United States
Environmental Protection
Agency
Industrial Environmental Research >rr'
Laboratory August 1978
Cincinnati OH 45268
Research and Development
c/EPA
Performance Testing of
the Tetradyne High Speed
Air Jet Skimmer
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2 Environmental Protection Technology
3 Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7 interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
Thts report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental 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.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-600/2-78-187
August 1978
PERFORMANCE TESTING OF THE
TETRADYNE HIGH SPEED AIR JET SKIMMER
by
William E. McCracken and Sol H. Schwartz
Mason & Hanger-Silas Mason Co., Inc.
Leonardo, New Jersey 07737
Contract No. 68-03-0490
Project Officers
Frank J. Freestone
John S. Farlow
Oil and Hazardous Materials Spills Branch
Industrial Environmental Research Laboratory
Edison, New Jersey 08817
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO A526S
-------
DISCLAIMER
The work described in this report was conducted under the sponsorship
of the U.S. Environmental Protection Agency. This report has been
reviewed by the Office of Research and Development, U.S. Environmental
Protection Agency, and approved for publication. Approval does not
signify that the contents necessarily reflect the views and policies of
these agencies, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
ii
-------
FOREWORD
When energy and material resources are extracted, processed, con-
verted, and used, the related pollutional Impacts on our environment and
even on our health often require that new and increasingly more efficient
pollution control methods be used. The Industrial Environmental Research
Laboratory - Cincinnati (lERL-Ci) assists in developing and demonstrating
new and improved methodologies that will meet these needs both efficiently
and economically.
This report describes performance testing of a research prototype,
air jet, thin film, high speed oil skimmer. Based on these results, a
number of design modifications are suggested. The methods, results, and
techniques described are of interest to those interested in specifying,
using or testing such equipment. Further information may be obtained
through the Resource Extraction and Handling Division, Oil and Hazardous
Materials Spills Branch, Edison, New Jersey.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
-------
ABSTRACT
The U.S. Environmental Protection Agency evaluated the performance
of the prototype Tetradyne High Speed Air Jet Skimmer at their OHMSETT
Test Facility at Leonardo, New Jersey. The skimmer depends on an air-
jet impacting the water surface at an angle and deflecting rapidly
moving, floating, spilled material laterally into a low-current chamber
for ease in recovery. The objective of the testing program was to
determine the ability of the Tetradyne skimmer to pick up a large area,
thin film (0.1-1.0 mm) spill of floating oil in water currents up to 3
m/s. The four test fluids used during the program, No. 2 fuel oil,
naphtha, and two lubricating stocks, encompassed a wide range of physical
properties. The recovery performance parameters determined were recovery
rate and throughput efficiency. The effects of film thickness, fluid
viscosity, fluid specific gravity, and fluid interfacial tension on
skimmer performance parameters under fast current conditions are presented.
Modifications for further improving performance are recommended.
This report was submitted in fulfillment of Contract No. 68-03-
0490, Job Order No. 23, by Mason & Hanger-Silas Mason Co., Inc., Leonardo,
New Jersey, under the sponsorship of the United States Environmental
Protection Agency. This report covers a period from May 11, 1976, to
May 13, 1976, and work was completed as of December 1977.
iv
-------
CONTENTS
Foreword ±±±
Abstract 'iv
Figures v±
Tables vi
Abbreviations and Symbols vii
List of Conversions viii
Acknowledgement lx
1. Introduction 1
2. Conclusions 3
3. Recommendations 5
4. Description of Tetradyne Skimmer 6
5. Test Plan 11
6. Test Procedures 15
7. Results and Discussion 18
References 25
Appendices
A. OHMSETT Description 26
B. Tetradyne Laboratory Testing and Skimmer
Design Data 28
-------
FIGURES
Number Page
1 Tetradyne High Speed Air Jet Skimmer under test in a
0.3 m Harbor Chop 6
2 Tetradyne High Speed Air Jet Skimmer in Calm Water .... 7
3 OHMSETT Modified Collector Configuration 8
4 Air and Water Current Interaction Moving Surface Oil ... 10
5 Sketch of Tetradyne Skimmer Test Arrangement 16
6 Maximum Throughput efficiency versus Tow Speed for the
Tetradyne Skimmer with Lube Oil 21
7 Throughput efficiency versus Lube Oil Slick Thickness
for the Tetradyne Skimmer 22
8 Tetradyne Skimmer throughput efficiency variation with changes
in specific gravity, interfacial tension and
viscosity 24
TABLES
1 Test Fluids Properties in Design Matrix 13
2 Actual Fluid Physical Properties at 12.8°C 13
3 Proposed Test Matrix Tetradyne Skimmer 14
4 Test Results Tetradyne Skimmer 20
vi
-------
ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
cm —centimetres
IFT —interfacial tension
kg —kilogram
kPa —kiloPascal
kw —kilowatt
m —metre
m3 —metre cubed
m/s —metre per second
m2/s —metre squared per second
m3/s —metre cubed per second
m3/hr —metre cubed per hour
ml — millilitre
mV —millivolt
ppt —parts per thousand
s.g. —specific gravity
Va —air velocity at water surface
Ve —towing velocity
VT —transverse oil velocity
SYMBOLS
°C —degrees Celsius
$ —angle of air jet to water
6 —angle of boom to skimmer centerline
3 —percent efficiency of oil movement
vii
-------
LIST OF CONVERSIONS
METRIC TO ENGLISH
To convert from
Celsius
joule
joule
kilogram
metre
metre
metre2
metre2
metre3
metre3
metre/second
metre/second
metre2/second
metre3/second
metre3/second
newton
watt
ENGLISH TO METRIC
centistoke
degree Fahrenheit
erg
foot
foot2
foot/minute
foot /minute
foo t-pound-force
gallon (U.S. liquid)
gallon (U.S. liquid)/
minute
horsepower (550 ft
Ibf/s)
inch
inch2
knot (international)
litre
pound-force (Ibf avoir)
pound-mass (Ibm avoir)
to
degree Fahrenheit
erg
foot-pound-force
pound-mass (Ibm avoir)
foot
inch
foot2
inch2
gallon (U.S. liquid)
litre
foot/minute
knot
centistoke
foot3/minute
gallon (U.S. liquid)/minute
pound-force (Ibf avoir)
horsepower (550 ft Ibf/s)
metre2/second
Celsius
joule
metre
metre2
metre/second
metre'/second
joule
metre3
metre3/second
watt
metre
metre2
metre/second
metre3
newton
kilogram
Multiply by
tc - (tp-32)/1.8
1.000 E+07
7.374 E-01
2.205 E+00
3.281 E+00
3.937 E+01
1.076 E+01
1.549 E+03
2.642 E+02
1.000 E+03
1.969 E+02
1.944 E+00
1.000 E+06
2.119 E+03
1.587 E+04
2.248 E-01
1.341 E-03
1.000 E-06
tc " (tF-32)/1.8
1.000 E-07
3.048 E-01
9.290 E-02
5.080 E-03
4.719 E-04
1.356 E+00
3.785 E-03
6.309 E-05
457
540
6.452
5,
1.
