流化床中单颗粒纤维素热解模型研究

MODEL OF CELLULOSE PARTICLE PYROLYSIS IN FLUIDIZED BED REACTOR

为了研究生物质热解过程 ,该文对纤维素这种生物质中最主要组份的流化床热解过程进行了数值模拟。模型在合理选取动力学模型的基础上考虑了单颗粒纤维素在流化床热解过程中由扩散和对流所引起的热量传递 ,包括了各种重要的气、液相热解产物的质量传递以及颗粒内部压力对过程的影响。计算结果显示 ,即使是对非常小的颗粒 ,热解反应热对热解过程的影响也至关重要 ;而无论是在大颗粒还是小颗粒中 ,热解液相中间产物流动对能量、质量传递的影响以及挥发份参加颗粒内二次反应的份额则可以忽略。计算还得到了不同粒径颗粒热解的产物分布。总体来说 ,该模型为我们提供了一个探究纤维素热解细节的机会。计算结果可以为实际热解反应器的设计和运行提供依据。

To study biomass pyrolysis processes, a numerical model is developed in this paper. It is dedicated to study the process of single cellulose particle pyrolysis in fluidized bed. The model includes the mass conservation of all of those important solid, liquid and gas products of pyrolysis and inter particle pressure distribution, all of the important heat and mass transfer caused by diffusion or convection are also taken into account. It can reveal the very detailed process of cellulose particle pyrolysis. By solving the model presented in this paper, the role of reaction heat during fluidized bed pyrolysis is proved to be very crucial, even for very small particle (r=1mm). The solid reaction time is determined and the influence of kinetic data on this time is also discussed quantitatively. The evolutions of the internal pressure and the flow of important products are analyzed comprehensively and the importance of particle permeability is identified. The calculation shown the flowing of active cellulose and inter particle secondary reaction play negligible roles during pyrolysis under fluidized bed conditions both for small and large particles adopted in the calculation. Additionally, yields of every pyrolysis products are also deduced. In general, the simulation provides a very good chance to peruse the inside detail of cellulose particle pyrolysis in fluidized bed reactor. The results achieved are very meaningful to those practial reactor design and operation.