multiple utilities2.pdf

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Typical Steam System

HP Steam

MP Steam

LP Steam

G

G

Furnace

Condenser

Fuel

Treated water

Condensing turbine

0.1 bara40 oC

Back pressure turbine



Typical Steam System (Cont’d)

Steam Boilers

100 barg Power Generation40 barg Normal maximum pressure for distribution40-10 barg Conventional distribution pressure levels

5 – 1.5 barg Low pressure steam from HP/MP steam or from w



Typical Steam System (Cont’d)

Steam is used extensively in most sites for:

indirect heating in steam heaters;steam tracing for pipes and storage tanks (i.e. steam pipes around the exteriothe materials inside from solidifying;direct heating of water through live steam injection;creation of vacuum in steam ejectors;

mass and heat exchange by live steam injection in distillation;reduction of partial pressure in gas-phase reactors;combustion processes to atomize fuel oil;injection into combustion processes to lower NO x emissions through reductitemperatureinjection into flares to assist the combustionpower generation in steam turbines.



Hot Oil Circuit

What is the minimum hot oil flowrate?

Furnace

Process DutyT return

T supply

T

H

T ret

T sup

Oil

Q



Furnace

TTFT= Theoretical Flame Temperature

T

H

T stack

QH

T TFT

StackLoss QFuel

T oFurnace

Tstack

Fuel

Air

T TFT

To



Refrigeration

W

Cooling Water

Expansionvalve

Expansionvalve

Level 1

Level 2



How do we TARGET for the BEST mix of utilities

THE GRAND COMPOSITE CURVE



Problem Table Algorithm (PTA)

Cascade DiagramPlot this on a T-H Di

T*intervalQHmin= 55

80

40

ZERO

30

45

QCmin = 20

Pinch



Cascade DiagramQHmin = 55

80

40

ZERO

30

45

QCmin = 20

T* QHmin = 55

QCmin

= 20



Relation with Composite Curve

T*

D H

QHmin = 55

QCmin = 20

T

Qcmin

D Tmin/2

D



The Grand Composite CurveQHmin = 55

80

40

ZERO

30

45

QCmin = 20

T* Hot Utility

Cold Utility

ExcesStream

Excess CStreams

‘Pockets’ of additiheat recovery



Grand Composite Curve (Cont’d)

The pinch divides GCC intoHeat SinkHeat Source

The grand composite curves

give the hot and cold utilityrequirements of the processboth in enthalpy andtemperatures

T* Hot Utility

Cold Utility

He

Heat



Utility Placement

T*

D H

HP Steam

Cooling Water

T*MP

Cooling Water

LP



Utility Placement

Each time a utility profiletouches the grand compositecurve

A new pinch (utility pinch ) iscreated

T*

MP

Cooling Water

LP





Utility Placement

T*

D HCooling Water

120 oC

CPmin

T supply = 300 oC290 oC

T return= 130 oC

D Tmin = 20 oC

T*

120 oC

CPmin

T supply =290 oC

D Tmin =

The pinch does nneed to be limiti



Utility Placement

Number of Steam LevelsMany levels – possibleCaution! – Each level costscomplexity

So, DON’T GO MAD!

T*

Pinc

QHmin



Utility Placement

Steam generation belo

T*

D

H

Pinch

QHmin~

~

180 oC

140 oC

100 oC

20 oC

Steam

60 oC

Cooling water



Utility Placement

Steam generation with boilerfeed water pre-heat andsuperheat

T*

Pi

QCmin

~~

180 oC

140 oC

120 oC

20 oC

Steam

60 oC Coo

160 oC

100oC

80 oC

40 oC

Evaporation

PreheatSuperheat



Utility Placement

Sometimes, the pocket should be used

IF (1) the pocket spans the temperature of two utilities

(2) The heat duty within the pocket is big enough to make it worthwhile

T*

D H

Pinch

QHmin~~

HP SteamGeneration

CW

T*

Pinc

QHmin~~

HP SteamGeneration

CW

LP SteamUsage



Utility Placement

Pinch temperature might be limiting stack temperature

T*

D H

CPmin

TTFT

T pinch

T acid dew

T o

Fu

Tstack

Fuel

Air

T TFT

T o



Utility Placement

Mixture of flue gas and steam*Note:Flue gas cooled down to pinch

T*

D H

FG

T*

FG

LP



Utility Placement - Refrigeration

What do you think the placement should be?





Utility Placement – Multiple Utilities

Utility and process can form an extra pinch – utility pinch

T*

D H

T Qhmn

Qcmin



Utility Placement

Where is the utility pinch?

We can’t always locate the utility pinch on the Grand Composite Curve (GC

T*

D H

T Qhmn

Qcmin



Utility Placement

The composite curves give the TRUE picture

we need to add the utilities back inform balanced composite curves



Balanced Composite Curves

Source and sink in perfect balanceAll utilities are includedAll pinches are shown

T

D H

FG

REFCW

ST



Balanced Composite Curves

Each utility pinch creates an additional design region within w

the appropriate utility is usedT

D H

HP

REFCW

LPUP

PP

UP

UP

UP

PP





Thank you for listening….



Multiple UtilitiesWorking Examples

l l l



Multiple Utilities

Problem Table ( D Tmin = 20 oC)

T* (oC) Cascade Heat Flow (MW)

540 30

510 42

490 44

390 24

310 0

190 60

150 52

90 64

50 56

M l i l U ili i



Multiple Utilities

1. Draw the Grand Composite Curve2. Determine how much steam can be produced at a saturation

temperature of 210 oC from boiler feedwater with tempera100 oC. (For steam D Hvap = 2000 kJ/kg, for boiler feedwate4.2 kJ/kg oC)

3. If flue gas is available (TTFT

= 1800 oC), determine the flu

W k h



Worksheet

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80

T* (oC)

D H (MW)



Solution – Multiple UtilitiesWorking Session

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multiple utilities2.pdf