Drying behaviors of low-rank coal under negative pressure: Kinetics and model

ABSTRACT

The drying behaviors of low-rank coal (LRC) under negative pressure were studied with a vacuum-drying oven under different pressures and temperatures. The results confirmed the feasibility of using the Page model to predict the drying behaviors of LRC under negative pressure. A new ideal radical ball model was proposed to further qualitatively analyze the influences of pressure and temperature on the drying behaviors. Reasoning based on the radical ball model combining the Kelvin formula, Fick’s first law of diffusion, Knudsen’s diffusion law, and transition diffusion region suggests that a higher negative pressure and temperature leads to a higher maximum dehydration rate, that larger pressure and temperature gradients cause smaller critical moisture contents, and that decreases in the drying pressure and increases in the temperature increase the instantaneous removal rate of bound water.

KEYWORDS:

• Drying behaviors
• kinetics model
• low-rank coal
• negative pressure