episode 60 : pinch diagram and heat integration

SAJJAD KHUDHUR ABBASCeo , Founder & Head of SHacademyChemical Engineering , Al-Muthanna University, IraqOil & Gas Safety and Health Professional – OSHACADEMYTrainer of Trainers (TOT) - Canadian Center of Human Development

Episode 60 : Pinch Diagram and Heat Integration

Introduction of Process Integration

Pinch Diagram and Heat Integration

Reference: Notes from course on “Modelling, design and control for process integration”, CAPEC, August 2000 (R.

Dunn)

Process Integration Tools Allow Analysis of the “Enterprise”

• The optimal allocation of mass and energy within a unit operation, process and/or site.• Optimal allocation can be based on economic, environmental or other important objectives.

Heating Cooling

Mass Integration (Mass Exchange Network – MEN) Energy Integration (Heat Exchange Network – HEN)

Power Pressure

ProductsFeed Stock

By-ProductsSolvents

Chemical Plant

(Enterprise)Effluents

Catalysts

Spent MaterialsMaterial for Utilities(Water, Coal)

Heating Power Cooling

Pressure

Process Integration Techniques

ReactiveMass Exchange ExchangeNetworks Networks(REAMEN’s)

Mass Exchange Networks (MEN’s)

Process Integration

Process Integration

Heat Exchange Networks (HEN’s)

Combined Heat and Reactive Mass Exchange Networks (CHARMEN’s)

Masswith Regeneration (MEN/REGEN)

Reverse Osmosis Networks (RON’s)

Heat-Induced

Waste Minimization Networks (HIWAMIN’s)

Energy-Induced Separation Networks (EISEN’s)

Pervaporation Network’s (PERVAP’s) Waste

Interception and Allocation Networks(WIN’s)

Heat-Induced Separation Networks (HISEN’s)

Energy-Induced Waste Minimization Networks (EIWAMIN’s)

4

Heat Exchange Network (HEN)

Want to Identify:– Optimal matching between hot and cold streams to

minimize utility consumption– Minimum number of heat exchangers needed

PlantUnit OperationsRaw Materials

Products&

By-Products

Hot Streams In

Cold Streams In

Cold Streams Out

Hot Streams Out

(Linnhoff, Grossmann et al, 1978-Present)A Heat Exchange Network is a System of One or More

Heat ExchangersHot and Cold Utilities

Heat Exchanger Network

Therefore, 10x103 BTU/hr must be supplied from utilities (if there are no restrictions on temperature driving force)

How can we check driving force restrictions? Second Law Analysis (You can not transfer heat from a lower temperature to a higher temperature)

5*Ref. Douglas, 1988, Conceptual Design of Chemical Processes, McGraw-Hill Publishers, p. 218.

Consider the problem of two hot stream and two cold streams:

First Law Analysis (Conservation of Energy):

Q F Cp T 4000 BTU (200 100)o F 400x103 BTU / hr hr o F

Q FCp T 1000 BTU (250 120)o F 130x103 BTU / hr hr o F

2 2 2 2

1 1 1 1

Calculate Q3 and Q4

Table 1*

Stream Q available

No. Condition FCp, BTU/(hroF) Tin Tout 103 BTU/hr

1 Hot 1000 250 120 1302 Hot 4000 200 100 4003 Cold 3000 90 150 -1804 Cold 6000 130 190 -360

-10

Shifted Temperature Scales (using Table 1 data):

100

Hot Temperature Scale Cold Temperature Scale

250

240

200

150

190

140

90

Sources Sinks

These streams need to be cooled

These streams need to be heated

Temperature Interval Diagram (TID)


250

240

200

140

100

190

130

90

160 150

120 110

Net Energy Required at Each Interval


Heat Duty Within IntervalsInterval, i250 240FCp 1000 4000 3000 6000 1000 Q

200

140 3 130

100 5

120 4 110

190

90

1 50

2 -40160 150

-80

40

20

Total = -10

Q (FCp) (FCp)

T

Q (1000 4000 3000 6000)(160 140) 80x103

3

Q (1000 4000 6000)(200 160) 40x103

2

Q (1000)(250 200) 50x103

1

cold ,i

i hot ,i

Therefore,

i

Heat Transfer to and from Utilities for Each Temperature IntervalHot Temperature Scale

250

Cold Temperature Scale

240

50200 190

Hot -40

Cold160

UtilityUtility 150

140 130

120 110

100 20 90

Cascade Diagram


250 240

200

140

100

190

150

130 Pinch

90

160

50

-40

-80

50Hot

UtilityCold

Utility10700

40 4020 60

11

Hot Composite CurveTable 2*

Hot streams, oF Cumulative H

Since FCp values are constant, we could have replaced the calculation for H2, H3, H4 with a single expression: H2,3,4=(1000+4000)(200-120)=400,000

Temperature (oF) Plot Becomes the Hot Composite Curve

Enthalpy (1000 BTU/hr)*Ref. Douglas, 1988, Conceptual Design of Chemical Processes, McGraw-Hill Publishers, p. 218.

T=100 H0=0 0

T=120 H1=4000(120-100)=80,000 80,000T=140 H2=(1000+4000)(140-120)=100,000 180,000T=160 H3=(1000+4000)(160-140)=100,000 280,000T=200 H4=(1000+4000)(200-160)=200,000 480,000T=200 H5=1000(250-200)=50,000 530,000

Hot Composite Curve

270

250

230

210

190

170

150

130

110

900 100 200 300 400

Enthalpy, 1000 BTU/hr

500 600

Tem

pera

ture

(deg

F)

Cold Composite CurveTable 2.3*

Cold streams, oF Cumulative H

Temperature (oF) Plot Becomes the Cold Composite Curve

Enthalpy (1000 BTU/hr)

*Ref. Douglas, 1988, Conceptual Design of Chemical Processes, McGraw-Hill Publishers, p. 218.

T=90 H0=60,000 60,000

T=130 H1=3000(130-90)=120,000 180,000T=150 H2=(3000+6000)(150-130)=180,000 360,000T=190 H3=6000(190-150)=240,000 600,000

Cold Composite Curve

210

190

170

150

130

110

900 100 200 300 400

Enthalpy, 1000 BTU/hr500 600 700

Tem

pera

ture

(deg

F)

Composite Curves

27025023021019017015013011090

Tem

pera

ture

, deg

F

Hot Composite StreamCold Composite Stream at 10 deg F minimum temperature driving force

0 200 400 600

Enthalpy, 1000 BTU/hrComputer Aided process Engineering - Lecture 11 (R. Gani)

Composite Curves

270

250

230

210

190

170

150

130

110

90

Tem

pera

ture

, deg

F

Hot Composite StreamCold Composite Stream at 10 deg F minimum temperature driving force Cold Composite Stream at 20 deg F minimum temperature driving force

0 200 400 600

Enthalpy, 1000 BTU/hrComputer Aided process Engineering - Lecture 11 (R. Gani)

Composite “Pinch” Diagram

Temperature Minimum Amount ofCold Utility Required

Minimum Amount of Hot Utility Required

Process to Process Heat Integration

“Pinch” orTminimum

EnthalpyComputer Aided process Engineering - Lecture 11 (R. Gani)

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