EPA-R2-73-115
FEBRUARY 1973 Environmental Protection Technology Series
A Small Vacuum
Oil Skimming System
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-115
February 1973
A SMALL VACUUM
OIL SKIMMING SYSTEM
by
Ralph H. Cross, III
Project 15080 FVP
Project Officer:
Frank J. Freestone
Edison Water Quality Research Laboratories, NERC
Edison, New Jersey 08817
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, B.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price SO cents domestic postpaid or 35 cents GPO Bookstore
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EPA Review Notice
This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environ-
mental Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
ii
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ABSTRACT
An oil-slick collection system suitable for use on harbor craft
is described. This system employs a pneumatic-powered vacuum
cleaner to collect oil from the water surface by entrainment in
a high-velocity air stream. The components are widely available
commercial items.
Tests show the system to be successful in picking up No. 4 fuel
and lighter oils. The collection rate depends chiefly on the rate
of oil supply to the skimmer.
This report was submitted in partial fulfillment of Project Number
15080 FVP under the partial sponsorship of the Water Quality Office,
Environmental Protection Agency.
iii
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TABLE OF CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Collection System Details 7
V Application 15
VI Field Experience and Data 17
VII Acknowledgments 19
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FIGURES
Number
1 Pick-up System 6
2 Oil Removal from Drum
with Vacuum Head 8
3. Horizontal Skimmer Head 11
4 Boom Corner Skimmer Support
Unit Assembly 14
vi
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SECTION I
CONCLUSIONS
The system described herein, for use by readily available harbor craft
to pick up floating oil, has been shown to be effective in picking up No.
4 fuel and lighter oil in tests. No. 6 fuel oil, especially when cold,
tends to clog the system. The components are generally available off-the-
shelf items. The only power required is compressed air, although in
large quantities.
Oil collection rates are limited (on small spills) primarily by the
rate of approach of oil to the intake.
By the proper operation of the system, oil leaks can be eliminated.
Operating personnel can, therefore, avoid physical contact with oil, and
slipping accidents on oily decks can be prevented.
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SECTION II
RECOMMENDATIONS
1. The pick-up system described herein was designed originally as
auxiliary equipment to enable the clean up of oil and other test
substances used in evaluating fire streams and various types of
boom as spill control devices. While it works extremely well with the
less viscous oils, the aperture and tubing diameters are probably too
small to enable the rapid pick-up of the viscous fractions such as
bunker "C"; therefore, development of a larger system is suggested.
2. When placed at the apex of a boom corner, with fire streams pushing
the oil into the corner, this device proved to be very efficient. The
effectiveness of any skimmer depends on the thickness of the oil layer
in its vicinity. We, therefore, recommend that any skimmer, whenever
possible, be operated as close as possible to the apex of a corner,
pocket, or cul-de-sac into which the oil is being herded.
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SECTION III
INTRODUCTION
The oil slick collection system described in this report is a vacuum-
operated system which entrains oil, water and small debris in a high-
velocity air stream for delivery to a vacuum tank separator, from which
the oil can be pumped to storage containers and the water discharged.
This system was designed to fill a perceived need for a system to pick
up harbor oil spills that would be adaptable to fireboats, towboats
and other available harbor craft.
The use of harbor craft for rapid initial response is attractive
primarily because of their availability. Fireboats, for example, are
on 24-hour call in many major ports, and can arrive within 10 - 15
minutes of a call (in New York Harbor). Coast Guard craft also have
emergency response capabilities, and towboats are generally available
in most ports. Moreover, these craft have other jobs to do; therefore,
the cost of maintaining craft exclusively for oil spill control is
avoided. This same fact poses complications, however. Equipment
cannot be stored on board that would impair these crafts' primary
functions, and both the equipment and method of operation should preclude
the spillage of oil on personnel or decks. Fireboats, in particular,
may have to respond to a fire from an oil spill, and oily 'decks would
pose a substantial safety hazard.
The system described in this report is an application of the air-
entrainment pick-up process found in the use of the vacuum-type catch
basin cleaners to pick up oil slicks, within the constraints generated
by the use of harbor craft. The particular prototype system con-
structed was designed around the facilities available on the fireboats
of the Fire Department of New York; while many variations are possible
to meet local conditions and take advantage of locally available
components, further development of engineering design criteria is
still underway.
