Cost-effective design of a draw solution recovery process for forward osmosis desalination

Abstract

The recovery process for the draw solution in a forward osmosis (FO) desalination plant is designed using the Aspen Custom Modeler (ACM). This system is cost-minimized around three draw solutes: ammonium bicarbonate, ammonium hydroxide, and ethanol. A method to dissolve gas phase draw solutions is proposed and optimized. Through control of the CO2 to NH3 mole ratio, the decomposed gas can be more easily dissolved. Cost-minimizing design specifications for each system are determined for improved energy efficiency. Water production costs and process specifications for each draw solute are compared, and the advantages of each system are discussed. The design takes into consideration the CO2 to NH3 mole ratio, the stripping column, heat exchangers, absorber, and flow configuration.