v>EPA
United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
EPA-600/7-78-060
April 1978
Research and Development
Performance Testing of
Oil MOP Zero Relative
Velocity Oil Skimmer
Interagency Energy-Environment
Research and Development Series
-------
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-600/7-78-060
April 1978
PERFORMANCE TESTING OF OIL MOP
ZERO RELATIVE VELOCITY OIL SKIMMER
by
Michael K. Breslin
Mason & Hanger-Silas Mason Co., Inc.
Leonardo, New Jersey 07737
Contract No. 68-03-OA90
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
U.S. Coast Guard
Washington, D.C. 20590
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 U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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FOREWORD
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 performance evaluation tests of a research
prototype skimmer based on an adaptation of existing commercial equipment.
The principle shows promise of being able to perform effectively at
relatively high speeds, thereby reducing cleanup time. This technique
will be of interest to all those interested in cleaning up oil spills in
inland and coastal waters. Further information may be obtained through
the Resource Extraction and Handling Division, Oil and Hazardous Materials
Spills Branch, Edison, New Jersey.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
iii
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ABSTRACT
This research test program was initiated by the U.S. Environmental
Protection Agency (EPA) and the U.S. Coast Guard (USCG) to determine the
ability of the Oil Mop Inc. (OMI) zero relative velocity (ZRV) oil
skimmer to recover oil from a water surface under various conditions.
A fast current (operating range up to 3 m/s (6 kts)), prototype
skimmer was designed and built by OMI and delivered to the Oil and
Hazardous Materials Simulated Environmental Test Tank (OHMSETT) to be
tested. The principle of operation was based on adsorbing oil onto
oleophilic fibers woven into a rope. The rope and fibers were then
squeezed by wringers to remove the oil into a recovery basin. The
device was rigged, trimmed and then towed into a controlled oil slick
while being operated and monitored for oil recovery. Device operating
speed, oil slick thickness, tow speed, and wave conditions served as
controlled independent variables. The fluid recovered was sampled
during and after the test run to determine device performance. Tests
were conducted in accordance with a test matrix developed by the USCG
and EPA. Results of the tests were evaluated in terms of recovery rate,
recovery efficiency, and throughput efficiency (i.e., the amount and
quality, or percent oil, of fluid recovered versus the amount of oil
distributed). Because of adverse weather and problems with the device,
the testing program was of short duration. Only a few tests were run,
so parameters could not be completely optimized.
This report was submitted in fulfillment of Contract No. 68-03-0490,
Job Order No. 29, by Mason & Hanger-Silas Mason Co., Inc., under the
sponsorship of the U.S. Environmental Protection Agency and the U.S.
Coast Guard. This report covers the period from November 29, 1976, to
December 3, 1976, when work was completed.
iv
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CONTENTS
Foreword ill
Abstract iv
Figures vi
Tables vi
Abbreviations and Symbols vii
Acknowledgments viii
1. Introduction and Objectives 1
2. Conclusions and Recommendations 2
3. Test Apparatus Description 3
• 4. Test Plan and Procedures 7
5. Results and Discussion 12
Appendices
A. Equations and definitions 19
B. Facility description 20
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FIGURES
Number
1 Top view of the OMI-ZRV skimmer 4
2 Side view of the OMI-ZRV skimmer 4
3 Schematic diagram of the tachometer and reduction wheels. . 5
4 Test set-up for the OMI-ZRV skimmer 10
5 Oil recovery rate of the OMI-ZRV skimmer as a function
of slick thickness, tow speed, wave condition, and
belt speed for Sunvis 7 (light) oil 15
6 Throughput efficiency of the OMI-ZRV skimmer as a function
of slick thickness, tow speed, wave condition, and
belt speed for Sunvis 7 (light) oil 16
7 Recovery efficiency of the OMI-ZRV skimmer as a function
of slick thickness, tow speed, wave condition, and
belt speed for Sunvis 7 (light) oil 17
TABLES
Number Page
1 USCG-EPA Oil Mop Test Matrix (Proposed) 8
2 Test Results - Oil Mop Inc., Mark II-9D Skimmer 9
vi
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ABBREVIATIONS AND SYMBOLS
C —Centigrade
cm —centimeter
EPA —Environmental Protection Agency
F --Fahrenheit
ft —feet
gal —gallon
gpm —gallons per minute
H.C. —harbor chop
H,L,T —height, length, period
in. —inch
kt —knot
m —meter
mm —millimeter
min. —minute
N —Newton
OMI —Oil Mop, Incorporated
OPT —optimum
ppt —parts per thousand
s —second
Sun or
Sunvis —Sun Oil Company registered brand names
TBD —to be determined
USCG —United States Coast Guard-
VDU —Vacuum Distillation Unit
ZRV —Zero Relative Velocity
vii
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ACKNOWLEDGMENTS
J.H. Getman, USCG, project officer for this test, and his assistant,
K.R. Goldman, are gratefully acknowledged for their guidance and assistance
during the test program.
