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 down

The 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

Pro

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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

Pro

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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

Pro

cess, En

ergy an

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OPER 03

T. Gundersen

Similarities/Analogies between Synthesisof Processes and Control Systems

Levels

Structure

Parameters

Various Topics for Heat Exchanger Networks

Pro

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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

Pro

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OPER 05

WS-1: What about Controllability?

T. Gundersen

Heat Integration − Introduction

Pro

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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

C

I 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

Pro

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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

Pro

cess, En

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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

Pro

cess, En

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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

Pro

cess, En

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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

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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

Pro

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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

Pro

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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

Pro

cess, En

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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

Pro

cess, En

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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

Pro

cess, En

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OPER 16

T. Gundersen EXP 01

Pro

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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

Pro

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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

Pro

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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

Pro

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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

Pro

cess, En

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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

Pro

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Expansions of Process IntegrationExpansions of Process Integration

Stages and Analogies in Methods

Heat PinchHeat Pinch

Mass PinchMass Pinch

Water PinchWater Pinch

Hydrogen PinchHydrogen Pinch

Data ExtractionData Extraction

AnalysisAnalysis

DesignDesign

OptimizationOptimization

ModelingModelingT

Q

HeatPinch

Graphical Diagrams

Representationsand Concepts

Performance Targetsahead of Design

Pinch Decomposition

T. Gundersen

Pro

cess, En

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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

Pro

cess, En

ergy an

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Water Pinch Demonstration

Wastewater Minimization

Graphical 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

Pro

cess, En

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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

Pro

cess, En

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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