•A ATEH I-OL'.VTIGN COVTROi. RKSEARTH STRIFE
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CONCEPT DEVELOPMENi ut-
HYDRAULIC SKIMMER SYSTEM
FOR RECOVERY OF FLOATING OIL
EN V I RON MEN TU PR<» !£(("[(> \
NV \T K R (i T V 1.1TY OFFICE
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes
the results and progress in the control and abatement
of pollution in our Nation's waters. They provide a
central source of information on the research, develop-
ment, and demonstration activities in the Water Quality
Office, Environmental Protection Agency, through inhouse
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Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Head, Project Reports
System, Office of Research and Development, Water Quality
Office, Environmental Protection Agency, Room 1108,
Washington, D.C. 20242.
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CONCEPT DEVELOPMENT OF A HYDRAULIC SKIMMER
SYSTEM FOR RECOVERY OF FLOATING OIL
Battelle Memorial Institute
Pacific Northwest Laboratory
Richland, Washington 99352
for the
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
Project # 15080FWP 04/71
Contract # H-12-884
April 1971
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EPA Review Notice
This report has been reviewed by the Water
Quality Office, EPA, and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies of
the Environmental Protection Agency, nor does
mention of trade names or commercial products
constitute endorsement or recommendation for
use.
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $1.25
Stock Number 5501-0068
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ABSTRACT
Efforts are being directed to develop effective counter-
measures against floating oil slicks. Mechanical recovery methods,
which do not cause additional environmental insult, are most attractive.
Such a concept, a hydraulic skimmer, was investigated.
Floating headers, providing a linear water spray pattern on
the water surface, are attached to an open sea workboat. Sea water is
pumped through spray nozzles mounted on the headers to move an oil slick
toward the boat. Side mounted chambers are positioned to collect the
concentrated floating oil. Recovered fluid is pumped to an onboard
separation system from which the oil is transferred to floating tanks or
barges and the water is recycled to the spray system.
Experimental work was directed toward component development
and evaluation of a large system model in a simulated environment. A
35 foot support vessel, a 40 foot spray header, and a 9 foot collection
chamber provided the 23 1/2 foot model sweep width. Speeds of advance to
five knots, random waves to 30 inches significant height and three oil
types were used in evaluating this system. Other equipment such as an
ultrasonic oil thickness gauge, process pumps and tankage were also used.
Model experiment results showed, for light oils, 80 to 100
percent effectiveness and oil recovery rates of 6600 to 8700 'gph.
Results with Bunker fuel were not as good, being on the order of 1300 to
1800 gph and 12 to 30 percent effective in recovering oil from the water
surface. However, program time constraints did not permit experimental
verification of modifications expected to increase performance on heavy
oils.
Further development of the concept, including additional model
testing with heavy oils plus open sea evaluation of a prototype system
was recommended.
This report was submitted in fulfillment of Contract No. 14-12-
884 between the Federal Water Quality Administration and Battelle-Northwest,
a division of Battelle Memorial Institute.
KEY WORDS: Concept, equipment development, oil skimmer,
open sea, evaluation, oily water, separation techniques, technical fea-
sibility, efficiencies, hydraulic studies, hydrodynamics, jets, math-
ematical studies, testing, water pollution treatment.
Ill
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CONTENTS
Section
I
II
III
IV
V
VI
VII
VIII
IX
Conclusions
Recommendations
Introduction and Summary
Spray Boom Development
Collection Chamber Development
Concept Evaluation Tests
Acknowledgments
References
Appendix
Page
1
3
5
15
47
65
83
85
87
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FIGURES
Number
1 Oil Recovery Concept 8
2 Process Flow Chart 9
3 Concept Evaluation Arrangement and Model 12
System Component Details
4 Illustration and Force Balance 16
Diagram of the Spray Induced Skimming
Mechanism
5 Illustration and Vector Velocity 20
Diagram of the Side-Skimming Arrangement
6 Speed of Advance as a Function of Boom 22
Configuration and Relative Oil to Water
Velocity
7 Speed of Advance Required for 50,000 gph 23
Oil Recovery
8 Flow and Pressure Requirements as a Function of 25
Speed of Advance
9 Maximum Skimming Speed as a Function of the 28
Relative Oil Density for Given Spray
Impingement Angles of 5, 10 and 20°
10 Spray Boom and Pivot Connections 29
11 Spray Boom Moments 31
12 Skimming Configuration During a Turning 32
Maneuver
13 Spray Simulator for Spray Nozzle Evaluation 36
14 Nomenclature of Spray Simulator Variables 39
15 Structural Connections Between Boom Sections; 44
Between the Boom and the Support Vessel;
Including Maximum Expected Forces and Reactions
16 Final Design of Model Spray Boom 46
Vl x
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Number Page
17 Side Entry Collection Chamber Concept 48
18 Collection Chamber Internal Circulation 59
Pattern Illustration
19 Collection Chamber Displacements Illustration 51
20 Flow Channel Test Section 53
21 Final Collection Chamber Arrangement 55
22 Internal Collection Chamber Effectiveness as a 56
Function of Free Stream Velocity
23 Spray and Chamber Effectiveness Tests 57
24 Spray and Chamber Effectiveness as a Function 59
of Free Stream Velocity
25 Schematic Showing One of Three Duplicate Oil 61
Pickup Arrangements and Its Relationship
to Other Parts of the Collection Chamber
26 Large Scale Model Collection Chamber 63
27 Concept Evaluation Model Operating in 30 to 67
36 Inch Waves
28 Oil Recovery Rate as a Function of Slick 73
Thickness
29 Oil Recovery Rate as a Function of Speed of 74
Advance
30 Empirical Factor as a Function of Oil 75
Recovery Rate
31 Model System Effectiveness as a Function 76
of Average Oil Slick Thickness
32 Model System Effectiveness as a Function of 78
Speed of Advance
33 Empirical Factor as a Function of Model 77
System Effectiveness
34 Oscilloscope Trace from Slick Thickness 88
Measuring Device
Vlil
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TABLES
Number Page
I Nozzle Characteristics 38
II Simulator Test Data 41-42
III Small Model Interior Chamber Effectiveness 53
Data
IV Small Model System Effectiveness Data 58
V Concept Skimming Performance Test Results 71-72
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SECTION I
CONCLUSIONS
1. The hydraulic skimmer system concept is a feasible approach to the
mechanical removal of floating oil from the open sea water surface.
The test program has proven the concept to have sound technical and
practical bases. Advancement of the concept to a full scale
operating oil pollution abatement tool has a high probability
of success. A modular system involving linear floating spray
headers, floating chambers to concentrate and collect the oil,
plus deck mounted equipment—pumps, tanks, winches, etc.—is con-
ceived to be easily and quickly transported to an oil spill cleanup
deployment site and then fitted to an existing workboat, barge or
tug.
2. System performance appears to be superior to known methods of oil
slick recovery in open sea environments. Conclusions are based on
experimental results from a half system model approximately 40 per-
cent of full scale (23 1/2 foot sweep width) operating on several
types of oil slicks on fresh water.
(a) Model performance varied with speed of advance with all
types of oil used in the experimental program. The follow-
ing values represent maximum performance achieved: 2.0 knots—
97 percent effectiveness and 6800 gph recovery rate; 3.0 knots—
55 percent effectiveness and 8700 gph recovery rate, and; 4.0
knots—24 percent effectiveness and 3000 gph recovery rate.
(b) Model performance was affected by the characteristics of the
oil being recovered. Performance on light oils ranged to
80 percent effectiveness and 6800 gph recovery rate for diesel
fuel (No. 2 fuel oil) and 100 percent and 8700 gph for crude
oil (40-42° API).
Operation was less efficient for heavy oil recovery—30 per-
cent effectiveness and 1870 gph recovery rate for Bunker
fuel (No. 5 fuel oil). Additional evaluation with heavy
oils and with system and component modifications would be
expected to show significant performance improvement. Time
constraints precluded such efforts.
(c) No model system performance degradation was detected with
operation in waves up to 30 inches significant wave height
(short "chop" partially suppressed). The ability of system
components to follow wave action indicated that longer and higher
waves would cause no detrimental effect.
3. An empirical factor involving system variables (spray flow rate,
spray pressure and speed of advance) and oil characteristics (oil
thickness and oil type—No. 2 fuel, No, 5 fuel, 40-42° API (crude)
became evident in data reduction. This factor^-sflow times the square
root of pressure divided by the product of oil thickness and
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and square of the rate of system advance—correlated with
effectiveness and oil recovery rate for the oil types used.
Extrapolation indicated system requirements for various levels
of performance for oil thicknesses for 1 to 3 mm. For No. 5 fuel,
the extrapolation was necessary over a range in system variables
not evaluated by model test, i.e., for an effectiveness greater
than 30 percent.
4. Measurement of system effectiveness for oil slick recovery techniques
is difficult especially in the presence of wind and waves. Con-
tinuous measurement of oil thickness was mandatory for such per-
formance evaluations and was used in this model test effort.
The ultrasonic method employed, although not optimized in this
program, represents a feasible method for instantaneous measure-
ment of oil layers down to 0.025 mm (.001 inch) thickness.
5. Recovered materials (oil, water and emulsion) are of adequate
quality to eliminate the need for sophisticated treatment equip-
ment, such as centrifuges, in the onboard process flow system. No. 2
and crude oil recovered contained from 11 to 46 percent free water
by volume. The oil-water mixture remaining when allowed to separate,
contained 3 to 70 percent water, 8 to 94 percent stable emulsion, and
3 to 25 percent free oil. No. 5 fuel oil (Bunker fuel) formed no
emulsion with water, although it did contain 8 to 43 percent air
by volume. An initial coalescence, in order to remove the free
water, plus pumping direct to tankage for eventual landside pro-
cessing and disposal is concluded to be an effective means of
handling recovered oil.
6. Behavior of the model system under dynamic conditions presented no
direct difficulties. Tests at speeds of advance to seven knots
without waves and to nearly three knots with waves produced no
instabilities or detrimental effects on performance of the system.
Evaluation of the high speed mode (boom angled to 10° of the vessel
centerline) at up to 3.75 knots proved not to be structurally
detrimental to the system. The effects of high intensity winds
were not evaluated by actual test. However, their effect cannot
be of the order of magnitude of the water currents and waves sus-
tained during testing on the low profile linear floating spray boom
and the low draft collection chamber. Maneuverability analyses
of a prototype oil recovery system mounted on a support vessel show
that low speed turns should be approached with caution. The
liklihood of overrunning one of the side mounted boom assemblies
can be decreased by operation of the spray system.
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SECTION II
EECOMMENDATIONS
1. It is strongly recommended that the concept be carried to the
next step of development—prototype design and development. The
following specific activities are recommended:
(a) Secure additional system requirement design data to ascertain
system performance improvements expected with minor system
changes and with heavy oils. Perform additional model testing.
(b) Develop a feedback device for automatic control of the suction
head level, with respect to the oil-water surface, within the
collection chamber. Model testing is recommended.
(c) Review vessel characteristics—length, deck space and dimensions,
horsepower rating, bulwark height above the deck and overall
freeboard—as bases for the design of components which must be
compatible with workboats, barges and tugs available in major
West Coast, Gulf Coast or East Coast ports as possible support
vessels. A vessel inventory is recommended.
(d) Design a full scale system such that it can be palletized and
air transported and then easily fit to existing available
vessels.
2. Advance the concept to a state of readiness for future oil pollution
incidents by performing the following recommended activities:
(a) Fabricate all required components of a total system prototype
for use in open sea test evaluation and for eventual use on
offshore spills.
(b) Plan and perform open sea tests to confirm the prototype system
performance, operability and seaworthiness.
(c) After minor system modifications, anticipated as a result of
open sea testing, plan and perform a demonstration for all
interested parties—federal representatives, oil company
industry conservation coordinators and major port authority
representatives. The presentation should include first-hand
observation of the system in operation, plus a plan of action
necessary for further use of the system in actual spill
incidents. The plan should be designed by the coordinated
efforts of government and industry.
(d) Prepare a complete set of installation, maintenance and
operating procedures of such simplicity and completeness
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that competence to operate the system is possible within a
very few hours by relatively inexperienced personnel.
Further develop the oil slick measurement device which was used
in this program. Potential applications include industrial process
control, enforcement of regulations regarding floating pollutants,
monitoring of oil spill cleanup progress, as well as evaluation of
oil spill abatement equipment.
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SECTION III
INTRODUCTION AND SUMMARY
The Federal Water Pollution Control Administration desires to
develop new and efficient devices and techniques for removing spilled
oil from the water surface in both protected and unprotected waters.
This study was directed toward the development and evaluation of a con-
cept for the recovery of oil from unprotected waters as defined in
Request for Proposal (RFP) No. WA 70-23, "Recovery of Floating Oil".
CONCEPT DESCRIPTION
The concept evaluated was based on the employment of generally
available vessels (workboats, barges or tugboats) of a class compatible
with open sea waters and capable of sustaining the speeds and environmen-
tal conditions to be encountered in oil recovery in such unprotected
areas.
The concept features a general "Vee-shape" arrangement formed by
linear spray headers on each side of a support vessel. The concentra-
ting effect of the advancing "Vee" is obtained by water spray which
induces surface currents toward a collection point on each side of the
vessel.
