Petrology, physicochemical and thermal analyses of selected cretaceous coals from the Benue Trough Basin in Nigeria

Abstract

Abundant coal resources that were previously neglected due to a crude oil boom need revitalisation and integration into the national electricity mix to address the energy demands of the Nigerian population. Selected coal samples from the Benue Trough sedimentary basin in Nigeria were examined by various techniques, including proximate and ultimate analyses, organic petrography, Fourier transform infrared ray spectroscopy, and thermogravimetric analysis. Based on vitrinite reflectance, the Lafia-Obi (OLB), Garin Maiganga (GMG), Imiegba (IMG), and Okaba (OKB) coals are classified as subbituminous, while the Lamja1 (LMJ1), Lamja2 (LMJ2) and Chikila (CHK) coals are high volatile B bituminous. The Enugu (ENG) coal is on the boundary between subbituminous and high volatile C bituminous. Organic petrographic results indicate vitrinite and fusinite contents steadily increase from the Lower Benue Trough coals to the Upper Benue Trough coals, while semifusinite and total mineral contents follow a reverse pattern. Thermal decomposition occurred in three stages, i.e., drying, devolatilization, and coke formation above 700°C; and the coal reactivity follows the following order, ENG [IMG[IGH[CHK[LMJ[OKB[GMG[LFB. The higher temperatures (above 900°C) are required to decompose the coals for efficient energy recovery. The LMJ1, LMJ2, OLB, CHK, GMG, and OKB coals can be exploited for electricity power generation. However, the Imeagha and Enugu coals are best suitable for both cement and power generation.

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

“…Furthermore, the AKZ and OME samples examined in this study have similar fuel properties with other lignites from Obomkpa, Ihioma, and Ogboligbo (Nyakuma 2019;Nyakuma et al 2019a) and Subbituminous coals such as Owukpa and Garin Maiganga in Nigeria (Ryemshak and Jauro 2013;Nyakuma and Jauro 2016b;Akinyemi et al 2020a). Lignite is an essential fuel source in many countries, where it is utilised for the production of electric power (79%), synthetic natural gas (SNG) (13%), fertilizer (7%), along with heating homes and oil drilling (Lignite Energy Council 2020).…”

“…Typically, the processing and utilisation of coal are hampered by high moisture content. In this study, the moisture content of below 10% observed for all the coal samples are within the acceptable limits for electric power generation or conversion into value-added products (Chukwu et al 2016;Akinyemi et al 2020a). In contrast, the volatile matter (VM) is an important factor for determining not only the coal rank but also its suitability for potential energy recovery from thermal processes such as combustion and pyrolysis (carbonisation) (Speight 2012;Nyakuma 2016).…”

“…However, this requires comprehensive characterisation of the fuel and energy properties of the nation's coal resources, particularly the newly discovered deposits around the country. It is envisaged that the findings will contribute to the existing literature on the geology and geochemistry (Ayinla et al 2017b;Akinyemi et al 2020a), petrology and petrography (Wuyep and Obaje 2012;Ayinla et al 2017a), mineralogy and sedimentology (Ogala et al 2012;Sonibare et al 2013) of selected Nigerian coals in the literature. Other studies have critically examined the physicochemical (Akinyemi et al 2020a), thermal and kinetic properties (Sonibare et al 2005;Nyakuma et al 2016) of selected Nigerian coals.…”

<em></em>Energy Recovery Potential of Obomkpa Coal

“…In addition, the outlined properties of coal provide insights into the thermal degradation behaviour, emissions profile, and potential environmental impact during energy recovery and electricity generation in power plants. However, the data on various Nigeria coals is limited to the geological, geochemical, petrographic, petrologic, sedimentology, and mineralogical properties as reported in the literature (Ayinla et al, 2017;Ogala, 2018;Akinyemi et al, 2020).…”

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

“…Previous studies have examined the source rock potentials (Akande et al 2007), mineralogy (Ogala et al 2012), petrology (Wuyep and Obaje 2012), sedimentology (Sonibare et al 2013), lithostratigraphy (Uzoegbu et al 2013), hydrocarbon potentials (Jauro et al 2014), geology (Ayinla et al 2017b), petrography (Ayinla et al 2017a), and geochemistry (Akinyemi et al 2020a) of selected Nigerian coals in the literature. Other studies have examined the physicochemical (Akinyemi et al 2020a), thermal conversion (Nyakuma et al 2016), major/trace elements (Sonibare et al 2013), and kinetic properties (Sonibare et al 2005) of selected coals from Nigeria. However, there are limited studies that comprehensively examine the fuel, material, and energetic characteristics of Nigerian coals particularly from the Benue trough where there have been numerous discoveries of large deposits in recent times.…”