spring/Summer 2021

ALPHA-CORR TYPE III ACID BRICK

AvAilAble

in the

USA todAy

From our strategic location in Houston, TX, we are able to supply a variety of brick shapes (straights, arches, wedges, keys) and sizes from stock for immediate purchase.

Please reach out to us for technical data and pricing.

Samples available upon request.

Meeting ASTM C279 standards for use in new construction and refurbishment of existing structures in sulphuric acid plants including towers, process vessels, floors, sumps, pits, etc.

A-103 MASTIC® A-103 Mastic® is Still Available and in Stock in warehouses in USA and Canada.

Made from the original recipe.

When your plant has a product that has proven successful for over forty years, why change? With this in mind, Alphatherm Inc. purchased the recipe of Pecora A-103 Mastic® to keep this integral piece of the Sulphuric Acid Tower lining system intact.

Made from the same ingredients with A DECADES OLD RECIPE, A-103 continues to be the workhorse membrane in Acid Plants worldwide.

Industrial Linings for Sulphuric Acid Plants.

Absorption Towers, Pump Tanks, Sulphur Pits, Secondary Containment, Acid Resistant Linings.

Acid Brick, Acid Resistant Mortar, Membranes, Carbon Brick, Polymer Concrete, Refractories, Teflon, Ceramic Paper and Blanket, Ceramic Rope, Borosilicate Block

Alphatherm Inc.

|

Accept No Imitations!

This is THE ONLY A-103 Mastic® made with the original Pecora recipe.

A-103 MASTIC is a registered trademark of Alphatherm Inc.

www.alphatherm.com

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Tel: (905) 948-9949

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Email: alphatherm@ilap.com

Feature

Special alloys changing how sulfuric acid plants are built and operated By: Nelson Clark, Joanes Barros, Matheus Sanchez, Bruno Ferraro, Gabriel Murakami, Lucas Camargo and Paulo Portilho, Clark Solutions, Brazil

Since the first industrial sulfuric acid plants were built in the early 1900s, very little change occurred in the materials used to handle the harsh conditions of the acid producing environment. More recently, the development and increased availability of special alloys has dramatically simplified the design and construction of the plants— small, skid-mounted plants can now be built and shipped to customers for installation with minimal field work and assembly.

Old school construction

The contact process was first patented in 1831, and the process variant for applying vanadium catalyst was developed by BASF in 1913. Until the late 20th century the materials of construction applied in sulfuric acid plants changed very little.

But in the later years of the last century, the development of new alloys and special materials as well as a reduction in their costs led to innovation throughout the contact section of acid plants.

Oxidation converters

SO2 oxidation converters are the core of any sulfuric acid facility. As a general rule, they are large, cylindrical, vertical vessels (though Clark Solutions has used horizontal vessels on small skid mounted plants.) They house 3, 4, or 5 catalytic beds where the SO2 to SO3 oxidation reaction takes place when the gases contact vanadium-based catalyst at reaction temperatures that range from 380-650 degrees C (7151200 degrees F).

The high temperatures associated with the presence of a small amount of water and a sulfur trioxide rich atmosphere make the converter environment extremely aggressive when temperatures fall below the dew point or there are steam/water leaks. Historically, the approach to handling the gases in these converters has been the use of a refractory brick lined carbon steel vessel shell coupled with high temperature resistant cast iron internals (support grids and posts).

Although construction can be excellent and long-lasting, carbon steel and cast iron have some disadvantages. The mechanical resistance of carbon steel is strongly affected in the temperature range above 500 degrees C (900 degrees F). Cast iron may suffer deformation in temperatures above 650 degrees C (1200 degrees F) (although some cast iron, such as Meehanite™, can withstand higher temperatures).

The industry and designers always aim to increase production with the smallest plant possible. This drove designs to increase SO2 concentration in the reactor PAGE 32

and thus increase operating temperatures.

First pass bottoms operating above 620 degrees C (1150 degrees F) that were unusual in the mid 1900s became the new standard. Some plants, at the expense of fast catalyst aging, would operate at 650 degrees C (1200 degrees F) continuously.

