Modification of KCS (Kalina Cycle System) 34g by replacing throttle valve with single-screw expander

Recovery of the energy loss caused by throttling plays an important role in improving the performance of a cycle. Based on the original Kalina Cycle System 34g, two redesigned cycles, which have different placement of single-screw expanders used to replace the throttle valve, are proposed in this paper. The thermodynamic performance of two redesigned cycles is analyzed and compared with the original Kalina Cycle System 34g. The results show that the thermodynamic performance of each redesigned cycle is better than that of the original Kalina Cycle System 34g and the IⅠ-redesigned cycle performs best. At a low and moderate evaporation pressure, there is an optimal ammonia-water concentration and it increases with the increase of evaporation pressure. With the concentration increases of ammonia-water, the performance advantage of the redesigned cycle system over the original Kalina Cycle System 34g gradually decreases. When the ammonia-water concentration is much lower than the optimal concentration, the single-screw expander produces much work and plays a positive role in net work output of cycle system. The highest cycle exergy efficiency of 54.14% can be obtained in the II-redesigned cycle when the evaporation pressure is 3.0MPa and ammonia-water concentration is 0.85.