&EPA
United States
Environmental Protection
Agency
Industrial Environmental Research EPA-600/7-80-020
Laboratory February 1980
Cincinnati OH 45268
Research and Development
OHMSETT
Evaluation Tests
Three Oil
Skimmers and a
Water Jet Herder
Interagency
Energy/Environment
R&D Program
Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-80-020
February 1980
OHMSETT EVALUATION TESTS: THREE OIL SKIMMERS AND A WATER JET HERDER
by
Douglas J. Graham and Robert W. Urban
PA Engineering
Corte Madera, California 94925
Michael K. Breslin and Michael G. Johnson
Mason & Hanger-Silas Mason Co., Inc.
Leonardo, New Jersey 07737
Contract No. 68-03-2642
Project Officer
John S. Farlow
Oil and Hazardous Materials Spills Branch
Industrial Environmental Research Laboratory
Edison, New Jersey 08817
This study was conducted in cooperation with the
U.S. Coast Guard
U.S. Geological Survey
U.S. Navy
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Industrial 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 OHMSETT Interagency Test Committee
or its member organizations, the U.S. Environmental Protection Agency,
the U.S. Coast Guard, the U.S. Geological Survey, and the U.S. Navy.
Mention of trade names or commercial products does not constitute en-
dorsement or recommendation for use, nor does the failure to mention or
test other commercial products indicate that they are not available or
that they cannot perform similarly to those mentioned.
ii
-------
FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even
on our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory
- Cincinnati (lERL-Ci) assists in developing and demonstrating new and
improved methodologies that will meet these needs both efficiently and
economically.
This report describes a number of operating techniques as well as
the results of performance testing of three commercial oil spill
cleanup devices and a water jet herder under a variety of controlled
conditions. The operating techniques described here will be of interest
to those involved in specifying, using, or testing such equipment. Further
information may be obtained through the Resource Extraction and Handling
Division, Oil & Hazardous Materials Spills Branch, Edison, New Jersey.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
ILL
-------
PREFACE
In February 1977, representatives of the U.S. Environmental Protection
Agency, U.S. Coast Guard, U.S. Navy, and U.S. Geological Survey met to
form the Interagency Test Committee (OITC) to sponsor tests of selected
oil pollution control equipment at the Oil and Hazardous Materials
Simulated Environmental Test Tank (OHMSETT) facility in Leonardo, New
Jersey. The primary motivations in forming the OITC were:
(a) To combine funds to study equipment of joint interest.
(b) To provide a formal focal point for interagency discussion and
comparison of oil pollution abatement programs.
Other interested U.S. and Canadian agencies have been invited to parti-
cipate in committee discussions, offer recommendations for selection of
test equipment, and share in test data results.
This report describes the performance testing of three selected oil
spill pickup devices and a water jet herder during the 1978 OHMSETT test
season. In addition to the complete technical details contained in this
written report, a 16-mm narrated motion picture report has been prepared
showing the dynamic nature of selected test runs and a summary of test
results.
As public agencies, the sponsors of this work hope that the test
results generated under this program can be utilized not only within
their own agencies but also by the public.
iv
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ABSTRACT
A series of performance tests was conducted at the U.S. Environmental
Protection Agency's oil and hazardous materials simulated environmental
test tank (OHMSETT) test facility with three selected oil spill pickup
devices (skimmers) and a water jet boom/skimmer transition device. Each
device was tested for a two-week period.
The objectives of the skimmer tests were to establish the range of
best performance for each device under the manufacturer's design limits
and to document test results on 16-mm film and by quantitative measures
of performance.
The three oil skimmers studied by the test committee during the
OHMSETT 1978 season, in order of testing, were the Offshore Devices,
Inc., Scoop skimmer, the Oil Mop, Inc., VOSS concept, and the Framo ACW-
402 skimmer.
During the 6-week skimmer test program, 148 individual data test
runs were made. Each skimmer was tested to the limit of its design
conditions, and beyond, to confirm the limit of effective oil slick
pickup. Extensive quantitative data were obtained for each skimmer and
are discussed in separate sections of this report. In reviewing the
test results for each skimmer, it should be kept in mind that trends or
rates of change of test results are often more important than the numerical
value of individual data points. These trends show to what extent
changing environmental conditions may affect performance.
The purpose of the more qualitative evaluation tests of the water
jet boom/skimmer transition was to determine whether the concept was
sufficiently effective to merit further development. This simple device
appears to have solved the problem of coupling two devices (a boom and
a skimmer) with radically different surface wave response functions
without losing much oil.
A motion picture report, "Testing Three Selected Oil Skimmers and a
Water Jet Boom/Skimmer Transition," is an important adjunct to this
report and illustrates the dynamic response of each device to selected
test tank conditions.
This report was submitted in fulfillment of Contract No, 68-03-
2642, Job Order No. 42, by Mason & Hanger-Silas Mason Co., Inc., under
the sponsorship of the U.S. Environmental Protection Agency, U.S. Coast
Guard, U.S. Geological Survey, and U.S. Navy. Technical direction was
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subcontracted to PA Engineering. This report covers a period from May
15, 1978, to November 17, 1978, and work was completed as of December
15, 1978.
vi
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CONTENTS
Foreword iii
Preface ...... iv
Abstract v
Figures viii
Tables ix
Abbreviations and Symbols ,....,.., x
Conversions ................ xi
Acknowledgments xii
1. Introduction 1
2. Offshore Devices, Inc. Scoop Skimmer 3
Conclusions and recommendations 3
Skimmer description 7
Test matrix and procedures 12
Test results and discussion 16
3. Oil Mop, Inc. VOSS Concept 24
Conclusions and recommendations . 24
Skimmer descriptions 28
Test matrix and procedures . . . 34
Test results and discussion 36
4. Framo 46
Conclusions and recommendations 46
Equipment description 49
Test matrix and procedures 51
Test results and discussion 55
5. Water Jet Boom/Skimmer Transition 64
Conclusions and recommendations 64
Equipment description 68
Test matrix and procedures 76
Test results and discussion 82
Appendices
A. OHMSETT facility description 87
B. Range of test oil properties for the 1978 OITC series ... 89
C. Skimmer technical descriptions 90
VI1
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FIGURES
Number Page
1 Offshore Devices, Inc. - Scoop skimmer components 8
2 Skimming struts - Scoop skimmer ......... 9
3 Operating principle - Scoop skimmer 10
4 OSD Scoop under test 11
5 Bow first testing configuration - OSD Scoop 15
6 TE trends - OSD Scoop 17
7 Underwater views - OSD Scoop 21
8 Artist view - TOSS system 29
9 Equipment components - Oil Mop VOSS concept 30
10 Operating principle - Oil Mop VOSS concept 31
11 Oil Mop Mark II-9D engine details 32
12 Oil Mop VOSS - deployment configurations 33
13 RE trends - Oil Mop VOSS (heavy oil) 39
14 RE trends - Oil Mop VOSS (light oil) 40
15 ORR trends - Oil Mop VOSS (heavy oil) 41
16 ORR trends - Oil Mop VOSS (light oil) 42
17 Test Bl: Calm, 0.76 m/s, configuration I - I mop 43
18 Test F5: 0.6 m HC, 0.76 m/s, configuration 1-2 mops . . 43
19 Test II: Calm, 0.76 m/s, configuration IV - 1 mop .... 45
20 Equipment components - Framo skimmer 50
21 Operating principles - Framo skimmer 53
22 Testing configuration - Framo skimmer ........... 54
23 RE trends - Framo (heavy oil) 59
24 RE trends - Framo (medium oil) 60
25 ORR trends - Framo (heavy oil) 61
26 ORR trends - Framo (medium oil) 62
27 Section view of water jet action 69
28 Single water jet producing a surface current 70
29 General test setup of water jets, boom, and skimmer .... 71
30 Water jets herding oil within booms and over the boom/
skimmer transition area 72
31 Close-up of boom/skimmer transition area with water jets
herding oil 74
32 Flexible curtains extending over the boom/skimmer transition
area 75
33 Typical water jet mounted on the Clean Water, Inc. boom . . 77
34 Side view of one of the two water jets mounted on the
oil skimmer 78
35 Tow speed versus final slick width for heavy oil 83
36 Tow speed versus final slick width for light oil 84
viii
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TABLES
Number page
1 Best Performance - OSD Scoop (Heavy Oil) 4
2 Best Performance - OSD Scoop (Light Oil) 4
3 Test Matrix - OSD Scoop 13
4 Test Procedures - OSD Scoop 14
5 Test Results - OSD Scoop (Heavy Oil) 18
6 Test Results - OSD Scoop (Light Oil) 19
7 TE vs. Separator Flowrate (Heavy Oil) 22
8 Best Performance - Oil Mop VOSS Concept (Heavy Oil) .... 25
9 Best Performance - Oil Mop VOSS Concept (Light Oil) .... 25
10 Test Matrix - Oil Mop VOSS Concept 34
11 Test Procedures - Oil Mop VOSS Concept 35
12 Test Results - Oil Mop VOSS Concept (Heavy Oil) 37
13 Test Results - Oil Mop VOSS Concept (Light Oil) 38
14 Best Performance - Framo ACW-402 (Heavy Oil) 47
15 Best Performance - Framo ACW-402 (Medium Oil) 47
16 Test Matrix - Framo ACW-402 51
17 Test Procedures - Framo ACW-402 52
18 Test Results - Framo (Heavy Oil) 56
19 Test Results - Framo (Medium Oil) 57
20 Best Performance - Water Jet (Heavy Oil) 65
21 Best Performance - Water Jet (Light Oil) 65
22 Test Matrix and Results - Water Jet Boom/Skimmer Transition
Device (Heavy Oil) 79
23 Test Matrix and Results - Water Jet Boom/Skimmer Transition
Device (Light Oil) . 80
24 Test Procedures - Water Jet Boom/Skimmer Transition
Device 82
ix
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LIST OF ABBREVIATIONS
kg —kilograms
kn —kilonewtons
kt —knots
m —metres
mm —millimetres
m3 —cubic metres
m/s —metres per second
m2/s —square metres per second
m3/s —cubic metres per second
s —seconds
V —oil collected by skimmer during steady state test time (m3)
t° —steady state test time (s)
V —total oil/water mixture collected by skimmer during steady
state test time (m3)
Q —rate at which test oil enters the front of the skimmer (m3/s)
ND* —No Data
HC —Harbor chop wave condition (nonregular wave condition achieved
by allowing waves to reflect off all tank side walls)
OHMSETT —Oil and hazardous materials simulated environmental test tank
OITC —OHMSETT Interagency Test Committee,
OSD —Offshore Devices, Inc.
ORR » V u
— —Oil recovery rate = volume of oil recovered by the skimmer
ss per unit time during steady state test (m3/s)
RE - V u -
— x 100 —Recovery efficiency = percent of oil in the oil/water
T mixture that is recovered from the water surface by
the skimmer (%)
TE = V ..
0 x 100 —Throughput efficiency = percent of oil that enters
^o ss the skimmer and is recovered from the water surface
(%) (advancing skimmers only)
VOSS —Vessel of opportunity skimmer system (an oil skimmer that
can be deployed from the deck of a vessel not dedicated to
oil pollution control work, such as an ocean-going tugboat or
offshore supply vessel)
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LIST OF CONVERSIONS
METRIC TO ENGLISH
To convert from
Celsius
joule
joule
kilogram
metre
metre
metre2
metre2
metre3
metre3
metre/second
metre/second
metre2/second
metre3/second
metre3/second
newton
watt
ENGLISH TO METRIC
centistoke
degree Fahrenheit
erg
foot
foot2
foot/minute
foot3/minute
foot-pound-force
gallon (U.S. liquid)
gallon (U.S. liquid)/
minute
horsepower (550 ft
Ibf/s)
inch
inch2
knot (international)
litre
pound-force (Ibf avoir)
pound-mass (Ibm avoir)
to
degree Fahrenheit
erg
foot-pound-force
pound-mass (Ibm avoir)
foot
inch
foot2
inch2
gallon (U.S. liquid)
litre
foot/minute
knot
centistoke
foot3/minute
gallon (U.S. liquid)/minute
pound-force (Ibf avoir)
horsepower (550 ft Ibf/s)
metre2/second
Celsius
joule
metre
metre2
metre/second
metre3/second
joule
metre3
metre3/second
watt
metre
metre2
metre/second
metre3
newton
kilogram
Multiply by
tc = (tF-32)/1.8
1.000 E+07
7.374 E-01
2.205 E+00
3.281 E+00
3.937 E+01
1.076 E+01
1.549 E+03
2.642 E+02
1.000 E+03
1.969 E+02
1.944 E+00
1.000 E+06
2.119 E+03
1.587 E+04
2.248 E-01
1.341 E-03
1.000 E-06
tc = (tp-32)/1.8
1.000 E-07
3.048 E-01
9.290 E-02
5.080 E-03
4.719 E-04
1.356 E+00
3.785 E-03
6.309 E-05
7.457
2.540
6.452
5,
1,
4,
144
000
448
4.535
E+02
E-02
E-04
E-01
E-03
E+00
E-01
xi
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ACKNOWLEDGMENTS
Acknowledgments are due, first and foremost, to the individual
manufacturers who willingly supplied skimmers and operator personnel
for the duration of these tests.
John S. Farlow, the OHMSETT Project Officer for the U.S. Environ-
mental Protection Agency, served as the OHMSETT Interagency Test Committee
(OITC) chairman and provided valuable assistance throughout the project.
Mason & Hanger-Silas Mason Co., Inc., the operating contractor for
OHMSETT, deserves a special note of thanks for the professional and innova-
tive support of their personnel at the OHMSETT test site. R.A. Ackerman,
General Manager, M.G. Johnson, Test Director, and the test engineers,
H.W. Lichte and M.K. Breslin, provided continual guidance and assistance
throughout the test program concerning detailed test procedures and sequence
to maximize the number of data runs obtained.
In the areas of data collection and reduction, S.H. Schwartz was
especially helpful in the rapid reduction of raw data on which to base
selection of test conditions for subsequent test runs.
Videotape coverage (a key element in making real time decisions between
test runs), 16-mm photography for the motion picutre, and 35-mm photography
for the written report were amply carried out (in spite of the usual diffi-
culties of weather conditions and electronic malfunctions) by the OHMSETT
photo/video electronics department.
Funds for this project were provided by the OHMSETT Interagency Test
Committee (OITC).
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SECTION 1
INTRODUCTION
This report describes the conduct and results of the 1978 OHMSETT
Interagency Test Committee (OITC) sponsored oil and hazardous materials
simulated environmental test tank (OHMSETT) tests. The oil spill control
and cleanup equipment tested in 1978, listed in order of testing, were:
1. Offshore Devices, Inc. Scoop skimmer
2. Oil Mop, Inc. VOSS concept
3. Frank Mohn, A/S, Framo ACW-402 skimmer
4. Water jet boom/skimmer transition
The Scoop and Framo skimmers are commercially available units. The
Oil Mop VOSS concept consists of commercially available equipment deployed
in an unconventional mode to simulate operation abeam an offshore supply
vessel or an ocean-going tug. The water jet boom/skimmer transition con-
sists of a commercially available pump with plumbing used to guide oil from
a boom into a skimmer while physically decoupling those two devices with
very different wave response functions.
Test objectives for the commercially available Scoop and Framo were to
collect quantitative and qualitative data in the areas of:
A. Best performance, as determined by the three quantitative
performance parameters described below.
B. Operating limits or oil loss mechanisms (either inherent in
the principle of operation or a result of a correctable mechanical
detail) that limit the application of each device.
C. Mechanical problems that may be of interest to a potential
user of the device.
D. Device modification that may improve skimmer operating limits
or increase best performance.
In addition to the above objectives, tests of the Oil Mop VOSS
concept and the water jet boom/skimmer transition concept were conducted
to answer the questions Does either the Oil Mop VOSS concept or the water
jet boom/skimmer transition concept merit further development?
Quantitative performance data to support conclusions of the above
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objectives are presented in terms of the three basic performance parameters
which have become standard for advancing (towed or self-propelled)
skimmers:
1. Throughput efficiency (TE). Percentage of oil entering the
bow of the skimmer which is picked up.
2. Recovery efficiency (RE). Percentage of oil in the oil/water
mixture,picked up by the skimmer.
3. Oil recovery rate (ORR). Volume of oil per unit time picked
up by the skimmer during steady state operation.
In addition, the trend of the above three parameters with variations
of skimmer setting, tow speed, wave condition, and oil type was found to
be as important as the numerical values when determining the range of
effectiveness of a given skimmer.
Sections 2, 3, 4, and 5 are each complete and self-contained descrip-
tions of the four devices, the testing procedures, conditions, and results,
and the trends of test results. It should be kept in mind that each device,
like all items sold commercially, is designed by its manufacturer to
operate most effectively within a certain range of environmental conditions.
Therefore, direct comparison of test results is not always possible.
The three appendices attached to this report present a description
of the OHMSETT test facility, a description of the range of oil properties
for each skimmer test, and a detailed technical description of the three
skimmers.
