EPA-R2-73-205
APRIL 1973 Environmental Protection Technology Series
The Development and Demonstration
of an Underwater
Oil Harvesting Technique
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
-------
EPA-R2-73-205
April 1973
THE DEVELOPMENT AND DEMONSTRATION
OF AN UNDERWATER OIL HARVESTING TECHNIQUE
By
Ralph A. Bianchi
George Henry
Contract #14-12-899
Project 15080 FWL
Project Officer
Thomas W. Devine
New England Basins Office
240 Highland Avenue
Needham Heights, Massachusetts 02194
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price $1.26 domestic postpaid or $1
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency,
nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
11
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ABSTRACT
Analytical studies and harbor tests were conducted to determine the
feasibility of harvesting oil beneath the surface of the water with the
use of inclined planes.
The analytical and laboratory investigations provided sufficient basic
information to design and build operational units aoid showed that this
kind of device could harvest both light and heavy oils between 3/4 knot
and 2 knots. Information was obtained regarding angle of incline,
length of collection well, and the design of a baffle grid. Tests, which
were performed in waves, showed that a platform could be designed so
that oil could be collected in waves and chop without seriously affecting
efficiency.
A 22-foot-long unit was designed, built, and demonstrated in Boston
Harbor. The results showed that the fixed-plane concept is highly
effective in areas where the vessel can travel through the slick.
Recovered oil is virtually water.free and, under representative con-
ditions of wind, waves, and current, and in one pass through an oil
slick, the unit recovered between 70% and 86% of the oil presented to
it. The quantities of oil collected in one pass could be greatly in-
creased if sweeping arms were used to increase the active area and
concentrate the oil.
Although the fixed inclined plane (SHOC) demonstrator unit works well
between 3/4 knot and 2 knots, in the interest of extending the velocity
range to from zero knots to over Z knots, it is recommended that a
modified operational unit employing a new principle of a moving
inclined plane be designed and built to work in actual spill situations.
It is also recommended that a set of effective sweeps to be directly
attached to the unit be investigated and developed.
111
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CONTENTS
Section Page
I CONCLUSIONS 1
fl RECOMMENDATIONS 3
III INTRODUCTION 5
IV ANALYTICAL AND EXPERIMENTAL* PR OCR AM 7
SHOC Concept 7
Literature Search 7
Theoretical Live atigations 7
Experimental Program 11
Circulating Tank Facility 11
Tow Basin Facility 17
Test Oils 17
Circulating Tank Tests and Results 20
Tow Basin Test Results 31
Some General Design Considerations 34
V DESIGN, FABRICATION, AND TEST 43
Description 43
Fabrication 45
-Slafeility and Wave Response 45
Harbor Tests and Evaluation 50
VI ASSESSMENT OF THE UNDERWATER
OIL COLLECTION TECHNIQUE 61
VII ACKNOWLEDGMENTS 63
Vim REFERENCES 65
IX APPEKDICES 67
Appendix A - Literature Search 67
Appendix B - Theoretical Basts of
ht- Experimental Design ol the
SHOC Concept 72
Appendix G - The JBF DIP Concept 84
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FIG USES
Figure Page
1 The SHOO Concept 8
2 Three Modes of Oil Collection 10
3 Oil Globule Size vs Oil- Water Relative Velocity 12
4 Well Length vs Oil-Water Relative Velocity 13
5 Circulating Tank Without Accessories 14
6 Circulating Tank Air -Driven Water Circulator 15
7 Circulating Tank Facility With Accessories 16
8 Tow Facility Building and Basin 18
9 Underwater Light and Wave Generator lor
Tow Basin 19
10 Plexiglass Model for Determining Velocity
Profiles 21
1 1 Test Positions for Determining Velocity
12 View Looking tip at the Action of Hydrodynamic
Forces on the Interfacial Wave ,? 23
13 Plexiglas Model of SHOC with Curved Incline
and Baffle Section 26
14 Baffle Section of Plexiglas SHOC Model 27
1 5 Circulating Tank Data for Various Oile> 28
16 Flow Guides for Test Model 29
1 7 Circulating Tank Data for No. 2 Oil, Flow
Guide Model 30
18 The Variable- Incline -Angle Model Being
Prepared for Testing 32
19 Tow Bamn Data for Various Incline Angles 33
20 Tow BWBin Model with Flow Guides and Baffle
Sections 35
21 Tow Basin Data With and Without FloW Guides 36
22 Tow Basin Model in Waves 37
23 Tow Basin Data for Model in Waves 38
24 Tow Hasia Data for Various Baffle Lengths 39
-------
Figure Page
25 Design Curves for SHOC Oil Skimmer 40
26 Outline Drawing of the SHOC Demonstration Unit 44
27 Side View of SHOC Hull Being Fabricated 46
28 Stern View of SHOC Hull Being Fabricated 47
•;>
29 The SHOC Being Launched in Boston Harbor 48
30 Scale Model of the 22-Foot SHOC Demonstration
Unit 49
31 Schematic of the SHOC Harbor Test Arrangement 51
32 Schematic of Oil-Level Measurement Technique 53
33 Collection Chamber Volume Calibration Chart 54
34 View of the SHOC Baffles After Nine Months
in the Water 59
B-l Oil Globule Size vs Oil-Water Relative Velocity 77
B-2 Well Length vs Oil-Water Relative Velocity 82
vii
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TABLES
Table Pape
1 Properties of Test 6tle 20
2 Horizontal Velocity Variations Around Narrow
Model (1-1/4 ft/sec Free-Stream. Velocity) 24
' '
and §lai& Velocity Variations
Around Narrow Model (3 ft /sec Free- Stream
Velocity) 24
4 Boston Harbor Tests of SHOC Oil Recovery
Effectiveness 56
"
B-l Critical Veloifilies for Various Oil Proper. tie s
Below llhich No Oil Droplets ^ are Formed 77
B-2 Terminal Velocities of Various -Size Droplets
for C3^1s of Different Specific Gravities and
Interfacial Tensions 81
viil
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SECTION I
CONCLUSIONS
1. The method pf collecting oil beneath the surface of the water
Using an inclined plane is feasible and practical.
2. The fixed inclined plane (SHOC) unit operates effectively at
vessel or water velocities of from 3/4 knot^to 2 knots.
3. For effective oil recovery, the inclined plane angle with
respect to the horizontal should not be greater than 30°.
4. Baffle grids between 3 and 4 inches square and 9 inches high
will capture both the high and low viscosity oils.
5. Baffle sections greater than 7 feet long will capture between
70% and 90% of the oil presented to the skimmer in one pass at
the operating velocities.
6. Vessels employing the fixed inclined plane principle can be
made as small or as large as desired. Size will be determined
by cost, use, and handling considerations.
7. Vessels employing the SHOC concept can harvest thin or thick
oil slicks over a very wide range of viscosities without any
serious effect on efficiency or performance.
8. The tow basin and harbor tests show that SHOC units can be
built that will collect oil effectively under severe wave con-
ditions.
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SECTION II
RECOMMENDATIONS
This program was limited to the investigation and harbor demonstra-
tion of the fixed inclined plane (SHOC) concept. It was not within the
scope of the program to design and build an operational unit. It is
recommended, however, that a full-sized, self-propelled operational
unit employing a new principle of a moving inclined plane be designed
and built to work in actual spills. The first part* of this recommenda-
tion, namely the design of an operational unit employing the new prin-
ciple, has been supported by the Environmental Protection Agency.
Effective sweeps for sweeping oil to the oil skimmer that are inte-
with the skimmer do not exist. The use of simple flat plates
;been unsuccessful because of their behavior in waves and their high
drag characteristics. It is recommended that a program be supported
to investigate and develop a set of integral sweeps to increase the
effectiveness of oil skimmers.
Conditions created by extreme operating maneuvers, such as rapid
changes in direction or sharp turns, may interfere with efficient
removal of oil from the collection well. Laboratory and harbor tests
should be performed to determine what alterations should be made in
and around the collection well to improve the efficiency of collection
during various maneuvers.
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SECTION III
INTRODUCTION
In 1970, JBF Scientific Corporation was awarded a contract to (1)
perform an investigation of the engineering principles involved in
collecting oil below the surface of the water by means of an inclined
plane, and (2) design and fabricate a demonstration unit for evaluation
in a realistic environment.
The development and demonstration of the concept was accomplished
in two phases. In the first phase, investigations were performed with
laboratory tests to develop design information for building the demon-
stration model. In the second phase, a demonstration unit was
designed, fabricated, and evaluated in Boston Harbor. A more
breakdown of the program is outlined below.
PHASE I - THE DEVELOPMENT OF DESIGN
INFORMATION USHK3 LABORATORY
MODELS f~~ir~
1. The Performance of Literature Review
2. The Design and Construction of a Circulating Tank
3. The Design and Construction of Models for the
Circulating Tank Tests
4. The Performance of Circulating Tank Tests
5. The Design and Construction of Models for Tow Basin
Tests
6. The Performance of Tests in the Tow Basin
7. The Development and Preparation of Design Data
PHASE II - THE DESIGN, CONSTRUCTION,
AND DEMONSTRATJbN OF A
UNIT IN BOSTON HARBOR
1. The Design of the Demonstration Unit
2. The Fabrication of the Demonstration Unit
3. The Design and Preparation of a Harbor Test Plan
4. The Evaluation of the Demonstration Unit
-------
The oil recovery technique developed under the contract is directed
at hydrodynamically funneling the oil slick down into the submerged
inlet of a collecting chamber. The principle involves forcing the
surface oil to follow the submerged contour of an inclined plane so
that the oil film is thickened and so that the thickened film is then
trapped in a well at the end of the inclined plane. The concept is
called, "The Submerged Hydrodynamic Oil Concentrator (SHOC). "
The behavior of the SHOC concept from the hydrodynamic viewpoint
is a complex phenomenon involving laminar and turbulent flow and two
fluids of different densities and viscosities. There are several pos-
sible non-dimensional groups involved in describing the process so
that a completely analytical approach is not possible. That is, none
of the dimensionless expressions occur in such a way as to be the
principle phenomenon that explains the entire collection process.
