Air and Effluent Quality Improvements Through Condensate Stripping, 1997 Pulping Conference Proceedings

The Weyerhaeuser mill in Grande Prairie, Alberta was faced with increasingly stringent effluent BOD5 requirements in the early 1990s. In addition, they were experiencing difficulties with effluent toxicity and community odor complaints. Condensate stripping was investigated as a means to deal with all of these problems.

As a basis for the process design, balances were developed for volatile BOD and TRS compounds in pulping and recovery, based on extensive sampling as well as theoretical considerations. Two main alternatives were developed: a Base Case, designed to treat a 3000 m 3 /d (550 USgpm) contaminated condensate stream, and an Alternative Case, which used further condensate volume reduction measures to treat 1700 m 3 /d (310 USgpm). Through heat integration with the evaporation plant, the net increase in steam demand was kept to a minimum.

Modeling indicated that condensate stripping would reduce the discharge of volatile BOD by 88% and TRS by 98.5% in the Base Case, while in the Alternative Case the reductions would be 72% and 96%, respectively. Mill management decided to proceed with the Base Case in order to get maximum benefits and to position the mill for future effluent reduction and ultimate mill water system closure.

The condensate stripping system was started up in September, 1993. It has met or exceeded all of its expectations: community odor complaints have dropped essentially to zero, sulfide-caused effluent toxicity has been eliminated, and the BOD in the raw mill effluent dropped by a surprising 12 kg/ADt; 6-8 kg/ADt had been expected based on volatile BOD balances. The rest has been attributed to improved liquor carryover control.