Abstract
Coal reserves at Mui and Taru in Kitui and Kilifi counties in Kenya are estimated to provide over 400 million tons. Being new discoveries, their properties were investigated using the ASTM standards, while the combustion characteristics were studied in a fluidized bed combustor (FBC). Proximate analyses of the Mui1, Mui2, and Taru coal samples were as follows: moisture content 3.75, 5.48, and 3.53%; volatile matter 59.25, 58.05, and 55.10%; ash content 9.25, 11.48, and 24.63%; and fixed carbon 27.80, 25.00, and 16.75%, respectively. Ultimate analysis for Mui1, Mui2, and Taru coal samples is as follows: sulphur wt.% 1.94, 1.89, and 1.07; carbon 65.68, 60.98, and 51.10%; hydrogen 5.97, 5.70, and 5.09%; nitrogen 0.92, 0.94, and 1.00%; and oxygen 11.62, 12.33, and 11.13%, respectively. Temperature–weight loss analysis showed that for Mui and Taru basin coal, devolatilization starts at 200°C and 250°C, and combustion was complete at 750°C and 650°C, respectively. The maximum temperature obtained in FBC was 855°C at 700 mm height, just above the point of fuel feed, while the minimum was 440°C at height of 2230 mm. Maximum pressure drop was 1.02 mbars at 150 mm, while minimum was 0.67 mbars at 700 mm from the base. Gross calorific values were Mui1 coal, 27090 kJ/kg (grade A), Mui2 coal, 25196 kJ/kg (grade B), and the Taru coal, 21016 kJ/kg (grade C). Flue gas analysis for Taru and Mui coal gave hydrogen sulfide as 20 ppm and 6 ppm, maximum carbon monoxide of 2000 ppm at 600°C, and a decrease in oxygen as combustion progressed to a minimum of 15%, followed by an increase to 20.3%, suggesting depletion of coal. Based on the findings, the coal samples were suitable for commercial use.
Highlights
Energy is one of the key sectors towards the development of any given region [1]
For a fluidized bed combustor (FBC), the silica sand was sieve analyzed, and an average particle size of 325 μm was used as bed material, since sand particle size of 300–3 mm is the best in FBC [18]
Other equipment used in this study included a digital gas analyzer (Altair 5x) to analyse oxygen, carbon monoxide, combustibles, and hydrogen sulfide in the flue gas, the artificial neural network (ANN) model [20] to determine the elemental organic components in the coal samples, the PTC furnace (Carbolite Gero) for proximate and temperature– weight loss analysis
Summary
Energy is one of the key sectors towards the development of any given region [1]. With Kenya’s vision 2030 [2], the country has to invest more in energy generation to meet future increase in demand. The Government of Kenya has been keen to increase the share of renewable energy sources in the country’s generation mix [3]. With the discovery of fossil fuels in the country including coal deposits at Mui in Kitui and Taru basin in Kilifi County, oil in Turkana County, and natural gas in Wajir, it is shifting towards a mixed approach encompassing development of both renewable energy plants and fossil fuel generators [4]. To increase the number of energy sources, coal is being explored by the government, since it is cheaper than hydro and geothermal despite known negative impacts on the environment such as generation of greenhouse gas, carbon dioxide, and air pollution due to sulphur oxides, nitrogen oxides, coal dust, coal combustion wastes, and coal sludge [8]
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