Multiple Effect Evaporator Condensate Segregation Options for MACT I Compliance, 1999 Pulping Conference Proceedings

Gerald R. Mittet

NLK Consultants

Richard Garber & Paul Baldwin

Boise Cascade Corporation

Compliance with the MACT I provisions of the EPA Cluster Rules requires treatment of selected foul condensate streams from digesters and evaporators in kraft pulp mills to remove methanol. The MACT I rules also require collection and treatment of vapors from washer hoods. Vapors from decker hoods must also be collected if contaminated condensate having a methanol concentration greater than 400 mg/l is used as wash water on decker showers. The latter requirements may be waived if condensates are segregated in a manner which makes the “Clean Condensate Alternative” applicable.

The total volume of condensate requiring treatment can be reduced by segregating foul condensates. Evaporator condensates may be segregated using external liquor heaters, secondary condensers, internal baffles, or by simply removing condensates from individual effects. The preferred option for condensate segregation is dependent on the costs of collecting and treating segregated condensate. Two options for condensate segregation have been evaluated for the Wallula mill, and methanol distributions throughout the mill have been calculated for each option. The total volume of segregated condensate is minimized by installing external heaters at the sixth effects and further segregating condenser condensates. However, process condensate reused on the brown stock washers and in the causticizing plant then has a relatively high methanol concentration. Process condensate with a much lower methanol concentration is produced by segregating a slightly higher volume of foul condensate taken from the evaporator sixth effects and condenser ejector trains. Total recovery of methanol in segregated condensate is also maximized when this is done.