introduction to pinch technology

Introduction to Pinch Technology

Introduction to Pinch TechnologyTopics

• Introduction

• Heating Curves

• Composite Curves

• Pinch Point

• Network Design

• Crude Distillation Check

• Quiz

Introduction to Pinch TechnologyIntroduction

Representation of exchangers and streams

Cold

Hot

H1

H2

H3

C1

C2

C3This diagram suitable

for two streams.For many streams, this diagram

provides a schematic.


Exercise

- Two Hot Streams

- Two Cold Streams

- Steam and Cooling Water

- Temperatures and Duties from Table

Stream WCp Tin Tout Q

H1 0.05 315 240 -3.75

H2 0.20 240 140 -20.0

C1 0.075 40 130 +6.75

C2 0.125 130 260 +16.25

Steam 350 350

CW 27 40

W = Mass

Cp = Heat Capacity

CW = Cooling Water

Q = Duty


Exercise

For the given Basis, calculate the following:

- How many exchangers are required?

- What size are the exchangers?

- How much steam and cooling water are required?


Exercise

Provide a solution using the ““Dumbbell” representation

Steam

C1

C2

H1

H2

CW

Steam Load

= 23 Units

CW Load

= 23.75 Units

350 350

130 40

260 130

40 27

315 240

240 140

What is downside of this scheme?

Formulate another exchanger network.


Exercise

Provide an alternate network solution reducing utility load

Steam

C1

C2

H1

H2

CW

350 350

130 40

260 130

40 27

315 240

240 140

Heat Exchanger A B C D

Calculate stream temperatures and duties.......

WCp=0.075

WCp=0.125

WCp=0.050

WCp=0.200


Exercise


Steam

C1

C2

H1

H2

CW

350 350

130 40

260 130

40 27

315 240

240 140


WCp=0.075

WCp=0.125

WCp=0.050

WCp=0.200

Duty=xxx

xxx

Duty=xxx

xxx

Duty=xxx

Duty=xxx


Exercise


Steam

C1

C2

H1

H2

CW

350 350

130 40

260 130

40 27

315 240

240 140


WCp=0.075

WCp=0.125

WCp=0.050

WCp=0.200

Duty=6.75

206

Duty=3.75

160

Duty=12.50

Duty=13.25


Questions

- Will both exchange networks work?

- Which is better?

- Is there a better network?

- How many combinations of exchange are there?

Conclusions

- Is there a need for an early systematic approach

to exchanger network design?

- The answer to a systematic approach is called

PINCH TECHNOLOGY. It will benefit the

process engineer by providing:

Better planning

Targets for the Utilities

Estimate exchanger targets early

Optimized designs


PROCESS UNIT OR

COMPLEX

Process Integration

Feed

Heat Reaction

Feed

Power

Energy

Recovery

Products

Products

Products

Cold

Utility

Hot

Utility

Once the basis of design is established, the Process Engineer

must do the engineering to define the structure within the box.

PINCH TECHNOLOGY is one of the modern tools available

for the Process Engineer.

Introduction to Pinch TechnologyHeating Curves

Construction of Heating Curves

- Two Fluids with constant Cp

- Two Fluids with changing Cp

- Two Fluids with hot and cold utilities

- Finding optimum approach of hot and cold curves


Two Fluids with constant Cp

600

500

400

300

200

100

0

0 0.2 0.4 0.6 0.8 1.0

Tem

per

atu

re

Fraction of Thermal Duty

Hot

Cold


Two Fluids with changing Cp

600

500

400

300

200

100

0

0 0.2 0.4 0.6 0.8 1.0

Tem

per

atu

re

Fraction of Thermal Duty

Cold

Hot


Two fluids with hot and cold utilities

600

500

400

300

200

100

0

0

Tem

per

atu

re

Hot

Cold

20 40 60 80 100

Thermal Duty, MMBTU/Hr

What is Hot Utility?

What is Cold Utility?

What is Exchanger

Duty?

What is Minimum

Temperature Approach?


Two fluids with hot and cold utilities with infinite exchange

600

500

400

300

200

100

0

0

Tem

per

atu

re

Hot

Cold

20 40 60 80 100

Thermal Duty, MMBTU/Hr

What is minimum

heating utility?

What is minimum

cooling utility?

What is temperature

approach?

Is this a reasonable

design?


