褐煤等温脱水热重分析

利用热天平热重和微分热重分析方法，进行了4种褐煤在氮气流下等温干燥实验，得到了样品蒸发速率与含水率关系曲线，并获得各脱水阶段的干燥机理方程。采用扫描电镜对脱水前后褐煤外观形貌进行分析。结果表明，热天平氮气吹扫条件下，褐煤体积收缩、外观发生变化；干燥过程分成2个阶段，其中含水率高于临介含水率阶段是褐煤较大孔结构中自由水/体积水蒸发析出过程，并伴随褐煤体积的收缩，按照Kelvin公式，该过程主要受毛细管作用力影响，蒸发速率逐渐降低；含水率低于临介含水率阶段对应褐煤内部微孔内水分的干燥，由于褐煤表面富含含氧官能团，并与水通过氢键连接，水的蒸发速率变得更低，蒸发过程主要受脱附/吸附以及氢键破坏作用控制。

Investigation on the Isothermal Dewatering of Brown Coal by Thermobalance

Using thermobalance, four kinds of brown coal were dried under the flow of nitrogen and isothermal conditions. With thermogravimetric (TG) and differential thermogravimetric (DTG) methods, the curves of evaporation rates versus moisture contents were plotted and the mechanism equations of different drying stages were obtained. Samples before and after drying were also analysed by scanning electron microscope (SEM). Results show that under the condition of nitrogen flow in thermobalance, coal bulk decreases as the micro-morphology changes; the drying process can be divided into two stages. At the first stage when moisture content X is larger than the critical value, Xc, water in bigger pores of brown coal is first evaporated, along with the shrinkage effect of coal bulk; according to the Kelvin formula, the evaporation rate decreases due to the increase of capillary force. At the second stage when X is smaller than Xc, water in the micropores is dried, such water is linked with the brown coal surface through hydrogen bond between oxygen-rich function groups and water moleculars; during such process, the evaporation rate becomes even smaller because it is controlled by the mechanism of adsorption and desorption also by the breakage of hydrogen bond.