Water-containing sludge must be removed from the settling tank before the
separation process starts, and must also be removed from the service tank
at regular intervals. The tank's ventilation system must be designed in such a
way that condensate cannot flow back into the tank.
If the vanadium/sodium ratio is unfavourable, the melting point of the heavy
fuel oil ash may fall in the operating area of the exhaust-gas valve which can
lead to high-temperature corrosion. Most of the water and water-soluble
sodium compounds it contains can be removed by pretreating the heavy fuel
oil in the settling tank and in the separators.
The risk of high-temperature corrosion is low if the sodium content is one
third of the vanadium content or less. It must also be ensured that sodium
does not enter the engine in the form of seawater in the intake air.
If the sodium content is higher than 100 mg/kg, this is likely to result in a
higher quantity of salt deposits in the combustion chamber and exhaust-gas
system. This will impair the function of the engine (including the suction func-
tion of the turbocharger).
Under certain conditions, high-temperature corrosion can be prevented by
using a fuel additive that increases the melting point of heavy fuel oil ash (also
see
Additives for heavy fuel oils).
Fuel ash consists for the greater part of vanadium oxide and nickel sulphate
(see above section for more information). Heavy fuel oils containing a high
proportion of ash in the form of foreign matter, e.g. sand, corrosion com-
pounds and catalyst particles, accelerate the mechanical wear in the engine.
Catalyst particles produced as a result of the catalytic cracking process may
be present in the heavy fuel oils. In most cases, these catalyst particles are
aluminium silicates causing a high degree of wear in the injection system and
the engine. The aluminium content determined, multiplied by a factor of
between 5 and 8 (depending on the catalytic bond), is roughly the same as
the proportion of catalyst remnants in the heavy fuel oil.
If a homogeniser is used, it must never be installed between the settling tank
and separator as otherwise it will not be possible to ensure satisfactory sepa-
ration of harmful contaminants, particularly seawater.
National and international transportation and storage regulations governing
the use of fuels must be complied with in relation to the flash point. In gen-
eral, a flash point of above 60 °C is prescribed for diesel engine fuels.
The pour point is the temperature at which the fuel is no longer flowable
(pumpable). As the pour point of many low-viscosity heavy fuel oils is higher
than 0 °C, the bunker facility must be preheated, unless fuel in accordance
with RMA or RMB is used. The entire bunker facility must be designed in
such a way that the heavy fuel oil can be preheated to around 10 °C above
the pour point.
If the viscosity of the fuel is higher than 1000 mm
2
/s (cSt), or the temperature
is not at least 10 °C above the pour point, pump problems will occur. For
more information, also refer to paragraph Low-temperature behaviour (ASTM
D 97.
If the proportion of asphalt is more than two thirds of the coke residue (Con-
radson), combustion may be delayed which in turn may increase the forma-
tion of combustion residues, leading to such as deposits on and in the injec-
tion nozzles, large amounts of smoke, low output, increased fuel consump-
tion and a rapid rise in ignition pressure as well as combustion close to the
cylinder wall (thermal overloading of lubricating oil film). If the ratio of asphalt
to coke residues reaches the limit 0.66, and if the asphalt content exceeds
8%, the risk of deposits forming in the combustion chamber and injection
Vanadium/Sodium
Ash
Homogeniser
Flash point (ASTM D 93)
Low-temperature behaviour
(ASTM D 97)
Pump characteristics
Combustion properties
2017-07-11 - de
Specification of heavy fuel oil (HFO) D010.000.023-05-0001
General
MAN Diesel & Turbo
010.000.023-05
D010.000.023-05-0001 EN 9 (13)
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