Fossil fuel energy resources of Ethiopia: Coal deposits

International Journal of Coal Geology

November 2007,

Abstract

The gravity of Ethiopian energy problem has initiated studies to explore various energy resources in Ethiopia, one among this is the exploration for coal resources. Studies confirmed the presence of coal deposits in the country. The coal-bearing sediments are distributed in the Inter-Trappean and Pre-Trap volcanic geological settings, and deposited in fluvio-lacustrine and paludal environments in grabens and half-grabens formed by a NNE–SSW and NNW–SSE fault systems. Most significant coal deposits are found in the Inter-Trappean geological setting. The coal and coal-bearing sediments reach a maximum thickness of 4 m and 300 m, respectively. The best coal deposits were hosted in sandstone–coal–shale and mudstone–coal–shale facies. The coal formations of Ethiopia are quite unique in that they are neither comparable to the coal measures of the Permo-Carboniferous Karroo Formation nor to the Late Devonian–Carboniferous of North America or Northwestern Europe. Proximate analysis and calorific value data indicated that the Ethiopian coals fall under lignite to high volatile bituminous coal, and genetically are classified under humic, sapropelic and mixed coal. Vitrinite reflectance studies confirmed 0.3–0.64% Ro values for the studied coals. Palynology studies confirmed that the Ethiopian coal-bearing sediments range in age from Eocene to Miocene. A total of about 297 Mt of coal reserve registered in the country. The coal reserve of the country can be considered as an important alternative source of energy.

Introduction

Energy is one of the basic inputs in economic development and human survival. Energy is needed as inputs in industry, agriculture, mining, construction, service giving organization etc. Where will the chemical industry find its raw materials when oil and gas run out? World reserves of oil are estimated to last for another 40 years, natural gas perhaps 60 years; and proven world reserves of coal, by contrast, are likely to last for at least 200–300 years at present rate of consumption (Maitlis and Rourke, 1993, Bowler, 1993). Now chemists are looking at ways of exploiting coal not only as a fuel but also as a long-term alternative source of basic materials for making important industrial chemicals (Maitlis and Rourke, 1993).

The ever-growing of the price of petroleum products affects all the countries of the world. Owing to the present world-wide energy crisis, low-grade fuel (coal, oil shale, tar sand etc.) is becoming an alternative resources in many countries of the world. Many countries in the world are beginning the processes of developing various coal fields.

For sound economic development and social progress, developing nations like Ethiopia require an adequate supply of energy at affordable prices. To meet the ever-growing need of energy in Ethiopia, successive studies are underway in various fields to establish plants of hydroelectric power, geothermal energy, natural hydrocarbon, solar energy, etc. The main sources of energy in Ethiopia are wood, oil and hydroelectric power for domestic, industrial and transportation sectors. The entire rural and a large segment of urban population in the country use wood as domestic fuel. The need of domestic fuel is the major factor for deforestation in Ethiopia, which creates environmental problems, such as soil degradation, desertification and destruction of natural ecosystem.

The coal deposits of Ethiopia are classified into Inter-Trappean and Pre-Trap volcanic geological setting (Wolela, 1991a, Wolela, 1991b, Wolela, 1992a, Wolela, 1992b). Two types of coal-bearing sedimentary successions are identified in Ethiopia. These include: (i) sandstone–coal–shale facies and (ii) siltstone/mudstone–coal–shale facies. The coal seams hosted in sandstone–coal–shale facies are thicker and persistent than those in the siltstone/mudstone–coal–shale facies. Significant amounts of coal deposits are found in the Delbi-Moye, Chilga, Yayu, Lalo-Sapo, Nejo, Wuchale and Mush Valley Basins (Fig. 1).

The coal deposits of the country can be used as an alternative source of energy. The exploration of coal deposits is an integral part in search of energy resources. Hence, the use of coal will have a great contribution to the energy sector: (i) to relieve the pressure of using wood as fuel for small-scale industries, (ii) as a substitution for imported crude oil and to save significant hard currency, and (iii) as a substitution for fire wood and wood-derived charcoals domestic fuel for rural and urban areas, (iv) power generation, (v) hydrocarbon extraction and (vi) production of fertilizer.

