Process for digesting and bleaching cellulosic material with reduced emissions

A method for the digesting and bleaching of cellulose-containing material wherein the emissions therefrom and the demand for fresh chemicals therefor are reduced, said method comprising the steps of (1) digesting cellulose-containing material in a digestion liquor containing sulfur and sodium, to thereby produce a digested pulp mixture and gases containing sulfur compounds, (2) removing said gases containing sulfur compounds from said digestion step;

• (3) combusting said gases containing sulfur compounds produced in the digestion step so as to convert sulfur therein to sulfur dioxide gas;
• (4) separating the digested pulp mixture into digested pulp and a waste liquor;
• (5) combusting said waste liquor so as to convert sulfur therein to sulfur dioxide gas;
• (6) generating chlorine dioxide gas and producing acid residual solution as a by-product therefrom;
• (7) bleaching said separated digested pulp with said chlorine dioxide gas;
• (8) absorbing sulfur dioxide gas from said combusting steps (3) and (5) in a scrubber containing an absorption liquor comprising an alkali metal salt solution substantially free of sulfur and sulfur compounds to thereby form a scrubber liquor;
• (9) mixing the resulting scrubber liquor with the acid residual solution from the chlorine dioxide generating step, whereby sulfur dioxide gas and a residual solution free from sulfur dioxide gas are produced;
• (10) separating the sulfur dioxide produced in step (9) from said residual solution free from sulfur dioxide;
• (11) precipitating non-chloride alkali metal salts from said residual solution free from sulfur dioxide to thereby obtain a sulfuric acid solution containing chloride;
• and (12) recycling said residual sulfuric acid solution containing chloride from step (11) to said chlorine dioxide generating step (6), whereby the chloride content of said residual sulfuric acid solution is utilized.