褐煤低温干燥表面收缩特性实验研究*

Experimental study on surface drying shrinkage characteristics of lignite under low temperature

摘要:

为明确褐煤低温（50 ℃以下）干燥引发表面干缩现象的发展规律，采用低温（20~30 ℃）低湿（40%~60%）空气干燥的方式，开展褐煤低温干燥干缩实验，分析干燥与表面收缩规律。结果表明：低温干燥过程中，对水分蒸发速率影响显著的因素是相对湿度而非温度，70%~90%的总水分散失量在干燥初期48 h内蒸发完成，平均含水率低至12.8%；低温干燥导致褐煤发生非均匀性表面干燥收缩，表面干缩经历热胀-快速干缩-收缩稳定3个阶段，水分快速蒸发散失的前48 h干缩率低，之后进入水分蒸发速率显著降低而干缩率持续升高，最终至收缩稳定，低速蒸发阶段发生显著干缩；表面干燥收缩率与散失水分质量具有显著的正相关性，与水分含量和蒸发速率具有显著负相关性。

Abstract:

In order to clarify the development laws of surface drying shrinkage caused by the low temperature drying (below 50 ℃) of lignite,the low temperature drying and drying shrinkage experiments were carried out by using the air drying with low temperature (20~30 ℃) and low relative humidity (40%~60%) to analyze the drying and surface shrinkage laws.The results showed that in the process of low temperature drying,the relative humidity,rather than temperature,was the significant influencing factor on the water evaporation rate.70% to 90% of the total moisture loss evaporated within the initial 48 hours of drying,and the average moisture content dropped to 12.8%.The low temperature drying engendered the non-uniform surface drying shrinkage of lignite,and the surface drying shrinkage went through three stages of thermal expansion,rapid drying shrinkage and stable shrinkage.In the initial 48 hours with rapid evaporation and loss of water,the drying shrinkage rate was low,and after that,the evaporation rate of water decreased significantly and the drying shrinkage rate increased continually,and the significant drying shrinkage occurred in the low-speed evaporation stage with the final stable shrinkage.There was a significant positive correlation between the surface drying shrinkage rate and the lost water quality,and a significant negative correlation between the surface drying shrinkage and the water content and evaporation rate.