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题名: 立体循环一体化氧化沟结构优化研究
作者: 杨宁
学位类别: 硕士
答辩日期: 2015-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 刘俊新
关键词: 一体化氧化沟,结构优化,计算流体力学,数值模拟,流场,integrated oxidation ditch, structural optimization, computational fluid ,dynamics, numerical simulation, flow-field
其他题名: Optimization on Structure of Integrated Oxidation Ditch with Vertical Circle (IODVC)
学位专业: 环境工程
中文摘要:     相比于传统氧化沟,立体循环一体化氧化沟(Integrated Oxidation Ditch with Vertical Circle,简称 IODVC)采用上下沟道的立体循环结构形式,且与固液分离区一体化,实现了沉淀污泥自动回流,因此能够减少占地面积和降低能耗。尽管IODVC已有一些研究和应用,但对  IODVC结构优化的研究开展较少。与传统氧化沟平面循环的流场不同,IODVC的立体循环结构使其具有独特的流场特性。目前,针对 IODVC流场的研究仅限于简单的仪器测试,在测量精度和装置尺寸方面受到了一定限制,IODVC的水力学特性尚不明确,在对  IODVC进行相关结构设计和优化时常采用经验或者半经验公式的方式,缺乏可靠的理论依据和设计参数,这些问题都制约着 IODVC的应用和推广。
    针对以上问题,本论文借助计算流体力学( Computational Fluid  Dynamics,简称 CFD)工具和 FLUENT计算方法,构建了  IODVC单相流场模型和污泥-污水固液两相流模型。并借助模型,系统开展了对 IODVC主沟和固液分离区结构的优化研究。取得如下主要结论:
(1)采用非结构化三角形网格生成方法对IODVC计算域进行网格划分,利用多重参考系(MRF)模型和风扇(Fan)模型分别定义曝气转刷和底部推流器的水力学行为,并借助 RNG k-ε湍流模型仿真IODVC内部流场的湍流变化;经试验验证,上述模型可准确描述 IODVC沟道内的流态特性。
(2)与无导流板情况相比,在IODVC弯道处加装导流板可提高全沟道的混合液流速。加装单层导流板,使混合液流速小于 0.15m/s的区域占比减少 22%,流速大于 0.25 m/s的区域占比增加  17%;加装双层导流板,可使高流速区域占比进一步增加 9.5%。加装导流板可有效改善 IODVC弯道处混合液的紊动程度,优化沟道隔板下方的混合液流速分布,使得右侧弯道出口处的回流低速区宽度占下
沟道宽度的比例减少 20%,同时显著提高了下沟道混合液的整体流速。因此,在相同功率输入的情况下,加装导流板有利于沟中液体达到良好的混合效果。
(3)导流板的布设位置对IODVC沟道内混合液流态影响较大,通过模拟得到了导流板位置的优化设置参数,即两侧导流板水平位移 180mm为宜。此外,将导流板末端适当延长可以进一步加强对水流的导控作用,对于防止隔板左侧上方污泥淤积有积极作用。导流板延长的长度等于导流板的半径时效果最佳。
(4)将固液分离区设置为45°的斜坡,可改善内部污泥分布,通过增加污泥沉淀面积达到改善 IODVC出水水质的目的,且斜坡的存在使固液分离区的沉淀污泥实现了自动回流,有利于 IODVC降低能耗。进水挡板的消能作用对于固液分离区的出水水质至关重要。无进水挡板时,沉淀效率会因主沟与固液分离区二者流场之间的相互作用而有所降低;适当缩减挡板长度可缓解进水水流对回流口附近区域的水力冲击,在一定范围内,挡板长度为 200mm时出水水质最优。
    上述研究及取得的结果可为 IODVC的进一步结构优化和工程应用提供科学依据和技术支持。

 
 
