FORFARANDE FOR MINSKNING AV BEHOVET AV FERSKA KEMIKALIER VID UPPSLUTNING AV CELLULOSAHALTIGT MATERIAL MED NATRIUM- OCH SVAVELHALTIGA LOSNINGAR

摘要

A process is provided for reducing the requirement of fresh chemicals without increasing emissions in the pulping of cellulosic material with alkaline sodium and sulfur-containing-sulfate pulping liquor, which comprises evaporating and burning spent sulfate pulping liquor; dissolving the resulting smelt in water to form a sodiumsulfide-sodium carbonate-containing solution (green liquor); regenerating pulping liquor (white liquor) containing sodium sulfide and sodium hydroxide from said solution; and recirculating said regenerated liquor to the pulping stage; oxidizing at least one of the resulting green and white liquors to form sodium thiosulfate therein; reacting the residual acid liquor from the manufacture of chlorine dioxide by reduction of an alkali metal with oxidized white and/or green liquor to form sulfur dioxide and sulfur; removing and recovering sulfur dioxide; and returning the residual liquor freed from sulfur dioxide to the pulping.