159
1 INTRODUCTION
1.1 Chemicalscharacteristics
The ability of a vessel to execute a successful tank
cleaning operation is what makes that vessel better
thanitscompetitor.Ifthetankcleaningissuccessful,
there is no waste. If the tank cleaning is not
successful, everyoane feels the impact: time,
manpower, cleaning chemicals, bunkers, equipment,
offspecificat
ioncargoandlossofearings.Thebasics
ofanytankcleaningprocedurearetipicallythesame.
There are technical publically tank cleaning
guidelines, like: MIRACLE (Supplied and produced
by Chemtec in Hamburg); Dr. Verway (CHEMTEC,
Hamburg);MILBROS(Q88Stamford,USA)(Sørensen
O. et al.1959). All of these published guidelines
basically provide the same informat
ions in order to
avoid the appearance of technological risks (Jensen
B.B.etal.2011‐2012;PanaitescuF.V.etal.2014).
Oneofthemostimportantaspectsofchoosingthe
correct tank cleaning procedure is to recognise and
understand the chemical properties of the previous
cargo:volat
ility,solubilityinwater,viscosity,colour,
drying cargo, polimerisable cargo, strong absorber.
The most important aspects of understanding the
chemical properties of the cargoes that are being
cleanedfrom:volatilecargoeswilltendtoevaporate,
butmayberetainedinorganiccoatings;non‐volatile
cargoestendto bepersistent,butarenotretainedin
organic coatings; water soluble cargoes do not need
cleaningchemicalstoremovethem,beca
usetheyare
completelyremovedjustusingwater;viscouscargoes
will usually need warmer washing water to make
themeasiertoremove;colouredcargoes/residueswill
probably need a colour remover‐bleach; drying oils
andpolymerisa
blecargoeswillalwaysneedambient
temperature water washing; strong absorbers are a
challenge.Someadditionalfactorsstronglyinfluence
the successful outcome of any tank cleaning
Performances in Tank Cleaning
F.V.Panaitescu&M.Panaitescu
M
aritimeUniversity,Constanta,Romania
V.A.Panaitescu
ThomeShipping,Constanta,Romania
L.Martes
RomanianSeafarersCenter,Constanta,Romania
ABSTRACT:Thereareseveraloperationswhichmustdotomaximizetheperformanceoftankcleaning.The
newadvancedtechnologiesintankcleaninghaveraisedthestandardsinmarineareas.Therearemanywaysto
realiseoptimalcleaningefficiencyfordifferenttanks.Theevaluationoftankcleaningoptionsmea
nstostart
with audit of operations: how many tanks require cleaning, are there obstructions in tanks (e.g. agitators,
mixers),whatresidueneedstoberemoved,arecleaningagentsrequiredoriswatersufficient,whatmethods
canusedfortankcleaning.Afterthesesteps,mustbeverifytheresultsandensuretha
tthebestcleaningvalues
canbeachievedintermsofaccuracyandreliability.Technologyadvancements havemadeiteasiertoremove
stubborn residues, shorten cleaning cycle times and achieve higher levels of automation. In this paper are
presented the performances in tank cleaning in accordance with legislation in force. If ta
nk cleaning
technologiesareeffective,thenoperatingcostsareminimal.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 12
Number 1
March 2018
DOI:10.12716/1001.12.01.18
160
operation: a) outside climate conditions; b) the
monitoring cleaning process; c) the pre‐loading
inspectionspecificationsforthenextcargo.Thereare
three levels of pre‐loading inspection: load on top
(LOT); visually clean/water white standard;
chemicallyclean/wallwashstandard.
1.2 Tankcleaningoperations
There are various parameter that contribute
to
effectivetankcleaning(SørensenO.etal.1959;Sinner,
H.1959). Thecontent oftankcleaning planis based
on the cleaning processes model: MARPOL wash
(AnnexI,AnnexIIhighviscosity)orsolvent;cold/hot
washto continue;wash withchemicals; rinse (when
chemical are used); repeat chemical wash/manual
cleaning; steaming/fresh water; manual cleaning
(CSM‐L&I‐IMEC.2016).
Tank cleaning operations are optimised when all
cleaningstepsaremonitoring.Afterthesesteps,must
beverifytheresultsandensurethatthebestcleaning
values can be achieved in terms of accuracy and
reliability.
2 OPTIMIZINGTANKCLEANINGOPERATIONS
2.1 Thesteps
ofcleaningoperations
Tank cleaning operationsare manually and
mechanically. If the operation is made manually,
changing to an automated method will yield many
benefits:moreconsistent,improvedworkersafetyby
removing contact with hazardous chemicals, faster
cleaning,reduceduseofwater, chemicalsandlower
wastewater disposal costs (http://www.tankjet.com,
2016).
