Physicochemical, Mineralogy, and Thermo-Kinetic Characterisation of Newly Discovered Nigerian Coals under Pyrolysis and Combustion Conditions

Abstract

In this study, the physicochemical, microstructural, mineralogical, thermal, and kinetic properties of three (3) newly discovered coals from Akunza (AKZ), Ome (OME), and Shiga (SHG) in Nigeria were examined for potential energy recovery. Physicochemical analysis revealed high combustible but low levels of polluting elements. The higher heating values (HHV) ranged from 18.65 MJ/kg (AKZ) to 26.59 MJ/kg (SHG). Microstructure and mineralogical analyses revealed particles with a rough texture, surfaces, and glassy lustre, which could be ascribed to metals, quartz, and kaolinite minerals. The major elements (C, O, Si, and Al), along with minor elements (Ca, Cu, Fe, K, Mg, S, and Ti) detected are associated with clays, salts, or the porphyrin constituents of coal. Thermal analysis showed mass loss (M L ) ranges from 30.51% – 87.57% and residual mass (R M ) from 12.44% – 69.49% under combustion (oxidative) and pyrolysis (non-oxidative) TGA conditions due to thermal degradation of organic matter, vitrinite, inertinite and liptinite macerals. Kinetic analysis revealed that the coal samples are highly reactive under the non-isothermal oxidative and non-oxidative conditions based on the Coats-Redfern Model. The activation energy ( E a ) ranged from 23.81 kJ/mol – 89.56 kJ/mol whereas the pre-exponential factor ( k o ) ranged from 6.77×10 -04 min -1 – 1.72×10 03 min -1 under pyrolysis and combustion conditions. In conclusion, the coals are practical feedstocks for either industrial applications or energy recovery.

Thermal Oxidative and Non-Oxidative Degradation Behaviour of Afuze Coal

“…Likewise, the lower ML but higher RM observed during non-oxidative degradation of AFZ could be ascribed to the largely endothermic nature of the process, as reported in the literature (Agroskin et al, 1972;Hanrot et al, 1994). Similar findings were reported for various ranks of coals from Nigeria (Sonibare et al, 2005;Chukwu et al, 2016;Nyakuma et al, 2021).…”

“…%) based on charge balance using the EDX software (AZTEC Oxford Instruments, UK). A detailed description of the SEM/EDX analyser and its operating conditions are presented in the literature (Nyakuma et al, 2021).…”

“…In this study, the temperature profile characteristics (TPCs) derived from the TG plots for AFZ degradation were; ignition temperature (Ti), midpoint temperature (Tm), offset temperature (Tf), mass loss (ML, %) and residual mass (RM, %), whereas the maximum drying peak (Td) and peak decomposition temperature (Tx) were deduced from the DTG plots. A detailed description of the procedures and guidelines for determining the TPCs are outlined in the literature (Nyakuma et al, 2021).…”

“…The loss of mass of AFZ could be ascribed to the thermal degradation of the maceral components (namely; vitrinite, inertinite, and liptinite) of the coal sample. The composition of vitrinites, liptinites, and inertinites typically range from 50% to 90%, 5%-10%, and 50%-70% based on source, rank, and classification of the coals (Speight, 2012;Nyakuma et al, 2021). Therefore, the mass loss of AFZ could be attributed to the thermal degradation of the maceral, lignitic and cellulosic plant materials (or organic fractions) or components present in the coal structure (Hayatsu et al, 1986;Košina and Heppner, 1984;Landais et al, 1989;Wu et al, 2017).…”

Demineralization and Characterization of Coal Deposit Found in Maiganga, Akko Local Government, Gombe State, Nigeria

“…Coal is a sedimentary rock composed of three types of materials: organic carbonaceous matter (macerals), non-combustible minerals from ash, and fluids (Behera et al, 2018). It is a fossil fuel that is used in electricity generation, firing kiln for cement production, iron and steel production, raw material for numerous applications (Ryemshak and Jauro, 2013;Nyakuma et al, 2021) and many other applications, however, there are high levels of ash and sulfur in raw coal (Meshram et al, 2015). But low ash content is needed to increase handling and burning capacity, decrease handling costs, and improves combustion and boiler efficiency while low sulfur is required since high sulfur content is associated with acid mine drainage, chimney corrosion and other equipment such as air heaters (Usman et al, 2019).…”