Hydrodynamics of High-Density Downer Reactors Using a Novel Solids Feeder
Hydrodynamics of High-Density Downer Reactors Using a Novel Solids Feeder
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DOI：
10.2202/1542-6580.1220
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发表时间：
2005-11
影响因子：
1.6
通讯作者：
Xuqi Song;X. Bi;Y. Bolkan
中科院分区：
文献类型：
--
作者：
Xuqi Song;X. Bi;Y. Bolkan
对于需要很短停留时间的反应，下沉反应堆比上升反应堆有许多优点。然而，在需要高固气比的反应中，它的应用受到充分开发区域的低固体含率（通常小于1%）的限制。在本文中，我们介绍了一个直径0.078 m，长3.2 m的高密度下料反应器的性能，该反应器配备了最近开发的新型固体进料系统。实验采用颗粒密度为1600 kg/m3，平均直径为133 mm的流体焦炭颗粒，固体通量为1400 kg/m3，表面气速为0 ~ 6 m/s。降料器以批处理方式运行，固体从降料器顶部的流化床内的固体给料器中进料，降料器的下端与接收料斗相连。固体流量由安装在下行器入口下方0.4 m处的蝶阀控制。空气通过位于蝶阀正下方的四个45度角喷嘴注入下行器。每次运行后，固体通过外部立管从底部受料斗提升到上部流化床。从电容探头得到的局部测量积分计算出的截面平均固含量是固体通量和表面气体速度的函数。在一定的表面气速下，固相含率随固相流量的增加而增加，而在一定的表面气速下，固相含率随气速的增加而降低。在Gs=1400 kg/m2s, Ug=2.0 m/s的工况下，在注入点以下3.0 m的轴向位置，截面平均固含率达到16.5%。高密度降火剂中固体径向分布的形状不仅随表面气速而变化，而且随固体通量的变化而变化。在较高的固体通量和较低的气体流速下，径向固体分布更加均匀。在高通量工况下（Gs=1400 kg/m2s, Ug=2.0 m/s），近壁区致密环消失。在固定固体通量约为400 kg/m2s的条件下，当气体流速从3.0 m/s增加到6.0 m/s时，径向固体含率曲线变得不均匀，靠近壁面的密度更大，而在中心区域则更稀，分布不均匀，这与文献报道的低固体通量条件下的流动模式有明显不同。
Downer reactors have many advantages over risers for reactions requiring very short residence time. However, its application for reactions where a high solid/gas ratio is required has been restricted by the low solids holdup in the fully developed region (typically less than one percent). In this paper, we present the performance of a 0.078 m diameter and 3.2 m long high-density downer reactor equipped with a recently developed novel solids feeding system.Experiments were carried out using fluid coke particles of particle density 1600 kg/m3 and mean diameter 133 mm, with solids fluxes up to 1400 kg/m2s and superficial gas velocities ranging from 0 to 6 m/s. The downer was operated under batch mode, with solids fed from a solids feeder installed inside a fluidized bed at the top of the downer and the bottom end of the downer connected to a receiving hopper. The solids flux was controlled by a butterfly valve installed 0.4 m below the downer entrance. Air was injected into the downer through four 45-degree-angled nozzles located right below the butterfly valve. Solids were lifted up from the bottom receiving-hopper to the upper fluidized bed through an external riser after each run.The cross-sectional average solids hold-up calculated from the integration of local measurements obtained from a capacitance probe was found to be a function of both the solids flux and superficial gas velocity. The solids hold-up increased with increasing solids flux at a given superficial gas velocity, but decreased with increasing gas velocity at a fixed solids flux. A cross-sectional average solids holdup of 16.5% was achieved at an axial position of 3.0 m below the air injection point under the operating condition of Gs=1400 kg/m2s and Ug=2.0 m/s. The shape of radial solids distribution varied not only with the superficial gas velocity but also with the solids flux in high-density downers. The radial solids distribution became more uniform under higher solids fluxes and lower gas velocities. The dense ring at the near wall region disappeared under the high-flux operating condition (Gs=1400 kg/m2s, Ug=2.0 m/s). The radial solids holdup profiles became less uniform, denser near the wall and more dilute and non-uniformly distributed in the central region, as the gas velocity increased from 3.0 to 6.0 m/s at a fixed solids flux of about 400 kg/m2s, which is significantly different from flow patterns reported in the literature under lower solids flux conditions.