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Sulphur recovery from smelter off gases

Summary

The clock is ticking for the many plants around the world that are still allowed to emit large quantities of SO2 because of their remote locations and the high cost of mitigation. As governments become more environmentally responsible, the industry is seeking an economical solution to control these SO2 emissions. Lisa Connock reports on the new generation of technologies being proposed to tackle the problem.

Abstract

When smelting sulphide ores, the sulphides are converted into oxides according to the following summary reaction:

MeS + 3/2 O2 ® MeO + SO2 [1]

Approximately one kilogram of sulphur dioxide is generated per kilogram of metal when iron, copper, nickel or zinc sulphides are roasted or smelted. Depending on whether air or enriched air is used, the concentration of SO2 in the smelter off gas is in the range of 8-30 vol-%. Clearly, if the sulphur dioxide is not removed from the smelter off gas, the environmental impact would be sizable with impacts in the form of acid rain over a wide area with its associated environmental and health concerns.

The conversion of SO2 off-gases to sulphuric acid for sale in the marketplace is the usual route to address the issue as the overall process generates excess heat energy and is a well-proven and reliable technology.

However, sulphuric acid production is not viable when the smelters are located in remote areas because costly acid storage and distribution are needed. In these cases, a viable alternative may be the reduction of SO2 to solid elemental sulphur. Elemental sulphur is easier to transport and distribute, it can be stored in exhausted mine sites or in dedicated storage facilities at relatively low cost and, when the market for sulphur is buoyant, it can be sold on the international market..

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Prospects for demand

Summary

The International Fertilizer Industry Association (IFA) has released its latest review and outlook for the phosphate fertilizers industry. Sulphur reports on current and future prospects among the world's biggest consumers of sulphuric acid.

Abstract

The next issue of Sulphur (the Sep­tember-October 2006 issue) will feature British Sulphur Consultants’ reg­u­lar appraisal of sulphur and sulphuric acid trade statistics. Whilst project development, partic­ularly in the base metals industries, is changing the shape and emphasis of global distribution of sulphur, the phosphate fertilizers industry continues to form the bedrock of demand for the element.

IFA’s Annual Conference in Cape Town, South Africa, in June provided sulphur producers and suppliers with an appraisal of their biggest customer’s performance in the past year. IFA’s appraisal of the phosphate fertilizer producers’ plans for expansion up to 2010 also gave the sulphur industry an insight into how much scheduled additional production of sulphur could be soaked up by new fertilizer plant – and whether the phosphates producers were heading for future surplus.

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Sulphur recovery in the LNG industry

Summary

Disulphide oils are by-products of mercaptans removal from propane, butane and pentane in LNG production complexes. Although the sulphur contained in mercaptans and disulphide oils is a small fraction of the total sulphur to be removed from natural gas, in many countries, it is necessary to recover a large part of the sulphur contained in these impurities to satisfy regulations. Lisa Connock reports.

Abstract

The goal of propane, butane and pentane treatment in a gas field is the extraction of hydrogen sulphide (H2S), carbon dioxide (CO2) and mercaptans (RSH) from the hydrocarbons streams, in order to meet the sulphur specifications of the final product to be sold.

The technology used for RSH removal may vary; one process route is to absorb RSH with a suitable solid bed absorbent, regenerate the absorbent and send the concentrated RSH released to the sulphur recovery unit.

Another process route utilises caustic soda wash in continuous mode for the removal of sulphur compounds. In order to improve the economics of the process, caustic soda is regenerated by direct oxidation of mercaptans to disulphide oil (DSO or RSSR) with air in the presence of catalyst.

The major chemical reactions involved in this process can be summarised as follows:

  • Extraction of H2S with caustic soda:
    H2S + 2 NaOH -> Na2S + H2O
  • Oxidation of sodium sulphide (Na2S) with oxygen:
    2 Na2S + 2 O2 + H2O -> Na2S2O3 + 2 NaOH
  • Extraction of mercaptans (RSH) with caustic soda:
    RSH + NaOH -> NaRS + H2O
  • Oxidation of sodium mercaptide (NaRS) with oxygen:
    NaRS + 1/2 O2 + H2O + NaOH -> RSSR + 2 NaOH

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Gulf energy exports drive up sulphur production

Summary

A shortage of world refining capacity and vast reserves of gas isolated from major markets have inspired unprecedented investment in new plant in the Middle East to deliver oil and gas products to international customers. After Qatar Gas last year, it was the turn of Saudi and Kuwaiti oil processors to announce major developments affecting sulphur production.

Abstract

Little more than a year ago the sulphur market was abuzz with news of vast quantities of product that would emerge in the following decade from Qatar’s plans to become the leading exporter of liquefied natural gas (LNG). The source of this sulphur – all of it premium, formed product – was to be the huge North Field gas reserves, offshore Qatar. Qatar Gas had no plans to reinject acid gas recovered at its LNG plants; in fact the company had detailed and sophisticated plans for a coordinated sulphur recovery, handling and exporting operation.

With the prospect of North Field’s Iran counterpart, South Pars, adding millions more tonnes to the region’s supply, albeit more slowly, by 2014 there would be a huge over-supply was the call from some quarters of the sulphur industry.

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