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Publication > Issue > Articles

Integrated heat exchangers for reduced SO2 emissions

Summary

In this article Karl H. Daum, Senior Process Engineer at Lurgi Metallurgie GmbH, reviews the heart of the sulphuric acid plant, namely the converter, and presents design concepts on the topic of integrated heat exchangers. He also presents a historical overview and offers a survey of the current state of the art.

Abstract

Sulphuric acid plants are frequently subject to public scrutiny with regard to their sulphur dioxide (SO2) emissions. Stricter emission regulations have been introduced progressively during the last decades, both in terms of actual emissions and ground level concentrations. It is a demanding task for plant operators to ensure that emissions are kept within limits, even during upset situations or start-up and shutdown transitions. Although the process of SO2 oxidation in multiple stage converter vessels has not principally changed during the last century, significant progress has been made in terms of reliability and performance of plant equipment.

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Biodesulphurisation: a serious contender for H2S removal

Summary

The Thiopaq process, which has been used to sweeten biogas since 1993, has now been further developed to remove H2S from high-pressure natural gas, synthesis gas and refinery gas streams. The new Shell-Paques/Thiopaq process can offer a safe and cost effective alternative to liquid redox processes and amine/Claus installations with sulphur loads of up to 45 t/d.

Abstract

The ThiopaqTM family of biotechnological processes removes and converts hydrogen sulphide (H2S) or sulphur oxides (SOx) from gas streams, aqueous streams or light hydrocarbons. The process operates at near ambient conditions using safe, naturally occurring, living micro-organisms as catalysts.

Sulphur compounds must be dissolved in an aqueous medium. When gas streams are treated, the gas is scrubbed with an aqueous sodium bicarbonate solution, which is regenerated in the Thiopaq bioreactor and recycled to the scrubber. In the regeneration process elemental sulphur is produced. When refinery spent caustic is treated with Thiopaq, sulphide can be converted to either sulphur or sulphate. Although the treated caustic is not regenerated, it is safe for disposal and light mercaptans are also converted.

The new Shell-Paques/Thiopaq process for H2S removal of gaseous streams offers:

  • Replacement for amine treating, Claus recovery and tail gas treatment or liquid redox processes.
  • Minimal chemical consumption.
  • Gas treatment as well as sulphur recovery.
  • 99.99% H2S removal for gas streams.
  • 100% conversion of sulphide in the bioreactor with 95-98% selectivity to S0.
  • No deactivation
  • Applies to H2S concentrations of 100 ppmv to 100 vol-% and pressures from 1-75 barg. Therefore, direct treatment and amine off-gas treatment are both possible.
  • High turndown ratio.

 

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Putting Claus catalysts to the test

Summary

In this article W.S Kijlstra of Shell Global Solutions and P.D Clark, N.I. Dowling and M. Huang of Alberta Sulphur Research Ltd present a new catalyst testing procedure that has been developed for the evaluation of Claus catalysts. The new testing procedure marks a significant improvement over previously published techniques as now linear, steady-state CS2 conversions are observed, allowing all commercial alumina catalysts to be compared on the same basis.

Abstract

In the past, a wide variety of pre-ageing techniques have been applied prior to testing catalysts to bring them to a state of mid- to end-of-life activity. Such procedures have lead to a variety of activity curves for carbon disulphide (CS2) conversion which are difficult, if not impossible, to compare. In this study, we have developed an ageing and experimental procedure, which gives a steady state CS2 conversion from the onset of the experiment. The procedures are based on a fundamental understanding of the mode of action of Claus catalysts, particularly with respect to the formation of sulphate on alumina catalysts.

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Elf refines its role

Summary

Elf Aquitaine boasted almost half a century as a producer and marketer of sulphur recovered from natural gas.With the formation of TotalFinaElf, the largest European-owned oil refining business, Elf has changed its identity and expanded its role as leading marketers of sulphur to embrace the output from the group's refineries and the prospect of a wider international stage for its operations.

Abstract

Much of the logic behind the consolidation of the world’s energy majors in recent years centres on an opportunity to increase efficiency in the oil refining and ­marketing sector. That is no less the case in Europe where the amalgamation of French majors Total and Fina, later joined by the Elf group, has delivered the region’s largest oil refining business.

Elf’s membership of TotalFinaElf is also making its mark on the sulphur market in North West Europe and beyond as a result of its unique position in the group as a major processor of sour gas. With production of 550,000 tonnes of sulphur from its gas processing operations in 2000, Elf Aquitaine maintained its role as a leading producer after 44 years of operations. But Elf Aqui­taine’s role in the new group is delivering a series of changes: through a product portfolio increasingly aligned to oil refining; through developing interests in worldwide sources of sulphur; and through a change in identity. Elf Aquitaine has become TotalFinaElf Sulphur Divis­ion, the primary source of expertise in sulphur marketing within a global energy group.

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Burning questions at Europe's biggest acid plant

Summary

Spain's leading fertilizer manufacturer became the European industry's most significant purchaser of brimstone when it replaced pyrites roasting with the continent's largest sulphur burner. Sulphur visited the riverside plant close to Spain's Atlantic coast.

Abstract

At the beginning of 2001 Spain’s leading fertilizer manufacturer, Fertiberia, took official delivery from Lurgi of Europe’s largest operational sulphur-burning plant. The significance of the 2,400 t/d acid plant for Fertiberia is a wholesale move from pyrites roasting to contemporary technology for the production of sulphuric acid for phosphoric acid manufacture. Apart from the gains in operating efficiency and flexibility expected from the new plant, the move also means a shift in Fertiberia’s position as an acid producer from being a purchaser of local supplies of raw materials to becoming the primary European outlet for international trade in brimstone.

To put the development in a wider context, the emergence of Fertiberia on the scene as a major consumer of traded sulphur helps significantly to redress significant losses to the market resulting from the closure of major phosphate fertilizer production in the Benelux region during 1999.

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Waterloo route to sulphuric acid

Summary

The University of Waterloo, Ontario, Canada has developed a novel catalyst and solvation process for the oxidation of sulphur dioxide and the subsequent recovery of sulphuric acid and other industrial products.

Abstract

Activated carbon is a remarkable catalyst for the oxidation of sulphur dioxide to sulphur trioxide, a reaction that is the basis for all sulphuric acid manufacturing processes. Certain carbons exhibit hourly production rates for SO3 at 25°C that approach 3 grams of SO3 (as H2SO4) per gram of catalyst. This rate appears to be several hundred times greater than the production rate over conventional vanadia catalysts operating between 300 and 400°C. Furthermore, at 25°C the oxidation goes to completion. By contrast, in the conventional process, single pass conversions are limited to approximately 95% and tail gas processing is necessary.

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