Keywords: finite time thermodynamics, irreversible CHP plants, two–stage intercooled CHP plants, regenerative reheated CHP plants, closed CHP plants, Brayton CHP plants, exergy output rate, exergy efficiency, power to heat ratio, combined heat and power, heat recovery, exergy performance
Exergy performance analyses of an irreversible two–stage intercooled regenerative reheated closed Brayton CHP plant
A combined heat and power (CHP) plant model composed of an irreversible constant– temperature heat reservoirs two–stage intercooled regenerative reheated closed Brayton cycle and a heat recovery device is proposed using finite time thermodynamics. By taking dimensionless exergy output rate and exergy efficiency as the objectives, the performance of the plant is investigated. The two cases with fixed and variable total pressure ratio are discussed. By means of detailed numerical calculations, the two intercooling pressure ratios, the two reheating pressure ratios and the total pressure ratio are optimised respectively, and the corresponding power to heat ratios are obtained. The effects of design parameters (such as compressors and turbines efficiencies, pressure drop losses, regeneration, intercooling and reheating degrees, etc.) on the exergy performances of the CHP plant are analysed. It is found that both dimensionless exergy output rate and exergy efficiency have double–maxima with respect to consumer–side temperature.