Characterization Of Maiganga And Okaba Coal Blend For Solid Fuel Combustion
This study was carried out on characterization of Maiganga and Okaba coal blend for solid fuel combustion. In this paper, characterization and ash chemistry of selected Nigeria coal samples were investigated to determine its suitability as a solid fuel. The three coal samples considered originated from Northern Benue trough, Central Benue trough and Anambra Basin of Nigeria where proven reserve deposits are found. The coal samples were analysed using various analytical methods such as thermogravimetric analysis (TGA) and X-ray Fluorescence spectroscopy (XRF) analyses. The ash chemistry indices used in predicting the performance of the coal samples includes basic to acidic oxide (B/A), silica ratio, iron index and sulphur slagging index (Rs).
The TGA profile suggests that Enugu coal showed high thermal stability than that of Okaba and Maiganga coals but had an ash content higher by a factor of 2.0 when compared with Okaba and Maiganga coals. Maiganga coal however has the highest heating value of 27.40 MJ/kg when compared to Okaba coal (25.74 MJ/kg) and Enugu coal (22.92 MJ/kg). The silica ratio indicated that Enugu coal has high slag volume, while the B/A suggest that all the coals were found to be less than 0.6 indicating low slagging potential. The comparison of the ash chemistry suggests that Maiganga coal has lowest slagging potential while Enugu coal highest slagging potential.
Table Of Contents
- Title page
- Certification page
- Table of content
- 1.1 Background of the study
- 1.2 Problem Statement
- 1.3 Objectives of the study
- 1.4 Scope of the study
- 1.5 Significance of the study
Two Literature Review
- 2.1 Previous Research on Nigerian Coals
- 2.2 Review of Theoretical Basis for Coal Analysis
- 2.3 Characterisation of Coal
- 2.4 Fundamentals of Coal Combustion
- 2.5 Influence of Coal Properties on Power Plant Design
- 2.6 Power Generation from Low Grade Coals
- 2.7 Coal Beneficiation
- 2.8 Research Gap
Materials And Methods
- 3.1 Coal Samples preparation
- 3.2 Proximate and ultimate analysis
- 3.3 Thermal and chemical characterization
- 3.4 Ash chemistry prediction
Results And Discussion
- 4.1 Proximate and ultimate analyses
- 4.2 Thermal analysis
- 4.3 Chemical analysis
- 4.4 Ash chemistry of coal samples
Conclusion And Recommendations
- 5.1 Conclusion
- 5.2 Recommendations
1.1 Background Of The Study
Power generation in any country is very essential to its economic growth, Nigeria generates about 4,000 megawatts(MW) of electricity (Ediri, 2014), but this is deficient as the country still faces the challenge of epileptic power supply, it is expected that power generation reaches 40,000 megawatts(MW) in the year 2020 (Ediri, 2014), to achieve this feat the government has planned the construction of various power generating stations of which coal would be a vital raw material used in some of these plants, although generation of energy from coal is accompanied by the emission of greenhouse gases, the development of clean coal technologies have helped to reduce this emissions. Coal which is a product of long periods of accumulation and subsequent physical and chemical alteration of plant material is an organic rock (as opposed to most other rocks in the earth’s crust, such as clays and sandstone, which are inorganic; it contains mostly carbon (C), but it also has hydrogen (H), oxygen (O), sulfur (S) and nitrogen (N), as well as some inorganic constituents (minerals) and water (H2O). (Radovic, 2009) Different types of coals are classified based on their composition of these constituent elements, based on this coal is classified as lignite, subbituminous, bituminous and anthracite. the combustion of coal under specified conditions leaves behind a residue known as ―ash‖ which is composed mainly of oxides and sulphate depending on the source of the coal sample. (Folahan , 2012).
