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H T Steam CW CP C =14 CP H =7 T=100 T=80 T=90 T=75 T=100 T=80 T=90 T=75 CP = 0.5 CP = 2.5 CP = 1 CP = 6 Figure B.1 within each enthalpy interval it is possible to design a network in (S - 1) matches. (From Ahmad and Simth, IChemE, ChERD, 67: 481, 1989; reproduced by permission of the Institution of Chemical Engineers.)
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Area Target
Section StreamPopulation
jk
Cold Streams
Hot Streams
H
T
Qj
enthalpy interval
kq
kq
j jk k
k
jlmtot h
qT
A ||1
,
Townsend, D. W. and B. Linnhoff, “Surface Area Targets for Heat Exchanger Networks”, IChemE Annual Research Meeting, Bath, England (April, 1984)
H
T Steam
CW
CPC=14
CPH=7T=100
T=80
T=90
T=75
T=100
T=80
T=90
T=75
CP = 0.5CP = 2.5
CP = 1
CP = 1
CP = 6
Figure B.1 within each enthalpy interval it is possible to design a network in(S - 1) matches. (From Ahmad and Simth, IChemE, ChERD, 67: 481, 1989; reproduced by permission of the Institution of Chemical Engineers.)
250240230220210200190180170160150140130120110100 90 0 200 400 600
Table 8.1-1Approach temperature = 10
+
++
+
++
+ +
+ +
+
Enthalpy, 1000 Btu/hr = Hot + = Cold
Temperature,
F
FIGURE 8.3-1Tempreature-enthalpy diagram.
176
Hotutility
Coldutility
1
2
2
21
1 1
1
2Number of cold streamsin this interval
j
Hot composite Curve
T (F) H (BTU/hr)103
100 0 120 80 140 180 160 280 200 480 250 530
Cold composite Curve
T (F) H (103 BTU/hr)
90 60 130 180 150 360 190 600
MINIMUM HEAT TRANSFER AREA IN INTERVAL j Stream No. CP 103 qk,j 103 TS TT and Type (BTU/hr.F) (BTU/hr) (F) (F)
1. Hot 1 36 176 140 2. Hot 4 144 176 140 3. Cold 3 - 60 130 150 4. Cold 6 - 120 130 150
Stream No. CP 103 qk,j 103 TS TT and Type (BTU/hr.F) (BTU/hr) (F) (F)
1. Hot 1 36 176 140 2. Hot 2/3 24 176 140 31/3 120 176 140 3. Cold 1.8 - 36 130 150 1.2 - 24 130 150 4. Cold 6 - 120 130 150
1
2
3
MINIMUM HEAT TRANSFER AREA IN INTERVAL j
MIN
42,32,31,
1112011241136hhThhThhT
Ajlmjlmjlm
j
4321,
12060144361hhhhT jlm
MIN
jN
k k
jk
jlmj h
q
TA
1
,
,
1
where
Nj = total number of process streams in interval j
jN
k k
jkN
j jlmtot h
q
TA
1
,
1 ,
1MIN
Thot-cold
Tcold
PINCH
(a)
A Screening Procedure For Detection of “Bad” Matches
T
Tcold
(b)
A Screening Procedure For Detection of “Bad” Matches
A Good Match
T
Tcold
(c)
A Screening Procedure For Detection of “Bad” Matches
Two Bad Matches
1-1 Exchanger (a) Temperature
Length
countercurrent
Figure 7.7 1-1 shells approach pure countercurrent flow, whereas 1-2 shells exhibitpartial countercurrent and partial cocurrent flow.
Q = UATLM
TH1
TH2TC2
TC1
TH1
TC2
TH2
TC1
TC2 TH1
TH2TC1
Q =(UATLM) FT FT = f (R,P)
H
C
CC
HH
CPCP
TTTTR
12
21
11
12
CH
CC
TTTTP
1-2 Exchanger (b) Temperature
Length
TC1
TC2
TH1
TH2
partial cuntercurrentpartial cocurrent
R=1
Figure 7.8
Figure 7.8 Designs with a temperature approach or small temperature cross can be accommodated in a single 1-2 shell, whereas designs with a large temperature cross become infeasible. (From Ahmad, Linnhoff, and Smith, Trans. ASME, J. Heat Transfer, 110: 340, 1988; reproduced by permission of the American Society of Mechanical Engineers.)
temperature cross large
P large
(a) A single 1-2 shell is infeasible.
Figure 7.10 A large overall temperature cross requires shells in series to reduce the cross in individual exchangers.(From Ahmad, Linnhoff, and Smith, Trans. ASME, J. Heat Transfer, 110: 340, 1988; reproduced by permission of the American Society of Mechanical Engineers.)
A
B
A B
temperature crosses smaller
Figure 7.10 A large overall temperature cross requires shells in series to reduce the cross in individual exchangers.(From Ahmad, Linnhoff, and Smith, Trans. ASME, J. Heat Transfer, 110: 340, 1988; reproduced by permission of the American Society of Mechanical Engineers.)
(b) Putting shells in series reduces the temperature cross in individual exchangers.