Multi-criteria optimization of a new geothermal driven integrated power and hydrogen production system via a new Index: Economic sustainability (EcoSI)

Abstract

This study investigates a new geothermal energy-driven hybrid system, including an organic Rankine cycle (ORC) for power generation and a proton exchange membrane electrolyzer (PEMEL) to improve the sustainability of issued geothermal energy sources. In this aim, 2400 designs were formed parametrically. The designs were optimized throughout the multi-criteria decision-making (MCDM) analysis named efficiency analysis technique with output satisficing (EATWOS). In the optimization, a new index named the economic sustainability index (EcoSI) was proposed as the objective function. EcoSI was then introduced into MCDM analysis along with the sustainability index (SI). Design 1-2-7-1-1 with a turbine inlet temperature of 100 degrees C and inlet pressure of 1950 kPa was determined as the optimal design. In this design, the optimal current density was determined as the minimum chosen value with 1000 A/m(2). The power supply rate was determined as the minimum chosen value of 10 %. The temperatures of the production and re-injection wells were determined as 133.5 degrees C and 111.99 degrees C, respectively. The exergy efficiency and power generation rate of ORC were determined as 21.11 % and 12.113 MW, respectively. The hydrogen generation rate and exergy efficiency of PEMEL were determined as 0.0057003 kg/s and 48.76 %, respectively. The exergy efficiency of the overall system was determined as 19.92 %. The investment cost was determined as 332.57 $/h. Exergy destruction, fuel and product costs were determined at 38312.99 $/h, 48272.40 $/h, and 24240.05 $/h, respectively. The sustainability index (SI) was determined as 1.249, whereas the economic sustainability index (EcoSI) was determined as 1.260.