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IN THIS ISSUE > > > > Market Outlook: Supply Critical for 2022 PAGE 10

Common pitfalls of sulfuric acid piping and ducting PAGE 14 Developing a Repair Method for Leaking Acid Towers PAGE 28

Sulfuric Acid

COVERING BEST PRACTICES FOR THE INDUSTRY

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Noracid: A decade of progress Page 7

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IN THIS ISSUE > > > > Market Outlook: Supply Critical for 2022 PAGE 10

Common pitfalls of sulfuric acid piping and ducting PAGE 32

FROM THE PUBLISHER

Developing a Repair Method for Leaking Acid Towers PAGE 28

On the Cover…

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Noracid marks tenyear anniversary manufacturing sulfuric acid at its plant in Mejillones, Chile

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 2022 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 are preparing this issue for press, we are also wrapping up the plans for our 2022 Sulfuric Acid Roundtable (SAR), April 4-7, in The Woodlands, TX. This will be our first conference since the coronavirus pandemic shut down most of the world in early 2020. This year’s SAR is packed with 2.5 days of informative technical presentations and panel discussions that will delve into topics such as: sulfuric acid operations, troubleshooting, acid towers, mist elimination, converters, catalyst handling, analyzers, NOx abatement, acid piping and ducting, sulfur melting, precipitators, heat exchangers, and hydrogen formation and risk mitigation. Fiona Boyd of Acuity Commodities will present the keynote address on the changing sulfuric acid market dynamics. Since Acuity Commodities’ last article in the Fall/Winter 2021 issue of Sulfuric Acid Today, many commodity prices have continued to firm. This includes sulfur and sulfuric acid, where supply remains overall snug and demand firm, which in turn is providing price support. Please see Acuity Commodities’ informative article ‘Supply critical for 2022’ on page 10 for further details.

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

Our cover story, on page 7, focuses on Noracid’s ten-year anniversary manufacturing sulfuric acid at its plant in Mejillones, Chile. Over the last decade, the facility has been stalwart in supplying local copper mining operations with the necessary ingredient for separating metal from ore. The plant has also been a model for longevity and plant availability. VIP International shares its experience with NOx abatement and mitigation (page 12); INTEREP shares some common pitfalls of sulfuric acid

Sincerely, Kathy Hayward

FEATURES & GUEST COLUMNS

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

piping and ducting (page 14); Elessent MECS Technologies shares some common and not so common containment failures and discusses indicators of pending failures, as well as root causes of ultimate failures, specifically in SO2 and SO3 process gas releases and steam equipment leaks (page 16); PVS Chemicals upgrades its Belgium acid operation with a new converter and with GEAR® Catalyst, waste heat boilers, and economizer (page 18); Sauereisen explains the benefits of their polymer concrete corrosion protection for pump pads, trenchless and process flooring (page 20); Chemetics® has designed and delivered 3,000 anodically protected sulfuric acid coolers (page 22); NORAM delivers another hot-sweep cold exchanger (page 24); Sulphurnet shares how sulfur quality affects melting & filtration (page 26); Knight Material Technologies developed a repair method for leaking acid towers (page 28); Beltran Technologies discusses WESP technology (page 30); CG Thermal explains the importance the recuperator design to avoid common failure modes found in an operating environment (page 32); and Clark Solutions explains how their CSX piping increases reliability, uptime, and safety (page 33).

I would like to welcome our new and returning Sulfuric Acid Today advertisers and contributors, including: Acid Piping Technology Inc., Acuity Commodities, BASF, Beltran Technologies, Breen Energy Solutions, Central Maintenance & Welding, CG Thermal, Elessent, INTEREP, Knight Material Technologies, Metso-Outotec, NORAM Engineering & Constructors, Optimus, Southwest Refractory of Texas, Savino Barbera, Spraying Systems Co., STEULER-KCH GmbH, Sulphurnet, VIP International, and Weir Minerals Lewis Pumps.

We are currently compiling information for our Fall/Winter 2022 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.

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Supply critical for 2022

EDITOR April Kabbash

12

NOx! The other acid gas

EDITOR April Smith

14

Common pitfalls of sulfuric acid piping and ducting

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PVS Chemicals upgrades its Belgium acid operation

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Polymer concrete: Corrosion protection for pump pads, trenchless &

MARKETING ASSISTANT Tim Bowers DESIGN & LAYOUT

process flooring 22

Chemetics—3,000 acid coolers and counting

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NORAM delivers another hot-sweep cold exchanger

281-545-8053

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How sulfur quality affects melting & filtration

Mailing Address: P.O. Box 3502 Covington, LA 70434 Phone: (985) 807-3868 E-Mail: kathy@h2so4today.com www.h2so4today.com

28

Developing a repair method for leaking acid towers

30

Wet electrostatic precipitator technology

32

Designing for reliability & efficiency in high temperature gas-to-gas heat

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

18

24

exchangers 33

Clark Solutions CSX piping increases reliability, uptime, and safety

28

Department

INDUSTRY INSIGHTS High Street Capital acquires Koch Knight

CANTON, Ohio—High Street Capital recently announced the acquisition of Knight Material Technologies (KMT), formerly Koch Knight, LLC, a Koch Engineered Solutions (KES) company and subsidiary of Koch Industries, Inc. Koch will remain a key customer of KMT, and the two companies will continue to maintain a strong relationship.

High Street Capital intends to invest in KMT’s technology, innovation plan, and infrastructure to grow its market share, relying on its existing management team and employees. The current management team will remain in place, and KMT has plans to ensure services and materials continue at current production levels without interruption.

“We look forward to this new opportunity,” said Kevin Brooks, president of KMT. “Knight Material Technologies will be in a position to take advantage of new opportunities and ideas in an entrepreneurial environment. In addition, the investment will enable us to expand manufacturing operations, including workforce and vendor relations.”

The transfer of ownership aligns with other companies in the High Street Capital portfolio of industrial manufacturers, processors, and service organizations. The equity firm has a long history of investing and growing niche manufacturing businesses.

“Knight Material Technologies is an

ideal partner for High Street Capital—they are a world-class service provider with superior products and an outstanding reputation, and that only comes from having really great people throughout the company,” stated Matt Laffey, principal at High Street Capital. “We anticipate supporting management’s growth plan immediately by investing in new product technologies and infrastructure to capture opportunities in the market.”

Demand for KMT products and services has been increasingly growing during the past few years. As a result of the change in ownership, the company will be well-positioned to expand manufacturing production, including the popular Flexeramic® ceramic structured packing systems and other proprietary materials.

For more information, visit www.

KnightMaterials.com.

International private equity consortium finalizes purchase of Clean Technologies business from DuPont

CHESTERFIELD, MO—New Year’s Day marked the beginning for Elessent Clean Technologies as an international private equity consortium, consisting of BroadPeak Global LP, Asia Green Fund, and The Saudi Arabian Industrial Investments Company, completed its transaction to purchase the Clean Technologies business of DuPont de Nemours, Inc. The new, independent company has been

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.

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PAGE 4

named Elessent Clean Technologies and is a global leader in process technologies to drive sustainability and carbon neutrality in the metal, fertilizer, chemical, and oil refining industries. Elessent retains exclusive rights to the technologies, expertise, products, and services to which these industries have grown accustomed from the Clean Technologies business over the years, including: MECS sulfuric acid and environmental technologies, BELCO scrubbing technologies, STRATCO alkylation technology, and IsoTherming hydroprocessing technology.

“We are excited about what the future holds for us as a standalone company,” said Elessent CEO, Eli Ben-Shoshan, “The strong global expertise of the group will accelerate our mission to deliver the technology and tailored solutions our customers need to more efficiently produce cleaner products for the world.”

Derived from the words “element” and “essential,” Elessent helps customers produce, optimize or separate essential elements every day. From the production of carbonless energy to the production of sulfuric acid for the metals and fertilizer industries, and from removal of sulfur from refined oil products to air pollution control, Elessent creates clean alternatives to traditional industrial processes to minimize the impact on the environment.

For more information, visit www. ellesentct.com.

IOCL Haldia Refinery completes BS-VI project of wet sulfuric acid unit

NEW DELHI—The BS-VI project at IOCL Haldia Refinery achieved a final milestone with the successful mechanical completion of the wet sulfuric acid unit.

The main objective of the sulfuric acid plant is to recover minimum 99.9% sulfur from H2S rich gases from ARU and SWS units. This unit is designed to produce 98.5% sulfuric acid from SWS and ARU units mainly from NH3 rich sour gases and acid gases respectively.

To meet this requirement a capacity of 325 TPD sulfuric acid unit has been envisaged at IOCL Haldia Refinery Hardeep Singh Puri. Haldia Refinery is one of the two refineries of IndianOil Group Companies producing Lube Oil Base Stocks (LOBS) situated 136 km downstream of Kolkata in the district of Purba Medinipur, West Bengal, near the confluence of river Hooghly and Haldi.

For more information, visit www.iocl.com.

Nornickel buys tech for sulfur capture

MOSCOW—Russia-based mining and metals company Nornickel is preparing to receive six shell-and-tube heat exchangers for sulfuric acid production as part of the sulfur program to capture sulfur dioxide emissions at its Nadezhda Metallurgical and Copper smelters.

The six heat exchangers were assembled and tested at a special site in St Petersburg and delivered to the Port of Dudinka in an ice-class vessel.

The company has prepared a “transport

corridor” to transport the heat exchangers to the sulfur program site. This includes engineering communications, plane structures, plus additional turning and reloading sites.

The sulfur program technology includes the intermediate production of sulfuric acid with a high degree of sulfur dioxide recovery. Nornickel said this is “the proven and most efficient way” of utilizing sulfur dioxide in the metal and mining industry. The company explained that the technology captures 99% or more of the gas from the units on which it is installed.

Additionally, it said the program will cut sulfur dioxide emissions in Norilsk, Russia’s northernmost city by 90% after 2025 In addition to the sulfur program, Nornickel said it would invest 63 million in 2022 on new machinery and equipment for the Kola Division. In total, the company will purchase 2,000 units of equipment, including 14 filter presses for the chemical and metallurgical shop. Its Kola MMC asset will include a mobile laboratory for air monitoring.

For more information, visit www. nornnickel.com.

Metso Outotec awarded $170 million order for Norway zinc project

HELSINKI—Metso Outotec, a frontrunner in sustainable technologies, has been awarded a $170 million contract for the delivery of key technology to the Boliden Odda zinc smelter expansion in western Norway.

With the expansion, Boliden Odda is planning to increase its annual production capacity of zinc metal from 200,000 to 350,000 tonnes. Several by-products will also be produced. The project is called Green Zinc Odda, and its energy consumption is based on fossil-free energy. Metso Outotec’s scope of delivery includes roasting and off-gas cleaning solutions and a sulfuric acid plant.

Metso Outotec will also supply hydrometallurgical equipment and technology for calcine leaching, solid liquid separation, solution purification, as well as process and plant engineering and site services. Metso Outotec deliveries will take place in 2022-2024.

“The Green Zinc Odda project paves way for more sustainable zinc production and is yet another important milestone in the many years of collaboration between Boliden and Metso Outotec,” said Jari Ålgars, president, Metals business area at Metso Outotec.

Metso Outotec’s industry-leading zinc processing technologies consist of several proprietary Planet Positive solutions. These sustainable and cost-efficient technologies and services enable efficient zinc and by-product recovery from a wide range of primary zinc raw material. In the roasting process, even electrical power is produced as a by-product.

For more information, visit www. mogroup.com.

SNC Lavalin to undertake feasibility study in Australia

MONTREAL—SNC-Lavalin Group Inc. will undertake a definitive feasibility study for Verdant Minerals Pty Ltd on their Sulfuric Acid Today • Spring/Summer 2022

Ammaroo Phosphate Project in the Northern Territory of Australia. SNC-Lavalin is providing engineering and procurement services to assess the feasibility of a 4,500-metric tonper-day sulfuric acid plant which will be part of a fully integrated mine and downstream processing facility to produce ammonium phosphate fertilizers.

This sulfuric acid plant will utilize DuPont MECS technologies to minimize SO2 emissions, rendering the plant more sustainable in the long-term. MECS® Heat Recovery System (HRS) technology will also be used to recover medium pressure steam from the sulfuric acid plant, an energy now captured instead of being wasted, providing the majority of energy requirements for the site and removing the need to have additional sources of energy. This will maximize energy efficiency while reducing the overall facility’s reliance on energy supply from external sources and overall lessen its carbon footprint.

“We are proud to be working with Verdant Minerals on this project to develop a world class sulfuric acid plant as part of its major new mine and processing development, ensuring the long-term sustainability of its operations,” said Patrick Sikka, Vice-President, North America, Mining & Metallurgy at SNC-Lavalin.

For more information, please www. snclavalin.com.

Nuberg EPC wins two sulfuric acid plant projects in Egypt and Ethiopia Leading Indian Global EPC and turnkey project management company, Nuberg EPC, has announced winning two sulfuric acid

WASTE HEAT RECOVERY BOILERS SUPERHEATERS ECONOMIZERS

plant projects in Gamasa City, Egypt and Oromia, Ethiopia. The 500 million tpd and 5 MW Rating STG Set in Egypt is scheduled to be delivered in 22 months and the 50 tpd sulfuric acid and 40 tpd aluminium sulfate revamp project in Ethiopia in 15 months from the contract LC opening date.

These projects are an acknowledgement of Nuberg EPC’s advanced sulfuric acid technology–double-contact double-absorption (DCDA) and execution capability. In this process the product gases, sulfur dioxide (SO2) and sulfur trioxide (SO3), are passed through absorption towers twice to achieve further absorption and production of higher-grade sulfuric acid. Before this the company has built more than seven sulfuric acid plants in Saudi Arabia, India, Egypt, Turkey, Bangladesh, and Oman. Over the years, Nuberg EPC has established itself as a world-class sulfuric acid EPC- LSTK supplier.

A. K. Tyagi, MD, Nuberg EPC, said: “We look forward to further strengthening the faith of the clients in our sulfuric acid turnkey project expertise and engineering talent. The whole industry faced challenging times last year and yet we managed to deliver to our commitments in time. We will be looking forward to delivering ahead of schedule for an early start to our clients.”

Nuberg EPC’s scope of services for these projects include process design and technology including product and technology development, process know-how and licensing, basic engineering, front end engineering design (FEED), construction management, operation and maintenance, detailed engineering, project management, commissioning, EPC & LSTK Solutions, heavy fabrication, and start-up of the plant.

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

Fertilizer industry mourns loss of icon FRESNO, California— Mack A. Barber, 94, passed away on December 2, 2021, in Fresno, CA. Born on July 31, 1927, in Wyaconda, MO, to John S. Barber and Pauline (McReynolds) Barber, Mack grew up on his family’s farm. He graduated from Wyaconda High School in 1945. After high school he enlisted in the U.S. Army Air Corps and was honorably discharged in 1947. He then graduated from the University of Missouri in 1953 with a bachelor’s degree in Chemical Engineering. Mack was an icon in the fertilizer industry all over the

Op�mus delivered its rst sulfuric acid plant waste heat recovery system in 1996. Across the power and process industries, we’ve produced more heat recovery boilers, HRSGs, superheaters, and economizers than any ac�ve company in the USA.