0

200

400

600

800

1000

1200

0 20 40 60 80 100

Utility

Capital

Total

Delta T Minimum (approach)

Find the optimum approach:

Tabulate Utility, Capital & Total Cost vs Approach


Conclusions

- Two Fluid System

Understandable

Simple

Minimum Calculations

- Extend to PINCH TECHNOLOGY

Many Streams

Overlapping Temperature Ranges

Many Utilities (Steam, CW, Air, Fuel Oil & Gas)

Algorithms for Matching Exchangers

Composite Curves

Plot all cooling services as a single composite curve

Plot all heating services as a single composite curve

T

T

T

T

Q Q

Q Q

Hot

Composite

Cold

Composite

Plot the hot composite streams on a Crude Distillation Unit

STREAMS TEMPERATURE, DEG F DUTY, Q

IN OUT MMBTU/HR

Reduced Crude

Gas Oil PA

Diesel PA

Gas Oil Net

Diesel Net

Kerosene Net

Overhead Vapor

665 175

590 440

530 380

570 120

510 120

400 100

285 140

167.6

40.0

60.0

27.0

22.5

29.1

186.7

Assumptions: Specific Heat constant from inlet to outlet temperature.

Step One: Line up intervals from lowest to highest.

100, 120, 140, 175, 285, 380, 400, 440, 510, 530, 570, 590, 665

Step Two: Determine which intervals are common to which streams.

Step Three: Determine the mean specific heat for each stream.

Step Three: Determine duty associated with each interval.

Step Four: Plot the temperature vs. duty composite curve.

Introduction to Pinch TechnologyComposite Curves

Reduced Crude

Gas Oil PA

Diesel PA

Gas Oil Net

Diesel Net

Kerosene Net

Overhead Vapor

100 120 140 175 285 380 400 440 510 530 570 590

120 140 175 285 380 400 440 510 530 570 590 665

38 32 7 14 24 7 14 7 26

19 5 11 5

8 16 28 8

1 2 7 6 1 2 4 1 2

1 2 7 6 1 2 4

2 2 4 11 10 2

45 142

(WxCp)

0.342

0.267

0.400

0.060

0.058

0.097

1.288

Total 2 4 53 205 54 19 34 79 21 27 12 26

Cumulative 2 6 59 264 318 337 371 450 471 498 510 536


0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900

Te

mp

era

ture

, D

eg

F

Duty, MMBTU/HR

Hot Composite Curve


0

100

200

300

400

500

600

0 20 40 60 80 100 120

Tem

per

atu

re

Thermal Duty

Hot

Composite

Cold

Composite

Practical use of composite curves

Minimum Delta T or Pinch


0

100

200

300

400

500

600

0 20 40 60 80 100 120

Tem

per

atu

re

Thermal Duty

Hot

Composite

Cold

Composite


Hot Utility Target


0

100

200

300

400

500

600

0 20 40 60 80 100 120

Tem

per

atu

re

Thermal Duty

Hot

Composite

Cold

Composite


Cold Utility Target


0

100

200

300

400

500

600

0 20 40 60 80 100 120

Tem

per

atu

re

Thermal Duty

Hot

Composite

Cold

Composite


Exchange between Hot and Cold Streams


0

100

200

300

400

500

600

0 20 40 60 80 100 120 140

Tem

per

atu

re

Thermal Duty

Hot

Composite


The cold composite can be drawn at any location along the

Q axis as long as T and slopes are maintained. What changes?



0

100

200

300

400

500

600

0 20 40 60 80 100 120 140

Tem

per

atu

re

Thermal Duty

Hot

Composite


The cold composite can be drawn at any location along the

Q axis as long as T and slopes are maintained. What changes?

Note:The change in the Pinch value is proportional to the change in total utility load.

Introduction to Pinch TechnologyPinch Point

0

200

400

600

800

1000

1200

0 20 40 60 80 100

Utility

Capital

Total

Delta T Minimum

Find the optimum “Delta T Minimum”

Tabulate Utility, Capital & Total Cost vs Delta T Minimum

Pinch Point


0

100

200

300

400

500

600

0 20 40 60 80 100 120

Tem

per

atu

re

Thermal Duty

Hot

Composite

Cold

Composite


Once pinch is set, optimum exchange layout must take

advantage of maximum temperature driving force.


Rules to maximize thermal driving force at desired PINCH POINT

•Maintain vertical driving force with exchanger selections

•Select matches with exchangers 100% above pinch

•Select matches with exchangers 100% below pinch

•Do not use cooling utility above pinch

•Do not use heating utility below pinch


Rules of Thumb for various processes

- Refrigeration 10 deg F Pinch

- Petrochemical 30 deg F Pinch

- Petroleum 50 deg F Pinch

- High Pressure Units 100 deg F Pinch

Remember once the Pinch is set

- Hot Utility is fixed

- Cold Utility is fixed

Remember exchanger constraints

- Some exchanger configurations are undesirable

- Constraints may prevent attaining desired Pinch

Introduction to Pinch TechnologyNetwork Design

Summary:

- Generate composite curves

Stream data

Temperature data

- Select optimum Pinch Point

Capital costs

Utility costs

- Rules for exchanger selection

No heat transfer across the Pinch Point

Start at Pinch Point and work outward(above & below)

Maintain maximum temperature driving force

Never let exchanger approach drop below Pinch Point


Software

- Is there software to help the Process Engineer?

