Ignition and Combustion of a Single Coal Particle under Pressurized Oxy-Coal Combustion Environments: A Modified Transient Coal Ignition Model

Pressurized oxy-coal combustion (POCC) is a next-generation oxy-coal combustion (OCC) technology for CO2 capture, and its high-pressure environments result in significantly different ignition behaviors. A modified transient ignition model of a single coal particle under POCC was developed by coupling CPD devolatilization, ARM gas combustion, and L-H-3 char combustion models applicable to pressurized conditions, with sufficient validation against experimental data under both atmospheric and pressurized conditions. Then, the coal particle ignition characteristics at pressures of 1–20 atm were numerically investigated at ambient gas temperatures Tg of 1473–1873K, oxygen concentrations XO2 of 10–40%, and particle sizes dp of 76.5–200 μm under O2/N2 and O2/CO2 environments. The numerical results revealed that elevating pressure prolonged the ignition delay time (τi) within the pressure range of 1–20 atm in both O2/N2 and O2/CO2 environments, with the ignition inhibition effect diminishing at higher pressures, which is primarily due to the inhibited coal devolatilization and gas-phase diffusion. Increasing Tg and XO2 both offset the negative effect of the pressure on τi, while increasing dp further delays τi at high pressures. The sensitivity analyses indicated that pressure had a relatively small effect on τi, though it affected the high-temperature volatile yield (Q-factor) of coal particles significantly, compared to Tg, XO2, and dp. Furthermore, the dimensionless parameters ητi and ηvol were proposed to quantify the variation of τi and Q-factor caused by the elevated pressure. The elevating pressure invariably prolonged τi under different operating conditions, with the greatest effect under low Tg, low XO2, and small dp conditions of 1473 K, 10% O2, and 76.5 μm. For dp = 76.5 μm, the Q-factor always decreased with pressure, especially at high Tg (1873K) and high XO2 (40% O2). These findings provide valuable insights into the coal particle ignition characteristics under POCC environments.