Heat Transfer Modeling And Study In A Single Wood Particle During The Pyrolysis Process

Wood fast pyrolysis technology is one of most promising methods to utilize wood resources. However, the mechanism is still in the stage of exploration. Heating up rapidly which is different from traditional pyrolysis is the prominent features of fast pyrolysis technology and affects the product. Heat transfer in wood particle is the key to optimize wood pyrolysis process for it controls the process of pyrolysis. In this paper, a 2-D transient heat transfer model in cylindrical to predict the thermal behavior in a single wood particle during the pyrolysis process in a fluidized bed has been made. Wood anisotropy and thermophysical properties was considered in this model, as well as the influence of the source phase including heat reaction and evaporation of moisture in wood on temperature distribution in wood particle, in addition, the effective convection heat transfer coefficient between the single particle and the bed was calculated. The ANSYS was used to solve the heat transfer equation. Based on the calculation of transient temperature in wood particle and the temperature distribution during the process of wood pyrolysis at different time, the influence of heat reaction, moisture content, l/d and thermophysical properties on the temperature changes of the result was investigated. In order to verify the validity of the model, three representative sample wood particles were selected to pyrolysis in thermal analysis equipment (HCT-1). After making a comparison between experiment results (the TG and DTG curves) and simulation results (the TG and DTG curves), it was found that this model fits the real situation well.Results are as followed:(1) A relatively perfect heat transfer model to predict the thermal behavior in a single wood particle during the pyrolysis process has been done. It is found that the heat transfer from outside to inside in a single wood particle during pyrolysis process, and the pyrolysis reaction associated with temperature was layered and handed in.(2)Also, moisture content and heat reaction have a significant influence on the temperature rising, existence of moisture and endothermic reaction hinder heat transferring from outside to inside. When l/d≥3, we can think that the heat transfer take place along the radial direction. When l/d<3, we can think that the heat transfer crisscross in vertical and horizontal. The calculation results are agreed with the previous literature and experimental results.(3) For the wood particle in cylindrical,When l/d<3, the heat transfer equation is: 1/r(?)/(?)r(krr(?)T/(?)r)+(?)/(?)z(kz(?)T/(?)z)+Φ=ρc(?T)/(?)τ And when l/d<3, the heat transfer equation is: 1/r(?)/(?)r(krr(?)T/(?)r)+Φ=ρc(?T)/(?)τ(4)A new method to validate the heat transfer model was established. The thermogravimetric analysis (TG) was used to measure the wood particle weight changes during the low pyrolysis. After modeling temperature distribution in a single wood particle under the above situation by the heat transfer model, we compared the simulated results with the measured results. This method provides a new mean to validate the heat transfer model in a single particle with small size.