Investigation of wet particle drying process in a fluidized bed dryer by CFD simulation and experimental measurement
Investigation of wet particle drying process in a fluidized bed dryer by CFD simulation and experimental measurement
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DOI：
10.1016/j.cej.2022.139200
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发表时间：
2022-09
影响因子：
15.1
通讯作者：
Q. Tu;Z. Ma;Haigang Wang
中科院分区：
文献类型：
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作者：
Q. Tu;Z. Ma;Haigang Wang
由于颗粒含水率的变化，湿法颗粒干燥过程十分复杂，对颗粒的气固性质、流动动力学以及传质换热行为都有很大影响。本文采用双流体模型(TFM)对颗粒在沸腾床干燥器中的干燥过程进行了数值模拟。同时，采用在线电容层析成像技术(ECT)测量固体颗粒浓度，离线水分仪测量颗粒水分。实验干燥曲线包括恒速期和降速期两个阶段。通过二维CFD模拟得到了连续干燥曲线。干燥速率在预增温阶段急剧增加，在恒速阶段达到最大值，在降速阶段先显著下降，然后缓慢下降。颗粒温度逐渐升高，直至达到空气温度并保持恒定。为了捕捉干燥过程中详细的流动动力学，对一定含水率下的干燥过程进行了三维CFD模拟。结果表明，模拟得到的颗粒截面体积分数为核心-环状结构，并得到了在线电容层析成像的验证。沿反应堆高度形成内循环。传质和换热主要发生在干燥器的下部和气泡与固相的接触区。随着颗粒含水率的降低，最小流态化速度减小，气泡上升速度增大。
Wet particle drying process is complex due to the change of particle moisture, which has big effect on the gas–solid properties, flow dynamics and mass and heat transfer behavior. In this research, a two-fluid model (TFM) coupled with the mass and heat transfer was used to simulate the particle drying process in a fluidized bed dryer. Meanwhile, online electrical capacitance tomography (ECT) was used to measure the solids concentration and off-line moisture meter was employed to measure the particle moisture. Two periods, i.e., constant-rate period and falling-rate period, were captured in the experimental drying curve. The continuous drying curve was obtained by the 2D CFD simulation. The drying rate increases sharply in the pre-warming period, reaches high in the constant-rate period, and decreases markedly in the falling-rate period at the beginning and then decreases slowly. The particle temperature increases gradually until it reaches the air temperature and keeps constant. In order to capture detailed flow dynamics in the drying process, 3D CFD simulations at certain moisture contents were performed. It is found that the simulated cross-sectional particle volume fraction shows core-annular structure and is verified by the on-line ECT measurement. An internal circulation is formed along the reactor height. The mass and heat transfer mainly happens at the lower part of the dryer and at the contact region between the bubbles and the solids phase. The minimum fluidization velocity decreases, and the bubble rising velocity increases when the particle moisture level decreases.