The so called "spray boom" is an array of spray nozzles pro-
viding a continuous spray impingement pattern on the water surface.
When the nozzles are arranged in a linear pattern and the spray is
directed generally perpendicular to the direction of travel, sweeping
of floating oil toward a collection point is affected. A continuous
floating manifold provides pressurized water to the nozzles. The con-
ceptual boom is a low profile floating assembly with relatively short
flat members pivoted at each connection. Attachment is to the support
vessel by mechanical pivot and flexible hose connections; the spray boom
orientation is maintained by cable rigging to the bow. A possible pro-
totype arrangement derived from this concept for three classes of off-
shore .support vessel is shown on Figure 1.
The "collection chamber" forms another major component of the
concept system. It consists of a deep, narrow and long hull shape with
an entry for floating oil at the side near the rear of the chamber. The
spray system is required to direct the oil into this side entry. Vertical
baffles and an open bottom, plus the use of internal spray nozzles pro-
vides for moving oil from the side entry location to the front stagna-
tion area. A floating suction head provides for recovery of the thickened
oil. A collection chamber is attached to the vessel at each side, toward
the rear of the vessel.
Finally, the concept must provide equipment which processes
the material recovered from each collection chamber into a high quality
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oil for storage and subsequent disposal. The oil recovery process employs
oil recovery pumping units, oily water separation units and tankage
filling units. The process flow chart in Figure 2 indicates the inter-
relationship of these units. One particular characteristic is that all
water from the separation unit may be recycled through the spray boom
and ahead of the skimmer. This approach makes it possible to reprocess
any oil which may be lost in the water discharge of the separator.
Oily water pumped from the oil-water separator may be dumped
to waste (land fill or incineration) or processed for bunkering or
refining. The use of landside polishing process units may be required.
Space and weight limitations on board typical support vessels will
likely preclude carrying such final process equipment.
Storage and transporting of recovered oil to a landside base
is assumed to be by moderately sized pillow tanks.
EVALUATION PROGRAM DESCRIPTION
Major concept components, the spray boom and the collection
chamber were developed separately by experimental model work. All
components and support facilities were then fabricated for evaluation
of the total system.
Development of the spray boom entailed analysis, experimental
component design, and evaluation. Analysis revealed the basic mechanisms
involved in the induced motion of oil slicks by water spray. System
parameters were determined from basic assumptions and were used as
initial design criteria.
A simulated spray boom, consisting of a mobile spray nozzle
manifold supplied with high pressure water, was cantilevered over the
side of a large water basin. It was used in determining nozzle char-
acteristics which most efficiently provide oil slick movement. This
simulator, mounted on a truck which could be driven parallel to the
basin wall, also provided reliable information on the most promising
spray flows, pressures, nozzle heights, and orientations. Additional
information was drawn from observation of a similar device undergoing
open sea evaluation at Santa Barbara. This device, as part of the
American Petroleum Institute-Federal Water Quality Administration sup-
ported Project Sea Dragon employed a spray boom. It was supported ,. „ „.
above the water surface by discretely spaced catamaran hull floats. ' '
The final design was accomplished and the 40 foot spray boom
was fabricated as shown in Figure 3 which follows:
Development of the collection chamber was an iterative pro-
cedure involving small models testing and analysis of the mechanisms
involved. Major deficiencies were overcome and a concept evaluation
model was designed by scale-up of the models tested. Figure 3 shows
the final design used to fabricate the nine foot long chamber.
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Figure 1
Oil Recovery Concept
-- x
7-8
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Water
Water
Pressure
Pump
Separator
Pillow Tank
Sludge or
Trash Pump
Support Vessel
Figure 2
Process Flow Chart
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The support vessel, spray pressure pumps, process pumps,
tankage, towing arrangements and interfaces were also designed for
use in the evaluation testing phase as shown on Figure 3.
CONCEPT EVALUATION
Concept evaluation was performed in a large water test basin
209 x 432 x 16 1/2 feet deep. A flap-type wave generator capable of
producing random three foot choppy wave patterns on the entire sur-
face was used. Support equipment included: electric power supplies, towing
harnesses, booms for restriction of oil spreading and devices to meas-
ure waves, currents and oil slick thickness.
Initial experiments were performed to identify minor modifi-
cations required for operability. Speeds of advance up to seven knots
were achieved on calm waters and speeds to approximately five knots
in waves to 36 inches significant wave height—average height of the one-
third highest waves, crest to trough.
Subsequent skimming evaluation experiments showed system
effectiveness—oil recovered versus oil encountered—to be up to
100 percent for crude oil and diesel fuel at speeds of advance in the
2.5 to 3.5 knot range. Recovery of Bunker fuel was less effective
with a maximum of only 30 percent. Oil recovery rates for the 23 1/2 foot
sweep width of the model system were 7000 to 8000 gph for light oils
and 1000 to 1500 gph for Bunker fuel. Improved skimming performance
on heavy fuels is likely based on spray boom performance analysis. At
the low temperatures during the heavy oil tests, 32 to 45°F, the high
viscosity Bunker fuel tended to be in the form of a cohesive mass which
sluggishly rolled beneath the water surface when being moved by the
spray system. Its high density also caused it to be more readily sub-
merged by impingement of the water spray. The sluggish motion combined
with the minimal buoyancy of the heavy oil contributed to this poor per-
formance. It is probable that empirical adjustment of parameters
(speed of advance, water pressure, water flow) would significantly improve
performance. Also, locating the spray nozzles at or near the water
surface so that the maximum horizontal spray force can be transmitted
to the slick would improve performance. However, time limitations pre-
vented experimental verification. It was concluded that there is no
inherent reason to prevent the efficiency of heavy oil recovery from
approaching that demonstrated for light oils.
The oil-to-water ratios in recovered materials varied consid-
erably. Some high oil-to-water ratios were obtained, however. This
suggests that adjustment of the system parameters and operation on a
continuous basis will result in good recovered oil quality. Formation
of emulsions did take place, but only on the liyht oil products. Proper
design of pumping systems and continuous, once through, recovery does
not appear to present problems of a significant magnitude, at least for
those oils used in this development project.
13
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SECTION IV
SPRAY BOOM DEVELOPMENT
Development activities entailed an initial analysis, followed
by model evaluation. A large scale device was then designed for overall
concept demonstration.
SPRAY BOOM ANALYSIS
In the concept under investigation, the floating spray boom has
two functions. First, it produces a water spray impingement on the water
surface. Second, it is the buoyant support of a spray header. The first
function produces the effect of moving an oil slick in a controlled direc-
tion and rate; the latter is an assembly arranged in a configuration to
support the header and to produce this effect. The two functions are
separately treated as; (a) spray effectiveness and, (b) boom stability
and integrity.
SPRAY EFFECTIVENESS
The movement of surface oil slicks has been characterized for
many wind and current situations and for several spreading regimes from
instantaneous spillages.(4,5,6) However, these empirical formulations
are not easily adapted to describe induced movement of oil slicks by high
pressure water sprays.
Consider an oil slick retained from following the underlying
current by the use of high pressure spray. The spray reaction force
arrests the surface flow of oil and thus contains the oil slick. This
is essentially the mechanism which produces the effect of oil skimming—
a spray manifold is angled into the direction of travel thus imparting a
side motion to the surface in such a way that oil travels down the boom
length and into a collection device.
The oil slick is assumed to be a flat plate slipping across the
underlying water column. The underlying current may be equated to advan-
cing the water spray at a rate equal to the hypothetical current. An
effective mass equal to the mass of oil is assumed. Vertical movements
of oil relative to the adjacent water would be effected by viscosity
(drag). However for this analysis such an effect is considered as
second order and is neglected.
Figure 4 illustrates the water spray skimming mechanism.
The force balance which causes the skimming effects can be
obtained by considering that, in the horizontal direction, the drag
force on a stationary oil lens due to an underlying water current (or
advancement of the spray) plus a force which resists the acceleration of
an effective mass of material must be balanced by a horizontal component
of the spray reaction force. This is also expressed by equation (1),
following. In the vertical direction, as a first approximation, assume
15
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F, (buoyancy)
F (spray)
^
(drag + inertia)
ty
(spray to I
surface angle) L- ^
v^^ 3
I
F + F.
ly
w
j
(weight + inertia)
Force Balance Diagram
>• Coordinate
system fixed
to spray
nozzle
direction of spray advance
water spray from
nozzle
water current.
(relative to spray nozzle)
Figure 4
Illustration and Force Balance Diagram of
the Spray Induced Skimming Mechanism
16
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that the vertical component of /the spray reaction force must be balanced
by the relative oil buoyancy in water and by a vertical acceleration of
the effective mass of material. This statement is expressed as equation
(2).
Fd + Fix - FsCos(V
Fb - Fw - Fiy = FsSin(ei} (2)
where,
F, = drag force between oil and water considering the slick
to be a rigid flat plate moving across the water surface.
= C. Area D (V 2)/2
f w ow
F. = Force to accelerate an effective mass in the horizontal
direction
= D T Area a /g
o x
F = Water spray reaction force generated through the concept
spray boom
F, = Buoyancy due to water displaced by the oil slick
i
D T Area, with no spray
D T Area, when oil is submerged
• w
F = Weight of oil slick
w
= D T Area
o
F. = Force to accelerate an effective mass in vertical direction
= D T(Area)a /g
o y
6.. = Angle of water spray impingement on the water surface
C = Drag coefficient
Area= Spray impingement area per foot of boom length
T = Oil slick thickness
V = Relative oil to water velocity
ow
0 = Spray flow rate per foot of boom length
H = Spray pressure at the nozzles
17
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g = Acceleration of gravity
D = Density of water
D = Density of oil
a = Acceleration of oil in horizontal direction
x
a = Acceleration of oil in vertical direction
y
The solution to force balance equation (1), the summation of
forces in the horizontal direction (x-direction) will imply the water
spray flows required to horizontally move an oil slick. Inserting the
force relations into equation (1) and algebraically manipulating the
result produces the following relationship:
a - ID /(D T)
x [ w x o '
(3)
Also now, assume that in order to retain the oil ahead of the
spray boom, the average acceleration a Avg. must be such that the
relative oil to water velocity is reduced to zero by the time it tra-
verses the first half of the spray impingement area. Average acceleration
over a given distance equals the relative velocity change squared divi-
ded by twice the distance, or ex (Avg.) = V ^/2x. In this case, x would
be half the spray impingement length or L. With this assumption and
after rearranging, note the following equation.
„ 0.5 [Area V 2 1 f D T C.'
H =| ow II. o + __f
D L 2
w
Equation (4) identifies the important variables and to what
extent they affect performance as follows:
• Increases in drag coefficient, possibly caused by eddy forma-
tion at the oil/water interface produces an added flow and
pressure requirement. Poor nozzle types could have this effect.
• Increases in oil slick thickness requires that a greater mass
be accelerated to retain the oil lens, thus increased flow
and pressure.
• Decreases in the effective spray impingement length (a function
of the spray pattern and height above the water surface) requires
greater acceleration of the oil as the spray advances.
• Increases in the relative oil-to-water velocity, V , have
important effects on the spray flow and pressure requirements.
High rates of advance are required to obtain a high oil recovery
rate. A trade off here is necessary—minimum speed for adequate
recovery rates, maximum speed for good performance with a given
spray flow and pressure.
18
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• Changes in spray angle (9,) near zero degrees for this
application have practically no effect on spray requirements.
• The relative oil density (D /D ) varies over a range of about
20 percent—suggesting that oil type has minimal effect on
spray flow and pressure requirements.
• Required hydraulic force for effective oil slick movement is
proportional to the spray flow rate and to the square root
of spray pressure. Therefore, arrangements which operate at
low pressure and high flow will require the least pumping
power for a given level of performance.
The previous analysis may be expanded to the case of a spray
boom angled from the direction of the current (or spray advance) by an
angle (9~) and with spray nozzles angled from this boom by (9_). Figure
5 illustrates this side-skimming configuration.
The vector summation of the velocities shown in Figure 5
results in the following:
V = V + V (5)
ov ow wv
where,
V = oil current vector
ov
V = water current vector
wv
V = relative oil to water current vector (same direction
as the spray forces)
The critical value of V is that velocity which results in
a vector of oil current in essentially the direction of the spray boom,
or 9- relative to the vessel. This is the situation depicted by the
velocity vector diagram of Figure 5. If the water current (speed of
advance) were increased and the spray force were reduced, the oil current
vector would have a reduced angle, resulting in oil escapement along
the length of the boom. Conversely, the reverse situation would result
in moving the oil well ahead of the spray, thus wasting pumping power.
Equation (5) when broken into sealer equations and when the
critical value of V is assumed, results in the following equation:
V = V Sin(90)/Sin(9_) (6)
ow wv 2. 3
This expresses the relationship between the vessel speed (V ), the
oil to water relative velocity (V ) and the spray boom configuration
(9«, 9_). From equation (6) it can be determined that to be the most
effective, the spray nozzles should be perpendicular to the boom
(9^ = 90e). This case enables the greatest value of vessel speed for
a given spray flow and pressure and level of effectiveness as in equation
(7).