Linhoff March

Advent

Hysim/Sim Sci

Spreadsheets

- Can software make the exchanger matches?

Yes, as good as the algorithms

Do not underestimate the human interface

- Let us go through with an example


Example

Start the grid by showing all the hot streams(requiring

cooling) to go from left to right and the cold streams

(requiring heating) to go from right to left.

Stream Type W x Cp TempIn TempOut

Cold 2.0 20 135

Hot 3.0 170 60

Cold 4.0 80 140

Hot 1.5 150 30

Plot the composites with a Pinch Point of 10 degrees.


0

20

40

60

80

100

120

140

160

180

0 200 400 600

Tem

per

atu

re

Thermal Duty

Example

Heating Utility = 20

Cooling Utility = 60

Pinch = 10


Example

Layout streams in a grid with the center line at the

Pinch temperatures.

170 90 90 60

150 90 90 30

135 80 80 20

140 80

W x Cp Duty

above below

3.0 240 90

1.5 90 90

2.0 110 120

4.0 240 -

(2)

(4)

(1)

(3)


Example

Start matching exchanger above the Pinch

170 90

150 90

135 80

140 80

W x Cp Duty

above

3.0 240

1.5 90

2.0 110

4.0 240

(2)

(4)

(1)

(3)

170 - 90

140 - 80

30 10

150 - 90

125 - 80

25 10

125 - 135

Q = 240 Q = 90

Q = 20

Hot Utility


Example

Match exchangers below the Pinch

90 60

90 30

80 20

W x Cp Duty

below

3.0 90

1.5 90

2.0 120

(2)

(4)

(1)

(3)

90 - 60

80 - 35

10 25

90 - 70

35 - 20

55 50

70 - 30

Q = 60

Q = 90 Q = 30

Cooling Utility

Introduction to Pinch TechnologyCrude Distillation Unit Design Check

The hot composite streams for the Crude Distillation Unit have

been plotted. Now plot the cold composite streams. Use the exiting

heater duty as the hot utility. What is the resultant Pinch Point?

IN OUT MMBTU/HR

STREAMS TEMPERATURE, DEG F DUTY, Q

Crude to Desalter

Crude to Heater

Crude to Flash Zone

Debut Reboiler

60 260

250 449

449 705

374 375

126.2

152.7

273.7

20.0

Introduction to Pinch TechnologyCrude Distillation Unit Design Check

Crude to Fl Zone

Crude to Heater

Crude to Desalter

Debut Reboiler

705 449 375 374 260 250

449 375 374 260 250 60(WxCp)

1.069

0.767

0.631

20.0

Total 274 57 21 87 14 120

Cumulative (536+274 = 810) 536 479 458 371 357 237

274

57 1 87 8

6 120

20


Crude Distillation Unit Design Check

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900

Te

mp

era

ture

, D

eg

F

Duty, MMBTU/HR

Hot Composite Curve


Crude Distillation Unit Design Check

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900

Te

mp

era

ture

, D

eg

F

Duty, MMBTU/HR

Composite Curves

Introduction to Pinch TechnologyQuiz

1. Based on the individual streams below, calculate the heat duty for the hot

composite curve in the 180-150 deg range.

Stream Q, MMBTU/H Tin Tout

1 20.0 200 100

2 4.5 180 150

3 12.0 160 130

a. 4.5 MMBTU/H

b. 22.5 MMBTU/H

c. 14.5 MMBTU/H

2. The complete composite curve for the streams in Problem 1 would consist

of how many separate temperature zones?

a. 5

b. 3

c. 1

3. The Pinch Point is determined as:

a. The point where the heating and cooling curve cross

b. The temperature difference between the two composite curves that

results in the optimum economic cost.

c. The point where the composite curves just touch


4. The physical significance of the reducing the Delta Tmin is to:

a. Increase the heat exchange surface area

b. Reduce capital cost

c. Decrease the heat exchange surface area

5. When designing an oil processing facility, a recommended target

pinch temperature is:

a. 70 deg F

b. 50 deg F

c. 20 deg F

6. When selecting the streams that should be used to exchange heat, which

rule of network design applies?

a. Do not exchange heat across the Pinch Point

b. Minimize vertical temperature driving force

c. Exchanger temperature differentials less than the pinch point

temperature are acceptable

7. Heating and cooling utilities are fixed when the pinch point temperature

is selected.

a. True

b. False


8. From the composite curves developed for the crude unit design, what

is the value of the pinch point temperature?

a. 200 deg F

b. 136 deg F

c. 155 deg F

9. If the cold composite curve developed for the crude unit design is repositioned

laterally to the left, what happens to the heating utility.

a. Increases

b. No change

c. Decreases

10. Pinch technology can be used to help and aid with the process flow scheme

selection.

a. True

b. False

introduction to pinch technology

Documents

duty introduction

cold curves introduction

heat exchanger

better network

alternate network solution

hot streams

cold streams steam

tablestream wcp tin