单颗粒褐煤高温烟气干燥过程研究

STUDY ON SINGLE LIGNITE PARTICLE DRYING PROCESS BY HOT GAS

以褐煤颗粒中水分蒸发界面为基础,将褐煤颗粒分为干区和湿区,干区考虑传热传质,湿区只考虑传热,并采用有限体积法,建立了一维球坐标系下单颗粒褐煤干燥脱水过程模型.利用Crank-Nicolson六点差分格式对其离散,模拟得到不同工况(初始烟温、停留时间和颗粒粒径等)下的单颗粒褐煤含湿量及其内部温度分布的动态变化.实验结果与模型模拟结果对比表明二者吻合度较好,所建干燥模型可以较好地反映褐煤干燥的实际过程.研究发现,初始烟温越高、停留时间越长以及颗粒粒径越小,干燥效果越好.当粒径为20mm的褐煤颗粒在初始温度为873K的热气流下停留131s时,其含水量即可从25.3%降到12%以下,此时颗粒表面的温度为537K,略高于挥发分初析温度(520K),此工况可以作为褐煤实际干燥过程中的最佳工况参照.

ABSTRACT Based on finite volume method, the model of the drying process of a single spherical lignite particle in hot gas was developed. In the paper, the lignite particle was divided into dry region and wet region by water evaporation interface. Crank-nicolson scheme was used to discretize the transport equations so that a single lignite particle dynamic process of moisture content and temperature distribution within the particle under different conditions （initial gas tem- perature, particle size, resident time） was identified. It is suggested that the model values are more closed to the experimental results and the actual drying process of lignite can be simulated successfully by the model. It was found that longer residence time, larger particle size and drying medium of higher original temperature lead to lower moisture lignite. At the initial gas tempera- ture of 873 K, the moisture content of the lignite particle size of 20 mm decreases from 25.3% to 12% within the residence time of 131 s and the surface temperature of lignite particle is just 537 K, a little higher than the initial evolution temperature of volatile （520 K）. Hence, it can be used as the reference of the actual drying process of lignite. KEY WORDS lignite, high temperature gas, drying, mathematical model