Thermohydrodynamic analysis of the vertical gas wall and reheat gas wall in a 300 MW supercritical CO2 boiler

Abstract

Supercritical CO2 (sCO2) Brayton cycle usually shows high efficiency and also has compact structure, which can be considered as a promising alternative in future coal-fired power plants. However, sCO2 boiler has different structures and configurations compared with the conventional steam boiler, especially for the arrangement of radiative heat transfer surfaces. Proper design of vertical gas wall and reheat gas wall is crucial to the success design of sCO2 boiler. In this study, a thermohydrodynamic model of radiative heat transfer surfaces was developed to predict pressure drops and wall temperature distributions. A sCO2 power cycle calculation model was employed to comprehensively analyze the influences of pressure drops on the thermal efficiency. A 300 MW sCO2 boiler was taken into account as the baseline case and thermohydrodynamic analyses of gas wall and reheat gas wall were carried out. The influences of flow directions and mass fluxes on wall temperature, pressure drops and thermal efficiency were obtained by the present models. Then, optimized structures of radiative heat transfer surfaces were proposed, i.e., vertical downward gas wall with tubes of φ34 × 4 mm and vertical upward reheat gas wall with tubes of φ57 × 6 mm. Accordingly, the net cycle efficiency achieved an optimized value of 50.07% under the conditions that the wall temperatures of radiative heat transfer surfaces did not exceed the allowable temperature.