They are all involved and there are transition zones. The approach
which was used to develop design data was to present a theoretical
framework to define the processes and to generate sufficient empirical
information to explain these processes and to make predictions of the
oil collection effectiveness for various size units. Based on these
predictions, several models were designed and a 22-foot-long SHOC
unit was built and demonstrated in Boston Harbor.
-------
SECTION IV
ANALYTICAL AND EXPERIMENTAL PROGRAM
SHOC Concept
The principle of the SHOC concept involves forcing the oil on the
surface of the water to follow the contour of an inclined plane to a
collection well located beneath the surface of the water.
Figure 1 is a schematic of the concept. Two side plates extend into
the water so that as the vessel moves forward, oil and water must
follow the contour of the incline without escaping to the side. The
principle is the same whether the vessel moves relative to the water
or the water relative to the vessel (i.e., water current).
Basically, there are two different zones of importance. In the first,
the concentration zone, the oil slick is concentrated as it flows along
the incline of the vessel. The oil is buoyant and has a higher viscosity
than water and, therefore, its flow is in sheets and globules along much
of the length of the concentration zone. This results in a stable layer
of oil flowing along the incline. As the oil flows down to the second
zone, the collection zone, the sheets and globules coalesce and are
trapped in a baffled well. In the collection zone, the oil which has
been flowing along the bottom of the vessel rises due to buoyant forces
into the baffles and the collection tank. The oil then concentrates into
a thick layer at the top of the well where it can be pumped off practi-
cally free of any water.
Literature Search
Prior to performing the theoretical and experimental work a search
was made to obtain pertinent information on the oil-on-water behavior
and on the practical aspects of oil recovery processes. For the
behavior of oil on water particular attention was paid to analyses that
has been performed concerning the instabilities of oil-water inter-
faces, the way that oil breaks up beneath the water surface, and the
trajectories of submerged oil globules. This information is referred
to in the text. The investigation of the practical aspects of oil recovery
processes was limited to readily available information on the physical
and chemical removal of oil slicks. This work provided insights into
the practical problems of recovering oil, such as the amounts of oil
spilled, the number of spills, film thicknesses, the spreading char-
acteristics, and the sweep and containment difficulties. This liter-
ature is listed in Appendix A.
Theoretical Investigations
The behavior of the SHOC concept from the hydrodynamic viewpoint
is a complex phenomenon involving laminar and turbulent flow regimes
-------
Side Plates
Bames
Concentration Zone—*•
Figure I. The SHOC Concept
8
-------
and boundary layers, coupled with wave interactions. There are five
different non-dimensional groups which appear in the equations des-
cribing the flow processes, and each of these has a different structure
in relation to the modelling parameters of characteristic length and
velocity. The Densimetric Froude Number relates inertial to buoyant
effects, the Reynolds Number relates inertial to viscous effects, the
Euler Number relates pressure or acceleration to inertial effects, the
Strouhal Number relates vortex spacing to a diameter, and the Weber
Number relates inertial to surface-tension effects. Unfortunately
none of these dimensionless expressions occurs in such a way as to
be the principal phenomenon that governs the entire oil collection
process. They are all involved, and there are transition zones so that
a completely rational expression for the collection process is not
possible. However, a combination of the analyses and the empirical
information developed is sufficient to quantify the process and make
predictions of the oil collection effectiveness for various size units.
Appendix B presents the development of the theoretical framework of
the SHOC concept and only a brief synopsis will be presented here.
Basically, there are three possible modes of collection for a device
employing the SHOC concept (see Figure 2). These modes are (a) the
oil-layer buildup extends sufficiently far in front of the plane to cause
the depth of oil to exceed the draft of the vessel; (b) the oil-water inter-
facial waves cause oil to shear off in sheets and globules that are trans
ported to the incline down to the collection zone; and (c) the oil shears
at the buildup region adjacent to the incline in sheets that travel with a
wave-like action.
The modes of prime concern in the design of SHOC units are shown in
Figure 2 (b and c), where the oil-water interfacial wave causes oil to
shear off in sheets, globules and droplets. The parts of Appendix B
that are useful in design are the critical Weber Number (which estab-
lishes the velocity at which oil begins to move down the incline) and the
governing relations for the globule size and collection well length as
a function of oil-water relative velocity.
The critical Weber Number is given by
P dV*
w =
c
where P = oil density
o
d = diameter of globules
V = critical relative oil-water velocity
o - interfacial tension between oil and water
9
-------
Full Oil Buildup
Collected Oil
(a)
Collected Oil
Sheets and Globules
(b)
Collected Oil
Sheets of Oil
(c)
Figure 2. Three Modes of Oil Collection
10
-------
A We approximately equal to 22 has been found by Wicks [l] to give
good agreement with tests. It is used to determine the critical velocity
for effective oil collection where oil moves relative to the plane.
Figure 3 shows oil droplet size for limiting values of surface tensions
and specific gravities plotted as a function of relative velocity between
the oil and water particles. It is used to determine the mean size of
oil globules which travel down the incline.
Figure 4 is a plot of collection well length versus water or vessel
operating velocity. It was obtained from calculations substantiated
in reference [1] and is used to determine the length of baffle section
required to collect the oil particles, whose size has been determined
above.
The cross-section and baffle height were determined on the following
basis. It is most desirable to have as small a cross-sectional area
as possible to minimize the size of the eddy within a baffle. The
smaller eddies or vortices do not tend to push oil out of the baffle and
back into the water stream. In theory the height of the baffle should
be at least twice the dimension of the cross-section width so that there
is a minimum of disturbance in the well above the top of the baffles.
The design values obtained using these rules have to be modified to
consider the size openings required to capture the more viscous oils,
and final design dimensions, therefore, were optimized experimentally.
Experimental Program
The literature search and the theoretical work discussed in the pre-
vious section provided the guidance for the experimental program. A
very important part of the tests was the recording of experimental
results on motion picture films for subsequent analysis. This visual
information was correlated with measurements of oil collection rates
for making many important decisions in the actual design of SHOC
units.
Two major test programs were carried out in the laboratory. The
first involved the use of a circulating tank and the second a tow basin.
Circulating Tank Facility
The circulating tank designed and built under this program is 15 feet
long, 5 feet wide, and 3 feet deep. Figure 5 is a photograph of the
tank without accessories. Water was circulated by the air-driven
propeller shown in Figure 6. The circulator provided the water vel-
ocities from 0 to 3 feet per second. Figure 7 shows the circulating
tank facility with all of the accessories. Oil was presented to the
water by means of a splash plate at controlled rates to provide varia-
tions in average oil film thickness. The oil harvested was pumped
11
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X - specific gravity
O - surface tension
.01
Mean Diameter of Oil Globule (in.)
Figure 3. Oil Globule Size vs Oil-Water Relative Velocity
-------
u
o
»*
V
> 3
!>
•«4
*•
It
I I I I III
Mill
CT = surface tension 0.0016 Ibs/ft
o
X a specific gravity
D = l/2 in.
6 8 10
Well Length (ft)
20
D = initial distance of oil
globule below well
60 80 100
Figure 4. Well Length vs Oil-Water Relative Velocity
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Figure 5. Circulating Tank Without Accessories
14
-------
^_
Circulating Tank Air-Driven Water Circulator
15
-------
Figure 7. Circulating Tank Facility With Accessories
-------
from the collection wells of the models to a separate oil storage con-
tainer, so that quantities of oil collected could be compared directly
with the quantities presented. Turning vanes were used to prevent
excessive turbulence in the straight test section, and plexiglas
sections provided the means of obtaining motion pictures of the under-
water oil collection process.
Free stream velocity in the circulating tank was determined by
inserting a calibrated water U-Toube manometer upstream of the
test model.
4
Tow Basin Facility
The towing facility to test the SHOC models is shown in Figures 8
and 9. Figure 8 contains photographs of the building and an overall
view of the tow basin. Figure 9 shows an underwater traveling light
source, which was used for taking still and motion pictures; the towing
cable and motor; and the wave generator. The tow basin is 5 feet
wide, 5 feet deep, and over 100 feet long. The wave generator is a
hinged paddle, driven through an electric cam by a variable-speed
electric drive. Models were towed at velocities up to 5 feet per
second and traveling waves up to 12 feet long and 6 inches high were
attenuated at both ends by means of inclined beaches. A known quan-
tity of oil was placed on the water and allowed to spread over the sur-
face to provide an average film thickness of 0. 5 mm to 1. 0 mm, and
models were towed between 1 and 4 feet per second. Measurements
were made of the amount of oil collected by removing the oil and some
•water from the well and placing the mixture into a graduated cylinder.
The oil level alone was a measure of the amount collected.
Test Oils
Petroleum oils (No. 2 and No. 6), silicone fluids, and castor oils
were tested. The silicone fluids and castor oils were used with
controlled amounts of dye, so that clear motion pictures could be
taken of the oil flowdown and the collection processes.
Table 1 shows the densities and viscosities of the test oils.
17
-------
Figure 8. Tow Facility Building and Basin
18
-------
Figure 9. Underwater Light and Wave Generator for Tow Basin
19
-------
TABLE 1
Properties of Test Oils
Type of Oil
Castor
Soybean
Silicone Fluid
No. 2 Oil
No. 6 Oil
Viscosity
(centistokes)
2,000
65
10, 000
10
10, 000
Specific
Gravity
0.98
0.92
0.98
0.85
0.98
Circulating Tank Tests and Results
Before testing with oil in the circulating tank, it was important to
establish the relevance of two-dimensional testing. This test tech-
nique greatly simplified the oil collection and efficiency measure-
ments as well as the methods of observing and filming the tests. The
first tests, therefore, were performed using a 4-inch wide model in
the 12-inch wide test section. Figure 10 is a photograph of the plexi-
glas model used. There were non-oil tests to determine the relative
velocities down the incline between the side plates around the model.
Figure 11 is a schematic showing the test point locations, and Tables
2 and 3 contain velocity variations in a 1-1/4 feet per second and
3 feet per second free-stream circulating velocity. The results
showed that testing models that were the full width of the circulating
annulus was justified since the flow velocities down the inclined plane
and under the baffles would be substantially the same as they would be
if flow were permitted around the sides of the model.
The first series of oil tests was designed to determine the effect of
incline angle on the oil buildup and flowdown. A flat plate was placed
in the test section and inclined at angles between 10° and 40°, and a
wide range of tests were performed using No. 2 and No. 6 oil at free-
stream circulating velocities of 0. 5 feet per second to 3 feet per second.
