Pilot Experiments And Simulation Study On Oxy-fuel Combustion Characteristic And Pollutant Emission Characteristic Of Pulverized Coal

Electric power production from coal-based fossil fuel combustion results in the emission of greenhouse gases which are dominant contributed by CO2. The rapid increasing amount of greenhouse gases exerts profound influence on the global environment, and global warming and climate changes it caused become progressively worse. Public awareness and legislation lead to a series of international cooperative agreements on reduction of greenhouse gas emissions which are represented by Kyoto protocol and the Intergovernmental Panel on Climate change. It also accelerates the development of the technologies on Carbon capture and storage (CCS). Compared with other current possibilities, however, oxy-fuel combustion is the most reliable and economical choice which was characterized by coal burned in pure oxygen and recycled flue gas (O2/RFG) instead of air.Current available research findings show that CO2concentration of exhaust gases is over90%during the process of coal oxy-fuel combustion, so it is possible to utilize and treat it without separation. Furthermore, the expense of pollutant disposal and thermal loss decrease because of the relatively small amount of flue gas volume. However, the flame temperature is lower and its stability is poorer while compared with the combustion process in air atmosphere. The pollutant emission characteristic is different too. But the flame temperature and furnace heat-transfer characteristic is enhanced effectively by adopting advanced burners or by adjusting air distribution. It has great potential on simultaneous removal of multi-pollutant. However, few studies focuses on these aspects such as the mechanism of coal oxy-fuel combustion and pollutant formation characteristics, operation parameters. O2/CO2burner designing, etc. Especially, the research that experimental investigation on pilot-scale or full-scale test facility still seems insufficient in depth and scope before this paper.Thermogravimetric-Infrared Interconnection method (TG-FTIR) was employed in the online measurement of combustion process of three kinds of coal and its char in O2/N2and O2/CO2atmosphere with different proportion of O2. particularly in measurement of CO concentration. Reaction kinetic parameters of the coals were obtained by analyzing the reaction curves and the combustion products under O2/N2and O2/CO2atmosphere, and the corresponding most probability mechanism function was acquired by using two different simulation calculation methods too. The influence of high concentration CO2on the reaction rates of the coals and the formation of pollutants was researched by analyzing the composition of flue gas.The first domestic pilot-scale oxy-fuel combustion test facility was designed and built in this work. The facility was characterized by a0.3MW vertical combustor. A series of combustion experiments have been carried out in this system in air, O2/CO2and O2/RFG atmosphere. The combustion characteristics and temperature fields were comparative analyzed at different oxygen concentration and different flue gase circulation ratio. Optimum operation parameters were determined to obtain the similar flame temperature and heat transfer under air and O2/RFG atmosphere and to gain a ready-to-recovery stream of flue gas. According to the characteristics of O2/CO2recycled combustion, a type of O2/CO2swirl burner was designed by using numerical simulation method combined with experimental approach. It got an insight into the methodology of designing O2/CO2burner. The cold-state experiment was carried out to test the aerodynamic performance of the burner and adjusted the flow expansion angle and the central recirculation region. The combustion tests under air and O2/RFG atmosphere were carried out to examine the performance of the burner in respect of combustion characteristics and pollutant formation characteristics. Studies showed the improved swirl burner has the virtue of operational flexibility and better combustion performances when it was applied to oxy-fuel combustion conditions. It presented important references for future researching and designing of O2/CO2burner.FLUENT was used to simulate the coal combustion process on the pilot test facility. The appropriate flow, combustion and heat transfer model were chosed to obtain the reasonable results which were compared with measured data. The simulation results had a good agreement with the experimental data. This demonstrates that numerical simulation could reflect the real combustion process. FLUENT was used to analyze the combustion process when the operational parameters changed, for example, the circulation ratio. The analytical results can guide the future operation of the experiments. Moreover, FLUENT was useful on determining the best swirl strength and blade fitting angle in designing process of O2/CO2burner.Theoretical analysis and experimental studies of the pollutant formation mechanism during coal oxy-fuel combustion process were conducted on the pilot test facility. The formation and emission mechanism of NOX and SO2was investigated under air and O2/CO2atmosphere. The in-furnace limestone injection technology was conducted to explore the possibilities of NOX and SO2co-capture during O2/CO2recycled coal combustion process. Numerical simulation was carried out to simulate the combustion process under air and O2/CO2atmosphere by using the commercial software FLUENT and CHEMKIN. Simulation results were analyzed to discover the mechanism of pollutant formation and decomposition. A lot of facters (such as temperature, O2concentration, reaction atmosphere, recycling mode) were taken into account to analyze their influences on pollutant emission characteristics. The numerical simulation results and experimental results agree well, and the pollutant emission index of oxy-fuel combustion was significantly lower than AIR condition. In addition, the pollutant removal rate of the improved burner was marked increased.