heat part3 retrofit
DESCRIPTION
heaterTRANSCRIPT
• Optimal Retrofit ≠ Optimal Grassroot § Optimal Reuse of installed Heat Exchangers § Requires accurate Modeling (“Rating”) § Shorter Paybacks (especially Energy Projects)
• Phases are the same, but Content is different § Data Extraction has been discussed already § Targeting with focus on Optimal Value for ΔTmin § Process Modifications more difficult than in Grassroot § Network Design is focused on reduced Heat Transfer
across the Pinch point (Process and Utility Pinches) § Optimization is used to maximize the Utilization of
Existing Heat Exchangers through Loops and Paths
What about Retrofit Design of Heat Exchanger Networks ?
T. Gundersen Retro 1
Process, Energy and System
Heat Integration − Retrofit Design
Penalty Heat Flow Diagram
Pinch
T Hot Streams
Cold Streams
ST
Hot Streams
Cold Streams CW
QP = QPP + QPH + QPC Q: What Pinch ? Which ΔTmin ?
T. Gundersen Retro 2
Process, Energy and System
Heat Integration − Retrofit Design
QPC
QPPQPH
Energy Target Plot
HRAT
QH,min
QH,exist
QH,new
HRATnew HRATexist
ΔE a
b
c
HRAT = Heat Recovery Approach Temperature
T. Gundersen Retro 3
Process, Energy and System
Heat Integration − Retrofit Design
Savings vs. Investments
Investment (US$)
Savings (US$/yr)
Invmax
a
b d c
PB=1 PB=2
PB=3
min HRAT subject to Inv ≤ Invmax and PB ≤ PBmax
T. Gundersen Retro 4
Process, Energy and System
Heat Integration − Retrofit Design
Examples of Cross-Pinch Heat Transfer
T. Gundersen Retro 5
Process, Energy and System
Heat Integration − Retrofit Design
H
C
H
mCpH
mCpC
TH,in
TC,out TC,in
TH,out
TP,H
TP,C
, , , ,XP H H in P H C C out P CQ mCp T T mCp T T⎡ ⎤ ⎡ ⎤= ⋅ − − ⋅ −⎣ ⎦ ⎣ ⎦> = 0 <
”Shifting” in Retrofit Design
T. Gundersen Retro 6
Process, Energy and System
Heat Integration − Retrofit Design
LP
C
HP QXP
QC
QH
LP
C
HP QXP
QC − QXP
QH − QXP
H
C
H
C
QH
QC
Example of an Existing Network Pinch180°
C2210° 160°
C1210° 50°
H2220° 60°
H1270° 160°
160°
Ca
2
2
H
1
1
1000 kW
2500 kW
Cb
980 kW
1320 kW
2200 kW
160°
214.4°
120°
mCp(kW/°C)
18.0
22.0
20.0
50.0
QPP = 22 • (220 - 180) = 880 kW QPC = 18 • (214.4 - 180) = 620 kW QP = 1500 kW = 2500 - 1000 QPH = 0 kW
T. Gundersen Retro 7
Process, Energy and System
Heat Integration − Retrofit Design
Changing Operating Conditions (“shifting”)
Pinch 180°
C2 210° 160°
C1 210° 50°
H2
220° 60°
H1
270° 160°
160°
Ca
2
2
H
1
1
1000 kW
2500 kW
Cb
360 kW
440 kW
2200 kW
160°
214.4°
80°
mCp (kW/°C)
18.0
22.0
20.0
50.0
180°
620 kW
880 kW
180°
“Releases” Heat above the Pinch by changing Operating Conditions (Temperatures) for Exchanger 2 and Cooler Ca
T. Gundersen Retro 8
Process, Energy and System
Heat Integration − Retrofit Design
Network After Modifications (Retrofit)
Pinch 180°
C2 210° 160°