Lyla and Mack Barber enjoying the 2012 AIChE conference in Clearwater, Florida.

world for nearly 70 years.

Mack married his high school sweetheart Lyla Jean (Fields) in 1947 at the Little Brown Church in the Vale, Nashua, IA. They were happily married for 74 years, raised 4 children, and traveled the world.

Mack is survived

Sulfuric Acid Today • Spring/Summer 2022

by his wife Lyla J. Barber, his sons Michael (wife Johnny) Barber of Houston, TX, Steven Barber of Fresno, CA, Jeffrey (wife Melinda) Barber of Parrish, FL, daughter Janene Barber of Valparaiso, FL, and granddaughter Maegan Barber of Houston, TX. q

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PAGE 5

Department

INDUSTRY INSIGHTS

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Cover Story

Noracid: A decade of progress

By: April Smith, Editor, Sulfuric Acid Today

N

oracid is marking its ten-year anniversary manufacturing sulfuric acid at its plant in Mejillones, Chile. Over the last decade, the facility has been stalwart in supplying local copper mining operations with the necessary ingredient for separating metal from ore. The plant has also been a model for longevity and plant availability.

Recently Noracid’s managers, together with representatives from the plant’s designer, Metso Outotec, reviewed the facility’s performance and cataloged its operational statistics. They reflected on the how the design and maintenance practices have driven the plant’s success; and consider what needs to happen next to keep the facility performing optimally in the decade to come.

Noracid’s founding

Noracid was founded in 2007 to supply sulfuric acid to the key mining companies in the northern region of Chile. The plant came online in 2012 and was the country’s first large-scale producer of sulfuric acid, which it manufactures from the combustion of elemental sulfur. The plant’s proximity to the Mejillones port on the Pacific Ocean facilitates the movement of supplies and products.

In addition to sulfuric acid, Noracid imports sulfur for use as feedstock and to sell to regional markets. The facility also generates electricity using heat released from the acid production process, and delivers it to the local power grid.

Noracid began as a business consortium between Grupo Ultramar and Belfi.

Grupo Ultramar provides marine port handling services, shipping, freight, and other logistics services. Belfi is an engineering and construction company; it provided the construction services that built the Noracid plant.

Metso Outotec was granted the contract to design and supply the plant in 2009, and construction began the following year.

The products

Noracid consumes 240K tons per year of sulfur as feed stock to its acid operation.

Bulk solid sulfur is also distributed to the iodine industry and boric acid manufacturing plants located in northern Chile and Argentina. On-site sulfur storage capacity is 100K tons.

Sulfuric acid manufacturing capacity is 720,000 tons per year with storage capacity at the Mejillones terminal of 40,000 tons.

From storage, 2,000 tons are transported daily, by trucks and trains, to mining operations in northern Chile.

The plant also generates electricity by channeling the heat released from acid production into a steam turbine. The cogenSulfuric Acid Today • Spring/Summer 2022

Noracid marks ten years of service at its sulfuric acid plant in Mejillones, Chile.

eration process has a capacity of 26 MW. Of this, 9 MW is consumed at Noracid’s facilities while the surplus 17 MW is delivered to the local power network. Operating independently from the local power supply provides the key benefit of enabling continuous operation in the event of an outage in the public power network.

Milestones

Noracid has logged a strong performance history over the last ten years. “Their results in terms of availability and utilization of the plant are very high, particularly with regard to availability,” said Collin Bartlett, Director of Business Development at Metso Outotec. “Average availability is greater than

98.5 percent and they’ve had few unscheduled shutdowns.”

From 2012 through 2021, unscheduled shutdowns averaged once per month for a period of 6 to 8 hours. And in all of 2020, unscheduled outages totaled only two days. These shutdowns were typically because of high vibrations of the sulfur burner, repairs to an expansion joint, or replacement of an acid recirculation pump.

The plant’s operational timeline shows long stretches of continuous production.

Since mid-2012, the plant has run for 24 to 36 months, pausing in between to carry out three main shutdowns.

How did the plant achieve this success?

Noracid and Metso Outotec credit two main factors: a robust design and an exacting maintenance protocol.

Design for longevity

Converter section (foreground) with sulfur melting and covered sulfur storage (background).

In 2009 when the design phase began, the term “sustainable” was not the buzz word it is today. Yet Noracid’s vision, carried throughout the project, was rooted in sustainable principles.

“From the beginning, Noracid focused on reliability and operational cost efficiency,” said Bartlett, “and they have been willing to consider incrementally higher capital cost to reduce operating costs over the lifecycle of the plant.”

A few of the ways in which these principles manifested was in a design that maximized electricity generation as well as minimized overall water consumption. For the electricity piece, the facility integrated a steam turbine, which has consistently powered the entire operation, while also supplying 17 MW/year to the local power grid. In terms of water usage, a plan was formed to minimize both water consumption and energy use.

Rather than implementing a water-based acid cooling system, which is standard for the industry, Metso Outotec designed an airbased cooling system instead. A water-based system would require desalinating the water before using it in the cooling process and then draining warmed effluent water into the Bay of Mejillones. Since local regulations at the time limited temperature increases in the bay, cooling by air made much better sense.

“It was a fairly unique solution in the acid industry,” said Hannes Storch, Vice President at Metso Outotec.

There was ample space on site for the cooling system, plus powering it from the facility’s own electricity supply provided an extra degree of plant independence.

Planning for long-haul efficiency also meant the design would be capable of meeting current and future SO2 emission standards.

Sustainable sulfur storage was another PAGE 7

Cover Story

significant feature. There were no sulfur pits, which eliminated the associated maintenance and emissions. Covered sulfur storage limited the amount of corrosive dust settling in the plant or migrating to the local township. Over time, ingress of salt and sand into the sulfur melter has been minimal, contributing to more stable plant operation and higher availability.

Overall, a robust process design and plant layout has enabled the plant to operate under very stable conditions with less chance of process upset and less wear on equipment.

Maintain for longevity—the four pillars

Birthing a plant is one thing. Care and feeding is everything else. Noracid has carried out strong maintenance protocols since the beginning with a strategy based on four key pillars: condition-based maintenance, well stocked critical spares, efficient turnarounds, and a support network of industrial specialists.

Pillar 1: Condition-based maintenance

Noracid’s maintenance program involves careful monitoring of three main conditions: vibration, corrosion, and temperature.

Vibration is monitored online using the Intellinova System on the main process equipment: sulfur burner, primary air blower, water feed pump, acid pumps, sulfur pump, and cooling system pumps.

Vibrations are viewed in the OSIsoft PI System and the data is collected to create history and equipment alarm set points.

The main blower is monitored and protected with the Bently Nevada system.

Noracid’s turbine-generator undergoes periodic vibration and oil analysis. It’s operating status is also continuously monitored via remote service that provides 24/7 support.

Corrosion is tracked by non-destructive testing (NDT) of components such as the drying tower, IAT, FAT, sulfuric acid piping, pressure leaf filter, sulfur tanks, sulfuric acid tank, etc. NDT techniques include ultrasound, long range ultrasonic testing (piping), phased array ultrasound, and eddy current (tube).

Temperature monitoring is accomplished using thermographic photography for transformers, electric motors, and checking levels in tanks and pipelines.

“Condition-based maintenance is of limited value if there’s no response to the condition,” said Bartlett. “What’s notable here is not all the monitoring systems, but that Noracid has been willing to drive its operational efficiency based on the results of such systems in a consistent manner.”

Noracid uses software management PAGE 8

Inside the covered sulfur storage facility.

tools to ensure spares are available and work is carried out at the appropriate time. A full software suite of tools (Infor EAM) helps plant personnel optimize maintenance tasks, including: managing scheduled procedures; entering corrective works; and tracking key performance indicators (KPIs), work orders, corrective/preventative ledgers, etc.

Pillar 2: Critical spare parts

Noracid’s remote location has driven maintenance protocols built on self-sufficiency, particularly with regard to spare parts availability. The core strategy is to have all major spare parts available at the plant. Plant personnel also meet regularly to reassess requirements for critical spare parts.

The strategy has served the operation well. Even pandemic-induced global supply scarcity was not an issue.

“Our strong inventory and outage planning team has allowed us to weather the pandemic and the associated supply chain issues with reasonable ease,” said Elio Barraza; Noracid’s Operation Manager. “In early March, we entered our plant shutdown with no real expectation of challenges.”

Pillar 3: Plant turnarounds

Noracid prides itself on their extensive plant turnarounds, which have taken place at ever increasing intervals. Their last shutdown, in early 2022, took place after 38 months.

Noracid’s carefully planned and fullyresourced turnarounds have ensured plant reliability and availability over the last decade.

Turnaround expenditures have averaged approximately 7M USD, of which 40 percent is associated with equipment and spares, and the rest associated with labor costs.

The scope of these turnarounds includes: • High priority tasks identified during the preceding operational period.

• Maintenance tasks to be performed only during a plant outage.

• Backlog tasks originating during the previous operational period.

• Inspection of components subjected to corrosion or wear.

• Improvements, upgrades, and design changes.

Converter section.

Pillar 4: Third-party specialist support

“Our overall maintenance strategy involves using only original spare parts and keeping a well-stocked inventory,” said Barraza. In many cases Noracid has direct contact with the fabricator of the spares, enabling them to have a guaranteed availability for turnarounds with the QA/QC accuracy of the original part.

The plant also maintains strong ties with technical specialists from key suppliers, often seeking and acting on their advice.

“These companies have committed to support us in the longer-term aims of the business and are available to support 24/7 for the short-term issues that emerge from time to time,” said Cristian Roempler, Development Manager at Noracid.

The next step

Having consistently achieved high plant availability and utilization for the better part of a decade, plant managers are looking ahead to the next ten years.

“Once we raised plant availability levels up a few years ago, it has been a big challenge to maintain them,” Barraza said. “As the plant gets older, we need to anticipate problems, seek them out, and remain organized so that we don’t get into a situation where issues become overwhelming.”

To improve performance further, the company is evaluating a ‘digital transforma-

Aerial view of the fin-fan water cooling farm.

tion’ of their operation via computer optimization. “Our wish to improve our productivity further requires us to invest in ‘next generation’ tools to assist us in reaching this goal,” said Roempler. “Without these tools further improvements can only be incremental.”

“Many of the optimizer concepts currently being considered for use in the acid industry already have proven roots in the metals mining industries that we serve,” said Storch.

“Metso Outotec’s optimizers are based on twenty years of continuous improvement as IT based technologies became available.”

Metso Outotec’s optimizer compares an aspect of sulfuric acid production to theoretical data, and, based on actual data on how that aspect of the process is trending, support operators with practical advice on corrective action.

“The optimizer allows customers to make process adjustments based on operational key performance indicators (KPIs),” said Bartlett. “Though KPI’s vary depending on client needs, electricity use is a common one. In some metallurgical plants, for example, the optimizer helps reduce electricity consumption over the entire process chain, starting from the feed bin of the metallurgical process and ending at the stack of the acid plant.”

Implementing an optimization system is a multi-step process requiring careful consideration. In keeping with its exacting operational standards, Noracid’s planners are assessing how the system would best serve the facility over the next ten years. q

Metso Outotec’s work scope Metso Outotec designed Noracid’s sulfuric acid plant and supplied the following equipment: • Sulfur melting and filtration area • Sulfur combustion area • Converter area • Drying and absorption area • Infrastructure, including air cooling systems, T/G set, etc.

Since plant commissioning, Metso Outotec has supported Noracid in plant operation, minor plant upgrades, and maintenance activities.

Sulfuric Acid Today • Spring/Summer 2022

Feature

MARKET OUTLOOK

Supply critical for 2022

Fiona Boyd, Acuity Commodities

Freda Gordon, Acuity Commodities

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

Since our last article in the Fall Winter 2021 issue of Sulfuric Acid Today, many commodity prices have continued to firm. This includes sulfur and sulfuric acid, where supply remains overall snug and demand firm, which in turn is providing price support.

Looking first at sulfur, the key raw material for most sulfuric acid production, throughout last year the market continued to rebalance following the impacts of the Covid-19 pandemic. One of the largest impacts of the pandemic was the loss of sulfur production due to lower by-product output of sulfur at the refinery level because of refined product demand destruction. On the other side, sulfur demand was not as negatively impacted as on the supply side, demand for most of these goods remained firm, or firmer.

As such, sulfur consumers spent 2021 readjusting to what supply was available and, in some cases, developing new trading partners.

Meanwhile throughout 2021, the rollouts of Covid-19 vaccines and fiscal support helped to boost investment and spending, spurring demand for various commodities including copper, cobalt, and fertilizers.

With all this came a squeeze in the supply chain and sulfur, like many other commodities, was experiencing shortages of supply and strong demand. At the same time, other raw material prices were growing, such as ammonia driven by increases in natural gas pricing. Prices of fuel and many items also grew, pushing inflation rates to new multi-year highs in many countries.

Many sectors have been successful, however, in passing higher costs on to consumers. This includes fertilizers, where faced with record-high ammonia and increasing sulfur prices, producers increased their end product prices accordingly. In turn, these higher input prices have been accepted by farmers due to strong grain economics with phosphate fertilizer applications ongoing to support yields.

We noted in our last article how the Tampa molten sulfur quarterly contract price jumped from $96/lt DEL in 1Q21 to $192/lt DEL in 2Q21. Today, the benchmark price is $282/lt DEL for 1Q and global pricing at the time of writing would suggest an increase for 2Q. This reflects the impact of ongoing tight supply availability and robust demand – higher prices.

The outlook for sulfur is somewhat clouded, however, by the developing situation in the Ukraine/Russia region.

Any developments there, including sanctions and Russia’s potential retaliation, could impact both sulfur and phosphate fertilizer availability and pricing as Russia is a key producer of both. Russia is also a key exporter of natural gas, copper, nickel, and wheat so any disruption to the country’s exports will influence not only its fertilizer and metal production, but the cost of food globally.

Outside of fertilizers, sulfuric acid demand remains firm. This includes copper leaching in the key import market of Chile. The ongoing strong fundamentals there PAGE 10

as discussed in our last article resulted in Acuity assessing the 2022 Chilean annual copper price as $235-244/t CFR Mejillones, up from $55-62/t CFR Mejillones for 2021. The settlement at this level followed business for 1Q22 delivery being concluded as far back as October 2021 in the mid $240s/t CFR for 1Q22 delivery, partly setting the tone for annual negotiations.

What was different, however, was because of the perceived high prices by the buy side, buyers were not in favor of typical fixed-price contracts, which resulted in some pricing flexibility in contracts. While the sell side was hesitant in agreeing after selling at negative FOB levels as recently as 2020, some suppliers did agree to nontraditional terms.

Much like sulfur supply, acid supply is constrained too with the situation most notable in Europe. In 4Q21, we saw supply availability tighten further when some producers reduced smelter operating rates due to high energy prices.

