433
1
INTRODUCTION
The problem of emergence, collection, storage and
separation of a multi‐phase flow of water with oil
products, referred to in the operating conditions of
watertransportvehiclesasshipʹsbilgeandoilywater
(BOW) is very actual and important. BOW during
vessel’soperationarethemostlarge‐tonnage
typeof
waste,andfortheirprocessingallshipsinaccordance
with regulatory requirements [14] have to be
equippedwithBOWseparators.
The outlet concentrationofimpuritiesinpurified
watershouldbelessthan15p.p.m.[14]andinabig
numberofspecialregionsoftheplanet,theoverboard
discharge of BOW is prohibited. With a
comprehensive analysis of this problem, it can be
stated that from an economic point of view the
secondaryoilproductsobtainedfromtheBOWareof
greatinterestasasourceofadditionalfuelresources
fortheship.
Bilge and Oily Water Treatment During Operation
of Vessel
O.V.Malakhov,O.M.Palagin,A.I.Naydyonov,K.A.Lykhoglyad&A.V.Bondarenko
NationalUniversity“OdesaMaritimeAcademy”,Odessa,Ukraine
ABSTRACT:Bilgeandoilywater(BOW)duringvessel’soperationarethemostlarge‐tonnagetypeofwasteand
fortheirtreatmentallships,inaccordancewithregulatoryrequirements[14],havetobeequippedwithspecial
equipment– oilywaterseparators.Under conditionsofsea
vesseloperationBOWareprocesseffluentsthat
occurintheengineroom,incargoholds,aswellasduringtheoperationofthedifferentequipmentanddeck
machinery.Atseavessel’soperatingconditionsthreemaindirectionsofBOWcleaningarenowused:physical,
chemicalandbiological.Inmosttechnologicalcases,
theyareusedincombinationwitheachother.Theanalysis
ofBOWseparationmethodsbasedonthesethreedirectionshasshownthattheyallcouldbecharacterizedby
one common drawback‐unidirectional cleaning. During separation the final product – water is only one
componentof multiphaseflow.Itisverydifficult
toobtainsecondarypetrochemicalproductswhenmodern
methodsofpurificationareusedontheseavesselduringseparation.Becauseofthisreasonintheresearch,a
new method for BOW separation was developed. It is based on the use of a hydrodynamic process of
supercavitation with artificial ventilation of the
cavitational cavern. With local origin in the flow of a
supercavitatingcavern,therewillalwaysbesaturatedwatervaporinsideofit.Theprocessofpermanentwater
vaporselectionfromthecavernwillultimatelycontributetotheproductionofhighlyconcentratedmixtureof
those petroleum products that form the initial mixture
of BOW. In research, an assessment of the spatial
stabilityofthecavitationalcavernintherangeofvariouscavitationnumberswasdone.Duringthestudyof
BOWseparationprocessitwasfoundthatdecreasingoftheworkingpressureinsidetheworkingchamberof
the cavitation separator havetobe
alwayscompensatedby an increasein the temperatureofthe processed
multiphaseflow.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 18
Number 2
June 2024
DOI:10.12716/1001.18.02.23
434
2
MATERIALSANDMETHODS
2.1
MainSourcesofBOW
BOW are process effluents that occur in the engine
room,incargoholds,aswellasduringtheoperation
ofthedeckanddeckmachineryundertheconditions
oftheshipʹsoperation.
According totheanalysisfulfilledforsea vessels
(bulkers,tankers,RO‐ROtypevessels,
etc.)operation,
it was found that the main generators of the
components that form the basis of the BOW, which
finallyendupinbilgewellsandtanks,are:condensed
liquids from cooling systems of main and auxiliary
engines; condensed liquids from starting and
auxiliary compressors for compressed air supply;
liquids condensated from the deck heater system;
distillate from refrigeration units and compressor
units servicing air conditioning systems; liquids
condensated from for oil tanks (separator tank,
incinerator tank, etc.) heating systems; leaks in
pipelines and ship auxiliary mechanisms, in
particular: sea water, fuel, oilandsteamsystems (in
most cases, such
leaks are typical for ships whose
constructionandoperationperiodexceedstenyears);
waste water with light chemical products after
cleaning or scrubbing the decks of the engine room
andpalletsofshipauxiliarymechanisms;productsof
washing or scouring of: decks, deck machinery,
processequipmentandauxiliaryequipment;running
water forpersonalhygiene of workersin the engine
room of large multi‐tonnage vessels; drainage of
rainwater from ship chimneys at the absence of
separatedischargelines;cargohold ortankwashing
productscollectedinaseparate,so‐calledSLOPtank;
products of oil spills during bunkering or during
loading
and unloading operations, collected in a
separate SLOP tank; drains from bow, stern and
centralshipwellsandgaters.
During operation of water transport facilities
quantitativechangesinthetotalvolumesofgenerated
BOW are determined by a combination of the
followingreasons:theoperationalintensityoftheship
power
plant; total power and number of auxiliary
boiler equipment; non‐uniform loading of the shipʹs
holds with the same type of cargo; the quality of
inspectionandrepairoftanksandfuelandoilsupply
systems,etc.
2.2
SpecificFeaturesofBOW
ThequalitativeandquantitativecompositionofBOW
isnotuniversalandineachcaseisavariablevalue.It
directly depends and is determined by the ship
technologicalprocessesthat generateit. Theaverage
statisticallistofthemainBOWcomponentsincludes:
dissolved gases; oils (industrial, used
machine oils,
etc.)withaconcentrationofupto1000mg/l;wasteoil
productsandtheircomponents,aswellasoilsludge
(concentration up to 8000 mg/l); detergents
(concentration up to 5‐10 mg/l); suspensions
(concentration up to 300‐500 mg/l); sulfates
(concentrationupto200mg/l);phenols(concentration
up
to50mg/l).
Alloftheabovecomponents,exceptforgases,are
characterizedbyalargespecificgravitycomparedto
thesameparameterforwater, whichis thebasis for
thefurtherprocessfortheirseparationfromtheBOW
flow.
IfweclassifyBOWcomponentsasgaseous,liquid
and solid we
can state that, depending on the ratio
between the densities of the separately considered
componentρc and waterρw, the following two
optionsforthebehaviorofthemixturearepossible:
in a stationary state, over time atρc<ρw, for a
certaintimeduring stratification,the components
oftheBOWwillfloatup;
inmotionwithabsenceofliftingforcesandρc>ρw,
thecomponentsoftheBOWwillprecipitate.
ConsideringBOWasamulticomponentflowbeing
processeditisworthtonote,thatwhenanalyzingthe
operation practice of separators, it was found that
high purification efficiency occurs ata concentration
of harmful
components only up to 100 mg/l [3, 19].
Exceeding this value leads to the complication of
methodsusedfortheirseparation.
2.3
BOWSeparationMethods
The general principles of technological schemes
functioningintendedforBOWseparationaredirectly
determined by the work processes used to separate
their constituent components. Three main directions
of water purification in the vessel operating
conditionscanbedistinguishedprincipally:physical,
chemicalandbiological.Inmostcases,theyare
used
incombinationwitheachother[1,3,11,13,16].
The basis of the physical direction is the use of
mass and less often surface forces. In this case, the
mass forces include the forces of inertia, gravity,
floating,etc.
