Combustion of agricultural residues : Application for Stirling micro-combined heat and power

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Access to energy services is crucial for the development of countries. Therefore, in developing countries, the access to modern conversion technologies would contribute to reduce the poverty, improve health services and promote the economy especially in rural areas. Around 2.5 billion people in these countries use biomass for cooking. However, major concerns are due to the unsustainable use of biomass and the inefficient conversion technologies employed in rural areas. Therefore, the use of locally available biomass in modern biomass conversion technologies would significantly reduce emissions and improve the energy efficiency. These modern technologies may include residential pellet stoves and boilers which at the moment only are used for heating appliances in industrialized countries. Their combination with a prime mover like a Stirling engine could a very attractive solution to produce combined heat and power (CHP) though still in prototype stage. In this context, this study is mainly focused on the development of an energy system fuelled by locally available biomass to produce heat and electricity based on a Stirling engine. The main objective is to perform experiments to find relevant parameters that characterize the energy system proposed.In the first stage of this work, the suitability of using agricultural residues in a pellet boiler was evaluated in comparison to commercial wood pellets. The agricultural residues used during the tests were: sugar cane bagasse, sunflower husks and Brazil nut shells. The first two residues were pelletized and the last one was reduced to a uniform size. Parameters and energy used during the pelletizing were found. Emission levels and boiler efficiency under steady-state and transient conditions were also presented for the different biomass sorts. In the second stage, the integration of the same pellet burner and the Stirling engine was characterized in terms of losses and efficiency calculations. Finally, the integration of the pelletizing, combustion, and heat and power generation was discussed based on experimental and predicted results.

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