Feasibility of Recovering Useful Salts from Irrigation Wastewater Concentrates Produced by Power Plant Cooling

摘要

The report evaluates the feasibility of a novel energy-conserving way to recover useful salts (sodium sulfate and calcium sulfate) from concentrated brines by evaporation/crystallization. The concentrated brines examined were cooling tower blowdown from agricultural wastewater and this blowdown after further concentration and use in ion exchange regeneration. Laboratory and pilot tests were made with both conventional evaporation/crystallization and interface-enhanced, vertical-tube foam evaporation which increases evaporation. Sodium sulfate and calcium sulfate recovery provides potential capital cost savings, about $2 million for a 1000-MWe power plant. Sale of these products is an added incentive to their recovery. The use of foamy vapor/liquid flow on the evaporating brine/crystal slurry enhanced heat transfer by up to 40% and enabled concurrent energy reductions of 28%, compared to conventional evaporation/crystallization of sodium sulfate in a 5000-gpd vapor-compression vertical-tube evaporation pilot plant. Consequently, the use of agricultural wastewater for power plant cooling in the San Joaquin Valley with ion exchange for pre-softening and wastewater regeneration solely with concentrated brine from blowdown appears technically feasible and economically attractive.