These tests were visually monitored and filmed, so that the results
could be repeatedly reviewed. Figure 12 is a photograph which shows
the buildup at the interface in front of the incline and one of the flow
patterns observed on the incline. Several critical observations were
drawn from the results of these tests.
20
-------
Figure 10. Plexiglas Model for Determining Velocity Profiles
-------
Water Line
9 +
+ 1
4-4
(a) Positions for 1-1/4 fps Free Stream Velocity
Water Line
+ 1
+ 3
+-6
6-H
+ 7
•1-7
(b) Positions for 3 fps Free Stream Velocity
Figure 11. Test Positions for Determining Velocity Variations
22
-------
Figure 12. View Loking up at the Action of Hydrodynamic Forces
on the Interfacial Wave
-------
Table 2. Horizontal Velocity Variations Around
Narrow Model
(1-1/4 ft/sec
Free-Stream Velocity)
Distances (in inches)
Test
Position
1
2
3
4
5
6
7
8
9
10
11
14
12
13
Table
Around
Position
1
2
3
4
5
6
7
8
9
dl
1.0
3.0
5.5
9.5
5.4
5.5
1.0
5.5
1.0
(see
^4
4.0
21.0
d2
+ 14.5
+ 14.5
+ 14.5
+ 14.5
-35.0
+14.5
below)
d5
1.0
.35
d3
0
0
0
0
0
4.0
0
d6
0
0
3. Horizontal and Slant Velocity-
Narrow
dl
(in)
1
5
_
_
_
15
20
1.25
5.5
Horizontal
Velocity
(ft/sec)
1. 1
1.2
1.2
1. 15
1.25
1.25
1.4
Slant Velocity
.7
-9
Variations
Model (3 ft/sec Free- Stream Velocity)
d2
(in)
7
7
-
-
_
12
center /tank
0
0
d3 d4
(in) (in)
0
0
0 4
0 21
0 21
0
0
4
4
dg Velocity
(in)
_
-
1
.25
1.25
-
-
-
-
(ft/sec)
2.8
2.8
3. 1 (slant)
3. 35 (slant)
3.35
2.75
3.0
3. 15
3.3
24
-------
Below about 1 foot per second oil will not tear off the
interfacial w^ave and. flow down the incline.
At angles less than 25° and at velocities approaching
1 foot per second all oils tend to travel down the incline
in large sheets and globules. At velocities between 2
and 3 feet per second oil tends to break up into finer
particles and droplets.
Gradually curving the incline at the base of incline to
the horizontal greatly improved the trajectories of oil
globules and particles, which is important for minimizing
collection well length.
From the results of the tests, the literature review, and the analyses
an engineering test model was designed and fabricated out of plexi-
glas. It consisted of a curved inclined surface with a nominal angle
of 23° and a collection well 34 inches long with the provision for
inserting a variety of baffle cross sections and spacings. The plexi-
glas model is shown in Figures 13 and 14. The particular model
shown has 1-inch square by 1-1/2 inch high baffle sections. It is free-
floating, twelve inches wide, and has a 7-inch draft. It also has a
reverse incline surface rising in the collection well to provide a con-
centration zone for pumping out the collected oil. Two-inch, three-
inch, and four-inch, square cross sections of baffles were also fabri-
cated and inserted in the collection well. The tests of the flow of oil
through these cross sections were made using the dyed silicone fluid
which closely simulates a typical No. 6 fuel oil. The heights of these
latter baffles were twice the dimension of the cross-section width to
minimize the disturbance in the well above the top of the baffles.
A series of tests were run at various water velocities with No. 2,
No. 4, and No. 6 type fuel oils. Figure 15 is a plot of the data.
The straight line represents the theoretical limit of rate of oil that
can be collected. Points to the left of the line are due to experi-
mental error. Tests were run below 1. 5-mm film thickness because
of the EPA contract requirement. All data was normalized to 1-mm
film thickness for comparison purposes.
In addition to the data plotted in Figure 15 a series of motion pictures
was taken and reviewed in considerable detail. The observations of
the No. 2 oil tests led to the idea of using a series of parallel flow
guides on the incline. It was reasoned that these flow guides would
provide a better control of the oil geometry on the incline and would
result in higher oil collection rates at higher velocities. Figure 16
is a photograph of the full set of flow guides that was tested. These
guides were tested from 1/2-inch spacing to 6-inch spacing, and the
results were compared with the data obtained on the 12-inch-model-
width tests. The results are presented in Figure 17.
25
-------
Figure 13. Plexiglas Model of SHOC with Curved Incline and Baffle Section
-------
Figure 14. Baffle Section of Plexiglas SHOC Model
27
-------
B
a
I
O - No. 2 Fuel Oil
0 - No. 4 Fuel Oil
& - No. 6 Fuel Oil
K
O
••H
•4->
U
O
a
O
O
8
Model Width - 1 foot
Average Oil Film - 1 mm
I
.5
1 1.5 2
Free Stream Velocity (fpe)
2.5
Figure 15. Circulating Tank Data for Various Oils
28
-------
Figure 16. Flow Guides for Test Model
-------
.. o -
A -
a -
60
J 2
«
o
3
o
O
g
Flow Guides-12 in. Spacing
Flow Guides—6 in. Spacing
Flow Guides-3 in. Spacing
Flow Guides-1.5 in. Spacing
Flow Guides-0. 5 in. Spacing
8
Model Width - 1 foot
Average Oil Film - 1 mm
I
1 1.5 2
Free Stream Velocity dps)
2.5
17. Circmlatittg TaiOc
for No. 2 Oil, Flow G^iide Model
30
-------
The conclusions drawn from our circulating tank tests were as follows:
(a) The oil collection rates are reasonably close to what
was predicted theoretically.
(b) The oil collection rate is not significantly affected by
introducing various flow guides at velocities up to
2. 5 feet per second.
(c) The baffle cross sections must be at least 3" x 3" in
order to pass the heavier fuel oils, and twice the
dimension of the cross section (6") area ample for
the height of the baffle to minimize the disturbances
in the well above the baffles.
(d) The towing tests should be designed to test the heavier
oils which are theoretically more difficult to collect at
velocities over 1-1/2 feet per second.
We also observed that the oil collected was not emulsified nor did it
contain any significant quantities of water.
Tow Basin Test Results
Because the majority of the circulating tank tests were performed
using the lighter oils, it was decided to run the tow tests using a
heavy, high-viscosity oil.
The first series of tests that were run in the tow-basin were to verify
the No. 2 oil results obtained in the circulating tank tests. The second
set of tests were conducted using castor oil to simulate residual oils
like No. 6. The simulation was excellent, not only in terms of den-
sity, viscosity, and surface tension but also its tackiness, wettability,
and its behavior on the incline and on the baffle surfaces. Castor oil
was used because it could be dyed to the desired color for visual obser-
vations and for taking motion pictures. The motion pictures taken
with No. 2 oil were compared with those taken in the circulating tank.
These observations showed that No. 2 oil circulating tank test data
would be the same as tow tank data.
Oil recovery rates were determined for four major test conditions.
The first was to determine the effect of using various angles of incline
on the collection rate. Figure 18 shows photographs of the variable
incline angle model being placed in the tow basin. Figure 19 is a plot
of the results of the tests performed. As can be seen in Figure 19*
the 12° angle was significantly more effective than the 23° angle
incline. A 16° angle was also tested at one velocity to establish a data
point between the 12 and 23° angle tests. The next runs were to
evaluate the use of flow guides. A spacing of 1 inch was selected as
31
-------
Figure 18. The Variable-Incline-Angle Model Being Prepared for Testing
32
-------
4
fi
a
BO
nJ
K
*
o
u
V
Oil Properties
Specific Gravity - .98
Viscosity - 2000 centistokes
Surface Tension 40 dynes/cm
X
12 Incline
23 Incline
A 16 Incline
X
Model Width &,;J foot
Average Oil Film - 1 mm
I
2 3
Tow Velocity (fps)
Figure J9. Tow Basin Data for Various Incline Angles
33
-------
optimum for the viscosity of 2000 centistokes. Figure 20 shows the
flow guides attached to the model at the tow basin. The results are
shown in Figure 21. The collection rate was actually much less with
the flow guides. A close examination of the motion pictures taken
revealed that the increase in resistance caused a significant buildup
of oil in front of the model, which was directed around the sides,
resulting in much lower recovery rates.
Another series of tests compared results with waves to results in
calm conditions. Since wave response models have an entirely dif-
ferent scaling relation from those associated with oil recovery, it
was not possible to simply scale the wave lengths and amplitudes with
the inclined plane model. Based on the advice of naval architects,
it was reasoned that if we could generate a combination of wave
lengths, wave amplitudes, and vessel velocity such that the model
heaved and pitched severely, then the simulation to full scale units
in relatively heavy seas would be realistic. The wave conditions
selected caused the model to heave and pitch at amplitudes of 50%
of the vessel draft. Vessels can and should be designed to meet this
requirement in 3- to 5-foot seas if they are to survive in anticipated
harbor environments. Figure 22 shows the models being tested in
waves. The results of the tests are plotted in Figure 23. The per-
formance in waves of this severity only caused a small percentage
change in the recovery performance. There is an anomaly at 4 feet
per second but this was caused by the test technician inadvertently
leaving the wave damper plate out of the baffled collection well at this
speed. This was not realized until after the test series was completed.
We later verified that this decrease in performance does occur when
the wave damper is removed, at the higher speed, in calm water.
The last test runs were to obtain design information on the length of
the collection well. Baffle length was varied by attaching additional
baffle sections to the model. This can be seen by referring again to
Figure 20. Figure 24 shows the effect of doubling the baffle length.
This data was particularly useful, because the oil recovery rate was
higher than was predicted from calculations using the information in
Appendix B. For a test oil of a viscosity of 2000 centistokes the
mean size of the globules was larger than predicted. As can be seen,
the increased baffle length increased the pick up rate at velocities
above 1-1/2 feet per second by approximately 25%.
Some General Design Considerations
Figure 25 contains a family of curves with collection well length as
the running parameter and was developed from the experimental data
and the information in Appendix B. The collection rates are normal-
ized to a unit (per foot) width of skimmer.