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SECTION 2
OFFSHORE DEVICES, INC. SCOOP SKIMMER
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
During the period May 15 to May 31, 1978, 33 oil pickup performance
tests were conducted with the Offshore Devices Scoop skimmer. A total
of 23 tests were run with high viscosity (heavy) oil and 10 tests with
low viscosity (light) oil.1 This section summarizes the conclusions of
the eight days of testing in four major areas:
1. Best Performance
2. Operating Limits
3. Mechanical Problems
4. Device Modifications
Best Performance—
Best ORR performance for the Scoop skimmer occurs with large amounts
of oil (greater than 4 m3) in the barrier catenary. Under these conditions,
recovery of pure oil is limited only by the pump capacity of 15.8 x 10~3m3/s,
The present tests were performed with smaller volumes of oil in the
barrier to evaluate Scoop operation near the end of a spill cleanup operation
and to determine how the separator and weirs function with thinner
slicks.
Best skimmer performance (highest numerical results) achieved
during these tests is presented, along with accompanying test conditions,
in Tables 1 and 2. As a result of the skimmer operating principle, the
highest value for each of the parameters TE, RE, and ORR did not occur
under the same test conditions. Of special interest in Table 1 is the
best performance exhibited by the oil/water separator (as measured by
the RE value). The separator was designed to fully separate oil and
water (RE = 100%) at a fluid (oil and water) flowrate no greater than
3.3 x 10-3m3/s. However, as shown in Table 1 a 100% RE value (indicating
that complete oil-water separation was taking place in the separator)
was obtained for a fluid flowrate of 13.6 x 10~3jn3/s with heavy oil, four
times the design flowrate.
Physical properties of both test oils are listed in Appendix B for each
skimmer test.
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TABLE 1. BEST PERFORMANCE - OSD SCOOP (HEAVY OIL)
Performance
parameter
TE
RE
ORR
Highest
value
100%
100%
3.2xlO~3m3/s
Tow
speed
Cm/a)
0.38
0.51
0.38
Wave
ht x length
(mxm)
0.6HC
0
0.3 x 9
0/W sep.
flowrate
(m3/sxlO~3)
6.3
13.6
4.3
Test
no.
27
19
15
TABLE 2. BEST PERFORMANCE - OSD SCOOP (LIGHT OIL)
Performance
parameter
TE
RE
ORR
Highest
value
89%
26%
2. 1x10- V/ a
Tow
Speed
(m/s)
0.38
0.38
0.38
Wave
ht x length
(mxm)
0
0
0
0/W sep.
flowrate
(m3/sxlO~3)
3.3
10.1
5.5
Test
no.
8
3
6
Operating Limits—
Based upon both quantitative and qualitative observations
during these tests, the operating limits of the Scoop skimmer appear to
depend on the following three factors:
1. Oil loss past a vertical containment barrier. Two oil loss
mechanisms of near-boom drainage and head-wave droplet entrain-
ment were both observed. The strengths of these two mechanisms
depended upon the initial precharge oil volume placed in the
barrier at the start of each test, the pumping rate during the
test, the tow speed, and the wave condition. Most oil
losses were observed to be a result of droplet entrainment.
Drainage failure was observed on only a few wave tests.
Visual observation of the area astern the Scoop barrier
catenary indicated that significant oil loss began at a tow
speed of about 0.51 m/s for light oil and at a slightly higher
speed of about 0.62 m/s for heavy oil. An insufficient number
of tests were conducted to determine these limits more precisely.
This could have been the result of the low interfacial tension
measured for the light oil used in the testing.
2. Oil/water separator volume. Performance of the present separator
exceeded its design maximum flowrate limit of 3.3 x 10~3m3/s
with heavy oil. No oil appeared at the separator water dis-
charge hose, indicating that complete settling of the oil/water
mixture was occurring for flowrates as high as 13.6 x 10~3m3/s.
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For light oil, incomplete settling (indicated by oil appearing
at the water discharge hose) was observed at the separator
design flowrate of 3.3 x 10~3m3/s. An increase in separator
volume would allow a higher throughput flowrate with more
complete settling for all types of oil. Such an increase in
flowrate would reduce the length of time required to pump a
given oil volume from in front of the weirs. Since the cumulative
oil lost under the Scoop barrier increases with time, a shorter
pumping time would mean less loss and higher throughput efficiency.
3. Workboat stern tow. One of the operating modes of the Scoop
skimmer is with the workboat towed stern to the towing direction
and the skimming barrier attached to the bow. The Scoop work-
boat tested at OHMSETT was obtained from the manufacturer before
a full height internal transom could be installed. The importance
of a full height internal transom forward of the outboard motor
space was confirmed when, while waiting for a test to begin, the
boat filled with water due to wave splash over the outboard motor
cutout. This caused the boat to fill with water and swamp.
Since these OHMSETT tests, the manufacturer has conducted an
inclining experiment to demonstrate the result that the riding
moment of the Scoop workboat is reduced by only 10% when the
onboard separator is filled with water.
Mechanical Problems—
There were no problems with the 21 m long skimming barrier during
the two week test. The barrier proved to be very rugged, and the attached
external tension lines did not snag or tangle during the many changes in
tow direction up and down the tank.
The light-weight flexible suction hose connecting the skimming
struts to the diaphragm pump was partially collapsed by the test crew in
the course of normal activity aboard the boat. In addition, it was
abraided against the workboat rails by the surging action of the diaphragm
pump.
The hydraulic control system that drives the double diaphragm pump
developed problems toward the end of the test series. Erratic operation
caused the pump flowrate (set at the beginning of the test) to drop
significantly and in some cases to fall to zero during the test run.
Despite several Interruptions the test series to clean out the control
elements (there was no filter in the hydraulic oil circuit) and to
reduce oil temperature with the addition of a coiled length of copper
tubing placed over the side, the problem was never completely resolved.
The manufacturer has subsequently evaluated this problem following the
OHMSETT test. The control problem proved to be related to a low viscosity
hydraulic oil which was used in the control system after the workboat
swamped and capsized following the light oil tests period. The manu-
facturer has redesigned the hydraulic control elements to eliminate this
viscosity dependence.
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The plexlglas separator vent standpipe was found to be quite fragile
and was accidentally broken off during initial Scoop assembly prior to
the start of testing. This plexiglas vent standpipe has now been replaced
with a stronger lexan pipe by.the manufacturer.
The standpipe height was insufficient for some of the heavy oil
tests, as shown when the separator discharge valve was moved from the
100% water to 100% oil position. Oil then surged up to overflow the top
of the standpipe because of the greater hydrostatic head required to
push settled heavy oil out of the separator into the OHMSETT collection
barrel onboard the workboat. The standpipe height might not be a problem
when the collapsible storage bag is used to received settled oil from the
separator. As the separator was designed, this collapsible storage bag
is at the waterline elevation, thereby reducing the head in the standpipe
above the separator necessary to push heavy oil into the storage bag.
Device Modifications—
The only modifications made to the Scoop (as supplied) was the
addition of a copper cooling coil for the hydraulic control system.
This modification did not improve the smoothness or reliability of the
hydraulic control circuit in operating the diaphragm pump.
Recommendations
Device modifications recommended to improve performance and reliability
of the OSD Scoop system are:
1. Improvement in the reliability of the hydraulic control circuit
for the diaphragm pump.
2. Removal of the fragile 2-m-tall plexiglas vent standpipe atop
the separator, replacing it with another design that would
allow for the slight pressurization of the separator necessary
to push settled heavy viscous oil through the oil discharge
port and hose into the Scoop oil storage bag. The manufacturer
reports that the plexiglas standpipe has been replaced with a
lexan version and that no breakage has been encountered during
regular field use.
3. Conduction of an inclining experiment, rolling the workboat to
the rail with the separator filled with water to determine
what reduction (if any) in roll stability is attributable to
the separator. The manufacturer reports that these tests have
recently been completed with the result that reduction in roll
stability (as measured by the righting moment per degree roll)
was reduced (by only 10%) when the separator was filled with
water.
Because of the operating principle of the Scoop system skimming
element (namely, a rigid containment barrier) it is felt that the maximum
useful tow speed cannot be significantly raised above 0.5 m/s. It is
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recommended that if any additional OHMSETT tests are to be conducted
using this concept, they be conducted with the larger Coast Guard skimming
barrier together with a larger version of the oil/water separator used
in Scoop system. A test of this combination of equipment may be of
great interest to OITC members concerned with offshore oil spill recovery.
Any future tests with the Coast Guard skimming barrier should also
measure throughput efficiency for comparison with that of the smaller
Scoop version.
SKIMMER DESCRIPTION
The Offshore Device Scoop skimmer system has five components (Figure
1): (1) a 21-m length of skimming barrier complete with four weir
skimming struts; (2) a uniquely designed hydraulically powered double
acting diaphragm pump able to pass debris; (3) an 8-m-long workboat; (4)
a 1.3-m3-capacity oil/water gravity separator; and (5) a 1.9-m3-capacity
separated oil pillow tank. Figure 1 is a schematic of the 8-m workboat
showing the 21-m skimming barrier stowed in the bow and the relative
positions of the oil/water separator, the diaphragm pump, and the oil
pillow tank. The square bow of the workboat contains a hinged door to
facilitate launching of the skimming barrier.
The Scoop operating principle is explained in the schematic drawings
of Figures 2 and 3. Figure 4 shows the device under test. Complete
technical details and capacities of all components are presented in
Appendix C.
The operating principle of the Scoop skimmer is illustrated in
Figures 2 and 3. A thick pool of oil is collected in the bottom of the
barrier catenary by forward motion of tow boats. Oil flows over weir
inlets built into four special struts, called skimming struts (Figure
2), in the bottom of the barrier catenary. The liquid level in the
skimming struts is lowered by the action of the diaphragm pump, allowing
an oil-rich mixture to flow over the strut weirs and into the bottom of
the oil/water separator (Figure 3). Two operator-controlled discharge
valves, joined together by a single lever, control the outlet streams
from the separator. With the control lever in the 100% water position
(Figure 3), settled water from the bottom of the separator is discharged
through a hose to the area in front of the skimming barrier so that any
contained oil can be reprocessed. With the control lever in the 100% oil
position, settled oil is discharged into the pillow tank being towed
alongside. The outlet control lever can be placed in any intermediate
position to allow discharge of both settled water and oil in varying
proportions.
A plexiglas vent standpipe on top of the separator (Figure 3)
allows any air ingested into the separator to be vented and gives the
operator an indication of pressure inside the separator. The maximum
flowrate through the separator is dictated by the height of the stand-
pipe and viscosity of the settled oil. With the outlet control lever
at the 100% oil position, the frictional resistance through the discharge
-------
(3) Workboat
(2) Diaphragm Pum
\
Hydraulic Pack
(1) Skimming Barrier
Oil/Water Separator Hinged Bow
Door
(5) Separated Oil
Figure 1. Offshore Devices - Scoop skimmer components.
-------
Oil Discharge
Skimming Strut
Float
Non-skimming Strut
Tow Direction
External Tension Line
Figure 2. Skimming struts - Scoop skimmer.
-------
Oil/Water Outlet Control Lever
"100% Water" Position | | ^^ Vent Pipe
Oil & Water
Diaphragm
Pump
"100%
Oil"
Position
Water Valve
Oil Valve
1.9 m3
Pillow Tank
Skimming
Strut
1.3 m3 Oil/Water Separator
Settled
Water
Figure 3. Operating principle - Scoop skimmer.
-------
Figure 4. OSD Scoop under test,
-------
valve and hose is much greater with heavy oil than with light oil.
Likewise, the liquid head required in the standpipe is higher for heavy
oil than for light oil. Indeed for some heavy oil runs during this test
series, the diaphragm pump flowrate had to be reduced to avoid overflowing
the open-top standpipe as the oil/water outlet control lever (Figure 3)
was moved from the 100% water to the 100% oil position.
TEST MATRIX AND PROCEDURES
Test Matrix—
Initial checkout tests were conducted without oil to establish the
maximum tow speed and wave conditions under which effective oil skimmer
performance 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 light oil were then conducted
in accordance with the matrix of test conditions listed in Table 3.
Test Procedures—
For initial checkout runs without oil, the procedure was simply to
set the wave condition and tow the Scoop down the tank at a tow speed
increasing from 0 to 0.75 m/s in various wave conditions. The test
procedure for oil data runs was rehearsed during these runs, and the tow
bridle lengths were adjusted to position the four skimming struts at the
bottom of the catenary.
For all test runs with oil, the procedure followed by the Scoop
operator was that which a. field operator would use to maximize the
quantity of oil picked up while minimizing its water content. A detailed
description of the procedure used is presented in Table 4. Briefly, in
order to pick up maximum oil with minimum water, the separator was
initially filled with water to minimize sloshing and turbulent mixing,
and the run began with the separator outlet valve in the 100% water
position. The valve was moved gradually to the 100% oil position only
if visible oil appeared in the settled water discharge (Figure 3). This
method ensured that the maximum amount of gravity separation occurred
inside the separator during the test run to maximize system RE. For
those test runs where less than 200% of the separator volume was pumped
through the separator, steady state was deemed not to have occurred, and
the system RE (water content of the settled oil layer) was not reported.
The relationship of the Scoop skimming barrier and workboat during
the tests is shown in Figure 5. The Scoop workboat was Initially towed
stern first, in compliance with the manufacturer's recommendation, to
allow a more direct path for the floating hoses from skimming struts to
diaphragm pump. This stern-first configuration was used for all tests
with light oil. However, the workboat was swamped by wave action over
the stern while waiting for a 0.6-m HC wave condition to develop at the
12
-------
TABLE 3. TEST MATRIX - OSD SCOOP
Tow
speed
(m/s)
0.38
0.38
0.51
0.51
0.38
0.63
0.25
0.25
0.38
0.63
0.63
0.38
0.38
0.51
0.63
0.38
0.51
0.63
0.51
0.63
0.25
0.38
0.51
0.38
0.38
0.38
0.38
0.38
0.38
0.63
0.51
0.51
0.38
Wave
ht x length
(mxm)
0.3 x 9
0.3 x 9
0
0
0
0
0
0
0
0
0
0.6 HC
0
0
0
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0.6 HC
0
0.3 x 9
0
0
0
0
0
0
0.3 x 9
0.3 x 9
Oil
precharge
volume
(m3)
1.16
1.13
1.14
1.14
1.12
1.15
1.15
1.15
0.90
1.15
1.15
1.15
1.15
1.15
1.16
1.15
1.16
1.15
1.16
1.16
1.15
1.15
1.18
0.60
0.61
0.62
1.35
0.60
0.61
1.17
1.18
1.21
1.24
No.
weirs
4
2
4
4
4
4
2
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
2
2
2
2
0/W
sep.
flowrate
(m3/sxlO-3)
4.3
4.3
7.1
13.6
13.6
4.7-13.6
3.0
10.1
3.1-6.6
6.3-10.1
5.5-6.3
6.3
1.6
3.1
3.1
3.1
3.1
3.1
9.5
6.3
6.3
10.1
6.8
10.1
10.1
10.1
5.5
7.1
3.3
3.3
3.3
3.3
3.3
Test
oil
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
13
-------
TABLE 4. TEST PROCEDURES - OSD SCOOP
1. Separator is pumped clear of separated oil from previous test and
filled with water. The discharge valve is set to the "100% water"
position (Figure 3).
2. After the diaphragm pump suction hose is placed over the side, the
pump flowrate is set by counting the stroke frequency and multiplying
by a calibration factor previously determined.
3. Tow is started and the oil precharge volume is deposited in the
barrier catenary. When the test slick has settled in the bottom of
the catenary with a straight leading edge, the pump on board the
workboat is activated, and discrete samples are taken at the separator
inlet.
4. The water discharge hose from the separator is monitored for visible
oil during the run. When oil appears at the water discharge hose,
the separator discharge valve is slowly adjusted to close off the
water flow and open the settled oil flow to the onboard collection
barrel (Figure 3). This adjustment is continued toward the "100%
oil" position until no oil is visible in the water discharge hose.
A column of oil then rises in the vent standpipe to a height necessary
to push settled oil out the separator top and into the collection
barrel placed aboard the workboat. The collection barrel is pumped
out continuously by a diaphragm pump into measurement barrels on
the auxiliary bridge (Figure 5).
5. At the end of the test tow, the Scoop diaphragm pump remains activated
for a period of time, depending on the flowrate, to insure that the
approximately 0.09 m3 of fluid contained in the hoses between the
skimming struts and the separator has been pumped into the separator.
6. The heights of the settled water layer (h ) and water/emulsion
layer (h ) are measured in the separator observation window (Figure
3) and a grab sample of the emulsion layer in the separator is taken
to determine the percent oil content. If any oil has been discharged
from the separator into the collection barrel during the run, this
volume is analyzed for water content using a standard OHMSETT
composite sample.
7. If a significant amount of oil remains in front of the barrier
after the run, it is directed into the skimming strut weirs with
fire hoses. An OHMSETT diaphragm pump is attached to the skimming
strut weir hoses, and this residual oil is pumped into measurement
barrels on the auxiliary bridge (Figure 5), where the oil volume is
determined using standard OHMSETT sampling procedures.
