Desulphurisation processes

The H2S formed in the hydro-desulphurisation process can be removed from the product stream in a variety of ways. Commonly used methods are chemical reaction with, for example, zinc oxide or iron oxide, caustic scrubbing and absorption processes. For the H2S decomposition processes treated in this chapter, only the absorption/desorption methods are of importance. Most used are absorber/stripper combination units with an alkanolamine as absorbing compound [2],... 

The solubility of PbS (Ks = 10 ) is much lower than that of PbC03 (Ks = or of Pb(OH)2 (Ks = 10" ). The conversion to PbS is practically 100 %, compared to the lower conversions obtained during the conventional desulphurisation process for example, 90 % conversion for the process with Na2C03 and 95 % for the one with NaOH. 

Alvarez-Ayuso E, Querol X, Tomas A. Environmental impact of a coal combustion-desulphurisation plant Abatement capacity of desulphurisation process and environmental characterisation of combustion by-products. Chemosphere 2006, 65, 2009-2017. 

BAT is to apply exhaust air desulphurisation processes based on catalytic oxidation with H2SO4 production (see Section 12.7.4)... 

Company history heavily sugar oriented. Decanters sold strongly into the chemicals sector, and for waste treatment, especially in flue-gas desulphurisation processes... 

Rosenburg, H.S. (1986) Byproduct gypsum from flue gas desulphurisation processes , Industrial and Engineering Chemistry Product Research and Development, 25(2), 348-355. 

Sulphuric acid is the largest volume chemical in the world with an annual production of about 180 mill, t/year which is used primarily for phosphate fertilizers, petroleum alkylation, copper ore leaching and in smaller quantities for a number of other purposes (pulp and paper, other acids, aluminium, titanium dioxide, plastics, synthetic fibres, dyestuffs, sulphonation etc.). The major sulphur sources for sulphuric acid production are sulphur recovered from hydrocarbon processing in the refineries and from desulphurisation of natural gas, SO2 from metallurgical smelter operations, spent alkylation acid, and to a minor extent mined elemental sulphur and pyrites. A simplified flow sheet of a modem double-absorption plant for sulphuric acid production from sulphur is shown in Fig. 1. 

Desulphurisation of hydrocarbon fuels has traditionally been carried out primarily as part of the refining and upgrading process. Accordingly by far the most advanced and best understood chemistry and technology is to be found in this area. Prior to the advent of major concern for environmental impact of fossil fuel combustion products relatively little was done to desulphurise hydrocarbon fuels (principally coal) prior to combustion and past effects of large scale consumption of high sulphur coals can still be seen in major industrialised areas around the world. 

The first major attempt at precombustion desulphurisation was in the coal gas industry and a number of efficient and effective techniques for removal of H2S, COS, CS2, mercaptans and other volatile sulphur containing products of the gasification process were developed. Many of these techniques found application in the subsequent development of sour natural gas processing where large volumes of hydrogen sulphide had to be removed from the hydrocarbon component. 

As costs of precombustion hydrodesulphurisation and post combustion flue gas clean-up have escalated and as environmental regulations have further limited the sulphur dioxide emission rates, there has been a growing interest in technology designed to effect fuel desulphurisation during the combustion process. Desulphurisation during fluidised bed combustion of coal has been a leading technique in these developments. 

Desulphurisation of hydrocarbon fuels prior to combustion has been seen to be primarily achieved by reducing the inherent sulphur values to hydrogen sulphide. In post combustion desulphurisation the sulphur values are almost exclusively in the oxidised SO2 form. While this is hardly surprising in view of the oxidative nature of the fuel combustion process, it does mean that essentially different chemistry is involved and the nature of the oxidant - air - introduces large volumes of inert diluent -nitrogen. 

Perhaps the most difficult task in reviewing and comparing themiltitude of processes that have been, and are being proposed for desulphurisation of effluent gas streams is that of finding a suitable framework upon which to organize the data. Without such a structure, the very volume of information is simply unmanageable. 

The Wellman-Lord Process is not, in itself, a conversion method, but rather a solution phase technique for concentrating a dilute SO2 effluent stream to provide a suitably rich feed for Claus redox conversion. When coupled with the Claus Process, it constitutes an overall desulphurisation system which involves all three phases gas, liquid solution, and solid crystalline. 

In a surprisingly large number of industrially important processes reactions are involved that require the simultaneous contacting of a gas, a liquid and solid particles 28 . Very often the solid is a catalyst and it is on the surface of the solid that the chemical reaction occurs. The need for three-phase contacting can be appreciated by considering, as an example, the hydro-desulphurisation of a residual petroleum fraction, i.e. of the liquid taken from the base of a crude oil distillation column. 

C—S bonds, a process which is exploited in the desulphurisation of organic sulphur-containing compounds. 

It may be necessary to improve membrane selectivities, so that further purification of the produced hydrogen before re-use in the desulphurisation units can be limited as far as possible. Moreover the membrane reactor can be optimised for various variables, such as H2S conversion, hydrogen recovery, membrane area and temperature. In a techno-economic evaluation combined with advanced process design the impact of different operating parameters on the investment and operating costs should be studied. 

Browne s Process,3 which is made use of by the Canadian Copper Company, consists in desulphurising copper-nickel-iron matte, whereby a product, containing 54 per cent, of copper and 43 per cent, of nickel, together ivith small quantities of iron and sulphur, results. Half of this is cast into anodes and the remainder is treated with chlorine in brine, whereby the metals are obtained in solution as chlorides. On electrolysing, copper is deposited on to cathodes of the sa,me metal until the proportion of copper to nickel is reduced to 1 in 80. Addition... 

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