IMPROVED DIAMETER, VELOCITY, AND TEMPERATURE-MEASUREMENTS FOR CHAR PARTICLES IN DROP-TUBE REACTORS

Coal combustion researchers have typically used the average temperatur e and residence time of a burning particle cloud to determine the high -temperature reactivity of coals and chars. These average values, howe ver, cannot account for particle-to-particle variations or their possi ble causes. Researchers at Sandia National Laboratories developed a py rometry technique to simultaneously measure the temperature, velocity, and diameter of individual char particles burning in a transparent-wa ll flat-flame facility. This work reports two significant advances rel ative to the optical pyrometry technique. First, pyrometer modificatio ns together with a new analysis technique now permit the particle prop erties to be measured for smaller/cooler particles. Second, the modifi ed pyrometer has been implemented in two heated-wall drop-tube reactor s, rather than transparent-wall, flat-flame burners. This is significa nt because drop-tube reactors allow greater flexibility/control of gas environments and operating pressures during char oxidation. Glowing r eactor walls, however, present some unique challenges for these optica l measurements. Means of overcoming these challenges are discussed, an d reliable in situ measurement of particle temperatures, velocities, a nd diameters is verified. The results of measurements made in these dr op-tube reactors, both for calibration tests and actual oxidation test s with Spherocarb and a Utah bituminous coal char, are also presented.