细粒级人造金红石流态化行为的模拟

【作者】 李波；

【导师】 徐瑞东； 杨仰军；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2011， 硕士

【摘要】 流态化技术是化学工程领域的一种重要的技术。气固流化床具有高效的传质和传热效率、床层温度分布均匀、反应容易控制、生产能力大、应用范围广等特点。气固两相流之间存在强烈的非线性和耦合性,其流体力学性质相当复杂。在流化床的机理方面,还存在许多模糊之处,有待人们继续的探究。本文以攀枝花生产的细粒级人造金红石为原料,利用欧拉模型进行模拟。在20mm宽和80mm高的二维流化床中,模拟了细粒级人造金红石在几个不同表观气速下的流体动力学特性。在u=0.004m/s时,呈现均匀的散式膨胀；当u=0.005m/s时,出现鼓泡现象,为聚式流态化,但气泡内固含率较高；提高表观速度至0.02m/s,床内空隙率增大。验证了欧拉模型的可靠性。在1m/s至40m/s的气速范围内,研究了在两种开孔尺寸下的单孔射流形态,再现了单孔射流的发展过程。结果表明：初始气泡当量直径、气泡上升速度、射流深度随操作气速的提高、开孔尺寸增大而增大；而初始气泡的频率随射流气速提高、开孔尺寸增大略有减小；仅当静床高较小时,才会对射流的形态产生影响。对双射流模拟结果显示：双射流可以分为孤立射流、过渡射流和相互作用射流；随着气速的提高和开孔间距的减小,射流作用强烈,当尾涡具有足够的相互吸引力时,射流发生合并。在三孔、四孔射流、不同开孔尺寸和气速下的模拟结果表明：在低气速下,气泡射流可以在分布板上方很短的距离内形成大量的气泡交互区域；而在高气速下,射流之间作用强烈,可以获得较好的湍流效果；不等速射流之间,由于尾涡卷吸力不同,气速较大的射流对气速较小的射流有吸引作用。根据细粒级人造金红石粒特性,利用稳定性压降原理计算了几种分布板开孔率,并对常用的几种分布板进行了压降与速度的模拟验证。可以为分布板设计提供一些参考：用于细粒级人造金红石流态化的气体分布板应采取高压降、低开孔率的分布板；锐孔速度取决于表观气速和开孔率；在高压降的条件下,等开孔尺寸的分布板的锐孔速度相当；采用边缘开孔率高、中心开孔率低的措施,可以在一定程度上消除边避效应。更多还原

【Abstract】 Fluidized bed is an important technology used in chemical engineering. Fluidized equipment has many advantages, such as more higher efficiency on heat and mass transfer process, better bed temperature distribution, easier for controlling and large-scale. But its hydrodynamics are extraodinary complicated because of the intensity non-linear and coupling between gas phase and solid phase. We still have a lot of dark in the fluidized bed law, and have to explore.In this paper, Eulerian-Eulerian Model is used to research the hydrodynamic behavior of fine artificial rutile particle with a density of 4000 kg/m3 and a diameter of 46μm in several different superficial gas velocity. Simulation is carried out in a two-dimensional fluidized bed with 20 mm in width and 80 mm in height. At the superficial gas velocity of 0.004m/s, it acts as a homogeneous fluidization. When the velocity is 0.005m/s, it performances as an aggregative fluidization and some bubbles turn up with some particles. While the superficial gas velocity is improved to 0.02m/s, the porosity increase. This simulations prove the Eulerian-Eulerian model is credible.Within 1 m/s and 40 m/s, researching characters of single jet with two different apertures and gas velocity indicates that initial bubble equivalent diameter, bubble velocity and jet depth increase when aperture and operating velocity augment. On the contrary, initial bubble frequency have a few decreasing. Only when the still bed height very small, it would affect jet forms.Simulations of the double jet system show that it could be classified into three categories:isolated jets, transitional jets, and interacting jets. With gas velocity rising and aperture distance decreasing, jet interacting aggravating. If its trailing vortex have enough appeal, jet will merge. Three and four jets simulations show that lots of bubbles will appear on the apertures around, with low gas velocity and high gas velocity can obtain a well turbulent flow effect. If the jets velocity unequal, the high velocity jet will pull the low velocity because of differ in appeal.According to the characters of fine artificial rutile, perforated rate of distributors are calculated with stability press drop method which is validated by simulations. It can propound some suggestion that we should adopt high press drop distributor, the velocity of gas pass the distributor is depend on superficial velocity and perforated rate, velocity of gas pass the distributor is equal when the apertures is equal in size, and the distributor which central zone has a low perforated rate but high in marginal area can eliminate wall effect.更多还原