PARTICULATE FOULING OF SENSIBLE HEAT EXCHANGERS by ALAN PAUL WATKINSON B ...

198 Pages·2011·10.96 MB·English

PARTICULATE FOULING OF SENSIBLE HEAT EXCHANGERS
by
ALAN PAUL WATKINSON
B. Eng., McMaster University, 1962
M.A.Sc, University of British Columbia, 1966
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
In the Department
of
CHEMICAL ENGINEERING
We accept this thesis as conforming to the
required standard
THE UNIVERSITY OF BRITISH COLUMBIA
September,1968
In presenting this thesis in partial fulfilment of the requirements for
an advanced degree at the University of British Columbia, I agree that
the Library shall make it freely available for reference and Study.
I further agree that permission for extensive copying of this thesis
for scholarly purposes may be granted by the Head of my Department or
by his representatives. It is understood that copying or publication
of this thesis for financial gain shall not be allowed without my
written permission.
Department
The University of British Columbia
Vancouver 8, Canada
Date 2.<\
i
ABSTRACT
Fouling by a petroleum gas o il and a dilute suspension of
sand in water was studied as a function of mass flow rate and
wall temperature. The experiments were carried out by circulating
the liquid through a single tube maintained at constant heat
flux by electrical heating. The change in fouling resistance
and pressure drop with time was measured. The fouling resistance
of the water and of the o il at low heat fluxes grows to an asymp
totic value. At higher heat fluxes the o il fouling resistance
increased almost linearly with time after an induction period.
The asymptotic fouling resistance of both the o il and the water
decreased with increasing mass flow rate. At constant clean tube
wall temperature the initial fouling rate of the o il decreased
with increasing mass flow rate. The initial fouling rate of the
water increased with increasing mass flow rate up to a critical
mass flow rate, and then decreased with further increases in
mass flow rate. At constant mass flow rate, the initial fouling
rate of the o il depended exponentially on the clean tube wall
temperature. An activation energy of 29 Kcal/mole was calcu
lated for the o il fouling process by fitting the initial fouling
rate data to an Arrhenius type of equation. The pressure drop
increase showed the same general trends with mass flow rate and
tube wall temperature as did the fouling resistance.
Fouling resistances for heated Kraft cooking liquor, cal
culated from pulp mill operating data and from a single fouling
experiment, appeared to follow similar trends to those, followed
in common by the gas o il and the water.
The experimental results of this study were compared to
the mathematical model of Kern and Seaton. While the shape of
most fouling curves was in agreement with that predicted generally
by this model, dependence of the initial fouling rate and of the
asymptotic fouling resistance of the gas o il on the mass flow
rate were both in disagreement with the detailed predictions of
the model. For low mass flow rates of the water, however, even
"the detailed predictions were borne out. It was, moreover,
possible to remove part of the sand deposit by increasing the
velocity of the water, in accord with the postulated removal
mechanism of Kern and Seaton, but the coke-like deposit from
the gas o il could not be similarly removed by increasing the o il
velocity.
Mathematical models are developed in which the deposition
term is written as the product of a material flux to the wall
region and a sticking probability, after Parkins, and the removal
term depends on the shear stress, after Kern and Seaton, Specific
cases are considered where deposition is controlled by transfer
to the surface, adhesion at the surface, and a combination of
both steps.. Where deposition is controlled partly by transfer
and partly by adhesion, the model predicts mass flow rate and
temperature dependence of the initial fouling rate in agreement
with the experimental results found for the oil. The observed
asymptotic fouling resistance of the o i l, however, depended less
strongly on the reciprocal of the mass flow rate than is predicted
by the model. Where transfer alone controls the deposition
process, the extended model reduces to a form similar to that
of Kern and Seaton.
iv
TABLE OF CONTENTS
Page
ABSTRACT i
LIST OF TABLES vi
LIST OF FIGURES viii
ACKNOWLEDGEMENTS x i :L
1. INTRODUCTION..... 1
2. PERTINENT PRIOR WORK 5
3. SCOPE AND METHOD OF PRESENT WORK 18
4. SELECTION OF WORKING FLUIDS. „, 2 0
5,0 APPARATUS 23
6. EXPERIMENTAL PROCEDURES 3 6
7. RESULTS AND DISCUSSION 39
a) Calculation Methods. 39
b) Initial Experiments on Gas Oil Fouling 46
c) Effect of Mass Flow Rate on Fouling of Oil.. 48
d) Effect of Wall Temperature on Fouling of Oil 60
e) Combined Effects.of Mass.Flow.Rate.and Wall.
