Energy, exergy, and cost comparison of Goswami cycle and cascade organic Rankine cycle/absorption chiller system for geothermal application

Abstract

Combined cooling and power production can improve the overall efficiency of a geothermal energy conversion system. Most systems have complex structures, characterized by a large number of devices resulting in a greater heat loss, low energy conversion efficiency and higher costs. This paper presents a geothermal system based on a modified Goswami cycle, aimed to produce cooling and power simultaneously in one loop. The proposed system has a simple structure with few components, and the heat rejected to the environment by the rectifier is internally recovered to preheat the strong solution, involving lower heat losses and higher conversion efficiencies. In order to investigate the exergy destructions and losses, the overall performances, and the total absolute component cost, the modeling of the proposed system is established in detail. The Goswami system performance is evaluated for the conditions of an actual application, the geothermal reservoir of Torre Alfina (Italy), and the results compared with those of a cascade system based on organic Rankine cycle coupled with a water/lithium bromide absorption chiller. Results show that for the same power output produced in both systems, the best scenario is the Goswami cycle system with an exergy efficiency of 35.53% against 32.77% of the cascade system case. In addition, the component cost analysis showed that the highest total absolute component cost is obtained for the cascade system case with a total of 14.6 M€, while the Goswami case showed a lower value with a total of 11.8 M€.