Understanding exhaust gas treatment systems · Understanding exhaust gas treatment systems Contents 1 Figures and tables 2 1 Introduction 3 2 How to use the key 6 3 Air pollution

Understanding exhaustgas treatment systemsGuidance for shipowners and operators

June 2012

Cover image: Downtown Seattle and port(These waters will form part of the North American Emission Control Area (ECA) once it enters into effect in August, 2012.)

First published June 2012

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Understanding exhaust gas treatment systems

ContentsUnderstanding exhaustgas treatment systems

Contents 1Figures and tables 2

1 Introduction 3

2 How to use the key 6

3 Air pollution regulations and controls 73.1. MARPOL Annex VI 7

4 Exhaust gas treatment systems (EGTS) 94.1 Flexibility 94.2 The risk of non compliance 94.3 Backpressure 94.4 EGTS bypass 104.5 Exhaust gas velocity 104.6 Integration of multiple combustion devices 104.7 Maintenance, crew training and workload 11

5 EGTS approvals 125.1 Statutory approvals 125.2 Class approvals 135.3 Independent verification 13

6 SOX scrubbers 146.1 SOX scrubber technologies 146.2 Wet SOX scrubbers 146.3 Wet SOX scrubbers – open loop 156.4 Wet SOX scrubbers – closed loop 15Case study 1 – Open loop SOX scrubber 166.5 Wet SOX scrubbers – hybrid 19Case study 2 – Hybrid SOX scrubber 206.6 Common aspects of wet SOX scrubbers 226.7 Dry SOX scrubbers 266.8 Comparing SOX scrubber technologies 28

7 NOX-reducing devices 317.1. Selective catalytic reduction (SCR) 327.2. Exhaust gas recirculation (EGR) 36

Appendix A1 Impacts of marine exhaust emissionson human health and the environment 40

Appendix B1 MEPC 184(59) – Exhaust GasCleaning System Guidelines 42

Appendix B2 NOX Technical Code 47Appendix B3 Regional, national and local regulations 48Appendix C Chemical reactions 50Acronyms and abbreviations 51References 52

1

FiguresFigure 1: The hierarchy of exhaust gas

treatment systems 6Figure 2: The key 6Figure 3: The MARPOL Annex VI fuel oil

sulphur limits 7Figure 4: Current and future Emission Control

Areas (ECAs) 8Figure 5: MARPOL Annex VI diesel engine NOX

control schedule 8Figure 6: ID fans in exhaust ducts 10Figure 7: Water vapour in exhaust gas plume after

passing through wet SOX scrubber 14Figure 8: Open loop SOX scrubbing system 15Figure 9: Closed loop SOX scrubbing system 18Figure 10a: Hybrid SOX scrubbing system in open

loop mode 19Figure 10b: Hybrid SOX scrubbing system in closed

loop mode 19Figure 11: 21MW hybrid scrubber during

installation on Ficaria Seaways 21Figure 12: Washwater treatment system with

GRE piping 22Figure 13: Multi-stage washwater treatment system

used with closed loop scrubbers 22Figure 14: Hydrocyclone liner 24Figure 15: Washwater instrumentation 25Figure 16: Dry SOX scrubber system 26Figure 17: Calcium hydroxide granules 27Figure 18: Marine SCR arrangement - four-stroke

medium-speed engine 32Figure 19: Catalyst element fouling 33Figure 20: SCR arrangement - two-stroke

low-speed engine 34Figure 21: EGR system arrangement -

two-stroke low-speed engine 36Figure 22: Graphic of the second-generation

EGR system 37Figure 23: Continuous emissions monitoring systems 44Figure 24: Washwater discharge pH limits 45


Figures and tables

2

TablesTable 1: Statutory approval requirements for EGTS 12Table 2: Typical stages in a closed loop washwater

treatment system 24Table 3: Comparison of SOX scrubber technologies 29Table 4: Fuel oil sulphur limits recorded in MARPOL

Annex VI regulations 14.1 and 14.4 andcorresponding emissions values 42

Table 5: Scrubber document requirements 43Table 6: Key regional, national, and local regulations 48Table 7: California fuel regulation requirements 49


3

Lloyd’s Register has been at the forefront ofunderstanding emissions to air from marine diesel enginessince we started our Marine Exhaust Emissions ResearchProgramme [1], which assessed the nature and magnitudeof shipping’s contribution to atmospheric pollution.

Exhaust emissions from marine diesel engines mainlycomprise nitrogen, oxygen, carbon dioxide (CO2) andwater vapour, plus smaller quantities of nitrogen oxides,sulphur oxides, carbon monoxide, various hydrocarbonsat different states of combustion and complex particulatematter (PM). It is these smaller quantities, together withCO2, that are of most concern to human health and theenvironment. Adverse effects are experienced at local,regional and global levels. Appendix 1 provides furtherinformation about these impacts, which includecontribution to climate change through increasingconcentrations of CO2 in the atmosphere; respiratorydamage; cancers and genetic mutation; and damageto the natural and built environment.

The regulatory frameworkIn response to these impacts the International MaritimeOrganization (IMO), through its Marine EnvironmentProtection Committee (MEPC), introduced regulationsfor the prevention of air pollution under Annex VI of theMARPOL Convention.

The Annex imposes a framework of mandatory limitson emissions of sulphur oxides (SOX) and nitrogen oxides(NOX) both globally and within designated sea areas,known as Emission Control Areas (ECAs). These areregions where neighbouring states have shown thatemissions to air have particular impacts on humanhealth and the environment.

In parallel with Annex VI, a number of regional, nationaland local regulators have introduced their own controls,leading to a patchwork of regulatory requirements.

Section 3 of this publication gives an overview of MARPOLAnnex VI, and Appendix B3 includes a summary of themain regional, national and local regulations. At Lloyd’sRegister we monitor and influence the development ofenvironmental regulations at MEPC as a participant innational and observer delegations.

Exhaust gas treatment systemsa

As emission limits become more stringent, compliancebecomes more challenging and costly. There are anumber of compliance options, each of which hasdifferent technical and operational challenges.

To meet reduced SOX emission limits, ships can operateon low-sulphur residual and distillate fuels, and in thelonger term alternatives such as LNG (liquefied naturalgas), biofuels, DME (dimethyl ether) and methanol mayprovide solutions. The alternative to these options areexhaust gas treatment sytems (EGTS) known as SOXscrubbers, which clean the exhaust gas to reduce SOXemissions to a level that is equivalent to the required fuelsulphur content. This offers the flexibility to either operateon low-sulphur fuels or to use higher sulphur fuels.

Exhaust gas treatment systems for NOX , known asNOX-reducing devices, provide the flexibility to operateships constructed after 1 January, 2016 inside EmissionControl Areas designated to control NOX emissions(ECA-NOX).

This guidance provides an understanding of: thedifferent exhaust gas treatment technologies; whatto consider when deciding whether or not to installan exhaust gas treatment system; and the practicalchallenges of installing and operating these systemson board ships.

Section 4 describes the issues common to both SOXscrubbers and NOX-reducing devices; section 6 coversSOX scrubbers; and section 7 coves NOX-reducing devices.

At the time of publishing this guidance, every effort hasbeen made to ensure that it reflects the current status ofEGTS technology and emission regulations. We will beupdating it regularly. To download the latest version visitwww.lr.org/eca or to purchase a hard copy visit theLloyd’s Register webstore: www.webstore.lr.org

We would like to thank Shipping EmissionsAbatement and Trading (SEAaT) for their valuableinput to this publication.

1. Introduction

a The term exhaust gas treatment system (EGTS) is used in this guidance to refer collectively to SOX scrubbers and NOX-reducing devices.This is to avoid confusion with the term ‘exhaust gas cleaning system’, which the MEPC uses to refer to SOX scrubbers only.

4

A ship leaving PortMiami, which will form partof the North American Emission Control Area (ECA)

5


6

2. How to use the key

A key is included throughout this guidance to show youwhich types of EGTS each section covers.

SOX scrubbers are indicated by solid yellow boxes whileNOX-reducing devices are indicated by solid blue boxes.

Grey boxes indicate EGTS that are not covered withinthe section.

Figure 1 shows the hierarchy of systems covered by theguidance while figure 2 shows how the key appears oneach page.

SOxscrubbers

NOxreducingdevices

WetSOxscrubber

DrySOxscrubber

SCR EGR

Openloop

Closedloop

Hybrid

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR

Figure 1: The hierarchy of systems covered by this guidance.

Figure 2: The key asit appears on each page.This section covers wetopen loop, closed loop andhybrid SOX scrubbers.


7

International, regional, national and local instrumentsregulate emissions of SOX, NOX and particulate matterfrom ships. In response to greater concern about airquality the extent and complexity of regulation haveincreased while emissions limits have become tougher.Annex VI of the IMO MARPOL Convention applies toall ships trading internationally and has been used asthe basis for many other regional, national and localregulations.

Once the lowest limits for SOX and NOX come intoforce, the exhaust emission limits for ships engagedin international trade will still be higher than thecurrent limits for emissions from land-based industry,land-based transportation and air freight, whenconsidered on the basis of sulphur content of fuelconsumed or an engine’s NOX emissions in g/kWh.However, when considered on the basis of unit ofemission per unit of transport work delivered (e.g. SOXper teu·km) the emissions of ships will be lower thanother forms of transportation due to shipping’ssignificantly higher transport efficiency.

3.1 MARPOL Annex VIMARPOL Annex VI regulates the emissionsfrom ships engaged in international trade andregulations 4, 13 and 14 are particularly relevant.

Regulation 14Regulation 14 places limits on the sulphur content offuel to restrict SOX and particulate matter emissions,and is applicable to all ships in service. The regulationspecifies different limits for operating inside and outsidean Emission Control Area for SOX (ECA-SOX) and thesefollow a stepped reduction over time, as shown inFigure 3.

Two ECA-SOX – the Baltic and the North Sea (whchincludes the English Channel) – are currently in effectand well established. From 1 August, 2012, a third – theNorth American ECA-SOX – will enter into effect, whilea fourth – the US Caribbean ECA-SOX – is intended toenter into effect in January 2014. Figure 4 shows thegeographical extent of these areas.

Regulation 4Regulation 4 allows flag administrations to approvealternative means of compliance that are at least aseffective in terms of emissions reduction as the prescribedsulphur limits. This means that a ship may operate usinga fuel with a sulphur content higher than that allowed byregulation 14 as long as an approved SOX scrubber canreduce the SOX emissions to a level that is equivalent to,or lower than, the emissions produced by compliant fuel.If a SOX scrubber is fitted, it must be approved and

3. Air pollution regulations and controls

■ 4.50%

■ 3.50%

■ 1.50%

1.1.2012

1.1.2020* 1.1.2025

■ 1.00%

■ 0.10%

1.7.20101.1.2015

Fuel oilsulphurlimits

■ 0.50%

Outside ECA-SOx

Inside ECA-SOx

*Depending on the outcome of a review of fuel oil availability,to be completed 2018, the 2020 date could be deferred to 2025

Figure 3: The MARPOL Annex VI fuel oil sulphur limits

verified as compliant in accordance with the IMOExhaust Gas Cleaning SystemsGuidelines (MEPC 184(59)– 2009 Guidelines for Exhaust Gas Cleaning Systems [2] ).

The Guidelines specify two testing, survey, certificationand verification schemes:• Scheme A – initial approval and certification of

performance followed by in-service continuousmonitoring of operating parameters plus daily spotchecks of the SO2/CO2 emission ratio; and

• Scheme B – continuous monitoring of SO2/CO2


8

emission ratio using an approved system within-service daily spot checks of operating parameters.

In either case any washwater discharged to sea mustalso be continuously monitored. Appendix B1 containsmore detailed information on these Guidelines.

Regulation 13Regulation 13 places limits on the NOX emissions ofmarine diesel engines. The limits are divided into three‘Tiers’ whose applicability depends on the ship’sconstruction date (or the date of installation ofadditional or non-identical replacement engines) andthe engine’s rated speed (n), as shown in Figure 5. TierI and Tier II limits are applicable to engines installed onships constructed on or after 1 January, 2000, andJanuary 1, 2011 respectively.

Subject to a review of enabling technologies, Tier III limitswill apply to ships constructed on or after January 1,2016 when operating inside an ECA-NOX. Currently, twoECA-NOX will be in effect in 2016; the North AmericanECA-NOX and the US Caribbean ECA-NOX. These willalso be ECA-SOX (see ‘Regulation 14’ on page 7).

NOX Technical CodeThe NOX Technical Code 2008[3] contains mandatoryprocedures for the testing, survey and certification ofmarine diesel engines. Further details are included inAppendix B2.

North American ECA-SOX

from August 1, 2012

North American and US CaribbeanECAs will also be ECA-NOX

from 2016

Baltic and North Sea ECA-SOX

US Caribbean ECA-SOX

from January 1, 2014

17.0

I45.n-0.2

II44.n-0.23

III9.n-0.2

14.4

7.7

3.4

2.0

NOxg/kWh

NOxg/kWh

9.8

2000 2011 2016

Ship construction date

Note: Both vertical axesUpper limit less than 130 rpm. Lower limit 2000 rpm and above.

Outside ECA-SOx

Inside ECA-SOx

n = engine’s rated speed

Figure 5: MARPOL Annex VI diesel engine NOX control schedule

Figure 4: Current and future Emission Control Areas (ECAs)

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For the purposes of this guidance, EGTS are dividedinto SOX scrubbers and NOX-reducing devices. Thereis at least one exhaust gas treatment system on themarket that claims to reduce SOX, NOX and CO2using electrolysis or electromagnetic techniques, butat the time of writing there is not enough informationavailable on the underlying technology to makeany meaningful comment on its applicabilityand operation.

Issues specific to SOX scrubbers and NOX-reducingdevices are covered in Sections 6 and 7, but thereare a number of issues, outlined in this section, thatapply to both.

4.1 FlexibilityOne of the benefits of EGTS is that they offeroperational flexibility. A SOX scrubber allows anoperator to meet emission limits by either usinglow-sulphur fuels or by using the SOX scrubber toclean the exhaust gas. NOX-reducing devices will offerships constructed after 1 January, 2016 the flexibilityto operate inside ECA-NOX (see section 3.1).

4.2 The risk of non-complianceConsideration should be given to both the likelihoodand consequences of the failure of an EGTS when it isused to comply with mandatory regulation.

The likelihood of failure will depend on the reliability ofthe system components and the redundancy included inthe system’s design. Building in redundancy reduces thelikelihood that the system as a whole will fail. Forexample, designing a wet SOX scrubber with threepumps each capable of meeting 50% of the washwaterpump demand would allow the scrubber to continue tooperate in the event of a single pump failure. Otherareas where redundancy can be built in include theexhaust gas and wash water monitoring systems.

The consequences of an EGTS failure will dependon whether the ship can employ alternative meansto comply with the requirements. For example, in theevent of a main engine SOX scrubber failing a shipmay be able to bypass the scrubber and use compliant

fuel. Sufficient compliant fuel will need to be storedon board if this is to be used in the event of ascrubber failure. However, if no compliant fuel isavailable the ship would no longer be able to complywith the applicable regulations. It is worth noting thatthe integration of multiple exhaust streams into asingle scrubber does exacerbate the consequences ofthe system failing.

How flag and port states will respond in the event thata ship cannot comply is not yet apparent, but onepossible outcome would be to require the ship to sailto the nearest port until either the EGTS has beenfixed or an alternative method of compliance isavailable. The commercial consequence of such a delaywill depend on the ship’s trading pattern.

Understanding the likelihood and consequences ofa failure of an EGTS will allow informed decisions tobe made on the amount of redundancy to be designedinto the system.

4.3 BackpressureEngine manufacturers include a permitted range ofexhaust backpressures within the technical specificationsof their engines – operating outside this range may leadto accelerated wear, greatly reduced maintenanceintervals, reduced power and increased fuelconsumption. In addition, an engine’s NOX Technical Filemay also specify a range of permissible backpressures –operating outside this range will invalidate the engine’sNOX approval.

EGTS intrinsically increase backpressure and systemdesigners need to understand the impact of this onthe engine. If the EGTS will increase backpressure toa level outside allowable operating limits, it may bereduced by adding an induced draft fan (ID fan) intothe exhaust duct (see Figure 6).

