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重 慶 理 工 大 學(xué)
文 獻(xiàn) 翻 譯
二級學(xué)院 機(jī)械學(xué)院
班 級 機(jī)械設(shè)計制造及其自動化第二專業(yè)
學(xué)生姓名 謝 兵 學(xué) 號 10905020133
時 間 2013年3月16日
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指導(dǎo)教師：
年 月 日
設(shè)計程序的混凝和絮凝
對混凝攪拌罐的設(shè)計，設(shè)計師應(yīng)首先知道快速混合用于凝血和緩慢攪拌絮凝?；旌?
利用機(jī)械設(shè)備經(jīng)常進(jìn)行。圖1顯示了典型的混合葉輪。
有機(jī)械混合，可以發(fā)現(xiàn)在標(biāo)準(zhǔn)的典型設(shè)計標(biāo)準(zhǔn)在水/廢水處理教材。表1的數(shù)據(jù)，2是從metcaff與渦流污水工程和其他來源。
凝聚和絮凝攪拌罐設(shè)計的步驟是什么？“常用的設(shè)計方法的基礎(chǔ)上的速度梯度（G）的概念?；谠O(shè)計者的經(jīng)驗，他選擇的混合時間（t），G值，和一個混合葉輪?；谒x噸，G，和葉輪，設(shè)計師使用他的工程知識計算設(shè)計參數(shù)如下：
·混合罐的體積和尺寸
·理論的電力需求
·葉輪的直徑和轉(zhuǎn)速
表3示出了選擇的設(shè)計參數(shù)和作者計算出的數(shù)據(jù)。
設(shè)計流程總結(jié)如下：
假設(shè)設(shè)計案例
我現(xiàn)在就用一個假設(shè)的例子來說明如何設(shè)計攪拌罐凝固和絮凝。南通項目的基礎(chǔ)上，我們有假設(shè)的情況下，流程配置：快速混合凝固后3個階段的慢組合進(jìn)行絮凝。
設(shè)計流量：Q= 5000立方米
溫度：15°C（冬季），35°C（夏季）
1． 快速混合罐凝血設(shè)計
從表1中，推薦的混合時間為20 - 60秒。我們選擇最大的混合
·計算容積：
·計算快速混合罐尺寸：
選擇一個方形的槽的深度與寬度之比為1.5。
快速混合罐的尺寸是：
寬度=1.33米;長度=1.33米;深度= 2米
·計算電源要求：
速度梯度的概念中使用的設(shè)計和操作的坦克機(jī)械攪拌裝置：
其中，G =平均速度梯度（S-1）
P=功耗（W）
μ=動態(tài)粘度（NSM-2）
V=罐容積（m3）。
重新排列上述方程，我們得到：
μ=15°時 C=1.14×10-3 NSM-2，
μ=35°時 C=0.76×10-3 NSM-2。
我們選擇μ在15°C，以確保在冬季提供充足的電力。
從表1，推薦G是500 - 2,500 S-1。我們選擇G值為1000 S-1。
P = mVG2 = (1.14 x 10-3 )(3.5)(1,000)2 = 4,000 W = 4 kW
假設(shè)齒輪箱的效率為90％，功率要求變得
·計算葉輪的直徑和轉(zhuǎn)速
我們選擇45°尖銳的刀片有4個葉片的渦輪。從表1中，推薦的比例葉輪直徑（D），以等效的罐直徑為0.25 - 0.4。我們選擇0.3。
葉輪的旋轉(zhuǎn)速度（n）可以從以下估計數(shù)學(xué)關(guān)系：
上面的方程適用于，如果雷諾數(shù)是在湍流的范圍內(nèi)（NR>10000）。的功率數(shù)Np是由于在圖1和水密度r在15（℃）=999kgm3。
·檢查雷諾數(shù)：
·檢查葉輪葉尖速度：
·檢查營數(shù)：
凝固用快速混合罐的設(shè)計是完整的。選定的設(shè)計參數(shù)和計算，如在表3中示出在表4中被再現(xiàn)。
表4中設(shè)計參數(shù)，并計算混凝池。
2． 緩慢混合罐設(shè)計第1進(jìn)行絮凝
從表2中，推薦的混合時間是20 - 60分鐘。我們選擇了一個總的混合時間30分鐘。因為我們有3絮凝池，每個罐將有10分鐘的混合時間。
·計算容積：
·絮凝池的尺寸計算：
選擇一個方形水箱與寬度比1.13width深度。
絮凝池的尺寸是：寬度= 3.14米，長度= 3.14米，深度=3.5
·計算功率要求
從表2中，推薦使用的G是20 - 80 s-1的。我們選擇G值為80 s-1的。
假設(shè)變速箱的效率為90％，功率要求變?yōu)椋?
