EPA-6 0 0 / 2-81-
September 1981
PERFORMANCE TESTING OF FOUR SKIMMING SYSTEMS
by
Henry W. Lichte, Michael K. Breslin and Gary F. Smith
Mason & Hanger-Silas Mason Co., Inc.
Leonardo, New Jersey 07737
and
Douglas J. Graham and Robert W. Urban
PA Engineering
Corte Madera, California 94925
Contract No. 68-03-2642
Project Officer
Richard A. Griffiths
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory - Cincinnati
Edison, New Jersey 08837
This study was conducted in cooperation with the
U.S. Coast Guard
U.S. Geological Survey
U.S. Navy
Environment Canada
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
ii
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FOREWORD
The U.S. Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health and
welfare of the American people. Noxious air, foul water, and spoiled land are tragic
testimonies to the deterioration of our natural environment. The complexity of that
environment and the interplay of its components require a concentrated and integrated
attack on the problem.
Research and development is that necessary first step in problem solution; it
involves defining the problem, measuring its impact, and searching for solutions. The
Municipal Environmental Research Laboratory develops new and improved technology
and systems to prevent, treat, and manage wastewater and solid and hazardous waste
pollutant discharges from municipal and community sources, to preserve and treat
public drinking water supplies, and to minimize the adverse economic, social, health,
and aesthetic effects of pollution. This publication is one of the products of that
research and provides a most vital communiations link between the research and the
user community.
This report describes performance testing of four commercial oil spill cleanup
devices under a variety of controlled conditions. Results of these tests are of interest
to those involved in improving the capability of devices to clean up oil spills as well as
to those interested in specifying, using, or testing such equipment. Further
information may be obtained through the Solid <3c Hazardous Waste Research Division,
Oil and Hazardous Materials Spill Branch, Edison, New Jersey.
Francis T. Mayo
Director
Municipal Environmental Research Laboratory
Cincinnati
m
-------
ABSTRACT
Performance tests were conducted at the U.S. Environmental Protection
Agency's oil and hazardous simulated environmental test tank (OHMSETT) on four
commercial oil spill cleanup devices: the Sapiens Sirene skimming system, the Oil Mop
remote skimmer, the Troii/Destroil skimming system, and the Versatile Bennett arctic
skimmer. The objective of the test program conducted during the 1979 test season
was to evaluate skimmer performance in collecting oil floating on water using several
wave conditions, tow speeds, and skimmer operating parameters.
Tests described in this report were sponsored by the OHMSETT Interagency
Technical Committee (OITC). Members of the 1979 OITC were the U.S. Environ-
mental Protection Agency, U.S. Navy-SUPSALV, U.S. Navy-NAVFAC, U.S. Coast
Guard, U.S. Geological Survey, and Environment Canada.
A 16-mm film report, entitled "600 Foot Ocean", was produced to summarize
the results presented in this report. This film is available through the U.S.
Environmental Protection Agency, Office of Research and Development, Oil and
Hazardous Materials Spills Branch, Edison, New Jersey 08817.
This report is submitted in fulfillment of EPA Contract No. 68-03-2642 by
Mason & Hanger-Silas Mason Co., Inc., under the sponsorship of the U.S. Environmen-
tal Protection Agency. Technical direction and evaluation of the Oil Mop remote
skimmer and the Versatile Bennett arctic skimmer were subcontracted to PA
Engineering, Corte Madera, CA. This report covers the period 3uly 9, 1979, to
October 19, 1979; work was completed as of December 1, 1979.
iv
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Tables vii
Metric Conversion Factors viii
Acknowledgments ix
1 Introduction 1
2 Sirene Skimmer System 3
Conclusions 3
Recommendations 5
Skimmer Description 6
Test Matrix 7
Test Procedures 13
Test Results 17
Discussion 17
3 Oil Mop Remote Skimmer 28
Conclusions 28
Recommendations 31
Skimmer Description 31
Test Procedures 34
Test Results 37
Discussion 37
4 Troil/Destroil Skimmer System 45
Conclusions 45
Recommendations 46
Skimmer Description 47
Test Procedures 47
Test Results 51
Discussion 54
5 Versatile Environment Products Arctic Skimmer 58
Conclusions 58
Recommendations 60
Skimmer Description 60
Test Procedures 61
Test Results 66
Discussion 72
References 75
Appendices
A Facility Description 76
B OHMSETT Oil Properties and Analysis Techniques 78
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FIGURES
Number
1 Sapiens Sirene skimming system 8
2 Cutaway view of the aft portion of the Sapiens Sirene skimming system . 9
3 Sapiens Sirene as rigged for OHMSETT testing 10
4 Example of a test (test 2*0 with a fairly constant recovery efficiency ... 14
5 Example of a test (test 45) with a constantly increasing
recovery efficiency 15
6 Throughput efficiency Sirene skimmer/boom - Circo X heavy oil 20
7 Recovery efficiency Sirene skimmer/boom - Circo X heavy oil 21
8 Oil recovery rate Sirene skimmer/boom - Circo X heavy oil 22
9 Throughput efficiency - Sirene skimmer/boom - Circo medium oil 23
10 Recovery efficiency - Sirene skimmer/boom - Circo medium oil 24
11 Oil recovery rate - Sirene skimmer/boom - Circo medium oil 25
12 Oil Mop remote skimmer - test schematic 32
13 Oil Mop remote skimmer - tow test 33
14 Oil spilling over transom of Oil Mop remote skimmer 33
15 Oil Mop remote skimmer - non-tow test 35
16 Recovery efficiency trends for Oil Mop remote skimmer . 40
17 Oil recovery rate trends for Oil Mop remote skimmer 41
18 Medium oil recovery rate for Oil Mop remote skimmer 42
19 Oil Mop remote skimmer test using crane to lift wringer out of water ... 44
20 Use of fire hoses to thicken oil slick in the mop area 44
21 Troil/Destroil skimmer system as tested at OHMSETT 48
22 Troilboom illustration 49
23 Destroil skimmer pump .. 50
24 Recovery efficiency for Troil/Destroil skimmer system preload oil volumes
for all oil types 55
25 Oil recovery rate for Troil/Destroil skimmer system 56
26 Versatile Environment Products arctic skimmer as
tested at OHMSETT 63
27 Versatile Environment Products arctic skimmer operating principle 64
28 Effect of water jets in concentrating oil slicks 65
29 Grab sample recovery efficiency for test 24 of the Versatile Environment
Products arctic skimmer 69
30 Throughput efficiency trends with Circo X heavy oil, Versatile Environment
Products arctic skimmer 70
31 Throughput efficiency trends with Circo 4X light oil for Versatile Environment
Products arctic skimmer 71
32 Versatile Environment Products arctic skimmer door settings versus tow
speed 73
33 Debris grate in the bow of the skimmer 74
vi
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TABLES
Number
1 Best Performance - Sapiens Sirene (Heavy Oil) 5
2 Best Performance - Sapiens Sirene (Medium Oil) 4
3 Sapiens Sirene Test Matrix 11
4 Sapiens Sirene Test Procedures 16
5 Sapiens Sirene Results (Heavy Oil) 18
6 Sapiens Sirene Results (Medium Oil) 19
7 Sapiens Sirene Pump Tests 26
8 Best Results - OMI Remote (Heavy Oil) 29
9 Best Results - OMI Remote (Medium Oil) 29
10 Test Procedures - Oil Mop Remote Skimmer (Towed Tests) 34
11 Test Procedures - Oil Mop Remote Skimmer (Maneuvering Tests) 36
12 Test Procedures - Oil Mop Remote Skimmer (Stationary Tests) 36
13 Towed Test Results - Oil Mop Remote Skimmer (Heavy Oil) 38
14 Towed Test Results - Oil Mop Remote Skimmer (Medium Oil) 38
15 Non-towed Test Results - Oil Mop Remote (Medium Oil) 39
16 Peak Performance - Troil/Destroil Skimmer System 45
17 Test Procedures - Troil/Destroil Skimmer System , 51
18 Troil/Destroil Test Results (Heavy Oil) 52
19 Troil/Destroil Test Results (Light Oil) 53
20 Peak Performance - Bennett Arctic Skimmer (Heavy Oil) 59
21 Peak Performance - Bennett Arctic Skimmer (Light Oil) 59
22 Test Procedures - Bennett Arctic Skimmer (Tow Tests) 61
23 Test Procedures - Bennett Arctic Skimmer (Oil Recovery Rate Test).... 62
24 Test Results Bennett Arctic Skimmer (Heavy Oil) 67
25 Test Results Bennett Arctic Skimmer (Light Oil) 68
vii
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LIST OF CONVERSIONS
METRIC TO ENGLISH
To convert from
Celsius
joule
joule
kilogram
metre
metre-
metre-
metre^
metref
metre
metre/second
metre^second
metre,/second
metre,/second
metre /second
newton
watt
ENGLISH TO METRIC
centistoke
degree Fahrenheit
erg
foot_
foot''
foot&ninute
foot /minute
foot-pound-force
gallon (U.S. liquid)
gallon (U.S. liquid)/minute
horsepower (550 ft Ibf/s)
inch-
inch
knot (international)
litre
pound force (Ibf avoir)
pound-mass (Ibm avoir)
pound/foot
to
degree Fahrenheit
erg
foot-pound-force
pound-mass (Ibm avoir)
foot
inch-
foot,
indi
gallon (U.S. liquid)
litre
foot/minute
knot
centjstoke
foot /minute
gallon (U.S. liquid)/minute
pound-force (Ibf avoir)
horsepower (550 ft Ibf/s)
metre /second
Celsius
joule
metre-
metre
metre&econd
metre /second
joule _
metre,
metre /second
watt
metre-
metre
metreijecond
metre
newton
kilogram
pascal
Multiply by
t = (t_-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
t = (tp-32)/1.8
17000 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
7.457 E+02
2.540 E-02
6.452 E-04
5.144 E-01
1.000 E-03
4.448 E+00
4.535 E-01
4.788 E+01
viii
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ACKNOWLEDGMENTS
The authors gratefully ackonowledge the support of the manufacturers and
suppliers, who provided the four skimmers as well as knowledgeable advisers for these
tests. Special thanks go to Jacques Vidilles (Sapiens Co.), Norm Tribe (Oil Mop
Pollution Control), Erling Blomberg (Troilboom Systems), Kjeld Jensen (DeSmithske),
Tom Mackey (Hyde Products), and Dave Houston (Versatile Environmental Products).
Guidance from the OITC members through Mr. 3.S. Farlow, Chief, Oil Spill
Staff, EPA, in developing test guidelines and providing funds for the tests was timely
and efficient.
The test team and support staffs of Mason & Hanger-Silas Mason Co., Inc. and
PA Engineering provided cost-effective and reliable test measurements, which
permitted completion of the four-part program on schedule.
ix
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SECTION 1
INTRODUCTION
Results and methods used for tests sponsored by the 1979 OHMSETT Inter-
agency Technical Committee (OITC) are presented in this report for the following
commercially-available spill cleanup equipment:
(1) Sapiens Sirene skimming system,
(2) Oil Mop Pollution Control, Ltd. remote skimmer,
(3) Hyde Products, Inc. Troil/Destroil skimming system, and
(4) Versatile Environment Products arctic skimmer.
Each system was shipped from a foreign country on loan to OHMSETT (see
Appendix A) for this test program. Tests were conducted to evaluate the test devices
for:
(1) best oil collection performance,
(2) environmental conditions limiting operation,
(3) mechanical problems, and
«0 device modifications to improve performance and/or operating limits.
Quantitative performance data to support conclusions in the above areas are
presented based on the following parameters calculated from steady state test results.
(1) Throughput Efficiency (TE) — Percentage of oil entering the skimmer
which is recovered. This parameter is important for advancing skimmers
in this report.
_P _ Flowrate of oil recovered _ xlOO%
Flowrate of oil distributed (encounter rate)
(2) Recovery Efficiency (RE)- -Percentage of oil in the fluid recoverd by the
skimmer. This parameter applies to all devices in this report and is
useful for evaluating storage required to contain fluid recovered at a
spill.
= Volume of oil recovered
_ _
Volume of total fluid recovered (oil and water)
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(3) Oil Recovery Rate (ORR)—Volume of oil recovered per unit time. This
parameter also applies to all devices in this report. Oil recovery rate is
useful to determine time needed to clean up a spill of known volume.
ORR - Volume oil recovered
Unit of time
Each of the following report sections is self-contained and describes the test
and results for one of the four devices. Direct comparison of test results should be
avoided because all skimmers were operated differently. The Oil Mop Pollution
Control, Ltd. remote skimmer and the Versatile Environment Products arctic skimmer
were operated as both stationary and advancing skimmers, while the other two were
operated as advancing skimmers only. Appendices A and B to this report describe the
OHMSETT test facility and the oil properties for each skimmer's test program.
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SECTION 2
SIRENE SKIMMER SYSTEM
CONCLUSIONS
During the period 9 to 20 July 1979, 43 oil recovery performance tests were
conducted with the Sapiens Sirene skimmer. A total of 31 tests were run with a high
viscosity oil (Circo X heavy) and 12 tests with a medium viscosity oil (Circo medium).
Oil properties are detailed in Appendix B. This section summarizes the conclusions
from the nine days of testing in four major areas:
(1) Best Performance—
(2) Operating Limits—
(3) Mechanical Problems—
(4) Device Modifications—
Best Performance—
Consistently, the highest values of RE, TE, and ORR were obtained during tow
tests with waves. This result was surprising since waves generally causes poorer
performance in oil skimmers.
The tests in heavy oil produced better results than the test in medium oil.
Medium oil was entrained and lost from the system more easily than the heavy oil due
to interfacial shear forces.
The best skimmer performance data (highest numerical results) achieved during
these tests are presented along with accompanying test conditions in Tables 1 and 2.
Due to the skimmer's operating principle, the highest values of TE, ORR and RE did
not occur under the same test conditions. Test oil logistics prevented the use of large
enough amounts of oil to have saturated the system over the entire tow test. Thus
absolute maximums for ORR and RE were not determined.
TABLE 1. BEST PERFORMANCE - SAPIENS SIRENE (HEAVY OIL).
Performance
parameter
TE
RE
ORR
-
Highest
value
100%
71.0%
39.7 nr/hr
Tow
speed
(kt)
0.50
1.25
1.0
Wave
Hx L
(m x m)
0
0.6 HC
0.6 HC
Test
no.
1
27
26
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TABLE 2. BEST PERFORMANCE - SAPIENS SIRENE (MEDIUM OIL).
