Topic 7 - Cooling Water System Design

7/18/2019 Topic 7 - Cooling Water System Design

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CBB 4323 : Plant Utility Systems

Semester May 2014

Utility Systems Design



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



!ass Exchanger Networ


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



0he Driving /orce Plot




)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




1 Strategies to conserve water

)ater +ecovery 0arget

+educe +euse +ecycle

2+

/resh

)ater

Discharge



0argeting minimum cooling water flowrate


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





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





?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





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



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.


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



Example &contd'#

0() &o('

96

-6

5 &)'6

66 966 =96

76


6

26

=6

0() &o('

96

-6

6

=96

76

6

26

=6

?imiting

(ooling )ater

Profiles

?imiting(ooling )ater

(omposite (urve

66 966



1 Parallel heat exchanger design with no water re@use


(P0otal ; Σ (Pi ; 26 )3o(

0()+ ; ?m() ; B

0()S ; 26o(

E@-

E@

E@2


m() ; 2637.-: ; 8. g3s ; 9.: t3h

0()+ ; &-6>96'<&-9>=6'<&9>=6' ; 9=.9o(

&7.-:>8.'

Example &contd'#



1 !inimum fresh cooling water supply m()

; B


(P ; =96 ) ; -.8 )3o(

26 o(


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'#



0argeting minimum water flowrate


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.



0argeting minimum water flowrate


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 &)'



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





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



1 )ater grid diagram F a typical parallel design option


/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


0 ; 76o(0 ; 6o(

0 ; 76o(0 ; 6o(

0 ; 76o(0 ; 6o(

0 ; 76o(0 ; 6o(

0 ; 6o(

0otal ()S flowrate ; -7=.7 t3h



1 )ater grid diagram F design at maximum inlet and outlet temperatures


/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


0 ; 76o(0 ; 6o(

0 ; 76o(0 ; 26o(

0 ; 89o(0 ; 26o(

0 ; 89o(0 ; 99o(

0otal ()S flowrate ; -7=.7 t3h




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


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(.




1 Design a%ove pinch

-766 )

(P ; 77.2

(P ; 76()+

Pinch

0 ; 76o( 0 ; 89o(

HE 2


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



Design of water networ for minimum freshwater water flowrate


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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Topic 7 - Cooling Water System Design