Significance of coal properties on the caking degree of coarse coal particles mined at Limpopo Province, Republic of South Africa

In this paper, a comprehensive coal property (chemical, mineralogical, physical, and petrographic) study was conducted using a caking coal from South Africa, density cuts and pyrolyzed samples to understand the % coal caking during pyrolysis. Coal particles of 4, 8, and 10 mm in diameters from the coal feed and its density cuts were pyrolyzed at 0.87, 15, and 30 bar and 450°C and 550°C in the North-West University Fischer assay oven under N₂ for 15 min. The results for the samples show that the effects of particle size, temperature, pressure, and vitrinite and inorganic element carboxylate contents on the % caking of coal particles contribute significantly during pyrolysis. The mechanistic model shows that float coal particles soften, swell, melt, and coalesce during the pyrolysis tests. This model also shows that kaolinite and inertinite in the sink and <1.9 g/cm³ float particles fragment to non-caking particles. The statistical model using Free-Swelling Index, petrographic, and electron microprobe results achieves the highest coefficient of R² = 0.99. These models can be used to predict coal caking degree and the non-caking of coal particles during pyrolysis.