19
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ow
Coordinate system fixed
to spray boom (or the
support vessel)
Vector Velocity Diagram
Support Vess 2
Spray Boom
Figure 5
Illustration and Vector Velocity Diagram
of the Side-Skimming Arrangement
20
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V = V Sin(e_) (7)
ow wv 2
By substituting equation (7) into equation (4) , derived for
the simplified case of a current perpendicular to a spray boom, a
relationship useful to the side-skimming technique is obtained:
0.5 rAreaveT Cl (8)
W 0 .0.5. ,- , ID L
(2g) Cos (6.^ w
Implications derived from equation (8) are:
• Reduced angles of boom to vessel require lower spray pressure
and flow.
• Reduced vessel speeds significantly reduces required spray pres-
sure and flow.
The effect of angling the skimming mechanism deserves additional
attention. Equation (7) is graphically expressed in Figure 6 to show
the effect of this variable on the vessel speed for given oil to water
relative velocities. (Also implied by a given oil to water relative
velocity, is a given spray flow and pressure requirement — see equation
(4)).
The sweep width is also directly related to the boom to vessel
angle for a given boom length. This would control the system capacity,
all other things being equal.
A simple derivation reveals the relationship of sweep width
to system variables as shown in equation (9).
wv
where :
W = sweep width
Q = oil recovery rate
V = vessel to water velocity
wv
T = oil thickness
This equation is shown graphically in Figure 7, using the
design goals of 50,000 gph oil recovery rate at an oil thickness of
1.5 mm and less.
Decreasing the spray boom angulation (99) , to achieve improved
skimming performance is constrained by the sweep widths required to
achieve the recovery rate goal and by the maximum boom lengths which
are practical for available support vessels. These vessels can be
expected to be normally about 100 feet in length and 30 feet in beam.
21
-------
10
Vessel Speed
V
wv
(knots)
0
V =10 ft/sec
ow
Vow = 5 ft/sec
.Sin(e2)
0 45
Boom to Vessel Angle (9 )- (degrees)
Figure 6
Speed of Advance as a Function of Boom Configuration and Relative
Oil to Water Velocity
22
I
90
-------
250
CO
*tJ
(D
(D
O.
o.
i
O
n>
(D
.0
o
*•
o
o
o
00
tt>
o
o
to
3
200
Beam of
Sweep - W
(ft) 150
H
100 __
50
t = 0.3
nun
Vessel Speed -
V (knots)
wv
-------
If the maximum practical boom length is taken to equal the vessel
length (to enable proper guy cable support), then the spray boom
angulation for oil collection from slicks 1.5 mm and less in thickness,
would be limited to about 45°.
Equation (4) and (8) can now be solved to obtain approximate
spray flow and pressure requirements as a function of oil to water
relative velocity or vessel speed. Equation (10) below expresses the
result of these equations using the following assumptions—(see
Figure 8 for a graphical expression of equation (10):
C. = Turbulent friction factor
- 0.74Re-°-2
Re = Reynolds Number
= D V L/y
w ow
D = 1.985 slugs/ft3
V =5.6 ft/sec for Reynold Number Determinations
ow J
L = 10 ft
y = sea water viscosity
= 2.5 x 10~5 Ib sec/ft2
2
Area = 10 ft /ft of boom
DQ = 1.786 slugs/ft3
T = 1.5 mm (0.06 inches)
g = 32.2 ft/sec2
QI = 10°
02 = 45°
Qw(gpm/ft)Hw°-5(Psi) = 67.6 V^Cft/sec)
°r 0 5 2
Q (gpm/ft)H (psi) = 78.5 Vessel speed (kts)
The solution to force balance equation (2), the summation
of vertical forces, suggest problems with oil loss resulting from
oil slick submergence and subsequent overruning. Since this represents
a possible failure mode, it was examined using the same general nom-
enclature given at the introduction of this section. By inserting the
force relations previously developed into equation (2) and algebrically
manipulating this result, the following equation results:
24
-------
500
Nozzle
Flow per foot
Floi
of boom
400
(gpm/ft)
300
200
100 _
ow = 5.8 ft/sec
Vessel Speed = 5 knots
4.6 ft/sec
4 knots
3,5 ft/sec
3 knots
2.3 ft/sec
2 knots
1.16 ft/sec
not
0.58 ft/sec - 0.5 knot
25
125
H , Nozzle Pressure (psi)
Figure 8
Nozzle Flow and Pressure Requirements as a Function of Speed
of Advance
25
-------
= (D /D ) lo (2gH)°'5Sin(e )/(gT Area) - (D -D )/D 1 (11)
W O I W W -L W O W I
a
y
where the oil is submerged and being accelerated downward (a ^ 0).
Overruning an oil slick will occur when the net oil buoyancy
(total buoyancy - weight) is overcome by spray forces and when sufficient
excess force is present to accelerate the slick to a depth where nozzle
sprays are not able to accelerate it horizontally.
As the density of the oil approaches that of water, several
limitations on system variables are indicated. A statement of this
is given in the following equation where the vertical ccceleration is
assumed to be zero, but where the oil layer is just stable—any
increased downward force would produce oil submergence.
(D -D )/D = Q (2gH )°'5Sin(e )/(g T Area) (12)
W O W W W X
Using this failure criteria, conditions which may enhance oil
submergence are indicated as possible system limits.
• As the relative oil to water density approaches zero, system
variables become quite limited where either the flow and pressure
must be reduced (this implies slower vessel speeds and thus
lower recovery rates—assuming equal slick thicknesses) or
the spray impingement angle must be reduced to approach zero.
• The effect of variations in impingement angle, for snail impinge-
ment angles, are quite significant—approximately proportional
to the absolute angle change—a change in angle of from 5 to 10°
would roughly double the downward spray reaction force component.
• Decreases in oil slick thickness decrease the buoyancy force
and thus cause a greater susceptibility to submergence of an
oil slick by a given spray condition.
• Decreases in the spray impingement area, such as would be the
case if shallow angle nozzles were used or when nozzle height
and impingement angles produce reduced areas, cause an increasing
tendency to submerge the oil. Wide pattern nozzles may be the
preferred type.
The implication of a speed-of-advance limitation as the
relative oil-to-waCer density is reduced is critical and must be further
treated. By combining the submergence criteria from equation (12) and
the skimming criteria from either equation (4) or (8), eliminating the
common spray term, 0 (2gH )' , and using the same assumed variables
(but letting 9.. vary), the following equation results:
D /D = (1-0.009 V 2tan 9.. )/(1+0.0035 V 2tan 9,) , or (13)
O W OW -L OW 1
26
-------
D /D = (1-0.012 Vessel speed2 tan 6 )/(1+0.047 Vessel speed2
tan 91) (13)
This equation is shown in Figure 9 for given spray impinge-
ment angles, thus relating the maximum vessel speeds to a given oil
type (density).
BOOM STABILITY AND INTEGRITY
Structural support of a spray header which produces the correct
spray effectiveness is required. Continuous rigid floating sections
with discretely flexible pivots is the support concept. Floats are
suspended as outriggers for additional roll stability. The total boom
length is supported at an appropriate angle to the vessel by cables from
each boom section to the support vessel bow. At the aft extreme of the
boom, attachment to the vessel is made with a free pivot and a lever
arrangement to allow for relative vessel to boom surges. The flexible
pivots between boom sections are free to rotate only in one plane and not
in the other two. Twist from one section to the next is constrinaed.
Boom sections are also prevented from forming other than the desired
straight length. Figure 10 shows the configuration derived from these
constraints.
The several possible hydrodynamic instabilities are considered in
the following paragraphs:
Instability No. 1 (roll in the plane of the end view of the
boom). Two stable conditions (2,4) and two meta-stable conditions (1,3)
are possible in considering this roll possibility as noted below in
generalized cross section views.
Condition 1 Condition 2 Condition 3 Condition 4
Condition 4 is the desired condition, applicable during skimming. Con-
dition 3 is possible if the boom front becomes submerged during forward
speeds and all counteracting moments (cable force moments, spray force
moments and roll stabilizer weight moment) are insufficient to prevent
the motion.
Figure 11 and the following discussion indicate how this
condition is prevented. The movement due to the spray reaction force is
a function of the nozzle flow and pressure characteristic and the moment
arm, height from boom center to nozzle. The moment arm is quite short,
thus producing a relatively small moment to counteract roll. The roll
stabilizer moment is a constant once the floating portions becomes
raised out of the water. For this condition it would be the stabilizer
weight times the moment arm from center of roll of the boom to center of
27
-------
LOOT
•H
CO
C
Q)
» 0.3 _L
•H
o
8> 0.2 4-
•H
0.0
in0 APT
0.9Q.25.70 API
0.804-45.3° API
0.7 170.6° API
0.6
0.5
0.4
9 = 10
9n = 20C
Skimming must be performed a
system variables consiste
with values below those s
by the curves.
5°.9729
10°.9457
20°.8898
it
lown
0.0
0.0
2.0
1.72
4.0 V
ow
3.44
Vessel Speed (kts)
Maximum Speed
6.0(£t/sec)
5.16
8.0
6.88
10.0
8.6
Figure 9
Maximum Skimming Speed as a Function of the
Relative Oil Density for Given Spray Impingement
Angles of 5, 10 and 20°
28
-------
Forward
Direction
on/
Support
Vesse
\ \
No Angulation along
the Length
Bcom-to-
Vessel Pivot
Support
Vessel
PLAN VIEW
ELEVATION VIEW
Free Rotation to
Follow Waves
Water Surface
Water Surface
Twist Between
Sections
END VIEW
Figure 10
Spray Boom and Pivot Connections
29
-------
gravity of the stabilizer (quite long). This moment is relatively large.
A moment due to the cable forces would be the tension force of the cable
times a moment arm which extends from the center of roll of the boom
to the cable attachment point and also multiplied by the Sin of the angle
between the direction of the cable force and the boom roll position (as
seen in the end view). Thus, the cable moment increases with cable
forces and with roll angle. The only positive moment which can produce
roll is due to drag and wave forces on the boom. The moment due to drag
will be a drag force resultant through the center of drag on the boom,
the moment arm being the distance from the center of drag to the center
of roll, multiplied by the Sin of an appropriate angle (boom roll position
to the equivalent direction of the drag force).
By a summation of forces, it is found that the cable forces
must be equal to the spray reaction force plus the drag force*, therefore
cable forces must necessarily exceed drag force. Also, the cable
moment arm will be longer than a moment arm due to drag forces. Logically,
therefore, a moment due to drag cannot exceed the counteracting cable
moment and no exaggerated rolling can be produced when the cables are
intact and properly adjusted. The effect of waves produces a similar
result with the exception of a rolling inertia which will allow small
momentary roll deviations from the equilibrium. Figure 11 graphically
expresses this inherent roll stability.
Condition 2 or the upside-down position is only possible if
condition 1 or 3 has been encountered first. Although condition 2 is
quite stable, considering that condition 3 is unlikely and condition 1
is quite doubtful (no significant moments would be present to cause this
condition), the inverted position will not likely occur in even quite
harsh wave conditions.
Catastrophic boom roll is considered to be quite unlikely from
the preceeding analysis and only small roll angles due to wave effects
are expected.
Instability No. 2 (rotation of the boom with respect to the
vessel): Two conditions are possible, either the boom is angled and
constrained from increased rotation relative to the vessel or forces
cause the boom to collapse against the side of the vessel. Condition 1
would be the skimming mode of operation characteristic of approximately
45° angle to the vessel and taunt cables. Condition 2 is a collapsed
boom angle with loose ineffective cables.
Condition 1 Condition 2
The cable forces which cause the condition 1 stable configuration are due
to spray forces and drag forces. The spray forces are a function of flow
and pressure characteristics of the nozzles only, while the force on
the boom due to drag is a function of speed -of advance and the boom-
to-vessel angle (advancing in a straight line) or boom-to-water current
30
-------
Center of Roll
F cable = F drag + F spray
F cable > F drag
Cable Moment = F cable X
c
Drag Moment = F drag X
X > X. d
c d
Therefore Cable Moment > Drag Moment
F cable
F spray
Figure 11
Spray Boom Moments
31
-------
angle (when turning). As the boom-to-vessel angle is decreased, the
drag term is likewise decreased. With significant water spray reaction
forces, it would be impossible to obtain a condition 2 situation while
advancing in a straight line.
In the case of a turning maneuver, the support vessel will
pivot about a point 1/4 the vessel length from the bow. The vessel will
also have a drift angle, (angle of vessel center line to the direction of
travel), similar to a slip angle for an automotive tire during a turn.
The stern will drift out on the turn. The following Figure 12 will
illustrate the turning maneuver.
When spray booms are attached to each side of a vessel, the
boom on the inside of the turn will be pulled sideways by the vessel at
an angle relative to the stationary water column. This angle is equal
to the vessel-to-boom angle plus the drift angle. The outside boom will
also be forced at an angle to the underlying water column. This angle
however is equal to the boom to vessel angle minus the drift angle. From
these observations, the outside boom would be in jeopardy if the drift angle
were to exceed the boom-to-vessel angle (in the absence of spray forces).
This could be considered a conservative limit for turning maneuvers when
spray forces are present.
