Resource Recovery from Bleach Plant Effluents: A Paradigm Shift?, 1996 Pulping Conference Proceedings

“Shri” Ananta Shrinath

Jaakko Pöyry Fluor Daniel

Brigitte Smith

Molten Metal Technology, Inc.

Alvin Tanner

Fluor Daniel

The Cluster Rules have lent a measure of urgency to finding ways and means of reducing bleach plant effluent discharges. Reduction in fresh water usage, and closure of bleach plant filtrates, is being widely recognized as the best way to address increasingly stringent environmental regulations. Various industry efforts in North America and Scandinavia are focusing on reduction, and ultimately, elimination, of bleach plant effluents through recycle of bleach filtrates to the pulp mill, with eventual integration into existing chemical recovery systems. However, integration of bleach filtrates, especially from chlorine compound-based bleach sequences , with existing chemical recovery loops, is fraught with problems, such as susceptibility to corrosion and pluggage in the recovery boiler, and increased sensitivity to upsets in the process due to tightly closed water circuits . The bleach chemical recovery process described in this paper is based upon an alternate approach to bleach plant closure. The process envisages a stand-alone bleach chemical recovery loop, distinct and separate from pulping chemical recovery systems. This separation is expected to allow mills to incorporate this process without disruption of their process, as described in this paper. The process, based on the perspective that bleach effluents constitute a resource stream from which valuable products can be derived and recycled to the pulp mill and bleach plant, utilizes a unique technology developed by Molten Metal Technology, called Catalytic Extraction Process (CEP). The process is expected to result in the return of useful resource streams, such as clean condensate and sodium hydroxide to the pulp mill and bleach plant. Another useful product generated by the process is syngas, which may be recycled for use as fuel in boilers. Deleterious components of the bleach effluent stream, such as chlorine and heavy metals, can be selectively captured in a non-leachable, vitreous phase.