UK P&I Club Catalytic Fines 1

In contrast to this apparent increase indamages, the incidence of fuels assupplied containing aluminium andsilicon above specification limits has notincreased. Shipowners are thereforereminded that consuming fuel that iswithin the ISO specification for catalyticfines, at the time of delivery, does notguarantee engines will not sufferunexpected wear.At high risk of wearare fuel pump plungers and barrels, fuelvalves, piston rings and cylinder liners.

What are catalytic fines?

Refineries use catalysts to improve theyield of high value products, such asgasoline, refined from crude oil.

Unfortunately, some of these fineparticles escape into side stream productsthat are used as blend components inthe production of residual grades ofmarine fuel.

This particulate matter, comprising ofaluminium and silicon oxides, isextremely hard and, if entrained in thefuel as it enters engines, can causesevere abrasive wear.

Specification limits

The ISO 8217 Specifications of MarineFuels set out upper limits for combinedlevels of aluminium and silicon for fuelsas delivered.The 2005 specification

upper limit of 80mg/kg was reduced to60mg/kg in the 2010 edition, and theupper limit has been kept at this levelin the latest ISO 8217 edition of 2017,for commonly utilised RMG & RMKfuel grades.

Unfortunately, many fuel supplierstoday still refuse to supply to ISO8217:2010 and only accept the 2005edition limits. Charter parties oftenincorporate the following bunker clause“Fuel to be compliant with ISO 8217 –latest version”.With this clause, itwould seem that a Charterer wouldneed to supply fuel with a combinedaluminium and silicon upper limit of60mg/kg but they may only be able topurchase fuel with an upper limit of80mg/kg. If the fuel is tested andcombined aluminium and silicon isreported to be greater than 60mg/kgbut lower than 80mg/kg, this problemcan lead to disputes.

The earlier upper limit of 80mg/kg wasset on the basis that if this was notexceeded in fuels as supplied, then onboard treatment by settling, purificationand filtration should reduce this to amaximum of 15mg/kg (the maximumrecommended by most engine makersto avoid excessive wear) by the time thefuel was injected into an engine. Someengine makers have suggested thatcombined aluminium and silicon shouldbe a maximum of only 10mg/kg. In anyevent, these low levels, at the point offuel injection, require the fuel treatmentprocess to be around 80% to 85%efficient, if the fuel supplied containsaluminium and silicon at total 80mg/kg.

In reality, tests of before and afterseparator samples have suggested thattypical, in service separator efficiency canbe, at best, 75%, and often much lower.

Reducing the risk of serious enginedamage caused by catalytic fines

Refinery catalytic fines in marine fuel oil are not a newproblem but in recent years there appears to have beenan increase in the frequency of engine damage causedby these highly abrasive particles.

TECHNICAL ADVICE

TECHNICAL ADVICE

The ISO 8217 working group took thisinto account when they developed the2010 edition of the standard and reducedthe maximum content of combinedaluminium and silicon for fuels suppliedto 60mg/kg, giving ship’s engines alittle more protection. Clearly, if a fuelas supplied contained 60mg/kg, and themaximum permitted at the engine was10mg/kg, a separator efficiency of 83%would be necessary (if 15mg/kg at theengine was accepted, then an efficiencyof 75% would be needed).

Fortunately, the vast majority of fuelssupplied have combined aluminiumand silicon levels well below 60mg/kg,nonetheless, effective fuel treatmentremains imperative.

On board treatment

Catalytic fines have a tendency to settletowards the bottom of a tank duringstorage; this process depends very muchon the fuel temperature and storagetime. In practice, settling out of catalyticfines in primary (storage) tanks (wherethe temperature would typically bearound 30˚C) is rather low and mostlikely less than around 10% of the totalsuspended catalytic fine content. So, afuel with 80mg/kg combinedaluminium and silicon at delivery maybe transferred from a storage tank to asettling tank with around 72mg/kg. Asthe fuel is held at around 70˚C in asettling tank, we may expect a greaterreduction in catalytic fines but thistends to be restricted when the ship isat sea and the tank is lowered and filledperiodically. However, when the ship isin port and consumption is low, dwelltime increases and settling will beimproved.Tests on bottom sedimentsamples from these tanks have shownvery high levels of catalytic fines. Levelsof several thousand mg/kg are notuncommon. Clearly, this situation ispotentially dangerous as if thesesediments are disturbed by the shiprolling and pitching in heavy weather,they could pass through the fuel systemto the engines, causing rapid wear.