Performance
parameter
TE
RE
ORR
Highest
value
99%
66.5% .,
39.8 nrr/hr
Tow
speed
(kt)
0.75
1.25
1.25
Wave
H x L
(m x m)
All waves
0.7 HC
0.7 HC
Test
no.
36, 40, 46
45
41
It is worthy to note that no oil was lost due to splashover of waves. The
cylindrical design of the continuous flotation elements caused the oil and water to be
splashed forward, in front of the boom. This was true even at the highest tow speed
run in the roughest wave condition. Another reason for lack of splashover was the
virtual absence of device heave with respect to the water's surface. The great amount
of flotation coupled with the concave skirt design, which tends to hold the device to
the water's surface, acted to maintain a relatively large, constant freeboard.
Operating Limits—
Based upon both quantitative and qualitative results obtained from these tests,
the operating limits of the Sirene skimmer appear to depend on the following three
items:
(1) Oil entrainment phenomena at tow speeds above 0.75 knots cause oil to
escape the skimmer before it can be pumped out. Such losses occurred
in three areas: (1) beneath the points of attachment between the side
sections and the rear collection section, (2) beneath the large floats on
either side of the oil/water inlet and (3) out the water outlet which is
located beneath the oil suction box in the aft end of the device.
(2) Limited pump capacity which allows the oil to build up in front of the oil
inlet and therefore be subject to entrainment and shedding due to water
flow beneath the oil.
(3) The inability of oil to flow easily to the oil suction box after it enters
the oil inlet. This allows the oil slick to be subjected to the water
passing below it for a longer period of time. Shedding and entrainment
of oil droplets is thus increased.
The pumping system did not severely emulsify the oil and water collected. This
is evidenced by the similarity between the recovery efficiency samples obtained by
allowing gravity to separate the oil and water and those obtained by centrifuging
oil/water samples.
TE was not affected by slick thickness while RE and ORR were directly
dependent.
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Mechanical Problems—
There were very few mechanical problems with the Sirene skimmer during the
test period. Although the device was rather large, it was easily deployed and rigged in
the test tank without the aid of a crane or mechanical hoist. Six men carried the
inflated sections to the edge of the tank and dropped them in the water. Men in small
boats secured the Sirene to the tow points and attached the offloading hose.
A small gasket in one of the system's two Warren Rupp Sandpiper Model SA-3
pumps was found to have been installed incorrectly by the manufacturer. The
correction did not change the pump rate significantly.
Towards the end of the test program a leak was discovered in the second stage
flotation element of the Sirene. It appeared that the test oil had caused the adhesive
at a seam to fail. A successful patch was made from excess material shipped with the
skimmer and fastened to the fabric with an instant glue. No other leaks in the system
were discovered. The owners are taking steps to improve the adhesive used in
assembling the Sirene.
Device Modifications—
By distributing a narrow slick down the center of the device and holding it there
using water jets, the rear oil collection section could be observed to function apart
from the rest of the Sirene system. The data from these tests (no. 9 and 9R) showed
about a fourfold increase in system performance over previous tests (no. 6 and 8,)
which employed a system-wide oil slick. The system-wide slick was six times as wide
and one-sixth as thick as the narrow slick. Observations from these tests and others
were that the most severe oil losses occurred at the attachment points of the side and
rear sections and under the flotation elements on either side of the oil inlet. There
were no noticeable losses observed from under the 14.5-m long side floats. This was
probably due to their slight angle to the current. If the tow points were separated
further to increase the sweep width, the angle of the side floats to the current would
also increase. When the component of current perpendicular to the boom sections
neared 0.8 knots, shedding would occur.
In an effort to diminish the oil losses at the attachment points of the side and
rear sections, one length (3.3 m) of oil boom (Clean Water, Inc., Harbor Boom 0.6 m
draft) was tied in front of each attachment point (tests 17, 18, 19 and 20). The
upcurrent portion of the boom sections was secured to the side sections of the Sirene
while the downstream end was secured to the rear section at the edge of the oil inlet.
The purpose of the catty-cornered arrangement of the boom sections was to break up
the severe change in angle betwen the side and rear sections into two smaller angles.
It was hoped that this would decrease oil shedding over 1 knot tow speed and channel
the oil directly to the oil inlet. The boom sections did not consistently improve the
system's performance. Oil was seen flowing around the boom sections into the
protected corner and shedding beneath the flotation elements.
RECOMMENDATIONS
Device modifications which are recommended for improving the performance of
the Sapiens Sirene system are:
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(1) Extend the oil inlet across the entire rear section of the device. The
floats on either side of the oil inlet could be eliminated or placed outside
the side flotation elements. The severe angle change which developed at
the point where the side sections join the rear section would no longer
exist since the oil would travel directly from the side sections into the
narrowing funnel behind the oil inlet.
(2) Improve the narrowing funnel behind the oil inlet to allow oil to move
more easily through it to the oil suction box. If oil could be transported
through the funnel area at the same flow rate it is encountered by the
system, there would not be a pool of oil which would be subjected to the
interfacial shearing forces of the water passing beneath it and out the
water exit. Longitudinally arranged flotation elements spaced across the
funnel would allow oil to pass easily by keeping the fabric above the
slick's surface.
(3) Increase system pumping capacity by improving the arrangement of the
two double-acting diaphragm pumps used to transfer the oil/water fluid
from the suction box to the collection barrels. According to the
manufacturer, Warren Rupp, the pumps would be 12% more efficient if
used independent of each other, rather than in a common inlet, common
outlet arrangement. A doubling of present pump capacity is
recommended.
(4) Replace the center torpedo float on the oil/water inlet with two floats,
spaced at 1/3 and 2/3 the distance across the mouth. This would
eliminate turbulence generated by the float directly upstream of the oil
suction box.
If the modifications which were recommended or ones that serve the same
purpose are incorporated into the system, another test program should be performed at
OHMSETT. The system shows promise through its innovations in design and material
use.
SKIMMER DESCRIPTION
The Sapiens Sirene as tested is a two-stage oil skimming system comprised of
five components (Figure 1). The first stage is the oil herding section (side floats) while
the second is the oil collection section (rear float, hoses, and pump). The five
components are:
(1) a 14.5-m long float of inflated flexible fabric with an increasing boom
draft from forward to aft (right side or wing section);
(2) a 7.5-m long oil inlet section which includes the narrowing funnel leading
into the suction box with a torpedo-like float supporting the oil/water
inlet in the center.
(3) another 14.5-m long float of inflated flexible fabric with the boom draft
increasing from forward to aft (left side or wing section);
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(4) an aluminum suction box with floats that is clamped onto the upper part
of the apex of the rear funnel to accept the oil collected; and
(5) 20 m oi 110-mm hose and two air-driven, double-acting diaphragm pumps
(162 m /hr capacity) to remove the collected fluid from the Sirene to
the collection barrels.
Figures 1 and 2 show the Sirene and the designed method of oil and water flow
through the inlet and funnel section. The normal field mode of operation has the
pumps located forward of the system in a towing vessel. For convenience of operation
during the OHMSETT tests, the pumps were positioned aft of the system, elevated on a
moving bridge.
Referring to Figures 1 and 2, the operating principle is as follows. By towing
the system as shown an oil slick is encountered and confined between the two side
members (first stage). The slick is gradually narrowed as it approaches the rear, oil
collection section (second stage). The oil is forced into the inlet of the rear section
and through the funnel-shaped fabric which narrows and thickens the oil slick. The aft
end of the funneled fabric is divided into an upper and lower exit. The small upper one
(oil outlet) is clamped onto the aluminum suction box which in turn is attached to the
suction hose. The lower, larger outlet allows water to exit.
Two interesting features in the Sirene system, not usually seen in booms, are
the adjustable length ballast chain and the variable boom draft. The skirt depth is
varied to eliminate drag where a skirt is not needed (i.e. the forward portion of the
side sections) and to confine oil where a skirt is needed (i.e. aft portion of side
sections and across the rear section). Any of the end links in the ballast chain can be
connected to the nylon towing strap so that the lower edge of the boom skirt can
develop the desired concavity under tow. The shorter the ballast chain, the greater
the skirt will cup. The concave skirt cups the water and tends to draw the boom into
the water as tow speed is increased. The greater the tow speed, the smaller amount of
curvature is needed in the boom skirt to keep-the boom from rising up from the water
and planing (a common boom failure mode). The large, flexible, inflated freeboard
section (inflation pressures 0-20 kPa) of the boom prevents boom submergence.
Together, the skirt and flotation form a self-stabilizing system which conforms easily
to waves.
TEST MATRIX
The Sirene oil recovery system was deployed in the test tank and rigged for
towing (Figure 3). Initial shakedown tests were conducted without oil to establish
maximum tow speed and wave conditions under which effective oil skimming perform-
ance was most probable and to set limits for subsequent oil performance tests.
Sampling procedures were also rehearsed during these initial tests. Performance tests
for both heavy and medium oil were then conducted in accordance with the matrix of
test conditions listed in Table 3.
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oo
Rear float (second
Oil suction hose stage).
Aluminum
floats and
transition
piece
Narrowing
fabric funnel
(second stage)
Starboard side float
(first stage)
Oil/water inlet
Torpedo float
Port side float (first stage)
^Variable depth skirt
Adjustable skirt
ballast chain
Direction of Tow
Nylon tension strap
Figure 1. Sapiens SIrene skimming system
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DIRECTION OF TOW
Rear Section Float i
Torpedo
Float
.Suction Box with Oil
Suction Hose
Fluid
Inlet
Boom Skirt
Water Outlet
Figure 2. Cutaway view of the aft portion of .the Sapiens Sirene skimming system.
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DIRECTION OF TOW
OIL DISTRIBUTION POINTS
U/W VIDEO
CAMERA
COLLEC
BARRELS
VIDEO BRIDGE
1. Oil Distributor
2. Test Director
3. Test Engineer
4. Skimmer Operator
5. Photographer*
6. Collected Fluids Handler*
7. Bridge Operator *
8. VDU/Filter Operator
9. Chemist *
* - Not Shown
Figure 3. Sapiens Sirene as rigged for OHMSETT testing.
10
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TABLE 3. SAPIENS SIRENE TEST MATRIX
Test
no.
SD1
SD2
SD3
SD4
1
2
3
it
5
6
7
8
9
10
Tow
speed
(kt)
0-1.5
1.5-3
0-1.5
1.5-3
0.5
0.75
1
1
1.5
1.5
2
2
2
2.5
Wave
H x L
(m x m)
___
—
—
—
—
—
—
—
—
—
—
—
—
Slick
thickness
(mm)
0
0
varied
varied
1.5
1.5
1.5
0.75
1.5
0.8
1.5
0.8
0.4
1.5
Sirene
pump
rate
(m3/hr)
max
max
max
max
max
max
max
max
max
max
max
max
max
max
Oil
dist.
rate
(m3/hr)
0
0
45.
45.
26.
38.
52.
26.
77.
38.
104
52.
26.
131
4
4
1
6
2
1
2
6
2
1
Total
oil
dist.
(m3)
0
0
TBD
TBD
0
1
1.3
0.7
1.9
1
1.7
0.9
0.4
2.2
Oil
type
___
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Comments
Shakedown
Shakedown
Shakedown
Shakedown
Calmwater
Dist. Rate
Dist Rate =
= Pump Cap.
= Kz Pump Cap.
Dist Rate greater than
Pump Cap.
Dist. Rate
Pump Cap.
Dist. Rate
Dist. Rate
Dist Rate =
Dist. Rate
less than
= 2*Pump Cap.
= Pump Cap.
= KzPump Cap.
greater than
2*Pump Cap.
11
12
13
14
15
16
17
18
2.5
0.5
0.75
1
1
1.5
1.5
0.5
—
0.3
0.3
0.3
0.3
0.3
0.3
0.6
HC
HC
HC
HC
HC
HC
HC
0.4
1.5
1.5
1.5
0.75
1.5
0.75
1.5
max
max
max
max
max
max
max
max
32.
26.
38.
52.
26.
77.
38.
26.
7
1
6
2
1
2
6
1
0.6
0.7
1
1.3
0.7
1.9
1
0.7
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Dist. Rate
Pump Cap.
HC tests
less than
(Continued)
-------
TABLE 3. (Continued)
Test
no.
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36-70
A
B
C
D
E
F
G
H
I
3
K
Tow
speed
(kt)
0.75
1
1
1.5
1.5
0.5
0.75
1
1
1.5
1.5
0.5
0.75
1
1
1.5
1.5
1
1
1
1
1
1
1
1
1
1
1
Wave
Hx L
(m x m)
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.3x15
0.3x15
0.3x15
0.3x15
0.3x15
0.3x15
0.6x15
0.6x15
0.6x15
0.6x15
0.6x15
0.6x15
—
—
—
0.3 HC
0.3 HC
0.6 HC
0.6 HC
0.3x15
0.3x15
0.6x15
0.6x15
Slick
thickness
(mm)
1.5
1.5
0.75
1.5
0.75
1.5
1.5
1.5
0.75
1.5
0.75
1.5
1.5
1.5
0.75
0.5
0.75
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Sirene Oil
pump dist.
rate rate
(m3/hr) (m3/hr)
max
max
max
max
max
max
max
max
max
max
max
max
max
max
max
max
max
Repeat of tests
max
max
max
max
max
max
max
max
max
max
max
38.6
52.2
26.1
77.2
38.6
26.1
38.6
52.2
26.1
77.2
38.6
26.1
38.6
52.2
26.1
77.2
38.6
1 to 35
52.2
52.2
52.2
52.2
52.2
52.2
52.2
52.2
52.2
52.2
52.2
Total
oil
dis±.
(m3)
1
1.3
0.7
1.9
1
0.7
1
1.3
0.7
1.9
1
0.7
1
1.3
0.7
1.9
1
with Medium
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
Oil
type Comments
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy Regular wave tests
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Oil
Medium Non-symmetrical Tests
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
-------
TEST PROCEDURES
A steady-state collection barrel was included among the oil collection barrels
on the auxiliary bridge. Its purpose was to receive the oil collected near the midway
portion of the test. It was assumed that the system would have reached steady state
oil collection and discharge before the oil was directed into the barrel and would have
maintained that steady state until the oil spigot was removed from the barrel (Figure
3). However, discrete samples taken at the pump outlet throughout the tests indicated
that very often a constant oil to water ratio was not achieved during the period when
the oil was being directed into the steady state barrel (Figure 3). Figures 4 and 5
illustrate trends in the system RE (percent oil in sample), during the tow tests as a
function of elapsed time. The net reported RE is selected near the highest peak as a
best case achieveable in normal skimmer operations.
