Study on the combustion characteristics of a two-dimensional particle group for coal char and petroleum coke particles

Abstract

The combustion characteristics of particle group are different from the combustion of a single particle, owing to the physicochemical effect and interaction among particles. The current work investigated the effect of the increasing particle concentration on the group combustion with the consideration of temperature and solid fuel type, including bituminous coal char and petroleum coke. A visual imaging technology was used to record and analyze the combustion process and group evolution of burning particles in the two-dimensional scale. Results showed that a delayed combustion phenomenon was found for both coal char and petroleum coke with the increasing particle concentration in a group. The burnout time increased in multiples from the combustion of a single particle, dispersed particles to a particle group. The total carbon conversion and combustion rate of the particle group significantly decreased with the increasing particle concentration in the group, especially for the bituminous char of a high reactivity. With increasing the combustion temperature, the burnout time was additionally prolonged from 20% to 80% between the internal and external particles in the particle group. The theoretical analysis with the consideration of Stefan flow, gas diffusion, and gas-solid reaction was used to propose the delayed combustion mechanism, and the results matched well with the experimental data. The increasing particle concentration in the group, which consumed the oxygen, generated the advance effect of Stefan flow, and hindered the oxygen diffusion, was the key factor to delay the group combustion. For the group combustion of petroleum coke with low reactivity, although the surface reaction was the controlling step, the reactant gas diffusion inside the group could not be ignored. For the group combustion of coal char particle with high reactivity, the diffusion of the reactant gas in the group was the dominant controlling step for the delayed combustion behavior.