M.G. Johnson is gratefully acknowledged for his efforts throughout
the test program and especially for designing and fabricating the needed
tow brackets.
Funds for this project were provided by the U.S. Coast Guard Oper-
ations and Environmental Technology Division, Office of Research and
Development, Washington, B.C., and the Edison, New Jersey, office of the
U.S. Environmental Protection Agency, Oil and Hazardous Materials Spills
Branch, Edison, New Jersey.
viii
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SECTION 1
INTRODUCTION AND OBJECTIVES
Oils are being handled by marine transportation and dockside equipment
in increasing amounts and variety. The growing potential for accidental
discharge of these materials poses a serious threat to the welfare of
the general public and environment.
Satisfactory devices for both control and cleanup of oil spills are
still in the developmental stage. For cleanup, a device must be efficient,
easy to deploy and operate, and able to perform under many environmental
conditions.
Oil Mop Inc. (OMI) has designed a new fast-current skimmer system
using endless-rope sorbent mops to adsorb spilled oil from the water's
surface. The moving skimmer processes the mops at about its own speed,
maintaining zero relative velocity (ZRV) between the rope mops and the
oil layer. The device has been tested at the U.S. Environmental Protection
Agency's (EPA) oil and hazardous materials simulated environmental test
tank (OHMSETT) facility, which was specifically designed to test prototype
oil control and cleanup equipment under simulated hydrodynamic environmental
conditions.
The purpose of this project was to evaluate the performance of the
prototype OMI-ZRV fast-current skimmer at tow speeds up to 2.54 m/s (5
kt) with Sunvis 7 and Sunvis 1650 oils under several wave conditions.
But freezing conditions resulted in lengthy start-up and shake-down
times; therefore Sunvis 1650, the heavier oil, was not tested. Since
the principle of operation of the device required the velocity of the
oil mops to be relatively close to the tow speed, the maximum tow speed
was limited by the maximum mop speed. And because of the lack of drive
power in the oil mop engines, the maximum tow speed tested was 1.78 m/s
(3.5 kt). This test was conducted with the rope-mop speed at 1.52 m/s
(3.0 kt).
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
The following conclusions were drawn from the evaluation of the
test data and observations of equipment performance.
The OMI-ZRV skimmer recovered oil best at slow speeds (1.02 m/s (2
kt)) in calm water with the belt running slightly faster or slower than
the tow speed. But before a definite appraisal of the system can be
made, several items support the need for further testing:
1. Because of initial set-up problems, weather conditions, and
problems with the device, only two days of testing were possible.
Consequently, there was no chance to analyze the data collected
and refine testing techniques.
2. The device's recovery efficiency improved toward the end of
each test run, suggesting that the samples were collected too
early in the test runs and before steady state conditions were
achieved.
3. Recovery time was not recorded until the second day of testing;
it was noticed then that a discrepancy (< 15 seconds) could
exist between it and distribution time.
4. A definite time for starting the rope mops could not be established.
Such unknowns make design analysis difficult.
The design shows promise but is still in the developmental stage.
The rope-mop and squeezer components of the skimmer have been used
successfully to recover oil from water at a fixed location with little
or no current. Successfully incorporating these components into a
moving system will require further study and modifications of the
present device. Such modifications should include a different shape for
the catamaran hulls and larger rope-mop drive engines. Gradual transition
between the main hull to the bow and stern would produce less headwave,
less drastic oil channeling, and less entrainment of missed oil after
the device passes. The rope-mop drive units used during testing could
not process the rope mops fast enough and sometimes stalled during
operation. These and other modifications are included under Results and
Discussion.
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SECTION 3
TEST APPARATUS DESCRIPTION
DEVICE DESCRIPTION
The OMI-ZRV skimmer was mounted on a 2.74-m (9-ft) wide aluminum
catamaran that was fitted with modified bows (Figures 1 and 2). The
craft was rigged and towed during this testing, but it can be equipped
with two outboard motors with steering controls. Two Mark II-9D mop
engines with wringer assemblies drove and wrung six oil mops. Each
engine was equipped with an oil collection pan, vertical guide idlers,
four rollers, and two adjustable springs for setting pressure on the
wringers. The drive on the Mark II-9D series mop engine consisted of a
positive chain drive going to one of the 22.86-cm (9-in.) polypropylene
rollers from a reduction gear. The rope mops were constructed of thin,
flat, oleophilic plastic fibers woven into a plastic rope base. The
fibers formed a thick nap along the entire length of the rope, which
floated on the oil/ water interface.
