# Three-Dimensional Numerical Analysis and Operational Optimization of High-Efficiency Sedimentation Tank

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Calculation Model and Methods

#### 2.1. Geometric Model

#### 2.2. Boundary Conditions and Grid Settings

^{−3}.

## 3. Results and Discussion

#### 3.1. Optimization of the Flocculation Zone

#### 3.1.1. Diameter of the Draft Tube

#### 3.1.2. Height of the Draft Tube

#### 3.2. Optimization of the Plug-Flow/Clarification Zone

#### 3.2.1. Height of the Water Tunnel

#### 3.2.2. Height of the Water-Retaining Weir

#### 3.3. Optimization of the Operation Parameters

#### 3.3.1. Dosage of Heavy Medium Particles

^{3}. In the coagulation and sedimentation process, the simultaneous addition of inert high-density powder (heavy medium) not only serves as the core for floc formation, but also significantly improves the settling performance of the flocs due to the higher density [29].

^{3}, 1118 kg/m

^{3}, 1236 kg/m

^{3}, and 1353 kg/m

^{3}, respectively.

#### 3.3.2. Stirring Rate

#### 3.3.3. Inlet Velocity

#### 3.4. Comparison between High-Efficiency Settling Tank and Conventional Clarifier

## 4. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Three-dimensional schematic diagram of (

**a**) flocculation zone, (

**b**) plug-flow and clarification zone, and (

**c**) the overall high-efficiency sedimentation tank.

**Figure 2.**Velocity distribution contour map of the YZ cross-section at different diameters of the draft tube: (

**a**) 2.4 m, (

**b**) 2.5 m, and (

**c**) 2.6 m.

**Figure 3.**The influence of different diameters of the draft tube on (

**a**) average turbulent kinetic energy k and (

**b**) average turbulent kinetic energy dissipation rate ε on a typical cross-section.

**Figure 4.**The contour profiles of velocities in the YZ cross-section for different heights of the draft tube: (

**a**) 3.4 m, (

**b**) 3.5 m, and (

**c**) 3.6 m.

**Figure 5.**The influence of different heights of the draft tube on (

**a**) average turbulent kinetic energy k and (

**b**) average turbulent kinetic energy dissipation rate ε on a typical cross-section.

**Figure 6.**The velocity distribution (

**a1**–

**c1**) and streamline diagram (

**a2**–

**c2**) of XY cross-section (Z = 0) at different water tunnel heights: (

**a1**,

**a2**) h = 0.9 m, (

**b1**,

**b2**) h = 1.0 m, (

**c1**,

**c2**) h = 1.1 m.

**Figure 7.**Distribution of turbulent kinetic energy (

**a1**–

**c1**) and turbulent kinetic energy dissipation rate (

**a2**–

**c2**) in the XY cross-section (Z = 0) at different heights h across the water tunnel. (

**a1**,

**a2**) h = 0.9 m, (

**b1**,

**b2**) h = 1.0 m, (

**c1**,

**c2**) h = 1.1 m.

**Figure 8.**The velocity distribution (

**a1**–

**c1**) and streamline diagram (

**a2**–

**c2**) of XY cross-section (Z = 0) at different heights of water-retaining weir: (

**a1**,

**a2**) l = 1.5 m, (

**b1**,

**b2**) l = 1.6 m, (

**c1**,

**c2**) l = 1.7 m.

**Figure 9.**The liquid phase velocity distribution (

**left**) and streamline diagram (

**right**) of XY cross-section (Z = 0) with different heavy medium particle dosages: (

**a1**,

**a2**) 0 mg/L, (

**b1**,

**b2**) 20 mg/L, (

**c1**,

**c2**) 40 mg/L, (

**d1**,

**d2**) 60 mg/L.

**Figure 10.**The volume solid holdup distribution of XY cross-section (Z = 0) with different heavy medium particle dosages: (

**a**) 0 mg/L, (

**b**) 20 mg/L, (

**c**) 40 mg/L and (

**d**) 60 mg/L.

**Figure 11.**The velocity distribution (

**a1**–

**c1**) and streamline diagram (

**a2**–

**c2**) of XY cross-section (Z = 0) at different stirring rates: (

**a1**,

**a2**) 25 rpm, (

**b1**,

**b2**) 30 rpm, (

**c1**,

**c2**) 35 rpm.

**Figure 12.**The volume solid holdup distribution of XY cross-section (Z = 0) at different stirring rates: (

**a**) 25 rpm, (

**b**) 30 rpm, (

**c**) 35 rpm.

**Figure 13.**The velocity distribution (

**left**) and streamline diagram (

**right**) of XY cross-section (Z = 0) at different inlet velocity: (

**a1**,

**a2**) 0.72 m/s, (

**b1**,

**b2**) 0.79 m/s and (

**c1**,

**c2**) 0.86 m/s.

**Figure 14.**Comparisons of the simulated and measured volume solid holdup of flocs at the outlet under different inlet flow rates.

Diameter of Draft Tube (m) | Turbulent Kinetic Energy k (m ^{2}·s^{−2}) | Dissipation Rate ε (m ^{2}·s^{−3}) |
---|---|---|

2.4 | 0.0236 | 0.0109 |

2.5 | 0.0289 | 0.0155 |

2.6 | 0.0285 | 0.0161 |

**Table 2.**Effect of draft tube height on average turbulent kinetic energy k and average turbulent kinetic energy dissipation rate ε in flocculation zone.

