發(fā)布時間：2019-06-15 06:36

【摘要】：氧化溝(oxidation ditch)工藝以其經(jīng)濟、簡便、高效的突出優(yōu)勢被廣泛應用于城市污水與工業(yè)廢水的處理中,但由于氧化溝的尺寸大,溝道中的流場復雜,氧化溝在動力不足時,污泥在低流速下容易發(fā)生沉積,影響氧化溝的正常運行。研究氧化溝內(nèi)部流場的分布特點,可分析出氧化溝中容易發(fā)生污泥沉積的區(qū)域以及氧化溝不同的結構形式對流場分布的影響,為氧化溝的設計以及運行提供參考。本文借助Pro/E軟件以及Fluent軟件,以武漢某污水廠的DE氧化溝為原型,建立與實際氧化溝尺寸相同的氧化溝幾何模型。同時利用Pro/E軟件建立氧化溝水下推流設備的三維模型,改進了以往數(shù)值模擬中采用風扇模型來實現(xiàn)對水下推流器簡化模擬的處理方法,使氧化溝內(nèi)流場的模擬更加精確。在Fluent平臺上采用RNG K-?湍流模型、滑移網(wǎng)格模型和SIMPLEC算法,模擬氧化溝內(nèi)部流場的分布特點。結果表明氧化溝內(nèi)擋流板的設置促進了上層水流和下層水流的垂直混合,使氧化溝內(nèi)流速分布更加均勻。而導流墻的設置避免了彎道內(nèi)壁附近水流呈現(xiàn)停滯回旋狀態(tài),確保了水流能平穩(wěn)通過氧化溝彎道,但在氧化溝底部依然存在低速區(qū),低速區(qū)主要集中在中隔墻兩端彎道水流下游處。實際工況下氧化溝內(nèi)部流速分布復雜,不同深度的水流速度分布不同,采用二維模型已無法實現(xiàn)對氧化溝的準確模擬。在Fluent軟件平臺上建立了安裝有水下推流器的長方形攪拌池溝渠模型,在污水-污泥兩相環(huán)境下對氧化溝中常用的低速大直徑水下推進器與高速小直徑水下攪拌器形成的流場進行了數(shù)值模擬。結果表明,兩種水下推流器均可產(chǎn)生明顯的推流作用,但低速大直徑水下推進器形成的攪動半徑更大,整體的推流流速高,污泥沉降率低,且在提供相同的推力時所需的功率更低,結果表明DE氧化溝中更適合安裝低速大直徑水下推進器作為氧化溝中的水下推流器。相關模型的數(shù)值模擬結果表明本文中的DE氧化溝需對導流墻進行偏置,導流墻圓心宜設置在上游溝道,最優(yōu)偏心距為0.5m,結果與原設計相同。通過數(shù)值模擬對氧化溝的結構優(yōu)化進行了研究,結果表明采用導流墻在下游方向延伸3m的方案,并沒有改善氧化溝內(nèi)的流速分布,而在彎道處設置兩道導流墻且導流墻圓心設置在上游溝道的方案能改善氧化溝內(nèi)的流速分布,縮小氧化溝底部低速區(qū)的面積,是氧化溝結構優(yōu)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.
【學位授予單位】：武漢理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：X703

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