14
-------
Collection Barrel
OHMSETT Pump
X
Main Bridge
Oil/Water In
Settled Water Out
Settled Oil Out
Oil/Water Separator
Oil Precharge
Auxiliary Bridge
Measurement Barrels
Four Skimming Struts
OOoo
Figure 5. Bow first testing configuration - OSD Scoop
-------
start of a test run. Subsequent tests (all with heavy oil) were conducted
with the workboat pointing bow forward (Figure 5).
The oil content of the oil/water mixture being pumped from the
weirs (weir RE) was measured by grab samples taken at the separator
inlet. Although weir RE is not representative of the complete Scoop
barrier/separator system, it was measured and reported as an indication
of skimming strut weir performance and, for certain runs, as a comparison
with the Scoop overall system RE as measured at the separator oil outlet.
As treated more fully later, the test tow time was insufficient to
establish steady state conditions in the separator for some tow speeds
and pump rates. For those runs where the total volume pumped through
the separator during the run was 200% or more of the separator volume,
system RE was reported. In these cases, if the separator discharge
valve remained at the 100% water position with no oil appearing at the
water discharge hose during the entire test tow, the system RE was
reported as 100%. For those runs in which the separator discharge valve
was moved toward the 100% oil position to eliminate visible oil in the
water discharge, the RE was determined by standard OHMSETT sampling of
the oil/water mixture discharged through the separator oil port into the
measurement barrel during the run (Figure 5).
None of the previous OHMSETT tests with the larger scale Coast
Guard skimming barrier measured throughput efficiency (TE). Since TE is
an important user parameter for any skimmer, regardless of operating
principle, it was measured in this OITC series by taking the additional
time necessary at the end of each test to fire hose all residual oil
remaining in front of the barrier into the skimming weirs to be pumped
to separate measurement barrels. The volume of oil available for pickup
(or encountered) during a run is then equal to the amount in front of
the barrier at the start of the tow (oil precharge volume) minus the
amount in front of the barrier at the end of the tow (residual oil
volume). With the end-of-test residual oil volume measured, the through-
put efficiency was then calculated by using the following formula:
Total oil volume collected
Oil precharge volume - residual oil volume
If no visible oil was lost past the barrier during the tow down
the tank, TE was recorded as 100%.
TEST RESULTS AND DISCUSSION
Test Results
Results of the performance parameters TE, RE, and ORR for all oil
tests are listed in Tables 5 and 6 for heavy oil and light oil respec-
tively.
Trends in the TE data are most easily seen when the tabular results
are plotted as in Figure 6. In this figure the highest TE values
16
-------
100
I
W
M
o
I—I
w
I
80
60
40
20
Heavy Oil, Calm
Heavy Oil, 0.3 m x 9 m reg. wave
Heavy Oil, 0.6 m harbor chop wave
O Light oil, Calm
/\ Light Oil, 0.3 m x 9 m reg. wave
0
I
I
0.1
0.2 0.3 0.4 0.5
TOW SPEED, m/s
Figure 6. TE trends - OSD Scoop.
0.6
0.7
-------
TABLE 5. TEST RESULTS - OSD SCOOP (HEAVY OIL) (1)
Test
no.
15
16
18
19
20
21
22
23
24
25
26
27
28
29
30
31R
32
33
34
35
36
37
38
Wave
Tow ht x
speed length
(m/s) (mxm)
0.38 0.3x9
0.38 0.3x9
0.51 0
0.51 0
0.38 0
0.63 0
0.25 0
0.25 0
0.38 0
0.63 0
0.63 0
0.38 0.6 HC
0.38 0
0.51 0
0.63 0
0.38 0.6 HC
0.51 0.6 HC
0.63 0.6 HC
0.51 0.6 HC
0.63 0.6 HC
0.25 0.6 HC
0.38 0.6 HC
0.51 0.6 HC
Oil
pre-
charge
(m3)
1.16
1.13
1.14
1.14
1.12
1.15
1.15
1.15
0.90
1.15
1.15
1.15
1.15
1.15
1.16
1.15
1.16
1.15
1.16
1.16
1.15
1.15
1.18
0/W
sep.
flowrate
No.
weirs
4
2
4
4
4
4
2
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
(m3/s
xlO~
4
4
7
13
13
4.7-13
3
10
5.1-6
6.3-10
5.5-6
6
1
3
3
3
3
3
9
6
6
10
6
3)
.3
.3
.1
.6
.6
.6
.0
.1
.6
.1
.3
.3
.6
.1
.1
.1
.1
.1
.5
.3
.3
.1
.8
Sep.
dis.
valve (2)
(3)
(3)
w
w
w/o
w
w
w/o
w
(3)
w
w/o
w
w
w
w
w
w
w
w
w
(4)
(4)
Vol.
pumped
through Weir
sep.
(m3)
(3)
(3)
1.84
3.47
4.90
(4)
1.36
4.24
(5)
(3)
(5)
1.96
0.52
0.89
0.69
1.13
0.95
0.76
2.55
1.51
3.03
3.18
1.94
RE
f°/ \
Y/o )
53
58
(4)
60
50
25
40
48
(4)
20
10
45
75
40
10
10
30
10
35
20
10
36
30
RE
(%)
(3)
(3)
(6)
100
87
(5)
(6)
57
(5)
(3)
(5)
(6)
(6)
(6)
(6)
(6)
(6)
(6)
95
(6)
100
(4)
(6)
TE
(%)
88
93
49
44
100
46
100
100
100
43
26
100
100
82
17
35
70
21
81
37
57
70
56
ORR
(m3/s
x!0~3)
3.2
2.7
1.8
1.8
2.8
0.8
2.5
2.6
(4)
(4)
1.7
(4)
(4)
1.2
0.9
1.1
1.5
0.8
2.5
1.8
1.3
1.9
1.6
1.
2.
3.
4.
5.
6.
Average viscosity:
1000 x
IQ-^rnVs.
Position of separator discharge valve
at the beginning of
water discharge hose
run ; it
clear
Test started with separator
No data.
then moved
of oil; w =
empty.
during
toward
valve
Pump hydraulic controls unsteady duringztest,
RE reported only if
separator reached
> 2 x (volume separator) =
2 x (1.3 m3
steady
) = 2.6
test
100%
lever
run was w/o = valve lever
oil discharge, as
remained
total volume
state
m3.
at 100%
to 100%
water
necessary, during run
water position during
discharge
to keep
entire run.
pumped not known.
during run — i.e.
volume
pumped through
separator
-------
TABLE 6. TEST RESULTS - OSD SCOOP (LIGHT OIL) (1)
Wave
Tow ht x
Test speed length
no.
3
4
5
6
7
8
10
11
12
13
(m/ s) (mxm)
0.38 0
0.38 0.3x9
0.38 0
0.38 0
0.38 0
0.38 0
0.63 0
0.51 0
0.51 0.3x9
0.38 0.3x9
Oil
pre-
charge
(m3)
0.60
0.61
0.62
1.35
0.60
0.61
1.17
1.18
1.21
1.24
No.
weirs
4
4
4
4
4
4
2
2
2
2
0/W sep.
flowrate
(m3/s
xlO-3)
10.1
10.1
10.1
5.5
7.1
3.3
3.3
3.3
3.3
3.3
Sep.
dis.
valve (2)
w/o
w/o
w/o
w/o
w/o
w/o
w
w
w
w
Vol.
pumped
through Weir
sep. RE
RE
TE
/3\ (9/\ (^\ ("/^
3
3
3
1
2
1
0
0
0
1
.48
.23
.23
.77
.68
.05
.65
.79
.75
.02
20
14
20
42
19
14
38
34
26(3)
26(3)
26
18
25
(4)
20
(4)
(4)
(4)
(4)
(4)
70
82
83
72
87
89
11
42
29
64
ORE
(m3/s
x!0~3)
1.2
1.0
1.4
2.1
1.0
0.8
0.6
1.4
1.1
1.0
1.
2.
3.
4.
Average viscosity:
17.8 x 10-
lBur/s.
Position of separator discharge valve
at the beginning of
water discharge hose
run.
run; it then moved
clear or
Samples recovered out of order
RE reported only if
separator
oil; w =
during test
toward 100%
valve lever
, boat capsized with
reached
> 2 x (Volume separator) = 2 x (1.3 m3
steady state
) = 2.6 m3.
run was w/o
= valve lever
oil discharge as
remained
samples
at
100%
to 100% water
necessary during
discharge
run to keep
water position during
from both Test 12
during run — i.e
. volume
and 13.
pumped through
entire
separator
-------
obtained for each set of test conditions are plotted.
Discussion
In discussing the test results of the OSD Scoop, it must be kept in
mind that there are two active elements of the Scoop system:
1. The skimming barrier and
2. The oil/water separator.
Presentation of a performance parameter for the skimming barrier is
straightforward while that for the oil/water separator depends upon a
number of variables which could not be fully adjusted during this test
series.
Skimming barrier performance is illustrated by the TE trend graph
(Figure 6) and the TE and weir RE entries (Tables 5 and 6). The ability
of the barrier to contain oil for pickup is directly indicated by the TE
value. The efficiency of the skimming strut weirs is measured by the
weir RE value, which is affected by the wave-following ability of the
weir lip and the oil pool thickness in front of the weirs. The rate at
which oil is pumped from the oil pool into the separator directly affects
the amount of oil collected and thereby the TE. In order to investigate
the effect of pump rate on the TE value, data results from Table 5 were
organized in order of increasing tow speed and separator flowrate and
presented in Table 7. Although available test time did not allow for
the number of runs necessary to investigate completely the effects of
tow speed, pump rate, and skimming strut weir behavior on skimming
barrier performance, the general indications are that:
1. TE rapidly falls below 50% as tow speed is increased above
0.51 m/s. This reduction is more rapid for light oil than for
heavy oil (Figure 6).
2. TE seems to be increased, for a given wave condition and tow
speed, if the pumping rate from the weirs is increased. This
tendency was observed more consistently as the tow speed
increased (Table 7).
3. Wave conformance of the skimming barrier is excellent, as
demonstrated by the only slight variation in weir RE and TE
results for the same tow speed in different wave conditions
(Figure 6 and Table 5).
Performance of the oil/water separator is not as straightforward as
skimming barrier performance. The separator operation depends on all of
the following in various degrees:
1. Presence of steady state flow conditions inside the separator.
2. Position of separator oil/water outlet valve.
20
-------
(a) Test 8: 0.38 m/s, Calm, TE = 89%
(b) Test 1: 0.63 m/s, Calm, TE = 11%
Figure 7. Underwater views - OSD Scoop
21
-------
TABLE 7. THROUGHPUT EFFICIENCY VERSUS SEPARATOR FLOW RATE (HEAVY OIL)
Test
no.
22
23
28
24
20
31R
27
37
15
16
29
18
19
32
38
34
30
26
25
21
33
35
Tow
speed
(m/s)
0.25
0.25
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.51
0.51
0.51
0.51
0.51
0.51
0.63
0.63
0.63
0.63
0.63
0.63
Wave
ht x length
(mxm)
0
0
0
0
0
0.6 HC
0.6 HC
0.6 HC
0.3x9
0.3x9
0
0
0
0.6 HC
0.6 HC
0.6 HC
0
0
0
0
0.6 HC
0.6 HC
0/W
sep.
flowrate
(m3/sxlO-3)
3.0
10.1
1.6
3.1-6.6
13.6
3.1
6.3
10.1
4.3
4.3
3.1
7.1
13.6
3.1
6.8
9.5
3.1
5.5-6.3
6.3-10.1
4.7-13.6
3.1
6.3
TE
(%)
100
100
100
100
100
35
100
70
88
93
82
49
44
70
56
81
17
26
43
46
21
37
22
-------
3. Character of oil/water emulsion pumped into the separator from
the weirs.
4. Oil properties.
5. Fluid flowrate through the separator.
The time available during this test series did not allow for a complete
investigation of the above factors, nor would this lengthy testing have
been in keeping with the test objective of obtaining maximum information
on performance of the total Scoop system.
For the data that was collected, the separator performance is
represented by the value of RE, measured at the separator oil outlet,
and a comparison with the weir RE, measured at the separator inlet
(Tables 5 and 6) can be made. Weir RE is an average of grab samples
taken at the separator inlet during the run. In Tables 5 and 6 the
value of the Scoop system RE, measured at the separator oil outlet, was
only reported for those tests runs during which the fluid volume pumped
through the separator was equal to or greater than 200% of the separator
volume. This criterion was taken as an indication that steady state
flow conditions existed within the separator for a sufficient portion of
the run. In reviewing Tables 5 and 6, the following observations can be
made:
1. For heavy oil tests, the separator yielded a 100% RE value
(indicating complete oil settling) for flowrates as high as
13.6 x 10 m3/s— more than four times greater than the design
value.
2. In all tests the value of RE (at separator oil outlet) was
greater than the value of weir RE (at separator inlet), showing
that the separator is effective in reducing the volume of
fluid which must be stored during cleanup of a spill.
Separator performance data obtained here should be considered
preliminary (Tables 5 and 6) since steady state operation of the separator
was achieved for only a few test runs. In addition, the RE results for
light oil (Table 6) appear suspect because they are so close to the
weir RE values measured at the separator inlet. If further interest in
the Scoop separator exists, light oil tests should be included. The
test setup should also include the Scoop skimming struts and diaphragm
pump since the physical character of the emulsion presented to the
separator inlet depends upon these two components.
23
-------
SECTION 3
OIL MOP, INC. VOSS CONCEPT
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
During the period July 10 to July 21, 1978, 41 oil pickup performance
tests were conducted to determine the feasibility of the Oil Mop, Inc.
VOSS (Vessel of Opportunity Skimmer System) Concept. A total of 22 tests
were conducted with high viscosity (heavy) oil and 19 tests with low
viscosity (light) oil. This section summarizes the conclusions of the
feasibility tests in four major areas:
1. Best Performance
2. Operating Limits
3. Mechanical Problems
4. Device Modifications
Best Performance—
Best skimmer performance (highest numerical results) obtained during
the feasibility tests is presented together with test tank and Oil Mop
VOSS deployment conditions in Tables 8 and 9. In accordance with the
operating principle of the oleophilic oil mop and the different deployment
configurations used, the highest value of the TE, RE, and ORR parameters
did not occur under the same test conditions. Test results demonstrate
that the Oil Mop VOSS concept shows excellent promise as an oil pickup
system for open ocean use. Based upon both visual observation and quantita-
tive data results, the concept consistently demonstrated:
1. Excellent wave conformance of the flexible rope mop.
2. Good retention of sorbed oil on the mop surface even when the
mop was submerged and subjected to local perpendicular currents.
3. ORR and TE values limited chiefly by the ability of the deploy-
ment technique to maximize the percentage of the oil slick
brought into contact with the mop.
Physical properties of both test oils are listed in Appendix B,
24
-------
TABLE 8. BEST PERFORMANCE - OIL MOP VOSS CONCEPT (HEAVY OIL)
Performance
parameters
TE
RE
ORR
Highest
value
25%
68% , o
3.09 x 10 m /s
Tow
speed
(m/s)
0.76
0.76
0.76
Wave
ht x length
(m x m)
0.6 HC
0
0.6 HC
No.
mops
2
1
2
Deploy.
con fig.
I
I
I
TABLE 9. BEST PERFORMANCE - OIL MOP VOSS CONCEPT (LIGHT OIL)
Per f ormance
parameter
TE
RE
ORR
Highest
value
37%
48% - ,
4.10 x 10 m/s
Tow
speed
(m/s)
1.52
0.76
1.52
Wave
Ht
(m
0.6
0
0
x length
x m)
HC
No.
mops
1
1
2
Deploy.
config.
IV
IV
I
Operating Limits—
Operating limits of the Oil Mop VOSS concept were not established
during these initial feasibility tests. More testing needs to be
performed with equipment especially designed for the VOSS application.
However, the concept's limits appear to depend on the single factor of:
Deployment method that determines percentage of oil slick con-
tacted by the mop(s).Within the time and budget constraints
of the present test series, different mop deployment methods
were studied, using both single and double lengths of oil mop. The
floating portion of the oil mop lengths in all configurations
appeared to be saturated very quickly by those portions of the
oil slick directly beneath or (in waves) within a distance of 1
to 12 mop diameters on either side of the mop(s). Other portions
of the slick outside these regions were too far away from the
mops to be brought into contact by the action of waves or by
the low velocity of the mops relative to the water. These por-
tions of (the slick were merely deflected out of the way and
lost behind the oil mops.
Secondary limiting factors, which were dealt with by temporary rigging
during the feasibility tests, were:
1. Loss of oil at squeezing mop engine. Some oil was scraped off
the saturated mops against the auxiliary bridge and mop engine
25
-------
structural members as the oil-laden mop was pulled out of the
water into the squeezing oil mop engine.
2. Non-uniform mop strand density. Jerking motion of the oil mop
during its travel around its deployment circuit caused a vari-
ation in tension, intermittently lifting the oil-soaked length
of mop up out of the slick. The jerking was caused by slight
bunching of oil mop strands at various points along the mop.
