Study On Thin-layer Drying Characteristics Of Brown Coal

The drying characteristics under isothermal condition of Hulun Buir pulverized brown coal with high moisture content was studied using thermo-gravimetric method. The effects of drying temperature and particle size on drying process were analyzed. The typical drying stage were divided according to the drying rate curve. The max drying rate, the critical moisture content and the equilibrium moisture content were obtained, and the effects of temperature and particle size on them were analyzed. The constant drying rate stage was obviously observed, and the characteristics were closely related to drying temperature and free water content. The drying rate decreased with the decrease of particle size, but the effect of particle size is not obvious when the coal particle is enough small. The critical and equilibrium moisture content decreased with the increase of temperature and particle size. When the temperature is between 80℃ and 100℃, the particle size arranges from 100 μm to 300 μm, the drying rate and efficient were high. The experimental results could provide the basis of selection and optimization of brown coal powder and drying process conditions.The thin-layer drying kinetics of Hulun Buir pulverized brown coal with high moisture content under isothermal condition was investigated using infrared moisture analyzer (Sartorius MA150).12 thin-layer drying models used to fit the experimental data, and the Page model was the best to describe the thin-layer drying process of Hulun Buir brown coal. According to Page model, the moisture content, drying rate constant (k) and drying rate at any time could be calculated. The effect of drying temperature and particle size on drying dynamics were studied. The effective moisture diffusivity (Deff) and drying activation energy (Ea) were determined by Fick’s second diffusion law and Arrhenius equation. Furthermore, an expression which described the relationship of drying rate and time was proposed. The calculated results and experimental data fitted well. It could provide the data basis for the selection and optimization of brown coal powder and drying process conditions.The water resorption process of Hulun Buir brown coal was studied using the constant climate chamber. The effects of relative humidity, particle size, and drying temperature on water resorption characteristics were analyzed. The effect of drying process on particle pore structure was shown directly with SEM. The water resorption characteristics affected by pore structure changing was explained. The relative humidity was the main driving force of water resorption. The smaller the particle size, the faster water resorption rate, and the higher equilibrium moisture content. The destroy degree of particle pore structure was large when the drying temperature was high.