257
1 INTRODUCTION
Shipping is by far the most important mean of
transporttoday,withapproximately90%oftheglobal
cargo.Shippingintensityintonsperkmisgrowingat
ratesof4to6%yearly[5]eveninarecessionscenario,
andisestimatedtocontinuethispath,asshippingis
recognized as the most cost effect
ive means of
transport. In this scenario there is an increasing
consideration for the environmental impact of
shipping. IMO leads the international exhaust
emissionregulationsforshipsthatmaybewaivedon
itsendorsementby member states or superseded by
morestringentlocalregulations[5],incertaincoastal
and port areas are being applied (ECA Emission
Cont
rolledAreas).ExistingECA’sare the BalticSea,
the North Sea, the coasts of the USA and Canada.
ECA’s in discussion are the coasts of Mexico, Black
Sea,MediterraneanSea (2014)andtheBay of Tokyo
(2015).
IMO’s 1997 protocol to amend MARPOL 73/
78
added Annex VI‐Regulations for the Prevention of
AirPollutionfromShips.Thisenteredintoforceon19
May2005.Regulation14includeda1.5%limitonthe
sulphurcontentoffueltobeusedinaSOxEmission
Control Area (SECA). Alternatively the use of an
a
pprovedExhaustGasCleaningSystemtoreducethe
totalemissionsfromtheshiptoanequivalentlevelof
0,6gSO
x/kWhwaspermitted.
Forthereductionandmonitoringof green house
gases (GHG) emissions the IMO developed and
adoptionregulations,suchas“InterimGuidelinesfor
Voluntary Ship CO
2 Emission Indexing for Using in
Trials(2005)” [5] and “Guidelines for Voluntary use
of the Ship Energy Efficiency Operational Indicator
Solution to Reduce Air Environmental Pollution from
Ships
H.T.Pham&T.M.Nguyen
VietnamMaritimeUniversity,Vietnam
ABSTRACT: Exhaust gas emissions from ships are increasingly polluting the air environment seriously.
Therefore, the MARPOL 73/78 Annex VI is applied for all ships from 2017, Annex VI provided that the
concentrationsofNOx,SOxCOcontainedinship’sexhaustgasesmustbelessthan6.4g/kWh,0.6g/kWh,and
5.5g/
kWh respectively. Today, there are many solutions to reduce pollution emissions from exhaust gas of
ships,suchasimprovingcombustion,usingoilemulsion,usingbiofuel,…However,thesesolutionsalsohavea
handfulofdisadventagessuchasbeingunabletothoroughlyresoulveproblems,highcost,andverydifficultto
improvethequalit
yofshipexhaustgasemissionsforoldships.
Exhaustgastreatmentmethodusesacentralizedtreatmentsystemwhereexhaustgasfromthethermalengines
istakeninacentralizedtreatmentsystembeforedischargingintotheair.Aftercentralizedtreatmentsystem,in
comparision with raw exhaust gas, soot can be reduced by 98%, NOx can be reduced by 75%, SOx can be
reducedby80%.Thismethodoftreatmentisnotonlylowcost,goodqualit
ybutalsomakemarineheat‐engines
stillusetraditionalfuelsaswellasneednotimproveitsstructure.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 9
Number 2
June 2015
DOI:10.12716/1001.09.02.14
258
(EEOI‐2010)” [5]. GHG emissions covered in these
regulations include carbon dioxide (CO
2), methane
(CH
4)andnitrousoxide(N2O).TheEUimplemented
similarregulationssettinglimitsonmarineemissions,
such as EU Sulphur Directive 2005/33/EC, setting
limitsforSO
xandPMemissionsfrommarinetraffic
inEUterritorialwatersandthesettingupofEmission
Control Areas (ECA) in line with MARPOL 93/97
Annex VI [5]. The international and European
legislation gave a real intent to reduce maritime
pollution through reductions of SO
x, NOx, PM and
CO
2, as well as CO, volatile organic compounds
(VOC;includingmethane)andN
2O.
This paper presents a technology utilized for the
abatement of sulphur oxides, particulate matter and
nitrogen oxides based on a centralized treatment
system as exhaust gas from the thermal engines is
taken in a centralized treatment system before
dischargingintotheair.
