Abstract:

Lignite drying is very important for improvement of lignite quality. In order to simulate evaporation process of water in lignite particle during drying in high temperature flue gas, a mathematical model was established for the unsteady drying process of single lignite particle at high and variable temperature using finite volume method, and the fundamental assumption made was that the lignite particle was spherical and could be divided into two parts in one-dimensional spherical coordinate system by water evaporation interface that migrates inwards during drying. The model was used to analyze the drying behavior of lignite particle with time and the effect of initial temperature of flue gas and particle size. The variation trend obtained by numerical simulation was similar to that did by experiments for drying process. It was found that the higher initial flue gas temperature and the smaller particle size lead to the faster migration velocity of the water evaporation interface, the lower moisture content of lignite particle and the shorter drying time. There is a linear relationship between the interface migration velocity and the initial flue gas temperature and lignite particle size.

Key words: single particle, lignite, high temperature flue gas, drying, heat transfer, mass transfer, numerical simulation

摘要：

褐煤干燥对于提高其品质具有重要意义。为了模拟高温烟气干燥这一高温差、变温差非稳态传热传质过程中褐煤内水分蒸发过程,采用有限体积法建立了一维球坐标系下蒸发界面向内迁移的单颗粒褐煤干燥数学模型,并利用该模型分析了初始烟气温度和颗粒粒径对单个褐煤颗粒干燥特性的影响。模型模拟结果与实验结果对比表明二者变化趋势一致,所建模型能较好地反映出高温烟气干燥过程中褐煤内水分蒸发过程。结果表明,初始烟气温度越高,颗粒粒径越小,蒸发界面向内迁移速度越快,水分脱除越快,干燥时间越短;蒸发界面平均迁移速度均与初始烟气温度和颗粒粒径呈线性关系;在初始烟气温度700℃下,较短的停留时间使得颗粒表面温度未达到挥发分析出温度,本研究中不同粒径褐煤颗粒在干燥过程中基本没有挥发分的析出。

关键词: 单颗粒, 褐煤, 高温烟气, 干燥, 传热, 传质, 数值模拟