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Operational Aspects. Typical : Processes are designed & optimized based on given (fixed) data (flowrates, temperatures, pressures, etc.) But : Processes (and Heat Exchanger Networks) are: − often operated “off” design (above/below) − subject to disturbances - PowerPoint PPT Presentation
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Operational AspectsTypical:Processes are designed & optimized based on given (fixed) data (flowrates, temperatures, pressures, etc.)But:Processes (and Heat Exchanger Networks) are: − often operated “off” design (above/below) − subject to disturbances − to be started up and shut downThe Result:The Process Engineer will over-design before the Control Engineer adds new Units for Manipulation
T. Gundersen OPER 01
Various Topics for Heat Exchanger Networks
Process, Energy and System
T. Gundersen
Various Operational Aspects• Controllability
Property of the Process, not the Control System Ability to handle operational Variations
• Flexibility Ability to cope with different Operating Conditions
• Start-Up and Shut-Down Starting up from “Cold” Conditions is challenging
• “Switchability” Change Operation from one Condition to another
• Environmental Aspects• Safety• Maintenance• “RAMS”
Reliability, Availability, Maintainability, Safety
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 02
T. Gundersen
Two important Aspects of Operability• Controllability of Processes
“Ability to handle Short Term Variations”
Withstand (unwanted) Disturbances Stability Issues
Follow (wanted) Set-Point Changes On-line Optimization
• Flexibility of Processes “Ability to handle Long Term Variations” Undesirable Variations
Fouling (or Scaling) in Heat Exchangers Deactivation of Catalysts
Desirable Variations/Changes New Raw Materials and/or new Products Changes in Production Volume
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 03
T. Gundersen
Similarities/Analogies between Synthesisof Processes and Control Systems
Levels
Structure
Parameters
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 04
• Production Site• Process• Equipment
• Choice of Units• Matching• Sequences
• Pressures• Temperatures• Flowrates
• Optimizing• Advisory• Basic Control
• Manipulators• Pairing• Controller Types
• Gain• Integral Time• Derivative Time
Process Control
WS-1: Heat Integration
T. Gundersen
Stream Ts Tt mCp ΔH°C °C kW/°C kW
H1 300 100 1.5 300H2 200 100 5.0 500C1 50 250 4.0 800
Steam 280 280 (var)Cooling Water 15 20 (var)
Specification:ΔTmin = 20°C
Find:QH,min , QC,min
Tpinch , Umin
Umin,MER
and Network
Notice:1) H1 and H2 provide as much heat as C1 needs (800 kW)2) Ts (C1) < Tt (H1,H2) − 20° and Ts (H1) > Tt (C1) + 20°
Heat Integration − Introduction
Process, Energy and System
OPER 05
WS-1: What about Controllability?
T. Gundersen
Heat Integration − Introduction
Process, Energy and System
OPER 06
mCp(kW/°C)
1.5
5.0
4.0
H1
H2
C1
200°C
250°C 50°C
100°C
100°C300°C
180°C
CI III
II
200ºC
150 20500
130
H130
217.5°C 55°C
186.7ºC
MER Design with QH = QH,min , QC = QC,min , U = Umin,MER
Consider: Disturbance for H1 inlet T, while controlling H2 outlet T
Flexibility in Heat Exchanger Networks
C2290° 115°
C1120°
H2
450° 280°
H1
310° 50°
280°240 kW
20 kW 330 kW
10 kW
290°1
2
1 3
3
2
C 285°
40°
mCp
1.0
2.0
3.0
2.0
T. Gundersen
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 07
C2290° 115°
C1120°
H2
450° 280°
H1
310° 50°
169.5°240 kW
241 kW 109 kW
231 kW
179.7°1
2
1 3
3
2
C 395.5°
40°
mCp
1.85
2.0
3.0
2.0
T. Gundersen
Various Topics for Heat Exchanger Networks
Process, Energy and System
Flexibility in Heat Exchanger Networks
OPER 08
C2290° 115°
C1120°
H2
450° 280°
H1
310° 50°
234.5°240 kW
111 kW 239 kW
101 kW
227.8°1
2
1 3
3
2
C 330.5°
40°
mCp
1.35
2.0
3.0
2.0
T. Gundersen
Various Topics for Heat Exchanger Networks
Process, Energy and System
Flexibility in Heat Exchanger Networks
OPER 09
In Summary:
The Network Structure was Flexible (Resilient) for the Cases when mCp was 1.0 and 1.85 for Stream H1, but did not work when mCp was 1.35 even with infinite Heat Transfer Area.
The Reason:
The Problem is Non-Convex, which happens when: − the Pinch point changes − there is a change in Mass Flowrates
T. Gundersen
Various Topics for Heat Exchanger Networks
Process, Energy and System
Flexibility in Heat Exchanger Networks
OPER 10
T. Gundersen
WS-5: Design for FlexibilityQ: How to handle Fouling ?