Oil Recovery Rate was determined by multiplying the RE by the pumping rate.
Pumping rate was determined from the amount of fluid collected in the "steady state"
barrel divided by the time in which it was collected. An investigation of the effect
that the percentage of oil had upon the pumping rate in these tests revealed the pump
rate remained nearly constant for all tests.
Throughput efficiency was obtained because it was considered to be a
parameter important to analyzing the effectiveness of the Sirene in combating oil
spills. If no oil loss was seen coming from the Sirene during the tow test, TE was
determined to be 100%. If a very minor amount of oil was seen exiting the boom, TE
was set at 99%. This could be considered as the threshold point of shedding failure. If
a significant quantity of oil was seen being lost from the boom, the amount remaining
in the boom was pumped to the collection barrels, quantified, and used in the
determination of TE. If no oil remained in the boom after completion of the tow test,
the oil collected during the test was used to determine TE. Throughput efficency was
calculated two ways. The first method looked at the test generally by saying the oil
collected by the boom was all oil, not lost from its confines during the test run. TE
was calculated by:
TF = • O^ collected under tow plus oil remaining in the boom X100%
Oil distributed
The second method looked specifically at what occurred during the time the system
was under tow. TE was calculated by:
c _ Oil volume collected during the test run _
_
Oil distributed minus oil remaining in the boom
To ascertain the amount of oil remaining in the Sirene after the tow test, fire hoses
were used to gently drive the oil into the oil/water inlet. Such oil was pumped into
separate collection barrels. The hosing of the oil into the device for collection after a
tow test was a difficult and delicate task. Often, some oil was lost outside of the
Sirene due to the inexperience of a hose handler. In addition, at the start of a test, a
small amount of oil was lost through the dump valve on the pump before a consistent
color of collected fluid appeared to be exiting and was then directed to the collection
barrels. The TE values obtained should not be considered as the maximum capability
of the system.
13
-------
A- SIRENE TEST #24
P
E
R
C
E
N
T
0
I
L
I
N
S
A
M
P
L
E
70
50
40
30
20
DETERMINED RE Ctl%)
STEADY STATE
•BARREL INTERVAL-
0
0
10 20 30 40 50 60
TIME (SECONDS)
70
80
90
100
Figure ^. Example of a test (test 21*) with a fairly constant recovery efficiency.
-------
P 70
E
R
C
E
N
T
60
0
I
L
I
N
S
A
M
P
L
E
50
40
30
20
10
0
A- SIRENE TEST #45.
DETERMINED RE C6SJO
STEADY STATE
BARREL INTERVAL-
I
0
10 20 30 40 50
TIME CSECONDS)
60
70
80
90
Figure 5. Example of a test (test **5) with a constantly increasing recovery efficiency.
-------
All oil collection tests were conducted according to the following procedures:
TABLE 4. SAPIENS SIRENE TEST PROCEDURES.
1. Set Scoreboard clock to 110 seconds.
2. Close valves on recovery collection barrels.
3. Position valve at pump outlet to dump position.
4. Position oil handling spigot over the 1.9 m barrel.
5. Regulate air pressure in the Sirene to obtain the correct inlet submersion and
adjust ballast chain for skirt concavity.
6. Set oil distribution rate in recirculation loop aboard main bridge.
7. Establish wave condition.
8. Start Sirene compressor and pump.
9. Begin tow, start pumps, and set valves to discharge back into the test tank,
start oil distribution (continue for 90 seconds).
10. When oil is seen being discharged ftom the pump move the valve from the dump
position to discharge into the 1.9 m barrel for 40 seconds, start the Scoreboard
clock, and begin grab sampling every 10 seconds.
11. After 40 seconds has elapsed, (70 seconds left on the clock) move the spigot
over the 0.95 m barrel (steady state barrel) for 40 seconds. Continue grab
samples.
12. After 40 seconds (30 seconds left on the clock) move the spigot over the 1.9 m
barrel again for 30 seconds. Continue grab samples.
13. After 30 seconds has elapsed (0 seconds left) the Scoreboard clock will sound,
the tow will be stopped and the air to the pumps will be shut off. Secure the
wave generator.
14. Move the spigot to the other 0.95 m barrel.
15. Gently hose the oil remaining in front of the boom into the pump inlet and pump
at a reduced rate (to minimize water content) into the 0.95 m barrel.
16. Lower the skimming booms on the bridges and skim any lost oil to the north end
to prepare for the next test.
These procedures were used for tests at 1.5 knots and below. Oil distribution time was
90 seconds. For tests at higher speeds the distribution time was 60 seconds, the barrel
collection times were 20 seconds, 30 seconds, 20 seconds, instead of the 40, 40, 30, and
16
-------
grab samples were taken once every 6 seconds instead of every 10 seconds. The time
of tow had to be shortened due to the limited useable length of the towing tank.
TEST RESULTS
Results of the performance parameters TE, RE, and ORR for heavy and medium
oil tests are listed in Tables 5 and 6.
Trends in the TE, RE, and ORR data are most easily seen when the tabular data
are plotted in graphs (Figures 6 through 11). In the case of duplicate tests, the higher
value was used in the plots. For the sake of clarity and comparison, only tests with a
3-mm thick oil slick in both medium and heavy oil have been plotted.
DISCUSSION
The most striking result of this test is the obvious improvement in device
performance in the presence of waves over that in calm water. The shape of the
flotation (cylindrical) appears to hinder the performance in calm water (by giving the
oil a gradual slope to follow down into the water and increase oil entrainment loss) and
aid performance in waves (the splash from the waves impacting the flotation throws a
wave curving up and away, carrying oil with it, thus keeping it in front of and away
from the flotation). The more confused the sea, the better the device performed. In
addition, the undulations in waves of the flexible funnel aft of the oil water inlet
probably aided in the passage of oil to the suction box.
The better performance in heavy oil tests over those in medium oil is due to the
tendency of medium oil to form droplets easier than the heavy oil. Medium oil is
therefore quicker to shed beneath a boom when subjected to interfacial shearing
forces. -iThe effects of water passing beneath an oil slick is documented in other
reports.
The other obvious trend was the fall-off of device performance with increasing
speed. Even the beneficial wave action could not stave off significant losses at tow
speeds above 1 knot. The isolation of the oil loss points by distributing a narrow slick
(tests 9 and 9R) showed that certain design changes could increase that significant loss
speed to at least 1.5 knots. The design changes have been listed in the Recommen-
dations. The oil that did pass either beneath the device or out the water outlet
generally consisted of droplets between 0.5- and 2.0-cm diameter. The lost oil was
dispersed fairly well over the 2.*-m depth of the test tank. This oil took about 5 to 10
minutes to completely rise to the surface. It should be understood that the
aforementioned results would vary depending upon the properties of the oil.
The results of tests 9 and 9R should be compared with the results of tests 6 and
8. The same amounts of oil were distributed in all four tests. Thus, essentially the
same oil slicks (0.8 mm) were used in these tests. Water jets were used to converge
and direct the oil slick into the inlet in tests 9 and 9R while the side floats were used
in tests 6 and 8. TE, RE, and ORR for tests 9 and 9R was three to four times that of
tests 6 and 8. The values for ORR and RE from the narrow slick tests plotted on the
graphs match the results of tests conducted in 3-mm thick, system-wide oil slicks.
17
-------
TABLE 5. SAPIENS SIRENE RESULTS - CIRCO X HEAVY OIL
Test
no.
1
2
3
4
5
5R
6
7
8
9
9R
10
17
18
19
20
21
22
23
2*
25
26
27
28
29
30
31
32
33
3*
35
Tow
speed
(knots)
0.5
0.75
1.0
1.0
1.5
1.5
1.5
1.25
1.5
1.5
1.5
0.75
1.25
1.5
1.25
1.5
1.25
1.5
0.75
0.5
0.75
1.0
1.25
1.5
1.75
2.0
2.0
2.0
0.75
1.25
1.75
Oil dist.
rate
(m3/hr)
25.7
39.4
52.3
108.3
78.7
76.5
41.7
33.3
39.1
39.4
37.9
38.9
31.8
39.7
32.7
78.1
129.9
148.4
77.1
53.0
78.0
128.7
134.6
127.2
157.5
170.4
174.9
169.2
79.5
112.4
157.2
Slick
thk.
(mm)
1.7
1.7
1.6
3.3
1.6
1.5
0.8
0.8
0.8
4.8
4.6
1.6
0.8
0.8
0.8
1.6
3.2
3.0
3.1
3.2
3.2
3.9
3.3
2.6
2.7
2.6
2.7
2.6
3.2
2.7
2.7
Waves
H x L
(m x m)
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.3 HC
0.3 HC
0.5x11.6
0.5x11.6
0.5x11.6
RE
(%)
7.0
23.5
20.5
42.0
15.5
13.5
8.5
9.0
5.5
27.5
23.5
26.5
8.5
4.0
8.0
7.0
48.5
25.5
22.5
13.0
31.0
58.0
71.0
57.5
49.5
25.5
19.0
12.5
27.0
54.5
25.5
TE
(%)
115.9
92.8
88.9
78.7
15.8
14.9
15.7
25.3
12.9
48.1
48.6
100.0
52.4
13.7
25.8
6.6
27.6
11.0
100.0
100.0
99.0
63.4
48.7
30.6
21.3
9.3
8.6
6.5
99.0
53.4
14.6
ORR
(m3/hr)
10.5
16.7
12.6
28.5
11.9
10.7
7.1
6.7
4.8
20.3
17.4
9.9
9.7
6.5
11.1
5.4
28.4
15.8
18.0
7.3
18.6
39.7
39.5
33.4
28.1
16.6
14.4
7.6
16.4
35.7
20.8
18
-------
TABLE 6. SAPIENS SIRENE RESULTS - CIRCO MEDIUM OIL
Test
no.
36
37
38
39
40
41
42
43
44
45
46
47
Tow
speed
(knots)
0.75
1.50
1.00
1.25
0.75
1.25
1.75
1.50
1.75
1.25
0.75
1.25
Oil dist.
rate
(m3/hr)
76.8
128.2
109.0
128.2
78.0
127.9
145.4
172.2
169.0
135.7
77.5
80.4
Slick
thk.
(mm)
3.1
2.6
3.3
3.1
3.2
3.1
2.5
3.5
2.9
3.3
3.1
2.0
Waves
HxL
(m x m)
Calm
Calm
Calm
Calm
0.5x11.6
0.5x11.6
0.5x11.6
0.5x11.6
0.7 HC
0.7 HC
0.7 HC
0.7 HC
RE
(%)
21.5
23.5
43.5
42.0
21.0
59.0
28.5
44.0
29.0
66.5
24.5
33.5
TE
(%)
99.0
10.6
68.2
38.2
99.0
50.7
13.9
20.1
13.3
55.6
99.0
40.7
ORR
(m3/hr)
16.6
14.0
35.2
12.6
15.7
39.8
15.8
27.4
16.6
24.6
15.7
19.4
19
-------
ru
o
T
H
0
U
S
H
P
U
T
108
80
70
50
40
E
F
F
I
C
I
E
N 30
C
Y28
10
0
0
A- CALM WATER
D- 0.5M X II.6M WAVE
0- 0.7M HC WAVE
+- CALM W/NARROW SLICK
0.5
Ov
\
v
D
I .5
TOW SPEED
Figure 6. Sirene skimmer/boom - Circo X heavy oil.
-------
ro
R
E
C
100
90
0
V 80
R
Y
E
F
F
I
C
I
E
N
C
Y
70
60
30
20
10
0
A- CALM WATER
D- 0.5M X 11.6M WAVE
0- 0.7M HC WAVE
+- CALM W/NARROW SLICK
o
0
0.5
t 1.5
TOW SPEED CKNOTS)
Figure 7. Sirene skimmer/boom - Circo X heavy oil.
-------
ro
0
I
L
R
E
C
0
V
E
R
Y
R
A
T
E
60
55
50
45
40
35
30
25
20
15
10
5
0
0
A- CALM WATER
D- 0.5M X 11.6M WAVE
0- 0.7M HC WAVE
f- CALM W/NARROW SLICK
R.
/ X
/
/ A
i
/\
\
\
\
\
\
D
\
\
\
\
O
0.5
1 1.5
TOW SPEED (KNOTS)
Figure 8, Sirene skimmer/boom - Circo X. heavy oil. (All values corrected to reflect performance in a
3-mm slick).
-------
ro
UJ
Tt00
H
o 80
u
6 88
H
P
U 70
T
60
50
40
E
F
F
I
C
I
E
N 30
C
Y20
10
0
0
0.5
A- CALM WATER
Q D- 0.5M X U.6M WAVE
\ 0- 0.7M HC WAVE
\
\
\
A\
\
U \
A V
•%
D
1 1.5
TOW SPEED CKNOTS3
Figure 9. Sirene skimmer/boom - Circo medium oil.
-------
ro
R
E
C
0
V
E
R
Y
E
F
F
I
C
I
E
N
C
Y
100
90
80
70
60
50
40
30
20
10
0
0
fl
A- CALM WATER
D- 0.5M X II.6M WAVE
0- 0.7M HC WAVE
0.5
t
1.5
TOW SPEED CKNOTS)
Figure 10. Sirene skimmer/boom - Circo medium oil.
-------
ro
0
I
L
R
E
C
0
V
E
R
Y
R
A
T
E
u>
60
55
50
45
40
35
30
25
20
15
10
5
0
0
A- CALM WATER
D- 0.SM X 11,6M WAVE
0- 0.7M HC WAVE
A
/ \
/A
D
A
a
0.5
1 1.5
TOW SPEED CKNOTS5
Figure 11. Slrene skimmer/boom - Circo medium oil. (All values corrected to reflect performance in a
3-mm slick).
-------
Pump tests were undertaken to determine whether enough air was suppied to
the diaphragm pumps from the air compressor. The results are given below.
TABLE 7. SAPIENS SIRENE PUMP TESTS.
Test
no.
11
12
13
1*
15
16
Pump(s)
used
1 (East pump)
1 (West pump)
2 (Complete set)
2 (Complete set)
2 (Complete set)
2 (Complete set)
Pump
rate (m
49
49
84.6
86.8
86
85.7
•3
3/hr)
Three 19-mm air hoses, 7.6-m long, were used to supply the ale during each
test. The manufacturer stated that each pump should put forth 52.2 m /hr of water.
