Experimental Study on the Effect of Heat-Retaining and Diversion Facilities on Thermal Discharge from a Power Plant - MDPI
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water
Article
Experimental Study on the Effect of Heat-Retaining
and Diversion Facilities on Thermal Discharge from a
Power Plant
Ruixia Hao, Liyuan Qiao, Lijuan Han and Chun Tian *
School of Water Resources Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China;
haoruixia@tyut.edu.cn (R.H.); qiaoliyuan9701@163.com (L.Q.); hanlijuan@tyut.edu.cn (L.H.)
* Correspondence: tianchun@tyut.edu.cn; Tel.: +86-136-0353-0613
Received: 29 June 2020; Accepted: 10 August 2020; Published: 12 August 2020
Abstract: In order to reduce the influence of thermal discharge from the power plant on the
surrounding water environment and the operation efficiency of the power plant, a distorted physical
model was presented and applied to Huadian Kemen Power Plant for studying heat transport and
analyzing the effects of heat-retaining and diversion facilities near the intake/outlet on the thermal
discharge for six scenarios. Field investigations were also used to validate the model. This study
is unique as it is the first to elaborate on the impact of heat-retaining and diversion facilities on
thermal discharge. The results indicate that the construction of heat-retaining and diversion facilities
can decrease the excess temperature at intake to meet the intake requirement and improve the
distribution of low temperature rise, but the area of high temperature rise has an increase. When the
heat-retaining wall and diversion dike were constructed, the maximum intake temperature rise of
Phase III decreased significantly by 1.0–1.3 ◦ C with an average decrease of 0.2 ◦ C, and the maximum
value of Phase I and II was reduced by 0.3 ◦ C with little mean change. A comparative experiment
with different construction heights was also conducted. Result analysis shows that when the crest
elevation was reduced from 3 to 2 m, the influence on the intake temperature rise of Phase I and
II could be ignored, and the average temperature rise of Phase III only had an increase of 0.1 ◦ C,
suggesting that constructions with 2 m play an effective role in reducing heat return to the intake.
Keywords: thermal discharge; heat-retaining and diversion facilities; physical model; excess temperature
at intake; tidal flows
1. Introduction
With the rapid economic development of coastal areas, more attention has been paid to
ocean exploitation to address growing energy demands. Large power plants combined with new
combustion/gasification technology [1–3] are often built in coastal areas and use the sea as cooling
water, discharging a large amount of waste heat into the nearby seas [4]. The rise in water temperature
and the water stratification caused by thermal discharge [5–7] have adverse impacts on the marine
ecological environment [8–11]. Thermal pollution caused mainly by industrial use of water as a cooling
agent has been regarded as a severe threat to ecological composition in coastal waters [12]. Meanwhile,
a portion of the heated water directly returns to the intake, which negatively affects the unit operation
efficiency [13,14]. The study on the hydraulic and thermal characteristics of thermal discharge is the
basis to analyze the above problems.
The physical model is an important method to study thermal discharge characteristics. The mixing
and dilution of heated water in near zones can be directly and truly reflected by experiments in the
laboratory. The problem studied has occurred mainly in heat transport and the layouts of the power
Water 2020, 12, 2267; doi:10.3390/w12082267 www.mdpi.com/journal/water
Water 2020, 12, 2267 2 of 15
plant intake and outlet. Shawky et al. [15] tested two alternatives for outfall configuration, the surface
open channel and multiport diffuser, to study the effect of thermal discharge by a scaled physical
model. They indicated that the outfall of the diffusers could improve the mixing process and reduce
thermal pollution to the allowable limits. Tian et al. [16] used the physical model with scale distortion
to discuss the influence of intake retraction to bank on temperature rise. Intake retraction shortened
the distance between intakes and outlets, the nearby water depth shoaled, the buoyant stratification
caused by the temperature difference weakened and the direct recurrent of hot water increased, so that
the intake temperature rise was more obvious, which is unfavorable to the plant. El-Ghorab [17]
investigated the effects of effluents, excess temperature and flow regime on the mixing zone using a
physical model, and established regression equations to predict the size of the mixing zone. The mixing
zone area increases as the effluent increases and decreases as the flow in the river increases. It was
found that the excess temperature at the outlet has more influence on the mixing zone. The work
in [12] also provided a discussion on the effect of water discharge and the temperature at the outlet
on the plume distribution. Zeng et al. [18] used the full-field physical model with scale distortion
and the local physical model with a normal scale to analyze the detailed heat exchange phenomenon
and discuss the effect of scale distortion. The results showed that compared with field measurements,
the water temperature in coastal water was a little oversimulated near the surface and was a little
undersimulated near the bottom of the heated-water layer by the full-field physical model. It was
also shown that the model with scale distortion was applicable for simulating turbulent tidal flow
and heat transport in coastal water in the case study. Shah et al. [19] used the physical model and
numerical simulation to analyze the influence of flow rate and wind speed on the thermal plume.
Shawky et al. [20] studied the effects of the main parameters such as the intake length, the distance
between the intake and outlet, the water depth under the intake skimmer wall and the water depth just
upstream the intake on the thermal characteristics using a physical model and numerical simulation.
Two mathematical formulas indicating the relationship between these parameters and the hot water
concentration at intake were deduced and verified.
At present, the majority of such studies have focused on the layout of the intake and outlet to
reduce the impact of thermal discharge [21–23], and the effect of heat-retaining and diversion facilities
has been ignored. The reasonable layout of the diversion dike and heat-retaining wall is an effective
way to control heat transport and decrease excess temperature at intake, but there is a lack of detailed
study on the effect of heat-retaining and diversion facilities. Therefore, in this paper, a distorted physical
model is established and validated with field measurements. The objective is to study the influence of
the construction and height of heat-retaining and diversion facilities near the intake/outlet on thermal
discharge characteristics, including the temperature rise distribution and excess temperature at intake
by scenario comparison. This paper is the first to present, in detail, the effects of heat-retaining and
diversion facilities. The results include important reference values for similar engineering applications
and scientific evaluation.
2. Project Overview
Luoyuan Bay is situated on the northeast coast of Fujian Province, China, surrounded by mountains
and facing the sea in the northeast. The bay is wide and shallow with an area of 188.6 km2 . The length
from the baymouth to the bayhead is about 25 km, and the maximum water depth is 74 m. The mean
width is 7 km and the mouth width is only 1.3 km. Luoyuan Bay is a typical semienclosed harbor that
exchanges water with the open sea only through the Kemen Channel (Figure 1). The wind and waves
are weak, and there is no obvious impact of rivers or tributaries. According to the observed data,
the tidal current featuring reciprocating flow is dominated by a regular semidiurnal tide. The mean
tidal range is about 4.94 m and the maximum is 6.91 m. The flow velocity at the baymouth is larger
than that in other areas. The maximum flood rate is 1.09 m s−1 and the maximum ebb rate is 1.17 m s−1 .
