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2018 International Conference on Civil, Architecture and Disaster Prevention IOP Publishing
IOP Conf. Series: Earth and Environmental Science 218 (2019) 012045 doi:10.1088/1755-1315/218/1/012045

Study on Structural Characteristics of Siphon Well Design in

a Power Plant

Shen Dongmei[1] , Yu Cairui [1] , Wu Shaoyang[2]

1
Architecture and Civil Engineering Department of West Anhui University, 237012
2
Central Southern China Electric Power Design Institute (CSEPDI) of China Power
Engineering Consulting Group Corporation，430071
Email of all the authors:
Corresponding Author: shendongmei; email:shdm9832@163.com;
phone:15855269832; fax:0564-3307059 ； yucairui; email:yucr_2000@163.com;
phone:13865643150; fax:0564-3307059:wushaoyang; email:285010685@163.com;
phone:15827222355; fax: 027-87811992

Abstract： The structural characteristics of siphon wells are important parameters to determine
the good operation of siphon wells. Based on the engineering data of a power plant and
combined with the physical model test of hydraulic characteristics, considering the hydraulic
characteristics, the foam pollution and the engineering cost，this design can avoid the defects of
simple theoretical calculation and has a strong reference value.

1.Introduction
The structural characteristics of siphon wells are important parameters to determine the good operation
of siphon wells.Siphon well could be deemed an important hydraulic structure in cooling water
drainage system of power plants, the rationality of its structure is not only closely related to the
realization of its own function, but also directly affects the safe and efficient operation of the whole
system . The weir crest elevation and cross-sectional area of siphon wells are the main structural
parameters affecting their own functions. If the weir crest elevation is too high, the siphon effect will
weak, the operation and maintenance cost will increase. Besides, the serious foam pollution will be
produced. If it’s too low, it is easy to cause the negative pressure to be too low and even the water
hammer will be destroyed. If the cross-sectional area is too large, the construction cost will be
increased, and if it’s too small, the negative pressure water hammer will probably appear if the water
pump is cut off suddenly [1-5].
At present, the siphon well structure design is obtained by referring to the relevant design manual,
and the design calculation is only analyzed unilaterally from the economic benefit. However, for
specific projects, due to the differences of specific sites conditions, the structural design parameters
may not be consistent with the actual engineering when they are initially determined. At the same time,
due to the serious foam pollution caused by the improper design of structural parameters, the
environment will be greatly damaged.
The physical model is based on the principle of similarity, and scaling down the prototype.
Through hydraulic tests, the defects of relying solely on theoretical calculation can be over come,
which can not only verify the rationality of theoretical calculation parameters, but also observe its

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2018 International Conference on Civil, Architecture and Disaster Prevention IOP Publishing
IOP Conf. Series: Earth and Environmental Science 218 (2019) 012045 doi:10.1088/1755-1315/218/1/012045

hydraulic characteristic. Water flow patterns and foam pollution. Therefore, in the actual engineering
design, the structural parameters of siphon wells can be determined by the physical model test of
hydraulic characteristics, which not only considers the economy, but also gives considerations to the
environmental protection and safety, and has the irreplaceable advantage of other methods.

2.Methods: engineering information and design

2.1Basic engineering information

A coal-fired power plant, near the Yangtze River, is located in a northern subtropical monsoon humid
climate,where the average annual temperature is 16.1℃-18.3℃. What is more, there is abundant
rainfall, ample sunshine, hot summer and cold winter. Installed capacity is 600 MW, set up two groups.
Taking the main plant of the power plant as zero meter floor and the relative elevation at the top of the
condenser is 5.50m. The circulating water quantity of a unit is 17.04 m3/s summer and 12.26 m3/s in
winter. The water level at the outlet of cooling water near the river is about 56.58 m in summer and
55.66m in winter.
2.2 Engineering design analysis

