EFFECT OF PRESSURE ON OXIDATION RATE OF MILLIMETER-SIZED CHAR PARTICLES

Mass losses and burnout times of large (0.1, 0.2 g) char particles at pressures of 101-760 kPa were measured in a newly designed high-pressure reactor. A cantilever balance measured instantaneous particle mass and an optical pyrometer measured particle temperature continuously. The process was also videotaped. Sixty-two combustion experiments were conducted with a bituminous coal and a iignite. The reactor air temperature was similar to 900 or 1200 K and the air flow Reynolds number was varied by a factor of two. Coal particles were placed in a platinum-wire basket inside the reactor at the end of the balance beam. An ash layer accumulated around the particles and receded as the char was consumed. In all tests a linear decrease in cube root of char mass with time was observed during oxidation until near the end of burnout, Changes in air velocity had little effect on oxidation time; increasing gas temperature or increasing pressure from 101 to 507kPa reduced oxidation times by about one-quarter. Further increase in pressure caused no further reduction in burnout time. Pairs of nearly equally sized particles of coal had oxidation times similar to those of single particles with the same total mass.