(574a) Pressurized Coal Pyrolysis and CO2 Gasification at High Initial Heating Rates

An understanding of the effects of pressure and initial heating rates on coal pyrolysis is critical to modeling gasification because the char structure can have a significant effect on apparent reaction rates. Previous studies at atmospheric pressure have shown that coal swelling reaches a maximum at heating rates of ~10⁴ K/s (the operating regime of conventional drop-tube reactors) and then decreases to an asymptotic minimum at ~10⁵ K/s (the operating regime of flat-flame burners). It is believed that the swelling behavior observed at 10⁵ K/s is more representative of industrial gasifiers, which operate at ~10⁶ K/s. The BYU High Pressure Flat-Flame Burner (HPFFB) has been rebuilt to be more suitable for gasification studies at heating rates of ~10⁵ K/s and pressures of 2.5 atm - 15 atm. The HPFFB has been used to conduct pyrolysis and gasification experiments on three bituminous coals and a subbituminous coal. Swelling of bituminous coals at high initial heating rates (10⁵ K/s) was found to exceed swelling from similar experiments at atmospheric pressure, but the measured swelling ratios were low compared to values reported from pressurized experiments conducted at lower heating rates (10⁴ K/s). Subbituminous coals produced highly porous chars with high reactivities. Swelling information from these tests has been combined with published data to develop a swelling correlation with heating rate dependence for CFD applications. Mass release information gained from these tests has been used to fit kinetic coefficients in a gasification model.