Comparison of Flame Stability Under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame

The flame characteristics of a pilot-scale swirl burner for air and oxy-fuel combustion of pulverized coal are investigated. The local burner air (or oxygen) ratio lambda and the oxygen concentration have been systematically varied. The investigated flames were characterized recording UV emissions originating from OH* chemiluminescence indicating the reaction zone in the gas phase, measuring the axial and tangential velocities using an laser Doppler velocimetry (LDV) system and analyzing the composition of the flue gas. A change of the flame structure was revealed from the conducted measurement: the "regular" flame for the investigated burner is characterized by a cone-shaped swirling combustion zone with a distinct inner recirculation zone. Reducing the oxidizer flows through the burner leads to a breakdown of the inner recirculation zone and a significant change of the flame pattern. This change was identified by the LDV measurements as well as from the chemiluminescence images, and it was found to be closely related to the momentum flow through the burner into the main combustion zone.