The six oil mops used on the device were each 22.86 cm (9 in.)
in diameter and about 15.24 m (50 ft) long. The continuous lengths of
rope mop were laid on the water beneath the center of the catamaran and
pulled on board at the stern to be squeezed by the wringers before being
returned to the water's surface.
VIDEO AND PHOTOGRAPHIC DOCUMENTATION
Cameras provided visual documentation of test layout, equipment,
and performance characteristics. A black-and-white TV camera in a
waterproof case provided underwater video, which was recorded on 2.54-cm
(1-in.) video tape using a recording deck. Topside and tank-side window
coverage was provided by two 16-mm movie cameras and a 35-mm slide
camera.
TACHOMETER DESCRIPTION
A magneto tachometer was mounted on the frame of a Mark II-9D
engine (Figure 3). A similar tachometer to measure the bridge speed was
mounted on the axle of the bridge wheel. The output of each tachometer
went into a differential voltmeter for measuring the relative velocities
between bridge speed and rope-mop speed. A separate voltmeter measured
the rpm of the 22.86-cm (9-in.) diameter squeegee roller, from which
rope-mop speed could be directly determined.
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Oil Mops
Outlet from Oil
Collection Pans
Shaft for Tachometer
Outboard Motor
Compartment
Bow Modification
Assembly
Figure 1. Top view of the OMI-ZRV skimmer.
Oil Containment Pans
Mark II-9D
Mop Engines
\\vCv
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Wringer Housing
23.87-cm (9.4-in.) Dia. Wheel
Magneto Tachometer
1
r
I 22.86-cm
v— (9-in.) Dia.
Squeezing
Roller
11
x 2
1 '
\
•
C~
> — 17
Di
3.87-
s — *
.78-(
.a. Wl
Contac
Point
Electrical Outlet
FRONT VIEW
SIDE VIEW
Figure 3. Schematic diagram of the tachometer and reduction wheels.
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TEST FLUID DESCRIPTION
Sunvis 7 oil was the sole test fluid distributed during the test
program. The properties listed below were determined in the OHMSETT
laboratory from a sample taken during testing:
Specific gravity 0.859
Interfacial tension .... 10.7 x 10~3 N/m @ 22.7°C (73°F)
(tested with OHMSETT tank water, 16 ppt salinity)
Surface tension 32.5 x 10~3 N/m @ 22.7°C (73°F)
% Water and Sediment 0.1% Sediment
Viscosity 65.0 x 10~6 m2/s @ 1.5°C
(tank water temperature)
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SECTION 4
TEST PLAN AND PROCEDURES
TEST RATIONALE
To fully evaluate and optimize device performance within the given
test time, a test matrix was developed to determine the optimum value
for a given parameter (Table 1), fix it there, and then test variations
of a second parameter. Tests with subsequent parameters were conducted
in a similar fashion. Because of time and weather conditions, some
parameters could not be investigated fully for optimization.
The tests were concerned with measuring the steady state or equili-
brium performance of the OMI-ZRV skimmer. Steady state testing was
qualitatively identified by visual observations during the tests. The
fluid collected by the device was continuously offloaded during a test.
When the color of this stream exiting the dump valves became consistent,
steady state was declared, and the fluid was collected.
At the end of a test run, the quantity of oil/water mixture collected
was measured, and the quality (% oil) was determined through laboratory
analysis. Oil recovery rate, throughput efficiency, and recovery efficiency
were then calculated (Table 2).
PROCEDURES
All performance testing was conducted at OHMSETT by the operating
contractor, Mason & Hanger-Silas Mason Co., Inc., with the guidance of
the OMI personnel. Figure 4 shows a general view of the test set-up and
personnel involvement.
Test fluid contained on the main towing bridge was pumped through a
manifold and nozzle system for distribution onto the water's surface
approximately 15.2 m (50 ft) forward of the test device. To ensure that
the oil did not mix into the water column upon delivery, a splashpan was
used with the nozzle, system and a smooth slick was laid on the water
surface. To ensure, a high percentage of encounter, 1.9-cm (0.75-in)
diameter polypropylene guide ropes were used to contain and direct the
oil into the device. Oil thicknesses were calculated from the speed of
tow, encounter width, and distribution rate.
A test run required that proper procedures were followed before,
during, and after the test. The rope mops were brought up to the desired
speed with the off-loading pumps operating and the dump valves open.
