Water production through CO2 capture in coal‐fired power plants

A novel integrated liquid absorbent‐based CO2 capture and desalination process is proposed. It is based on the use of a forward osmosis operation replacing the trim cooler in the capture process. This cooler controls the absorption liquid inlet temperature to the absorber. In the forward osmosis operation water is transferred from a saline solution to the absorption liquid. It can be recovered in two ways: via the overhead condenser of the desorber or via an intercooling operation by flashing the absorption liquid under vacuum, followed by condensation of the water vapor produced. In both cases the energy requirement for the water production process is considered negligible as it is part of the energy requirement of the capture process. The amount of produced water and its quality is such that it can be used as makeup for flue gas desulphurization and/or cooling tower makeup. Thus, it can provide a resolution for the increase in specific cooling water requirement as a result of a CO2 capture retrofit to an existing coal‐fired power station. Monoethanolamine and sodium glycinate solutions were evaluated as absorption liquids in this study. Amino acid salt solutions are preferred because of the high osmotic pressure and low vapor pressure, providing the best option for high water quality. Inclusion of a forward osmosis in an amine‐based postcombustion CO2 capture plant integrated in a power plant is able to produce significant amounts of freshwater from seawater. Process modeling and laboratory‐based evaluation of commercially available membranes indicate that it can provide a resolution for the increase in specific cooling water requirement as a result of a CO2 capture retrofit to an existing coal‐fired power station.