4.
144
000
448
4.535
E+02
E-02
E-04
E-01
E-03
E+00
E-01
viii
-------
ACKNOWLEDGMENTS
The authors wish to acknowledge the efforts of Mr. Frank J. Freestone,
U.S. Environmental Protection Agency, for his direction and planning of
this study and Mr. M.G. Johnson, Mason & Hanger-Silas Mason Co., Inc.,
for his expertise in the design and fabrication of the test device.
-------
SECTION 1
INTRODUCTION
PREVIOUS WORK
In considering resolutions to the problem of a large-area, thin-
film oil slick floating on the surface of a river, harbor, or estuary,
it becomes apparent that physical removal of the oil from the surface of
the water is most environmentally desirable. To collect a large-area
slick in a short period of time, one may treat either a wide swath at a
slow or moderate speed or a relatively narrow swath at a higher speed.
Sorbent deployment and retrieval techniques have been developed by the
U.S. Environnmental Protection Agency to advance the state-of-the-art of
slow and moderate speed technology. Hitherto, cleanup has been ineffective
at high speeds where the relative velocity of the oil and water normal
to the pickup or control device exceeds about 1.0 m/s. These high speed
conditions are found in rivers, harbors, or open estuaries with high
currents, or whenever pickup of the slick is attempted as quickly as
possible by successive passes.
The speed limitation of present devices is invariably caused by
their unfavorable interactions with the flow regime of oil and water
moving relative to them. If efficiency at higher speeds is to be
achieved, the hydrodynamic flow conditions around the device must be
taken into account and, if possible, used or altered to advantage.
In 1974 the United States Environmental Protection Agency (EPA)
sponsored two separate research contracts in the field of high-speed
devices for the recovery of thin-film oil spills (1, 2, 4). Both projects
involve deflecting oil that is moving relative to the device by means of
an air jet so that the resulting oil and water spray can be captured and
separated. Additionally, the U.S. Coast Guard sponsored a fast current
study in 1975 (3).
The project conducted by Tetradyne Corporation of Richardson,
Texas, used air jets to concentrate and, subsequently, deflect oil into
a sump for gravity separation. According to their report this device
achieved up to 86% (vol/vol) throughput efficiency at a speed of 1.8 m/s
in towing tank tests of a full-scale prototype; it was relatively
insensitive to waves, small debris, and changes in oil viscosity (1).
SCOPE
This report describes performance tests of the Tetradyne skimmer
-------
with oil and floating hazardous materials in the EPA OHMSETT test tank
facility (Appendix A). Test conditions and procedures were designed to
correspond with typical inland and harbor waterways. The test fluids
selected for this project were Lube oil (Sunvis 75), No. 2 fuel oil,
Sunvis No. 31, Sunvis No. 7, and Naphtha, which together provided a wide
range of physical properties.
-------
SECTION 2
CONCLUSIONS
The test results indicate that the Tetradyne Air Jet skimmer needs
further development to effectively recover thin film (=0.1 mm) slicks in
fast currents (2.0-3.0 m/s). Skimmer performance deteriorated in calm
water with tow speeds above 1.5 m/s, and during a single test with the
0.3 m (height) harbor chop moving at 1.5 m/s, performance deteriorated
until the skimmer became completely ineffective.
Previous laboratory test and tow tank test results with this skimmer
were not confirmed by the tests at OHMSETT. Throughput efficiency was
typically below 50% and recovery rates were below 2.3 m3/hr, as con-
trasted with those previously reported by Tetradyne (4).
Possible reasons for the lower performance were:
inadequate air supply to maintain a constant and uniform
nozzle velocity > 12 m/s
inadequate instrument and air flow controllers to measure and
maintain the air flow to the booms
inadequate oil distribution and collection techniques to
accurately measure and control the rate and volume of oil lay-
down and removal at the end of each run.
However, despite these quantification deficiencies in thin-film
testing technique, qualitative data (films, slides and observations)
confirmed that even when the nozzle velocity was strong enough to cause
a 0.6 m spray, the throughput efficiencies never were near the pre-
viously reported values (80Z). Stronger air velocities appeared to
cause both air bubble and oil droplet entrainment at the fast-current
speeds. Black and white underwater video documents this gross entrain-
ment problem. Design changes could possibly overcome this difficulty by
directing the air jet more parallel to the water surface.
Tests using a variety of test fluid thicknesses did indicate a
definite performance break point at about 0.2 mm. With thinner slicks,
throughput efficiency was significantly higher.
Although the experimental errors were larger than normal, order-of-
magnitude changes in oil viscosity and interfacial tension did seem to
-------
affect performance significantly. As the viscosity and interfacial
tension were each made larger (while the other two properties and test
conditions were held constant), the throughput efficiency increased
significantly. Although varying the specific gravity from 0.75 to 0.85
has no significant effect, it is felt that specific gravity above 0.85
(near 1.0) would become critical and cause excessive oil entrainment, as
has been shown with other skimmers and test projects at OHMSETT (5).