Build up of deposits within the EGTS components(for example soot clogging of demisters or depositson selective catalytic reduction (SCR) catalysts) willincrease backpressure while the ship is in operation.

4. Exhaust gas treatmentsystems (EGTS)

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR


maintenance of the EGTS while the associatedengine(s) is running (although care should be taken asthe bypass damper is not a secure means of isolatingthe EGTS chamber).

4.5 Exhaust gas velocityThe introduction of EGTS may slow the exhaustgas and any cooling will slow it down further.Consequently, to ensure the exhaust gas clearsthe ship, the exhaust duct outlet may have to beredesigned to increase the velocity of the gas asit exits the funnel. While relevant to all ships, this isparticularly important for cruise ships and ferries. Caremust be taken to ensure that the resulting increase inbackpressure is acceptable (see section 4.3).

4.6 Integration of multiple combustiondevicesIt is possible to combine the exhausts from a numberof different combustion devices into a single EGTS.This may be necessary due to space restrictions, orsimply to reduce the cost of the installation.

Monitoring the pressure differential across the EGTSwill indicate if cleaning is required. Some of thesedeposits can present a significant health and safety riskto people entering the EGTS to carry out maintenanceand cleaning activities.

4.4 EGTS bypassA bypass provides an alternative path for the exhaustgas so that it avoids the EGTS. When the bypass is‘closed’ exhaust gas will pass through the EGTSand when it is ’open‘ the exhaust gas will exit the shipwithout passing through the EGTS. Some wet SOXscrubbers are designed to 'run dry' whereas others maybe damaged if hot exhaust gas is passed through themwhile they are not operating. For systems not designedto run dry, the bypass damper can be interlocked withthe EGTS controls to provide a failsafe protection.

Opening the bypass when the EGTS is not operatingwill prevent a build up of soot and unburnedhydrocarbons within the system. When the bypassis open it might also be possible to undertake

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Figure 6: ID fans in exhaust ducts (image courtesy of Hamworthy-Krystallon)


11

The practice of combining exhausts is uncommonwithin the marine industry where typically eachengine has its own independent intake and exhaust.Concerns arising from combining exhausts include:

• backflow of exhaust gas into the exhaust ductof combustion devices that are not operating

• increased backpressure when two or morecombustion devices are combined that havedifferent exhaust gas flow characteristics; and

• designing the EGTS to operate effectively overa wide range of exhaust gas flow rates.

Dampers might be required for each exhaust topreclude the back flow of exhaust gas into theexhaust of combustion devices that are not operating.Monitoring is required to confirm that the backpressureon each device remains within allowable limits.

4.7 Maintenance, crew training and workloadIt is important to understand the impact of EGTSmaintenance on system availability. For instance,annual inspection and cleaning of the SCR chamberwill result in the SCR system not being available for

a period of time, which may impact the availabilityof the ship to operate in an ECA-NOX. The cleaningwill either need to be scheduled while the ship isoperating in locations where the SCR system is notrequired or the ship might have to be taken outof service.

Hazardous chemicals are used in a number of EGTSand adequate controls should be put in place toprotect ships’ staff. There is also a possibility of furtherhazardous chemicals and compounds (such asammonium bi-sulphate in SCR systems) beinggenerated. These will require robust procedures andcrew training, as well as adequate signage andpersonal protective equipment (PPE).

Crew training should cover the normal operation ofthe EGTS, including bunkering of any chemicals(consumables), calibration of sensors and routinemaintenance, as well as the procedures to be followedin case of system failure and deviation from normaloperation.

The additional workload associated with systemoperation and maintenance should be assessed. If itis significant, measures may need to be implementedto prevent crew fatigue.


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As with most shipboard equipment installed to meeta regulatory requirement, EGTS require both statutorycertification (issued by, or on behalf of, a flag administration)to show that the equipment meets the requiredperformance criteria, and classification society approval(class approval) to show that the equipment does notpresent an unacceptable risk to the ship and the essentialequipment required for the ship’s continued operation.

There are a number of different statutory and classapprovals associated with exhaust gas treatment systemsand their ship-specific installation. In addition to theseformal approvals equipment manufacturers andoperators may also wish to undertake independentverification of the performance of either a givenequipment design (Type Approval) or the performance ofa ship-specific installation (verification of performance).

5.1 Statutory approvalsTable 1 shows the statutory approval requirementsfor EGTS. These are described in more detail inAppendices B1and B2.

Scheme A statutory approval of SOX scrubbers issometimes referred to as ‘type approval’. Note: this isdifferent to Lloyd’s Register Type Approval, described insection 5.3, which involves independent verification ofperformance against standards specified by theequipment manufacturer.

For statutory approval, the equipment manufacturershould provide equipment with all of theapproved documentation required to demonstratecompliance.

5. EGTS approvals

Statutory – flag state ship-specific approval

(May be delivered by the ship’s class society acting as a recognised organisation if authorised by the flag state)

SOX

scrubberIMO MEPC 184(59) – 2009 Guidelines for Exhaust Gas Cleaning Systemsb 2.

Scheme A:Technical and Operating Manuals including SECPInitial shop or onboard test of scrubberDaily monitoring of SO2/CO2Continuous monitoring of key operating parametersContinuous monitoring of washwater

Scheme B: Technical & Operating Manuals including SECPNo shop or onboard test of scrubberContinuous onboard monitoring of SO2/CO2Daily monitoring of key operating parametersContinuous monitoring of washwater

Deliverable: Approved documentation (including Scheme A Certificate if applicable) and post-installationInitial Survey

NOXreducingdevice

Engine specific - certified entity is ‘engine + device’

Reviewed against NOX Technical Code 2008

Technical File (including Onboard NOX Verification Procedure)Engine group / family certificationPre-certification Survey

Deliverable: ‘engine + device’ certificate supported by approved documentation and post-installationInitial Survey

Table 1: Statutory approval requirements for EGTS

b These Guidelines apply to wet systems; it is anticipated that guidelines for dry scrubbers will be submitted at MEPC 64 in October 2012

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR


13

5.2 Class approvals

Class unit approvalEquipment manufacturers may ask Lloyd’s Registerfor a class unit approval to assess the impact of theirequipment on the safety of a generic ship and itsassociated systems by checking for compliance with ourRules and Regulations for the Classification Of Ships (theLR Rules). Specific Rules for EGTS will be included withinthe LR Rules from July 2013; these will ensure that EGTSare comprehensively and consistently approved, and willprovide stakeholders with information on Lloyd’sRegister’s requirements.

Class unit approval is a desk top review and includesan assessment of all of the hazards introduced by thesystem and any proposed mitigation measures. Typicallythe documentation required for the review is a mixtureof equipment construction drawings and schematicdrawings of associated systems and is not basedon an actual installation. In all cases the equipmentmanufacturer is required to submit a comprehensiverisk assessment for their system. Hazards mightinclude backpressure, corrosion, loss of containmentof hazardous chemicals, fire, overpressure and flooding.

Class unit approval may take a long time to completeand require a number of additional documentsubmissions as the approval progresses. Completionof class unit approval will significantly streamlineship-specific class approvals of subsequent installations.

Class approval of ship-specific EGTSinstallationClass approval of a ship-specific installation is requiredfor a ship to remain in ‘class’ with its classificationsociety. The approval includes a document review andonboard survey, and is informed by the class unitapproval. The approval focuses on the impact of thesystem on the safety of the ship and covers ship-specificpiping installations, electrical and control installations,and structural modifications.

5.3 Independent verification

Lloyd’s Register Type ApprovalLR’s Type Approval service provides equipmentmanufacturers with independent confirmation of theperformance of their products. It is applicable to seriesproduction of equipment whose critical componentsremain unchanged and typically the units are surveyedon a sample basis (as opposed to surveying every unit).The scope of the approval is specified by the equipmentmanufacturer and agreed by Lloyd’s Register. For EGTSthe scope of the Type Approval might include one ormore of the following:

• compliance with statutory requirements(performance standard)

• class unit approval (to confirm that the unit doesnot present unacceptable risk to the ship)

• compliance with specified maintainability anddurability standards.

To apply for Type Approval the equipment manufacturersubmits documents and plans and, depending on thescope of the approval, performance tests may also berequired. As Type Approval does not follow a definedscope it is important to note what the equipment-specific Type Approval documents state; Type Approval isnot a panacea.

Note: aspects such as EGTS functionality, reliability anddurability are not included within any of the statutoryapprovals, class unit approval or class approval of ship-specific installation.

Verification of performanceLR can also provide independent verification of EGTSin-service performance. This service is delivered byexhaust emissions specialists experienced in exhaust gasmeasurement, analysis and legislative interpretation,who are familiar with working on board ships.

To meet SOX emisson limits, ship operators currentlyhave two main options: using low-sulphur fuels or usinga SOX scrubber, if permitted (see table 5 in AppendixB3). The choice depends on a number of factors,including the cost of compliant low-sulphur fuels, thecapital expenditure (CAPEX) and operating expenditure(OPEX) of the SOX scrubber, and the amount of timethat the ship is expected to spend inside ECA-SOX.

We have developed the ‘ECA Calculator’ to helpoperators understand the costs associated withdifferent compliance options. Visit www.lr.org/eca todownload your copy.

6.1 SOX scrubber technologiesCurrently there are two main types of SOX scrubber:

• wet scrubbers (section 6.2) that use water(seawater or fresh) as the scrubbing medium; and

• dry scrubbers (section 6.7) that use a dry chemical.

Wet systems are further divided into:

• ‘open loop’ systems (section 6.3) that use seawater

• ‘closed loop’ systems (section 6.4) that use freshwater with the addition of an alkaline chemical;and

• ‘hybrid’ systems (section 6.5), which can operatein both open loop and closed loop modes.

Section 6.8 and Table 3 provide a comparison of thedifferent types of SOX scrubber.

6.2 Wet SOX scrubbersWet SOX scrubbing is a simple, effective technologythat has been used in industrial applications for manyyears. Wet SOX scrubbers broadly comprise thefollowing components:

• a scrubber unit – a vessel or series of closely coupledcomponents, which bring water into intimatecontact with the exhaust gas from one or morecombustion units. The unit is typically mounted highup in the ship in or around the funnel

• a treatment plant for conditioning of washwater beforedischarge overboard

• a residue handling facility for sludge separated fromthe washwater

• a scrubber control and emissions monitoring system.

These components will be interconnected by pipeworkwith various pumps, coolers and tanks, depending onthe scrubber system configuration. One piping systemand washwater treatment plant may service more thanone scrubber. There will also be a monitoring and controlsystem, with instrumentation either dedicated to a singlescrubber or shared across an integrated system.

Within wet SOX scrubbers there is a need to intimately mixwashwater with the exhaust without creating abackpressure that exceeds the combustion unitmanufacturer's limits and, if applicable, the engine’s NOXcertification limits. There are, however, incentives to makethe scrubber unit as small as possible, as this will reduce thespace required for installation and will also reducemanufacturing costs. The design should therefore makeoptimum use of the minimum practical washwater flow todissolve sulphur oxides, to bring emissions down to therequired level while retaining sufficient buffering capacity.Too little effective flow, mixing or alkalinity and the requiredreduction in SOX is not achieved. Conversely, too muchwater is inefficient in terms of pumping power andcomponent size and weight.

A wet SOX scrubber system may also include a reheaterto increase the exhaust gas temperature above the dewpoint, and a demister to remove fine water droplets.


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6. SOX scrubbersSOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR

Figure 7: Water vapour in an exhaust gas plume after passingthrough a wet SOX scrubber (image courtesy of Alfa Laval)


15

6.3 Wet SOX scrubbers – open loopIn wet open loop SOX scrubbing systems (includinghybrid systems operating in open loop mode – seesection 6.5) seawater is pumped from the sea throughthe scrubber, cleaned (see figure 8) and thendischarged back to sea. Washwater is not recirculated.The washwater flow rate in open loop systems isapproximately 45m3/MWh.

A SOX removal rate close to 98% with full alkalinityseawater should be expected, meaning emissions froma 3.50% sulphur fuel will be the equivalent of thosefrom a 0.10% sulphur fuel after scrubbing. In thedesign process seawater temperature also has to beconsidered as SO2 solubility reduces at higher seawatertemperatures. Equipment manufacturers shouldprovide guidance on the maximum sulphur content offuel that can be consumed by an engine or boiler witha scrubbed exhaust, so that emissions remain withinapplicable limits, together with any seawatertemperature limitations that may apply.

6.4 Wet SOX scrubbers – closed loopAll marine closed loop SOX scrubbers (including hybridSOX scrubbers when operating in closed loop mode –see section 6.5) use fresh water treated with sodiumhydroxidec (NaOH) as the scrubbing media. This results inthe removal of SOX from the exhaust gas stream assodium sulphate. The chemical reactions are shown inAppendix C. Rather than the once-through flow of anopen loop scrubber the washwater from a closed loopscrubber passes into a process tank where it is cleanedbefore being recirculated (see figure 9).

Control of pH by dosing with sodium hydroxide enablesthe washwater circulation rate and therefore powerconsumption to be about half that of open loop systemsat approximately 20 m3/MWh and between0.5 – 1% of the power of the engine being scrubbed.Closed loop systems can also be operated when the shipis operating in enclosed waters where the alkalinity wouldbe too low for open loop operation.

c Also known as caustic soda or lye

Scrubber

Pump

Exhaustgas

Watertreatment

Sludge tank

Seawater

Open loop washwater

Treated washwater

Sludge

Figure 8: An open loop wet SOX scrubbing system

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR


16

The installation made use of much of the pipeworkand infrastructure that had been installed for aprevious unsuccessful scrubber system, but it stillrequired the removal and realignment of a sectionof the existing exhaust ducting. The conversion wascompleted in a couple of days.

The costs of the scrubber and installation were coveredby HKL who wanted to test their scrubber on board aship, and demonstrate to clients that their technologyoperates successfully in a shipboard environment.

GRE (glass reinforced epoxy) piping had been usedfor the earlier scrubber installation and was retainedfor the washwater system due to the corrosive natureof warm, acidic washwater. Originally there were anumber of failures of the bonded flanges of the GREpiping when the system was subject to the fulloperating pressure and flow rate. The re-bondedflanges proved reliable and did not leak.

The ship's staff controlled the scrubber using a touch-screen and a 'green button and red button' (start/stop)approach. In addition to turning the system on and off,ship's staff had to monitor washwater dischargeparameters and pressure drop across the scrubber andperiodically check the uptake spaces for leakages. Whenthey identifed a problem they generally shut down thesystem and called HKL to make repairs, rather thanrepairing the system themselves. This was partly due tothe developmental nature of the installation, and partlydue to the ready availability of the HKL team.

One aspect of the scrubber that evolved during thetrial was the ‘de-plume’ heat exchanger arrangement.The de-plume heat exchanger was fitted after thescrubber chamber to reduce the visible exhaust plume,in conjunction with a de-mister. The initial de-plumedesign would slowly clog up with deposits of calciumsalts resulting in increased backpressure on the engine.The design steadily evolved to prevent this occurrence.

In addition, when the scrubber was operating, ship'sstaff reported that the exhaust from the scrubbedengine was clearer than that of the other engines,suggesting that there was no carry over of washwater

and that a proportion of the particulate matterwithin the exhaust was also being removed.

While in port at berth, reaction water in the formof cooling water from auxiliary engines was addedto the discharge stream to correct the pH. This wasnot required when the ship was at sea. Typically thequantity of dilution water was 1.5 times thewashwater flow rate.

The multi-cyclones were de-sludged once every24 hours. While the accumulation of sludge was small(estimated to be approximately 0.14 kg/MW·day) itdid depend on the water the ship was operating in andthe combustion quality of the engine. It was noted thatthe amount of sludge increased when operating in Calaiswhere there is increased sand and silt in the harbourwater. On Pride of Kent the sludge from the generatorwas combined with the sludge from the fuel oil purifiersand landed ashore, but on subsequent system designsthe sludge is stored separately in dedicated IBC tanksthat can be taken ashore for disposal.

