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 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 ranged from 18.65 MJ/kg (AKZ) to 26.59 MJ/kg (SHG). Microstructure and mineralogical analyses revealed particles with a rough texture, surface, 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 (ML) ranges from 30.51% to 87.57% and residual mass (RM) from 12.44% to 69.49% under combustion (oxidative) and pyrolysis (non-oxidative) TGA conditions due to thermal degradation of organic matter and macerals (vitrinite, inertinite and liptinite). Kinetic analysis revealed the coals are highly reactive under the oxidative and non-oxidative conditions based on the Coats–Redfern Model. The activation energy (Ea) ranged from 23.81 to 89.56 kJ/mol, whereas the pre-exponential factor (ko) was from 6.77 × 10–4/min to 1.72 × 103/min under pyrolysis and combustion conditions. In conclusion, the coals are practical feedstocks for either energy recovery or industrial applications.

Thermodynamic Analysis of In Situ Underground Pyrolysis of Tar-Rich Coal: Primary Reactions

“…The first peak of C 6 H 6 generation is usually a result of the degradation and cleavage of coal macromolecular structures. In contrast, the second peak is the product of condensation reactions between aromatic and hydrogenated aromatic structures in coal. , It was reported that with the increase of pyrolysis temperature, the content of monocyclic aromatic hydrocarbons in the tar fraction decreased, while the range of polycyclic aromatic hydrocarbons and their derivatives kept increasing . The heavy-fraction content increased, mainly because the higher pyrolysis temperature caused the dehydrogenation and recondensation of aromatic hydrocarbons in the tar; related scholars found the same pattern in their experiments, and as the final temperature of pyrolysis increased from 550 to 750 °C, the content of benzene substances decreased.…”

“… 23 , 54 It was reported that with the increase of pyrolysis temperature, the content of monocyclic aromatic hydrocarbons in the tar fraction decreased, while the range of polycyclic aromatic hydrocarbons and their derivatives kept increasing. 55 The heavy-fraction content increased, mainly because the higher pyrolysis temperature caused the dehydrogenation and recondensation of aromatic hydrocarbons in the tar; related scholars found the same pattern in their experiments, and as the final temperature of pyrolysis increased from 550 to 750 °C, the content of benzene substances decreased. Some even disappeared with an increase in temperature, while the naphthalene substances increased with an increase in temperature.…”

Three-Dimensional Physical Similarity Simulation Experiments for a Transparent Shaft Coal Pocket Wall in Coal Mines

“… 33 Nyakuma et al through microstructure and mineralogical analyses revealed particles with a rough texture, surface, and glassy luster. 34 These issues should be clarified to reveal the deformation, damage, and failure mechanism of the shaft coal pocket wall. The effective means to investigate these issues was a three-dimensional physical similarity simulation test, which further revealed the deformation, damage, and failure mechanism of the shaft wall.…”

“…Hood and Yalcin et al studied about the organic fraction of the coals; Guatame and Rincón analyzed the coal facies changes in the depositional conditions of the sequence in the Eastern Cordillera of Colombia . Nyakuma et al through microstructure and mineralogical analyses revealed particles with a rough texture, surface, and glassy luster . These issues should be clarified to reveal the deformation, damage, and failure mechanism of the shaft coal pocket wall.…”