Temperature 62
f) Local Fouling Rates 68
g) Nature of Deposits in Gas Oil Fouling „ 69
h) Reproducibility of Gas Oil Results and
Somparison with Tabulated.Fouling Factors... 75
i) Sand-Water Fouling................ 76
j) Kraft Liquor Fouling 89
8. EXTENSION OF EXISTING FOULING MODELS 95
9. CONCLUSIONS 124
10, RECOMMENDATION FOR FURTHER WORK.. 12 7
11. LIST OF REFERENCES 12 9
12. NOMENCLATURE 134
Appendix 1. Calibration of Equipment. 1-1
a) Thermocouple Calibration 1-1
b) Differential Pressure Cell Calibration 1-6
c) Orifice Plate Calibration 1-10
Appendix 2. Calculation.of.the.Heat.Transfer Coef
ficient 2-1
a) Determination of the Heat Flux 2-1
b) Inside Tube Wall Temperature 2-3
c) Determination.of the Mean Temperature
Difference 2-3
d) Sample Calculation 2-5
e) Dimensions of Test Sections II and III 2-10
Appendix 3. Experimental Data 3-1
vi
LIST OF TABLES
Table Page
I, Properties of a Typical Gas Oil Blend 22
II. Location of Thermocouples on Test Sections 30
i l l. Comparison of Calculated and Measured Water
Heat Transfer Coefficients 47
IV. Fit of Gas Oil Fouling Data to Equation 6 55
V. Linear Fit of Initial Fouling Rate Data 55
VI. Gas Oil Deposit Weights 71
VII. Approximate Size Distribution of Particulates
in Oil 72
VIII. Estimated Thermal Conductivity of Gas Oil
Deposits from Readings at End of Run 74
IX. Reproducibility of Initial Fouling Rates 75
X. Fit of Sand-Water Fouling Data to Equation 6 86
XI. Estimated Thermal Conductivity of Sand Deposits 88
XII. Fouling Models for Thin Deposits for W Constant 105
XIII. Fouling Models w'ithil.Bloc&age.'ffo& W Constant 106
XIV. Fouling Models with Blockage for Constant
Pressure Gradient 114
XV. Quotient Fouling Models with Blockage for W
Constant 119
Appendix 1
Table 1-1 Resistance Thermometer Data 1-3
l-II Thermocouple Calibrations-Test Section I 1-4
V ll
l-III Thermocouple Calibrations - Test 1-5
Section I II
1-IV Calibration of Orifice Differential
Pressure Cell 1-8
1-V Calibration of Tube Differential Pres
sure Cell 1-9
1-VI Calibration of Orifice Plates 1-12
1-VII F it of Regression Equations for
Orifice Plates 1-13
Appendix 3
Table 3-1 Operating Conditions and Clean Tube
Coefficients for Fouling Expeximents 3-4
3-II Inside Wall Temperature Profiles and
Fouling Data 3-5
3-III Comparison of Clean Tube Heat Transfer
Coefficients with Sieder-Tate Equation 3-10
3-IV Pressure Drop and Deposit Thicknesses 3-11
3-V Particulate Levels in Fouling Experi
ments 3 -13
viii
LIST OF FIGURES
Figure Number Page
0 Computed Fouling Curves for Kerris
Example 2 12
1 Diagram of Heat Transfer Loop 24
2 Orifice Plates and Flanges 25
3 Diagram of Test Section I 27
4 Pressure Taps and Electrical Terminals 28
5 Photograph of Test Section II 31
6 Outlet Mixing Chamber 3 3
7 Tube Wall Temperature Profiles and Terminal
Fluid Temperatures 43
8 Comparison of Measured Clean Heat Transfer
Coefficients and Predictions of the Sieder-
Tate Equation for Gas Oils 45
9 Heat Transfer Coefficient versus Time for.
T « 295°F-Oil A 50
Wc
10 Heat Transfer Coefficient versus Time for
Tw « 295°F-Oil B 51
c
11 Heat Transfer Coefficient versus Time for
E.W 346°F-Oil B 53
w c
12 Fouling Resistance of Oils versus Time for
T «295 (Solid Lines are Least Squares Fit
w
tocEquation 6) 54
13 Fouling Resistance and Pressure Drop Increase
versus Time for T ,« 346°F-Oil "B 57
T>
w c
14 Variation of Parameters of Equation 6 with Mass
Flow Rate of Oil (log-log) 58