The Pride of Kent scrubber was not fitted with abypass but operational experience has convincedHKL that a bypass should be offered as an optionto enhance the availability of scrubbed engines.

After 30,000 hours of operation during the pastsix years the scrubber has now been removed. Thescrubber worked, achieving the 98% SOX reductionrequired to reduce emissions from 3.50% sulphur fuelto the equivalent of 0.10% sulphur fuel.

The design has formed the basis of the HKL scrubbersfitted to all subsequent newbuilds. There is continuingresearch and development at HKL’s test facility inNorway to reduce maintenance requirements andmanufacturing costs.

P&O Ferries have learned a lot from the project andhave a much better understanding of the challengesassociated with the design, installation and operationof scrubbers. They can confidently assess which oftheir ships are suitable for retrofitting to comply withthe forthcoming 0.10% ECA-SOX limit. �

Case study oneInstallation of a Hamworthy-Krystallon open loop scrubber onP&O Ferries’ Pride of Kent crubber installed on P&O Ferries Prideof KentIn 2005, Hamworthy Krystallon Ltd. (HKL) approached P&O Ferries with a request to install and test aprototype scrubber on board Pride of Kent. P&O Ferries agreed and in December 2005 a scrubber wasinstalled on a 1MW auxiliary generator. Due to the constraints of Pride of Kent’s fuel system, and as thescrubber was only cleaning a small proportion of the installed power, it was not used used to achievecompliance with regulations and the ship operated the scrubbed generator on compliant heavy fuel oil.

17

Neil Farquhar,Technical OperationsManager, P&O Ferries

Lee Bracegirdle,Marine TechnicalAdvisor, HamworthyKrystallon Ltd.

P&O Ferries' Pride of Kent (image courtesy of P&O)

Closed loop systems discharge small quantities of treatedwashwater to reduce the concentration of sodiumsulphate. If uncontrolled, the formation of sodiumsulphate crystals will lead to progressive degradation ofthe washwater system. Information from scrubbermanufacturers suggests that the washwater dischargerate is approximately 0.1 m3/MWh.

The rate of fresh water replenishment to the system is notonly dependent on the discharge to sea but also losses tothe exhaust through evaporation and via the washwatertreatment plant. The rate of evaporation is influenced byexhaust and scrubbing water temperatures, which in turnare governed by factors such as engine load and thetemperature of the seawater supply to the systemcoolers. Some of the water vapour incorporated withinthe exhaust may be captured after the scrubber andreused to reduce fresh water consumption.

With the addition of a washwater holding tank, closedloop systems can operate in zero discharge mode for aperiod of time (the exact length of time depends on thesize of the holding tank). This flexibility is ideally suited tooperation in areas where there is sensitivity to washwaterdischarges, such as ports and estuaries.

By being able to operate in zero discharge mode, closedloop systems also provide a measure of mitigation againstwashwater discharge regulations that may come intoforce in the future.

Closed loop systems typically consume sodiumhydroxide in a 50% aqueous solution. The dosage rate isapproximately 15 litres/MWh of scrubbed engine power ifa 2.70% sulphur fuel is scrubbed to equivalent to 0.10%.

The density of 50% sodium hydroxide aqueous solution is1530 kg/m3 at 15oC and storage tanks must be designedaccordingly. The choice of materials for pipework, fittingsand tanks is also an important consideration as sodiumhydroxide is corrosive to aluminium, brass, bronze, tin,zinc (including galvanised coatings) and glass. Mild steelcan experience corrosion cracking at over 50oC; stainlesssteel is resistant at higher temperatures.

Sodium hydroxide is usually delivered by road tankerat a transportation temperature of around 40oC. Thetemperature when pumping must be above 20oC, as theviscosity rapidly rises below this temperature. However, itshould not be above 50oC to prevent corrosion crackingof mild steel pipework. Onboard storage temperature istherefore between 20oC and 50oC.

If onboard temperature is regulated by cooling watersystems then the risk of a heat transfer coil failing(leading to cross contamination of the cooling systemwith sodium hydroxide) should be recognised. Sodiumhydroxide has a pH of 14 and is hazardous. It can causesevere skin burns, respiratory damage and eye injury.Robust procedures are required for handling sodiumhydroxide, including use of appropriate personalprotective equipment (PPE) if there is risk of exposure.Reference should be made to material safety datasheets(MSDS).

Closed loop systems require more tankage than openloop systems. A process or buffer tank is required in thescrubbing water circulation system, a holding tank isrequired for zero discharge mode (size dependent on shiprequirements) and loading facilities, storage tanks anddosing equipment are required for sodium hydroxide.


18A container ship passing under Bay Bridge, San Francisco

Scrubber

Exhaustgas

NaOHunit

Watertreatment

Sludge

Sodium hydroxide (NaOH)

Fresh Water

Sludge tank

Fresh water

Process tank

Seawater

Closed loop wash water

Treated wash water

Holding tank

Cooler

Pump

Pump

Figure 9: A closed loop wet SOX scrubbing system

SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR


19

6.5 Wet SOX scrubbers – hybridHybrid systems can be operated in either open loopmode (see section 6.3) or closed loop mode (seesection 6.4). This provides the flexibility to operate inclosed loop mode (including zero discharge mode)where the water alkalinity is insufficient or where thereis sensitivity to, or regulation of, washwater discharge,and in open loop mode without consuming sodiumhydroxide at all other times.

The arrangement offers advantages in that sodiumhydroxide is only used when necessary, reducinghandling and storage and associated costs. Freshwater consumption is also reduced.

Hybrid scrubbers are, however, more complex thanopen loop or closed loop SOX scrubbers. Figures 10aand 10b show the layout of a typical hybrid system,in open and closed loop modes.

Scrubber

Exhaustgas

NaOHunit

Watertreatment

Sludge tank

Fresh water

Process tank

Holding tank

Cooler

Pump

Watertreatment

Pump

Sludge


Fresh Water

Seawater

Open loop washwater

Treated washwater

Figure 10a: A hybrid SOX scrubbing system, operating in open loop mode

Scrubber

Exhaustgas

NaOHunit

Watertreatment

Sludge tank

Fresh water

Process tank

Holding tank

Cooler

Pump

Sludge


Fresh Water

Watertreatment

Seawater

Closed loop washwater

Treated washwater

Pump

Figure 10b: A hybrid SOX scrubbing system, operating in closed loop mode

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR


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DFDS and Alfa Laval divided the work between them.Alfa Laval designed the scrubber and oversaw itsinstallation and commissioning, supplying all of theequipment needed for the installation; DFDS oversaw theinstallation of the supporting systems including pumps,piping and cabling as well as the steelwork modificationsassociated with the extension of the funnel. Figure 11shows the scrubber unit during installation.

The scrubber is a hybrid, capable of operating in bothopen loop and closed loop modes. It includes an exhaustgas bypass to allow the ship to continue to operate attimes when the scrubber is being maintained or repaired.When the scrubber bypass is in the open position the shipis operated on compliant fuel.

The washwater system design includes a single 200kWwashwater pump which means that the scrubber has tobe shut down while the pump is being maintained orrepaired. For any future wet scrubber installations DFDSwould install three pumps, two of which would berequired to operate the scrubber. This would allowoperation to continue while one pump is beingmaintained or repaired.

Throughout the design and installation phases DFDSencouraged the active participation of the staff on boardFicaria Seaways. This included temporarily installingwashwater piping and asking ship's staff how it could beimproved. Based on their feedback the pipework designwas revised to reduce pressure drop in the system,improve support arrangements, and minimise impact onthe spaces that the piping is routed through.

DFDS have experienced good co-operation fromthe Lloyd’s Register Copenhagen team for the approval ofupdated plans and manuals. In addition to the standardclass approval of piping systems and equipment, theship’s Loading Manual and Stability Manuals have hadto be re-approved due to the impact of the scrubber andits associated systems on the ship’s lightship weight andvertical centre of gravity. Alfa Laval has also submitted

a risk assessment that identifies the risks associated withthe scrubber and any mitigation measures that have beenimplemented to manage these risks.

As the scrubber was fitted on Ficaria Seaways as part ofa technology demonstration, the Danish EnvironmentalProtection Agency (EPA) has temporarily permitted theship to operate on non-compliant heavy fuel oil whenthe scrubber is operating. Lloyd’s Register (acting as arecognised organisation on behalf of the EPA) approvedthe content and format of the SOX Emissions CompliancePlan, the Onboard Monitoring Manual and the TechnicalManual for Scheme B compliance. Ship's staff will be ableto use these documents to demonstrate compliancethrough continuous monitoring of the exhaust gasand washwater.

The scrubber was initially commissioned in May 2010and was operational from June 2010 to December 2010.During this time the system suffered from somewashwater piping leaks. The leaks occurred due to failureof the coating on the inside of the pipes, which exposedthe steel beneath to the warm, acidic, and hence highlycorrosive, washwater. These failures occurred in spite ofprecautions taken to ensure adequate coating thicknessby grinding welds on the internal surfaces before thepipes were coated by qualified painters. In December2010, DFDS took the decision to replace all of the steelpiping with GRE piping; at this time the washwaterholding tank was also replaced with a GRE tank. Thescrubber has been back in action since July 2011 andthere have been no leaks from the new pipework. (DFDSdid note that GRE piping requires more support and hasa larger bend radius than the equivalent in steel.)

For the ship’s staff the operation of the scrubber system isstraightforward: pressing the green button starts thescrubber and pressing the red button stops the scrubber.The control system uses a feed from the ship’s GPS toautomatically switch from open loop mode to closed loopmode when entering port and when operating in Swedishwaters. (It was agreed with the Swedish maritime

Case Study twoAlfa Laval hybrid scrubber installed on DFDS Ferry Ficaria Seaways

In 2008, Alfa Laval approached DFDS to explore the possibility of installing a prototype scrubber on boardFicaria Seaways. The ship was an attractive proposition for two main reasons: she operated exclusivelywithin an ECA-SOX; and she was due to commence an extensive refit.

21

authorities that the ship would only operate in closed loopmode while in Swedish waters.) Alfa Laval is happy withthis arrangement as it means they get good information onthe operation of the scrubber in both open and closed loopmodes while in passage. In part due to their earlyinvolvement, the staff on board Ficaria Seaways tookresponsibility for the scrubber system soon after it wascommissioned and now undertake maintenance andrepairs as for any other system on board the ship.

When operating in closed loop mode 50% sodiumhydroxide solution is used to control the pH of therecirculating washwater. At this concentration sodiumhydroxide is a very hazardous chemical. It is broughton board in 1,000 litre IBC tanks and hoses to the tanksare connected and disconnected manually by ship’s staff.DFDS require that the staff wear full protective equipmentwhen handling the chemical. The current storage capacityfor sodium hydroxide solution is not sufficient forcontinuous operation in closed loop mode and DFDS isconsidering the use of larger tanks for future installations,ideally a dedicated tank integrated into the ship’s structure.

In July 2011, the exhaust ducting after the scrubber wasaltered to increase the velocity of the exhaust gas toensure that the exhaust plume clears the ship.

A large number of sensors for various parametersincluding temperature and pressure have been fitted tothe scrubber to gather data on its performance. Inevitablythere have been some failures and it has been necessaryto carry a number of spares. The issue has beenexacerbated as the prototype control system does

not make an assessment of the severity of the fault –it simply goes into a failure mode. Production versionsof the scrubber not only contain fewer sensors but alsoa more intelligent fault handling system that respondsappropriately to the identified failure event.

When operating in closed loop mode the scrubbersystem periodically discharges a quantity of washwaterto reduce the build up of sulphate. The system is toppedup with fresh water and condensed water vapour takenfrom the exhaust gas after the scrubber, which isreintroduced into the recirculating washwater. Coolingthe washwater increases the amount of water vapourthat can be condensed.

The Danish EPA has produced a report on theenvironmental impact of washwater discharges, in partusing data based on samples taken from Ficaria Seaways.Alfa Laval believes that washwater criteria should bereviewed, and improved as necessary.

Both DFDS and Alfa Laval have learned a lot from the trialinstallation on board Ficaria Seaways. Both are confidentthat the scrubber technology works. DFDS have a strongunderstanding of the costs of installing and operatinga scrubber and have also been able to apply theirunderstanding to assess which of the other ships in theirfleet could be retrofitted with scrubbers. Alfa Laval haveused the experience gained from the trial to gather muchdata, which they now use to precisely design scrubbers fora range of different engine sizes. They have also been ableto develop individual components of the system to operateeffectively and reliably. �

Figure 11: The 21MW hybrid scrubber during installation on Ficaria Seaways (image courtesy of Alfa Laval)

Kasper MoosVice President,Technical OrganisationDFDS A/S

Jens Peter HansenR&D Manager,Exhaust Gas CleaningAlfa Laval

6.6 Common aspects of wet SOX scrubbers

Wet SOX scrubber system materialsWashwater in wet SOX scrubbers is highly corrosive andthe scrubber components that come into contact withit should be constructed of suitable corrosion-resistantmaterials. Glass reinforced epoxy (GRE) piping (the blackpiping shown in figure 12) has been used successfullyin a number of installations. GRE piping is lightweight,which makes it easier to handle during retrofits, butits reduced rigidity makes it necessary to installappropriate bracketing – in excess of that required forsteel pipe. The relevant LR rules should be followed, e.g.,use of steel transition pieces, fitted with suitable closingdevices where GRE piping passes through watertightdoors. GRE piping close to the scrubber must also beprotected from exposure to hot exhaust gases. frastr

Experience indicates that coated steel piping may not besuitable as it can suffer rapid localised corrosion typicallyat welds and flanges, where there is an increased risk ofbreakdown of the coating. Stainless steel 316L may alsobe subject to rapid corrosion, particularly in open loopsystems using seawater, which has a moderately high


22

temperature after scrubbing and a low pH. In thesecases, nickel alloys with a higher pitting resistanceequivalence number (PREN) may be used.

Typically, it is not necessary to change the materials ofthe exhaust duct and systems downstream of a wet SOXscrubber if the exhaust gas temperature is kept abovethe dew point. If this is not the case, corrosion-resistantmaterials should be used.

During the class unit approval and the ship-specificclass approval (see section 5.2) the materials used inthe construction of the SOX scrubber and its associatedsystems, including chemical storage and handling systems,will be reviewed for compliance with class Rules.

Washwater treatment plantThe technology and techniques used for washwatertreatment are influenced by the overboard dischargerate. The low discharge rate of closed loop systems(0.1 m3/MWh) enables use of centrifugal separators (similarto those used for fuel and lubricating oil) or multi-stageoily water separators. Wärtsilä's washwater treatmentplant (shown in figure 13) is an example of the latter.

SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCRFigure 12: Washwater treatment system with GRE piping(image courtesy of Hamworthy-Krystallon)

Figure 13: Multi-stage washwater treatment system used with closed loop SOX scrubbers(image courtsey of Wärtsilä)

23

For open loop systems with a higher discharge rate(≈45 m3/MWh), cyclonic separation is appropriate.This technique is widely used in onshore and offshoreindustry and may also be encountered in ships’ ballastwater treatment systems.

The heavy fractions are moved outward and downwardto the outlet (underflow) at the bottom of the device.The light fractions move toward the central axis andupward to the outlet (overflow) at the top of the device.A hydrocyclone is a tapered device that converts velocityof a liquid into a rotary motion. It does this by means of atangential inlet or inlets near its top. This causes the entirecontents to spin, creating centrifugal force in the liquid.

Hydroyclones can either consist of a single vessel or a'nest' of hydrocyclone 'liners' within a vessel (see figure14). The latter, which may be either horizontally orvertically orientated, is arranged with a plate (similar toa tube plate in a cooler) at each end. The overflowplate holds the overflow end of each liner in placewhile the underflow plate holds the underflow ends.

Retrofitting of a closed loop scrubber with bypass(image courtsey of Wärtsilä)

Depending on design, hydrocylones can separatesolids from liquid or liquids of differing densities.Combinations can therefore be used to separate bothparticulate matter and hydrocarbons from washwater.The velocity of the washwater is either imparted by apump or by the height of the scrubber above thewashwater plant in the engine room, if sufficient.

