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Abstract

A process and an apparatus in black-liquor evaporation for the selective removal, by liquid absorption, of hydrogen sulphide from the generated gas (3) containing hydrogen sulphide as well as carbon dioxide, an disclosed. In the process, the gas is counter-currently brought into multistage contact, preferably comprising three stages (6, 7, 8), with circulating carbonate-containing alkaline solutions, preferably sodium carbonate solutions (25), the pH of which is adjusted during the absorption to about 9-12 by the addition of a hydroxide, preferably a sodium hydroxide solution (26, 27, 28). It is preferred that the gas flow is turbulent and the liquid flow is laminar when contacted with one another. The apparatus comprises a container (1) having a gas inlet (2), a gas outlet (4), and a packing (9) arranged in several successive stages (6, 7, 8). The apparatus has means (25) for supplying a carbonate-containing solution to the last stage and through this stage countercurrently to the gas, and for recycling the solution across this stage; conduits (29, 30) arranged between the stages for supplying a partial flow of the solution from one stage to a preceding stage; means (26, 27, 28) for supplying a hydroxide to the carbonate-containing solution in at least one of the stages (6, 7, 8); and an outlet conduit (31) from the first stage, as seen in the feed direction of the gas, for discharging a sulphide-containing liquid.

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First Claim