The prevalence of these shifts became possible with the popularization of different grades of stainless steels. The carbon steel and cast iron construction has slowly but steadily been replaced by special 304 stainless steel grades, more resistant to the thermal stress and corrosion than the carbon steel.

The new material has also led the industry to change converter design. While in the past the first catalytic pass had to be placed on top of the reactor due to thermal stress and increases in pressure drop increase, stainless steel construction (not as affected by thermal stress as carbon steel) allowed the first pass to be positioned wherever it made more sense to the designer. Many designers chose to install the first catalytic bed at the bottom of the reactor to simplify. Also, superheaters could be located on the ground level, which saved on ducting and supports.

The heavy duty high temperature resistant cast iron castings used for catalyst support and internals of the converter have also been replaced by special grades of 304 or 321 stainless steel, the latter in the hotter areas.

With proper design, the new materials of construction allowed the refractory brick to be partially or completely eliminated, depending on process conditions, making the vessels cheaper and lighter than prior versions.

Gas-gas heat exchangers

Another traditional piece of equipment in double absorption plants that has benefited from improved and more accessible materials is the gas-gas heat exchanger.

Heat exchangers cool the gases prior to entering the interpass absorption tower while at the same time re-heating the cold gases exiting the absorption tower. In the hot side of the exchanger temperatures and SO2/SO3 laden gas are the challenges; on the cold side acid mist and SO3 slippage are potential problems. In a way, the same problems afflicting the converter affect hot gas-gas heat exchangers.

Temperatures that could surpass 500 degrees C (900 degrees F) and the SO3 laden gas requires that hot heat exchangers use high temperature resistant materials of construction. An early solution was metallized carbon steel, a strategy to make the base material bear the hot and harsh conditions. The metallization process is

extremely difficult, though, and if done improperly can actually shorten tube life.

What happened with hot gas-gas heat exchangers has its parallel in cold gas-gas exchangers. For nearly one century gas-gas heat exchangers have been built in plain carbon steel. The material selection is perfect and should last a very long time with regular design operating conditions of the exchanger. The only problem is that actual operation does not always go by the book.

When engineers design a plant, they choose materials that operate at the design conditions. The problem with these designs is the non-expected operating conditions: low capacity operation, poor air/gas drying performance, unexpected mist carryover from the interpass absorption, improper SO3 absorption, and water or steam leakage.

When one of these conditions exist, the cold exchangers are pushed beyond their design limits. Hot, strong, and corrosive acid will completely change the dynamics of corrosion. When this happens, the consequences are the same: accelerated corrosion, sulfate formation and pressure drop build up, gas leaks, increased emissions, reduced capacity, and earlier than expected plant shut down. This is why cold gas-gas heat exchangers are among the most frequent maintenance items and shutdown drivers in a double-absorption plant.

The answer? Stainless steel construction in gas-gas heat exchangers increases equipment life, reduces corrosion and sulfate formation in upset conditions, and saves money on cleaning and maintenance.

When properly designed and operated, stainless steel exchangers last longer and will pay for the extra cost on a “total cost of ownership” basis.

Strong acid piping

For more than a century hot strong sulfuric acid piping was designed and built using cast iron piping and connections. Cast iron grades changed from place to place, from country to country. Some places use 250# class piping and fittings to provide extra wall thickness for corrosion.

Conventional cast iron fittings and gravity cast parts have chaplets to separate the molds—another weak point that in many situations is the starting point of a leak.

In the end, the corrosion resistance of cast iron allied to the thick walls has for a long time been the only option to strong acid piping despite the natural shortfalls.

Thus, the development of special alloys and steels, such as Clark solutions CSX™ family of high silicon stainless steels, was very welcome.

Special alloys are designed to operate with corrosion rates below 0.02-0.04

Corrosion of different alloys.

CSX™ Isocorrosion curve.

mm/year (1-2 mils/year), while even the best cast irons will show corrosion rates at average transport velocities in the range of 0.15-0.30 mm/year (5-10 mils/year). The thick walls guarantee a long lifetime, at expense of substantial iron being captured by the acid.