-------
SECTION 3
RECOMMENDATIONS
An optimum air jet skimmer design can only be achieved through a
better understanding of the interaction of the air jet with the floating
oil. Since the amount of kinetic energy transferred to the oil slick
depends upon the angle of incidence of the air jet, it is doubtful that
this type qf skimmer would be effective in waves characterized by short
periods and large amplitudes.
Further testing of this skimmer at OHMSETT is recommended, provided
certain design changes are implemented. The most significant improve-
ment would be the use of an air supply adequate to maintain an air jet
velocity of at least 12 m/s. Air flow control dampers should be used to
carefully control the air flow to the diverter and collector booms.
Fitot tubes or other similar instrumentation should also be used to
measure the air velocity in each of these booms. The optimum design
would utilize controls to automatically regulate the air flow dampers,
air blower, and nozzle angles in order to maintain the jet velocity.
Boom angles and nozzle angles should be made easily adjustable within
certain ranges above and below the optimum suggested equipment settings.
-------
SECTION 4
DESCRIPTION OF TETRADYNE SKIMMER
The original prototype Tetradyne skimmer (1974) was damaged in
transit from Texas and then rehabilitated for these tests (Figures 1, 2,
and 3). The skimmer was constructed from an aluminum boat hull. The
38.1 cm wide by 40.6 cm high flow-through channel was made from aluminum
sheet. This unit incorporated a false bottom with two collection chambers
and utilized air flow to hold the oil in the chambers. The diverter and
collector booms and nozzles were also constructed from sheet metal.
Figure 1. Tetradyne High Speed Air Jet Skimmer under test in a
0.3 m harbor chop.
-------
Figure 2. Tetradyne High Speed Air Jet Skimmer in calm water.
-------
Plan View
oo
1 Collector boom
2 Flow thru channel
3 Diverter boom
4 Air weir
5 Honeycomb
6 Bulkhead
7 Primary separation area
8 Secondary separation area
9 False bottom
10 Water discharge
Cross Section
Figure 3. OHMSETT modified collector configuration.
-------
Tetradyne's Air Jet Skimmer (1) depends on the simple principle
that an air stream directed at an angle to the surface of the floating
oil may be used to move the oil rapidly and horizontally across the
water. If this air stream consists of an elongated air curtain, it can
sweep a large area and concentrate the oil for collection. Figure 4
schematically shows the conditions which occur when air impinges on an
oil/water interface with a relative velocity of 12 to 18 m/s between the
boom air and the oil/water combination. This may result from the move-
ments of the air stream, the boom itself, the water, or any combination
of these relative to the earth.
Two factors help to direct the oil. First, the impinging air acts
directly on the oil to move it with the air flow. Second, the surface
of the water is distorted into a trough with a standing wave in front of
it. This standing wave also helps to prevent the oil from passing
through the air curtain. Also, a water current is generated which helps
to move the oil.
Tests have shown that winds blowing horizontally across the water
surface move oil at approximately two percent of the wind velocity.
This relatively poor interaction is largely due to a thick boundary
layer of slower moving air near the water. Tests with the air sweep
system show that it causes a much stronger interaction to occur between
the oil and the air stream, because the air is directed downward at the
water surface, overcoming the boundary effect. Air booms have been used
to hold oil directly against currents up to 0.9 m/s; however, at higher
speeds an oil headwave forms and entrainment occurs.
In these tests, it was decided that 1.3 cm boom nozzles would be
utilized, although the 1.9 cm nozzles would be used for larger models.
This decision was based on the limited capacity of the blower and the
air compressor available to supply air to the nozzles. The key parameter
which had to be held constant during the tests was the air velocity at
the water surface.
-------
Water Surface
Water Drops
Current Retains Oil
Figure 4. Air and water current interaction moving surface oil.
-------
SECTION 5
TEST PLAN
TEST RATIONALE
For the Tetradyne skimmer, thin film oil recovery is based upon
four principles:
1. A low pressure air jet directed at a 45° angle to the surface
of water will move oil by means of an induced water surface
current and by the surface drag of the rapidly moving air on
the oil film (Figure 4).
2. A strong air jet directed onto the surface of water with a
floating film of oil will "rip" the oil and some of the sur-
face water from the main body and transport the oil and water
in the form of a spray for a short but useful distance.
3. This oil/water spray can be separated by gravity.
4. The oil cannot be satisfactorily collected if it is permitted
to pass through hydraulic disturbances such as bow waves or
hydraulic jumps.
The above-mentioned low pressure jet (see 2) Is used to herd the
oil and thicken it into a windrow of chosen width. The windrow of oil
is then passed into the body of the device by means of an open-top
channel that has no changes in cross section, originates well ahead of
the bow wave caused by the pickup unit, and passes completely through
the pickup unit. The strong jet (see 2) is used to rip the windrow
of oil from the surface of the water in the channel and direct it into
the body of the pickup unit. The oil and water are then separated by
gravity within the pickup unit.
Previous prototype testing of this device has indicated a direct
relationship between performance and the following variables (see
Appendix B): .
1. towing velocity; Ve
2. collector boom settings; 0, $, and h» the nozzle height above
water
3. diverter boom settings; 0d, * , and h^
11
-------
4. air velocity at the water surface; Va (12.2 m/s)
Tests conducted at OHMSETT were aimed at measuring the skimmer's
pil pickup capabilities with various waves, currents, and differing test
fluids. First, a series of tests was designed to use a lube oil to
optimize the skimmer's design parameters (including its trim) while
varying film thickness, tow speed, and wave conditions. Then, the
skimmer was tested with other fluids for pickup performance and de-
pendence upon such slick properties as viscosity, specific gravity and
interfacial tension.
TEST MATRIX DESIGN
Two test series were designed to accomplish the above-mentioned
objectives:
1. Skimmer performance versus tow speeds (up to 3 m/s) at various
film thicknesses (less than 1.0 mm) and wave conditions
2. Skimmer performance versus fluid properties such as viscosity,
specific gravity (s.g.) and interfacial tension (IFT) at
various tow speeds under calm water conditions.
