OCR Text |
Show 1 INTRODUCTION The combustion of pulverized coal in industrial burners typically occurs as an air deficient jet of suspended coal particles entraining secondary air from the surroundings. The fuel is initially heated in an environment with insufficient oxygen to react completely with the carbon and hydrogen, and the gases devolatized from the coal reflect this incomplete chemistry. It has been hypothesized that the environment surrounding the coal particle during the early stages of pyrolysis may have a significant effect on the form in which the coal-nitrogen takes. Hence, the mixing process possibly may be used to advantage to minimize the formation of certain pollutant species. The pulverized coal flame cannot be considered a true diffusion flame in the sense associated with natural gas jets; but neither is it premixed nor perfectly-stirred. The experimentalist cannot rely on a single configuration to model such a complex process. As a result, many different approaches have been used to gain an understanding of pulverized coal pyrolysis and combustion, including flat-flame burners [1,2, 3], tunnel reactors [4,5,6], and electrically heated metal grids [7,8]. The opposed-flow diffusion flame was first used to study coal combustion by Chin and Sawyer [9] in an experiment with a compressed column of pulverized particles. Graves and Wendt [10,11] have demonstrated that this flow configuration is also suitable for pulverized coal-cloud/oxygen flames. The main advantage of an opposed-flow burner arrangement is that the environment surrounding the coal particles can be carefully controlled while at the same time subjecting the fuel to conditions closely akin to actual furnace flames. Graves and Wendt [11] concluded that an opposed-flow diffusion flame (OFDF) can be viewed as represent- |