2.2.1Hydraulic characteristic physical model test

(1) Choice of intersection
The section area of siphon well is an important parameter in structural design,it is affected greatly
by site limitations in actual engineering. The circulating water quantity of this project was relatively
small, therefore, the siphon well size was also smaller. Considering the small occupation of
thin-walled Weir, it was determined that thin-walled Weir was used as overwater structure. There are
three kinds of common thin-walled Weir: orthogonal Weir, skew Weir and folded Weir. For the project
was limited by the site ,consideration was given to the use of skew Weir. Due to the intersection angle
of skew Weir is a main factor affecting its flood discharge capacity, determining a suitable intersection
angle is the key of Siphon Well design. In order to determine the suitable intersection angle, a thin wall
weir flow model was established in the laboratory (see Figure 1 below). The discharge experiment of
skew Weir at the intersection angle of 15°,30°,45°,60° was studied experimentally. By measuring the
water head of the Weir under different working conditions, the water surface profile of various
condition was shown in Figure 2 below.

outlet

inlet

Fig 1. Discharge test plan of thin-walled weir

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2018 International Conference on Civil, Architecture and Disaster Prevention IOP Publishing
IOP Conf. Series: Earth and Environmental Science 218 (2019) 012045 doi:10.1088/1755-1315/218/1/012045

Fig 2. Relationship between water flow at different angles and head of weir
It can be seen from Fig.2 that under the same flow rate，with the increase of intersection angle，the
head of Weir decreases and the discharge capacity of weir becomes stronger. However, is the bigger
the angle,the better. When the flow rate increases, the water head on the weir increases more slowly，
but what about the downstream water flow pattern and whether there will be foam pollution or not
should be further combined with the downstream water flow pattern analysis.
（2）Analysis of water flow pattern
If Weir crest elevation is high，a large amount of gas will be doped in the water flow behind the
siphon well，forming a large amount of foam which has a great impact on the environment 5 .In
［ ］

response to the above problems, based on the discharge test plan of thin-walled weir, the flow pattern
and foam transport in siphon wells were analyzed, and the hydraulic performance of siphon wells was
optimized.
The experimental results show that in the case of free discharge, when the angle of intersection of
skew Weir increases from 30° to 60°, the current scour tended to be intense, the turbulence of
downstream flow enhanced, and the amount of foam is increased. Combined with the flow-head curve,
considering the discharge capacity and foam pollution, a skew Weir with an intersection angle slightly
greater than 30° was preliminary determined.

2.2.2 Design calculation

The discharge of submerged Weir is
,
qv = σm0 ⋅ b 2 g H 1.5 （1）
where parameter are expressed as:c
b——the width of overflow Weir，m
σ ——Submergence coefficient，According to table 1
q——rate of flow，m3/s
g——acceleration of gravity，
it can be concluded that the Weir is a non-submerged Weir, and the flow coefficient of Weir can
be obtained by calculating CH ≥ 0.5H, H ≥ 0.1m(CH -Weir height ,H- weir head),then
,
m0 = 0.402 + 0.054 H C H (2)

3
2018 International Conference on Civil, Architecture and Disaster Prevention IOP Publishing
IOP Conf. Series: Earth and Environmental Science 218 (2019) 012045 doi:10.1088/1755-1315/218/1/012045

Table 1 Submergence coefficient σ

Condition computational formula
H h, 3 Z
0.15 ≤ ≤ 1.90 σ = 1.05(1 + 0.2 )
CH CH H
H h, 3 Z
0.15 ≤ ≤ 0.25 σ = 1.008(1 + 0.2 )
CH CH H

calculation. Finally, determining the angel of skew Weir was ϕ = 340 , the width of overflow Weir was
21.633m, the length of siphon well was 20m and the width of siphonc was 9m. Siphon horizontal
profile was presented in figure 3 as below.

B-B

Fig. 3 Siphon profile of a power plant

3.Results and discussion

3.1 Design optimization analysis

4
2018 International Conference on Civil, Architecture and Disaster Prevention IOP Publishing
IOP Conf. Series: Earth and Environmental Science 218 (2019) 012045 doi:10.1088/1755-1315/218/1/012045