·計算葉輪的直徑和轉(zhuǎn)速：
我們選擇45°尖銳的刀片有4個葉片的渦輪。從表2中，推薦的比例
葉輪直徑（D），以等效的罐直徑為0.35 - 0.45。我們選擇0.3，稍
的最低值以下。
·檢查雷諾數(shù)：
·檢查葉輪葉尖速度：
·檢查營數(shù)：
3． 緩慢混合罐設(shè)計第2進(jìn)行絮凝
從表2中，推薦的混合時間是20 - 60分鐘。我們選擇了一個總的混合時間
30分鐘。因為我們有3絮凝池，每個罐將有10分鐘的混合時間。
·計算容積：
·絮凝池的尺寸計算：
選擇一個方形水箱與寬度比1.13width深度。
絮凝池的尺寸是：
寬度= 3.14米，長度= 3.14米，深度=3.55米
·計算電源要求：
從表2中，推薦使用的G是20 - 80 s-1的。我們選擇G值為60 s-1的。
假設(shè)變速箱的效率為90％，功率要求變?yōu)椋?
·計算葉輪的直徑和轉(zhuǎn)速：
我們選擇45°尖銳的刀片有4個葉片的渦輪。從表2中，推薦的比例
葉輪直徑（D），以等效的罐直徑為0.35 - 0.45。我們選擇0.3，稍
的最低值以下。
·檢查雷諾數(shù)：
·檢查葉輪葉尖速度：
·檢查營數(shù)：
4． 緩慢混合罐設(shè)計第3進(jìn)行絮凝
從表2中，推薦的混合時間是20 - 60分鐘。我們選擇了一個總的混合時間30分鐘。因為我們有3絮凝池，每個罐將有10分鐘的混合時間。
·計算容積：
·絮凝池的尺寸計算：
選擇一個方形水箱與寬度比1.13width深度。
絮凝池的尺寸是：寬度= 3.14米，長度= 3.14米，深度=3.55米
·計算電源要求：
從表2中，推薦使用的G是20 - 80 s-1的。我們選擇G值為40 s-1的。
假設(shè)變速箱的效率為90％，功率要求變?yōu)椋?
·計算葉輪的直徑和轉(zhuǎn)速：
我們選擇45°尖銳的刀片有4個葉片的渦輪。從表2中，推薦的比例葉輪直徑（D），以等效的罐直徑為0.35 - 0.45。我們選擇0.3，稍的最低值以下。
·檢查雷諾數(shù)：
·檢查葉輪葉尖速度：
·檢查營數(shù)：
進(jìn)行絮凝3慢速混合罐的設(shè)計是完整的。選定的設(shè)計參數(shù)如在表3中示出計算出的被再現(xiàn)于表5-7中
表5中。設(shè)計參數(shù)選擇和絮凝池＃1計算。
表6中。設(shè)計參數(shù)選擇和計算絮凝池＃2。
表7中。選擇的設(shè)計參數(shù)，和為絮凝池＃3計算。
至于我可以告訴葉強和天津的設(shè)計，設(shè)計過程通過研究所沒有考慮速度梯度的概念。在本次會議在新加坡檢討南通設(shè)計，我問葉七盎的設(shè)計是否凝血和絮凝池G值的概念的基礎(chǔ)上。葉強證實他知道的速度梯度的概念。但最近，葉強說，有沒有文檔/計算，以證明該設(shè)計確實是基于速度梯度。
天津設(shè)計院提供的信息是基于葉強的個人經(jīng)驗。葉強轉(zhuǎn)交了一份由設(shè)計院完成的計算，對我來說，看到附加的文檔。但沒有提到在文檔中，它的速度梯度的設(shè)計過程似乎是反向的上述設(shè)計過程。葉輪直徑和轉(zhuǎn)速是任意選定的。這些選定的值，然后用于計算功率要求，參見下圖。這是顯而易見的，該程序是正好相反的是什么通常使用的設(shè)計師的凝聚和絮凝流程。
通過葉強和天津設(shè)計院設(shè)計過程在概念上不正確的。不過，這并不意味著擬建的規(guī)?；炷托跄趯嵺`過程將失敗。的原因是，已經(jīng)廣泛的速度梯度在文獻(xiàn)中提出了混凝，絮凝設(shè)計。因此，安全邊際巨大的。不過，葉嶈作為一個過程的設(shè)計人員應(yīng)該學(xué)習(xí)的正確方法廢水處理工藝設(shè)計。設(shè)計程序和適當(dāng)?shù)奈募嬎闶潜仨毜摹?
