Patent ID: 7291245
Filing Date: 2007-11-06
Classification: C01D,C01F,C01P,D21C,Y02P,Y10S

Abstract:
1. A process for causticizing green liquor in chemical recovery from black liquor in alkaline pulping, comprising the procedures of: (1) slaking lime with water or weak wash water to form a lime slurry containing lime grits; separating rough lime grits from the lime slurry to obtain the rough lime grits and a lime slurry from which the rough lime grits has been removed; sifting the thus obtained lime slurry with a 180-800 mesh sieve screen (excluding 180 mesh sieve screen) to obtain siftings and a fine lime slurry for causticization; and the siftings and the rough lime grits are mixed to obtain lime grits that can be used as a mineralizer when coal is burned in a coal burning boiler; (2) adding green liquor obtained by dissolving a smelt formed by evaporating and burning black liquor in alkaline pulping into a depurator; adding to the depurator a green liquor depurating agent whose active component is Ca (3) conducting a first causticization step by adding the fine green liquor obtained in procedure (2) and the fine lime slurry obtained in procedure (1) into a causticiser at a reaction temperature between 0° C. and 70° C. (excluding 70° C.), wherein the quantity of CaO contained in the fine lime slurry is 1-1.6 times of the theoretical quantity needed for causticization reaction; subjecting the mixture obtained after the first causticization step to a solid-liquid separation to obtain an alkali liquor that is commonly called as white liquor and solids; conducting a second causticization step by adding the fine green liquor obtained in procedure (2) into the solids obtained after the first causticization step at a reaction temperature between 0° C. and 70° C. (excluding 70° C.), wherein the ratio of the weight of Na