4175° 20°
3175°
2
155° 90°
1
200° 115°
138°
170°1
4
1 3
3 4 134°
20°
H 2
2
84°
120
81
6 12 Time(months)
U1 (W/m2K)
Exchanger 1has fouling
above 125°C
Ref.: Kotjabasakis and Linnhoff, Oil & Gas Jl., Sept. 1987
73°
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 11
T. Gundersen
WS-5: Fouling in Heat Exchangers1: The Traditional Approach
4175° 20°
3175°
2
155° 90°
1
200° 115°
138°
170°1
4
1 3
3 4 134°
20°
H 2
2
84°
New Area:148 m2
Energy Usage:Constant (the same)73°
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 12
T. Gundersen
WS-5: Fouling in Heat Exchangers2: An alternative Solution
4175° 20°
3175°
2
155° 90°
1
200° 115°
138°
170°
1
4
1 3
3 4 134°
20°
H 2
2
84°
New Unit:Heater on Stream 3
Energy Usage:From 1850 to 2140 kW
H
73°
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 13
T. Gundersen
WS-5: Fouling in Heat Exchangers3: Use Network Interactions
4175° 20°
3175°
2
155° 90°
1
200° 115°
138°
170°1
4
1 3
3 4 134°
20°
H 2
2
84°
New Area:103 m2
Energy Usage:15% Reduction !!73°
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 14
T. Gundersen
WS-5: Fouling in Heat ExchangersSummary
“Method/Approach” ΔArea ΔEnergy
Traditional Approach 148 m2 0
Alternative Solution New Heater + 13%
Network Interactions 103 m2 - 15%
Best Result obtained by using a “Systems Approach”
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 15
T. Gundersen
Summary of Operability
• Plant Operation is often “Off-Design”
• Controllability (Short Term Variations)
• Flexibility (Long Term Variations)
• A new Design Strategy for Fouling
• The importance of Topology (Flowsheet or Network Structure) has been proven
• Process Integration has a Focus precisely on the Structural Aspects of Process Plants
Various Topics for Heat Exchanger Networks
Process, Energy and System
OPER 16
T. Gundersen EXP 01
Process, Energy and System
Expansions of Process Integration
Expansionsof PA & PI
Objectives from Energy Cost to Equipment Cost to Total Annualized Cost and also Operability, including
Flexibility Controllability Switchability
Start-up & Shut-down New Operating Conditions
and finally Environment, including Emissions Reduction Waste Minimization
T. Gundersen EXP 02
Process, Energy and System
Expansions of Process IntegrationExpansions of Process Integration
Scope from Heat Exchanger Networks to Separation Systems, especially
Distillation and Evaporation (heat driven) to Reactor Systems to Heat & Power, including
Steam & Gas Turbines and Heat Pumps to Utility Systems, including
Steam Systems, Furnaces, Refrigeration Cycles to Entire Processes to Total Sites to Regions
Expansionsof PA & PI
T. Gundersen EXP 03
Process, Energy and System
Expansions of Process IntegrationExpansions of Process Integration
Plants from Continuous to Batch and Semi-Batch
Projects from New Design to Retrofit to Debottlenecking
Thermodynamics from Simple 1st Law Considerations to Various 2nd Law Applications
Exergy in Distillation and Refrigeration
Expansionsof PA & PI
T. Gundersen EXP 04
Process, Energy and System
Expansions of Process IntegrationExpansions of Process Integration
Methods Pinch based Methodologies from Analogies
from Heat Pinch for Heat Recovery and CHP in Thermal Energy Systems
to Mass Pinch for Mass Transfer / Mass Exchange Systems
to Water Pinch for Wastewater Minimization and Distributed Effluent Treatment Systems
to Hydrogen Pinch for Hydrogen Management in Oil Refineries
Other Schools of Methods was discussed on a previous slide
Expansionsof PA & PI
T. Gundersen EXP 05
Process, Energy and System
Expansions of Process Integration
DetailedEngineering
StrategicPlanning
ConceptualDesign
HeatIntegration
Pinch
Analysis
Optimization
Methods
Combined
Methods
Expansionsin ProcessIntegration
Process Integration is muchmore than Pinch Analysis for Heat Exchanger Networks
T. Gundersen EXP 06
Process, Energy and System
Expansions of Process IntegrationExpansions of Process Integration
Stages and Analogies in Methods
Heat Pinch
Mass Pinch
Water Pinch
Hydrogen Pinch
Data Extraction
Analysis
Design
Optimization
ModelingT
Q
HeatPinch
Graphical Diagrams
Representationsand Concepts
Performance Targetsahead of Design
Pinch Decomposition
T. Gundersen
Process, Energy and System
Water Pinch Demonstration
Wastewater Minimization
Topic: Efficient Use of Wastewater
Reuse, Regeneration and Recycling- both Targets and Design
Methods: Water Pinch (discussed here)Mathematical Programming
Ref.: Wang and Smith “Wastewater Minimization”,Chem. Engng. Sci., vol. 49, pp 981-1006, 1994
EXP 07
T. Gundersen
Process, Energy and System
Water Pinch Demonstration
Wastewater MinimizationGraphical Representation
H
T
ΔH = mCp ΔT
mass/heat
analogy
C
Δm = mH2O ΔC
m
Cpr,in
Cpr,out
Cout,max
Cin,max
1
23
EXP 08
T. Gundersen SUM 01
Process, Energy and System
Final Summary
Main Results from Pinch Analysis
• The Concept of Composite Curves Applicable whenever an “Amount” has a “Quality” Heat & Temperature, Mass & Concentration, etc.
• A Two Step Approach: Targets ahead of Design• A fundamental Decomposition at the Pinch
T
H
C
m
HeatPinch
WaterPinch
QC,min
QH,min
Watermin
T. Gundersen SUM 02
Process, Energy and System
Final Summary
Objectives for using Process Integration
• Minimize Total Annual Cost by optimal Trade-off between Energy, Equipment and Raw Material
• Within this trade-off: minimize Energy, improve Raw Material usage and minimize Capital Cost
• Increase Production Volume by Debottlenecking• Reduce Operating Problems by correct rather
than maximum use of Process Integration• Increase Plant Controllability and Flexibility• Minimize undesirable Emissions• Add to the joint Efforts in the Process Industries
and Society for a Sustainable Development