In US submissions to the IMO supporting theintroduction of the North American ECA [7], test datashowed PM10 emissions being dependent on fuelsulphur levels, with emission rates of 0.23 g/kWh withdistillate fuel (0.24% sulphur content) and 1.35 g/kWhwith residual fuel (2.46% sulphur content) – whichaccorded well with the findings of LR’s Marine ExhaustEmissions Research Programme [1].

If a scrubber removes 70% of the particulate matter,then approximately 500kg of sludge may be expectedfor every 100 tonnes (t) of residual fuel consumed bya diesel engine. This is dependent on removal rate atthe scrubber and the efficiency of the washwatertreatment, both in removing PM and not includingexcess water. Wet SOX scrubber manufacturers typicallyrecommend a sludge tank of around 0.5m3/MW ofscrubbed engine power.

Residue removed from SOX scrubber washwater mustbe stored on board, landed ashore and disposedof appropriately; it is not permitted to incinerate itor discharge it to sea.


24

Washwater dischargesFigure 15 shows the position of instruments that canbe fitted to an open loop system for the monitoring ofwater quality at system inlet and overboard discharge.The IMO Exhaust Gas Cleaning System Guidelinesrequire the following to be continuously monitored forcomparison with the quality of the receiving waters:

• pH as a measure of acidity• polycyclic aromatic hydrocarbons (PAHs) as

a measure of harmful oil components• turbidity as a measure of particulate content.

A salinity meter may also be fitted at the system supplyas the IMO Exhaust Gas Cleaning Systems Guidelinesrequire details of the “minimum inlet water alkalinity“and “salinity levels or fresh water elements necessary toprovide adequate neutralizing agents“ to be recordedin the SOX scrubber's Technical Manual (ETM-A orETM-B) – see Appendix B1.

Continuous monitoring of alkalinity is not practical onboard ship, but pH and salinity can be used as anindirect reference. Seawater usually has a pH ofbetween 8 and 8.4 so a low salinity and/or pH wouldsuggest entry to brackish water and therefore thepotential for loss of scrubbing efficiency. It should benoted that even fresh water may have sufficientbuffering capacity for scrubbing, although SOX removalefficiency can be reduced. Continuous monitoring ofwashwater will therefore give assurance that thesystem is able to function when operating in enclosedwaters.

In addition to PAH monitoring, a 15 ppm oil-in-watermonitor (of the type normally associated with bilgewater separation) may be fitted at the system dischargeas a further confirmation of the quality of thedischarged washwater.

Figure 14: Hydrocyclone liner

Underflowplate

Overflowplate

Light phaseoverflow Mixture

Tangentialinlets

Heavyphaseunderflow

Table 2: Typical stages in a closed loop washwater treatment system

Stage Process/technique

Stage 1 Using dissolved air, oil contained within the washwater is floated to the surface, where it is skimmed off.

Stage 2 Suspended particulate matter is removed using coagulation and flocculation processes. Coagulants are used toneutralise negative charges, causing particles to repel each other so that they are unable to agglomerate.Flocculent then combines the neutrally charged particles into larger masses.

Stage 3 Dissolved air flotation is again used to separate and remove particles from the washwater.

Stage 4 Before discharge, the washwater is finally subjected to active carbon filtration. The carbon has a very high surfacearea because of its micro-porosity and is effective at removal of organic compounds, including PAHs by adsorption.


25

Typical washwater instrumentation is shown in figure15 and includes:

Point 1 washwater system inlet• pH (optional; depending on which method is

chosen to determine pH at discharge – seeAppendix B1.4)

• PAH• turbidity• salinity (optional)

Point 2 (after washwater treatment plant and beforeany pH correction)• PAH• turbidity

Point 3 (before discharge after any pH correction)• pH.

If chemicals are added or created in the system to treatwashwater, the IMO Exhaust Gas Cleaning SystemGuidelines require a specific assessment of the effect ofthose chemicals on the quality of the dischargedwashwater. The SOX scrubber manufacturer will have toprovide details of any parameters to be monitored thatare additional to those specifically listed in theGuidelines.

The position, care, calibration and survey requirementsfor washwater monitoring instruments must becontained within an approved Onboard MonitoringManual (OMM). Further information is included inAppendix B1. Short periods of instrumentdowntime are allowed for maintenance and cleaningbut only when the ship is not in ports, harboursor estuaries. This may have commercial implicationsif there are tasks that have to be undertaken atsea requiring attendance by the manufactureror specialists.

The IMO Exhaust Gas Cleaning Systems Guidelinesstate the washwater discharge criteria areintended to act as initial guidance and that as moredata becomes available the criteria should be revised,taking into account any advice given by GESAMPd.Ship operators, in conjunction with the scrubbermanufacturer, are requested to analyse a minimumof three sets of samples of system inlet water,washwater before treatment and washwater dischargeover a two year period. Analysis should include pH,PAH, oil, nitrate, nitrite and metal content, althoughthe tests can be varied as knowledge develops.Analysis data, together with relevant scrubbingsystem and engine operating parameters, are thento be forwarded by the ship's flag administration tothe IMO.

Information on national and local restrictions onwashwater discharges that might apply on a ship’strading pattern can be obtained from the relevantauthorities. Any controls are likely to apply to restrictedwaters rather than open water. Closed loop SOXscrubbers (and hybrid SOX scrubbers in closed loopmode) mitigate the effect of washwater restrictions, asthey are able to operate for a period of time in zerodischarge mode. Washwater restrictions are notapplicable to dry SOX scrubbers.

A key compliance requirement already in place isthe US Environmental Protection Agency's (EPA) VesselGeneral Permit (VGP) for discharges incidental to thenormal operation of ships. Ship's with exhaust gascleaning systems must have a VGP in order to dischargeSOX scrubber washwater. Washwater must not containoil, including oily mixtures in quantities that may beharmful as defined by MARPOL Annex I – i.e., thedischarge must comply with the 15ppm oil-in-waterlimit [19]. Sludge generated from scrubbing must not bedischarged to sea. The EPA also recommends that shipsfollow the washwater criteria set out in section 10 ofthe IMO Exhaust Gas Cleaning SystemsGuidelines. Thepermit is applicable to “waters of the United States,including the contiguous zone or ocean”. The EPA isplanning to introduce a revised VGP in 2013.

Scrubber

Watertreatment

pHcorrection

32

1

Figure 15: Washwater instrumentation

d GESAMP - Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection – an advisory body to the UN (seewww.gesamp.org)

6.7 Dry SOX scrubbersDry SOX scrubbers have been widely used in land-based industry since the 1970s. Figure 16 showsa typical dry SOX scrubber comprising the followingmain components:

• A scrubber unit, in this case known as an'absorber', which brings the exhaust gas fromone or more combustion units into contact withcalcium hydroxide granulese. Unlike the majorityof wet scrubbers, the exhaust gas entry isperpendicular to the vertical downward flow of thescrubbing medium. No heat is removed from theexhaust gas during scrubbing (in fact the reactionis exothermic and releases heat) so dry scrubberscan be positioned before waste heat recovery andSCR equipment.

• A granule supply silo and screw conveyorfor discharge, positioned at the top and bottomof the absorber respectively. A pneumaticconveyor system enables granules to betransported from and returned to onboard storagefacilities. The use of flexible pipework facilitatesthe storage of granules at various locationson board.


26

• A scrubber control and emission monitoringsystem. Removal of the used granules andany exhaust-related particulate matter isan automated process and may either becontinuous or intermittent to ensure the correctflow of fresh granules under gravity downthrough the absorber.

Dry scrubbers typically operate at exhausttemperatures between 240°C and 450°C. Calciumhydroxide granules are between 2 and 8 mm indiameter (see figure 17) with a very high surfacearea to maximise contact with the exhaust gas.Within the absorber, the calcium hydroxide granules(Ca(OH)2) react with sulphur oxides to form gypsum(CaSO4·2H2O). Details of the chemical reactionscan be found in Appendix C1.3. Trials on a 3.6MWengine using up to 1.80% sulphur content fuel arereported to show a 99% and 80% reduction in SO2and particulate matter emissions respectively. It shouldbe noted that the PM reduction was tested accordingto DIN51402 (rather than either of the methodsmentioned in section 6.8) whereby particulate iscaptured on a filter of silica fibre material.

SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR

Figure 16: A dry SOX scrubber system (image courtesy of Couple Systems)

SCR (DeNOX)

Funnel

Bypass damper

Control cabinet

Monitoringsystem

Pneumaticconveying

Flexiblepipeline

Used granulate (variableposition and size)

Connection to external(disposal of granulate)

Connection to external(supply of granulate)

Supply silo

Absorber

e Also known as slaked lime

27

The filter is then assessed either visually or byphotometer, which compares the intensity of reflectedlight with that from the original light source, enablinga smoke number to be derived by a standardconversion procedure.

To reduce SOX emissions to those equivalent tofuel with a 0.10% sulphur content, a typical marineengine using residual fuel with a 2.70% sulphurcontent would consume calcium hydroxide granulesat a rate of 40 kg/MWh and, based on a density of800kg/m3, the volume of granulate required wouldbe approximately 0.05 m3/MWh (i.e., a 20MW enginewould require approximately 19 tonnes of granulateper day with a volume of 24m3). Electrical powerconsumption is lower than for wet systems atapproximately 0.15 – 0.20% of the power of theengine being scrubbed.

Unlike wet scrubbers, dry scrubbers have norequirement for washwater treatment systems andtheir associated pipework, tankage, instrumentationand controls. This simplifies installation and operation,and makes dry scubbers ideally suited to areas wherethere is increased sensitivity regarding discharges tosea. However, as with closed loop operation of a wetsystem, there is a need for storage and handling ofconsumables. Used granules must also be storedbefore disposal ashore.

The scrubber manufacturer can co-ordinate thelogistics of supplying, removing and disposing ofgranulate.

Fresh granules can be supplied to the ship by siloroad tankers fitted with pneumatic delivery systemsor in 'Big Bags' to smaller ships (although this is nota preferred method). Strategic logistics centres arealso planned for the delivery and reception of newand used granules in special 15 tonne containers.These can be handled in the same manner as standardshipping containers and located at convenientpositions on board. Each container is divided intocompartments so it can store both fresh andused granules.

Calcium hydroxide is a strong alkali and appropriatecare should be taken when handling it on board, withreference to material safety datasheets (MSDS).

Figure 17: Calcium hydroxide granules(image courtesy of Couple Systems)


The chemical is classed as harmful to eye and skinand the inhalation of dust should be avoided.Although calcium hydroxide has hazardous properties,it is considerably less hazardous than 50% aqueoussodium hydroxide solutions typically used in wetscrubbing systems. It should be kept dry and awayfrom contact with acids. It is also important thatused granules remain dry, and fully contained storageand handling systems are therefore an advantage.If a ship's own storage is used, advice should betaken as to appropriate alkali-resistant coatings.

While dry scrubbing does not reduce NOX emissionsby itself, it is ideally suited for use in conjunctionwith SCR systems (see section 7.1) which requirehot exhaust gas to attain an operating temperatureof above 300oC and SOX concentrations less thanthose of a fuel with a 1.0% sulphur content.Higher sulphur fuels (> 1.0%) can lead to pluggingof the SCR catalyst, which diminishes NOX reductionefficiency and potentially shortens the life ofthe catalyst.

An optional downstream fan can be fitted so that theengine is not subject to excessive backpressure and thecomplete arrangement can be bypassed.

6.8 Comparing SOX scrubber technologies

Operation in fresh waterAlkalinity or the buffering capacity of seawater is a keyparameter for the effective operation of wet open loopSOX scrubbers (including hybrid SOX scrubbers whenoperating in open loop mode). When exhaust gas ismixed with seawater inside the scrubber, sulphur oxidesare dissolved, increasing the acidity and lowering the pHof the washwater. Alkalinity is a measure of the ability toresist changes in pH; in seawater, alkalinity is naturallyprovided by bicarbonates, carbonates, borates andanions of other 'salts' in more minor quantities. Detailsof the chemical reactions can be found in Appendix C.It is not the sodium chloride content of seawater thatfacilitates scrubbing. Hence, salinity (a measure of allsalts present) only indirectly indicates that sufficientalkalinity is present.

Some natural fresh water can be highly alkaline andsuitable for scrubbing, although efficiency may bereduced. The water in the Great Lakes and areas withinthe Baltic Sea does not have sufficient alkalinity tosupport the operation of wet, open loop SOX scrubbers.Closed loop wet SOX scrubbers (including hybrid SOXscrubbers operating in closed loop mode) and dry SOXscrubbers do not use seawater as their scrubbingmedium; therefore they are unaffected by the propertiesof the water the ship is operating in.

Operation without discharge to seaThe high washwater discharge rate (≈45m3/MWh) ofopen loop systems (and hybrid systems in open loopmode) means that when operating they have todischarge washwater into the sea continuously. Themuch lower discharge rate (0.1m3/MWh) of closed loopsystems (and hybrid systems operating in closed loopmode) means that it is possible to retain washwater tobe discharged on board for a limited period of time(i.e., operate in zero discharge mode). Dry SOX scrubbershave no discharges to sea.

Being able to operate in zero discharge mode is idealfor areas where there is sensitivity to wash waterdischarges, such as ports and estuaries. In addition,while many authorities may be expected to acceptwashwater discharges meeting the requirements of theIMO Exhaust Gas Cleaning System Guidelines (seesection 6.6 and Appendix B1), regional, national and


28

local regulators may decide to impose a stricter regimefor ships operating within their coastal waters. Beingable to operate closed loop systems in zero dischargemode for a limited period provides a measure ofprotection against the possibility of future washwaterdischarge regulations. Dry SOX scrubbers are unaffectedby washwater discharge requirements.

WeightThe filled dry SOX scrubber unit for a 20 MW engine isheavier (≈200 tonnes) than comparable exhaust capacitywet scrubbers (30-55 tonnes). However, the overallweight of wet and dry systems may be similar once thewashwater systems, such as the processing tank, holdingtank and chemical storage, are taken into account.

As most of the weight of the dry scrubber system isinstalled relatively high up in the ship, the impact of thesystem on the vertical centre of gravity (VCG) of the shipis likely to be greater than for wet SOX scrubbers, wheremany of the components may be lower down. Wheninstalling a SOX scrubber on an existing ship, theresulting change in lightship weight and/or VCG maynecessitate the revision of the ship’s stability manuals.

Power consumptionThe washwater flow rate in an open loop SOX scrubberis higher (≈45m3/MWh) than a closed loop SOX scrubber(≈20m3/MWh) because the buffering capacity ofseawater is less than the buffering capacity of freshwater dosed with sodium hydroxide. Consequently,open loop SOX scrubbers require larger pumps and havehigher power requirements.

The power requirement of dry SOX scrubber systems ismainly associated with a screw conveyor that moves thecalcium hydroxide granules through the scrubber unit(known as an absorber). The power required is thereforesignificantly less than for wet SOX scrubbers.

The energy consumption associated with SOX scrubbersdoes not adversely impact a ship’s attained EnergyEfficiency Design Index (EEDI) value as, for almostall conventional cargo ships, the auxiliary powerconsumption will be calculated as a fixed proportion ofthe installed main engine power, and is unrelated to theactual auxiliary power consumption. However, if theinstallation of the system reduces cargo carrying capacitythen the EEDI will be affected.

SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR


29

The energy consumption will affect any operationalenergy efficiency key performance indicators (KPIs) thatinclude actual energy consumption of auxiliary systems,such as the Energy Efficiency Operational Indicator (EEOI).

Compatibility with waste heat recovery unitsand SCR systemsAll wet SOX scrubbers significantly cool the exhaust gasand are therefore not suitable for installation before awaste heat recovery unit. For the same reason, it wouldnot be possible to install a wet SOX scrubber beforean SCR system (see section 7.1) unless a reheaterwas fitted after the wet scrubber to raise the exhaustgas temperature back up to around 300oC – thetemperature required for SCR systems to work effectively.

Dry SOX scrubbers do not cool the exhaust gas so theyare suitable for installation before both waste heatrecovery units and SCR systems.

