Professor Barry Crittenden Department of Chemical Engineering

Professor Barry Crittenden

Department of Chemical Engineering

University of Bath, Bath, UK, BA2 7AY

INTENSIFIED HEAT TRANSFER TECHNOLOGIES FOR ENHANCED HEAT RECOVERY - INTHEAT

INTHEAT KICK-OFF MEETING 17 DECEMBER 2010


1. Bath and its University

2. INTHEAT work packages

3. Experimental capability

4. CFD capability

5. Fouling & threshold model capability

6. Compensation plot

OUTLINE


Population 85,000(with two Universities)

UNESCO World Heritage City

Excellent transport links

40 km from Bristol International Airport

160km west of London

CITY OF BATH


Received Charter in 1966

Located on a hill overlooking the City of Bath

13,000 students, including 3,400 international students

from over 100 countries

THE UNIVERSITY OF BATH

Modern campus-based university on a 81 hectare site

Consistently within the top 10 UK universities in national league tables

Research-driven, with high quality teaching and a small, friendly campus

Three Faculties:Engineering & Design

Science Humanities & Social Science

&School of Management

Department of Chemical Engineering

(9 West)


Work Package

Title Months(Bath)

WP1 Analysis of intensified heat transfer under fouling*

14

WP2 Combined tube-side & shell-side heat exchanger enhancement

1

WP3 Heat exchangers made of plastic material 0

WP4 Design, retrofit and control of intensified heat recovery networks

9

WP5 Putting into practice 4

WP6 Technology transfer 4

WP7 Project management 0

INTHEAT WORKPLAN TABLES

* Lead: Bath


Overall objective: Enhancing our understanding of heat exchange under fouling

▪ To develop an advanced CFD tool to improve the heat exchanger performance by adjusting both operating conditions and equipment geometry

▪ To gain in-depth understanding of fouling mechanisms and kinetics of fouling through experiments

Task 1.1: Experimental fouling investigation

Task 1.2: CFD research on heat transfer

Task 1.3: Testing of possible anti-fouling additives

Deliverable D1.1: Report on technical review of fouling and its impact on heat transfer (Month 3)

Deliverable D1.2: Report on experimental fouling investigation and CFD research on

heat transfer enhancement (Month 12)

Participant Short name Person-months

1 PIL 1.5

2 CALGAVIN 4

3 SODRU 2.5

4 MAKATEC

5 OIKOS

6 UNIMAN 3

7 UNIBATH 14

8 UPB 2

9 UNIPAN 6

10 EMBAFFLE

Total 33

INTHEAT WORK PACKAGE 1


FOULING CAN BE VERY COMPLEX AND EXPENSIVE


23

0 m

m a

ppro

xim

ate

ly

t wb t ws

t bulk

INS

UL

AT

ION

INS

UL

AT

ION

© 2008 University of Bath, England

t wm

Fil Level

Finger (Mild Steel)BS 070M20

Section A-A

26.00 Ø

73

.00

twm

twb

tws Hea

ted

Re

gio

n0

– 60

0 W

Heat Flux0 – 120 kW m2

Fouling Region

19.00

A A

Up to 30 bar

Up to 300oC bulk

Up to 400oC surface

Up to 120 kW/m2 flux

q

TTR sostf

EXPERIMENTAL FACILITY


TYPICAL FOULING CURVE (CRUDE B, ≈ 6 WT% ASPHALTENE)

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0 1 2 3 4 5 6 7

Time (hours)

Rf

m

2 K

kW-1

Rf Petronas (b) - Asphaltene 6 % wt

Linear (y = 0.0181x - 0.021 R2 = 0.9193)

-

http://www.imperial.ac.uk/crudeoilfouling20 February 2008

B.D.Crittenden, M.Yang, A.Young & W. Hall

NB tso ≈ 375 ºC,tbulk= 260 ºC

Shear Stress ≈ 0.5 Pa

= 5.0 E -06 m2 K kJ -1

Stirred cell conditions: 500 W & 200 rpm (Tso≈ 375oC; Reynolds Number = 12700)

