Abstract: An improved method for removing malodorous sulfur compounds from flue gases generated in kraft or sodium sulfite pulping operations and the like by the absorption process using green liquor, an aqueous solution containing sodium sulfide and sodium carbonate. The malodorous gas compounds, including hydrogen sulfide, methyl mercaptan, and dimethyl sulfide are preferentially absorbed by the sodium sulfide forming sodium hydrosulfide and methanol. Any sulfur dioxide in the gas is absorbed and neutralized by sodium carbonate. In this method carbon dioxide absorption is minimized and the formation of sodium bicarbonate is limited. Sodium bicarbonate formation is minimized in order to avoid its reaction with sodium hydrosulfide which would then release undesirable hydrogen sulfide during absorption, as well as to forestall the need to increase chemical and lime kiln capacity requirements when the green liquor returned to the kraft recovery process contains excess amounts of sodium bicarbonate.

Abstract: An improved method for recovering sulfur from flue gas which contains sulfur dioxide formed from burning sulfur containing fuels. The method first involves the reduction burning of auxilary fuel in the presence of sodium sulfite to convert it to smelt containing sodium sulfide and sodium carbonate. The smelt is dissolved, and the solution reacted with carbon dioxide, hydrogen sulfide and water vapor forming sodium hydrosulfide. The sodium hydrosulfide is reacted with a high concentration of recycled sodium bicarbonate and stripped with carbon dioxide to form sodium carbonate and release the sulfides as hydrogen sulfide from the stripper. The hydrogen sulfide released is then converted to sulfur dioxide, sulfuric acid or elemental sulfur. Pressurized carbon dioxide is used for pressure carbonation of recycled solution from the stripper to convert the sodium carbonate to the high concentration of recycled sodium bicarbonate used for stripping.

Abstract: An improved method for recovering spent sodium and sulfur components in sodium sulfite and sodium bisulfite pulping operations. The method involves reduction burning of spent liquor to convert it to smelt and the treatment of this smelt in a sequence of operations that accelerate the reaction steps used to produce sodium hydrosulfide, hydrogen sulfide, sulfur dioxide, sodium carbonate, sodium bicarbonate and to recover sodium sulfite, sodium bisulfite, sodium carbonate and/or sodium hydroxide while preventing formation of sodium thiosulfate.