Particulate matter (PM) removalSOX scrubbers can be an effective means of reducingPM (see section A1.5 in Appendix A1), both indirectly byremoval of SOX and by direct mechanical cleaning whenparticles come into direct contact with either washwateror chemical granules. SOX scrubber manufacturerstypically claim between 70% and 90% removal rates.

The sulphates, which make a significant contribution toPM, are formed post-combustion in the exhaust plume.Oxidation of SO2, followed by further oxidation andcondensation processes, contributes to the growth ofcomplex particles after the cylinder [4] and the majority ofsulphates form in reactions after release from the stack [5].

Wet scrubber, open loop Wet scrubber, closed loop Wet scrubber, hybrid Dry scrubber

Main systemcomponents

•Scrubber•Washwater piping•Washwater pumps•Washwater treatmentequipment•Sludge handling equipment

•Scrubber•Washwater piping•Washwater pumps•Washwater processing tank•Washwater holding tank•Sodium hydroxide storagetank•Washwater treatmentequipment•Sludge handling equipment

•Scrubber•Washwater piping•Washwater pumps•Washwater processing tank•Washwater holding tank•Sodium hydroxide storagetank•Washwater treatmentequipment•Sludge handling equipment

•Absorber•Fresh granulate hopper•Used granulate hopper•Granulate transport system•Additional granulatestorage (new and usedgranules)

Operation infresh water

� � �(Only when operatingin closed loop mode)

�

Operationwithoutdischarge to sea

No For a limited time dependingon the size of the washwaterholding tank

For a limited time dependingon the size of the washwaterholding tank

Yes

Weight

Typical valuesfor a 20MW SOXscrubber

30-55t(Excluding washwater system andtreatment equipment)

30-55t(Excluding washwater system,treatment equipment, washwaterprocessing tank and washwaterholding tank)

30-55t(Excluding washwater system,treatment equipment, washwaterprocessing tank and washwaterholding tank)

≈200t(Including granules storedadjacent to the absorber butexcluding additional granulatestorage)

Powerconsumption (%of max. scrubbedengine power)

1-2% 0.5-1% 0.5-2%(Depending on whether it isoperating in open or closedloop mode)

0.15-0.20%

ScrubbingChemicalconsumable

No consumable Sodium hydroxide solution

(≈6 l/MWh·%S)

Sodium hydroxide solution(Only when operating in closedloop mode)(≈6 l/MWh·%S)

Calcium hydroxide granules

(≈10 kg/MWh·%S)

Compatibilitywith waste heatrecovery system

Yes, provided the scrubberis installed after the wasteheat recovery system



Yes. Can be placed beforeor after the waste heatrecovery system

Compatibilitywith SCR system

No, unless a reheateris fitted after the wetscrubber to raise theexhaust gas temperature



�

Compatibilitywith EGR system

� � � �

Particulatematter removal

� � � �

Table 3: Comparison of SOX scrubber technologies

The IMO Exhaust Gas Cleaning System Guidelines requiremonitoring of the SO2 to CO2 ratio in the exhaust gas butdo not require PM monitoring as this is not necessary todemonstrate equivalence with fuel sulphur content limit.The in-service measurement of particulate matter can bechallenging; methods involving weighing deposits onfilters are difficult to measure continuously on board.

Ship operators should note that the 'wet' method forcollecting PM on filters contained in ISO 8178f includessulphates and any incompletely burned hydrocarbons,whereas the 'hot/dry' technique contained in ISO 9096g

does not. Significantly different results will therefore beobtained from the same engine operating under thesame conditions consuming the same fuel, with ISO 8178tests reporting a greater mass of particulate. Scrubbermanufacturers have used differing methodologies duringtheir trials, which make it difficult to compare like for likethe PM reduction performance of various scrubbers.

Visible smokeSmoke is a collection of airborne solid and liquidparticulates and gases, together with entrained air.Visible smoke from combustion devices on ships islargely comprised of black carbon, heavy metals fromthe ash content, and water vapour.

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Some countries impose ‘smoke’ control measures onshipping in their coastal waters. For example, withinthree miles of the Alaska coastline, visible emissions,excluding condensed water vapour, must not reducevisibility through the exhaust of a marine vessel by morethan 20 percent. Short defined periods of increasedemissions are, however, permitted in port, at anchoror when manoeuvring [6]. A visible plume may alsobe undesirable for commercial reasons.

All SOX scrubbers reduce the black carbon andash from the exhaust (see section 6.8 - particulatematter removal). But wet SOX scrubbers may increasethe water vapour content in the exhaust stream,resulting in a highly visible white plume unless theexhaust is kept well above the dew point (see figure 5).Wet SOX scrubber manufacturers should provideguidance on how this will be controlled.

Attenuation of engine noiseSOX scrubbers are commonly installed in the place ofthe silencer when converting existing ships. Equipmentmanufacturers have differing views on the attenuationthat their equipment might provide. For wet SOXscrubbers this attenuation will change depending onwhether or not the SOX scrubber is in operation.

A ferry operating in the Baltic ECA-SOX

f the international standard for reciprocating internal combustion engines – exhaust emission measurementg the international standard for stationary source emissions – manual determination of mass concentration of particulate matter


31

NOX is the collective term for nitric oxide (NO) andnitrogen dioxide (NO2) emissions. (Nitrous oxide (N2O) isnot a NOX..) Nitric oxide is a precursor for nitrogendioxide; approximately 5% NO is oxidised to NO2 in theexhaust after leaving the cylinder. The major componentof NOX on exit from the ship is nitric oxide, which readilyoxidises in the atmosphere.

Nitric oxide is formed in the cylinder during combustionby two main mechanisms.• Thermal NO(x)• Fuel NO(x)

Thermal formation is the principal mechanism bywhich nitric oxide is produced. Fuel NO(x), formed fromnitrogen containing fuels, can also be a significantcontributor to the total. The proportion attributable toeach mechanism depends on the combustionconditions, which in turn are determined by thecombustion unit type, configuration and operation,together with the fuel's grade and composition.

Thermal NO(x) is primarily formed in high temperaturereactions between nitrogen and oxygen in the chargeair. Formation is dependent on temperature, exposuretime of the combustion gases to high temperature, andavailable oxygen. Above 1,500oC the rate of formationrises exponentially.

Fuel NO(x) is formed from the oxidation of the nitrogencompounds predominantly contained in residual fuel oilsand biofuels. The process is dependent on the air fuelratio (i.e., available oxygen) and the quantity of fuel-bound nitrogen and, to a lesser extent, combustiontemperature and the nature of the nitrogen compounds.

As the largest component of NOX is formed through theThermal NO(x) mechanism, it is not possible toeffectively reduce NOX emissions by controlling the fuelconsumed. NOX reduction is therefore achieved byreducing thermal NO(x) by one of the following:

• primary NOX control, which reduces the formation ofthermal NO(x); and

• post-combustion abatement in which the exhaust gasis treated to remove NOX.

Primary NOX control aims to reduce the formationof nitric oxide at source (i.e., in the engine's cylinders).This can be achieved through engine design and byoperational adjustments of parameters and componentssuch as fuel injection (pressure, timing, rate, nozzleconfiguration), valve timing, charge air (temperature,pressure) and compression ratio. The engine builder ishowever presented with a challenge as there is also aneed to minimise fuel consumption, and hence CO2emissions, by maximising combustion efficiency.Increasing efficiency typically increases combustiontemperature, which has the undesirable effect ofincreasing NOX emissions. Using primary controlstherefore results in a trade-off between fuelconsumption and NOX emission performance.

Other at-engine measures can enable furtherreductions of NO at source by reducing localtemperatures and oxygen content in the combustionzone. These include various 'wet' technologies,such as: water-in-fuel (WIF); fuel water emulsion (FWE);direct water injection to the combustion space (DWI);water sprays into the charge air (humid air motor(HAM)); and scavenging air moistening (SAM)).

Tier II limits under MARPOL Annex VI, Regulation 13(see section 3.1) can be achieved using primary controls,with compliance being managed by the engine builder.However, with conventional petroleum-based fuel oils,it appears that Tier III limits are only likely to be achievedusing either selective catalytic reduction or exhaustgas recirculation.

Subject to an imminent IMO review of availabletechnologies, Tier III NOX limits will apply to all shipsconstructed on or after 1 January, 2016, with enginesover 130kW that operate inside an ECA-NOX. Unlike thesulphur limits in Regulation 14 of MARPOL Annex VI,the Tier III NOX limits will not retrospectively apply toships constructed before 1 January, 2016 (except inthe case of additional or non-identical replacementengines installed on or after 1 January, 2016).

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR

7. NOX-reducing devices


32

Figure 18: Marine SCR arrangement – four-stroke medium-speed engine(image courtsey of Wärtsilä)

NOX measurementand control

To stack

Engine

Compact SCR

Aqueaous ureacontrol

Aqueaous ureadosage pump

Aqueaous urea injection

Aqueaous ureasolution storage tank

Gassamplepump

SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR

7.1 Selective catalytic reduction (SCR)Selective catalytic reduction is a relatively maturetechnology, widely used for NOX control in land-basedindustry and land-based transportation. SCR can reduceNOX emissions by 80-90% to below 2g/kWh. SCR systemsare currently fitted to four-stroke medium-speed engineson a number of ships in service which are able to gaincommercial advantage from reduced NOX emissions.

The SCR system converts nitrogen oxides into nitrogenand water, by means of a reducing agent injected intothe engine exhaust stream before a catalyst. Urea is thereductant typically used for marine applications. Itdecomposes to form ammonia in a mixing duct beforeadsorption onto the catalyst that facilitates the reductionprocess. Details of the chemical reactions can be foundin Appendix C2.1.

An SCR system comprises the following maincomponents:• a pumping unit for transfer of urea solution from

storage• a urea dosing unit• a mixing duct with urea injection point• a reactor housing containing replaceable

catalyst blocks• a control system• a soot/ash cleaning system.

SCR systems also offer ship-operators a potential fuelsaving benefit when operating outside an ECA-NOX, asit is possible to use the SCR to meet Tier II NOX limits.This would allow the engine settings to be adjusted foroptimum efficiency (Tier II engines are typically 4 – 4.5%less efficient than Tier I engines), resulting in reduced


33

fuel consumption and lower CO2 emissions. For this theSCR control system would require control set points foroperation inside and outside of ECA-NOX. It may bepossible to apply this CO2 saving when calculating aship’s EEDI.

SCR systems fitted to four-stroke mediumspeed enginesThe exhaust temperature dictates the position of thereactor containing the catalyst. To date, virtually allmarine SCR systems have been installed on four-strokeengines, as there is a sufficiently high exhausttemperature to allow efficient catalyst operation afterthe turbocharger. In this arrangement the reactor isfitted before any waste heat recovery system. When theSCR is not required, reactors may be run dry without theneed for a bypass.

Effective catalytic reduction typically requires an exhausttemperature of over 300oC, but below 500oC to preventthermal damage to the catalyst. It is possible to run atlower temperatures but the sulphur content of the fuelneeds to be reduced to prevent deposits, which canplug the catalyst. The warming up period after enginestart is typically 30 – 90 minutes (unless pre-warmingequipment is fitted). This assumes that the engineloading is high enough to heat the SCR to its operatingtemperature. Extended operation at low loads will resultin longer start up times and may result in the SCR notreaching its operating temperature. It is not yet clearhow authorities will view ships that are non-compliantduring the warming up period.

The reactor and mixing duct are installed as integralparts of the engine exhaust system; it is crucial that ureamixes completely with the exhaust gas before enteringthe SCR reactor.

The catalyst has a finite life and part of the maintenanceregime for the SCR should be periodic analysis ofcatalyst activity. Empirical evidence from oil fired powerplant SCR indicate that the two principal elementscausing accelerated catalyst deactivation are potassiumand sodium.

The mechanism for deposit formation involves anundesirable parallel reaction (to the NOX conversion) atthe catalyst whereby sulphur dioxide in the exhaust isoxidised to sulphur trioxide (SO3), which can then reactwith ammonia to form ammonium sulphate andbisulphate. Deposits reduce the effective area andshorten the lifespan of the catalyst, with fuel-relatedhydrocarbon and particulate matter adding to thefouling. As conditions deteriorate, NOX reduction isimpaired and more un-reacted ammonia will slip pastthe catalyst. Figure 19 shows clean, partially fouled, andheavily fouled catalyst elements.

Manufacturers endeavour to minimise the oxidation ofsulphur dioxide with their reduction catalyst materialsand by specifying that only fuels with a sulphur contentof less than 1.00% should be used. This not onlyprevents the formation of ammonium sulphates, butalso sulphuric acid. Systems capable of operating withhigher sulphur content are possible but higher exhausttemperatures are required. As an alternative tolow-sulphur fuel, a SOX scrubber fitted before thereactor may be used. When installed after a wet SOXscrubber the exhaust gas would require reheating fromaround 50oC to at least 300oC. No reheat would berequired for a dry scrubber.

An additional undesirable parallel reaction willtake place if calcium is present, resulting in calciumsulphate deposits.

An oxidation catalyst may be included in the reactorafter the reduction catalyst. Its purpose is to oxidisecarbon monoxide (CO) and unburned hydrocarbons(HC) to water and carbon dioxide or act as a 'slipcatalyst', oxidising un-reacted ammonia to nitrogenand water. An oxidation catalyst may also be fittedbefore the reactor to convert NO to NO2, increasingthe rate of NOX reduction and allowing a reducedreactor size and lower operating temperature.Sulphur in the fuel is a concern, however, and mustbe limited for systems using oxidation catalysts, asoxidised SO2 compounds form, deactivating anddamaging the catalyst.

Figure 19: Catalyst element fouling

SCR systems fitted to two-stroke low-speed enginesTo date, a very small number of two-stroke low-speedengines have been equipped with SCR systems[8,9].For low-speed engines, the reactor is typically placedupstream of the turbocharger to provide the catalystwith a sufficiently high exhaust temperature. Figure 20shows a two-stroke engine fitted with an SCR system.This type of installation is more challenging than for four-stroke engines because of space constraints and a needto bypass the reactor during various engine operatingmodes. The reactor in this configuration is relativelysmaller than a downstream unit because the exhaust gasdensity is higher.

The catalyst has a significant heat capacity which meansthat for two-stroke engines the reactor must bebypassed at start-up and when rapidly accelerating toensure sufficient energy reaches the turbocharger. Bypassmay also be required when decelerating to preventexcess heat energy at the turbocharger. Despite theposition of the reactor, the exhaust temperature mayalso be too low for efficient catalyst operation and forpreventing ammonium sulphate deposits when theengine is operating at low loads on residual fuel.

As an alternative the reactor can be placed after theturbocharger on a two-stroke low speed engine if aburner is fitted to increase the exhaust temperature tothe required level [10].

Urea and catalystTypically, a 40% urea solution is injected as a fine sprayinto the mixing duct before the catalyst by means ofcompressed air. Effective dispersion of the urea in the

34

exhaust stream is critical to efficient SCR performance;this may be achieved by suitable injection nozzles,atomising air, high-pressure injection (typically 25 Bar),duct design, or a combination of all four. The ureaconverts to ammonia before entering the reactor.

Regular cleaning of filters in the urea handling systemand the injection nozzles is an important part of thesystem maintenance requirements. Urea is classed asnon-hazardous and can be stored in existing tanks ifepoxy-coated. It is used because of the difficulty with thestorage and direct handling of ammonia, which is bothtoxic and corrosive. Using poor quality urea doesdegrade the performance of the SCR. A standard forMaritime Grade Urea Solution based on work by theEuropean Chemical Industry Council (CEFIC) is availablefrom the International Association for Catalytic Controlof Ship Emissions to Air (www.IACCSEA.com).

The rate of urea injection must be sufficient to reduceNOX emissions to the required level but not so great thatun-reacted ammonia exits the ship. 15 litres/MWh istypical for a 40% solution. Control is based on the loadand speed of the engine with active feedback providedon some systems by NOX and ammonia emissionsmonitoring. At engine start-up urea injection is initiatedonce the catalyst reaches operating temperature, whichis key for effective NOX reduction performance, depositprevention and to avoid ammonia slip.

