Recovery of black liquor

Abstract

Abstract WEAK BLACK LIQUOR DERIVED FROM WOOD PULP PROCESSING AS A RESULT OF PULP WASHING, IS CONCENTRATED,AND SOLID SALTS ARE PRODUCED FOR THE PREPARATION OF GREEN LIQUOR WHICH IS RECYCLED TO THE WOOD PULP PROCESS. THE WEAK BLACK LIQUOR IS CONCENTRATED BY DIRECT CONTACT WITH HOT AIR, AND THE CONCENTRATED LIQUOR IS REACTED WITH PROCESS AIR AT ELEVATED TEMPERATURE IN A FLUIDIZE BED TYPE OF REACTOR, TO PRODUCE SOLID SODIUM SULFATE AND SODIUM CARBONATE SALTS FOR RECYCLE AND A HOT FLUE GAS. THE HOT FLUE GAS IS PASSED IN INDIRECT HEAT EXCHANGE WITH AMBIENT OR INITIALLY WARM AIR, TO PRODUCE THE HOT AIR BLACK LIQUOR CONCENTRATION. THE SOLID SALTS, CONSISTING MOSTLY OF SODIUM SULFATE AND SODIUM CARBONATE, ARE REACTED AT ELEVATED TEMPERATURE WITH A REDUCING TYPE GAS IN A CHEMICAL REACTOR, TO PRODUCE A SODIUM SULFIDE-CARBONATE MIXTURE WHICH IS DISSOLVED IN AN AQUEOUS LIQUID, SUCH AS WATER OR DILUTE WASH LIQUOR, TO PRODUCE GREEN LIQUOR. THE HOT GAS STREAM DISCHARGED FROM THE SALTS REDUCTION STEPS IS PREFERABLY COMBINED WITH THE HOT FLUE GENERATED DURING SOLID SALTS PRODUCTION FROM CONCENTRATED BLACK LIQUOR, AND THE COMBINED GAS STREAM IN THEN EMPLOYED TO PREHEAT AIR. THE PROCESS IS PREFERABLY APPLICABLE TO A KRAFT PULP PROCESS.

Inventors

• 👤 Indravadan S Shah

Bibliographic Details