Heat and Power Integration
CHEN 4460 – Process Synthesis,
Simulation and Optimization
Dr. Mario Richard Eden
Department of Chemical Engineering
Auburn University
Lecture No. 10 – Heat and Power Integration: Network Design
November 6, 2012
Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel
Lecture 9 – Objectives
Given data on the hot and cold streams of a
process, you should be able to:
 Compute the pinch temperatures  Last time!
 Compute the Maximum Energy Recovery
(MER) targets using graphical and/or algebraic
methods  Last time!
 Design a simple Heat Exchanger Network
(HEN) to meet the MER targets
Reviewing Simple Example
30°
60°
120°
100°
ΔH=160
ΔH=162
180°
80°
ΔH=100
Utilities:
Steam @ 150 oC, CW @ 25oC
Stream
TS
(oC)
TT
(oC)
H1
H2
C1
C2
180
130
60
30
80
40
100
120
CP
H
o
(kW) (kW/ C)
100
1.0
180
2.0
160
4.0
162
1.8
130°
40°
ΔH=180
Design a network of steam heaters,
water coolers and exchangers for the
process streams. Where possible, use
exchangers in preference to utilities.
Simple Example - Targets
40°
100°
ΔH=18
ΔH=60
30°
60°
120°
130°
ΔH=162
180°
80°
ΔH=100
Units:
Steam:
Cooling water:
4
60 kW
18 kW
Are these numbers optimal??
Reviewing Simple Example
30°
60°
120°
100°
ΔH=160
ΔH=162
180°
80°
ΔH=100
130°
40°
ΔH=180
T
T
1.0
1.0
180
180
CP =
CP =
H=50
130
H=150
C
C
P
=
2.
0
130
=3
P
.0
H=150
P
=
H=80
C
Not to
scale!!
2.
0
80
80
40
H=50
40
H
Not to
scale!!
H=80
H
Reviewing Simple Example
30°
60°
120°
100°
ΔH=160
ΔH=162
180°
80°
ΔH=100
130°
40°
ΔH=180
T
T
CP =
CP =
H=36
100
100
H=232
60
C
=5
P
.8
H=36
H=232
60
Not to
scale!!
1.8
=
P
4 .0
H=54
CP =
C
30
1. 8
120
1.8
120
30
H
Not to
scale!!
H=54
H
Temperature
Reviewing Simple Example
200
180
160
140
120
100
80
60
40
20
0
QHmin = 48 kW
QCmin = 6 kW
Maximum Energy Recovery
(MER) Targets!
THpinch = 70
TCpinch = 60
0
50
100
150
200
Enthalpy
250
300
350
Reviewing Simple Example
Near Optimal Solution
H1
H2
80oC
180oC
130oC
100oC
120oC
40oC
C
7
60oC
H
49
111
100
30oC
62
60°
C2
100°
ΔH=49
80°
30°
C1
120°
ΔH=62
ΔH=100
180°
40°
ΔH=7
ΔH=111
Reviewing Simple Example
HEN Representation (Grid Diagram)
180 C
80oC
130oC
40oC
o
H1
H2
100oC
o
120 C
C
7
60oC
H
49
111
100
30oC
62
C1
C2
HEN Grid Diagram
Thot
H1
H2
H
Thot
Thot
Tcold
Tcold
Tcold
Tcold
C
C1
C2
The pinch divides the HEN into two parts:
 the left hand side (above the pinch)
 the right hand side (below the pinch)
At the pinch, ALL hot streams are hotter
than ALL cold streams by Tmin.
MER Network Design
CP
170oC
60oC
3.0
150oC
30oC
1.5
H1
H2
135oC
20oC
140oC
80oC
C1
2.0
C2
4.0
Step 1: MER Targeting
Pinch at 90° (Hot) and 80° (Cold)
Energy Targets:
Total Hot Utilities:
Total Cold Utilities:
20 kW
60 kW
MER Network Design
Step 2: Divide the problem at the pinch
CP
170oC
H1
o
H2
150 C
135oC
140oC
90oC
90oC
60oC
3.0
90oC
90oC
30oC
1.5
80oC
80oC
20oC
80oC
C2
C1
2.0
4.0
MER Network Design
Step 3: Design hot-end starting at the pinch
Pair up exchangers according to CP-constraints.
Immediately above the pinch
Pair up streams such that: CPHOT  CPCOLD
(This ensures that TH TC  Tmin)
CP
H1
3.0
H2
1.5
C1
2.0
C2
4.0
Meets Tmin
Violates
Tminconstraint
constraint
Tmin
MER Network Design
Step 3 Cont’d: Complete hot-end design, by ticking-off
streams.
CP
H1
QHmin = 20 kW 
H2