2 EMISSIONFROMMARINETHERMALENGINES
Significant amounts
of the concerning emissions are
produced from the main diesel engines used to
provide propulsion and generate power. Other
sources,suchasonboardincineratorsandboilers,can
contribute to emission levels from ships, depending
on their operation, but these are at relatively low
levels compared to those produced from the
main
power and propulsion diesel engines [5]. The
emissions levels from marine engines typically
dependonfivefactors,whichare:
1 Typeoffuelbeingconsumed;
2 enginetype;
3 engineefficiency;
4 powerandpropulsiondriveconfiguration;
5 operationandworkloadoftheengines.
Marinefuelsareheavier, moreviscous
thantheir
land based equivalents, traditionally with longer
carbonchainsandhighersulphurmasscontent.The
three most commonly used marine fuels are marine
diesel oil (MDO); marine fuel oil (MFO) and heavy
fuel oil (HFO). Figure below introduces correlation
betweentheair,fuelandlubricantconsumptionrate
tothe
emissionoftoxicsubstancesinexhaustgasofa
fourstrokemarinedieselenginewithmediumspeed
usingHFOcontaining2,2%sulphur[5].
Figure1.Typicalexhaustgascomposition–mediumspeed
fourstrokeengineusingHFO
3 EXHAUSTGASCLEANINGPROCESS
3.1 ProcessreducesNO
xintheexhaustgas
TheSCRprocessmakesitpossibletoreducethelevel
ofnitrogenoxidesbymeansofthereactionsshownin
abroadtemperaturerangebetweenabout160°Cand
just under 600
0
C, depending on flue gas conditions
andcatalysttype.Highselectivitiesof almost 100 %
are obtained in the reaction of ammonia and, if
required,NO
xconversionsofwellabove90%canbe
achieved.
Nitrogen oxides are reacted stoichiometrically
withureaaccordingtothefollowingreactions[2,3]:
NO+NO
2+(NH2)2CO→2N2+CO2+2H20 (1)
(NH
2)2CO+H20→2NH3+CO2 (2)
The major part of the nitrogen oxides, which is
generallypresent as NO, is reacted according to the
followingreaction[2,3]:
4NO+4NH
3+O2→4N2+6H2O (3)
AslongasamixtureofNOandNO
2ispresent,the
following somewhat faster reaction proceeds in
parallel[2,3]:
NO+NO
2+2NH3→2N2+3H2O(4)
Inprinciple,thesereactionscanalsobecarriedout
withoutcatalystinasmalltemperaturerangearound
900
0
C.However,undertheseconditionsasignificant
proportionoftheammoniaisburnedtoformnitrogen
oxides, which severely impairs the efficiency in
respectofammoniaconsumptionandtheachievable
NOxconversion.
Usually catalysts for treating NO
x are based on
Cu‐Zeolite alloy in form of catalytically active
anatase.Thissupportmaterialisacid‐resistantandis
therefore particularly suitable for use in acid flue
259
gases.System for NO
x cleaning process is taken in
figure2.
Figure2.NOxcleaningsystem
3.2 ProcessreducesSOxintheexhaustgasusing
CalciumHydroxide
The large‐scale proven processes for the
desulphurization of flue gases are based these days
on absorptive processes. Normally lime based
materialssuchashydratedlime[Ca(OH)
2]areinuse.
Particularly in small and mediumsized combustions
dryandsemi‐dryprocessesbasedcalciumhydroxide
arewellestablishedbecauseofthelowercapitalcosts,
the operating safety and the smaller footprint
comparedtowetprocesses.Theseunitsareoperated
attemperaturesbetween80
0
Cand250
0
Cbasedonthe
fact that a preferably high amount of the latent
availableheatisusedforgeneratingsteam.Thelower
operatingtemperature,themoreexhaustgasheatcan
beused,especiallyifthecombustionunitisusedasa
combined heat and power unit. For that reason low
temperatures
are preferred. The selected operating
temperature depends in the first place on the
concentration of the acidic exhaust gas components
SO
2, HCl and HF as well as on the concentration of
thehygroscopicsaltsformedwiththeabsorbens.
For temperatures below the dehydration
temperature the reaction step for calcium hydroxide
withSO
2canbedescribedasfollows[2,3]:
Ca(OH)
2+SO2→CaSO3+2H2O (5)
Asideotherreactionsaretakingplace:
Ca(OH)
2+SO2+O2→CaSO4+H2O (6)
Ca(OH)
2+SO3+H2O→CaSO4+2H2O (7)
which means that during the absorption of sulphur
oxides calcium sulphite and calcium sulphate are
generated..