This was reduced due to the 2.5 m height of the pump inlet above the water line as
well as the increased viscosity of the oils over that of water. According to the pump
tests run at OHMSETT, the arrangement of the pumps with a common inlet and outlet
reduce the combined output by about 12%. Attention should be paid to the efficiency
of the pumping system and the rate at which the oil is drawn from the suction box.
Comparing the results of test number 10 (a single pump test) with test number 2 (a
double pump test) one can see that the slight increase in RE using both pumps; possibly
due to the slower withdrawal of fluid from the suction box which allows more oil than
water to accumulate. At tow speeds of 0.75 knots and less, these would be agreeable;
but, at higher tow speeds, it is better to remove the oil from the system quickly to
prevent loss from droplet shedding.
Test no. 47 was conducted with the left wing slightly in advance of the right
wing. The oil collection inlet was angled 75 degrees to the direction of tow rather
than the usual 90 degrees. The reason for the test was to simulate a field use error
when one tow vessel advances ahead of the other. The results indicate a slight
decrease in TE and a significant decline in RE and ORR. The device still functioned
during this test, however safeguards should be installed to avoid this from happening in
the field.
The results from test no. 28 were lower than might be expected. An abnormal
dip in the curves representing performance in the 0.7-m harbor chop can be seen in
Figures 7, 8, and 9. The low values for this test are probably attributable to a poor
sample being taken from the oil/water mixture collected in the barrels. All other
aspects of the test appear normal.
All but one of the properties of the test oils were generally within the
acceptable ranges specified by ASTM. Interfacial tension was very low. Such an
interfacial tension would allow oil droplets to form more easily when mixed with
water. The results of testing a boom/skimmer device in such an oil would be a slight
26
-------
decrease in performance due to shedding of oil droplets beneath the skirt and a
tendency for the oil/water mixture collected to emulsify easily. It does not appear
that such effects greatly influenced the overall performance of the Sirene system.
A ready solution to the problem of oil flow hindrance in the funnel leading from
the oil/water inlet to the suction box might be elongating the funnel so the oil's
convergence is not as abrupt. However, towing the Sirene system produces currents
which converge behind the second stage. During the development of the system the
designers found that if the funnel section were longer, the converging currents would
collapse the fabric passage and thus allow no oil to flow to the suction box. The
designers are examining other methods to improve oil flow through the funnel.
27
-------
SECTION 3
OIL MOP REMOTE SKIMMER
CONCLUSIONS
During the period 6-10 August 1979, nineteen oil pickup performance tests were
conducted with the Oil Mop remote skimmer. A total of six tests were conducted with
high viscosity oil (Circo X Heavy) and thirteen using medium viscosity oil (Circo
Medium). Appendix B contains oil property data.
The primary test objective was to generate design information for future
construction of a larger version of the Oil Mop remote skimmer to be built for Arctic
service in Canadian waters. The following are test conclusions relating to the design
criteria for the larger skimmer:
(1) At least three powered rollers must be provided to prevent slippage of
the oil mop, especially when saturated with high viscosity oils.
(2) The mop-oil slick contact length and rotational mop speed of the full-
scale skimmer should be selected after conducting a series of oil mop
saturation te"sts with the various viscosity oils expected to be
encountered. The oil mop saturation times can be compared with various
values of skimmer length divided by mop roller surface speed.
Time available during the single week of testing was not sufficient to
determine mop-oil saturation time for the two test oils. However, as an
example of how performance is affected by mop-oil slick contact time,
it was shown that in tests with oils of 185 cSt viscosity, oil pickup
performance (ORR) was unaffected by reducing the mop-to-oil slick
contact length from 1.9 meters to 1.2 meters. ORR performance did fall
off rapidly, however, when the contact length was reduced to 0.6 meters.
(3) To maximize oil recovery rate the full-scale skimmer hulls should be
open on the sides, if possible, to allow oil to enter from the sides as well
as the front. This will increase the ORR by allowing more oil to come in
contact with the tops of the oil mops, which float above the water
surface. The skimmer beam should be maximized to increase the oil mop
surface area being laid down on top of the slick as it enters the front of
the skimmer.
W A positive displacement type offloading pump is necessary to ensure
rapid offloading of collected oil over a wide oil viscosity range.
28
-------
Best performance—
The objective of these tests was to obtain design information for a larger
unmanned Oil Mop remote oil skimmer. The highest numerical results obtained in
these tests may not be the maximum obtainable with the full-scale Oil Mop skimmer.
The highest numerical values of the three performance parameters of TE, RE, and
ORR for the present OHMSETT tests are summarized in Tables 8 and 9.
TABLE 8. BEST RESULTS - OMI REMOTE (HEAVY OIL).
Performance
parameter
TE
RE
ORR
Highest
value
30%
96%
2.6 m3/hr
Tow
speed
(kt)
0.5
0.5
1
Waves
HxL
(m x m)
0.3 x 4.2
0
0
Slick
thk.
(mm)
9
6
6
TABLE 9. BEST RESULTS - OMI REMOTE (MEDIUM OIL).
Performance
parameter
TE
RE
ORR
Highest
value
43%
93%
2.7 m3/hr
Tow
speed
(kt)
0.5
0.5
1
Waves
HxL
(m x m)
0.3 x 1.2
0.2 x 7.0
0
Slick
thk.
(mm)
9
9
9
Operating Limits-
Based upon numerical and qualitative test results, the operating limits for this
skimmer appear to depend upon two factors:
(1) oil mop-to-oil slick contact area
(2) slippage of oil-soaked mops through the squeezing roller assembly
29
-------
Regarding the first factor, it was noticed during stationary tests with medium
viscosity oil that areas of clear water appeared under the point where the oil soaked
mops were lifted out of the water at the stern of the skimmer. This indicated that the
mops, at least on the side facing the oil slick, were fully saturated with test oil. The
ORR performance of the device was seen to increase when the entire skimmer hulls
were lifted clear of the water by an overhead crane, thereby exposing the tops of the
floating oil mop to splashing contact with oil from the sides. In the full-scale device,
the oil pickup rate (ORR) can be increased by maximizing the skimmer beam and
opening the skimmer hulls along the length of the skimmer to allow oil to splash onto
the mops from the sides.
Regarding the second factor, it is essential that future skimmers include three
powered rollers instead of two as provided in the present Oil Mop remote unit. Two
rollers are needed to squeeze oil from the saturated rope mop. A third roller
operating against one of the other two rollers, is needed to provide the mop tension to
maintain the oil mop rotational speed. By visual observation, it was apparent that in
almost all tests with heavy oil and some tests with medium oil slippage of the mops
occurred at the two squeezing rollers. This resulted in the mops remaining on the oil
slick after they had become fully saturated, reducing the net oil pickup per unit time.
Mechanical problems—
The following mechanical problems which limited the performance of the unit
and its deployment ease were encountered during the test week:
(1) Slippage of the oil-saturated mops while going through the squeezing rollers.
(2) Extreme changes of skimmer pitch in the presence of waves as collected oil
sloshed to the stern.
(3) Low thrust of the two electrically-driven propellers, causing the unit to be
unmaneuverable in some wave conditions.
(4) Entanglement of the remote control umbilical as the unit was maneuvered along
a 300 degree arc inside the boomed test area.
(5) Inability of the supplied submersible pump to offload collected oil fast enough
to prevent its overflowing the stern of the skimmer.
Testing was interrupted to correct the above mechanical difficulties, as time
would permit.
Slippage of the oil-soaked mops through the two-roller squeeze/rotational drive
assembly reduced the oil pickup rate of the unit, especially in towed tests where, in
some cases, the mop rotational speed dropped to one-fourth of the forward tow speed.
A number of roller squeeze tension adjustments were attempted but without effect.
The problem was minimized to the extent possible during the tests by shortening the
oil mops by 1.2 meters. This reduced the weight of oil-soaked mop which the
squeeze/drive rollers had to pull from the skimmer stern.
30
-------
The pitching of the skimmer in waves was made worse by the fore and aft
sloshing of recovered oil along the collection pan between the catamaran hulls. This
was solved by adding a plywood transverse bulkhead amidships in the collection pan
and boring a second 51-mm diameter drain hole from the collection pan to the
submersible offloading pump well to minimize the oil remaining in the collection pan.
The low thrust of the two props and the entanglement of the umbilical when
attempting rotational maneuvers were not solved during the one week of testing.
The inability of the electric, onboard centrifugal pump to offload recovered oil
was solved by connecting the suction of an OHMSETT-supplied 51-mm diaphragm
pump to the discharge of the skimmer pump. Prior to the connection of the OHMSETT
pump the inlet screen holes of the skimmer pump were enlarged from 6 to 9 mm
diameter, but the pumping capacity with the 380 cSt test oil still proved to be
insufficient to keep up with the rate of oil pickup by the mops.
All of the mechanical problems described above have been passed on to the
equipment manufacturer, who was present during the entire week of tests.
RECOMMENDATIONS
It is recommended that the full-scale Oil Mop remote skimmer incorporating
the four design criteria itemized in the Conclusions section be retested at OHMSETT.
SKIMMER DESCRIPTION
The Oil Mop remote skimmer model was fabricated by Oil Mop Pollution
Control Ltd. as a preliminary model of a full size unit to be used for Arctic oil spill
recovery service. The skimmer is designed as an unmanned unit controlled by an
umbilical electric cable. The operating principle is that of oil slick sorption onto a
bank of polypropylene rope mops, rotating in the vertical plane to produce zero
velocity relative to the surface of the water during forward motion of the skimmer.
A schematic drawing of the skimmer tested during this OITC series is shown in
Figure 12. A photograph of the skimmer during a tow test is shown in Figure 13. The
unit is comprised of a set of catamaran hulls, 1.9 meters long with a 1.3 meters beam.
The two 254-mm diameter oil mop ropes are deposited on the water at the skimmer
bow and pulled up from the water over the unpowered stern roller through the action
of two squeeze/drive rollers located in the bow. The two bow rollers are driven by a
220 volt, 4.2 ampere, 373 watt, electric motor. The rollers have a fixed surface speed
of 0.* knot. These rollers pull the jnop around the entire circuit and squeeze the oil
sorbed onto the mop into a 0.06 m collection pan beneath the rollers which extends
aft to the skimmer stern. As originally delivered for testing, the skimmer offloading
pump was fed by a 51-mrn diameter gravity drain tunnel extending from the stern of
the skimmer to the submersible pump well on the starboard pontoon (see Figure 12).
Soon after the start of testing, a plywood bulkhead (Figure 12) was added to prevent
oil sloshing aft and weighting down the stern so that recovered oil spilled over the
transom (see Figure 14). A second 51-mm diameter drain tunnel was bored into the
pump well from the collection pan forward of the bulkhead (Figure 12) to direct
recovered oil into the pump well. The pump supplied with the skimmer model is a
31
-------
CO
Sump pump
51-mm drain hole
added for tests
i- Drive rollers
Sump pump
Rotatable
\£ prop
Foam-filled hulls
Drive rollers
Uncovered roller
TOW DIRECTION
Uncovered
I>t roller
Plywood bulkhead added for tests
Sump pump
\
Fixed Drop
Unpowered roller
Mop/slick contact length
Figure 12. Oil Mop Pollution Control Ltd. remote skimmer - test schematic.
-------
Figure 13- Oil Mop remote skimmer - tow test.
Figure 1H. Oil spilling over transom of Oil Mop remote skimmer.
33
-------
TSURUMI submersible pump having a rated capacity of 7.2 m /hr and taking suction
through an inlet screen with a hole size of 6-mm diameter.
The unit is provided with two independently operated stern propellers, one fixed
and the other rotatable to reduce the turning radius. The propellers are powered by a
110 volt, 15 ampere power source.
TEST PROCEDURES
The skimmer was tested in both towed and non-towed modes. Figure 13 shows
the skimmer undergoing a tow test, while in Figure 15, a non-tow test is being
conducted.
For towed tests, the procedures listed in Table 10 were followed.
TABLE 10. TEST PROCEDURES - OIL MOP REMOTE SKIMMER (TOWED TESTS)
1. Empty skimmer pump well and collection hose of oil using OHMSETT positive
displacement diaphragm pump located on the main bridge.
2. Accelerate skimmer to test tow speed; at a predetermined mark on the tank
wall, start test oil distribution.
3. When test oil slick reaches the skimmer bow, activate mop rotation, skimmer
pump and main bridge OHMSETT diaphragm pump. During the run, direct the
oil discharge of the skimmer into a 0.9 m sampling barrel.
4. Secure test oil distribution at a predetermined spot along the tank wall.
Continue towing and pumping until the trailing edge of the test slick arrives at
the sternmost point where the oil mops leave the water. Stop tow but continue
pumping until the unsaturated portion of the mop reaches the bow rollers.
Record oil distribution time as the steady state operating time for the test.
5. Continue pumping as necessary to empty the onboard collection sump of
recovered oil.
The non-towed tests were divided into two deployment modes: maneuvering, in
which the skimmer propellers were remotely operated to give a forward way to the
skimmer; and stationary, in which the skimmer was lifted clear of the water by an
overhead crane to determine performance with different rope mop oil slick contact
lengths. Both types of non-towed tests were conducted in a boomed enclosure having a
circular shape of 10.1 meters diameter (see Figure 15). Test procedures for the
maneuvering tests are itemized in Table 11 and those for the stationary tests are
listed in Table 12.
-------
Figure 15. Oil Mop remote - non-tow test.
35
-------
TABLE 11. TEST PROCEDURES - OIL MOP POLLUTION CONTROL, LTD.
REMOTE SKIMMER (MANEUVERING TEST)
1. Pump skimmer sump and collection hose dry with OHMSETT positive displace-
ment diaphragm pump located on the main bridge.
2. Pump a volume of test oil necessary to achieve a slick approximately 12 mm
thick into the enclosed boom area.
3. Activate a stopwatch, the skimmer and OHMSETT pumps, mops and propellers.
During the test period, maneuver the skimmer along a 300 degree arc against
the smooth edge of the containment boom. Secure the stopwatch when the
skimmer reaches the end of the 300 degree arc. Reactivate the stopwatch
after the skimmer has been turned around and as it begins the 300 degree
counterclockwise arc along the boom.
4. Continue maneuvering in this fashion until the test slick takes on the appear-
ance of patches of floating oil. At the end of a complete 300 degree arc secure
the stopwatch.
5. Continue pumping to empty the skimmer collection sump of recovered oil.
TABLE 12. TEST PROCEDURES - OIL MOP POLLUTION CONTROL, LTD.
REMOTE SKIMMER (STATIONARY TEST)
Pump skimmer sump and collection hose dry with OHMSETT positive displace-
ment diaphragm pump located on the main bridge.