With European smelters a key source of acid supply for regions such as the Americas, we saw more product from other regions moving in its place. This included Asian acid moving to Latin America and the United States, with high freight for the trade routes providing some price support.

As planning for 2022 was underway, we did see more offers of acid from Chinese smelters emerge, and at slightly lower levels compared with product from Japan or South Korea. As we discussed in our last article, the acid market in China is unpredictable and what will be key this year is domestic pricing versus what is achievable offshore. Logistics are a notable issue in China, however, which could constrain vessel movements. The country’s zero-Covid policy, if maintained for the remainder of the year, could continue to cause logistical disruptions to cargoes going in and out of China.

In the meantime, it became evident that the supply of acid from Europe would not improve in 1Q22, in part as copper smelters prepare for major turnarounds in 2Q and zinc smelters continuing to run at reduced rates.

In the United States, less acid was imported in 2021 with pricing out of Europe a key constraint. This is because unlike other markets, such as Chile, where acid is imported for direct consumption, most imported acid in the United States is for distribution. This is largely against domestic contract business for a variety of downstream applications, such as pulp and paper. With annual pricing agreed at the end of the year for the following year, domestic pricing was not at a level to cover the costs of imported material.

While North American suppliers did increase 2022 contract pricing notably, it was still not enough to support the level of pricing needed to make imports workable, along with lower overall availability. This means dependency on domestic supply is critical this year, and we have already seen supply disruptions and a heavy planned maintenance schedule, particularly in 1H. Despite price resistance being seen globally, in the end business is usually concluded due to a lack of other options.

This is highlighting what has carried over from 2021 – supply is tight and higher input prices are being accepted because of firm downstream fundamentals.

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. For North America, we offer a bi-weekly report on sulfur and sulfuric acid as well as a monthly report on industrial chemicals, including caustic soda and hydrochloric. In addition, Acuity does bespoke consulting work. Please visit www.acuitycommodities.com for detailed information. q Sulfuric Acid Today • Spring/Summer 2022

David W. Bailey 1953-2022

You will be missed

With considerable sorrow CMW shares the news with our Sulfuric Acid family of the passing of our mentor, colleague and good friend David Bailey. David enjoyed a long career as a boilermaker, including 35 years with us at CMW leading our chemical field crews. It was always a treat to see David interact with new clients and see their reactions at the realization as he talked that, not only did he speak the sulfuric acid language, but he had seen it, done it and fixed it, whatever ‘it’ was many times and more times than not had the solution for which they were looking. He was adamant that CMW deliver quality work, safe solutions and on schedule performance. So much of our reputation is due to him. David was well renowned for his food, and delighted to cook for his crews while they were out of town to bring them a taste of home on long turnarounds. Always available to answer a call and find a solution, David will be sorely missed by our industry and certainly missed by those of us honored to work alongside him.

Feature

NOx! The other acid gas

By: Darwin Passman, CSP, Safety Director, VIP International Inc.

NOx is an unwanted by-product created in three areas of a sulfuric acid plant. The first and primary place NOx is created is the furnace.

Higher operating temperatures coupled with increased oxygen enrichment and longer residence time form nitrogen oxides. This type of formation is referred to as thermal NOx and represents the majority of nitrogen oxides formed in the gas. Nitrogen oxides may also be present in the fuel or feedstock used in the furnace. This type of NOx is referred to as chemical NOx. A third source of NOx, specific to smelters, results from the operation of wet electrostatic precipitators (WESPs). Electrical arcing in the WESPs causes the formation of nitrogen oxides.

The nitrogen oxides react with sulfuric acid to form the compound nitrosylsulfuric acid (HNOSO4). NOx, in the gas stream, is readily absorbed by the submicronic acid mist particles due to the high surface area to volume ratio. Therefore, most of the nitrosylsulfuric acid is concentrated in the acid draining from the mist eliminators. The mist eliminators are saturated with this NOx-laden acid and sulfates. This acid is readily soluble in sulfuric acid at low temperatures and accumulates in the acidic sulfates of cold exchangers and the false bottom of the stack.

Exposure to NOx is most prevalent during a turnaround. Once the system has been purged

and cooled down, the system is de-energized and prepared for inspections and repairs. Inspection entry points are opened on the dry side as well as the wet side. Due to the natural draft of the plant, ambient air is drawn into the entry points.

The humidity in the ambient air is absorbed by the nitrosylsulfuric initiating a reaction that releases NOx primarily as nitrogen dioxide (NO2). NO2, unlike sulfur dioxide, does not have adequate warning properties at low but toxic concentrations; therefore monitors with electrochemical NO2 sensors must be used for detection and quantification of NO2. It’s worth noting that atmospheric testing of any confined space must follow the OSHA procedure for testing in the following order: OSHA exposure limits: • Percent oxygen: 19.5 - 23.5% • Lower explosive limit: 0.0 - 10.0% • Toxics: carbon monoxide, sulfur dioxide, hydrogen sulfide, or nitrogen dioxide.

Initially there may be a low or no reading of NOx. The nitrosylsulfuric is relatively stable until it begins to absorb moisture. Once exposed to moisture, the reaction begins to release NOx and produces heat. The reaction increases as the acid gets hotter and absorbs more moisture. As a result of this delayed process, we often see NOx levels start out low at the beginning of a turnaround and increase as time progresses.

Areas of significant exposure are from sulfate buildup in the cold exchangers, stack, and other areas of potential sulfate buildup. The gas outlet section of the interpass absorption tower and final tower, including the tube-sheet and mist eliminators, can also be primary sources of NOx exposure.

• The OSHA permissible exposure limit (PEL) for nitrogen dioxide is 5 ppm.

• The Cal OSHA (PEL) is 1 ppm.

• The immediately dangerous to life and health exposure (IDLH) is 20 ppm.

NOTE: Nitrogen dioxide interferes with the sulfur dioxide electrochemical sensor on the atmospheric monitor. For example, if the nitrogen dioxide level is 25 ppm and the sulfur dioxide level is 0 ppm the electrochemical sensor for sulfur dioxide will read -25 ppm or negative 25 ppm. Sulfur dioxide does not interfere with the NO2 electrochemical sensor.

When attempting to mitigate NOx exposure consider the following: • Vessels being entered for inspection or work.

• The actual work being performed.

• Isolating NOx laden equipment.

• Hydrogen buildup.

Since NOx emissions increase when nitrosylsulfuric acid is exposed to moisture, a

plan to minimize that exposure during turnaround should be created to decrease emissions.

Removal of material (sulfates on mist eliminators) at the beginning of the turnaround will decrease the NOx exposure. Also, isolation of specific equipment that is NOx laden will keep the rest of the equipment free of contamination but may also increase the risk of hydrogen build up in a dead zone area.

Once the material is removed, the NOx can be treated with a process that breaks it down to free nitrogen (N2) and weak sulfuric acid (H2SO4).

When working in a potential NOx environment, proactive monitoring is the first step to minimizing exposure. If NOx is present, ventilation is a possible remedy for removal while working in the vessel. If an immediate source of NOx is in the vessel, ventilation may increase the exposure risk by injecting humid air. If NOx is present and work must be performed, immediately dangerous to life and health (IDLH) protocol must be followed. This requires training, experience, and the equipment to safely enter and work in an IDLH atmosphere. The goal in any IDLH entry is to reduce the atmospheric conditions to non-IDLH as quickly and safely as possible.

If NOx is here to stay, mitigate exposure when possible, educate the workforce, and provide training in the safe handling and atmospheric exposure during a turnaround.

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

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Feature

Common pitfalls of sulfuric acid piping and ducting

By: CJ Horecky, Executive Director, INTEREP

Keeping a sulfuric acid plant operating efficiently is a delicate science. Almost every piece of equipment in operation has the potential to bring the whole plant offline if it fails. And each piece of equipment is usually complicated in its own right. Understanding the intricacies of the way each piece interacts with adjacent systems in a plant adds a whole other level of complexity. Thankfully, piping and ducting systems are simple, straightforward, and don’t ever bring plants offline, right? Taking an unplanned shutdown because of a failure in piping or ducting systems is embarrassing.

Sure, the ductwork, like a network of veins and arteries, ties everything together, but it’s more of a peripheral feature. Ductwork is not the core equipment that the whole plant runs on, it’s just a system connector, so there is little grace for plant managers who experience a ductwork failure, and even less for maintenance managers who didn’t see it coming.

As King Solomon said, “there is nothing new under the sun.” The saying applies to acid plants as well. Technology has come a long way in the last 40 years, but INTEREP has consistently found the same telltale signs of imminent piping and ducting failures. Watch for these, and avoid an unplanned shutdown.

Hidden leaks

Acid pooling on the ground, corroded structural steel, plumes in the air… these are all signs of a positive pressure leak, and need to be fixed fast to avoid all kinds of damage, safety issues, and environmental hazards. What about negative pressure leaks though? They’re just as detrimental in the long term, yet tend to be overlooked.

“Out of sight, out of mind,” right?

A negative pressure leak means ambient air being sucked into the system, and what’s doing the sucking? The ID fan/blower. If the ID fan/blower is pulling in ambient air, it’s pulling in less process-gas or using more electricity—both cause trouble. Now let’s talk about that ambient air: it’s wet.

Even in the Sonoran Desert of the Southwestern US (home to several acid plants) the average relative humidity is 38.5%, double that number if you live outside that area. So, your unseen leak is now bringing water into the sulfur gas stream, and making sulfuric acid in places it shouldn’t be.

This will exhibit itself in the following symptoms: • Slow drips or crystalline minerals/acids running from beneath insulation or from gaskets/expansion joints.

PAGE 14

Low-point acid collection found by INTEREP during an inspection at an acid plant in North America.

•

Loss of fan capacity (or becoming ID fan/blower limited in worst-cases).

• Internal corrosion in non-acid containing equipment.

• Elevated O2 process gas levels.

These are the most common hidden leak points: • Fabric expansion joints that have outlived their useful life.

• Fabric expansion joints that have not been properly spliced.

• Holes in ductwork that are hidden beneath insulation.

• Loose flanges or equipment connections.

• Equipment doors/manways upstream (dry gas area).

• Expansion joints that have been insulated over and not documented.

Signs of hidden leaks found by INTEREP during an inspection at an acid plant in Southeast Asia.

Low points

Galvanic metallurgical corrosion found by INTEREP during an inspection at an acid plant in Europe.

Condensation and precipitation getting into a ducting system is an issue. But what about when liquid gets out? Liquid seeks the lowest point in your piping and ducting systems. This often occurs near elbows, in the bottom of vessels, or in the convolutions of horizontal expansion joints. If there is a sagging area in the ductwork, or a low elbow or bend, a drain can be installed to tap this dilute acid off into a sump, until the system can be properly leveled at the next major shutdown. However, if it’s in a metal bellows expansion joint (ubiquitous across the large diameter ductwork in sulfuric acid plants), what can be done? A drain can’t simply be added because there may be as many as 20 or 30 convolutions (the accordion shaped expanded pieces of a metal bellows) which are all their own low points and which will collect dilute acid that gets into the system.

What to do if acid is pooling in a horizontal expansion joint: • Externally insulate the expansion joint (check to verify metallurgy temperature first) to bring everything above dew point.

• Change the metallurgy to something that can handle the dilute acid and will last between shutdowns.

• In certain circumstances, it may be possible to add a drain to the bottom of a “heavy wall” single convolution expansion joint.

• Upgrade to 2-ply designs with a monitoring system that will alert operations when the inner ply fails, so a routine maintenance system can be developed.

• Add either steam or electrical tracing to increase the bellows temperature above dew point.

Metallurgical corrosion

Carbon steel, high-nickel alloy, FRP, thermoplastics—you’ve seen it all, and you know what you like to use. Most plants have a specification for the type of steel to use in piping and ducting systems, and it’s probably followed fairly well. Here’s where things sneak though: piping and ducting accessories. Does the pump vendor know that the flanges should be made of 316L to match the adjacent piping? Does the expansion joint vendor know that the T304 metal bellows are getting welded onto carbon steel? Does the damper manufacturer build shaft packing glands to the same spec as the ductwork is built to? It’s easy to end up with a slew of different pieces of equipment in the system, and it’s hard to vet them all first. Obviously, try to replace any piece that has an incompatible metallurgy with an upgraded one, but sometimes the downtime or the upgrade cost is simply too much.

What are the options if ductwork accessories are corroding and the plant can’t come offline?

• Determine if the part is acting as a heat-sink and dropping the process gas within below dew point.

• Determine if the area upstream is airtight or if there are any major infiltration points contributing to the issue.

• Check metallurgical compatibility between accessory and adjacent ductwork.

• Take UT readings to determine corrosion rate and projected lifespan.

• Perform thermal scans to look for hot and cold spots or potential failure points.

For more information, visit INTEREPinc.com. CJ Horecky of INTEREP will also be leading a deeper discussion of this topic at the Sulfuric Acid Roundtable, April 4th-7th in the Woodlands, TX. q Sulfuric Acid Today • Spring/Summer 2022

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sulfuric acid group products & services Looking ahead

Department

LESSONS LEARNED: Case histories from the sulfuric acid industry

Acid plant troubleshooting issues By: J. McCreight and W. M. Weiss, Elessent Clean Technologies

Typical acid plant metrics revolve around safety, emissions, production capacity, and reliability. Engineering design works to maximize these metrics by keeping process fluids inside vessels and piping. Loss of containment, either to the environment or inside a vessel, compromises these metrics. The ability to recognize and troubleshoot problems quickly can avoid or significantly reduce mishaps that can result in environmental releases, injuries, and major damage to the plant. This article shares some common and not so common failures and discusses indicators of pending failures, as well as root causes of ultimate failures, specifically in SO2 and SO3 process gas releases and steam equipment leaks. These lessons learned are from true incidents and the thoughts are meant to help operations and maintenance personnel avoid the same issues at their plants. Ultimately, readers should be able to better troubleshoot plant issues and gather tips on how to improve reliability.

SO2 / SO3 releases

Fugitive gas leaks (containing SO2 / SO3) from ducting, equipment, and valves are a constant source of frustration and problems.

They are safety hazards for employees on site and potentially for third parties either on or off site. They can be an environmental issue and require self-reporting to appropriate environmental agencies.

Leaks do not generally just happen. They result from corrosion or from thermal stresses related to shutdowns and startups. Normally this will occur over time. Corrosion may result from either internal or external issues. Who has not dreaded the aftereffects of a thunderstorm with driving winds? New leaks are usually found after the storm has passed as condensation occurs within ducting and equipment— especially in dead legs. Rainwater hitting and quenching hot metal will eventually cause it to crack and these cracks will start to leak gas.

Cracks do not self-heal but continue to propagate. New gas leaks may also result from acid tower carryover, collection of condensate in difficult-to-purge areas such as low points, or stress/fatigue near nozzles, joints, and elbows.

