Multi-level sulfide content white liquor production and utilization in cellulose pulping

A method of producing kraft pulp by cooking comminuted cellulosic fibrous material with white liquor to produce kraft pulp and black liquor, comprising the steps of:

• (a) treating a slurry of cellulosic fibrous material in a plurality of consecutive stages with white liquor, including at least first and second stages, using a first supply of white liquor on the first stage and a second supply of white liquor on another stage;
• (b) subjecting the material treated with white liquor to cooking conditions in at least one of the stages to effect kraft cooking thereof, and producing black liquor;
• (c) removing and treating sulfur from the black liquor and making at least two streams of white liquors from the remaining black liquor, and wherein the second stream of white liquor is used as the second supply of white liquor;
• (d) adding the treated sulfur to the first stream of white liquor to produce the first supply of white liquor with a sulfur content greater than the sulfur content of the second supply of white liquor;
• and
• wherein steps (a), (c) and (d) are practiced by:
• (i) pressure heating the black liquor at a temperature and for a time period such that substantial volumes of off gases containing organic sulfur compounds are produced;
• (ii) treating the off gases from step (i) to produce primarily hydrogen sulfide and methane;
• and (iii) using the hydrogen sulfide to produce the first supply of white liquor.