34
-------
OJ
Figure 20. Tow Basin Model with Flow Guides and Baffle Sections
-------
1
s
a.
M
4>
a
«
o
o
V
Oil Properties
Specific Gravity - .98
Viscosity - 2000 centistokes
Surface Tension - 40 dynes/cm
X
i
<
X
w
/
/
\.
Model Width - 1 foot
Average Oil Film - 1 mm
\
v
No Flow Guides
A Flow Guides- 1.5 in. Spacing
2 3
Tow Velocity (fps)
Figure 21. Tow Basin Data With and Without Flow Guides
36
-------
Figure 22. Tow Basin Model in Waves
37
-------
8
£
6
o.
JU?
V
13
05
u
«
«
Oil
Specific Cavity - .9$
Viscosity - 2000 centis&Sfkes
Surface Tension - 40 dynes /cm
\ -*
,. . y -
Model "W I4th - 1 foot \
Oil Filftj - 1 mm \
\
• Calm Conditions
A Waves IZ ft long, 4 in. high
2- • •'••' ' '- •••'••"'- 3
Tow Velocity (fps)
Figure 23. Tow Basin Data for Motel in Waves
38
-------
a
S.
7 2
t*
o
u
0)
Oil Properties
Specific Gravity - .98
Viscosity - 2000 centistokes
Surface Tension - 40 dynes /cm
x
Model Width - 1 foot
Average Oil Film - 1 mm
• 3-foot-long Baffle Section
A 6-foot-long Baffle Section
1 2
Tow Velocity (fps)
Figure 24. Tow Basin Data for Various Baffle Lengths
39
-------
Film Thickness
10mm 5mm 1 mm
I I
40
30
*>
a
e*
w
o
u
20
10
— 20
— 15
— 10
No. 2 Fuel Oil
No. 6 Fuel Oil
L = Baffle Section Length
I
I.I.I
234
Vessel or Free Stream Velocity (fps)
Figure 25. Design Curves for SHOC Oil Skimmer
40
-------
The straight-line portion of the curve is based on the circulating tank
tests with No. 2 oil. The data points shown were taken using No. 2
oil, No. 6 oil, and simulated No. 6 oil at oil film thicknesses between
0. 5 mm and 8 mm. The projected parametric curves presented for
the No. 6 oil were obtained from data available on submerged oil path
trajectories. This information is presented in Appendix B.
The curves presented in Figure 25 show that a SHOC unit operates
best at speeds between 1 and 4 feet per second. Below 1 foot per
second oil will not go down the incline and above 4 feet per second the
oil collection rate decreases rapidly. The larger the baffled section
the more effective the collection. It should be recognized, however,
that when relative velocities between the oil and water exceed 3 feet
per second, the oil breaks up into fine particles and becomes entrained
in the water column. However, at vessel velocities of 3 to 4 feet per
second the actual relative velocity between the oil and water, since the
oil is also moving, is much less than 3 feet per second. Assuming that
a design will be operated near optimum speed, therefore, the oil
recovery rate can be increased by (1) making the unit wider, (2)
using a longer collection well, or (3) increasing the oil slick thickness
in front of the device.
41
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SECTION V
*
DESIGN, FABRICATION AND TEST
In order to best show the possible performance characteristics of a
SHOC unit, it was felt that the demonstration unit should be as large
as possible within our budget and time limitations. A unit on the
order of twenty feet long and eight feet wide could easily be trans-
ported, could carry several people in the Boston Harbor environment
without danger, and appeared to be within our budget. Within this
dimensional framework it was decided to make the well 7. 5 feet long
and the incline angle 15°, with a well depth from the waterline of
21 inches. These basic dimensions were derived from the test data and
the design curves to have a unit that would operate effectively between
1 and 2 knots vessel velocity.
Description
Figure 26 contains an outline drawing of the SHOC demonstration unit.
The hull is partitioned into compartments, which are used for flotation
and ballast. The flotation tanks were filled with sufficient foamed
material to prevent the vessel from sinking in the event the tanks
were ever ruptured. The ballast tanks were positioned so that the
vessel could be trimmed in roll, pitch, and draft, using either solid
ballast or sea water. A 275-gallon tank was also built into the hull
to provide storage for the test oils.
The side view shows some of the details of the collection well. The
baffles are 3 inches square by 9 inches high. These dimensions were
selected from tests in the circulating tank, where a variety of geo-
metries were examined. The well is truncated so that a deep pocket
of oil concentrates at the top, where it is pumped to the storage tank.
The top view of the unit shows the oil handling system, which consists
of a gasoline engine-driven screw pump that could operate at several
speeds, pump a wide variety of oils, and handle 0. 4 inch diameter
particles. The system was capable of pumping oil from the collec-
tion well and transferring it to the Storage tank or pumping oil from
storage and deploying it in front of the vessel, as was done for demon-
stration purposes. The demonstration unit also has viewports for the
purpose of observing the oil being collected in the well as the vessel
moved through an oil slick.
Propulsion was provided by two 12. 9 hp Crysler outboard gasoline
engines with dual steering controls and individual throttle and shift
controls, all located on a central console. Electricity was generated
on board to power the running lights and charge the battery.
43
-------
21" FREEBOARD
r
PUMP AND PUMP
DRIVE ASSEMBLY
OIL COLLECTION rVIEW PORTS/-FUEL TANKS
WELL
9 HP. GASOLINE
ENGINE WITH
CLUTCH
TRANSMISSION
7
\
MOYNO 116
OIL PUMP
CONTROL CONSOLE
KEEL PLATES
OIL STORAGE OIL COLLECTION WELL
26' OVERALL
7'-9" BEAM
13 H.P. OUTBOARDS
3" x 3- x o" BAFFLES
Figure 26. Outline Drawing of the SHOC Demonstration Unit
-------
Fabrication
The demonstration unit was fabricated completely out of aluminum,
and the dry weight of the hull and accessories was 5000 Ibs. The unit
fully ballasted and at its design draft and trim weighed 11, 000 Ibs.
This weight represents a considerable amount of water ballast which
could be used as oil storage capacity on an operational unit. Figures
27 and 28 are photographs of the hull, taken while it was being fabri-
cated. Figure 29 is a photograph of the completed unit being launched
at the Coast Guard Base, Boston Harbor. Figure 30 is a photograph
of a scale model which shows the pump handling system and some deck
details.
Stability and Wave Response
As described in previous sections, tests on plastic models have been
conducted in the tow basin to determine the effects of waves on the oil
collection rate. The results of these tests showed that there was little,
if any, loss in recovery rate when the vessel heaves and pitches at
single amplitudes equal to one-half the draft of the vessel.
In the design of the demonstration unit stability and wave response
characteristics were calculated. A summary of these characteristics
is given below.
Stability
Transverse Metacentric Height 3. 75 ft
Longitudinal Metacentric Height 26. 00 ft
Sinkage 855 Ibs/in
Response Period Exciting Wave Length
Heave 2. 1 sec. 22. 3 ft.
Pitch 2. 55 sec. 33. 2 ft.
Roll 2. 3 sec. 27. 9 ft.
The values of metacentric heignts show that there is good stability in
both the transverse and longitudinal direction. Two men and equip-
ment would encounter only a few degrees of roll. The sinkage in
pounds per inch of draft increase indicates that 5 men on board
increased the draft by only 1 inch.
45
-------
^
**mK f"
^^^^^^v
Figure 27. Side View of SHOC Hull Being Fabricated
-------
4-
-J
Figure 28. Stern View of SHOC Hull Being Fabricated
-------
00
:. .»•]
Figure 29. The SHOC Being Launched in Boston Harbor
-------
••-O
Figure 30. Scale Model of the 22-Foot SHOC Demonstration Unit
-------
The response of the vessel to waves in heave, pitch, and roll have
natural frequencies, with a period of 2.1 to 2. 55 seconds. Twenty to
thirty-five foot wave lengths will excite one or another of three fre-
quencies when the vessel is moving at its slow operating speeds. The
most severe excitation wave length (twice the length of the vessel) is
44 feet, which does not coincide with any of the heave, pitch, and roll
response wave lengths.
In protected waters, therefore, the vessel will in general respond
well to the normal wave heights encountered, and there was little,
if anyj wave effects on oil collection during the harbor* tests. Motion
pictures taken of the vessel response were analyzed and showed that
the calculations were correct. Measurements of oil collection in
Boston Harbor also showed little, if any, wave effects on the oil
collection process.
Harbor Tests and Evaluation
Figure 31 is a schematic of the SHOC unit outfitted for the tests that
were conducted in Boston Harbor. A set of confinement arms was
designed to confine the oil in front of the unit. The oil was deployed
in front of the unit on a splash plate between the confinement arms.
These arms in no way affected the oil collection process or the oper-
ation of the vessel. They were simply used for test purposes so that
no significant oil would be lost around the unit to the environment.
The side view in Figure 31 shows the deployment of the oil onto a
splash plate. The oil travelled between the confinement arms down
the incline between the keel plates, and was collected and concentrated
in the baffled well.
Prior to performing the tests a test plan had to be prepared and
approved by EPA, the Commonwealth of Massachusetts and the U.S.
Coast Guard. The approval was granted on the basis that most of the
testa employed biodegradable oils. Since it was not advisable to spill
excessive quantities of either biodegradable or petroleum oils, it was
decided to use a mixture of oils that would approximate a crude oil.
The properties (density and viscosity) of the mixtures that were used
in the tests, are presented below:
Viscosity
Oil (centistokes) Gravity
Bio Mixture
(Crtt4e simulant) 200 0.95
Petroleum Mixture
(Crude simulant) 250 0.92
50
-------
(TO
CO
o
er
o
&
ft-
ff
en
ffi
Confinement Arms
SHOC Unit-
Splash • "
Plate
•Cross Members
ffi
D)
rf
Oil Deployment Pipe
Water
Line
•Hinge Tubing
-------
It was decided to re-use oil that was picked up for tests since it would
provide for testing aged oil, and oil that might have been emulsified
from the spilling and redeployment processes. There was no attempt,
however, to control these variables.