The implementation of chemical processes in the
BOW separation
is based on the use of various
reagents in combination with electrochemical
oxidationoftheprocessedflow[2,12].
ThebiologicaldirectionofBOWseparationimplies
theuseofmicroorganismsthatensurethedestruction
of the constituent components of petrochemical
productsduringthetimeoftheirlifeactivity[20,25].
During
research,ageneralstructuralclassification
of existing methods for the BOW separation was
developed (Fig. 1). It was done in the form of a
diagram, which shows that all ship technological
schemes for BOW processing are based on twelve
differenttechnologies.
The analysis of their performance indicators has
shown that
during the vessel’soperation,separators
which operate on the principle of centrifugal flow
separation are most widely used. The main
disadvantageofmarinecentrifugalseparatorsistheir
limitedcapacity,i.e.inabilitytoprocesslargevolumes
of BOW in short periods of time. Basically, such a
limitation is caused by the length
of the path that
particlesofoilyimpuritieshavetopassbybeforethey
hit the free surface of water or stick to the contact
surfaceoftheseparator.
During separation of BOW, pre‐filtration of the
processedmultiphaseflowisusedalways.Itisbased
on the physical cleaning
method and is founded on
435
theuseofpressureornon‐pressurefiltration.During
filtration,anon‐selectivereversibleprocessisused.It
isbasedontheuseofvanderWaalsforces‐theforces
ofintermolecularinteractionbetweenthemoleculesof
the filtering materialand the molecules of the BOW
components[21].
Figure1.MethodsofBOWseparation
2.4 CavitationinBOW
AdetailedanalysisofallmethodsforBOWseparation
in Fig. 1 allows to conclude, that they are
characterizing by one common drawback‐
unidirectional cleaning. During the separation, the
output product is only one mixture component‐
water.Whenusingthesepurificationmethodsduring
separation, it is very difficult
to obtain secondary
petrochemical products. For this reason, during the
research, it was concluded that it is necessary to
develop a new method for theBOWseparation and
theexpediencyofusinginthiscasethehydrodynamic
processofsupercavitationwithartificialventilationof
thecavity.
Withlocalorigin in
theflow ofasupercavitating
cavern, there will always be saturated water vapor
insideofit[24].Theprocessofcontinuousselectionof
water vapor from the cavern will ultimately
contributetotheproductionofahighlyconcentrated
mixture of those petroleum products that form the
initial content of the BOW.
An example of a
supercavitationalcavernforstationarywaterflowone
canseeinFig.2[18].
Figure2.Stationarysupercavitationcavern[18].
Themainadvantageoftheproposednewmethod
for BOW flow separation using the supercavitation
process with artificial cavity ventilation is the
possibility of purifying the flow with a high
concentrationofharmfulimpurities.Thismethodcan
beusedasanalternativetoelectrochemicalseparation
methods, which are currently considered to
be
practicallytheonlyeffectivemethodsthatcanbeused
atimpurityconcentrationsinwaterexceeding1g/l[2,
17].
2.5
SpecificofCavitationalFlowsandCaverns
The main feature of the occurrence of cavitation
cavernsonrigidboundarieslocatedinamovingflow
isthebeginningofcavitation‐themomentwhenthe
cavitationnumberΩbecomesequaltotheminimum
pressure factor С
рmin. On the outflowing surface, the
value of this factor is determined bythe position of
the point (line) where the maximum rarefaction is
observed [6]. Near such a region of minimum
pressure,nucleation,accumulation,andassociationof
initially formed bubbles of water vapor and gases
dissolvedintheliquidoccur
[5,6,10].Theinfluence
ofthedesign(itsgeometricconfiguration,thedegree
ofcurvatureoftheconstituentelements,theangleof
attackoftheflow,theamountofoverlapattheinlet
and outlet, etc.) of the working chamber of the
cavitation channel always increases with the
developmentof
cavitation[26,27].Thequalityofsuch
influence is directly determined by the shape and
location of the surface on which the cavitational
cavernisformed.
Since cavitation in a liquid is the formation and
stableexistenceofcavitiesfilledwithvaporandgases,
theratioofthecontentofgas
andvaporinthecavity
maybedifferentwithalocaldecreaseinpressure.
Depending on the concentration of steam or gas
insidethecavern,cavitationcavernsaredividedinto
twotypes‐steamandgaseous[5,18,27].
Due tothecomplexity of the processes occurring
during artificial cavitation, there
is currently no
clearly formulated theory that describes the
relationship between the main characteristics of this
flowand hydrodynamic forcesthataffectthespatial
dimensions of the cavity. There are also no known
data that indicate how the air flow and pressure
which goes to supply cavity ventilation affect these
values
[15].
The value of the static pressureРSt has a direct
impactonthestabilityofthesupercavitationalcavern.
With an increase in the value ofРSt, the decreasing
volumeofthecavitationcavernwillperceivealarge
value oftheabsolutepressure.Accordingly, the rate
of decrease in volume
will be higher, other things
beingequal,andasaresult,thepressureofthevapor‐
gasmixtureinsidethecavitywillincrease,eventually
leadingtovaporcondensation.
Aspecificfeatureofsupercavitationinmultiphase
flows is the absence of influence of the physical
propertiesoftheflowontodynamicsof
thecavitation
cavern existence [18]. In particular, such two
important factors as the surface tension coefficient
and the viscosity of the flow do not change the
dimensions of the cavitation cavern with the
invarianceofthecavitationnumberoftheflow.Thus,
forexample,theinfluenceofviscositybeginsto
affect
when its value exceeds by two orders of magnitude
(at100andmoretimes)theanalogousvalueforpure
water[28].
The spatial behavior of cavitation caverns is
directly determined by the geometry of the flow in
436
whichtheyareformed.Thecavityshapecanchange
significantly under the influence of closely spaced
hydrodynamic features [18]. In this case, depending
on their intensity and location in relation to the
cavitation cavern, it is possible to obtain a different
degreeofdeformationofitsboundaries.Atthesame
time,inthecaseofveryhighrelativeflowvelocities,
theinfluenceoftheforcesofgravity(weight)ofliquid
on the geometry of the cavitational cavern is
practicallyabsent.
The presence of rigid walls near the cavern can
leadtotheappearanceofasymmetryofitsboundaries
withrespect
tothehorizontalsection.Inthepresence
ofahorizontalchannelwall,themaximumlengthof
the cavitational supercavern depends on the
cavitationnumber.Ifacavityappearsbehindthedisk,
thenitslengthcanbedescribedbyarelation[7]
1, 66
Ω
max
min
d
L
(1)
d – diameter of disk, m;Ω
min‐minimal number of
cavitation.
Thevalueoftheminimumdistancehbetweenthe
wall and the boundaries of the cavity at which its
destructionwillnotbeobservedcanbedescribedas
[7]
4
3
0,375
d
h
F
r
(2)
Fr–Froudeparameter.
According to the experimental results [7], the
minimal distance h depends on the velocity of the
nozzle or the main flow around the nozzles. In the
practically demanded range of Froude numbers, i.e.
whenFr
≈5‐10thevalueofhshouldexceed5%ofthe
lengthofthesupercavitationalcavern.Inaccordance
with this range, the deformation (the ratio of the
abscissainthemaximumsectionofthecaverntothe
diameterofthenozzlebehindwhichitwasformed)of
the cavitation cavern near
a solid surface [7] is
proposedtobefoundas
0.05
1
c
y
h
L
(3)
L–lengthofcavitationalcavern,m.