-------
TABLE 1.
oo
Test
no.
1-1
1-2
1-3
1-4
2-1
2-2
2-3
2-4
3-1
3-2
3-3
3-4
4-1
4-2
4-3
5-1
5-2
6-1
6-2
6-3
6-4
7-1
7-2
7-3
7-4
Oil
type
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun ,7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 7
Sun 1650
Sun 1650
Sun 1650
Sun 1650
Sun 1650
Sun 1650
Sun 1650
Sun 1650
Tow
speed
1.0
1.5
2.0
2.5
OPT
OPT
OPT
OPT
1.0
1.5
2.0
2.5
2.5
2.5
2.5
OPT
OPT
1.0
1.5
2.0
2.5
1.0
1.5
2.0
2.5
Oil*
thick
nun
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
5
8
3
3
3
3
3
3
3
3
Dist. Wave
rate
x(10~3m3/s)
4.16
6.24
8.33
10.41
TBD
TBD
TBD
TBD
4.16
6.24'
8.33
10.41
10.41
10.41
10.41
TBD
TBD
4.16
6.24
8.33
10.41
4.16
6.24
8.33
10.41
Calm
Calm
Calm
Calm
Calm
Calm
Calm
Calm
0.6 m*
0.6 m
0.6 m
0.6 m
Reg 1
Reg 2
Reg 3
Calm
Calm
Calm
Calm
Calm
Calm
0.6 m
0.6 m
0.6 m
0.6 m
Belt
speed
ZRV
ZRV
ZRV
ZRV
+
OPT
OPT
OPT
OPT
OPT
OPT
OPT
OPT
OPT
ZRV
ZRV
ZRV
ZRV
ZRV
ZRV
ZRV
ZRV
ZRV
ZRV
: •* *
Tension
Initial
Initial
Initial
Initial
Initial
Initial
+
OPT
OPT
OPT
OPT
OPT
OPT
OPT
Initial
Initial
Initial
Initial
Initial
Initial
Initial
Initial
Initial
Initial
Wave Generator
Stroke RPM
cm
7.6
7.6
7.6
7.6
11.4
51.2
19.0
7.6
7.6
7.6
7.6
35
35
35
35
30
24
15
35
35
35
35
Wave
H,L,T
m,m,s
0.5, 5.2, 1.9
0.42, 10.7,2.7
0.36, 20.1,4.6
+, - Slight increase or decrease in belt speed or tension from initial setting
* Harbor chop
-------
Teit
no.
Tow
bpced
01/3
Wave
cund.
Uist.
vul .
m1
Dlst./Rec,
time/time
bee/sec
Dlst.
rate
x(10"!m5/
Slick
thick.
y ) mm
Hop X Enc.
bpeed
m/a
DUcrece
Sam. A
* oil
bumplut* Furfurmance chtiracierlutica
Sum. i)
2 oil
Oil
rec.
m1 :
Oil rac.*
rate
n(lO~i/m>/a)
Rec.*
eft.
t
Throughput*
efficiency
X
1-2
2-1
2-2
5-1
3-1
3-2
5-1R
5-2
1.54,
1.7d
1.27
1.54
1.03
1.54
1.54
1.54
Culm
Culm
Calm
Calm
0.6 m
0.6 in
Calm
Calm
0.50
0.50
0.44
0.82
HC+ 0.35
HC 0.50
0.83
1.39
59.8
50.0
60.2
60.6/56.8
60.1/63.6
60.2/50.0
60.0/48.2
59.7/62.8
8.39 3
10.03 3
7.23 3
13.58 5
5.76 3
B.24 3
13.91 5
23.21 8
1.54
1.54
1.54
1.54
1.03
1.54
1.54
1.54
100
100
100
100
90
85
90
95
4.7
20.9
20.6
17.4
10.2
10.5
18.1
17.5
12,6
27.3
24.8
29.7
19.4
10.2
21.3
30.6
0.047
0.102
0.117
0.088
0.08 A
0.066
0.104
0.1J2
0.78
2,04
1.94
1.55
1.32
1.33
2.15
2.11
8.7
24.1
22.7
23.6
U.8
10.4
19.7
24.1
12.4
27.2
J5.8
14.2
35,5
20.7
18,6
13.3
*See Appendix A fur tltf init ton.
•Htarbor ctuip.
-------
Bridge Drive Motor
Offices/
Lab/Shop
Building
Test Director
Oil Distribution
Recovery Pump
Underwater Video
Photographies
OMI Personnel
OMI Personnel
Filter/VDU Operator
M)) Bridge/Wave
Operator
(lO) Chemistry lab
Uj) Project Engineer
Control Tower
(5)
Auxiliary Bridge
Collection
Barrels
Pumps
///„/' / „' i1,' /•
X/xv
acuum
Oil Distribution
Manifold"
Wave Flaps
TJF
n.2) Data Analysis
Filter
System
Figure k. Test set-up for the OMI-ZRV skimmer.
