Performance of Kalina cycle with single-screw expander for low-temperature geothermal energy utilization

Abstract

Recovering the expansion work by replacing throttle valve with expander may improve the performance of a thermodynamic cycle. Based on Kalina Cycle System 11, 34, and 34 g, different redesigned cycles with single-screw expander are proposed in this paper. I-redesigned cycle has a single-screw expander which replaces the throttle valve and is located between absorber and regenerator. In II-redesigned cycle, the single-screw expander is located between regenerator and separator, and the original throttle valves is removed. The thermodynamic performance of two redesigned cycles is analyzed and compared with their corresponding original cycle. It can be found that two redesigned cycles perform better than their corresponding original cycle system. II-redesigned cycle is better than I-redesigned cycle. When comparing the redesigned cycle of the same type, the performance ranking from good to bad is Kalina Cycle System 34, 11, and 34 g. II-redesigned cycle for Kalina Cycle System 34, 11 and 34 g can reach the maximum thermal efficiency of 11.44%, 11.14%, and 10.85% respectively at the evaporation pressure of 3.0 MPa. It can be seen that the series connection of regenerator and evaporator is better than the parallel connection and the increase in the number of regenerators can improve the thermodynamic performance of the cycle.