Ecologically Balanced Kraft Pulp Production - The Chemical Balance, 1996 Minimum Effluent Mills Symposium Proceedings

Ingrid Oskarsson

Stora Corporate Research AB

Kenneth Näslund

Stora Billerud AB

Stora is working towards ecologically balanced production of kraft pulp. The goals for pulp production are to obtain a pulp of good quality, a clean environment and a cost-efficient process. It is thereby important to close flows from the wood room, clean the condensates, reduce the volume of spill and have low carry-over of dissolved substances to the bleach plant. The chemical balance (s, na, cl, k) in the kraft mill is one issue that must be dealt with to achieve this goal the levels of potassium and chloride together with runnability concerns establish the lower limit for the input of chemicals. This limit often exceeds the losses at a modern mill and excess chemicals must be purged. Normally, the most efficient way is to purge electrostatic precipitator ash. Potassium and chloride levels are then reduced. An input of inorganic chemicals with no value as make-up chemicals for cooking liquor preparation means that more excess chemicals must be purged. This will occur if high amounts of spent acid or alkaline bleach plant filtrates are taken to the recovery area in a kraft mill with low losses.