Externally fired gas turbine cycle based on biomass gasification gas as fuel

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Energy services are essential for the development of societies, reduce poverty, and improve the living standards of inhabitants. The conventional routes to provide energy services employ fossil fuels. However, this involves environmental and availability concerns. Environmental issues and the need for energy security demand the use of alternative energy sources. Biomass is a renewable energy source that is advantageous because of its dispatchability and local availability worldwide. Local generation at small scales is interesting because it reduces energy losses when transporting electricity and heat. The development of sustainable decentralized small scale heat and power plants (CHP) using biomass is thus important.In this context, this work is mainly focused on the development of an energy conversion technology based on an externally fired gas turbine using biomass gasification gas as fuel. Although this system is not new, its applicability with biomass gasification gas has not been widely studied. This work is divided in three parts. In the first part, the effect of the fuel composition and fuel inlet temperature on the performance of an externally fired gas turbine prototype is analyzed through simulations. Then, the performances of two types of heat exchangers are compared under the operational conditions of the prototype taking into account different thicknesses of deposit materials. The results shows that the composition of the fuels and the corresponding flue gas temperatures affect the electrical power output of the system. However, this is limited by the operating temperature of the heat exchanger. It is also reported that a decrease in the effectiveness of the heat exchanger has a greater influence on the electrical power output than an increase in the pressure drop as a result of deposit materials. High pressure drops in the hot side of the heat exchanger slightly affect the electrical power output. If biomass gasification gas is to be used after the gasifier with reduced cleaning steps, the effect of contaminants such as tar in the combustion performance is important. The last part in this work describes experimental studies of the effect of benzene as tar representative in the combustion performance of a surrogate mixture of biomass gasification gas. Polyaromatic hydrocarbons such as benzene, present in tar in biomass derived gas, affect the combustion emissions depending on their concentration in the fuel gas.

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