Skimmer performance parameters were defined as follows:
Throughput efficiency (TE) - volume of oil recovered by the
skimmer divided by the volume of oil actually encountered.
Oil recovery rate (ORR) - volume of oil recovered divided by
test time interval during.which it was recovered.
During the first series of tests (with lube oil), the following
design parameters were adjusted to optimize skimmer pickup performance:
1. air flow, cfm,
2. height of nozzles above the water,
3. angle of the nozzles with respect to the water,
4. trim of the skimmer vessel under tow, and
5. length of the collector boom nozzle opening.
The test conditions for this series covered the following ranges:
1. oil thickness: 0.05 mm to 1.0 mm
2. oil slick width: 3.5 mm
3. oil type: lube 100 x 10-6m2/s, 0.85 s.g., 7 x 10~3N/m IFT
4. wave conditions: calm, 0.3 m harbor chop
5. tow speeds: 1.5, 2.0, 2.5, and 3.0 m/s
During the second series of tests, various fluids were used to
achieve significant differences in viscosity, specific gravity, and
interfacial tension of the slick. The goal was to change one of the three
properties independently while holding the other two constant and
12
-------
repeating the test conditions in each case; thus, the only variable
affecting the skimmer performance would be the property of the specific
oil. The planned and actual test fluid properties for this series are
given in Tables 1 and 2.
TABLE 1. TEST FLUID PROPERTIES IN DESIGN MATRIX*
Property
varied
Viscosity
Specific Gravity
Interfacial Tension
Viscosity
x 10~6m2/s
10
100
10
10
25
25
Specific
gravity
0.85
0.85
0.75
0.85
0.85
0.85
Interfacial
tension
x 10- 3 N/
10
10
10
10
30
10
m
*Nominal property values are listed.
TABLE 2. ACTUAL FLUID PHYSICAL PROPERTIES AT 12.8°C
Type Test
code fluid
A Lube oil
B No. 2 fuel oil
C Naphtha (low
pressure)
D Sunvis 7 oil
E Sunvis 31/#2
Viscosity
x 10~6m2/s
102.0
7.0
5.0
25.0
25.0
Specific
gravity
0.850
0.845
0.780
0.850
0.860
Interfacial
tension
x 10" 3 N/m
7.0
5.0
7.0
24.0
5.0
Water
content
%
0.2
0.2
0.2
0.2
0.2
The proposed test matrix is given in Table 3.
13
-------
TABLE 3. PROPOSED TEST MATRIX TETRADYNE SKIMMER
Test no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21*
Test fluid type
A
A
A
A
A
A
A
A
A
A
A
A
B
B
C
C
D
D
E
E
E
Slick thickness
nun
0.1
0.5
1.0
0.1
0.5
1.0
0.1
0.5
1.0
0.1
0.5
1.0
0.1
0.1
0.1
0.1
0.5
0.5
0.5
0.5
0.5
Tow speed
m/s
3.0
3.0
3.0
2.5
2.5
2.5
2.0
2.0
2.0
1.5
1.5
1.5
1.5
2.5
1.5
2.5
1.5
2.5
2.5
2.5
1.5
*Test No. 21 was conducted with 0.3 m harbor chop waves.
were in calm water.
All other tests
14
-------
SECTION 6
TEST PROCEDURES
GENERAL TEST PROCEDURES
Prior to testing, the skimmer was deployed in the tank according to
the manufacturer's recommendations. The following unique features of
the Tetradyne skimmer (Figure 3) required special attention:
1. Collection boom nozzle - 1.27 cm width, 10 cm height (h) above
the water, 45° angle of air jet to water (*), 1.8 m long, and
angled horizontally 15° to the longitudinal center line of the
skimmer (0).
2. Diverter boom angled (horizontally) 45° to the longitudinal
center line of the skimmer.
3. Air flow rate - air dampers were used to regulate air flow to
the air Jet booms to maintain Vfl _> 12 m/s (horizontal air
velocity at the water surface).
The test device was connected by ropes between the main tow bridge
and the video truss. Figure 5 schematically shows the general test
arrangement and the manpower distribution.
First, air flow to the skimmer collector and diverter booms was
checked. After all systems were verified as being in operation, a
series of shakedown runs was performed to confirm the stability of the
device when under tow. Next, performance testing began, with the surface
conditions, tow speed, and oil distribution was varied in general accordance
with the proposed Test Matrix (Table 3).
The tow tests were conducted in the following manner. An oil slick
was laid down from the main bridge onto the water surface several feet
ahead of the skimmer under tow. The device encountered the 1.5 m wide
slick at various speeds from 1.5 m/s to 3.0 m/s. At the end of each
test run, the recovery time and the temperature and volume of the
recovered fluid were measured.
Total recovery rate was determined from the total volume of recovered
oil/water mixture and the duration of the recovery time.
Samples of the oil/water mixture were analyzed in the chemistry
15
-------
t
Direction of Tow
Tetradyne Test Skimmer
Recovered Oil Hose
Reverse Tow Line
t.
Cs) G)
Video Truss
P
V
I
Manpower Distribution
(I) Test Director
(2) Fluids Dispensing Operator
(5) Valve Operator
(4) Recovery Technician
(T) Photographer
(T) Data Documentation Officer
Figure 5. Sketch of Tetradyne skimmer test arrangement(plan view)
16
-------
laboratory to determine accurate oil and water percentages. Oil recovery
rate was calculated by multiplying the total recovery rate by the percent
oil.
As is shown below, throughput efficiency was measured using total
oil collected and total oil distributed (the device encountered all the
test oil):
TE = volume of oil collected
volume of oil distributed.