By analogy with thin cavitating airfoils,
approximatelythevalueoftheliftforcefactoracting
on the rectilinear thin boundary of the cavitation
caverncanbedetermined,dependingontheangleof
attackoftheflow,bytheBetzformula
2Ω
1
2
y
C
(4)
–angleofattack;Ω‐cavitationnumber.
Forthecasewhencavitationflowisformedinside
achannelwithrigidboundaries,formula(4)willgive
moreaccurateresultsifinsteadoftheangleofattack
oftheflow,theangleofitsbevelisused.Thisvalueis
theratioof
themaximumvalueoftheverticalvelocity
componentatthesupercavityinterfacetothevelocity
oftheoncomingmainflowandcanbecalculatedas
y
max
V
V
(5)
A decrease in the number of cavitation, which is
equivalenttoanincreaseintheflowvelocity,always
leads to the association of finely dispersed vapor
bubbles into an integral supercavitation cavern. For
thisreason,itisimportanttoknowthespeedatwhich
the first stage of cavitation
will occur inside the
working chamber of the cavitator. It corresponds to
the nucleationofsmallbubbles filledwithsaturated
watervaporandcanbecalculatedas
..
2
ct i
max
PghP
V
(6)
P
i‐pressurealongthesurfaceoftheworkingchamber
ofthecavitator,Pa;P
c.t.‐pressureinthestoragetank,
Pa;h‐heightofthestoragetanklocationinrelationto
the axis of symmetry of the cavitation working
chamberoftheseparator,m;ξ
max–maximalfactorof
localhydrauliclossesofthecavitatorchamber.
During cavitational separation of BOW it is
importanttoknowtheamountofwatervaportaken
off.Thevapormassinthefirstapproximationcanbe
foundusingtheHertz‐Knudsenformula
1
2
..
2
ss
M
GP
Rt
(7)
G‐massofvaporevaporatingorcondensingperunit
timeonaunitsurface;α‐accommodationfactor(for
waterα=0.04...1.0); P
s.s.‐pressure of saturated water
vaporinsidethecavity,Pa;M‐molecularweightof
water vapor; R‐universal gas constant; t‐absolute
temperature,°C.
For an approximate evaluation of timeτ, during
whichasphericalcavitationsupercavernwithradiusr
willbecompletelyfilledwithsaturatedwatervapor,
canbefound
as
1
2
2
3
rM
Rt
(8)
The destruction time of this spherical cavern can
becalculatedusingtheempiricalRayleighformula
0.915
max
tr
P
(9)
rmax – maximalradius,m;
‐initialdensityofBOW
flow,kg/m
3
;P
‐initialpressureoftheBOWflow,Pa.
437
When the cavity expands, the vapor pressure
inside of it will not always correspond to the
saturatedvaporpressure.Tosatisfytheirequality,itis
necessarytoaccomplishaninequality
1
2
2
3
max
s
r
M
t
Rt
(10)
ts–timewhencavernformsstableposition,sec.
Evaluationofexpression(10)showsthatataBOW
temperatureequalsto20°C,thewatervaporpressure
insidethecavernwillbeequaltothesaturatedvapor
pressure, subject to the following inequality r
max/ts
17,8m/sec.
Since dissolved gases are always present in the
BOW, theirmass mustalsobe taken into accountat
theinitialstageofcavityformation.Forthecasewhen
the outer boundaries of the cavitation cavern are
limited by a flat rectangular channel, the mass of
dissolvedgasesis
equalto
3
4
3
g
g
C
GbL
K
(11)
G
g‐massofgasinsidethecavernatthetimewhenit
reachesastablestate;C
g‐initialgasconcentrationin
the BOW flow; K‐Henryʹs constant; b and L –
thicknessandlengthofthecavern.
2.6
ArtificialSupercaverns
Initially, artificial supercaverns were used in
experimental studies of phenomena associated with
thehigh‐speedmotionofbodiesinafluid.Artificial
supercaverns,incomparisonwithcavernsthatoccur
during natural cavitation, have distinctive features:
theflowmovement inwhich cavitationisartificially
createdisalwayscharacterizedbylower
valuesofthe
averagevelocity;duetothedifferenceinthedensities
of liquids and air, which is always much less than
unity, artificial supercaverns always have a clear
interface between the areas of the moving flow; the
beginning of an artificial supercavern always has a
uniquespatiallyfixedposition;
themovementof the
vapor‐gas mixture inside the artificial supercavern
can be neglected and it can be assumed that the
outflowingofthecavityisprovidedbypotentialflow.
For the case of artificial blowing of air into the
cavitation supercavern, in the first approximation,
without considering the discontinuity of
the main
flow of the BOW, the dependence of the velocity at
the boundary of the supercavern on the blowing
velocitywasestimated.Ifweacceptthatattheinletto
the working chamber of the cavitator: the values of
thevelocityandpressureoftheBOWflowarePbow,
Vbow;thevelocityandpressureoftheairarePa,Va;
velocity and pressure at the boundary of the BOW
flowcavernarePc,Vc,thenthe flowvelocity at the
cavernboundarycanbefoundas
2
1Ω
2
aa
cbow
V
VV
(12)
a‐density of theair, kg/m
3
; Va‐velocityoftheair
supply,m/sec.
Since low cavitation numbers correspond to high
motion velocities [7, 22], it can be written
approximately that
11
2
. In this case, the last
expression can be simplified to an approximate
formula
2
Ω
1
22
aa
c bow
V
VV
(13)
Analysisof(13)allowsonetomakeconclusionthat
velocitycausedbythehydrodynamicfeaturesinside
thecavitationchannel,attheboundaryofcavern,will
be determined mainly by the velocity horizontal
componentsoftheairandthetreatedBOWflow.In
thiscase,theprevailingcontributiontothe
valueofVc
informula(13)comesfromthetermV
bowΩ/2.
Whenoneconsidersspatialandtemporalstability
ofanartificialcavitationsupercavern,theoptimalair
supply rate used for its ventilation is of great
importance. Its value can be found if we accept the
hypothesis that the air movement occurs due to the
pressuredropintheendsections
oftheairflow.Such
sectionscanbethecavityclosureplaneandtheinlet
sectionoftheairchannel.Inthiscase,theoptimalair
flowrateisequalto
2
atm
a
a
P
V
l
P
d
(14)
P
atm‐atmospheric pressure, Pa;
p
‐pressure factor
behindthecross‐sectionofairinletintothecavern;λ
–hydraulicfrictionfactoroftheairsupplychannel;l,
d–lengthanddiameteroftheairsupplychannel,m;
Oneofthemainfactorsdeterminingthenecessity
to use artificial supercavitation during BOW
separation is
the hysteresis in the occurrence of
natural cavitation vapor bubbles [27]. It has been
experimentally stated that, at the initial moment of
time,thegrowthofbubblesoccursduetoadecrease
in pressure in the liquid to the threshold value P
cr,
which is always less than the saturated vapor
pressure [26]. In the future, the growth of the gas‐
vapor bubble is prevented by the added mass of
liquid, static pressure and surface tension pressure.
