Effects of pressure on coal pyrolysis and char morphology

A better understanding of high-pressure coal pyrolysis is needed to design advanced coal gasification combined-cycle systems. High-temperature, high-heating-rate, and high-pressure pyrolysis experiments were conducted on three bituminous coals and a lignite, to more fully understand the effects of pressure on resultant char properties, A flat-flame burner was designed and used inside a high-pressure drop-tube reactor to provide a high-temperature, high-heating-rate environment that is representative of industrial processes. Chars were prepared at four different pressures, ranging from 0.85 atm to 15 atm. The measured total volatiles yields compared well with predictions of the Chemical Percolation Devolatilization (CPD) model. The physical properties of the char samples were analyzed, including swelling ratio, morphology, and internal surface areas. Chars produced at high pressure were determined to be in the early stage of foam structure evolution and have a higher porosity but denser skeleton. The internal surface areas of chars decreases as the pressure increases, which contributes mostly to the lower intrinsic reactivity of chars that are formed at high pressure.