Set mop/oil slick contact length by adjusting the overhead crane to lift the
skimmer hulls clear of the water. Pump a predetermined volume of test oil to
achieve the desired slick thickness or to replace the (estimated) volume of oil
picked up during the prior test. Set the selected wave condition.
Activate a stopwatch, oil mop rotation and offloading pumps. Activate fire
hoses (some tests) to direct the oil into the region of the boom area where the
skimmer is positioned. Visually estimate the area covered by the test oil and
held in that area by the fire hoses during the conduct of the test.
At the end of a 10 minute period, secure the stopwatch and place the skimmer
in an area of the tank free of test oil. Continue pumping to empty the skimmer
collection sump of recovered oil. Analyze the collected oil/water mixture in
the sample barrel.
-------
TEST RESULTS
Results of the numerical performance parameters are itemized in Table 13 for
heavy oil and Tables 14 and 15 for medium oil. Throughput efficiency was calculated
only for the towed tests. Accurate measurement of the test oil slick volume entering
the bow of the skimmer (necessary to calculate TE) was possible only during tow tests.
Since the Oil Mop remote skimmer is intended for use primarily inside boomed
areas, the two most important performance parameters are recovery efficiency, RE,
and the net oil recovery rate, ORR. By maneuvering within a boomed area, the
skimmer can encounter parts of the oil slick which may have passed through the device
uncollected on previous passes. Therefore, calculation of throughput efficiency is of
less importance for the Oil Mop remote skimmer than would be the case with a
skimmer operating on a slick unconfined by containment boom.
RE results are plotted for all tests (towed and non-towed) in Figure 16. Lines
connecting data points having test conditions differing only by the wave condition
show the trend of RE values as a function of wave condition.
ORR results for all towed tests are graphed in Figure 17 as a function of wave
condition ranging from calm to the 0.3-m x 4.2-m regular wave condition.
Non-towed test results with medium oil are shown in Figure 18. In these tests
the mop/slick contact length and means of bringing oil to the mops was varied. In
some tests, the skimmer was maneuvered through the slick using its own propulsion; in
other tests the mop/slick contact length was changed by lifting the skimmer with a
crane and using fire hoses to keep a thickened test oil slick against the rotating oil
mops.
DISCUSSION
Although this brief one week test series allowed only enough time to test a few
deployment modes and mop/slick contact lengths, the ^trends of numerical results do
reinforce the conclusions of earlier OHM SETT tests using the oleophilic oil mop
operating principle in different skimmer platforms. Referring to the data points and
trends plotted in Figure 16, 17, and 18 the oil mop oleophilic principle has the
following significant characteristics:
1. RE is relatively independent of wave steepness.
2. ORR is limited primarily by the rate at which oil mops can be brought in
contact with the slick.
Both of the above characteristics appear to be due to the degree of oleophilic
nature of the mops and their tenacity for hanging onto oil, once wetted with oil, even
when momentarily submerged by a passing or breaking wavelet.
37
-------
TABLE 13. TOWED TEST RESULTS - OIL MOP REMOTE (HEAVY OIL)
Test
no.
T01R
TO4
TO2R
T05
T06
T03
Tow
speed
(kt)
0.5
1.0
0.5
1.0
1.0
0.5
Slick
thickness
(mm)
6
6
9
9
9
9
Waves
HxL
(m x m)
0
0
0.2 x 7.0
0.2 x 7.0
0.3 x 4.2
0.3 x 4.2
Mop
speed
(kt)
0.1
0.25
0.15
—
—
—
Mop/roller
slippage
yes
yes
yes
yes
yes
yes
RE
%
96
81
70
86
76
74
TE
%
16
17
27
16
16
30
ORR
(m3/hr)
1.2
2.6
1.8
2.4
2.3
1.9
OJ
co
TABLE 14. TOWED TEST RESULTS - OIL MOP REMOTE (MEDIUM OIL)
Test
no.
T10
T14
T12
T13
Tow
speed
(kt)
0.5
1.0
0.5
0.5
Slick
thickness
(mm)
9
9
9
9
Waves
HxL
(m x m)
0
0
0.2 x 7.0
0.3 x 4.2
Mop
speed
(kt)
0.4
0.4
0.4
0.4
Mop/roller
slippage
Intermittent
n
M
II
RE
%
90
88
93
86
TE
%
42
18
31
43
OJRR
(m3/hr)
2.1
2.7
2.1
2.4
-------
TABLE 15. NON-TOWED TEST RESULTS - OIL MOP REMOTE (MEDIUM OIL)
u>
Test
no.
SO4
SO5
SO6
SO7
SOS
S09
S10
Sll
S12
Tow Slick Waves Mop
spd. thickness H x L spd. Mop/roller
(kt) (mm) (m x m) (kt) slippage
(1) 6 0 — Intermittent
(1) 9 0.2x7.0 — "
0 11 o — "
0 13 0 — "
0 14 0 — "
0 47 0 — "
0 45 0.3 x 4.2 — "
0 47 0.4 x 0.8 — "
0 52 0.4 x 0.8 — "
Mop/sJick
contact
length
(m)
1.9
1.9
1.9
1.2(5)
0.6(5)
0.6(5)
1.2(5)
1.2(5)
1.9
(2)
Deploy.
mode
M
M
S
S
S
5(4)
5(4)
5(4)
5(4)
(3)
RE TE
% %
67
80
36
60
82
93
89
92
65
ORR
(m3/hr)
1.5
2.0
0.4
0.7
0.6
0.6
2.0
1.9
1.1
NOTES:
(1)
(2)
(3)
(4)
(5)
Variable (unknown) forward speed in maneuvering mode
M = maneuvering with remote control props
S = stationary (props not operated)
Not calculated (calculated only for towed tests)
Fire hose used to direct oil slick against mops
Skimmer hulls lifted out of the water by crane
due to intermittent operation of props.
-------
120
R
E
0
E
R
Y 90
F80
F
I 70
C
j5 60
N
C 50
Y
X 40
30
20
A
B
D
A
O
A-
0-
0-
+ .
HEAVY OIL-TOWED
MEDIUM OIL-TOWED
MEDIUM OIL-MANEUVERING
MEDIUM OIL-STATIONARY
D
4-
CALM .2/7 .3/4 .4/ 8
WAVE CONDITION CM X M)
Figure 16. Recovery efficiency trends for Oil Mop remote skimmer.
-------
L*.o
R
E 2
C
0
*,.s
R
Y
R
A
T
E0.5
&
LO
A- MEDIUM OIL - 0.5 KNOTS
D- HEAVY OIL - 0.5 KNOTS
0- MEDIUM OIL - I.0 KNOTS
+- HEAVY OIL - 1.0 KNOTS
A •• ^— •" "l" mmm m^m ,mm wmm i_
o
n
CALM .2/7
WAVE CONDITION CM X M>
.3/4
Figure 17. Oil recovery rate trends for Oil Mop remote skimmer.
-------
-tr
tV)
A- MANEUVERING
D- STATIONARY
0- WITH FIRE HOSE
S A
\
D
8.6
1.2
MOP/SLICK CONTACT LENGTH CM)
Figure 18. Medium oil
recovery rate for Oil Mop remote skijnmer.
-------
Referring to Figure 16, of the 19 tests conducted in the various deployment
modes, fifteen demonstrated a RE equal to or greater than 70%. In addition, lines
connecting data points whose tests conditions differ only by wave condition show the
recovery efficiency actually increased or was reduced by only 10% or less as the wave
steepness increased.
The trends of Figure 17 also demonstrate an insensitivity to wave steepness.
Although the number of data points is small, this figure reinforces the results of past
Oil Mop QHMSETT tests that the ORR falls off only slightly with increase in wave
steepness as more oil is brought into contact with the mop. Figure 17 also illustrates
the oil mop characteristic that the ORR is limited by the rate at which the oil slick
can be brought into contact with the mops. The higher of the two tow speeds brought
the mops in contact with the slick at a greater rate, thereby yielding higher ORR
values.
Figure 18 demonstrates the change in oil pickup performance with the variation
in mop to oil slick contact length. The sketches of Figure 18 show, to scale, the
various mop/slick contact lengths. For the 0.6 and 1.2 meter contact length, (see
Figure 19) the skimmer was lifted clear of the water by an overhead crane, thereby
allowing oil to contact mops from the sides as well as the front. For the contact
length of 1.9 meters shown to the extreme right, the unit was floating in its design
condition (as it was for the rest of the tests) with the hulls preventing any oil from
contacting the rotating mops from the side. The two trend lines in Figure 17
connecting data points differing only by the contact length show the effect of the hulls
in reducing ORR value. The effect of two other factors which increased the rate of
oil contact with the mop, and thus the ORR value are also evident in Figure 17. First,
the increase in ORR due to getting more oil to the rnops is clearly shown by the two
triangular data points obtained when the unit was operated in a manuevering mode
with its onboard propulsion. Second, the increase in ORR due to increase in slick
thickness is evident when comparing the diamond data points with the square data
points. The diamond data points represent stationary tests in which fire hoses were
used to thicken the slick locally in the area of the mops (see Figure 20).
-------
Figure 19. Oil Mop remote skimmer test using crane to lift wringer
out of water.
Figure 20. Use of fire hoses to thicken oil slick in the mop area.
-------
SECTION 4
TROIL/DESTROIL SKIMMER SYSTEM
CONCLUSIONS
The Troil/Destroil Skimmer System was tested at OHMSETT 15-24 August 1979.
The tests were conducted to measure the recovery performance of the combined boom
and skimmer system and observe the interaction of the boom and floating skimmer.
Best Performance-
Table 16 shows the best skimmer performance for heavy and light oils. Oil
specifications can be found in Appendix B. Skimmer performance parameters,
Recovery Efficiency (RE) and Oil Recovery Rate (ORR), were at their highest when
the boom preload oil volume was at the test maximum. Because of the high skimmer
pump capacity it was necessary to change the preload charge volume. Tests were
conducted with various boomed preload volumes to detemine performance changes and
guidance for operator control.
TABLE 16. PEAK PERFORMANCE - TROIL/DESTROIL SKIMMER SYSTEM
Performance
parameter
Highest
value
Tow
speed
(kt)
Boom
Preload
m
Waves
HxL
(m x m)
CIRCO HEAVY OIL--
Test No. 22
RE
ORR
93% ,
20.9 irT/hr
0.75
0.75
3.8
3.8
0.26 x 4.2
0.26 x4.2
CIRCO 4X LIGHT OIL--
Test No. 33
RE 91% , 0.75 3.8 calm
ORR 23.7m:7hr 0.75 3.8 calm
-------
Operating limits —
The Troil/Destroil skimmer system, as tested, has the following operating
limits:
(1) The maximum towing speed at which the Troilboom can retain collected
oil without significant loss is 1 knot.
(2) The maximum pumping rate of the Destroil skimmer pump is approxi-
mately 37.4 m /hr.
At a boom towing speed of 1 knot the Troilboom lost oil at a visually estimated
rate of approximately 2.3 m /hr. When the towing speed was increased to 1.25 knots
the visually estimated oil loss rate increased to approximately 23 m /hr. Oil losses
were consistently observed to be the result of vortex shedding occurring near the side
walls of the skimmer collection pocket.
The Destroil skimmer has an advancing screw pump capable of pumping very
thick oil in the range of several tens of thousands of centistokes. The maximum
viscosity of the test oil used at OHMSETT was approximately 925 cSt. The test series
did not determine the pumping capabilities of the skimmer with higher viscosity
mixtures. The skimmer pump was capable of ingesting a quantity of floating debris
deposited during one of the test runs. The boom and skimmer system showed good
wave-following in test waves up to 0.47 m harbor chop. The independent towing bridle
allowed the boom to maintain a relatively constant waterline while in the wave. There
were several mechanical failures of the boom during one 1.5 knot tow test. Two boom
stiffeners broke and five rope eyelets split. The split eyelets were repaired by
sandwiching metal washers to accept the rope line. The boom stiffeners were
replaced.
RECOMMENDATIONS
The Troil/Destroil skimmer system, as tested, should be used at speeds not
exceeding 1 knot. The device can be used in moderate waves without significant
performance reduction. Once rigged, a single operator can control the recovery
operation by adjusting pumping rate and skimmer height. Skimmer performance of
recovery efficiency and oil recovery rate can be increased if the operator allows a
precharge oil volume to remain in the skimmer pocket while operating the pump. At
least 3.8 m is necessary to provide an appropriate precharge volume in the boom
pocket for good performance.
The oil recovery rate of the skimmer is limited by the pump capacity. A larger
pump with about three times the pumping capacity should be considered for the
Troil/Destroil skimmer system. The boom and skimmer must be able to survive a
variety of weather and towing conditions. Towing bridles and boom stiffener battens
should be made stronger so that the boom can survive greater towing loads. The bridle
attachment points should be redesigned to provide for quick rigging adjustments to
allow a proper boom towing attitude.
-------
SKIMMER DESCRIPTION
The Troil/Destroil skimmer system assembled for OHMSETT testing combined
the Troilboom Giant 1.5 metre oil boom manufactured by Trelleborg AB, Sweden and
the Destroil Model DS210 Skimmer Pump manufactured by DESMI A/S, Denmark. The
boom and skimmer are shown in Figure 21 as deployed at OHMSETT.
The Troilboom consisted of four 6.4-m sections of 1.5-m high collection boom.
Figure 22 is an illustration. At the center of the boom is a 3.5-m wide opening at
which is attached an additional section of boom that provides a pocket to collect the
swept oil and contain the floating skimmer pump. The boom panels are supported by
curved fiberglass battens which provide a concave boom profile while under tow. The
boom is towed by an independent external load line which connects to the battens by
individual bridles. This arrangement allows each boom section to conform to waves
and maintain a nearly constant waterline.
The Destroil skimmer pump is a hydraulicaliy-driven screw pump. Oil is
recovered as it flows over the central hopper weir into the exposed pump screw.
Skimmer flotation is provided by two fixed-position floats and one which is adjusted by
remote ballasting with compressed air. The skimmer pump is shown in Figure 23. The
pump is driven by a remote diesel-hydraulic power pack which provides pump power and
air ballast control. The pump discharges through a 127-mm flexible discharge hose.
The screw and hopper have a macerator cutting edge for chopping debris that may
enter the pump with the oil.
