Exergy and economic analyses of an innovative integrated system for cogeneration of treated biogas and liquid carbon dioxide using absorption–compression refrigeration system and ORC/Kalina power cycles through geothermal energy

Abstract

Nowadays, it is undeniable that applying renewable energy kinds with the approach of maximizing the performance of energy systems owing to the rising trend of energy demand in the world. In this research, an innovative integrated structure for the cogeneration of biomethane (bioCH4) and liquid carbon dioxide (CO2) by unrefined biogas and exhaust fumes from power plants is developed. The cryogenic biogas upgrading process and CO2 capture cycle are used for the treatment of unrefined biogas and the exhaust fumes from the power plants, respectively. The absorption–compression cooling process and organic Rankine/Kalina power units through geothermal energy are used to provide refrigerate and power. The present integrated process generates 0.8434 kg/s bioCH4 and 2.631 kg/s liquid CO2 by receiving 2.368 kg/s untreated biogas, 21.32 kg/s flue gas, and 7922 kW heat flow from geothermal energy. The thermal and total exergy efficiencies of the hybrid system are achieved at 59.94% and 73.10%, respectively. Exergy analysis depicts that the heat exchangers (4043 kW) and distillation columns (1857 kW) have the most exergy destruction in the among of equipment, which is 39.12% of the total system destruction. The heat exchanger network related to the multi-stream exchanger HE16 is extracted by pinch method. The economic assessment illustrates that the return period and the prime cost of the product are equal to 4.45 years and 0.8189 US$/ m3 bio-methane, respectively. The sensitivity investigation illustrates that the total thermal efficiency increases up to 72.50% and geothermal heat duty decreases to 7808 kW with the increase of methane composition in the untreated biogas from 55 mol% to 75 mol%. The return period increases up to 2.235 years and the net annual benefit decrease to 16.73 MMUS$/year when the bio-methane cost decreases from 2.5 US$/m3 to 0.5 US$/m3.