Ifthecleaningismadewithmachines,maybe
ableto improve cleaningefficiency by making some
simple changes or using different equipment.
Technology advancements have made it easier to
remove stubborn residues, shorten cleaning cycle
times and achieve higher levels of automation
(http://www.tankjet.com,2016).
The new advanced technologies in tank
cleaning
have raised the standards in marine areas.There are
many waysto realiseoptimal cleaningefficiency for
different tanks. The evaluation of tank cleaning
optionsmeanstostartwithauditofoperations:how
manytanksrequirecleaning,arethereobstructionsin
tanks(e.g.agitators,mixers),whatresidueneedstobe
removed,
are cleaning agents required or is water
sufficient,whatmethods canusedfor tankcleaning.
After these steps, must be verify the results and
ensurethatthe bestcleaning valuescanbe achieved
intermsofaccuracyandreliability.
Inspection of the cargo tanks is very important
becauseitisthe
bestindicatoraboutwhethertheload
port inspection will be successful or not (CSM‐L&I‐
IMEC,2016).Ifthecargotanksandthedecklookand
smell clean and are well organised, the load port
inspectorwillhaveabetterfeelingaboutvesseland
thefinalresultswillbefavorable.
Inspection of the cargo tanks includes: a) tank
hatch (hatch gaskets, odour when the hatch is first
opened, overall appearance of the hatch, the
conditions of coating, signs of corrosion); b) deck
head(signofcondensation,cargoresidues,visiblesalt
crystals, coating breakdown); c) access ladder or
platforms; d) bulkheads (check
for evidence of
previous cargo, discoloured patches, corrosion,
coating breackdown/condition of the steel, other
surface debrs, tank cleaning machine “shadow”
areas); e) cargo lines (first foot samples are critical,
because they are the first measure of how clean the
cargo lines are; always clean them in the same way
that
the cargo tanks are cleaned cold water/hot
water/cleaningchemicals,steaminglinescleaningfree
frominorganicchlorides;thisstepincludesalsoflexi
cargohoseswhichareusedduringcargooperations;
aftercleaningandpriortoloadingmustverifiedthat
alldrainvalvesarekeptopen;attheendofcleaning,
thelines
mustbeblownbacktothetanks).
2.2 Theselectionofequipments
Itis importantto optimisethetankcleaning process
toensurerepeatabletankcleaningperformanceinthe
shortestpossibleamountoftime(Jensen,B.B.B.etal.
2011‐2012).
Forthis,tankcleaningprocessmustbeautomated.
Process control
depends upon reliable real‐time in‐
line measurements using electronic sensors to
monitorandverifytheperformanceoftankcleaning
systems.Itisimportanttochoosingtherightsystem
to monitor and control tank cleaning automated
system and to define the objectives for monitoring
and control. These help to understand the
available
options and advantages (cleaning consistency,
reducedlabourcostsand increasedproduction time,
less downtime, higher energy savings and reduced
waterandcleaningfluidconsumption).
There are many possibilities to choose tank
cleaning products and the maximum tank diameter
eachunitcanclean(http://www.tankjet.com,2016).
Finaldecisionwillbedetermined
bytanksizeand
level of cleaning required. For the selection process
there are the folowing things which must comply
(http://www.tankjet.com,2016):
High impact cleaning is required to remove
stubborn residues such as layers of a dried
substance(tankcleanersinthiscategorygenerally
usehighpressureand/orhighflow);
Medium impact cleaning is required when good
impingement is neededto remove residues (tank
cleaners that provide medium impact generally
use solid stream nozzles at medium flows and
pressures);
Lowimpactcleaningisusedforlightcleaningwhen
some impact is required (low flow/medium
pressure and high flow/low
pressure nozzles are
usedtoachievelowimpactcleaning);
Rinsing is used when distributing cleaning
solution throughout the tank without impact
providessufficientcleaning.
