Xian Wu, Ziwen Dong, Lifeng Sun, Tinggui Jia
College of Safety Science and Engineering, Liaoning Technical University, Fuxin, Liaoning 123000, China.
School of Safety Engineering, Ningbo University of Technology, Ningbo, Zhejiang 315211, China.
ACS Omega. 2022 Mar 16;7(12):10029-10038. doi: 10.1021/acsomega.1c05575. eCollection 2022 Mar 29.
Low-temperature and humid drying experiments [temperatures of 20-30 °C; relative humidity (RH) of 40-60%] were conducted to investigate the drying shrinkage of lignite at low temperatures. The moisture content and volume variations of lignite during low-temperature drying were measured to analyze the change in the water content and volume drying shrinkage rate under low-temperature drying conditions. The results show that in the first 48 h of drying, the water evaporated rapidly. The amount of external water evaporated and lost accounted for 70-90% of the total water lost during the entire low-temperature drying period, and the average water content is reduced to about 12.8%. When the rapid loss of external water decreased to less than 12.8%, the water adsorbed on the external surfaces, the movable water between large particles was completely lost, and saturated lignite underwent heterogeneous volume shrinkage. The drying shrinkage was slow during the first 48 h, accounting for 20.8% of the total drying shrinkage in the entire low-temperature drying process. The volume shrinkage occurred in four stages as the water content decreased with time. With increasing drying time, the decrease in the water content occurred in four stages: the thermal expansion stage, rapid shrinkage stage, slow shrinkage stage, and stable shrinkage stage. The dry shrinkage rate has a significant positive correlation with the water evaporation quality and significant negative correlations with the water content and evaporation rate. The lower the evaporation rate, the greater the dry shrinkage rate when the saturated lignite is dried under low-temperature and humid conditions (temperature of <30 °C; RH of <60%). There is a time lag between volume shrinkage and water loss, and there is also a difference in their quantities. The volume shrinkage is lower than the water loss, and the difference is largest about 48 h into the initial stage of low-temperature drying. As the low-temperature drying time increases, the shrinkage due to drying becomes stable, and the moisture content remains unchanged. The larger the ratio of RH to temperature, the larger the stable shrinkage.
进行了低温和潮湿干燥实验（温度为20 - 30°C；相对湿度（RH）为40 - 60%），以研究褐煤在低温下的干燥收缩情况。测量了褐煤在低温干燥过程中的水分含量和体积变化，以分析低温干燥条件下水分含量的变化和体积干燥收缩率。结果表明，在干燥的前48小时内，水分迅速蒸发。蒸发和损失的外部水分占整个低温干燥期间总失水量的70 - 90%，平均水分含量降至约12.8%。当外部水分的快速损失降至低于12.8%时，吸附在外部表面的水分、大颗粒之间的可移动水分完全丧失，饱和褐煤发生非均匀体积收缩。在最初的48小时内干燥收缩缓慢，占整个低温干燥过程中总干燥收缩的20.8%。随着水分含量随时间降低，体积收缩分四个阶段发生。随着干燥时间的增加，水分含量的降低分四个阶段：热膨胀阶段、快速收缩阶段、缓慢收缩阶段和稳定收缩阶段。干燥收缩率与水分蒸发质量呈显著正相关，与水分含量和蒸发速率呈显著负相关。在低温和潮湿条件下（温度<30°C；RH<60%）干燥饱和褐煤时，蒸发速率越低，干燥收缩率越大。体积收缩和水分损失之间存在时间滞后，并且它们的量也存在差异。体积收缩低于水分损失，在低温干燥初始阶段约48小时时差异最大。随着低温干燥时间的增加，干燥引起的收缩变得稳定，水分含量保持不变。RH与温度的比值越大，稳定收缩越大。