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FROM AIR SUPPLY
VAC-U-MAX
2 VACUUM HOSE
55 GAL. VACUUM DRUM
RETURN TO
SKIMMER AREA
FROM AIR
SUPPLY
PUMP
FIGURE I
PICK-UP SYSTEM
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SECTION IV
COLLECTION SYSTEM DETAILS
The system can be broken down into the following components: skimmer
head, delivery hose, vacuum/separating tank, vacuum pump, water
removal pump, plumbing connections, and oil storage containers
(Fig. 1). The analysis and construction of each component, and the
interaction between components, are detailed below.
Vacuum/Separating Tank
The purpose of the vacuum/separating tank is twofold; first, to
separate the oil-water mixture from the air, which then passes out
through the vacuum pump; and second, to provide adequate residence
time for the oil and water to separate. The air-liquid separation
poses no difficulty, especially with the commercial vacuum cleaner
head used. (It is designed to match the top of a 55 gal. drum). As
the oil-water mixture does not pass through pumps or valves, the
formulation of stable emulsions is avoided, and gravity separation
occurs within a minute or two. In batch processing (using, say,
several 55 gal. drums, and moving the vacuum head with the pickup hose
attached from one to the next as each fills), a waiting period of 2 - 5
minutes should be allowed before decanting the water from beneath the
layer of collected oil. The drum must be designed to take the maximum
vacuum with a closed or clogged inlet without collapse.
The vacuum head is a pneumatically powered commercial unit manufactured
by Vac-U-Max, Belleville, New Jersey, model 55-2D, with two venturi
jets. Air requirements are approximately 84 SCFM at a minimum of
60 Ib/in , and it will pull a vacuum up to 13 inches of mercury, or
approximately 15 feet of water. It is fitted with a float control
which breaks the vacuum when the liquid level nears the top of the drum
beneath. The pneumatic powered unit was chosen for the following reasons:
1. Adequate compressed air is available on the fireboats.
2. No sparks, heat or moving parts in the head, minimizing fire
hazards and simplifying maintenance.
3. Light weight (about 45 Ibs).
4. No hazardous electric extension cords or gasoline required -
minor air leaks are of ho consequence.
Data on air flow rate vs. vacuum for the unit do not appear readily
available, but it was found that with a 2 in. inside diameter hose,
water and No. 4 fuel oil were swept directly along, with no visible
ponding or accumulation of water in low spots in the hose (transparent
plastic), while a section of 3 in. hose connected in the pickup line
during the same test showed a substantial amount of ponding. Some
rough estimates based on the fall velocity of large drops, and the
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OIL DELIVERY HOSE
55 GAL.
VACUUM DRUM
VACUUM HOSE-
FROM AIR SUPPLY-
55 GAL.
STORAGE DRUM
FIGURE 2
OIL REMOVAL FROM DRUM WITH VACUUM HEAD
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suction and entrainment at the pickup head suggest that the air velocity
in the 2 in. hose was at least 75 - 100 ft/sec, for an air flow rate
of at least 90 - 120 cfm. The rated flow at no vacuum is approximately
200 cfm.
Water Removal Pump
Where large amounts of water xjill be collected with the oil, it is
advantageous to have a pump to remove water more or less continuously
from the bottom of the drum, through a fitting mounted there. Although
oil water separation will take place in the tank while the vacuum head
is operating, some simple baffling to enhance this process is recommended,
when operating in this way.
The pump selected and obtained for test purposes was a pneumatic double-
diaphragm pump, manufactured by Wilden Pump and Engineering Co., Colton,
California, Model M-15.
This unit was selected since it is self-priming, relatively non-clogging,
capable of extracting water against the vacuum in the tank, and has a
pneumatic power source.
For the batch processing mode of operation, the vacuum cleaner head was
modified to allow it to pull a vacuum on the 3/4" vent hole of a standard
oil drum. This makes it possible to transfer the oil from the open-
ended drum into standard drums for storage. The vacuum hose is connected
to the 2" fill hole of the standard drum. (See figure 2)
Hose
The hose used in the prototype system was a 2 in._I.D. clear plastic
vacuum hose with spiral stiffening coils, also made by Vac-U-Max. The
hose leads directly from the skimmer head to the tank, with no valves in
the line, to avoid excessive emulsifying effects on the water-oil mixture.
