The Experiment Study And Modeling On The Gasification Of Typical Biomass

Bioenergy is an ideal renewable energy with advantages of low sulfur, low nitrogen and CO₂ zero-emission. The prospect of producing clean, sustainable powering substantial quantities from bioenergy is now arousing interest, stimulated by increasing concern over the environmental consequences of conventional fossil and nuclear fuel use. The development and research of biomass gasification technology that can convert low-quality bioenergy to higher-quality fuel gas can not only relieve the demand pressure of power fuel for China, but also improve China energy structure. For the above mentioned purposes, the experiment study and modeling on the gasification of typical biomass was performed.In the thesis, at first, using calcium oxide, magnesia and ferric oxide as catalyst, the properties and reaction kinetics of typical agriculture biomass catalytic gasification were investigated in a thermogravimetric analyzer under ambient pressure. The homogeneous model (HM) and shrinking core model (SCM) were used to correlate the relationship between conversion (α) and temperature (T). The results indicated that in the range of 820℃～1000℃,calcium oxide could make the activation energy of rice husk higher.On the contrast, magnesia and ferric oxide could make the activation energy lower by more than 32.6%å’Œ17.9% separately. In the low temperature range (pyrolysis), the homogeneous model was better than the shrinking core model. It was opposite in the high temperature range (gasification).Secondly, the reaction kinetics of the pyrolysis and gasification of rice husk were investigated in the thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer with various atmospheres. The gas products evolved from rice husk were detected on-line by Fourier transform infrared spectroscopy (FTIR). The main gas products were H₂O, CO, CH₄, CxHy(x>1)and some organics carbohydrate mixtures. H₂O was released at the lower temperature, whereas CH4 and CO were appeared at the higher temperature. There were similar characteristic temperature and emission tendency between the releasing curve of CO and the reaction rate curve of rice husk.Thirdly, the characteristics of biomass ash were studied. On the basis of element analysis of biomass ash for four biomasses, the experiment indicated that cotton straw ash was prone to slagging and deposition and rice straw ash and maize straw ash had light proneness to slagging and deposition with comparison with rice husk ash. X-ray diffraction experiments showed different biomasses ash had different XRD characteristics.Finally, a biomass gasification model was developed by the method of Gibbs free energy minimization. The model provided a very good agreement with the experimental results from a fluidized bed gasifier. We found that the model was effective to simulate the pilot fluidized bed and gasification power plant.