An experimental study on binderless briquetting of Chinese lignite: Effects of briquetting conditions

• Chinese lignite was dried in nitrogen and briquetted without binder.
• Different parameters in the binderless briquetting process were studied.
• The optimum briquetting parameters were obtained.
• The study of the chemical structure of coal showed oxidation affects briquette strength.
• Hydrogen bonds were proved to play an important role in briquetting.

Technology development of lignite upgrading involving drying and binderless briquetting is important to the efficient utilization of lignite resources. In this study, the effects of briquetting conditions, i.e., briquetting pressure, temperature, coal properties and pretreatment, on the compressive strength of briquettes were systemically investigated using a lab-scale briquetting testing rig. The experimental results indicated that the compressive strength of briquettes increased with increasing the compression pressure. An optimum strength was obtained at the briquetting temperature of 150 °C. There also existed an optimum moisture content of 14–16% at which the highest compressive briquette strength was achieved. The increase in the amount of –125 μm size fraction in the feed sample increased the briquette strength. FTIR analysis showed that the oxygen-containing functional groups have a significant influence on the compressive briquette strength due to the ability of forming more hydrogen bonds.