(1) Economic optimization analysis

Affected by the actual site, the well width was too large, the siphon well occupied too much space ,
the construction quantity and the cost increased. so it is not suitable to adopt the large-angle Skew
Weir in the view of the engineering economy.
(2) Optimization analysis of environmental protection
During the free discharge of siphon wells, severe water vapor adulteration was produced, and the
foam pollution of drainage outlet was serious. From the physical model test of hydraulic
characteristics, it can be seen that when the intersection angle of skew Weir increases gradually, the
turbulence of flow enhanced, the distance of return to normal gradually increased, and the amount of
foam produced increased. In order to eliminate sensory pollution caused by foam, many power plants
often add defoamer to the drainage system. This will not only increase the operating cost of the power
plant, but also defoamer will cause secondary pollution to the receiving water environment[6].From the
aspect of environmental protection, the angle of siphon well should not be too big.
(3) Security optimization analysis
The higher the siphon utilization is, the more significant the economic benefits are. If the other
dimensions of siphon wells are invariant and the siphon utilization height of the siphon well in the
power plant is increased by 2m, the pump head will be reduced by 2m.
If the number of hours used per year is calculated at 5000, the factory electricity price is 0.4 yuan /
kW*h, the annual operating cost of the water pumps of the two units will be reduced as follows:
Pump shaft power increase×number of hours used per year × electricity price =(KγQH/102/η)
×5000×0.4=1.05×1000×((17.04×7+12.26×5)/12)×2×2×5000×0.4/(102×0.85) ＝ 145.80(Ten thousand
yuan)
It can be seen from the above formula that when the siphon height was increased by 1 m, the
annual operating cost of the power plant could be saved by about 730000 yuan. But in terms of safety,
siphon utilization is not the higher the better. Due to the circulating water pipe is a closed space, if
the distance from the circulating water outlet to the condenser outlet is more than 10 meters (a column
of water at atmospheric pressure), it will lead to the cut off of the circulating water backwater pipeline,
and the consequences will be very serious. In order to make the backwater flow smoothly, the
circulating water pump will do more work, thus consuming more electricity, the effect is
counterproductive. According to the practical results of previous projects, from the point of view of
safety analysis, the siphon utilization height is generally used 7 m.
Synthesis of the above three aspects of optimization analysis, the angle of skew Weir ϕ = 34 0
and the siphon height of 7 m is reasonable.

3.2 Engineering validation

The design has completed construction and operation, after a period of observation, the system ran
smoothly and produced little foam pollution . When the siphon wells were adopted, the annual
operating cost could be reduced by about 10million yuan during two years, which shows that the
method of determining the structural parameters of siphon wells combined with the physical model
test of hydraulic characteristics is reasonable and feasible.

4.Conclusion
The structural characteristics of siphon wells are important parameters to determine the good operation
of siphon wells.The rationality of its structure is not only closely related to the realization of its own
function, but also directly affects the safe and efficient operation of the whole system. The structural
parameters derived from the design manual are often inconsistent with the actual site. And the power
plants are mostly close to the river. The foam pollution caused by cooling water will cause great
damage to the environment. In this study, the physical model test of hydraulic characteristics is carried
out in the laboratory. Considering the discharge capacity and hydraulic flow pattern, the oblique weir
with an angle of slightly more than 300 is preliminarily drawn up. In the design process, the design
parameters are optimized and analyzed from three aspects to determine the siphon well size. Finally,

5
2018 International Conference on Civil, Architecture and Disaster Prevention IOP Publishing
IOP Conf. Series: Earth and Environmental Science 218 (2019) 012045 doi:10.1088/1755-1315/218/1/012045

through engineering verification, the comprehensive design layout is reasonable. The structural
characteristics of siphon wells are studied by combining theoretical derivation with laboratory physical
model, which provides a new idea for engineering design.

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engineering ,2013( 10) : 55－58
[3] ChenFushan,SunHaiyan,ChenYunhuai. Assign optimization and design of siphon well in a power
plant circulating water［J］.Huadian technology，2012( 12) : 18－20
[4] ChenFushan,SunHaiyan,HanQin. Study optimization and design of siphon well parameter in a
power plant circulating water［J］.Huadian technology，2012( 8) : 56－58
[5] Zhang Guopeng. Research on hydraulic characteristics of siphon well in cooling water system of
Power plant［D］．Handan: Hebei University of Engineering
[6] ZengLinggang.The causation and countermeasure to the foam in seal pit of coastal power plant
［J］．China science and technology information , 2009（18）:67-68