Effect of oxy-fuel combustion on flame characteristics of low calorific value coal gases in a small burner and combustor

Currently, using oxygen instead of air in a combustion process is being widely discussed as an option to reduce fuel consumption and utilization of oxygen is expected to improve the thermal efficiency and combustion performances. The main goal of this study is to determine the combustion behaviors of low calorific value coal gases under oxy-fuel combustion conditions and to compare with the results of air-fuel combustion conditions in the existing burner and the combustor. The coal-derived low calorific value coal gases (syngases) have been properly oxy-combusted using the existing burner within the present study. Temperature and emission values have been experimentally measured and investigated on different axial and radial positions by using thermocouples and a flue gas analyzer throughout the combustion chamber. All experiments have been performed under a thermal power of 10 kW and an excess oxygen coefficient of lambda = 1.2 combustion conditions for both turbulator distances of 7 cm and 2 cm. The burner walls were overheated due to using of pure oxygen instead of air during combustion when the turbulator position of the burner was further to the burner exit (7 cm). Because of that, the turbulator position of the burner has also been changed as a small modification to alleviate overheating of the burner walls and hence, it was drawn near to the burner exit (2 cm). Therefore, it can be said that the burner either can be used with modification or the burner material should be changed to be withstood higher temperature levels. It is consequently concluded that the flame that has emerged under combustion condition with 2 cm of the turbulator distance is wider and smoother than that of the flame showing up under combustion condition with 7 cm of the turbulator distance. CO, CO2 and NOX emissions have also been determined on different axial and radial positions. According to the measurements, it has been demonstrated that CO2 and NOX decrease while CO increase on the axial measurements as the turbulator distance is draw near to the burner exit. When the oxy-fuel combustion results are compared with the air-fuel combustion results, it can be concluded that the oxy-fuel combustion performances of the coal-derived syngases are better than that of the air-fuel combustion, which corresponds to an increment of about 22% in their flame temperatures. However, it has been obtained that oxy-fuel NOX values are not lower than that of the air-fuel values due to the higher flame temperatures. It has been revealed that oxy-fuel CO emission values are lower and oxy-fuel CO2 emission values are higher (approximately 30%) than values of the air-fuel combustion due to the absence of nitrogen in the oxidizer.