Comprehensive Analysis of Coal Combustion Characteristics and Kinetic Parameters of Botswana Coal, Morupule, Mmamabula and Mabesekwa Coalfields

Botswana coal found within the Karoo Basin has received little attention primarily due to limited data on its properties. Several previous researches have been conducted using data for South African coal. However, coal is a heterogeneous material with properties varying not only across different geographic sites but also in iso-seams. Thus, it is important to conduct a study on Botswana coal to determine its combustion characteristics and reactivity. Thermogravimetric analysis was used to study thermal decomposition and determine coal kinetic parameters of coals from the Morupule, Mmamabula and Mabesekwa coalfields. Coal samples were subjected to non-isothermal heating at a heating rate of 25 °C/min in an oxygen atmosphere until a maximum temperature of 1000 °C was reached. Different combustion parameters such as combustion temperatures, and maximum combustion rate were determined from thermogravimetric analysis/derivative thermogravimetric curves. Also determined were the five comprehensive combustion indices for further appreciation of the samples’ combustion traits. Furthermore, the samples were classified based on the chemical composition of the ash. Combustion temperatures were found to be 512.93 ± 3.53 °C to 532.571.36 ± °C ignition temperature, 524.431.17 ± °C to 689.40.56 ± °C peak maximum temperature and 662.771.42 ± °C to 749.73 ± 0.86 °C burnout temperature. Basic oxides in ash could be used to establish the similarities between the coal ash samples via principal component analysis. Proximate-ultimate properties were used to characterize the coal samples into high volatile bituminous and lignite coal. Coal kinetics calculated using pseudo-first-order Arrhenius method yielded activation energies between 42.31 and 60.11 kJ mol⁻¹.