Leaks may not necessarily result from mechanical failures of steel and loss of duct/ equipment integrity. Leaks may come from valves such as sample points that do not fully seal; from shafts on duct dampers that are not provided with adequate purge air to the stuffing box; from blower shaft seals in spent acid or metallurgical plants that are not properly sealed; and from gas cleaning systems dripping fluids that contain dissolved acid gases.

It is important to check for unusual sights and smells during operator rounds. To assist, many plants are using ambient fence line gas monitors for SO2. Coupled with wind direction, this can help pinpoint the source of the leak.

Leaks of SO3 gas are visible as a white or grey plume that does not readily dissipate while leaks of SO2 gas are colorless and impossible to detect visually. SO2 has a characteristic pungent PAGE 16

odor which most people can detect at around one ppmv. IDLH concentration of SO2 is 100 ppmv. Gas leaks in some parts of the plant may contain both gases.

A quick self-survey: • How well are you maintaining the insulation and cladding on heated equipment?

Some small plants build rain roofs over troublesome areas. Has your site installed rain shields/ covers over critical equipment and ducting junctions (think of first pass exit nozzle for example)? Are you maintaining these rain covers?

• Are your maintenance teams promptly replacing insulation and cladding after maintenance work? Is the replacement performed per design standards? For instance, insulation needs to be placed across gussets and not between them. If placed between gussets, the gussets behave as cooling fins resulting in thermal stresses that have a propensity to tear them off at the base weld. Banding should be applied as needed and at the proper tension, so they do not slump or tear off with heating and cooling. Banding should be checked from time to time. Cladding should be reapplied to keep the insulation dry, and the cladding should use the proper attachment devices and be properly sealed.

• Are duct and equipment wall thicknesses examined during shutdowns? Do you perform plant walk-throughs looking for discoloration spots (that dreaded greenish corrosion color) on the insulation cladding as evidence of potential leak sites underneath that are small and not readily visible? A preemptive replacement of ducts, expansion joints, and equipment sections may be preferred to waiting for failure and leaks.

• What about those small white puffs of “smoke”? What about your sense of smell?

Are you detecting the distinctive odor of SO2? Do you react quickly to these detected leak points and address them while they are still small or wait until they become more problematic?

Gas leaks need to be addressed quickly as they can lead to employee safety issues and possible environmental deviations from your operating permit. On-line patching of gas leaks can buy operating time, but eventually an outage will need to be planned and scheduled to make permanent repairs.

It has been observed that some owners collect the gas leaks and route them to a suction drying tower using piping or flex hoses.

The leak is encapsulated to the extent needed and the gases are pulled away by the drying tower vacuum. This “shop vac” approach can be effective in the short term. The encapsulation may have some impacts on the thermal expansion capability of the duct or vessel and stress cracking may develop in the area around the encapsulation. The drying tower is not normally designed for removal of SO3. This gas will produce unexpected submicron mist in the tower which may carry downstream to the blower and the converter section.

Steam equipment leaks

Steam equipment leaks eventually occur.

Sulfur-burning plants have steam jacketed spray nozzle assemblies as well as boiler(s), superheater(s), and economizers. All are potential leakage points, as shown in the photographs presented here. Often, metallurgical plants have no steaming equipment with no risk of steam leaks. Spent acid regeneration plant steaming equipment might be limited to the wet gas section in the front end. The focus here is on steaming equipment leaks occurring after the drying tower.

Some leaks may start slowly and be difficult to detect, while others may be instantly obvious. The extent of corrosion damage is a function of leak size and begins to increase in magnitude as the leak grows. Preventative maintenance during turnarounds (by visual inspection, eddy current testing, and checking thickness of U bends) is key in early detection or identification of thin spots which may be addressed/repaired during plant shutdowns.

Once a leak occurs, quick detection and proper mitigation responses are important aspects to protect process equipment, safeguard personnel, and minimize releases to the environment.

Hot weak acid in contact with steel components will lead to corrosion and hydrogen formation.

Leak locations can be identified by a review of process trends such as dilution water, boiler feedwater, and steam flow rates; visual inspection; and by listening for internal equipment hissing. The response may vary depending on the leak point and the extent of leakage.

Shutting down the plant and depressurizing the steam system are normal recommendations.

This requires isolation from the site steam header and venting the steam after the superheaters. Boiler feedwater flow should be maintained as required to maintain boiler level. This is to keep the tubes cool from furnace gases.

However, a low water level in the boiler should not be corrected by adding water while the furnace is hot and the steam drum is pressurized.

Exposed boiler tubes in this condition will be excessively hot and soft. Collapsed tubes will result from this early water addition. Allow the tubes to cool first.

Once steam enters the dry section of the

Overheated sulfur cracked and leaking.

spray

assemblies,

Leaking boiler tube to tubesheet welds.

A Tyndall Beam Test can detect water vapor in process gas.

acid plant, it reacts with SO3 gas to form sulfuric acid This can condense in cool sections of the plant and will dilute the acid contents to concentrations where corrosion rates may be extremely high. The presence of water vapor may be detected by commercially available dew point analyzers or with a more simple Tyndall Beam Test shown below. A dried flask will become cloudy in the presence of acid mist droplets to the extent that these are present.

This corrosion from weak acid leads to thinning of plate and potential release of containment; it leads to corrosion of vessel internals which can affect process performance or mechanical support; it generates iron sulfate sludge which plugs packing, piping, and ducts; and it generates hydrogen gas which may reach its LEL concentration in high points of the process if not properly purged.

Steam leaks do not manifest in just a liquid phase. Steam exists as a vapor and the vapor content of the process increases as the sulfuric acid becomes hotter and weaker.

Recharging cooled strong acid to a pump tank and initiating circulation over a packed tower with high water vapor content will rapidly absorb this water vapor. This can result in a sudden generation of vacuum and collapse of tower sections. Manways should be opened to allow large amounts of air ingress if the blower purge is not still functioning once acid circulation begins. Blower purge is highly advised to sweep water vapor downstream as well as any hydrogen accumulation.

Training with acid plant operation simulators (MECS® Acid Plant Simulator for example) and/or developing operational experience by running “what-if” drills with operations and maintenance personnel will help prepare the operations team for when that day arrives. The key is to plan, review, and revise those plans for the eventuality. Managers and operators should discuss and practice responses focusing on how to keep employees safe; minimizing equipment damage and environmental releases; and how to prevent hydrogen from accumulating within the plant. Focus should be on early detection of a leak and identifying the proper responses to secure both the leak and the plant quickly. It is important to think about where the weak acid could have collected and how / where to properly drain it. If warranted, neutralize those areas to prevent on-going corrosion damage if the plant is to be down for any appreciable amount of time. Materials and equipment for this will need to be available and ready for service. A tabletop exercise may help point out areas of misunderstanding that need to be addressed before an “event” occurs. Turnaround planning may be enhanced with the review of plant operating data to sense the presence of a leak before it is found during inspection.

For more information, please visit www. elessentct.com or email Walter Weiss at WALTER.M.WEISS@dupont.com. q Sulfuric Acid Today • Spring/Summer 2022

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Feature

PVS Chemicals upgrades its Belgium acid operation PVS Chemicals Belgium recently marked its one-year anniversary producing sulfuric acid using upgraded SO2 conversion and heat recovery systems.

In February of 2021, the company’s sulfuric acid operation started up with a new four-pass converter and steam generation equipment. Since that time, PVS Belgium has increased uptime while creating green energy.

About PVS

PVS Chemicals Belgium NV is located on the canal in Port of Ghent, Belgium. The company specializes in manufacturing and distribution of sulfurbased specialty chemicals, with a focus on high-purity products.

Products include chlorosulfonic acid, oleum, and other high purity sulfuric acids such as ultra pure, chemically pure, and technically pure grades; along with ammonium bisulfite, sodium bisulfite, and sodium bisulfate. The variety of offerings serve diverse industries from batteries and electronics to food, fertilizers, and water treatment.

Within both the industrial grade and high purity acids, PVS Belgium produces many customized variations. Food-grade sulfuric acid is customizable from between 1 and 98 percent solution. The same is true for high-purity acids, such as chemically pure sulfuric acid used in pharmaceuticals; electronic grade sulfuric acid used in the manufacture of printed circuit

Process flow prior to replacing old converters and heat exchangers.

boards; and ultra-high pure sulfuric acid used in the production of microchips, semiconductors, and pharmaceutical and photovoltaic applications.

The company’s size, about 40 employees, with multiple integrated specialty units and a state-of-the-art onsite laboratory, enables flexibility in fulfilling custom orders. This flexibility sets PVS Belgium apart from other suppliers and has made the company successful in the European sulfuric acid market and beyond.

PVS Chemicals Belgium is owned by PVS Chemicals, Inc., which was founded in 1945 under the name Pressure Vessel Service (PVS). Headquartered in Detroit, the parent company is a global manufacturer, distributor, and marketer of chemicals and transportation services with operations in Asia, Europe, and North America.

Aging equipment & downtime

Prior to the upgrade, the plant was equipped with two parallel converter trains with air coolers between passes. The converters were at the end of usable life and the plant was experi-

Fourth beds of aging twin converters. Converter 2 (bottom) shows bed three falling through.

PAGE 18

New MECS® four-pass converter replaced aging twin converters.

encing multiple shutdowns, both planned and unplanned, resulting in production losses and costly repairs.

Several repairs had to be made to the converters, heat exchangers, and ducting.

Additionally, the equipment was housed inside a building, which made access for maintenance and repairs extremely difficult.

New economizer (left) and waste heat boilers (center) saves roughly the same amount of CO2 annually as planting 195K trees per year.

The solution

In a preliminary study that began in April 2018, MECS® technology experts worked with PVS plant managers on a design that replaced the failing twin converters and provided an efficient heat recovery process to produce steam. The design featured a single stainless steel four-pass converter, three waste heat boilers, and an economizer.

“Though the upgrade would increase capacity from 220 TPD to 300 TPD, main drivers for the project were to improve operational reliability and generate green energy,” said Omar Sinaph, Managing Director of PVS Chemicals Belgium.

The new converter was designed to be used with MECS® GEAR® catalyst. Because of its shape and size, less GEAR® catalyst is required than MECS® XLP® catalyst to achieve the same conversion. This in turn translates to a smaller converter and thus reduced capital cost.

Two types of catalyst were loaded. GEAR® 310, the smaller of the two and more active, was installed in beds 2, 3, and 4. The slightly larger GEAR® 330 was used in bed 1 for better dust management.

The new economizer and the four new waste heat boilers allow for heat recovery of up to 5

Schematic of new converter and heat recovery process at PVS Chemicals Belgium.

MM Kcal/hr. This saves approximately 11,700 TPA CO2 and is roughly equivalent to planting 195,000 trees per year.

Installation & startup

“The Covid pandemic created some delays at the fabrication workshop for the steaming equipment,” Yves Herssens, MECS® Technology representative, said, “but accurate monitoring of their progress was put in place to limit the impact for our customer.”

The old converters remained in service during construction.

The indoor location that for so long frustrated maintenance efforts became an advantage during the transition. “The new equipment is located outside the building but close enough so that it could be connected to the rest of the plant. This allowed us to install and load the new converter while the old equipment was still operating,” said Sinaph.

Cold shutdown for final tiein and startup was completed

in three weeks despite snow and freezing temperatures.

Commissioning and startup were completed on time in February 2021. Since that time, the plant has performed stably, producing high quality acid per design, and delivering a regular supply of high pressure steam for internal use and for its industrial neighbor.

“Uptime has significantly improved,” said Herssens, “which allows PVS to serve more clients reliably and in predictable timeframes. Saturated steam output has almost doubled.”

“The intensive support from the MECS® technology experts for the commissioning and start-up was of great help,” said Sinaph. “Reliability of the plant has significantly improved.

And steam production is highly beneficial, especially since the cost of energy has dramatically increased.”

For more information, please visit www.pvschhemicals.com or www.elessentct.com. q

Sulfuric Acid Today • Spring/Summer 2022

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Feature

Polymer concrete: Corrosion protection for pump pads, trenchless & process flooring By: John E. Davis, Inside Sales and Marketing Specialist, Sauereisen Inc.

Polymer concretes are designed to give superior mechanical properties like that of masonry. Because of chemical resistance throughout the entire thickness, polymer concretes may preclude the necessity of barrier coatings and linings. Polymer concretes offer a one-step approach to solving corrosion and provide superior compressive, flexural, and tensile strength. In addition, select fillers enable physical properties such as absorption and freeze-thaw durability to far exceed most inorganic counterparts.

Polymer concrete is one of the most durable, long-lasting, and corrosion-resistant materials available for industrial infrastructure.

This class of products consists of a matrix composed of heavy-duty aggregate and either chemical-resistant resin or cement binder.

These castable materials may offer up to five times the physical strength compared to standard Portland-based concrete.

Application of polymer concrete also offers the advantage of developing strength rapidly. Most castables in this category are set through a catalyzed chemical reaction. This thermo-setting process occurs within 24-48 hours, primarily. Compared to the 28-day hydration downtime of standard concrete, construction may proceed much more rapidly.

Understanding the capabilities and limitations of the different fillers and resin systems within the polymer concrete family is impor-

tant. As technologies evolve, the chemistry of various formulations proliferates as well. Engineers, architects, maintenance personnel, and contractors can create a value-added solution to their corrosion problems when knowing what to recommend. When properly specified and installed, polymer concrete provides a solution for some of the most difficult corrosion problems.

The wide variety of polymer concrete formulations can make selecting the correct materials a challenge. Ultimately, selecting the right chemistry can translate into substantial cost savings as determined by increased longevity or decreased construction downtime.

A few of the more common formulations of polymer concretes include silicates, epoxies, and vinyl esters. Sauereisen, Inc. of Pittsburgh, PA, specializes in corrosion resistant materials and produces a broad selection of polymer concretes to supplement other product lines including refractories, mortars, and monolithic barriers of various thickness. For environments subject to the highest temperatures and acid concentrations, potassium silicate polymer concretes provide optimum protection.

The silicates can withstand temperature ranges more than 1,400o F (760o C). This chemistry will also withstand most solvents, oils, acids, and acid salts (except hydrofluoric) over a pH range of 0.0 to 7.0.

For years, silicate-based refractories have

ULTIMATE CORROSION PROTECTION for Secondary Containment Wherever extensive corrosion conditions exist, we have a system to offer long term asset protection. …Since 1899

P: 412.963.0303 • E: info@sauereisen.com sauereisen.com PAGE 20

provided thermal insulation and chemical protection for flue gas structures subject to hot, acidic gasses commonly found in coal burning power generation facilities. Recently, polymer concretes have been specified for horizontal applications, such as chimney floors, where greater compressive strength is beneficial compared to the gunite-applied refractory. In either case, these acidproof concretes possess resistance to full concentrations of sulfuric acid. Other applications are construction of sumps, containment pads, dikes, trenches, support columns, and bases.

Pump pad cast with polymer concrete for added corrosion protection.