The maximum velocity near the plant is about 0.70 m s−1 . During the spring tide, the maximum rate of
the residual current is 0.13 m s−1 , and during the neap tide, the maximum is 0.06 m s−1 . The residual
Water 2020, 12, 2267 3 of 15
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current
maximum
maximum near
is the plant
is 0.06
0.06 m
−1.comes
m ss−1 . The along the
The residual
residual channel
current
current nearto
near the
the
the inner
plant
plant bay, along
comes
comes which is consistent
along the
the towith
channel to
channel the flood
the inner
the inner bay,
bay,
current
which is
which direction.
is consistent
consistent with
with thethe flood
flood current
current direction.
direction.
Figure 1.
Figure 1. Location
Location of
of Luoyuan
Luoyuan Bay
Bay and
and power
power plant.
plant.
Huadian
Huadian Kemen
Huadian KemenPower
Kemen PowerPlant
Power Plant
Plant is located
is located
is locatedon theon south
on the south
the bank bank
south of Luoyuan
bank Bay (Figure
of Luoyuan
of Luoyuan 1).
Bay (Figure
Bay The capacity
(Figure 1). The
1). The
of Phase I and II is 2400 MW, with the cooling water circulating at 81.68 m 3 s−1 .3 The capacity of
capacity of Phase I and II is 2400 MW, with the cooling water circulating
capacity of Phase I and II is 2400 MW, with the cooling water circulating at 81.68 m s . The capacity at 81.68 m 3 s −1. The
−1 capacity
Phase III is 2000 MW, and the units require a cooling flow of 65.66 m 3 s3 −1−1. The phases of the power
of Phase III is 2000 MW, and the units require a cooling flow of 65.66
of Phase III is 2000 MW, and the units require a cooling flow of 65.66 m3 s−1. The phases of the power m s . The phases
plant
plant use
use seawater
use seawateras
seawater asthe
as thecooling
the coolingwater
cooling waterthrough
water through
through their
their
their intakes
intakes
intakes and discharge
and
and discharge
discharge thetheheated
the heated
heated waterwater
waterintointothe
into
bay at a temperature of 8.5 ◦ C above the ambient temperature through their outfalls. Figure 2 shows
the bay at a temperature of 8.5 °C above the ambient temperature through their outfalls. Figure 22
the bay at a temperature of 8.5 °C above the ambient temperature through their outfalls. Figure
shows
the
shows thelayout
plane
the plane of
plane layout
intakes
layout of intakes
of intakes and outfalls.
and outfalls.
and outfalls.
The intake Theheads
The intakeofheads
intake heads ofI Phase
Phaseof Phase
and Phase II and
andIIPhase
Phase
are setII IInext
are set
are set next
to each
next
to each
other, andother,
the and
joint the joint
outlet is outlet
built on is built
the on
northeast the northeast
side of the side of
plant.
to each other, and the joint outlet is built on the northeast side of the plant. The layout of the deep the
The plant.
layout The
of layout
the deep of the
intake deep
and
intake
surface and surface
discharge isdischarge
adopted is
in adopted
the in
prophase the prophase
projects. Theprojects.
bottom
intake and surface discharge is adopted in the prophase projects. The bottom elevation of the intake The bottom
elevation ofelevation
the intake of the
is intake
−15.6 m
is −15.6
and
is −15.6
1.9 m maway
m and 1.9
and 1.9
from mthe
m away
awaybottomfromofthe
from the bottom
thebottom
harbor of of
basinthe to
the harbor
prevent
harbor basin to prevent
prevent and
sedimentation
basin to sedimentation
sediment from
sedimentation and
and
sediment from entering. The top elevation of
−6.6 the intake is
sediment from entering. The top elevation of the intake is −6.6 m, which is 4.2 m away from low
entering. The top elevation of the intake is m, which is −6.6
4.2 m m,
away which
from is
the4.2 m
annual away from
average the
the
annual
tide average
level. The low
diversion tide level.
ditch is The
used diversion
to connect ditch
the is
intake used
and
annual average low tide level. The diversion ditch is used to connect the intake and the pump to
theconnect
pump the
house. intake
An and
open the
channel pump for
house.isAn
intake
house. Anusedopen
open channel
in Phase
channel for
III,for intake
andintake is used
the outlet
is used in Phase
Phaseon
is arranged
in III,the
III, and
andeast the
the outlet
side is arranged
of the
outlet is arranged outlet.
prophase on the
on the The
east bottom
east side of
side of
the prophase
elevation of theoutlet.
open The bottom
channel is elevation
about −10.3 of the
m. open
In channel
addition,
the prophase outlet. The bottom elevation of the open channel is about −10.3 m. In addition, the is
the about
outlets −10.3
of m.
Phase In
I, addition,
II and III the
are
outlets of
equipped
outlets of with
Phasediffusion
Phase I, II
I, II and
andfacilities
III are
III are equipped
equipped
to dissipate with
with diffusion
energy facilities
and reduce
diffusion facilities toexit
theto dissipate
velocity.
dissipate energy
The baffle
energy and reduce
and reduce
sill with the
a
the
exit elevation
top
exit velocity. The
velocity. The
of −2.5baffle sill
m issill
baffle with
setwith
at theaa top
top elevation
tail of the outlet,
elevation of −2.5
of −2.5
and m m isstone
theis set at
set atapron
the tail
the tail
withof the
of the outlet, and
an elevation
outlet, and the stone
−3.0stone
of the m is
apron
set with
behind an
the elevation
baffle sill. of −3.0 m is set behind
apron with an elevation of −3.0 m is set behind the baffle sill. the baffle sill.
Figure 2. Layout
Figure Layout of intakes,
intakes, outlets and
and heat-retaining and
and diversion facilities.
facilities.
Figure 2.
2. Layout of
of intakes, outlets
outlets and heat-retaining
heat-retaining and diversion
diversion facilities.
3. Materials
3. Materials and
and Methods
Methods
Water 2020, 12, 2267 4 of 15
3. Materials and Methods
3.1. Model Design
• For wide and shallow waters, it is necessary to adjust the model scale and use the distorted
physical model [24,25]. Factors such as the simulation range, terrain condition, laboratory size
and water supply capacity should be considered in determining the distorted scale. Due to the
great amount of heated water discharged from the Huadian Kemen Power Plant and strong heat
accumulation in Luoyuan Bay, the simulation range is relatively large. Generally, the average
isotherm of 0.3 ◦ C should be included in the model area. Based on the early numerical simulation
results [26], the simulation range of 20 km × 8 km was determined (see Figure 1). Because of the
great topographic variation and the large shoal waters in the range, the distortion ratio cannot be
too small. However, considering the mixing properties in the near zone, a large distortion should
also be avoided [27]. Finally, the distorted scale of 3.33 was selected with a horizontal scale of 400
and a vertical scale of 120 by comprehensive consideration.