There is a considerable quantity of engineering data in the literature for each
component in this skimming system. The Troilboom was tested in the Swedish State
Shipbuilding Experimental Tank, was evaluated by Warren Spring Laboratory in the
United Kingdom, the Swedish Coast Guard, and the Norwegian Ship Research Institute
Ship Model Tank. The Destroil skimmer was tested in the Danish Ship Research
Laboratory Test Tank. Various parts of the skimming system have documented
experience in the Amoco Cadiz, Eleni V, and Ekofisk spill cleanups. After the
OHMSETT program, the system was scheduled for testing by the U.S. Navy and
Environment Canada.
TEST PROCEDURES
The Troil/Destroil skimmer system was rigged in the test tank between the
towing bridges and towed by the main bridge. The boom sweep width was 18 m. The
skimmer was towed directly by the main bridge and positioned to respond freely within
the boom collection pocket. Several preliminary test runs were performed with and
without oil to determine the maximum oil containment speed, towing loads, and
boom/skimmer interaction.
The procedures used various preload oil volumes and a constant oil distribution
rate which approximated the maximum pump capacity. The use of an oil preload and
suitable oil distribution rate would allow the skimmer to perform as it would be
operated in the field. The test procedures were designed to examine the steady state
performance of the skimmer. To do this, the oil mixture collected during the middle
of the test run was kept separate from that collected at the beginning and end of the
test run. In this way, steady state conditions could be approximated. Table 17
describes the test procedures used for the data collection runs.
-------
Figure 21. Troil/Destroil skimmer system as tested at OEMSETT.
-------
Bridle lines
External load line
Fiberglass battens
Boom panels
Figure 22. Troilboom.
-------
Remotely adjustable air ballast float
Mechanically adjustable floats
vn
o
Screw
Honper
f—Pump discharge
Figure 23. Destroil skimmer pump,
-------
TABLE 17. TEST PROCEDURES - TROIL/DESTROIL SKIMMER SYSTEM
1. Distribute the metered preload volume from the main distribution manifold.
2. Start the towing bridge and begin the oil distribution.
3. Start the skimmer pump when the preload and constant oil slick have reached
the collection pocket (approximately 60 seconds).
4. Start the oil collection in barrel //I one minute after pumping begins.
5. Shift to collection barrel #2 after one minute.
6. Stop the oil distribution 21.9 m before the end of the tow.
7. Shift to collection barrel no. 1 one minute after the towing bridge stops.
8. Continue pumping and cleanup remaining oil into slop barrel.
9. Tow back to head of tank.
TEST RESULTS
During the preliminary shakedown tests, the maximum towing speed at which
oil could be retained by the boom was observed to be 1 knot. The rate of oil loss from
the boom was visually estimated from the remaining volume in the boom pocket to be
approximately 2.3 m /hr at towing speeds up to 1 knot. When the towing speed was
increased to 1.25 knots the rate of oil loss quickly increased to approximately 23
m /hr.
Towing loads were measured from the main bridge to be 330 kg at 1 knot in
calm water. A maximum load of 1,134 kg was measured at 1.5 knots in waves. At this
load, damage was sustained by several boom bridles and battens as the boom began to
submerge at this towing speed.
The skimmer pumping rate was measured to be a maximum of 37A m /hr while
recovering the heavy test oil, Circo X Heavy with a viscosity.of 850 cSt. The pumping
rate, averaged for all data runs, was approximately 22.6 m /hr with the pump screw
turning at a set rate of 425 rpm. The results of the data runs are shown in Tables 18
and 19.
The Troil/Destroil skimmer system combines several interesting features of the
boom and floating skimmer. The independent towing bridle of the boom provides for
good wave conformance in a variety of sea states. The center collection pocket
provides an oil storage area to thicken the oil layer and a convenient place for the
floating skimmer or several skimmer pumps to be placed. The Destroil skimmer is an
interesting application of a screw pump to an oil skimmer. The skimmer can be
controlled remotely by an operator at the hydraulic console. The pump has
51
-------
TABLE 18. TROIL/DESTROIL TEST RESULTS (HEAVY OIL)
Test
no.
Tow
speed
(kts)
Slick
thk.
(mm)
Boom
Preload
(m3)
Waves
Hx L
(m x m)
RE
ORR
(m3/hr)
Comments
11R
12
12R
13
14R
w 15
16
17
18
19
20
21
22
23
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0
25
0
0.75
1.0
0.75
1.25
0.75
5.3
4.7
4.7
5.0
4.8
4.8
3.6
2.8
3.7
4.6
3.6
4.7
2.9
3.4
1.89
0.95
0.95
0.38
0.95
0.95
0.95
89
89
89
89
0.95
0.95
79
79
3.
3.
0.95
calm
calm
calm
calm
0.47 HC
0.47 HC
0.19x7
calm
0.26 x 4.2
0.26 x 4.2
calm
0.19x7
calm
0.26 x 4.2
0.26 x 4.2
0.26 x 4.2
79
70
75
49
59
59
67
70
60
46
78
40
64
93
70
58
18,
18,
17.4
.6
,3
,7
.9
10.
12.
10.
14.
16.0
12.9
9.7
17.9
8.3
15.7
20.9
14.8
9.6
Average of barrels
Average of barrels
Average of barrels
Value discarded out of range
-------
TABLE 19. TROIL/DESTROIL TEST RESULTS (LIGHT OIL)
VJ1
U)
Test
no.
25
26
27
28
29
30
31
32
33
34
Tow
speed
(kts)
0.75
0.75
0.75
0.75
0.75
0.75
1.25
1.25
0.75
1.0
Slick
thk.
(mm)
4.8
4.8
4.7
4.7
4.7
4.7
2.9
2.9
4.7
3.7
Boom
Preload
(m3)
0.38
0.95
1.89
0.38
0.95
1.89
1.89
3.79
3.79
3.79
Waves
HxL
(m x m)
calm
calm
calm
0.26 x 4.2
0.26 x 4.2
0.26 x 4.2
0.26 x 4.2
0.26 x 4.2
calm
0.26 x 4.2
RE
(%)
50
76
91
26
47
61
72
66
91
62
QRR
(m /hr) Comments
12.0
17.3 Recalculated from data
20.6
5.3
8.7
14.6
12.3 Value discarded small volume collected
16.7
23.7
19.8
-------
demonstrated an ability to handle debris and would appear to be able to pump a wide
range of viscosities.
The test parameters were selected to examine the effects of the boom preload
oil volume, waves, and speed on the skimmer performance measurements of Recovery
Efficiency (RE) and Oil Recovery Rate (ORR). Skimmer performance was not greatly
affected by the different test oils as shown by the overlap of the data of the different
oils.
Figure 24 shows the plot of the recovery efficiency versus preload oil volumes
for the combined heavy and ligh± oil data. The graph shows a minimum RE of 50%
wi±h a preload volume of 0.4 m while the skimmer is towed in calm water. The 0.4
m preload was considered minimum acceptable before pumping. RE increases-to 90%
at a preload of 3.8 m . RE is reduced to 23% in waves with a preload of 0.4 m . With
a larger preload of 3.8 m , the RE in waves increases to 84%. Figure 26 also shows
the effects of the combination of waves and higher towing speeds of 1.25 knots to
reduce skimmer RE. At this speed, the system performance would be reduced not only
by the lower RE but by the significantly increased oil loss rate from the collection
boom.
Figure 25 shows the plot of the Oil Recovery Rate (ORR) versus the preload oil
volume for the combined heavy and light oil data. The ORR in calm, water increases
from L0.6 rn /hr at a preload of 0.4 m to a recovery rate of 23.7 m /hr at the higher
3.8 m preload. The ORR shows a relative increase of 37% between the 1.9 m
preload volume and the 3.8 rn preload volume. In contrast, the same preload change
results in a recovery efficiency increase of only 25%. The more rapid improvement in
ORR is the result of the increased pumping rate of the skimmer pump as the viscosity
of the collected mixture increases. Figure 25 also shows the reduced skimmer
performance in waves. A further reduction of ORR is shown by performance in waves
at 1.25 knots tow .speed. At this speed, the oil loss rate of the boom, previously
estimated at 23 m /hr exceeds the ORR of the skimmer. The test results show the
importance for the skimmer opertor to maintain a good volume of oil in the skimmer
pocket and to maintain towing speeds below 1 knot.
In developing the data for Figures 24 and 25, performance data was averaged
for all runs with towing speeds of 1 knot and below because the boom performance
appeared to be similar for these speeds. The performance data for all wave types
were averaged as the the boom and skimmer showed a similar response for all the
wave types. The tested skimmer system was relatively large and the test method not
precise enough to distinguish subtle differences in speed and wave characteristics.
A debris test was performed to examine the solkis handling ability of the screw
pump. During this test, the pump digested 0.2 m of mixed trash (cans, wood,
styrofoam, plastic bags, a raincoat, polypropylene rope) and 3m of Petro-Fiber
sorbent material, along with the collected oil.
DISCUSSION
The ORR of the skimmer pump is at its maximum when the preload of oil in the
boom pocket is thick enough to allow the skimmer to maintain high j-ecovery
efficiency. It is important that the skimmer operator maintain a 0.4 m preload
-------
VJl
R
E
120
110
0
V100
R
Y 90
E
F
F
I
C
I
E
N
C
Y
80
70
60
50
40
30
20
0
D
0.5
A
D
O
n
n
A- 0.74 KNOTS
D- 0.74 KNOTS
. 00 KNOTS
. 00 KNOTS
. 24 KNOTS
0 - 1
- I
0 - I
CALM
WAVES
CALM
WAVES
WAVES
2
o
1.5 2
PRELOAD VOLUME
2.5
8
o
o
3.5
Figure 2k. Recovery efficiency for Troil/Destroil skimmer system preload oil volumes for all oil types.
-------
0
I
L
R
E
C
0
V
E
R
Y
R
A
T
E
0
LO
25
20
15
10
A
A
a
A
A
O
a
n
B
A- 0.74 KNOT
D- 0.74 KNOT
,00 KNOT
,00 KNOT
0-
+ -
1
1
0- 0.64 KNOT -
CALM
WAVES
CALM
WAVES
WAVES
£
A
n
6
o
o
0.5
1 1.5 2 2.5
PRELOAD VOLUME CCUBIC METERS)
3.5
Figure 25. Oil recovery rate for Troil/Destroil skimmer system.
-------
volume in the pocket. The operator can make best use of his oil storage tank capacity
and skimmer pumping rate by maintaining the preload throughout recovery operations.
During the test, it was observed that at tow speeds near 1 knot, a 3.8 m preload was
maintained when the oil collection pocket was completely filled with oil and an oil
head wave extended three feet forward from the pocket mouth. A smaller 1.9 m
preload was maintained when the oil volume just filled the oil collection pocket.
During testing it was observed that the Troilboom was lightweight and could be
easily handled by two men. It was necessary several times to adjust towing bridle
lengths and considerable effort was spent in making these adjustments. Bridle
adjustments could be speeded up by providing quick adjustable fasteners for the towing
bridles. Some of the bridle splices loosened during towing as the oil reduced the splice
strength of the polypropylene rope. The fiberglass batten stays of several boom panels
snapped at high towing speed of 1.5 knots. At this speed, the boom submerged
dramatically and rapidly increased the towing load.
The oil collection pocket at the apex of the boom provides a holding area for
the oil and a place for the floating skimmer. Oil was observed to circulate within the
pocket at all towing speeds. Oil did not concentrate in the back of the pocket but
circulated towards the left and the right wall near the middle where the skimmer was
located.
57
-------
SECTION 5
VERSATILE ENVIRONMENT PRODUCTS ARCTIC SKIMMER
CONCLUSIONS
The Versatile Environment Products arctic skimmer was tested at the
OHMSETT test facility from 15 to 23 October, 1979. This skimmer is an air-
transportable remotely-controlled version which incorporates the original Bennett oil
collection principle. A larger Bennett skimmer, the Mark 6E, was tested during the
1977 OHMSETT test season. The Arctic Skimmer is a prototype version developed for
Environment Canada intended for use in cold weather. The Arctic Skimmer
incorporates several improvements over the Mark 6E Skimmer.
The objectives of the Arctic Skimmer tests were to observe skimmer operation
in regards to operator control and mechanical performance. Skimmer performance
was measured over several tank test conditions to gain operator control experience to
maximize skimmer performance.
The following conclusions were determined from the test series:
(1) The skimmer can be controlled from either onboard with the power pack
mounted on the skimmer or remotely with the power pack removed and
connected to the skimmer through the hydraulic control lines. The
several adjustable skimmer settings can be preset for remote skimmer
operation.
(2) The water jet nozzles can effectively concentrate and sweep oil into the
skimmer at speeds from 1 knot to 4 knots in both calm and wave
conditions.
(3) The settings of the three adjustable skimmer doors are critical for
maximum performance at each speed. A graph of skimmer door settings
was developed from performance tests.
Tables 20 and 21 lists the best skimmer performance for heavy and light oils
respectively. In addition to regular towing tests with a 3-mm slick, several tests were
performed to establish the maximum oil recovery rate (ORR) of the skimmer. In these
tests at least 25.0 mm thickness of oil was presented to the skimmer and the skimmer
then adjusted for maximum recovery rate.
-------
TABLE 20. PEAK PERFORMANCE - BENNETT ARCTIC SKIMMER (HEAVY OIL).
Performance
parameter
TE
RE
ORR
Highest
value
96.3%
85.0.%
20 rri /hr
Tow
speed
(kt)
2
0
0
Waves
H x L
(m x m)
calm
calm
calm
Slick
thk.
(mm)
3.4
25.0
25.0
TABLE 21. PEAK PERFORMANCE - BENNETT ARCTIC SKIMMER (LIGHT OIL).
Performance
parameter
TE
RE
ORR
Highest
value
99.4%
97.4%
19.4 nT/hr
Tow
speed
(kt)
1
0
0
Waves
H xL
(m x m)
calm
calm
calm
Slick
thk.
(mm)
2.8
25.0
25.0
Operating Limits—
Each of the performance parameters can be maximized by the operator as
follows:
1. To maintain high throughput efficiency, the skimmer should be operated at
speeds not greater than 2 kt. The maximum safe skimming speed in calm water
is 5 kt.
2. To maintain high recovery efficiency, a thick oil layer should be maintained at
the collection belt. The belt should be raised to be even with the oil/water
interface.
3. The oil recovery rate of the skimmer is limited by the maximum pumping rate
of the skimmer pump. The actual rate will vary with the viscosity and
discharge hose requirements. Maximum pumping rates observed for the 80-mm
discharge hose with 4.5-m head was 23.6 m /hr.
The Arctic Skimmer was tested in waves 0.18-m high by 9.4-m long. The
maximum height of wave in which the skimmer can perform is about 0.3-m high, which
is about the maximum depth of the bow door. As the skimmer is able to respond to
longer period waves, the actual height of the wave can increase if the relative wave
height at the skimmer mouth remains near 0.3 m.
