GB1349196A - Flue gas desulphurization process - Google Patents

Abstract

1349196 Desulphurization of flue gas ESSO RESEARCH & ENG CO 1 June 1971 [1 June 1970] 18237/71 Heading C1A In a process for desulphurizing an SO 2 and O 2 containing flue gas in which a small amount of S<SP>VI</SP> is formed in the course of absorbing SO 2 in an aqueous absorbent containing NH 3 and/ or NH 4 <SP>+</SP> and in which at least a part of the absorber effluent (containing S<SP>IV</SP> and S<SP>VI</SP>) is acidified with NH 4 HSO 4 to form SO 2 and an aqueous mixture of (NH 4 )SO 4 and (NH 4 )HSO 4 , the major portion of the (NH 4 ) 2 SO 4 content of said mixture is decomposed to form (NH 4 )HSO 4 and NH 3 and a major portion of the (NH 4 )HSO 4 thus produced is returned to the acidifier where it is used for acidification of the absorber effluent, a minor portion being returned to the furnace, in which the flue gas is produced, where it is decomposed into a gaseous mixture of N 2 , SO 2 and water thereby reducing the S<SP>VI</SP> content of the system. It is preferred that the amount of bisulphate returned to the furnace is equivalent to the sum of the amount of S<SP>VI</SP> formed and the amount of SO 3 present in the flue gas, that the absorbent contains ammonium sulphite as solute. Liberated SO 2 may be converted into useful products such as S or H 2 SO 4 and ammonia liberated in the decomposition stage may be reacted with a second portion of the absorber effluent which is not acidified, to produce fresh absorbent. In the drawing the flue gas leaving furnace 10 is cooled by exchange with combustion air in heat exchanger 12 before passing up absorber tower 20 against a stream of aqueous ammoniacal absorbent solution. Desulphurized gas containing <10% of the original SO 2 content is vented at 23. The absorbent passes to holding tank 25 and from there a portion is passed to acidifier 30 where it is treated with ammonium bisulphate via 31. The slurry produced on acidification and after liberation of SO 2 via 32 is passed into a stream of hot gas 34 and decomposer 35 where water is evaporated and the ammonium sulphate content of the slurry is decomposed to yield gaseous ammonia and ammonium bisulphate. The ammonium bisulphate is returned in major proportion to acidifier 30 via line 31, the minor proportion being returned via line 50 to furnace 14, either in molten state or as a particulate solid, where it is decomposed to produce SO 2 , N 2 and H 2 O. Ammonia leaving decomposer 35 is returned to ammoniator 40 where it is contacted with absorber effluent taken from line 28 and diluted with water in liner 41-42 to produce fresh absorbent which is recycled via lines 43 and 46 to absorber 20 via holding tank 21. Line 40 and cooler 45 are employed for circulation and cooling of the regenerated absorbent from 40 in order to maintain a desired temperature in said ammoniator.