15-21
15.16 (a)
QB = (4 + 3 – 3)(20) = 80 kW
QC = (4 + 3 – 3 – 5)(50) = – 50 kW
From interval A
(
4
)(
50
)
–
(
mc
p
)
3
(
50
)
= 50
(
mc
p
)
3 = 3
From interval D
(mcp)2(20) – (3+5)(20)=-100
(mcp)2 = 3
(b)
(c) Tpinch, hot = 160 C
Tpinch,cold = 140 C
(d) Above Pinch
A
Q = 50
B
Q = 80
50
1
480 kW
2
270 kW
HU
20 kW
420 20 270 20
15-23
Design above pinch
Design below pinch
15-24
15.17 (a)
Stream
Number 1 2 3 4
FhrBTU
Cm P2 4 5 4
Temperature
(ºF)
Temperature
(ºF) hrBTU
Q
400 380
200 A 250 -50
(b)
A
-50
HU
50
50
15-25
(c)
Above pinch
2 exchangers
(d) Above pinch PCPH CmCm
Stream Number 1 2 3 4
FhrBTUCm P 2 4 5 4
HU
50
2
200
3
250
50 200
15-26
(e) Below pinch PCPH CmCm
Stream Number 1 2 3 4
FhrBTUCm P 2 4 5 4
41
100
15.18 (a)
Stream
Number 1 2 3 4
CkW
Cm P4 5 4 3
Temperature
(ºC)
Temperature
(ºC) kW
Q
(b)
A
0
0
B
-90
HU
90
90
15-28
(c)
Above pinch
Below pinch
4 exchangers
1
80
1
200
2
200
2
90
15-29
(d) Above pinch PCPH CmCm
Stream Number 1 2 3 4
CkWCm P 4 5 4 3
two possible solutions (there are more if split streams)
4
Q4 = 140 kW
250
4
230
4
Q4 = 155 kW
250
211.25
4
Q3 = 45 kW
230
191.25
210
(e) Utility constraint not only makes direct match impossible, but is also makes minimum
number of exchangers impossible to meet
(f) Below pinch PCPH CmCm – at least two possible solutions without splitting streams
Stream Number 1 2 3 4
CkWCm P 4 5 4 3
180
5
Q5 = 80 kW
200
180 200
160
180
5
Q6 = 30 kW
15-31
15.19 (a)
Stream
Number 1 2 3 4
CkW
Cm P5 2 3 2
Temperature
(ºC)
Temperature
(ºC) kW
Q
280 260
200 A 120 80
(b)
A
80
80
B
0
80
15-32
(c)
Above pinch
4 exchangers
1
300
HU
220
3
480
4
240
300 180 40
2
200
200
15-33
(d) Above pinch PCPH CmCm
Stream Number 1 2 3 4
CkWCm P 5 2 3 2
(e) Below pinch PCPH CmCm
Stream Number 1 2 3 4
CkWCm P 5 2 3 2
HU Q4 = 40 kW
220
4
280
260
2
Q2 = 300 kW
15-34
15.20 (a)
Stream
Number 1 2 3 4
C)(kW/
Cm P2 2 3 3
Temperature
(ºC)
Temperature
(ºC) kW
Q
30
(b) A
20
20
15-35
(c)
Above pinch
4 exchangers
1
180
2
200
HU
10
3
120
4
270
120 10
200
60
15-36
(d) Above pinch PCPH CmCm
Stream Number 1 2 3 4
CkWCm P 2 2 3 3
HU Q4 = 10 kW
4
240
Q3 = 80 kW
236.7
3
HU Q4 = 10 kW
4
260
3
240
15-37
(e) Below pinch PCPH CmCm
Stream Number 1 2 3 4
CkWCm P 2 2 3 3
120
5Q5 = 80 kW
160 150
5
150
110
21
120
5Q5 = 80 kW
160 150
5
150
110
15-38
15.21 (a)
Stream
Number 1 2 3 4
C)(kW/
Cm P2 3 4 2
Temperature
(ºC) Temperature
(ºC) kW
Q
250 240
20 A 20 0
240 230
60
(b) A
0
0
B
-40
HU
40
40