Coking of waste kraft pulping liquors at lowered pH - by blowing liquors with sulphur dioxide prior to coking

摘要

Alkaline kraft pulping liquors are treated by (a) flowing the liquors to an adsorbing zone and adding SO2 to lower the pH to 7 (b) coking under autogenous pressure in a coking zone to form coke, H2S-contg. gas and aq. effluent (c) burning the coke to produce SO2 for recycle to step (a), and (d) adding lime and H2S to the effluent in a second adsorbing zone to form new kraft cooking liquor. Reducing the pH to 7 in step (a) lowers coking chemical O2 demand (COD) and shortens coking residence time.