Development of a novel geothermal trigeneration system utilizing modified organic-flash cycle and zeotropic mixtures: Environmental assessment and optimization

Abstract

Due to the rise in global energy demand caused by growth in the human population and standards of living, renewable energy-based trigeneration systems have gained importance recently. Owing to this, an innovative geothermal-powered trigeneration system is presented to produce electricity, H2, and cooling simultaneously. Also, its performance is scrutinized from the thermodynamic, environmental, and sustainability outlooks to find the best zeotropic mixtures. A two-objective optimization is conducted, taking into account both energetic and exergetic efficiencies as objectives to detect the optimized working conditions. The used mixtures include Butane/Pentane, Butene/Pentane, Isobutene/Pentane, Isobutane/Pentane, R142b/Pentane, R236ea/Pentane, and R245fa/Pentane. Based on studies of the mass fraction of Pentane, the Isobutene/Pentane mixture exhibits the best performance among the zeotropic mixtures. For the Isobutene/Pentane mixture, a rising flash tank temperature leads to reduced net electricity and produced H2 rate, whereas the cooling load goes up. Furthermore, the energetic efficiency of the system has an increasing trend with increments in the temperature of the evaporators in the design. With increasing temperature of the evaporators and flash tank temperature, the CO2 emissions rate has an increasing trend. Finally, there is a considerable amount of exergy destroyed by the vapor generator in both optimal and base operating conditions.