Experimental Research And Simulation Of Biomass Gasification With Oxygen-Enriched Air And Steam In Fluidized Bed

Biomass is a widely available, renewable and CO2-neutral resource, considered to be a promising alternative energy. Gasification in a fluidized bed is one of the most efficient ways of converting the energy embedded in biomass. Biomass gasification with air is widely used in industrial applications. However, air gasification has some disadvantages such as low LHV, high content of tars and low gasification efficiency due to nitrogen dilution, which make it less competitive in business. While gasification with enriched air or enriched air-steam instead of air can promote reduction reactions in fluidized bed, improve gasification performance and obtain higher LHV gases with few tars. In the thesis, both experimental research and simulation are combined together to study bimass gasification characteristics with enriched air and enriched air-steam, in order to provide theoretical reference and technical support for utilization of combustible solid waste in high quality.Gasification of two kinds of RDF is performed on a bench-scale fluidized bed gasifier with enriched air and enriched air-steam as fluidizing and oxidizing agents, respectively. The effects of gasification temperature, equivalence ratio, volume fraction of oxygen, bed material properties, fluidization volecity and S/B on gas composition, LHV, gas yield, carbon conversion and gasification efficiency were investigated through a series of experiments. Results show that the following order of gasification performance is calcined limestone> bauxite> attapulgite clay with three different bed materials. Rising temperature enhances the formation of H2 and CO and improves gasification efficiency. Higher ER can cause gas quality to degrade for more oxidization reactions. In the experiental study, the optimal value of ER was about 0.2 under the conditions. The LHV of gases and gasification efficiency in the optimal conditions are 7.88MJ/m3 and 41.5% with enriched air, respectively. It really improves biomass gasification performance compared to air gasification with LHV of 3.43MJ/m3 and gasification efficiency of 25.5%. Morever, introduction of enriched air -steam as the gasification medium promotes the steam reforming reaction. The LHV of gases and gasification efficiency in the optimal conditions are 7.75MJ/m3 and 61% with enriched air-steam. Compared to enriched air gasification, the gasification efficiency with enriched air-steam is improved significantly again.Based on element balance, chemical equilibrium and energy balance with considering char, the thermodynamic equilibrium model of biomass gasification with enriched air in a fluidized bed gasifier has been developed. The equilibrium constants of steam reforming reaction and methanation reaction are modified by multiplying coefficients. Compared the predicted results with the experimental data, results show the error of original model data is really far and that of the revised model satisfactorily agrees with the experimental data with average RMS of 1.64 and the maximum relative error less than 20%. The developed model is then used to study the effects of biomass moisture content and S/B on rice husk enriched air gasification.