Heat Exchanger Network Synthesis (Pinch Analysis)

Rangan Banerjee

Department of Energy Science and Engineering

IIT Bombay

Lecture in KIC-TEQIP programme on Energy Management and Energy Efficiency - IITG - 24th May 2016

Heat Exchanger Network Synthesis (Pinch Analysis)

200C

Steam 1200C

800C

2kW/0C

Heating

200C

2kW/0C

800C

Steam 1200C

Source: Linnhoff

2

Heat Exchanger Network Synthesis (Pinch Analysis)

300C

900C 1500C

1500C

300C

900C

500C

2kW/0C

2kW/0C

Cooling500C

Source: Linnhoff

3

Alternative Network

120kW

120kW

900C 1500C

800C 200C

900C

200C 800C

1500C

Source: Linnhoff

4

TUAQ Integration

As decreases, expect Area to increase

But if Q decreases, Area may also decrease

120 = (UA) 70

UA = 1.7 kW/k

Total UA = 3.4 kW/k

In earlier case total UA = 6.44 kW/k

Hence cost energy

T

Area and Energy

5

Problem Definition

Grass root design

t

s

T

T

ST HTTCPCPdTQ )(

6

Problem Definition

Stream No. Type CP (kW/0C) Ts0C Tt

0C

1 C 2.0 20 135

2 H 3.0 170 60

3 C 4.0 80 140

4 H 1.5 150 130

CT 0

min 10 Utilities steam at 2000C cooling water at 150C

Source: Linhoff

7

Parallel grid representation

H 2

H 4

C 1

C 3

1700C

1500C

1350C

1400C

600

300

200

800

3.0

1.5

2.0

4.0

CP (kW/0C)

8

Data Specification

Set of hot streams to be cooled and set of cold streams to be heated

Inlet and outlet temperatures (Tin, Tout) of steams

Flow rates (m) of streams

Specific heats (Cp) and heat transfer Coefficients with dependence on temperature

Allowable

Additional constraints

Plant layout, safety, flexibility, controllability, operability.

P

9

Temperature – Enthalpy diagram

Tt

H = CP(Tt-Ts)

T

kWH

Ts

0C

CPdt

dH

CPdH

dT 1Slope =

If Ts > Tt Hot stream

Ts < Tt Cold stream

10

Cold Streams

11

Cold Composite Curve

12

Hot Streams

13

Hot Composite Curves

14

Pinch Analysis

0

20

40

60

80

100

120

140

160

180

Enthalpy (H)

Te

mp

era

ture

(o

C)

HCC

CCC

15

Pinch Analysis

0

20

40

60

80

100

120

140

160

180

Enthalpy (H)

Te

mp

era

ture

(o

C)

∆T=10oC

QC=60 kW

QH=20 kW

16

Design rules

No heat transfer across Pinch

No cold utilities above Pinch

No hot utilities below Pinch

17

Pinch

H

T

Pinch H

C

C

QC,min

C-C Cold Composite

H-H Hot Composite

QH,min

18

19

H=-60kW

H=-2.5kW

H=+82.5kW

H=-75kW

H=+15kW

1650C

550C

850C

1450C

1400C

250C

1

2

4

5

3

0 kW

-20 kW

55 kW

40 kW

60 kW

62.5 kW

20 kW

82.5 kW

0 kW

75 kW

60 kW

80 kW

To Cold Utility To Cold Utility

From Hot Utility From Hot UtilityHEAT CASCADE

20

2

4

1

3

1700 900 900600

800

1400

900 900

800200

300

800

1350

1500

4.0

2.0

1.5

3.0

QC MIN =60 kW

PINCH QH MIN = 20 kW

CP kW/0C

21

DESIGN

H

2 I III

4 CII IV

1

3

1700 900 600

1500900 700 300

13501250 800 350 200

1400 800

240kW

90kW 90kW 30kW

60kW

20kW

22

Eulers Theorem

23

Targeting no of units

24

Energy Relaxation

25

H

2 I III

4 CII

1

3

1500T2 300

1350 650 200

240

120-X 90

60+X

20+X

PATH

26

H

2 I III

4 CII

1

3

1500300

1350 650 200

240

112.5 90

67.5

27.5

u = uMIN = 5

750

6009001700

1210

1400800

27

28

29

30

31

References

1. B. Linhoff, User Guide on Process Integration for the Efficient Use of Energy IChem E (1984), London.

2. U. V. Shenoy, Heat Exchanger Network Synthesis, Gulf Publishing Company, Houston, Texas, 1995.

32