PHOENICS数值模拟平流式二沉池流场

本文利用CFD商用软件PHOENICS,模拟平流式二沉池内的流线和速度分布.结果表明池内的实际流场与理想沉淀池之间存在着很大的差异,特别是在挡板前后存在着两个极为明显的涡流区,影响二沉池的沉淀效果.并且还考虑了不同的回流比对二沉池流态产生的影响.     

强化生物脱氮的生活污水处理厂改造工艺研究

在传统生物脱氮除磷工艺基础上,增加污泥膜生物反应器(SMBR),组成一种强化的生物脱氮工艺。通过对部分二沉池回流污泥进行SMBR延时曝气处理,并在SMBR中营造一个适合硝化细菌生长的环境,再将富集硝化细菌的污泥回流至好氧池内,大量且高活性的硝化菌大幅提升硝化效率,SMBR出水回流至缺氧池内进行反硝化,或用于厂内回用。此种强化生物脱氮工艺,可减少好氧池的水力停留时间,又能提高污水处理厂的脱氮效率,还可减少并稳定二沉池的剩余污泥,适用于新建污水厂,也可用于现有污水处理厂的提标改造。     

基于CFD的竖流式二沉池实际工况的模拟

为了探究实际工况下竖流式二沉池的流场变化及污泥质量浓度分布情况,利用RNG k-epsilon湍流模型和mixture模型,对其进行二维瞬态数值模拟,比较不同负荷、不同回流比对二沉池内部的流场变化和污泥质量浓度分布的影响。结果表明:q=0.5 m~3/(m~2·h)是竖流式二沉池比较理想的设计表面负荷;回流比对二沉池的稳定运行具有一定的影响,竖流二沉池的进口部分设计参数应当结合回流比进行适当的调整。     

溶气气浮池气液两相流二维数值模拟

采用计算流体力学软件FLUENT对溶气气浮池进行了二维数值模拟,分别对液相单相流动和气液两相流动进行了研究。模拟采用了RNG k-ε湍流模型,气液两相流的模拟采用了欧拉模型。计算得到了溶气气浮池内液相流场情况和气相在溶气气浮池内的体积分数分布,模拟结果与实验结果符合。     

针对污水厂化学除磷工艺的系统优化

为提高除磷药剂的利用率,研究了化学除磷产生的污泥(以下简称"化学除磷污泥")对二沉池出水水质的影响效果。结果表明:投加化学除磷污泥可有效去除二沉池内的TP,去除率可达16%,减少了后续深度除磷药剂的消耗量,节省了运营成本。同时,化学除磷污泥可改善二沉池内污泥沉降性能及出水水质,其中SVI降低了7%,SS,COD的去除率分别达到18%,10%。因此,化学除磷污泥的回用是一种有效可行的降低污水厂运营成本的办法。     

二沉池两相流数值模拟及混合液流变性质的影响

基于实际二沉池尺寸、流变性质、回流等工况,采用数值模拟方法对二沉池固液两相动力学行为进行模拟研究。结果表明,二沉池内存在多个漩涡,且分布于二沉池上部、中部和下部;混合液的流动速度在二沉池上部和污泥斗区域较低,在二沉池中下部较高;污泥高含量区分布于污泥斗及二沉池底部区域,且越靠近二沉池右侧壁面污泥层厚度不断降低。混合液流变性质模型为拟合污泥含量的赫谢尔-巴尔克莱模型时,模拟得到的速度及污泥层厚度与牛顿流体(水)模拟得到的结果较为相近且与实验结果误差不显著,但牛顿流体对二沉池底部的污泥含量预估较低,当混合液流变性质为赫谢尔-巴尔克莱模型时(与污泥含量无关)速度及污泥含量的模拟结果均较差。     

高温气体穿越液池过程气液传热传质数值分析

建立气液二相间动量、热量及质量同时传递数学模型,数值模拟了高温气体穿越液池气液直接接触热质传递规律。模型中考虑了气泡破碎、聚合以及冷却水蒸发等因素的影响。数值模拟获得了液池内气液二相温度变化规律,探讨了液池内表观气速、气泡尺寸以及进入液池气体温度等因素对液池内气液二相温度分布特性的影响。计算结果与实验值吻合较好,验证了模型的可行性。数值模拟结果表明:高温气体在进入液池后,首先经历一个剧烈的气液热质交换过程,存在一个较大的温度梯度变化,而随后气体温度变化趋于平缓;随着液池内表观气速的降低,池内气体温度降低;最大冷却水蒸发速率和最高气体温度均出现在靠近下降管出口的区域。     