2.3 Methodsofresearch
Therearethreeclasicalmethodsofapplyingcleaning
chemicals to the cargo tanks and a new vision for
monitoringandtestanalysis
ofsamples‐VISIBLEand
161
ULTRA‐VIOLETspectroscopy(UV‐VIS)(table1).The
clasicalcleaningmethodsare:re‐circulation(figure1),
injection (figure2), direct spraying (CSM‐L&I‐IMEC,
2016). The important objectives for cleaning by
recirculationare:theprocesscan’tstopped(once the
cleaning has started, it is very straightforward to
handle); work easy facilities
(easy calculation for
cleaningchemicalsdependingonworksolution);easy
to maintain heat during recirculation (unless the
vesselisequippedwithheatingcoilsoraqnextremely
efficientheatersystem).The importantobjectivesfor
cleaningbyinjectionare:providesaconstantsupply
of “fresh” cleaning solution; utilises maximum
washing water temperatures;
depending on the
efficiencyofinjectionpump;theconcentrationofthe
cleaningchemicalmixtureisnotreallyconfirmed(the
cleningchemicalconcentrateispumpedintoawater
moving volume); can use much higher volumes of
cleaning chemicals concentrate; the contact time
between cleasning chemical solution and cargo tank
surface is much
lower (30 ... 60 minutes). Direct
sprayingisprimarilyusedforspotcleaning ofareas
thatareintheshadowofthetankcleaningmachines,
unless the tank cleaning machines are damaged or
broken.
For monitoring and test analysis of samplesin
theVSIBLEregionofthelightspectrum,regular
glass
sample cells should be used. They are marked with
“G’letter. The apparatus is spectrometer. For
monitoring and test analysis of samplesin the
ULTRA‐VIOLET region of the light spectrum, only
sample cells made from quartz glass can be used.
Theyaremarkedwith“Q”letter.Itisimportanttouse
thecorrectsamplecell,otherwisethedatagenerated
mightnotbevalid.
Tankcleaningresulttestsare:PermanganateTime
Test‐PTT (is based on the ability of potassium
permanganate, KMnO
4, to oxidise hydrocarbon
impurities that could be present in the wall wash
liquid; ifPTT is a reactionina neutral solution, the
valueofKMnO
4issmallandchangesitscolourfrom
pink‐orange to yellow‐orange)(MARPOL);
Hydrocarbons Test (water miscibility)(is the
qualitative detection of non‐water‐soluble
contaminants; Chloride Test (is used the judge the
presence of chlorides on bulkheads; Chloride levels
vary from 0.1 ppm to 5 ppm); Colour Test(APHA);
UV‐Test
(is used to identify hydrocarbons and
chemicals);TheAcidWashTest(isusedtodetermine
the presence of Benzene, Toluene, Xylenes, refined
SolventNaphthas,similarindustrialaromatic
hydrocarbons, impurities in metha nol); NVM (Non
Volatile Matters) Test (isused to determine if there
are non‐volatile impurities on the tank surface by
weights).
Table1.VISIBLEandULTRA‐VIOLETspectroscopy.
______________________________________________
Tankcleaning
TestVIS UV
__________ _____________
Unitswavelenght(nm),
AbsorbanceAbsorbance(A)
______________________________________________
1.Inorganic ppm*** Cargoqualityfor
chloridespotableethanolmethanol
2.PTT
*
%SHELLCHEMICAL
Analyse
(alcohols,ketone)
3.APHAcolour APHA routinewallwash
inspectionpriorto
loadingpotableethanol
andHMD*****
4.Hydrocarbons FTU
***
 waterinsoluble
hydrocarbons
______________________________________________
*PTT=permanganatetimetest
**APHA=colourtest
***ppm=partspermiliioninorganicchlorides
***FTU=formazineturbidityunit
*****HMD=Hexamethylenediamine
Figure1.TheprincipleofRe‐circulation.
Figure2.Theprincipleofinjection.
Thetestprocedure foranalysismay varyslightly
from place to place, but the principle is always the
same. In this case study are used for each test
different samples where are mixed with different
solution for relevant presence of residues (on
chlorides, silver nitrate solution, on PTT, potassium
permanganate solution,
the hydrocarbons test
containstracesofhydrocarbonbasedcargoesthatare
solubleinthemethanoloracetone).
Inthechemicaltankerarea,UVspectroscopyisa
more widely accepted technique for analysing the
quality of loaded cargo. When a UV light source is
passedthrough atestsample, thedifferent
chemical
162
groups that make up the sample, absorb different
amounts of the UV light (absorba nce) (CSM‐L&I‐
IMEC, 2016). Each chemical substance has its own
uniqueUVfingerprintandthispermittoidentifythe
presence of these chemical substances in the test
samples.
The most commonly chemicals are: methanol,
benzene,styrene
monomer,phenol,fattyacidmethyl
ester‐fame, pyrolysis gasoline, acetone, multiple
hydrocarbons,unknows.
3 EXPERIMENTALDATAANDRESULTS
3.1 Visiblespectroscopytests
Visible spectroscopy tests are: inorganic chlorides,
PPT, APHAcolour, hydrocarbons. In this paper, for
eachtestareuseddifferentquantitiesoftestsample,
putintoseparate,cleanmeasuring
cylindersandadd
different solutions to identified chemical products.
