International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

This article presents the thermodynamic analysis of a 17.5 MW gross electric geothermal power plant based on binary cycle technology with isobutane. The geothermal power plant comprises two separate closed loops: the geothermal fluid flows in one loop and the Organic Rankine Cycle (ORC) fluid flows in the second loop. The geothermal fluid is extracted from a depth of 2500-3000 m with a temperature of 170 °C and a pressure of 25 bar. Two production wells supply geothermal fluid (brine and steam) with a high fraction of noncondensable gases (NCG). A separator extracts NCG from the geothermal fluid. Isobutane is preheated and evaporated before entering the ORC turbine with a temperature of 133 °C and a pressure of 28 bar, where expands to the condenser pressure of 4 bar. Electricity is generated by a 17.5 MW axial ORC turbine and additionally by a 1.5 MW NCG turbine. The analysis revealed that the configuration without NCG turbine achieves a net efficiency of 12.73% and a net electric power of 13.68 MW while the configuration with NCG turbine achieves a net efficiency of 14.04% and a net electric power of 15.16 MW but with much higher CO2 emissions into the atmosphere.

This paper investigates the performance of post-combustion carbon capture and storage (PCCS) for pulverized coal-fired power plants. The PCCS units comprises CO2 absorption by 30 wt% monoethanolamine (MEA) solution and CO2 compression at 150 bar for permanent storage or enhanced oil recovery. The specific CO2 emissions per unit of generated electricity is 733 kgCO2/MWh in the reference power plant without PCCS while the power plant with integrated PCCS achieve specific emissions lower than 100 kgCO2/MWh, assuming a carbon capture rate of 90%. However, PCCS technology needs substantial amounts of thermal energy for absorbent regeneration and electricity for carbon capture, CO2 compression as well as for the operation of other parasitic electricity consumers. The PCCS energy requirements vastly affect the overall power plant performance. The reference coal-fired supercritical power plant (without PCCS) achieves a net efficiency of 45.1%. On the other hand, the PCCS integrated power plant achieves a net efficiency of 34.6%, a 10.5%-pts net efficiency loss over the reference scenario, when the PCCS specific energy demand is 3.5 MJth/kgCO2 for absorbent regeneration, 0.35 MJel/kgCO2 for CO2 compression and 0.15 MJel/kgCO2 for carbon capture and cooling water pumps. The corresponding electricity output penalty caused by the PCCS unit is 352 kWhel/kgCO2. PCCS technology shows promising potential for decarbonization of the power industry, but further development is necessary to improve its reliability, cost-effectiveness and to diminish its impact on the power plant performance.