MEASUREMENTS
Various measurements are made during the testing. These measure-
ments generally include: Air—wind speed, direction, temperature;
Water—temperature at the tank surface and mid-depth, specific gravity,
chemical content (test fluid), wave height and length; Test fluid--
temperature during the test, viscosity at that temperature, specific
gravity, surface tension, interfacial tension with tank water, distri-
bution volume, slick thickness; Recovered Material—total volume,
volume of test fluid, volume of water, temperature; Time—duration of
test fluid distribution, equilibrium time, total test time, various
interval times; speed of the bridges; and distance traveled both during
total run and at equilibrium. In addition to written records of the
above measurements, 16 mm color movie and 35 mm color slide records were
made of the testing. Underwater black and white videotapes were also
made to record oil entrainment and flow characteristics in the oil
recovery zone.
17
-------
SECTION 7
RESULTS AND DISCUSSION
GENERAL
The first series of test runs concentrated on adjusting the con-
trolled variables for optimum oil pickup at tow speeds up to 0.3 m/s and
in waves. The following adjustments resulted from these tests:
1. Air flow rate was increased to the maximum by combining the
compressor and blower.
2. Height of collector nozzles above the water was decreased to
=5.1 cm.
3. Length of the collector nozzle was decreased from 2.7 m to 1.8
1.8 m.
Nozzle air velocity, V& (from the above adjustments), resulted in
observed air-impingement-spray heights equal to those documented previously
(1).
A. Angle of jets to water was adjusted to =45°.
5. Trim of the skimmer was fixed such that the height from the
top rear edge of the skimmer was =0.3 m above the water
surface.
Wave tests were run to determine skimmer stability and response in
0.3 m and 0.6 m harbor chop waves, and in a 0.6 m x 9.1 m 3.0 sec
regular wave. After several shakedown runs, each involving a different
trim adjustment, it was concluded that the prototype skimmer as designed
could not operate in these waves. With the air jet nozzles set at 5.1
cm of the mean (still) water level, the test waves washed up above the
nozzles, submerging them and rendering the air jet ineffective. The air
impingement velocity varied significantly with wave height as the nozzle
height above the water surface went from zero to =0.6 m in the large
waves tested. Only one wave test was run with oil (test No. 21); performance
dropped significantly below that in an equivalent calm water test.
Recovery rates were low (maximum » 15.6 x 10~5m3/s) for the following
reasons:
18
-------
1. The Tetradyne device is a thin film Air Jet skimmer. Thin
film skimmers are designed to recover oil slicks spread so
thin that other conventional skimmers would either be unable to
pickup or suffer low performance unless the oil was thickened
with booms. Thin film testing requires low oil distribution
rates, especially for a skimmer sweeping (i.e. for 0.1 mm
slick, 1.5 m wide, traveling 3.0 m/s, the oil distribution
rate was 46.7 x 10~5m3/s).
2. Difficulty was experienced in removing the small volumes of
recovered oil from the Tetradyne collection wells for mea-
surement.
Greater air delivery capacity would definitely improve the skimmer's
performance, permitting the use of longer collector booms and promoting
higher recovery rates.
TOW SPEED TESTS
Throughput efficiency (the ratio of oil recovered to oil encountered)
was considered the most meaningful and measurable performance parameter
for this skimmer. Throughput efficiency of 100% means that the skimmer
was picking up all of the oil it encountered during the test run.
Performance was measured in calm water under fast current test condi-
tions (1.5 to 3.0 m/s). As shown in Table 4 and Figure 6, throughput
efficiency dropped sharply as tow speed approached 2.5 m/s and was
nearly zero (within measurement accuracy) at 2.5 m/s and 3.0 m/s. It
appeared that as tow speed increased, more air flow (higher nozzle
velocity) was needed to offset the increased momentum of given volumes
of floating oil encountering the skimmer at higher relative velocities.
SLICK THICKNESS TESTS
Since the Tetradyne skimmer was designed for thin film operations
and no^practical upper limit existed on slick thickness to define "thin
films," tests were run to measure throughput efficiency versus slick
thickness. As shown in Table 4 and Figure 7, throughput efficiency
dropped sharply for slick thickness beyond 0.2 mm. Therefore, at least
for this skimmer, with the low air flow rates tested, thin film-oil
slicks should be defined at _< 0.2 mm thickness.
Accuracy of the slick thickness on the water surface was a matter
of continuing concern during testing, especially for films < 0.2 mm
thick. Inaccuracies might have been introduced in the following ways:
1. Oil volume distribution—the positive displacement flow meters
used were not designed for accurate measurements below 63.1 x
10~ m /s. Therefore, even though volumes could be measured,
accurate flow rates could not be maintained.
2. Tow Speed—periodic checks on actual versus tachometer tow
speeds indicated some differences (i.e. 3.02 m/s versus 2.83
19
-------
TABLE 4. TKST KISIILTS TETKAIHNE SUHMKH
twit
5/11
5/11
5/11
5/11
S/U
5/11
s;u
5/11
5/12
5/12
5/12
1/12
5/U
5/n
5/12
5/12
5/12
5/12
5/13
5/13
5/13
5/13
5/13
5/13
J/13
5M3
5/13
5/13
5/13
5/13
5/13
Time
1)10
1334
U15
1455
1515
1620
IMS
17,-i
1015
15)45
1140
1255
1320
U45
1410
1505
1600
1640
1120
1310
1110
IH.'S
IliO
1625
IMS
092S
1
-------
ISJ
40
30
U
M
fe
fa
W
H
P
PM
§
20
10
0.0
0.5
.2 mm slick thickness
Q . 1 mm
J_
1.02
1.52 2.03
TOW SPEED
.2 mm
2.54 3.05 m/s
Figure 6. Maximum throughput efficiency versus tow speed for the Tetradyne Skimmer with Lube
Oil.
-------
40,-
30
KJ
U
3 20
1
10
0
0.0 0.2
0.4
1.0
_l
1.2
Figure 7
0.6 0.8
SLICK THICKNESS mm
Throughput efficiency versus Lube Oil slick thickness for the Tetradyne Skimmer.
-------
m/s actual for a 6.7% error).
Though these inaccuracies affect the character of the tests, per-
formance (throughput efficiency) was measured volumetrically, independent
of flow rates and film thickness inaccuracies.