The non‐linearity of the behavior of the phase
equilibrium leads to a decrease in the
average
temperature of the vapor bubble relative to the
temperatureof thesurroundingliquid.Theresult of
suchatemperatureimbalanceistheflowofheatfrom
theliquidintothebubblewiththeevaporationofthe
liquidintotheinteriorandthesubsequentgrowthof
thebubble.Anincrease
inhydrostaticpressureleads
toadecreaseinthetimeofcollapseofthecavitation
cavern and an increase in the intensity of shock
waves.Also,inthiscasecavitationerosiontakesplace
[8].
In accordance with the experimental data [7], at
moderate relative flow velocities, stable regimes of
artificial supercaverns
with stable hydrodynamic
438
characteristicsareobservedintherangeofcavitation
numbers0
0.2.
Aspecificfeatureofartificialsupercavernsistheir
dependenceontherelativevelocityofthemainflow
in which they are formed. For a given cavitation
number,adecreaseintheinjectedgasflowratecanbe
compensatedbyanincreaseintherelativevelocity.At
the same time,
at excessive flow rates of the blown
gas,thecavitywillbesaturatedwiththisgaswiththe
appearance of boundary instability or complete
destruction of the cavern. In accordance with
experimentalresults[7],thecriticalcavitationnumber
at which high‐frequency spatiotemporal oscillations
oftheexternalcontourofthecavern
beginsatisfiesthe
inequalityΩ
cr<0.19Ωnat.
2.7
CavityDimensionsandFlowTemperatureInfluence
onSeparation
During separation of BOW flow by the proposed
method of cavitation evaporation of the water
component, an important question is the spatial
stability of the supercavern when water vapor is
removed outside from it. Due to the change in the
volumeofthe
cavitationcavity,itsoutercontourwill
constantlyoscillateintheverticalplanerelativetoits
stable stationary position. These fluctuations will be
affected by the ratio between the pressure values
insidethecavernandinthemovingflowoftheBOW.
Inthiscase,itisalwaysnecessarytomake
anassessof
astableequilibriumatwhichthecavitycanreturnto
itsmaximumsizeorviceversawillcometothestate
ofavapor‐gascavernthatdoesnotparticipateinthe
cavitationprocess.
If we consider the cavern as spherical, then the
value of the critical radius
of the cavitation cavern
withrespecttothepressurePinthemainflowofthe
BOWwillbedeterminedas
4
3
cr
ccav
r
PP
(15)
– factorofsurfacetension; Pc‐pressureinsidethe
cavern;P
cav‐thresholdpressurecorrespondingtothe
occurrenceofcavitation(atfirstapproximation,itcan
be takenequalstothesaturatedvapor pressureata
giventemperature).
Below the value calculated by expression (15),
thereisnosensetoprovidetheprocessofremoving
watervaporduringtheseparationoftheBOW.
Inthis
casethecavitywillnolongerbeabletorecovertoits
originalsize.
The temperature factor also plays an important
roleduring cavitationalseparationofBOW. Withan
increase in temperature, due to a decrease in the
solubilityof gases,theirreleaseandtransferintothe
interiorof
thecavitywillbemuchmoreintense.The
second factor that will influence the increase in the
size of the supercavitational cavern with increasing
flow temperature is the drop in the value of the
surface tension factor. At a constant value of static
pressure, an increase in temperature invariably will
produce an increase in the dimensions of cavitation
cavern.
When considering supercavitation in an ordinary
homogeneous flow, the growth of the temperature
factor will lead to negative consequences‐the
destruction of the cavitation cavern due to a quick
increaseinthemassofwatervaporandpressuredrop
inside of it.
From the point of view of the BOW
separation process, this drawback is an advantage,
sinceauniformselectionofwatervaporwillonlylead
to stabilization of the spatio‐temporal dimensions of
thecavityandanincreaseintheproductivityof the
separation process in terms of the amount
of
separatedwater.
According to the experimental results [23], the
optimal temperatureatwhich spatial stabilityof the
cavity dimensions is observed answers the range of
55–60°С.
Accordingtotheexperimentaldata[9],anincrease
inpressureduringcavitationwillalsoleadtoashift
in the flow temperature
at which the cavitation
process will remain stable. In particular, for pure
water, the maximum cavitation effect is at 4 atm of
excessivepressurewasobservedattemperatures85‐
95°C.
2.8
LocalNumbersofCavitation
Theproblemofstabilityofartificialsupercavernswas
consideredby[7],whereitwasshownthatairsupply
toasupercavitatingcavernispossibleinonecaseonly
‐ when its dimensions reach certain values. Such
dimensionsofthe cavern correspondtoits complete
formation in accordance
with the conditions of the
experiment. With artificial ventilation, the initial air
entry is accompanied by a characteristic sound click
andanalmostinstantaneousincreaseinthesizeofthe
cavitationalcavernwith anincreaseintheintakeair
flow rate. The cavitation number drops significantly
andthenremainsconstantand
doesnotdependona
furtherincreaseinairflow.
A good criterion in the analysis of artificial
supercaverns can be an estimate of local cavitation
numbers.Inaccordancewiththeexperimentalresults
[7] in unrestricted flow an integral cavitation
supercavern appears when the cavitation number
correspondstothevaluesΩ
=0.5‐0.3.Suchcavernsare
characterized by the absence of clear and stable
boundaries.
With a cavitation number equals toΩ=0.2, the
cavitational cavern shrinks in size and, due to the
occurrenceofareversejet,canbreak.Inthecasewhen
Ω<0.13,thedimensionsofthecavernincreasewith
the
appearanceofclearandtransparentboundaries. The
cavitational cavern in this case assumes a stable
spatio‐temporalstate.
From the point of view of stability, cavitation
caverns withΩ>0.13 are characterized by a strong
dependenceonthevalueofthedynamicpressurein
theflowandareunstable.
Oneof
thereasonsfortheviolationofthedynamic
instabilityofthecaverncanbe:exceedingthecapacity
oftheworkingchannelofthecavitationchamber;the
appearance of a large counter pressure behind the
workingchamber;externaldynamicperturbations.
439
3
INVESTIGATIONOFBOWSEPARATION
3.1
InitialPostulates
Amathematicalmodeldescribingdynamicalbehavior
ofacavitationsupercavernwithconsiderationofthe
process of its artificialventilation was developed on
thebasisofthefollowinghypothesis:
BOWflowisideal(withoutanytypesturbulence)
andhasaweight;
theflowoutsidethecavityisincompressible;
thebeginningandtheendofthecavitationcavern
arealwaysknownandcorrespondtotheentrance
andexittotheworkingareaoftheseparator;
theweightofthegascomponentinsidethecavity
can be considered by means of hydrostatic
pressure.
atthebeginningoftheseparationprocess,airfor
cavitational cavern ventilation enters it at each
pointofitsinitialcross‐section.
the main flow of the BOW is flat and one‐
dimensional.