Epoxy polymer concretes, as a group, offer low permeability and broad chemical resistance. Epoxies exhibit greater bond strength, lower porosity, and more broad chemical resistance than inorganic varieties. Typically, the compressive strength of epoxies is greater than 10,000 psi. This classification of polymer concretes shows tolerance to a wide spectrum of acids and alkalis over a pH range of 0.0 to 14.0.

These products are often categorized as either general purpose epoxy polymer concrete or as a novolac epoxy. The novolac epoxy resin possesses a greater degree of cross-linking than the standard Bisphenol-A epoxy. Consequently, the novolac resin system offers an upgrade in properties. Among epoxies, novolac systems tolerate greater chemical concentrations while exhibiting compressive strength of 16,000 psi.

The organic polymer concretes in the vinyl ester family are specified where certain chemicals such as bleaches or oxidizing solutions are present. Like epoxy-resin based polymer concrete, vinyl ester polymer concretes can be of a general-purpose grade as well as a novolac vinyl ester formulation. Often the temperature environment is a determining factor in selecting one of the organic polymer concretes.

Sauereisen’ s epoxy, novolac epoxy, vinyl ester, and novolac vinyl ester polymer concretes resist maximum service temperatures of 1,500o F, 1,800o F, 2,200o F, and 2,500o F, respectively.

Chemical facility floor poured with Sauereisen Epoxy Polymer Concrete No. 265.

Application of polymer concrete

Standard mortar mixers and tools are used for mixing and placing polymer concretes. A familiarity with the working properties of basic concrete is all that is required. Typical reinforcement is incorporated where appropriate. Pencil vibrators can aid consolidation of the material.

Minimal finishing is required. The workability of polymer concrete makes it a good choice for the construction of sumps, trenches, floors, walls, and structural supports.

Continuous mixing is often utilized to complete the placement of material even quicker. Mixing by this method delivers up to 20,000 pounds or 5 cubic yards of material per hour.

For projects on an extra fast track, polymer concrete offers the versatility of being formed into pre-cast structures, too.

Polymer concretes may be used as overlays for Portland cements or as a stand-alone system.

In either case, the polymer concrete will need some type of reinforcement. Most manufacturers of polymer concretes recommend a thickness of at least 1” or more. The reinforcement selected depends on the application thickness, anticipated shrinkage, thermal load expected as well as maximum temperatures during cure.

The reinforcements must be anchored to the substrate when used as an overlay. Typical recommended reinforcements are epoxy coated, stainless or galvanized rebar as well as various types of mesh.

As polymer concretes typically will cure faster than Portland-based concrete, it is important that all equipment, forms, and other materials are ready before beginning the mixing process. Most polymer concretes will release heat during cure and this exothermic reaction can reduce working time when mixed in large quantities, therefore reducing the time required to mix, place, and finish the material.

Using Portland cements in the chemical processing facility typically requires protecting the concrete for corrosion. This protection can be a few mils of a corrosion-resistant coating up to a brick and mortar system. The service life of the coating is related to the chemistry and thickness of the coating. The thinner the coating the increased likelihood of the corrosive material penetrating the barrier, requiring the repair of the concrete substrate, replacement of the coating, disposal of contaminated concrete, and additional downtime.

Polymer concretes will provide a substantial corrosion barrier and a service life many times greater than protected concrete.

Sauereisen has 121+ years of experience in corrosion protection and engineered solutions. The company maintains a global presence with a network of technical sales representatives throughout the world, with manufacturing and warehouse facilities located in the United States, Europe, the Pacific Rim, and Latin America providing worldwide product distribution. Sauereisen remains dedicated to solving the problems requiring specialty materials with the expertise in the restoration of infrastructure and the prevention of corrosion. For more information, please visit www.sauereisen.com. q Sulfuric Acid Today • Spring/Summer 2022

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Feature

Chemetics— Chemetics —3,000 acid coolers and counting

By: Robert Maciel, Senior Business Development Manager, Chemetics Inc.

Few developments in the manufacture of sulfuric acid can eclipse the importance of the Chemetics® anodically protected sulfuric acid cooler. First introduced in 1967 by Chemetics’ parent company, Canadian Industries Limited (CIL), and popularized in the 1970s and 1980s, the Chemetics design revolutionized the conventional method of acid cooling and continues to set the global standard for reliability and performance. Developed out of the need to improve plant reliability, the CIL cooler, as it was once known, revolutionized conventional methods of acid cooling, led to uninterrupted operation, compact plant layouts, vastly reduced maintenance, greatly improved acid plant reliability, and the ability to recover valuable low-grade energy.

In 2021 Chemetics celebrated yet another significant milestone in the long history of the sulfuric acid cooler: the delivery of the 3,000th unit. The cooler was supplied to a North American client to replace an original Chemetics cooler from the 1970s. One might think it would be an extraordinary circumstance to encounter an acid cooler with half a century of service. This is commonplace,

though, as several of the original 1970s Chemetics acid coolers remain in service to this day.

This is a testament to the quality design and fabrication that Chemetics has become known for. As the originators and leaders in acid cooling technology, Chemetics has continued to introduce developments in anodic protection, thermal and mechanical design, manufacturing methods/ techniques, as well as materials of construction.

Chemetics acid coolers are fully designed and fabricated in a state-of-the-art facility located in Pickering Ontario, Canada, which is owned/operated by Chemetics, ensuring complete control of quality and schedule.

Many of the fitters and welders have continuously worked on Chemetics acid coolers for their entire careers (40+ years). If one were to line up all the tube-totubesheet welding executed by Chemetics the result would be a continuous weld that could reach the International Space Station.

This unparalleled know-how and experience results in the highest possible weld quality, which in turn allows for the industry’s most robust/reliable and safe acid cooler. Chemetics also stocks significant quantities of acid

1970s Chemetics acid cooler production.

cooler materials (tubing, plate, ANOTROL® electronics, etc.) with tubing made to Chemetics specifications to maximize corrosion resistance. In-house fabrication in combination with stock materials allows for competitive pricing and fast delivery times.

The demand for Chemetics equipment and its high level of fabrication quality has continued to increase globally. To meet this increasing demand, Chemetics is presently investing in a major expansion to the Pickering fabrication facility.

Since the introduction of the original stainless steel anodically protected acid cooler, Chemetics has also developed proprietary materials and designs to address various applications and challenges. Chemetics developed proprietary CIRAMET® and CIRAMET+ allowing for acid cooling with water containing high levels of chlorides (from brackish water to seawater).

SARAMET®, developed by and proprietary to Chemetics, is available in multiple grades (SARAMET 23, 25, 35, HT™

and HT™+). Acid coolers made of specific SARAMET grades allow for operation without anodic protection due to SARAMET’s exceptional corrosion resistance in hot sulfuric acid, with HT and HT+ grades specified for higher temperature energy recovery applications. Grades are custom selected for each service to maximize performance and reliability while minimizing cost.

With the milestone of the 3,000th acid cooler, Chemetics and the sulfuric acid industry celebrates one of its most important landmark developments. This milestone acid cooler has been installed and the client is looking forward to enjoying another 50 years of trouble-free service.

While we take time to appreciate this achievement, the focus continues to be on the future.

Chemetics continues to lead by prioritizing technology development that will benefit sulfuric acid plants and the individuals who operate and maintain them.

Chemetics also provides spare parts and site technical services globally to support acid cooler inspections, maintenance, and troubleshooting.

For more information, please contact Chemetics at chemetics. equipment@worley.com. q

Chemetics has delivered 3,000 acid coolers so far.

PAGE 22

Sulfuric Acid Today • Spring/Summer 2022

Feature

NORAM delivers another hot-sweep cold exchanger

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

Leaking exchanger reduces capacity

Our client approached NORAM after they found they had to reduce the plant sulfuric acid production rate to maintain their target SO2 emissions due to severely leaking tubes in the cold interpass (IP) gas exchanger. A few years before, the client had installed a NORAM Hot Sweep cold exchanger in a sister acid plant and was well satisfied with the performance.

It was therefore a relatively easy decision to replace the leaking exchanger with a NORAM Radial Flow Hot Sweep cold exchanger.

The existing exchanger was built in the 1990s as a carbon-steel double segmental exchanger. This exchanger type has a shell full of tubes and large bustles for the shell inlet and shell outlet gases. The heat transfer coefficient, an indication of the effectiveness of the tube surface area, for a double segmental exchanger is about 50% of that of a radial flow style exchanger.

Also, the coldest SO3 gas is adjacent to the cool SO2 gas stream resulting in cold metal temperature that promotes condensation,

corrosion, and sulfate fouling.

NORAM’s design

The shell-side gas in NORAM’s RF™ radial flow design flows at right angles across the tubes, which provides a high heat exchanger effectiveness or, in heat transfer terms, a high film coefficient. Thanks to the No Tubes In Window (NTIW) baffle design, there is reduced shell gas flow parallel to the tubes, which prevents areas of low heat transfer.

To eliminate potential cold-end condensation, NORAM’s SF™ split flow exchanger incorporates a patented hot-sweep feature that keeps the cold end temperatures above the dew point of sulfuric acid vapor.

The result is the bottom of the exchanger is warmed well above the dewpoint temperature, reducing the chance of condensation and corrosion. NORAM has been supplying this popular style of gas exchanger and the first is still operating after 20 years. Refer to Fig. 1 for the flow arrangement.

Making it fit

It is relatively easy to design a new exchanger. However, the art of the design for a replacement lies in minimizing the changes required for the installation, such as ducting and foundations. Matching the foundation is easy as the radial flow exchanger is generally smaller in diameter and lighter. A structural steel framework, called grillage, is often used to connect the new exchanger

Old exchanger (left) with top bustle removed.

to the existing foundation, eliminating the need to do any concrete work.

For the ducting, NORAM optimizes the exchanger design to minimize the ducting changes and re-use as much of the existing ductwork as possible. For this project, NORAM designed and supplied a short-shell inlet duct and some interconnecting pieces to connect the new exchanger to the existing ducts, minimizing installation costs.

Doing more with less

The client planned to increase acid plant capacity. A NORAM study, completed a few years before the implementation of this project, generated a process flow diagram for the future production case that was used for the design of the new cold IP gas exchanger. The new exchanger was designed for lower pressure drop and increased heat transfer. In addition, the new exchanger design achieved this with less tube surface area than the old exchanger, as

New NORAM Hot Sweep Cold IP Gas Exchanger.

demonstrated in the table below.

The savings were dramatic: the new exchanger had 50% fewer tubes, 50% less tube surface area, was 50% lighter, and had 40% lower pressure drop compared to the existing. Also, unlike the old exchanger, the new exchanger is designed to meet the requirements of the future increased capacity case.

And that’s a wrap

The gas exchanger was fabricated in a high-quality, local shop that NORAM used on previous projects. Delivery, in one piece, was on schedule. The start-up was uneventful, the exchanger has been in service for close to a year and the plant is no longer limited in production capacity by a cold IP gas exchanger, resulting in excellent economics for this project.

For more information, please visit www.noram-eng.com. q

Table: Exchanger Comparison Fig. 1: Flow arrangement for Cold IP with Hot Sweep, Red Stream: hot SO3 Gas. Blue Stream: cool SO2 Gas

The baffle cage of the new exchanger, prior to tube stuffing.

Parameter

Old Exchanger

New Exchanger

Shell configuration

Double segmental baffles

Radial flow with hot sweeps

Material of construction

Carbon steel

304 stainless steel

Tube gauge

11

14

No of tubes

2,900

1,100

ft2

68,000

33,000

m2

6,300

3,100

lbs

110,000

51,000

kg

243,000

113,000

inches

29

17

mm

737

432

Tube area

Weight

Pressure drop, WC Built offsite, the exchanger was delivered in one piece, reducing build time.

PAGE 24

Sulfuric Acid Today • Spring/Summer 2022

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Feature

How sulfur quality affects melting & filtration

By: Nuria Pascual Vasco, Lucia Kisic, and Jan Hermans, Sulphurnet

Sulfur is distributed in liquid as well as in solid form. Refineries are the main source of liquid sulfur, providing the best quality on the market. The Claus process produces liquid sulfur with minimum impurities. The only impurity that could possibly affect the quality of liquid sulfur is the presence of H2S due to the lack of a complete degassing process. The transportation distance of liquid sulfur is limited due to the solidification process—exceeding 500 KM causes sulfur to solidify and trucks must be pre-heated to re-melt the sulfur.

When larger distances are involved, refinery sulfur is solidified and distributed in forms such as prilled, granulated, or flaked sulfur. Each has its own characteristics regarding angle of repose and conveyor belt incline, and the likelihood of breakage and formation of powder.

Another form of solid sulfur comes from Frash mining. To Sulphurnet’s knowledge, two mines are still in operation, one in Jaltipan, Mexico, and the other in the Machów mines of Poland. We will go deeper into mined sulfur later.

Currently, the sulfur market is very dynamic and sulfur prices are rapidly increasing. The supply chain is disturbed because of price movement and increased demand, resulting in lower sulfur grades entering the market. Using more contaminated sulfur risks interfering with melting and filtration processes, potentially jeopardizing the sulfur section’s throughput capacity. Poor quality sulfur can also decrease catalyst lifetime and increase production cost. Parameters affecting the sulfur quality and the melting process are the H2S, level of organics, acidity, and elevated ash levels. Additionally, safety issues can arise from different qualities of sulfur.

When receiving sulfur specifications, the following information will almost certainly be provided: • Sulfur minimum 99,7% • Ash <0,02% • Organics <0,04% • Water content <1% • Acidity < 0,001% • Metals (As, Te, Se) <1 ppm The first thing to consider is that the quality is measured on the location of solidification. So, when the sulfur arrives at the melting plant the composition is changed drastically due to various parameters which we will discuss later.

In Sulphurnet’s experience, metals such

Mined vs. refinery sulfur.

PAGE 26

as arsenic, tellurium, and selenium are not present in refinery sulfur. In the past, pyrite was used as a sulfur source. Pyrite has higher concentrations of various metals, including arsenic, tellurium, and selenium. So due to historical reasons these were analyzed but are not present in today’s quality sulfur.

A special emphasis should be placed on sulfur produced by the Frash Mining Process. These sulfur grades are heavily polluted with high viscous organics (Carsul), with concentrations reaching as high as 0.7%.

This complicates the prilling process and interferes with sulfur melting and purification processes. The sulfur has a darker color, indicating the level of organics, which is far from bright refinery sulfur.

When analyzing sulfur that arrives on site, it often doesn’t meet the specifications as stated on the original datasheet. The main reasons are these changes in the following: • Transportation: With land transport, frequent loading and unloading increases ash. Sulfur can also break and create dust. With transport by sea, water and ash content increases. FeSx might be formed causing further corrosion.

• Rain: Humidity and rain decreases sulfur quality. Though under roof storage is costly, it is a good practice.

• Acidity: The presence of Thiobacillus bacteria in the sulfur in combination with air and water forms sulfuric acid. Its production rate depends on the humidity and local temperature. The more acid the higher the bacteria’s activity.

The sulfuric acid industry requires clean sulfur to protect the catalyst. A close examination of the listed impurities in the sulfur melting and purification process reveals that a variety of issues can arise. Here is a summary of the potential issues:

Frequent moving increases sulfur ash and dust.