乙烯生产废水处理工艺技术改造实践

某石化企业由于所在地区排污标准的提高,导致原有污水处理工艺出水水质难以达标,为满足新排污标准,对原污水处理工艺进行技术改造.工艺改造包括:高盐系列新建预沉池、均质池、中沉池、三沉池、综合提升泵和曝气生物滤池;低盐系列新建预曝池、反应池、一沉池、A池、二沉池和过滤装置,其它均为旧池部分改造或利旧.介绍了新工艺流程,改造后工艺试运行效果良好,达到了设计要求及改造目的.     

某污水处理厂氧化沟射流曝气工程改造效果分析

某污水处理厂将管式微孔曝气系统改造成射流式曝气系统。本文对曝气系统改造前后的工艺参数进行了全面分析,结果表明:射流曝气改造后曝气池溶解氧从1.4 mg/L上升到2.9 mg/L,水中溶解氧量明显增加,且气水比与改造前相比下降11%,但改造后二沉池出水COD值、SS值分别较改造前出水COD值高出15.4%、84.9%。终沉池的COD去除能力得到了显著提升,终沉池去除率从29.9%提高到55.3%。     

含磷废水提标工艺改造

针对含磷废水提出"电解塔+多元协同催化氧化"技术对来水进行预处理,在充分利旧的前提下,将原生化池一组三个池子中的一个改造为缺氧池,预处理后水经缺氧池-好氧池后进入二沉池。现有二沉池系统缺乏刮泥装置,新增二沉池刮泥设备,减少二沉池污泥上浮现象。二沉池出水后经混凝沉淀池加药沉淀,去除污水中的磷,好氧池上加药装置不再使用。     

Influence of flow field on sedimentation efficiency in a circular settling tank with peripheral inflow and central effluent

The paper presents an experimental study of suspension flow patterns and velocity field inside a circular settling tank with continuous operation. Research was focused on the impact of a specific flow pattern on the sedimentation efficiency of the prototype settling tank. The latter differed from a common circular settling tank in that it was peripherally fed and had the central draw-off. Experiment was carried out on a settling tank section made of plexiglass and represented a radial slice of a prototype settling tank. The flow field and local suspension concentration was determined by computer-aided visualization. Sedimentation efficiency was assessed relatively by comparison of the amount of settled particles (sludge height measurements) between different types of flow in a certain time period of the settling tank operation. Results showed that there were two types of flow in the settling tank that were initiated by a horizontal or vertical inflow from the distribution ring. The type of inflow (horizontal or vertical) was a function of the suspension height in the settling tank. Significant differences in sedimentation efficiency were observed between both types of flow, particularly at lower inlet suspension concentrations. Horizontal inflow proved to be less efficient in terms of settling.     

Continuous‐Flow Surface Aeration Systems

An aeration process in an activated sludge plant is a continuous‐flow system. In this system, there is a steady input flow (flow from the primary clarifier or settling tank with some part from the secondary clarifier or secondary settling tank) and output flow connection to the secondary clarifier or settling tank. The experimental and numerical results obtained through batch systems can not be relied on and applied for the designing of a continuous aeration tank. In order to scale up laboratory results for field application, it is imperative to know the geometric parameters of a continuous system. Geometric parameters have a greater influence on the mass transfer process of surface aeration systems. The present work establishes the optimal geometric configuration of a continuous‐flow surface aeration system. It is found that the maintenance of these optimal geometric parameters systems result in maximum aeration efficiency. By maintaining the obtained optimal geometric parameters, further experiments are conducted in continuous‐flow surface aerators with three different sizes in order to develop design curves correlating the oxygen transfer coefficient and power number with the rotor speed. The design methodology to implement the presently developed optimal geometric parameters and correlation equations for field application is discussed.     

Characterization on the hydrodynamics of a covering-plate Rushton impeller

A modified Rushton impeller with two circular covering-plates mounted on the upper and lower sides of the blades was designed. There are gaps between the plates and the blades. The turbulent hydrodynamics was analyzed by the computational fluid dynamics (CFD) method. Firstly, the reliability of the numerical model and simulation method was verified by comparing with the experimental results from literature. Subsequently, the power consumption, flow pattern, mean velocity and mixing time of the covering-plate Rushton impeller (RT-C) were studied and compared with the standard Rushton impeller (RT) operated under the same conditions. Results show that the power consumption can be decreased about 18%. Compared with the almost unchanged flow field in the lower stirred tank, the mean velocity was increased at the upper half of the stirred tank. And in the impeller region, the mean axial and radial velocities were increased, the mean tangential velocity was decreased. In addition, the average mixing time of RT-C was shortened about 4.14% than the counterpart of RT. The conclusions obtained here indicated that RT-C has a more effective mixing performance and it can be used as an alternative of RT in the process industries.     

