Mechanism And Experimental Study On Biomass Gasification And Pyrolysis

The increasing use of biomass resources in efficient way can alleviate the pressure on the demand of clean energy and environmental protection. The pyrolysis-gasification technology, in terms of technical and economical acceptable, is playing the significant role in converting biomass into available energy products.The thesis presents thermo-chemical reaction properties of biomass focusing on gasification process. The systematical analysis and experiments were carried out to illustrate physical and chemical characteristics, and associated key factors during the gasification process. An optimized process is presented aiming at obtaining clean fuel gas of less tar content thereby improving its quality of syngas.The effect of physical and chemical properties of biomass on thermal chemical reaction were investigated including chemical and biochemical compositions, heating value, density and ash melting point etc. The properties of biomass used as bio-energy in terms of thermo-chemical behaviour is therefore evaluated and can be further referred to other biomass fuels.Thermogravimetric (TG) experiments using different biomass as feedstocks were carried out without air. Dynamic behaviour was investigated based on the dynamic experiments on TG and afterwards dynamic biomass pyrolysis model was established. Results show that different feedstocks show almost the same tendency with temperature due to the consistent reaction mechanism. Pyrolysis reaction order is 1 and activation energy is in the range of 60~90kJ/mol.K.The tube furnace was chosen as main experimental equipment to pyrolyze the corn core and straw at atmospheric pressure. The effects of pyrolysis temperature and reaction time on the distribution of the pyrolysis products were discussed in details. The mass ratio of gaseous products rose from <15% to >60% when temperature increased from 400℃to 800℃, which implied that the higher temperature is helpful to crack more tar.TG analyzer was operated under the different conditions such as isothermal TG and constant temperature-rising rate, to investigate the effects of different conditions on the deoxidization reaction. With the favor of experiment and model, the analysis to the whole process and determining factors could reveal that the temperature is the key factor in the deoxidation reaction with 850℃as the turning point. Additonally, the rate of deoxidation reaction is obviously slower than that of pyrolysis reaction, which is the determining factor when designing the gasifier load.A two-step biomass gasification process was proposed based on the systematic analysis for various biomass materials covering the following aspects, such as physical & chemical characteristics, chemical reaction dynamics of pyrolysis and gasification etc. The process conditions and reactor structures could meet the requirements of the biomass gasification and tar crack. This process can produce the fuel gas with the tar content less than 20 mg/Nm3 when the temperature in the combustion area was kept higher than 920℃.