Experimental Study Xilin Hot Lignite Drying Kinetics And Moisture Readsorption Characteristics

In recent years, with the economy rapid development, the high-quality coalresources shortage, people are turning to relatively abundant, inexpensive lignite,but the characteristics of high moisture, low calorific value affects its widerapplication. For lignite drying upgrading, on the one hand increases the calorificvalue and its use efficiency, while also reduces transportation costs. Therefore, thestudy of lignite drying kinetics and moisture reabsorption characteristics hasimportant practical significance.The thesis studys the drying kinetics and moisture migration diffusioncharacteristics under isotherm and non-isothermal conditions, focusing on theeffects of temperature, dry atmosphere on the lignite drying characteristics andmoisture reabsorption characteristics, in order to investigate the drying process andmoisture reabsorption mechanism. Conclusions are as follows:As the temperature increases, the lignite drying rate increases, but the law issimilar. The drying stage can be divided into constant rate drying period and fallingrate drying period, falling period may be divided into the first reduction stage andthe second. In the constant rate and the first drying period, the bound water andcapillary water are dehydrated, in the second reduction stage, the multilayer waterand monolayer water, connected to lignite oxygen-containing functional group byhydrogen bonds, are removed. When the dry basis water content is less than10%, inaddition to230℃, the drying rate is almost same under different temperatures,indicating that this part of water is difficult to remove.Lignite isothermal drying characteristics is studied by the Weibull distributionfunction, there is a good correlation with experiment data, indicating that theWeibull distribution function can be well described lignite drying process. The scaleparameter is greatly affected by temperature and sample thickness, however, littleimpact on the shape parameter. It means that in the experiment, the sample mass andtemperature influence the drying rate, but the water evaporation diffusionmechanism has little effect.The paper studied the drying kinetics of two lignitics on the thermobalance, andthe result showed that the activation energy of the two lignitics had the similarvariation trend, which was the activation energy decreased at first and thenincreased with the temperature growing.In the hole dehydration process, thedesorption energy of different formals of water was different because of thebinding effect of capillary tube and the adsorptive action of cellular structure.The drying rate of lignite in CO2was samll than that in N2and air, when it was dryed in air below200℃, the concentration of groups like carboxy increased whilethe concentration of methylene decreased, which showed that the oxidation processmainly happaned on the side chain of the aliphatic hydrocarbon.The moisturereabsorbing result of the coal sample dried in three drying mediums showed, at thetemperature of140℃, the reabosorbing amount of the coal sample was quitedifferent, the reabosorbing amount of the coal sample dryied in air is the larggest,and the coal sample dried in N2was the last one. However, then the temperature is200℃, the reabosorbing amount of the coal sample was close. which showed that ata low temperature, the drying medium effected largely on the drying characteristicsand structure of coal sample, while at high temperature the temperature plays themain role in the drying process.