When a boom-to-vessel angle of, say, 10°, compared to 45° is used,
such as during high speed transport between slicks, smaller drift angles
will produce the unwanted instability. However, high speeds result in
smaller drift angles thus indicating that high speeds can probably be
sustained in most situations. Low speed maneuvers are consistent with
large drift angles, making hazardous situations possible. Therefore,
during low speed cases with small boom-to-vessel angles or normal skim-
ming angles with no spray present, careful and considered vessel handling
would be required.
Instability No. 3 (rotation in elevation view plane due to
boom end forces). Forces along the length of a jointed boom will tend
to cause it to collapse. The buoyancy and weight distribution of the
boom sections will counteract this tendency. As the water level
raises and lowers on the boom, the weight and buoyancy produce restoring
forces.
ss ^<^^
fc *s.
* ^
^^^^ n —
\s
I^UIIU_LI_J-U11 X
Condition 2
Condition 3
Condition 3 will be the equilibrium position in calm waters. Condition 1,
though exaggerated, is the correct performance boom shape in a wave
situation. Condition 2 would result only from the endmost boom section
diving due to a combination of hydrodynamic conditions (waves and current).
32
-------
Direction of Travel
Right Turn
Propulsion or Rudder Direction
Drift Angle
Figure 12
Skimming Configuration During a Turning Maneuver
33
-------
The boom sections are considered to be approximately half
submerged during an equilibrium condition. Total buoyancy will be
approximately twice the total weight for a symmetrical body floating
half submerged. Such a floating device would act as a spring—a given
vertical force applied would cause a displacement which is proportional
to the force. The maximum force possible would be either equal to the
weight, if the device is lifted from the water, or equal to the net
buoyancy (total buoyancy minus total weight) when the device is com-
pletely submerged. Consider that equal vertical forces are applied to
each end of a boom but in opposite directions. This produces a list
or angular deflection and a counter moment. By applying a summation of
moments equal to zero (a stable list) and by considering a half sub-
merged object, a list angle can be determined for any value of this
vertical force. The following equation is evident:
F = I2w B tan 9 (14)
24
where:
F = vertical force
1 = length of object
w = width of object
9 = list angle of object relative to the water surface
(in length direction)
B = either the net buoyancy or the total weight per unit volume
Forces along the length of a jointed floating device will
produce alternating vertical force components (force up at one joint
and down at the next).
It can be seen that for a given buoyancy or weight per unit
volume, stability is enhanced by increases in width and length. As
the rotation angle is increased, as is the case for steeper and steeper
waves, the instability is worsened.
The end force on the boom is due to several contributing
factors; boom drag, spray reaction forces and cable forces. The spray
force will tend to reduce the end forces and will dominate (producing
tension along the length of the device rather than compression forces)
during very slow speeds. The cable force will definitely reduce the
end forces—but only on the boom sections at the aft portion of the system.
Cables attached to the outward extreme boom connections may have a
small component which adds to the end force due to drag. The location
of the"front vessel, cable mounting and the length of the floating boom
will drastically change this effect. The major difficulties which may
arise will be from high speed travel, with low spray forces and will be
more likely at the extreme inboard joint.
34
-------
Diving of the end boom is possible and should be considered
in the final boom design. Greater buoyancy or hydrodynandc fins may
be reasonable preventative approaches.
The above instability characteristics imply that speed
of advance in both the skimming and speed modes of travel should be
restricted. Trailing of the booms will therefore become necessary
above a characteristic speed and in combination with waves which produce
large rotation angles.
WAVE AND SPRAY INTERACTIONS
Waves will obviously affect both spray effectiveness and the
boom motions and stability. The nozzle action on a choppy sea is
such that the spray impingement angles vary as a wave passes through
the spray impingement area. The significance of this effect is
indicated on Figure 9, which shows maximum speed of advance as a function
of spray impingement angle which can be sustained without submergence
of an oil slick. The dynamic action of a floating boom in waves,
producing transient changes in both the relative nozzle elevation above
the water and impingement angles due to rolling; surging, is also of con-
sequence. Boom sections should be designed to closely follow the wave
profiles which they encounter. Rolling of boom sections from one to the
next would be constrained; therefore the boom-to-water surface angle
will be at some average value over the entire boom length. Spray
nozzle distribution angles should be such as to allow for considerable boom
roll and surge and still produce a wide spray impingement area. Longer
period (long wave length) waves will have little effect here because of
the shallow slopes of such waves. For example, the whole boom assembly
can follow a five foot wave which has a 100 foot wave length. The
larger the wave, the easier it is for the boom-to follow it. The short
period "chop" or fresh wind waves will cause the greatest difficulties
from both the spray effectiveness and the boom wave following aspects.
Model testing should be performed in a "short chop" wave environment.
SPRAY BOOM DEVELOPMENT TESTS
Experimental verification and parameterization of spray nozzle
characteristics, flows, and pressures on oil slick motion were necessary
for a firm design basis of the model system. A spray boom "simulator"
was designed and fabricated for this work. The spray simulator as it
was called, Figure 13, consisted of a cantilever structure supporting
a manifold on which various nozzles were mounted. This structure was
supported by a jib crane arrangement from a truck. A pump and tank
located on the truck provided pressurized water to the spray manifold.
The truck was driven along the test basin wall with the boom
overhanging the water adjacent to the wall during the experiment.
Water spray from the manifold was directed at floating oil slicks with
various combinations of nozzle types, pressures, and flows. A portion
35
-------
Spray Manifold
Spray Simulator
After Test Run
Before Test Run
Figure 13
Spray Simulator For Spray Nozzle Evaluation
36
-------
of the basin was enclosed by a floating boom and used for testing.
The simulator provided for nozzles at six inch centers or multiples thereof
for a length of 20 feet. The manifold could be positioned at any
desired angle to the direction of travel and the nozzles could be
oriented at any desired angle to the water surface or to the manifold.
The effect of the water spray on the oil during each run was recorded
photographically and the geometrical and hydraulic parameters for
each run were recorded. Qualitative visual observations supplemented
recorded data.
The search for a viable combination of test parameters
resulted in a system judged to be sufficiently effective for design of
a scale model prototype.
Table I is a summary of nozzles evaluated using the spray
simulator. Figure 14 shows the nomenclature for the various operating
components of the spray simulator.
The distance of the nozzles above the water surface was
about 30 inches when the simulator was in a level position. Irregu-
larities in the roadway along which it was driven allowed the manifold
to vary from ^36 inches above the water surface to within M.2 inches
of the surface. It was observed that effective combinations of nozzles
and angles worked inspite of these height variations.
Basic conclusions drawn from this effect pertain to spray boom
effectiveness in moving an oil slick without overruning it. Empirical
trials were made for various A, B and C angles (see Figure 14 for
definitions). Nozzle types were evaluated and flows and pressures were
varied. Runs were made up to 3.0 knots speed of advance, 24 inch
significant wave height and different oil types (Texaco Crude Oil 42-
44° API and diesel fuel oil).
Conclusions from this phase of the work were as follows:
• Nozzle height had no apparent effect upon skimming efficiency
within the range of 12 to 36 inches above the water
surface.
• The optimum boom angles appeared to be: A = 67 1/2°, B = 45°
and C = 10°.
• The most effective nozzle type for moving surface oil
slicks of those tested was the 2HH30350 full jet style
(Spraying Systems Co., Bellwood, Illinois).
• Twenty gpm per foot of boom and 100 psi was required to move
oil in 24 inch waves and at a 3.0 knot speed of advance.
37
-------
Full Jet Nozzles
Flat Jet Nozzles
3/4 P35200*
TABLE I
NOZZLE CHARACTERISTICS
Nozzle No.*
3/4 H4
1 H10
1 1/4 H14
2 HH 30350
Flow
12.4 gpm
31.4 gpm
41 . 4 gpm
50 gpm
at Pressure
80 psi
80 psi
80 psi
80 psi
Spray Angles
63°
71°
73°
30°
28 gpm
80 psi
Fabricated Nozzles (flattened pipe couplings)
3/4 A 50 gpm 80 psi
40°, 22'
20°,
A
r*\
Full Jet Nozzle
Flat Jet Nozzle
Fabricated Nozzle
* Spraying Systems Co., Bellwood, Illinois
36
-------
Cantilever Structure
Spray Nozzle
Manifold
Direction of
Travel
Principle Spray Direction
Water Surface
PLAN VIEW
Principle Spray Direction
Direction
of Travel
END VIEW OF MANIFOLD
Figure 14
Nomenclature of Spray Simulator Variables
39
-------
With two exceptions, the nozzles tested were not effective
at speeds above 2.8 knots in calm water. The fabricated nozzles were
more effective than most nozzle types. However, they produced an
irregular spray impingement pattern and required large flows and
pressures. Most variation in performance was attributed to the char-
acteristic spray exit angle for the particular nozzle. Flatjets are
not appropriate because of their small spray impingement area. Wide
angle, fulljets fail because of energy transfer inefficiencies inherent
in the wide angle (60°) spray impingement on the surface. The model
2HH30350 has only a 30° spray exist angle in a full cone distribution
pattern, thus providing the required surface current without undue
turbulence.
The flow and pressure requirements determined from these
experiments are based on a cantilivered boom and not a wave following
(floating) spray boom. Also the visual observations and photographs
of the skimming operation require subjective judgment for interpre-
tation—thus, resulting conclusions should be considered qualitative.
Detailed test data are given in Table II.
SPRAY BOOM DESIGN
Spray boom design was performed as several tasks, each rep-
resenting a performance aspect: hydraulic, hydrodynamic and structural.
HYDRAULIC
Spray boom simulator experiments showed that approximately 20
gpm/foot of boom and 100 psi was sufficient to obtain 80-90% spray
effectiveness in two foot waves and speeds to 3.0 knots. These criteria
were used in sizing pumps and piping for the model system.
A total length of 40 feet in five 8-foot sections was chosen
for the boom model. The water requirements of this boom are therefore
800 gpm total flow with a 100 psi capability for pressure.
Choice of pipe diameter was made from hydraulic pressure drop
data for schedule 40 steel pipe. For 800 gpm, a pressure drop of 4.43
psi/100 foot length (5" pipe) or 1.75 psi/100 ft. (6" pipe) can be
expected. The choice was made to use two 4-inch pipes interconnected
along the boom length. This is equivalent in cross-sectioned area to
one 5.65 inch pipe and results in about 1 psi loss within the spray
boom length. This is a conservative estimate because of the reduction
of flow along the boom length. Vertical uprights at 6-inch centers
are provided for the spray nozzle connections, thus allowing for easy
changes iu nozzle spacing and other piping. Flexible hose connections
between boom sections provide for 20 to 30° angular deflection.
A diesel-driven centrifugal pump, capable of 1400 gpm at
120 psi C2400 rpm) , was used as the water supply. This pump was
mounted on a 35-foot steel hull lifeboat to simulate a support vessel.
40
-------
TABLE II
SIMULATOR TEST DATA
Test
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Water
Speed Pressure
(knots) (psig)
5.0
1.6
(no data)
2.5
1.5
1.5
3.0
3.0
1.5
3.0
(no data)
(no data)
(no data)
3.5
2.8
(no data)
2.8
40
40
40
40
40
40
30
30
30
80
38
50
Spray Oil Angle
Flow Type
(gpm)
270 Crude
270 "
140
140
240
240
335
335
335 "
700
316
285 "
Thickness Nozzle A
(mm)
.7 3/4 P35200 80°
" " " 80
.6 3/4 H4 90
1.2 " " 90
1H10 90
1.8 " 90
1 1/4 H14 90
II M II gQ
M i. •• 90
.7 3/4 A 90
.6 45
1.2 3/4 P35200 45
B
35°
0
45
45
45
45
45
45
60
45
45
45
C E
20°
20
20
20
20
20
20
20
20
10
10
10
If f ectiveness
(percent)
0
0
0
50
50
0
0
90
30
90
70-90
75
-------
TABLE II (Continued)
SIMULATOR TEST DATA
Test
No.
18
19
20
21
22
23
24
25
26
27
Speed
(knots)
2.8
2.0
1.5
1.5
1.5
3.0
3.0
3.0
3.0
3.0
Water
Pressure
(psig)
100
100
100
100
100
40
118
80
80
118
Spray Oil
Flow Type
(gpm)
400 Crude
400 "
400 "
400 "
400
250 Diesel
500 "
350 "
350
500
Angle
Thickness Nozzle A
(mm)
1.0 3/4 P35200 45
n n it 45
.6 " " 45
.4 2 HH30350 67
.2 " " 67
.8 " " 67
67
67
n n n 67
67
B
45
45
45
45
45
45
45
45
45
45
C Effectiveness
(percent)
10°
10
10
10
10
10
10
10
10
10
85
90
80
85- 90
80- 90 with
2 ' waves
50- 80
80- 90
80
80
85
-------
Water was supplied to the pump suction from the basin via a bulkhead
fitting through, the boat hull. Discharge was through twin flexible
hoses, 4" in diameter, to connections at the inboard end of the spray
boom assembly.
HYDRODYNAMIC
Current and wave forces on the boom sections could only be
estimated at this stage in the development effort. For a determination
of expected maximum forces, the following was assumed: a single floating
boom section 8 feet long, 36 inches wide, and 8 inches deep (rounded
ends), a wave characteristic of 3.0 feet (3.9 sec.) superimposed on a
5 knot speed of advance, no wind effect, and a cable rigging which will
withstand the forces with little elasticity. With these assumptions,
the maximum force due to waves was calculated to be 340 pounds and due
to the current, 510 pounds. Superposition of these conditions results
in a total maximum force of 850 pounds per boom section due to hydro-
dynamically induced forces.