H2S sulfur flour

Nowadays, concerns about the environmental impact of industrial processes are increasing, causing stricter regulations being applied to liquid sulfur melting facilities, where special attention needs to be paid to the maximum H2S emissions.

Emitting H2S into the environment has a negative impact on both animal and plant life. According to the United States department of labor (OSHA), exposure to 2-5 ppm can already cause nausea, eye tearing, and airway problems. Its characteristic odor of rotten eggs can already be smelled at concentrations as low as 0.01 ppm but becomes stronger at higher concentrations. Because

of its high toxicity and flammability, many authorities have limited maximum emissions.

Thus, sulfur obtained from the Claus process must contain below 10 ppm of H2S, and the maximum emission in Europe is commonly around 3 mg/Nm3.

In a sulfur melting plant, the melting tank is the main point of emissions. Inside, the fresh solid sulfur is continuously melted, and the water content is evaporated. The water vapor aided by the existing airflow through the tank drags part of the H2S to the stack, where it is released into the atmosphere or treated by a gas cleaning system. The water effect together with the liquid-vapor equilibrium reached by the H2S gives the H2S gaseous emission.

Sulphurnet has studied the H2S emission thoroughly and developed a sulfur melting technology that reduces emissions from 10 ppm in the solid sulfur to the strict EC regulations of 3 mg/Nm3.

The gas stream also contains sulfur flour. This is liquid sulfur that evaporates from the melting tank due to its vapor pressure at the high process temperature. When the sulfur vapor cools down, it condensates and desublimates, forming sulfur flour which can then be defined as a submicron aerosol (mixture of sulfur in the form of droplets, particles, and vapor). Once sulfur flour touches cold surfaces, it solidifies and sticks to them causing various issues such as instrument failure, blockage of untraced piping and equipment, scrubber blockage, etc.

Different types of H2S scrubbers have been used to minimize these emissions, but they often fail because of the high solid loads.

This is due to the characteristics of the sulfur vapor, or sulfur flour, which causes parts of the scrubber, such as the demister and spray nozzles, to block.

Sulfur solidification can cause the metal parts of equipment to corrode and form iron sulphide, especially considering that in presence of water, air, and high temperature, the corrosion process is accelerated.

To prevent all these issues, piping, nozzles, and instruments should be jacketed, and all equipment should be kept at process temperature. However, the deposition of sulfur flour cannot be prevented in all areas; and in these places corrosion resistant materials and regular inspection should be applied.

Organics

Organics cause a variety of issues during the melting process. They settle in poorly agitated tanks, forming layers that block heat exchangers and, as a result, reduce melting capacity. Also, liquid sulfur pumps can be damaged by accumulation of organics in the submerged pump impellor.

When it is not possible to drain a melting tank, the pit must be emptied, and remaining sulfur must cool down. This entails shutting down for at least a week to clean the pits.

A well-designed melting tank avoids these costly production losses.

Melted organics have different proper-

Organic matter in sulfur can foul equipment.

ties that interfere with the filtration process.

The organics with a high viscosity are jelly products that tend to clog the filtration area.

This means that the filtration flows should be reduced to avoid a rapid pressure incline and filter cake blockage. This leads to more frequent filter cleanings and sulfur losses, but it also endangers the production capacity because flow rates can drop as low as 60% of capacity when compared to good bright sulfur.

In those cases, a body feed can be used to improve process performance. A body feed is a filter aid addition to unfiltered sulfur. It provides a filter cake with open pores that prevents large flow drops. Still, a 40% reduction in flow rate must be considered.

Using body feed requires an additional investment that should not be underestimated, as it requires a body feed vessel, a body feed pump, and additional piping and valves to make this process work properly. As can be seen, there are numerous reasons to thoroughly investigate the sulfur source used in the process.

Liquid sulfur pump damaged from poor sulfur quality.

High water content

Wet sulfur consumes a lot of energy during the sulfur melting process. Water vaporization requires nearly five times the energy of sulfur melting. Furthermore, wet sulfur (5%) causes foaming. That is not a big deal as long as the foaming is controlled in the melter, but large amounts of foam can escape and pollute the environment while also increasing fire risk.

Ash

Ash in the sulfur melting process causes substantial issues both in melting as well as filtration processes. To keep solids suspended Continued on page 27

Sulfuric Acid Today • Spring/Summer 2022

Feature

Continued from page 26

in the melter, good agitation is essential.

Lack of agitation causes the ashes to settle.

This is especially problematic with in-ground pits, where they rapidly sediment in the dead zones. In that scenario, the process must be interrupted for cleaning, and the sulfur should first solidify before getting drilled out. This operation is time- and labor-intensive and interrupts production.

Settled ashes can cover the heating coils in the melter, limiting its heating capacity.

They can also enter and block the pump.

As ash level in the filter rises, the filter cycle time begins to shorten. Because of these shorter cycles, the filter must be cleaned more frequently.

Acidity

Corrosion is well known in sulfur processing, and has two main causes.

Sulfur solidification in equipment steel, piping, or valves produces FeS, which, combined with air and moisture, initiates a corrosion process. Equipment can be destroyed in a matter of weeks, depending on local conditions, humidity, and temperature.

The presence of acid in sulfur at temperatures as high as 150 degrees Celsius makes the acid extremely aggressive. These conditions are unsuitable for stainless steel or super duplex steel. A brick lined melter in addition to an excellent neutralization process are required to reduce acidity. Dosing with lime in the form of Ca(OH)2 is a must. To control corrosion, frequent acidity analyses

before and after neutralization are needed.

To obtain reliable results, good analytical procedures must be used. Both melting and filtration processes will be affected by acidity due to the fact that longer residence time is required to obtain a good neutralization process, which reduces the melting capacity.

The extra addition of lime rapidly increases the formation of filter cake, which reduces the filtration cycle. This results in higher sulfur losses and increase in OPEX.

Conclusion

As a result of the concerns discussed here, we advise that pricing should not be the most important factor to consider when purchasing sulfur for the melting and filtration plant. Given the current status of the market, people need to be aware of the risks of high volumes of low-quality sulfur. It’s more crucial than ever to look at factors like ash, acidity, and organics levels in sulfur. When sulfur with a high content of these components enters the market, it causes major process interruptions and equipment damage. Savings made by buying lower cost sulfur grades will be offset by OPEX costs in the sulfur melting section and can eventually reduce a plant’s capacity and operational lifetime. Sulphurnet can assist with solving these issues as well as adapting and modifying existing equipment to any sulfur quality level.

For more information, visit www.sulphurnet.com. q

A NEW DAY FOR KNIGHT

You’ve known us for over 100 years.

You’ve relied on our technology and services, and now, it’s a new day for Knight, as Knight Material Technologies.

With newly-expanded access to resources, we’re positioned to bring our customers an even greater vision for industry leading products and services.

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Sulphuric Acid Coolers Experience: • Originally developed and patented by Chemetics • Industry standard best-in-class design since 1968 • More than 2000 in service worldwide with frequent 30+ year service life • CIRAMET® seawater coolers and SARAMET® silicon stainless steel options Features and Benefits: • Custom designed for optimal performance and reliability • Designed and fabricated in our state-of-the-art Canadian facility • ANOTROL® anodic protection, advanced proportional control with true continuous duty rated power supply • Now with MEMORY SEAL™ cathode gland for improved reliability World-wide technical and inspection services to maintain safe operation and uptime in your plant.

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Sulfuric Acid Today • Spring/Summer 2022

chemetics.equipment@worley.com | Business Development: +1 905 619 5200

PAGE 27

Feature

Developing a repair method for leaking acid towers By: Matthias Walschburger, Knight Material Technologies

During the sulfur conference in Berlin in November 2012, Knight Material Technologies (KMT) was approached

by Rick Davis, President of Davis & Associates Consulting. He wanted to know if KMT had a repair method for a leaking absorption tower that had an uncontrolled energy release (hydrogen explosion) earlier in 2012. The tower had started leaking only weeks after the startup of the plant. The owner, Noracid, wanted a temporary solution until the installation of a new bricklined tower could take place, which was planned several months down the road.

KMT met with the original equipment designers during the conference to gain some insight into the lining design. All absorption towers for this acid plant were designed without any type of acid-resistant membranes to protect the steel shell, such as Pecora Mastic, Rhepanol ORG, or PYROFLEX® acid-resistant sheet lining.

The original designers believed that only a layer of ceramic paper soaked in potassium silicate solution would suffice for this purpose.

Knight Materials was tasked with finding a solution to leaks in a Noracid-owned acid tower in 2012.

In further discussions following the meeting, it was disclosed that leakage of acid in one of the heat exchangers was caused by an uncontrolled energy release.

During the startup of the acid plant, the instruments in the control room never showed a decrease in pH value in the cooling water circuit of the heat exchanger, and therefore, the plant never would have shut off.

KMT explained to the OEM engineers the idea of injecting resin into the interstice between the brick and the steel PAGE 28

shell of the intermediate absorption tower that had suffered the damage. At the time, they were not convinced that an injection of resin could be the solution. They were concerned about the level of acid resistance of the resin in that harsh an environment and the uncertainty of how the interaction of the steel shell and brick lining with an intermediate layer of hardened resin would work. KMT’s take on the structural implication was that the injection material, once solidified, would create a combined structural system with the brick. As the injection would be executed under ambient temperature, the void between brick and steel would be the maximum and filled with resin, leaving very little or no space between the shell and brick. When heated up under operation, the thermal expansion would create an annular compression load on the brick and a radial load from the brick on the shell, closing any void. This would reduce the possibility of acid flowing in this interstice and causing damage to the shell.

To test the extent of the damage, Noracid performed several plate thickness measurements and detected a reduction in steel thickness in several areas of the steel shell. In the areas where they detected reduced thickness, they welded steel plates over the thinning shell to reduce the possibility of leakage and further structural instability. While the structural stability was less of a concern, the leaks continued, so this solution was viewed as a limited success. Noracid had just finished the construction of the acid plant the year prior and had already performed several repairs to the acid plant to get it running.

Now they were under pressure to prove to their shareholders that they could expect production and associated revenue as soon as possible. This meant that Noracid was in dire need of a permanent repair as soon as possible, and finding a solution had to start immediately.

KMT’s sulfuric acid specialist, Matthias Walschburger, had previously performed similar injections in Turkey, Colombia, and Mexico. He was confident that with the right resin design, KMT could fill the voids created by the acid flowing in the gap between the brick and steel, stopping the degradation of the steel shell.

Regarding potential tower repairs, such as welding a steel box to the outside of the shell and filling it up with potassium silicate and injecting Pecora Mastic through injection ports, both had shortcomings.

Trying to stop corrosion/degradation of the steel shell by filling a box weld to

Pecora Mastic injection

EPOXIGARD HC injection

the tower’s exterior with potassium silicate and hoping that gravity would make the potassium silicate flow into the gap created by corrosion would not work. The silicate would react with the acid, hardening immediately. The problem is the silicate can’t reach the inside of the tower. Instead, it creates a patch on the outside, and the acid begins flowing in that space, damaging the steel shell around the corroded hole even more.

Another alternative was to inject Pecora Mastic into the void. This needs to be done at a high temperature with solvents present to dilute the Pecora to achieve the required low viscosity to penetrate the narrow space between the steel shell and the brick. The inherent problem of this type of injection is that solvents and flexibilizers— VOCs—evaporate, leaving small evaporation channels inside the resin. This hasn’t solved the issue as the acid can flow back to the steel shell, continuing to deteriorate the steel. Therefore, this strategy will work only for a limited period. Furthermore, during wind and seismic activity, if the injected material starts cracking due to the loss of flexibilizers, as is common in Chile, those cracks can contribute to a quicker propagation of the acid attack to the shell.

KMT needed to find a type of resin for its injection system that would not result in the shortcomings of previous techniques—the acid hardening injection materials immediately or leaving evaporation channels when fully reacted and hardened. The ideal resin needed to stay fluid when coming into contact with acid, stay elastic, not leave evaporation channels after hardening, and also not crack under load. KMT would use the reaction of the epoxy resin turning red when contacting the acid as an indicator to control the progress of our injection when emanating from aeration holes and continue injecting resin until it emerged clear from this aeration hole. This means the void has been filled in its entirety. Due to the low viscosity, the resin will flow in every direction where it finds a path, and it is nearly impossible

to limit the expansion to a predetermined section of the tower. That is why we recommend injecting the whole vessel when using this repair method. The only issue uncovered was after injecting some towers, the resin that got into the tower’s interior and into contact with the freshly produced acid would change the color of the acid to a light pink. However, the coloring would not affect the quality of the acid produced and would disappear after several days of operation.

KMT started looking into possible resin formulations available on the market but was unable to find one that could fit our requirements of low viscosity, 100% solids with no VOCs, and sufficient acid resistance. After spending significant R&D time testing various formulations to address each of the issues the customer described, we commenced testing a series of resin mixtures we had already developed for high chemical resistant secondary containments. From there, we modified these to achieve the low viscosity required and developed a proprietary epoxy resin with low viscosity, high chemical and heat resistance, and zero VOC as injection material.

This resin would lose little, if any, of its components and would not retract or create new flow channels due to evaporation of VOCs, therefore creating a more durable chemical barrier.

The resin was injected into voids in the tower.

While developing the formulation, KMT also needed to create the technology to deliver this new formulation into the gap between the brick and steel without causing additional damage to the brick lining, as other methods have done in the past. Therefore, they developed a delivery Sulfuric Acid Today • Spring/Summer 2022

Sulfuric Acid Today • Spring/Summer 2022

The injection process starts at the bottom of the tower and works up.

drilling the injection ports. The injection process started from the bottom of the tower, working to the top. In ten days, we had filled the voids previously detected by the sounding, and the plant started up shortly thereafter. With great anticipation, the plant personnel waited to see how the resin would perform and for how long, as the tower had deteriorated so badly.

There will always be some areas the resin will not reach during the initial injection, but newly found hollow spots and/ or leaks can be easily repaired during a follow-up visit. Noracid asked KMT four months later to perform some minor touchup work at a few injection points, which we were able to complete in two days.

To date, we have not injected a tower under running conditions. We determined that it would be too dangerous for the operators to perform an injection as acid could come out at high pressure when drilling the ports into the shell, risking serious harm. Towers working under negative pressure (suction) may be injected. However, due to the associated safety risks, we will not perform this task. With safety being the highest priority, it is always recommended that the towers are idle during injection activities.

News of this new repair method traveled quickly around the acid-producing companies with acid plants in Chile, including Codelco Ventanas, who had contacted KMT the same year requesting an injection repair. The following year, Codelco Altonorte were among some of the customers asking for similar injections. Other markets noticed the excellent results and development work KMT had performed, and this technology expanded into the pulp and paper industry, the phosphoric acid market, and other mixed acid applications. We have performed this

work in multiple countries around the globe, including Chile, Mexico, Korea, the Philippines, Australia, Peru, Brazil, and the United States, to name a few.