Theeffectsand resultsareanalysedwith
spectrometer, at different reaction times (minutes)
(Table2).
Table2.Visiblespectroscopytests
_______________________________________________
TestAddsolution Time  Results
____________ ____________________
ml/%/gminutes nm,A,ppm,
%,FTU
_______________________________________________
1.Inorganic 25(5dropssilver 15  420nm
nitrate(2%/5%)+50.099A
*
drops20%1.0ppm
nitricacid)
chlorides
2.PPT500<20 <32%
(0.02%KMnO
4+ >50 >32%
0.1gsolidKMnO4)530nm
3.APHAcolour methanol/acetone5...15APHA
(lowlevels)
4.Hydrocarbons10015...20 400nm
(solvent+water)0.025A
1...2FTU
(slighthydr.)
3...600FTU
(increasinghydr.)
_______________________________________________
*Absorbance
3.2 UVspectroscopytests
The typical “aromatic”activity was tested for
chemicals:methanol,benzene,styrene,phenol, more
UV traces of chemical cargoes (figure 3, figure 4,
figure 5, figure 6, figure 7) with spectometer. One
important aspect of UV spectroscopy is the
concentrationoftheidentifiedgroups(i.g.tobeable
to
quantify how much benzene is present in the
sample). For this, was analysed how 10 ppm of
benzene, styrene and phenol in methanol not only
give different shaped peaks, but also different sized
peaksaswell(figure8).
Figure3.Puremethanol.
Figure4.Benzeneinmethanol.
Figure5.Styreneinmethanol.
Figure6.Phenolinmethanol.
163
Figure7.Fameinmethanol.
Figure8.Theconcentrationoftheidentifiedgroups.
The grafic interpretations have shown that UV
spectroscopy is very important to identify chemical
groups and to determine concentartions of these
groups(CSM‐L&I‐IMEC,2016).
4 CONCLUSIONS
In general, the tank cleaning monitoring procedures
depend on the cargoes properties to be cleaned, on
the surrounding conditions, on the available
equipment
andlastbutnotleasttherequirementsof
the products to be loaded. A variety of chemical
cleaning agents is available for most application
problems.Cleaning agents must be IMO approved.
Afteranaliseofexperimentaldata,canobserve:
1 Forvisiblespectroscopy
atinorganicchloridestest‐after15minutes
outof
direct sunlight, any presence of a white colour
indicates the presenceof inorganic chlorides in
the test samples and using spectrometer, can be
quantifiedthese;
at PPT , after 10 minutes visually check the
appearance of each sample (typically is 50 ... 60
minutes);after50minutes,if
wasfound>32%,the
resultshouldbereporedasPTTisgreaterthan50
minutes; ifthetest sample was analysed after20
minutes and the was found < 32%, the result
shouldbereporedasPTTislessthan20minutes.
Incasestudy,thespectrometerreadingto
howthe
colourofamethanolwallwashfades,regardingat
32%‐stillcontainsatraceofpinkandregardingat
21 %‐is closest to the recommended colour.
Without the spectrometer, the method of
determining of PTT is to prepare the colour
standarddescribedbyrequirements.
at colour test,
the result is in accordance with
requirementsinunitsAPHA;
athydrocarbonstestresults(Table2),candirectly
readingonspectrometer,inunitsofturbidityFTU,
if it is a slight presence of hydrocarbons, or it
indicatesanincreasing presenceof hydrocarbons;
inthiscasestudy,beacceptedas
“pass”.
2 ForUVspectroscopy
forbenzene inmethanoltherearetwoareaswith
strongactivitybetween200...220nm(benzeneisa
purehydrocarbon)and240...260nm(threesmall
peakswithpurebenzeneandtheindicativeofall
Aromatics);
for styrene in methanol there is strong UV
activityin
two specific regions at 210 nm
(hydrocarbon, ethylene group) and between
240...260nm(Aromatics);
for phenolinmethanolthere isAromatic activity
around240...260nm,butinthiscasestudy,ithas
beenshiftedtohigherwavelenghtareas,260..280
nm (because the OH group from formula of
phenol is directly attached to the benzene ring
(Sørensenetal.2016).
There are
more UV traces of chemical cargoes
(fatty acid methyl ester‐fame, pyrolysys gasoline‐
pygas,acetone,multiplehydrocarbons,unknows).
In literature are published more informations
about additional poits for UV tests (NVM‐Non‐
volatile‐ matter, AWC‐acid wash colour test) and
washing water analysis (http://www. alfalaval. com.
2016).
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