甘肃窑街油页岩等温干燥机理分析

Investigation on isothermal drying mechanism of Yaojie oilshale

采用甘肃窑街油页岩颗粒作为原料,利用电热鼓风箱和电子天平及红外温度测定仪,测定油页岩样品在外界温度恒定条件下的含水率和干燥速率曲线,并讨论各段的干燥机理方程,分析温度、粒径大小对甘肃油页岩干燥效果的影响。结果表明:干燥速率曲线上明显存在拐点,由此可知干燥过程存在不同的干燥机理,当含水率大于拐点含水率时,主要是大孔隙中的自由水和束缚水脱除过程且伴随着体积的缩小,由Keliven公式,这一过程受到毛细管作用影响,蒸发速率逐渐降低;含水率小于拐点含水率阶段对应着油页岩内部更细小孔内水分的受热过程,当水分子动能达到一定值后突然汽化逸出引起含水率下降并引起油页岩干燥后期的热破碎现象。

Yaojie oil shale particles were taken as sample to determine water content and drying rate with electric heating box,electronic balance and infrared temperature measuring instrument. The drying mechanism in each section was discussed,and the effect of temperature,particle size on oil shale drying was analyzed. On the drying rate curve,an inflection point existed obviously,which suggested that the drying process was divided into two stages. When water content was higher than the one of the inflection point,the main process is the removal of free water and bound water in large pores accompanied with shrinkage. According to the Kelvin equation,this process was influenced by the capillary effect,which reduced the evaporation rate gradually. When water content was less than the one of the inflection point,water in the smaller pores was heated,water molecular escaped when its kinetic energy reached a certain level,causing the decrease of moisture content and thermal breakage during the later period of oil shale drying.