Thermo-economic comparison of Kalina and CO2 transcritical power cycle for low temperature geothermal sources in China

Abstract

Over 3200 geothermal spots have been discovered in China. With purpose of evaluating the performance of enhanced geothermal systems, a thermal-economic comparative analysis is conducted between CO2 transcritical power cycle (CTPC) and Kalina cycle driven by the low temperature geothermal water. The two cycles are compared through six indicators: net power output, thermal efficiency, exergy efficiency, total heat exchanger area, cost per net power (CPP) and the percentages that heat exchangers occupied in the total cost (PHC). Moreover, the single indicator is optimized by means of genetic algorithm (GA) and the optimum value of each indictor is compared between the CTPC and Kalina cycle. Geothermal water with the same temperature and mass flow rate is chosen as the heat source for both the systems. The results show that the Kalina cycle presents a higher net power output and thermal efficiency while the exergy efficiency of the Kalina cycle is less than that of the CTPC. In addition, the Kalina cycle presents a lower CPP and PHC which represent a better economic performance than the CTPC. Therefore, the adoption of the Kalina cycle may be reasonable in the low-temperature geothermal sources due to the better thermo-economic performance in contrast to the CTPC.