Comparative analysis on off-design performance of a novel parallel dual-pressure Kalina cycle for low-grade heat utilization

Abstract In this paper, a novel parallel dual-pressure Kalina cycle system is presented to utilize the low-grade geothermal energy. In order to highlight the performance of the proposed cycle, the comparison of parallel dual-pressure Kalina cycle system and the basic Kalina cycle system is conducted and set at the same boundary conditions. The maximal net power output of cycle is considered as the single-objective function based on particle swarm optimization algorithm. The exergy analysis and economic cost for both cycles are investigated at design conditions. Furthermore, as operating at off-design conditions, the variation ranges of geothermal energy mass flux and inlet temperature are 7.5–14 kg/s and 136–150 °C, respectively. The sliding pressure regulation strategy is applied to response to the variations of geothermal energy parameters. The two-levels evaporation pressures in the parallel dual-pressure Kalina cycle are adjusted to remain the invariable temperature difference between geothermal energy inlet temperature of evaporators and the corresponding turbine inlet temperature. The results show that, at design conditions, the maximal net power output of parallel dual-pressure Kalina cycle and basic Kalina cycle is 329.62KW and 274.94KW, the corresponding exergy efficiency is 44.52% and 33.39%. Besides, the condenser contributes to the largest exergy destruction ratio in parallel dual-pressure Kalina cycle and basic Kalina cycle, which are 33.96% and 44.94% of overall exergy destruction, respectively. According to the off-design performance investigation, it is shown that the higher geothermal energy mass flux and inlet temperature are in favor of the larger net power output for both cycles. The thermodynamic evaluation shows that the proposed parallel dual-pressure Kalina cycle exhibits a more excellent performance in terms of net power output and exergy efficiency than basic Kalina cycle.