The Use Of High Temperature Flue Gas Pyrolysis Forming Carbon Biomass Research

Biomass briquettes have high energy density and are also convenient for transportation and storage. The utilization of biomass briquettes is bene-ficial to develop biomass energy on large-scale. Carbonization of biomass briquettes is a very important way for the use of biomass. There is much flue gas whose temperature is high in industry process. To use the flue gas as a heat source for carbonization can make sufficient use of waste heat of the flue gas. This paper focused on carbonization of biomass briquettes using flue gas whose temperature was high.Firstly, biomass materials for producing char had been selected after analyzing the two aspects’influences on biomass carbonization. The two aspects are respectively the results of proximate analysis and lignin content of biomass materials. Biomass materials which have ash of low content and lignin of high content should be selected. The quality of biomass char is high when biomass materials have ash of low content. The yield of biomass char is largh when biomass materials have lignin of high content.Secondly, the caloric requirement of carbonization at different heating rates had been studied. When heating rates were different, pyrolysis process and heat of reaction varied.Then caloric requirement were different.When the range of final temperature was450-465℃, the caloric requirement from small to large were obtained at heating rates of5,20,10℃7min. When the range of final temperature was465～596℃, the caloric requirement from small to large were obtained at heating rates of20,5,10℃/min. When the range of final temperature was596～700℃, the caloric requirement from small to large were obtained at heating rates of20,10,5℃/min. When heating rates were5℃/min,10℃/min respectively, the final temperature shouldn’t higher than550℃,600℃. If the final temperature was too high, the slope of caloric requirement curve would increase quickly and caloric requirement was large. Thirdly, kinetics of biomass briquettes was investigated through experiments. Decomposition rate first increased and then decreased in pyrolysis process of biomass briquettes. When heating rates of biomass were6,11,22℃/min respectively, temperature of biomass briquettes at maximum decomposition rate were319,336,396℃.Maximum decomposition rates were-2.32,-4.29,-6.24%/min. The activation energies were21.50,23.94,28.10kJ/mol.They all increased with heating rate.Maximum decom-position rate and activation energy of biomass briquettes were both less than these of small size biomass when heating rates of their pyrolysis process were the same. Main pyrolysis stage of biomass briquettes accorded with second order reaction mechanism.Heat exchange for biomass carbonization utilizing flue gas had been designed using DSC curves. The accuracy of heat transfer design method is improved through the introduction of micro-element method and the function of temperature of biomass. By analysis of the relationship of the caloric requirement and temperature, the relationship between the tem-perature and the location of the biomass in the heat exchange, we concluded that the heat flux density was a constant in some range of temperature. Then heat transfer to moving biomass from flue gas whose temperature was high could transform into heat transfer to static biomass from a constant heat flux.Finally, biomass briquettes’s carbonization homogeneity was studied. Biomass briquettes’s size is larger than that of small dimension biomass and carbonization in whole biomass is different to some extent. But endothermic and exothermic effect in pyrolysis process and mass transfer of volatile are beneficial to carbonization homogeneity. When biomass average heating rate becomes larger, the maximum temperature difference of surface and inside becomes larger, besides that the temperature of biomass is higher when biomass briquettes’s carbonization is homogeneous.Maximum tem-perature differences were30,76,137℃respectively when biomass average heating rates were5,10,19℃/min. In order to ensure homogeneity, carbonization should reach the temperature which lignin decomposes strongly at releasing heat violently. Carbonization temperature should be higher than450℃. Besides, biomass average heating rate shouldn’t be too high and it should be under19℃/min.