Characterization of the fuel value of peat deposits for potential development of a peat fired power plant in Uganda

Abstract

Peat is a renewable energy source that can be harnessed as an additional source of energy. Although Uganda’s biomass resources are substantial, biomass consumption for domestic and industrial energy is at an unsustainable rate, leading to annual deforestation rate of 1.44%, one of the highest in sub–Saharan Africa. This study aimed to evaluate the energy potential of peat in Katuna village, Kabale district, for a possibility of establishing a peat-fired power plant in Uganda. Physical and chemical laboratory analyses of the peat samples were conducted to assess their suitability as an energy source. A bomb calorimeter was used for calorific value analysis while geophysical techniques were used to estimate the volume of peat deposits in Katuna and their energy potential. Aspen Plus modeling determined the energy output and efficiency of the two thermochemical conversion processes, gasification and combustion. Sensitivity analyses scrutinized the impact of parameters such as equivalence ratio, steam to fuel ratio and pressure on process efficiency. Bomb calorimetry revealed average calorific value of 19.53 MJ/kg, while proximate analysis showed organic carbon content of 52.44%, moisture content of 61.09%, volatile matter of 69.29% and ash content of 7.54% on dry basis. Ultimate analysis showed sulphur and nitrogen contents of 0.55% and 1.32% respectively. Aspen Plus simulation presented gasification as the superior pathway, with a carbon conversion rate of 98% compared to 95% for combustion. Gasification had a power output of 215 MW compared to 201 MW of combustion at an equivalent feedstock of 100,000 kg/hr. To obtain this power output, the total energy input per unit mass of fuel was 5.13 MJ/kg for gasification and 4.83 MJ/kg for combustion. The peat volume was estimated to be 59.6 km3 indicating sufficient quantities for exploitation. Estimation of the energy potential indicated that gasification with an overall efficiency of 36.75% exhibited potential of generating 112.3 MW of energy for the next 25 years. In contrast, combustion with an efficiency of 33.25% indicated potential of generating 101.6 MW of energy for the same period. Sensitivity analysis indicated that an optimum equivalence ratio of 0.29, steam to fuel ratio of 1, pressures below 20 bars and particle size range of 0.1mm to 0.5mm enhanced the overall efficiency of gasification. These findings established gasification as the most efficient pathway, with an entrained flow gasifier as the most suitable type of gasifier for converting this peat to energy. The study underscored peat's potential in providing Uganda with a viable energy source for a resilient and sustainable energy future.