Three years ago, we were asked by the Chilean paper mill CMPC to inject their two bleaching towers. This application required a different resin-based system: a Vinyl Ester for which KMT had been completing research and development work for implementation. We were asked to inject two bleaching towers, 7.3 m in diameter by 60 m in height. Due to the short turnaround time given, we set up an injection schedule using four injection pumps working in parallel. Due to the high volume to be injected, this job was divided into two separate injections executed over two planned turnarounds.

In conclusion, a theoretical short-term repair to get a client a few months of serviceability for a tower that experienced a significant event (uncontrolled energy release) has now been in operation for over eight years. In fact, the tower is still in operation, being monitored yearly, and shows no sign of deterioration that would warrant replacement.

During the 2019 sulfur conference in Houston, we met with Noracid plant manager Cristian Roempler and one of the owners. During this conversation, they confirmed KMT’s solution has been more than what they had expected in the beginning and has saved them the installation of a new tower. We sent a questionnaire to Noracid to gain additional insight into the performance of our injection solution. Here are our questions and Noracid’s replies: Had Noracid considered an alternative repair method before contacting Knight Material Technologies? Noracid replied: “We evaluated a partial exchange of the brick lining and the steel shell. We

welded several patches on the outside of the tower, which in this case was not a problem as the acid protection installed was a ceramic paper soaked in potassium silicate. These we tried to backfill with mastic.

“During the CRU sulfur conference in Berlin, we found out about this concept of doing a resin injection into the tower and got excited about this alternative. Further down the road, we implemented it during the upcoming main outage at the beginning of 2014.”

How has the injection repair held up?

Noracid replied: “In the beginning, we were not sure about the outcome as there was not much of an experience using the injection method, but under the alternative to replace the tower or giving it some additional months of service before deciding to exchange the tower, we went with this strategy.

“The injection was performed with no setback, and we were able to start up our plant.

“KMT always were following up on our requests and delivered a well-prepared service, which over time and with every injection cycle, became more effective in dealing with new leaking points.

“The tower is still in service after 8 years without any major inconveniences and we have done steel shell thickness measurements over this period and have not detected any loss in thickness so far.

“We never expected this repair to be a definitive solution to our problem, but it turned out to be a definitive repair in our case. We had expected this to be a short interim solution for us to build a new tower.

Over the years, KMT has become more efficient in implementing improvements to the technology, and we would like to recommend to them to find a more definitive solution to the final sealing of the injection holes.’’

Have there been any major earthquakes in the Mejillones area that may have affected the performance of the tower? Noracid replied: “There have been several earthquakes, but without major repercussions related to the tower operation. We have not had any major earthquakes so far and no adverse effects either.”

Seeing the success and the need for enforcing tower strength, KMT has been developing more sophisticated injection ports and final sealing methods to provide continuous improvement to the tower injection process and performance.

For more information, contact Matthias Walschburger at matthias. walschburger@knightmaterials.com. For information on KMT products and solutions, visit www.knightmaterials.com q PAGE 29

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system utilizing a static mixer and an appropriate injection nozzle system to push the resin into the voids inside the tower with high enough pressure to get the material flowing into the void. With the right combination, the formula would permeate into the fractures or cracks of the brick or mortar joints while avoiding a pressure peak that could damage or dislodge the brick lining.

The traditional way of pre-mixing a two-component resin product and injecting it via a pressure pot was a possibility but having to deal with a short resin gel time mixing and injecting could only be done in small batches. This would result in additional material loss during the injection process and extend the shutdown time unnecessarily. The challenge was finding a delivery system that included a twocomponent injection pump with enough throughput volume to shorten the shutdown time.

KMT started injecting its materials into the towers with great success while continuing to look for ways to improve the injection system. We realized that the mixing ratio utilizing an electric injection pump was inconsistent due to the breakage of actuating springs in the ball-valves, which needed improvement. While keeping in mind the need to adequately control the injection pressure to be less than 2 bar going into the tower, we started to investigate different injection equipment available on the market. We found a pneumatically driven injection pump that was able to control the injection pressure, deliver an adequate injection volume, and have the advantage of handling the resin to hardener ratios consistently.

KMT’s first approach to deliver resin into the void area of the towers used packers–a hollow threaded tube with a rubber hose mantle around a set of washers and screws at each end that, when tightened, compresses the rubber hose, forcing it to expand into the bore hole. During subsequent procedures, we concluded this solution was more effective for thicker steel shells. The packer could have an adequate thread count for a sufficient grip in the shell so it would not be ejected during the injection. However, with the thin steel shells where the acid plants were designed, we had to go to a solution with a threaded delivery port.

Noracid was keen to have the material injected into their tower quickly to meet their tight deadlines, so KMT airfreighted the new product to Chile before the end of 2013.

Noracid had already built the scaffold around the tower, looking for other ways to save time. Once on-site, KMT was ready to begin sounding the tower, marking the hollow regions behind the steel shell, and

Feature

Wet electrostatic precipitator technology By: Gary Siegel, Marketing Director, Beltran Technologies Inc.

Acid mist precipitators or Wet Electrostatic Precipitators (WESPs) are used in metallurgical acid plants to protect the catalyst beds. These plants are usually nonferrous smelters, processing copper, zinc, lead, nickel, molybdenum, zirconium, and gold ores. WESPs are also used in spent acid recovery sulfuric acid plants where reprocessed or “spent” acid is converted into SO2 feedstock for the formation of new sulfuric acid. Another application for WESPs is to protect the sulfuric acid plants used to reduce SO2 and SO3 emissions from heavy oil and coal-fired boilers where the fuel has high concentrations of sulfur.

WESPs efficiently collect sub-micron dusts and acid mists. These fine particulates usually contain heavy metals, such as, arsenic, lead, zinc, cadmium, and other metals depending on the content of the ores. The emission from these metallurgical processes can contain flotation oils used to separate the various constitutes in the ore, such as sulfides. These oils evaporate in the high temperature of the metallurgical process and condense into mists in the quenching section of the gas cleaning plant and are then collected by the WESP. WESPs are also used for tail gas cleaning where it is necessary to remove particulate, mists, and aerosols, as well as reduce visible emissions.

Advantages of WESPs

The advantages of using a WESP versus other types of gas cleaning equipment is that WESPs combine high efficiency collection of submicron particulate, mists, and aerosols with low pressure loss since the internal structure is open tubes, which are not easily plugged to restrict gas flow. Another advantage of WESPs is that they can remove dusts that are conductive or have high resistivity, which are problematic for dry ESPs. Since a lot of metallurgical dusts have high resistivity, the wet environment of the WESP coats the particulate with moisture, which makes the dust conductive and collected with high efficiency.

WESPs operate by charging and collecting the particulate, mists, and aerosols with a corona formed by the collector surfaces and sharp pointed discharge electrodes. High voltage power charges the WESPs, usually between 30 and 75 kilovolts, depending on the WESP design and the process gas conditions. The WESP is usually formed with a collector of tubes or plates with discharge electrodes held in the center of the collector structure by a high voltage frame, supported by non-conducting insulators. Since the process gases are saturated and contain electrically conductive mists and aerosols, the insulators have to be operated dry, being PAGE 30

At Hindustan Zinc in Udaipur, India, WESPs are arranged in two parallel trains, with each train comprised of two WESPs in series.

purged by dry, clean, and heated purge gases, usually ambient air. The WESP can be operated by the collection of liquid acid droplets, mists, and aerosols, flushing the collector plates, or by the operation of continuous fogging sprays into the collector section. WESPs usually have deluge or wash nozzles mounted to periodically wash the WESP of solids and collected particulate, which may not be removed by the draining acid/water collected by the WESP.

WESP design

The collection efficiency of WESPs is expressed in the DA equation and is an exponential function of the three parameters: 1) collector surface area (A); 2) gas flow rate (F); and 3) drift velocity (w). These are really two parameters, A/F, which is related to the size of the WESP box, and which is proportional to the electrical power applied to the process gases. Since the efficiency is proportional to the product of these two parameters, it is possible to design a WESP with either a large box and low power, or a smaller box and higher power, for the same efficiency. Since electrical power consumption of WESPs is usually low compared to other gas cleaning equipment, such as venturi scrubbers, bag filters, or other types of high pressure devices, and WESPs are constructed of expensive corrosion resistant materials, it is better to maximize w and minimize

Zambian copper smelters, operated by Mopani Copper Mines, have ten WESPs designed and engineered by Beltran Technologies for sulfuric gas cleaning.

A/F (the size of the WESP). The exponent in the DA equation can be substituted with the parameters voltage, tube- or plate-length, inter-electrode spacing, and gas velocity through the collector. Efficiency increases with greater field strength (operating voltage divided by inter-electrode spacing), collector length, and reduced process gas velocity.

The collection efficiency of WESPs varies with the size of the particulate, mist, or aerosol. Since gas phase reaction and evaporation/condensation form particles around 0.1 to 1.0 microns, considerable acid mist and particles form in this size range. As particles increase in size from the submicron range, they are more easily collected since field charging increases. Also, as particles decrease in size from the submicron range they are more easily collected, since diffusion charging increases. Therefore, the collection efficiency curve versus particle size forms a U-shaped with its minimum in the submicron range. The collection efficiency is also related to corona power of the WESP, with the minimum efficiency increasing with greater corona power. To minimize the size of the WESP and maximize the operating efficiency, the WESP should be designed to maximize w, the drift velocity, or the rate at which particulate, mists, and aerosols move to the collector plates.

WESPs can be designed with various collector shapes: flat plates, vertical round tubes, hexagonal tubes, or square tubes.

Historically, WESPs were built with round tubes and flat plates. The original acid mist WESPs were built with round tubes at the beginning of the last century. However, as the flow rate increased, the diameter of the tube became larger, which required higher operating voltages. Electrical power supplies at that time were limited in design and could not operate reliably at very high voltages, above 80 kilovolts. After that, WESPs were built with multiple smaller tubes or flat plates. Early WESPs were built from lead to resist the corrosion of sulfuric acid, so it was more economical to use larger diameter tubes and reduce their number, since lead construction was problematic due to lead’s low mechanical properties and high density.

More modern WESP designs, utilizing other corrosion resistant materials such as conductive graphite composites or chrome-nickelmolybdenum alloys, can be built in more efficient and economic configurations.

The round tube design has the disadvantage of wasting space in the vessel due to the nesting of the round tubes. So round tube WESPs require larger size vessels, otherwise gas will flow through at a greater velocity requiring longer tubes for comparable collection efficiencies. This then requires the WESP to be considerably taller and the tubes

longer for the same efficiency. This has a further disadvantage in that the high voltage discharge electrodes are longer and the electrodes have a greater likelihood of swinging or vibrating during operation. This causes sparking and the WESP to operate at lower field strengths and voltages, lowering operating power and efficiency. In addition, longer tubes are more difficult to clean, since the wash sprays have more difficulty penetrating the high L/D tubes. Dust builds up in the tube increasing sparking and reducing operating voltage, operating power, and collection efficiency.

There is a major economic disadvantage of designing WESPs with round tubes: the surface area on the outside of the round tube is wasted. Only the surface area of the inside of the tube is utilized for collection; therefore, the round design has to use twice the collector material to obtain the same collector surface as the flat, hexagonal, or square tube design.

The obvious feature of the round tube is the uniformity of the distance from the collector surface to the discharge electrode.

Early lead designs utilized lead wires, supported by a metal core. In that case, since a wire was the discharge electrode, the spacing between the collector and corona wire was constant around the circumference. However, wires are problematic since they break and short out the WESP, creating unreliable performance. Also, wires had to use lead weights at the bottom to keep the wires straight and aligned in the center of the tubes. This type of structure is susceptible to swinging, which causes poor WESP efficiency and unreliable operation. Most modern round tube WESPs use spiked discharge electrodes or solid pipe masts; however, this defeats the purpose of having a round tube design, since the spikes produce an asymmetric distance from the spike to the round wall, with the resulting asymmetric field strength and build-up of solids on the tube wall.

Thus, modern WESPs designed with advanced materials of construction use other shape collector tubes, such as the hexagonal and square tube. Flat plate electrostatic precipitators have operated efficiently since the early part of the last century. This design does not have uniform field strength since the field is greatest opposite the discharge electrode wire or spike and weakest at the area between the discharge electrodes. This difference is overcome by making the plate length slightly longer to compensate for the field asymmetry. Flat plate ESPs have operated at high efficiency for over 100 years.

The hexagonal tube design has the advantage that its shape is almost the same as a round tube (field strength symmetry) but it takes advantage of the fact that both sides Sulfuric Acid Today • Spring/Summer 2022

Sulfuric Acid Today • Spring/Summer 2022

Tubular electrostatic precipitator

increasing corona power. Multi-pointed star discharge electrodes are utilized to maximize corona power and WESP operating efficiency. Multi-pointed star discharge electrodes overcome the problems of current suppression of space charge effect, whereby the corona power is significantly reduced by the high concentration of submicron particles, mists, and aerosols present in the process gases. This reduces the corona power of the WESP operation and can lower the collection efficiency. The multi-pointed stars charge and repel some of the submicron particles, and then enable the next star to increase its corona power, repeating this phenomenon almost 100 times as the gases flow up the

tube. This type of electrode can produce considerable efficiency in single or multiple pass WESPs, usually utilized in acid plants.

WESPs can be utilized in various configurations, such as: single WESPs; two WESPs in series; two WESPs in parallel; and multi-WESPs in parallel and two in series. Smaller gas flows are usually treated with one WESP. This also depends upon the efficiency requirements; however, one WESP unit can produce reliable service at 99.5% efficiency for smaller flows. Typically plants have two WESPs in series so that one WESP can be washed while one operates.

Sometimes two WESPs are designed to be utilized in parallel, for similar purpose.

Two in series has the advantage of the first WESP overcoming the current suppression condition, while the second WESP operates at full power. This will depend on the gas flow rate, inlet and outlet process conditions, amount of particulate, mist and aerosol at inlet and outlet, etc. Larger plants will require more WESPs in parallel and usually two WESPs in series so one WESP can be taken offline for washing or maintenance, or washed online.

Materials of WESP construction

As mentioned previously, early WESPs were mostly built of lead. Modern WESPs

are built of metal alloys, thermoplastic materials, thermosetting materials, and conductive graphite composite materials. Metal alloys are expensive and have extended delivery time, but their biggest disadvantage is the unreliable performance with regard to corrosion. The sulfuric acid WESP operates in highly corrosive environments, including sulfuric, hydrochloric, and hydrofluoric acid and other impurities, as well as increased temperature. Because of the high cost of more robust chrome-nickel-molybdenum alloys, like C-276, C-22, and C-2000, designers are attempting to use less corrosion resistant alloys like AL6XN and SMO 254, with resulting corrosion problems in some applications and conditions.

