High intensity combustion of coal

A vertical tunnel furnace has been used to burn coal and char under conditions of intensemixing obtained by using impinging jet streams at the top of the furnace. Combustion in all cases was rapid, with 99% burn-out in about 300 msec. for the coals and 1200 msec. for the char. Burning times in other furnaces are typically reported as 1 to 2 sec. In all cases, the burn-out curves were well predicted by a simple mixing model with diffusional kinetics. The predicted curves were insensitive to temperature. The difference between the coal and char was primarily the rapid loss of mass by the coal (Q-factor 1.8) due to pyrolysis, so that there was relatively greater solid mass at higher density to be burned-out in the case of the char. Comparison with predictions from other tested kinetic schemes indicates that the chemical kinetics must be so substantially enhanced by the firing conditions that the chemical reaction resistance becomes unimportant compared with the diffusional resistance. The firing condition identified as that most likely to be the source of the rate of enhancement is the rate of heating, at about 10 6 K/S compared with the more usual value of about 10 4 K/S in slower burning flames.