OIL PROPERTIES TESTS
Skimmer performance is definitely a function of the physical properties
of the oil encountered (6) . Therefore, tests were run to determine the
effects of specific gravity, interfacial tension, and viscosity on
throughput efficiency.
Test results shown in Table 4 and Figures 8a, 8b, and 8c indicate
the effects of the physical properties on throughput efficiency. The
results are summarized below:
1. Specific gravity—there appeared to be no significant effect
on throughput efficiencies when S.G. varied from 0.75 to 0.85.
2. Interfacial tension (between oil and sea water)—throughput
efficiency increased sharply as IFT increased from 5 to 25 x
10~3 N/m.
3, Viscosity—throughput efficiency Increased significantly as
oil viscosity increased from 10 to 110 x 10~6m2/s.
Although, not measured, the interfacial friction between the air
jet and the oil would significantly effect performance. This factor
depends, among other things, on the angle between the air jet and the
water surface. Therefore, in rough or wavy waters, this angle could
change rapidly, randomly and drastically, causing erratic skimmer per-
formance.
MEASUREMENT ACCURACY
There are inherent difficulties in accurately measuring small
volumes when conducting large scale tests. Even though 1,000-ml grad-
uated laboratory cylinders were used when appropriate, the difficulty of
removing collected oil from the secondary separation area of the skinner
caused uncertainties. A thin coating remaining on the walls might
amount to as much as 1.9 x 10~3m3, which is 5Z of a typical recovery
volume of 3.8 x 10~"2m3.
23
-------
20
td
M
0
M
10
I
§
No waves, 1.5 m/s
Avg. Film Thickness = 0.27 mm
IFT = 10 x 15-3N/m Viscosity = 10 x 10-6m*/s
0.75 0.80 0.85
(a) SPECIFIC GRAVITY
25
U
a
W
CM
W
o
ED
§
No waves, Thickness
S.G. = 0.85
Viscosity = 10 x 10 6m2/s
0.29 mm
1
I
5 15 25
(b) INTERFACIAL TENSION (xlO~3N/m)
20 — -°
O
H
10
No waves, Thickness = 0.23 mm
S.G. - 0.85, IFT = 10 x 10~3N/m
HROUGHPUT
D
i f
t
M 0 20 40
(c) VISCOSITY
I
60
(xlO-6m2
1
100
/s)
,1
120
Figure 8. Tetradyne Skimmer throughput efficiency variation with changes
in specific gravity, interfacial tension and viscosity. (Plotted
data points are average of two test runs).
24
-------
REFERENCES
1. Anderson, R.A. Air Sweep - The Development of a High - Velocity
System for Rapid Removal of Large Area Oil Spills. Technical
Memorandum. Contract No. 68-03-0327. U.S. Environmental Pro-
tection Agency, Edison, N.J.
2. Freestone, F.J., R.A. Anderson, and N.P. Trentacoste. United
States Environmental Protection Agency Research in High-Speed
Devices for the Recovery of Thin-Film Oil Spills. In: Proceedings,
Conference on Prevention and Control of Oil Pollution. American
Petroleum Institute, Washington, D.C. 1975. pp. 409-419.
3. Mueller, F.N. Fast Current Oil Response System. CG-D-115-75, U.S,
Coast Guard, Washington, D.C., 1975.
4. McCracken, W.E., and S.H. Schwartz. Performance Testing of Spill
Control Devices on Floatable Hazardous Materials. EPA-600/2-77-
222, U.S. Environmental Protection Agency, Cincinnati, Ohio, 1977.
139 pp.
5. Trentacoste, N.P. Surface Effects Skimmer Development.
U.S. Environmental Protection Agency, Cincinnati, Ohio, 1974.
(Available from NTIS, Springfield, Virginia, NTIS PB 242391/AS)
6. Wilkinson, D.L., Dynamics of Contained Oil Slicks. In: Proceedings
American Society of Civil Engineers: Journal of the Hydraulics
Division. June 1972. pp. 1013-1030.
25
-------
APPENDIX A
OHMSETT TEST FACILITY
Figure A-l. OHMSETT Test Facility.
GENERAL
The U.S. Environmental Protection Agency is operating an Oil and
Hazardous Materials Simulated Environmental Test Tank (OHMSETT) located
in Leonardo, New Jersey (Figure A-l). This facility provides an environ-
mentally safe place to conduct testing and development of devices and
techniques for the control of oil and hazardous material spills.
The primary feature of the facility is a pile-supported, concrete
tank with a water surface 203 metres long by 20 metres wide and with a
water depth of 2.4 metres. The tank can be filled with fresh or salt
water. The tank is spanned by a bridge capable of exerting a force up
to 151 kilonewtons, towing floating equipment at speeds to 3 metres/second
26
-------
for at least 45 seconds. Slower speeds yield longer test runs. The
towing bridge is equipped to lay oil or hazardous materials on the
surface of the water several metres ahead of the device being tested, so
that reproducible thicknesses and widths of the test fluids can be
achieved with minimum interference by wind.
The principal systems of the tank include a wave generator and
beach, and a filter system. The wave generator and absorber beach have
capabilities of producing regular waves to 0.7 metre high and to 28.0
metres long, as well as a series to 1.2 metres high reflecting, complex
waves meant to simulate the water surface of a harbor or the sea. The
tank water is clarified by recirculation through a 0.13 cubic metre/second
diatomaceous earth filter system to permit full use of a sophisticated
underwater photography and video Imagery system, and to remove the
hydrocarbons that enter the tank water as a result of testing. The
towing bridge has a built-in skimming barrier which can move oil onto
the North end of the tank for cleanup and recycling.
When the tank must be emptied for maintenance purposes, the entire
water volume, of 9842 cubic metres is filtered and treated until it
meets all applicable State and Federal water quality standards before
being discharged. Additional specialized treatment may be used whenever
hazardous materials are used for tests. One such device is a trailer-
mounted carbon treatment unit for removing organic materials from the
water.
