Composite Curve (Smith, R., 2005) Two-stream heat recovery problem
VIII
HEAT INTEGRATION
Dr. Eng. Yulius Deddy Hermawan Department of Chemical Engineering UPN “Veteran” Yogyakarta
Outline
1. Heat Exchanger Network
2. Reactor Heat Integration
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
VIII.1
HEAT EXCHANGER NETWORK
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Composite Curve (Smith, R., 2005)
Two-stream heat recovery problem Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
T-H Diagram
160 150 140 130 120 110 10090
80
70
60
50
40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
D
H (MW)T ( o
C)
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
A simple recovery problem with one hot stream and one cold stream Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
HE stream data for two hot streams and two cold streams
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
A simple flowsheet with two hot streams and two cold streams
The hot streams can be combined to obtain a composite curve
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
The cold streams can be combined to obtain a composite curve
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Plotting the hot and cold composite curves together allows the
targets for hot and cold utility to be obtained
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Increasing DT min from 10 o
C to 20 o
C
increase the hot and cold utility targets o
- 1
- (
- (
CP (MW.K
80
27.0 0.30 145 235 Reactor 2 product Hot 200 80 -30.0 0.25 195
75 Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
The Problem Table Algorithm: Stream Population
Interval temp.245 250
235 240 230
195 200 190 200 185 180 190 180 190 145 140 150 140 15075
70
80
30
35
0.20 25 185 Reactor 1 product Hot 250 40 -31.5 0.15 245
40
25
1
3
2
4
35 Reactor 2 feed Cold 140 230
32.0
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
T
Shifted temperatures
D T min= 10 o
C Stream Type Supply temperature T
S
(
o
C) Target temperature T
(
C) Reactor 1 feed Cold 20 180
o
C) D H (MW)
Heat capacity flowrate
) Shift temperature T
S
o
C) Shift temperature T
T
20 Stream Population
- ∑CPH [MW.K
- 1
- 7.5
- 1
- 1
2.0
2.5
2.0
2.0 Deficit
0.20
10
20
25
12.0
2.0
4.5
2.0
2.0 Deficit
0.05
40
40
30
10.0 Q
Cold Utility
Cmin
1. Dividing the problem at the pinch, and designing each part separately
4. Maximising exchanger load
(below)
≥ CP COLD
(above) CP HOT
≤ CP COLD
3. Immediately adjacent to the pinch, obeying the constraints: CP HOT
2. Starting the design at the pinch and moving away
3. Don’t use hot utilities below Design is produced by:
Cold Utility
2. Don’t use cold utilities above
1. Don’t transfer heat across the Pinch
Simple Design for Maximum Energy Recovery
To produce minimum utility load:4 Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
2
3
1
Stream Population
35
70 -0.20 -14.0 Surplus -14.0 6.5 -14.0 14.0
80
C
245 250
Utility MW
Utility MW Hot
Deficit Hot
[MW] Surplus/
INTERNAL
] DH
C) ∑CP
10 -0.15 -1.5 Surplus -1.5 1.5 -1.5
o
(
INTERNAL
DT
Interval temp.