STRUCTURAL
Constraints on boom motion and maximum forces are important
to the ultimate boom performance and boom interface structures. Each
boom section must be capable of withstanding the forces which are imposed
under the worse case encountered during its operation. The spray
reaction force was found to be 80 pounds per boom section considering
the requirement of 20 gpm per foot of boom, 100 psi spray pressure and
a nozzle efficiency of 75%. This in combination with hydrodynamically
induced forces must be offset by cable forces and the boom to vessel
interface pivot.
By making the assumption that cable forces are balanced (no
moments are encountered at the connection between boom sections), forces
as shown in Figure 15 result.
Considerable compressive force (up to 3300) pounds between boom
sections is evident. Cable forces range up to approximately 1000 pounds
tensio'n for the balanced force case; 2500 to 3000 pounds should be the
maximum requirement of anyone cable as a worst case (unbalanced forces).
The front and rear connections to the support vessel will also require
considerable strength in resisting the maximum forces.
Unbalancing of the cable tensions will result in bending
moments in the affected boom sections in addition to those created by
the drag and spray reaction forces. If the outermost cable becomes
loose, a bending force is applied at the connection between the outboard
boom sections. Inserting the expected maximum forces into appropriate
equations produces a maximum moment in the boom section of 660 ft Ib
at the connection. With balanced cable forces a maximum of only 335 ft Ib
is reached. Considering the possible problems in rigging, 130 ft Ib
for bending and 4000 Ib compression in each boom section is considered
a practical design critera.
43
-------
2870#
2940#
Figure 15
Structural Connections Between Boom Sections
and Between the Boom and the Support Vessel;
Including Maximum Expected Force and Reactions
44
-------
Other possible forces due to wave action must be considered.
A wave could possibly lift a central portion of a boom section
resulting in both ends being lifted from the water. The weight of the
boom would then produce a bending moment. The buoyancy would produce an
upward force at the center and the unsupported ends would produce a
downward weight. Forty pounds of force per foot of boom would produce
a maximum moment of 160 ft Ib in this plane.
Since the boom sections are constraiined from relative twist
between sections, twisting torque will be randomly applied to the boom
sections due to wave action. For design purposes, a 60 pound weight
on one stabilizer at a distance of 8 ft from the center of boom roll
was assumed to give a maximum twisting torque. The boom length which
would be affected must sustain a torque of 240 ft Ib.
The boom sections were designed, fabricated and tested for
loads in excess of these expected maximum values. Figure 16 is a
photograph of the final design arrangement used in concept evaluation
tests. Vessel to boom structural connections were made by a lever
arrangement which compensates for relative vessel to boom surges.
45
-------
Figure 16
Final Design of Model Spray Boom
46
-------
SECTION V
COLLECTION CHAMBER DEVELOPMENT
Collection chamber development, as in the case of the spray
booms, was performed by analytical treatment followed by model experi-
mentation. Concept evaluation equipment was then designed for system
evaluation.
COLLECTION CHAMBER ANALYSIS
Development of the collection chamber concept was based on the
environmental conditions in which it must function and the program
design goals. Performance factors were classified as effectiveness,
stability, and wave following characteristics.
COLLECTION EFFECTIVENESS
Recovery of floating oil which is "swept" by a hydraulic
spray boom is not simple. Retrieving a small quantity of oil while
avoiding pumping a large quantity of water requires the oil to be con-
centrated in a stagnant area or stilling chamber. Collection or reten-
tion chambers which have open fronts to admit incoming oil and water
and then retain only the oil are subject to the phenomenon of under-
flow and draining. This phenomenon has been extensively studied in the
laboratory and attempts have been made to predict analytically the , _.
underflow behavior and provide a physical explanation for the effect. '
A side entrance oil collection chamber scheme was employed for concept
development to circumvent the difficulty of underflow. The rationale
is basically to minimize the quantity of water which must flow into and
out of the chamber. For example, in calm water, the only flow of fluid
into the chamber is that induced by the spray nozzles. In wave motion,
however, there will be a variable flow of water into and out of the
chamber as it heaves with the waves. Figure 17 illustrates the collec-
tion chamber concept and it is further explained as follows:
• The concentrated oil reaching the inboard boom section is
driven into the side entryway of the collection chamber by
induced spray current.
• Once inside the chamber, the oil is out of the influence of the
free stream flow and is moved forward by a series of internally
mounted spray nozzles.
• At the forward most location within the collection chamber (the
oil recovery zone), the oil stagnates until oil suction pumps
operate to pump the oil on board the support vessel.
47.
-------
Surface
Oil Flo
Lines
Collection
Chamber
Spray Boom Sections
Direction of Current
(Vessel Direction)
Figure 17
Side Entry Collection Chamber Concept
48
-------
The flow below the chamber open bottom will cause cells of
induced circulation. It was expected that a chamber having a series of
internal baffles would provide a controlled liquid circulation pattern
within the chamber as it is towed. Correct positioning of baffles
and the use of a short bottom plate at the front was intended to pre-
vent oil underflow. The front portion of the chamber is closed at the
bottom thus forming a stagnant oil recovery zone. Figure 18 shows the
flow patterns expected in this arrangement.
This concept was verified by developmental testing on a model
scale. Several spray nozzles were arranged to provide additional
impetus to thicken the oil.
CHAMBER STABILITY AND INTEGRITY
As in the case of the floating spray boom, the chamber is subject
to all the relative water surface displacements of any floating object.
The collection chamber was considered for each instability mode. Figure
19 illustrates the expected induced motions of the collection chamber.
Instability No. 1 (Rotation of Chamber with respect to vessel
axis). The relative rotation of the collection chamber must be con-
strained by the use of an appropriate linkage system. Connections to
the vessel are made at fore and aft locations on the chamber. Thus no
relative rotation is possible.
Instability No. 2 (Heaving of the Chamber). The connection
links between the vessel and chamber will allow for considerable vari-
ation of the relative elevations of the chamber and vessel. The relative
displacement permitted must be consistent with the expected sea state
environmental conditions. The chamber is essentially free to follow
encountered wave profiles. To minimize the relative heave of the chamber
with respect to the water surface a minimum weight or inertial mass and
a maximum feasible buoyancy were desired. By the use of such a design,
displacements from equilibrium by a wave will produce large restoring
forces. The larger the restoring force, the quicker the response and
the smaller the heave.
Instability No. 3 (Chamber Roll). Modeling studies produced
a configuration which is much deeper than wide. This shape is sensitive
to rolling because there are large areas to produce hydrodynamic side
forces but a small distance between floatation cells (width of chamber)
to counteract the moments produced. It therefore evolved that the chamber
be connected to either the vessel or the first boom section in such a
way that the chamber is constrained to roll with these more stable members.
A linkage is feasible in producing this constraint while still allowing
for correct positioning and debris removal requirements.
WAVE AND OIL COLLECTION RELATIONSHIPS
The effect of waves on the collection system has been considered
and means of compliance to the wave environment have been described.
49
-------
Top View
• Oil Recovery Zone
Side View of
Collection Chamber
Direction of Advance
Figure 18
Collection Chamber Internal Circulation Pattern Illustration
50
-------
X
Rotation with respect to vessel axis
Plan View
1
Heave
1
1 ---- 1
l. Water surface
Elevation View
Water surface
Figure 19
Collection Chamber Displacements Illustration
51
-------
The effect of waves on the collection system is manifested both in
the oil collection effectiveness and in the chamber motion (stability
and integrity).
First, the potential effect of waves on collection effective-
ness is due to the water level changes within the chamber. With the
fast response of the concept chamber, this will be of little consequence
except in waves containing a large, short period energy distribution.
This will be the case only for locally active storms producing choppy
wind wave conditions. If this situation is encountered, it will cause
heaving of the chamber and distortion of the circulation patterns within
the chamber. These short period waves are characteristic of smaller waves
(on the order of 2 foot significant wave height) and will have little
effect on a chamber of greater depth. Another effect of heaving on
chamber effectiveness is the resulting flow in and out of the entry door
with surge. If the chamber bottom were completely sealed, this effect
would produce gross inefficiencies; with the present concept chamber
(roughly 80% open bottom) no appreciable in and out flow with heaving
is expected. A quick operating control mechanism for recovery of
the floating oil in the chamber is suggested, whereby the suction pickup
is automatically kept within a small deviation from the surface of
the watar at the front of the chamber.
Stability and integrity in the presence of waves requires a
system which can withstand the expected forces. The present' concept
affords no major shortcoming or limitations in this respect.
COLLECTION CHAMBER SMALL MODEL EXPERIMENTS
Small model tests were made of the spray boom alone, the
collection chamber alone and the boom and chamber together. Larger
scale tests to determine full scale nozzle requirements for the spray
boom were also made prior to concept model design as described in
Section IV.
Scaled models of collection chamber geometries were evaluated
in a 24-inch wide by 48-inch deep flow channel. The free stream flow
velocity of the channel was regulated by a 20 hp outboard motor mounted
on the periphery of a 15 foot diameter circular channel. Fresh water
flows past two flow straighteners and through a straight section used
for testing. The honey-comb flow straightsner reduce turbulence and
provide reasonably uniform flow for testing. Surface velocities were
determined from pitot tube pressure readings taken 3 inches below the
water surface at the center of the channel.
CHAMBER MODEL TESTS
Verification of the concept geometry was by a series of flow
channel experiments in which' small plexiglas scale models of collection
chamber concepts were evaluated. Figure 20 is a photograph of the flow
channel with an experimental chamber adjacent to the viewing window.
52
-------
Figure 20
Flow Channel Test Section
53
-------
Both open front and side entry chamber types were evaluated.
It was soon evident that there would be major difficulties in isolating
the oil slick from the large quantities of water entering the open front
model. The side entry model was therefore chosen early in the development
testing.
Testing of this chamber concept showed that oil losses occurred
and were attributable to an unwanted circulation pattern within the
chamber. This circulation was found to be produced by high stream
velocities beneath the open bottom chamber. Incoming oil was entrained
in a. downward circulation and escaped. As was analytically predicted,
the installation of vertical baffles at specific locations along the
length and a bottom baffle at the front of the chamber significantly
reduced the internal turbulence and provided an essentially calm region
at the front for oil recovery. Figure 21 shows the final arrangement.
Effectiveness of the collection chamber was measured by flow
channel experiments as the quantity of oil moved to the oil recovery
zone divided by the quantity of oil entering the chamber. Experiments
were performed with crude oil in which a known quantity of oil (500 ml)
was administered at the opening and after equilibrium was reached, the
quantity of oil remaining in the recovery zone was measured. Figure 22
shows the result as a function of the free stream velocity. The rela-
tively high internal chamber effectiveness suggest that once oil enters
the chamber it is not likely to escape.
COMBINED SPRAY AND CHAMBER SMALL MODEL EXPERIMENTS
The operation of the hydraulic oil recovery system, including
the spray boom, collection chamber and oil pickup device, was simulated
in small scale model tests. A manifold with 12 small spray nozzles
approximated the spray boom for the purpose of visually observing the
oil flow patterns and streamlines in the vicinity of the collection
chamber side entrance. Oil slick simulation was accomplished by metering
a quantity of oil through a linear manifold one inch above the water
surface with outlet holes on one inch centers. This configuration allowed
oil to spread to a uniform slick before entering the spray region.
Figure 23 shows the floating oil slick being moved into the
small model collection chamber by the model spray boom. The view of
the oil entrained as a result of turbulence caused by the spray and
corresponding surface current impinging on the opposite side of the chamber
is shown through the side window of the flow channel. This form of
turbulence was prevalent during all of the experiments and was the
primary reason for the observed loss of oil out the bottom of the chamber.
Once oil droplets entered the chamber, they were moved forward by
chamber spray nozzles to the stagnant region. Figure 23 also shows the
calm region towards the front of the chamber. The maximum depth of oil
contained within this region during experiments was 1 3/4 inches.
54
-------
Honeycomb Flow
Straightener
.ection
(j_ Plexiglass Col
Chamber
•Internal Baffles
Flow Channel Plexiglass Window
Figure 21
Final Collection Chamber Arrangement
55
-------
100 __
Internal Effect
Percent
90 _
80 _
70 _
60
.veness
Lagunillas Crude Oil
(Venezuela Heavy)
f
1
I
2
i
3
Free Stream Velocity
(Knots)
Figure 22
Internal Collection Chamber Effectiveness as a
Function of Free Stream Velocity
56
-------
Top View of
Test Chamber
showing
Lagunillas
crude being
skimmed into
a simulated
collection
chamber.
Side View of
Test Chamber
showing
Lagunillas
crude oil
entrained at
the wall due
to spray sur-
face velocities
Figure 23
Spray and Chamber Effectiveness Tests
57
-------
Effectiveness for the model system was defined as the percent
of floating oil moved into the chamber and forward to the stagnant
collection area. Several nozzles with different spray patterns were
tried with a square pattern jet showing the greater utility. As shown
on Figure 24, effectiveness at 1.2 knots with the square jet spray nozzles
was 100 percent. At higher free stream velocities, the efficiency
declined. Flatjets proved to be less effective. It was also noted
that oil could escape before reaching the chamber if the model spray
boom was not properly positioned. Also, at the higher free stream
velocities, the model spray system could not attain the spray pressure
and flow required to move all of the oil into the collection chamber.
