The influence of gasification reactions on char consumption under oxy-combustion conditions: Effects of particle trajectory and conversion

Abstract

The effects of char gasification reactions during oxy-combustion of pulverized coal are dependent on the boundary conditions and are not fully understood. In this study, a CFD simulation of lignite coal combustion in a pilot-scale oxyfuel test facility with a 29% oxygen feed are used to determine representative regions (pre-flame, flame, and post-flame) in which char particles are burned. Coal particle trajectories are analyzed to extract representative time-dependent boundary conditions to which char particles are exposed as they traverse the furnace. These realistic boundary conditions are then employed in a detailed, single particle char consumption model to evaluate the influence of the local environment and char conversion on the importance of the gasification reactions to the overall rate of char consumption, using apparent initial reaction rates of char oxidation and gasification in-line with the literature estimates. In the pre-flame region, gasification reactions are of little importance; in the flame region char gasification reactions should not be neglected; while in the post-flame regions, the impact of gasification depends on the particle’s trajectory. When gasification is non-negligible, its significance depends on the particular char’s physical, and especially kinetic, properties. As conversion proceeds, gasification reactions, when significant, can alter the location within the particle where char consumption occurs, further affecting the rate of char consumption. Their impact can induce structural changes that may accelerate conversion via peripheral fragmentation.