Catalysts have considerable heat capacity so the timetaken to reach the injection trigger temperature isdependent on a number of factors including theminimum catalyst operating temperature recommendedfor the fuel type, the period of cool down since theengine was last operated, the size of the catalyst and theengine load pattern at start-up. Injection can begin up to30 minutes after a fully cold start, whereas it may beginwithin 10–15 minutes if the catalyst is still warm fromrunning in the previous 6–10 hours.

There will be similar considerations when entering anECA-NOX if the reactor has been bypassed, as thecatalyst will need to be brought online and reach therequired temperature before injection can commence.While these figures are indicative for both pre and postturbocharger catalysts, those fitted before turbochargerson two-stroke engines are relatively more compact andtherefore should heat up more quickly.

In marine SCR systems the catalyst is typically madeup of porous titanium dioxide (TiO2) ceramic material inlayers of replaceable honeycomb blocks. The highsurface area construction acts as a carrier for the

Figure 20: SCR arrangement – two-stroke low speed engine(image courtesy of MAN Diesel & Turbo)


35

catalyst's active compounds such as vanadium pentoxide(V2O5) and tungsten trioxide (WO3). The reactor andblocks can be orientated so the exhaust gas passes eithervertically or horizontally, with the former favoured forhigher particulate/dust applications. Regular cleaning bycompressed air soot blowers or sonic horn is used toreduce fouling of the gas passages and catalyst surfaces.It should be noted that urea injection and soot blowingwill likely require the installation of additional aircompressor capacity sized for all SCR systems on board.

SCR catalyst material is susceptible to fouling,plugging and poisoning:

Fouling is a general deposition of material and isobvious when carrying out a visual inspection. Thefouling masks the catalyst, preventing contact betweenthe catalyst surface and the reactants. Fouling can beaddressed by soot blowing and should not affect the lifeof the catalyst.

Plugging does not refer to plugging of the catalysthoneycomb (see figure 18) but rather the plugging ofthe catalyst pores. The catalyst is a very porous material,and to work effectively these pores must be open asthey give the catalyst a very large contact area with thereactants. Plugging may not be seen during a visualinspection, as it can occur without there being a heavydeposition on the catalyst.

Poisoning refers to chemical attack of the activeelement of the catalyst. The activity of the catalyst willdecay with age but it can be deactivated by attack fromphosphorous or alkaline/heavy metals.

Catalyst lifespan depends on a number of factorsthat result in physical plugging of the catalyst pores,including combustion conditions, engine operating (load)regime, exhaust temperature and fuel sulphur level.In addition 'poisoning' can occur when fuel- andlubricating oil-related compounds in the exhaust areadsorbed onto the catalyst resulting in progressivechemical deactivation. These compounds are formedfrom alkali metals (sodium, potassium), alkaline earthmetals (calcium, magnesium), phosphorus or zinc.Manufacturers may have strict limits on concentrationsin the exhaust gas and as such it is important to followrecommendations regarding fuel and lubricating oils.Excessive lubricating oil consumption should be avoided,and certain biofuels, for example, could have a high levelof alkali metals/alkaline earth metals.

Typical lifespan figures for catalyst blocks are betweentwo and five years with replacement undertaken by theSCR vendors or authorised contractors. In Californiaspent catalyst elements require specialist disposal becauseof the vanadium content. Generally, however, thematerial is not considered to be hazardous; metals arerecycled and waste is removed to landfill.

The ongoing monitoring of catalyst condition isimportant, not only to ensure NOX reduction ismaintained but also to make sure that the injected ureais fully utilised to avoid ammonia slip. Emissionsmonitoring can also be utilised; increased urea feed toobtain the required NOX reduction indicates a loss ofcatalyst efficiency, as does an increase in un-reactedammonia at the catalyst outlet.

A container ship passing under Bay Bridge, San Francisco, which will form part of the North American ECA

7.2 Exhaust gas recirculation (EGR)Exhaust gas recirculation is a mature technologywithin the automotive market, but new to ships.A proportion of the exhaust from before theturbocharger is reintroduced to the cylinders withthe charge air. This lowers the oxygen content of themixture and increases its heat capacity. This results ina reduction of peak combustion temperatures andhence the formation of thermal NO(x) is suppressed.As such, EGR is a method of primary NOX controlrather than a true exhaust gas treatment system.


36

Test engine work by MAN Diesel & Turbo has shown that,with 40% recirculation, EGR has the potential to reduceNOX down to Tier III levels on a two-stroke low-speedmarine engine and that increased fuel consumption,carbon monoxide emissions and PM emissions resultingfrom reduced combustion efficiency are manageable withengine adjustments. It is also reported that specific fuelconsumption is much improved when using EGR toreduce NOX down to Tier II limits, when compared withusing engine adjustments to achieve the same level ofemissions, particularly at part load. No high-speed ormedium-speed engine manufacturer currently offers EGRNOX abatement technology.

Figure 21: An EGR system arrangement - two-stroke low-speed engine (image courtsey of MAN Diesel & Turbo)

Exhaust outlet

Prescrubber

Blower

Scrubber

CoolerWMC

NaOHtank

FW

On/offvalve

Stopvalve

NaOHpump

Buffertank

Sea

Shut down valve

Change over valve

Dischargecontrol valve

Sludgetank

Scrubberpump

MixcoolerWMC

Water

cleaning

Polishing

SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR


37

The main components of an exhaust gas recirculationsystem are shown in figure 21, and comprise:

• a high pressure exhaust gas scrubber fitted beforethe engine turbocharger

• a cooler to further reduce the temperature of therecirculated gas

• a water mist catcher (WMC) to remove entrainedwater droplets

• a high-pressure blower to increase recirculatedgas pressure before reintroduction to the enginescavenge air

• automated valves for isolation of the system.

The scrubber in the EGR system is used to removesulphur oxides and particulate matter from the recirculatedexhaust, to prevent corrosion and reduce fouling of theEGR system and engine components. An EGR scrubberis more compact than a similar capacity scrubber afterthe turbocharger as the exhaust gas density is higher.The main washwater components are typical of a closedloop system using fresh water with sodium hydroxidetreatment and comprise:

• a buffer tank with fresh water make-up• a sodium hydroxide dosing device• a circulating pump• a water treatment plant with sludge collection.

A first generation MAN EGR has undergone a trialonboard M.V. Alexander Maersk. Initial issues withmaterials [11] required material upgrades and improvedsodium hydroxide dosage because of iron and sodiumsulphate deposits in the main engine air coolers,and corrosion of EGR system components includingthe cooler casing and blower. It has been reportedthat with an exhaust recirculation rate of 20% thetarget NOX reduction of 50% was exceeded using3.0% sulphur residual fuel without affecting thecylinder condition.

MAN is now constructing a second generationEGR system (see figure 22) based on the experiencefrom the first trial. This will be installed on a larger

engine with the scrubber, cooler, water mist catcherand blower integrated into a single unit designedto be fitted in the same way as a charge air cooler.40% exhaust recirculation is planned to achieveTier III compliance.

Unlike selective catalytic reduction, fuel sulphur contentand low load operation are not constraining factorsfor EGR systems. It should be noted, however, thatalthough the EGR scrubber has been found to removeup to 80% of sulphur oxides in the recirculated gas, afurther scrubber could be needed in the exhaust systemafter the turbocharger to be compliant in an ECA-SOXwhen using high-sulphur fuel.

EGR systems can result in increased CO and particulateemissions, which may be controlled using additionaltechniques such as water in fuel to achieve anoptimum balance between NOX, CO and PM. Dueto the nature of EGR systems' primary engine controls,system malfunction or deviations from normaloperation can significantly reduce engine efficiencyand increase CO and PM. There is also a risk of greatlyaccelerated engine wear and increased maintenancerequirements if the scrubber does not clean and coolthe exhaust gas to the required levels.

Figure 22: Graphic of the second-generation EGR system. The orangesections are the EGR system components, integrated into the engine(image courtesy of MAN Diesel & Turbo)

38

Cargo ships near Kiel in the Baltic ECA-SOX

39

40


A1.1 Carbon dioxide (CO2) and water vapourCO2 and water vapour will be formed in allcombustion processes in which complete or nearcomplete combustion of a hydrocarbon fuel takesplace. As such, the production of CO2 and watervapour is a function of the quantity of fuel burnt.Climate change resulting from increasedconcentrations of CO2 in the atmosphere is a welldocumented global concern. The input of watervapour (also a principal greenhouse gas) to theatmosphere is currently of little concern since theglobal average concentration is not changing and ithas a relatively short lifespan.

A1.2 Sulphur oxides (SOX)Sulphur oxides derive directly from the sulphurcontent of the fuels used. The sulphur in thecombustion chamber is oxidised, principally formingsulphur dioxide (SO2) with a minor proportion ofsulphur trioxide (SO3).

Relatively close to the source and in the absence ofrain, fog and snow, the 'dry precipitation' of gaseousSO2 and acidic sulphate containing particulate matteris detrimental to human health and the environment,causing respiratory problems and damagingvegetation.

At sometimes considerable distances from the sourcethe 'wet precipitation' of acid rain, fog or snow canhave a directly negative impact on plant life andindirect effects on wider ecosystems. Damage tominerals used in the construction of buildings andother architecture can also occur.

A1.3 Nitrogen oxides (NOX)The formation of nitrogen oxides occurs as a result ofoxidisation of molecular nitrogen in the combustion airor, to a lesser extent, in the fuel. Adverse effects dueto NOX are diverse. Nitrogen dioxide (NO2) causesrespiratory problems and damage to vegetation, aswell as contributing significantly to acid deposition.In addition, NOX and non-methane hydrocarbons(nMHCs) are involved in a series of photochemicalreactions leading to increased tropospheric ozone,which in turn may adversely affect human health, cropyield and natural vegetation.

A1.4 HydrocarbonsThe gaseous hydrocarbon fraction of exhaust gaswill predominantly consist of unburned or partiallycombusted fuel and lubricating oils. Individualcomponents may be present in either vapour orparticulate phases. The diverse nature of hydrocarbonfraction components makes it difficult to both quantifythe emissions and identify specific health andenvironmental problems. Polycyclic aromatichydrocarbons (PAHs) are of particular note in thisrespect and are present in particulate emissions fromall types of combustion sources.

As regards wider environmental effects, the non-methane hydrocarbons (nMHCs) are of concern onaccount of their involvement in photochemicalreactions leading to the formation of troposphericozone (see nitrogen oxides above). Additionally, anysignificant methane emissions will be of concernbecause of both stratospheric ozone depletion and (asmethane is a principal greenhouse gas) global climatechange.

A1.5 Particulate matter (PM)The particulates fraction of exhaust emissionsrepresents a complex mixture of sulphate withassociated water, non- or partially combustedhydrocarbon components, black carbon and heavymetals as represented by the ash fraction. Some flakesor deposits from the exhaust system may also bepresent. With the exception of the latter the majorityof diesel particulates are likely to be less than 1µm indiameter and readily transportable by air currents.Potentially detrimental effects may thus beencountered outside the immediate vicinity of theexhaust gas stack.

Although study of marine diesel particulate exhaustcomposition is limited, extrapolation of results fromother diesel applications would suggest that generalrespiratory problems as well as more serious toxic,mutagenic and carcinogenic effects might beencountered.

Appendix A1Impacts of marine exhaust emissions onhuman health and the environment

41

Black carbon is detrimental to human health (fineparticles can penetrate deep into the lungs causingincreased respiratory and heart problems) and is nowrecognised as being of concern in terms of globalwarming. When deposited on to snow and iceparticularly in Arctic regions, light surfaces aredarkened, albedo (reflectivity) is reduced and there isan increase in heat energy absorbed. Similarly, airborneblack carbon particles absorb heat from sunlight, sowarming the atmosphere.

In July 2011, the IMO agreed a work plan regardingblack carbon, including actions to:

• develop a definition for black carbon emissionsfrom international shipping

• consider measurement methods for black carbonand identify the most appropriate method formeasuring black carbon emissions from internationalshipping

• investigate appropriate control measures toreduce the impact of black carbon emissions frominternational shipping; and submit a final report tothe IMO in 2014, when MEPC should agree on theappropriate action(s).

MEPC is currently considering future controls on PMemissions, particularly for the most damaging fine andultra fine particles of less than 2.5 microns (PM2.5) and100 nm (PM0.1) respectively.


42

MEPC 184(59) – 2009 Guidelines for Exhaust GasCleaning Systems specifies the requirements for thetest, certification and in-service verification of SOXscrubbing systems.

MARPOL Annex VI requires that SOX emissions limits bemet by controlling the sulphur content of the fuelbeing combusted. SOX scrubbers are approved asequivalent to the use of controlled fuels by the ship’sflag administration or by a classification societyacting as a recognised organisation on the flagadministration’s behalf. In principle, this approvalof equivalency, supported by approved onboarddocumentation and records, should be accepted byport states as demonstrating compliance with MARPOLAnneix VI. However, if the ship changes flag there is noguarantee that the receiving administration will acceptthe original approval and they may decide to requestadditional evidence on the performance of the systembefore issuing their approval.

The Guidelines apply to any SOX scrubber fitted tofuel oil combustion machinery (excluding incinerators)as an alternative method of compliance with Annex VI,Regulation 14. There are two schemes available:Scheme A under which the SOX scrubber is subjectto initial certification of SOX reduction performancefollowed by continuous monitoring of operatingparameters and a daily spot check of emissionsperformance; or Scheme B in which there is norequirement for initial certification, but continuousemissions monitoring using an approved system and adaily spot check of operating parameters are required.

Currently the EC only accepts continuous emissionsmonitoring and the US Coastguard also appears tobe predisposed to continuous emissions monitoring.Therefore, for those ships that either currently tradeinto EU or US waters, or may do so in the future,Scheme B approval would appear to be thesensible option.

The majority of sulphur oxide in an exhaust system isSO2, which is almost entirely derived from the fuel'ssulphur content. Unlike NOX its formation is notrelated to engine design, operation or combustionconditions. The majority of CO2 in the exhaustof a diesel engine is also derived from the fuel.The ratio of SO2 to CO2 therefore gives a measure ofSOX emissions in proportion to the sulphur contentof the fuel consumed. This is very helpful as it allowsfor a significant reduction in the complexity of themonitoring system, as there is no need to integrateother engine operating parameters, such as speedand fuel consumption. It also readily allows themonitoring of other types of combustion unitssuch as boilers, which do not directly producea kW load.

The Guidelines therefore enable compliance withRegulation 14 to be demonstrated on the basis of theSO2/CO2 ratio values listed in table 4 below. (This isonly applicable to the combustion of petroleum-baseddistillate and residual fuel oils.)

Table 4: The fuel oil sulphur limits recorded in MARPOLAnnex VI Regulations 14.1 and 14.4 and correspondingemissions values

Each ship fitted with a scrubbing system will requirea SOX Emissions Compliance Plan (SECP). The plan,prepared by the ship operator, must demonstratehow the ship in its entirety will comply withRegulation 14 and must be approved by theadministration. It is required to cover all fuel oilcombustion units on the ship, whether fitted withscrubbers or not.

Appendix B1

MEPC 184(59) – Exhaust Gas Cleaning System Guidelines

Fuel oil sulphur content(% m/m)

Ratio emission,SO2 (ppm)/CO2 (% v/v)

4.50 195.0

3.50 151.7

1.50 65.0

1.00 43.3

0.50 21.7

0.10 4.3

42

Ships in the Baltic Sea near Kiel, Germany (The Baltic ECA entered into effect on January 1, [ ].


SOX

Open

Closed

Hybrid

Dry

NOX

EGR

SCR

Table 5 summarises the documents required for SchemeA and Scheme B. These will be provided by theequipment manufacturer.

B1.1 Scheme A complianceScheme A for SOX scrubbers is similar to EIAPPcertification and the Parameter Check Method forNOX. The basis of the procedure is that theperformance of the scrubber is certified before goinginto service. Then, if all relevant components andoperating parameters are within those in the approvedEGC system – Technical Manual (ETM-A), the emissionsreduction performance of the scrubber is within thatrequired without the need for continuous exhaustemission measurements on the ship.

