Characterization of high-density gas–solids downward fluidized flow
Characterization of high-density gas–solids downward fluidized flow
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DOI：
10.1016/s0032-5910(00)00276-x
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发表时间：
2001-03
影响因子：
5.2
通讯作者：
Weizao Liu;K. Luo;Jesse Zhu;J. Beeckmans
中科院分区：
文献类型：
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作者：
Weizao Liu;K. Luo;Jesse Zhu;J. Beeckmans
实验是在一个专门设计的5米高，0.025米内径。高密度气固下行流化床，以测量沿下行床沿着的轴向压力梯度分布和充分发展区域中的实际固含率。采用流化催化裂化（FCC）颗粒（ρp=1300 kg/m3，dp=70 μm）和两种玻璃微珠（ρp=2500 kg/m3，dp=123和332 μm）。从压力梯度分布图中，沿柱沿着确定了颗粒加速区和充分发展区。在充分发展区，固含率随气速的增加而减小，随循环量的增加而线性增加。后者的结果在几乎恒定的颗粒速度在一个大范围的固体通量在给定的气体速度。颗粒速度也随气体速度线性增加。颗粒的性质似乎对颗粒的平均速度影响不大，但较小和/或较轻的颗粒会产生较大的固含率。固含率高达10-20%。将实验结果与上升管实验结果进行比较，发现两种气固并流系统具有内在的相似性。在充分发展的区域，从压力梯度计算的表观固含率同意与实际固含率测量的一对夹管阀下不是很高的气体速度，但低估了在较高的气体速度，由于壁面摩擦损失增加。
Experiments were carried out in a specially designed 5 m tall, 0.025 m i.d. high-density gas–solids downflow fluidized bed to measure the axial pressure gradient profiles along the downer and the actual solids holdup in the fully developed region. Fluidized catalytic cracking (FCC) particles (ρp=1300 kg/m3, dp=70 μm) and two types of glass beads (ρp=2500 kg/m3, dp=123 and 332 μm) were used. A particle acceleration region and a fully developed region were identified along the column from the pressure gradient profiles. In the fully developed region, solids holdup decreases with the gas velocity but increases linearly with the solids circulation rate. The latter results in nearly constant particle velocities over a large range of solids flux at given gas velocities. Particle velocity also increases linearly with the gas velocity. Particle properties seem not to affect the mean particle velocity much, but smaller and/or lighter particles give larger solid holdups. A solids holdup as high as 10–20% has been achieved. Comparison of the results obtained here with those from an upflow riser shows inherent similarities between the two gas–solids co-current flow systems. In the fully developed region, the apparent solids holdup calculated from the pressure gradient agreed well with the actual solids holdup measured by a pair of pinch valves under not very high gas velocities, but was underestimated at higher gas velocities due to the increased wall friction loss.