双曲面搅拌器反应池内流态分布及其影响因素分析

发布时间：2018-03-01 16:44

本文关键词： 双曲面搅拌器计算流体力学数值模拟现场测定流场　出处：《西安建筑科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：厌氧池和缺氧池作为城市污水A2/O处理工艺的主要构成,其运行状态对脱氮除磷效果至关重要。在厌氧池和缺氧池内通过设置的搅拌器转动带动流体旋转使混合液处于悬浮和混合状态,完成活性污泥与污染物的混合与反应过程。双曲面搅拌器作为一种新型的搅拌设备具有能耗低、搅拌效果好等特点,被广泛用于厌氧池和缺氧池,但有关双曲面搅拌池的设计、搅拌器的选型以及池内流态分布尚不十分清楚,主要依赖于工程师的经验,导致搅拌器与池型的不配套,从而使得大多数搅拌池未能处于最优的工作状态。随着计算流体力学技术的发展,通过数值模拟可十分方便地获得搅拌池内的流态。本文以西安市第四污水处理厂内正在运行的三类缺氧池为对象,首先测定池内的实际流速分布,分析混合状态,在此基础上,应用FLUENT计算流体力学软件,利用多重参考系法(MRF)和标准k??模型对流场进行数值模拟,探讨搅拌池尺寸、搅拌器结构、安装高度及搅拌功率等因素对混合效果的影响,为双曲面搅拌器的设计、选型及反应池流态优化提供依据。主要研究成果如下:(1)双曲面搅拌器由于其特殊的结构,可将流体导入池底,从而在池内形成稳定的环流,池内流速呈现底部高、上部次之、中部最低的不均匀分布规律,具有能耗低、混合效果好的特点。(2)通过对单个矩形(正方形和长方形)双曲面搅拌池数值模拟得出的流场速度分布与实测结果进行对比,两者较为接近,表明模拟方法切实可行。缺氧池中的最大流速出现在距池底200mm处;距离池壁1.0~1.5m处流速最低;搅拌叶轮的作用范围集中在距池底200~400mm的区域,表明双曲面搅拌器的工作原理为利用小部分的流体带动整个池内的流体循环流动。(3)通过对搅拌池尺寸、搅拌器结构、安装高度、搅拌功率等因素的研究,表明双曲面搅拌器的直径D与搅拌池边长L的比值(D/L)为0.188~0.250、搅拌器直径与搅拌器高度B的比值(D/B)为2.5、搅拌器安装高度h为500mm以及搅拌功率为2~4W/m3时,混合效果最佳。(4)在廊道式好氧池内安装多台双曲面搅拌器将其改造为无隔墙缺氧池的方法切实可行。依据模拟结果,对西安市第四污水处理厂廊道式缺氧池的进一步改造和优化提出了建议,将现有的5台叶轮直径为2500mm、功率为5.5kW的搅拌器改为10台叶轮直径2000mm、功率为2.0kW的搅拌器,在不增加能量消耗的前提下,搅拌池底部最大流速可由0.093m/s增加到0.241m/s,不仅可获得更佳的搅拌效果,而且还能有效防止污泥在底部形成积泥和表面的浮渣。
[Abstract]:Anaerobic and anoxic tanks are the main components of A2 / O treatment process for municipal sewage. The operating state is very important for the removal of nitrogen and phosphorus. In the anaerobic and anoxic tanks, the mixture is suspended and mixed by rotating the agitator to drive the fluid to rotate. As a new type of mixing equipment, hyperbolic agitator is widely used in anaerobic and anoxic tank because of its low energy consumption and good agitation effect, but the design of hyperbolic agitator is related to the design of hyperbolic agitator. The type selection of agitator and the distribution of flow state in the tank are not very clear. It mainly depends on the experience of the engineer, which leads to the mismatch of agitator and pool type. As a result, most of the agitators are not in optimal working conditions. With the development of computational fluid dynamics, The flow state in the mixing tank can be easily obtained by numerical simulation. In this paper, three kinds of anoxic tanks in Xi'an 4th sewage treatment plant are taken as the object. The actual velocity distribution in the tank is first measured, and the mixing state is analyzed. Using the FLUENT computational fluid dynamics software, the multiple reference system method and the standard k? ? Numerical simulation of the model flow field is carried out to investigate the influence of mixing tank size, agitator structure, installation height and mixing power on the mixing effect, which is the design of the hyperbolic agitator. The main research results are as follows: 1) because of its special structure, the hyperboloid agitator can introduce the fluid into the bottom of the tank, thus forming a stable circulation in the pool. The velocity of flow in the tank is high at the bottom, followed by the upper one. The lowest non-uniform distribution law in the middle of the region is characterized by low energy consumption and good mixing effect. The velocity distribution of the flow field obtained by numerical simulation of a single rectangular (square and rectangular) hyperboloid mixing tank is compared with the measured results. The results show that the maximum velocity of flow in anoxic tank is 200 mm from the bottom of the pool, the velocity of velocity is the lowest at 1.0 ~ 1.5 m from the wall of the pool, and the range of action of the impeller is 200 ~ 400 mm from the bottom of the pool. It shows that the working principle of hyperbolic agitator is to use a small part of fluid to drive the fluid circulation flow in the whole tank. Through the study of the size of the mixing tank, the structure of the agitator, the installation height, the mixing power and so on, The results show that the ratio of D / L of the hyperbolic agitator is 0.188 ~ 0.250, the ratio of the diameter of the agitator to the height of the agitator is 2.5, the installation height h is 500mm and the mixing power is 2 ~ 4 W / m ~ 3, the ratio of D / L is 0.1888 / 0.250, and the ratio of the diameter of the agitator to the height of the agitator is 2.5. The method of installing hyperbolic agitator into anoxic tank without partition wall is feasible. Some suggestions are put forward for the further improvement and optimization of the corridor anoxic tank in Xi'an 4th sewage treatment Plant. The existing five impellers with a diameter of 2500mm and a power of 5.5 kW are changed into 10 impellers with a diameter of 2000mm and a power of 2.0kW. Without increasing energy consumption, the maximum flow velocity at the bottom of the mixing tank can be increased from 0.093 m / s to 0.241 m / s, which can not only obtain better stirring effect, but also effectively prevent sludge from forming mud and surface dross at the bottom.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X703

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