170o
150o
90
3.0

90o

135o
140o
H
20
o
80o
90

80o
1.5
C1
2.0
C2
4.0
240
Add heating utilities as needed (MER target)
MER Network Design
Step 4: Design cold-end starting at the pinch
Pair up exchangers according to CP-constraints.
Immediately below the pinch
Pair up streams such that: CPHOT  CPCOLD
(This ensures that TH TC  Tmin)
CP
H1
3.0
H2
1.5
C1
2.0
Violates
Meets
TT
constraint
constraint
minmin
Tmin
MER Network Design
Step 4 Cont’d: Complete cold-end design, by ticking-off
streams.
CP
H1
H2

90o
60o
90o
C
60
80o

35o
90

30o
20o
C1
3.0
1.5
QCmin = 60 kW 
2.0
30
Add cooling utilities as needed (MER target)
MER Network Design
Completed Design
CP
H1
H2
170o
150
90o
o
135o
H
140o
60o
90o
20
80o
125o
90
30o
70o
C
60
20o
35o
90
30
80o
3.0
1.5
C1
2.0
C2
4.0
240
Note that this design meets the MER targets:
QHmin = 20 kW and QCmin = 60 kW
Steps in MER Network Design
 MER targeting: Define pinch temperatures, Qhmin and QCmin
 Divide problem at the pinch
 Design hot-end, starting at the pinch: Pair up exchangers
according to CP-constraints. Immediately above the pinch,
pair up streams such that: CPHOT  CPCOLD. “Tick off” streams
in order to minimize costs. Add heating utilities as needed
(up to QHmin). Do not use cold utilities above the pinch.
 Design cold-end, starting at the pinch: Pair up exchangers
according to CP-constraints. Immediately below the pinch,
pair up streams such that: CPHOT  CPCOLD. “Tick off” streams
in order to minimize costs. Add heating utilities as needed
(up to QCmin). Do not use hot utilities below the pinch.
Simple Example Revisited
Near Optimal Solution
H1
H2
80oC
180oC
130oC
100oC
120oC
40oC
C
7
60oC
H
49
111
100
30oC
62
60°
C2
100°
ΔH=49
80°
30°
C1
120°
ΔH=62
ΔH=100
180°
40°
ΔH=7
ΔH=111
Simple Example Revisited
Utilities: Steam @ 150 oC, CW @ 25oC
Stream
TS
(oC)
TT
(oC)
H1
H2
C1
C2
180
130
60
30
80
40
100
120
H1
CP
H
o
(kW) (kW/ C)
100
1.0
180
2.0
160
4.0
162
1.8
H2
180oC
80oC
130oC
40oC
100oC
120oC
C
7
60oC
H
49
111
100
30oC
C1
C2
62
CP
H1
QHmin=48 
H2

180oC
80oC
130oC
100oC

120oC 40


80oC
70oC
43oC
60 C
H
H
8
120 60oC
100

54
40 C

C
o
6
o
1.0
2.0
QCmin=6
o
60 C
30oC
C1
4.0
C2
1.8

Summary – Heat Integration
Given data on the hot and cold streams of a
process, you should be able to:
 Compute the pinch temperatures  Last time!
 Compute the Maximum Energy Recovery
(MER) targets using graphical and/or algebraic
methods  Last time!
 Design a simple Heat Exchanger Network
(HEN) to meet the MER targets
Other Business
•
Next Lectures – November 13 & 27
–
•
Class review
Simulation Project Reports
–
•
Due Thursday November 29
Final Exam – December 3
–
–
Ross 136
8:00 AM – 10:30 AM