• The model was designed according to the Froude number similarity (Equation (1)), and it was also
required to meet the densimetric Froude number similarity (buoyancy effect, Equation (2)) [28–30].
p
(F r )r = V/ gH ) r = 1 (1)
s
∆ρ
(F d )r = V/ gH ) r = 1 (2)
ρ
where Fr is Froude number, Fd is densimetric Froude number, V is velocity, g is gravity acceleration,
H is water depth, ρ is fluid density, ∆ρ is the density difference between heated water and ambient
water and the subscript “r” denotes the ratio between prototype and model.
Based on the Froude number similarity, the densimetric Froude number similarity means that
the relative density difference in both the prototype and model is equal. Assuming that the density
difference linearly changes with the temperature difference, a temperature rise scale of 1 is required to
meet the heat similarity.
According to the Froude number similarity, the velocity, time, discharge and roughness scales can
be determined as follows:
Velocity scale : Vr = Hr1/2 (3)
Time scale : tr = Lr /Vr (4)
Discharge scale : Qr = Vr × Hr × Lr (5)
Roughness scale : nr = Hr2/3 /L1/2
r (6)
where Vr is velocity scale between prototype and model, Hr is vertical scale, tr is time scale, Lr is
horizontal scale, Qr is discharge scale, nr is roughness scale.
The important model scales are shown in Table 1.
Table 1. Physical model scale.
Parameter Notation Value Parameter Notation Value
Horizontal scale Lr 400 Time scale tr 36.51
Vertical scale Hr 120 Discharge scale Qr 525,600
Velocity scale Vr 10.95 Roughness scale nr 1.22
Considering the similarities of turbulence and heat diffusion, the Reynolds number of the model
exceeds the critical value. The flow is turbulent, and the flow pattern is similar.
Water 2020, 12, 2267 5 of 15
3.2. Model Set-Up
Water 2020, 12, x FOR PEER REVIEW 5 of 15
According to the bathymetric and topographic survey, the bed level and horizontal outline of
According
the model to the bathymetric
were determined. and topographic
Afterwards, the physicalsurvey,
modelthe
wasbed level and
carefully horizontal
shaped with aoutline of
horizontal
the of
scale model
400 were
and adetermined. Afterwards,
vertical scale of 120. the
Thephysical model of
bed surface was carefully
the model shaped with awith
was coated horizontal
cement
mortar, and the concrete structures, such as outlets and wharfs, were made of plexiglass tomortar,
scale of 400 and a vertical scale of 120. The bed surface of the model was coated with cement meet the
and the concrete structures, such as outlets and wharfs, were made of plexiglass to meet the
roughness similarity.
roughness similarity.
Figure 3 is the original photograph of the physical model, and the model panorama can be seen in
Figure 3 is the original photograph of the physical model, and the model panorama can be seen
Figure 3a. The length of the model was 50 m and the width was 20 m. The maximum water depth was
in Figure 3a. The length of the model was 50 m and the width was 20 m. The maximum water3 depth
about 0.62 m. The flow rate of the cooling water was 0.00028 m3 s−1 to simulate the 147.34 m s−1 rate
was about 0.62 m. The flow rate of the cooling water was 0.00028 m3 s−1 to simulate the 147.34 m3 s−1
of Phase I, II and III in the prototype.
rate of Phase I, II and III in the prototype.
Figure
Figure 3. 3. Photographsofofthe
Photographs thephysical
physical model:
model: (a)
(a) the
the panoramic
panoramicphoto
photoofofthe
themodel;
model;(b)(b)
thethe
closed
closed
circulating
circulating heating
heating system;(c)
system; (c)the
thevelocimeter;
velocimeter; (d)
(d) the
the temperature
temperature measuring
measuringprobes.
probes.
TheThe physicalmodel
physical modelwaswasconstructed
constructed toto study both
both the
the tidal
tidal currents
currentsand
andthe
thetemperature
temperature
distribution.The
distribution. Thetidal
tidalcurrent
currentwas
wasgenerated
generated byby the
the tide
tide supply
supplysystem,
system,which
whichwaswascomposed
composed of of
a a
reservoir, pumps and valves. The tidal current was simulated by 64 submerged pumps,
reservoir, pumps and valves. The tidal current was simulated by 64 submerged pumps, which were which were
setset
ononthethe upstream
upstream andand downstream
downstream open
open boundariestotocontrol
boundaries controlinflow
infloworor outflow,
outflow, and
and thethe flow
flow rate
rate was provided by numerical prediction. The closed circulation system for cooling
was provided by numerical prediction. The closed circulation system for cooling water (Figure 3b)water (Figure
3b) consisted of the micropump, electric heater and float flowmeter.
consisted of the micropump, electric heater and float flowmeter.
Automatic tracking level meters with a precision of 0.02 mm were selected to measure the water
Automatic tracking level meters with a precision of 0.02 mm were selected to measure the water
level. The VECTRINO velocimeters (Figure 3c) were used for tidal flow measurement. Figure 4a
level. The VECTRINO velocimeters (Figure 3c) were used for tidal flow measurement. Figure 4a shows
shows the layouts of the T1–T3 water level sites and the A1–A4 velocity sites. T1 and A1–A4, which
the layouts of the T1–T3 water level sites and the A1–A4 velocity sites. T1 and A1–A4, which are the
are the same as the observation sites, can be used for model validation. T2 and T3 were added to get
same as the observation sites, can be used for model validation. T2 and T3 were added to get the
the water level at different positions in the whole simulation range. The LMT multipoint digital
water level at
scanning different positions
temperature recordersinwere
the whole simulation
used for range. Themeasurement.
water temperature LMT multipoint digital scanning
According to the
different influences of thermal discharge, 256 temperature measuring probes (Figure 3d) with a
Water 2020, 12, 2267 6 of 15
temperature recorders were used for water temperature measurement. According to the different
Water Water
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615
influences of thermal discharge, 256 temperature measuring probes (Figure 3d) with a precision of
±0.06 ◦ C were set and most of them were set near the surface, as shown in Figure 4b. Due to the
precision
precision
precision
precision of
ofof precision
±0.06of ±0.06
±0.06
±0.06 °C
°C°C of
°C±0.06
were
were
were were
set and
setset °C
andset
andwere
and
most
most
most set
most
of
ofof and
them of most
them
them them
were
were
were of
setthem
were set
near
setset near
near were
near
thethe
the set
the near
surface,
surface,
surface, asthe
surface,
as surface,
as shown
shown
as shown
shown in asFigure
shown
in
Figure
inin
Figure Figure
4b.
4b. in
Due
4b.
Due Figure
4b.
Due Due 4b. Due
to the
to to the
large
the largelarge
to
large
tidalthetidal
tidaltidal
range range
large
range tidal
range
in in inthe
theinthe
rangestudy
the
study
studyin
study area,
the
area,
area, the
study
area,
the the probes
thearea,
probes were
probes
probes the
were
were installed
probes
were
installed on
were
installed
installed on the
ontheautomatic
installed
on
the the on tracking
the
automatic
automatic
automatic tracking elevatortracking
automatic
tracking
tracking with a
to the large tidal range in the study area, the probes were installed on the automatic tracking
precision
elevator of ±0.1–0.2
withof mm to fit the water depth variation. In addition, five vertical measuring lines,
elevator
elevator
elevator
elevator with
with
with awith a precision
a precision
aprecision
precision ofaofprecision
of ±0.1–0.2
±0.1–0.2
±0.1–0.2
±0.1–0.2 mm
mmof
mm ±0.1–0.2
mm
to
to fit
to to
the
fitfit
the mm
fit the
water
the towater
water
water fit
depththedepth
depth
depth water
variation.depth
variation.
variation.
variation. In variation.
