Abstract
Environmental requirements and demands from the coal industry have resulted in a boom in briquetting technology in China. In this work, a low-volatility bituminous coal from the Changcun mine and bentonite binders are used for briquetting. The compressive strength, impact strength, and thermal stability of briquettes made using different binder concentration are determined. The morphology and distribution of binders in briquettes are studied by optical microscopy and digital image-processing technologies. The concept of roundness is introduced to indicate the pressure to which the binders are subjected during briquetting. The influences of binder morphology on briquette strength are discussed. The binders are mainly in aggregated and dispersed forms, present in similar proportions in the briquettes. Aggregated binders with large differences in size are not well-distributed. Binder roundness values are concentrated between 1.5 and 4.0, which indicates that most aggregated binders are compressed and conform well to the surfaces of coal particles. A few binders had roundness value approximating 1 or above 4, which indicated that these were under little pressure or overloaded, respectively. The relationships between briquette strength and binder morphology show that aggregated binders are detrimental to mechanical strength while dispersed binders benefit briquetting.
Highlights
In 2013, 3.7 billion tons of coal sample were mined and 3.61 billion tons of coal were consumed in China
Two forms of binders were found in the briquettes examined by optical microscopy
Small particles and dark colors were seen in the dispersed binders, which made quantitative analysis difficult, so this study focused on agglomerated binders
Summary
In 2013, 3.7 billion tons of coal sample were mined and 3.61 billion tons of coal were consumed in China. As more emphasis is placed on cleaner production and controlling air pollution, cleaner utilization of coal is a strong direction of future development. Bai Key State Laboratory for Coal Mining and Clean Utilization, Beijing 100013, China. Research concerning relationships between the microstructure and the macroscopic properties is necessary to model and improve the performances of materials. The morphology and distribution of the binders have a strong effect on their performance. The microstructures (morphology and distribution) of binders in briquettes and their influence on briquette strength are discussed. The morphology and distribution of binders in briquettes can be characterized by optical microscopy. Optical microscopy and digital processing technology were chosen to study the binder microstructures in the briquettes
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