Testing at the facility is served from a 650 square metres building
adjacent to the tank. This building houses offices, a quality control
laboratory (which is very important since test fluids and tank water are
both recycled), a small machine shop, and an equipment preparation area.
This government-owned, contractor-operated facility is available
for testing purposes on a cost-reimbursable basis. The operating con-
tractor, Mason & Hanger-Silas Mason Co., Inc., provides a permanent
staff of fourteen multi-disciplinary personnel. The U.S. Environmental
Protection Agency provides expertise In the area of spill control tech-
nology, and overall project direction.
For additional information, contact: John S. Farlow, OHMSETT
Project Officer, U.S. Environmental Protection Agency, Research and
Development, lERL-Ci, Edison, New Jersey 08817,201-321-6631.
27
-------
APPENDIX B
TETRADYNE LABORATORY TESTING AND SKIMMER DESIGN DATA*
AIR NOZZLE TESTS
One of the primary factors in developing a usable air jet system
involves the determination of the air velocities and volumes necessary
to meet the operational requirements. Once these factors are known, it
is possible to determine power and weight requirements for a skimmer
vessel.
To provide the basis for the design of the air booms, nozzles and
blowers, a test program was undertaken using a simulated air boom with
an adjustable nozzle opening. The specific objective of this test
series was to obtain data to permit selection of an optimum boom-nozzle
configuration and size; to determine blower size, pressure and power
requirements and determine the required boom diameters.
This test boom was positioned vertically and was supplied with air
from a large blower. A Prandtl tube was mounted on a frame in front of
the boom nozzle. Signals from a pressure transducer and a displacement
potentiometer were fed directly to an X-Y plotter. With this arrange-
ment, it was possible to plot a pressure profile across the air stream
directly by traversing the tube in front of the nozzle. Figure B-l is a
sample of a plot for the instrument.
Using this apparatus, 172 test runs were made, testing nozzle
widths of 0.6 cm, 1.3 cm, and 1.9 cm. For each of these nozzles widths,
velocity profiles were prepared at distances of 0.3 cm, 15.2 cm, 0.3 m,
0.6 m, 0.9 m, 1.2 m, 1.8 m, 2.4 m, and 3.0 m from the nozzle. At each
distance, six values of boom air pressure were tested to determine
performance at various initial air velocities. The boom air pressures
generally ranged from approximately 2.5 to 25 cm of water, although the
pressure was varied in some tests to match the conditions.
One relationship which was clearly established in the test series
is that the larger (1.9 cm) nozzlopening projects an air stream a
significantly greater distance than the narrower nozzles. This wider
nozzle also requires less pressure and power to project high velocity
air over distances up to 3.05 m.
*From Reference 1 (Section III, pp. 9-19)
28
-------
TETRADYNE CORPORATION
DYNAMIC PRESSURE
Figure B-1. Sample plot from X-Y plotter.
. . , .
. ,
,
. _
.
~ ,^^-
: _^_
. i .
!
1 ' - :
.
— i — r
— :~~| — '~r~
,
1 : : i
i , •
: ,
i
' : 1 .
. ' ' '
• ' • '~
'
•~ • •
•
ujXj ~^;_
l_i_ft— vA^l V
i , i I;
n'Jr
! 1 J
i
• '
1
i ' i ll
IP
i J r
- T <
"^T"
T
i
! ; ' I
Tv^F
I
ffi
ii
if
r
if-
,
r '
V- i •
V '
_ L—
—— r-
i — . —
...
r-
i
[— ._ , ^ j ^+_+
1 •
• * i * *
1
. :
1 1 •
• • i : t
I'M
'
r
X
— r-*"
•
I
r;
i
1
r.
,
'V
1 i • T
, . y .v,
I
•- rA.
i
-
tfr-
"^
-
»J
1
-
' 1 "
1 • . 1 :
i
I
, 1
1 t —
! I !
' • ! i
• '
1 .
— -i— -|
i •
i
• i
; i i
f
i
Ju
nay*
jr'T
• f •
• : i '
FT
' ' i 1 i v
'
*IV
f
^ '
'! • ' '
*T W-1
JV v ""«
1 ,
1 1 I •-
Test No
Boom P
Press. I
Displ. F
Peak Dy
Peak Ai
Air Stre
1.9
0.6
151
Date 10/25/73
ressureO.9 RPa
'acto
actoi
•n. Pr
r Vel
am \
cm N
m
r 2.44 cm
defl./cm water
.167 cm defl./cm trav.
PCS 0.2 kPa
Vidth(50% Pfr.R )10'2 cm
ozzle
from Nozzle
| •
i
if ! i
~^FJ —
/ i
t u
». y ,
•
, [
I/,
, , n
L32 !
1 T
. . ; • ] •
•
• ' i
ATI
rf—
f
i i
• j
i ' •
! ' '
• '
— »— t — i — i —
' i I i
i ' • — i —
1
j •
— J — i —
— U
i
• j '
' i ! :
• • — i —
- 1 !
i I
"'iTv V <*J"v — uv-w 1
.1 1 -
• • • • 1 — (— ' — >—
; ' ' •
! ,
— • — ) — ' — i — '
!
H
,
f t
• |
• ' i -
—1 — p-i — H-
' '
'
1 i
1 — i . ! ' '
i , , .
1 i T
i
1
]
; , :
,
! — 1
1 ; !
1 : '
' i '
1 1 !
i !
-—
]
-------
As a comparison, at 1.2 m from the nozzle and at a nozzle pressure
of 1.8 kPa, the 0.6 cm nozzle produced a peak velocity of 9.1 m/s, the
1.3 cm nozzle produced a peak velocity of 11.9 m/s, and the 1.9 cm
nozzle produced a peak velocity of 11.9 m/s.
Examining the requirements for an air sweep skimmer moving through
the water, calculations indicated that a boom angle, Q = 30* from the
centerline of the skimmer unit will permit a 9.1 m wide collection
configuration with 9.1 m long booms, while not requiring excessive
transverse velocities for the oil. Figure B-2 shows the relationship of
skimmer velocity to boom angle 0 and transverse oil velocity VT.
