Heat and Power Integration

CHEN 4460 – Process Synthesis, Simulation and Optimization

Dr. Mario Richard EdenDepartment of Chemical Engineering

Auburn University

Lecture No. 10 – Heat and Power Integration: Network DesignNovember 6, 2012

Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel

Lecture 9 – Objectives

Compute the pinch temperatures

Compute the Maximum Energy Recovery (MER) targets using graphical and/or algebraic methods

Design a simple Heat Exchanger Network (HEN) to meet the MER targets

Given data on the hot and cold streams of a process, you should be able to:

Last time!

Last time!

Reviewing Simple Example

Stream TS

(oC) TT

(oC) H

(kW) CP

(kW/oC)

H1 180 80 100 1.0 H2 130 40 180 2.0 C1 60 100 160 4.0 C2 30 120 162 1.8

Design a network of steam heaters, water coolers and exchangers for the process streams. Where possible, use exchangers in preference to utilities.

Utilities:Steam @ 150 oC, CW @ 25oC

30° 120°

180° 80°

130° 40°

60° 100°

ΔH=162

ΔH=160

ΔH=100

ΔH=180

Simple Example - Targets

30° 120°

180° 80°

40°

60°

ΔH=162

ΔH=60ΔH=18130°

ΔH=100

100°

Units: 4Steam: 60 kWCooling water: 18 kW

Are these numbers optimal??

H=150

H

180

130

CP = 3.0

80

40

H=50

H=80

C P =

1.0

C P = 2.

0

T

30° 120°

180° 80°

130° 40°

60° 100°

ΔH=162

ΔH=160

ΔH=100

ΔH=180

H=150

T

H

180

130

C P =

1.0

C P = 2.0

80

40

H=50

H=80Not to scale!

!

Not to scale!

!

Reviewing Simple Example

H=232

T

H

120

100

CP = 5.8

60

30

H=36

H=54

C P =

1.8

C P =

1.8

30° 120°

180° 80°

130° 40°

60° 100°

ΔH=162

ΔH=160

ΔH=100

ΔH=180

H=232

T

H

120

100

C P =

1.8

CP = 4.0

60

30

H=36

H=54Not to scale!

!

Not to scale!

!

Reviewing Simple Example

020406080

100120140160180200

0 50 100 150 200 250 300 350

Enthalpy

Temperature

QCmin = 6 kW QHmin = 48 kW

TCpinch = 60

THpinch = 70

Maximum Energy Recovery (MER) Targets!

Reviewing Simple Example

Reviewing Simple Example

Near Optimal Solution

30°

40°

60°

ΔH=62

ΔH=49100°

120°

ΔH=100

ΔH=7180°

80°

ΔH=111

H1

H2

C1

C2

180oC 80oC

130oC

100oC

120oC

40oC

60oC

30oC111

H

49

62

7C

100

Reviewing Simple Example

HEN Representation (Grid Diagram)

H1

H2

C1

C2

180oC 80oC

130oC

100oC

120oC

40oC

60oC

30oC111

H

49

62

7C

100

HEN Grid Diagram

H1

H2

C1

C2

Thot

H

CThot

Tcold

Thot

Tcold

Tcold

Tcold

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 hotterthan ALL cold streams by Tmin.

MER Network Design

H1

H2

C1

C2

170oC 60oC

150oC

135oC

140oC

30oC

20oC

80oC

CP

3.0

1.5

2.0

4.0

Step 1:MER TargetingPinch at 90° (Hot) and 80°

(Cold)

Energy Targets: Total Hot Utilities: 20 kWTotal Cold Utilities: 60 kW

MER Network Design

Step 2:Divide the problem at the pinch

H1

H2

C1

170oC 60oC

150oC

135oC

140oC

30oC

20oC

80oC

CP

3.0

1.5

2.0

4.0C2

80oC 80oC

90oC90oC

90oC 90oC

MER Network DesignStep 3:Design hot-end starting at the pinch

Pair up exchangers according to CP-constraints.

Immediately above the pinchPair up streams such that: CPHOT CPCOLD(This ensures that TH TC Tmin)

H1

H2

C1

CP

3.0

1.5

2.0

4.0C2

Violates Tmin constraint

H1

H2

C1

CP

3.0

1.5

2.0

4.0C2

Meets Tmin constraint

Tmin

MER Network DesignStep 3 Cont’d: Complete hot-end design, by ticking-off streams.

H1

H2

C1

CP

3.0

1.5

2.0

4.0C2

170o

150o

135o

140o

90o

90o

80o

80o

90

240

H

Add heating utilities as needed (MER target)

QHmin = 20 kW

20

MER Network DesignStep 4:Design cold-end starting at the pinch

Pair up exchangers according to CP-constraints.

Immediately below the pinchPair up streams such that: CPHOT CPCOLD(This ensures that TH TC Tmin)

H1

H2

C1

CP

3.0

1.5

2.0

Violates Tmin constraint

H1

H2

C1

CP

3.0

1.5

2.0

Meets Tmin constraint

Tmin

MER Network DesignStep 4 Cont’d: Complete cold-end design, by ticking-off streams.

H1

H2

C1

CP

3.0

1.5

2.0

90o

90o

80o20o

60o

30o

C

Add cooling utilities as needed (MER target)

QCmin = 60 kW

3090

6035o

MER Network Design

Completed Design

H1

H2

C1

CP

3.0

1.5

2.0

4.0C2

170o

150o

135o

140o

90o

90o

80o

80o

240

9020

H125o

90 30

6035o

70o

20o

60o

30o

C

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

30°

40°

60°

ΔH=62

ΔH=49100°

120°

ΔH=100

ΔH=7180°

80°

ΔH=111

H1

H2

C1

C2

180oC 80oC

130oC

100oC

120oC

40oC

60oC

30oC111

H

49

62

7C

100

Simple Example Revisited

Stream TS

(oC) TT

(oC) H

(kW) CP

(kW/oC)

H1 180 80 100 1.0 H2 130 40 180 2.0 C1 60 100 160 4.0 C2 30 120 162 1.8

Utilities: Steam @ 150 oC, CW @ 25oC

H1

H2

C1

180oC 80oC

130oC

100oC

120oC

40oC

60oC

CP

1.0

2.0

4.0

1.8C2

60oC

70oC

60oC 30oC

QHmin=48 QCmin=6

80oC

H54

C

120

43oC

6

100

H

8

40

H1

H2

C1

C2

180oC 80oC

130oC

100oC

120oC

40oC

60oC

30oC111

H

49

62

7C

100

Compute the pinch temperatures

Compute the Maximum Energy Recovery (MER) targets using graphical and/or algebraic methods

Design a simple Heat Exchanger Network (HEN) to meet the MER targets

Given data on the hot and cold streams of a process, you should be able to:

Last time!

Last time!

Summary – Heat Integration

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