Thermo-enviro-economic analysis of different power cycle configurations for green hydrogen production from waste heat

In this study, thermodynamic, thermo-economic and enviro-economic analyses of green hydrogen production with biomass waste heat -Steam Rankine Cycle (SRC) -Organic Rankine Cycle (ORC)-Proton Exchange Membrane electrolyzer (PEME) combined system were carried out. After the high -temperature biomass waste heat is used in the SRC unit, the mid -low temperature waste heat released is used in the ORC unit, which is more suitable for these temperatures, to generate electricity. Hydrogen production was investigated by transferring the power generated in the SRC and ORC unit to the PEME unit. Eight different configurations were created by using two organic fluids (R245fa-dry and R152a-wet) in four different layouts of the ORC unit. These layout are basic, regenerative, recuperative, regenerative with recuperator. The effect of turbine inlet temperature variation on system efficiency and hydrogen production rate at different evaporation pressure/critical pressure (Pe/Pcr) ratios in the ORC unit was determined. After determining the maximum hydrogen production point in each configuration, thermo-economic and enviro-economic analysis was performed. With the thermo-economic analysis, the payback period of the system, specific investment cost (SIC -$/kW) and levelized cost of hydrogen (LCOH-$/kg) were determined. For this, the amount of hydrogen produced per year, purchase equipment and other costs (installation, structural, contingencies, etc.) were taken into consideration. Finally, an enviro-economic analysis was carried out to determine the amount of CO2 reduction and the corresponding carbon credit gain (CCG-$). As a result of the study, the best performance was obtained in Conf-4a (Biomass waste heat -SRC -Regenerative recuperator ORC with R245fa-PEME). The amount of hydrogen produced per year, LCOH and CCG were 93.81 tons, 1.74 $/kg and 37,527 $, respectively.