Under Scheme A, each scrubber must have a SOXEmissions Compliance Certificate (SECC). This certifies itis capable of meeting an SO2/CO2 emissions value on acontinuous basis at the specified exhaust gas flow rateand the maximum fuel oil sulphur content (typically3.50% or higher), for the range of system operatingparameters in the Technical Manual. The SO2/CO2emissions value, the exhaust gas flow rate and themaximum fuel oil sulphur content are specified bythe manufacturer.

The 'certified value' must be suitable for a ship'soperating pattern, with the SO2/CO2 emissions beingat least the equivalent of the applicable fuel sulphurlimit under Regulation 14. (Generally the certifiedvalue for most scrubbers should be expected to be theequivalent of using 0.10% sulphur fuel.)

Certification testing can be carried out either on thetest bed or after installation on board. Test datatogether with the Technical Manual is submitted bythe manufacturer for approval. The scrubber must betested over the defined range of exhaust gas flowrates with one or more fuel oils to demonstrate itsoperational performance and that the certified valuecan be achieved. On approval the SOX EmissionsCompliance Certificate is issued. (The Guidelines alsogive the methods by which identical, serially producedunits and those of the same design, but of differentcapacity, from a production range may be certifiedwithout the need for repeat testing.)


A scrubber unit must be fitted to an engine or boiler forwhich it is rated. A survey is required after installationon board and the scrubber system is also subject toperiodic survey. The Technical Manual must contain averification procedure for the surveys and details of thecombustion unit to which it is fitted. To ensurecompliance in service there is a requirement for certainsystem operating parameters to be continuouslyrecorded and daily spot checks of emissions are alsorecommended. It should be noted that if the scrubbersystem manufacturer cannot guarantee that thecertified value or better will be met between surveys, orif the surveys require specialist equipment orknowledge, then it may be preferable to demonstratecompliance through continuous emissions monitoring(i.e., Scheme B rather than Scheme A).

Parameters that must be continuously recorded includescrubbing water pressure and flow rate at the scrubberunit inlet, exhaust gas pressure before and pressure dropacross the scrubber unit, fuel oil combustion equipmentload, and exhaust gas temperature before and after thescrubber. A record of chemical consumption must alsobe maintained. Limits and applicable ranges of theseoperating values must be contained within the TechnicalManual. The parameters are intended to ensure waterflow and chemical addition are at an optimum forscrubbing, that the back pressure imparted by thescrubber on the exhaust does not adversely impactengine operation, that the scrubber is not for somereason becoming blocked and that exhaust is notbypassing the scrubbing process. The Technical Manualmust contain details of action to be taken in the event ofthe applicable SO2/CO2 ratio being exceeded.

An approved Onboard Monitoring Manual (OMM) isrequired to give details of the monitoring sensors andtheir position, and the care and calibration needed todemonstrate compliance. Continuously recorded data,including standard time and ship’s position, must besecurely stored for at least 18 months and be availablefor inspection as necessary to confirm compliance.Component adjustments, maintenance and servicerecords, together with chemical consumption, ifapplicable, must be recorded in the system’s EGC RecordBook, which also must be approved. Alternatively, ifapproved, maintenance and service records can berecorded in the ship’s planned maintenance system.

Document Scheme A Scheme B

SOX Emissions Compliance Plan (SECP) X X

SOX Emissions Compliance Certificate (SECC) X

EGC system – Technical Manual for Scheme A (ETM-A) X

EGC system – Technical Manual for Scheme B (ETM-B) X

Onboard Monitoring Manual (OMM) X X

EGC Record Book or Electronic Logging System X X

Table 5: Scrubber document requirements

43

44

B1.2 Scheme B complianceUnder Scheme B, a continuous emissions monitoringsystem (see figure 23) is required to show that theSO2/CO2 ratio of the scrubbed exhaust is less than orequal to the required SO2/CO2 ratio at any load point,including during transient operation, and thuscompliant with Regulation 14.

The scrubber system is in effect treated as a 'blackbox' and unlike Scheme A there is no need for SOXreduction performance to be certified before thescrubber is used in service. The continuous emissionsmonitoring system must, however, be approved and issubject to an initial survey at installation and periodicsurveys thereafter.

As with Scheme A, Scheme B requires an approvedOnboard Monitoring Manual (OMM) containing detailsof the monitoring sensors and their position, and thecare and calibration needed to demonstratecompliance. Continuously recorded data, includingstandard time and ship’s position, must be securelystored for at least 18 months and be available forinspection as necessary to confirm compliance.

An EGC System – Technical Manual (ETM-B) is also tobe approved. Like Scheme A this must contain detailsof the combustion unit to which the scrubber is fitted,applicable operating values and limits, and action tobe taken in the event of the relevant SO2/CO2 ratiobeing exceeded. Daily spot checks of variousparameters required to verify proper operation of thescrubber must be logged in the system’s EGC RecordBook or the engine room logger system.

B1.3 Washwater and treatment residueRegardless of the Scheme used, the condition of anywashwater discharged to sea must be continuouslymonitored and data for the following parameters mustbe securely logged against time and ship’s position.

• pH (a measure of acidity),• PAH (a measure of the harmful components of oil);

and• turbidity (a measure of particulate matter).

A test for nitrate content is also required at eachrenewal survey.

Systems that require the addition of chemicals for thepurpose of scrubbing or conditioning of washwaterbefore discharge are required to undergo a specificassessment and, if necessary, additional washwatercriteria should be established.

Residue from washwater treatment may not beincinerated and must be landed ashore. In some casesthis sludge is landed in dedicated portable storagetanks (IBC). In others, the water is extracted from thesludge and it is carried ashore in bags for disposal, andin other cases the washwater sludge is piped into thesludge tank and disposed ashore with the sludge fromthe fuel oil purifiers.

Figure 23: Continuous emissions monitoring systems (Image courtesy of Hamworthy-Krystallon)


45

B1.4 Washwater discharges – pHLow pH water can have a detrimental impact onecosystems and organisms such as shellfish, and cancause corrosion issues on the ship. The washwaterimmediately after scrubbing can have a pH of 4 or less.However, the Guidelines require the pH to comply withone of the following standards (also see Figure 25):

1. ”The discharge washwater should have a pH of noless than 6.5 measured at the ship’s overboarddischarge with the exception that during manoeuvringand transit, the maximum difference between inletand outlet of 2 pH units is allowed measured at theship’s inlet and overboard discharge”; or

2. ”During commissioning of the [scrubber] unit(s) afterinstallation, the discharged washwater plume shouldbe measured externally from the ship (at rest inharbour) and the discharge pH at the ship’s overboardpH monitoring point will be recorded when theplume at 4 metres from the discharge point equals oris above pH 6.5. The discharged pH to achieve aminimum pH units of 6.5 will become the overboardpH discharge limit recorded in the ETM-A or ETM-B.”

While it is generally recognised that no environmentalharm will arise from short-term exposure of organisms toseawater down to pH 6.5 [12], the rationale for the twolimits in the first option is that discharged washwater willreadily mix in a ship's wake, very quickly correcting thelower pH. However, this is not possible with a stationaryship so a tighter limit is applied.

In order to comply with the pH 6.5 limit, particularly at theship's side in port, seawater can be used to dilute thewashwater. A specific pump can be used for this purpose.However, it may also be possible to reduce energyconsumption by using seawater that has already beenused for cooling purposes in other engine room systems.


B1.5 Washwater discharges –particulate matter and oilAs particulate matter and potentially harmfulcomponents of oil could be discharged to sea within thewashwater, the IMO Exhaust Gas Cleaning SystemsGuidelines require turbidity and the concentration ofpolycyclic aromatic hydrocarbons (PAH) to becontinuously monitored. Instruments have to be fittedafter the washwater treatment plant but before anyaddition of fresh seawater or other treatment for pHcorrection.

PAHs are produced from a wide range of activities thatinvolve the combustion of fossil fuels and hence may bepresent in the seawater taken up by the ship. The IMOGuidelines take this into account and allow PAH andturbidity readings at system inlet to be deducted fromdischarge figures.

The IMO Guidelines have limits for just one PAH –phenanthrene – which is prevalent in diesel exhaustand an indicator for the possible presence of others.In order to control the quantity of PAH at discharge,limits on concentration above the system inlet level aregiven at various washwater flow rates, with a higherconcentration being allowable at low discharge rates andvice versa. The Guidelines also prescribe the measurementtechnologies that should be employed to ensure thatinstruments with an appropriate sensitivity are used.Instruments either detect:• the amount of ultra violet light absorbed by PAHs at

high concentrations and low washwater flow rates, or• the intensity of the light emitted by PAHs

(fluorescence) at low concentrations and highwashwater rates.

Turbidity is a measure of the loss of transparency of aliquid because of the particulates suspended within it.Although this can be used to monitor the removal ofexhaust-related material by the washwater treatmentplant, sediment entrained in the seawater at scrubbersystem inlet can impact the validity of readingsparticularly whilst the ship is manoeuvring. TheGuidelines therefore have turbidity limits based on arolling 15-minute average of the difference betweenturbidity at inlet and discharge.

Figure 24: Washwater discharge pH limits (image courtsey of EGCSA)

IN

IN

OUT

Vessel moving: (pH IN – pH OUT) ≤ 2

Vessel stationary: pH OUT ≥ 6.5

Vessel stationary:pH 4m ≥ 6.5pH OUT to be recorded in ETM as limit

Discharge pH limits 1

Discharge pH limit 2

OUT

IN

OUT

46


B1.6 Washwater discharges – nitratesNOX is comprised mainly of nitric oxide (NO) formedduring combustion, with a small amount of nitrogendioxide (NO2) formed by oxidation of NO in the exhaust.The solubility of NO is poor, whereas NO2 reacts withwater to form nitric acid (HNO3) together with areduction back to NO. This means conventional wetscrubbing will remove a small amount of NOX fromexhaust gas (generally less than 5%). The little that isremoved is converted to nitrate, and also nitrite in SOXscrubbers that use sodium hydroxide (NaOH).

Nitrates are important nutrients that promote the growthof organisms, but excess levels of nitrates, phosphates andsediment can lead to eutrophication in aquatic ecosystems,resulting in excessive growth of some organisms such asalgae. Algal blooms can be toxic, reduce water clarity andstarve water of the oxygen needed for fish, shellfish andplants to survive below the surface.

In near-shore waters, phosphates are available fromindustrial, agricultural and domestic activities; typicalsources include detergents, sewage and run-off fromfertilised land. The introduction of nitrates in largequantities is therefore undesirable.

Because the quantity of NOX removed by conventionalwet scrubbers is small, the Guidelines do not requirecontinuous monitoring of overboard nitrate emissions.However, to mitigate the risk of eutrophication thereis a nitrate limit based on scrubbing 12% of the NOXfrom an exhaust stream (significantly more than is usuallyachieved). It is required that laboratory analysis of awashwater sample is undertaken in the three monthsleading up to each five yearly renewal survey and thatthe results are retained in the Exhaust Gas CleaningRecord Book, so they are available for flag and port stateinspections. The Scrubber Technical Manual (ETM-A orETM-B) must contain details of the sampling and analysisprogramme and typical nitrate levels if above 80%of the limit figure.

B1.7 Washwater discharges –other effects on seawaterThere are a number of other effects not specificallymentioned in the Guidelines. When dissolved in watersulphur oxides undergo a process of ionisation andoxidation to form sulphate. The reaction is buffered bythe alkalinity of the scrubbing water, which is naturally

imparted by seawater in open loop systems and by theaddition of sodium hydroxide in closed loop systems.There is a common misconception that the transfer ofsulphur to the ocean in the form of sulphate is in itselfdetrimental to ecosystems. In fact, sulphate is a majorand stable constituent of seawater, a significant sourcebeing natural volcanic activity and seafloor degassing. Itis relatively easy to estimate the total sulphur content ofglobal oceans for comparison with the total sulphurcontent of all known oil reserves, to show how minorthe contribution of the latter is.

While scrubbing prevents damaging sulphur oxides andparticulate matter entering the atmosphere, the processinvolves two other reactions that should be considered.

Firstly, the formation of sulphate requires oxygen and soincreases chemical oxygen demand (COD). This isindirectly addressed by the IMO Exhaust Gas CleaningSystemsGuidelines as it has been independently shownthat oxygen levels will rapidly recover to within 1% ofthe receiving waters if pH limits are met. An exceptionto this occurs in warmer open seas, where up to 50%extra dilution is required for oxygen levels to normalise [12].This dilution is readily available particularly as the shipwill almost certainly be underway, causing the dischargeto be mixed with fresh seawater in the ship's wake.

The other consideration is the impact that discharges oflow pH washwater may have on receiving waters. Thereaction below shows the ocean carbonate system andillustrates the interaction of carbon dioxide withseawater. Atmospheric CO2 dissolves in the sea to formcarbonic acid. Carbonic acid then dissociates by losinghydrogen ions to form bicarbonate. The increase inhydrogen ion concentration lowers the pH of the water,thereby increasing acidity. Available carbonate fromshells and skeletons of marine organisms that are eitherdissolved in the seawater or deposited in sediments thencombine with the hydrogen ions to resist furtherchanges in pH. Using bicarbonate and carbonate tobuffer washwater moves the reaction to the left and socauses increased acidity. Independent study has howevershown that this is an order of magnitude smaller thanthat caused by CO2 emissions from fossil fuelconsumption [12].

Ocean carbonate system:CO2(g)�CO2(aq)�H2CO3 (Carbonic acid)�H1+ HCO3-(bicarbonate)�H1+CO3

2- (carbonate)

47

The NOX emissions of Tier I and Tier II (see section 3.1)engines do not require NOX-reducing devices, as NOXis controlled using primary, in-engine controls toconstrain the combustion temperature and hence theformation of NOX. Certification of Tier I and Tier IIengines is issued following successful test bedmeasurements of the relevant load points for thetest cycle that is applicable for the function andconfiguration of the engine. There are three methodsfor confirming that the engine’s in-service NOX emissionsremain within the applicable limits.

By far the most common is the parameter checkmethod. A pre-certified engine is surveyed wheninstalled and then periodically thereafter. The principleof this approach is that if all relevant components andoperating parameters are within those included andapproved in the engine’s Technical File, then the NOXemissions will not exceed the approved values.The simplified measurement method is similar topre-certification testing, but with some simplification.However, it does require the engine to be run over thewhole of the applicable duty cycle at each survey orport state inspection.

Under the direct measurement and monitoring methodan approved emissions monitoring system is usedto measure NOX while the engine is in service. Usingthese measurements, as well as other engine operatingparameters and typically CO2 concentration todetermine exhaust flow rate, the specific g/kWh NOXemissions are calculated at the relevant engine test cycleload and speed points. Data have to be compiled within30 days of survey in order to be considered current.Under new guidelines that were adopted at MEPC 63the SCR system is recognised as being a component ofthe engine; therefore pre-certification of the combinedarrangement (engine + SCR) would typically be ona test bed before installation on board. This is referredto as Scheme A.

If it is not possible to test an engine and SCR together,either on a test bed or on board because of the sizeor construction of the arrangement, an alternativeScheme (Scheme B) allows for the engine and SCRto be tested separately subject to the agreement of theAdministration. The NOX emissions from the engine aretested as usual in accordance with the appropriate testcycle. The NOX reduction performance of the SCR canbe based on modelling tools using data from eithera full size or scaled down version. The overall NOXemission value (g/kWh) is calculated by combining theengine emissions and SCR emission reduction rate ateach load/speed point in the test cycle. Data is thenentered into the engine's Technical File and the parentengine EIAPPh certificate. A final and simplerconfirmation test is carried out on board whereby theemissions concentration (parts per million (ppm)) ismeasured at the inlet and outlet of the SCR chamberand compared with the Technical File entries.

With this approach there are concerns as to thereliability and robustness of the modelling of the SCR’sperformance and the associated scale model testingwhich would be used to calculate the estimated NOXemission value entered on the Supplement to theEIAPP Certificate. These concerns arise particularlybecause the confirmation test is only to be undertakenon the parent engine after installation on board andhence may not fully reflect all the influencing factorswhich in practice could affect the performance ofindividual SCR units. Given these concerns, shipowners,who will be responsible for the ongoing in-servicedemonstration of compliance, may, irrespective ofthe engine’s NOX certification status, be looking tosee that a confirmation test is satisfactorily completedon each and every SCR-fitted engine, even identicalengines, as part of the ship trials before acceptance.

