Hydrodynamics in high-density downer reactor
Hydrodynamics in high-density downer reactor
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发表时间：
2005
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通讯作者：
L. Hongzhong
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作者：
L. Hongzhong
实验在高5.6 m、内径降液管0.08 m的特制循环流化床中进行。玻璃珠(ρ p=2480 kg·m -3,d p=131 μm)、FCC催化剂颗粒(ρ p=992 kg·m -3,d p=82 μm)和两种硅胶(ρ p=750 kg·m) 分别采用d p=128 μm和572 μm)，固体通量最大为600 kg·m -2·s -1 ，固含率高达0.14。结果表明，高密度运行时的瞬态固体浓度特性与低密度运行时不同。低密度运行时,概率密度分布(PDD)曲线有一个峰值,而高密度运行时,PDD曲线顶部出现一条水平线。固体浓度随着固体流量的增加而增加。较小、较轻的颗粒可以获得较高的固体浓度，而流动性好的、较重的颗粒可以获得较高的固体流量。下降器整体压力梯度为正，颗粒加速区长度约为1.5—2.0 m。根据出口结构的不同，下降器可分为两个区域：颗粒加速区和低密度运行时的发达区或三个区域。 区域：粒子加速区域、发达区域、高密度运行的出口区域。
Experiments were carried out in a special circulating fluidized bed of 5.6 m in height, 0.08 m in ID downcomer.Glass beads(ρ p=2480 kg·m -3,d p=131 μm),FCC catalyst particles (ρ p=992 kg·m -3, d p=82 μm)and two kinds of silica gel (ρ p=750 kg·m -3, d p=128 μm and 572 μm) were used.The maximum of the solids flux was 600 kg·m -2·s -1 and a solids holdup as high as 0.14 was achieved.The results showed that the characteristics of the transient solids concentration at high-density operation were different from those at low-density operation. Under low-density operation, the probability density distribution (PDD)curves had one peak,but under high-density operation,there was a horizontal line around the top of the PDD curves. Solids concentration increased with increasing solids flux.Smaller and lighter particles could achieve higher solids concentration, while the good fluidity and heavier particles could achieve high solids flux.The pressure gradient was positive in the overall downer and the length of particles acceleration zone was about 1.5—2.0 m.Depending on the structure of the exit, the downer could be divided into two regions:particle acceleration region and developed region under low-density operation or three regions:particle acceleration region, developed region, and exit region with high-density operation.