Development of Vertical Tube Foam Evaporation for Desalination.

摘要

A vertical tube evaporation (VTE) pilot plant facility capable of testing full-sized distillation tubes in an 18-tube bundle to provide comparative data,under process conditions relevant to projected large plant operation,is described. Double-fluted and spiral-corrugated distillation tubes were tested in the upflow mode with fresh water,brine and seawater feeds. A novel,proprietary method of brine-side enhancement was applied:The interface enhancement method (1) produced overall VTE heat transfer coefficient and distillate productivity rate enhancements of up to 200percent over and above VTE performance data obtained with these enhanced tubes under comparable standard upflow process conditions. This interface enhancement method depends upon the addition of selected surfactants to the feed brine in a few parts per million (ppm) concentration and upon establishing a foamy two-phase flow condition over the heat transfer surface. Overall heat transfer enhancements of about 100percent were reproducibly demonstrated under realistic upflow VTE conditions with both double-fluted and spiral-corrugated distillation tubes using seawater feed having about 5ppm of a fully biodegradable commercial surfactant added thereto. Simultaneous tubeside pressure drop reductions by a factor ranging from 3to 10,and significant upflow VTE stabilization effects were also demonstrated.