Recirculation of Bleach Plant Waste Liquors, 1993 Environmental Conference Proceedings

The discharge of bleach plant waste liquors is considered to be the most important remaining environmental issue for kraft pulp mills. In this study the possibilities of treating the waste liquors internally to allow the water to be reused in the process are assessed. The main emphasis is on bleach plants using chlorine-containing bleaching agents, although the results can be equally applicable in combination with non-chlorine bleaching technologies.

The study included desktop work to redesign the bleach plant with the aim of separating problem substances into the acidic waste liquor and reducing the amount of spent liquors. Laboratory testing and a long-term trial run of a pilot version of a special type of evaporator showed that the acidic waste liquor can be purified and recirculated within the bleach plant. A method for safe incineration of problem concentrates was developed. Vendor contacts and economic calculations show that the proposed solutions are feasible.

It is concluded that it would be technically possible to recirculate all bleach plant waste liquors in a modem kraft pulp mill even without refraining from using chlorine-containing bleaching agents.