Insight into the combustion effect of the high-reactivity char particle on the low-reactivity char particle in a hot O2/CO2 atmosphere

Abstract

Based on the pseudo-steady-state approach, the combustion effect of high-reactivity char (i.e., HR-char) on low-reactivity char (i.e., LR-char) is investigated numerically in a hot O2/CO2 atmosphere under two arrangements (LR-LR case: the upstream and downstream particles are LR-char, HR-LR case: the upstream particle is HR-char and the downstream particle is LR-char). This paper is aimed to study the influence of oxygen concentration (from 2% to 30%) and ambient temperature (1300 K, 1400 K, and 1500 K) on the combustion effect under the condition with dominated oxidation reaction and weak gasification reaction, and explain the mechanism in aspects of the temperature, specie concentration, and reaction rate. The numerical results are carefully validated against experimental data published in the literature. The results show that under these studied ambient temperatures, the char-O2 oxidation-reduction brings a more pronounced effect than the char-CO2 gasification enhancement for char consumption owning to the dominant role of the char oxidation reaction. The upstream HR-char particle combustion under the HR-LR case produces a higher temperature, lower oxygen, and higher CO2 atmosphere ahead of the downstream char than under the LR-LR case, which significantly inhibits the downstream LR-char particle combustion. In addition, lower oxygen concentration or higher ambient temperature decreases the difference in temperature, oxygen, and CO2 between the HR-LR and LR-LR cases ahead of the downstream char, resulting in the lower difference in the downstream LR-char oxidation consumption rate between the HR-LR and LR-LR case. Consequently, the weaker combustion inhibitive effect of the high-reactivity char on the low-reactivity char is observed. The findings shed light on the interaction effects observed during blended coal combustion in O2/CO2 mixtures.