| Under the great pressure brought by the energy crisis and environmental pollution, the development of clean, economical and efficient biomass thermochemical conversion technology has become a social consensus. Under the present situation, developing a clean and efficient biomass utilization technology need further study and grasp the law of biomass pyrolysis. The instrument called Micro Fluidized Bed Reaction Analyze (MFBRA), which designed by the Institute of process engineering, Chinese Academy of Sciences, is essential suitable to analyze the rapid reactions of thermally unstable substances. However, the biomass pyrolysis involves a series of reactions of the liquid substances such as tar. The experiment of liquid sample can’t be conducted in the present MFBRA, which limits its application in the field of biomass energy. Under the support of National Special Project for Development of Major Scientific Equipment, the function extension of MFBRA was carried out according to the characteristics of biomass pyrolysis. At last the extended MFBRA was applied in the biomass pyrolysis study in this paper.One of the shortages of MFBRA in the analysis of the reaction of liquid phase is that the MFBRA can’t realize the sampling of the liquid sample. Moreover, the resident time of the liquid sample tends to be too short to react completely due to the present structure of the reactor. In this paper the function of the MFBRA was upgraded based on the characteristic of the biomass pyrolysis. In order to achieve the fast and accurate trace liquid material feeding, a sampling device of liquid samples was designed. Moreover, the height of the reaction zone of the reactor was extended so as to prolong the residence time of the sample. Through the above improvement, the application scope of the instrument was expanded from solid raw to both solid and liquid raw. The developed apparatus can make up for the shortage of the available instruments in the reaction analysis of liquid material.Two major focuses in the field of biomass pyrolysis-the co-pyrolysis of biomass and lignite and the cracking of biomass tar, were studied by using the developed apparatus.The co-pyrolysis characteristic of biomass and lignite were investigated under isothermal condition in MFBRA. The synergetic effect was evaluated by comparing the experimental gas yields and distributions with the calculated values, and iso-conversional method was used to calculate the kinetic parameters of formation of each gas component. The results showed that synergetic effect was manifested in co-pyrolysis. It was found that with the change of mixing ratio of biomass, the synergistic effect showed promoting or inhibiting effect to the co-pyrolysis. The mechanism of synergistic effect was analyzed as well. For the range of conversion investigated, the activation energies for H2, CH4, CO and CO2 were 72.90 kJ/mol, 43.90 kJ/mol,18.51 kJ/mol and 13.44 kJ/mol, respectively; the reactions for CH4 and CO2 conformed to 2 order chemical reaction model, and for H2 and CO conformed to 1.5 order chemical reaction model; the pre-exponential factors for CH4, CO2, H2 and CO were 249.0 s-1,5.290 s-1,237.4 s-1 and 2.693 s-1, respectively. The discrepancy of the kinetic parameters implied that there were different pathways for forming the different gas. The synergy effect shows that the properties of good mass transfer and rapid temperature rising of MFBRA have obvious advantages in the rapid reactions.At the back of the paper, the characteristics and kinetics of biomass tar cracking was investigate. The carbon balance, carbon conversion, temperature of the reaction zone and the differential pressure between the inlet and the outlet of the reactor were measured to estimate the performance of the developed apparatus, and the results showed good reproducibility and reliability. H2, CH4 and CO comprised the vast bulk of producer gas and the total volume fraction of them increased from 69.85% to 93.62% (973-1173 K). It was observed that the thermal conversion rate of the tar increased significantly with the increase of reaction temperature. Kinetic parameters, including reaction order, pre-exponential factor and apparent activation energy, were studied with isothermal method. The reaction orders varied greatly with temperatures, suggesting that temperature significantly affected the reaction mechanism. The pre-exponential factors for H2, CH4, CO and gas mixture were in the range of 2.37*103-2.87*105 s-1, while the apparent activation energies of them ranged from 62.96-100.2 kJ/mol. Compared to the fixed bed experiments, the derived results were obvious higher. According to the Arrhenius equation, we can know that the high values are closer to the intrinsic reaction, which demonstrates the applicability and superiority of the expanding instrument in the reaction analysis of liquid... |
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