The effectiveness or efficiency of the oil recovery process was deter-
mined by measuring the amount of oil deployed and comparing it with
a measure of the volume of oil in the collection tank. The oil volume
deployed was determined by measuring the difference in oil level in the
storage tank before and after the test, with a steel tape. The deter-
mination of the oil volume collected was complicated by the irregular
shape of the chamber and by the location of the oil-water interface.
The oil volume collected, therefore, had to be determined by combin-
ing the oil-level measurement and the volume calibration for the
collection chamber. The level of oil was obtained by measuring the
immersion distance of a conductivity probe below the oil surface. The
conductivity probe is in a continuity loop with an ohmmeter as is shown
in Figure 32. The volume calibration for the collection chamber is
shown in Figure 33 in terms of the immersion depth, h, and the exposed
probe length, h'.
The procedure for measuring oil volume involved setting the end of the
probe so that it just contacts the liquid surface. The exposed probe
length, h's, was measured and the volume above the liquid surface was
obtained from Figure 33.
After connecting the ohmmeter circuit as shown in Figure 32, the
probe was removed slowly downward until its sharp point pierced the
oil-water interface. This event was identified by the meter needle,
which moves from an open circuit to a short condition. The exposed
probe length was measured, and the volume above the oil-water inter-
face was obtained from Figure 33.
The oil volume in the collection chamber was obtained by subtracting
the volume obtained in the previous measurements. Samples of the
oil were extracted from the well, placed in a plastic cylinder and
allowed to stand for several hours. Some oil samples were placed in
a centrifuge and subjected to a 1, 200 g acceleration for 10 minutes to
determine the water content.
The boat velocity was measured relative to the water, using the Signet
Scientific Mark 9 Knotmeter, 0-12 knots full scale. The resolution of
the instrument is better than . 1 knots, and is linear below 1/2 knots as
determined by velocity calibrations over a measured course.
The oil flow rate was measured with a 1-1/2 inch Hersey-Sparling
meter, which was mounted in line with the Moyno oil pump. The meter
was calibrated with a large graduate. This measurement was checked
by noting the time of the run and the total volume deployed. Oil deploy-
ment rates were such that an average film thickness of between 0. 5
mm and 1. 5 mm was presented to the device.
52
-------
Conductive Probe
Measured
Height
Insulator
Bushing
Seawater
Ohmmeter
Packing
Gland
Hull
Figure 32. Schematic of Oil-Level Measurement Technique
53
-------
200
180
160
140
_ 120
n
O
BO
100
80
60
40
20
i 1 1 1 1 1 r
Bottom Edge of
Truncated Section
Top of Collection
Chamber
Water Surface
at 21-in. Draft
_ Top of Baffles
Probe
Length
10
12
22
24
4 A
,1
A
A
A 2'
b 28
30
h'(in.) for 30-in. Probe
Figure 33. Collection Chamber Volume Calibration Chart
54
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Because of the restrictions placed on the total amount of oil that could
be spilled in any one test and the environmental damage associated with
spilling oil, we did not carry out any more tests than were necessary to
demonstrate the principle and to establish the design limits. A total of
14 tests were performed in Boston Harbor. The results of these tests
are presented in Table 4.
It should be emphasized that the indicated efficiency number presented
in the table is that associated with the oil recovered in one pass and
that the oil collected contained no visible traces of water. From the
centrifuge test it was determined that there was less than 1% water in
the oil.
The first three runs shown on the table were performed in very calm
water between two piers in an area approximately 1, 000 feet long by
200 feet wide between Pier 6 and 7 of the South Boston Annex to the
Boston Naval Shipyard. During these tests, a significant amount of
oil leaked by the confinement arms to the side of the skimmer and was
not presented to the inclined plane. This explains the relatively low
indicated efficiencies. The reason for leakage was a poor seal where
the confinement arms joined the front of the skimmer. Another reason
for the relatively low readings of oil collection was that the propulsion
was turned off before all the oil on the incline was allowed to travel to
the collection well. These losses were eliminated in runs 4 through
14. The only other losses noted during the tests that caused errors
were losses due to very rapid turns and maneuvers causing some of
the oil that was deployed to be spilled to the side rather than in front
of the vessel and some oil in the well to be drawn out of the bottom of
the well.
Buns 4 through 14 were run in the main channel of Boston Harbor,
where waves from 1 to approximately 3 feet high were encountered.
Many days were windy, and a significant chop was present on the waves
as well. In this typical open-water harbor environment the oil recovery
effectiveness was not reduced.
Combining the results of Table 4 it can be shown that of the 958. 3
gallons spilled, 691* 5 gallons were recovered, resulting in an overall
one-pass efficiency of 72.1%. If runs in which known experimental
errors were eliminated (Runs 1, 2, 3, 5, and 12), then of the 600.9
gallons spilled, 467. 5 gallons were recovered, resulting in an overall
one-pass efficiency of 77. 7%*
In addition to the specific controlled tests that were performed in
Boston Harbor, there were a number of practical observations made
during the tests* These are discussed below.
The confinement arms were originally designed as straight flat wooden
plates, 2 feet high by 8 feet long, with a 4 inch by 4 inch longitudinal
stiffening member. The arms created an excessive amount of drag
55
-------
TABLE 4. Boston Harbor Tests of SHOC Oil Recovery Effectiveness
Reference
Run
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Vessel
Velocity
(knots)
1.0
1.0
1.0
1.5
1.5
1.5
1. 5
1.5
1.5
1.5
1.5
2.0
2.0
2.0
Oil Mixture
Bio Mixture
ii M
ti M
II M
II II
II It
M II
II II
It II
Petroleum Mix.
it it
Bio Mixture
it it
Petroleum Mix.
V olume
Spilled
(gallons)
75.5
64.7
89.6
74.4
65.0
60.5
62.5
54.0
66.0
54.0
65.0
62.6
86.5
78.0
958.3
600.9
V olume
Recovered
(gallons)
43.0
35.5
62.5
62.5
48.0
46.0
43.0
40.0
55.0
40.0
56.0
35.0
69.0
56.0
691.5
467.5
Efficiency*
(%)
57
55
70
84
74
76
69
74
83
74
86
56
79
72
72. 1
77.7
Remarks
Oil lost during deployment
Oil lost during deployment
Oil lost during deployment
No loss during deployment
Turning loss
No losses
No losses
No losses
No losses
No losses
No losses
Turning loss
No losses
No losses
*Effeciency = ratio of the amount of oil collected in one pass to the amount
mouth of the demonstrator
of oil presented to the
-------
and turbulence on the back side. When they were angled outward
approximately 30° to create a sweeping action, there was a consider-
able amount of additional turbulence created at the extremities. This
turbulence resulted in an increased drag and what appeared to be a
premature loss of oil under the sweep at all velocities. The forces
were so high that at one point the 1-1/2 inch diameter stainless-steel
hinge tubing, which held the confinement arms in front of the unit, and
the joints of the cross members used to steady the arms in front of the
unit failed.
These elements are indicated in Figure 31. The straight arms, which
were 12 inches into the water, had to be redesigned so that they were
tapered to the forward tip and with additional buoyancy so that their
maximum draft did not exceed 6 inches. The sweeping mode was
abandoned and the arms were returned to a 0° sweep angle and used
strictly as confinement arms. The important observation made here
is that considerable work needs to be done before effective broad-
angle sweeps can be integrated with a skimmer.
Some other important observations were made while maneuvering the
unit during the oil pickup tests. A sharp turn to change or reverse the
direction of the unit caused a cross eddy in the collection well which
resulted in some loss of oil from the well itself. Additional investi-
gations of the well geometry and the geometry around the side plates
(keels) can and should be made to minimize these losses. These man-
euvers also created considerable turbulence between the confinement
arms. This turbulence caused oil between the arms to become entwined
in the water and to travel beneath the confinement arms to the side of
the unit.
Although wave heights and wave lengths during the harbor tests were
not precisely measured, there were a wide variety of conditions
encountered. Several tests were run in chop and stiff winds, some
were run with relatively closely spaced 2-foot waves, and others were
run in long, high swells. The unit was directed at an angle to the wave
pattern? as well as normal to them. As was expected, the most severe
oil collection conditions occurred when the vessel heaved and pitched
due to its response to a given wave system. When this occurred, the
flat plane would splash water and oil in front of the vessel. This
splashing action did not affect the oil collection process. After the
splash occurs, the vessel advances into the disturbed region and carries
the oil down the plane to the well. Once the oil is beneath the water
surface, the buoyant forces cause the oil to come in contact with the
plane and slide down the well entrance, where it is collected. The oil
deployed was immediately collected, and there was not any visible
trace of water in the oil at the top of the well. Samples of this oil
were allowed to stand overnight for these observations.
57
-------
After 9 months of intermittent use in Boston Harbor, the demonstration
unit was removed from the water for final disposition. It was noted
that the baffles themselves were practically free of any fouling or
clogging problem. * Figure 34 is a photograph showing the condition of
the baffles when the unit was just removed from the harbor.
*A11 submerged portions of the vessel had been painted with marine
anti-fouling paint.
58
-------
U1
sO
Figure 34. View of the SHOC Baffles After Nine Months in the Water
-------
SECTION VI
ASSESSMENT OF THE UNDERWATER OIL COLLECTION TECHNIQUE
The goal of this program was to establish the feasibility of the SHOC
concept or, more generally, the whole idea of harvesting oil with
inclined planes beneath the water surface.
The specific goal of early laboratory and analytical work was to obtain
data to make important design decisions, such as the angle and length
of incline, the cross-section height of the baffles, and the length of the
baffle sections, and to establish the recovery rUtes for various oil film
thicknesses. Sufficient tests were performed to indicate that skimmers
would remain effective in waves typically found in protected waters and
that skimmers could be made of a large size. In general, all our
analytical and experimental work indicated that there was nothing in
the inclined plane underwater collection process to limit the upper size
of a unit and thus, vessel size could be determined by other consider-
ations. Our results showed that the operating velocities for effective
oil collection were in the range from 3/4 knot to 2 knots and that this
type of device will harvest thin (0. 10 mm) oil films as well as thick
(50 mm) oil layers. Waves typically found in harbor channels and
protected waters did not adversely affect the oil harvesting process,
and a properly designed vessel incorporating the principle should remain
effective in 3 to 5 foot high waves.
When the SHOC is operated near the optimum speed, the oil recovery
rate can be increased by (1) making the unit wider, (2) using a longer
baffle, or (3) increasing the oil slick thickness in front of the device.