The Problem Table Algorithm: the problem table cascade
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
7.5 Q Hmin 235 240 230
9
80
40
70
75
0.0
4.0
4.0
4.0 Deficit
0.10
145 140 150 140 150
195 200 190 200
4.0
10 -0.10 -1.0 Surplus -1.0 -3.5 -1.0
185 180 190 180 190
3.0
6.0
6.0 Deficit 6.0 -4.5
0.15
40
5. Supplying external heating only above the pinch, and
external cooling only below the pinch
Example problem stream data, showing pinch
CPPinch
[MW.K ]
250 150 150
40
0.15
2 200 150 150
80
0.25
4 180 140 140
20
0.20
1 230 140 140
0.30
3 Q
7.5 Q
10.0 Hmin Cmin
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Heat Exchanger Above the Pinch
Pinch250 150 203.3
2
Starting the design at the pinch and moving away
200 150
4
Immediately adjacent to the pinch, obeying the constraints:
180 140
CP ≤ CP (above)
HOT COLD
7.0 MW CP ≥ CP (below)
HOT COLD
230 205 181.7 140
H
12.5 MW
7.5 MW
7.0 MW
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Heat Exchanger Below the Pinch
Pinch150 106.7
40 C
Starting the design at the pinch and moving away
10 MW
150
80
Immediately adjacent to the pinch, obeying the constraints:
CP ≤ CP (above)
140
52.5
20 HOT COLD
1 CP ≥ CP (below)
HOT COLD
17.5 MW 6.5 MW
140
3 Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
A design that achieves the energy target:
Grid Diagram
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
1.0
T (
o
5 Cold 110 110
4 Cold 80 130 2.5 0.050
3 Cold 30 110 1.4 0.018
90
1.0 0.0202 Hot 140
40
3.0 0.0251 Hot 160
)
CP (MW.K
Heat capacity flowrate
D H (MW)
C) Heat Duty
T
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
C) Target temp.
S ( o
T
Stream Type Supply temp.
3. Develop grid diagram (heat exchanger network) for this case ! Stream data for Assignment 8.1.
C !
= 10 o
2. From the composite curves, determine the target for hot and cold utility
for DT minC !
= 10 o
1. Sketch the composite curves for DT min
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Assignment: 8.1.
A design that achieves the energy target:
Process Flow Diagram with Energy Integration Scheme
VIII.2
REACTOR HEAT INTEGRATION
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Characteristics of Reactor Heat Integration
1. Adiabatic Operation: leads to an acceptable temperature rise for exothermic reactors or an acceptable decrease for endothermic reactors.
2. Heat Carriers: If adiabatic operation produces an unacceptable rise or fall in temperature, then the option is to introduce a heat carrier. The operation is still adiabatic, but an inert material is introduced with the reactor feed as a heat carrier.
3. Cold Shot: Injection of cold fresh feed for exothermic reactions or preheated feed for endothermic reactions to intermediate points in the
reactor can be used to control the temperature in the reactor.
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Reactor Heat Integration
Effluent (Reactor Products) HEATERFeed REACTOR
(UTILITIES) FEHE COOLER (UTILITIES)
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
A Complex Energy Integrated of HDA Process
Gas recycle Purge
Compressor Cooler
H feed
2 Furnace
Separator Toluene
FEHE-2 FEHE-3 FEHE-1
PFR feed Quench
Fuel
e
Methane
cl cy
CR
re e en
Product
lu
Column Benzene
Recycle
To
Column Stabilizer
R3 R2 R1 Column
Diphenyl
Source: Terrill, D. L. and Douglas, J. M. (1987), A T-H Method for Heat Exchanger Network Synthesis. Ind. Eng.
Chem. Res. 26, 175-179
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
4841 lbmole/hr 1150 o
F 521 psia
4841 lbmole/hr
146 oF 600.5 psia
69 MMBtu/hr
Feed of Reactor need to be heated
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Effluent of Reactor need to be cooled
4944.3 lbmole/hr 1150 oF 504 psia
74.83 MMBtu/hr
4944.3 lbmole/hr 113 oF 469.2 psia To next process
65.7 MMBtu/hr
Heat Duty of Heat Exchanger Processes
(Comparation between process WITH and WITHOUT energy integration)
65.46
9.1 FEHE -
74.83
3.36 Condenser
69
Furnace
With Energy
Integration
Without Energy IntegrationHeat Exchanger Heat Duty (MMBtu/hr)
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY
Process flow diagram of Feed-Effluent-Heat-Exchanger
4944.3 lbmole/hr 1150 o9.1 MMBtu/hr
F 469.2 psia
F 564.7 psia 4944.3 lbmole/hr 113 o
F 564.7 psia 4841 lbmole/hr 1150 o
F 600.5 psia 4841 lbmole/hr 1106 o
F 472.4 psia 4841 lbmole/hr 146 o
3.36 MMBtu/hr 4944.3 lbmole/hr 222 o
F 504 psia
Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY