The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically.In order to increase the accuracy in the prediction of flame temperature and ignition position,eddy dissipation concept(EDC)model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter.Simulation was conducted under six oxidant stream conditions with different O2/N2/CO2molar ratios:21/79/0,30/70/0,50/50/0,21/0/79,30/0/70 and 50/0/50.Results showed that O2enrichment in the primary oxidant stream is in favor of combustion stabilization,acceleration of ignition and increase of maximum flame temperature,while the full substitution of N2by CO2in the oxidant stream delays ignition and decreases the maximum flame temperature.However,the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream.Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30%O2and 70%CO2in the oxidant stream,indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one.The swirl burner with a specially designed preheating chamber can increase flame temperature,accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion.Also,qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain O2enrichment and oxy-coal combustion conditions against the air-coal combustion.
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