ENERGY-EFFICIENT EVAPORATION PROCESS WITH MEANS FOR VAPOR RECOVERY

In a process for the recovery and reuse of heat contained in the wet exhaust gases emanating from a solids dryer or liquor concentrator (1), particularly one in which drying or concentration is facilitated by purging the vapor with some noncondensable gas such as as air or nitrogen, water or solvent vapor in the moist exhaust mixture is separated from the noncondensable gas or gases by preferentially passing the vapor through a semipermeable membrane (2). The water or solvent vapor is then compressed and subsequently condensed in a heat exchanger (4), permitting recovery of its latent heat of vaporization for reuse in the evaporation process. In a drying process, this recovered energy is conveniently used to reheat the dry gases that exit from the membrane separator (2) permitting the hot, dry gases to be recirculated through the dryer (1). Alternatively, an indirect heat exchanger may be used to transfer this heat to the material being dried. In an evaporative process for the concentration of a liquor, the recovered energy may be used either to preheat the dry purge gases or to heat the dilute liquor being concentrated.