1. Catalytic Fines in Residual Fuels
Presented to Rigel Shipping Canada Senior Officer’s Conference, Shediac, N.B. 26 September
2006
By Doug Hankinson, Chief Engineer, M/V EMERALD STAR
Where They Come From and What They Are
(Show slide of page 3 micrograph from Separation Standard)
As a consequence of the relentless increase in demand for distillate fuels, refineries have
incorporated more sophisticated processes in order to extract as much as possible of distillate
feedstock from a barrel of crude oil. In 1990 approximately 20% of a barrel of crude remained for
processing into residual fuel oil, compared to 14% today (mid-2005).
Fluid bed catalytic cracking was pioneered in the early 1940s and today there are numerous grades
and manufacturers of catalyst. The common denominator of material for all catalysts used in the
approximately 740 refineries in the world is a matrix of alumina (Al2O3), silica (SiO2) bonded
together with clay or some other zeolite.
This catalytic cracking process is very useful because it converts gas oil and residual oil into high-
octane gasoline and diesel fuel.
Large cat crackers contain about 500 metric tons of expensive catalyst. For as much as refiners try to
reclaim catalyst elements small amounts of this material escapes the reclamation process to be
delivered in the heavy fuel oil we receive on our ships.
Particle Size & Count
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2. Catalytic Fines in Residual Fuels
In a catalytic cracker the generally spherical particles of catalyst that are in the order of 20 to 100
microns in size. These particles are in constant motion at relatively high velocities colliding with
each other and their containment vessels. As a result of these collisions break-up of the spheres leads
to production of smaller catalyst fines.
Both ISO 8217 – 1996 and the latest ISO standard, 8217 – 2005 for fuel quality list the maximum
allowable limit of aluminum and silicon combined in RMG 35 (our heavy fuel) as 80 ppm. Any
content of aluminum and silicon betrays a presence of cat fines related solids of at least double that
concentration. Material that is present but is not tested for is the clay which binds the alumina and
the silica to each other.
In September 2004 the fuel testing arm of Classification Society Det Norske Veritas published
statistics indicating the percentage of bunker fuel deliveries that contained specific ranges of
aluminum and silicon. These details are presented below.
Al + Si (mg/kg) % of deliveries
> 80 0.3
> 60, < = 80 1.7
> 20, < = 60 19
< 20 79
Regardless of the content of cat fines in the fuel supplied to the vessel engine builders expect the
particle count of cat fines to be reduced to 15 parts per million (ppm) before the fuel is supplied to
the engine.
Data compiled from investigations by British Petroleum (BP) Marine regarding the size distribution
of cat fines possibly found in fuels is presented below.
Size (micron) 5 – 10 10 – 15 15 - 35 35 - 100
Quantity (%) 57 27 15 1
A simple shipboard check for the presence of abrasive contaminants to place a sample of fuel
between two smooth glass plates. Applying pressure while rotating one plate against the other will
scour the plates if there is any grit present.
Expected Damages
(Show slide of micrograph, piston rings with cat fines imbedded)
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3. Catalytic Fines in Residual Fuels
One or more of the engine operating difficulties listed below can be expected when consuming
residual fuel containing excessive amounts of catalytic fines:
- fuel filter clogging;
- abnormal wear or seizure of fuel injectors and fuel pumps;
- high operating temperatures of exhaust gas, scavenge air, jacket cooling water and piston
cooling oil;
- abnormal wear of and probable breakage of piston rings creating blow-by;
- scavenge box and trunking fire;
- exhaust system fire;
- heavy fouling of turbocharger nozzle ring and exhaust side rotor blades;
- surging of turbocharger;
- turbocharger vibration;
- turbocharger bearing failure;
- damage to exhaust side of turbocharger rotor;
- damage to turbocharger due to overrunning;
- cracked cylinder liners.
Fuel Handling To Minimize Damages
Fuel storage tank temperatures are to be maintained at a point where the fuel is pumpable. To high a
temperature will turn these tanks into settling tanks.
