Post on 13-Jan-2020
Prof Barry Crittenden, Dr Mengyan Yang
FOULING THRESHOLDS IN BARE TUBES AND TUBES FITTED WITH INSERTS
University of Bath
Department of Chemical Engineering
Sustainable Thermal Energy Management Conference
SusTEM2010
Newcastle 2-3 November 2010
OUTLINE
1. The crude oil fouling problem
2. Experimental results from bare tube and
tube fitted with a hiTRAN insert
3. Computational fluid dynamics3. Computational fluid dynamics
4. Equivalent linear velocity for tubes fitted
with inserts
5. Fouling model & threshold modelling
6. Conclusions
PARTNERSHIP
Centre for Process IntegrationSchool of Chem Eng & Analytical Science
University of Manchester
PO Box 88, Sackville Street
Manchester M60 1QD
Prof Robin Smith
Dr Jin-Kuk Kim
Cal Gavin Ltd
Minerva Mill Innovation CentreStation Road
Alcester B49 5ET
Dr Jin-Kuk Kim
Dr Igor Bulatov Martin Gough
Department of Chem Eng
University of Bath
Bath BA2 7AY
Prof Barry Crittenden
Dr Mengyan Yang
Embaffle B.V
Coengebouw
Kabelweg 37, 1014 BA
Amsterdam
Stuart Oakley
Eric van der Zijden
CRUDE OIL PREHEAT EXCHANGER TRAIN
Between 16 and 60 shell & tube exchangers in the pre-heat train
DEPOSITS IN CRUDE PREHEAT EXHANGER TRAINS
DOWNTIME, BUNDLE PULLING AND CLEANING
01E102 rf
0.02
0.025
0.03
TYPICAL GROWTH IN HEAT EXCHANGER FOULING RESISTANCE
Thermal resistance
0
0.005
0.01
0.015
01/0
8/20
0401
/09/
2004
01/1
0/20
0401
/11/
2004
01/1
2/20
0401
/01/
2005
01/0
2/20
0501
/03/
2005
01/0
4/20
0501
/05/
2005
01/0
6/20
0501
/07/
2005
01/0
8/20
0501
/09/
2005
01/1
0/20
0501
/11/
2005
01/1
2/20
0501
/01/
2006
01/0
2/20
0601
/03/
2006
01/0
4/20
06
01E102 rf
Date
SCHEMATIC OF THE PILOT-SCALE PARALLEL TUBE APPARATUS
0
0.0002
0.0004
0.0006
0.0008
0.001
0 1 2 3 4 5
Linear velocity (m/s)
Fo
ulin
g r
ate
(K
m2W
01h
-1)
523K 538K 543K 553K
0
0.0001
0.0002
0.0003
0.0004
0 0.5 1 1.5 2 2.5
Liner velocity (m/s)
Fo
ulin
g r
ate
(K
m2W
-1h
-1)
523K 538K
Bare MDI insert
EXPERIMENTAL CONDITIONS
Velocity Re Initial (clean) surface temperature
(m/s) 250°C 265°C 270°C 280°C
0.5 3600 Bare & MDI Bare & MDI N/A Bare
0.8 5800 Bare N/A N/A Bare
1.0 7300 Bare & MDI Bare & MDI Bare Bare
1.5 11000 Bare & MDI Bare & MDI Bare Bare
1.8 14500 Bare & MDI Bare Bare Bare
2.0 21800 Bare Bare Bare Bare
3.0 26200 Bare Bare Bare Bare
4.0 29000 Bare Bare Bare Bare
hiTRAN TUBE INSERTS
Reproduced from www.calgavin.com
FOULING THRESHOLD CONDITIONS
Temperature
(K)
Linear velocity
bare tube
(m/s)
Linear velocity
tube with insert
(m/s)
523 4.01 2.23
538 4.16 2.43
543 4.48 No data
553 4.58 No data
Over the surface of heat exchanger tubes, in particular with tubes fitted with inserts, it is desirable to know:
The velocity distribution
The shear stress distribution
The temperature distribution
NEED TO KNOW
The temperature distribution
The heat flux distribution
CFD simulation can provide answers for both bare tubes and tubes
with inserts
k-ε model – basic equations
Equation of continuity
Equation of momentum
Equations of turbulent kinetic energy (k) and dissipation rate of turbulent energy (ε):
CFD SIMULATION USING COMSOL SOFTWARE
( ) ( )[ ] ρεησ
ηηρ
ρ−∇+∇+
∇
+⋅∇=∇⋅+
∂
∂ 2T
T
k
T uukkut
k
k
( ) ( )[ ]k
CuukCCut
TT
2
2
2
1
ερρε
σ
ηηερ
ερεµε
ε
−∇+∇+
∇
+⋅∇=∇⋅+
∂
∂
For the heat transfer equations, the turbulence results in an effective
thermal conductivity keff :
keff = ko + kT
kT = CpηT/PrT
CFD SIMULATION FOR FLUID FLOW IN BARE TUBE
Velocity field for flow in bare tube of 19 mm ID
Axial symmetric geometry, the upper boundary
represents the central axial.
Left end: inlet; Right end: outlet
Inlet velocity: 1m/s, bulk temperature: 423K
Shear stress can be calculated from the turbulent viscosity and velocity gradient obtained by CFD.
