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Sulphur's growing Gulf

Summary

British Sulphur Events' 2nd Sulphur Middle East Conference in Bahrain brought together the big stories behind the region's continued fast-paced development as an exporter of sulphur, and ­examined the leading demand stories of the coming years. Chris Cunningham reports.

Abstract

Middle Eastern sulphur supply had been at the centre of worldwide debate during 2005 to determine when an expected surge in supply would emerge and whether prices could continue their steady move­ment upwards. Most of the answers, in the immediate and longer term, lay within the Gulf region. So it was with especially appropriate timing that British Sul­phur should bring to the second in its series of Sulphur Middle East conferences in May a panel of speakers equipped with the detailed information that underlies those answers.

The timing of the conference, held in Bahrain’s Regency Inter-Con­tinental Hotel, was also appropriate in terms of the development of the energy industries which generate the yellow by-product. Higher levels of production of Middle Eastern sulphur may in future be attributed as much to higher levels of energy processing – to provide low-sulphur pro­ducts for the world’s markets – as they will be to basic processing of new oil and gas finds.

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Five years of brimstone trade

Summary

The International Fertilizer Industry Association has published its forecast for the supply-demand balance from 2005-2009 covering products and raw materials. Here Sulphur reviews some of the issues raised and predictions made surrounding the global supply of brimstone over the next five years.

Abstract

The Sulphur 2005 conference issue of Sulphur will feature a comprehensive account of international trade in sulphur and sulphur­ic acid during 2004. Meanwhile the Inter­national Fertilizer Industry Asso­­cia­tion’s (IFA) production and inter- national trade committee has published its estimates for last year’s trade in brimstone and forecasts for the next five years of supply and demand.

Buoyant demand from primary customers maintained a strong market for sulphur worldwide during 2004, with year-on-year growth in deliveries rising by 7 per cent to a global total of 46.4 million tonnes, according to IFA’s production and international trade committee. This healthy picture was skewed considerably by rapidly increasing demand from China where imports grew by 35 per cent. Actual global production from gas processing, oil refining and Frasch mining was 46.0 million tonnes during the year.

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Using methanol in a sulphur plant

Summary

This article explores the use of meth­anol as a source of hydrogen in the Claus converter train and for reducing tail gas units. Use of methanol to increase the H2S/SO2 ratio either in the Claus furnace or in the first converter are also discussed by Peter D. Clark and colleagues.

Abstract

Availability of hydrogen in a Claus process gas stream is an important factor in sulphur recovery systems that have tail gas units which operate by reduction of sulphur values (SO2, sulphur vapour) to H2S, which is then recycled to the reaction furnace. In some plants, particularly those operating with a high H2S content in the acid gas, a considerable portion or all of the required hydrogen is produced in the reaction furnace either by dissociation or partial oxidation of H2S.

2 H2S -> 2 H2 + S2
2 H2S + 1/2 O2 ->  H2 + H2O + S2

In other cases, the amount of hydrogen reaching the reducing tail gas unit is insufficient to support complete conversion of all sulphur compounds to H2S and supplemental H2 must be supplied by either using a clean hy­dro­gen stream or manufacturing a CO/H2 mixture in a reducing gas generator. In the latter instances, me­th­­ane or very clean fuel gas is partly oxidised to H2 and CO in a burner system under defined fuel/O2 ratios. Careful operation of these systems and addition of steam to the fuel gas feed may be required to prevent solid carbon formation in the burner. Solid carbon formation must be avoided, as it will end up clogging the top layer of catalyst in the reducing tail gas unit impairing its efficiency. The chemistry of reducing gas generator combustion units is very complex, but the major reactions yield the needed H2 together with byproduct CO, CO2 and H2O. The combustion processes produce some or all of the heat ener­gy required for reheat of the process gas. Some of the basic combustion processes are:

  • CH4 + 2 O2 -> CO2 + 2 H2O + heat
  • CH4 + 3/2 O2 -> CO2 + H2O + H2 + heat
  • CH4 + O2 -> CO + H2O + H2 + heat
  • CH4 + 1/2 O2 -> CO + H2
  • CH4 + H2O -> CO + 3 H2

Efficient mixing of fuel and air in a reducing gas generator is very important as localised hot spots cause decomposition of the CH4 to solid carbon and H2: CH4 -> C + 2 H2

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Burning issues for SRUs

Summary

Choosing efficient combustion equipment for the SRU is critical for maximum sulphur recovery rates, reliable trouble-free operation, flexibility, production of bright yellow sulphur and longer catalyst life. Lisa Connock reports.

Abstract

Combustion equipment is requir­ed in multiple locations in sulphur recovery units (SRUs). Typical applications of burners include the main burner for the reaction furnace, the incinerator burner, and in-line burners to reheat gases to the catalytic reactors and the tail gas treating reactor. As sulphur plants have become more sophisticated and air emission regulations more stringent, good burner design has become increasingly important.

The modified Claus process takes place in two steps:

  • Thermal step: one-third of the total H2S in the acid gas is oxidised to SO2 in the thermal reactor. H2S + 3/2O2 ® SO2 + H2O
  • Catalytic step: the SO2 formed in the thermal step reacts with the remaining H2S to form elemental sulphur and water in the catalytic stages.
    2H2S + SO2 -> 3/2S2 + 2H2O

All contaminants, such as ammonia, hydrocarbons and mercaptans in the feed gas should be destructed in the main reaction furnace to prevent problems downstream.

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Assuring acid quality

Summary

High quality sulphuric acid commands better prices on the market. Klaus Hasselwander of Outokumpu Technology discusses current technologies for assuring the quality of sulphuric acid from both sulphur burning and metallurgical sulphuric acid plants and Dr Hanno Hintze of Norddeutsche Affinerie reports on the improvements to acid quality at NA's smelting facilities in Hamburg.

Abstract

The quality of sulphuric acid has become of greater importance to many acid manufacturers who are influenced by the need to maintain acceptable acid prices. This applies to acid produced from burning sulphur (premium acid), and especially to sulphuric acid produced from SO2 gas in non-ferrous smelt­ers, as these gases often contain many contaminants, dust and fumes that need to be removed to avoid contamination of the product acid.

Typical requirements for sulphuric acid are listed below:

Appearance: water clear
Colour: 40 Hazen
Mercury (Hg): <0.5 ppm
Iron (Fe): <25 ppm
Nickel (Ni): <1 ppm
Chromium (Cr): <1.5 ppm
Manganese (Mn): <0.3 ppm
Sulphur dioxide (SO2): <30 ppm
Chloride (Cl-): <2ppm
Fluoride (F-): <5 ppm
Ammonium (NH4+): <1 ppm
Nitrate (NO3-): <5 ppm
Arsenic (As): <0.2 ppm
Copper (Cu): <0.2 ppm
Cadmium (Cd): <0.02 ppm
Lead (Pb): <0.3 ppm
Zinc (Zn): <0.1 ppm
Antimony (Sb): <0.02 ppm
Bismuth (Bi): <0.02 ppm
Selenium (Se): <0.1 ppm

 

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