3.3 Processreducesootintheexhaustgas
Process of cleaning soot in exhaust gas is
implementedinsootremovaldevicewhichistypeof
porous layers and water spray (scrubber). This
equipment
consists of a rectangular tank where
porouslayersmadebycopperalloyareplacedinside
andwatered(showninfigure3)[4].
Exhaust gas Exhaust gas
Water nozzle
Porous layers Sludge tank
Figure3.Scrubber
Principleofsootcleanerisasfollows:Exhaustgas
is leaded into scrubber, through the porous layers
aftermoistering, soot will stick to the surface of the
porouslayerswhiletheexhaustgasgoesthroughit.
Almostallsootwillbesweptawayintosludgetank.
The amount of soot remaining
on the surface of
porouslayerswillbeperiodicallywashedwithwater.
Theexhaustgasgoingthroughttheporouslayers
lossesitsenergybecauseofaerodynamicresistanceof
porouslayers,thislossisdifinedasfollows[5]:
OmmH
dS
v
Hp
t
kk
2
0
2
,
2
(8)
m
S
S
d
a
t
,
4
0
(9)
ak
k
k
S
v
0
4
Re
(10)
IfRe
k<80:
85,0
Re
400
k
;80<Rek<400:
45,0
Re
70
k
;
Re
k>400:
2,0
Re
5,16
k
;
where:
rate of aerodynamic resistance force of
porouslayers;Hporouslayerheight,m;v
kvelosityof
exhaustgasthroughtporouslayers,m/s;
k
density
of the exhaust gas, kg/m
3
; S0 sectional area of 1 m
2
hollow, m
3
/m
3
; dt

equivalent
diameter of porous
layer,m;S
aexposedsurfaceareaof1m
3
porouslayer,
m
2
/m
3
;
k
dynamicviscosityofexhaustgas,Pa.s.
Capacityofwatersprayintoequipmentisusually
inrange0,15÷0,51l/m
3
.Effectofsootcleaningcanbe
upto90%withsootsizes
m
2 .
Effectofsootcleaningisdeterminedby[5]:
)
))(1(
exp(1
0
Stk
d
H
qS
on
(11)
0
2
18 d
v
Stk
k
bk
(12)
260
Where:
experimental constant dependent on
porous material; d
0 special parameter of porous
phases,m;
man
Sq
,m
3
/m
3
;
m
thiknessofwater
membraneonsurfaceofporouslayers,mm;StkStoke
standards for soot and exhaust system with special
parameter d
0 of porous phase, mm. Raschig phase,
saddle‐stitched Berl, intalox phase d
0=12,7mm,
=0,192; berl phase, Raschig phase, Pall phase
d
0=25,4mm,
=0,19.
Inordertoincreasetheabilityofremovingsootin
exhaust gas, soot and water can be loaded opposite
charge. Soot paticles are positively charged in a
devicenamedPMcharge,thenareletintothesecond
chamber where water is negatively charged. As a
result, soot paticles are attracted
by water due to
Coulomb attraction with high efficiency. In this
chamber,mostofsootwithsmallsizearekept.Soot
treatment diagram by charging method is described
infigure4
Figure4.sootstreatedbyPMcharge
Soottreatmentefficiencybyelectromagneticforce:
[1]
Where water is neutralization and shoot is
charged:
4,0
2
0
2
2
3
.
89,2
wkM
MC
E
dvd
qC
(13)
Wheresootandwaterarecharged:
0
2
3
.
4
kM
wMC
E
vd
qqC
(14)
Total Soot treatment efficiency is determined by
thefollowingformula[1]:
.
)(
.3,0exp11
0 kw
w
wk
w
TB
vv
v
d
h
Q
Q
N
N
(15)
Where:N:densityofsootafterfiltrationchamber,
kg/m
3
; N0: density of soot on filtration chamber,
kg/m
3
;Qk:exhaustgasflowintothetreatedchamber
(m
3
/s); Qw: flow of water injection into treated
chamber,(m
3
/s);dw:diameterofdroplets,m;h:height
of the scrubber, m.
k
v : velosity of the exhaust gas
flow,m/s;
w
d isparticlediameterofwater,m;
M
d
is
diameterofsoot,m;C
C:theCunninghamslip;
is
theviscosityofair(kg/m.s);q
M:chargeofsoot,C;qw
is charge of water, C;
0
is allowed vacuum
coefficient.