In addition,
addition,
InIn addition,
addition, Infive
five
five addition,
five
vertical
vertical
vertical five vertical
vertical
measuring
measuring
measuring C1–C5,
measuring
lines,
lines,lines,were
C1–C5, C1–C5,
C1–C5, arranged
lines,
were
were C1–C5,
were to
arranged measure
were
arranged
arranged to tothe
arranged
measure water
measure to
the temperature
measure
the
water water
temperature at different
thetemperature
water at atdepths
temperature atnear
different
different depths the
different
depths
near intake/outfall.
depths near
near
measuring lines, C1–C5, were arranged toto measure
measure the
the water
water temperature
temperature atat different
different depths
depths near
near
C1–C4 were the same as the observation sites, and C5 near the intake of Phase III was added to get the
the intake/outfall. C1–C4 were the same as the observation sites, and C5 near the intake of Phase III ofIIIPhase III
the the the
intake/outfall.
the intake/outfall. intake/outfall.
intake/outfall.C1–C4
C1–C4C1–C4
were
were C1–C4
were
the the
same
the were
samesame
as the
the
as as same
the
observation
the as the
observation
observation observation
sites, sites,
sites,and and and
C5 sites,
near
C5 C5
nearand
near
the C5
the
intake
the near
intake
intake of the of
Phase
of intake
PhasePhase
IIIIII
intake temperature.
waswas
was was
added
added
added towas
added
to get
togettoadded
the
get get
the thetointake
intake
the intake
intake get thetemperature.
intake temperature.
temperature.
temperature.
temperature.
FigureFigure
4.
Figure
Figure The
4. 4.
The Figure
4. The
layout
Figure
The layout4.
layout4.of
layout
The
of The
of oflayout
measuring
layout of
measuring
of measuring
measuring
measuring measuring
sites: sites:
(a)
sites:
sites: (a)
water
sites:
(a)(a) sites:
water
water water
level
(a) (a)sites
water
level
level water
level
level
sites
sites ( level
(sites)) and
( sites and sites
)(( andand (velocity
) velocity
and ) sites
velocity
velocity and
velocity (velocity
sites
sites sites ((b)
( (();); );(b)
sites sites
(b)
(b) (b)( ); (b)
); temperature
temperature
temperature temperature
temperature
probes probes
probes
probes ( (
temperature probes ( ). ( ( ). ((
). probes
( ). ( (:: ).
the
:
the ( :
open
the
openthe
open open :
boundary the
boundary
boundary open
boundary
with boundary
with
with with
the
the the
pumps)
the pumps)
pumps).
pumps) with
pumps) the pumps)
3.3. 3.3.
Model
3.3. 3.3.
Model Model
Model Validation
3.3.Validation
Validation
Model Validation Validation
3.3. Model Validation
The The The
observed
observed The
The
observedtidal observed
observed
tidal tidal
current
current tidal
tidal
current
and and current
current
and
waterwater water and
temperature water
watertemperature
andtemperature
temperature temperature
data data data
werewere were data
data
obtained were
were
obtained
obtained from obtained
fromobtained
from
aa field
afield from
from
a survey
fieldfield aathat
field
survey
survey thatsurvey
field surveythat
that that
The observed tidal current and water temperature data were obtained from survey that
was was
wasperformed was
was
performed performed
byperformedby theby the
by
Third Third
the ThirdInstitute
Institute of
Institute Oceanography,
of Oceanography,of Oceanography, Ministry
Ministry of
Ministry
of Natural
Natural of Resources
Natural
Resources from
ResourcesNovember
from from
was performed
performed bybythethe theThird Third
Third Institute
Institute
Institute of
ofofOceanography,
Oceanography,
Oceanography, Ministry
Ministry
Ministry of
ofofNatural
Natural
Natural Resources
Resources
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fromfrom
to December,
November to 2012
December, with the
2012 operation
with the of Phase
operation I and
and
of II.The
Phase The I heated
and II. The water heated discharge
water atthe
the outlet of
November November
November to to to
December, December,
December,
November to December, 2012 with the operation 2012 2012 2012
with
with with
the the the
operation operation
operation
3 −1
of Phase
of of
Phase Phase
I and
I I and
II. The
II.
of Phase I and II. The heated water II. The
heated heated
heated waterwater
3
water
discharge discharge
discharge
discharge
−1
at the the at the
at discharge
the
at at
outlet outlet
outlet
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ofofPhase ofPhase
Phase
Phase outlet
Phase
II and Iof
I and
and
and Phase
IIIIIand
was
II
was
IIwas
IIwaswas
0.00016
0.00016
0.00016
I 0.00016
and IImmwas
0.00016 m−10.00016
3 ss3−1
3m sm−1s
to
to3 to −1totom
ssimulate simulate
simulate
simulate the
thethe the
3 s−1 to simulate
simulate the
discharge discharge
discharge
discharge the
discharge
of of
81.68
ofof of81.68
discharge
81.68
81.68 81.68
mm3m
m
3 ss3−1of
sm
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inin
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−1381.68
the
in
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the m the
the prototype.
3 s−1 in the prototype.
prototype.
prototype.
prototype.
prototype.
ItIt It
was It found
was wasfound It was
Itby
foundwas
by found
byfound
experiment
experiment by experiment
bythat
experiment experiment
that that
the the that
the
floodfloodthat the
flood
tide tideflood
the flood
tide
current
currenttide
current
wascurrent
tide
was current
was
mainly was
mainlymainlymainly
was
divided
divided mainly
divided divided
into into divided
into
two twointo
two two
streamsinto streams
streams
streams after
two streams
was found by experiment that the flood tide current was mainly divided into two streams
afterafterafter
passing
passing passing
after
passing
through
through through
passing
through the the the
Kemen the
through
Kemen Kemen
Kemen the
Channel.
Channel. Channel.
Kemen
Channel. One One One
Channel.
One
stream
stream stream
One
stream
flowed
flowed flowed
stream
flowed
along
along along
flowed
along
the the the
thealong
northwest northwest
northwest
northwest the andand and
northwest
and
thethe the
the
other other
otherand
other reached
the other
after passing through the Kemen Channel. One stream flowed along the northwest and the other
reached reached
reached the the the
the southwest
reached
southwest southwest
southwest the bayhead.bayhead.
southwest
bayhead.
bayhead. During During
bayhead.