As an example, while some of the most frequently used cast irons have wall thicknesses as high as 22 mm (0.9 in), CSX piping uses wall thicknesses of 4 mm (0.2 in) or 6 mm (0.3 in) while still providing 20 or more years of service.

The thinner walls make special alloy piping lighter, but this is not the only advantage. Cast iron piping is generally operated with acid at velocities of 1.0-2.0 m/s. Corrosion rates on cast iron increase with transport velocity. CSX and special alloy piping are normally designed for around 3 m/s for long runs and 5 m/s for short runs. The special alloys’ corrosion rates are not sensitive to transport velocity, so the design is limited only by acceptable pressure drop.

Another advantage is welding capability. Welded lines substantially reduce the number of flanges used, which significantly reduces the risk of leaks at flanged connections. Even better, in the event of a leak or failure special alloy lines can be locally welded. No cranes, no replacement of large parts, no new gasketing or tightening. This saves a huge amount of time and energy when compared to cast iron lines, which may cost one or two days of production loss.

In Brazil, where Clark Solutions designed and replaced cast iron pipelines with CSX, the customer reported gains in plant operation and up to 60-80% less downtime compared to prior operation.

Sulfuric Acid Today • Spring/Summer 2021

Drying and absorbing towers and tanks face the harshest conditions in an acid plant. As a result, it is this equipment that industry experts have the most disagreement about. The traditional approach to preventing corrosion is to build a bricklined carbon steel vessel to avoid direct contact of acid with the metal.

Every technology vendor has its special recipe. The basic concept around surface protection of this equipment is the installation of a resin or polymeric material, a rubber, an asphaltic mastic, or a special resin in contact with the carbon steel shell sometimes followed by an adhesive PTFE film over which potassium or sodium mortar is applied with acid resistant brick.

Lining a carbon steel vessel to operate with hot strong acid is a work of art.

It requires extremely skilled installers and attention to detail. Properly done, a good lining system may last as long as 35-40 years. Skilled masons are becoming more scarce and expensive; and quality work takes time.

In addition, resins and polymers are not all the same—their resistance to acid varies. Sometimes shelf life affects performance. Improper mixing or installation may leave weak spots where acid attack will initiate.

Bricks and mortars are permeable—it is a question of time when acid will contact the liners. If the installation was not properly done or if the materials were not properly chosen, the lining may last for just a few years.

Brick-lined towers and tanks are extremely heavy, requiring extremely

Without brick lining, this 310M™ tower increases the gas/liquid free-flow cross sectional area by 15%.

Sulfuric Acid Today • Spring/Summer 2021

strong foundations and in most cases requiring the lining service to be constructed in place.

New materials eliminate the need for lining, PTFE, and brick. Towers and tanks, just like piping, can be in direct contact with the hot and strong acid.

Special alloys including Clark Solutions’ CSX or Outotec’s SX are the premium option for metal tower construction. Special grades of 310 stainless steel, such as Clark Solutions 310M can be used with good performance and long life in 98.0-98.5% strong acid and in heat recovery towers, where acid can be as hot as 240 degrees C and at concentrations as high as 99.5% in heat recovery systems, such as in Clark Solutions Safehr®.

Lighter metal towers can quickly replace brick-lined towers, without requiring new foundations. In some replacement situations, eliminating the brick lining while keeping the outside diameter the same can increase cross-sectional area, which can mean a substantial capacity gain.

Of course, nothing is perfect. Alloy towers do require proper concentration and temperature controls. While a shortterm concentration or temperature excursion may be tolerated and won’t lead to substantial corrosion, long-term excursions may accelerate corrosion and lead towers to an early failure.

square meter for some special applications. For sulfuric acid plants, given the nature of the service and the packing used, distribution densities with special alloy will usually vary from 25 to 50 points per square meter.

The 2-5 times denser irrigation allows substantial reduction in packing heights, not only shortening tower heights but also reducing pressure drop across packing or allowing the design of smaller towers running at the same pressure drop.

