In-situ investigation of coal particle fragmentation induced by thermal stress and numerical analysis of the main influencing factors.

Particle fragmentation influences thermochemical coal conversion processes in different ways, which is of great significance for process design and control. Different mechanisms are proposed for fragmentation characterization, but direct and substantial optical evidence supporting these theories is rarely reported. In the present study, the fragmentation process of two anthracites with low volatiles is investigated in-situ with the aid of an optical system. The observed fragmentation phenomenon confirms that the thermal stress is the main driving force for the fragmentation of the investigated anthracite particles. Together with a model analysis, a fragmentation pattern different from previous reports is proposed. The tensile stress causes the particles to fragment from the center. Fine particles are produced by multiple tensile failure rather than by the spalling of particles' outer shell caused by compressive stress. Based on the model, the impact of various process- and particle-related factors on the maximum thermal tensile stress and its appearance time are quantitatively evaluated, which significantly reduces the required time and effort in comparison to experimental analysis of the fragmentation. This study provides direct visual evidence and numerical validation of the fragmentation mechanism, which can be utilized to predict the coal particle behavior and the resulting particle size distribution. • Particle fragmentation of anthracites is investigated in a drop-tube reactor. • Fragmentation is monitored in-situ with a high-speed optical monitoring system. • A preferred fragmentation mechanism and pattern is ascertained. • Fine particles are caused by multiple tensile breakup rather than spalling. • Impact of various factors on the thermal stress is modeled and evaluated. [ABSTRACT FROM AUTHOR]