Key issues and practical design for cooling wall of supercritical carbon dioxide coal-fired boiler

摘要

When supercritical carbon dioxide (S-CO2) Brayton cycle is used for coal-fired power plants, the significantly increased mass flow rate and endothermic temperature of S-CO2 boiler leads to the over-temperature and high pressure drop on the cooling wall (CW). This paper presents a mathematic flow and heat transfer model of S-CO2 in combustion chamber CW. The results show that reducing the tube diameter can effectively reduce the temperature difference in cooling wall and reduce the effect of high heat flux on the temperature difference. The pressure drop decreases exponentially with the increase of tube diameter and boiler expansion factor. Increasing partial flow numbers will decrease the boiler pressure drop and improve system cycle efficiency in spite of increasing the temperature difference of CW. The change of flow direction has no obvious effect on temperature distribution of CW and has opposite effect on gravity and buoyancy force. Three boiler layout strategies, including partial flow strategy, flow symmetry strategy and boiler local expansion strategy are proposed in order to coordinate the pressure drop and uneven temperature distribution, which can not only decrease boiler heat exchange surface temperature difference but also reduce the boiler pressure drop to prevent the over-temperature and improve system performance. (C) 2019 Elsevier Ltd. All rights reserved.