DE氧化沟流场的数值模拟与优化研究

发布时间：2019-06-15 06:36

【摘要】：氧化沟(oxidation ditch)工艺以其经济、简便、高效的突出优势被广泛应用于城市污水与工业废水的处理中,但由于氧化沟的尺寸大,沟道中的流场复杂,氧化沟在动力不足时,污泥在低流速下容易发生沉积,影响氧化沟的正常运行。研究氧化沟内部流场的分布特点,可分析出氧化沟中容易发生污泥沉积的区域以及氧化沟不同的结构形式对流场分布的影响,为氧化沟的设计以及运行提供参考。本文借助Pro/E软件以及Fluent软件,以武汉某污水厂的DE氧化沟为原型,建立与实际氧化沟尺寸相同的氧化沟几何模型。同时利用Pro/E软件建立氧化沟水下推流设备的三维模型,改进了以往数值模拟中采用风扇模型来实现对水下推流器简化模拟的处理方法,使氧化沟内流场的模拟更加精确。在Fluent平台上采用RNG K-?湍流模型、滑移网格模型和SIMPLEC算法,模拟氧化沟内部流场的分布特点。结果表明氧化沟内挡流板的设置促进了上层水流和下层水流的垂直混合,使氧化沟内流速分布更加均匀。而导流墙的设置避免了弯道内壁附近水流呈现停滞回旋状态,确保了水流能平稳通过氧化沟弯道,但在氧化沟底部依然存在低速区,低速区主要集中在中隔墙两端弯道水流下游处。实际工况下氧化沟内部流速分布复杂,不同深度的水流速度分布不同,采用二维模型已无法实现对氧化沟的准确模拟。在Fluent软件平台上建立了安装有水下推流器的长方形搅拌池沟渠模型,在污水-污泥两相环境下对氧化沟中常用的低速大直径水下推进器与高速小直径水下搅拌器形成的流场进行了数值模拟。结果表明,两种水下推流器均可产生明显的推流作用,但低速大直径水下推进器形成的搅动半径更大,整体的推流流速高,污泥沉降率低,且在提供相同的推力时所需的功率更低,结果表明DE氧化沟中更适合安装低速大直径水下推进器作为氧化沟中的水下推流器。相关模型的数值模拟结果表明本文中的DE氧化沟需对导流墙进行偏置,导流墙圆心宜设置在上游沟道,最优偏心距为0.5m,结果与原设计相同。通过数值模拟对氧化沟的结构优化进行了研究,结果表明采用导流墙在下游方向延伸3m的方案,并没有改善氧化沟内的流速分布,而在弯道处设置两道导流墙且导流墙圆心设置在上游沟道的方案能改善氧化沟内的流速分布,缩小氧化沟底部低速区的面积,是氧化沟结构优化的方向。
[Abstract]:Oxidation ditch (oxidation ditch) process has been widely used in the treatment of municipal sewage and industrial wastewater because of its outstanding advantages of economy, simplicity and high efficiency. However, due to the large size of oxidation ditch and the complexity of flow field in the channel, the sludge in the oxidation ditch is prone to deposition at low flow rate when the power is insufficient, which affects the normal operation of the oxidation ditch. By studying the distribution characteristics of the flow field in the oxidation ditch, the influence of the area prone to sludge deposition in the oxidation ditch and the different structural forms of the oxidation ditch on the flow field distribution can be analyzed, which provides a reference for the design and operation of the oxidation ditch. In this paper, with the help of Pro/E software and Fluent software, taking the DE oxidation ditch of a sewage plant in Wuhan as the prototype, the geometric model of the oxidation ditch with the same size as the actual oxidation ditch is established. At the same time, the three-dimensional model of the underwater push flow equipment in the oxidation ditch is established by using Pro/E software, and the fan model is improved to realize the simplified simulation of the underwater thruster in the previous numerical simulation, which makes the simulation of the flow field in the oxidation ditch more accurate. Using RNG K on Fluent platform? Turbulence model, slip grid model and SIMPLEC algorithm are used to simulate the distribution characteristics of flow field in oxidation ditch. The results show that the setting of the baffle in the oxidation ditch promotes the vertical mixing of the upper flow and the lower flow, and makes the velocity distribution in the oxidation ditch more uniform. The setting of the diversion wall avoids the stagnant circumflex state of the flow near the inner wall of the bend and ensures that the flow can pass through the bend of the oxidation ditch smoothly, but there is still a low speed zone at the bottom of the oxidation ditch, and the low speed area is mainly concentrated in the downstream of the bend at both ends of the middle partition wall. Under the actual working conditions, the velocity distribution in the oxidation ditch is complex and the flow velocity distribution at different depths is different. The accurate simulation of the oxidation ditch can not be realized by using the two-dimensional model. A rectangular mixing tank ditch model with underwater thruster installed on Fluent software platform is established. The flow field formed by low speed large diameter underwater thruster and high speed and small diameter underwater agitator commonly used in oxidation ditch is numerically simulated in sewage-sludge two-phase environment. The results show that both kinds of underwater thrusters can produce obvious push flow effect, but the stirring radius of low speed and large diameter underwater thrusters is larger, the overall push flow velocity is high, the sludge sedimentation rate is low, and the power required when providing the same thrust is lower. The results show that DE oxidation ditch is more suitable for installing low speed and large diameter underwater thrusters as underwater thrusters in oxidation trenches. The numerical simulation results of the related model show that the DE oxidation ditch in this paper needs to bias the diversion wall, the center of the diversion wall should be set in the upstream channel, and the optimal eccentricity is 0.5m, and the result is the same as that of the original design. The structural optimization of the oxidation ditch is studied by numerical simulation. The results show that the scheme of extending the diversion wall in the downstream direction of 3m does not improve the velocity distribution in the oxidation ditch, but the scheme of setting two diversion walls at the bend and setting the center of the diversion wall in the upstream channel can improve the velocity distribution in the oxidation ditch and reduce the area of the low velocity zone at the bottom of the oxidation ditch, which is the direction of the optimization of the oxidation ditch structure.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X703

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