The clear plastic was chosen to permit observation of flows inside. This
worked well except when picking up No. 6 fuel oil, in which case the
inside of the hose was coated with an opaque film of oil.
An estimate of the air flow rate required for a given hose diameter can
be obtained as follows:
Consider the free-fall velocity of a large drop of water or oil, in air;
the upward air velocity must exceed that. For a 1/2 in, diameter spherical
drop, the fall velocity is approximately 60 ft/sec.
Skimmer Head-Vertical Pipe
This skimmer head, in its simplest form, consists of a short piece of
2 in. pipe on the end of the vacuum hose. With careful handling, this
arrangement minimizes the amount of oil on the. outside of the equipment,
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and thus the amount of oil liable to get on the boat deck after retrieval.
This skimmer head is essentially a model of catch basin vacuum cleaner
truck pick-up, often used in a variety of ways for oil slick pick-up.
The problem of entraining oil and water in the air stream entering the
skimmer and vacuum hose is similar to the problem of selective
withdrawal from a density-stratified fluid, except that the density
difference is much larger than in the cases usually studied.
The basic entrainment mechanism is based on the pressure drop in the
inlet to the vacuum line, equal to the "velocity head" of the air flow
in the pipe. When the inlet is near the water surface (say, half a
pipe diameter away) the surface responds to this pressure drop by
rising towards the inlet, where the liquid is entrained in the air
flow. As the inlet moves closer to the water surface, the flow area
of the cylindrical surface between the pipe end and the water decreases
until it becomes less than the cross-sectional area of the pipe; these
two areas are equal when the pipe end is half a pipe radius R away from
the water surface. As the pressure drop is governed by the maximum
velocity into the pipe, and this velocity increases as fhe cross-section
decreases, the pressure drop will be approximately four times that with
the inlet well away from the water surface. Thus, it appears that the
end of the inlet should be fixed between 0.5 R and 1.0 R above the water
surface, with the air flow rate adequate to give an inlet pressure drop
(in, say, feet of water) equal to or greater than the clearance.
Mounting the inlet is subject to these criteria:
1. The clearance between the pipe end and the water surface should,
as much as possible, be controlled within the above limits.
2. The mounting system must not obstruct the flow of oil or air
to the inlet.
The common way of mounting the intake pipe from a catch basin vacuum
truck is to suspend the pipe from the truck over the edge of a dock;
depending on the operator's vision, attention, and judgment to main-
tain the proper clearance. In practice, this has two major drawbacks:
operator inattention, and the inability to respond to waves. These
systems also have a rather low static lift (typically 36 - 60 inches
of vrater), so that when the end of the pipe goes under the water
surface, flow ceases; moreover, the suspension system usually "gives"
enough so that the pipe is pulled down, and tends to stay underwater.
The prototype system requires more careful control for effective
performance, as the dimensions are smaller; however, the penalty for
immersion of the pipe end is much less, as the static lift (approximately
15 feet of water) is generally enough to clear the pipe. Moreover, the
unit is small enough so that only relatively small, unobstructive floats
are required to control the clearance, allowing occasional immersion
with passing "chop", or locally-generated wind waves.
10
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TO VACUUM TANK
FOAM FLOAT BLOCKS
FIGURE 3
HORIZONTAL SKIMMER HEAD
11
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Skimmer Head - Horizontal Pipe
Basically this skimmer consists of the open end of a short, horizontal
section of 2 in. pipe at the water surface, vacuum tubing, and flotation
(Fig. 3). Since part of the opening is below the surface, fluid will
continue to flow through it so long as the water, levels on either
side are unequal. The suction hose, by constantly drawing off the
fluid, maintains the flow of fluid into the pipe. In this respect,
the horizontal suction head behaves like a miniature veir type skimmer.
However, the suction has an additional important function. It creates
in the immediate neighborhood of the orifice, a rather high velocity
air flow which strongly augments the inward flow of fluid. The flota-
tion is needed to keep the orifice at the air/water interface.