3.1.1
BasicEquationsandCalculationScheme
In the Euler form, the motion of the main flow
outsidethecavitywaswritteninthefollowingform
1
VV P
Vgy
tx x
(16)
Motion of the steam‐water mixture inside cavern
hastheanalogicalview
1
s
tst st
st st
st
VV P
Vgy
tx x
(17)
AttheboundarybetweenmainBOWflowandthe
supercavitationcavern,conditionsshouldbesatisfied
alwaysinthefollowingform
s
t
P
P
x
x
(18)
s
t
V
V
x
x
(19)
Rigid boundary conditions modeling the direct
influenceoftherigidwallsoftheworkingchamberof
the cavitation channel. On rigid walls of the
separatorʹsworking chamber itis necessarytofulfill
theconditionofcompleteimpermeabilityin contrast
to the free interface surface, corresponding to the
outer
boundaryofthesupercavernwiththeprocessed
BOWflow,Inthis case,the boundaryconditions for
equations(16)‐(17)are:
rigidwallsonthesideofmainBOWflow:
PP
nx
(20)
0
V
x
(21)
rigidwallsinsidecavitationalcavern:
.
st
s
st
P
P
x
(22)
0
st
V
x
(23)
t‐time, sec; n‐surface normal coordinate, m; P
st –
pressure of the steam, Pa; P
s.st – pressure of the
saturatedsteam,Pa.
To describe the process of artificial ventilation of
the supercavitation caverna calculationscheme was
developed(Fig.3)inrelationtomathematicalmodel.
Thedesignoftheworkingchamberofthecavitation
channel implies a clear closure of the boundaries of
thesupercavern
totheoutletplate(allothercasesare
consideredasnon‐working).Thiscalculationscheme
for the process of extracting the water component
fromthe BOWallowsthesolutionofthedifferential
equationsofthemathematicalmodelusingthefinite
differencemethod.
The velocity at the cavitational cavern boundary,
which in
Fig. 3 is a curve connecting the inlet and
outlet plates of the working chamber, is considered
equals to the flow velocity in the calculated section,
whichcoincideswiththeinletplate.Thisconditionis
consistent with the experimental results [7], and in
thiscase,theinfluenceofnon‐stationary
phenomena
in the tail part of the cavitational cavern on the
conditionsofflowarounditsheadpartisabsent.
Figure3.Calculationscheme
Theadvantageoftheproposeddesignschemeisto
overcometheBrillouinparadox‐attheboundaryof
cavern,thevelocityisaconstantandnon‐zerovalue.
In its tail part, it contains a critical point with zero
velocity,whichinthiscasephysicallycorrespondsto
the upper edge of the
output plate. Due to such a
fixed point, the Zhukovsky‐Chaplygin condition is
satisfied‐duringthecalculations,asmoothdescentof
the flowlines from the surface of the output plate
takesplace.
Thefinitedifferencemethodwasusedtosolvethe
differential equations of the mathematical model of
the BOW
separation process. In accordance with
calculation scheme (Fig. 3) the entire computational
domainwasdividedintocomputationalsectionswith
auniformstep.ThestepvaluealongtheOXandOY
axes was chosen on the basis of the results of
preliminary calculations and was usually
4
1
10
ii
xxL
and
6
1
10
ii
yyH
.
440
As convergence criteria during calculations was
used divergence between left and right parts in
equations (16) and (17). Its maximal value in all
calculationpointsneverexceededvalue10
‐8
.
All terms of the equations of the mathematical
model correspond to a homogeneous continuous
BOWflow.Whenusingthefinitedifferencemethod,
which implies the replacement of a continuous
medium by a discrete one, they were written using
their differentialanalogs.Depending onthelocation
of the computational point in
relation to the rigid
boundariesofthecomputationaldomain,central,left‐
sided,andright‐sideddifferencesofthesecondorder
ofaccuracywereused.
4
RESULTS
4.1
GeometryofCavitationalCavern
DuringmodelingtheprocessofBOWseparation,the
dependence of the elongation of the cavity L in
relationtothewidthoftheworkingchannelBofthe
BOW cavitation separator was determined. The
calculation was carried out without considering air
injection,since,inaccordancewiththe
conclusionsof
[7], neither the method of creating the cavitational
cavernnortheshapeofthebodybehindwhichitwas
formedaffectthegeometryofthecavity.Theresults
of the calculations (Fig. 4) show that a drop in the
flow rate, corresponding to an increase in the
cavitation
number on the plot, leadstoa significant
reduction in the size of the cavitational cavern. The
workingdimensionsofthecavitationcavernanswers
the range of cavitation numbers from 0.1 to 0.15. In
this case, the length of the cavern is from 5 to 4
calibersofthewidthof
cavitator’sworkingchamber.
Tocontrolthecalculateddataonthegrowthofthe
cavitationcavern inthecrosssectionalongitsentire
length,theresultsof[7]wereused.Forthecaseofan
unbounded flow, this author proposes the use of
followingrelation
0.955
Ω
max
D
d
(24)
D
max–maximaldiameterofthecavitationalcavern,m;
d‐diameterofthenozzlebehindwhichthecavitation
caverniscreated,m.
During the calculations there was done an
assessment of the degree of influence of the rigid
horizontal boundary of the working chamber of the
cavitational channel onto deformation of
the lower
contourofthecavitationalcavern.Thecavityprofile
ordinates were calculated for three values of the
relative height
h
of the cavitator’s inlet plate. This
valuewascalculatedastheratiooftheplateheighth
to the height of the cavitation channel itself H. The
calculationresultsareshownin Figure5,whereone
can see that a decrease in the value leads to the
alignmentofthe
cavityboundarytoaflatshape.
ThehorizontalaxisinFigure5correspondstothe
relative elongation of the cavity
x
x
L
, and the
verticalaxiscorrespondstothechangeinitsrelative
ordinate
y
y
H
.
Figure4. Influence of flow velocity onto the length of
cavitationalcavern
Figure5. Influence of flow geometry onto the contour of
cavitationalcavern
1– h =0.1;2– h =0.4;3– h =0.6
4.2 QuantitativeEvaluation
A specific feature of BOW separation process is
determined by the detection of BOW main physical
property‐viscosity. The main oil‐containing
componentsdonotanswerthewell‐knownNewtonʹs
law[6].Forthisreason,themultiphaseflowstructure
must be consideredas agrid containing water. This
grid, in turn, consists of a set of paraffin and resin
molecules randomly arranged among themselves [4,
13].
In case when the viscosity of the BOW flow is
unknown, it can be found at first approximation by
the values of the viscosity of the n mixture
components,consideringtheirvolumetric
contentai.
11 2 2
nn
aa a (25)
Due to the strictly expressed non‐linearity of
reological properties, there is always a strong
resistance to tangential shear stresses in the BOW
flow. For this reason, most constructions of shipʹs
bilge water hydrodynamic separators use flat
channels, inside which density stratification of the
processedflowoccurs[11,
19].Duringcalculations,an
estimate was done for the value of pressure drop
inside a two‐dimensional flat channel, the walls of
whichrepresenttwoparallelplanes.Thevaluesofthe
kinematic viscosity of the BOW flow were taken
identicalandequaltoν=2∙10
‐6
m
2
/sec.
441
FordifferentvaluesoftheBOWflowdensitythere
was created a nomogram which depicts the
dependence between pressure drop and velocity of
theprocessedflow.ItisshowninFigure6,whereone
can see that during flow motion an increase in the
flowdensityofthe BOW
leadstoan increase inthe
valueofpressuredrop.Withregardtotheproposed
methodofhydrodynamiccavitationseparation,itcan
be stated that ceteris paribus in this case, the
beginning of the cavitation process should be
expectedatlowerspeeds.Undertheseconditionsthe
valueofvelocityisdirectly
determinedbythevalue
of excessive pressure. The higher the excessive
pressureinthepumpedmixtureofBOWisthehigher
will be the effect of cavitation onto efficiency of the
technologicalseparationprocess.
