Intrinsic gasification kinetics of coal chars generated in a high-pressure, high-temperature flow reactor

An understanding of the intrinsic gasification rates of chars generated at high temperatures and elevated pressures is crucial for the design and optimization of gasifiers. Therefore, a widely used Pittsburgh No. 8 coal was partially gasified in a CO₂/N₂ atmosphere at 1300 °C at a range of pressures (3.4, 6.2, 11.3, 15.5, and 21.7 bar) in a high-pressure, high-temperature flow reactor to generate char. The intrinsic reaction rate of those chars with CO₂ was obtained using a high-pressure thermogravimetric analyzer. The kinetic parameters were obtained using an n^th-order model. The results show that the intrinsic reaction rate was less affected by the char generation pressure, while the apparent reaction rate was primarily dependent on the surface area evolution during the gasification process. The apparent reactivity reached a maximum for the char generated at 6.2 bar and decreased with further increases in pressure. Among the kinetic parameters, the activation energies were not affected over the range of char generation pressures (3.4–21.7 bar), while the pre-exponential factors were within similar orders of magnitude. The order of reaction was determined by varying the CO₂ partial pressure. The order of reaction decreased with increasing char generation pressure and closely followed the surface area at that conversion in most cases.