59
-------
Mechanical Problems—
No serious mechanical problems were encountered during the test series.
Several minor problems occurred which were quickly corrected by the OHMSETT test
crew, as follows:
(1) Overheating of hydraulic fluid occurred after continuous operation.
Additional temporary cooling was provided by hanging hydraulic hoses in
the tank water.
(2) Several hydraulic leaks occurred in the hydraulic hose bundle where hose
couplings had loosened during shipment.
(3) Lock nuts on the mid gill door adjustment screws loosened and jammed
the opening mechanism.
RECOM MENDATION5
The OHMSETT test program resulted in the following suggestions for the
manufacturer to consider later in his development program.
(1) The arctic skimmer is intended to be transported partially disassembled.
The skimmer could arrive with the belt mechanism removed and lowered,
flotation collars removed, and additional equipment stored within the
skimmer. Clear rigging, reassembly, and system check-out procedures
should be fixed on the skimmer to facilitate quick deployment.
(2) The skimmer operating manual should be updated to include optimal
skimmer door settings, belt speed and pump control calibration curves.
(3) An auxiliary cooler should be provided for the hydraulic reservoir for
extended operation in warm weather.
(it) The rigging for the water jet sweep booms should be simplified to allow
quick adjustment from the skimmer.
(5) The squeeze belt collection sump could be enlarged to contain belt
splashover at high speed.
(6) The adjustment screws for the aft and middle gill door should be
modified to make readjustment quicker.
SKIMMER DESCRIPTION
The Versatile Environment Products arctic skimmer is a non-self-propelled
advancing weir skimmer with an adsorbent rotating belt. The skimmer is equipped
with a hydraulic power pack which powers the collection belt mechanism, the oil
offloading pump, and a water pump for ballasting and powering the water jet booms.
The skimmer is similar in design to the larger Bennett Mark 6E skimmer that was
60
-------
tested during the 1977 OITC test program. The skimmer can be operated with the
power pack and control station onboard the skimmer or with the power pack removed
and remotely controlling the skimmer means of a 27.4-m umbilical hose bundle.
The device is shown in Figure 26 as it is rigged in the test tank. It is shown
with the power pack mounted on the skimmer. The skimmer is 7.92-m long with a
beam of 2.9 m. The beam is increased by flotation collars, which increase stability.
The skimmer weighs 5117 kg with an additional 650 kg for the power pack. The power
pack is powered by a 55.9 kW VM diesel.
Figure 27 shows the operating principle of the skimmer. As the skimmer
advances, the upper layer of oil and water enters the skimmer over the adjustable bow
ramp. As the water and oil mixture enters the device, water exits through the mid and
aft gill doors. The adsorbent polyester/wool rotating belt faces aft and collects oil off
the water surface. The collected oil is squeezed from the belt by a secondary squeeze
belt. Collected oil is recovered in the sump and transferred off the skimmer by the
discharge pump. The skimmer has been simplified from earlier Bennett versions by the
absence of the aft secondary collection weir and the manual door adjustments.
The skimmer is equipped with two water jet booms mounted either side of the
bow ramp. Each boom is 6.1-m long with a single 20-mm water nozzle at the end
directed downward. Water is provided by the onboard hydraulically driven pump which
can provide approximately 2 m /hr at 69 kPa. The water jet booms can control and
concentrate oil slicks as the skimmer advances. With these, oil can be concentrated
into the skimmer mouth without the use of external floating sweep booms. The water
jet boom is an OHMSETT innovation to control oil slicks. This is the first commercial
application of the water jets. Figure 28 shows the effect of the water jets of
concentrating the oil slick.
TEST PROCEDURES
The arctic skimmer was rigged in the tank between the main and auxiliary
bridges. The skimmer pump discharged through the 80-mm hose up to the auxiliary
bridge into one of the three 0.95 m collection barrels.
The skimmer was tested in two operating modes: first with the operator and
power pack onboard the skimmer, and then remotely with the power pack connected
to the skimmer by the 27.*f-m umbilical hose bundle.
The majority of tests were performed with the skimmer towed from the main
bridge with an oU distribution set for a 3-mm slick.
Towing tests used the following procedure:
TABLE 22. TEST PROCEDURES - BENNETT ARCTIC SKIMMER
(TOW TESTS).
1. Start the diesel engine and set all door settings.
2. Start the tow at the test speed and begin oil distribution.
61
-------
3. Start the oil collection belt when the oil has reached the belt surface. Set the
belt speed.
4. Begin pumping when sufficient oil is collected in the sump. Collect the pump
discharge in one collection barrel on the auxiliary bridge.
5. Stop the oil distribution after 91.4 m, continue towing.
6. Near the end of the tank, as the tow is gradually slowed to a stop, keep the oil
inside the skimmer with the fire hose from the main bridge.
7. Continue the oil collection with the belt until oil is no longer being recovered.
8. Pump down the oil sump and clear the discharge hose. Mark the collection
barrel and begin mixing for oil samples.
The oil recovery rate of the collection belt and discharge pump were tested
with the following procedures:
TABLE 23. TEST PROCEDURES - BENNETT ARCTIC SKIMMER
(OIL RECOVERY RATE TEST).
1. With the bow ramp and gill doors closed, place an oil distribution hose from.the
main bridge inside the skimmer containment area and preload with 0.76 m of
oil.
2. Begin the collection of oil with ±he collection belt at maximum rpm. Begin
constant oil distribution at 28.4 m /hr.
3. Begin the discharge pump when sufficient oil has collected in the sump and
discharge into collection barrel number 1. Adjust belt speed and height as
necessary for maximum recovery.
4. After 100 seconds, transfer to collection barrel number 2.
5. After an additional 100 seconds, transfer the discharge hose to collection barrel
3.
6. After an additional 100 seconds, 300 seconds total, stop the discharge pump,
collection belt and oil distribution. Measure all collection barrel volumes and
take oil samples.
Tests were conducted with both Circo X heavy oil with an average viscosity of
2100-cSt and with Circo 4X light oil, with an average viscosity of approximately 35 cSt
(see Appendix B).
The majority of tests were performed in calm water to establish a performance
baseline and limits under ideal conditions. Tests were performed in waves that were
62
-------
Figure 26. Versatile Environment Products arctic skimmer as tested
at OHMSETT.
-------
Os
-fc"
Aft
N Oil discharge
Gill doors
Figure 2?. Versatile Environment Products arctic skimmer operating principle.
I i
-------
Figure 28. Effect of water jets in concentrating oil slicks.
-------
approximately 0.18-m high by 9.4-m long. This wave provided considerable skimmer
movement with good oil movement within the skimmer. The relative height of the
wave was close to the maximum depth of the bow ramp. In open water such a wave
would be considered near the limits of operator and skimmer safety.
TEST RESULTS
The results of the performance test runs are listed in Tables 24 and 25. The oil
recovery rate tests are noted in these tables in test 15 for the heavy oil and tests 27
and 27R for the light oil tests.
The data show the peculiarities of testing the arctic skimmer within the
constraints of OHMSETT. The relatively short towing length of the tank makes it
difficult to achieve constant operating conditions, or steady state, for each test run.
The skimmer has many internal surfaces and areas which must be saturated with oil to
operate at its maximum. As a result, several test runs at similar conditions must be
performed to average skimmer performance.
The test procedures that were used for the towing tests provide reasonably
accurate throughput efficiency (TE) at the expense of accuracy of recovery efficiency
(RE). For this skimmer, the TE measures how well the skimmer can contain and hold
oil as it moves down the tank. To measure this accurately it was necessary to ensure
that all oil that was captured was transferred to the collection barrel. To do this, the
collection belt was run until all possible oil was recovered. During the cleanup of each
test run, the collection belt gradually recovered more and more water which caused
the recovery efficiency to decrease. The recovery efficiency numbers shown in Tables
24 and 25 reflect more of a lower average for each test run.
Recovery efficiency (RE) is mostly a measure of how well the adsorbent belt
picks oil up off the water surface. This is a function of the thickness of the oil layer
in front of the collection belt more than either tow speed, wave, or oil viscosity. A
skimmer operator can control RE by waiting for oil to collect inside the skimmer
before starting the collection belt. Peak recovery efficiencies for the skimmer are
best shown in the oil recovery rate (ORR) tests.
Figure 29 shows a plot of RE for test number 24. In this case, the graph shows
a peak RE of 63% where the average barrel sample showed only 42.1%. The steady
state RE for most of the tow tests could be expected to be from 10 to 20% higher than
the average value shown in the tables.
Throughput efficiency versus towing speed is shown in Figures 30 and 31. For
the heavy oil, TE stayed above 90% at speeds up to 2 knots and gradually declined to
about 50% at 4 knots. A test was conducted at 4.5 knots which proved to be the
towing limit of the device as the bow ramp caused the device to begin to submerge. In
waves, TE was reduced to about 70% at speeds up to 2 knots.
In light oil, TE remained above 90% at speeds up to 2 knots but was reduced
more quickly at higher speeds, where at 3 knots performance was reduced to 50%. At
4 knots, TE was reduced to approximately 40% and demonstrated clear failure at this
condition. In waves, TE was reduced to about 75% from 1 knot to 2 knots. Skimmer
performance seemed similar for TE for both of the test oils. However, at speeds
66
-------
TABLE 24. TEST RESULTS - BENNETT ARCTIC SKIMMER (HEAVY OIL)
Os
-4
Test
no.
4
4R
4C
4D
5
5R
5C
6
6R
6C
7
7R
g
8R
10
10R
11
11R
11C
15
Tow
speed
(knots)
1.0
1.0
1.0
1.0
2.0
2.0
2.0
3.0
3.0
3.0
4.0
4.0
4.0
5.0
1.0
1.0
2.0
2.0
2.0
-0-
Slick
thk.
(mm)
2.6
2.5
3.3
3.0
3.6
3.5
3.3
2.7
2.6
2.9
2.8
3.0
3.1
2.9
3.1
3.2
3.0
3.0
2.7
25.0
Waves
HxL
(m x m)
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
0.18 x 9.4
0.18 x 9.4
0.18 x 9.4
0.18 x 9.4
0.18 x 9.4
calm
TE
%
73.0
72.0
94.5
86.8
59.3
110.5
82.1
61.1
81.8
73.4
50.7
59.4
48.9
42.1
59.4
76.5
72.3
72.3
83.8
ND
RE
%
61.0
66.9
64.5
62.0
72.6
67.2
70.0
71.9
76.0
74.9
72.1
71.9
70.0
65.9
63.9
70.0
75.1
71.5
72.0
85.0
Comments
data discarded - making adjustments
data discarded - making adjustments
data discarded - making adjustments
data discarded - making adjustments
started at 5.0 knots
a
Oil recovery rate = 20 m /hr
-------
TABLE 25. TEST RESULTS - BENNETT ARCTIC SKIMMER (LIGHT OIL)
Os
OO
Test
no.
21
21R
21C
21D
22
22R
22C
23
23R
23C
23D
23S
24
24R
24C
24D
25
25R
25C
25D
26
26R
26C
27
27R
Tow
speed
(knots)
1.0
1.0 .
1.0
1.0
2.0
2.0
2.0
3.0
3.0
3.0
3.0
3.0
4.0
4.0
4.0
4.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
-0-
-0-
Slick
thk.
(mm)
2.8
2.8
2.8
2.8
2.7
2.7
2.7
2.8
3.0
2.8
2.8
2.9
2.8
2.8
2.8
2.8
3.2
3.3
3.3
3.1
4.5
2.8
2.9
25.0
25.0
Waves
HxL
(m x m)
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
calm
0.18 x 9.4
0.18x9.4
0.18 x9.4
0.18 x9.4
0.18 x 9.4
0.18 x 9.4
0.18 x 9.4
calm
calm
TE
%
112.3
99.4
98.0
105.6
85.5
92.7
91.2
52.1
44.0
49.1
48.9
51.5
41.2
31.9
40.5
36.8
70.6
68.5
84.9
93.1
61.9
73.2
74.3
ND
ND
RE
%
67.0
65.0
59.0
63.0
64.0
67.0
70.0
56.7
49.7
48.3
49.7
47.7
42.1
31.1
40.5
34.4
41.0
45.8
52. 4
48.3
52.4
55.9
52.5
97.0
94.4
Comments
data discarded priming run with
light oil
o
Oil recovery rate = 18.4 m./hr
Oil recovery rate = 19.4 m /hr
-------
<•£>
R
E
C
0
V
E
R
Y
E
F
F
I
C
I
E
N
C
Y
90
70
60
50
30
20
0
0
A- DISCRETE SAMPLES
60
120 180 240 300 360
SAMPLE PERIOD CSECONDS>
420
480
540
Figure 29. Grab sample recovery efficiency for test 2^ of the Versatile Environment Products
arctic skimmer.
-------
T 110
H
0
U
G
H
P
U
T
E
F
F
I
C
I
E
N
C
Y
90
80
70
60
50
40
30
20
10
0
A
A
a
D
A
A- CALM WATER
D- 0.2M X 9.4M WAVE
8
D
A
A
A
A
0
2 3
TOW SPEED CKNOTS>
Figure 30. Throughput efficiency trends with Circo X heavy oil, Versatile Environment Products
arctic skimmer.
-------
T100
H
0 90
U
G
H
P
U 70
T
60
80
50
E
F
F
I
C
I
E
N 30
C
Y
20
10
0
D
D
B
A- CALM WATER
D- 0.2M X 9.4M WAVE
D
A
A
0
2 3
TOW SPEED CKNOTS>
Figure 31. Throughput efficiency trends with Circo **X light oil for Versatile Environment Products
arctic skimmer.
-------
above 2 knots the light oil mixes more easily and losses occur out the aft and mid gill
doors.
The oil recovery rate tests showed the rate was limited by the discharge pump
rather than the oil collection belt. Differences in rate are not that pronounced and
the belt and pump are closely matched In capacity. The rigging of the discharge hose
which required a 4.5 m rise to the collection barrels, may have limited maximum
discharge pump rate.
DISCUSSION
Performance of the arctic skimmer is the result of operator control in adjusting
skimmer controls. These controls include: bow ramp height, middle and aft gill door
settings, collection belt height, belt speed, discharge rates, and water jet boom width
and pressure.