C1 210° 50°
H2
220° 60°
H1 270° 160°
160°
Ca
2
2
H
1
1
1000 kW
1000 kW
Cb
360 kW
440 kW
2200 kW
160°
214.4°
80°
mCp (kW/°C)
18.0
22.0
20.0
50.0
180°
620 kW
880 kW
180° 4
3
4
3
190°
The Project requires Purchase of 2 new Units and additional Area (new shell ?) to Unit 2 (smaller ΔT )
T. Gundersen Retro 9
Process, Energy and System
Heat Integration − Retrofit Design
A simpler Retrofit Solution
The Project requires Purchase of only 1 new Unit, while the Energy Savings is 620 kW (versus 1500)
T. Gundersen
Pinch 180°
C2 210° 160°
C1 210° 50°
H2 220° 60°
H1 270° 160°
160°
Ca
2
2
H
1
1
1000 kW
1880 kW
Cb
360 kW
1320 kW
2200 kW
160°
214.4°
120°
mCp (kW/°C)
18.0
22.0
20.0
50.0 3
3
620 kW
180°
172.4°
Retro 10
Process, Energy and System
Heat Integration − Retrofit Design
WS-7: A simple Retrofit Problem
T. Gundersen Retro 11
Process, Energy and System
Heat Integration − Retrofit Design
H1
C1 220°C 70°C
50°C 250°C
120°C
4000 kW
H
C I
I
8000 kW
12000 kW
170°C
mCp (kW/ºC)
100
80
Given: ΔTmin = 5ºC U = 1.0 kW/(m2K) CST = 0.1 NOK/kWh CCW = 0 NOK/kWh
Further: Steam available at 250ºC, Cooling Water at 20ºC (constant) 8000 Operating Hours per Year Cost of new Exchanger: Chex = 0.5 + 0.01·A (m2 and MNOK) Cost of moving/repiping existing Exchanger: Chex = 0.5 MNOK Maximum Payback: PBmax = 3 years
Targeting by using Pro_Pi Software
T. Gundersen Retro 12
Process, Energy and System
Heat Integration − Retrofit Design
Result: For ΔTmin ≤ 30ºC: QH,min = 0 kW, QC,min = 8000 kW
Demand Curves
0
2000
4000
6000
8000
10000
12000
0 10 20 30 40 50 60 Global temperature difference (K)
Q (k
W)
WS-7 (cont.): Alternative Retrofit Projects
T. Gundersen
Process, Energy and System
Heat Integration − Retrofit Design
Retro 13
H1
C1220°C 70°C
50°C250°C
120°C
4000 kW
H
CI
I
8000 kW
12000 kW
170°C
mCp(kW/ºC)
100
80
Existing Design: PB = n.a.
I = 0 MNOK, ΔE = 0 MNOK/yr
H1
C1220°C 70°C
50°C250°C
922.9 kW
H
CI
I
11077.1 kW
8922.9 kW
139.23°C
mCp(kW/ºC)
100
80208.46°C
Project # 1: PB = 0.20 yr = 2.4 months
I = 0.5 MNOK, ΔE = 2.46 MNOK/yr
Project # 2: PB = 0.38 yr = 4.6 months
I = 1.23 MNOK, ΔE = 3.2 MNOK/yr
H1
C1220°C 70°C
50°C250°C
120°C
4000 kW
CI
I
8000 kW
8000 kW
170°C
mCp(kW/ºC)
100
80
II
II
130°C
Project # 3: PB = 0.46 yr = 5.5 months
I = 1.47 MNOK, ΔE = 3.2 MNOK/yr
H1
C1220°C 70°C
50°C250°C
120°C
4000 kW
CI
I
8000 kW
8000 kW
170°C
mCp(kW/ºC)
100
80
II
II
130°CH
H
WS-7 (cont.): Alternative Retrofit Projects
T. Gundersen
Process, Energy and System
Heat Integration − Retrofit Design
Savings MNOK/yr
Investment MNOK 0
1.0
2.0
3.0
0.5 1.0 1.5 0
PB = 2.4 months
PB = 4.6 months
ΔPB = 11.8 months
Retro 14
The Optimum
WS-10: Retrofit
Optimization with Loops and Paths
T. Gundersen Retro 15
Process, Energy and System
Heat Integration − Retrofit Design
