Sulphuric acid double absorption process

In case of sulphuric acid plants, the earlier single-conversion single-absorption process was replaced by the double-conversion double-absorption process for most of the new plants. The SO2 % in gases at converter inlet was increased from 7.5-8.0 % to 11.0-11.5 % which could reduce the volume of gases to be handled for the same production rate. The power required by the air blower got reduced as a result. 

Figure 7.8 Sulphur-burning double absorption sulphuric acid process...

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. 

Second lau analysis is applied to a 100 tonnes per day double-contact double-absorption (DC-DA) sulphuric acid plant in order to bring out true energy conversion efficiencies and consumptions based on uork availability of various streams. Second lau efficiencies are compared uith those of first lau to pinpoint true losses and inevitable consumptions in energy conversion processes. 

The Zincor process is based on the roast-leach-electrowinning process. The zinc sulphide concentrate is roasted in four Lurgi fiuo-solids roasters to produce zinc oxide and sulphur dioxide gas. The SO2 gas is fed to two Monsanto double absorption acid plants. 

Process engineers are thus seen to have been able to provide practical solutions to the problems of reducing atmospheric emissions in sulphuric acid plants. They have also achieved a further halving of both wastage and pollution by designing plants that operate at pressure. Increased pressure favours increased conversion because there is a volume contraction on reaction. In France a double absorption plant has been operated at 4 bar for over ten years. 

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