Ache-high Pour Point Feb11

8/2/2019 Ache-high Pour Point Feb11

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THERMAL DESIGN OF

WITH HIGH POUR POINT FLUID

. .

Consultant, Equipment Engineering (Heat Exchangers)Foster Wheeler, Chennai, India

ec n ca resen a on

13th

HTRI CC Meet, Chennai, India14th February 2011

2011 Foster Wheeler. All rights reserved.


2/21

To develop Thermal Designas per HTRI program for

Air Cooled Heat Exchanger Unitfor fuel oil cooling having

high pour point, with an aim to illustrate the use of a simple

practical idea avoiding costly appurtenance.

2011FosterWheeler.Allrightsreserved.


3/21

Fuel oil conditions

Fluidname HighSulphurFuelOil(HSFO)

Parameter Units Case1 Case2

.

(allliquid)

.

(allliquid)

Temperature in/out DegC 131/84 129/65

*

Allowable pressuredrop

Kg/cm*2

.

3.5

.

2.5

Specific heat in/out Kcal/kgC 0.47/0.42 0.46/0.42

. . .

Thermalconductivity in/out Kcal/mhrC 0.09/0.1 0.09/0.1

Density

in/out Kg/m*3 973.4

/989 904

/923

Liq.surfacetension in/out Dyne /cm 30.7/33.7 27.5/32

Foulingresistance C hrm*2/Kcal 0.001 0.001


ourpo n eg


4/21

Air side conditions

Forced draft fan arrangement.

Design ambient air temperature = 42 C (Summer)

Minimum air temperature = 11 C (Winter)



5/21

Design compliance: Standards & Specifications

Design to comply with requirements of

API 661 / ISO 13706

and relevant project specifications



6/21

Design compliance: Minimum tube wall temperature API 661

As per API 661, when fluids with high pour points are handled, theminimum tube wall temperature attained during the operation shall bemaintained at or above the specified minimum tube wall temperature.

The specified minimum tube wall temperature shall be 14 C abovethe pour point of the fluid handled. Refer Table C.2.7 Table C1 ofAPI- 661 category 5.



7/21

HTRI Xace, program

Design modelling is done in HTRI Xace, for both the given cases atboth summer and winter ambient air conditions.



8/21

Salient features of the modelling

Bare tubes are used instead of conventional high fin tubes, as finned

surface did not help in improving heat transfer co-efficient of highv scous u .

A combination of bare tube & finned tubes also did not provideimprovement.

Hot air recirculation is not used, as suitable temperature control isobtained with tube side fluid flow reversal (co-current flow) in winter,without enhancin the set oint of desi n ambient air tem erature.

Counter-current air flow in summer and co-current air flow in winter isused to control minimum tube wall temperature in winter within API

For proper operation in both cases, a bay is isolated from operationin one case.



9/21

Salient features of the modelling

A distributed pass-type tube layout (two passes in a row) is used tohave even flow with proper velocity (at least 0.3 m/s) in tubes of highviscous fluid.

Tube inserts are not used since proprietary devices are not preferredby the user.



10/21

Controlling case

The controlling Case is Case 2 with higher heat duty.

However Case 1 is found to be pressure drop controlling.

Design performed for Case 2 with suitable geometry & configurationand then it is checked with Case 1 for passing.

Final design is one that passed both the cases with same geometryand configuration with required air flow control for each case.



11/21

Performance parameters

Parameter Units Case1 Case2

Flowrate Kg/hr Summer Winter Summer Winter

Designambient

air

Deg

C 42 11 42 11

empera ure

Flowpattern CounterCurrent

Co-

Current

Counter

Current

Co-

Current

Heatdut MM 4.138 5.572

Kcal/hr

No.ofBays(with2bundles) 4 5

Airfacevelocity m/s 0.85 0.42 2.5 0.69

Totalairflow 1000Kg/hr 955.6 467.2 3491 971.75

Mintubemetaltemp(HTRI

finalresults

line

8

DegC 59.2 65.6 48.03 46.8

Allowablemin.tubemetal

temperature

DegC 49 42

(AsperAPI661=Pourpoint+14C)


H2O

. . . .

Tubepressuredrop Kg/Cm*2 3.0 1.16 1.495 1.511


12/21

HTRI Minimum tube wall temperature Summer, Counter currentna es gn


A

partial

screen

shot

of

HTRI

output

of

the

case.


13/21

HTRI Minimum tube wall temperature Winter, Counter current

e ow e

specified

minimum

.

Thedesignisnot

acceptable


Apartial

screen

shot

of

HTRI

output

of

the

case.


14/21

HTRI Minimum tube wall temperature Winter, Co-current

Final Results

Released to the following HTRI Member Company:

Foster Wheeler Energy Ltd

FWEL

. .

HTRI CC 13

ACHE HIGH POUR POINT. CASE 2 WINTER(CO-CURRENT)

Simulation-Horizontal air-cooled heat exchanger forced draft co-current to cross flow

1 Process Data Airside Tubeside

u name

3 Fluid condition Sens. Gas Sens. Liquid4 Total flow rate (1000-kg/hr) 971.753 198.000 *

5 Weight fraction vapor, In/Out (--) 1.000 1.000 0.000 0.000

6 Temperature, In/Out (Deg C) 11.00 34.88 129.00 65.00

, . . . .

8 Wall temperature, Min/Max (Deg C) 46.73 83.42 46.80 83.77

9 Pressure, In/Out (kgf/cm2A) 1.033 1.033 6.033 4.523

10 Pressure drop, Total/Allowed (mmH2O) (kgf/cm2) 1.508 0.000 1.511 2.500

11 Pressure Drop, A-frame reflux section (kgf/cm2)- . .

13 - In/Out (m/s) 0.31 0.31

14 Film coefficient, Bare/Extended (kcal/m2-hr-C) 28.39 28.39 32.39

15 Mole fraction inert (--)

16 Heat transfer safety factor (--) 1 1

17 Fouling resistance (m2-hr-C/kcal) 0.000000 0.001000


ApartialscreenshotofHTRIoutputofthecase.


15/21


16/21


17/21

Bundle configuration: Pass arrangement

Passes

1

Tubesidein

VentRows

3 3

66

4

7

5

2

3

4

510 9

7 810

SPLITBUNDLESDrain

Vent

A

7

6

8

9

12

13

11

14

15

18

11

14

15

18

16

17

TubesideoutDrain

1919 20

ViewA


Bundle

is

split

into

two,

due

to

weight

limitations


18/21

Other accessories for operation

A steam coil and outlet louvres are suggested so that the bundlecan be warmed for start-up and to unfreeze if there is congealingin the tubes.

Variable Frequency Drive (VFD) control of air flow for processoutlet temperature.



19/21

Schematic arrangement of the Air Cooled Heat Exchanger

ALL DIMENSIONS IN mm

T1 V

OUTLET

LOUVRES

BUNDLES

T2

D

(COLUMN CENTRES)

HTRI Model

Apartialscreenshotof

HTRIoutput

.

(COLUMN

OneBay

neB

undle

CENTRES)O



20/21

Conclusion

The final design is an optimised unit which avoided the need ofcostly boxed-up hot air recirculation cabins.

It is recommended that for every case of high pour point fluid

cooling, counter current / co- current design shall be examinedfirst before deciding the need of hot air recirculation.

When the pour point is high enough, and not able to obtain acontrol of minimum tube wall temperature as per API 661, hot air

recirculation must be used.


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Ache-high Pour Point Feb11

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