This paper discusses the geological setting, integrated surface and sub-surface studies, depositional environments, chemical characteristics and reserves of the coal deposits of Ethiopia and provides quality data to help promote the use of coal as the major energy source for rural and urban areas. The geology of each coal deposit is discussed separately. Proximate analysis, ultimate analysis, scanning electron microscopy, vitrinite reflectance and palynology studies were carried out to determine the characteristics of the Ethiopian coals.

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Section snippets

Methodology

Rock outcrops and logged boreholes data are used to determine the lateral and vertical variation of the coal seams, chemical characteristics and reserves evaluation. Representative core and outcrop coal samples were collected for different types of analyses. Proximate analysis was performed on 1 g of coal sample using Fisher Model-490 Coal Analyser to determine moisture, volatile matter, ash and fixed carbon. The gross calorific value of the coal samples was determined according to ASTM method, 

Chilga Basin

The basin is situated at 12°25′–12°38′N and 37°03′–37°11′E latitude and longitude, respectively (Fig. 1, Fig. 2). Chilga is located 52-km southwest of Gonder, and 100-km NW of Lake Tana. The basin is found at altitude of between 1600 and 2100 m above sea level. The coal at Chilga is one of the most extensively studied deposits in the country. The perennial and intermittent streams drain from the Chilga Highland, and enter to the Blue Nile River. Twelve boreholes were drilled in the central part 

Delbi-Moye Basin

The Delbi-Moye Basin is situated at 7°19′–7°24′N and 36°48′–36°53′E latitude and longitude, respectively (Fig. 1, Fig. 5). Delbi is 390 km west of Addis Ababa, and 45 km south of Jimma city. The coal in this basin is the second-most studied deposits in the country. The basin is found at an altitude between 2060 and 2240 m above sea level. Twenty-one boreholes were drilled in the Delbi-Moye Basin within an area of 25 km².

Mush Valley

Mush Valley is situated 159 km northeast of the Addis Ababa along Addis Ababa–Dessie road (Fig. 1). The area is found between 2600 and 2800 m above sea level. The Inter-Trappean coal-bearing lacustrine sediments were predominantly composed of sandstones, siltstones, carbonaceous shales and coal seams. The succession in the Mush Valley lies on the Miocene–Pliocene basaltic substratum (Babu and Getahun, 1981). Two coal seams are interbedded at different levels of the coal-bearing sediments. The

Microscopy studies

The Moye coal deposit is humic in type, whereas the Delbi coal deposit is dominated by sapropelic coal. Moye coals are generally rich in vitrinite and liptinite macerals and have moderate sulfur content (Table 5). The sapropelic coals in the Delbi area are predominantly boghead with minor amounts of cannel coals, whereas the humic coals in the Moye area are dominated by vitrite and clarite lithotypes. The Chilga, Wuchale and Nejo coals are characterized by mixed coal, and defined by vitrite and 

Chemical characteristics of Ethiopian coals

The studied coals have 11.5–46.53% volatile matter, 11.5–56.9% fixed carbon and 5.3–58.3% ash content (Table 6). The vitrinite reflectance (Ro) values and sulfur contents range from 0.3 to 0.64% and 0.2 to 2.39%, respectively. The calorific values of the studied coals range from 2626 to 6743 cal/g (Table 6). The hydrogen, carbon, nitrogen and oxygen contents range from 4.2–6.57%, 60.3–80.22%, 0.8–2.27% and 15.98–32.69%, respectively (Table 7).

The coals in the Delbi area are characterized by

Summary and conclusions

There are strong evidences that the NNW–SSE and NNE–SSW fault systems provided the tectonic configuration for the development of grabens and half-grabens for the sedimentation of the coal-bearing sediments. The coal deposits are classified into Inter-Trappean and Pre-Trap geological settings. Most of the significant coal deposits of Ethiopia are found on the southwestern plateau of Ethiopia, in the Inter-Trappean geological setting.

The coal measures of Ethiopia are Tertiary, with minor amounts

Acknowledgement

Earlier drafts of the manuscript were read by Mr. G. J. Bae and A. Assefa. The constructive and valuable comments are gratefully acknowledged. The manuscript benefited substantially from critical commentary by Dr. J. Parnell, Dr. E. Gierlowski-Kordesch, and Dr. M. Tilahun, and an anonymous reviewer of the journal. The author acknowledges the Ethiopian Geological Surveys and Petroleum Operations Department, Ministry of Mines and Energy for their support and help to carry out this research work.Recommended articles

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