Fuel Treatment Onboard Ship

These residual fuels contain a number of impurities such as catalytic fines, rust, dust, sand and water that the ship’s fuel treatment system needs to eliminate, before it can be safely used. 

ISO 8217 is the International Standard specifying the standards for petroleum fuels to be used in marine diesel engines
and boilers. Numerous cases of machinery damage have occurred
over the years due to poor fuel oil quality combined with improper fuel oil treatment on board.

 

Generally the fuel supplied meets the ISO 8217 standards absolving the supplier of any responsibilities for damage to the machinery.

Following the guidance below will minimize risk of damage to machinery components by ensuring that the fuel is efficiently treated prior to it being consumed:

1) Fuels of different grades and from different suppliers should,
to the extent possible, be kept segregated to avoid the potential problem of incompatibility. If fuel grades need to be mixed, this
should be kept to a minimum and engineers should be cautious
during the use of this fuel as increased amount of sludge could
result. Transfer small quantities at a time to the settling tank monitoring settling tank drain, separator operation and filters
closely.

2) A system of daily draining of the settling and service tanks,
and periodic internal inspection and cleaning of the tanks is
essential to prevent the build-up of particulate sediment. If the settling and service tanks are not drained regularly, there is a risk
that agitation of these tanks at sea will allow the contaminants
to progress through into the fuel system. Catalytic fines are hydrophilic, i.e. in case of water in the fuel, the water will attract
the catalytic fines. The draining of sludge and water in the settling
and service tanks is thus very important to reduce accumulation
of Catalytic fines.

3) ISO 8217:2012 regulates the amount of catalytic fines permitted
in HFO, expressed as Al+Si, to 60 mg/kg. However, due to the
abrasive nature of these particles, most engine manufacturers limit
the maximum amount of catalytic fines in the fuel injected into the
engines to 15 mg/kg. Since the catalytic fine value cannot be
assessed on board, whenever cat fines (Al+Si) are noted in excess of 35mg/kg in the fuel analysis report the stand-by separator must be started and run in series or parallel as arrangement provided till the entire batch of fuel is consumed.

While running the separators in series, the flow rate will need to
be the minimum possible to meet the consumption of the engine.
When run in parallel, they should be run with corresponding divided feed rates such that the combined throughput of both the separators matches the fuel oil consumption per day.

4) Carry out periodical cleaning and maintenance on the separators
making sure that the disc stack is cleaned at that time. If the interval between sludge discharges is too long, there will be a possibility of built up of deposits on the discs. The clear area between the discs will be reduced, resulting in the increase of flow velocity, which carry the particles/contaminants with the liquid flow towards the center. This leads to a reduced separation performance and carry over of impurities. Decrease the desludging interval if deposits are seen on the bowl discs during regular inspections.

5) During rough seas the Cat fines settled in the settling tank can be agitated and fed to the centrifuges. This could influence the efficiency of the separators, leading to carry over of catalytic fines to the service tank. Using the standby fuel centrifuges at
minimum divided throughput during heavy weather will improve
the separation efficiency reducing the Cat fine carry over.

6) In case the purification is found insufficient as indicated by fuel
fine filters clogging frequently, due consideration should be
given to reduce the Main engine load/rpm, thereby reducing the
consumption as a temporary measure. The separators must
be opened up for inspection and cleaning to verify their efficient
operation and be restarted at minimum throughput to match with the reduced consumption. Once the condition stabilizes the main engine RPM can be increased to the normal range. Bypassing the fine filters is not a solution, as it can result in serious and extensive damage to engine components.

7) Run the separators at optimum temperature of 98 deg C for fuels
above 180cSt (at 50 deg C). For example, a centrifuge operating
with an inlet temperature of 90°C would require a reduction in the throughput of min. 15% to 20% to obtain the same cleaning efficiency as with a 98°C inlet temperature. Arrange to have the heat exchangers cleaned and in the interim run two separators
in parallel with corresponding divided feed rates if unable to
maintain optimum temperature of 98 deg centigrade.

8) Monitor and record fuel oil filter back-flushing cycles per day. Fuel oil fine filters are designed to automatically back flush by fuel every hour. Back flush cycles exceeding 24 cycles per day when set to back flush every hour indicates clogging of filter elements and manual cleaning of filter elements should be carried out at the earliest.
Before switching to the bypass filter ensure that the bypass filter is clean, its element is not damaged and is of an equivalent or acceptable micron rating.

9) Periodical monthly inspection of filter elements is necessary
as elements can be damaged in service. Filter elements should be
renewed at intervals described in manufacturers’ instructions.
The candle elements should be handled very carefully as often
they are damaged whilst cleaning. Periodical analysis of fuel oil
Samples from the system will help the ship’s crew identify a faulty
condition early enabling them to take the necessary preventive action. Any sudden machinery damaged eg. Fuel pump seizure
should also be followed up by a filter elements inspection and
any damaged element should be replaced with the equivalent
quality and rating filter mesh.

10) Study the fuel change over procedure on board your ship and
follow it diligently To ensure that fuel switching takes place without loss of power or damage to engine components, the temperature and viscosity of the fuels must be carefully monitored during the change over process. Time should be allowed to maintain the temperature gradient recommended by the engine
manufacturer, e.g. 2˚C/minute, in a controlled manner. This will
in many cases be necessary in order to avoid a thermal shock
to the system, e.g. seizure of fuel injection pumps, and/or other operational problems that may occur due to low viscosity and/or
rapid temperature changes.