Figure6. Influence of velocity onto pressure drop in the
flow
1–ρ=800kg/m
3
;2–ρ=900kg/m
3
;3–ρ=1100kg/m
3
;
4–ρ=1200kg/m
3
When in the BOW flow cavitation occurs at the
hydromechanical approach the resulting cavern can
be considered as local resistance. In this case it is
worth to estimate the value of its resistance
coefficient. This parameter can be considered as the
sumofinductiveandtwoprofileresistances
.. ..x x ind x t w x b l
CC C C
(26)
C
xind‐inductive resistance, depending on the
elongationofthecavityandtheangleofattackofthe
flowonit;C
xt.w.‐profilecavitationresistancecaused
bytheturbulentwakebehindthecavityandthenon‐
stationary mode of closing of its boundaries; C
xb.l.‐
profile viscous resistance, caused in the presence of
rigidobstaclesbytheboundarylayerarisingonthem.
All terms of expression (26) are directly
determined by the processes of vortex formation at
the interface of the cavitational cavern. Inductive
resistanceiscausedmainlybylongitudinalvorticesat
theboundariesof
thecavitationalcavern,andprofile
resistance‐bytransversevorticesatitsboundaries.
4.3
ExperimentalEvaluationoftheMainParameters
During experimental researches, it was studied how
the dynamic pressure at the inlet to the working
chamber of the cavitator affects the quality of the
BOW separation process. All experiments were
carriedoutforthreeflowtemperatures:30°С,50°С
and90°
С.Amixtureofwaterwithfueloilintheratio
of50%waterto50%fueloilwasusedasaBOW.The
mainmeasurementresultsareshowninFigure7.The
graph shows that the effect of dynamic pressure
growth onthe cavity length l is directly determined
by the temperature factor. The maximum length
correspondingtothelength ofthe workingchamber
ofthecavitatorLwasobserved,respectively,at:
TemperatureBOW,°C Pressure,Pa
30406250
50381591
90320113
Figure7. Influenceofdynamicpressureinthe flow on the
relativelengthofthecavity
1 – temperature is 30 °С; 2‐temperature is 50 °С; 3‐
temperatureis90°С.
Ananalysisofthestatedvaluesallowsustodraw
an unambiguous conclusion‐a decrease in the
operating pressure must always be compensated by
anincreaseinthetemperatureoftheprocessedflow.
It should also be noted that with an increase in
temperature, the solubility of gases in the BOW
decreases, which, as a result, are released from the
treated flow at the first stage of cavitation, i.e. even
beforethebeginningofthesupercavitationprocess.
An increase in the temperature of the supplied
BOW at a constant value of the static and dynamic
pressuresledtoanincreasein
thesizeoftheemerging
supercavernandanincreaseinthemassofthesteam
inside of it. The consequence of the growth of the
masswillalwaysbeadecreaseinpressureinsidethe
cavitational cavern. An increase in temperature, on
theonehand,increasesthecavitationzone,buton
the
other hand, reduces the intensity of the cavitation
effect. Under normal conditions, the value of the
optimaltemperatureatwhichthefirstfactorprevails
overthesecond,asestablishedexperimentallyis55‐
60°C.
Despite the same nature of the change in the
obtainedcurvesinFigs.7one
canseethatatelevated
temperatures,thetreatedBOWflowcanbesubjected
toaseparationprocessatamuchlowerpressure.Asa
result, therequirements for theselection of injection
equipment can be reduced in terms of reducing its
flowrateand pressure characteristicsand the quality
ofmaterialsused
inthemanufactureoftheworking
chamberofthecavitationchannel.
Ifitisnecessarytoincreasethetotalproductivity
of a separation unit containing several working
chambers,thequality ofthe cleaning processcan be
greatly influenced by their totalhydraulic resistance
442
whenworking onasinglepipelineoftheseparation
circuit. For this reason, during the experiments, the
dependence of the volumetric flowrate of purified
water on the number of simultaneously connected
workingchamberswasstudied.ItisshowninFigure
8,whereonecanseethatanincreaseinthe
numberof
working chambers N did not lead to a directly
proportional increase in the performance of the
separator.Withthedimensionsofcavitationchannel:
length 1 m, width 0.3 m and depth 0.01 m and the
inlet headof theBOWflowequals to 46 m.w.h. the
optimalnumber
ofworkingchambersshouldbethree
units.Furtheradditionofworkingchambersleadsto
a general increase in the pressure drop across the
separatoranddoesnotgiveasignificantchangeinits
total productivity. During the experiments, it was
foundthatinthiscase,thehydraulicresistanceofthe
main
pipeline, which constitutes the main
technological circuit for processing BOW, also
increases.
Figure8.Dependencebetweenperformanceandnumberof
workingchambers
Aneffectivewaytoinfluencethehydromechanical
characteristicsoftheflowistochangeitsstructureby
blowingair.Inthiscase,artificialcavitationiscreated
intheflow,andduringtheexperimentsitwasfound
thatairsupplyshouldstartbeforethebeginningof
thesecondstageofcavitation,i.e.
whenthevapor‐gas
bubble‐film cavitation (the first stage) passes into a
continuoussupercavern(thesecondstage).
During the experiments, there was found the
dependence between resistance factor of the inlet
rectangular plate in the working chamber of the
cavitator and the cavitation number of the supplied
flow. It
is showninFigure 9. The graph shows that
startingfromthecavitationnumberequalsto0.1,i.e.
with the release of the artificial supercavern to its
stationaryspatialdimensionsthisdependencetookon
aself‐similarcharacter.
Onthebaseofexperimentalresults,itwasfound
that hydraulic resistance during
cavitation is
determined by only two factors: the size of the
cavitational cavern and the number of cavitation. In
thiscase,itwasconcludedthathydraulicresistanceof
cavitational cavern does not depend in any way on
themethodof itscreationand isidenticalbothwith
naturalcavitationand
withcreationofcavitationdue
toairblowing.
Inartificialcavitation,theeffectofthesuppliedair
flowrate on the hydrodynamic characteristics of the
resultingsupercavernisimportant.Anincreaseinthe
ventilation air flowrate leads to an increase in the
dimensionsofthecavity.Thevaluesofthevolumetric
air
flowrate in experiments were respectively
Q=0.00012m
3
/secandQ=0.0002m
3
/sec.
Duringexperiments,itwasfoundoutthatarapid
increaseinthesizeofthecavityuptothelengthofthe
working section of the separation chamber can be
obtainedinthecasewhentheflowrateofthesupplied
airisintherangefrom5to8%of
theflowrateofthe
treatedBOWflow.Exceedingthespecifiedrangeled
tothe collapseofthecavitywith negativecavitation
numbers corresponding to the case when the air
pressureinsidethecavityexceededthepressureatthe
interfacebetweentheliquidandvaporphases.
During experiments there was studied
how the
directionofairsupplymakesinfluenceonthestability
ofthecavitationalcavern.AsonecanseeinFigure10,
air supply was carried out in three different ways:
perpendiculartotheflowoftheB)W,againstthemain
flowoftheB)Wandinsidethecavitationalcavern.
