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Topic 7 - Cooling Water System Design
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7/18/2019 Topic 7 - Cooling Water System Design
http://slidepdf.com/reader/full/topic-7-cooling-water-system-design 1/23
CBB 4323 : Plant Utility Systems
Semester May 2014
Utility Systems Design
7/18/2019 Topic 7 - Cooling Water System Design
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Utility systems is an important lifeline to the process plant.
Design of utility systems requires a holistic view of the total process.
Lecture 6 Utility Systems Design
Systematic Design Procedures
Heat Exchanger
Networ
!ass Exchanger
Networ
Heat "ntegration !ass "ntegration
7/18/2019 Topic 7 - Cooling Water System Design
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!ass Exchanger Networ
Lecture 6 Utility Systems Design
Definition# $ networ comprising mass transfer %ased operations to
selectively remove mass &and energy' from a stream.
Evaporative (ooling )ater Distri%ution Networ
()S*
cool()+*
warm
Dry
$ir
Humid
$ir
U,- U,/resh
)ater Discharge
7/18/2019 Topic 7 - Cooling Water System Design
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0he Driving /orce Plot
Lecture 6 Utility Systems Design
7/18/2019 Topic 7 - Cooling Water System Design
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)ater +ecovery 0arget
Lecture 6 )ater Networ
E-
()S
E
()+ ()S
()+
E-
E
"mpact of water recovery on cooling water networ#
(ooling tower efficiency
∆0 heat exchangers
∆P heat exchangers
1 (onventional water distri%ution 1 )ater distri%ution usingwater recovery concept
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Lecture 6 )ater Networ
1 Strategies to conserve water
)ater +ecovery 0arget
+educe +euse +ecycle
2+
/resh
)ater
Discharge
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0argeting minimum cooling water flowrate
Lecture 6 )ater Networ
1 (onsider four water using operations
HeatExchangers
0()*in
&o('
0()*out
&o('
(P&)34'
5&)'
- 6 76 6 766
26 76 -66 -666
2 26 89 76 -:66
7 99 89 -6 66
89
0 &o
('
99
76
6
5 &)'
6
766 -766 266 2766
26
0hese are maximum temperatures that can
%e operated %y the heat exchangers
7/18/2019 Topic 7 - Cooling Water System Design
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0argeting minimum cooling water flowrate
Lecture 6 )ater Networ
1 "f all unit operations use fresh cooling water &i.e. in parallel arrangement'#
5 ; (P x ∆0
(P0otal ; Σmi(pi
; 6 < -66 < 76 < -6
; -86 )3o
(m0 ; -86 ; 76.8 g3s ; -7=.7 t3h
7.-:
()+ temperature*
m0hcwr ;
Σmihi0()+ ; &6>76'<&-66>76'<&76>89'<&-6>89' ; 96.2o(
&7.-:>76.8'
HE -
()SHE
()+
HE 2
HE 7
7/18/2019 Topic 7 - Cooling Water System Design
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0argeting minimum cooling water flowrate
Lecture 6 )ater Networ
?imiting (ooling )ater
(omposite (urve
89
0 &o
('
99
76
6
5 &)'
6
766 -766 266 2766
26
?imiting (ooling )ater
Profiles
89
0 &o
('
99
76
6
5 &)'
6
766 -766 266 2766
26 a c t u
a l f l o w r a t
e m i n i m
u m f l o
w r a t e
7/18/2019 Topic 7 - Cooling Water System Design
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0argeting minimum cooling water flowrate
Lecture 6 )ater Networ
1 ?imiting cooling water composite curve is used to target minimum cooling water
flowrate for the given heat exchangers.
"n the composite curve*
Pinch point# 0 ; 76o(
5 ; -766 < 76&76@26' ; -:66 )
(Pmin ; -:66 ; A6 )34&76@6'
()+ temperature0()+ ; 0()S < 5
"f 0()S ; 6o(*
m()*min ; A6 ; -.9 g3s ; 88.9 t3h
7.-:
(P
0()+ ; 2766 ; 98.:o(
A6
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Example#
Data for three heat exchanger units are shown %elow#
Draw the limiting cooling water composite curve. 0hen calculatethe total fresh cooling water requirement if no water reuse
strategy is implemented.
Lecture 6 )ater Networ
Heat Exchangers0()*in
&o('
0()*out
&o('
(P&)34'
5&)'
E@- 26 96 -6 66
E@ 76 =6 -9 266
E@2 26 =6 9 -96
7/18/2019 Topic 7 - Cooling Water System Design
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Example &contd'#
0() &o('
96
-6
5 &)'6
66 966 =96
76
Lecture 6 )ater Networ
6
26
=6
0() &o('
96
-6
6
=96
76
6
26
=6
?imiting
(ooling )ater
Profiles
?imiting(ooling )ater
(omposite (urve
66 966
7/18/2019 Topic 7 - Cooling Water System Design
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1 Parallel heat exchanger design with no water re@use
"n the composite curve*
(P0otal ; Σ (Pi ; 26 )3o(
0()+ ; ?m() ; B
0()S ; 26o(
E@-
E@
E@2
Lecture 4 )ater Networ
m() ; 2637.-: ; 8. g3s ; 9.: t3h
0()+ ; &-6>96'<&-9>=6'<&9>=6' ; 9=.9o(
&7.-:>8.'
