GB783608A - Improvements in or relating to processes of digestion of fibres of raw material for the production of pulp or cellulose - Google Patents

Abstract

A process for producing chemical or semi-chemical pulp from fibrous raw materials having a moisture content of 10-12 per cent, such as bamboos, grasses and bagasse, comprises rapidly impregnating chips or stems of the raw material, before the major chemical or mechano-chemical treatment of digestion and delignification, by preheating the cooking liquor, which contains 20-70 grams or more per litre of alkaline or neutral reagents, such as a mixture of caustic soda and sodium sulphide, to an elevated temperature, e.g. 162-170 DEG C., before forcing it under steam pressure into a digester containing the chips or stems. The temperature in the digester is raised to the optimum for impregnation, and simultaneously the steam pressure is boosted to over 100 p.s.i., the temperature and pressure being maintained, with circulation of liquor, for a period sufficient for the chips or stems to become substantially impregnated and softened, whereafter the boosted pressure is relieved and the chips or stems are subjected to the chemical or mechano-chemical processes of digestion and delignification to produce hard bleaching or semi-chemical pulp. Preferably the charge of raw material in the digester is subjected to steam or acid hydrolysis before the cooking liquor is forced into the digester and, after the impregnation is complete, the boosted steam pressure is relieved only to the optimum conditions for digestion and the chips or stems are digested with the liquor for a period sufficient to produce pulp of the desired characteristics. This pulp may then, as before, be mechano-chemically defibred and delignified, and may be subsequently processed for washing, screening, and bleaching.