| Pyrolysis technology is regarded as one of the main ways of biomass conversion and utilization of clean, which can convert biomass into combustible gas, bio-oil, biochar and other clean energy and has vast applied prospects. Up to present, the research on biomass pyrolysis has gained some progress and made certain achievements, however, there is still an absence in the systematic research on gas evolution and kinetic characteristic analysis during the process of biomass pyrolysis. Exactly, it is the foundation of in-depth investigation on the pyrolysis technology and it can exposit the basic principle of gas evolution during pyrolysis of biomass in theory. So it is an integral part of biomass pyrolysis research. Investigating the pyrolysis conversion properties of biomass and exploring the reaction mechanism of gaseous products evolution and effect laws that the key parameters affect biomass pyrolysis process, and establishing the biomass pyrolysis kinetic model can provide the basis for the development of new pyrolysis technology and the design of advanced pyrolysis equipment.The basic characteristics of biomass feedstock was studied and the basic parameters of fluidized bed was analysed and optimized. Then pyrolysis experiments were done using the fluidized bed to study the parameters of temperature and pressure drop.The results indicated that temperature remained stable in the reactor and the error was maintained below 0.16 percent, the pressure drop in the fluidized bed was about 14500Pa and the fluctuations were not more than 881.3Pa in the whole pyrolysis process,which proved the fluidized bed can reach well stabilization. Key parameters, including bed height and flow rate of the fluidizing gas that impact the effect of biomass pyrolysis process were analyzed.The results showed that higher aspect ratio and flow rate of the fluidizing gas benefited the gas producing during the pyrolysis process, within a certain range. The optimization results suggested that aspect ratio of fluidized bed was 0.32 and the flow rate of the fluidizing gas should be higher than 0.4L/min.Based on the optimization results, characteristics and kinetics of gas evolution during biomass pyrolysis under isothermal conditions, which refer to H2, CH4, CO and CO2 were studied. The results indicated temperature influenced not only the release order of gas but also the relative amount of each single content. At the operating temperature range of 600℃-800℃, the first available gas was CO2 and H2 was the last one. In addition, a higher temperature made the release order of gas more apparent. The relative contents in percentage of H2 and CH4 increased and the relative contents in percentage of CO first increased and then decreased with the increase of temperature, and for CO2 the relative contents in percentage first decreased and then slightly increased. Meanwhile, the results suggested that CO had the highest amount in the gas products. The relative contents in percentage of CO, CH4 and H2 decreased and that of CO2 increased with the increase of biomass particle size from 0.15mm to 1.00mm, and the change values were 5.6%,1.7%,1.8% and 9.1% respectively. In the biomass isothermal fast pyrolysis process, participation of oxygen made the pyrolysis reaction time more longer and the reaction process more complex, at the same time the relative contents of CO2 increased with the increase of oxygen concentration. The kinetics results suggested that higher temperature benefited the reaction rate of generating four gas products, and the effect caused by temperature change was the most obvious for H2. The biomass isothermal fast pyrolysis process was divided into three stages and the datas that came from stage II were used to analyse kinetic parameters, using the chemical reaction model to describe pyrolysis process. With varied temperatures (600℃-850℃), the reaction order of CO2 increased from 0.97 to 1.27, and for the CH4 it increased from 0.88 to 1.25. As for H2 and CO, the change regulation of reaction orders remained non constat, they both achieved the minimum at the temperature of 600℃ with values of 1.10 and 0.97, and achieved the maximum at the temperature of 850℃ with values of 1.38 and 1.31. The values of activation energy for generating H2, CO, CO2 and CH4 were 18.90,12.05,10.48 and 11.31 kJ/mol respectively. The results indicated that H2 was the most difficult to form due to the highest activation energy. The values of reaction order with respect to gas mixture were in the range of 1.20-1.33 under the inert gas conditions, as for oxygen conditions the values were in the range of 0.94-1.11, the average were 1.26 and 1.06 respectively. The values of activation energy for generating gas mixture was 16.74 kJ/mol, corresponding to the value of pre-exponential factor was 4.24s-1 under the inert gas conditions, as for oxygen conditions the values were 22.22 kJ/mol and 6.-1. The values of activation energy and pre-exponential factor with respect to gas mixture were more higher in the presence of oxygen. |
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