Plan View
I
Skimmer velocity 3.1 m/s
VT m/s
Figure B-2. Skimmer velocity—boom angle relationships.
Boom
x
Section View
Water
Figure B-3. Impingement angle relationships.
For relatively small values of $ (=50°) the air is deflected by the
water surface and Va is assumed to be the horizontal air velocity.
From Figures B-2 and B-3.
Va (Required) = VT
6
where 0 « % efficiency of oil movement defined as B
Y Oil
V Air
30
-------
One of the primary objectives of the wet tests was to measure 3 at
various values of Va and <)> and at various water flow velocities.
Data from EPA tests indicate values of 3 = .1 for light oils moved by
surface winds; however, under these conditions, the boundary layer near
the water surface is large. By directing the air stream at the water surface,
at the optimum angle, values of 3 near .2 may be reached. If & = .2 is
assumed, then Figure B-4 indicates the relationship of required boom length
and oil velocity for various values of 0.
3.0
2.4
H
1.2
Boom Length
L
15.2
12.2
9.1
6.1
10
20
30
40
e
s^
J3
00
(3
0)
•J
S
o
0
fQ
50
Figure B-4. Boom length and transverse oil velocity versus boom angle
0 for a 9.1 m wide sweep pattern.
Assuming 0 = .2, Q - 30°, and = 45°, the required air velocity at the
water surface Va = 12.6 m/s. These primary estimates were to be verified
in the wet tests.
Figures B-5 and B-6 are plots of test results used for preliminary
system analysis. This chart compares horsepower required per 0.3-m
section of boom with V at 1.2 m from the boom. The distance of 1.2 m
31
-------
•H
O
O
1-1
OJ
6
o
63.5
50.8
OJ
u-\
O
n
o
m
4J
QJ
i
•H
6
o
o
38.1
25.4
•H
cd
S
12.7
6.1
9.1 12.2
-------
1.83 r-
LJ
TD
QJ
Vj
•H
D
cr
0)
OS
1.53
C
o
4-1
u
g 1.22
o
M
0.92
0.61
0.31
6.1
11.8 m3/s C? 19.38 cm Water
49.53 cm Max. Diameter
14.1 kw
14.2 m3/s @ 8.25 cm Water
54.61 cm Max. Diameter
14.1 kw
9.1
9.1
12.2
15.2
V at L = 1.2 m/s
ci
Figure B-6. Power requirement chart.
-------
was selected as the critical distance considering wave heights of 0.6 m
and values of 4> of approximately 45°. It is clear that the larger
nozzles require less pressure and power to reduce velocity at a given
distance. The 0.6 cm nozzle is not capable of producing the assumed
required velocity of 12.5 m/s at 1.2 m from the boom. This velocity
requirement was modified by later model testing.
A trade-off decision was required between the 1.3-cm nozzle and the
1.9-cm nozzle, while the power required is greater for the 1.3-cm nozzle
and it produces lower velocities. This decision was necessary prior to
further model design and testing.
Curves of required boom diameters have been plotted on Figure B-
5, assuming air velocity in the boom at 30.5 m/s. The shaded area in
Figure B-6 represents the estimated air velocity range.
At Va = 12.2 m/s, the 1.3-cm nozzle requires 11.8 m3/s at 19.3 cm
of water boom pressure; it indicated a maximum boom diameter of 49.5 cm
and requires a total of 21.7 kw.
Under the same conditions, the 1.9-cm nozzle requires 14.2 m3/s 8.3
cm of water boom pressure; it indicates a maximum boom diameter of 54.6
cm and requires a total of 14.1 kw. Tapered booms will be used to
reduce weight and provide the best structrual support.
It was decided that the 1.9-cm nozzle has a much greater capacity
to produce higher velocities at greater distances, and it appeared to be
the best selection.
With the selection of these preliminary values for the air system,
work proceeded on to the development of a flow table and scale models
for testing the system.
34
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-600/2-78-187
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Performance Testing of the Tetradyne High Speed Air
Jet Skimmer
5. REPORT DATE
August 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
William E. McCracken and Sol H. Schwartz
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Mason & Hanger-Silas Mason Co., Inc.
P. 0. Box 117
Leonardo, New Jersey 07737
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
68-03-0490
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final 5/11-13/76
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT ~~ — -
The U.S. Environmental Protection Agency evaluated the performance of the pro-
totype Tetradyne High Speed Air Jet Skimmer at their OHMSETT test facility at
Leonardo, New Jersey. The skimmer depends on an air-jet impacting the water sur-
face at an angle and deflecting rapidly moving, floating, spilled material
laterally into a low-current chamber for ease in recovery. The objective of
the testing program was to determine the ability of the Tetradyne skimmer to
pick up a large area, thin film (0.1-1.0 mm) spill of floating oil in water
currents up to 3 m/s. The four test fluids used during the program, No. 2
fuel oil, naphtha, and two lubricating stocks, encompassed a wide range of
physical properties. The recovery performance parameters determined were re-
covery rate and throughput efficiency. The effects of film thickness, fluid
viscosity, fluid specific gravity, and fluid interfacial tension on skimmer
performance parameters under fast current conditions are presented. Modifica-
tions for further improving performance are recommended.
This report was submitted in fulfillment of Contract No. 68-03-0490, Job Order
No. 23, by Mason & Hanger-Silas Mason Co., Inc., Leonardo, New Jersey under
the sponsorship of the U.S. Environmental Protection Agency.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
(•.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Water pollution
Performance tests
Oils
Skimmers
Air flow
Air jet skimmer
Oil skimmer
Oil spill cleanup
Protected waters
Skimming vessel
13B
RELEASE TO PUBLIC
19. SECURITY CLASS {This Report)
UNCLASSIFIED
EPA Form 2220-1 (t-73)
20. SECURITY CLASS (This page}
UNCLASSIFIED
21. NO. OF PAGES
45
22. PRICE
35
•its.
------- |