The evolution of char surface area along pulverized coal combustion

Pulverized (36-75 mu m) samples from three coals were fed to a drop tube furnace (DTF) operated at 1300 degrees C under different O-2/N-2 mixtures. From the obtained set of char samples, one low burnout char from each parent coal was re-entered into the DTF under varying gas compositions. The aim of this work is to monitor the textural changes of the chars along pulverized coal combustion, with special care to isolate the variations of surface area attributable to char combustion from those arising from early char/oxygen interactions during the pyrolysis stage. The burnout, helium density, and CO2 and BET surface areas of the combusted and refired chars were determined, and the patterns of variation of the textural parameters were established for these two types of unburned material. It was found that the presence of oxygen in the vicinity of pyrolyzing coal particles affected the development of surface area of the newly formed chars and that this effect was both rank- and maceral-dependent.