英文摘要:     Compared with traditional oxidation  ditches, vertical and circulatory structure of which the  channel is divided  into upper and  lower parts  is adopted in  the Integrated Oxidation Ditch with  Vertical Circle (IODVC), in  addition, the main ditch  and solid-liquid separation zone are integrated, so it can not only realize automatic circumfluence of  deposited   sludge,  but   also  decrease   the  occupation  area   and  reduce   energy consumption. Although there have been some research and application  about IODVC,there is few study on structural optimization of IODVC. Being different from the plane circulatory flow-field in traditional  oxidation ditches, IODVC possesses unique flow-field characteristics  because of  its  vertical and  circulatory structure.  At present,  the research on  flow-field  of IODVC  is limited  to  simple instrument  test, and  to some degree, measurement  accuracy  and size  of device  are  also greatly  limited. For  that reason, hydraulic characteristic  of IODVC is still unclear. Besides  that, empirical and semi-empirical formulas are  adopted in the related  structural design and optimization of IODVC. It results in the lack  of reliable theoretical basis and design parameters, all above problems restricting application and popularization of IODVC.
      To cure  the above issues,  computational fluid dynamics  (CFD) technique  along with a Fluent code were used to build single-phase flow-field model and sewage-sludge solid-liquid two-phase flow model in  this paper. By virtue of models, optimization  on structure of  main ditch  and  solid-liquid separation  zone of  IODVC was  carried out systematically. Main conclusions can be summarized as follows:
(1)   Computing mesh was generated by the software, and unstructured  triangular mesh was utilized here.  Moving Reference Frame (MRF) model and  Fan model were used to define the hydraulics behaviors of brush running  and impeller, respectively. In addition, RNG k-ε turbulence  model was used to  simulate the turbulence variation of flow-field in  IODVC. The  experiment verifies that  the above  models can accurately describe the flow characteristics of ditches in IODVC.
(2)   Compared   with  the  situation   that  there   is  no  guide -plate  in  IODVC, implementation of  guide-plates in  bend channel  can enhance  the velocity  of mixing liquid in ditches. Implementation  of single guide-plate can decrease the  percentage of flow  regime that  the  mixing  liquid  velocity was  lower  than  0.15m/s  by 22%  and enhance the percentage of flow regime that the liquid velocity was higher than 0.25m/s by 17% correspondingly;  implementation of double  guide-plates can further  increase the percentage of high  flowing velocity by 9.5%.  Implementation of guide-plates can effectively improve turbulence degree  of mixing liquid in  bend channel and optimize the velocity distribution of mixing liquid below the diversion-plate, which consequently reducing the percentage that width of reversed-flow region in outlet section of the right side  of bend  channel is  divided  by width  of  lower ditch  by 20%.In  the  meantime, implementation of  guide-plates can  significantly increase  the monolithic  velocity of mixing  liquid  in  lower ditch.  Therefore,  in  the  case  of  the same  input  of  power, implementation of guide-plates is beneficial to achieve a good mixing effect.
(3)   The  flow   pattern  will   varied  substantially    with  different   position   of guide-plates  in  ditches  of  IODVC,  and  optimal  settings  parameter  of  position  is obtained  by  numerical  simulation.  Optimal  condition  occurs  when  the  horizontal displacement-distance of  bilateral  guide-plates is  180mm. In  addition, appropriately prolonging  the length  of  the end  of  guide-plates  can further  guide  the  liquid flow behavior and prevent the sludge from depositing on the left side of diversion-plate. The findings also suggest  that when the  extended length equals  to the radius value  of the guide-plates, the flow behavior in the reactor is relatively optimum.
(4)   Setting  a  slope  of  45°  in solid-liquid   separation   zone  can improve   the distribution of sludge  and promote water quality  discharged by add deposited  area in IODVC.  In  the  meantime, the  solid-liquid  separation  zone  can  achieve  automatic circumfluence  of   deposited  sludge   by  slope,   along  with   the  reduce   of  energy consumption. The function that the  baffle plays a role of energy dissipation  is of vital importance  to water  quality  discharged  of solid-liquid  separation  zone.  Deposition efficiency goes down  when there is  no baffle, which  is caused by  the interactions of flow-field between main  ditch and solid-liquid  separation zone. Hydraulic shock  that entered  flow  generates  on  region  around  return  flow  section  can  be  relieved   by
appropriate shrinkage of the length of baffle. The research results also indicate that the water quality discharged is relatively optimal when the length of baffle is 200mm within certain realms.
    Overall, the  above-mentioned outcomes  derived from  this research can  provide guidance for both the further  optimization on structure and application to  engineering of full-scale IODVC systems.
 
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34456
Appears in Collections:水污染控制技术研究室_学位论文

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Recommended Citation:
杨宁. 立体循环一体化氧化沟结构优化研究[D]. 北京. 中国科学院研究生院. 2015.
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