The effect of particle size on the strength parameters of German brown coal and its chars

An experimental study on the compressive strength and Young's modulus of German brown coal from Schleenhain mine was carried out in order to determine the non-empirical mechanical properties required for the development of close-to-reality models of the stress-induced fragmentation of coal particles. A series of uniaxial compression tests was conducted on irregularly shaped coal specimens with diameters in the range of 0.8-6.3 mm, which are typical for industrial-scale coal utilization processes. According to the test results, the compressive strength and Young's modulus of coal particles significantly increase as the specimen size decrease. The data obtained show reasonable agreement with results published in the literature. Additionally, the mechanical properties of chars produced by coal pyrolysis at temperatures in the range of 400-1000 °C were measured in order to quantify the influence of the thermal treatment on mechanical properties. The compressive strength and Young's modulus of the chars increase to a maximum at a thermal treatment temperature of about 800 °C and then decrease as the temperature further increases.