Figure9.Dragcoefficientoftheinletplateduringartificial
cavitation
Themoststablestatecavitationalcaverntookplace
in the latter case, when air was supplied into the
interiorofthecavity.Thetransitionattheinitialstage
frompartialto completeventilationofthecavitation
cavernoccurredabruptlywithoutpressurebreaksin
theworkingareaofthecavitatorchamber.In
firsttwo
cases,duringexperiments,thefailureanddestruction
of the cavitational cavern was observed practically
alwaysevenattheinitialstageofitsinception.
Figure10.Schemeofairsupplytothecavitationalcavern
The principle of operation of the proposed
cavitationalmethodforBOWflowseparationisbased
ontheconstantselectionofartificiallyblownairand
watervaporfromthesupercavitationalcavern.Inthe
course of experiments, it was investigated how the
flowrateofthesteamtakenoffwithairQ
extaffectsthe
behaviorofthecavitationalcavern.Themainresults
443
are shown in Figure 11, where one can see that the
dependence between the change in the cavitation
number for various values of the flowrate of the
extractedsteamcanbeapproximatedbyalinearlaw.
Figure11.Influenceofsteamextractiononsupercavity
Onthebaseofthisdependence itwasconcluded
that the flowrate of water vapor taken from the
cavitationalsupercaverndoesnothaveanyeffecton
thecavitationmodeexistingintheworkingchamber.
Theratioofcavitationnumbersduringtheextraction
of steamΩ
ext in the case of ordinary (not artificial)
cavitationΩto the ratio of the flowrate of the
extracted steam Q
ext to the total flowrate Q obeys a
linear relationship with a change within an error
equalsto3.8%.Asimilarconclusionwasobtainedalso
on the basis of the performed experiments for the
dimensions of the cavitational supercavern. The
lengthofthecavitationalcavernduringtheselection
ofsteamand
airfromitdidnotchange.
4.4
AirSupplySystem
Themaintechnicalquestionsintheimplementationof
the proposed method of BOW separation in the
operatingconditionsofthevesselshouldbeaimedat
increasing its productivity. All optimal dimensions
and output power of the separator should be
determined by only one performance indicator‐its
flowcapacity.
One of the perspective options to increase the
productivity of separator is the use of artificial
ventilationofthecavitationalcavern,whichisbased
on blowingairinto theinside of the cavern. On the
base of stated above results it has been established
thattheartificialventilationofthe
supervacuitycavity
hasadirectimpactonitsdimensionsand,asaresult,
on the final performance of the shipʹs separation
plant.
Thecalculationoftheairsupplysystemshouldbe
infactalwaysreducedtothehydrauliccalculationof
a converging nozzle (cone nozzle) and to the
determination of
its cross‐sectional area for a given
flowrate and pressures before and after the nozzle.
Thefrictionofairpassingthroughthenozzlecanbe
neglectedduetoitsinsignificance.
When calculating the jet nozzle, the mass air
flowrateshouldbedeterminedbytheexpression
out out out
QSV (26)
‐flowratefactor;Sout‐outletarea,m
2
;Vout–velocity
attheoutputsection,m/sec.
Thevelocityatthenozzle’soutletcanbecalculated
using the Bernoulli’s energy equation for a one‐
dimensionalflow
21 1
out out inlt
out inlt
VPP
kk
gk k
(27)
andtheadiabaticexpansionequation
1
k
out out
inlt inlt
P
P
(28)
as
1
2
1
1
k
inlt
k
out
out
P
gk
V
kP
(29)
=Pout/Pinlt ; Рinlt and Рout – pressure at the inlet and
outletofthenozzle,Pa;ρ
inltandρout–airdensityatthe
inletandoutletofthenozzle(canbefoundfromstate
tablesordiagrams);k–adiabaticexponent.
Insertion of (29) into(26) withconcerningof(28)
gives
21
2
1
k
kk
out inlt
gk
QS P
k
(30)
Inexpressions(27)‐(30),moreaccurateresultscan
beobtainedifinsteadoftheadiabaticexponentk,we
usethevolumetricadiabaticexponentk
vofair.
2
v
T
T
kk
k
P
RT p
(31)
– aircompressibilityfactor;μT‐deviationfactor(its
diapason of change is from 0.04 to 2) depending on
thegradientofthechangeinairvolumevbymeansof
pressurepataconstanttemperatureT.
To ensure high‐quality air supply inside the
cavitationalcavern,itisnecessarytoprovideoptimal
taper angles
αduring manufacture of a conical jet
nozzle. At these angles, an irrotational flow of air
supplied to the ventilation of the cavern will be
provided.Thedependenceofthetaperangleαonthe
ratio of the inlet and outlet diameters of the cone
nozzlepresentedinTable1andFigure
12.
Table1.Optimalvaluesofthenozzletaperangleα
________________________________________________
(Dinlt/Dout)
2
1,5 2 2,5 3 3,5 4
________________________________________________
28° 22° 16° 12° 9° 6°
________________________________________________
444
Figure12.Optimumvalueofthenozzletaperangle
5 DISCUSSION
Researches described in the article were mainly
directedtothe solution of a veryurgent problemof
technical and environmental improvement in the
processofseavesselsoperating.Theuseofsecondary
energy resourcesonavessel,in our case BOW, will
always lead to additional income and reduction of
environmentalemissions.
Onabaseofallresultsobtainedintheresearchof
thecavitationprocessinapplicationtotheseparation
of a multi‐phase flow on sea vessels, in fact, it is
proposed to create a new type of separation
equipment.Thistypeofequipmenthasthepotential
to
be used not only on ships, but also in other
industries.
The problemofutilization of multiphase flows is
veryactualandwillnotloseitssignificanceformany
decades.Theproposedseparationmethodisuniversal
andcanbeusedinthefuturenotonlyonseavessels,
but also for
treatment facilities at energy plants, in
medicinewhendisposingofchemicallyorbiologically
hazardousreagents,etc.
The versatility and reliability of the proposed
method of hydrodynamic separation based on the
cavitation process is mainly based on the invariable
implementation of the basic laws of physics. In this
case,the intensity
of theprocess of evaporationofa
moving stream will always directly depend on its
pressureandtemperature.
The main areas of further research, which still
remain undiscovered, include methods for creating
stable caverns in clearly spatially fixed areas of a
movingflow.Inthiscase,itisnecessarytopay
special
attentiontotwoareas:methodsofsealingtheworking
chamber of the cavitation channels; simplification of
thetechniqueformonitoringthevacuumvaluealong
the cavity with modern measuring equipment.
Critical pressure jumps on the surface of cavitation
channels from low vacuum to local zones with a
pressure exceeding
100 MPa require the creation of
new materials. In addition to such materials, it is
necessarytocreatenewmechanismsforproducinga
spatially stable cavitation zone with clearly fixed
boundariesinamovingflow.
6
CONCLUSIONS
ModernmethodsofBOWseparationonvesselshave
onecommondrawback.Whentheyareworkingona
ship, the cleaning of the BOW is always
unidirectional. During the separation process, only
onewatercomponentistheoutputproduct,andthe
secondarypetrochemicalproductswithahighdegree
ofconcentrationare
verydifficulttoobtaininapure
formandcannotbeusedinfurther.