The unit width is primarily determined by its anticipated usage. For
instance, it is difficult to transport by rail, air or road a unit wider
than 12 feet unless this is done in a disassembled configuration.
Similarly, it is difficult to maneuver a unit in the harbor if it is wider
than say 20 feet. In open waters, a very wide configuration could be
used.
Increasing the baffle length increases the recovery rate by providing a
longer path over which the buoyant forces can act to bring the oil up
into the well. A SHOC with a draft of 2 to 3 feet for the angles of
interest would contain an incline ten feet long. Assuming a 10 foot
plane length; a 25 foot long SHOC could then have a 12 foot baffle
section. A 35 foot long SHOC would have a 15 foot long incline, and a
20 foot baffle section. For the harbor and nearshore environment it
is not unrealistic to consider using a 25 to 35 foot long SHOC.
Since the SHOC recovery rate varies linearly with slick thickness, one
way to increase the recovery rate is to use sweeps in front of the SHOC
to increase the effective width of the unit. Sweep technology is not very
advanced at the present time. The sweeps have to be towed at a speed
61
-------
such that the oil velocity component normal to the sweeps does not cause
the oil to go under them. A number of sweep studies have been con-
ducted but these have not resulted in a viable solution to the problem.
Prior to the start of the program to evaluate the SHOC concept, a new
oil-harvesting concept was developed by JBF Corporation. This new
concept involved the use of a moving inclined plane. As in the SHOC
concept, oil is collected beneath the surface of the water, however, in
the new concept an endless belt travels over the inclined plane and
carries any floating material downward into the water and up into the
collection well. The floatables (usually oil or sorbents, but it could
be any material) are held against the plane by a combination of hydro-
dynamic, buoyant, and cohesive forces. The oil and sorbents are
collected in the well, and any residual material is scraped off the belt
as it passes through the well volume. The principle allows collection
while there is no current or vessel movement, and it carries sorbent
materials to the well as effectively as it carries oil alone. A more
detailed description of this concept, which is called the DIP (Dynamic
Inclined Plane), is presented in Appendix C.
Laboratory tests indicate that the DIP may work more effectively than
the SHOC at higher velocities because the motion of the plane does not
require that the oil slide in shear on the incline, which could result
in less oil breakup.
The DIP concept was presented to EPA, and as a result, the SHOC
contract was extended to include the design of an operational harbor
unit incorporating a moving plain. The unit will be self-propelled,
30-35 feet long, and will have on-board storage sufficient to handle
practically all harbor spills. The results to date indicate that the use
of a moving plane results in a significant improvement in the under-
water oil collection process.
In summarizing, it can be said that the methods of collecting oil
beneath the surface of the water have the advantages that the process
concentrates the oil and separates it from the water as it harvests,
and there is a minimal effect due to waves and chop. Additional
investigations should be made to fully develop the dynamic inclined
plane (DIP) concept, to develop an effective set of sweeps, and to
improve the collection effectiveness during maneuvers and turns.
62
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SECTION VII
ACKNOWLEDGEMENTS
The support and assistance of the Project Officer, Mr. Thomas Devine
of the Environmental Protection Agency, are acknowledged with sincere
thanks. In addition, the suggestions of Mr. R. T. Dewling and the
assistance of Mr. S. Dorrier of EPA, Edison, have been appreciated.
The authors wich to acknowledge the efforts of Mr. James H. Farrell
and Mr. E.E. Jchanson for their numerous beneficial technial contri-
butions to the project, Dr. William T. Hogan for the initial theoretical
work on the SHOC concept, and Dr. Ronald P. Murro for his theoretical
work and the experimental design of the circulating tank test program.
The cooperation and assistance of the U.S. Coast Guard has been grate-
fully acknowledged through Cdr. J. Fournier, Lt. H. Schmecht, and
several crews of the First Coast Guard District, Boston, for their
important contribution to the harbor test program.
63
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SECTION VHI
REFERENCES
[l] Wicks, M., "Fluid Dynamics of Floating Oil Containment by-
Mechanical Barriers on the Presence of Water Currents, " Pro-
ceedings of the Joint Conference on Prevention and Control of
Oil Spills, Purdue Univ. t Lafayette, Ind. (December, 1969).
[2] Keulegan, G. H., "The Motion of Saline Fronts in Still Water, "
National Bureau of Standards, Report 5831 (1958).
[3] Von Karman, T., Bulletin Amer. Math. Society, 46, 618-83 (1940),
[4] Benjamin, T. B., "Gravity Currents and Related Phenomena, Journal
of Fluid Mechanics, 31, 209-48 (1968).
[5] Hinze, J. O., "Fundamentals of the Hydrodynamic Mechanism of.
Splitting up in Dispersion Processes, " A. I. Ch. E. Journal, 1,
289 (1955).
[6] Hu, S., and Kintner, R. C., "The Fall of Single Liquid Drops
Through Water, " A. I. Ch. E. Journal, _1, 42(1955).
[7] Christiansen, R. M., and Hanson, A. N.; Ind. and Eng. Chem.,
49, 1017-24, ,1957.
65
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APPENDIX A
LITERATURE SEARCH
The literature on oil pollution is very extensive. This search was
restricted to those works that dealt with the physical and chemical
removal of oil from the surface of the water, at the initiation of this
program.
Altenburg, Kirk and Co., Annual Report On Testing And Evaluation
Of Oil Spill Recovery Equipment, Maine Port Authority,
October 1969, 43 p.
American Petroleum Institute, Investigation Of The Behavior Of Oil-
Water Mixtures in Separators, Final Report, August 1951, 89 p.
American Petroleum Institute, Recommended Practice For Cleaning
Petroleum Storage Tanks, Safety and Fire Protection Committee,
API RP 2015, September 1968, 14 p.
Anonymous, Pneumatic Air Barriers; Effective Defense Against Oil
Pollution, Dockand Harbor Authority, September 1968.
Anonymous, Air Barrier Contains Spills, Oil and Gas J., December 9,
1968
Anonymous, The Treatment And Disposal Of Floating Oil» Report No.
RR/ES/40, Warren Spring Laboratory, Ministry of Technology,
United Kingdom, April 1963.
Barr, Bruce A., Reclamation Of Oil In A Large Industry, Purdue
University, Proceedings of the Fourth Industrial Waste Conference,
September 21-22, 1948, Ext. Ser-68, pp. 285-9.
Battelle Memorial Institute, Pacific Northwest Laboratory, Oil Spillage
Study Literature Search And Critical Evaluation For Selection Of
Promising Techniques To Control And Prevent Damage, Preliminary
report for U.S. Department of Transportation, Coast Guard,
November 1967, 301 p.
Battelle Memorial Institute, Study of Equipment and Methods For Removing
Oil From Harbor Waters, Report No. CR 70.001, August 25, 1969,
178 p.
Beduhn, George E., Removal Of Oil And pebris From Harbor Waters,
Civil Engineering Laboratory, Tech. Note N-825, n.d., 20 p.
67
-------
Blokker, P. C. , Spreading And Evaporation of Petroleum Products
On Water, Shell Oil Laboratory Report, Amsterdam, (date
unknown, but after 1961).
Bulson, P.S., Currents Produced By An Air Curtain In Deep Water,
Dock And Harbor Authority, May 1961, pp. 15-22.
Crown Zellerbach Corporation, Unpublished Research Memorandum
on Combating Oil Tanker Spills With Reclaimed Fiber From
Primary Treatment Plant Clarifiers, Camus, Washington, 1968.
Culbertson, T. L. , and A. L. Scott, Chemical Treatment Of Oil Spilled
On Harbor Waters, Technical Note N-983. Naval Civil Engineering
Laboratory, August 1968.
Dennis, JohnV., The Relationship Of Ocean Currents To Oil Pollution
Off The Southeastern Coast Of New England, American Petroleum
Institute, Transportation Division, January 1961, 30 p.
Dorrler, S.J., Limited Oil Spills At Naval Shore Installations, Utilities
Division, Atlantic Division, Naval Facilities Engineering Command,
Norfolk, Virginia, March 25, 1969.
Engineering-Science, Inc., Determination And Removal Of Floatable
Material From Waste Water, Prepared for U.S. Public Health
Service, Div. of Water Supply and Pollution Control, November
1965, 122p.
Executive Office of the President, The Oil Spill Problem, First report
of the President's Panel on Oil Spills, n.d. 25 p.
Fay, James A. , The Spread Of Oil Slicks On A Calm Sea, Massachusetts
Institute of Technology, August 1969, 14 p.
Federal Water Quality Administration, Chemical Treatment Of Oil Slicks,
A status report on the use of chemicals and other materials to
treat oil spilled on water, by Edison Water Quality Lab.
DAST-18, March 1969, 20 p.
Federal Water Quality Administration, Chemical Treatment Of Oil Spills,
by E. Struzeski, Jr., and R. T. Dewling, Edison Water Quality
Lab. Presented at Joint API-FWPCA Conference on Prevention
and Control of Oil Spills, December 15-17, 1969, New York City,
CWSP 10-23. December 1969, 20 p.
Federal Water Quality Administration, Oil Sampling Techniques, Progress
I eport, by Edison Water Quality Lab, DAST-12, RD-15080FHT12/69.
December 1969, 62 p.
Federal Water Quality Administration, Oil Skimming Devices, by Edison
Water Quality Lab. May 1970, 95 p.
68
-------
Federal Water Quality Administration, 1969, A Status Report On The
Use of Chemicals And Other Materials To Treat Oil Spilled On
Water, Northeast Region Edison, New Jersey.
Federal Water Pollution Control Administration, Use of Chemicals And
Other Materials To Treat Oil On Water, (Status Report),
Northeast Region Research and Development Program, February 24,
1967.
Giles, R. N., Oil-Water Separation, Purdue University Proceedings of
the Sixth Industrial Waste Conference, February 21-23, 1951,
Ext-ser-76, p. 1-9.
Glude, John B., and John A. Peters, Recommendations For Handling Oil
Spills Similar To That From The Tanker Torrey Canyon,
June 1967, 24 p.
Hawthorne, W. R., The Early Development Of The Dracone Flexible
Barge, Institute Of Mechanical Engineers, The Thirty-Third
Thomas Lowe Gray Lecture, 1961, 34 p.