我決定用一個假設(shè)的例子來說明凝固在設(shè)計所涉及的步驟絮凝過程的一個原因。我想葉期骯遵循給定的設(shè)計實例上述重新計算凝聚和絮凝的設(shè)計參數(shù)為南通項目并檢查設(shè)計參數(shù)是否導(dǎo)致速度梯度值的范圍內(nèi)可接受的范圍內(nèi)。
Design Procedure for Coagulation and Flocculation
To design mixing tanks for coagulation and flocculation, the first thing the designer should know is that rapid mixing is used for coagulation and slow mixing for flocculation. Mixing is often carried out by using mechanical devices. Figure 1 shows typical mixing impellers and their power numbers.
There are typical design criteria for mechanical mixing that can be found in standard text books on water/wastewater treatment. The data in Tables 1 and 2 are taken from Metcaff& Eddy Wastewater Engineering and other sources.
What are the steps involved in designing mixing tanks for coagulation and flocculation? The commonly used design approach is based on the concept of velocity gradient (G). Based on the designer’s experience, he selects a mixing time (t), a G value, and a mixing impeller. Based on the selected t, G, and impeller, the designer uses his engineering knowledge to calculate the following design parameters:
· Mixing tank volume and dimensions
· Theoretical power requirement
· Impeller diameter and rotational speed
Table 3 shows the design parameters selected and the design parameters calculated by thedesigner.
Table3. Design parameters selected and calculated by the designer.
Hypothetical Design Case
I will now use a hypothetical case to illustrate how to design mixing tanks for coagulation and flocculation. The hypothetical case is based on the Nantong project where we have the following process configuration: a rapid mix for coagulation followed by 3 stages of slow mix for flocculation.
Design flow rate: Q = 5,000 m3/day
Temperature: 15 °C (winter), 35 °C (summer)
1. Design of a rapid mix tank for coagulation
From Table 1, recommended mixing time is 20 – 60 s. We select the maximum mixing time of 60 s.
· Calculate tank volume:
· Calculate dimensions of rapid mix tank:
Select a square tank with a depth to width ratio of 1.5.
Dimensions of rapid mix tank are:
Width = 1.33 m; Length = 1.33 m; Depth = 2 m
· Calculate power requirement:
The concept of velocity gradient is used in the design and operation of tanks with mechanical mixing devices:
where G = average velocity gradient (s-1), P = power requirement (W), μ = dynamic viscosity (Nsm-2), and V = tank volume (m3). Rearranging the above equation we get:
μ at 15 °C = 1.14 x 10-3 Nsm-2, μ at 35 °C = 0.76 x 10-3 Nsm-2. We select μ at 15 °C to ensure adequate power is provided during winter.
From Table 1, recommended G is 500 – 2,500 s-1. We select a G value of 1,000 s-1.
Assuming the gearbox efficiency is 90%, the power requirement becomes:
· Calculate impeller diameter and rotational speed:
We select 45° pitched-blade turbine with 4 blades. From Table 1, the recommended ratio of impeller diameter (D) to equivalent tank diameter is 0.25 – 0.4. We select 0.3.
The rotational speed of the impeller (n) can be estimated from the following
Mathematical relationship:
The above equation applies if the Reynolds number is in the turbulent range (NR > 10,000). The power number Np is given in Figure 1 and water density r at 15 °C = 999 kgm3.
· Check Reynolds number:
· Check impeller tip speed:
· Check Camp number:
The design of a rapid mix tank for coagulation is complete. The design parameters selected and calculated as shown in Table 3 are reproduced in Table 4.
2. Design of slow mix tank #1 for flocculation
From Table 2, recommended mixing time is 20 – 60 min. We select a total mixing time of 30 min. Since we have 3 flocculation tanks, each tank will have a mixing time of 10 min.
· Calculate tank volume:
· Calculate dimensions of flocculation tank:
Select a square tank with a depth to width ratio of 1.13width.
Dimensions of flocculation tank are:
Width = 3.14 m; Length = 3.14 m; Depth = 3.55 m
· Calculate power requirement:
From Table 2, recommended G is 20 – 80 s-1. We select a G value of 80 s-1.
Assuming the gearbox efficiency is 90%, the power requirement becomes
· Calculate impeller diameter and rotational speed
We select 45° pitched-blade turbine with 4 blades. From Table 2, the recommended ratio of impeller diameter (D) to equivalent tank diameter is 0.35 – 0.45. We select 0.3, slightly below the minimum value.