Results of flow channel small model system experiments are
summarized in Tables III and IV following:
TABLE III
SMALL MODEL INTERIOR CHAMBER EFFECTIVENESS DATA
Run No.
1
2
3
4
Quantity of
Oil Added
(a*)
500
500
500
500
Quantity of
Oil Retained*
(in.)
13/16
13/16
12/16
11/16
Velocity
Knots
0.87
1.60
2.80
3.70
TABLE IV
SMALL MODEL SYSTEM EFFECTIVENESS DATA
Pitot Tube
Reading
Test No. (in. of oil)
(Flatjet)
//1/8P3504**
5
6
7
(Square Jet)
#1/8GG3004**
8
9
0.12
0.31
0.85
0.30
0.50
Velocity
Knots
0.85
1.30
2.16
1.30
1.75
Quantity of
Oil Added
500
500
500
500
500
Quantity of
Oil Retained*
(in.) %Eff
12/16
9/16
8/16
13/16
12/16
92.5
69.0
61.5
100
92
Flow =2.5 gpm, tests 5,6 & 7; flow - 3.5, tests 8 & 9
* 13/16 inches retained is equivalent to 500 mJl
** Spraying Systems Co., Bellewood, Illinois
58
-------
100
Effect3veness
System
(percent)
80 _
60 -
40
20 -
1.0
Free Stream Velocity (knots)
Figure 24
Spray and Chamber Effectiveness as a Function of
Free Stream Velocity
From Small Model Experiments
59
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COLLECTION CHAMBER DESIGN
A large scale model collection chamber was designed and fab-
ricated based on the preceding developmental work.
HYDRAULIC
Spray nozzles were used to induce surface flow toward the
forward oil recovery zone of the chamber. Manifolds were designed
for orientation, nozzle types, and spray impingement angles consistent
with those of the small developmental model. Piping arrangements pro-
vided for pressure and flow measurement at the nozzles.
Oil suction piping and recovery pumps were sized for a recovery
rate of 260 gpm. To achieve this pumping rate, 3 pumps (diaphram type)
of 85 gpm each were employed. Diaphram pumps were used rather than cen-
trifugal pumps to avoid excessive emulsification of oil-water mixtures.
Each pickup pump was provided with an individual suction line
(two inch flexible neoprene-lined hose). Each was also attached to a
counterweighted recovery device which pivoted at the chamber center and
floated in the water in the oil recovery zone of the chamber. Oil could
enter any one of the three floating suctions. An arrangement including
flotation material and a horizontal baffle provided vertical position
control. See Figure 25 for details.
HYDRODYNAMIC
The drag forces on a deep and narrow object, such as the
collection chamber are from waves, currents, and the forward motion
of the system. These forces were calculated as 765 pounds for a three
foot wave (3.9 sec. period) and 285 pounds from a five knot (8.45 ft/sec.)
relative velocity (speed of forward motion plus current). By super-
position, the maximum frontal force would be 1050 pounds. Since large
scale basin experiments were to involve only straight ahead travel, side
forces were not determined.
STRUCTURAL
The model test chamber was constructed of plywood with
angle iron reinforcement at all corner locations. Buoyancy was pro-
vided by closed cell styrofoam held in place by 1/4 inch bolts and
large plywood washers. Buoyancy material was positioned in the front
and rear for nearly the full depth of the chamber. Additional buoyant
material was positioned at and just above the neutral water line to
provide large restoring forces against perturbations (waves).
Ballast (220 pounds) in the form of lead bricks was attached
to the bottom of the chamber. This reduced the center of mass sig-
nificantly below the center of buoyancy, therefore enhancing roll
stability. The total chamber weight (including ballast) was 440 pounds
6Q
-------
To diaphram pump
Pivot for oil recovery
piping -^
Oil recovery piping
Flotation Material
(polyurethane
foam)
v^ ^ X. ^f" -^J "'->->•
\\ o „• ~ \ foam>
—^A Suctxons \
^i ri i
Chamber Side-entry
|
Figure 25
Schematic Showing One of the Three Duplicate Oil Pickup
Arrangements and Its Relation to Other Parts
of the Collection Chamber
61
-------
and the total buoyancy 880 pounds. Buoyancy was equally divided between
material for restoring force and direct chamber weight compensation.
A photograph of the large scale model test chamber as designed
and fabricated is shown on Figure 26.
62
-------
Figure 26
Large Scale of the Model Collection Chamber
63
-------
SECTION VI
CONCEPT EVALUATION
The basic system components, previously described, were fab-
ricated and combined for experimental evaluation. A thirty-five foot
lifeboat was used as the support vessel. It was attached to a trolley
that was supported by the test basin wall. A model spray boom, 40 feet
long and a 9 foot long collection chamber were attached to the support
vessel. The assembly was towed by a tractor driven parallel and exter-
nal to the basin wall. The system model simulated one-half of a scaled
(approximately 40 percent scale) model hydraulic oil skimmer. (See Figure
3 for system arrangement and construction details of the major com-
ponents—spray boom and collection chamber.) Oil was purposefully spilled
in a boomed off area to be swept by the system. During testing, the
instantaneous oil thickness was monitored as the area was swept, thus
enabling measurement of the amount of oil encountered. Spray flows and
pressure and vessel speed were monitored. Recovered oil and water were
evaluated for each test to determine system effectiveness and oil
recovery rates. During all tests, system integrity and stability was
noted.
The main considerations in evaluating concept performance were
(a) structural integrity and stability and (b) oil recovery performance.
STRUCTURAL INTEGRITY AND STABILITY
Before oil recovery experiments were attempted, several test
runs were made in order to identify any weak design characteristics
or system instabilities in waves or under high speed conditions. Minor
problems could then be solved before they could impede subsequent per-
formance testing.
HIGH SPEED PERFORMANCE
Several tests were performed in which the support vessel, with
the concept system attached, was towed (in the absence of waves) at
progressively higher speeds. The collection chamber and boom were
separately evaluated. It was initially found that at a speed of three
to four knots and the boom angled at 45° to the vessel (no spray),
sections of the boom began to dive or "porpoise". This affect was
caused by the bow wave formed in front of the boom (estimated as six
inches to one foot in height). When these experiments were repeated
with the spray system in operation, this effect did not become apparent
until speeds greater than five knots were reached. Additional boom-to-
vessel cable connections and adjustment of tension in each partially
corrected the problem. The roll stability floats for each boom section
were adjusted to increase the lift with forward motion. Fifty pounds
of additional ballast (per boom section) were also added to each roll
65
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stability float. Following these modifications, tests up to and inclu-
ding seven knots revealed no instability or undesired motions.
The speed mode of operation, which might be used for example
in moving from one oil patch to another, was evaluated. The boom-to-vessel
angle was set at 10° to the vessel centerline and a light spray action
was applied to hold the boom in position. One test at a speed of advance
of 3.75 knots was made without stability or other problems. A slight
tendency toward buckling between boom sections was noted, although it
was clearly safe and stable, showing only a few degrees of rotation from
one boom section to the next.
No collection chamber instability was noted up to speeds of
advance of seven knots. A bow wave occasionally overtopped the chamber
front at higher speeds.
PERFORMANCE IN WAVES
Several structural tests were made with waves up to 36 inches
(significant) wave height. Initial tests were statically performed.
Several minor changes were required in the interfaces between the
vessel and collection chamber and between the vessel and boom. See
Figure 27 for photographic evaluation of the concept system performance
in waves. Experiments were then performed with the system in motion
at speeds up to five knots. With the modifications derived from earlier
high speed runs, the presence of waves resulted in no inherent diffi-
culties. The boom sections followed the waves quite well even at the
higher speeds. The collection chamber also reacted well to waves. The
stilling action of the collection chamber resulted in quite small surges
in the chamber oil recovery zone (less than six inches). Some of the
bow waves overtopped the front of the chamber just as in the earlier tests.
No correction was made, although it was noted for change in the event
another similar device is built.
OIL RECOVERY PERFORMANCE
Once the system was found to be structurally sound and stable,
oil recovery performance experiments were performed. The system per-
formance was to be characterized with respect to the following criteria:
• oil recovery rate
• system effectiveness
• oil-to-water ratio
• recovered oil properties.
The important system variables were evaluated relative to these
criteria in order to determine the system operating characteristics and
66
-------
Spray Boom
Collection
Chamber and
Support
Vessel
Spray Boom
and Boom to
Vessel Connection
Figure 27
Concept Evaluation Model Operating in a 30" to 36V Wave Condition
67
-------
performance limitations. Three types of oil were used; diesel (No. 2
fuel), crude oil (Texaco, Anacortes - 40-42° API) and Bunker (No. 5 fuel).
A considerable range in speeds and several tests with waves were made
with each oil type.
As in the integrity and stability tests, the system was towed
along the test basin wall by a wheel tractor. The average speed of
advance of the model was obtained by timing the travel over the length
of a test run. The test area was a rectangle, bounded by booms, approxi-
mately 60 feet by 360 feet in length. The performance test length was
203 feet, to accommodate acceleration and deceleration of the system.
The effective skimming width was found to be 23 1/2 feet for the 40 foot
boom angled at 45° to the vessel and correcting for end effects. The
oil thickness was monitored along the test length using a pulse-echo
ultrasonic transducer. Thickness was obtained by using an oscilloscope
to monitor the time between sound echoes from the oil/air interface and
the oil/water interface. The thickness readings were integrated to deter-
mine the average slick thickness encountered by the skimmer. A full
description of the oil thickness system used in evaluating the oil skimmer
concept is appended.
During acceleration (before the test length was entered), the
boom spray pressure was adjusted to the value expected to be appropriate
during early nozzle development tests. It was maintained at a value
which was visually observed to move oil to the correct position adjacent
to the collection chamber inlet. Also within this test length, oil
suction pumps were started; the inlets at the pickup device in the
collection chamber were held manually from contacting the oil and water
in the chamber. Once the collection chamber entered the test length,
the pickup inlets were dropped into the chamber to remove the collected
oil. Throughout each run, the spray pressure remained the same as that
set at the beginning and the pickup device remained operating in bringing
the oil and water on board and into a large recovery tank. When the end
of the test length was reached, the system was decelerated, the spray
nozzle pressure was diminished and the suction pickup device allowed to
pick up any residual oil left in the chamber.
After each run, data were recorded including all pertinent geo-
metrical relationships as well as nozzle pressures, speeds of advance
and oil thickness measurements. An oil sample was taken of the oil at
the surface of the recovery tank. This sample was measured promptly
for oil, emulsion and water volumes. Later evaluations of these samples
indicated the water, oil and entrained air contents. The depth of
water, emulsion and oil was also monitored in the large recovery tank
and used later in determining system performance.
When tests were made in waves, the significant wave height was
manually measured. The significant wave height was the measured peak
to trough of the highest 1/3 waves of a random sea. This height was
estimated by visual observation of the water height on a meter stick.
68
-------
Definitions of performance measures and their determination were
as follows:
Oil recovery rate is the volume of oil or emulsified oil recovered
on board the support vessel (in the recovery tank) per unit time. This
represents the rate of continuous oil recovery from the model system under
the condition existing during the test.
System effectiveness relates the oil encountered within the skim-
ming area (as implied by the pulse-echo ultrasonic oil thickness measure-
ments) to the oil recovered on board the support vessel (in the recovery
tank). A 100 percent effective system would be able to recover 100 per-
cent of the oil encountered under conditions prevailing during a test.
Fifty percent effectiveness would imply that fifty percent of the oil
encountered is recovered.
Oil-to-water ratio is the amount of oil (and emulsified oil)
recovered divided by the amount of free water recovered on board.
Recovered oil properties were from samples taken directly after
each test run. After a static holding period for coalescence, the
oil, emulsion and water volumes were measured for each sample. Oil
concentration in emulsions and entrained air volume were also measured.
Test results are included in Table V following. This Table
includes all data relating to oil recovery rates and system effectiveness,
i.e., the practical system operating characteristics. Data which relate
oil-to-water ratios recovered and recovered oil properties to system
variables are also included. Such information is required to delineate
the fluid processes necessary for effective stream quality program goals.
Explanation of the tabulated data is necessary for complete
understanding of these results. First, experiments were performed at
an outdoor facility during the late fall and early winter. In addition
to the discomfort to operating personnel, the low ambient temperature
of test basin water (32 to 50°F) prevented oil spreading at rates
typical of more moderate conditions and considerably influenced other
oil properties such as oil viscosity and pour points of Bunker fuel. In
addition, equipment freeze-up periodically prevented prompt initiation
of experiment runs. Also, when winds occurred, the slick was frequently
swept out of the path of the test apparatus against the basin wall.
Work was periodically delayed for up to five days. The net result of
these environmental difficulties was to slow the rate of experimental
evaluation, although such difficulties may be quite likely in actual use
of the system. It is believed that considerable knowledge of the
possible effects of adverse conditions was gained during this work.
The first twelve test runs were performed with No. 2 fuel oil.
