Low-temperature geothermal energy utilization improvement based on the addition of a second vapor-liquid separator in Kalina cycle systems

Due to the low thermal-to-power conversion efficiency of low-temperature geothermal energy, low-temperature geothermal energy driven Kalina cycle system (KCS) 11, 34, and 34g were designed and have been widely studied. Two reconstructed systems installing a second vapor-liquid separator are proposed for each of the above three Kalina cycle systems in this paper. In the A-reconstructed system, the second separator is positioned between the original separator and regenerator (regenerator-1 in KCS 34). In the B-reconstructed system, the second separator is placed downstream of the original absorber. Thermodynamic performance comparison of these systems shows that the two reconstructed systems of KCS 34 and KCS 34g are superior to their respective original systems. The B-reconstructed system of KCS 11 only outperforms the original system at high evaporating pressures and with a high ammonia mass concentration. The B-reconstructed system performs better when used for KCS 34, while the A-reconstructed system performs better when used for KCS 34g, and the two reconstructed systems perform close to each other when used for KCS 11. Comparing three original cycles and their respective two reconstructed cycles, it can be observed that KCS 34 and its two reconstructed cycles exhibit the best performance, KCS 34g and its reconstructed systems exhibit the worst, while have a wider ammonia mass concentration range. Evaporators contribute the largest exergy loss in all systems. The highest thermal efficiencies of 10.99 %, 12.65 %, and 10.92 % and the highest exergy efficiencies of 54.38 %, 62.59 %, and 54.03 % can be obtained at an evaporating pressure of 3 MPa, corresponding to B-reconstructed system of KCS 11, B-reconstructed system of KCS 34, and A-reconstructed system of KCS 34g, respectively.