Study On The Heat Transfer And Thermal Effect Of Biomass Pyrolysis With Gas Heat Carrier

The pyrolysis of biomass can produce a variety of high value products,especially for the preparation of biomass pyrolysis carbon,which is an important way to product activated carbon.The pysolysis of biomass is an endothermic process,The source and heat demand for pyrolysis have an important influence on the design of pyrolysis process and the research and development of pyrolysis equipment.From the perspective of heat transfer,pyrolysis heating can be divided into: radiation,convection and conduction.Among them,the heating method of gas heat carrier has the advantages of flexible heat source,high heating efficiency and no solid phase material consumption,etc.,so it is of great significance to study the heat transfer law of this process.To profoundly analyze the pyrolysis process of biomass,the biomass carbon under the action of different factors was prepared by tube furnace and analyzed by industrial elemental analyzer,specific surface area analyzer,scanning electron microscope,XPS,infrared spectrum analyzer and other instruments.It was found that the characteristics of biomass carbon were obviously different with different kinds of raw materials.The higher the temperature is,the deeper the pyrolysis degree of biomass carbon will be,and the content of surface functional groups will gradually decrease,and the biomass carbon will gradually aromatize and melt.Under the same pyrolysis condition,the larger the particle size of biomass,the lower the degree of pyrolysis.With the increase of the heating rate,the volatilization rate of biomass pyrolysis increases,which leads to the differences in the pore structure distribution of biomass carbon.Compared with other influencing factors,heating rate has less influence on biomass carbonization process.Then,A thermogravimetry and differental scanning calorimetry(TG-DSC)and a laboratory bench for the pyrolysis of large biomass particles were employed to investigate the instrinsic pyrolysis characteristics of furfural reaidue,and the pyrolysis heat demand of large furfural residue particle under different pyrolusis temperature,particle sizes and carrier gas flow rates.From the experimental results,the heat absorption during the intrinsic process of the slow pyrolysis could be divided into two phases,namely thermolysis of raw materials as well as degassing and reconstruction of semi-coke,with a lower heating rate indicating a higher degree of overlap between the two phases.Through analysis,it was found that under the operating condition of 30 ℃/min,the pyrolysis of furfural residue required 739 k J/kg,which reflects the heat demand in the actual pyrolysis process at a highly accurate level.The pyrolysis heat demand of furfural residue particle were lower than the result from the differential thermalanalysis,and showed positive correlations with pyrolytic temperature and particle size while had little relation with carrier gas flow.It is thus concluded that the pyrolysis of particles is closely associated with internal heat transmission.Finally,a simple biomass pyrolysis heat transfer model was established based on the previous work.Simulation results under the condition of 600 ℃ and 700 ℃ with the experimental comparison fit well,but has obvious deviation under 800 ℃,indicating the rise of temperature change mode of heat transfer inside biomass particle.