During these test runs, data acquisition techniques were developed,
operational sequences devised, equipment was run-in, and numerous
empirical adjustments were made. The latter entailed relocating the
69
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collection chamber position, enlarging its oil entrance aperture, and
"tuning" the spray pressure and flow to best correspond to the speed of
advance. This tuning was not possible during the performance of a
test run(which lasted for only one to two minutes) and had to be done
from run to run. This break-in period was much longer than had been
anticipated and performance results from the first 12 runs were poor.
Effectiveness ranged from 1.5 to 12.8 percent and recovery rate from
60 to 1920 gph. Because of the aforementioned reasons and because of
later highly promising test results, the first twelve runs are not con-
sidered to be representative of concept system capabilities. Data from
the subsequent experiments (13 through 29), are analyzed in the following
discussion.
OIL EECOVERY RATE
The effect of changes in slick thickness for the three oil
types is shown on Figure 28. Bunker and diesel fuels are little
effected, however crude oil tests show a marked increase in recovery
rate with increased oil thickness. Figure 29 relates speed of
advance with oil recovery rates. Up to 1870 gph was achieved for the
speed of advance range of 1.2 to 4.5 knots for Bunker fuel. Crude
oil recovery rates as great as 8700 gph were achieved between 1.0 and
4.2 knots and for diesel fuel, 7500 gph up to 3.0 knots. System
limitations became apparent especially for the crude oil above 3.0 to
3.5 knots. Oil recovery rates are limited at low speeds by the amount
of oil available for recovery, rather than system deficiencies.
spray pressure divided by thi
squared, or OH °'5/(T V2) ii
A semi-empirical factor which combines vessel speed, oil
thickness and spray flow pressure characteristics is used to evaluate this
system. This performance parameter (spray flow times square root of
the product of oil thickness and vessel speed
. „_ . . is of similar form to equation (4) or equation
(8) in the spray boom performance analysis. The analysis provided the
basis for selection of this combination of variables. Data obtained
from concept evaluation tests shows a correlation with this empirical
factor for the range in variables tested.
Oil recovery rates for Bunker and diesel fuels, are rather
insensitive to variation of this factor as shown on Figure 30. Recovery
rates of crude oil increased from 3000 to 8000 gph as the empirical
factor increased from approximately 15 to 25. A value of 25 would
produce 1500, 7000 and 8000 gph oil recovery rates for Bunker, diesel
and crude oils, respectively.
SYSTEM EFFECTIVENESS
Effectiveness is defined as the percentage of oil encountered
which is collected by the system and brought onboard for processing.
Average slick thickness is plotted against effectiveness in
Figure 31. Singular relationships, "if they exist, are obscured by
70
-------
TABLE V
CONCEPT SKIMMING PERFORMANCE TEST RESULTS
Test Run*
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
13
x9
20
21
22
23
24
25
26
27
28
29
Time/Date Spill
Material
11:30/12/3 Diesel Fuel (#2)
12:10/12/3
10:30/12/4 "
12:00/12/4
1:30/12/4
2:30/12/4 "
11:15/12/5
12:00/12/5
1:00/12/5
2:30/12/5
9:30/12/8 Bunker Fuel (#5)
10:30/12/8
2:00/12/8
9:00/12/9
10:00/12/9
10:00/12/10
11:00/12/10
10:00/12/11
11:30/12/11
.11:30/12/12 Crude Oil
(40-42° API)
1:00/12/12
2:30/i^/::
11:00/12/13
12:00/12/13
1:00/12/13 "
11:30/12/14 Diesel Fuel(//2)
12:00/12/14
1:00/12/14
2:00/12/14
Slick
Thickness
(mm)
.8
3.8
.8
1.3
.6
.9
2.3
1.4
.8
.8
1.5
1.9
1.1
1.3
2.4
2.1
0.5
1.1
1.4
1.2
1.7
1.7
1.0
1.6
1.0
3.0
2.5
2.5
1.5
Wave Condition
(height /period)
calm
n
n
n
n
n
n
it
18"/2.5 Sec.
24"/3.0 Sec.
calm
n
"
n
n
"
n
28"/3.0 Sec.
28"/3.0 Sec.
calm
"
n
n
14"/3.5 Sec.
14"/2.5 Sec.
calm
30"/3.5 Sec.
calm
30"/3.5 Sec.
Speed of
Advance
(knots)
.5
.9
1.3
2.0
2.9
0.8
3.3
3.6
1.4
2.6
0.8
1.4
2.1
2.7
3.0
1.4
4.5
1.2
2.8
1.6
3.0
4.2
2.0
2.0
1.0
1.5
2.0
3.0
0.9
System
Effectiveness
7.2
12.5
7.4
9.8
9.4
2.5
1.5
2.1
12.8
5.3
3.0
4.2
10,4
6
12
13
6.5
8.7
30
84
55
24
40
97
100
56
39
41
81
Oil Recovery
Rate (gph)
140
1920
520
910
590
60
430
360
530
390
130
480
1870
1170
1420
820
1500
420
1380
7700
8700
3000
4670
6800
4900
7500
6700
6640
68LO
Oil/Water
Ratio
.05
.52
.12
.40
.05
.03
.03
.03
.10
.03
.03
.05
.12
.34
.16
.07
.20
.06
.08
7.7
2.4
.6
6.8
7.5
2.3
1.5
1.2
1.2
4.9
% Water (air)
in Recovered Oil
—
8
22
56
60
77
38
30
50
(25), 7
(17), 7
(36)
(25)
(4)
(27)
(12)
(12)
(13)
70
67
64
13
3
3
1.5
3.1
6.9
3.2
Empirical Factor
Q^H 0.5/(T v2) gph/ ft
psi°-5/(mm kts2)
488
36.3
72.2
25.4
34.8
67.7
7.9
11.6
51.9
32.4
61.3
20.1
27.3
17.3
9.2
25.9
27
47.2
14.0
34.8
11.1
9.2
20.3
15.0
69.8
19.6
14.3
7.3
53.4
* Test runs 1 through 12 are not considered to indicate system performance;
Test runs 13 through 29 will be considered to indicate __ -tern
concept.
but were made to determine necessary modifications.
for the particular arrangement tested. It does not indicate optimum performance of basic
71-72
-------
CO
o
o.
60
0)
J-l
13
0)
O
a
a
•H
O
10
9
8 .
5 .
O
A
O
Bunker Fuel
Crude Oil
Diesel Fuel
Darkened Forms Indicate Tests
with Waves (14-30")
0.5 1.0 1.5
Average Slick Thickness Encountered (mm)
2.0
2.5
Figure 28
Oil Recovery Rate as a Function of Slick Thickness
73
-------
P.
60
3
&
M
-------
50
40
•*]
ml
n-it
F
H
-------
c
-------
such variations as the emulsification of the oil by recycling from run
to run and nonuniformities in slick thickness. As is expected, system
effectiveness decreases with increases in speed of advance (see Figure
32). This is a result of both inefficiencies in skimming at higher
speeds and limits in system variables such as spray flow and pressure
at increasing speed. Bunker fuel showed relatively poor system effec-
tiveness. During evaluation tests, low temperatures caused this
material to congeal so that it did not physically resemble the slicks
of the other materials. It appeared very sluggish and tended to roll
along near the surface rather than flowing on the surface as did the
other material. Several possibilities exist for improving performance
on Bunker fuels. The most attractive is to provide the capability for
adjusting the height of the spray nozzles so that spray water exits just
at the water surface. Such a reduced spray impingement angle would be
expected to substantially improve effectiveness on heavy oils. This
conclusion is supported by the spray boom performance analysis in con-
sideration of the submergence phenomenon caused by spray impingement on
heavy oils.
Figure 33 shows system effectiveness as a function of the
previously defined empirical factor. The correlation defined in Figure
33 is consistent for the three oil types. An empirical factor of
approximately 25 is required for recovering 100 percent of crude oil
encountered. Extrapolation of the diesel test data shows a value of
40 for 100 percent recovery.
Bunker fuel tests also show a correlation, but at a lower range of
effectiveness. Extrapolation far beyond the experimental parameter
range should be done with caution. Considerable increase in the empirical
factor is necessary in order to increase system effectiveness for Bunker
fuel to the levels observed for the lighter materials. Approximately
20 percent system effectiveness was obtained at an empirical factor
value of 40. Changes in the system would be expected to change the per-
formance correlation.
OIL-TO-WATER RATIO
The relative quantities of oil, emulsified oil and water
recovered on board the model test support vessel varied considerably.
Since the oil recovery pumps (3) were all operated continuously for
each full test run at their maximum pumping rate (no attempt was made
to optimize the oil to water relative pickup rates), variations in
the quantities of oil, emulsion and water recovered occurred. Exper-
iments were performed over a broad range of speeds of advance, over
varying slick thicknesses, with different oils (pumping Bunker fuel
would be slower due to viscosity effects). With waves, some pumping
of air occurred (the suction device would frequently raise above the
surface and elementarily pull in air). All of these would affect
the relative quantities of oil (and emulsion) and water being recovered
by the pumping system.
77
-------
c
CD
o
M
0)
P.
CO
CO
c
cu
0
cu
M-t
4-1
W
-------
50
m
o
M
I
H
m
•
o
o
4J
O
u
•K
cx
40
30
20
10
O
A
D
_L
Bunker Fuel
Crude Oil
Diesel Fuel
Darkened forms indicate
tests with waves
(14-30") /
A
_L
J_
JL
J_
_L
0 10 20 30 40 50 60 70
System Effectiveness (percent)
_L
80
90 100
Figure 33
Empirical Factor as a Function of Model System Effectiveness
79
-------
With continuous operation of a large prototype system, the
rate of pumping of the oil recovery pump system could be readily con-
trolled. Approximate maximum oil-to-water ratios for Bunker fuel,
crude oil and diesel fuel were found to be 1/3, 20/1 and 4/1, respec-
tively. It is also probable that frequent and appropriate "tuning"
of the system would achieve oil-to-water ratios on a continuous basis
as were obtained during the best test runs. Bunker fuel oil-to-water
ratios would possibly be increased from the 1/3 value for continuous
operation. Greater ratios would be possible if recovery rates were
increased or pumping rates reduced. Here, continuous operation implies
oil recovery over a time period on the order of an hour rather than
the short duration test runs of one to two minutes.
RECOVERED OIL PROPERTIES
Characteristics of recovered oil were implied by sampling
recovered oil and allowing the constituents to coalesce. Thus, a
determination of the extent of emulsification and air entrainment
was possible.
Bunker fuel (No. 5, P.S. 300 grade) showed no tendency to
emulsify. Volume was found to decrease with time, however. This
decrease was observed to be caused by air entrainment in the spraying
and pumping operations. Air entrainment varied from 4 to 36 percent
in the recovered oil product: for the test runs evaluated, averaging 19
percent over the seven tests. This represents a decrease in effective
density of on the order of 19 percent, i.e.,Bunker of density 1.0 would
have an effective density of 0.81.
Both diesel fuel (No. 2) and the crude oil (40-42° API) samples
showed varying degrees of emulsification, primarily water-in-oil type.
Water concentrations ranged from three to 70 percent and 1.5 to 9.6
percent for crude and diesel fuel, respectively. Crude oil samples
averaged 37 percent water, while diesel oil samples averaged only
3.7 percent. For both fuels, it was impossible to distinguish free
oil from emulsified material in the samples when initially examined.
Crude and diesel oils showed no tendency to capture entrained
air, probably due to their relatively low viscosities. Bunker fuel, on
the other hand, was quite viscous, almost to the pour point of the mater-
ial, and showed no emulsion with water.
Continued cycling of the oils resulted in added emulsification
from one test to the next, as was noted in the initial 12 test runs
with diesel fuel.
SYSTEM PERFORMANCE ASSESSMENT
The following paragraphs compare the measured or extrapolated
concept system evaluation test with design goals as specified in the
request for proposal.
80
-------
(1) Skim in 5 foot waves with 20 mph winds and 2 knot currents
superimposed
Skimming with the complete system at approximately 40 percent of
full prototype dimensions was performed in random waves of three feet
height with little or no degradation in system performance. Waves in
the area covered by surface oil slicks were suppressed to about 30 inches
in height. It is believed that the short chop waves encountered by the
concept system during testing are probably more detrimental to performance
than longer waves of the 5 foot size. This is because of the ability of
the floating components to follow the longer wave profiles. Component
interfaces will be designed to be compatible in displacement and strength
to the expected environmental effects of a five foot sea.
The effect of wind on performance (structural and stability) was
not determinable during the high wind conditions periodically experienced
during model testing. These winds did, however, force the oil slick
against the test boundaries and out of the skimmer path, thus making it
impossible to test for skimming performance during such periods. All
exposed components are of a low profile to the wind and the sea. It is
therefore believed that winds of 20 mph will have little effect other
than to cause a surface oil movement with respect to the water column.
Currents of 2 knots are assumed to be relative velocity values
between the system components and the water column. Since skimming was
quite successful at greater values than 2 knots, this was met.