Example &contd'#
7/18/2019 Topic 7 - Cooling Water System Design
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1 !inimum fresh cooling water supply m()
; B
"n the composite curve*
(P ; =96 ) ; -.8 )3o(
26 o(
Lecture 4 )ater Networ
5 &)'
0() &o('
96
-6
6
=96
76
6
26
=6
?imiting
(ooling )ater
(omposite (urve
66 966
0()+ ; 26 < =96 ; =6o(
-.8
m()+ ; -.837.-: ; -:.8 t3h
Example &contd'#
7/18/2019 Topic 7 - Cooling Water System Design
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0argeting minimum water flowrate
Lecture 4 )ater Networ
0() &o('
5 &)'6
1 )hat is the minimum fresh cooling water flowrate for these
operationsB
Note# Slope of fresh cooling water supply
line correlates to the flowrate of the
fresh water supplyC
Higher /lowrate
?ower /lowrate
(aution
(rossing the composite
curve yields infeasi%le
design.
7/18/2019 Topic 7 - Cooling Water System Design
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0argeting minimum water flowrate
Lecture 4 )ater Networ
6
1 )hat is the minimum fresh water flowrate for these operationsB
!inimum fresh cooling water consumption is
limited %y the pinch point.
)ater Pinch
Note# /inal temperature
due to water reuse.
0() &o('
5 &)'
7/18/2019 Topic 7 - Cooling Water System Design
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Design of cooling water networ for minimum freshwater water flowrate
Lecture 6 )ater Networ Design
1 0he significance of pinch location
)ater Pinchelow
Pinch
$%ove
Pinch
?imiting (ooling )ater (omposite (urve
for a 7@heat exchanger pro%lem
89
0 &o('
99
76
6
5 &)'
6
766 -766 266 2766
26
m i n i m
u m f l o
w r a t e
7/18/2019 Topic 7 - Cooling Water System Design
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Design of cooling water networ for minimum freshwater water flowrate
Lecture 6 )ater Networ Design
1 0he significance of pinch location
89
0 &o('
99
76
6
5 &)'
6
766 -766 266 2766
26
m i n i m
u m f l o
w r a t e
7/18/2019 Topic 7 - Cooling Water System Design
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1 )ater grid diagram F a typical parallel design option
Lecture 6 )ater Networ Design
/resh
(ooling
)ater
Supply
from
(ooling
0ower
&()S'
0 ; 76o(
HE -
HE 7
HE 2
(ooling
)ater+eturn to
(ooling
0ower
&()S'
(P ;
-86 )34
(P ; 6
HE
(P ; 96
(P ; A6
(P ; -6
Design of cooling water networ for minimum freshwater water flowrate
0 ; 76o(0 ; 6o(
0 ; 76o(0 ; 6o(
0 ; 76o(0 ; 6o(
0 ; 76o(0 ; 6o(
0 ; 6o(
0otal ()S flowrate ; -7=.7 t3h
7/18/2019 Topic 7 - Cooling Water System Design
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1 )ater grid diagram F design at maximum inlet and outlet temperatures
Lecture 6 )ater Networ Design
/resh
(ooling
)ater
Supply
from
(ooling
0ower
&()S'
0 ; 96.2o(
HE -
HE 7
HE 2
(ooling
)ater+eturn to
(ooling
0ower
&()S'
(P ;
-86 )34
(P ; 6
HE
(P ; -66
(P ; 76
(P ; -6
Design of cooling water networ for minimum freshwater water flowrate
0 ; 76o(0 ; 6o(
0 ; 76o(0 ; 26o(
0 ; 89o(0 ; 26o(
0 ; 89o(0 ; 99o(
0otal ()S flowrate ; -7=.7 t3h
7/18/2019 Topic 7 - Cooling Water System Design
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Lecture 4 )ater Networ Design
1 Design %elow pinch
y interpolation
-766 < &76@26'x&76'
; -:66 )
766 )
-666 )
(P ; 6
(P ; 96()S
Pinch0 ; 6o( 0 ; 76o(
HE -
HE
Design of cooling water networ for minimum freshwater water flowrate
89
0 &o('
99
76
6
5 &)'
6
766 -766 266 2766
26
m i n i m
u m f l o
w r a t e
(P ; A6 )34
∆0 ; 6o(
(P ; A6
766 )
(P ; 6HE 2
Note# 766 ) reaches
76o(. Need another
-766 ) to reach
89o(.
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Lecture 4 )ater Networ Design
1 Design a%ove pinch
-766 )
(P ; 77.2
(P ; 76()+
Pinch
0 ; 76o( 0 ; 89o(
HE 2
Design of cooling water networ for minimum freshwater water flowrate
89
0 &o('
99
76
6
5 &)'
6
766 -766 266 2766
26
m i n i m
u m f l o
w r a t e
(P ; A6 )34
∆0 ; 29o(
(P ; A6
66 )
(P ; 9.8 HE 7
-:66
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Design of water networ for minimum freshwater water flowrate
Lecture 4 )ater Networ Design
1 /inal )ater networ design
/resh
(ooling
)ater
Supply
from
(ooling
0ower
&()S'
Pinch0 ; 6o( 0 ; 98.:o(0pinch ; 76o(
HE -
HE 7
HE 2
(ooling
)ater+eturn to
(ooling
0ower
&()S'
(P ;
A6 )34
(P ; 6
HE
(P ; 96
(P ; 6
(P ; 9.8
(P ; 77.2
(P ; 6
0otal ()S flowrate ; 88.9 t3h
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