3. Jamming of the oil mop engine. On a few runs the low tension
mop portion leaving the squeezing engine became entangled in
the mop entering the engine. The entrainment caused the mop
to wrap around a squeeze roller, stalling the movement of
mop(s) around the deployment circuit.
Mechanical Problems—
No problems were encountered during the two week test series with
any of the mechanical components of the MK II-9D oil mop engines. The
diesel engine proved to be very reliable, and the roller assemblies were
easily worked on in the few cases of mop engine jams.
The MK II-9D engines and mops used in these tests were operated before
arrival at OHMSETT at the Oil Mop, Inc. plant in Belle Chasse, Louisiana
to determine the maximum non-jamming rotational speeds with the standard
gearing and two lengths of oil mop. It was demonstrated in these check-
out tests that two 50-m mop lengths could be powered around a triangular
circuit without jamming at speeds up to 1,52 m/s. The checkout tests,
however, could not be performed with oil.
During the oil tests at OHMSETT, a few jams of the MK II-9D engines
were experienced because of the tendency of the mop to stick to protruding
metal structural supports of the OHMSETT bridge and to the oil mop
engine as it was pushed out of the engine after being squeezed.
Smooth, uniform speed adjustment of the mop sections floating in
the oil slick was difficult because of a variation in mop strand density
along its length. This bunching of the mop strands caused tugging and
sudden changes in tension as the mop was pulled through the squeeze
rollers. The presence of the lube-type test oil, especially the heavy
oil, lubricated the mop/squeeze roller contact area, contributing to
a loss of tension control. A compressed air jet was used to more
completely remove oil from the mop and to reduce slippage of the mop
against the rollers, but this was not successful.
The non-powered mop tail pulleys provided for the feasibility tests
were designed for low-speed operation while floating on the water surface.
In these tests, the pulleys were suspended at various angles above the
water by tying them off the video truss and operating at higher than
normal speeds. Oil mop jams at the tail pulleys occurred until they
were modified.
26
-------
Device Modifications—
The modifications performed during the two-week feasibility tests
and the effect they had on observed performance were:
1. Polyethylene chutes. A 3-mm-thick polyethylene sheet attached
to each MK II-9D mop engine below the rollers reduced friction
of the squeezed mop when it was pushed out of the lead engine
and reduced scrape-off oil loss of the oil-laden mop when it
was lifted off the surface by the trailing engine. These two
sheets were instrumental in minimizing the number of oil mop
jams experienced during the two weeks. Because of the changes
in vertical angle of the oil-soaked mop when it was lifted out
of the water under various wave conditions, placement of the
polyethylene sheet was not optimal for some tests. The result
was that a small amount of oil had to be scraped off the mop.
2. Modified non-powered tail pulley. A piece of tubing was placed
across the top of the fiberglass non-powered pulley wheel to
prevent the oil from jumping over the top and jamming between
the support axle and rotating pulley. This was effective in
eliminating the jamming of the oil mop at the tail pulleys.
Recommendations
Oil pickup concepts which have the highest probability of success
for rough weather, open ocean use are those using a non-surface piercing
oil pickup element with good wave conformance. Because the Oil Mop VOSS
concept tested here exhibited excellent wave conformance and insensitivity
of ORR and RE values to wave conditions at a set tow speed in the range
of 0.76 to 1.52 m/s (some results were higher in wave conditions than
calm), the concept merits further development. The next step in the feasibi-
lity process should consist of design, construction, and test of a full-size
prototype employing larger 45-cm diameter oil mops and hydraulically driven
rollers. This equipment would be first tested at OHMSETT and, if successful,
deployed from an offshore supply boat or other suitable vessel in actual
open water tests first without and then with spilled oil. Further
design efforts include work on the following:
1. A deployment scheme to maximize the rate and area coverage of
the oil mop dropping onto the oil slick (i.e., to maximize the
oil encountered by the oil mop lengths).
2. Squeeze roller assemblies with high torque and fine speed adjust-
ment in the linear speed range of 1.0 to 2.0 m/s.
3. Squeeze roller mounting frames to allow the squeezed mop rope
when it is pushed out of the machine with zero tension to fall
1(Investigation of Extreme Weather Oil Pollution Response Capabilities.
Seaward International USCG DOT-CG-80372-A, U.S. Coast Guard, Washington,
D.C., July 1978).
27
-------
freely onto the slick without danger of bunch-up and jamming.
SKIMMER DESCRIPTION
The basic elements and operating principle of the Oil Mop VOSS
concept is shown in the schematics of Figures 8, 9, 10, and 11. Figure
8 is an artist's conception of the concept when it is deployed from an
oil industry offshore supply vessel. Figure 9 shows the basic components
of the OHMSETT feasibility test configuration and the arrangement of the
two mop engines. The lead engine installed on the main bridge provides
tension to pull the oil mop out of the trailing engine situated on the
auxiliary bridge. Throttle controls on both lead and trailing engines
were used to adjust the location of the contact point the and contact
length of the mop in the test slick. The trailing engine squeezes the
oil-soaked mop after its transit through the oil slick. The unpowered
tail pulley enables the return lengths to the lead engine to be kept
above the water surface. Figure 10 is an elevated view (to scale) of
the test setup. The simple operating principle of the oil mop is
illustrated in the three enlarged inserts of Figure 10. Oil is first
sorbed by the mop as it falls on the slick from above (A). Visual
observation indicated that the oil appeared to be retained by the mop as
short wave-length waves washed over it (B). Oil was also picked up by
the mop as it resurfaced through the trough of a wave (C).
Figure 11 is a schematic of the MK II-9D mop engine used for these
tests. Complete dimension and weight information is contained in Appendix
C. The standard MK II-9D engines were modified by Oil Mop, Inc. before
shipment to OHMSETT to include a special throttle control cable. Both
rollers and the offloading pump are chain driven through a transmission
attached directly to the single-cyclinder diesel engine. The offloading
pump shown in Figure 11 was not used; oil and water squeezed from the
mop into the collection pan of the trailing engine in Figure 9 was
offloaded by an OHMSETT pump into adjacent measurement barrels.
The artist's conception of (Figure 8) is only one example of how an
oil mop system (actually a "sorbent on a string") might be deployed.
Figure 12 summarizes the different deployment configurations tested
during this feasibility series. Whenever possible, the configurations
were tested with both one and two lengths of oil mop. For each con-
figuration, the position of the deployment vessel is shown by dashed
lines. Configuration I is an approximation of the artist's conception
shown in Figure 8. The powered roller assembly to the side of the
deployment vessel in Figure 8 is modeled by the leading mop engine.
Configurations II and III were tried to investigate the possibility of
using a non-powered pulley outboard of the vessel. This would be easier
to rig and more reliable to use in the field. Configuration IV was run
since conclusions of previous testing indicated that the single most
important limitation of this concept is the ability to get a maximum
amount of oil mMop in contact with the slick.
28
-------
-
*
Figure 8. Artist view - VOSS system.
-------
Trailing Mop
Engine
Measurement
Barrels
Auxiliary Bridge
Figure 9. Equipment components - Oil Mop VOSS concept.
30
-------
Trailing Mop Engine
Tow Direction
Lead Mop Engine
u>
Aux.
Bridge
Main Bridge
Clean Mop
Oil^Soaked Mop
Unpowered Tail Pulley
Polyethylene Sheet
Contact Point
Mop Pulled
Through Slick
Breaking Wave
Clean Mop
Oil Saturated
Mop
Figure 10. Operating principle - Oil Mop VOSS concept.
-------
Fine Throttle Control
Contact Point with Oil Slick
Figure 11. Oil Mop Mark II-9D engine details,
32
-------
/—
voss
Vessel
Configuration I
Configuration II
|VOSS
(Vessel
Configuration III
Configuration IV
Figure 12. Oil Mop VOSS -- deployment configurations,
33
-------
TEST MATRIX AND PROCEDURES
Test Matrix
Performance tests with both heavy and light oil were conducted in
accordance with the matrix of test tank conditions and mop deployment
configurations listed in Table 10.
TABLE 10. TEST MATRIX - OIL MOP VOSS
Tow
speed
(m/s)
0.76
1.27
1.52
0.76
1.27
1.52
0.76
1.27
1.52
0.76
0.76
0.76
1.27
1.52
0.76
1.27
1.52
0.76
1.52
0.76
1.52
0.76
1.52
0.76
1.52
0.76
Wave Nominal
ht x length slick thk.
(m x m) (mm)
0
0
0
0.15 x 3.3
0.15 x 3.3
0.15 x 3.3
0.6 HC
0.6 HC
0.6 HC
0
0.6 HC
0
0
0
0.6 HC
0.6 HC
0.6 HC
0
0
0
0
0.6 HC
0.6 HC
0
0
0.6 HC
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
No.
mops
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
Deploy.
config.
(Figure 12)
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
II
II
III
III
III
III
III
III
III
Test
oil
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
Light
(continued)
34
-------
TABLE 10 (continued)
Tow
speed
(m/s)
0.76
1.52
0.76
1.52
Wave
ht x length
(m x m)
0
0
0.6 HC
0.6 HC
Nominal
slick thk.
(mm)
5
5
5
5
No.
mops
1
1
1
1
Deploy
config.
(Figure 12)
IV
IV
IV
IV
Test
oil
Light
Light
Light
Light
Test Procedures
Initial checkout tests without oil were conducted with the oil mop
deployed in configuration I (Figure 12), using one 45-m-long oil mop
length with the lead engine at an angle of 10 degrees to the right of
the trailing engine. These tests were used to familiarize lead and
trailing engine operators with the hand signals necessary to communicate
throttle adjustments between the two engines for control of the oil mop
slick contact length and the degree to which the oil mop assumed a "J"
shape in front of and beneath the trailing engine (Figure 9). It was
obvious from these tests that the encounter width would be too small for
field use. The lead engine was then moved to the righthand edge of the
main bridge in an approximate 30-degree angle to the trailing engine
(Figure 12). All oil tests using configuration I then were conducted
with the lead engine 30 degrees to the right of the trailing engine.
Procedures for all oil tests in each of the deployment configurations
are itemized in Table 11.
TEST PROCEDURES - OIL MOP VOSS
1. Collection pan
water.
of trailing mop engine is pumped dry of oil and
2. Wave condition required is established in the tank, and selection of
tow speed is made.
3. At the start of test tow both mop engines are actuated simultaneously.
4. Test oil slick distribution is started. During the test run the
speed of the lead and trailing mop engines is continuously adjusted
as necessary to maintain a constant mop-slick contact length. When
the mop-slick contact length is nearly uniform during the run, a
visual estimate is made of the encounter width (Figure 9).
5. Near the end of the test tow, the test oil slick distribution is
halted, but the mop engines are operated until all oil-soaked
(continued)
35
-------
TABLE 11 (continued)
lengths of the oil mop have passed through the trailing engine and
squeezed free of sorbed oil. The total oil distribution time is then
recorded as the total test time.
The oil and water mixture in the collection pan under the trailing
engine wringer assembly is offloaded by the OHMSETT pump into
measurement barrels where standard OHMSETT procedures are used to
determine the total volume of the recovered oil/water mixture and
the percent of oil in the mixture (RE).
TEST RESULTS AND DISCUSSION
Test Results
Results for the performance parameters TE, RE, and ORR are listed
in Tables 12 and 13 for heavy and light oil respectively.
The throughput efficiency was determined using the formula:
Total oil volume collected
TE
(Total test oil laid down) x (visual estimate of % test
oil hitting mops)
Determination of the visual estimate of test oil encountered (necessary
to apply the above equation) was not possible for all test runs (especially
those involving waves). As a result, the TE value was only obtained for 17
of the 41 oil tests.
Unlike the TE values, the RE values were determined by direct
measurement. The total oil and water mixture collected during the run
was measured and the percent oil measured directly, ORR values were
obtained by multiplying the RE value by the total volume of oil and
water in the measurement barrel and dividing by the test oil distribution
time. Consequently, the RE and ORR results are the most reliable indicators
of the Oil Mop VOSS concept performance.
Trends in the RE and ORR data are most easily seen when plotted
(Figures 13, 14, 15, and 16).
Discussion
Figures 13 and 14 are plots of the RE trends for heavy and light
oil respectively. In these figures, the RE is seen to be consistently
higher for deployment configurations using just one mop (small symbols)
than those using two mops (large symbols). This conclusion was verified
by visual observations in tests with one mop (Figure 17) and tests with
two mops (Figure 18). In tests with two mops, the downstream mop was
shadowed from effective contact with the oil slick by the leading mop
36
-------
TABLE 12. TEST RESULTS - OIL MOP VOSS CONCEPT (HEAVY OIL) (1)
Test
no.
Al
A2
A3
A4
A5
A6
A7
A8
Bl
B2
B3
B4
B5
B6
B7
B8
B9
Cl
C4R
C5
E2
E3
Tow Wave Total Oil Oil
speed ht x length oil dist.(2) No. deploy. picked up
(m/s) (m x m) (m3) mops conf ig. (3) (m3)
0.76 0
0.76 0
0.76 0
0.76 0.15 x 3.
0.76 0.15 x 3.
1.27 0
1.27 0
1.52 0
0.76 0
0.76 0
0.76 0.15 x 3.
1.27 0.15 x 3.
1.27 0.15 x 3.
1.52 0.15 x 3.
0.76 0.6 HC
1.27 0.6 HC
1.52 0.6 HC
0.76 0 ,
0.76 0
1.27 0
0.76 0
0.76 0.6 HC
1.44
1.32
1.37
3 1.36
3 1.39
1.21
1.36
1.43
1.57
1.42
3 1.41
3 1.42
3 1.34
3 1.29
1.09
1.23
1.36
1.34
1.43
1.23
1.42
1.34
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0.142
0.126
0.149
0.187
0.176
0.132
0.129
0.115
0.107
0.134
0.215
0.121
0.182
0.104
0.193
0.112
0.084
0.150
0.149
0.157
0.262
0.354
RE
34
68
67
63
62
59
50
35
50
68
58
54
51
55
54
49
46
57
57
59
37
51
ORR
RE(4)(m3/s
(%) xlO~3)
19
14
18
16
19
——_
23
15
13
15
25
25
1.20
1.07
1.26
1.58
1.45
1.83
1.77
1.89
0.88
1.13
1.77
1.64
2.52
1.77
1.64
1.58
1.39
1.26
1.26
2.18
2.21
3.09
1.
2.
3.
4.
Average viscosity: 793
Nominal slick thickness
Refer to Figure 12.
Mop(s)-to-slick contact
„ i /\_6_2 /_
x ID m /s.
of 5 mm.
length variable
over run .
TE reported only when
visual
estimate
of
encounter percentage was available.
-------
TABLE 13. TEST RESULTS - OIL MOP VOSS CONCEPT (LIGHT OIL) (1)
CXI
Test
no.
F2
F3
F4R
F5
F6
F7
SI
S2
Tl
T2
T3
T4
11
12
13
14
110
111
112
Tow Wave Total
speed ht x length oil dist.(2)
(m/s) (m x m)
0.76
1.27
1.52
0.76
1.27
1.52
0.76
1.52
0.76
1.52
0.76
1.52
0.76
1.52
0.76
1.52
0.76
1.52
0.76
0
0
0
0.6
0.6
0.6
0
0
0
0
0.6
0.6
0
0
0.6
0.6
0
0
0.6
HC
HC
HC
HC
HC
HC
HC
HC
(m3)
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
34
32
30
53
39
37
40
24
61
24
47
34
35
27
18
31
33
31
19
No.
mops
2
2
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1
1
Deploy.
Oil
picked up RE
config.(3)(m3) (%)
I
I
I
I
I
I
II
II
III
III
III
III
IV
IV
IV
IV
IV
IV
IV
0.349
0.231
0.246
0.397
0.145
0.155
0.105
0.103
0.216
0.150
0.264
0.166
0.224
0.121
0.271
0.196
0.147
0.072
0.134
45
41
39
38
19
26
23
38
38
38
35
34
45
35
48
47
48
43
43
ORR
TE (m3/s
(%) xlO~3)
2
3.
4.
3.
2.
9
z. .
25 0.
21 1.
1.
0
i- •
2.
2.
1.
19 2.
3.
37 3.
19 1.
14 1.
1.
90
22
10
31
02
59
88
70
77
52
21
78
89
02
03
28
20
20
51
1.
2.
3.
4.
Average viscosity:
15 x
Nominal slick thickness
Refer to
Figure 12
*
Mop (s) -to-slick contact
encounter
percentage was
10~BnT/
of 5 mm.
s.
length variable over
run.
TE reported only
when visual
estimate of
available.
