EFFECT OF PRESSURE ON THE DEVOLATILIZATION AND SWELLING BEHAVIOR OF A SOFTENING COAL DURING RAPID HEATING

Pyrolysis of an Illinois no. 6 bituminous coal was studied under rapid heating conditions in two entrained-flow furnaces at pressures from 0.1 to 3.8 MPa N2. Increasing the pyrolysis pressure slowed the global release rates of volatiles, lowered the asymptotic volatiles yields and promoted secondary reactions of the volatiles which reduced the tar yield and changed the gas yield. The extent of swelling and the volatiles transport mechanism were found to be sensitive to the applied N2 pressure. At 0.1 MPa N2, insignificant swelling occurred and the particle morphologies indicated that bubble transport had not occurred. The coal swelled most extensively with large blow holes observed on the particle surfaces when pyrolysed at 0.8 MPa, an indication that volatiles transport occurred by bubble movement. Further increase in pressure reduced the swelling and the number and size of the holes formed on the particle surfaces. The observed swelling behaviour was attributed to the combined effect of fluidity development and swelling resistance which was a function of the applied pressure. The swelling behaviour at elevated pressure could not be predicted from data taken at atmospheric pressure.