Amendments to the NOX Technical Code 2008enabling the Scheme B pre-certification procedure wereadopted at MEPC 63. However, detailed proceduresdemonstrating ongoing compliance based on emissionmonitoring are expected to be further developed.

Appendix B2NOX Technical Code

h Engine International Air Pollution Prevention

SOX

Open

Closed

Hybrid

Dry

NOX

SCR

EGR


48

Table 6 shows the major regional, national and localregulations that currently apply to international shipping,none of which control NOX emissions. Furtherinformation is provided in the sections below.

B3.1 European UnionEuropean Council Directive 1999/32 as amended byEC 2005/33 relates to the sulphur content of marinefuels. In addition to incorporating the Baltic ECA-SOXand North Sea ECA-SOX (which includes the EnglishChannel) into national law, European Union memberstates are directed to ensure all ships, regardless of flag,use fuel containing no more than 0.10% sulphur ‘atberth’, which is defined as including ships at anchorwithin port. Any fuel changeover operation must occuras soon as possible after arrival at berth, and as late aspossible before departure, and be logged. The Directivealso requires that during 'regular' service betweenmember state ports and in EU waters, passenger shipsmust use fuel containing no more than 1.50% sulphur,unless in ECA-SOX in which case the lower ECA-SOXlimit applies. Further information can be found in the LRFAQs on the EC Directive requirements [13].

EC 2005/33 allows technologies such as SOX scrubbersto be used either during a trial approved by an EUmember state or as an alternative to complying with fuelrules, if the equipment has been properly approved,taking into account the IMO MEPC 184(59) Exhaust GasCleaning System Guidelines.

If used, scrubbers must continuously achieve emissionreductions that are at least as low as those achieved bythe Directive's sulphur-in-fuel limits. Scrubbing systemstherefore have to be fitted with continuous emissionsmonitoring equipment (i.e., use MEPC 184(59) SchemeB), and ships must ”document thoroughly that anywaste streams discharged into enclosed ports, harboursand estuaries have no impact on ecosystems”.

EC 1999/32 and 2005/33 are no longer fully alignedwith Annex VI following its revision in 2008.The Commission is therefore consulting with industrystakeholders and EU governments on amendmentsto the Directive, and an update is due to be finalisedduring 2012[14]. Aspects in which the EC requirementsmay differ include: applying the 0.50% sulphur limit

Appendix B3Regional, national and local air quality regulations

SOX SOX scrubberspermitted?

NOX Comments

EuropeEC Directive 1999/32as amended by2005/33

"Sulphur Contentof Marine Fuels"

Includes specific low-sulphur fuel rulesfor ships in port andpassenger ships onregular service in the EU

�

(with continuousemissions monitoring)

No regulation The Directive iscurrently under reviewto improve alignmentwith MARPOL Annex VI.However, it is likely thatthe Directive may alsoinclude additionalrequirements (seesection B3.1).

USATitle 40 of theUS Code of FederalRegulations,CFR Part 1043

Control of SOX andPM from ships subjectto MARPOL Annex VI

� No regulation The requirements areunder review. There areindications that in futurethe US may not acceptexhaust gas treatmentsystems unless they arefitted with continuousmonitoring of exhaustemissions.

California(Title 13 CaliforniaCode of Regulations,CCR section 2299.2)

Fuel sulphur and otheroperational requirementswithin California watersand 24 nautical milesoff the California coast

� No regulation Specific low-sulphurfuel rules for shipsvisiting California

Table 6: Key regional, national, and local regulations


49

outside of ECA-SOX in 2020, irrespective of theoutcome of the IMO review in 2018; and that theremay be no allowance to use fuel with a sulphur contentgreater than 3.50% with certain types of scrubber.

B3.2 North AmericaUnder United States federal marine air pollutionregulation, the Environmental Protection Agency (EPA)defines three categories of engine, subdivided bycylinder displacement and engine power or speed. Eachsub division has Tiers of reducing emission limits forNOX, particulate matter, carbon monoxide andhydrocarbons and a model year from which the limitswill apply to domestically operated engines [15].

Title 40 of the US Code of Federal Regulations, CFR Part1043 [16] incorporates MARPOL Annex VI into US Law.The regulation applies to all US flagged ocean-goingships operating worldwide including the United Statesand foreign flag ships while in US waters. As such,emissions of SOX, PM and NOX are controlled from thelargest category 3 marine engines with a per cylinderdisplacement of over 30 litres and approved exhaust gascleaning systems are allowed as an alternative. Smallercategory 1 and 2 auxiliary engines on ships withcategory 3 propulsion engines are also permitted tocomply with MARPOL Annex VI under 40 CFR Part1042.650 and Part 80[17, 18].

B3.3 CaliforniaIn addition to US federal emission controls based onAnnex VI, California has its own Regulation on Fuel


Sulphur and Other Operational Requirements forOcean-Going Vessels within California Waters and 24Nautical Miles of the California Baseline [20]. The fuel rulewas updated by the Air Resources Board (ARB) followingthe adoption of the North American ECA-SOX andapplies to all main and auxiliary engines and auxiliaryboilers (but not emergency engines) unlessa ship is on passage through regulated waters or ifcompliance would put the ship and people on boardin danger due to extraordinary circumstances. If shipsare to berth or anchor within California Waters or enteran inland waterway or estuary the requirements inTable 7 apply.

California only permits the use of exhaust controltechnologies, including SOX scrubbers, in trials as partof a research programme officially approved by theCalifornian authorities. Before the end of the trial theship must be brought back into full compliance withfuel rule requirements.

The regulation also includes provision for its owntermination, which states the fuel requirements willcease to apply if the USA adopts and enforces controlsthat yield equivalent emissions reductions. California,however, specifies the use of distillate fuels, with animplementation timeline that differs in part to thefederal legislation enacting Annex VI. It thereforeappears that this will not happen before 1 January,2015, when it will be necessary to comply with the0.10% sulphur limit by using distillate fuel in the NorthAmerican ECA.

Fuel requirement Effective date Fuel grade requirement and sulphur limit

Phase 1 1 July, 2009 Marine gas oil (DMA/DMZ) at or below1.5% sulphur; orMarine diesel oil (DMB) at or below0.5% sulphur

1 August, 2012 Marine gas oil (DMA/DMZ) at or below1.0% sulphur; orMarine diesel oil (DMB) at or below0.5% sulphur

Phase 2 1 January, 2014 Marine gas oil (DMA/DMZ) or marinediesel oil (DMB) at or below 0.1% sulphur

Table 7: California fuel regulation requirements

50


C1.1 Wet open loop SOX scrubber (includinghybrid system operating in open loop mode)SOX scrubbing media is seawater. Sulphur dioxide (SO2)is dissolved and ionised to bisulphite and sulphite, whichis then readily oxidised to sulphate in seawatercontaining oxygen. Similarly sulphuric acid, formed fromSO3, and hydrogen sulphate dissociate completely tosulphate.

For SO2:• SO2 + H2O � 'H2SO3' (sulphurous acid) � H+ +

HSO3- (bisulphite)

• HSO3- (bisulphite) � H+ + SO3

2- (sulphite)• SO3

2- (sulphite) + 1/2 O2 � SO42- (sulphate)

For SO3:• SO3 + H2O � H2SO4 (sulphuric acid)• H2SO4 + H2O � HSO4

- (hydrogen sulphate)+ H3O+ i

• HSO4- (hydrogen sulphate) + H2O � SO4

2- (sulphate)+ H3O

+

C1.2 Wet closed loop SOX scrubber (includinghybrid system operating in closed loopmode)SOX scrubbing media is fresh water dosed with sodiumhydroxide (NaOH). Sulphur oxides are dissolved andreact to form sodium bisulphite, sulphite and sulphate.The proportion of each is dependent on the pH andavailable oxygen.

For SO2:• Na+ + OH- +SO2 � NaHSO3 (aq sodium bisulphite)• 2Na+ + 2OH- + SO2 � Na2SO3 (aq sodium sulphite)

+ H2O• 2Na+ + 2OH- + SO2 + 1/2 O2 � Na2SO4 (aq sodium

sulphate) + H2O

For SO3:• SO3 + H2O � H2SO4 (sulphuric acid)• 2NaOH + H2SO4 � Na2SO4 (aq sodium sulphate) +

2H2O

C1.3 Dry SOX scrubberIn a dry SOx scrubber using calcium hydroxide (Ca(OH)2)the reaction with sulphur dioxide forms calcium sulphite:• SO2 + Ca(OH)2 � CaSO3 (calcium sulphite) + H2O

The sulphite is then oxidised and hydrated in theexhaust stream to form calcium sulphate dihydrate,or gypsum:• 2CaSO3 + O2 � 2CaSO4 (calcium sulphate)• CaSO4 + 2H2O � CaSO4·2H2O (calcium sulphate

dihydrate - gypsum)Similarly for SO3:• SO3 + Ca(OH)2 + H2O � CaSO4·2H2O (calcium

sulphate dihydrate - gypsum)

C2.1 Selective Catalytic ReductionUrea decomposition before the catalyst:• (NH2)2 CO (urea) � NH3 (ammonia) + HNCO

(isocyanic acid)• HNCO + H2O � NH3 + CO2

(Note the resulting quantity of CO2 is minor whencompared with that resulting from fuel combustion)

NOX reduction at the catalyst:1. 4NO + 4NH3 + O2 � 4N2 + 6H2O2. 2NO + 2NO2 + 4NH3 � 4N2 + 6H2O3. 6NO2 + 8NH3 � 7N2 + 12H2O

Equation 1 shows the main SCR reaction as nitric oxidedominates in the exhaust. The reaction shown atequation 2 occurs at the fastest rate up to an NO2:NOratio of 1:1. However, at higher ratios the excess NO2reacts slowly as per equation 3.

Appendix CChemical reactions

i Hydronium is a water molecule with an extra hydrogen ion attached to it (H2O + H+ � H3O+). An acid is any compound that yields

hydrogen ions (H+) or hydronium ions (H3O+) when dissolved in water

51


DME Dimethyl ether – a synthetic fuel formedfrom natural gas or biofuel

ECA-NOX Emission control area for nitrogen oxidesunder MARPOL Annex VI

ECA-SOX Emission control area for sulphur oxidesunder MARPOL Annex VI

ECA-SOX /NOX Emission control area for sulphur oxidesand nitrogen oxides under MARPOLAnnex VI

EEDI Energy Efficiency Design Index

EEOI Energy Efficiency Operational Indicator

EPA Environmental Protection Agency

EGR Exhaust gas recirculation – enginetechnology to reduce NOX formation byreintroducing cleaned exhaust gas intothe charge/scavenging air

EGCS Exhaust gas cleaning system – the termused by MEPC to refer to SOX scrubbers

EGCSA Exhaust Gas Cleaning SystemsAssociation www.egcsa.com

EGTS Exhaust gas treatment system – the termused in this guidance to refer to eitherSOX scrubbers or NOX scrubbers

ETM-A EGCS – Technical Manual for Scheme A –the manual containing all the relevantcomponents and operating parametersfor an EGCS to meet MARPOL Annex VISOX limits under the Scheme Aapproval process

ETM-B EGCS – Technical Manual for Scheme B

GESAMP Joint Group of Experts on theScientific Aspects of MarineEnvironmental Protectionwww.gesamp.org

GRE Glass reinforced epoxy – a corrosion-resistant material that can be used forthe construction of SOX scrubberwashwater pipes, process tanks andholding tanks

HAM Humid air motor

IBC Intermediate bulk container

IMO International Maritime Organization

LNG Liquefied natural gas

MEPC Marine Environment ProtectionCommittee

MSDS Material Safety Data Sheet

OMM Onboard Monitoring Manual – theapproved manual that details themonitoring sensors used to demonstratecompliance with MARPOL Annex VISOX limits

PAH Polycyclic aromatic hydrocarbon

PM Particulate matter

PPE Personal protective equipment

SAM Scavenging air moistening

SEAaT Shipping Emissions Abatement andTrading – a cross-industry group whosemission is to encourage and facilitateefficient reduction of harmful emissionsto air from shipping

SECC SOX Emissions Compliance Certificate –certifies that a scrubber will reduce SOXemissions to the required level when fueloil of a specified maximum sulphurcontent is consumed

SECP SOX Emissions Compliance Plan – thePlan describing how the overall ship willmeet MARPOL Annex VI SOX limits

SCR Selective catalytic reduction

VCG Vertical centre of gravity

VGP Vessel General Permit

Acronyms and abbreviations

52

1. Lloyd’s Register Marine Exhaust Emissions ResearchProgramme. Final Report, Lloyd’s Register.

2. MEPC 184(59) – 2009 Guidelines for Exhaust GasCleaning Systems

3. NOX Technical Code. IMO Resolution MEPC.177(58)

4. Marine Engineering Practice Series, Volume 3 Part 20– Exhaust Emissions from Combustion Machinery.Wright. Publisher: IMarEST, 2000.ISBN 1-902536-17-7

5. MEPC 59/INF.15: Study Pertaining to Ship Emissions’Impact on Climate Change and Air Quality. UnitedStates. International Maritime Organization, 2009

6. Alaska Opacity and Excess Emissions Regulations

7. MEPC 59/6/5: Proposal to Designate an EmissionControl Area for Nitrogen Oxides, Sulphur Oxidesand Particulate Matter. United States and Canada.International Maritime Organization, 2009

8. IMO Tier III solutions for Wärtsilä 2 stroke engines –Selective Catalytic Reduction (SCR)

9. Tier III Compliance. Low Speed Engines. MAN Diesel& Turbo

10.World’s First SCR NOX Removal System Installed onCoal Bulker Built by Oshima Shipbuilding – Aimingto Meet the IMO’s Tier III NOX Emission Controls.NYK Line et al. June 2011

11. Developments in Engine Technology for GreenShip Designs. Clausen MAN Diesel & Turbo.October 2010

12. Seawater Scrubbing – Reduction of SOX Emissionsfrom Ship Exhausts. Karle and Turner. The AllianceFor Global Sustainability Gothenburg, 2007


13. The Practical Applications of the ‘At Berth’Requirements, Lloyd's Register.www.lr.org/sectors/marine/documents/175157-the-practical-applications-of-the-at-berth-requirements-faq.aspx

14. EU policy on ship emissions.http://ec.europa.eu/environment/air/transport/ships.htmhttp://ec.europa.eu/environment/air/transport/pdf/sulphur_standard_shipping.pdf

15. EPA policy on ship emissions:www.epa.gov/otaq/oceanvessels.htmwww.epa.gov/otaq/marine.htm

16. Electronic Code of Federal Regulations e-CFR Title 40Protection of Environment Part 1043 Control of NOX,SOX and PM Emissions from Marine Engines andVessels subject to the MARPOL Protocol -www.gpoaccess.gov/ecfr/index.html

17. Electronic Code of Federal Regulations e-CFR Title 40Protection of Environment Part 1042 Control ofEmissions from New and In-Use MarineCompression-Ignition Engines and Vessels -www.gpoaccess.gov/ecfr/index.html

18. Electronic Code of Federal Regulations e-CFR Title 40Protection of Environment Part 80 Regulations offuels and fuel additives -www.gpoaccess.gov/ecfr/index.html

19. Electronic Code of Federal Regulations e-CFR Title 40Protection of Environment Part 110 Discharge of oilwww.gpoaccess.gov/ecfr/index.html

20. California policy on ship emissions:www.arb.ca.gov/ports/marinevess/ogv.htm

21.Market-based Instruments for NOX Abatement in theBaltic Sea, Per Kågeson.

References

For further information pleasecontact us atmarine [email protected]

For futher information about ourexhaust emissions services visitwww.lr.org/eca

www.lr.org

June 2012

Lloyd's Register is a trading name of the Lloyd's Register Group of entities.Services are provided by members of the Lloyd's Register Group. For details see www.lr.org/entities

Documents

Understanding exhaust gas treatment systems · Understanding exhaust gas treatment systems Contents 1 Figures and tables 2 1 Introduction 3 2 How to use the key 6 3 Air pollution