-------
OJ
vo
§
M
CJ
M
O
0
W
80
-------
.ts
O
-LUU
80
«
B
§ 60
o
M
It,
W
O
0
20
o
O
9
D
O
/K
- ^^
IU_
—
1 1 1
0
Calm, Config. I (2 mops)
0.6 HC, Config. I (2 mops)
Calm, Config. II (2 mops) ^J Calm, Config. IV (1 mop)
Calm, Config. Ill (2 mops) ^ 0.6 HC, Config. IV (1 mop)
0.6 HC, Config. Ill (2 mops)
A~~ — A
X^P^^<''^^^^™^^^™™"™l""""'"^"'^™^""1^™^"tf?''^r"x~^
^^ ^^^*»s. ^f\/
D^^\3^-«
1 1 1 1 I 1 1 1 1 1 1 1 1 I 1 1
0.5 1.0 1.5 2.0
TOW SPEED, m/s
Figure 14. RE trends - Oil Mop VOSS (light oil).
-------
i 5
o
co
w
H
S '
I
I
O Calm, Config. I (1 mop)
O 0.6 HC, Config. I (1 mop)
• 0.15 x 3.3, Config. I (1 mop)
Calm, Config. I (2 mops)
0.6 HC, Config. I (2 mops)
I
I
0
0.5
1.0
TOW SPEED, m/s
1.5
2.0
Figure 15. ORR trends - Oil Mop VOSS (heavy oil).
-------
£\ Calm, Config. I (2 mops)
\9 0.6 HC, Config. I (2 mops)
L J Calm, Config. II (2 mops)
\J> Calm, Config. Ill (2 mops)
0.6 HC, Config. Ill (2 mops)
NJ
^ 4
w
H
w
O
CJ
A Calm, Config.. IV (1 mop)
^ 0.6 HC, Config. IV (1 mop)
0
1
1
1
1
i
0
0.5 1.0
TOW SPEED, m/s
Figure 16. ORR trends - Oil Mop VOSS (light oil).
1.5
2.0
-------
Figure 17. Test Bl: Calm, 0.76 m/s, Configuration I - 1 mop,
Figure 18. Test F5: 0.6 m HC, 0.76 m/s, Configuration 1-2 mops.
43
-------
(Figure 18). The leading mop kept oil from the downstream mop by
three mechanisms: (a) absorbing the oil as it encountered the leading
mop, (b) deflecting the oil slick by flow along its length, or (c)
breaking the oil slick into droplets, only a portion of which impact the
downstream mop.
Figures 15 and 16 show the ORR for heavy and light oil respectively.
In Figure 15 the deployment configuration with two mops (large symbols)
showed a consistently higher ORR value than the configurations using one
mop (small symbols), the reversal of the situation for RE seen in Figures
13 and 14. Heavy oil tests were run only with configuration I (Figure
12).
Of most significance is the performance of a single mop in configuration
IV with light oil (Figures 14 and 16). Figure 19 shows one test run
with configuration IV. Configuration IV was at or near the top in RE
and ORR performance even when compared to other configuration using two
mop lengths. Furthermore, although the accuracy in determining the TE
is subject to the uncertainties of visual estimates of oil encounter
percentage, the results of Table 13 show that configuration IV had the
highest estimated TE of all the configurations studied (Figure 12).
Configuration IV (Figure 19) is recommended for further development,
including OHMSETT tank testing and full-scale field tests. Development
tasks should include a large diameter (45-cm) mop and deployment equipment
to broadcast a large amount of mop on top of an oil slick.
44
-------
Figure 19. Test II: Calm, 0.76 ra/s, Configuration IV - 1 mop,
45
-------
SECTION 4
FRAMO ACW-402 SKIMMER
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
The Framo ACW-402 open sea high-capacity oil skimmer was tested
during the period of October 23 to November 3, 1978. A total of 74 oil
pickup performance tests were conducted; 36 tests were run with high
viscosity (heavy) oil, and 38 tests were run using medium viscosity
(medium) oil.1 This section summarizes the conclusions of the two-
week test series in the four major areas of:
1. Best Performance
2. Operating Limits
3. Mechanical Problems
4. Device Modifications
Best Performance—
The Framo skimmer was designed for high volume recovery of spilled
oil from thick slicks held inside offshore containment barriers. Due to
the constraints of oil volume and tank time the maximum oil recovery
rate was not obtained for the FRAMO unit during this test series. If
the oil slick is thick enough, the recovery rate is bounded only by the
maximum pump flow rate under the existing conditions of oil (emulsion)
viscosity and the discharge hose head losses. Pump curves for various
viscosity oils appear in Appendix C. A maximum flow-rate test with
water was conducted near the end of this test series, yielding a maximum
pump rate against a 5-m head of approximately 146 x 10~3m3/s. Oil tests
run during this series used slick thicknesses from 6 mm to 160 mm. The
best skimmer performance (highest numerical results) obtained is shown
in Tables 14 and 15. Since the Framo skimmer is a stationary skimmer,
the throughput efficiency was not calculated. Because of the Framo
operating principles of both overflow weirs and rotating discs, the
highest value of the RE and ORR parameters presented in Tables 14 and 15
did not occur under the same test conditions.
Physical properties of both test oils are listed in Appendix B.
46
-------
TABLE 14. BEST PERFORMANCE FRAMO ACW-402 (HEAVY OIL)
Performance
parameter
RE
ORR
Highest
value
96% , ~
27 x 10" V /s
Wave
ht x length
(mxm)
0
0
Average
s Ik. thk
(mm)
73
79
Weir
ht
(cm)
0
-2
Disc
speed
(RPM)
4
20
Test
no.
18
23
TABLE 15. BEST PERFORMANCE - FRAMO ACW-402 (MEDIUM OIL)
Performance
parameter
RE
ORR
Highest
value
92%
53 x 10"3m3/s
Wave
ht x length
(mxm)
0
0
Average
slk. thk
(mm)
73
138
Weir
ht
(cm)
0
-5
Disc
speed
(RPM)
10
20
Test
no.
31
42
The test results consistently demonstrated that— depending on slick
thickness, wave conditions, operational time available at the spill site,
and available storage capacity for the recovered oil/water mixture—
the skimmer may be operated with:
A. Overflow weir above the still water surface, resulting in a
high RE value but a reduced ORR value (for thin slicks, short
waves or limited storage capacity).
B. Overflow weir below the still water surface to achieve maximum
ORR at the expense of the RE value (for thick slicks, long waves,
or large storage capacity).
In almost every wave and test slick thickness condition, moving the
Framo skimmer head around in the slick increased the RE and ORR over the
values obtained with the skimmer held stationary in a stationary mode.
Operating Limits—
Operating limits of the Framo ACW-402 skimmer depend upon the following
factors:
1. Slick thickness. For slick thicknesses greater than those used
in this test series (160 mm), the ORR (m /unit time) is limited
only by the oil (or emulsion) viscosity and the head loss through
the discharge hose. For operation in thin slicks, the weir
is raised above the water surface, and only the discs are used
to collect oil. This method maintains a high recovery
47
-------
efficiency, but at a sacrifice in the oil recovery rate.
This was verified by a single test at a slick thickness of 6
mm. In this test the RE was measured at 85%.
2. Waves with periods less than 6 seconds. The in-phase heave
response of the skimmer head is limited to waves with periods
of 6 seconds or greater impacting the skimmer head at right
angles to the disc assemblies. This is because of the design
of the following components:
a. the passive hydraulic compensating circuit in the control
arm for wave following and
b. the mass and floatation area of the skimmer head.
Waves of periods less than 6 seconds and small breaking wavelets
were observed breaking through the disc assemblies and carrying
water directly into the interior weir box of the skimmer.
Mechanical Problems—
No problems were encountered during the two week test series with
any of the mechanical or hydraulic components of the Framo skimmer. The
skimmer was operated for a total of 26 engine hours during the two-week
test series. Near the end of the test series it was noticed that some
plastic wipers had worked loose from the disc assemblies. Although incom-
plete scraping of the discs occurred as a result, the discs still seemed to
perform their primary function of thickening the slick at the overflow
weir lip.
From the control cab of the skimmer, it was easy to operate the five
skimmer control settings:
1. Disc speed,
2. Disc rotation,
3. Pump speed,
4. Movement of the skimmer head about a horizontal plane, and
5. Pressure on the lifting cylinder that controls the wave response
capability of the floating skimmer head.
Device Modifications—
No modifications were necessary to improve oil pickup performance.
However, addition of a vertical elevation indicator for the weir lip position
that could be seen from the control cab would assist the operator.
The manufacturer is considering certain modifications for future
Framo skimmers including:
1. A smoother profile shape floatation collar to minimize wave
slap and the consequent pushing of oil away from the rotating
discs by short wave-length waves.
48
-------
2. A new and sturdier wiper material.
3. A longer 17-m control arm with active hydraulic feedback control
to allow faster heave response of the skimmer head for a wider
range of wave periods.
{.ecommendatians^
These tests have shown the degree of opertional control possible
with a Framo unit in two instances. In thin slicks with the weir raised
a high percentage of oil content (RE) stream can be picked up, and in
thick slicks with the weir lowered a high volume stream can be recovered
(with a consequent reduction in RE value).
The skimmer operator can effectively control the quantity and quality
of the outlet stream from the skimmer depending on whether or not operational
conditions (such as barge volume available for storage, amount of operating
time available on site, and oil slick thickness) are satisfactory.
The next logical step in the evaluation of the Framo skimmer should
be the actual ocean deployment from an offshore boat or other large deck
area floating platform. This test would investigate such things as operator
control and visibility of the skimmer head, wave response of the control
arm from a moving platform, and performance of the skimmer with a weathered
oil product most resembling the oil likely to be encountered in a large-
scale oil pollution incident.
Any additional OHMSETT testing could be used only to verify wave
response of the skimmer head in waves having periods less than 6 seconds,
and to demonstrate large oil pickup rates (approximately 150 x 10 m /s)
using massive amounts of test oil (slick thicknesses of 200 mm).
SKIMMER DESCRIPTION
The Framo ACW-402 skimmer system is manufactured by Frank Mohn, A/S,
Bergen, Norway. The unit is shown in cross section, (Figure 20) mounted
on the roadway of the OHMSETT tank for testing. The skimmer consists
of:
A. A floating skimmer head containing rotating discs, an overflow
weir, and a submerged centrifugal pump.
B. A control arm containing all hydraulic control lines and the
15-cm-diameter oil transfer tube as well as a hydraulic lifting
cylinder with pressure relief valve that allows the skimmer
head to follow waves with periods greater than 6 s.
C. An enclosed control cab housing control levers for the skimmer
adjustments of pump speed, weir depth, disc rotation, and skimmer
head motion.
49
-------
(C) Control Console
(D) Power Pack
(B) Control Arm
(A) Skimmer Head
Containment Boom
Figure 20. Equipment components - Framo skimmer.
-------
D. A powerpack (equipped with a hydraulic/pneumatic accumulator
for automatic starting) containing diesel prime mover and
hydraulic pumps to power the submersible pump and the various
skimmer head adjustments.
The entire system— including the powerpack, control cab, control
arm, skimmer head— has a total weight of 7,000 kgs. The skimmer is
intended to be deployed from the flat deck area of an offshore supply
boat or ocean-going tug. Oil and water picked up by the skimmer head
flows through the hollow control arm and out through a 15-cm-diameter
oil transfer hose. A high flow rate is possible using the 120-hp submer-
sible centrifugal pump suspended beneath the skimmer head. The 168
aluminum discs have a total area of approximately 60 m2 and a diameter
of 500 mm. More complete technical details are presented in Appendix C.
The heart of the Framo ACW-402 is the floating skimmer head shown
in cross section in Figure 21. The skimmer head contains two mechanisms
for recovering oil-rich mixtures from floating oil slicks. In the
presence of thin slicks or short, choppy waves, the overflow weir is
raised, and oil is recovered using the discs only. This method minimizes
the water content of the recovered oil/water mixture and reduces the
volume flowrate of recovered oil. In the presence of thick slicks,
the weir lip is controllable when it is lowered to allow flow over the
weir and directly into the skimmer pump inlet. With the weir in this
lower position, the rotating discs serve to thicken the oil slick in the
vicinity of the weir lip so that a more oil-rich mixture flows over the
weir than would without the discs.
TEST MATRIX AND PROCEDURES
Test Matrix
Performance tests with both heavy and medium test oils were conducted
under the conditions listed in Table 16.
TABLE 16. TEST MATRIX - FRAMO ACW-402
Wave
ht x length
(m x m)
0
0
0
0
0
0
0
0
Nominal
slick thk.
(mm)
30 to 80
90
80
40
50
70
70
40
Weir
ht
(cm)
-.5
-2
-2
-2
-2
0
0
+8
Disc
speed
RPM
20
20
20
10
10
20
4,7,10
10
Test
oil
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Heavy
Skimmer
head
deployment*
S
S
M
S
M
S
S
S
(continued)
51
-------
TABLE 16 (continued)
Wave
ht x
(m x
0.19
0.17
0.52
0.48
0
0
0
0.48
0.52
0.17
length
m)
HC
x 2.
x 12
x 17
x 17
65
.04
.56
.56
x 12.04
x 2.
65
Nominal
slick thk.
(mm)
80
75
100
80
65
130
6
60, 120,
100
90
-5,
-5,
-5,
-5, -2,
160 -5,
-2,
-2,
Weir
ht
(cm)
0.+8
-2,0
-2,0
-2,0
-2,0
0,4-8
+8
-2,0
0,+8
0,+8
10,
10,
10,
10,
10,
Disc
speed
RPM
20
20
20
20
20
20
10
20
20
20
Test
oil
Heavy
Heavy
Heavy
Heavy
Medium
Medium
Medium
Medium
Medium
Medium
Skimmer
head
deployment*
S
S
S
M
S
M
S
M
M
M
&
&
&
&
&
S
S
S
S
S
*S = Skimmer head held stationary in test oil slick.
M = Skimmer head moved about in test oil at operator's discretion to
maximize ORR.
Test Procedures
All tests were conducted inside the boomed area shown in Figure 22.
To simulate the presence of a current and to determine the effect on
collection performance, the skimmer head was moved around the boomed
area during some tests. The surface area of the boomed configuration
was determined by direct measurement to be approximately 65.7 m . The
procedure used for all tests is itemized in Table 17.
TABLE 17. TEST PROCEDURES - FRAMO ACW-402
1. Skimmer head is submerged outside boomed test slick and pump is
operated until clear water appears at the end of the 15-cm discharge
hose into the 1.9-m3 collection barrels. The discharge hose is
placed over an empty slop barrel,
2. Initial slick thickness is determined either by direct measurement
with the OHMSETT conductivity probe or calculation based on quantities
of oil picked up by the skimmer and distributed from the main
bridge during previous tests.
3. The wave condition is established and skimmer weir depth and disc
speed are set.
4. Test oil distribution into the boomed area is begun. The skimmer
pump is activated.
5. When an oil-rich mixture appears at the end of the 15-cm-diameter
hose discharging into the slop barrel, the hose is moved to direct
(continued)
52
-------
Universal Joint
Thin Slicks
Weir Up
Skimmer Head
Discs (168)
Pump
Thick Slicks
Weir Down
Figure 21. Operating principles - Framo skimmer.
53
-------
Main Bridge
Oil Added During Test
Boomed Area
Video Truss
100 m Oil Discharge Hose
.9 i ' Measurement Barrels
Auxiliary Bridge
Figure 22. Testing configuration -• Framo skimmer,
54
-------
TABLE 17 (continued)
flow into a measurement barrel and activate the stopwatch. During
the run 4 to 6 oil/water grab samples are obtained from the skimmer
pump discharge.
6. When the 1.9-m3 collection barrel is filled, stopwatch is stopped,
the skimmer pump is secured, and total test time and barrel oil/water
volume are recorded.
7. The final slick thickness is determined by direct measurement.
8. The skimmer head is submerged outside the boomed area and pump
remaining oil into a slop barrel until water appears at the end of
the 15-cm-diameter discharge hose.
9. The volume of oil collected is determined by measuring the total
oil/water volume collected and multiplying by the average percent
oil value (RE) obtained from laboratory measurement of the discrete
samples.
TEST RESULTS AND DISCUSSION
Test Results
Numerical results of the two performance parameters— RE and ORR—
for all tests are listed in Tables 18 and 19 for heavy and medium oil
respectively. Trends in skimmer performance are plotted out in Figures
23, 25, and 26.
Discussion
When overhead observation was made of the action of the discs, it
seemed that the interfacial surface tension of the reprocessed heavy oil
used initially was reducing the adherence of the oil to the discs. To
test for this possibility, a load of new heavy oil with an interfacial
tension of 30 x lQ-3N/m was loaded onto the bridge. For some runs the
new oil did in fact increase the percentage of oil in the recovered
mixture. However, sufficient test time was not available to determine
the degree of dependence of recovery efficiency on heavy oil interfacial
tension.
Both Figure 23 (heavy oil) and Figure 24 (medium oil) show the
general trend of increase in recovery efficiency when the weir elevation
is increased above the still water line (oil recovery taking place via
the disc and wiper assemblies only).
A trend opposite to that observed in Figures 23 and 24 occurs when
the oil recovery rate (ORR) is plotted against weir height (Figures 25
and 26). The oil recovery rate rises dramatically as the weir is lowered
55
-------
TABLE 18. TEST RESULTS - FRAMO SKIMMER (HEAVY OIL) (1)
Ui
Test
no.
