Integrated systems
Water production from CO2-capture
Seawater desalination integrated into amine-based CO2-capture process
A new concept for seawater desalination integrated into an amine-based CO2-capture (PCC) process has been investigated, based on the use of forward osmosis (FO) to transfer water from seawater into the absorption solution via a membrane.
Core to the concept is the FO technology that enables the selective transfer of water directly from a saline cooling water stream to the CO2 absorption liquid. Subsequently the water can be recovered from the absorption liquid loop in the CO2-desorber by condensation of the steam exiting together with CO2, as part of the normal operations and hence without additional energy requirement. Water can also be recovered from the absorber using a membrane distillation process, making use of the heat generated during the CO2-absorption process.
Concept of FO process showing the direction of water permeation in the combined CO2 capture desalination process
Water consumption in thermal power stations, such as coal fired power plants, is a critical concern as these plants require substantial cooling, which is typically achieved through the evaporation of water in cooling towers or flow-through cooling using seawater. Adding CO2-capture to a coal-fired power station to reduce emissions increases the cooling water requirement. Water is needed to cool down the flue gases and the capture plant requires water for cooling and other functions. In the combined CO2 capture desalination process the FO unit will also replace trim cooler and operate as a Forward Osmosis Heat Exchanger (FOHEX) unit.
Forward Osmosis Heat Exchanger (FOHEX)
The technology was demonstrated with real flue gas, in partnership with Delta Electricity’s PCC pilot plant at Vales Power Point power station, which was 3000 times larger than the laboratory size equipment. The source of saltwater can be seawater, water from aquifers, lake water or brines from reverse osmosis desalination operations.
Techno-economic assessment
The preliminary techno-economic assessment of the overall process indicated a cost of A$1.77/m3 of water produced from a saline water stream, typical of seawater, slightly over 30per cent cheaper than the equivalent reverse osmosis desalination plant. The water production of 4368 m3/day would be able to supply 60 per cent of the plant’s cooling water needs.
