Hot-air drying behavior of lignite and quantitative characterization for its surface damage

Abstract

Cracking and fragmentation problems that occur during lignite drying limit its utilization value. In this study, the dehydration, surface damage, and pulverization behaviors of lignite were investigated under hot-air drying conditions, and the effect of the dewatering process on shrinkage cracking was analyzed. Cracks first appear at the edges of the lignite, then gradually extend inward until they spread over the entire surface of the lignite, before beginning to shrink, and eventually stabilize. The crack rate exhibited three stages: rapid development, shrinkage, and stabilization. The crack rate and shrinkage percentage increased significantly with increase in the drying temperature. The moisture content had a greater influence on the crack rate and shrinkage percentage of the samples than the surface temperature. A uniaxial compression test revealed that lignite with different degrees of dryness exhibited different degrees of breakage. The drying process drives the lignite toward finer grain sizes and, with moisture content below 0.8 g/g, the degree of breakage increases significantly. Thus, the main factor affecting the shrinkage and cracking of lignite was the moisture content. Cracks occurred when the tensile strain caused by shrinkage was greater than the tensile strength of the lignite.

Keywords:

• Lignite
• drying
• crack
• shrinkage
• fragmentation

Acknowledgment

The authors gratefully acknowledge the financial support for this research by the Natural Science Foundation of China (No. 51904274), the Open-Fund of Henan Key Laboratory of Coal Green Conversion (CGCF202104), Henan Province Key Research and promotion special (science and technology research) project, Training Program for Young Key undergraduate Teachers of Zhengzhou University, and Program for Innovative Research Team (in Science and Technology) in University of Henan Province (No. 19IRTSTHN028).

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.