93
94
95
96
97
98
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Slick
thick
(mm)
79
84
64
72
79
76
74
76
85
94
97
107
100
81
75
126
68
51
38
40
64
67
79
73
70
76
79
82
79
63
Wave
ht x length
(m x m)
0.19 HC
0.19 HC
0.19 HC
Calinwater
Calmwater
Calmwater
0.17 x 2.65
0.17 x 2.65
0.17 x 2.65
0.52 x 12.04
0.52 x 12.04
0.52 x 12.04
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Weir
height
(cm) (2)
8
0
-5
0
-5
-5
-5
0
-2
-2
0
-2
0
-2
-2
0
-2
-2
-2
-5
5
-5
0
0
0
0
0
0
-2
0
Disc
speed,
(RPM)
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
10
10
20
20
20
20
7
7
20
20
10
20
10
Skimmer
deploy-
ment (3)
S
S
S
S
S
S
S
S
S
S
S
S
S
M
S
S
M
M
S
S
S
S
S
S
S
S
S
S
S
S
Oil
rec.
(m3)
1.69
1.49
0.88
1.60
0.99
1.00
0.43
1.33
0.31
0.21
0.20
0.18
0.96
0.91
0.13
0.51
1.21
1.45
1.11
0.92
1.77
1.50
1.80
1.17
0.42
0.54
0.77
0.66
1.16
1.78
RE
(%)
82.3
76.0
42.0
78.8
48.0
50.7
21.5
69.8
15.3
10.3
10.0
8.7
47.0
42.7
6.4
24.7
59.3
68.0
54.7
45.3
86.7
74.0
88.7
95.8
95.2
87.6
90.4
94.2
57.4
86.7
ORR
m3/s
xlO~3)
1.9
4.2
7.4
1.9
22.0
9.9
2.7
2.1
2.2
1.9
1.1
1.3
1.6
10.1
1.4
2.7
7.1
6.9
2.2
12.3
3.5
15.8
3.1
4.0
3.1
3.2
4.7
3.4
26.9
15.4
(Continued)
-------
TABLE 18 (continued)
Test
no.
25
26
27
28
29
30
Test
no.
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
Slick
thick
(mm)
43
39
33
33
41
47
Slick
thick
(mm)
73
65
65
62
63
43
122
118
122
127
133
138
143
151
135
104
Wave
ht x length
(m x m)
Calmwater
Calmwater
Calmwater
Calmwater
0.48 x 17.56
Calmwater
TABLE 19. TEST
Wave
ht x length
(m x m)
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
0.52 x 12.04
Weir
height
(cm) (2)
8
0
-2
-2
0
0
RESULTS -
Weir
height
(cm) (2)
0
0
-2
-2
-5
-5
_c
_c
-2
-2
-2
-5
8
8
_c
-2
Disc
speed,
(RPM)
10
20
10
20
10
10
Skimmer
deploy-
ment (3)
S
S
S
S
S
S
FRAMO SKIMMER (MEDIUM
Disc
speed,
(RPM)
10
20
10
20
10
20
20
20
20
20
20
20
20
10
10
20
Skimmer
deploy-
ment (3)
S
S
S
S
S
S
S
S
S
M
M
M
M
S
M
S
Oil
rec.
(m3)
0.87
1.06
0.30
0.37
0.11
0.28
OIL) (5)
Oil
rec.
(m3)
0.71
0.66
0.67
0.24
1.13
0.77
0.90
0.83
0.59
1.10
1.67
1.17
0.65
0.48
2.20
0.25
RE
(%)
92.9
88.4
16.0
34.7
5.3
13.5
RE
(%)
91.9
82.6
87.3
47.3
55.5
38.0
46.0
41.4
31.4
53.4
81.3
56.7
80.7
88.8
56.0
12.4
ORR
m3/s
xlO~
2.7
2.9
3.8
9.2
1.8
1.3
ORR
m3/s
xlO~
4.4
5.5
15.2
5.4
22.5
25.7
41.0
20.9
14.1
21.6
17.9
53.3
13.8
4.1
46.9
4.2
3)
3)
(Continued)
-------
TABLE 19 (continued)
co
Test
no.
47
48
49
50
51
52
53
54
55
57
58
59
60
61
62
63
64
70
71
73
74
75
Slick
thick
(mm)
106
100
94
94
93
97
97
101
103
6
94
89
86
85
68
51
55
159
156
155
158
160
Wave
ht x length
(m x m)
0.52 x 12.04
Calrawater
0.5 x 12.04
0.5 x 12.04
0.5 x 12.04
0.5 x 12.04
0.17 x 2.65
0.17 x 2.65
0.17 x 2.65
Calmwater
0.17 x 2.65
0.17 x 2.65
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
0.48 x 17.56
Caltawater
Weir
height
(cm) (2)
0
0
-2
-2
0
8
-2
8
-2
8
0
0
-2
-2
0
0
8
-5
-5
-5
-5
-5
Disc
speed,
(RPM)
20
20
20
20
10
10
20
10
20
10
10
10
20
20
10
10
10
20
20
20
20
20
Skimmer
deploy-
ment (3)
S
S
S
M
S
S
M
M
M
S
S
M
M
S
M
S
S
S
M
M
S
S
Oil
rec.
Cm"
0.
1.
0.
0.
0.
0.
0.
0.
0.
ND
0.
0.
0.
0.
0.
0.
0.
0.
0.
1.
0.
1.
3)
17
05
16
31
18
21
43
32
49
73
56
33
16
43
41
43
99
83
28
96
30
RE
ORR
m3
/s
(%) x!0~3)
8
51
8
15
9
17
21
71
25
85
36
26
17
7
21
20
75
48
39
49
48
65
.0
.3
.0
.0
.0
.0
.0
.0
.0
.0
.0
.3
.0
.7
.7
.0
.0
.7
.7
.3
.7
.7
1.
15.
2.
5.
2.
1.
16.
1.
18.
9
0
5
3
5
6
1
0
9
ND
6.
8.
6.
3.
4.
3.
2.
25.
14.
49.
30.
40.
6
4
2
2
5
8
2
4
9
3
8
7
Footnotes for Tables 18 and 19
1.
2.
3.
4.
5.
Average viscosity
: 1900 x 10-6mz
/s.
With respect to still water line.
S = Skimmer head
stationary during entire
M = Skimmer head moved inside boomed area
Average viscosity
: 480 x 10-6m2.
test.
by operator
for maximum oil
p ickup .
-------
100 »-
80
20
A-
0
-5
(max down)
A
O Calm
\/ 0.48 m x 17.56 m reg. wave
/ \ 0.52 m x 12.04 m reg. wave
0.19 m HC wave
Calm, 6 mm thin slick test
0
(SWL)
WEIR ELEVATION FROM STILL WATER LINE (SWL), cm
Figure 23. RE trends - Framo (heavy oil).
+8
(max up)
-------
100 .
90 _
80 _
B^S
>-"
z
w
M
u
M
In
fc
M
70 -
o
0
I 1 1 1 1 1 1 1 1
Calm
0.48 m x 17.56 m reg.
1 1 1 1
30 -
20 -
10 -
0
-5
(max down)
0
(SWL)
WEIR ELEVATION FROM STIL1 WATER LINE (SWL), cm
+8
(max up)
Figure 24. RE trends - Frame (medium oil).
-------
50
40
-5
(max down)
D
Calm
0.48 m x 17.56 m reg. wave
0.52 m x 12.04 m reg. wave
0.19 m HC wave
0
(SWL)
WEIR ELEVATION FROM STILL WATER LINE (SWL), CM
Figure 25. ORR trends - Framo (heavy oil).
-------
60
O Calm
O 0.48 m x 17.56 m reg. wave
1
1
1
1
i.
-5
(max down)
0
(SWL)
WEIR ELEVATION FROM STILL WATER LINE (SWL), cm
Figure 26. ORR trends - Framo (medium oil).
+8
(max up)
-------
below the still water line. This increase in performance is at the
expense of oil recovery efficiency (Figures 23 and 24).
A detailed study of the numerical data values in Tables 18 and 19
and the observable trends as plotted in Figures 23 to 26 can be summarized
with the following statements:
A. The skimmer performs best in thin slicks by operating with the
weir above the still water line and with a disc speed of 10
RPM. This method maximizes RE, thus reducing the storage
volume requirement for recovered oil and water.
B. The skimmer performs best in thin slicks by operating with the
weir in the maximum down position, 5 cm below the water line
and with the discs at maximum speed of 20 RPM. This method
maximizes ORR, thus reducing the on-station operating time to
pick up a given size of spill.
63
-------
SECTION 5
WATER JET BOOM-TO-SKIMMER TRANSITION SYSTEM
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
During the period November 6 to November 17, 1978, a total of 53
performance tests were conducted with a vertical water jet boom-to-skimmer
transition system. The water jet devices and mounting brackets were
fabricated by OHMSETT operating personnel. The U.S. Navy Supervisor of
Salvage provided the lengths of oil containment boom and LPI, Inc., provided
the oil skimmer towed behind the Navy boom. This section summarizes the
conclusions of the two week test series in four major areas:
1. Best Performance
2. Operating Limits
3. Mechanical Problems
4. Device Modifications
Best Performance—
OHMSETT testing of the water jet device was conceived, planned and
executed in a two-week period.
Due to the experimental nature of the concept and the short time
period available for component fabrication, the best possible performance
of the water jet boom-to-skimmer transition device has not been firmly
established.
Although inconclusive, the best performance of the concept, as
measured by the percent reduction in slick width at the skimmer bow over
the value when no jets are operating, is presented in Tables 20 and 21
for heavy and light oils. These values are derived using the following
equation:
W - W.
% Reduction Slick Width = -^ i
o
Where: W = Slick width at skimmer bow, no jets operating
(measured data)
W. = Slick width at skimmer bow, "j" jets operating
(measured data)
64
-------
TABLE 20. BEST PERFORMANCE - WATER JET (HEAVY OIL)
Performance
parameter
Highest
value
Tow Wave
speed ht x length
(m/s) (mxm)
Number of
water .lets
% Slick width
reduction
73%
1.0
Calm
TABLE 21. BEST PERFORMANCE - WATER JET (LIGHT OIL)
Performance
parameter
Highest
value
Tow
speed
(m/s)
Wave
ht x length
(mxm)
Number of
water jets
% Slick width
reduction
66%
1.5
Calm
Based on the performance observed during these brief tests, it appears
that a system of vertical water jets, properly sized and positioned on the
converging boom and/or bow of a skimmer is superior to the traditional
solid skirt boom/skimmer connection in concentrating and directing an oil
slick into the skimmer.
Operating Limits—
The operating limits of the water jet boom/skimmer transition device
need to be more clearly defined with future tests. However, based on the
results of this initial feasibility test, the operating limits of the water
jet boom/skimmer transition device appear to depend upon the following
factors:
1. The number and position of water jets appeared to be more
important than changes in water supply pressure.
2. Although non-breaking waves do not affect water jet performance,
breaking waves can overpower the oil slick holding capability of
the jets and entrain oil downward in the water jet stream.
3. Trailing vortices at the boom catenary opening at higher tow
speeds have an effect on the oil slick exiting the boom in
spite of the presence of the water jet.
4. When the water jets became angled backward toward the boom
65
-------
skirt due to the top-heavy boom tipping forward and planing,
oil was entrained by the jets. When the jets were angled
forward so that the floating oil slick first encountered a
water surface elevation ahead of the jet impact point, the oil
was usually directed around the jet impact point with little
oil entraimnent.
Mechanical Problems—
The primary problem encountered in this initial feasibility test
was the tendency of the boom, made top-heavy with the attachment of the
water jet piping, to roll forward and plane during the test tow. This
was corrected by employing tie lines at the top and bottom of the booms
across the "V". If the booms were allowed to plane, the water jet would
be directed away from a vertical position to a more horizontal, backward
facing one. This could cause the jet to draw parts of the oil slick
into the jet impact zone rather than drive oil away from the point of
impact as is the case when the water jet is vertical to the water surface.
It is felt that with more time available for rigging, the water jet
technique can be retested at various angles of jet impingement with the
water surface.
Device Modifications—
Presence of the converging booms caused strong currents and vortices
near the boom and also tipping of the jets from their downward facing
vertical attitude (boom planing), A modification of this concept which
merits further testing is to employ vertical water jets alone to con-
centrate and herd an oil slick into a trailing skimmer. Without a boom
present, the water jets could be maintained in a more nearly vertical
attitude and the vortices and local turbulence caused by water flow
along the boom catenary and at the opening in front of the skimmer would
be eliminated. Wave chop buildup in front of the skimmer due to wave
reflection off the converging boom lengths would also be eliminated.
Whether mounted on a skimmer, length of boom, or separate float,
additional tests should be conducted using water jet mountings designed
so that the near-vertical attitude of the jet can be maintained at all
times. This seems to be important to maintain a radial zone around the
impact point so that the oil slick is diverted away from the impact
point instead of being drawn into the impact point and emulsified into
the water column.
Recommendations
The present short series of tests have gone a long way toward
defining the probability of success of a water jet device and the areas
that require further effort to optimize this technique to concentrate,
thicken, and direct an oil slick into the mouth of a pickup skimmer.
There are many unanswered questions as to the best method of water
jet positioning, their use with booms, and limits of performance in
66
-------
various wind and wave conditions. These questions should all be pursued
with further testing and analytical study of the vertical, forward moving
water jet.
Specific recommendations to most quickly determine the properties of
water jets in deflecting slicks are to:
1. Conduct tests with water jets and only one boom and also without
any booms to determine the effect of booms on the concentrating
effect of the water jets.
2. Place a set of water jets forward of the boom/water jet system
tested. The use of jets forward of the boom could be effective
in keeping oil from building up in thick layers against the boom
and being lost by vortices or entrainment into jets mounted on
the boom.
3. Fabricate water jet mounting hardware using gimbaled fixtures
or other means to allow the water jet to remain more nearly
vertical to the water surface when mounted on boom, aboard
a skimmer or on an independent float.
4. Investigate the oil slick concentration and deflection effects
in various wave and tow speed conditions as functions of water
jet variables such as spray pattern, degree of aeration, volu-
metric flow and nozzle pressure, design, and placement.
Wave reflection between the two containment booms, formation of
vortices at the exit throat in front of the skimmer, the development of
a strong current along the upstream boom face, and the uncontrollability
of the water jet vertical attitude all contributed to oil entrainment losses
in some runs. Wave reflections could be minimized or eliminated if only
one boom were used or if booms were eliminated altogether.
Positioning of water jets upstream of a boom could help reduce oil
entrainment into the water jets as the oil flows along with the contain-
ment boom. Entrainment seemed to occur when a thick slick was built up
and carried down alongside the boom. The forward current produced by
the jets could not divert such a moving slick and the oil was drawn into
the turbulence of the jet impact point. Different vertical angles of
the water jets should also be investigated.
A study for optimized construction and sizing of water jet hardware
for different wave and tow speed application should also be undertaken.
This would involve a study of hardware mounting designs to attach jets to
a boom, to a skimmer, or to individual floats. Other properties of the
water jet ability to deflect oil slicks should also be investigated. For
example, since it appears that one of the primary mechanisms in keeping
oil away from the impact point is the local free surface elevation height
around the impact point, adjusting the amount of air entrained into the
jet before it impacts the water may be important.
67
-------
Breaking waves were observed to be detrimental to the oil slick de-
flection abilities of the water jet. Obviously, the energy present in a
breaking wave must be overcome by the energy of the free water surface
disturbance imparted by the water jet in order for the jet to maintain
deflection control of the slick over the disturbing forces of a breaking
wave. With an optimum combination of water jet pressure, flowrate, degree
of jet aeration and spray pattern, a system can be developed which could
allow successful oil diversion in various breaking waves. Since breaking
waves, in the form of wind generated waves, short waves from wave slap of
a heaving skimmer bow or wave reflection from a containment boom are common
occurrences, it is important that this aspect be investigated.
EQUIPMENT DESCRIPTION
A cross sectional schematic of the water jet oil slick diversion con-
cept is shown in Figure 27. A photograph of the water surface motions
caused by a stationary water jet is shown in Figure 28. Use of the water
jet in the boom/skimmer transition system tested here is shown in the
sketch of Figure 29 and the photograph of Figure 30. Referring to Figure
27, a vertical water jet directed downward onto a water surface produces
a current on the water surface via two phenomena which act to move an oil
slick away from the point of impact.
The first phenomenon is a creation of a crater at the free surface
and a surface elevation ring around the point of impact complete with a
water splatter which moves up, over, and radially outward from the point
of impact. The local free surface elevation of the crater ring and the
water splatter moving radially outward act together to push an oil slick
away from the impact point.
