Fourth-generation fluid effect in geothermal-based hydrogen production combined system

Abstract

In this study, hydrogen production using a Proton Exchange Membrane Electrolyser (PEME) integrated with a geothermal based dual Organic Rankine Cycle (ORC) designed using different organic fluids is investigated. Five dry fluids (R245fa, R600, R600a, butene and isobutene) were used in the medium-temperature ORC-1 unit. In the low temperature ORC-2 unit, fourth-generation ultra-low global warming potential (GWP) fluids (R1243zf, R1225ye(Z) and R1234ze(E)), whose role in hydrogen production has not been determined before, were used as organic fluids. In addition to these fluids, the conventional wet fluid R134a and zeotropic R450A (42% R134a-58% R1234ze(E)), which is a mixture of wet and fourth-generation, were added for performance comparison. In the study, it was aimed to increase hydrogen production by using low temperature geothermal heat from the medium temperature ORC-1 unit in the ORC-2 unit with organic fluid open heater (OFOH), determine the organic fluid effect on hydrogen production by using fourth-generation fluids with low critical temperature and determine the ideal fluid pair among the fluid groups used in two ORC units. It is also planned to analyze the effect of OFOH utilization on hydrogen production in ORC-PEME integration. The contribution of 25 different fluid pairs formed as a result of the 5*5 matrix to hydrogen production through PEME was determined. The best fluid pair was R245fa-R1234ze(E) while the lowest performance was obtained in R600a-R134a duo. In the best fluid pair, it was determined that the amount of natural gas preserved (NGP) was 3018 tons per year and the levelized cost of hydrogen (LCOH) was 1.901 $/kg with 104.4 kg hydrogen production per hour. The minimum specific investment cost (3270 $/kW) was reached in this fluid pair. Compared to the worst fluid pair; it was determined that LCOH was reduced by 8.15% with the best fluid pair. For the best and worst fluid pairs, a difference of 412 tons per year was found between the NGP considering the CH4 consumed versus the hydrogen produced based on the steam methane reforming (SMR). Carbon credit gain (CCG) was determined by enviro-economic analysis, while R245fa-R1234ze(E) has 365.8 k$ carbon recovery, this value decreases to 315.8 k$ in R600a-R134a duo.