Abstract: A gas scrubber is provided which is particularly useful for scrubbing flue gas and condensate effluent from a kraft pulp mill. The scrubber comprises a first chamber having inner and outer looped parallel side walls, and first and second end walls extending therebetween. A gas inlet is positioned so as to direct gas passing through it between the side walls. Fluid nozzles on the inner wall are directed to spray liquid toward the outer wall. A gas outlet is provided which has at least a portion angularly spaced from the gas inlet. The walls of the first chamber are preferably arranged to provide an incremental volume between them which decreases with angular distance from the gas inlet. The gas outlet is dimensioned so that the velocity of the gas flowing between the walls is substantially constant. Preferably, the side walls are concentric, substantially circular and each of constant diameter. In addition, the first end wall is substantially planar and the second end wall is helical in configuration.

Abstract: A composition is provided which comprises an aqueous alkaline solution of a metal salt and black liquor, the metal salt being selected from the group consisting of iron, chromium, cobalt and nickel salts. This composition is useful in a process described for absorption of hydrogen sulfide from flue gas, followed by subsequent oxidation of dissolved sulfide to thiosulfate, if desired. The presence of the metal ions and black liquor synergistically catalyzes the overall reaction of absorption of hydrogen sulfide, followed by oxidation of the sulfide. Preferably, prior to scrubbing to remove hydrogen sulfide with the solution, the flue gas is first cooled to near its dew point, and then scrubbed with water to remove particulates. Additionally, the effluent flue gas from the absorption step is usefully scrubbed with water to recover heat, following which it is used to scrub condensates from a kraft pulp mill. The metal salt in the solution is preferably an iron salt at a concentration of about 0.002 M.