COMPARISON OF THE SHEAR STRESS OBTAINED
BY CFD AND FRICTION FACTOR METHODS
Velocity (m/s) Shear stress
CFD
(Pa)
Shear stress
Friction factor
(Pa)
Re Friction factor
0.5 0.8 0.8 6909 0.0087
1 2.9 2.8 13818 0.00731 2.9 2.8 13818 0.0073
2 9.9 9.3 27636 0.0061
3 19.2 18.9 41455 0.0053
4 32.2 31.3 55273 0.0052
CFD SIMULATION FOR FLUID FLOW IN TUBE WITH INSERTS
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
WALL SHEAR STRESS DISTRIBUTION
20.00
30.00
40.00
50.00
60.00
Sh
ea
r s
tre
ss
(P
a)
0.00
10.00
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
COMPARISON OF THE SHEAR STRESS VALUES BETWEEN BARE TUBE AND TUBE WITH INSERTS OBTAINED BY CFD
Velocity (m/s) Wall shear stress
Bare tube (Pa)
Lowest wall shear stress
Tube with insert (Pa)
0.5 0.8 1.3
1.0 2.9 6.4
2.0 9.9 38
PRESSURE DROPS OBTAINED BY CFD SIMULATIONAND MEASURED BY CAL GAVIN
Linear velocity
(m/s)
Pressure drop (kPa/m)
hiTRAN® data
Pressure drop (kPa/m)
CFD simulation
0.5 2.53 4.43
0.8 5.94 6.880.8 5.94 6.88
1.0 9.00 13.12
1.6 21.91 25.33
2.0 33.76 38.46
EQUIVALENT VELOCITY OF THE TUBE FLOW WITH MEDIUM DENSITY INSERTS
Equivalent velocity = 0.2461x2 + 1.1369x
R2 = 0.999
2
2.5
3
3.5
4
4.5
5
Eq
uiv
ale
nt
bare
tu
be
velo
cit
y (
m/s
)
15
20
25
30
35
40
45
Sh
ear
str
ess (
Pa)
■: Velocity; ¤: Shear stress
0
0.5
1
1.5
2
0 0.5 1 1.5 2 2.5 3
Velocity - Tube with inserts (m/s)
Eq
uiv
ale
nt
bare
tu
be
velo
cit
y (
m/s
)
0
5
10
15
Sh
ear
str
ess (
Pa)
APPLICATION OF THE MODEL DEVELOPED FOR FOULING
IN BARE TUBE TO TUBE WITH INSERTS
• Modify 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.
• Use the equivalent linear velocity in the fouling growth term:
• Adopt the concept of equivalent linear velocity which will allow the fouling
data obtained from experiments with a bare tube to be used for prediction
of the fouling inside a tube fitted with an insert.
wm
ssfm
sfmfC
RTETCuB
TuCA
dt
dRτ
µρ
µρ−
+=
−−
−
)/exp(13/23/13/123
3/43/23/2
COMPARISON OF EXPERIMENTAL DATA AND MODEL FITTING
Bare tube
0.00010
0.00020
0.00030
0.00040
Fo
uli
ng
rate
(K
m2/W
h)
0.00000
0 1 2 3 4 5
Linear velocity (m/s)
Fo
uli
ng
rate
(K
m2/W
h)
Experimental data: fouling rate of Maya crude at constant
wall temperature (523K) for the bare tube (Don Philips 1999).
Model parameter E: 50.2 kJ/mol
COMPARISON OF EXPERIMENTAL DATA AND MODEL FITTING
Tube with medium density hiTRAN insert
0.0001
0.0002
0.0003F
ou
lin
g r
ate
(K
m2W
-1h
-1)
0.0000
0.0001
0 0.5 1 1.5 2 2.5 3 3.5
Equivalent Linear velocity (m/s)Fo
ulin
g r
ate
(K
m
Experimental Model fitting
MODEL APPLICATION
0.0001
0.001
Pre
dic
ted
fo
uli
ng
rate
(K
m2/w
h)
0.00001
0.00001 0.0001 0.001
Actual fouling rate (Km2/wh)
Pre
dic
ted
fo
uli
ng
rate
(K
m
Experimental data: Fouling test results of Maya crude in bare tube and tube fitted with medium density insert (Crittenden et al. 2009).
Model parameter E: 50.2 kJ/mol by curve fitting
THRESHOLD CONDITIONS
Bare tube and tube with insert
520
530
540
550
560
Th
resh
old
tem
pera
ture
(K
)
500
510
3.00 3.50 4.00 4.50 5.00
Velocity/Equivalent velocity (m/s)
Th
resh
old
tem
pera
ture
(K
)
Experimental Model predicted
Experimental data: Fouling test results of Maya crude in bare tube
and tube fitted with medium density insert (Don Phillips 1999).
CONCLUSIONS & FUTURE
Parallel tube apparatus has provided crude oil experimental data as a function of linear velocity and surface temperatures with and without
hiTRAN inserts fitted.
CFD modelling allows prediction of surface shear stresses for both bare tubes and tubes fitted with inserts.
The concept of equivalent velocity can be used in Yeap’s fouling model
to draw together the fouling experimental results for Maya crude oil in to draw together the fouling experimental results for Maya crude oil in both a bare tube and a tube fitted with a hiTRAN insert.
The modified Yeap model can also be used to predict he fouling
threshold conditions for both bare tubes and tubes fitted with inserts.
Further CFD simulation will be carried out for the temperature
distributions in bare tubes and tubes fitted with hiTRAN inserts.
The research will be repeated with the Embaffle system, although validation of the CFD predictions will be much more difficult.