Study On Numerical Simulation Of Pressurized Oxy-fuel Combustion Characteristics And Scale-up Rule Of Fluidized Bed

Pressurized oxy-fuel combustion（POFC）technology can help to zero carbon emission for coal-fired power plants,and have higher net efficiency due to it achieve cascade utilization of system pressure by increasing the combustion pressure.Therefore,the POFC technology has broad industrial application prospects.However,the oxy-fuel combustion fluidized bed system is a complex system in which multiphase flow,mass and heat transfer and multiphase reaction are coupled.Its internal complex gas-solid flow,combustion and heat and mass transfer characteristics are difficult to study thoroughly by experiments.In addition,the influence of operating parameters on flow structure and combustion state are still unclear in the pressurized combustion state and large-scale process of oxy-fuel combustion fluidized bed,which brings challenges to the scale-up design and safe operation of oxy-fuel combustion fluidized bed.The complex flow and combustion process,the insufficiency of experimental research,the scale-up design of the device and the scale-up rule of parameters can be studied by numerical simulation.In this study,a comprehensive three-dimensional numerical model of pressurized oxy-fuel combustion fluidized bed coupled with multiphase flow,heat and mass transfer and chemical reaction was developed based on the Eulerian-Lagrangian framework.A multi-scale pressurized oxy-fuel combustion numerical simulation platform was constructed,which couple gas-solid two-phase flow and oxy-fuel combustion reaction.The influence of key operating parameters on the oxy-fuel combustion process was clarified in this work.The design method and scale-up rule of oxy-fuel circulation fludized bed were proposed to provide the design theory and operation guidance for scale-up design and operation optimization of oxy-fuel combustion fludized bed reactor.Based on the MP-PIC method in the Eulerian-Lagrangian framework and previous researches,a comprehensive three-dimensional numerical model of pressurized oxy-fuel combustion fluidized bed coupled with multiphase flow,heat and mass transfer and chemical reaction was developed.The applicability and accuracy of the model in terms of pressurized oxy-fuel combustion,gas-solid flow and pollutant generation were solved in this model.The three-dimensional numerical models of fluidized beds of different sizes were integrated to build a unified multi-size pressurized oxy-fuel combustion numerical test platform,and the accuracy and progressiveness of the model were demonstrated by the gas-solid flow and pressurized oxy-fuel combustion reaction.Based on the multi-size pressurized oxy-fuel combustion numerical test platform,which established 100 k W_th oxy-fuel circulation combustion fluidized bed,15 k W_th pressurized fluidized bed,and 12 MW_th pilot-scale pressurized circulation fluidized bed,the gas-solid flow,heat and mass transfer and combustion reaction characteristics of fluidized beds under pressurized oxy-fuel combustion has been systematically studied.The influence of key parameters such as combustion pressure and oxy-fuel atmosphere in the oxy-fuel fluidized bed on the oxy-fuel combustion process was clarified.The increasing combustion pressure helped to reduce the emission of CO and NO,improved the combustion efficiency and increased the CO₂ concentration in the flue gas.According to the requirements of this work,a modified correlation based on Wen-Yu correlation was proposed to predict the minimum fluidization velocity of Geldart B particles under high temperature and high pressure.The 150 MW_e and 330 MW_e industrial-scale oxy-fuel circulation fluidized bed systems were designed in this work.The particle motion,temperature distribution and the concentration distribution of gas components during the process of oxy-fuel combustion in the industrial-scale circulation fluidized bed were studied.The numerical simulation of oxy-fuel combustion process in circulation fluidized bed from 0.1 MW_th to 12 MW_th,150 MW_e and 330 MW_e was carried out on the multi-scale numerical simulation platform.The oxy-fuel combustion characteristics of circulation fluidized bed during the scale-up process were studied and compared by simulation results.Considering the factors such as the furnace structure,size,heating surface layout and operating parameters,the design method and scale-up rule of oxy-fuel combustion fluidized bed were summarized and proposed,which provided design and operation guidance for the industrial application of oxy-fuel circulation fluidized bed boilers.According to the proposed design method and scale-up rule of oxy-fuel circulation fluidized bed boiler,a 600 MW_e supercritical carbon dioxide（S-CO₂）power cycle oxy-fuel circulation fluidized bed boiler was designed.The differences in gas-solid flow,heat and mass transfer,and oxy-fuel combustion processes were compared under the S-CO₂ cycle and the steam cycle.The effects of different power cycle modes,oxy-fuel atmosphere and combustion pressure on combustion reaction and gas-solid flow characteristics in industrial circulation fluidized bed were studied.The results showed that the designed industrial-scale S-CO₂ cycle oxy-fuel circulation fluidized bed boiler could enrich the carbon dioxide in the flue gas and reach the design index of the S-CO₂ cycle.The progressiveness of the model and the universality of the scale-up method were further confirmed by the simulation results,which cloud provide the guidance for the design and application of new oxy-fuel combustion fluidized bed technologies in the future.