Use of high salinity water in a power plant by connecting a direct contact membrane distillation (DCMD) to a steam-injected gas turbine (STIG)

Abstract

Unlike steam turbines, electricity production in gas turbines is inherently independent of freshwater consumption. However, the thermal efficiency of gas turbines decreases as the temperature of input air increases. As a result, many methods of cooling the inlet air require the use of fresh water. Moreover, when it comes to humid gas turbine technology, the practice of injecting steam or humid air into the turbine to improve its thermal efficiency and output power consumes a substantial amount of freshwater. Therefore, reducing the use of fresh water to enhance the output power and thermal efficiency of gas turbines can be a necessary option, especially in hot and dry regions. Alternatively, considering the significant amounts of waste heat in gas turbines, one solution to reduce fresh water consumption is to connect them to thermal desalination units. However, conventional thermal desalination is only practical for seawater desalination in coastal areas. Therefore, this study explores the possibility of linking a direct contact membrane distillation (DCMD) unit to a Steam-injected gas turbine (STIG), which can use high salinity water sources like reverse osmosis (RO) brine in inland regions. The freshwater generated by the DCMD is used to chill the input air to the compressor and produce steam injected within the turbine. Simulation results show that this connection can raise the net output power by [9 to 17.2] MW and thermal efficiency by [3.3 to 15.6] % for compressor pressure ratios between [5 to 30], when compared to a simple gas turbine.