Bed modeling of a biomass grate-firing furnace: a numerical study
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Date
2018
Authors
Taban, Zahra
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Abstract
Biomass is a renewable source of energy that can play a vital role in achieving a more sustainable energy supply. It can also substitute fossil fuels in many applications such as heating. Biomass combustion in grate firing furnaces is a conventional approach to convert biomass fuel into heat and electricity. However, this technology is associated with some challenges such as low efficiency and pollutant emissions. Most of the published studies on biomass combustion are focused on gaining a better understanding of thermal conversions occurring in the bed section and subsequent chemical reactions taking place in the freeboard. Nevertheless, the conversion of solid biomass in the bed section of a furnace is a very complex phenomenon; and still requires further research. In this thesis, a numerical study is performed to describe the conversion of solid fuel in the bed section. Four different bed models are introduced and tested. For each model, a separate MATLAB code containing physical equations and chemical sub-models is developed to predict species mass fraction and temperature over the bed surface.
To test the performance of these models, and due to the lack of experimental data, the bed models outlets are applied as boundary conditions to the freeboard simulation modeled by the eddy dissipation concept (EDC). Then, the freeboard numerical results are compared with the experimental measurements at furnace outlet. The results show that the predicted released mass fraction and temperature from the furnace with the application of 1-D three-zone bed model are in better agreement with experiments. The results also indicate that the temperature distribution in the freeboard strongly depends on the adopted bed model.
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Keywords
Biomass, Grate-firing