Experimental study and modelling of pressurized oxy-coal combustion: Effect of devolatilization conditions on the physical structure and combustion characteristics of char particles

Abstract

Pressurized oxy-coal combustion has been regarded as a promising carbon capture and storage (CCS) technology, and the combustion characteristics of char particles under pressurized oxy-fuel combustion conditions have been extensively investigated. However, most previous studies used the char samples prepared under the atmospheric N2 condition rather than under the pressurized CO2 condition, which may lead to the misunderstanding of the combustion characteristics. In this study, the effects of devolatilization atmosphere and pressure on the physical structure of char particles were experimentally investigated. The char particles produced under different devolatilization conditions were then used for the oxy-char combustion experiments conducted in a fluidized bed with the operating pressure between 0.1 and 0.5 MPa. In view of the limitations of the experiment, an experimental verified particle-scale char combustion model was further used for predicting the char particle’s combustion reactivity and temperature, and the influence of physical structure on the combustion characteristics was analyzed. The results obtained from the experiments demonstrated that higher devolatilization pressure led to larger mean pore sizes and specific surface areas of char particles. The char particles obtained with CO2 atmosphere had larger specific surface areas but smaller mean pore sizes than those obtained with N2 atmosphere. Besides, increasing devolatilization pressure resulted in shorter burnout times of char particles. The simulation results showed that using the char samples prepared under the atmospheric N2 condition for the pressurized oxy-fuel combustion experiments led to the underestimations of char combustion reactivity and peak temperature.