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.
Highlights
Coal is a biogenic sedimentary rock derived from complex biochemical and metamorphic processes termed coalification in the earth’s crust (Grabner 2014)
The N and S content indicate the conversion of the coals examined could potentially generate hazardous emissions of nitrous (NOx, NHx) and sulphurous (SOx, HxS where x = 1, 2, ..., n) gases during thermal conversion
The thermal conversion of coal and its associated greenhouse gas (GHG) emissions are potentially dangerous to human health, safety, and environment exacerbating climate change and global warming (Reddy 2013)
Summary
Coal is a biogenic sedimentary rock derived from complex biochemical and metamorphic processes termed coalification in the earth’s crust (Grabner 2014). The growing demand for a cheap and reliable supply of electricity has stimulated significant investments in coal-fired power (Tang et al 2018) in developing countries such as India, China, and South Africa (Hancox 2016). Vietnam, Cambodia, and Mozambique have begun to invest heavily in coal-fired electricity generation due to the growing energy demands required to catalyse socio-economic growth and infrastructural development (Baruya 2017). Over the years, such investments have ensured a steady supply of low-cost and consistent energy (IEA 2018), which have stimulated fiscal growth, infrastructural development, and poverty alleviation (IEA-CCC 2020)
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