PROCEDE ET INSTALLATION POUR LE BLANCHIMENT DE TISSUS CELLULOSIQUES DE FABRICATION CHIMIQUE

摘要

Chemically produced pulp is in the prior art bleached with chlorine in a reactor where the mixture of pulp suspension and of chlorine solution remains for up to 60 minutes. The remaining lignin is then extracted with sodium hydroxide solution; the relatively dark fibrous mass is bleached with hypochlorite or the like in a multi-hour process to produce a saleable half-stuff. This gives rise to chlorine-containing, organically polluted waste liquors containing a high BOD and difficult-to-biodegrade materials. The bleaching process of the invention comprises mixing chemically produced pulp with ozone while the pulp is at the same time subjected to a fibre individualisation (separation, fiberisation) process. This accelerates the rate of bleaching, even though only relatively small quantities of ozone are consumed. Especially the yield is increased and the COD of the overall bleach is appreciably reduced. The energy required for grinding also decreases significantly.