立管窜气对旋风分离器分离效率的影响

发布时间：2018-12-12 06:00

【摘要】：旋风分离器是循环流化床锅炉的重要组成部件,其作用是利用高速旋流对炉膛出口的高温灰颗粒进行筛分,保证煤颗粒的充分燃烧和炉膛内颗粒粒度稳定。筛选后的颗粒通过旋风分离器底部的立管进入返料装置,同时在立管内形成料封。如果返料装置内的风量设置不当或者料封不稳定,气体可能通过立管进入分离器,该现象即立管窜气。立管窜气将影响旋风分离器的性能,特别是分离效率,而目前相关研究还比较少,因此研究窜气量对旋风分离器分离效率的影响具有重要意义。本研究分为实验和数值模拟两部分。实验部分为小型旋风分离器的冷态实验,获得不同入口风速、不同入口颗粒浓度和不同窜气速度条件下的分离效率、分级分离效率、压降等数据;数值模拟部分利用CFD软件Barracuda实现LES及MP-PIC方法的气固数值模拟,重点分析窜气对分离器内气相流场、压力场、颗粒分布的影响。实验结果显示:旋风分离器压降受入口风速的影响较大,随入口风速的增高而增高,受窜气速度的影响很小,随窜气速度的增高变化规律不明显;旋风分离器的分离效率在窜气速度低时下降较小,较高速窜气时下降很大;高入口风速工况下分离效率的下降幅度要小于低入口风速的情形,特别是在低速窜气时,前者几乎没有下降,后者可观察到较明显的下降;入口颗粒浓度较高工况的分离效率一般也较高,但对于入口风速较低的情况,这一规律不适用;细颗粒相对于粗颗粒更容易受到窜气的影响,对应的分级分离效率下降更明显。数值模拟结果显示:通过数值模拟所得压降、分离效率和分级分离效率均能与实验值较好吻合,具有较高的可信度;窜气将削弱旋风分离器内的旋转流动,使得向下旋流提前转化为向上旋流并扩大向上流动的区域,促使分离器锥段处形成相对高压区;窜气会携带颗粒向上,使分离器内远壁区域颗粒分布增多,还会增强分离器内颗粒的循环流动,使分离器内的总颗粒保有量增高,对旋风分离器的分离作用造成不利影响。
[Abstract]:Cyclone separator is an important component of circulating fluidized bed boiler. Its function is to sift the high-temperature ash particles at the outlet of the furnace by high-speed swirl flow to ensure the full combustion of coal particles and the stability of particle size in the furnace. The selected particles enter the return device through the riser at the bottom of the cyclone separator and form a material seal in the riser. If the air volume in the return device is not set properly or the material seal is unstable, the gas may enter the separator through the riser, which is the phenomenon of riser gas channeling. Riser gas channeling will affect the performance of cyclone separator, especially the separation efficiency, but there are few related studies at present, so it is of great significance to study the effect of gas channeling on the separation efficiency of cyclone separator. This research is divided into two parts: experiment and numerical simulation. The experiment part is the cold state experiment of the small cyclone separator. The data of separation efficiency, step separation efficiency and pressure drop are obtained under different inlet wind speed, different inlet particle concentration and different gas channeling velocity. In the part of numerical simulation, the gas-solid numerical simulation of LES and MP-PIC method is realized by CFD software Barracuda, and the influence of gas channeling on gas phase flow field, pressure field and particle distribution in the separator is analyzed. The experimental results show that the pressure drop of the cyclone separator is greatly affected by the inlet wind speed, increases with the increase of the inlet wind speed, and is little affected by the gas channeling velocity, but does not change obviously with the increase of the gas channeling velocity. The separation efficiency of cyclone separator decreases slightly when the gas channeling velocity is low, and is much lower than that with high speed gas channeling. Under the condition of high inlet wind speed, the decrease of separation efficiency is smaller than that of low inlet wind speed, especially in the case of low velocity gas channeling, the former has almost no decrease, and the latter can be observed a more obvious decrease. The separation efficiency of high inlet particle concentration is generally higher, but this rule is not applicable to the case of lower inlet wind speed, and fine particles are more easily affected by gas channeling than coarse particles, and the corresponding separation efficiency decreases more obviously. The results of numerical simulation show that the pressure drop, separation efficiency and step separation efficiency obtained by numerical simulation are in good agreement with the experimental values and have high reliability. The gas channeling will weaken the rotating flow in the cyclone separator, make the downward swirl flow transform into upward swirl flow ahead of time and expand the area of upward flow, and promote the formation of relative high pressure area at the cone section of the separator. Gas channeling will bring the particles upward, increase the particle distribution in the far wall of the separator, enhance the circulating flow of the particles in the separator, increase the total particle holding in the separator, and adversely affect the separation of the cyclone separator.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.8

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