For comparison: BP Rotterdam; Downey et al., 1992

Initial fouling rate = 3.5 E-07 m2K kJ-1;Tso = 260oC; Re = 30,000


ARRHENIUS PLOT FOR PETRONAS B (@ 200 RPM)

y = -5.9629x - 3.2528R2 = 0.9182

-12.8

-12.6

-12.4

-12.2

-12

-11.8

-11.6

-11.4

1.4 1.42 1.44 1.46 1.48 1.5 1.52 1.54 1.56 1.58 1.6

ln (

dR

fo/d

t)

EA = 49.47 kJ mol-1

ln (dRf / dt) = A – E/RT

1000/T (K)


EFFECT OF SURFACE SHEAR STRESS ON FOULING RATE (CRUDE A)

Shear stresses are obtained by CFD simulation for different stirring speeds

-1.00E-08

-8.00E-09

-6.00E-09

-4.00E-09

-2.00E-09

0.00E+00

2.00E-09

4.00E-09

6.00E-09

8.00E-09

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Surface shear stress (Pa)

dR_f

/dt (

m^2

K J^

-1)

600 K 610 K 620 K 630 K 640 K 650 K 660 K

Increasing the wall shear stress decreases the rate of fouling for any given surface temperature.

Negative fouling with existing deposits can occur for low surface temperatures and high surface shear stresses; this means fouling deposit being removed by surface shear stress.


PETRONAS B: 2D CFD SIMULATION FLOW & TEMPERATURE FIELDS

200 rpm, 500W, 106 kW/m2

Streamlines are shown in both gas and oil phases


SIMULATION FOR ACTUAL 3-D GEOMETRY

Petronas B, 500W, average heat flux: 106 kW m-2, 200 rpm

Velocity field Temperature field


Velocity field

Z (flow direction)

0 0.013

Tube (19mm ID) with medium density inserts (hiTRAN)

Linear flow rate: 1m/s, bulk temperature: 423K

Vertical slice

CFD SIMULATION FOR FLUID FLOW IN TUBE WITH INSERTS


WALL SHEAR STRESS DISTRIBUTION

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016

Position in z direction

Sh

ea

r s

tre

ss

(P

a)

0.5m/s 0.7m/s 1m/s 1.5m/s

Shear stress data are obtained from the velocity gradient and the turbulent viscosity by CFD simulation

Z position begins at just behind the loop edge, ends at the same position of the next loop


PARTICLE SEDIMENT TEST AT CAL GAVIN

Sediments seem to form behind the loop where the shear stress is a minimum


EQUIVALENT VELOCITY CONCEPT FOR ENHANCED SURFACES

Equivalent velocity = 0.2461x2 + 1.1369xR2 = 0.999

00.5

1

1.52

2.53

3.5

44.5

5

0 0.5 1 1.5 2 2.5 3

Velocity - Tube w ith inserts (m/s)

Eq

uiv

alen

t b

are

tub

e ve

loci

ty (

m/s

)

0

5

10

15

20

25

30

35

40

45

Sh

ear

stre

ss (

Pa)

■: Velocity; ¤: Shear stress

Obtain equivalent bare tube velocity by matching surface shear stress of enhanced surface with that of a bare tube

Example: hiTRAN medium density insert


APPLICATION OF THE MODEL DEVELOPED FOR FOULING IN BARE TUBE TO TUBE WITH INSERTS

▪ Modified Yeap’s model – replace the velocity in the fouling suppression term with wall shear stress. This model is capable of modelling the effect of velocity more accurately including the velocity maximum behaviour seen for Maya crude

▪ Using equivalent linear velocity in the fouling growth term:

▪ Adopting the concept of equivalent linear velocity would allow the fouling data obtained from experiments with bare tubes to be used for prediction of the fouling in tubes with inserts.

wm

ssfm

sfmf CRTETCuB

TuCA

dt

dR

)/exp(1 3/23/13/123

3/43/23/2


MODEL APPLICATION

0.00001

0.0001

0.001

0.00001 0.0001 0.001

Actual fouling rate (Km2/wh)

Pre

dic

ted

fo

uli

ng

rate

(K

m2/w

h)

Experimental data using Maya crude oil in both a bare tube and a tube fitted with medium density hiTRAN insert (Crittenden et al. 2009).

