Mill Closure - Decreasing the Solid Discharge, 1997 Minimum Effluent Mills Symposium Proceedings

In 1992 Millar Western’s Meadow Lake mill started up as the world’s first zero liquid effluent mill. In 1996 the next step in zero discharge was taken, the closure of the solids loop. Laboratory tests proved that dissolved smelt provided a suitable alkali source for partial substitution of caustic in the process. Purified sodium carbonate trials were successful in the mill, demonstrating its ability as a suitable alkali replacement. The smelt utilisation team was empowered to determine the methodology for introducing smelt into the process. After trying several smelt preparation techniques a dissolving trough and a liquor clarifier were determined to be the proper equipment. The system was automated and winterised. The smelt has been evaluated in several different areas of the mill. The evaporators run continuously on green liquor as alkali makeup for pH control. At present, the usage of green liquor in the mill accounts for a mass reduction to landfill of approximately 40%. Once all the system difficulties are resolved it is anticipated that 70% of the smelt can be recycled.