Hazel, C.R., First Progress Report -- Development Of Testing Procedures
For Evaluating Oil Spill Cleanup Agents, State of California,
Fish and Game Water Pollution Central Laboratory, 1969.
Hoult, David P., Oil On The Sea, Proceedings Of a Symposium, May 16,
1969, Cambridge, Mass., Plenum, 1969, 114 p.
Hoult, David P., 1970, Containment Of Oil Spills By Physical And Air
Barriers, AIChE Meeting Presentation, San Juan, Puerto Rico,
May 20, 1970.
Hoult, David P., 1969, Containment And Collection Devices For Oil
Slicks, p. 65 in Oil On The Sea (David P. Hoult, editor), Plenum
Press, New York, New York.
Houston, B.J., Investigation of Materials And Methods For Use In
Removing Surface Layers Of Oil On Water, Miscellaneous Paper
C-68-5, Department of the Army, U.S. Corps of Engineers,
U.S. Army Engineer Waterways Experiment Station, Vicksburg,
Mississippi, September 1968.
Howland, W. E., Oil Separation In The Disposal Of Refinery Wastes,
Purdue University, Proceedings of the fourth Industrial Waste
Conference, September 21-22, 1948, Ext. Ser. 68pp. 278-84.
Kondo, G., M. Hayashi, and Y. Murakami, Studies On The Method Of
Collecting Oil From The Surface Of The Water, Osaka Industrial
and Technological Laboratory Quarterly, Vol. 18, No. 1, May 1967.
69
-------
Lane, F. W. , et al, Typical Methods and Devices for Handling Oil-
Contaminated Water From Ships and Industrial Plants, Mines
Bureau, Tec. Paper 385, 1926, 66 p.
Mannheimer, Richard J. , and Alan A. Johnston, Controlled Spreading
On A Water Surface Applied To Military Uses, Fuels and
Lubricants Research Laboratory, Report No. FLRL-2, May 1967,
13 p.
Morgan, M.J., Some Problems Of Oil Refinery Waste - Collection And
Segregation, Purdue University, Proceedings of the Second
Industrial Waste Conference, January 10-11, 1946, Ext. Ser-60.
pp. 144-6.
Petroleum Magazine, Oil Disposal With Foam, pp.197, 206, 209-227,
September-October 1967.
Ries, Herman E. , and James F. Grutsch, Removal Of Surface Con-
taminants From Refinery Waste Water, Presented April 5, 1968
at the 155th National Meeting of the American Chemical Society,
San Francisco, California (Symposium on Petroleum Environmental
Chemistry), 1968, 19 p.
Scott, A. L. , andS.E. Gifford, Removal Of Oil From Harbor Waters.
Naval Civil Engineering Laboratory, Technical Note N-964;
Port Hueneme, California, February 1968.
Secretary of the Interior and the Secretary of Transportation, Oil-
Pollution - A Report To The President. A report on pollution
of the nation's water by oil and other hazardous substances,
February 1968, 31 p.
Sigvolt, R., The Forces Causing Spreading Of Petroleum Products On
Water And Their Neutralization By Fatty Oils, Compt. Rend,
Vol. 259, No. 3, pp. 561-564, July 20, 19&4.
Smith, J. W. , Problems In Dealing With Oil Pollution On Sea And Land,
Journal of Institute of Petroleum, November 1968.
Stroop, D.V., Behavior Of Fuel Oil On The Surface Of The Sea,
Report on oil pollution experiments, December 1927, 29 p.
Swift, W. H. , et al. Oil Spillage Prevention, Control, And Restoration -
State Of The Art And Research Needs, Battelle Memorial
Institute, Pacific Northwest Laboratory, 1968, 59 p.
United Nations, Oil Wastes Treatment At A Hungarian Petroleum Works,
In Economic Aspects of Treatment and Disposal of Certain
Industrial Effluents - Vol 3, 1967, pp. 31-2.
70
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Walkup, P. C. , et al, Oil Spill Treating Agents - A Compendium, by
Battelle-Northwest for the American Petroleum Institute,
May 1970.
Wallace, A. T. , et al, The Effect Of Inlet Conditions On Oil-Water
Separators At Sohio1 s Toledo Refinery, Purdue University,
Proceedings of the Twentieth Industrial Waste Conference,
May 4-6, 1965, Ext. Ser-118, pp. 618-25.
Water Pollution Research Laboratory, Treatment Of Waste Oil-In-Water
Emulsions , Water Pollution Research 1955, pp.1 71-2.
Weiss, S.J., and C.W. Davis, Oil Slick Removal By The Absorption
Method, Technical Note N-106, Naval Civil Engineering Laboratory,
August 1952.
71
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APPENDIX B
THEORETICAL BASIS FOR EXPERIMENTAL
DESIGN OF THE SHOC CONCEPT
The basic principle which is responsible for the operation of the SHOC
Concept is that material which is less dense than water will, if sub-
merged, rise to the water surface and float. Thus, oils having specific
gravities less than one are capable of being collected. A schematic
drawing of a vessel with an inclined plane illustrating the principle of
operation is shown below. The forward velocity v, of the vessel causes
oil layer buildup
>il being
driven down
the incline
ill be
oil being concentrated
in collection well
Schematic Illustration of the Fixed Plane Concept
the oil to be driven down the underside of the unit. The positive buoyant
forces cause the oil to eventually rise, in the well. The nature of the
oil-layer buildup in front of the plane, the flow of oil down the incline
and subsequent collection in the well depends directly on the geometry
and velocity of the vessel as well as on the physical properties of the
oil. These three flow regimes are not independent of each other and
from a hydrodynamic viewpoint manifest themselves in a complex
method of oil collection.
72
-------
Recognizing the complexity of the collection mechanism and the need
for a thorough understanding of it so as to permit rational scaling to
large prototypes, a comprehensive literature search was conducted.
The results of the survey and a discussion of the analyses describing
the collection are presented in the following sections.
By the nature of its operation the SHOC concept requires that oil on
the water surface move relative to the vessel so as to flow down the
incline to the draft of the unit. The conditions for successfully
collecting oil are:
(a) When the oil-layer buildup extends sufficiently far in front
of the plane to cause the depth of oil layer to exceed the
draft of the vessel;
(b) If operating conditions are such that the oil buildup in front
of the plane shears off in globules that become transported
by the water and flow down the inclined surface;
(c) When sufficient shear stresses are developed between the
water and oil layer adjacent to the incline, causing the
oil to travel in sheets with a wavelike action.
These conditions are shown schematically in Section IV (Figure 2).
Condition (a) would occur at very low operating velocities. It is not
an effective mode of operation for a fixed plane and is, therefore, not
considered here.
As the vessel moves through the water the oil slick will progressively
thicken. The hydrodynamics of the buildup and subsequent behavior of
the oil is typical of two fluids intruding on one another, e.g. , a cold
front entering into warm air or salt water into fresh water. Thus, the
mode of operation associated with the breakup of the oil layer (condition
(b) ) can best be understood by considering the unstable behavior of a
layer of fluid intruding with velocity v on a more dense fluid (e.g. , oil
on water), as shown below.
intruding oil layer
73
-------
For such a system a head wave develops and thickens to a little over
twice the mean height of the oil layer. There is a turbulent zone on
its leaward side after which the interface becomes somewhat horizontal.
[2] An approximate relation between the mean height h and the velocity
vr can be obtained from Bernoulli's equation resulting in [3]
<"
where g = local gravity constant
p = mass density of water
p = mass density of oil
o
The stability of the layer behind the head wave has been investigated by
Benjamin by considering the effects of a perturbation at the interface [4] .
kh coth kh > 4- I 1 + —
where k = - (2)
\ = wavelength
which is satisfied for alt real values of k, meaning that the flow is un-
stable to all small disturbances. Such an instability is manifested
physically either as a spatially periodic disturbance that grows
exponentially with time or where a disturbance grows with distance
downstream. At relatively small velocities the amplitude of the inter-
facial waves is small because of the damping effects. However, as the
relative velocity of the two layers is increased, the amplitude increases
because of greater energy being transmitted to the oil layer. As the
amplitude progressively increases, globules and eventually droplets
of oil will be torn off the interface and become entrained in the water.
The velocity at which oil is torn off the wave face can be estimated
using the equation developed by Hinze for breakup and formation of
globules of a dispersed phase. [5]
This relationship is based on the critical Weber Number, W
c
74
-------
« prtd v
22 *= ° c (3)
v = critical relative velocity between the oil
and water
d = diameter of oil droplets
0" = interfacial tension between the two liquids
Weber's number, W , is approximately equal to 22 and has been found
to give good predictions for oil-water systems [6 ]. The equation
relates, for a given fluid (fixing p0 and 0"), the diameter of droplets
formed at various velocities. Now the maximum diameter of a stable
droplet can be estimated using the results of Christiansen and Hixson
obtained for breakup of liquid jets in denser liquids, viz. , [7]
Now combining Equations (3) and (4) one then obtains critical relative
velocity below which no droplets are formed
v =
c
1/4
(5)
where X = Specific Gravity of oil
Typical values of (Tare . 0016 Ibs/ft to .0024 Ibs/ft for oil and the range
of X0 which is of interest is . 85 to . 97. The results obtained from
Equation (5) using the above cited ranges of oil properties are given
in Table B-l.
The results contained in the table indicate lower bounds of the velocity
for droplet formation, i. e. , no droplet will form below . 45 ft/sec
regardless of the type of oil. It should be noted the specific gravities
in the order of .85 are indicative of #2 fuel oil and specific gravities
of . 97 are indicative of the residue oil such as #6, Furthermore, it
should be realized that the velocity values given in the table do not
mean that oil droplets will form at those velocities but are values below
75
-------
Table B-l.
Critical Velocities for Various Oil
Properties Below Which No Oil
Droplets are Formed
CT
Ibs/ft
.0016
.0024
.0016
.0024
\
o
.85
.85
.97
.97
V
c
ft/sec
.72
.79
.45
.50
which no droplets are expected to form. In order for the droplets to
form, sufficient undulation of the oil-water interface will be necessary
which may well require significantly higher relative velocities to over-
come damping in the oil buildup system. Velocities may be 50 to 100
per cent above those given in the table, viz, in the order of 1 to 1.5
ft/sec. Also indicated by the results in Table B-l is that the more
dense oils will tend to break up more easily.
