Optimal integration of recompression supercritical CO2 Brayton cycle with main compression intercooling in solar power tower system based on exergoeconomic approach

Abstract

Despite the emerging interest in applying the supercritical CO2 (S-CO2) Brayton cycle to solar power towers (SPTs), its unique characteristics necessitates a specific thermoeconomic consideration in the integration of this cycle in SPT plants to obtain a competitive electricity generation cost. In this work, the exergoeconomic approach is utilized to address the optimal integration of the recompression S-CO2 Brayton cycle with main compression intercooling in the SPT plant. Firstly, exergoeconomic optimization using a genetic algorithm is performed on six crucial variables of S-CO2 Brayton cycle to minimize the total unit exergy cost of the SPT system (cp,tot). The results are then compared with those obtained by thermodynamic optimization aiming at maximal SPT energetic efficiency. Secondly, a sensitivity analysis model is established, the effects of the cost and design conditions of solar components on the optimal S-CO2 cycle integration are investigated with this model. Finally, linear regression models are established to predict the optimal cp,tot under various conditions of solar component capital cost and design with a deviation less than 2%. Results indicate that the optimal cp,tot is reduced by 8.94% according to the exergoeconomic optimization relative to the conventional thermodynamic optimization. The integration of reheating is not justified for the cycle due to the significant decreased temperature change across the primary heat exchanger and the consequent reduction in the exergoeconomic performance of the SPT plant. Sensitivity analysis highlights the effects of cost and design conditions of solar components on the optimal integration of the S-CO2 cycle, and indicates that the optimal cycle layout may degrade from the recompression cycle to the simple recuperating cycle under certain cost and design conditions of solar components.