Performance analysis of the Kalina Cycle System 34 with the addition of a second separator

• A modified cycle based on KCS 34 with a second separator was proposed. • The modified cycle attains a highest thermal efficiency of 13.54%. • The modified cycle attains a highest exergy efficiency of 50.27%. • The modified cycle demonstrates a maximum efficiency improvement of 1.333%. Based on the Kalina Cycle System (KCS) 34, this article proposes a modified Kalina Cycle System (MKCS), which incorporates a second separator and a second expander. The cycle’s performance was evaluated under low-grade heat sources and a standard working fluid mass flow rate in terms of net power output, thermal efficiency, exergy efficiency, and economic performance at different evaporator outlet temperatures and pressures. The results indicate that, in comparison with the original Kalina Cycle System (OKCS), the MKCS consistently delivers superior performance. Under the optimal operating conditions of a basic ammonia-water concentration of 0.65, an evaporator outlet temperature of 413.15 K, an evaporating pressure of 4.0 MPa, and an intermediate pressure of 1.32 MPa—corresponding to the geometric mean of the evaporating and condensing pressures—the net power output increased by 2.20% and reached 83.0 kW, while the thermal efficiency and the exergy efficiency rose to 11.51% and 43.44%, respectively. At other evaporator outlet temperatures, the maximum performance improvements are 1.84%, 2.12%, and 1.95%, respectively.