细粒褐煤在振动重介质流化床中的干燥特性研究

发布时间：2018-04-03 05:18

  本文选题：褐煤　切入点：振动重介质流化床　出处：《中国矿业大学》2015年硕士论文

【摘要】：我国褐煤资源丰富,约占全国煤炭储量的13%,但其含水率高、热值低,使褐煤利用效率低,经济性差,并导致环境污染。因此,深入研究褐煤干燥及清洁高效利用技术迫在眉睫。本论文在普通流化床基础上引入振动和重介质(磁铁矿粉),针对褐煤的流化特性、混合度及干燥特性进行实验,结合薄层干燥模型分析干燥过程中有效水分扩散系数、活化能、干燥速率和热量利用,着重研究了褐煤在振动重介质流化床中的干燥特性。通过对褐煤与磁铁矿粉混合物在振动流化床中的流化特性及混合度的研究发现,随着振幅和频率的增大,床层最小流化气速先减小后增大;随着介质量的增多,床层最小流化气速先减小后不变;温度的升高及褐煤颗粒粒径的减小也会减小床层最小流化气速;床高对振动重介质流化床的最小流化气速影响不大。床层混合度随着风速和振动强度的增大先减小后增大,最后达到稳定的较大值;随着介质量的增多而增大,随着床高的增高先增大后不变。在80-160℃条件下,对四种状态(无振动无介质、无振动加介质、加振动无介质、加振动加介质)进行了干燥实验,并对结果进行拟合分析:Midilli-Kucuk模型最适用于描述胜利褐煤的干燥;由于温度的升高,使褐煤干燥速率增大,有效水分扩散系数增大,其值在7.38×10-9-5.37×10-8 m2/s范围内;同时,振动和介质的加入使活化能减小,四种状态下活化能分别30.20KJ/mol、29.40 KJ/mol、30.04 KJ/mol、24.47 KJ/mol。褐煤在振动重介流化床的干燥过程中,外水干燥速率受振动强度、风速、粒径、温度及介质量的影响较大,受床高的影响较小;内水干燥速率受温度影响最大,受其他因素影响很小。因此,干燥外水适用于中温高气速及适量的介质,干燥内水时适用于高温低风速条件。对干燥过程中热量衡算发现,水分蒸发所需要的热量、颗粒升温所需热量以及热效率均随着湿含量降低而降低,在湿含量降低到10.11%时,平均热效率为52.15%,而当褐煤湿含量由10.11%至干燥完全,其平均热效率仅为4.48%;而尾气温度随含湿量降低而升高,尾气带走热量也增大,尾气中水汽少,因此,在干燥褐煤内水时可考虑循环使用尾气,减少能耗。
[Abstract]:China is rich in lignite resources, accounting for about 13% of the national coal reserves, but its high moisture content and low calorific value make lignite use efficiency low, economy poor, and lead to environmental pollution.Therefore, it is urgent to study the drying and clean and efficient utilization of lignite.In this paper, vibration and heavy medium (magnetite powder) are introduced on the basis of ordinary fluidized bed. Experiments on fluidization, mixing degree and drying characteristics of lignite are carried out. The effective moisture diffusion coefficient and activation energy are analyzed in combination with thin-layer drying model.The drying characteristics of lignite in a vibratory heavy medium fluidized bed were studied in terms of drying rate and heat utilization.The fluidization characteristics and mixing degree of the mixture of lignite and magnetite powder in a vibratory fluidized bed are studied. It is found that with the increase of amplitude and frequency, the minimum fluidization gas velocity of the bed decreases first and then increases, and with the increase of the medium mass,The minimum fluidized gas velocity of the bed will decrease first and then remain unchanged, the increase of temperature and the decrease of the particle size of lignite will also decrease the minimum fluidized gas velocity of the bed, and the bed height will have little effect on the minimum fluidized gas velocity of the vibrating heavy medium fluidized bed.With the increase of wind speed and vibration intensity, the mixing degree of the bed first decreases and then increases, and finally reaches a larger value of stability, and increases with the increase of the medium mass, increases first with the increase of the bed height, and then remains the same with the increase of the bed height.Under the condition of 80-160 鈩，

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