Waste Heat Evaporation of Paper Mill Process Waters, 1996 Environmental Conference Proceedings

A demonstration plant for evaporation of paper mill process waters was installed in 1995 at Enso-Gutzeit Oy Kotka Mills. The plant was intended to provide a mill scale demonstration of the approach to closing the paper mill water circulation by utilization of waste heat. The mill scale purification system comprises new evaporation and flotation/filtration technologies supplied by Ahlstrom Machinery. The falling-film, multi-effect vacuum evaporator consists of three effects and a surface condenser. The plant utilizes low temperature waste heat from the mills’ black liquor evaporation and the latent heat of the TMP filtrate. Condensing takes place in four stages and the segregated condensate of the waste steam is added to the total clean condensate volume. The new evaporator construction, ZEDIVAP TM , effectively segregates salts and volatile components without accumulation of harmful substances in the circulation water. A small amount of concentrate produced is mixed into weak black liquor and the foul condensate is utilized for biogas generation in the mills’ anaerobic wastewater pre-treatment system.