Thermo-economic evaluation of various bottoming ORCs for geothermal power plant, determination of optimum cycle for Sabalan power plant exhaust

Thermo-Economic analysis was applied to four different arrangements of Organic Rankine Cycle, using dry organic fluid as working fluid. These cycles were designed to use the geothermal outlet of the Sabalan flash cycle as a heat source. Evaluations were made for the proposed systems to determine the effects of important operating parameters such as turbine inlet pressure, condenser temperature, pinch point temperature and mass flow rate of geofluid on energy and exergy efficiencies, as well as total production cost. Moreover, objective functions of this parametric study were to maximize energy and exergy efficiency levels and to minimize the total production cost. Optimal values of operating parameters were determined by EES optimization using the "variable metric" searching method and defining bounds for each variable as constraints. Among cycles, the maximum energy and exergy efficiency of 20.57% and 63.72% were calculated in the IHE-ORC. The obtained results from the cost optimization, revealed that the lowest energy production cost and the lowest total energy cost were calculated to be related to the R-ORC (25.1 $/GJ) and B-ORC (2.47 M$/year), respectively. The main aim of this study was to use of Fuzzy TOPSIS as Multi-Criteria Decision Making (MCDM) technique to rank cycles based on problem criteria of thermodynamic and economic performance. These criteria include: energy efficiency (N1), exergy efficiency (N2), net power output (N3), production cost (N4) and total cost rate (N5). The method of Interval Shannon's Entropy was used to determine weight values of the criteria automatically. Thus multi-criteria analysis showed that the IHE-ORC was the best system in Sabalan. Additionally, the Basic, Regenerative and Dual fluid ORC were ranked second, third and fourth respectively.