Composite Curve (Smith, R., 2005) Two-stream heat recovery problem

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Department of Chemical Engineering - UPN “Veteran” Yogyakarta Page 1 of 15

VIII

HEAT INTEGRATION

Dr. Eng. Yulius Deddy Hermawan

Department of Chemical Engineering

UPN “Veteran” Yogyakarta

Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY

Outline

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Department of Chemical Engineering - UPN “Veteran” Yogyakarta Page 2 of 15 Dr. Eng. Y. D. Hermawan – ChemEng - UPNVY

VIII.1

HEAT EXCHANGER NETWORK

Composite Curve (Smith, R., 2005)

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T-H Diagram

160 150 140 130 120 110 100 90 80 70 60 50 40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

D

H (MW)

T (

o

C)

(4)

HE stream data for two hot streams and two cold streams

(5)

The hot streams can be combined to obtain a composite curve

(6)

Plotting the hot and cold composite curves together allows the

targets for hot and cold utility to be obtained

Increasing

D

T

min

from 10

o

C to 20

o

C

(7)

Shifted temperatures

D

T

min

= 10

o

C

Stream

Type

Supply

temperature

T

S

(

o

C)

Target

temperature

T

(

o

C)

D

H

(MW)

Heat capacity

flowrate

CP

(MW.K

-1

)

Shift

temperature

T

S*

(

o

C)

Shift

temperature

T

T*

(

o

C)

Reactor 1 feed

Cold

20

180

32.0

0.20

25

185

Reactor 1 product Hot

250

40

-31.5

0.15

245

35

Reactor 2 feed

Cold

140

230

27.0

0.30

145

235

Reactor 2 product Hot

200

80

-30.0

0.25

195

75

The Problem Table Algorithm: Stream Population

Interval temp.

245 250

235 240 230

195 200 190 200 185 180 190 180 190

145 140 150 140 150

75 70 80 80

(8)

The Problem Table Algorithm: the problem table cascade

Interval

temp. DTINTERNAL (o_C)

∑CPC

-∑CPH

[MW.K-1_]

DHINTERNAL

[MW]

Surplus/

Deficit _{Utility MW}Hot _{Utility MW}Hot

245 250 0 7.5QHmin

235 240 230 10 -0.15 -1.5 Surplus -1.5 1.5 -1.5 9

195 200 190 200 40 0.15 6.0 Deficit 6.0 -4.5 6.0 3.0

185 180 190 180 190 10 -0.10 -1.0 Surplus -1.0 -3.5 -1.0 4.0

145 140 150 140 150 40 0.10 4.0 Deficit 4.0 -7.5 4.0 0.0

75 70 80 80 70 -0.20 -14.0 Surplus -14.0 6.5 -14.0 14.0

35 30 40 40 0.05 2.0 Deficit 2.0 4.5 2.0 12.0

25 20 10 0.20 2.0 Deficit 2.0 2.5 2.0 10.0QCmin

Cold

Utility UtilityCold Stream Population

1

3 2

4

Simple Design for Maximum Energy Recovery



To produce minimum utility load:

1. Don’t transfer heat across the Pinch

2. Don’t use cold utilities above

3. Don’t use hot utilities below



Design is produced by:

1. Dividing the problem at the pinch, and designing each part

separately

2. Starting the design at the pinch and moving away

3. Immediately adjacent to the pinch, obeying the constraints:

CP

HOT

≤

CP

COLD

(above)

CP

HOT

≥

CP

COLD

(below)

4. Maximising exchanger load

(9)

Example problem stream data, showing pinch

Pinch

[MW.K

CP

-1

]

250 150 150 40 0.15

200 150 150 80 0.25

180 140 140 20 0.20

230 140 140 0.30

Q

Hmin

7.5

Q

Cmin

10.0

2

4

1

3

Heat Exchanger Above the Pinch

Pinch

250 203.3 150

200 150

180 140

230 205 181.7 140

2

4

H

7.0 MW

12.5 MW

7.0 MW

7.5 MW



Starting the design at the

pinch and moving away



Immediately adjacent to

the pinch, obeying the

constraints:

CP

_HOT

≤

CP

_COLD

(above)

(10)

Heat Exchanger Below the Pinch



Starting the design at the

pinch and moving away



Immediately adjacent to

the pinch, obeying the

constraints:

CP

_HOT

≤

CP

_COLD

(above)

CP

_HOT

≥

CP

_COLD

(below)

Pinch

150 106.7 40

150 80

140 52.5 20

140

1

3

C

17.5 MW 6.5 MW

10 MW

A design that achieves the energy target:

(11)

A design that achieves the energy target:

Process Flow Diagram with Energy Integration Scheme

Assignment: 8.1.

1. Sketch the composite curves for

D

T

_min

= 10

o

C !

2. From the composite curves, determine the target for hot and cold utility

for

D

T

_min

= 10

o

C !

3. Develop grid diagram (heat exchanger network) for this case !

Stream data for Assignment 8.1.

Stream Type Supply temp.

TS (oC)

Target temp.

TT (oC)

Heat Duty

D_{H (MW)}

Heat capacity flowrate

CP

(MW.K-1)

(12)

VIII.2

REACTOR HEAT INTEGRATION

Characteristics of Reactor Heat Integration

1. Adiabatic Operation

:

leads to an acceptable temperature rise for exothermic reactors or

an acceptable decrease for endothermic reactors.

2. Heat Carriers

:

If adiabatic operation produces an unacceptable rise or fall in

temperature, then the option is to introduce a heat carrier. The

operation is still adiabatic, but an inert material is introduced with

the reactor feed as a heat carrier.

3. Cold Shot

:

(13)

Reactor Heat Integration

HEATER

(UTILITIES)

REACTOR

COOLER

(UTILITIES)

FEHE

Feed

Effluent (Reactor Products)

A Complex Energy Integrated of HDA Process

Separator

PFR Cooler

Furnace

Quench H2feed

Compressor Purge Gas recycle

Fuel

Benzene Product Column

FEHE-1 FEHE-2 FEHE-3

Diphenyl Toluene feed To lu en e re cy cl e Recycle Column CR Methane Stabilizer Column

R3 R2 R1

(14)

4841 lbmole/hr

1150

o

F

521 psia

4841 lbmole/hr

146

o

F

600.5 psia

69 MMBtu/hr

Feed of Reactor need to be heated

Effluent of Reactor need to be cooled

4944.3 lbmole/hr

1150

o

F

504 psia

74.83 MMBtu/hr

4944.3 lbmole/hr

113

o

F

469.2 psia

(15)

Process flow diagram of Feed-Effluent-Heat-Exchanger

4944.3 lbmole/hr 1150 o_F

504 psia

3.36 MMBtu/hr

4944.3 lbmole/hr 222o_F

472.4 psia 4841 lbmole/hr

146o_F

600.5 psia

4841 lbmole/hr 1106 o_F

564.7 psia

4841 lbmole/hr 1150 o_F

564.7 psia

4944.3 lbmole/hr 113 o_F

469.2 psia 9.1 MMBtu/hr

65.7 MMBtu/hr

Heat Duty of Heat Exchanger Processes

(Comparation between process WITH and WITHOUT energy integration)

Heat

Exchanger

Heat Duty (MMBtu/hr)

With Energy

Integration

Without Energy

Integration

Furnace

69

3.36

Condenser

74.83

9.1