Performance Analysis And Optimization Of Cooling Wall Tube For Supercritical CO₂ Coal-Fired Power Plants

Coal-fired power generation is an important guarantee for China’s power supply.It is urgent to develop efficient and clean coal-fired power systems with low emission of pollutants and CO2 and high efficiency through theoretical innovation.Supercritical CO2(S-CO2)cycle is a promising alternative to steam based Rankine cycle for coal-fired power plant.S-CO2 cycle has a series of advantages such as high efficiency and low cost at low pressure,which may be a breakthrough of the design theory for conventional coal-fired power systems.The cooling walls are key component of supercritical CO2 coal-fired power plants.The safety of cooling walls in a S-CO2 boiler is a challenging issue.Compared with traditional water walls,the convective heat transfer coefficient of S-CO2 is lower and the working temperature is higher,leading to non-uniform circumferential temperature distribution,which affects the performance of the cooling walls.Supported by the National Natural Science Foundation of China,the researches mainly including the performance analysis and optimization of the cooling walls,have been carried out in this dissertation.1.A three-dimensional multiphysical coupling model,including energy,fluid flow,mass conservation governing equations,and static structure calculation,is proposed to analyze the performances of the cooling wall tubes in a S-CO2 boiler.The distributions of temperature,stress,and deformation of cooling wall tubes are determined numerically.2.A novel cooling wall-tube structure is proposed to improve thermal-structural performance via changing eccentricity,which matches the heat flux level to its thermal resistance.The traditional and novel structures are compared.The critical operating parameters affecting heat transfer performance are discussed.The novel structure can reduce maximum temperature and circumferential temperature difference effectively.Furthermore,the structure will facilitate the safety and economics of the tube.3.To break through the key designing technology for the cooling wall of an S-CO2 boiler,the mechanisms of heat transfer and fluid dynamics in the parallel pipes are considered in developing a novel multiphysics coupling model thus achieving a suitable simulation method coupling heat transfer,fluid dynamics and thermal stress.Multi-objective optimization and operation parameter matching are carried out from aspects such as the structure and layout of the cooling wall,operating parameters,thermal physical properties of S-CO2.The optimal design of the cooling wall in the S-CO2 boiler is implemented to innovate the configuration and optimization design method of the cooling wall in the S-CO2 boiler.