4E comparison and optimization of natural gas or solar-powered combined gas turbine cycle and inverse Brayton cycle in hydrogen and freshwater multi-generation systems

Replacing fossil fuel-based systems with renewable energy resources is a method to enhance the performance of the layout and reduce environmental pollution. The gas turbine cycle (GTC) is one of the main sources of consuming natural gas (NG) in a combustion chamber (CC). In the present study, the theoretical performance of a 500 kW CC-based gas turbine cycle is improved by replacing the NG CC with a solar power tower (SPT) and converting it into a multi-generation system. The waste heat recovery of GTC is done by a hot water unit and an inverse Brayton cycle (IBC), and then the energy of the heat rejection stage of IBC and the exhausted gas of the system is recovered by a thermoelectric generator (TEG) and an absorption chiller. Afterwards, the produced power of IBC and TEG is fed to a proton exchange membrane electrolyzer and a reverse osmosis desalination unit for hydrogen and potable water outputs. 4E optimization shows that the exergy efficiencies of the CC-based system (Configuration 1) and the SPT-based system (Configuration 2) are equal to 37.2% and 9.12%, respectively. However, the economic performance of Configuration 2 is better. In this case, the total cost rate and unit cost of multi-generation in Configuration 2 are 142.1 $/h and 15.14 $/GJ in comparison with 145.5 $/h and 31.58 $/GJ for Configuration 1. In addition, the fossil fuel consumption and emissions of Configuration 2 are zero, while the fuel and environmental cost rate make up 54.76% of the total cost rate of Configuration 1.