For maximum effectiveness any pick-up device must be in the vicinity
of the highest oil concentration. Yet, such a device tends to reduce
the thickness of oil around it, and, if left to itself, it becomes
increasingly inefficient as it thins out the oil layer near it. If
the area is large enough and the oil thin enough, it will eventually
cease to draw any oil at all, and pick up only water. There must be
either a means of moving oil to the pick-up device (e.g., fire streams
or a chemical herder at the edge of the oil slick) or a means of moving
the pick-up device to the highest oil concentration. Ideally, both should
be available.
The main effort in the development of this type of head has been directed
towards improving its controlability. In this respect it has some
advantage over an orifice which remains suspended above the water, be-
cause the flotation automatically assures proper vertical positioning,
and only the horizontal position need be controlled. However, the
bobbing of the device in waves tends to force oil away from it.
In practice, this type of head has usually been affixed to the end
of a long aluminum or rigid plastic tube (a part of the suction tubing)
by which it can be moved as needed from the deck of a boat or from a
pier or dock. Also it can be fitted to the apex of the floating boom
corner which is described in the next section.
Some slight advantage can be realized by flattening the orifice. This
will cause the lower lip to be nearer the surface and tend to improve
the oil/water ratio a little. But elaborate flattened heads which
provide an orifice area substantially larger than the cross sectional
area of the vacuum tubing are counter-productive because the air
velocity into the orifice is so reduced that it provides no significant
assistance to the oil flowing in, and the entire apparatus becomes a
rather inefficient weir type skimmer. While it is true that low
vacuum at the orifice tends to cause less mixing, eventually the oil
and water must enter tubing where the air velocity is much greater
(especially if a substantial lift is required) and the two fluids will
thoroughly mix there. Furthermore, as mentioned elsewhere in this report,
12
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stable emulsions are not formed in the high vacuum hoses, and
decanting is only a minor problem.
13
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3/4 THINWALL
CONDUIT
SPREADERS
FLATTEN END 8
SCREW TO fX3"
2" PLASTIC PIPE
CONN. TO VAC. HOSE
2"X6° BEVELED
30°EACH EDGE
SHELF BRACKET
STYROFOAM
FLOATS
WATERPLANE AREA
I FT.2-X 8"HIGH
MARINE OR EXT. GRADE
AB PLYWOOD
WEIGHTS
'/4"MASONITE ON OUTER FACE —
BOLT THRU TO '/2" PLYWOOD,
'4" THREADED ROD.
1X3" GLUED a NAILED TO PLYWOOD
FIGURE 4
BOOM CORNER SKIMMER SUPPORT UNIT ASSEMBLY
14
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SECTION V
APPLICATION
The above concepts and prototype system can be applied in several ways:
hand-held, from a small boat or pier near the water level; fitted, with
appropriate mounts, into a moored boom system; and as part of a moving
skimmer to be mounted on a boat.
Hand-Held
For hand use, the operator must have a fairly stable platform just above
the water line, as from a small boat alongside the harbor craft. Exper-
ience has shown that adequate control cannot be achieved manually from
a deck several feet above the water with the vertical head system.
Moored
A floating "boom corner" mount has been designed and constructed for the
system, as shown in Fig. 4. The V-shape is intended to be fitted between
sections of boom, so the oil can be herded conveniently to the skimmer
head with fire streams, currents, etc. Each 1/2" plywood panel is 3 ft
high by 4 ft long, and designed to float with a draft of two feet. The
styrofoam float blocks are 8 in. high with a water plane area of 1 ft?
each, and are through-bolted with a 1/4 in. masonite cover plate to the
plywood. The spreaders are 3/4 in. thin wall conduit, flattened on the
ends for fastening. For preliminary trials, the boom (Kane boom, 36"
high) fabric was screwed to the panels and backing blocks with wood
screws and fender washers. The components shown in Fig. 4 were selected
for availability, so that the boom corner could be rapidly assembled in
the field from locally available materials. Construction time was a few
hours (with one man) for the corner, with spray painting.