The second phenomenon (also depicted in Figure 27) and the one which
can result in long oil slick retention times even after the jet has moved
on, is a current produced by the rising bubbles of air which were entrained
into the water by the jet. As the bubbles rise, their diameter increases,
causing an increase in buoyant force and velocity. Water is pushed from
on top and to the sides of the bubble and, in the case of a single bubble,
is swept up under the rising air sac. To maintain a mass balance, water
is drawn in from the sides of the path of the bubble. As the bubble
reaches the surface and before it bursts, it pushes the last level of
water radially outward, and brings some entrained water to the surface which
is also radially dissipated after the bubble bursts. A relatively large
outward flowing, radial surface current is established locally while
small underwater currents are directed inward and upward to maintain the
mass balance. It is also possible to view the rising, bubble-laced plume
of water as a less dense fluid rising in a more dense fluid and spreading
at the surface.
An indepth theoretical analysis of the surface piercing water jet
phenomena was not possible during this test program. In any event, it is
believed that this radial current action, the strength of which varies in
some way with the pressure, degree of jet aeration and flowrate, can be
68
-------
Water Jet Nozzle
Coherent Water
Stream
Radial
Current
a
vo
Entrained
Air Bubbles
Depiction of Current Produced by
Rising Air Bubbles
I
1. Bubble pushes water from on top of it
aside and entrains water as it rises.
2. As bubble reaches surface it pushes
the last layer of water radially outward
along the surface.
3. The bubble bursts and the entrained
water is carried by its own momentum to
the surface and radially dissipated.
Figure 27. Section view of water jet action
-------
Figure 28. Single water jet producing a surface current,
-------
Color video on tower
Main Bridge
TOW DIRECTION
Oil
Storage
Fire hose pump
and 40 HP motor
Main
Bridge
House
with
valve and
pressure
gauge
A-?x;S&r?x
5cm 0 Flexible hose
Boom mounted water
jets
MARCO boom skirts
(5 tests only)
1. Test Director
2. Test Engineer
3. Oil Distributor
4. Photographer
5. Video Technician*
6. VDU Operator*
7. Filter Operator*
8. Control Room Operator*
*Not shown
LPI-OSED Skimmer-
Anti-planing and sub-
mergence tie lines
Skimmer mounted water jet
JTee with valve and
pressure gauge
"Centrifugal pump
\
to • B ——• » ——pr—
Auxiliary Bridge'
Figure 29. General test set up of water jets, boom, and skimmer
71
-------
Figure 30. Water jets herding oil within booms and over the boom/skimmer
transition area.
72
-------
effective in deflecting and concentrating oil slicks not only near the
point of water jet impact but for some distance along the wake of the
moving jet.
The motivation for tests with the current boom/skimmer configuration
shown in Figure 31 was the hope that the water jet could solve the problem
of directing floating oil slicks from a pair of converging booms into the
bow of a following oil skimmer without having to use mechanical side
curtains between the boom and trailing skimmer (see Figure 32). During
pickup of oil slicks in open water areas, it is common practice to attempt
to concentrate and thicken the slick before it is fed into the oil pickup
skimmer. Thicker slicks are easier for any skimmer to pick up and greatly
increase the oil pickup rate. The usual configuration (see Figure 32) is
to deploy a floating oil boom in a "V" configuration with a skimmer
attached to the boom at the apex of the "V". Problems with this arrange-
ment arise when the boom/skimmer combination is towed at a critical
speed through waves. At this speed, depending on wave height and
frequency, the skimmer and booms begin to heave up and down at different
frequencies and magnitudes. Because the skimmer is usually much more
massive than the boom, a heaving skimmer has been known to lift the con-
tainment booms completely out of the water or submerge them in the region
immediately forward of the skimmer bow with accompanying oil slick loss
around the sides of the skimmer. Another problem with closed catenary
boom/skimmer arrangement is the formation of a wave "chop" which forms in
front of the skimmer. Long wavelength waves entering the boom catenary
are reflected back and forth across the decreasing width of the boom "V"
shape until they form a short wavelength breaking wave chop at the bottom
of the "V" in front of the skimmer bow. Oil droplet formation by these
breaking waves can cause oil to be lost past the skimmer.
A successful "transition device" between a "V" shape boom assembly
and towed skimmer must have the following characteristics:
1. Allow skimmer and boom lengths to oscillate and heave freely,
independent of one another.
2. Put minimal energy into the oil slick as it flows between
the concentrating booms and skimmer mouth to minimize oil
droplet formation.
3. Be reliable under wave and tow conditions which result in
sizeable out-of-phase skimmer and boom heave motions.
4. Reduce formation of standing wave chop caused by reflective
waves in the region in front of the skimmer bow.
5. Be readily available, easy to rig and operate, and inexpensive.
The vertical water jet oil herding concept shows potential for satisfying
all of the above characteristics.
The equipment collected and fabricated at OHMSETT to test the feasl-
73
-------
Figure 31. Close-up of boom/skimmer transition area with water jets herding oil.
-------
Ln
Figure 32. Flexible curtain extending over the boom/skimmer transition area.
-------
bility of a water jet boom/skimmer transition device is displayed schemati-
cally in Figures 29, 33, and 34. In Figure 29, the overall test arrange-
ment can be seen in which a total of 8 jets were rigged; three along
each side of the containment boom "V" shape, and two deployed from the bow
of the towed skimmer. The boom lengths, each 17 m long with attached
water jet assemblies, were secured to the main towing bridge a distance
of 15 m apart. The booms, supplied by the U.S. Navy Supervisor of Salvage
for the purpose of these tests, are made by Clean Water, Inc. Pneumatic
floatation elements are integral with a continuous strip of heavy rubberized
fabric*
Figure 23 is a close-up schematic of the water jet/boom mount fabri-
cated for these tests and attached to the boom in three locations along
each 17 m length. These six water jets were all pressurized with a fire
pump (40 hp, 7.62-cm centrifugal) located on the main bridge. All boom
.water jet nozzles were fabricated from straight lengths of standard pipe
with an inside diameter of 1.55 cm. Each pipe nozzle is 7.5 cm long.
The nozzles were attached to the boom and were angled forward as shown
in Figure 33 about 10 degrees from the vertical to minimize oil entrain-
ment by the water jets. Cross-bridle lines were connected between tops
and bottoms of the water jet assembly mounting frames on opposite sides
of the boom "V" configuration to assist in keeping the boom upright and
the water jets vertical during the tow.
The two water jets mounted on the skimmer are shown in Figure 34.
Water was supplied to these jets by a 2.5 hp centrifugal pump mounted
on the skimmer. Standard pipe lengths 15 cm long with a 1.55 cm inside
diameter formed the water jet nozzles. The nozzles were mounted vertically
with solid piping and unions which allowed swiveling in a horizontal plane
to position them at outer edges of the oil slick exiting the "V" boom
opening (Figure 29). A reference board marked into quarter meters was
hung from the front of the skimmer as a reference to determine the final
slick width as it entered the skimmer.
Tests were recorded on video tape, 16 mm movie film and 35 mm still
film. A color video camera was located topside on the main bridge tower
and a black and white video camera was at the underwater window alongside
the test tank. Movie film and still photography was taken by hand-held
cameras from both topside and underwater window positions.
TEST MATRIX AND PROCEDURES
Test Matrix
An initial shakedown of the boom with attached cross bridles and
water jets was conducted with the skimmer before oil tests were begun.
With the skimmer and its nozzles attached to the boom, performance tests
with both heavy and light oil were conducted in accordance with the matrix
of test conditions listed in Tables 22 and 23.
76
-------
Front view
5 cm Flexible hose
Steel strap
bolted to
aluminum strut
and welded to
the reducer.
Aluminum supporting
strut
Boom
Ballast
Chain
Figure 33- Typical water jet mounted on the Clean Water, Inc. boom.
-------
CO
Water supplied from onboard
centrifugal pump
\
5 cm 0 Flexible hose
Camlock fittings
z
5 cm Std. pipe
3.7 m
1.27 cm
15 cm
1.2 m
Figure 3*t. Side view of one of the two water jets mounted on the oil skimmer.
-------
TABLE 22. TEST RESULTS - WATER JET BOOM/SKIMMER TRANSITION DEVICE (HEAVY OIL)
VO
Test
no.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Tow
speed
(m/s)
1.0-1.5
1.0
1.5
1.5
1.0
1.5
0.5
0.5
1.0
1.0
1.5
1.5
0.5
1.0
1.5
1.5
0.5
0.5
1.0
1.5
1.0
1.5
1.0
1.5
1.0
1.5
0.5
1.0
1.5
Wave
ht x length
(m x m)
Calmwater
Calmwater
Calmwater
Calmwater
Calmwater
Calrawater
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
0.5 x 12
Calmwater
0.5 x 12
0.5 x 12
0.5 x 12
Calmwater
Calmwater
0.5 x 12
0.5 x 12
Calmwater
Calmwater
1.0 HC
1.0 HC
1.0 HC
No.
jets(l)
4
4
4
0
0
0
0
4
4
0
0
4
2
2
2
2
2/0
6
6
6
6
6
8
8
8
8
8
8
8
Initial Water jet
slick nozzle pressure
thick . skimmer boom
(mm) (Kpa) (Kpa)
0.6
1.3
1.3
1.3
1.3
1.2
1.4
1.3
1.2
0.7
0.6
0.5
0.6
0.5
0.7
0.6
0.7
0.7
0.6
0.6
0.8
0.6
0.5
0.7
0.6
0.6
0.5
0.6
0.5
34
34
34
0
0
0
0
69
34
0
0
34
69
34
34
69
34
34
34
34
34
34
34
34
34
34
34-103
34-103
34
69
69
69
0
0
0
0
69
69
0
0
69
0
69-0
0
117-0
0
69-21
69-21
69-21
69-21
69-343
69-21
69-21
69-21
69-21
69
69
69
Slick
width (2)
(m)
0.6
0.75
0.75
1.75
2.75
1.25
1.25
1.5
1.75
3.00
3.00
2.00
1.25
2.50
3.00
3.00
1/1.5
0.75
1.75
2.25
1.00
1.00
2.50
3.00
1.00
1.25
1.00
2.00
3.00
Slick
thickness (2)
(m)
varied
25.8
25.0
6.1
6.0
13.9
5.7
12.9
5.6
2.9
2.5
3.4
7.6
3.1
3.6
2.8
6.4
13.6
2.8
2.6
11.8
8.8
3.1
3.1
8.5
6.6
7.6
2.7
2.7
(continued)
-------
TABLE 22 (continued)
Test
no.
30
31
32
33
34
Tow
speed
(m/s)
1.0
0.5
1.0
1.5
1.0
Wave
ht x length
(m x m)
1.0 HC
1.0 HC
1.0 HC
1.0 HC
1.0 HC
No.
jets(l)
8
0
0
0
6
Initial
slick
thick.
(mm)
0.5
0.5
0.5
0.5
0.5
Water jet
nozzle
skimmer
(Kpa)
207
0
0
0
34
pressure
boom
(Kpa)
310
0
0
0
69-346
Slick
width(2)
(m)
1.00
2.50
2.50
3.00
2.00
Slick
thickness (2)
(m)
8.2
3.0
3.2
2.6
4.2
The accounting system for the number of water jets in service was based upon starting with the
jets on the skimmer (2 nozzles in service) and moving into the boom nozzles. The jets were always
used in pairs. Example— 6 nozzles in service meant all but the pair farthest from the skimmer
were being used.
At skimmer bow.
00
o
TABLE 23. TEST RESULTS - WATER JET BOOM/SKIMMER TRANSITION DEVICE (LIGHT OIL)
Test
no.
40(3)
41
42
43
44
45
46
47
48(3)
49
50
51
Tow
speed
(m/s)
1.0
1.0
1.5
1.5
1.0
1.5
1.5
1.0
1.0
1.0
1.5
1.0
Wave
ht x length
(m x m)
1.0 HC
1.0 HC
1.0 HC
1.0 HC
0.0
0.0
0.0
0.0
1.0 HC
0.5 x 12
0.5 x 12
0.5 x 12
No.
jets(l)
0
8
0
8
0
0
8
8
2
8
8
0
Initial
slick
thick.
(mm)
0.6
0.8
0.6
0.5
0.6
0.5
0.5
0.5
0.5
0.5
0.5
0.6
Water jet
nozzle
skimmer
(Kpa)
0
34
0
34
0
0
34
34
34
34
69
0
pressure
boom
(Kpa)
0
69
0
69
0
0
69
10-207
0
69
69
0
Slick
width(2)
(m)
3.00
2.50
3.25
2.25
1.50
2.30
0.75
0.75
1.75
2.25
3.00
Slick
thickness (2)
(m)
3.0
4.5
2.3
4.0
5.5
3.1
10.7
10.7
2.4
3.5
2.5
(continued)
-------
TABLE 23 (continued)
oo
Test
no.
52
60(4)
61
62
62R
64
65
Tow
speed
(m/s)
1.5
1.0
1.0
1.5
1.0
1.0
1.5
Wave
ht x length
(m x m)
0.5 x 12
0.0
0.0
0.0
0.0
0.5 x 12
0.5 x 12
No.
jets(l)
0
0
8
0
0
0
0
Initial
slick
thick.
(mm)
0.5
0.6
0.6
0.4
0.4
0.6
Water jet
nozzle
skimmer
(Kpa)
0
0
34
0
0
0
0
pressure
boom
(Kpa)
0
0
69
0
0
0
0
Slick
width(2)
(m)
3.10
2.00
0.75
2.75
2.75
3.00
Tore up boom.
Slick
thickness (2)
(m)
2.3
4.2
11.2
2.5
2.5
2.8
Aborted.
1. The accounting system for the number of water jets in service was based upon starting with the
jets on the skimmer (2 nozzles in service) and moving into the boom nozzles. The jets were
always used in pairs. Example— 6 nozzles in service meant all but the pair farthest from the
skimmer were being used.
2. At skimmer bow.
3. The forward splash of the skimmer affected the oil between the booms too much for the water
jets to reduce the slick. Subsequently, no more harbor chop tests were conducted.
4. Test numbers 60 through 65 were conducted using the flexible skirt to maintain the oil slick
from the booms' exit to the skimmer.
-------
Test Procedures
The procedures for all runs are summarized in Table 24.
TABLE 24. TEST PROCEDURES - WATER JET BOOM/SKIMMER TRANSITION DEVICE
1. Oil distribution is set at a predetermined rate to distribute
a 15-m wide oil slick of about 0.5-mm thickness at the desired
tow speed.
2. Establish the desired wave condition.
3. Clear most of the oil from previous test out of boom area. It
is not necessary to be pristine in this matter because oil
collection is not monitored.
4. Activate water jets at the desired pressure by regulating valves
in the water supply line.
5. Begin the tow and bring the main bridge up to the desired tow
speed.
6. Begin oil distribution and continue for a distance of 45.5 m.
7. Observe and photograph the interaction between the water jets,
oil slick, and boom. Record the final slick width going into
the skimmer bow. During certain tests change the water jet
pressure to compare subsequent reactions of the oil slick.
8. Continue the tow for about 15 m after the end of the oil slick
has reached the oil skimmer. Lower the main bridge skimming
boom, skim oil back to clear the tank for the next test.
TEST RESULTS AND DISCUSSION
Test Results
Results of all tests are listed in Tables 22 and 23 for heavy and
light oil respectively. The primary performance indicator is the final
slick width at the skimmer bow. The double values in either the skimmer
or boom nozzle pressure columns indicate a change in nozzle pressure
during the test tow to see its effect on slick width reduction. These
changes in pressures did not make a great deal of difference. The nar-
rowest slick width was recorded in all cases. Summary plots of the percent
slick width reduction (with jets vs. without jets) at the skimmer bow
versus tow speed is presented for the various conditions of waves and
number of nozzles in Figures 35 and 36. In these figures, results obtained
using the configuration of water jets which produced the lowest final slick
width are compared to tests under the same conditions but without jets.
82
-------
oo
p
E
R
C
E
N
T
R
E
0
U
C
7
I
0
N
130
90'
70
60 '
SO'
40'
30*
20'
10'
Q
CALM - CALM WATER.
RE6. - REGULAR WAVE.
H.C. - HARBOR CHOP.
4 NOZZLES CALM
8 NOZZLES H.C.
4 NOZZLES RES.
2 NOZZLES RE6.
I
B.5
1
1.5
TOW SPEED
Figure 35. Tow speed vs slick width for heavy oil.
-------
oo
180
98
88
p 78
R 6*
'58
N 48
R
38
28
8
c
T
1-18
0
N-28
-38
-48
8
CALM - CALM WATER
RE6. - REGULAR WAVE
H.C. - HARBOR CHOP
A-IMPROVEMENT IN SLICK
WIDTH REDUCTION USING
8 NOZZLES VS. THE BOON
ADAPTERS.
8 NOZZLES,CALM
8 NOZZLES.REG.
8 NOZZLES,H.C.
BOON ADAPTERS,CALN
8.5
1
1.5
TOW SPEED Ctn/*>
Figure 36. Tow speed vs slick width for light oil
-------
The heavy oil graph includes a test in which a tow-jet configuration was
used in calm water. This shows that an advantage is gained if only two
jets are used. The light oil graph includes data points recorded using
the flexible skirt to connect the concentrating boom and skimmer. Due to
time constraints and the desire to examine the system at the higher tow
speeds, no tests were conducted below one knot with light oil.