The combustion of coal produces sulphur and some other gases and a solid residue known as coal ash or fly ash. Fly ash is either deposited as dry or hydraulic ash, the sulphur content of coal varies considerably with the nature and origin of the fossil deposits (Folahan , 2012) the utilization of coals for both energy production and various coal conversion processes is limited by the presence of sulphur in the coal, sourcing for the right type of coal and inconsistency in composition. Many of these plants will not be able to source for coal that meet up to their specification and will have to combine samples available to them to obtain the required quality of coal. The high sulphur dioxide emissions caused by the utilization of coals as a major fossil fuel leads to worldwide environmental problems. When coal is burnt its sulphur content combines with oxygen to form sulphur dioxide (SO2), which contributes to both pollution and acid rain. Acid rain resulting from SO2 has a harmful effect on agriculture and destroys the ecological balance. Also naturally occurring elements in the environment become part of the coal structure through the coalification process. The use of large quantity of coal results in significant emissions of these trace elements, although these trace elements are present in small amounts in the coal. Another serious problem of sulphur in coalis the formation of clinker in furnaces. The causes of clinker formation are low quality coal having low gross calorific value, more ash content, high mineral content, low fusion temperature of ash below 1500 C, and over-firing of the molten slag.
The presence of sulphur in coal also reduces the quality of metallurgical coal (Folahan, 2012). Blending of coals results in a combination of characteristics from each of the individual coals in the blend. Some coal characteristics, such as ash, sulphur and moisture content, are additive and can be calculated from the proportions of the different coals in the blend, it is therefore necessary to know the characteristics of the individual samples and that of the final blend before it is used in any power plant, this will enable a plant to understand the advantage and problems related to each blend of coal. The work done involves the chemical andthermo-gravimetric analysis of maiganga and okaba coal blend.
1.2 Problem Statement
The heat content in a fluidized bed or furnace of a power plant may be reduced greatly due to the presence of slags or foul formed as a result of the deposition of some constituent compounds in coal such as sulphur, alkalis and some trace metals, it is therefore important to find solutions to the usage of low quality coal by blending them with another sample that complement for the lacking quality.
There are only a few experimental investigations on the combustion profile of Nigerian coals and investigation their slagging potentials are even rarer. An in-depth understanding of the characterization and ash chemistry of the Nigerian coals is necessary in order to assess indigenous coal combustion efficiency. In this study, characterization and ash chemistry of selected Nigerian coals were carried out. The selection of coal sample was done in view of disparity of coal properties from different geographical locations as coal formation largely depends on constituent’s formation, compression temperature and pressure.
1.3 Objectives of the study
The main objective of the study is to examine the characterization of Maiganga and Okaba coal blend for solid fuel combustion.
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.
1.4 Scope of the study
To blend two coal samples and perform physical, chemical and thermal analysis on the blend obtained.
1.5 Significance of the study
The quality of the coal used affects most of the costs associated with coal-fired power plants. Proper evaluation of the combustion performance of the coal to ensure optimum utilisation and minimum costs is therefore essential.
This research will help determine the suitability of some Nigerian coals for use in coal-fired power plants, not only in Nigeria, but as an export commodity to other coal-consuming countries around the world. This will assist the potential investor in Nigeria’s power sector to make a decision on areas of the coal’s performance that may be suspect, requiring further investigation by a larger-scale form of testing (pilot-scale simulation or full-scale testing) and also serve as a justification for investment in such a larger-scale testing.
The significance of this research is further underscored by the present dependence of Nigeria on natural gas- and hydro-powered electricity. The unreliability of natural gas supply due to frequent disagreement over appropriate pricing and pipeline vandalism and the susceptibility of hydro-electric power to weather has made the inclusion of coal-fired electricity into Nigeria’s electricity generation mix imperative. The argument for nuclear power has been punctured by recent safety concerns arising from the Fukushima nuclear disaster as raised in the website of Green Peace International (http://www.greenpeace.org).
With world industrial giants such as the United States of America, Peoples Republic of China, Germany, Australia, India and South Africa among countries heavily dependent on coal for electricity generation, Nigeria cannot exclude itself from benefitting from this resource which it has been richly endowed with.
Conclusion And Recommendations
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.
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 pulverised coal combustion 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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