It is worth noting that it may be desirable to intentionally induce damping
by the addition of surfaces in the vicinity of the incline. This would tend
to raise the velocity for a given size oil particle to occur.
Having obtained estimated minimum operating speeds for oil globule
formation, resulting in oil becoming entrained in the water stream, it
is now necessary to examine the trajectories of such formations in order
to estimate the length of the collection well. Since the oil globule paths
are directly governed by the forces acting on them, and since a signifi-
cant force, viz, the drag force, is a function of the size of the globule,
Equation (3) must be used to obtain a value of a mean globule diameter.
The globule size is a function of velocity for typical values of oil density
and surface tension. Figure B-l contains a plot of mean oil globule
diameter as a function of operating speed, vr, for typical limiting
values of surface tensions and specific gravities. It is interesting to
note that a limiting value of the relative velocity will be in the order of
3 to 4 it!Bee, since above this velocity range the particles sizes are
in the order of .025 inches which will cause problems in extracting
them from the water. It should be recognized that oil flowing on the
plane has a velocity so that the actual operating velocity of the vessel
or the water velocity can be higher than 4 fps.
Droplet Motion
Let it be assumed, for calculation purposes, that droplets form
sufficiently close to the inclined surface such that the downward velocity
imparted to the droplet is given by:
76
-------
-j
-a
U 1
3,
"3
> .8
.4
.01
A - specific gravity
O - surface tension
A0 = . 97
a = . 0024
A0=.85
a = .0024
. 1
Mean Diameter of Oil Globule (in. )
Figure B-l. Oil Globule Size vs Oil-Water Relative Velocity
1 ,
1
ll.
1
1
,1,
, 1 ,
-------
v ~ v sin 9
PY
where v = imparted downward velocity
PY
8 = incline angle of the plane
Such an assumption results in an upper bound on the magnitude of im-
parted downward velocity since many particles will form at some
distance from the inclined surface and consequently have a lower value
of downward velocity. Furthermore, it is reasonable to assume that
the flow of water can be described by potential flow theory. Once the
droplets become entrained in the water their motion will be governed
by the various forces acting on them. The significant vertical forces
acting on a droplet are shown below.
BF
D
BF = buoyant force
W = weight
D = drag force
W
An additional sidewise force exists because of velocity gradients but
such a force is small compared to the others shown and consequently
will not be included [ l] . The implicit assumption of uncoupling the
vertical and horizontal motion will also be used which is justified in
Stokes1 region.
The buoyant and weight forces are:
BF =
W.
(6)
(7)
78
-------
where d_is the diameter of the oil droplet
The drag force on a liquid particle can be determined from the work of
Hu and Kintner [6 ]. They investigated various immiscible liquid
systems and found that the motion of liquid drops differs from that of
rigid spheres because of deformation and oscillation of the drops as
well as flow on the drop surface and internal circulation. Their investi-
gation resulted in the following relationship between the drag coefficient,
densities,
'D
_4/3[Re/P -13 + .75]
. 15
We P
. 15
1.275
(8)
dv p
v
where Re = — *
Reynolds' Number
We =
vzdp
V "W
I rr Weber1 s Number
P =
P (0")
rw '
gM.
= drag coefficient
The drag force is
~ 1 ^ 2
D = •- p C v —r
Z rw v 4
(9)
being given by Equation (8)
The sum of all the forces in the vertical direction must be equal to the
rate of change of momentum of the particle plus the effect of virtual mass,
Hence, combining all the forces, one obtains
BF - W + D = (m + mv) -^
(10)
79
-------
where m = virtual mass of droplet
v = vertical velocity
by substitution
u w • w dv
p- + . . 1 = - 1 + _
Equation (11) is a first order non-linear differential equation which when
solved, gives the vertical velocity as a function of time which can be re-
lated to a horizontal position through
v • (t) = v (-)
y * ' y X V '
x = horizontal distance
t = time
the velocity profile can then be integrated to give vertical position as a
function horizontal position. Following such a procedure with approp-
riate initial conditions, particle trajectories can be obtained. Such an
approach was used by Wicks [l] considering droplets to have an initial
downward velocity Vpy of which •% which would correspond to an incline
angle of 30°. His results were surprising in that it was shown that
no significant error exists if it is assumed that the droplets have no
initial downward velocity and achieve terminal speeds instantaneously.
Thus, the right side of Equation (11) can be set equal to zero resulting in
P0 gpo
=0 (12)
where v t is the terminal vertical velocity
Using the value of C_. given by Equation (8) one obtains a cubic
equation on v , viz.
80
-------
Civyt+cz=°
(13)
where C. a 858 m
1 V P,
C =-9.34
7 '
p
p d
^
Equation (13) has been solved in Wicks [1] , and the results are pre-
sented in Table B-2 for various values of oil densities, interfacial
tensions, and particle diameters. The results from Table B-2 can
Table B-2. Terminal Velocities of Various-Size Droplets
for Oils of Different Specific Gravities and
Interfacial Tensions
Drop dia.
Inches
.002
.004
.010
.020
.040
. 100
.200
.400
Interfacial tension = . 00 14 Ibs /ft
Sp.Gr. =.85
Term. Vel.
ft /sec
.0054
.0109
.0272
.0544
. 1087
.2578
.3719
Sp. Gr. =.97
Term. Vel.
ft /sec
.0017
.0035
.0088
.0176
.0353
.0878
. 1668
.2394
Interfacial tension = . 0027 Ibs /ft
Sp.Gr. =.85
Term. Vel.
ft /sec
.0051
.0101
.0254
.0508
. 1015
.2471
.3962
.4329
Sp. Gr. = .97
Term. Vel.
ft /sec
.0016
.0033
.0082
.0165
.0329
.0821
. 1601
.2554
be used with critical droplet size from Figure B-2 to determine required
collection well lengths. For example, oil droplets of a No. 6 oil
(Sp. Gr. 97) at a relative velocity of 2 ft/sec have a terminal rise
velocity of about .061. Thus if such particles were in front of and
1 inch below the level of the collection well, the required well length L,
would then be
= 1 in
.061 ft/sec
x 2 ft/sec •» 2.8. ft
-------
00
n
i i 111
i i i 11
0- s surface tension 0.0016 Ibs/ft
o
X. =» specific gravity
D = 1/2 in.
2 4 6 8 10
Well Length (ft)
Figure B-2. Well Length vs Oil-Water Relative Velocity
D a initial distance of oil
globule below well
80 100
-------
Because of the difference in Sp. Gr. of the No. E and No. 6 oils, the
well lengths must be governed by the behavior of the No. 6 oil.
Figure B-2 contains a plot of required well length versus relative
velocity for oil droplets having a Sp. Gr. of . 97 (T = . 0016 Ibs/ft and
which are various distances below the bottom of the well.
It should be kept in mind that these collection-well lengths are based
on the assumption that the oil layer breakup and oil droplets become
entrained in the flow. There is, however, condition (c) where the
relative velocity between the oil layer and water i6 such that a sheet
like flow is obtained on the incline. Such a condition occurs at
shallow incline angles, with dense oils since the contribution of the
buoyant forces to resistance of flow down the incline is small.
83
-------
APPENDIX C
THE JBF DIP CONCEPT
The principle of operation of the JBF DIP (Dynamic Inclined Plane)
oil harvesting device is best described by reference to the figure below.
An inclined plane is located beneath the surface of the water, and there
are vertical plates on either side of the plane so that the water and oil
are confined between the plates. As the device moves through the oil,
the oil cannot move to the sides because it is confined by the side plates,
and thus it is concentrated at the intersection of the inclined plane and
the oil/water surface. The oil is then forced on the incline and carried
beneath the water, either by the forward movement of the device (or the
flow of water) or by the downward movement of the plane itself. This
movement of the plane is accomplished by operating an endless belt
over the rollers, as is schematically shown above. Oil is held against
the plane by a combination of hydrodynamic, buoyant, and cohesive
forces. The oil is collected in the well, and any residual oil is scraped
off the belt.as it passes through the well volume * Buoyant forces cause
JBF Scientific Corporation has patents pending on this device.
85
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the oil to surface in the well, forcing water out the bottom. As the
oil collects it is pumped off to storage tanks. Separation occurs
automatically, and virtually no water is collected.
Since the oil is beneath the water surface, waves and rough water
have a minimal effect on oil collection.
ft U. S. GOVERNMENT PRINTING OFFICE : 1973—Slfc-1 55/299
86
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1
Accession Number
w
5
2
Subject Field & Group
05G
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
JBF Scientific Corporation
2 Ray Avenue, Burlington, Massachusetts 01803
Title
The Development and Demonstration of an Underwater
Oil Harvesting Technique
10
Authoi(u)
Bianchi, Ralph A.
Henry, George
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Project Designation
15080 FWL
Note
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Citation
Environmental Protection Agency report
number, EPA-R2-73-205, April 1973.
22 I Descriptor* (Starred Fiat)
*Water Pollution Control, Oil;
Pollution Abatement
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Identifiers (Starred Pint)
^Mechanical Clean Up, Oil Spills;
*Oil Recovery Systems, JBF Scientific Corporation
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Abstract
Analytical studies and harbor tests were conducted to determine the feasibility of
harvesting oil beneath the surface of the water with the use of inclined planes.
The analytical and laboratory investigations provided basic information to design
and build units and showed that this kind of device could harvest both light and heavy
oils between 3/4 knot and 2 knots. Information was obtained regarding the geo-
metry of the device. Tests showed that oil could be collected in waves without
seriously affecting efficiency.
A 22-foot-long unit was designed, built, and demonstrated in Boston Harbor.
The results showed that the fixed-plane concept is highly effective in areas where
the vessel can travel through the slick. Recovered oil is virtually water free and
the unit recovered between 70% and 85% of the oil presented to it.
The fixed inclined plane (SHOC) demonstrator unit works between 3/4 knot and
2 knots. To extend the velocity range down to zero knots and over 2 knots, it is
recommended that a moving inclined plane be used. It is also recommended that
a set of effective sweeps be investigated and developed.
AbaiMcfor
Ralph A. Bianchi
Institution
JBF Scientific Corporation
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