Process Modeling of Hybrid Forward Osmosis-Distillation Desalination Systems

摘要

Forward osmosis (FO), also known as engineered osmosis, is two step process for desalinating seawater and other complex aqueous feed streams. The first step, the passive diffusion of water across a polyamide thin-film composite membrane (similar to that used in reverse osmosis) is driven by an osmotic gradient between the feed stream and a high osmotic pressure draw solution. When using a thermolytic salt, the second step of draw solute recovery uses low-temperature heat to recycle the draw solution and produce a permeate stream of fresh water. Compared to alternative techniques for water desalination this process does not require electricity to power high-pressure pumps (as in reverse osmosis) or high grade thermal energy to evaporate the water (as in multistage flash distillation). One promising draw solute/recovery pair are the thermolytic salts created by ammonia and carbon dioxide (NH4HCO3, (NH4)2CO3, and NH2CO2NH4) which can be driven out of water at relatively low temperatures (<70°C) in distillation columns.