THERMODYNAMIC OPTIMIZATION OF RECUPERATED S-CO_2 BRAYTON CYCLES FOR SOLAR TOWER APPLICATIONS

摘要

Supercritical carbon dioxide (S-CO_2) Brayton cycle represents significant advantages in solar tower application. Various configurations of S-CO_2 Brayton cycle employing recuperation, recompression, intercooling and reheating have been investigated. The thermodynamic performance of each cycle configuration is optimized by using Genetic Algorithm in which the maximum cycle efficiency is defined as the objective function. The optimization process is comprehensive, i.e., the decision variables such as temperature and pressure of turbines, compressors, re-heaters, inter-coolers, and the pinch point temperature difference are optimized simultaneously. The recompression inlet temperature and mass flow fraction are also optimized along with other decision variables where that is the case. The main limiting factors in the optimization process are maximum cycle temperature, minimum heat rejection temperature, and pinch point temperature difference. The maximum cycle pressure is also a limiting factor in all studied cases except the simple recuperated cycle. The optimized cycle efficiency can vary from 55.77% to 62.02% where the highest value is obtained for the recompression recuperated cycle with reheating and intercooling. The optimization is based on thermodynamic analysis only, even though decision making for practical systems should be based on thermo-economic optimization.