In operation, with fire streams herding the oil towards the "boom corner"
and with the suction head operating at its apex, this system proved to
be extremely efficient.
15
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SECTION VI
FIELD EXPERIENCE AND DATA
Horizontal Head
The horizontal head proved effective in picking up No. 4 fuel oil in
calm water. Attempts at picking up patches of No. 6 fuel oil, however,
were thwarted by clogging of the vacuum line with a mixture of debris
and the extremely viscous oil, and by difficulties in maneuvering the
fireboat. The mobility of the skimmer was found to be a definite asset;
however, the oil-soaked floats and pipe end were messy when retrieved.
Vertical Head
Field experience with vertical-pipe vacuum skimmers is limited to obser-
vations of catch-basin vacuum trucks and to operational tests of the
boom corner skimmer. The most significant observation is that the oil
collection rate in either case is limited by the rate at which oil is
brought to the skimmer.
Catch-basin trucks do pick up oil, with or without sorbents. Examination
of films taken of the intake end show entrainment when the clearance
between the pipe end is less than approximately six inches, half the
diameter of the pipe. Since the advertised air velocity is nearly 300
ft/sec, corresponding to an inlet pressure drop of 20 in. of water, it
is clear that this proximity is required for entrainment and collection.
The boom corner skimmer was mounted in one corner of a closed boom moored
in a triangular shape. Clearance was adjusted to 1/2 - 3/4 in. Pickup
trials were run by dumping 2 gals, of No. 4 fuel oil inside the boom.
The wind blew the oil into the corner, except for some trapped in the
lee of the upwind boom section. As fast as oil would run into the corner,
within an inch or two of the pipe, it would be picked up. Waves occasional-
ly submerged the pipe end, resulting in water being pumped. The vacuum
system was then operated for about two additional hours, with the 54 cu
ft vacuum box ending up about two-thirds full of water, with essentially
all the oil floating on top.
17
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SECTION VII
ACKNOWLEDGMENTS
Practical tests of the system at actual spills and at numerous test
exercises were conducted with the aid of the officers, men and equip-
ment of the Marine Division of the New York Fire Department.
The guidance of Mr. Howard Lamp'l, EPA Project Officer, and the
cooperation of the City of New York and the U. S. Navy in providing
the test basin at Wallabout Creek, Brooklyn, New York, is gratefully
acknowledged.
ft U. S. GOVERNMENT PRINTING OFFICE : 1973—514-153/219
19
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No.
2.
w
4. Title
A SMALL VACUUM OIL SKIMMING SYSTEM
7. Authorfs)
Cross, Ralph H.
9. Organization
Alpine Geophysical Associates, Inc.
tinder contract to
New York City Fire Department
5. Report Date
6.
8. £ ,--Tforming Organization
Report No.
15080 FVP
Type / Repo. •. and
Period Covered
12.
Ewrlr«OMnt*l Protection Agency, ¥.Q.O.
Environmental Protection Agency report
number, EPA-R2-73-115, February 1973.
16. Abstract
The Oil-slick collection system suitable for use on harbor craft is described. This
system employs a pneumatic-powered vacuum cleaner to collect oil from the water sur-
face by entralnment in a high-velocity air stream. The components are widely availdsle
comaercial items.
Tests show the system to be successful in picking up No. 4 fuel and lighter oils. The
collection rate depends chiefly on the rate of oil supply to the skimmer.
This report was submitted in partial fulfillment of Project Number 15080 FVP under the
partial sponsorship of the Water Quality Office, Environmental Protection Agency.
17a. Descriptors
17b. Identifiers
*0il Spills, *Skimming, "Oil-Water interfaces, *Entrainment, "Harbors
!
"Vacuum Skimming Unit, "Compressed Air, "Floating Corner Skimmer
"Fire Department, "Emergency Service, Oil-Water Separation
Herding
lie. CO WRR Field & Group Q5D
18. Availability
• .. ..
f5. Security Class.
(Repor.)
•>0. Sec-'jityCi.ss.
(Page)
21. No. of - Q
Pages **
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Abstractor Ralph H. CrOSS
institution Alpine Geophysical Assoc.. Inc. for
WRSIC 1O2 (REV JUNE 1971}
N.Y.F.D.
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