During Duringthe thethe
ebbtheebb
During
ebb ebb
tide, tide,
tide,the
tide,
the the
theebb thecurrents
currentstide, the
currents
currents dominated
currents
dominated dominated
dominated by by
dominated
the the
by two
the
two streams
by
two
streams the converged
streams streams
two
reached the southwest bayhead. During the ebb tide, the currents dominated byby the the twotwo streams
streams
in front of the channel and flowed to the open sea. The flood and ebb currents flowed in flowed
opposite
converged converged
converged
converged inconverged
in front
in in front
front
front of
ofof the
the in
the front
ofchannel
the
channel
channel ofand
channelthe
and and channel
and
flowedflowed
flowed flowed
toand
totothe
the flowed
to
the the
openopen
open tosea.
open
sea.
sea. the
sea.
The
TheTheopen
The
flood sea.
flood
flood flood
and
and The
and ebband
ebb flood
ebb ebb
currents and
currents
currents ebb
currents
flowed currents
flowed
flowed flowedinin in
in in
opposite opposite
opposite directions
opposite
directions directions
directions and andand
directions
theand
thethe theproperty
property and
property
property the
of of reciprocating
property
of
reciprocating
of reciprocating of
reciprocating flow flow
reciprocating
flow flow
was was
was was obvious,
flow
obvious, was
obvious,
obvious, whichwhich
obvious,
which which
was waswas was consistent
which
consistent was
consistent
consistent with with
with withprevious
consistent with
opposite directions and the property of reciprocating flow was obvious, which was consistent with
previous studies
previous
studies [31–34].
studies
[31–34]. Due Due tospace
[31–34]. space
to Due
space limitations,
tolimitations,
spacethis this
limitations,
thispaper paper only
this shows
paper
only showsonlythe validation
shows
the the
validation results
validation
results of tide level,
results of
previous
previous
previous studies
studies
studies [31–34].
[31–34].
[31–34]. Due
Due Due to
totospace
space limitations,
limitations,
limitations, this
this paperpaper
paper only
onlyonly shows
shows
shows the
the the validation
validation
validation results
results
results ofof of
of
tide
tidetide tide
level,
level,
level, level, tide
velocity
velocity
velocity level,
velocity
and
andand velocity
and
direction
direction
direction and
direction
at
atat direction
at station
station
station
station T1/A2 at T1/A2
T1/A2
T1/A2 station
near
nearnear theT1/A2
near
thethe the
power near
power
power power theplant
plant
plant
plant power
during
during
during plant
during
the
the the during
the
spring spring
spring
spring and
andtheneap
and spring
and
neapneap neap and neap
tides, tides,
tides,
tides, as
asasshownas
shown
shown tides,
shown
in
inin as in
Figure shown
Figure
Figure Figure
5.
5.5.Thein
The Figure
5.
The The
model
model
model 5.
model The
simulation model
simulation
simulation
simulation is simulation
in
is is
inin is
good in
good
good good is
agreementin
agreement
agreement good
agreement withagreement
with
with with
the
the the the
fieldfield
field with
field the
measurement. field
measurement.
measurement.
measurement. measurement.
ItIt was
It
was Itconcluded
was was
concluded
concluded It was
concluded that concluded
that
that that
the
the the the
model
model
model that
model
can
can the
can be
becanmodel
beused
used be for
used can
used
for be
for
further
for used
further
further
further for studies
studies
studies
studies further
on
ononheatstudies
on
heat
heat heat
transport on
transport
transport heat
transport and
and andtransport
and
diffusion.
diffusion.
diffusion. and diffusion.
diffusion.
Water 2020, 12, 2267 7 of 15
velocity and direction at station T1/A2 near the power plant during the spring and neap tides, as shown
in Figure 5. The model simulation is in good agreement with the field measurement. It was concluded
that the model can be used for further studies on heat transport and diffusion.
Water 2020, 12, x FOR PEER REVIEW 7 of 15
Figure 5. Comparison of water level (a,d), velocity (b,e) and direction (c,f) simulated by the physical
Figure 5. Comparison of water level (a,d), velocity (b,e) and direction (c,f) simulated by the physical
model with field measurements during the spring tide and neap tide.
model with field measurements during the spring tide and neap tide.
TheThetemperature
temperatureanalysis
analysis showed
showed that that during
during the the observation
observationperiod period(in(inwinter),
winter),thethe
water
water
temperature in the bay was lower than the external temperature, and the surface water temperature
temperature in the bay was lower than the external temperature, and the surface water temperature was
was lower than that of the bottom. The water temperature was greatly affected by the tide. The
lower than that of the bottom. The water temperature was greatly affected by the tide. The temperature
temperature variation with time, presented as two peaks and two lows in a tidal day, was
variation with time, presented as two peaks and two lows in a tidal day, was synchronous with flux
synchronous with flux and reflux. The water temperature was higher at a high tide level and lower
and reflux. The water temperature was higher at a high tide level and lower at a low tide level.
at a low tide level.
Because some units did not operate in some observation periods of the spring tide and middle tide,
Because some units did not operate in some observation periods of the spring tide and middle
thetide,
average output of
the average the power
output of theplant
power only
plantaccounted for 42% offor
only accounted the42%
installed
of thecapacity.
installed The temperature
capacity. The
rise area caused by thermal discharge was relatively small. It was
temperature rise area caused by thermal discharge was relatively small. It was approximatelyapproximately considered that
thermal
considered that thermal discharge had little impact on the temperature rise at the far sites of C1 andthe
discharge had little impact on the temperature rise at the far sites of C1 and C4, and
natural
C4, and climate was the
the natural mainwas
climate reason for temperature
the main change at C1
reason for temperature and C4
change forand
at C1 the C4
period. The
for the natural
period.
temperature
The naturalvariation
temperature of C2 near theofintake
variation C2 near was theobtained
intake was by data interpolation
obtained of C1 and C4.
by data interpolation Then,
of C1
theand
measured
C4. Then, the measured values of temperature rise at the intake were acquired using the naturaland
values of temperature rise at the intake were acquired using the natural temperature
observed data of
temperature C2observed
and at adverse theofneap
data C2 attide (output
adverse theofneap
1464tide
MW). Tableof
(output 2 shows the comparison
1464 MW). Table 2 showsof the
the comparison
intake temperature of rise
the intake
of Phasetemperature rise of Phase
I and II between I and II between
the experimental the experimental
simulation simulation
and field measurement.
Theand field measurement.
depth-averaged values Theof depth-averaged
the model were values in good ofagreement
the model were in good
with field agreement with
measurements. fieldwas
There
measurements. There was a deviation in the surface temperature rise, but the
a deviation in the surface temperature rise, but the relative error was less than 20%. Due to the complexrelative error was less
than 20%.
influence Due to climate
of natural the complexchange influence
and actual of natural climate change
plant operation and actual
conditions, plant
etc., the operation
deviation was
conditions, etc., the deviation was within a reasonable range. The model
within a reasonable range. The model is thus available for predicting thermal discharge characteristics. is thus available for
predicting thermal discharge characteristics.
Table 2. Comparison of intake temperature rise of Phase I and II between experimental simulation and
Table
field 2. Comparison of intake temperature rise of Phase I and II between experimental simulation
measurement.
and field measurement.
