Fresh Water Usage Reduction Through Concentration of Pulp Mill Effluent Using a Gas Hydrate/Evaporation Hybrid, 1999 Pulping Conference Proceedings

Jason B. Smith, Wei Wang, Jeffery S. Hsieh & Peter X. Long

Georgia Institute of Technology

Reducing the amount of fresh water used in the pulp and papermaking process continues to be an avenue of investigation. As regulatory and industrial pressures have grown, the pulp and paper industry has expanded its efforts to more non-traditional approaches to reducing the volume effluent from a mill. One approach that has demonstrated promise was the application of freeze concentration, but there were unexpected limitations associated with this process. In 1997 Long and Hsieh applied gas hydrate technology as a method of eliminating the drawbacks associated with freeze concentration. After applying gas hydrate technology, the research expanded to include the application of a gas hydrate/evaporation hybrid process as a complete method for wastewater volume reduction.

Alkaline bleach plant effluent was processed through two separate processes and analyzed to determine its final properties. Falling film evaporation was used as a baseline and gas hydrate freeze concentration followed by falling film evaporation was used as a comparative process. This research examined the initial and final qualities (i.e. total suspended solids, total dissolved solids, and chemical oxygen demand) of all exiting streams from each process. It was found that the hybrid process reduced energy usage by 30%, operating costs by 10%, and additional stripper load by 80%.