Mechanical Properties and Brittleness Characterization Method of Low-Rank Coal and Its Char Particles under a Uniaxial Compression Test

Abstract

The mechanical properties of low-rank coal and its char particles are of great significance in many energy and chemical process applications. The 2.8–4.0 mm narrow size range irregularly shaped particles of Shenhua sub-bituminous coal and Huolinhe lignite and their 800 °C chars were studied by using a uniaxial compression test. The results showed that their mechanical properties such as effective elastic modulus, crushing force, crushing energy, and tensile stress fitted well with Weibull and logistic distributions. Statistically, the strength of both kinds of coal chars was higher than that of raw coal. The distribution of mechanical parameters of lignite and its char particles was more dispersed and had a wider range of variation. The brittleness index composed of compressive stiffness and breakage energy could well describe the particle failure mode, and the brittleness of sub-bituminous coal was greater than that of lignite. Image-based particle size distribution analysis revealed that samples with higher brittleness and strength would produce less volume of fragments conforming to fractal distribution during the crushing process. This indicates that the crushing process of coal particles with brittleness and high strength is relatively fast and their cracks are not fully developed.