Experimental investigation into the influence of the oxygen concentration on a pulverized coal swirl flame in oxy-fuel atmosphere

One of the significant advantages of oxy-fuel combustion is the added degree of freedom, given by the possibility of choosing the O-2 partial pressure in the oxidizer within a reasonable range, allowing the operation of such combustion systems to be fine-tuned for higher efficiency. However, the influence of the O-2 content in the oxidizer on flame structure and characteristic parameters (e.g.: flame temperature, chemical composition) is not fully understood. Therefore investigations were carried out to unveil these effects in a coal flame. For this purpose a swirl burner specifically designed for oxy-fuel combustion was utilized in a pilot scale test furnace (40 kW(th)). Thereby concentration of oxygen in the oxidizer was varied between 23 and 33 vol% while keeping the total volume flows (inlet velocities) constant. To investigate flame structures, a narrow-band radiation signal was captured using a CCD-camera with an image intensifier and an optical filter. Besides the flame structure, local particle temperatures and gas compositions were examined. The local gas composition was analyzed using an oil-tempered suction probe connected to an FTIR-(Fourier-Transform-Infrared-) spectrometer. Additionally, particle temperatures were estimated from analysis of emitted radiation in the visible part of the spectrum. It was found that the flame structure remains the same for all flames. However the O-2 concentration (stoichiometry) influences the local intensity of the combustion. Further, differences in the local gas composition are observed and maximum particle temperatures were found to increase linearly with increasing O-2 content in the oxidizer.