Oxy-fuel Combustion Characteristics And The Global Chemistry Mechanism For Methane Diffusion Flame

Oxy-fuel combustion is a major developing technology for solving the global warmingproblem. Meanwhile, the combustion characteristics are quite different from that of aircombustion. So, it is necessary to conduct the theoretical study of the oxy-fuel combustion.Due to the tremendous changes in the gas inlet condition and fuel combustion condition,chemical reaction in the oxyfuel combustion changes greatly. So, for numerical simulationof combustion, the global chemical reaction mechanism under conventional air combustiondoes not adapt very well. Modification and improvement of prediction accuracy for theglobal mechanism under oxy-fuel condition are imperative.As known, differences between oxy-fuel combustion and air combustion are mainlydue to the replacement of N2by CO2. In the present research, the physical and chemicalproperties of CO2are specially focused on. It is found that the thermal characteristics,chemical characteristics, transmission characteristics of CO2will reduce the flametemperature and CO increasing. Moreover, the impact of radiation characteristics onmethane combustion is little.Beside of the great change for the mole fraction of CO2in the oxidant, the O2and H2Oconcentration are also changes a lot. In this paper, the flame cover, temperaturedisctribution and CO emission under different mole fractions of O2and H2O conditions.Under the same O2concentration environment, the flame cover of oxy-fuel combustion isbigger than that of air combustion. Both the changes of temperature, CO concentration aredifferent. It mainly blames the interactive influence of O2, H2O, CO2.The JL, WD and the improved mechanisms, etc are chosen under the oxy-fuelcombustion to be modified. At the same time, due to the sensitivity of the globalmechanism to environment change, dry recirculation of oxy-fuel combustion and highoxygen combustion are considered to distinguish this problem. A half premixed flamemodel is selected to simulate the boiler dry and wet circulation flue gas with methane andoxygen combustion. The heat release, reaction rate under the oxy-fuel dry and wetcirculation combustion are detailed analysed and the global mechanisms are modifiedaccording to that. Finally, the most suitable global mechanisms are got for both wet and dryoxy-fuel combustion conditions. The temperature and species concentrations can wellpredicted by using them. Moreover, it is found that combustion is rapidly burned in highoxygen concentration environment. It is different from the dry and wet circulationcombustion. Therefore, he IFRF pure oxygen experiment data is used to modify the globalmechanisms. Also, the temperature distribution and component distribution are predictedby suitable mechanism for high oxygen environment.