10
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The bridge was brought to speed, and then oil distribution was begun.
The dump valves were closed when it was seen that the pumps were pumping
not just water but a consistent oil/water mixture. The fluid was then
pumped from the device to collection barrels on the auxiliary bridge.
Recovery efficiency samples were taken from near the pumps' discharges
at the midpoint and near the end of the test run. Oil was distributed
for about 1 min. for each test run. After the device passed over the
end of the slick, the rope mops were stopped and the bridge brought to a
halt. The oil containment pans were then flushed with 19 liters (5 gal)
of water, and pumping was continued until the pans were empty. The
amount of sample collected was determined by measuring the fluid height
in the collection barrels and converting that height into volume.
Thirty minutes were allocated for oil/emulsion/water separation by
gravity. The water was then drained, and the remaining oil/emulsion
height measured. A sample was taken from the emulsion layer for labor-
atory analysis. The remaining oil/emulsion was mixed for 5 min. and
then sampled again. Each collection barrel was measured and sampled
similarly. Data taken during the tests were: test number, date, time,
tow speed, rope-mop speed, oil distribution rate, oil distribution time,
recovery time, wave condition, and type of oil.
Problems encountered with the weather and the device prevented the
above-mentioned procedures from going smoothly. The two main factors
were the ice that formed on the rope mops overnight and the inability of
the wringers to consistently drive the full complement of ice-free rope
mops at speeds exceeding 1.5 m/s (3 kt). In the morning, the rope mops
had to be broken free of the ice that formed in the deck trays. Sometimes
not all of the ice was removed from the nap of the rope. This ice would
catch in the wringer and delay or interrupt a test. By afternoon, the
ice was removed completely, but the drive engines could not readily
engage the rope mops immediately. They had to be coaxed up to speed by
running the mops in water, thus wringing and throwing any precharge of
oil out of them. During a test, the drive engines would occasionally
slow or be slowed to prevent stalling.
11
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SECTION 5
RESULTS AND DISCUSSION
Because of the short test time and amount of data available, the
OMI-ZRV skimmer must be examined qualitatively. Eight oil-collection
test runs were made over 2 days. Two of those runs were subjected to
steady state interference such that the data collected were non-represen-
tative of the device capability. Test run 1-2 was made before the
catamaran was adequately trimmed. Under tow, the craft nosed down
sufficiently to dip the forward cross member into the oil slick and
create turbulence. Oil entrainment into the water column occurred
before the rope mops contacted the oil slick. During test run 5-1, the
rope mops were slowed down and sped up continuously to prevent engine
stall. This probably occurred because it was the first run of a cold
day after a very cold night during which ice had formed on the rope
mops. Near the end of the test, the far port-side rope mop parted,
and that engine was stopped. The 5-1 test run was repeated; 1-2 was
not.
Some difficulties were discovered during testing that affected the
analysis. Recovery time was not recorded until the second day of
testing, where a discrepancy was noted between it and distribution time.
Also, a definite time for starting the rope mops could not be established.
Such unknowns make quantitative design analysis difficult.
DEVICE DISCUSSION
The contact/collection area beneath the catamaran was not adequately
covered by the rope mops or protected from the wake developed by the
bows. Even with the bow modifications, enough wake was produced to
channel the oil to the center of the device. This effect proved dis-
advantageous because the rope mops were divided into two groups of three
each. One group was driven and wrung by the port oil mop engine and the
other by the starboard engine. The inner mops of the two groups were
separated about 38.5 cm (15 in.), centerline to centerline, upon coming
over the stern roller and returning to be wrung. A good deal of oil
escaped down between the groups of oil mops, either because of poor
oil/rope-mop contact or inadequate oil retention power of the inner most
rope mops. Hardly any oil was left on the port or starboard sides
beneath the craft after the slick reached the stern. The outboard rope
mops appeared to contribute only water to the collection pan, as was
evidenced by the color of the "rooster tails" that sprayed up from the
rope mops as they came over the stern roller. The outer sprays were
white, but the center ones were a dark pink from the dyed oil. Throughput
12
-------
efficiency for each test run was calculated based on 75% rope-mop coverage
of the area beneath the catamaran. With the bow wave, perhaps this per-
centage is sufficient, but the center area should have the greatest
coverage.
