Novel Matching Strategy for the Coupling of Heat Flux in Furnace Side and CO₂ Temperature in Tube Side to Control the Cooling Wall Temperatures

Required by the supercritical carbon dioxide (sCO₂) coal-fired power cycle, sCO₂ entering a boiler has a high temperature and can cause overheating of tubes. To eliminate the pressure drop penalty effect, the sCO₂ boiler consists of several modules, each having different heat flux received from the furnace side (q) and different CO₂ temperature in the cooling wall tube (T_f). We aim to search for the best matching strategy coupling furnace side and tube side to obtain the lowest temperature of tubes. By theoretically analyzing the wall temperature influenced by q, T_f and a comprehensive thermal resistance C, two matching methods are introduced: the heat flux-temperature matching (HTM) which matches higher q with lower T_f, and the heat flux-heat flux matching (HHM) that matches higher q with higher allowable-heat-flux at the temperature limit of tubes. HTM is a conventional method but HHM is newly proposed here. We show that, if C is identical for different modules, the two methods coincide; otherwise, HHM is recommended. For a sCO₂ boiler driving 1000 MWe power plant, smaller cooling wall temperatures are obtained by HHM than HTM. Based on HHM, the mid-partition wall, heat transfer enhancement, and downward flow are comprehensively used, decreasing the wall temperature significantly.