Thermal Analysis On Mixtures Of Biomass And Its Char

Abstract:Mixing biomass and it’s pyrolysis product-semi-char will change the combustion characteristics. Researching the impacts of mixing on combustion characteristics is of great significance in improving thermal conversion technology.The wood biomass and the charcoal——semi-coke of wood were selected in this paper, five samples were obtained:wood, charcoal, their mixtures in three ratios:1:4,1:1,4:1.To probe the effects of mixing on pyrolysis and combustion characteristic parameters, thermogravimetric analysis was used to get the weight loss data in nitrogen and air. The initial, maximum and final reaction temperatures as well as the volatile release characteristic index were obtained, the synergistic effect within the components was discussed. Results show, mixing influences the above characteristics. In nitrogen, the maximum and final reaction temperature of charcoal are much higher than wood, the volatile release characteristic index of wood is much higher than charcoal. The mixtures’maximum and final reaction temperature are nearly the same with wood and charcoal respectively. As the charcoal increases, the initial reaction temperature increases, the maximum weight loss rate decreases. There is synergistic effect restraining the reaction between the components. In air, with the charcoal increase, the initial and final reaction temperature increase, maximum weight loss rate decrease. There is synergistic effect accelerating the reaction between the components.To analyze the relation between the mixing ratio and kinetics as well as get mixtures’weight loss rate in any ratio, the kinetics were determined by homogeneous and shrinking core model, in addition, a weight loss model was used to calculate the mixtures’weight loss. Results show, in nitrogen and air, to charcoal and the mixture owning highest charcoal contend, homogeneous model is better than shrinking core model, the other three are opposite. In nitrogen, as the charcoal increases, the fitting range presenting reaction region transits from low to high temperature. In air, charcoal and the mixture owning highest charcoal contend fit at high temperature, that is their reaction region, while the other three samples fit at both high and low temperature. The weight loss model’s results accord with the experimental results well, indicating that the mixtures’ weight loss rate can be calculated approximately with the model on the basis of the components’weight loss data.To research the relation between the fuels’functional group and their characteristics, the fourier transform infrared spectrometer (FTIR) was used, functional groups are the main reaction position. Results show, with the wood increases, the oxygenic groups increase. The graph including the characteristic parameters and the peak number of wood and charcoal shows that the sample’s reactivity is greater when its oxygenic groups are multiple.In conclusion, mixing of biomass and its char is of great significance to pyrolysis and combustion characteristics. In nitrogen and air, There are synergistic effect restraining and accelerating the reaction between the components respectively. The weight loss model can predict the mixtures’ weight loss well. Different mixing ratios have different functional group, which lead to different reactivity.