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Subcritical organic ranking cycle based geothermal power plant thermodynamic and economic analysis

This paper is focused both on the thermodynamic and economic analysis of an Organic Rankine cycle based geothermal power plant. The analysis is applied to a case study of the geothermal field Rečica near the town Karlovac. Simple cycle configuration of the Organic Rankine cycles was applied. Thermodynamic and economic performance of an Organic Rankine cycle geothermal system using 8 working fluids (R134a, isobutane, R245fa, R601, R601a, R290, R1234yf, and R1234ze(E)) with different critical temperatures are analyzed. The thermodynamic analysis is performed on the basis of the analysis of influence of the operation conditions, such as evaporation and condensation temperatures and pressures, and evaporator and condenser pinch point temperature difference, on the cycle characteristics such as net power output, and plant irreversibility. The economic analysis is performed on the basis of relationship between the net power output and the total cost of equipment used in the Organic Rankine cycle. Mathematical models are defined for proposed Organic Rankine geothermal power plant, and the analysis is performed by using the software package Engineering Equation Solver. The analysis reveals that the working fluids, n- pentane and Isopentane, show the best economic performances, regardless the evaporation temperatures, while the working fluid R1234yf and R290 have the best thermodynamic performances. In addition, each analysed working fluid has its corresponding economically optimal condensation temperature (and condensation pressure). Economically optimal pinch point temperature difference of evaporator has different values, depending on the working fluid, while pinch point temperature difference of condenser has similar values for all analysed working fluids. Analysis results demonstrate that the subcritical Organic Rankine Cycle geothermal power plant represents a promising option for electricity production application.

Organic Rankine Cycle, ORC, geothermal power generation, thermodynamic analysis, economic analysis

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