重质大颗粒在非均匀布风流化床内停留时间

Residence time of a large heavy object in a fluidized bed with an uneven air distribution

用电容层析成像(ECT)示踪法研究了单个球形重质大颗粒在流化床密相区的停留时间分布特性及随流化风速变化时运动状态的演化过程。通过对实验结果的概率统计分析和对大颗粒受力特征的分析,揭示了大颗粒在床内运动行为的统计规律性和随机性。研究发现:大颗粒在床内的平均停留时间随流化风速的降低先缓慢增大,当流化风速低于某一临界值后,停留时间急剧增大,并过渡到以一定的概率到达布风板低侧,直至最终滞留在床中间;大颗粒密度越大,演变过程对应的流化风速越大。由于周围两相流压力场、速度场随时间的随机脉动性,大颗粒在床内的停留时间分布很宽。

The influence of the superficial gas vdocity on the residence time distributions （RTDs） of large spherical objects of different densities in the dense phase of a fluidized bed was studied using electrical capacitance tomography （ECT） tracing technique. The regularity and randomness of the motion of a large object were decided by a probabilistic statistical analysis to investigate the mechanical characteristics of an object in a bed. The results show that decreasing the fluidization velocity first slowly reduces the residence time. When the gas velocity is lower than a critical value, the residence time sharply increases until the object does not reach the low side of the air distributor. Heavier objects have higher critical gas velocities. The RTD curves are very broad due to the stochastic pressure and velocity pulsations in the fluidization bed.