Ammonia and hydrogen sulphide removal from gases - with two-stage hydrogen sulphide scrubbing and combined acid gas stripping

摘要

Removal of NH3 and H2S from gases (esp. coke-oven gas) is effected by scrubbing with water to remove NH3 and 2-stage scrubbing with a NH4OH soln. and an alkali metal hydroxide soln. to remove H2S, with the improvement that the liquors from both H2S scrubbing stages are combined and freed of H2S and HCN in at least one stripper column. The gas is passed successively through 4 scrubbers. The 1st is operated with deacidified NH3-contg. recycle water and liquor from the 2nd scrubber to remove 30-60% of the H2S. The 2nd scrubber is operated with recycled NH3 gas and liquor from the 3rd scrubber to remove 30-80% of the H2S. The 3rd scrubber is operated with water to remove NH3. The 4th scrubber is operated with NaOH soln. to remove residual H2S. The liquors from the 1st and 4th scrubbers are combined and introduced into 2 parallel stripper columns for removal of H2S and HCN. The bottoms stream from one column is recycled to the 1st scrubber and the bottoms stream from the other column is passed to a NH3 stripper column, and the NH3 is recycled to the 2nd scrubber. The process uses no more than the optimum amt. of alkali metal hydroxide.