Method of manufacturing bleached chemi-mechanical and semichemical fibre pulp by a two-stage impregnation process

Abstract

Chemimechanical pulp is produced from lignocellulosic material in a process in which the material is impregnated in two stages. The material is treated in the first stage with alkaline and, subsequent to passing an intermediate draining and reaction step, in the second stage with a solution that contains peroxide. The quantities of alkali and peroxide charged are fully optional and are independent of one another. The material is then optionally subjected to a further drainage and reaction step, and thereafter pre-heated at a temperature of between 50.degree. C. and 100.degree. C., whereafter the material is refined in one or two stages. The optimal brightness of the processed pulp for a given peroxide consumption is achieved by a balanced division of the peroxide charge between chip impregnation and bleaching.

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