· Check Reynolds number:
· Check impeller tip speed:
· Check Camp number:
3. Design of slow mix tank #2 for flocculation
From Table 2, recommended mixing time is 20 – 60 min. We select a total mixing time of 30 min. Since we have 3 flocculation tanks, each tank will have a mixing time of 10 min.
· Calculate tank volume:
· Calculate dimensions of flocculation tank:
Select a square tank with a depth to width ratio of 1.13width.
Dimensions of flocculation tank are:
Width = 3.14 m; Length = 3.14 m; Depth = 3.55 m
· Calculate power requirement:
From Table 2, recommended G is 20 – 80 s-1. We select a G value of 60 s-1.
P = mVG2 = (1.14 x 10-3 )(35)(60)2 = 144 W = 0.14 kW
Assuming the gearbox efficiency is 90%, the power requirement becomes:
· Calculate impeller diameter and rotational speed:
We select 45° pitched-blade turbine with 4 blades. From Table 2, the recommended ratio of impeller diameter (D) to equivalent tank diameter is 0.35 – 0.45. We select 0.3, slightly below the minimum value.
· Check Reynolds number:
· Check impeller tip speed:
· Check Camp number:
4. Design of slow mix tank #3 for flocculation
From Table 2, recommended mixing time is 20 – 60 min. We select a total mixing time of 30 min. Since we have 3 flocculation tanks, each tank will have a mixing time of 10 min.
· Calculate tank volume:
· Calculate dimensions of flocculation tank:
Select a square tank with a depth to width ratio of 1.13width.
Dimensions of flocculation tank are:
Width = 3.14 m; Length = 3.14 m; Depth = 3.55 m
· Calculate power requirement:
P = mVG2
From Table 2, recommended G is 20 – 80 s-1. We select a G value of 40 s-1.
P = mVG2 = (1.14 x 10-3)(35)(40)2 = 64W = 0.064 kW
Assuming the gearbox efficiency is 90%, the power requirement becomes:
· Calculate impeller diameter and rotational speed:
We select 45° pitched-blade turbine with 4 blades. From Table 2, the recommended ratio of impeller diameter (D) to equivalent tank diameter is 0.35 – 0.45. We select 0.3, slightly below the minimum value.
· Check Reynolds number:
· Check impeller tip speed:
TS =pnD =p (0.32)(1.06) = 1.1 ms-1 1.8 < TS < 2.4 ms-1 (Table 2), Not OK
· Check Camp number:
Gt = (40)(600) = 24,000 20,000 < Gt < 200,000 (Table 2), OK
The design of 3 slow mix tanks for flocculation is complete. The design parameters selected and calculated as shown in Table 3 are reproduced in Tables 5-7.
Table 5. Design parameters selected and calculated for flocculation tank #1.
As far as I can tell, the design procedure adopted by Ye Qiang and the Tianjin Design Institute did not consider the concept of velocity gradient. During our meeting in Singapore to review the Nantong design, I asked Ye Qiang whether the design of coagulation and flocculation tanks was based on the concept of G value. Ye Qiang confirmed that he was aware of the velocity gradient concept. But recently, Ye Qiang stated that there is no documentation/calculation to demonstrate that the design is indeed based on velocity gradient.
The information supplied to the Tianjin Design Institute was based on Ye Qiang’s personal experience. Ye Qiang forwarded a copy of calculations done by the Design Institute to me, see document attached. There is no mention of velocity gradient in the document and it seems that the design procedure is the reverse of the above design procedure. The impeller diameter and rotational speed are arbitrarily selected. These selected values are then used to calculate the power requirement, see diagram below. It is obvious that the procedure is the exact opposite of what is normally used by designers of coagulation and flocculation
processes.
The design procedure adopted by Ye Qiang and the Tianjin Design Institute is conceptually incorrect. But it does not mean that the proposed full-scale coagulation and flocculation processes will fail in practice. The reason is that a wide range of velocity gradient has been proposed for coagulation and flocculation design in the literature. So the safety margin is huge. Nevertheless, Ye Qiang as a process designer should learn the proper way of designing wastewater treatment processes. Proper documentation of design procedure and calculation is a must.
I decided to use a hypothetical case to illustrate the steps involved in designing coagulation and flocculation processes for a reason. I want Ye Qiang to follow the design example given above to re-calculate coagulation and flocculation design parameters for the Nantong project and to check whether the design parameters lead to velocity gradient values that fall within the acceptable range.