A novel method of vertical tube evaporation (VTE) to improve heat transfer performance was applied to the concentration of three types of industrial wastewaters. This method, interface enhancement, relies upon the addition of a few parts per million of a selected surfactant to the wastewater feed followed by imposed two-phase foamy liquid-vapor flow over the heat transfer surfaces. Applied to the concentration of power plant cooling tower blowdown and boiler blowdown, interface-enhanced VTE provided an approximate 120 percent increase in the usual VTE heat transfer performance, using a 5,000 gpd pilot plant having double-fluted aluminum-brass distillation tubes, under process conditions that are realistic for large industrial plants. Acidic mine drainage water, concentrated by double-fluted titanium evaporator tubes provided about a 60 percent heat transfer performance enhancement. Beneficial side effects of the surfactant additive were to inhibit the crystallization of solutes, permitting concentration of the wastewaters to smaller volumes. This work indicates feasibility and improved economics for renovation-recycle of each of the three types of wastewater examined.

"Project Number R-2753." Report prepared by Sea Water Conversion Laboratory, University of California, Richmond, California. Includes bibliographical references (page 58).