A qualitative solution to the problem of BOW
disposalcanbethe use ofanew separationmethod
that uses a hydromechanical approach. When
artificiallycreatedbyblowingairintothecavitational
caverninthemoving
flowoftheBOW,itispossible
to continuously select the resulting saturated water
vapor from the cavern and thus obtain the highly
concentratedoilycomponentsoftheBOW.
When creating an artificial supercavern by
injectingairtotheBOWflow,thevelocitycausedby
the hydrodynamic features inside the cavitation
channel at the cavern boundary will be mainly
determined by the horizontal components of the air
velocitiesandtheprocessedflowoftheBOW.
During the use of the cavitation process for the
separationoftheBOW,theoperatingpressureshould
be reduced and this reduction should be always
compensated
byanincreaseinthetemperatureofthe
treatedBOWflow.
REFERENCES
[1]Amran,N.A.,Adibah,S.M.,2020.Oil‐WaterSeparation
Techniques for Bilge Water Treatment. Resources of
Water. DOI% 10.5772/intechopen.91409. Available at:
https://www.intechopen.com/chapters/72671
[2]Bard, A. J., Faulkner, L. R., 2001. Electrochemical
methods: fundamentals and applications, 2nd Edition.
John Wiley & Sons. Available at:
http://www.nanoer.net/d/img/巴德+电化学方法+原理与
应用+2nd+Edition英文版+非扫描
557716.pdf
[3]Bashan, V., Demirel, H., Celik, E. 2022. Evaluation of
criticalproblemsofheavyfueloilseparatorsonshipsby
best‐worst method, Proceedings of the Institution of
MechanicalEngineersPartMJournalofEngineeringfor
the Maritime Environment 236(3). Available at:
https://www.researchgate.net/publication/361172923_Ev
aluation_of_critical_problems_of_heavy_fuel_oil_separa
tors_on_ships_by_best‐worst_method
[4]Beychok, M. R.,Milton
R.,1967. AqueousWastes from
PetroleumandPetrochemicalPlants,1stEdition.John
Wiley & Sons. Available at:
https://www.academia.edu/4388891/Aqueous_Wastes_fr
om_Petroleum_and_Petrochemical_plants_Milton_R_Be
ychok_John_Wiley_and_Sons_Inc_New_York_1_967_37
0_pages_12_75
[5]Brennen, C. E., 2014. Cavitation and BubbleDynamics.
Cambridge University Press. Available at:
https://authors.library.caltech.edu/25017/5/BUBBOOK.p
df
[6]Douglas, J. F., 2005. Fluid Mechanics. Pearson; 5th
edition. Available at: https://smartbukites.com/wp‐
content/uploads/2019/04/FLUID‐MECHANICS‐BY
‐
DOUGLAS00052.pdf
[7]Egorov, I.T., 1971. Artificial cavitation. Leningrad:
Shipbuilding.
[8]Fivel,M.C.,Franc,J‐P.,2018.CavitationErosion.Totten,
George E. ASM Handbook, Volume Friction,
445
Lubrication, and Wear Technology, pp.290‐301.
Availableat:https://hal.science/hal‐01697361/document
[9]Hickling, R., 1963. Effect of termal conduction in
sonoluminescence. Journal of the Acoustical Society of
America, V. 37, No 7, pp. 967–974. Available at:
https://doi.org/10.1121/1.1918641
[10]Knepp, R.,Daly, J.,Hammit F., 1974. Cavitation,
Moscow:Mir.
[11]Kolmetz,K.,2011,
Separatorvesselsselectionsizingand
troubleshooting, Handbook of Process Equipment
Design. Available at:
https://www.researchgate.net/publication/338832170_
[12]Madkour, L. H., 1993. ELECTROCHEMISTRY
Principles, Methods, and Applications, New York:
Oxford University Press. Available at:
https://www.academia.edu/14750398/ELECTROCHEMI
STRY_Principles_Methods_and_Applications
[13]Manning,F.S.,1991.OilfieldProcessingofPetroleum.
Natural Gas, PennWell Books. Available at:
https://toaz.info/doc‐view
[14]MARPOL 73/78‐International Convention for the
Prevention of Pollution from Ships, 1973. Available at:
http://www.mar.ist.utl.pt/mventura/Projecto‐Navios‐
I/IMO‐Conventions%20%28copies%29/MARPOL.pdf
[15]Matveev, K. I., 2002. On the limiting parameters of
artificial cavitation. Ocean Engineering. Volume 30,
Issue 9, June 2002, P. 1179‐1190. Available at:
https://doi.org/10.1016/S0029‐8018(02)00103‐8
[16]Md,S.
K.,2015.Prevention ofPollutionof the Marine
Environment from Vessels. Springer. Available at:
https://link.springer.com/book/10.1007/978‐3‐319‐10608‐
3
[17]Mutch, G. A., 2022. Electrochemical separation
processes for future societal challenges. Cell Reports
Physical Science. Volume 3, Issue 4. Available at:
https://doi.org/10.1016/j.xcrp.2022.100844
[18]Nesteruk, I., 2012. Supercavitation: Advances and
Perspectives
Acollectiondedicatedtothe70thjubileeof
Yu.N. Savchenko, Springer. Available at:
http://www.springer.com/978‐3‐642‐23655‐6
[19]Oily Bilgewater Separators. United States
EnvironmentalProtectionAgencyOfficeofWastewater
Management Washington, DC 20460. November 2011.
Available at:
https://www3.epa.gov/npdes/pubs/vgp_bilge.pdf
[20]Panwar,N.L.,Paul,A.S.,2020.Anoverviewofrecent
development in bio‐oil upgrading and separation
techniques. Environmental Engineering Research 26(5).
Available at:
https://www.researchgate.net/publication/346080210_An
_overview_of_recent_development_in_bio‐
oil_upgrading_and_separation_techniques
[21]Parsegian, V. A., 2006. Van Der Waals Forces: A
Handbook for Biologists, Chemists, Engineers, and
Physicists,NewYork:CambridgeUniversityPress,2006.
Available at:
https://doi.org/10.1017/CBO9780511614606
[22]Pellone, C. 1988. Effect of Separation on
Partial
Cavitation 1988, Journal of Fluid Eng. No 2. – P. 182.
https://doi.org/10.1115/1.3243532
[23]Plesset, M. S., 1972. Temperature effects in cavitation
damage,BasicEngng.No3.pp.559–566.Availableat:
https://doi.org/10.1115/1.3425484
[24]Ranade, V.V., 2022. Hydrodynamic Cavitation‐
Devices, Design and Applications. Wiley‐VCH Verlag
GmbH.
[25]Seader, J. D., Henley,
E. J., Roper, D. K., 2011.
Separationprocessprinciples:chemicalandbiochemical
operations.3rd ed.John Wiley &Sons, Inc.Available
at:https://imtk.ui.ac.id/wp‐
content/uploads/2014/02/Separation‐Process‐Principles‐
Third‐Edition.pdf
[26]Trevena,D.H.,1987.CavitationandTensioninLiquids
Bristol&Philadelphia:CrcPress.
[27]VanWijngaarden,L.,1976,Hydrodynamicsinteraction
betweengasbubblesinliquid,J.Fluid.Mech.V.77,P.l.,
pp. 27–44. Available at:
https://doi.org/10.1017/S0022112076001110
[28]Zaher, M, 2015. Cavitation and Supercavitation.
CreatespaceIndependentPublishingPlatform.
