Study On Drying Characteristics Of Fine-lignite In The Vibration Fluidizedbed With Medium

Lignite resources are abundant in China,which accounts for 13% of coal reserves, but its high moisture content and low calorific value make the lignite low utilization efficiency and economical efficiency, and cause environmental pollution. Therefore, further study on drying and cleaning technique of lignite is imminent. In this paper, vibration and heavy medium(magnet) was introduced into normal fluidied bed, experiment based on the fluidization characteristics,mixing degree, and drying characteristics, combined with thin layer drying model analyses the effective moisture diffusivity, activation energy, the drying rate and heat utilization in the drying process,and focus on the drying characteristics of lignite in the Vibration Fluidized Bed with Medium.Through the study on the fluidization characteristics and mixedness of lignite and magnetite powder in the VFB(Vibration Fluidized Bed),we found that the bed minimum fluidizing gas velocity decreases firstly and then increases with the increase of amplitude and frequency; the bed minimum fluidizing gas velocity decreases firstly and then hardly changes along with the increase in the quantity of medium;the rise of temperature and the decrease of the lignite particle size will decrease the bed minimum fluidizing gas velocity;the impact of bed height for the minimum fluidizing gas velocity of the VFB with medium is small.And that with the increase of vibration intensity, the bed mixing degree reduces firstly,then increases and finally achieves the larger value of stability; the bed mixing degree increases along with the increase in the quantity of medium and increases firstly and then changes hardly as the increase of bed height.Drying experiment was carried out in the four states(non-vibration & non-medium,non-vibration & medium,vibration & non-medium,vibration & medium) under the condition of 80-160 ℃. and the results were fitting analysis: Midilli-Kucuk model is best suited for describing Shengli lignite drying; The rise of temperature makes lignite drying rate and effective moisture diffusion coefficients increase,and the effective moisture diffusion coefficients are in the range of 7.38×10-9-5.37×10-8 m2/s. At the same time, adding vibration and medium make the activation energy decrease,and the values are 30.20KJ/mol,29.40 KJ/mol,30.04 KJ/mol and 24.47 KJ/mol in the four states.In the process of drying lignite in the VFB with medium,the drying rate of external water was influenced greatly by the vibration intensity, gas velocity, particle size, temperature and medium quantity,but it is less affected by bed height.The drying rate of inner water was most affected by temperature and little affected by other factors.Therefore,drying external water applied to middle temperature,high gas velocity and amount of medium and drying inner water applied to high temperature and low gas velocity.Base on the heat banance in the drying process,the heat required to evaporate the water, the heat required for heating the particles and thermal efficiency decreased with the decrease of moisture content, while the moisture content decreased, exhaust gas temperature raised, the heat taken away by exhaust gas also increased,and the water vapor in exhaust gas was less,so when drying inner water of lignite we can consider recycling the eshaust gas to reduce energy consumption.