Activation energy E = 50.2 kJ/mol by curve fitting


THRESHOLD CONDITIONS

For a bare tube and tube fitted with an insert

500

510

520

530

540

550

560

3.00 3.50 4.00 4.50 5.00

Velocity/Equivalent velocity (m/s)

Th

resh

old

tem

per

atu

re (

K)

Experimental Model predicted

Experimental data using Maya crude in bare tube and tube fitted with medium density insert (Don Phillips 1999).


COMPENSATION PLOT FOR ALL CRUDE OIL FOULING

-20

-10

0

10

20

30

40

50

0 50 100 150 200 250 300

EA (kJ mol-1)

ln[A

(m2 K

/ kJ

)]Crude ACrude BMaya crude oil (Crittenden et al. 2009)Kuwaiti crude oil (Bennett et al. 2009)Desalted crude oil (Knudsen et al. 1999)Shell Westhollow crude oil (Panchal et al. 1999)Exxon refinery crude oil (Scarborough et al. 1979)Shell Wood River crude oil (Panchal et al. 1999)

baEAn A

□: New points added – Crude A

Whether the effect is “true” or “false” is not known at present but is probably “false”.

Crittenden B D, Kolaczkowski S T, Takemoto T and Phillips D Z, Crude oil fouling in a pilot-scale parallel tube apparatus, J Heat Transfer Eng, 30: 777-785, (2009)


ISSUES RELATING TO APPARENT ACTIVATION ENERGY

Apparent activation energies increase with increasing wall shear stress (ie with velocity & Re).

Phenomenon has been observed before for reaction and crude oil fouling systems:

Crittenden B D, Hout S A, Alderman N J, Model experiments of chemical reaction fouling, TransIChemE 65A: 165-170, (1987).

Crittenden B D, Kolaczkowski S T, Takemoto T and Phillips D Z, Crude oil fouling in a parallel tube apparatus, J Heat Transfer Eng 30: 777-785, (2009).

Bennett C A, Kistler R S, Nangia K, Al-Ghawas W, Al-Hajji N and Al-Jemaz A, Observation of an isokinetic temperature and compensation effect for high temperature crude oil fouling, J Heat Transfer Eng 30: 794-804, (2009).

Young A, Venditti S, Berrueco C, Yang M, Waters A, Davies H, Hill S, Millan M and Crittenden B D, Characterisation of crude oils and their fouling deposits, J Heat Transfer Eng (in press, 2011).

Apparent activation energies increase also with fouling threshold temperatures.

Threshold fouling models must use apparent activation energies; if actual activation energies are used then they must be modified using shear stress (or velocity or Re) such as Ebert & Panchal.

This begs the question: how can the actual activation energy be determined for use in the Ebert & Panchal, Epstein, and Yeap models?


CONCLUSION

Batch stirred cell can be used to provide crude oil experimental data under various conditions of bulk temperature, surface temperature and surface shear stresses. Threshold conditions can be obtained. Chemicals can be added but long-term non-fouling experiments are not desirable. Within limits, the cell can be used with enhanced surfaces.

3-D CFD modelling allows predictive study of geometric changes including the use of enhanced surfaces.

Using the concept of equivalent velocity, a model that has been validated for a bare tube can then be applied to a tube with enhanced surfaces. Moreover, the fouling threshold conditions can be predicted.

Temperature and heat flux distributions can also be simulated by CFD.

Enhanced external surfaces need to be studied in much the same way. Some experimental validation would, in principle, be possible by adding a simple enhancement to the heat transfer surface of the batch stirred cell.


QUESTIONS?

Date post:	07-Jan-2016
Category:	Documents
Upload:	giolla
View:	39 times
Download:	0 times

Professor Barry Crittenden Department of Chemical Engineering

Documents