The Beltran WESP manufactured with conductive graphite composite materials have the following advantages: • Highly corrosion resistant • Have good mechanical properties • Electricallyconductive • Homogenous • Do not require water/acid film to ground WESP • Fire retardant and thermally robust • Cost effective For more information, contact Beltran Technologies, Inc., at (718) 338-3311 or info@ beltrantechnologies.com;or visit the company website at www.beltrantechnologies.com. q

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of the hexagonal wall material are utilized for the collection surface. However, when hexagonal tubes are nested into a round, square, or rectangular housing vessel, because of the nesting shape of the hexagonal tubes, about 15% of the cross-sectional area is wasted.

This requires an increase in tube length to compensate for the increased velocity, for the same collection efficiency.

The most efficient design when considering collection efficiency, compactness, and economic design is the square tube collector configuration. The square tube collector completely utilizes the cross-section of a square or rectangular vessel, and can be effectively used in a round vessel, as well as the hexagonal. Due to the square tube’s high utilization of the vessel cross-section, it can be operated at a lower velocity so that the required tube length is lower, making it more efficient and easier to wash, since the wash sprays penetrate the collector. The high voltage frame is also more rigid, does not swing, and stays more accurately aligned, resulting in more efficient and reliable performance.

Because of the shorter tube length, lower stabilizing insulators are not required, and the insulators can be mounted on the clean gas side of WESP, reducing the requirement for heated purge air and resulting in more reliable WESP operation.

As previously mentioned, the WESP collection efficiency is increased with

Feature

Designing for reliability & efficiency in high temperature gas-to-gas heat exchangers By: Joan A. Bova, VP, Sales & Marketing, CG Thermal LLC and Keith Robinson, Lead Process Designer, AirBTU, Inc.

High-temperature gas-to-gas heat exchangers are commonly found in sulfuric acid plants functioning as interchangers or preheaters for the catalyst bed and as preheaters at the sulfur furnace. These recuperators see very high temperatures and high temperature differentials. Typically, at least one if not both gas streams are highly corrosive if allowed to condense.

It is imperative to thoroughly evaluate the intended application and design the recuperator with these operational demands to avoid common failure modes found in this operating environment. The issues need to be addressed during the design phase so that reliability and efficiency can be designed into the recuperator.

Common failure modes

If a standard shell-and-tube design is employed, several failure modes will most likely occur, including cold-end corrosion, cold-end fouling, stress failures, and unanticipated pressure drop.

With cold-end corrosion, the cold gas stream often enters the heat exchanger at a temperature below the dew point of the constituents contained in the hot gas stream.

This creates a potential for material surface temperatures below that dewpoint. These are commonly referred to as cold spots. If a gas stream is in contact with a cold spot, condensation will occur. The resulting acid will cause localized corrosion commonly referred to as cold-end corrosion.

tube bundle. This results in uneven forces exerted on the tubesheet by the tubes and ultimately failure of the tubesheet welds.

In the event of a pressure drop that is higher than anticipated, the operational flow rate will be less than anticipated as well.

All of these failure modes impede the performance of the recuperator and ultimately the performance of the entire plant.

Once in operation, the remedy or repair is very costly and time consuming. If not remedied, the operational life in between maintenance could be as short as several years.

The solution: designing with CFD and FEA analysis

A thorough analysis of the unit is essential to address cold spots, uneven stresses, and pressure drop before the unit is manufactured so that costly adjustments and repairs are avoided and overall operating life and productivity is maximized.

Computational fluid dynamics (CFD) and finite element analysis (FEA) are at the core of the thorough evaluation that is required to verify pressure drop, heat transfer rates, temperatures, and flow though the recuperator. Experience provides the starting point when determining tube pitches, and baffle and plenum arrangement. The design is adjusted based on initial analysis until they are proven by subsequent runs. This analysis is the difference between a 5-year operating life and a 20+ year operating life.

Simplified techniques

Identifying cold spots is one of the first steps in analysis.

In cold-end fouling, cold spots in an SO3 rich gas stream cause the SO3 to precipitate. The SO3 creates a tenacious bond with the metal tube wall. These deposits continue to build up and if the unit is not shut down for maintenance, the resulting blockage of the gas stream will lead to obvious capacity issues.

Stress failures occur when high-temperature gas-to-gas recuperators experience rapid and extreme temperature changes.

This results in rapid and significant material expansion and contraction. With standard shell-and-tube designs, the tubes will most likely expand at different rates due to uneven temperature distribution within the PAGE 32

Using this example, the inlet temperature is 100°F and exits out of the top at about 1100°F. On the tube side, the inlet temperature is 1475°F, is cooled and exits at around 495°F. Therefore, the area of interest is located at the tube-side outlet and shellside inlet.

The analysis of this area of interest involves a very complicated array of surfaces including the gas flow on the interior and exterior of the tube and a detailed model of the tube wall itself. Completing the anaylsis for every tube across the bundle is very time consuming and cumbersome.

To provide initial/budgetary sizing and arrangements, a simplified approach is needed for an initial screening. For initial screening, assumptions can be made for the gas flows based on a standard boundary layer and convective heat transfer coefficients. Assumptions can also be made to model the tubes as a single surface.

With this simplified model, an analysis of the “area of interest” can be completed relatively quickly to confirm the suspicion of cold spot potential in that region. The recuperator design can then be modified and reanalyzed. With the simplified model, it is practical to run several iterations to zero in on the most advantageous arrangement.

CFD and FEA programs have become more powerful throughout the years and are capable of analyzing very large models with a very fine mesh. They can analyze heat transfer models that are very sensitive and difficult to converge. However, this takes considerable computer time, which is not always possible when a rough budgetary price is needed for a project in the initial stages of design work.

There are techniques to simplify modeling that involve focusing on areas of most concern. Experience tells us that these are typically in low-temperature regions, since these are most frequently the location of failures.

Design example

Temperature profile of section of tubes near cold gas inlet provided by CFD modeling.

Magnified view showing fluid boundary layer and tube wall temperature

Several tubes closest to the cold air inlet were closely analyzed. The cold gas is entering at a temperature lower than dew point of the tube side stream. The outer rows of tubes are exposed to this temperature. The magnified view provides the temperature profile of the fluid boundary layer and tube wall to confirm the potential for a cold spot.

Based on the findings from the initial analysis, the tube pitch was modified to allow more uniform flow on the shell side and more uniformity across the tube sheet.

The air inlet was relocated further up the shell to coincide with warmer tube wall

Fig. 1 Baffle design.

temperatures. The baffle arrangement was adjusted to accommodate this unique inlet location.

The baffles will first guide the air in a co-current arrangement, running parallel to the hot gas. This is followed by a section of crossflow, with the remainder of the flow being directed in a counter flow to the hot gas in the tubes (See Fig. 1). The baffles are also evaluated to minimize pressure drop.

Addressing issues in the design phase is key to success

In conclusion, addressing potential for cold-end corrosion and fouling, minimizing uneven stresses, and evaluating pressure drop during the design phase is crucial to long-term cost savings and maximum operating life. This is best accomplished with experience aided by CFD and FEA analysis. With this attention to detail in the design phase, the result will be a recuperator with exceptional life, with a number of field installed units exceeding 20 years.

For more information, please contact Joan Bova at joanb@cgthermal.com or visit www.cgthermal.com. q Sulfuric Acid Today • Spring/Summer 2022

By; Lucas Camargo and Alexandre Bastida, Clark Solutions

One of the largest fertilizer producers in the world with several sites in Brazil was looking to improve plant reliability and uptime. After careful analysis they found that one of the most important contributors to plant downtime was the piping system. This specific site used cast iron piping in the strong acid system.

Frequent failures used to take place, due to corrosion, thermal expansion/contraction induced cracks, mold chaplets in the curves, and connection bodies, as well as flange leaks. In addition, the corrosion rate of cast iron in

ever increasing acid temperatures was increasing acid iron content and conferring it a turbid, “milky” color.

With new process requirements and the emergence of new construction materials, it is expected that industries from various sectors switch to materials with longer service life. Clark Solutions CSX™ is a special metal alloy that, given its superior corrosion resistance and parts fabrication specifications, offers a very low corrosion rate with greater reliability, uptime, and safety in strong acid systems, extending acid plants uptime and reducing maintenance costs.

The customer and Clark Solutions started a project aiming to improve the acid distribution lines. This project aimed to lower stock levels of fittings, as well as save time in scheduled maintenance, mainly considering reduction of weights, flanges, and simplification of arrangement of these new pipes.

The project

Clark Solutions was hired to perform a comprehensive system analysis, evaluation, and upgrade of the cast iron piping at the sulfuric acid plant.

The project consisted of reviewing and resizing acid lines, simplifying routing, and reducing flanged connections and overall maintenance requirements. The project was part of an integrated modernization project for the acid plant.

Sulfuric Acid Today • Spring/Summer 2022

The services provided for this project were: Field survey Routing analysis Resizing and rerouting Flow analysis 3D modelling Flexibility analysis Assembly interferences review Piping manufacture Cast iron piping disassembly CSX piping assembly The project tackled 6-10 major lines for the plant, including connection pipes between towers, tanks, and heat exchangers.

A key success driver is communication between companies. Plant access, drawing review, supply and manufacture, updated schedules, maintenance crew histogram, and other project aspects must be thoroughly discussed and aligned on a recurring basis.

The site historically used cast iron in this mill. Cast iron, however, offers neither high corrosion resistance nor high erosion resistance in sulfuric acid service. Pipe or fittings lifespan is therefore a function of wall thickness, and, consequently, thicker and heavier piping or equipment is necessary to counterbalance this disadvantage. In fact, pipe thickness in sulfuric acid industry is commonly twice as bulky as standard 150# class values found across other industrial.

Fittings tend to corrode more easily due to higher local velocities caused by fouling, especially as cast iron is not resistant to erosion. Because of lower erosion resistance, ductile cast iron pipes are designed for lower velocities, increasing diameter, weight, and thus material and installation costs.

A leaking spool or fitting is a condemned piece; it cannot be welded and cannot be reused. When an acid leakage occurs, maintenance time may be long, sometimes taking days, depending on the size and diameter of the failed pieces. A new adjustment spool will be needed, all gaskets will have to be re-tightened, and some replaced. Very heavy equipment handling also requires extra safety precautions.

As cast iron parts are unique, it is not feasible to cut small spools from a standard spool. The plant must have a large spare parts inventory. Sometimes, fittings are specially sized, or the pipe supplier is from abroad and there is a long shipping lag. Day-long stops mean plant cooling.

Moisture and condensation occur, and corrosion will take place. Re-heating may be necessary.

When shipping takes longer than the maintenance shutdown, some plants have to emergency-fit parts that differ in size from the originals, so that the plant can continue operating until the correct parts arrive. This often leads to a change in line flexibility. Size difference and altered thermal expansion for this temporary solution may cause the system to behave in ways that create more leakage points.

CSX™, on the other hand, forms a passive silicon oxide layer that increases corrosion resistance. CSX™ piping is also lighter and easier to assemble since it can be welded, reducing flanged connections up to 80% and reducing leakage risks.

Its higher corrosion resistance enables using thinner pipe walls, greatly reducing weight and assembly costs.

Lower corrosion means less iron in the product acid.

Clark Solutions-designed acid plants report less than 5 • • • • • • • • • •

ppm iron in product acid.

In acid plants, significant production losses and safety risks are associated with cast iron pipes. We estimate that for a 2,000 MTPD plant capacity, losses may accrue in the $1.5 million per year range, when one includes acid and energy production losses due to downtime, maintenance costs, re-heating costs, safety risk, etc.

Case example comparison

Within the options for replacement product lines, one was remarkably identifiable for its position. A before and after comparison was made to showcase this line as a notable example. This example had few interferences and was a DN24” line with 6 curves.

Fig.1: Cast iron line example.

Fig. 2: CSX™ High Silicon line example.

The following table compares the main differences: Parameter

Cast iron line

CSX™ High Silicon line

Flange quantity

34

8

Bolts quantity

680

100

Nuts and washers 2x 1.360 quantity

2x 200

Weight (kg)

7.780

2.620

Thickness (mm)

22

6

Replacement time (days)

6

3

Table 1: Comparison for example line replacement.

Only 4 field welds were performed, and total assembly time was 3 days.

Continued on page 34

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Feature

Clark Solutions CSX piping increases reliability, uptime, and safety

Feature

Continued from page 33

The discussed example was easy, but several lines may bring some difficulties related to interferences, and 3D models are used to solve assembly issues. Some flanges are still necessary for either assembly or transport constraints.

The 3D modeling also serves as a basis for isometric drawings and flexibility calculations, expediting project time. This example produced 7 drawings, including manufacturing detail drawing, using fewer than 100 hours.

Overall results

As a planned maintenance stop, and as a new development for this specific site, the project had a much longer timeframe than conventional. With a lead time of 6 months, from field measurements, 3D modeling, analysis, drawings approval, manufacturing, testing, and delivery for total of 6-10 major lines.

Some positive points were: • 3 to 4 times lighter lines • Ease of assembly and disassembly • Ease of maintenance • Drastic inventory reduction for emergency or scheduled maintenance

Fig. 3: New CSX™ High Silicon line 3D model.

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• • •

Longer lifetime Possibility of reducing line diameters using same pumps Alternatively, possibility of increasing flow rates using same pumps Parameter

Cast iron line

CSX™ High Silicon line

Weight

Higher

Lower

Downtime

Higher

Lower

Complexity

Higher

Lower

Maintenance costs

Higher

Lower

Acid product quality

Lower

Higher

Spare parts inventory

Larger

Smaller

Table 2: Overall project advantages.

Conclusion

Acid leakage is a relevant concern in the sulfuric acid industry, in terms of both personnel safety and the economics related to increased maintenance. High silicon alloy stainless steel piping systems such as CSX are becoming more popular since their proven maintenance and safety advantages shows a cost-benefit for long term operation.

High corrosion resistance, thinner wall thickness and weldability are benefits that allow higher acid flow rate, smaller diameter, lower weight, quicker maintenance, fewer flanges, and fewer leakage points, all of which increase plant reliability and facilitate operation. q

AIChE resumes technology conference in Florida CLEARWATER, Fla. – The AIChE Central Florida Section will resume its annual conference after a two-year hiatus due to COVID-19.

Colleagues from all over the world gather at Clearwater Beach to share ideas concerning chemical process technology, specifically the production of phosphoric acid, phosphate fertilizers, and sulfuric acid. The Sheraton Sand Key Resort in Clearwater will once again be the site for this anticipated event, scheduled for June 10-11, 2022.

This year’s event will include workshops and presentations on a variety of topics affecting the industry. Participants can earn Professional Development Hours for attending.

As always, the convention also provides a relaxing getaway with friends and family, good food, and a lot of fun. Social and networking events are planned during the event, with a little something for everyone.

For more information, please visit www. aiche-cf.org. q

Sulfuric Acid Today • Spring/Summer 2022

A NEW DAY FOR KNIGHT You’ve known us for over 100 years.

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ACID-RESISANT CONSTRUCTION TOWER INTERNALS HEAT TRANSFER MEDIA MASS TRANSFER PACKING ENGINEERING SERVICES INSTALLATION SYSTEMS

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