NUMERICAL COMPARISON OF HEAT TRANSFER CHARACTERISTICS BETWEEN HEATING FULL-TUBE AND HALF-TUBE IN AN S-CO2 COAL-FIRED BOILER

The aim of the present work is to reveal the heat transfer characteristics of S-CO2 tube and flue gas in the S-CO2 coal-fired boiler. According to structural features of wall heaters of the S-CO2 boiler, the wall heaters are modeled as the full-tube/half-tube. The heat transfer characteristics of full-tube and half-tube are compared by the numerical methods. For different coal-fired flue gas temperatures, the distributions linking the wall temperature, the bulk temperature, the bulk velocity, and the local heat transfer coefficient along the tube were obtained. The results show that the wall temperature of the S-CO2 tube is approximately 50 K higher than that of the S-H2O tube, and the temperature difference between the outer wall temperature and the bulk temperature is about 50-100 K. Besides, the local heat coefficient of the full-tube is about 1.7 times that of the half-tube. It would further enrich the heat transfer mechanism of the unique characteristics of S-CO2 tube above pseudocritical temperature and provide a theoretical basis for the optimal design and safety operation of S-CO2 coal-fired applications.