Observation of the tests from the underwater window revealed that
the unrecovered oil was entrained well into the water after the device
passed. If the catamaran had been propelled with the optional outboard
motors, entrainment would have been more severe.
The drive motors should be larger to improve rope-mop handling
capability and increase rope-mop speed above 1.54 m/s (3 kt).
Ice that formed on the rope mops had to be removed largely by hand
before the motors could be coaxed into completing the job. Only then
could testing resume. New rope mops could not be processed until they
were run singularly through the wringer for flattening. Occasionally
during testing, the motors would nearly stall, so the speed of the mops
would be decreased and then brought up again to keep them running.
Before additional testing, the skimmer should be trimmed properly.
Weights were placed in the outboard motor compartments, and a towing
bracket was fabricated to prevent the device from nosing down under tow.
During the first test, the front cross member of the catamaran made
contact with the oil slick.
The oil collection pan beneath the port wringer would not drain as
rapidly as the starboard pan. Thus the pump sucked air from the empty
pan rather than fluid from the full pan. The loss of oil overflowing the
full pan was minimal— about 7.6 liters (2 gal)— because the device
recovery time was only 1 min. Longer operation would drastically increase
the loss, because the overflow began near the end of the test run. The
collection pans should not be drained to a "Y" coupling and pumped from
there. Two separate drains or one collection pan should be used.
A catch-basin on the stern of the catamaran should be installed to
recover the fluid that is flipped from the rope mops as they travel over
the stern roller and head toward the wringers.
In the future, the rope mops should be installed before the testing
at the correct lengths. Trial and error adjustments in rope-mop length
required over half a day in tank time, and the adjustments, which required
finger dexterity to tie and untie the wet rope, had to be done in sub-
freezing temperatures.
OPERATION DISCUSSION
The rope mops should not be run before the oil slick passes beneath
the device. Continuously running the rope mops in water and wringing
them strips the necessary precharge of oil from the fibers and loads the
collection pans with water. This effect is evidenced by the oil slick
distributed by the rope mops after the end of the distributed oil slick
is behind the device. In such an instance, oil is lost to the water
13
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from the rope mops. When a non-precharged rope mop encounters an oil
slick, time is required to displace the water and develop a sufficient
oil film on the fibers. Evidence of this fact exists in the increase of
oil content shown in the second discrete sample over the first. Running
the rope mops slightly slower or faster than ZRV should be examined more
closely. The data indicate that such operation improves performance.
Such improvement would stand to reason because the oil would be forced
onto the fibers and into apertures too small for the oil to enter on its
own accord.
Maximum recovery efficiency was possibly never reached in testing.
An increase in the percentage of oil collected was noticeable in the
discrete samples taken toward the end of the test runs. The average
increase was 28% (discounting tests 5-1 and 1-2) over a period of about
30 s. Even that oil percentage was still low (-20%) and probably would
have increased somewhat if longer runs had been made. This result indicates
that a precharge of oil is necessary on the rope mops.
DATA ANALYSIS
A qualitative data analysis (Figures 5, 6, and 7) discloses the
following trends peculiar to the device operating under the given conditions.
Recovery Rate
1. The recovery rate did not appear affected by towing the device
slower or faster than the belt speed. Thus specific factors
must be examined further before a trend can be identified.
These factors could have individually affected device performance
and thus possibly interacted to cancel or complement each
other. They are: (a) greater oil encounter rate was seen by
the device at the faster-than-ZRV tow speed in order to maintain
slick thickness (positive,effect); (b) more fibers were processed
for a given volume of oil at the slower-than-ZRV tow speed
(positive effect); (c) a greater wake was produced at the
faster-than-ZRV tow speed, which left less oil to contact the
outboard rope mops (negative effect); and (d) one or more of
the previous conditions could give the rope mops the necessary
and sufficient precharge more quickly and thus increase efficiency
(positive effect).
2. The recovery rate did not appear'to be affected by tow speed
in a harbor chop condition. The wave condition alone appeared
to affect recovery rate. The change in slick thickness at
1.54 m/s (3 kt) in calm water did not drastically alter results,
while a slightly shallower slick in waves did. A similar test
in calm water is needed to confirm whether the wave condition
caused the change or the rope mops were at their saturation
level in a 5 mm slick.
14
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co
o
B
o
o
X
a
3
M
O
2.50
2.00
1.50
1.00
0.50
0.00
TEST NO.
BELT SPEED = 1.54 m/s
NO WAVE
SLICK THICKNESS = 3tnm
BELT SPEED = ZRV
0.6m H.C.