After the settling tank, the fuel shouldbe treated by centrifugal separation.

Although the makers of separators claimthat their equipment should be capableof reducing catalytic fines by around75%-80%, tests on fuel samples takenfrom before and after separators inservice, have shown efficienciessubstantially lower. In some cases,Brookes Bell have encountered this to beas low as 45% and have found typicalefficiency to be around 65%. Poorseparation efficiency can be a result ofusing incorrect gravity discs (in a‘conventional’ separator), too low fuelinlet temperature and/or too high a feedrate.Clearly, if a fuel entering a separatorcontained 80mg/kg combinedaluminium and silicon and the separatorefficiency was down to 65% or lower,then the fuel leaving the separatorwould contain at least 28mg/kg, wellabove the recommended maximum of15mg/kg at engine injection.

The importance of correct operationand maintenance of separators cannotbe overstated. It is recommended thatthe manufacturer’s maintenanceprocedures are included in the ship’splanned maintenance schedule and thatthe equipment is correctly operated. Inaddition to the proper operation andmaintenance of the separators, regulardrainage (‘dewatering’ or ‘desludging’)of service and settling tanks will assist inthe fuel treatment process.

For effective residual fuel oil treatment,separators should be operated atminimum flow rate, consideringconsumption, and the fuel inlettemperature should be 98˚C. It shouldbe ensured that the correct gravity discis fitted (if applicable) with reference tothe density of the fuel in use.

It is suggested that before and afterseparator samples are taken when fuelsas supplied contain more than 40mg/kgaluminium plus silicon. Indeed, at leastone engine manufacturer nowrecommends this testing when fuels assupplied contain more than 25mg/kgaluminium plus silicon. Sending thesesamples for ash, water, density andaluminium plus silicon testing andcomparison of the results between thesamples, will indicate the efficiency of

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the separator.Any significant reductionin efficiency should be investigated.

After centrifuging, the fuel will bestored in a service tank. Settling ofcatalytic fines in this tank will againdepend on how long the fuel is stored.As this fuel will be at around 98˚C afterpurification, some catalytic fines willdeposit out and over time the bottomof this tank will become rich incatalytic fines. If the ship is in heavyweather, pitching and rolling, thesedeposits may be disturbed, entering thefuel system and passing to the engines.Ordinarily the only line of defenceafter the service tank is the supplysystem fuel filters.

Typically, the fuel supply line to themain engine will be equipped withauto-backflush filters with a mesh sizeof between 35 and 50 microns(although some operators are installing10 micron filters in main enginesystems).The auxiliary engine fuelsystems may be equipped with 10micron fuel filters. However, it must notbe assumed that filters will take out allremaining catalyst particles afterpurification.

Particle size

The size (and shape) of catalytic finesvaries, probably due to the service lifeof the particles in the refineryprocesses.The data below shows therange of particle sizes against thepercentage for each size range.The firstcolumn shows results from tests on aship’s sample and the second columnshows typical data according to adocument published by Alfa Laval, BPMarine and MAN B&W Diesel1.

Particle size Ship Sample BPMicrons % %

0-10 31 5710-15 32 2715-35 35 1535-100 0.7 1

It can be seen from the above, that themajority of catalytic fines have aparticle size of less than 15 micron and

1 ‘Marine diesel engines, catalytic fines and a new standard to ensure safe operation – Separation PerformanceStandard’, written by Alfa Laval, BP Marine and MAN B&W Diesel.

TECHNICAL ADVICE

a considerable amount are in the range15-35 micron.Obviously, filters with amesh size larger than this will notremove these small particles.The imagebelow shows catalytic fines embeddedin a piston ring.The size of theseparticles is up to around 15 microns.