Surface Depth Average (above 6 m)
Temperature Rise Surface Depth Average (above 6m)
Temperature Rise Maximum
Maximum Minimum
Minimum Mean
Mean Maximum
Maximum Minimum
Minimum Mean Mean
Simulation ◦ C)
Simulation( (°C) 2.10 2.10 0.17 0.17 0.730.73 1.12
1.12 0.170.17 0.48
0.48
Measurement ◦ C)
Measurement( (°C) 1.77 1.77 0.00 0.00 0.860.86 1.05
1.05 0.000.00 0.48
0.48
Relative error (%) 18.6 / 15.1 6.7 / 0
Relative error (%) 18.6 / 15.1 6.7 / 0
4. Model Scenarios
4.1. Layout Principle of Heat-Retaining and Diversion Facilities
In addition to the direct removal by environmental water and heat exchange with air, part of
the waste heat returns to the intake, resulting in an increase in intake water temperature and a
decrease in plant efficiency. Therefore, in the engineering design stage, building a heat-retaining
Water 2020, 12, 2267 8 of 15
4. Model Scenarios
4.1. Layout Principle of Heat-Retaining and Diversion Facilities
In addition to the direct removal by environmental water and heat exchange with air, part of the
waste heat returns to the intake, resulting in an increase in intake water temperature and a decrease in
plant efficiency. Therefore, in the engineering design stage, building a heat-retaining wall near the
intake to reduce the heated water recycling is often considered. The diversion dike is usually arranged
near the outlet to control the flow direction. It can be made into a curved type and a linear type, and the
crest elevation is generally not lower than the design water level. In the study of thermal discharge,
the diversion dike can not only be used to guide the flow and affect the heated water zone, but also can
function as a heat-retaining wall.
4.2. Scenario Description
The construction of heat-retaining and diversion facilities can promote heat diffusion downstream
and reduce the direct heat return, but it may also cause heat accumulation in the near-field. In this paper,
combined with the Huadian Kemen Power Plant, a physical model was conducted to study the
influences of heat-retaining wall and diversion dike when Phase I, II and III were all in operation.
As shown in Figure 2, the heat-retaining wall was set on the side of the Phase III intake open channel
close to the outlet, and the diversion dike was arranged near the outlet. Because the measured
maximum water level was 3.04 m, the constructions could fully operate when the crest elevation was
3 m. However, the engineering cost should also be considered in practice. In order to explore the
effect of the constructions and their heights on the thermal discharge characteristics, 6 scenarios were
designed, and 12 tests, including the spring tide and neap tide, were carried out, as listed in Table 3.
Table 3. Scenario description.
Scenario Tidal Type Height (m) Layout Instruction Others
Spring tide Without heat-retaining
1 3
Neap tide and diversion facilities
Spring tide
2 3 With diversion dike
Neap tide
Spring tide Phase I, II and III; cooling
3 3 With heat-retaining wall
Neap tide water of 147.34 m3 s−1 ;
Spring tide With diversion dike and temperature rise at outlet
4 3 of 8.5 ◦ C
Neap tide heat-retaining wall
Spring tide With diversion dike and
4-1 2 heat-retaining wall
Neap tide
Spring tide With diversion dike and
4-2 1 heat-retaining wall
Neap tide
5. Results and Discussion
5.1. Thermal Properties without the Constructions
Before the construction of heat-retaining and diversion facilities (Scenario 1), the heated water
could easily transport and diffuse upstream and downstream under the influence of reciprocating
current and residual flow. Figure 6 shows the distribution of the maximum and average temperature
rises at the surface during the spring and neap tides. Due to the high-velocity flow of the baymouth
and north deep-water area, the heated water was mainly accumulated in the south shore with a zonal
distribution. Compared with the neap tide, the tidal dynamic of the spring tide was stronger, which led
to greater heat transport with the tide. The heat accumulation was obvious in the bay during the
neap tide. The area of temperature rise was affected by the above two conditions. Under the present
installed capacity, the temperature rise area of 0.5 ◦ C in the spring tide was larger than that in the
Water 2020, 12, 2267 9 of 15
neap tide, but the heat still did not reach the north bank of the baymouth. The area of 1 ◦ C had little
difference and the 4 ◦ C area in the neap tide was larger than that in the spring tide (Figure 7).
The excess temperature at the intake varied periodically with the tide, and the variation trends
Water 2020, 12, x FOR PEER REVIEW 9 of 15
of the spring and neap tides were similar. The maximum occurred at the early stage of the flood
tide. At this time, the high temperature rise zone flowed towards the intake with the flood current.
About two hours after the low tide level, the intake temperature rise of Phase I and II reached the
About two hours after the low tide level, the intake temperature rise of Phase I and II reached the highest
highest point, about 1.34–1.53 °C in the spring and neap tides, and the mean was 0.75–0.90 °C.
point, about 1.34–1.53 ◦ C in the spring and neap tides, and the mean was 0.75–0.90 ◦ C. Because of the
Because of the distance of the intake of Phase III from the outfalls, the maximum lagged by a half
distance of the intake of Phase III from the outfalls, the maximum lagged by a half hour. The intake
hour. The intake temperature rises of the spring tide and neap tide were the same, and the
temperature rises of the spring tide and neap tide were the same, and the maximum was 2.15 ◦ C with
maximum was 2.15 °C with a mean of 0.98 °C (Table 4).
a mean of 0.98 ◦ C (Table 4).
In general, for the semienclosed bay, heat accumulation was more obvious with an increase of
In general, for the semienclosed bay, heat accumulation was more obvious with an increase of
thermal discharge, and neap tide was the adverse tide.
thermal discharge, and neap tide was the adverse tide.
According to the measured data, the highest natural water temperature in summer was 31.2 °C,
According to the measured data, the highest natural water temperature in summer was 31.2 ◦ C,
so the highest intake temperature of Phase I and II was 32.7 ◦°C, and the maximum of Phase III was
so the highest intake temperature of Phase I and II was 32.7 C, and the maximum of Phase III was
33.4 °C which did not meet the cooling water intake requirement of the steam turbine unit (≤33 °C)
33.4 ◦ C which did not meet the cooling water intake requirement of the steam turbine unit (≤33 ◦ C) [35].
[35]. In order to ensure normal unit operation, the intake temperature rise should not exceed 1.8 °C
In order to ensure normal unit operation, the intake temperature rise should not exceed 1.8 ◦ C. Therefore,
Therefore, it is necessary to build heat-retaining and diversion facilities to reduce the intake
it is necessary to build heat-retaining and diversion facilities to reduce the intake temperature.
temperature.
Figure 6.
Figure 6. Distributions
Distributions ofof maximum
maximum and
and mean temperature rise
mean temperature rise at
at surface:
surface: (a)
(a) maximum
maximum distribution
distribution
during the spring tide; (b) mean distribution during the spring tide; (c) maximum distribution
during the spring tide; (b) mean distribution during the spring tide; (c) maximum distribution during
during the neap tide; (d) mean distribution during the
the neap tide; (d) mean distribution during the neap tide.neap tide.
