Thermodynamic and economic analysis of organic Rankine cycle combined with flash cycle and ejector

Abstract

Increasing the net output power of the Organic Rankine Cycle (ORC) can increase the possibility of developing low-medium temperature heat sources. It is equally important to effectively control the system's economy. So, subcritical double-pressure ORC combined with flash cycle and ejector (S-EFDPORC) and transcritical ORC combined with flash cycle and ejector (T-EFDPORC) are proposed in present work. The thermodynamic and economic analyses on five proposed systems within the heat source temperature range of 100 °C–200 °C are conducted. The net output power and levelized energy cost (LEC) are treated as optimization objectives in thermodynamic and economic performance comparisons, respectively. The non-dominated sorting and three multi-objective optimization methods (LINMAP, TOPSIS, and Shannon Entropy) are used to perform the multi-objective optimization. The results show that S-EFDPORC and T-EFDPORC can both effectively improve the net output power compared with subcritical double-pressure ORC (S-DPORC) and transcritical double-pressure ORC (T-DPORC), while subcritical ORC combined with flash cycle and ejector (S-EFORC) can only improve the net output power within a certain temperature range. When the optimization objective is the net output power, compared with S-DPORC and T-DPORC, the growth rate of net output power in S-EFORC is more than 20% when the temperature is below 160 °C. When the temperature of the heat source is below 160 °C or above 180 °C, the growth rates of net output power of S-EFDPORC and T-EFDPORC increase more than 25%. When LEC is treated as optimization objective, compared with S-DPORC and T-DPORC, S-EFORC reduces LEC by more than 10%. S-EFDPORC and T-EFDPORC increase the LEC of the system, and the maximum growth rates of LEC are 30% and 60% respectively, resulting in worse economic performance. With three multi-objective optimization methods, both S-EFDPORC and T-EFDPORC can increase net output power, but their economy will deteriorate at most heat source temperatures. Although S-EFORC increase the net output power when the heat source temperature is below than 177 °C, LEC reduces throughout the heat source temperature range.