Careful adjustment of door and ramp settings is important to maintain high TE
for various towing speeds. The doors allow the skimmer to capture and hold oil for
recovery by the collection belt. Figure 32 shows the various successful door settings
used during the test program. The depth of water cut is controlled by the bow ramp; it
must be reduced as the towing speed increases. Water pressure is relieved by the aft
and mid doors, which if opened too far, will cause the collected oil to be washed out
from the skimmer. In waves, the bow ramp must be lowered to capture the full height
of the wave.
It was observed during the test runs that the collection belt was most effective
in recovering thin oil slicks when the belt was just touching the water surface. In
thicker slicks, the belt should be lowered no deeper than the oil/water interface.
Submerging the belt deeper in the water will cause lower RE as more water is
collected by the belt. If there is sufficient oil to be recovered, belt speed should be
about 3.1 knots for thick oil slicks and 1.1 knots for thin oil slicks, or less, to maximize
RE. At the higher speed, the oil collection belt and squeeze belt tend to throw oil
outside the collection sump. Belt speed should be adjusted to keep the oil falling in
the sump.
The pump discharge rate can be adjusted so that oil remains in the sump.
However, it is difficult for the operator to tell, particularly in remote operation, how
much oil remains in the sump. When operated remotely, the operator must guess if the
pump rate is sufficient to stay ahead of the collection belt or to prevent the pump
from running dry and possible damage.
The water jet booms were found to be effective at all speeds and wave
conditions. Water jets are not affected by waves as long as the booms are kept high
enough to clear the wave height. The 6.1-m water jet booms can be spread to a
maximum sweep width of 7.3 m. During a test run, it was observed that at 0.5 knot
and a pressure of 241 kPa, the booms could reduce the slick width about 80%. At a
speed of 1 knot, slick width was reduced to about 40% of the original width.
The bow of the skimmer is protected by a debris grate (Figure 33) which is
designed to force debris and ice down underneath the skimmer and keep itjout of the
collection area. During a test run using debris consisting of small 0.3 m pieces of
-------
OJ
40
D
0
0
R 30
0
P
N 20
I
N
G
~ 19
0
-10
A- BOW DOOR
D- MID GILL DOOR
0- AFT GILL DOOR
2 3
TOW SPEED CKNOTS)
Figure 32. Versatile Environment Products arctic skimmer door settings versus tow speed.
-------
wood, the skimmer was towed at speeds up to 2 knots. At the end of the run it was
observed that some of the debris had entered and was trapped inside the skimmer
having worked around the edge of the bar screen. None of the wood debris was forced
underneath the device at 2 knots.
The Versatile Environment Products arctic skimmer was tested in 52 test runs
in five test days. The skimmer collected oil both in a manned and unmanned operating
mode. Within known operating conditions, the operator does have adequate controls
from the remote station to operate the skimmer once initial settings have been made.
Figure 33. Debris grate in the bow of the skimmer.
-------
REFERENCES
1. Lindenmuth, W.T., E.R. Miller ^ and C.C. Hsu. Studies of Oil Retention Boom
Hydrodynamics, Hydronautics, Incorporated Technical Report 7013-2, 1970. 78
pp.
2. McCracken, W.E. Hydrodynamics of Diversionary Booms, EPA-600/2-78-075,
U.S. Environmental Protection Agency, Cincinnati, Ohio, 1978. 46 pp.
3. Breslin, M.K. The Use of Coherent Water Jets to Control Oil Spills, U.S.En-
vironmental Protection Agency, Cincinnati, Ohio, 1980 (in preparation).
*. Graham, D.J., R.W. Urban, M.K. Breslin, and M.G. Johnson. OHMSETT
Evaluation Tests: Three Oil Skimmers and a Water Jet Herder, U.S. Environ-
mental Protection Agency, Cincinnati, Ohio, 1980. 110 pp.
5. McCracken, W.E. Performance Testing of Selected Inland Oil Spill Control
Equipment, EPA-600/2-77-150, U.S. Environmental Protection Agency, Cincin-
nati, Ohio, 1977. 113pp.
75
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APPENDIX A
FACILITY DESCRIPTION
Figure A-l. Aerial view of OHM SETT Facility.
The U.S. Environmental Protection Agency operates the Oil and Hazardous
Materials Simulated Environmental Test Tank (OHMSETT) located in Leonardo, New
Jersey. This facility provides an environmentally safe place to conduct testing and
development of devices and techniques for the control and clean-up of oil and
hazardous material spills.
The primary feature of the facility is a pile-supported, concrete tank with a
water surface 203 meters long by 20 meters wide and with a water depth of 2A
meters. The tank can be filled with fresh or salt water. The tank is spanned by a
bridge capable of exerting a horizontal force up to 151 kilonewtons while towing
floating equipment at speeds to 6.5 knots for at least 40 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 meters ahead of the device being tested, so that
reproducible thicknesses and widths of the test slicks can be achieved with minimum
interference by wind.
76
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The principal systems of the tank include a wave generator, a beach, and a
filter system. The wave generator and absorber beach can produce regular waves to
0.6 meter high and to *f5 meters long, as well as a series of 0.7 meters high reflecting,
complex waves meant to simulate the water surface of a harbor. The tank water is
clarified by recirculation through a 410 cubic meter/hour 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 oil barrier which is used to skim oil to the
North end of the tank for cleanup and recycling.
When the tank must be emptied for maintenance purposes, the entire water
volume of 9800 cubic meters 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.
Testing at the facility is served from a 650 square meters 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 contractor, Mason & Hanger-
Silas Mason Co., Inc., provides a permanent staff of eighteen multi-disciplinary
personnel. The U.S. Environmental Protection Agency provides expertise in the area
af spill control technology and overall project direction.
For additional information, contact: Richard A. Griffiths, OHMSETT Project
Officer, U.S. Environmental Protection Agency, Research and Development, MERL,
Edison, New Jersey 08837, telephone number 201-321-6629.
77
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APPENDIX B
OHMSETT OIL PROPERTIES AND ANALYSIS TECHNIQUES
OHMSETT test fluids (light, medium, and heavy oils) are sampled and analyzed
several times during the process of using them in testing. The steps and analyses are
detailed below. Some test programs do not use ail sample procedures, and sampling
frequencies are often different.
FLUID PROPERTIES BEFORE TESTING
The test fluids in the bridge storage tanks are sampled at least once daily.
Some test programs require more frequent sampling when test fluids are pumped onto
the bridge more than once a day. Samples are analyzed for the properties detailed in
Table B-l.
TABLE B-l. OIL PROPERTIES
Sample
Property
Viscosity
Surface
Tensions
Interfacial
Tension w/
Tank Water
Specific
Gravity
Temp
Method °C
ASTM D-88 Room
ASTM D-341 and
ASTM D-2161 75
ASTM D-971 Room
ASTM D-971 Room
ASTM D-287 Room
ASTM D-1298
Output
Vise. vs.
Temp Chart
dynes/cm
dynes/cm
Sp.Gr.
(§60/60
Acceptable Range
Light Medium Heavy
cSt
3-10
(§25°C
24 to 34
@25°C
26 to 32
@25°C
0.83-0.91
cSt
100-300
@25°C
24 to 34
@25°C
26 to 32
@25°C
0.90-0.94
cSt
500-2000
@25°C
24 to 34
@25 C
26 to 32
@25°C
0.94-0.97
Bottom Solids ASTM D-96 Room % BS&W
and Water ASTM D-1796
less than 1%
78
-------
FLUIDS RECOVERED BY OIL CLEANUP DEVICES (SKIMMERS)
Fluids recovered by skimmers typically contain both oil and water in an
emulsion. The stability of the emulsion is affected by many factors such as
temperature, viscosity, interfacial tension, particles, oil and water percentages in the
mix, and the amount of mixing energy imparted to the mix. Samples are taken of the
recovered fluid and analyzed for oil and water content in order to determine recovery
and throughput efficiencies.
COMPOSITE SAMPLING
Recovered fluid is pumped from the skimmer to calibrated storage tanks either
during or after the test. The volume of total fluid is measured, any free water is
drained off and then the volume is measured again. Tanks are mixed for five minutes
using electric motor-drive propellers, then a sample is taken during mixing for
analysis. This sample is analyzed by ASTM Methods D-96 and D-1796, Water in Oil by
Centrifuge for oil and water percentage in the recovery tank. Frequently, test
programs use several recovery tanks on each test in order to separate the fluid
recovered during steady state operation, fluid recovered prior to steady state and fluid
recovered after steady state. Steady state is defined as the time during a test when
the skimmer is operating in conditions equivalent to operating in a limitless oil slick.
The percent of oil contained in the steady state recovery tank is then the recovery
efficiency (R.E.) of the device.
Oil volume recovered is found for each recovery tank by the following equation:
Test Oil (m3) = Total Oil In Tank (m3) * % Test Oil In Tank
When more than one tank is used during a single test, the tank volumes are added
together to get the total test fluid recovered. Calculation of throughput efficiency
(TE) is then performed using:
TF Q, Test Oil (m) .Recovered in All Tanks
(Test Fluid m Distributed During Test) multiplied by xlOO%
(% Test Fluid Oil Encountered By Skimmer)
DISCRETE SAMPLING
Since segregating the recovered fluid into pre-steady-state, steady-state and
post-steady-state recovery tanks is not always possible, a second method of obtaining
recovery efficiency is used in this case. Discrete samples are taken out of the
skimmer or from the hose connecting the skimmer to the recovery tanks. A tap is
placed in the line to obtain a cross-sectional sample of the fluid flowing through the
line. Samples are taken at specific times during the steady state test period and
analyzed for percent oil and water. Recovery efficiency is obtained by analyzing plots
of percent oil in each sample versus sample period time.
79
-------
TABLE B-2. SIRENE OIL PROPERTIES
Date
3uly
1979
10
11
12
13
16
17
18
19
20
Oil Type
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo Medium
Circo Medium
Viscosity
cSt
(3 Water
Temp
680
625
480
550
580
500
400
160
195
SFT
IFT
dynes/cm
37.0
36.4
36.7
36.2
37.0
35.8
36.0
35.3
35.2
9.0
9.0
11.1
6.8
7.2
5.8
6.1
4.8
6.2
Specific
Gravity
0.937
0.937
0.932
0.935
0.936
0.935
0.935
0.925
0.924
%
Bottom
Solids
and
Water
0.15
0.25
0
0.15
0
0
0
0
0.1
SFT - Surface tension of the oil.
IFT - Interfacial tension between the oil and OHMSETT tank water
TABLE B-3. OIL MOP REMOTE OIL PROPERTIES
Date
Aug
1979
7
8
8
9
10
Oil Type
Circo X Heavy
Circo X Heavy
Circo Medium
Circo Medium
Circo Medium
Viscosity
cSt
(d Water
Temp
380
490
145
185
170
SFT
IFT
dynes /cm
35.1
35.8
34.6
34.6
34.4
9.5
9.4
7.5
6
6.1
Specific
Gravity
0.934
0.935
0.923
0.925
0.924
%
Bottom
Solids
and
Water
0.8
0.75
0.25
0.3
0.2
SFT - Surface tension of the oil.
IFT - Interfacial tension between the oil and OHMSETT tank water
80
-------
TABLE B-4. TROIL/DESTROIL OIL PROPERTIES
Date
Aug
1979
16
17
20
21
22
23
Oil Type
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo 4X Light
Circo 4X Light
Viscosity
cSt
@ Water
Temp
925
800
800
710
8.3
9.*
SFT
IFT
dynes/cm
35.5
36.5
36.6
36.1
32.8
33
3.3
6.1
9.6
3.4
1.2
2.5
Specific
Gravity
0.938
0.9*0
0.937
0.936
0.885
0.890
%
Bottom
Solids
and
Water
0.4
0.4
0.275
0
0
0
SFT - Surface tension of the oil.
IFT - filter facial tension between the oil and OHM SETT tank water
TABLE B-5. BENNETT SKIMMER OIL PROPERTIES
Date
Aug
1979
16
17
18
19
22
23
Oil Type
Circo X Heavy
Circo X Heavy
Circo X Heavy
Circo 4X Light
Circo 4X Light
Circo 4X Light
Viscosity
cSt
(g Water
Temp
2,100
2,400
1,800
42
33
31
SFT
IFT
dynes/cm
31.7
32.1
32.0
29.7
31.5
31.3
6.6
9.3
8.5
4.4
3.2
4.2
Specific
Gravity
0.939
0.939
0.939
0.912
0.909
0.906
%
Bottom
Solids
and
Water
0.3
0.4
0.4
0.3
0.1
0.1
SFT - Surface tension of the oil.
IFT - Inter facial tension between the oil and OHM SETT tank water
81
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
J. REPORT NO.
EPA-600/2-81-y.ff
3. RECIPIENT'S ACCESSION'NO.
4. TITLE AND SUBTITLE
Performance Testing of Four Skimming Systems
5. REPORT DATE
TQftT
8. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Henry W. Lichte, Michael K. Breslin and Gary F. Smith,
Douglas J. Graham and Robert W. Urban*
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Mason & Hanger-Silas Mason Co., Inc.
P.O. Box 117
Leonardo, New Jersey 07737
10. PROGRAM ELEMENT NO.
INE-823
11. CONTRACT/GRANT NO.
68-03-2642
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory_Cin.
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
OH
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Douglas J. Graham and Robert W. Urban with
PA Engineering, Corte Madera, California 94925.
Project Officer: (201)
Richard A. Griffiths 321-6629
16. ABSTRACT
Performance tests were
oil and hazardous simulated
oil spill cleanup devices:
conducted at the U.S. Environmental Protection Agency's
environmental test tank (OHMSETT) on four commercial
the Sapiens Sirene skimming system, the Oil Mop remote
skimmer, the Troil/Destroil skimming system, and the Versatile Bennett arctic
skimmer. The objective of the test program conducted during the 1979 test season
was to evaluate skimmer performance in collecting oil floating on water using
several wave conditions, tow speeds, and skimmer operating parameters.
Tests described in this report were sponsored by the OHMSETT Interagency
Technical Committee (OITC). Members of the 1979 OITC were the U.S. Environmental
Protection Agency, U.S. Navy-SUPSALV, U.S. Navy-NAVFAC, U.S. Coast Guard, U.S.
Geological Survey, and Environment Canada.
A 16-mm film report, entitled "600 Foot Ocean", was produced to summarize
the results presented in this report. This film is available through the U.S.
Environmental Protection Agency, Office of Research and Development, Oil and Hazardous
Materials Spills Branch, Edison, New Jersey 08837.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Performance Tests
Skimmers
Water Pollution
Oil
Spilled Oil Cleanup
Protected Haters
Harbor Waters
Icy Waters
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
92
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
82
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