5.2. Effect of Heat-Retaining and Diversion Facilities on Temperature
TemperatureRise
RiseDistribution
Distribution
The influences
influencesofofheat-retaining
heat-retainingand anddiversion
diversion facilities were
facilities studied
were studied by comparing
by comparing Scenarios 1–4.
Scenarios
Figure 7 shows the scenario comparison of maximum and average temperature
1–4. Figure 7 shows the scenario comparison of maximum and average temperature rise areas at the rise areas at the surface
during
surface the springthe
during and neap tides.
spring In order
and neap to explore
tides. In order thetoinfluence
explore on thetheinfluence
vertical temperature rise
on the vertical
near the power
temperature plant,
rise neartemperature rise variations
the power plant, of different
temperature depths atof
rise variations C2different
are presented
depths in at
Figure 8.
C2 are
The relative
presented in Figure 8.position between the facilities and outlets was the key factor affecting the high
temperature rise area.
The relative The diversion
position between dike near the outlet
the facilities (Scenario
and outlets was2) blocks
the keythe heat diffusion
factor affecting upstream
the high
and leads to the heat distribution close to the shoreline. The high temperature
temperature rise area. The diversion dike near the outlet (Scenario 2) blocks the heat diffusion water is concentrated in
the shallowand
upstream waters
leadsbehind
to thethe wharfs,
heat and the area
distribution closehas
to an
theobvious increase.
shoreline. The highCompared with Scenario
temperature 1,
water is
the maximumin
concentrated area 4 ◦ C in the
theof shallow spring
waters and neap
behind the tides
wharfs,increased
and the by area
0.4–0.6 haskman 2 with an increase of
obvious increase.
59%, and the
Compared average
with Scenario 4 ◦maximum
area1,ofthe C increasedarea by 0.2–0.3
of 4 °C km
2 , about three times larger. Because the
in the spring and neap tides increased by
heat-retaining
0.4–0.6 km2 with wallan(Scenario
increase3)ofwas a little
59%, and fartheaway fromarea
average the outlet,
of 4 °Cthe effect onby
increased the0.2–0.3
high temperature
km2, about
rise ◦ 2
threearea waslarger.
times small.Because
The maximum area of 4 C
the heat-retaining had(Scenario
wall a slight increase
3) was aof 0.1–0.2
little km with
far away fromthethechange
outlet,
range not exceeding 20% of Scenario 1, and the average area variation was
the effect on the high temperature rise area was small. The maximum area of 4 °C had a slight inconspicuous.
increase of 0.1–0.2 km2 with the change range not exceeding 20% of Scenario 1, and the average area
variation was inconspicuous.
For the area of low temperature rise, there was a general decreasing trend when the
heat-retaining and diversion facilities were constructed. The diversion dike accelerated the heat
transport to the baymouth where the heat exchange was stronger, so the low temperature rise area
Water 2020, 12, 2267 10 of 15
For the area of low temperature rise, there was a general decreasing trend when the heat-retaining
and diversion facilities were constructed. The diversion dike accelerated the heat transport to the
baymouth where the heat exchange was stronger, so the low temperature rise area was reduced,
especially in the spring tide. Compared with Scenario 1, the maximum area of 1 ◦ C had a 44% reduction,
Water 2020, 12, x FOR PEER REVIEW 10 of 15
about 6.9 km2 . The average area of 1 ◦ C during the spring and neap tides had a 30% reduction,
about 0.7–1.5 km2 . However, because the heat retention between the intake and outlet was caused
a 30% reduction, about 0.7–1.5 km2. However, because the heat retention between the intake and
by the heat-retaining wall, the area of low temperature rise in Scenario 3 had an increase during the
outlet was caused by the heat-retaining wall, the area of low temperature rise in Scenario 3 had an
unfavorable neap tide. The increase was relatively small and the change of maximum and mean
increase during the unfavorable neap tide. The increase was relatively small and the change of
temperature rise areas of 1 ◦ C was about 16%–23% of Scenario 1.
maximum and mean temperature rise areas of 1 °C was about 16%–23% of Scenario 1.
When the diversion dike and the heat-retaining wall were constructed (Scenario 4), the two effects
When the diversion dike and the heat-retaining wall were constructed (Scenario 4), the two
were superimposed. Compared with Scenario 1, the low temperature rise area was reduced but the
effects were superimposed. Compared with Scenario 1, the low temperature rise area was reduced
high temperature rise area had an increase. The maximum area of 1 ◦ C during the spring and neap
but the high temperature rise area had an2 increase. The maximum area of 1 °C during the spring
tides had a 39% decrease, about 3.6–8.5 km . The mean area of 1 ◦ C was reduced by 0.5–1.3 km2 with
and neap tides had a 39% decrease, about 3.6–8.5 km 2. The mean area of 1 °C was reduced by
the reduction of 24%. The maximum area of 4 ◦ C increased by about 0.5 km2 with an increase of 53%,
0.5–1.3 km2 with the reduction of 24%. The◦ maximum area of 4 °C increased by about 0.5 km2 with
and the average temperature rise area of 4 C increased by 0.2 km2 .
an increase of 53%, and the average temperature rise area of 4 °C increased by 0.2 km2.
In the vicinity of the power plant (C2), the water depth changes greatly along the transverse
In the vicinity of the power plant (C2), the water depth changes greatly along the transverse
direction. This belongs to the heat transition zone with great buoyancy effects. As shown in Figure 8,
direction. This belongs to the heat transition zone with great buoyancy effects. As shown in Figure 8,
the thermal stratification was very obvious in Scenario 1. After building the heat-retaining and diversion
the thermal stratification was very obvious in Scenario 1. After building the heat-retaining and
facilities, vertical mixing was stronger and the thermal stratification was weakened. In addition,
diversion facilities, vertical mixing was stronger and the thermal stratification was weakened. In
the temperature rise changes greatly with time in a tidal day. Because C2 is located on the west side of
addition, the temperature rise changes greatly with time in a tidal day. Because C2 is located on the
the outlets, the heated water discharged flows to C2 under the influence of the flood current, leading to
west side of the outlets, the heated water discharged flows to C2 under the influence of the flood
the significant fluctuation of water temperature at C2 during the flood tide.
current, leading to the significant fluctuation of water temperature at C2 during the flood tide.
Figure
Figure 7.
7. Scenario
Scenario comparison
comparison of
of the
the maximum
maximum (a)
(a) and
and mean
mean (b)
(b) temperature
temperature rise
rise areas
areas at
at surface.
surface.Water 2020, 12, 2267 11 of 15
Figure 7. Scenario comparison of the maximum (a) and mean (b) temperature rise areas at surface.
Figure 8. Time series of temperature rise of different depth at C2.
5.3. Effect of Heat-Retaining and Diversion Facilities on Excess Temperature at Intake
Table 4 shows the scenario comparison of the intake temperature rise. Except for Scenario 1,
the results all met the limit of 1.8 ◦ C. Figure 9 shows the scenario comparison of temperature rise
variations at the intake in the adverse neap tide.