Acid coolers

The first acid coolers used in the sulfuric acid industry were cast iron construction. Huge installations used very large areas where water would wet the external surface of the hot cast iron tube banks while hot acid was flowing inside. The water cooled the tubes by evaporation and convection, and the tubes cooled the acid flowing inside.

The long lengths added a lot of iron to the product acid. This additional iron can be a problem, depending on the industry.

And cast iron coolers, like piping, also used dozens and dozens of flanges and connection points, each a potential leak source.

Acid distributors

As in piping, improved alloys also took over acid distributor manufacturing. Cast iron distributors corrode, which means sulfate in the tower and iron in circulating acid. Sulfate on top of the packing may increase pressure drop and in extreme cases compromise drying or absorption efficiency.

Alloy distributors are currently built in different forms and designs, and are lighter weight, simpler to install, and less prone to corrosion. They also allow more design flexibility. Old standard irrigation densities used in cast iron distributor equipped towers are usually around 10 to 15 distribution points per square meter.

This calls for increased packing heights to guarantee proper liquid distribution across the total height of the ceramic packing.

Special alloy distributors can be made of smaller parts that allow a much richer liquid distribution. Clark Solutions has built distributors with up to 500 points/

High efficiency Clark Solutions trough and downcomer sulfuric acid distributor installed in a 6m ID tower in Brazil.

Cast iron acid coolers.

The first attempt to replace the cast iron coolers started in the early 1980s with the introduction of anodically protected (AP) acid coolers. These shell and tube heat exchangers, with acid flowing on the shell and water in the tubes, operate with an impressed current that guarantees that the metal exposed to the flowing acid is always on a passive region.

One of the few disadvantages of the anodically protected acid coolers is that the corrosion protection film formed by the passivation current film is temperature sensitive. An increase in the temperature may cause the metal to move from a passive state to an active state, accelerating corrosion. Luckily this is a rather unusual occurrence, especially when trained operators are in charge.

The development of new alloys brought a myriad of options to the sulfuric acid producer. Shell and tube heat exchangers do not need anodic protection anymore.

They can be built out of CSX, 310M, Alloy 3033, and others. Any of these are adequate for some process conditions.

Alloyed shell and tube heat exchangers give the operator the same benefits of anodically protected acid coolers with the advantage of not requiring the instrumentation and controls needed by AP acid coolers. Kept and operated properly, alloy shell and tube coolers will have a long ser-

Feature

Drying, absorption towers & pump tanks

CSX shell and tube strong acid cooler.

vice life with little maintenance.

But the shell and tube were not the only heat exchangers to benefit from new alloys. Gasketed, semi-welded, and fully welded plate and block exchangers can also be made of special alloys, such as Hastelloy D-205 or Alloy 33. Plate exchangers are smaller and cheaper than shell and tube exchangers.

However, 0.3 mm distance between 0.5 mm thick plates require good quality water treatment as well as an acid with little or no dissolved silica or other materials and ions that may foul, clog, or precipitate corrosion on the plates.

Alloy plate coolers also work fine at temperatures as high as 150-160 degrees C in 98-98.5% acid and without issues maintaining cooling water temperature or flow.

Both shell & tube and plate exchangers in stainless steel construction are much more forgiving in this regard compared to AP coolers.

More recently Clark Solutions and Alfa Laval developed a fully welded 310M block exchanger designed to handle high temperatures and concentrations of the Safehr® heat recovery system. The newly designed 310M Compabloc® systems have now been in service at 99.0+% acid and 220-240 degrees C with no sign of corrosion and no loss of performance.

Conclusion

All the improvements provided by the development and application of new materials in the sulfuric acid industry combined to simplify, reduce weight, and increase capacity of the new plants. These features allowed plants to be built faster, at lower costs, and with less field labor.

Shop manufactured modular acid plants require minimal field work.

As materials science progresses, we expect even more improvements that will add to the simplification and reliability of new and future sulfuric acid plants. Plants are getting lighter, more energy efficient, and more reliable, and will continue to do so.

For more information, please visit www.clarksolutions.com. q PAGE 33