Recycling of bleach plant filtrates by electrodialysis removal of inorganic non-process elements.

Abstract

Water use in the pulp and paper industry is very significant, and the U.S. pulp and paper industries as well as other processing industries are actively pursuing water conservation and pollution prevention by in-process recycling of water. Bleach plant effluent is a large portion of the water discharged from a typical bleached kraft pulp mill. The recycling of bleach plant effluents to the kraft recovery cycle is widely regarded as an approach to low effluent bleached kraft pulp production. The focus of this work has been on developing an electrodialysis process for recycling the acidic bleach plant effluent of bleached Kraft pulp mills. Electrodialysis is uniquely suited as a selective kidney to remove non-process elements (NPEs) from bleach plant effluent before they reach the chemical recovery cycle. Using electrodialysis for selective NPE removal can prevent the problems caused by accumulation of inorganic NPEs in the pulping cycle and recovery boiler.

High frequency pulsed electrodialysis of acidic filtrate in kraft pulping

“…The acidic filtrate stream, coming from the bleaching of fiber, is compatible with electrodialysis, showing a low potential of fouling based on previous studies (Tsai et al, 1997). The acidic pH of the stream (~3) hinders the occurrence of colloids, and consequently the fouling of membranes in ED.…”

Recycling of cleach plant filtrates by electrodialysis removal of inorganic non-process elements.

“…This causes a strong need for a specific purge of inorganics (Rapson, 1967;Reeve, 1976). Additional discussions on water reuse in bleached kraft pulp mills were given earlier (Tsai et al 1997;Tsai et al 1999;Pfromm et al 1999). …”