4 CENTRALIZEDTREATMENTSYSTEM
Figure 5 shows a diagram of exhaust gas treatment
system which is used for treating exhaust gas of
thermalenginesonlaboratoryofMarineengineering
faculty of VMU. The system consists of three
treatmentchambers,theyareAchamber,Bchamber
and
Cchamber.
Figure5.Centralizedtreatmentsystem
A chamber is NOx neutralizated chamber using
urea solution. Second chamber is SO
x neutralization
chamber using hydrated lime (Ca(OH)
2), in which
soot is treated by neutralizated water and soot
charged.Thethirdchamberischamberwheresootis
removedbychargingsootandwateroppositely.
5 RESULTSANDDISCUSSION
Figure6.Influenceofchargingmodetotreatsootquality
261
Figure7.Soottreatedquality
Resultsoftheoreticalcalculationsandexperiments
showed that spraying regimes influence on soot
removed efficiency in treated chamber (figure 6). If
weemployonlyneutralwaterforweedingoutsoot,
effect achieves quite low, at best 65%, the soot
particleswhicharesmallerthan1μmperformanceis
only20%.When
sootparticlesarechargedoppositely
or both soot and water are charged, soot removed
efficiencysignificantlyincreases,reaching98%.
Resultsoftheoreticalcalculationsandexperiments
on the soot treatment quality of treatment system
witherrorsnegligiblearepresentedinfigure7.
Table1. NOx mesurement resultsbefore and after the
teatingequipment
_______________________________________________
mesurementsAfter1After3After5After8
hour hourshourshours
_______________________________________________
NOxmesurementresultsbefore30 35  35 34
thetreatingequipmentg/kWh
NO
xmesurementresultsafter 7 5 4 3,5
thetreatingequipment,g/kWh
SO
xmesurementresultsbefore 1,51,41,51,5
thetreatingequipmentg/kWh
SO
xmesurementresultsafter 0,4 0,35 0,35 0,3
thetreatingequipment,g/kWh
_______________________________________________
NOx treatment method absorbed by ingestion of
ureasolutionwithlowtreatmentcostandinvestment
and high treatment efficiency (efficiency can reach
75%,table1).
SO
2, SO3 treatment method with aqueous lime in
treating gets a very high efficiency (can be effective
from 70 to 80%, table 1), low treatment and
investmentcost,simpletreatmenttechnology.
Exhaust gas treatment method usingtreatment
systemasabovecanapplytocentrilizedtreatmenton
ships.
6 CONCLUTION
Exhaust gas treatment
system combines NOx, SOx
neitralizeandsoottreatmentthatsootandwaterare
opposite charged with very high efficiency. The
treatment quality of the system cansatisfy
standardsofIMOandEUROIVemissionsothatit
shouldbeappliedfortreatingexhaustgasonships.
Thecostoftreatmentandinstallationislow,
very
suitblefortreatingexhaustgasonships.Shipswhich
are equipped with centrilized exhaust gas treatment
system may not have to use fuel with low sulfur
contentinspecificareasoftheworld.Theenginescan
stillusetraditionalfuelswithlowcost.Theseengines
neednotimproveinterm
ofstructure.
Exhaust gas treatment system can be focused
widelyonshipsinthefuture.Itoffersgreatbenefits
to shipowner when installing this system because
shipscanstillusetraditionalfuelswithlowcostand
itneednotuseshoreexhaustgastreatmentsystemat
ports.
REFERENCES
[1]HongConHoang,KimLoanDong”Exhaustgastreating
techonology”. Hanoi 2006, Published by National
UniversityPublisher.
[2]Hong Ha Tran “calculated and measured soot
concentration in the exhaust gas of boiler before and
after treatment with charing water tower”, 2011,
PublishedbyMarinescienceandtechnologyjournals.
[3]Kim
CoHoang“Dustfiltrationandexhaustgasclean”,
2001,PublishedbyScientificandtechnicalPublisher.
[4]Ngoc Chan Tran“ Air pollution and air pollution
control”, 2001, Published by Scientific and technical
Publisher,
[5]Ralf Juergens, Couple Systems GTmbH, Deutscchland
“First operational experiences with a combined dry
desulphurization plant and SCR
unit downstream of a
HFOfueledmarineengine”,2013,PublishedbyCIMAC
Congrass,Shanghai.