气固流化床中颗粒的夹带和扬析特性

在内径0.5 m、总高6 m的流化床中对玻璃珠和白刚玉颗粒的夹带和扬析现象进行了实验研究，两种颗粒通过筛分配比得到不同粒径分布的实验物料，以0.25~0.76 m/s的速度分批进行流态化试验，考察了表观气速、床层物料粒径分布以及颗粒粒径对颗粒夹带和扬析速率的影响，得到了颗粒的扬析速率常数(Ki*)。实验结果表明，夹带量和扬析速率常数随着表观气速呈指数增加；扬析速率常数随着颗粒粒径减小先增加，达到一个临界粒径(dcrit)后，扬析速率常数会随着粒径减小趋于平缓或降低。提出了一组经验关联式，分别用于预测临界粒径两侧颗粒的扬析速率常数，关联式能很好地预测本工作实验条件下的数据，误差在30%以内，并且关联式能够对文献中的实验数据进行较好的预测，可以用于流化床装置的放大。

Entrainment and elutriation of particles in a gas-solid fluidized bed

The experimental work on the entrainment and elutriation of glass beads and white fused alumina powder with a wide particle size distribution was carried out in a fluidized bed with an inner diameter of 0.5 m and a total height of 6 m. The two powders were passed through the sieve distribution ratio to obtain experimental materials with different particle size distributions belonging overall to the Geldart groups A or B particles. Fluidization tests were carried out in a steady state at velocities of 0.25~0.76 m/s, the effects of superficial gas velocity, bed material particle size distribution and particle size on particle entrainment and elutriation rate were investigated. The elutriation rate constant of the powders under different conditions was obtained. In order to ensure that the transport disengaging height (TDH) was reached under various conditions, the entrained particles in the fluidization column were sampled axially and analyzed for particle size distribution. The experimental results showed that an increase of the concentration of fine particles in the experimental materials increased the total entrainment flux, but reduced the elutriation rate constant (Ki*). The total entrainment flux and the elutriation rate constant increased exponentially with increases of the superficial gas velocity. In addition, at a given superficial gas velocity, the elutriation rate constant first increased with the decrease of particle size, until reaching a critical particle size (dcrit), after which the elutriation rate constant would tend to flatten or decrease, that changes in the elutriation rate may be attributed to the interparticle adhesion forces. A new empirical correlation was proposed based on the experimental results and theory of dimensional analyses to estimate the elutriation rate constant of particles below the critical particle size. The correlation could agree well with the experimental data. The proposed empirical correlation can be used to scale up fluidized beds.