A comparative thermodynamic analysis of Organic Rankine Cycles (ORC) and kalina cycle for low-grade energy resources

Abstract

This work aims to contribute to the issue of producing electrical power and reducing the emissions of gases into the atmosphere by utilizing low grade energy sources such as solar energy, geothermal energy and the energy that is rejected from industrial processes. The Organic Rankine Cycle (ORC) and Kalina are two cycles used to utilize low-grade energy sources. Each of them differs in the structure and in the working fluids. The organic Rankine cycle uses organic materials as working fluids, such as benzene, R-600a, methanol, propane, R-245f, i-pentane and ammonia while Kalina cycle uses a mixture of ammonia and water as a working fluid. A comparative analysis is implemented to study the thermodynamic performance of the proposed cycles. For the organic cycles, the analysis reveals that benzene and methanol have the best thermodynamic performance compared to the other tested organic fluids. The thermodynamic findings of the organic Rankine cycles are compared with those obtained from the thermodynamic analysis of Kalina cycle of a binary solution of 70% ammonia and 30% water. For instance, the results showed that the methanol and benzene cycles are more efficient than Kalina cycle where the exergy and energy efficiencies of Kalina amounted to 9.41% and 6.224%, while the exergy and energy efficiencies of methanol cycle (ORC) were 18.85% and 12.83%, respectively.