Development of a Numerical Model of Syngas Expansion in a Gas Turbine Utilizing Mui Basin Coal

Abstract

The global energy demand has been increasing over the years and is still expected to increase by 25% in 2040. The rise in demand is being accelerated by economic growth and industrialization of developing countries in Africa and also due to the projected global population increase to 9 billion by 2040. Fossil fuels have been the major source of global energy. By the end of 20th century they accounted for 85% of the total energy consumed. Combustion of the fossil fuels to run machines productes greenhouse gases. Hence there is need for clean, cheap and reliable source of energy to meet the rise in demand. Coal is a cheap, dirty source of energy that is currently used to generate 41.5% of the world electricity and to meet 26.5% of global primary energy needs. Technologies have been developed to reduce emissions from coal power plants such as flue gas scrabing, clean coal, and the use of alternative fuel like natural gas. Clean coal technologies include; pressurized fluidized bed combustion, Integrated Gasification Combined Cycle (IGCC),carbon capture and storage. Fluidized bed combustion have reduced emissions but it is difficult to fluidize fine particles while further studies are still being done on coal gasification. Kenya discovered 400 million tonnes of coal ranging from lignite to sub-bituminous having calorific values between 16 and 27 MJ/kg in Mui Basin Kitui county. Construction of coal power plants is underway in Kenya and hence studies are needed on clean and efficient utilization of the available resource. Research on gasification of the coal to produce syngas has already been done. The current research is on simulation of syngas combustion gases expansion in a gas turbine rotor. The main objective of this study was to develop a numerical model for simulation of syngas expansion in a gas turbine utilizing mui basin coal. To achieve this a gas turbine rotor model was developed and Computational fluid dynamics (CFD) software was used to simulate the flow. Syngas used was from gasification of lignite coal while simulation fluid was combustion gases of hydrogen and carbon monoxide. The rotational speed, pressure ratio and inlet temperature of turbine were varied while performance of the rotor was being recorded. Results of this study showed that efficiency increased with increase in pressure ratio, rotational speed and inlet temperature up to maximum then started to decrease. Power was directly proportional to temperature and rotational speed while it was inversely to pressure ratio. The maximum efficiency of 92.7% and power of 2.5 kW was attained at rotational speed of 10,000 rpm, pressure ratio of 10, and inlet temperature of 900 K.