Discussion
This test series was intended primarily as a feasibility project.
The authors know of no previous experimental work having been done using
vertically directed water streams in conjunctions with a boom and skimmer
in a combined oil collection system. It is recognized that there have
been reports published on the use of fire hose streams to move oil on
water (Katz, R. and Cross, R., Use of Fire Streams to Control Floating
Oil, EPA-R2-73-181, U.S. Environmental Protection Agency, Cincinnati,
Ohio, 1973, 36 pp. and Roverts, A.C., Using Fire Streams with a Self-
Propelled Oil Skimmer, EPA-R2-113, U.S. Environmental Protection Agency,
Cincinnati, Ohio, 1973, 27 pp.), but these were based on the premise that
the vertical component of a water jet or stream has no value in moving an
oil slick.
It was seen that some oil herding effects were developed by the booms
themselves, without water jets. Each boom developed horizontal vortices
due to water passing beneath the skirt and coming up behind the boom. The
result was two currents opposing each other at the exit area. These
currents served to help keep the oil slick from spreading over the distance
between the booms and the skimmer. The effect of these currents varied
depending upon tow speed and wave condition. The flexible boom adapters
prevented these currents from herding the oil and thus the performance of
the adapters depicted on the graphs is in the negative range.
The overall outcome of this test series seems to point to using as
many jets as possible at high pressure. This must be tempered with the
effect of the jets on the oil slick. It has been shown that converging
a slick too violently can deteriorate oil recovery by a skimmer, (Breslin,
M.K., Testing the LPI Raked Bow Oil Skimmer, U.S. Environmental Protection
Agency, Cincinnati, Ohio, In preparation). Since oil collection by the
skimmer was not measured during these tests, such water jet effects cannot
be discussed in this report.
The boom, waves, tow speed, wind, and oil skimmer all interacted to
affect water jet performance. The boom did not remain perfectly upright
during all of the tests, but listed as if beginning to plane. In doing
so, the water jets were directed at an angle back toward the boom
skirt. Waves rebounding from the boom fabric splashed oil into the water
jet causing oil to be entrained in the jet. Forward tow of the "V" boom
forced oil against the boom and moved it down into the water jets in a
thick slick for runs at speeds greater than 0.51 m/s. Wind affected jet
performance by either disturbing a low pressure water jet before it hit
the water's surface or by hindering movement of the oil slick in response
to the jets. During wave tests, the raked bow of the LPI skimmer produced
85
-------
a forward splash and wave which would act to entrain and spread the oil
slick even before it exited the boom (e.g. test no. 48). The effects of
all these interactions is not precisely known since they were sporadic
and time constraints did not allow for detailed investigation. In spite of
these interactions a good picture of the water jets' abilities and potential
was obtained. Remedies for some of the interactions are listed in the
Device Modification paragraph of this report.
86
-------
APPENDIX A
OHMSETT TEST FACILITY
Figure A-l. OHMSETT Test Facility.
GENERAL
The U.S. Environmental Protection Agency is operating an Oil and
Hazardous Materials Simulated Environmental Test Tank (OHMSETT) located
in Leonardo, New Jersey (Figure A-l). This facility provides an environ-
mentally safe place to conduct testing and development of devices and
techniques for the control of oil and hazardous material spills.
The primary feature of the facility is a pile-supported, concrete
tank with a water surface 203 metres long by 20 metres wide and with a
water depth of 2.4 metres. The tank can be filled with fresh or salt
water. The tank is spanned by a bridge capable of exerting a force up
to 151 kilonewtons, towing floating equipment at speeds to 3 metres/second
87
-------
for at least 45 seconds. Slower speeds yield longer test runs. The
towing bridge is equipped to lay oil or hazardous materials on the
surface of the water several metres ahead of the device being tested, so
that reproducible thicknesses and widths of the test fluids can be
achieved with minimum interference by wind.
The principal systems of the tank include a wave generator and
beach, and a filter system. The wave generator and absorber beach have
capabilities of producing regular waves to 0.7 metre high and to 28.0
metres long, as well as a series to 1.2 metres high reflecting, complex
waves meant to simulate the water surface of a harbor or the sea. The
tank water is clarified by recirculation through a 0.13 cubic metre/second
diatomaceous earth filter system to permit full use of a sophisticated
underwater photography and video imagery system, and to remove the
hydrocarbons that enter the tank water as a result of testing. The
towing bridge has a built-in skimming barrier which can move oil onto
the North end of the tank for cleanup and recycling.
When the tank must be emptied for maintenance purposes, the entire
water volume, of 9842 cubic metres is filtered and treated until it
meets all applicable State and Federal water quality standards before
being discharged. Additional specialized treatment may be used whenever
hazardous materials are used for tests. One such device is a trailer-
mounted carbon treatment unit for removing organic materials from the
water.
Testing at the facility is served from a 650 square metres building
adjacent to the tank. This building houses offices, a quality control
laboratory (which is very important since test fluids and tank water are
both recycled), a small machine shop, and an equipment preparation area.
This government-owned, contractor-operated facility is available
for testing purposes on a cost-reimbursable basis. The operating con-
tractor, Mason & Hanger-Silas Mason Co., Inc., provides a permanent
staff of fourteen multi-disciplinary personnel. The U.S. Environmental
Protection Agency provides expertise in the area of spill control tech-
nology, and overall project direction.
For additional information, contact: John S. Farlow, OHMSETT
Project Officer, U.S. Environmental Protection Agency, Research and
Development, lERL-Ci, Edison, New Jersey 08817, 201-321-6631.
88
-------
APPENDIX B
TEST OIL PROPERTIES
Differences in the physical properties of the same oil designation
listed in Table B-l are the result of:
1. Differences in temperature at the time of testing and/or
2. Contamination or property changes due to the reprocessing
procedure of vacuum distillation of used test oil.
TABLE B-l. RANGE OF TEST OIL PROPERTIES FOR THE 1978 OITC SERIES
Surface
Oil Viscosity(l) Specific tension
designation (xlO-6m2/s) gravity (xlO~3N/m)
OSD SCOOP
Circo X heavy 1000-1210 0.933-0.939 35.2-35.3
Circo 4X light 17.8 0.897 27.1
OMI VOSS
Circo X heavy 768-1018 0.937 35.3-35.4
Circo 4X light 15.6-17.1 0.900 30.6-31.5
FRAMO
Circo X heavy 1900-2800 0.936-0.938 28.9-35.3
Circo medium 420-550 0.922-0.926 32.4-35.5
Interfacial
surface tension
(xlO-3N/m)
14.4-23.0
6.0
11.7-13.6
2.2-4.7
5.8-30.3
9.2-13.8
1. Measured at temperature of OHMSETT tank water.
89
-------
APPENDIX C
SKIMMER TECHNICAL DESCRIPTIONS
OFFSHORE DEVICES SCOOP
The Scoop system employs a surface following boom equipped with four
integral skimming weirs connected to a 250 gpm hydraulically driven
diaphragm pump which delivers recovered oil, water and debris to a 350
gallon onboard oil/water separator, all mounted in a fast, shallow draft,
trailerable 26 ft by 8 ft boat (Figure C-l).
Figure C-l. Scoop 250 gpm spill recovery vessel.
The boat is capable of reaching the scene of a spill at speeds over
20 knots dependent on power options. On scene, the 65 foot skimming barrier
is deployed through the bow door ramp and taken in tow by a workboat. The
45 foot sweep of a skimming boom is towed into the spill at a relative
speed of one knot (Figure C-2). The pump, which is capable of handling
collected solids up to 2 inches, conveys recovered material to the on-
board separator. Separated water is returned into the skimming boom and
oil is offloaded from the separator to a separate barge or a rubber pillow
tank towed alongside (Figure C-2).
90
-------
Figure C-2. Scoop deployed in stern-first skimming mode.
Specifications
Skimming Boom—
24 in x 68 ft
Draft: 13.5 in
Freeboard: 10.5 in
Construction: Curtain material is elastomer coated 2-ply nylon flexible
sections held upright or rigid reinforced with 20 rigid
sections of 6061 aluminum with external cylindrical etha-
foam floatation. Cast lead ballast. 6000 Ib tensile poly-
ester tension line. Four skimming weir sections with 17 in
x 2 3/8 in opening.
Weight: 7 Ibs/ft. 525 total.
Pump—
Hydraulically driven double acting diaphragm pump.
Capacity: variable to 250 gpm to 50 ft head.
Size: 17 in x 20 in x 32 in
Type: Fetters Model ACl diesel 6 hp.
Borg-Warner Model S-15-5 gear pump
7 gallon reservoir 5 micron filter
Weight: with fluid: 400 Ibs.
Oil-Water Separator—
350 gallon, 12 compartment gravity separator
Design Flow Rate: 50 gpm
Dwell Time: 5 minutes at 50 gpm
Air Removal: 3 inch diameter x 6 foot clear standpipe
Construction: 1/2 inch welded polypropylene. Lexan windows.
Dimensions: 42 in x 54 in x 48 in high.
Weight: dry 250 Ibs; full 3050 Ibs.
Response Vessel—
26 ft x 8 ft beam hand laid fiberglass.
Draft: 12" without engines.
91
-------
MARK 11-9 MECHANICAL DESCRIPTION: The Mark 11-9 is a skid mounted wringer unit with an
intermediate storage capacity of 4.33 barrels. The rope mop is wrung twice during each pass
through the machine by two nine inch diameter squeegee rollers. The lower roller is mount-
ed with adjustable spring mechanisms for pressure setting the rollers. A quick release lever
permits roller separation to facilitate set-up and
adjustment. The diesel driven unit consists of a
single cylinder engine coupled to a speed reducer
through an industrial clutch. The electric unit
consists of an explosion proof variable speed
motor drive. A chain and sprocket mechanism is
used to power both squeegee rollers and a spring
loaded tensioner is used to take up the slack in
the chain as the lower roller moves.
•TV
Courtesy of: OIL MOP, INC.
Rope mop--
Rope mops are manufactured in several types as designated by catalog numbers,
The code is as follows:
0 — designates a concentric mop; the rope core is in the center of the
fibers.
C — designates a "compact" weave necessary on the mops with small rope
cores.
y — designates "weedless" in the sense that is mitigates entanglement with
debris and flotsam.
1st digit — designates the core rope diameter in eighths of an inch.
2nd digit • - designates the maximum mop diameter in inches.
For instance OCW 6- 12 is a concentric weedless mop consisting of a 3/4
inch core rope with a maximum overall mop diameter of 12 inches (fiber
length is approximately 6 inches from core rope).
Rope Mop
Type
OCW 3-4
OCW 4-6
OCW 4-9
OCW 4-12
OCW 6-12
new 6-18
OCW 6-24
OCW 6-36
Standard
Length
10C
100'
100'
100'
100'
100'
100'
1 00' ....
Box
Size
2'x2'x2'
2'x2'x2'
2'x2'x4'
2'x2'x4'
2'x2'x4'
65"x35"x30"
65"x35"x30".
4'x4'x4'
Mop Weight
Lbs/Ft
... .14
... .32
... .38
... .46
... .60
... .75
... .90
... 1.50
Shipping
Weight, Lbs.
25
50
80
92
100
135
175
213
92
-------
DESCRIPTION: The rope is a continuous
length of mop made of oleophilic fibers
carefully woven to a core, forming an oil
sorbing device of unequalled efficiency.
Specific gravity of the OCW mop is
approximately 0.90.
Working temperature 210°F to -40°F.
Manufacturing tolerances ± 10 per cent.
Courtesy of: OIL MOP, INC.
OIL MOP Inc.
Engineers Road, Post Office Drawer P, Belle Chasse, La. 70037, U.S.A. ,
24 hour telephone—(504) 394-6110, Cable address—OILMOP, NEW ORLEANS, Telex • 58 7486 COM I
FRAMO ACW-402
The Framo ACW-400 is designed for high volume recovery of oil
contained in booms on water. A new combination of weir and adhesion
skimming principles improves the overall efficiency and is particularly
advantageous for handling of high viscosity emulsified oil.
The ACW-400 is a self-contained unit that can be instantly installed
on a wide range of vessels from harbour tugs and ferries to offshore
supply vessels and tankers. The recovery operation at Ekofisk during
the "Bravo" blowout proved successful operation from an offshore supply
vessel in sea state 4-5 Beaufort.
The recovery system is controlled by one man from an operation
cabin. The skimmer head is mounted on a hydraulically-balanced extension
arm which incorporates both oil transfer and hydraulic transmission
lines thus eliminating all hose handling problems. From parked position
on the deck the skimmer's head is launched and positioned in the oil
slick by the extension arm. When in position, an automatic load compensation
system is engaged allowing the arm and the head to follow the main wave
movements at an ideal stable skimming draught. The skimmer head can be
moved sideways and the extension adjusted independent of the automatic
vertical movement. The skimmer head can be lifted back on deck in
seconds allowing the recovery vessel to retreat immediately if required
in emergency.
93
-------
The system includes a portable submersible pump primarily intended
for discharge and transfer of the collected oil. This pump is designed
for entering tanks through butterworth-size openings and is also ex-
cellent for emergency offloading of disabled vessels to prevent pollution.
Being made from stainless steel the pump can feed fire monitors at 9
bar. The pump is hydraulically driven from the powerpack on the recovery
unit. This powerpack can easily be disconnected for separate use with
the portable pump.
As optional, the extension arm can be fitted with a hydraulically
driven dredge pump for recovery of contaminated sand, mud, or reed with
solids of 0 100 mm. This mini dredge arrangement is also recommendable
for regular harbour and canal maintenance work.
Specifications
Skimmer head—
The complete self-contained powerpack can be disconnected for
emergency offloading operations, etc. All hydraulic connections are
fitted with valved snap-on couplings.
The skimmer head is constructed in SW-resisting aluminum. Four
recovery drums are assembled in a square configuration outside the
adjustable weir/pumpwell. All functions are hydraulically operated and
adjusted from the operator cabin.
Drum speed: 0-30 rpm
Pump speed: 0-2000 rpm
Weir level: Water line — 45 m to +80 mm
Material: A57S
The skimmer head is connected to the extension arm by a universal
joint. All hydraulic connections are by valved snap-on couplings.
The recovery unit is assembled on a steel base. Prior to operation,
the base must be welded or bolted to the deck.
In parked position, the arm and the skimmer head is secured on the
base and the complete ready to start unit can be transported.
Overall dimensions: L=6.8m H=3.4m B=2.5m
Total weight: 7000 kgs
Operator cabin, powerpack and the extension arm with skimmer head are
mounted on a swing loader body.
Prime mover: Diesel or electric 160 HP
Hydraulic system pressure: Maximum 250 kp/cm2
Arm extension: Maximum 10.5 m
Maximum base level above water line: 3 m
Initial lift impulse (load compensated arm): 60 kp
94
-------
Loader body swing: 360°
Under favorable conditions of a calm sea and a thick oil slick, the oil
pickup capacity is only limited by the ability of the TK6 pump used in
the Framo ACW-402 skimmer to pump oil at the given viscosity of the
slick. Figure C-4 graphs the results of a test of the TK6 pump to
establish this upper limit of the Framo ACW-402 system to pickup oil
slicks.
95
-------
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96
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PUt/P & GEAR WORKS
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97
-------
TECHNICAL REPORT DATA
{Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-80-020
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
OHMSETT EVALUATION TESTS:
and a Water Jet Herder
Three Oil Skimmers
5. REPORT DATE
February 1980 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Douglas J. Graham, Robert W. Urban
Michael K. Breslin and Michael G. Johnson
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.
EHE 623
11. CONTRACT/GRANT NO.
68-03-2642
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab.-Gin,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13, TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
Douglas J. Graham and Robert W. Urban with Pollution Abatement
Associates, Corte Madera, California 94925
16. ABSTRACT • ,,,_.__.
A series of performance tests was conducted at the U.S. Environ-
mental Protection Agency's OHMSETT test facility with three selected
oil spill pickup devices (Skimmers) and a water jet boom/skimmer
transition device. The objectives of the skimmer tests were to
establish the range of best performance for each device under the
manufacturer's design limits and to document test results on 16-mm
film and by quantitative measures of performance.
The three oil skimmers studied by the test committee during the
OHMSETT 1978 season, in order of testing, were the Offshore Devices,
Inc., Scoop skimmerj the Oil Mop, Inc., VOSS concept; and the Frame
ACW-402 skimmer. During the 6-week skimmer test program, 148
individual data test runs were made.
The purpose of the more qualitative evaluation tests of the water
jet boom/skimmer transition was to determine whether the concept was
sufficiently effective to merit further development. This simple
device appears to have solved the problem of coupling two devices (a
boom and a skimmer) with radically different surface wave response
functions without losing much oil.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Performance tests
Skimmers
Water pollution
Oils
Spilled oil cleanup
Protected waters
Coastal waters
Diversionary boom
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
110
2O. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
98
U.S-GOVERNMENT PRINTING OFFICE: IMO-657-14&/5580
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