Height of Draft Tube (m) | Turbulent Kinetic Energy k (m ^{2}·s^{−2}) | Dissipation Rate ε (m ^{2}·s^{−3}) |
---|---|---|

3.4 | 0.0256 | 0.0133 |

3.5 | 0.0289 | 0.0155 |

3.6 | 0.0244 | 0.0125 |

**Table 3.**Effect of water tunnel height on average turbulent kinetic energy k and average turbulent kinetic energy dissipation rate ε in plug-flow/clarification zone.

Height of Water Tunnel (m) | Turbulent Kinetic Energy k (m ^{2}·s^{−2}) | Dissipation Rate ε (m ^{2}·s^{−3}) |
---|---|---|

0.9 | 0.7787 × 10^{−4} | 0.1245 × 10^{−4} |

1.0 | 0.7533 × 10^{−4} | 0.1205 × 10^{−4} |

1.1 | 0.7500 × 10^{−4} | 0.1224 × 10^{−4} |

**Table 4.**Effect of heavy medium particle dosage on average turbulent kinetic energy k and average dissipation rate ε.

Dosage of Heavy Medium Particles (mg/L) | Flocculation Zone | Plug-Flow/Clarification Zone | ||
---|---|---|---|---|

k (10^{−2} m^{2}·s^{−2}) | ε (10^{−3} m^{2}·s^{−3}) | k (10^{−4} m^{2}·s^{−2}) | ε (10^{−5} m^{2}·s^{−3}) | |

0 | 1.97 | 6.94 | 1.89 | 1.34 |

20 | 1.96 | 6.96 | 3.48 | 2.16 |

40 | 2.11 | 7.25 | 4.09 | 2.90 |

60 | 1.88 | 7.05 | 7.42 | 6.46 |

**Table 5.**The effect of inlet velocity—on the average turbulent kinetic energy k and the average turbulent kinetic energy dissipation rate ε.

Inlet Velocity (m/s) | Flocculation Zone | Plug-Flow/Clarification Zone | ||
---|---|---|---|---|

k (10^{−2} m^{2}·s^{−2}) | ε (10^{−3} m^{2}·s^{−3}) | k (10^{−4} m^{2}·s^{−2}) | ε (10^{−5} m^{2}·s^{−3}) | |

0.72 | 2.11 | 7.247 | 4.09 | 2.902 |

0.79 | 1.96 | 6.996 | 4.43 | 3.553 |

0.86 | 1.99 | 6.796 | 4.73 | 3.755 |

**Table 6.**Comparison between high-efficiency settling tank and conventional mechanically accelerated clarifier.

Parameter | Conventional Mechanically Accelerated Clarifier | High-Efficiency Settling Tank | |
---|---|---|---|

(Without Ballast) | (Use of Magnetite as a Ballast Material) | ||

Dosages of additives NaOH | adjust pH to 9.8 | adjust pH to 9.8 | adjust pH to 9.8 |

Na_{2}CO_{3} (mg/L) | 60~80 | 60~80 | 60~80 |

Polyferric coagulant (Fe^{3+}, mg/L) | 12 | 10 | 6 |

Polyacrylamide flocculant (mg/L) | 1.5 | 1.2 | 0.5 |

Sludge return | hydraulically stimulated passive circulation | forced circulation | forced circulation |

Removal efficiency of hardness (%) | 40~50 | ~80 | >90 |

Removal efficiency organic substances (%) | 20~30 | 20~50 | 20~60 |

Suspended solid’s concentration in produced water (mg/L) | <10 | <10 | <5 |

Hydraulic surface loading (m^{3}/(m^{2}·h)) | 3~7 | 10~15 | 15~20 |

Floor area (m^{2}) | about 240 | about 104 | about 64 |

Construction cost | $342,398 | $273,918 | $168,460 |

^{3}/h) for circulating water sewage in a power plant in North China.

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## Share and Cite

**MDPI and ACS Style**

Ye, Z.; Kang, S.; Wang, Z.; Jiang, Q.; Zhang, J.; Zheng, B.; Wang, J.
Three-Dimensional Numerical Analysis and Operational Optimization of High-Efficiency Sedimentation Tank. *Water* **2023**, *15*, 3656.
https://doi.org/10.3390/w15203656

**AMA Style**

Ye Z, Kang S, Wang Z, Jiang Q, Zhang J, Zheng B, Wang J.
Three-Dimensional Numerical Analysis and Operational Optimization of High-Efficiency Sedimentation Tank. *Water*. 2023; 15(20):3656.
https://doi.org/10.3390/w15203656

**Chicago/Turabian Style**

Ye, Zhian, Shaoxin Kang, Zhengjiang Wang, Qi Jiang, Jiangtao Zhang, Bin Zheng, and Jinlei Wang.
2023. "Three-Dimensional Numerical Analysis and Operational Optimization of High-Efficiency Sedimentation Tank" *Water* 15, no. 20: 3656.
https://doi.org/10.3390/w15203656