Method for producing green liquor in sulfate and sulphite pulp mill chemical recovery

摘要

PCT No. PCT/SE93/01028 Sec. 371 Date Jun. 5, 1995 Sec. 102(e) Date Jun. 5, 1995 PCT Filed Nov. 29, 1993 PCT Pub. No. WO94/12723 PCT Pub. Date Jun. 9, 1994When producing green liquor for later manufacture of cooking liquor, it is endeavoured that the green liquor shall be readily clarified and/or readily filtered. This endeavour is achieved with the present invention, which relates to a method of producing green liquor in which waste liquor separated from cellulose pulp and derived from a cooking stage and possibly from one or more bleaching stages is worked up including known treatment stages such as evaporation, combustion, smelt dissolving and other green liquor preparation, and in which a calcium containing chemical is added to the waste liquor prior to combustion, or is added at the combustion of the waste liquor. The method is characterized in that carbon deriving from the smelt is caused to equal at most 0.3 weight promillage, calculated on the smelt after combustion, when and after dissolving the smelt in liquid; and in that the addition of calcium is controlled so that the amount of calcium added together with the amount of calcium that is already present will equal at least +E,fra 3/4+EE of the amount of magnesium present in the waste liquor calculated in mol; and in that the addition is at most 10% by weight of the sodium plus sulphur present in the waste liquor.