Table 4 and Figure 9 show that the diversion dike built near the outfall (Scenario 2) effectively
reduced heat return to the intake of Phase I and II by discharging heated water downstream. Compared
with no diversion dike, the maximum decreased by about 0.3 ◦ C, and the average value was reduced
by about 0.1 ◦ C. Because the diversion dike is far away from the intake open channel, it has little
impact on the intake temperature rise of Phase III during the neap tide. Figure 9 indicates that except
for the difference of maximum, the intake temperature rise variations of Phase III were mostly the
same before and after the construction of the diversion dike.
When the heat-retaining wall was constructed on the side of the intake open channel (Scenario 3),
the heated water was blocked outside the wall during the flood tide, which directly prevented the heat
return to the intake channel. Compared with Scenario 1, the intake temperature rise of Phase III had an
obvious decline, and the maximum decreased by 1 ◦ C with an average reduction of 0.2 ◦ C. As shown in
Figure 9, the peak decreased distinctly after the construction of the heat-retaining wall and the variation
tended to be gentle. The temperature rise fluctuation was small, and the difference between maximum
and minimum was less than 0.5 ◦ C. The rule of temperature rise varying with tide was unapparent.
For the intake temperature rise of Phase I and II, due to the barrier of the wall, the retention time of
heated water between the intake and outlet was prolonged, and the heat accumulation during the
spring tide was enhanced slightly. The time increase in high temperature at intake led to the average
temperature rise of 0.1 ◦ C.
The diversion dike near the outlet mainly reduced the intake temperature rise of Phase I and II,
while the heat-retaining wall near the open channel had the main influence on Phase III. When the
heat-retaining wall and diversion dike were built (Scenario 4), the two effects were superimposed and
the combined effect was the best. Compared with Scenario 1, the intake temperature rises of Phase I,
II, and III were improved and the influence on Phase III was more prominent. The blocking effect
of the heat-retaining wall and the leading of the diversion dike effectively decreased the direct heat
return to the intake of Phase III. The peak of the intake temperature rise was clearly decreased and the
temperature rise varied slowly with the tide. The maximum of Phase III was reduced by 1.0–1.3 ◦ C
and the mean reduction was 0.2 ◦ C. For the intake temperature rise of Phase I and II, the temperature
rise variation with the tide was basically the same as Scenario 1. The two effects of the heat-retaining
wall and the diversion dike were partially offset, resulting in the maximum being reduced by about
0.3 ◦ C and an average effect that was not obvious.Water 2020, 12, 2267 12 of 15
Table 4. Scenario comparison of intake water temperature rise.
Phase I, II (◦ C) Phase III (◦ C)
Scenario Tide Type
Maximum Minimum Mean Maximum Minimum Mean
Spring tide 1.34 0.41 0.75 2.15 0.61 0.97
1
Neap tide 1.53 0.44 0.90 2.10 0.59 0.98
Spring tide 1.01 0.35 0.66 1.79 0.45 0.85
2
Neap tide 1.19 0.30 0.75 1.80 0.56 0.95
Spring tide 1.31 0.27 0.84 1.10 0.63 0.82
3
Neap tide 1.27 0.36 0.92 1.19 0.73 0.91
Spring tide 1.07 0.33 0.74 0.89 0.55 0.72
4
Neap tide 1.22 0.36 0.89 1.03 0.60 0.81
Water 2020, 12, x FOR PEER REVIEW 12 of 15
Figure 9.9. Scenario
Scenariocomparison
comparisonofof temperature
temperature riserise variation
variation at intake
at the the intake during
during the tide:
the neap neap(a)
tide: (a)
intake
intake temperature
temperature rise ofI,Phase
rise of Phase II; (b)I,intake
II; (b) temperature
intake temperature rise ofIII.
rise of Phase Phase III.
5.4. Effect of
5.4. Effect of Construction
Construction Height
Height on
on Excess
Excess Temperature
Temperatureat
atIntake
Intake
In
In addition
addition toto ensuring
ensuring thatthat the
the constructions
constructions were were fully
fully effective,
effective, thethe engineering
engineering investment
investment
also
also should be taken into account in actual engineering. Considering the crest elevations of 33 m,
should be taken into account in actual engineering. Considering the crest elevations of m, 22 m
m
and
and 1 m, the impact on the intake temperature rise was examined. Through contrastive analysis of
1 m, the impact on the intake temperature rise was examined. Through contrastive analysis of
Scenarios
Scenarios 4,4, 4-1
4-1 and
and 4-2,
4-2, the
the effect
effect of
of the
the construction
constructionheight
heightwaswasstudied.
studied.
With the reduction of the crest elevation, overtopping
With the reduction of the crest elevation, overtopping occurs during occurs during thethe
highhigh
tide.tide.
Then,Then,
the
the heat-retaining effect is reduced, and the thermal stratification is weaker
heat-retaining effect is reduced, and the thermal stratification is weaker with stronger vertical with stronger vertical
mixing.
mixing. Figure
Figure10 10shows
showsexcess
excess temperature
temperature variations
variationsat the intake
at the during
intake the spring
during and neap
the spring and tides.
neap
When
tides. the crest elevation had reduced to 2 m (two-thirds of the high tide level), the overtopping
time When
was aboutthe 4–6 h during
crest elevation the spring
had reducedand neap to tides.
2 m Due to the short
(two-thirds duration,
of the high thetideunfavorable
level), the
impact was relatively small. For Phase I and II, the intake temperature
overtopping time was about 4–6 h during the spring and neap tides. Due to the short duration, rise variation of 2 m crest
the
elevation was generally consistent with that of 3 m. The difference of Phase III between
unfavorable impact was relatively small. For Phase I and II, the intake temperature rise variation 2 m and 3 m crest
of
elevations had a slight
2 m crest elevation increase
was and consistent
generally it was morewith obvious
thatduring
of 3 m.the
The rising tide. The
difference of maximum increased2
Phase III between
by 0.1–0.3 ◦ with a mean increase of 0.1 ◦ C. The small difference indicates that the constructions with
m and 3 mC crest elevations had a slight increase and it was more obvious during the rising tide. The
2maximum
m crest elevations
increasedstill effectively
by 0.1–0.3 reduce
°C with heat return.
a mean increase of 0.1 °C. The small difference indicates that
the constructions with 2 m crest elevations still effectively reduce heat return.
When the crest elevation had reduced to 1 m (one-third of the high tide level), the effects of
heat-retaining and diversion facilities were greatly reduced. The overtopping time was about 10 h,
accounting for about two-fifths of a tidal day. Compared with the 3 m crest elevation, the period of
high temperature rise at the intake increased significantly and the vertical mixing was stronger,
resulting in the apparent increase of intake temperature rise. The average intake temperature rise of
Phase I and II increased by 0.15 °C, and the mean of Phase III increased by 0.3 °C. The minimum
and maximum also increased greatly. The results show that the crest elevation of 1 m could notYou can also read
