Supercritical Carbon Dioxide Coal-fired Boiler Characteristics Study Of Heat Transfer And Combustion Based On Supercritical Carbon Dioxide Power Cycle

High efficiency,cleanness,low carbon and flexibility are the major needs of the current coal-fired power generation system.The traditional power generation system based on the steam Rankine cycle is limited by the characteristics of steam and materials resistant to 700°C,which makes it difficult to further improve the system efficiency.Supercritical carbon dioxide（S-CO₂）coal-fired power generation technology is a new generation of transformational technology,which has become the important research direction of efficient and clean coal power in China.This paper mainly studies the following aspects:Firstly,system models and analysis methods of S-CO₂ coal-fired power generation plants were established,and the accuracy of unit models was verified.And the key parameters related to coal-fired boiler under different times of reheating were analyzed to obtain the influence on cycle efficiency,which laid the foundation for the subsequent research on system integration and optimization of S-CO₂ coal-fired power generation system.Secondly,on the issues of full temperature zone utilization difficulty and cycle heat sink loss,integration models of S-CO₂ coal-fired power generation system were constructed and evaluation parameter of system integration was proposed.The results show that the exergy efficiencies of S-CO₂ internal-splitting and top-bottom-circulating coal-fired power generation systems increase by 8.6%and 8.4%compared with the ultra-supercritical steam unit of 605^oC/603^oC/27.4 MPa.And exergy efficiencies of S-CO₂ double-path recompression coal-fired cogeneration unit increase by 9.8%and 1.0%compared with that of S-CO₂ recompressed cogeneration unit under 0%and 100%heating conditions,when the T-250/300-23.5 steam cogeneration unit is taken as the prototype.Thirdly,the flow and heat transfer model of S-CO₂ was constructed for analyzing the effects of the CO₂ purity,boiler grades,furnace configurations and heating surface layouts on the flow and heat transfer characteristics in the S-CO₂ cooling wall.The results are as follows:S-CO₂ boiler of high-capacity grade is not suitable for the singly small-diameter heating surface layout.The double-furnace configuration is conducive to reducing boiler pressure drop and temperature difference between the outer wall and working fluid.The split flow arrangement will lead to a certain proportion of increase in the outer wall temperature,while the pressure drop of the working fluid decreases exponentially.Then,the combustion and heat transfer characteristics of S-CO₂ boiler were studied,and the key issues of S-CO₂ boiler coupled with S-CO₂ cycle were explored.The results are as follows:although the expansion of boiler size and adoption of large proportion flue gas recirculation can effectively reduce boiler heat duty,expansion of boiler size is not conducive to ignition,stable combustion and peak regulation.And large proportion flue gas recirculation can shorten the residence time of pulverized coal and reduce furnace burnout rate.The lower furnace size of"T"typed boiler does not change to ensure the high efficient combustion of the main combustion zone,and double furnace configuration can increase the heating surface area,which makes the heat duty distribution uniform.Lastly,the combustion and heat transfer thermodynamic calculation method of the S-CO₂ boiler adapted for multi-zone furnace was studied and established.Thermodynamic calculation shows that S-CO₂"T-typed symmetrical flow double furnace"boiler configuration can effectively reduce furnace heat duty and make wall temperature distribution more uniform,which can effectively ensure the safe operation of 1000 MW S-CO₂ boiler and provide a basis for the design of S-CO₂ boiler.