Stream Ts Tt mCp ΔH °C °C kW/°C kW
H1 250 120 40 5200 H2 200 180 80 1600 C1 130 290 50 8000 C2 140 240 20 2000
Steam 320°C (condensing) Cooling Water 20°C à 30°C
ΔTmin = 10ºC QH,min = 4000 kW QC,min = 800 kW
Grand Composite Curve
100
150
200
250
300
350
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Q (kW)
T (°C) Grand Composite Curve
100
150
200
250
300
350
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Q (kW)
T (°C)
TPinch = 200ºC/190ºC and 140ºC/130ºC
WS-10: Existing Network
T. Gundersen Retro 16
Process, Energy and System
Heat Integration − Retrofit Design
mCp (kW/ºC)
[40]
[80]
[50]
[20]
H1
H2
C2
C1 Ha
C
200º
190º 130º
140º
130º
120º 165º 200º
200º 180º
158º 190º 290º
250º
240º 140º Q=5000
Q=2000
Q=1600 Q=1400
Q=1800
I
III
II
Targeting for ΔTmin = 10ºC: QH,min = 4000 kW , QC,min = 800 kW
Cross Pinch Heat Transfer: QXP,I = 1000 kW , QXP,C = 1000 kW
H1 C
WS-10: Retrofit Network
T. Gundersen Retro 17
Process, Energy and System
Heat Integration − Retrofit Design
mCp (kW/ºC)
[40]
[80]
[50]
[20]
H2
C2
C1 Ha
130º
120º 140º 175º
200º 180º
158º 190º 290º
250º
240º 140º Q=1600 Q=1400 [1400]
UA=106.1 [36.5]
Q=800 [1800]
I
III
II 200º
Q=1000 [2000] UA=50.1 [71.7]
Q=3000 [5000]
Q=2000 UA=138.6
Hb
Q=1000 UA=9.7
230º
190º
IV
Investments: New Exchangers IV and Hb and Additional Area for Existing Exch. II
Savings: 1000 kW Reduction in Steam and Cooling Water
WS-10: Summary
T. Gundersen Retro 18
Process, Energy and System
Heat Integration − Retrofit Design
a) Unchanged Energy Consumption Loop A: Ha (+x) → IV (-x) → I (+x) → Hb (-x) b) Better Use of Existing Ha and I
c) Reduces the Area for new Hb and IV
a) Unchanged Energy Consumption Loop B: IV (+y) → II (-y) b) Better Use of Existing I
c) Area increase in IV > Area saved in II
a) Increased Energy Consumption Path C: Ha (+z) → IV (-z) → C (+z) b) Reduces Area for Exchangers IV & II
c) Less (!!) Use of Existing I
a) Increased Energy Consumption Path D: Ha (+w) → II (-w) → C (+w) b) Reduces Area for Exchangers II & IV (This path is dependent – Combine B and C) c) Less (!!) Use of Existing III
a) Reduced (!!) Energy Consumption Path E: Hb (-v) → I (+v) → C (-v) b) Better Use of Existing I
c) Increased Additional Area for II
Loop A most promising, possibly combined with Path C if Existing Exchanger I becomes limiting
Optimization with 4 DOFs
T. Gundersen
Heat Recovery and Iterative Design
R S H U
R = Reactor System S = Separation System H = Heat Integration U = Utility System
Decomposition
R
S
H
U
Interactions
Proc. Mods. 1
Process, Energy and System
Process Modifications
Process Modifications
The “ Plus / Minus “ - Principle
T
Q QC,min
QH,min
T. Gundersen Proc. Mods. 2
Process, Energy and System
Process Modifications