(2) Capable of 8 knot speeds in 10 foot waves and 38 mph winds
and capable of 12 knot speeds under the condition of (1)
(not while skimming)
The configuration of the system in this mode of travel would be
such that the booms would be towed in a trailing position. The low pro-
file of the booms and their ability to follow the sea surface are expected
to make them quite suited to towing. The outrigger floats are expected
to present some resistance to such speeds. However, with adequate design
of the connection to the booms, these floats will handle 8 or 12 knot
travel. Problems may arise at the joints between boom sections and
between the boom sections and the support vessel. Design of these inter-
faces must make provision for expected environmentally induced forces.
Total travel for the vessel boom interface must be suited to the
wave heights encountered. Quick breakaways or other similar devices
might be necessary for protection of the vessel and personnel under
severe storm conditions.
(3) Storage of 1,000,000 gallons of oil
Storage requirements were beyond the experimental phase of this
concept development program although pillow tanks are presently available
and capable of filling this demand.
81
-------
(4) Able to recover oils ranging from light diesel to Bunker C
Test runs with, diesel fuel CNo. 2), Bunker fuel (No. 5) and
with a crude oil (40-42° API) showed capability for handling each type.
The recovery rate for Bunker fuel was at about one sixth the rate for
crude oil and diesel fuel recovery. Test runs involving Bunker fuel
showed that the spray jet tended to aerate this material so that it
exhibited a lower density than it would have otherwise. This enhances
the ability of the system to recover heavy fuels as compared to con-
cepts involving only gravity.
(5) Capable of recovery 50,000 gallons per hour under design
environmental conditions as stated in (1)
Recovery rates of 50,000 gph can be accomplished by a prototype
recovery system based on the concept developed in this program. Test
data show that 1500 gph of heavy oil or 7000 to 8000 gph of light oil
(crude oil or diesel fuel) can be recovered by the concept model which
covered a 23.5 foot sweep width. Simple scale-up shows that 50,000 gph
can be recovered using a skimmer boom combination which has a 140 foot
sweep width for light oils and 780 foot for heavy oils. As previously
mentioned, flexibility for optimal placement of nozzles closer to the
water surface, should enhance performance for heavy oils. Further tuning
of the spray pressure and boom-to-vessel angles may also improve on these
scale-up predictions. Concept evaluation tests were performed on contained
slicks. Linear extrapolation to the prototype system would be expected
to be conservatively in error because of the boundary effects associated
with boomed areas as contrasted to large unrestricted slicks.
(6) Operate on slicks of 1.5 mm in thickness^ or less
The concept system recovered oil throughout the range of oil
slicks employed in evaluation tests (0.465 to 3.75 mm).
(7) The recovered oil shall not contain more than 10 percent
sea water and the effluent water shall not contain more
than 10 mg/liter of oil
Additional equipment, such as centrifugal separators, coalescers,
or settling tanks, will be required to meet these goals. The develop-
ment of these was beyond the scope of the present program. Features
of the proposed concept which tend to enhance the oil-water separation
process are: (1) the entrainment of air in the heavier oils makes
them more buoyant (air floatation may be a natural process in the system);
(2) water effluents from separation processes may be recycled through
the pressure spray system and; (3) recovery pumping rates can be "tuned"
to produce a consistently high proportion of oil in the recovery product
pumped from the collection chamber.
82
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SECTION VII
ACKNOWLEDGMENTS
Experimental analysis and design phases of the study were
performed by a team from Battelle Memorial Institute's Pacific Northwest
Laboratories at their hydrodynamic testing facility in Richland,
Washington. Acknowledgment must be given to those organizations which
assisted in this effort. The assistance of the Texaco and Shell Oil
Companies in providing test oils is greatly appreciated. Local material
fabrication contractors and equipment purveyors also must be given
credit: Keltch Construction Company, Metalfab Company, R and N Inc.,
W I and M Fuel Company and Felton Oil Company are but a few who made
contributions.
The authors gratefully acknowledge the support and guidance
given by personnel from the Water Quality Office of the Environmental
Protection Agency, specifically, Mr. John J. Barich, III, who served
as project officer and Mr. Harold Bernard and Mr. Kurt Jakobson of
the Agriculture and Marine Pollution Control Branch.
Mr. John R. Blacklaw
Mr. Elaine A. Crea
Mr. Roy C. Kelley
Dr. E. Roger Simonson
Mr. P. C. Walkup
Battelle Northwest
83
-------
SECTION VIII
REFERENCES
1. "Oil/Water Separation System with Sea Skimmer," a report by the
Garrett Corporation to the Environmental Protection Agency
(Project 15080 DJP), October 1970.
2. "Final Report, Sea Dragon Oil Spill Containment and Removal
Systems>" Airsearch Report 70-6787, September 1970.
3. "Final Report, Development of a Water Jet Device for the
Collection of Floating Oil Slicks," a report by Battelle
Northwest for the Garrett Corporation, September 30, 1970.
4. S. A. Berridge, R. A. Dean, R. G. Fallows, and A. Fish, "The
Properties of Persistent Oils at Sea," J. Inst. Petrol, Vol. 54,
No. 539, November 1968.
5. P. C. Blokker, "Spreading and Evaporation of Petroleum Products on
Water," Paper presented at the Fourth International Harbor Con-
ference, Antwerp, June 22-27, 1964.
6. H. G. Schwartzberg, "The Spreading and Movement of Oil Spills,"
summary of report number 15080 EPL 4/70 in the Water Pollution
Research Series of the Environmental Protection Agency, April
1970.
7. M. Wicks III, "Fluid Dynamics of Floating Oil Contained by Mechan-
ical Barriers in the Presence of Water Currents," Proceedings,
Joint Conference on Prevention and Control of Oil Spills, spon-
sored by the American Petroleum Institute and the Federal Water
Pollution Control Administration, Dec. 15-17, 1969.
8. W. H. Trask and B. D. Bingham, "The Conduct of a Feasibility
Study of the Inverted Weir Oil Collector Concept," prepared by
Battelle-Northwest for the U. S. Coast Guard, 1970.
85
-------
SECTION IX
APPENDIX
Ultrasonic Oil Thickness Measurement Device
An ultrasonic system was assembled and used during concept
evaluation tests of the floating oil recovery system employing a spray
boom and side-entry collection chamber. It was operated in waves varying
from essentially calm conditions to 3.0 foot short chop waves and in
currents up to 4.5 knots. Considerable difficulty was experienced with
the system as assembled at the maximum environmental conditions experienced.
The concept involves a specially designed ultrasonic trans-
ducer which obtains oil/water and oil/air interface signals for further
processing. Detection of the two interfaces is accomplished by using
a pulsed ultrasound signal and monitoring the return reflected pulse.
The time delay between return pulses is an indication of the presence
and thickness of an oil slick. All that is necessary to cause a reflected
pulse is to have a significant abrupt density change at an interface.
The photographs shown on Figure 34 of an oscilloscope trace
of the pulse-echo signal train for diesel fuel on tap water illustrates
the ultrasonic technique. In the first photograph, tn denotes the trans-
mitter pulse or time 'O1, t.. represents the reflected sound energy from
the water-oil interface, t_ represents the oil-air interface, and t«,
t,, . . . . represents the reflected trapped sound in the oil layer. The
time between t and t« and t_, etc. is directly proportional to the oil
thickness. Calibration of tne instrument would involve determination of
the velocity of sound in oil, thus, the time measurement may be con-
verted directly to oil thickness. The second photograph represents near
the minimum thickness (near 10 mils) which can be measured with commer-
cially available ultrasonic instrumentation.
A support must be provided to hold the transducer within a
given distance of the surface. A floating catamaran pontoon was used as
the support principally because of the wave following capability of such
structures.
Processing of signals can be by many approaches depending upon
the required accuracy and the wave conditions present. With any
appreciable waves, a time delay, a pulsing system and electronic gates
are employed so that only the time difference between signals from the
two interfaces is monitored. This method and monitoring of compressed
signals was used in the work described herein.
High accuracy measurements or measurements of very thin slicks
require high quality signal processing equipment and appropriate trans-
ducers. Testing was accomplished with a thickness accuracy of approxi-
mately 1/16 inches. Equipment presently available may be assembled to
measure down to 1/100 inches and further refinements may make a resolu-
tion of 1/1000 inches possible.
87
-------
Diesel Fuel
(No. 2) 3.0 mm
thick, on tap
water
Diesel Fuel
(No. 2) 0.3 mm
thick, on tap
water
Figure 34
Oscilloscope Trace from Slick Thickness Measuring Device
-------
BIBLIOGRAPHIC:
c KortWeal Laboratories, laticlle Mrarlal Inatltate. Concept
for (b* Cnvlrooatt&tal frorec
1SOW rwr 4/71. Aft 11 1971.
ABSTRACT
S1J« »ount*d
1« pnapid to an onboard separation ayites fro* which the oil la transferred to
flMtlne. tanks or bar^ea and the water IB recycled to the spray sy»tn.
ExperlBental work vta directed toward coponcot development and evalutlon
Mo4rl mp*rlm*nt ruult* ihowcd. for ll^-it elli, 6O to 100 pcrcccC cff*ctl*«
1 all rtco-itrj iat*i of ttOO to 67CW gph. fLeiulc* with luiuct fuel wer« DOC
.Further Irvclopaent of the concept. Including •ddltlotial Mdtl t**Ct«t
•ftb heavy Bill plui cp*o •*• *T«l«atlo« ( all illck*. Nachinieal tccowrr MthodB. which do aot eai»« addltlorul
f»e«, «r« »tt*chnl to an op«» •» vorkbeat. 5** «*t«t l« f»c?*4 through »pi*T
»otll«» wounterf ot» the h»ad*r» to BO«« ca oil click toward th> boat. Sil Frotcctlon A(eac;t U*tcr Quality .01 Clce. trotte* k'i«Bv*
IXIK FVT 4/71. April 1971.
ABSTRACT
Cffort* ore fcelae. directed to develop effectln cei0t«r*eoaure« «|iln*t
H»«tlB| •!! allcfca. Mechanic*! recovery Bethod*. which do aot c»u«« additional
*•* lnv««tl|at*d.
floating header*! providing • linear water ffitj pattern on the water »<
lac*. *r« *ttached la an open tea workboat. Sr* water 1* pJip*4 through *puy
rtMrtt•] work w** directed touaid co*pomat 4«v«lop«e9t aad avaliMtloa
P«rmtt e>p«rla«atal vrrlflcatlaa of aodlf leal totiB >ap«ct*d to lucre*** perfai
#* heavy olla.
Further ocvelcp^eni
ACCESSION NO.
KEY WORDS:
Concept
Equipment Development
Oil Skimmer
Open Sea
Evaluation
Oily Water
Separation Techniques
Technical Feasibility
.atjpe »j»ttm VM r
-------
* A <. ves;, /on .Vumber
Q Subject Field &. Group
05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Pacific Northwest Laboratories of Battelle Memorial Institute
Title
Concept Development of a Hydraulic Skimmer System for Recovery of Floating Oil
10
Authors)
Blacklaw, John R.
Crea, Elaine A.
Simonson, E. Roger
Walkup, Paul C.
16
Project Designation
21
Note
22
Citation
Environmental Protection Agency, Water Quality Office, Program Number 15080 FWP
4/71, April 1, 1971 } 88 pp.
Descriptors (Starred First)
Evaluation*, Oily Water*, Separation Techniques*, Technical Feasibility*,
Efficiencies, Hydraulic Systems, Hydrodynamics, Jets, Mathematical Studies,
Testing, Water Pollution Treatment
25
Identifiers (Starred First)
Concept, Equipment Development, Oil Skimmer, Open Sea
27
Abstract Efforts are being directed to develop effective countermeasures against floating
oil slicks. Mechanical recovery methods, which do not cause additional environmental insult,
are most attractive. Such a concept, a hydraulic skimmer, was investigated. Floating headers-,
providing a linear water spray pattern on the water surface, are attached to an open sea work-
boat. Sea water is pumped through spray nozzles mounted on the headers to move an oil slick
toward the boat. Side mounted chambers are positioned to collect the concentrated floating oil.
Recovered fluid is pumped to an onboard separation system from which the oil is transferred to
floating tanks or barges and the water is recycled to the spray system. Experimental work was
directed toward component development and evaluation of a large system model in a simulated
environment. A 35 foot support vessel, a 40 foot spray header, and a 9 foot collection
chamber provided the 23 1/2 foot model sweep width. Speeds of advance to five knots, random
waves to 30 inches significant height and three oil types were used in evaluating this system.
Other equipment such as an ultrasonic oil thickness gauge, process pumps and tankage were also
used. Model experiment results showed, for light oils, 80 to 100 percent effectiveness and
oil recovery rates of 6600 to 8700 gph. Results with Bunker fuel were not as good, being on
the order of 1300 to 1800 gph and 12 to 30 percent effective in Recovering oil from the water
surface. However, program time constraints did not permit experimental verification of mod-
ifications expected to increase performance on heavy oils. Further development of the con-
cept, including additional model testing with heavy oils plus open sea evaluation of a proto-
LV »« UVULl
Abstractor
ittt-
wau —
John
•t
R.
umnutiemat
Blacklaw
Institution
Pacific
Northwest
Laboratories,
Battelle
Memorial
Institute
it R: 1 02 (REV JUV.V
VR Sr C
SEND TO'- VtATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S DEPARTMENT OF THE INTERIOR
WASHINGTON, D. C 20240
i V. S. GOVERNMENT PRINTING OFFICE : 1971 O - 428- 628
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