科研之友
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摘要
By the growing usage of geothermal energy as an alternative approach to produce useful work such as electricity, the emission of global greenhouse gases could be reduced because of its environmentally friendly. In this paper, the thermodynamic and economic performances of three systems which contain a basic Organic Rankine Cycle (ORC), a Regenerative Organic Rankine Cycle (RORC) and a Two-Stage Evaporation Organic Rankine Cycle (TSEORC) are investigated in order to generate electrical power from geothermal sources. For operating the considered cycles, three types of pure organic working fluids including dry (R600a, R601a), wet (R152a and R134a) and isentropic (R11 and R123) ones are selected. Firstly, according to thermodynamic aspect, Peng Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state are used to determine thermodynamic properties of mentioned working fluids and geothermal water, respectively. Furthermore, the operating parameters involving evaporator and regenerative temperatures, degree of superheat and pinch point temperature difference in evaporator are optimized with three optimization methods. Objective functions are exergy efficiency, Specific Investment Cost (SIC) and a combination of exergy and SIC for thermodynamic, economic and exergoeconomic optimizations. The amount of boundary conditions constituting of heat source inlet temperature, heat sink inlet temperature, heat source inlet pressure, heat sink inlet pressure temperature of condenser, pinch point temperature in condenser and heat source mass flow rate are 423.14 (K), 293.15 (K), 5 (bar), 2 (bar), 308 (K), 5 (K) and 50 (kg/s) respectively. Optimizations results show that among all considered operating parameters, degree of superheat ranged between 0 and 20 is the most effective parameter which is almost obtained at lower, upper and in the middle range of optimization bounds in the thermodynamic, economic and exergoeconomic investigations respectively. Secondly, from economic view point, three economic indicators: Levelized Cost Of Electricity (LCOE), Return On Investment (ROI) and Payback Period (PBP) are utilized so as to focus on the economic performance of three mentioned ORC configurations based on exergoeconomic results for twenty countries with geothermal resources as well as different cost of electricity production and tax rates. The results indicate that Australia has the maximum amount of ROI making up a bit more than 100% and minimum amount of PBP accounting for lower than four years when R123 is applied as the working fluid in TSEORC system. Also, the maximum and minimum values of LCOE are obtained in basic ORC-R134a and RORC-R123 (0.1474 and 0.0493 respectively). In addition, the investigation of impact of operating parameters on economic indicators for Iran illustrate that the ROI value dramatically rise by increasing the evaporator temperature and degree of superheat. In contrast, pinch point temperature difference leads to a decline in the amount of ROI. This note should be taken in to account that ROI and PBP show the reverse results.
- 出版日期2018-1