SLICK THICKNESS = 3mm
TOW SPEED = 1.54 m/s
BELT SPEED = ZRV
NO WAVE
(2-2) (2-1)
1.27 1.78
TOW SPEED (m/s)
(3-1) (3-2)
1.03 1.54
TOW SPEED (m/s)
(5-1R) (5-2)
5.0 8.0
SLICK THICKNESS (mm)
Figure 5. Oil recovery rate of the OMI-ZRV skimmer as a function of slick thickness,
tow speed, wave condition, and belt speed for Sunvis 7 (light) oil.
-------
6-2
B
M
ft,
PH
W
H
33
I
BELT SPEED = 1.54 m/s
NO WAVE
SLICK THICKNESS = 3mm
TOW SPEED = 1.54 m/s
BELT SPEED = ZRV
NO WAVE
BELT SPEED = ZRV
0.6m B.C.
SLICK THICKNESS = 3mm
(2-2) (2-1)
1.27 1.78
TOW SPEED (m/s)
(3-1)
1.03
TOW SPEED
(5-1R) (5.2)
5.0 8.0
SLICK THICKNESS (mm)
Figure 6. Throughput efficiency of the OMI-ZRV skimmer as a function of slick thickness,
tow speed, wave condition, and belt speed for Sunvis 7 (light) oil. (See
Appendix A for method of calculation).
-------
W
Ł
W
§
u
25.0
20.0
15.0
10.0
5.0
0.0
TEST NO.
BELT SPEED = 1.54 m/s
NO WAVE
SLICK THICKNESS = 3mm
BELT SPEED = ZRV
0.6m B.C.
SLICK THICKNESS = 3mm
TOW SPEED =1.54 m/s
BELT SPEED = ZRV
NO WAVE
(2-2)
1.27
(2-1)
1.78
TOW SPEED (m/s)
(3-1) (3-2)
1.03 1.54
TOW SPEED (m/s)
(5-1R) (5-2)
5.0 8.0
SLICK THICKNESS (mm)
Figure 7. Recovery efficiency of the OMI-ZRV skimmer as a function of slick thickness,
tow speed, wave condition, and belt speed for Sunvis 7 (light) oil.
-------
Throughput Efficiency
1. Throughput efficiency decreased when the device was towed
faster than the rope-mop speed. Although a greater oil encounter
rate was seen by the rope mops during the test, it was probably
in a thick, narrow slick in the center of the device because of
the greater wake at the higher speed.
2. Throughput efficiency was inversely affected by tow speed at
ZRV belt speed. This effect seems logical, since the rope
mops had a longer contact time with the oil and less wake was
produced by the catamaran at the slower tow speed.
3. Throughput efficiency was inversely affected by slick thickness.
This result is reasonable, since the oil is channeled by the
wake to the center rope mops, which are limited in the amount
of oil they can retain. In addition, throughput efficiency is
inversely proportional to the amount of oil distributed.
Recovery Efficiency
1. Recovery efficiency was unaffected by towing the device faster
or slower than ZRV. Again, as discussed with recovery rate,
many factors could have interplayed to produce such a result.
2. Recovery efficiency was inversely related to tow speed in a
harbor chop wave condition. This result was possibly due to
the increased wake and surface disturbance created by the
hulls at the higher speed. Such disturbances would wash water
over the rope mops, exposing all of the fibers and thus collecting
more water. The addition of a harbor chop condition would
have extended any speed effect above the limit found in calm
water. At the slower speed, the surface disturbance was not
as great and the rope mops were being processed more slowly,
so contact time was increased.
3. Recovery efficiency was directly related to slick thickness.
This effect is reasonable since more oil was available and the
fibers were oleophilic.
18
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APPENDIX A
EQUATIONS AND DEFINITIONS
1. Oil Recovery Rate (m3/s)
Procedure A -
O.R.R. oil recovered
oil distribution time
*Procedure B -
O.R.R. _ oil recovered
recovery time
2.** Throughput Efficiency (%)
T.E. _ oil recovered
(oil distributed) (%enccounter) ( . 75)
3. Recovery Efficiency (%)
R.E. _ % oil content in samples taken at
pump discharge
*Recovery Time - time from the first contact of oil with the mop
to the last. This definition was used for test 5-1 and following tests.
**Based on 9-in. mop diameter x 6 mops = 54 inch coverage width.
54 inch mop coverage ^75
72 inch hull separation ="
19
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APPENDIX B
FACILITY DESCRIPTION
The OHMSETT facility, owned by the U.S. Environmental Protection
Agency, is located in Leonardo, New Jersey. The facility provides an
environmentally safe place to test and develop devices and techniques
for the control and cleanup of oil and hazardous materials spills.
