Statistical Analysis of Coal Production in Nigeria (1990-2020)
CHAPTER ONE
Objectives of the study
The main objective of the study is to examine the statistical analysis of coal production in Nigeria (1990-2020).
The specific objectives of the study are to:
- To carry out proximate, ultimate and ash composition analyses of the coal samples.
- The determination of calorific value of the coal samples.
- To compare results of the above analyses with reference values of coal properties for power generation in order to determine the suitability of the coal samples for power generation.
CHAPTER TWO
LITERATURE REVIEW
Previous Research on Nigerian Coals
Olaleye (2003) investigated some Nigerian coals and showed that the relatively low ash and moisture contents, low sulphur content and medium to high calorific value, make Nigerian coals compare favourably with other sub-bituminous coals in coal-producing countries of the world, thereby making them a good export commodity. They are superior as regards ease of ignition, combustion characteristics and freedom from clinker. The coals burn with a long flame and require large combustion space. They are acceptable boiler fuels if used in suitable appliances such as chain grate stokes or as pulverized fuel. Nigerian coals are suitable as energy fuel for electricity generation for the abandoned Oji Power Station in Enugu State and other proposed power stations at Kogi, Benue, Anambra and Delta States. With the current deregulation of power generation in the country, necessitated by the lack of sufficient power generation by the Power Holding Company of Nigeria (PHCN), Independent Power Producers stand better opportunities.
Kibiya (2012) collected and analysed five (5) coal samples from Lafia-Obi (Nasarawa State), Okaba (Kogi State), Lamja (Adamawa State), Okpara and Onyeama (Enugu State) to determine their properties and classify them by rank using proximate analysis. Auto-ignition temperatures, reactivity and activation energies of the various coal samples were also determined. Results obtained showed that Lafia-Obi coal could be ranked the highest as bituminous (low volatile) coal. Okpara and Onyeama coalsboth were both bituminous A coals, while Okaba coal was found to be sub-bituminous B coal. Lamja coal was found to be a lignite A coal. Findings also revealed a dependence of coal density, reactivity and activation energies on coal type and particle size. The study concluded that Lafia-Obi, Okpara and Onyeama coals may be used for power generation. Lamja and Okaba coals were not recommended for power generation because of their low calorific values.
Laudan (2008) analysed coal samples from Enugu State (Okpara West Area, Okpara West Bank and Onyeama) and Gombe State (Doho and Gamawa) to determine their physical properties and to classify them by rank using proximate analysis. An electric furnace fitted with a 3kW heating element capable of generating heat to a temperature of 900oC was constructed and used to determine the auto-ignition temperatures, reactivity and activation energies of the various coal samples. Findings revealed that the reactivity and activation energies of the various coal samples depend on the coal type, source and particle size. While for some coals, the reactivity and activation energies increase with decrease in particle size (Okpara West Bank coal), in others, reactivity and activation energies decrease with decrease in particle size (Onyeama, Okpara West Area and Doho coals). However, in all cases, reactivity increases with increase in temperature.
Jauro and Chukwu (2011) investigated three Nigerian coals (Onyeama, Lafia-Obi and Gairin Maiganga) to determine their suitability in developing formed coke for use as blast furnace coke. Parameters that were usedincluded the shatter index, expressed as percentage stability and friability and mecum index. The highest cumulative percentage stability and the lowest cumulative percentage friability were observed in Lafia-Obi with values of 67.54% and 32.46%, followed by Onyeama with 66.92% and 33.08% and then Garin Maiganga with 55.04% and 44.96% respectively. Medium and low temperature carbonisation of Onyeama and Lafia-Obi coal samples gave an improved and satisfactory percentage stability and friability for semi-cokes.
CHAPTER THREE
MATERIALS AND METHODS
Coal Samples preparation
The coal samples used were sourced from Maiganga (Northern Benue trough), Okaba (Central Benue trough) and Enugu (Anambra Basin) respectively. All samples were initially crushed and pulverized. The coal samples were sieved to a particle size of 150 micrometer in preparation for further analysis.
Proximate and ultimate analysis
The moisture, volatile matter and ash contents were determined based on American Society for Testing and Materials D3172-13. The fixed carbon (dry basis) in the coal samples was obtained by subtracting the percentages of moisture, volatile matter and ash from 100. The ultimate analysis (sulphur, nitrogen, carbon and hydrogen) were also based on D3176-15. The High heating value (HHV) of coal was calculated using the correlation by Sami et al. (2015).
HHV = 0.3491C + 1.1783H + 0.1005S – 0.1034O – 0.0151N – 0.0211A (MJ/Kg) (1)
where; C = carbon, H = hydrogen, S = sulphur, O = oxygen N = nitrogen and A = ash
Thermal and chemical characterization
Thermal Characterization: The thermal degradation of the coal samples was performed using thermogravimetric analyser (Perkin ElmerTGA-4000). The samples were analyzed in pure nitrogen environment with a nitrogen flow rate of 20 ml/min, pressure of about 2.5 bars and a constant heating rate at 10oC/min for a temperature range of 23oC to 950oC. Five (5) gram of the coal samples each of particle size less than 150µm was accurately weighed and placed on to a clean crucible. The coal sample was heated until a constant weight was observed. The Pyris manager software was used to plot the degradation profile.
CHAPTER FOUR
RESULTS AND DISCUSSION
Proximate and ultimate analyses
Table 1 displays the result obtained from the proximate analysis carried out on the three (3) coal samples (Okaba, Maiganga and Enugu samples).
Moisture content: The result of moisture content of coal showed that the moisture contents ranges from 5.17 % to 6.200 %. Enugu coal has the highest moisture content (6.2%) followed by Okaba coal (5.44%) and then Maiganga coal sample (5.17%) respectively. These values revealed that the three coal samples are of low moisture content. The low values obtained are within the range considered for good coking coals. Low moisture content is an indication that the coal is of a high rank and good quality, possibly the rank of bituminous grade. Low moisture content also represents a significant improvement in coal’s quality because moisture affects the calorific value, the concentration of other constituents, decreases system capacity and increases operational cost. The moisture content of coal depends on the degree of maturity. Therefore Maiganga coal sample with the lowest moisture content (5.171%) may be the most matured, followed by Okaba and then Enugu coal samples.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
Conclusion
The different geographical locations as well as mode of occurrence coal constituents play a major role in coal formation. Hence three coals were selected from Northern Benue trough, Central Benue trough and Anambra Basin. The coal samples were first characterized and then combusted to ash samples. The thermal profiles suggest that Enugu has higher thermal stability and lower calorific value than Maiganga and Okaba coals. The ash chemistry indices used to predict the performance of the coal samples prior to combustion shows that silica ratio indicated that Enugu coal high slagging tendency, B/A suggest that all the coals were found to be less than 0.6 indicating low slagging potential. The ash chemistry suggests that Maiganga coal has low slagging potential while Enugu coal has severe slagging potential.
Recommendations
From the conclusion of the International Energy Agency that developing economies have a particularly strong dependency on coal for power production, electricity generation from coal is the most feasible solution to the power supply problem bedeviling Nigeria. In keeping with its published Roadmap for Power Sector Reform, it is needful for the government to aggressively exploit Nigeria’s abundant coal reserves for this purpose. Both pulverized coal production and fluidized bed combustion technologies may be deployed to ensure that Nigerian coals are used for generation of much-needed electricity.
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