Numerical simulation of flow field characteristics in a gas-liquid-solid agitated tank

Computational fluid dynamics simulation was carried out to investigate flow field characteristics in a gas-liquid-solid agitated tank. The Eulerian multifluid model along with standard k-ε turbulence model was employed in the simulation. A multiple reference frame approach was used to treat the impeller rotation. Liquid velocity, gas holdup and solid holdup distributions in the agitated tank were obtained. The effect of operating conditions on gas and solid distributions was investigated. The predicted flow pattern was compared with results in literature. The simulation results indicate that local hydrodynamic behaviors such as velocity, gas and solid holdup distribution, are strongly influenced by operating conditions. Within the scope of our study, increasing gas inlet rate caused liquid circulation to be weakened and was not in favor of gas dispersion. Solid holdup in the upper part of the tank, especially near the wall region decreased. Adding solid loadings resulted in liquid mean velocity near the surface region decreased, gas dispersion and solid suspension becoming worse.     

搅拌槽内黏性流体流动的DPIV测量与CFD模拟

搅拌槽是化学工业及其相关工业广泛应用的设备之一,由于其内部流动的复杂性,搅拌混合操作目前尚未形成完善的理论体系．对搅拌槽的设计和放大,主要是依赖半经验的方法,对其内部流场有必要进行更深入的研究．目前对不同黏性流体的流动测量及计算流体力学模拟工作见诸报道较少,而     

活性污泥沉降速率模型的研究进展

活性污泥沉降速率是二沉池模型的核心内容,以固体通量理论为基础的沉降速率模型主要包括幂函数模型、指数模型、Cho模型、双指数模型和颗粒分类沉降模型。在二沉池模拟中,指数模型和双指数模型较为实用且应用较多。指数模型的参数估计可通过模型参数与SVI关联实现,而双指数模型的参数则需将批沉降试验与最优化技术相结合才能确定。对活性污泥沉降速率模型的进一步研究工作提出展望。     

电场强化层流搅拌的荧光可视化试验及模拟分析

在层流搅拌中,搅拌桨的周期性扰动使搅拌槽内出现封闭、孤立的环状隔离流场。隔离流场严重阻碍了搅拌介质之间的有效交换,降低了搅拌效率。本文提出外加电场以强化层流搅拌的方案,利用电流体动力学效应改变流场的对称结构,消除混合死区。试验采用平面激光诱导荧光（planner laser induced fluorescence, PLIF）技术实现了搅拌槽内流场结构的实时可视化,并通过自编程程序识别并计算出非混合区域面积百分比。结果表明,随着电场强度的增大,混合效率逐渐提升,当电场强度为1.5kV/cm时混合效率可达98%。研究建立了基于有限元法及浓度扩散模型的混合搅拌模拟平台,探究搅拌槽内部流场结构时空演变规律。通过模拟分析发现,当外加平行板电场强度达到0.5kV/cm以上时,搅拌槽内部出现明显的二次涡流。二次涡流的出现与径向混合相互作用从而不断削弱隔离流场。在电场强度不变的条件下,外加周期性电场可以进一步提高搅拌效率,电场强度1kV/cm条件下的外加周期性电场可以使搅拌效率提升至98%以上。     

Theoretical and experimental study of sedimentation in vertical flow tanks

Settling characteristics of four different suspensions were measured by batch settling tests (glass spheres in glycerol-water mixtures and CaCO₃) and by continuous settling test in a bench-scale vertical flow tank (activated sludge and kaolin in water), including the measurement of solids concentrations inside the tank. The characteristics could be described by different correlation functions which now include all the information about the settling behaviour of ideal suspensions. Continuous settling experiments in a bench-scale vertical flow tank were carried out with the same four material systems. These results correspond with sufficient accuracy to those from the theory of limiting flux if the settling characteristics determined earlier are considered.     

加强圈在大型真空罐上的应用

指出在70m3 PVC混料槽筒体上设置3道加强圈可将其改造成沉析槽,通过计算确定了加强圈的规格及改造后设备的稳定性。