Pyrolysis and Gasification of Coals by Use of Rapid Heating Method (I)

Abstract

Eight kinds of coals were pyrolyzed and gasified simultaneously by use of a rapid heating method in nitrogen, steam or CO2 atmosphere. Coal particles (1.0mm in diameter) enclosed in a platinum mesh basket were dropped into the reactor which had been heated to a desired temperature (750, 800 or 850°C), and were heated rapidly at the rate of ca. 1600°C/min to reach the final gasification temperature in about 30 seconds. The amount of the evolved gas (AEG) and the decrease in the mass of coal (DMC) in the course of the experiment were measured in detail. First this experiment was performed in a nitrogen atmosphere, the pressure of which was kept at 1, 2. 5, 5, 10 or 20atm, to obtain the AEG and the DMC owing to the pyrolysis. Then the same experiment was performed in a steam or in a CO2 atmosphere. In this experiment the pyrolysis and the gasification of the coal proceeds simultaneously. The AEG and the DMC owing to the gasification were estimated by subtracting the AEG and the DMC owing to the pyrolysis from those obtained in the latter experiment. The gasification rate was found to be nearly proportional to the pore surface area of the unreacted sample. Then the gasification rate was formulated by use of Bhatia and Perlmutters' model in which the change in pore surface area was taken into account. By use of this model the initial gasification rates were easily estimated. The validity of the model was experimentally verified. It was also clarified that the gasification rate increases little when the steam pressure exceeds 1 atm.