The primary feature of the facility is a pile-supported, concrete
tank with a water surface 203.3 m (667 ft) long by 19.8 m (65 ft) wide,
and a water depth of 2.44 m (8 ft). The tank can be filled with fresh
or salt water. It is spanned by a towing bridge that can tow loads up
to 15,400 kg (34,000 lb) at speeds up to 3.05 m/s (6 kt) for a duration
of 45 s. Slower speeds yield longer test runs. The towing bridge is
equipped to lay test fluid on the surface of the water several feet
ahead of the device being tested, such that reproducible thicknesses and
widths of slicks can be achieved with minimum interference by wind.
The principal systems of the tank include a wave generator, absorber
beach, and filter system. The wave generator and absorber beach can
produce regular, minimum-reflection waves up to 0.61 m (2 ft) high and
24.38 m (80 ft) long, as well as a series of reflecting, complex waves
meant to simulate the water surface of a harbor or estuary. The water
is clarified by recirculation through a 0.13 m3/s (2,000 gal/min) diato-
maceous earth filter system. Clarification permits underwater photo-
graph and video imagery, and removes the hydrocarbons that enter the
tank during testing. The towing bridge has a built-in skimming board
that moves expended test fluid to the north end of the tank for cleanup
and recycling.
Tests at the facility are supported from a 650-m2 (7,000-ft2)
building adjacent to the tank. This building houses offices, a quality
control laboratory (for test fluids and tank water), a small machine
shop, and an equipment preparation area.
The government-owned, contractor-operated facility is available for
testing purposes on a cost-reimbursable basis. The operating contractor,
Mason & Hanger-Silas Mason Co., Inc., provides a staff of eleven multi-
disciplinary personnel. The U.S. Environmental Protection Agency provides
expertise in the area of spill control technology and overall project
direction.
20
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
I RtPOHT NO.
EPA-600/7-78-060
4 HI LL ANO SUBTITLh
Performance Testing of Oil Mop Zero Relative
Velocity Oil Skimmer
6..PEHFOHMING ORGANIZATION CODE
7 "AUTHOHIS)
Michael K. Breslin
8. PERFORMING ORGANIZATION REPORT NO.
9 PfcRFOHMING ORGANIZATION NAME ANO ADDRESS
Mason & Hanger-Silas Mason Co., Inc.
P. 0. Box 117
Leonardo, New Jersey 07737
12. SPONSORING AGKNCY NAME AND ADDRESS
Industrial Environmental Research Laboratory-Gin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
April 1978 issuing date
10. PROGRAM ELEMENT NO.
1NE623
11. CONTRACT/GRANT NO.
68-03-0490-
13. TYPE OF REPORT AND PERIOD COVERED
Final 11/29/76 - 12/3/76
14. SPONSORING AGENCY CODE
EPA/600/12
15 SUPI'LtMtNTARY NOTES
This study was co-sponsored by the U.S. Coast Guard.
16. ABSTRACT
This research test program was initiated by the U.S. Environmental Protection
Agency (EPA) and the U.S. Coast Guard (USCG) to determine the ability of the Oil Mop
Inc. (OMI) zero relative velocity (ZRV) oil skimmer to recover oil from a water surface
under various conditions.
A fast current (operating range up to 3 m/s (6 kts)), prototype skimmer was de-
signed and built by OMI and delivered to the'Oil and Hazardous Materials Simulated
Environmental Test Tank (OHMSETT) to be tested. The principle of operation was based
on adsorbing oil onto oleophilic fibers woven into a rope. The rope and fibers were
then squeezed by wringers to remove the oil into a recovery basin. The device was
rigged, trimmed and then towed into a controlled oil slick while being operated and mon
itored for oil recovery. Device operating speed, oil slick thickness, tow speed, and
wave conditions served as controlled independent variables. The fluid recovered was
sampled during and after the test run to determine device performance. Results of the
tests were evaluated in terms of recovery rate, recovery efficiency, and throughput
efficiency (i.e., the amount and quality, or percent oil, of fluid recovered versus the
amount of oil distributed). Because of adverse weather and problems with the device,
the testing program was of short duration. Only a few tests were run, so parameters
could not be completely optimized.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Water pollution
Performance tests
Oils
Adsorbents
Boats
b.lDENTIFIERS/OPEN ENDED TERMS
Oil skimmer
Oil spill cleanup
Protected waters
Skimming vessel
MOP ZRV
COSATI Field/Group
68D
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
29
20. SECURITY CLASS (This page)
UNCLASSIFIED
22 PRICE
EPA Form 2220-1 (9-73)
A U.S. GOVERNMENT PRINTING OFFICE: 1978-260-880/39
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