Different sized particles can createdifferent risks with the potential tocause damage at different locations inthe fuel system. For example, particlescan be small enough to pass throughfuel pump barrel/plunger clearances, orlarge enough not to enter those sameclearances. In either case, they will notcause abrasion at the fuel pumpbarrels/plungers, whereas those of a sizecomparable to the relevant clearanceswould be expected to cause damage inway of the fuel pumps.

Consider reducing risk byincorporating the followinginto management systems

1. Insist on a maximum combinedlevel of aluminium and silicon infuel deliveries of 60mg/kg. (ISO8217:2010 or later versions).Thismay be incorporated into a timecharter party or an order direct witha bunker supplier.

2. Sample and test all deliveries.Ensure a representative bulk dripsample is taken throughout eachdelivery and that this bulk sample isthoroughly mixed before pouringinto sub-sample bottles. Failure todo this can result in an unevendistribution of catalytic fines in eachof the sub-samples. Ensure the crewfully understand this process. Ideally,do not use the bunkered fuel untilthe analysis results are known.

3. Always operate separators withminimum acceptable flow rate(with consideration toconsumption) and with a fuel inlettemperature of 98˚C. Ensure thecorrect set up of the separator,including (where appropriate) theselection of the appropriate gravitydisc to suit the density of the fuel.Consider the operation of twoseparators in parallel.

4. As general guidance, take samplesbefore and after the separators eachtime the delivery sample analysisshows combined aluminium andsilicon above 40mg/kg. It should,however, be noted that some enginemanufacturers may recommendinstigating testing at lower levels, forexample above 25mg/kg;OEMadvice and service letters/bulletinsshould be considered as applicable.Send these samples for testing tocheck separator efficiency. Considerroutine separator efficiency analysisand the use of on board test kits.

5. Review and adhere to the auto-backflush filter manufacturer’soperating instructions, ensuringshipboard operational procedurescover such requirements.

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6. Manually clean and thoroughlyinspect the condition of all fuelfilters on a regular basis, and whenhigh differential pressures areobserved or auto-backflush periodsstart to increase.

7. Ensure a complete set of sparefilter elements is available on boardat all times.

8. Regularly ‘dewater/desludge’settling and service tanks.

9. Routinely open and clean thebottom of settling tanks and servicetanks (possibly to coincide withinterim/special surveys, for example).

10. Routinely open and clean thebottom of primary storage tanks(possibly to coincide with specialsurveys, for example).

11. As well as regular scavenge/under-piston space inspections take mainengine cylinder oil scrape downsamples every two months and sendfor analyses.Monitor the trend ofiron content as this will provideearly indication of piston ring andcylinder liner wear.

12. If it becomes necessary to renewpiston rings due to unusual wear,obtain replicas of cylinder liners forexamination. Embedded catalyticfines will need to be removed byhoning of the liners to preventfurther wear of new piston rings.

13. Keep detailed records of all theabove and of fuel consumptionhistory. Such evidence is crucial andmay be decisive if fuel relatedengine damage is suspected.

THE AUTHORS

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Brookes Bell Group provides comprehensivetechnical and consultancy services worldwideacross all the major maritime, engineeringand scientific disciplines.

Founded in Liverpool in 1903, Brookes Bellnow operate in London, Glasgow, Shanghai,Hong Kong and Singapore. Brookes Bellexperts are highly qualified and experiencedin their respective disciplines, includingmaster mariners, marine engineers, navalarchitects, metallurgy/material scientists, fireinvestigators, loss adjusters, consultingscientists and civil engineers.This wealth ofpractical experience is combined withcutting-edge in-house technology.

Brookes Bell Group’s reputation for excellenceis built upon integrity and proficiency and weare proud to provide our services to the world’smost eminent P&I Clubs, Shipowners,Charterers, Underwriters, Cargo Owners,Lawyers, Salvors, Shipyards,AverageAdjusters and Government Departments.