In the order of good housekeeping practice it is imperative that at least daily the drains of day and
settling tanks are checked for water. In the event of water being discovered than draining must
continue until the water has been removed.
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4. Catalytic Fines in Residual Fuels
For settling tanks to be effective maintain their temperature in the range of 65 to 70ºC.
Results from experimental work on the centrifuge treatment of today’s residual fuel qualities have
shown the best cleaning effect, particularly in regard to removal of catalytic fines, is achieved when a
pair of centrifuges are operated in series, i.e. in purifier/clarifier mode.
For fuels of a viscosity higher than 180 cSt @ 50ºC it is especially important that the highest
possible temperature, 98ºC, is maintained at the centrifuge inlet.”
In concert with this temperature the flow rate of fuel through the purifier/clarifier should be just
enough to keep the plant running plus about 10%. This setting ensures the greatest centrifuging effect
possible.
Assuming a heavy fuel oil supplied with a total cat fine count of 80 ppm, shipboard fuel handling
equipment must be operating at about 85% effectiveness to reduce that level to the engine makers’
recommended maximum allowable limit of 15 ppm.
Catalyst Fines are highly hydrophilic (they are attracted to water) and in the case of when there is
water in the fuel oils, are readily taken into water droplets. If the water cannot be sufficiently
separated from the fuel then the removal rate of the catalytic fines deteriorates.
If it is known that a high level of fines are present but there is negligible water, two centrifuges could
be run in parallel, each on a reduced output so that the combined output treated equals the
consumption.
Treatment of water laden fuel with an emulsion breaker will improve centrifuge efficiency with
respect to removing cat fines.
Inclusion in the fuel of significant volumes of used lube oil may also limit the effective removal of
fines. The desludging additives of lube oil ensure solids in an engine are carried in suspension while
that lube oil is in service. Heavy fuel contaminated with used lube oil (ULO) is likewise effective at
desludging storage, settling and day tanks as solids in those tanks will be picked up by the ULO
additives as they pass to the engine.
With respect to shipboard storage, settling and day tanks, experience dictates how often it will be
necessary to open and clean these tanks. The less sludge available means less are the chances of lube
oil additives picking up sludge particles when bunkers are taken on board that contain ULOs.
The increasing possibility of finding ULOs in fuel oils has been acknowledged on the international
level as a problem. Maximum allowable limits have been set for additives typically found in lube oils
in the recently issued fuel standard, ISO 8217 – 2005.
Each STAR ship of the COT 12.5 class is fitted with a Boll & Kirsch automatic backflushing unit
which has candle filter mesh size rated at 34 micron. This unit is located in the supply line from the
HFO day tank to the main engine and so is the last line of defence before fuel reaches the engine. (It
is uncertain if this is a ‘nominal’ rating or an ‘absolute’ rating.) Even at an absolute rating of 34
micron this capability is inadequate for reducing fuel born particle size to the recommended 15
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5. Catalytic Fines in Residual Fuels
micron. It has been the EMERALD experience that the most effective way in which to clean both the
candle and side filters is by wet ultrasonics.
Issued Warnings and Case Histories
DNVPS aluminum and silicon alert (85 ppm average) for Gibraltar supplier, 7 August 2006.
DNVPS aluminum and silicon warning (70 mg/kg) for Salalah, Oman supplier, 11 September 2006.
(Show slide of one year St. Rom supplied HFO)
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6. Catalytic Fines in Residual Fuels
DNVPS case history nr 2. (Use only page 1 of this case history.)
DNVPS case history nr 9
DNVPS case history nr 10
Given the trend of refiners trying to squeeze every saleable ounce of clean petroleum product from a
barrel of crude oil it is likely that we shall see an increasing incidence of fuels supplied to us pushing
the 80 ppm limit.
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7. Catalytic Fines in Residual Fuels
DNVPS case history nr 2. (Use only page 1 of this case history.)
DNVPS case history nr 9
DNVPS case history nr 10
Given the trend of refiners trying to squeeze every saleable ounce of clean petroleum product from a
barrel of crude oil it is likely that we shall see an increasing incidence of fuels supplied to us pushing
the 80 ppm limit.
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