The learning objective of this chapter is that the learner will know the range
of marine fuels which are available
Oh
there are a number of different marine fuel oils which can be used on board a
ship they can generally be classed into two groups distillate fuels and residual
fuels full details of the specification of both of these groups are given in the
ISO eight to one seven marine fuel standard the source of these fuels and
the characteristic properties are covered in detail in Siegel CBT module
number 179 marine fuel properties - we will make reference to some of the
properties in this module but you should refer to module number 179 if you need
further information the actual fuel being used will to some extent determine
the components in the fuel system as a general rule distillate fuels can be
used directly from the service tank with only basic filtration needed whereas
residual fuels will require greater filtration and will also need to be
heated to control the viscosity at the point of final use we will look at some
of the common fuels next
distillate fuels strictly speaking are those fuels obtained directly from the
distillation process as a result of crude oil refining some of the Moline
distillate fuels are however blends of pure distillates and heavier fuel oils
the full specifications for the four grades of marine distillate fuel are
given in the ISO 82 1:7 marine fuel standard which at the time of writing is
in its third edition DMX grade marine distillate is a high grade pure
distillate which is used only for special applications such as operation
of emergency diesel engines DMA grade usually referred to as marine gas oil is
also a pure distillate fuel it is normally used on small vessels such as
tugboats conditioned vessels only simple filtration is needed before use to
remove any dirt picked up during storage or transport as with all distillate
fuels heating is not normally required the other two grades dlb and DMC often
referred to as marine diesel oil are the distillate grades most commonly used by
commercial shipping usually as fuel for auxiliary diesel engines or for cold
start of main diesel engines and boilers click on a button to learn more about
marine diesel oil
marine diesel oil is the name given to the to marine distillate grades DM b and
d MC which are blends of pure distillate and heavy or residual fuel oil DM b
grade is essentially dirty marine gas oil with only a trace of heavy or
residual fuel content whereas DM c grade is a blend of distillate with up to 20%
heavy or residual fuel it should be obvious that cleaning and filtration is
required for both these grades before they can be used in a diesel engine
Marine residual fuels are a byproduct of the
finding process and are obtained from the residues of the various distillation
processes they are generally considered as low quality fuels the return grades
specified in the iso 8 to 1 7 fuel standard defined by various physical
properties including viscosity and the type of level of contaminant content
residual fuels require extensive pretreatment before use this will
include heating to bring the viscosity down to an acceptable level residual
fuels are commonly used for large two-stroke and four-stroke Moline diesel
engines and also marine boilers many auxiliary engines have now been designed
to operate on residual fuels where the residues of the refining process are
unsuitable for fuel purposes then blending is often carried out to bring
the fuel within a recognized specification click on the button to
learn more about blended fuels
marine fuels often have some so content which during combustion can
produce oxides of sulfur Sox recent changes in legislation in particular
MARPOL annex six have highlighted the need to reduce the Sox content of diesel
engine exhaust emissions the main focus in achieving this have been to place
limits on the sulfur content of marine fuels in addition other authorities
notably the European Union have issued directives or imposed regulations
requiring much stricter limits for vessels operating in their waters as an
alternative to using these low sulfur fuels approved treatment facilities such
as exhaust gas scrubbers are permitted which reduce the Sox content of the
exhaust gases we will look at some of the issues related to the use of these
fuels later in the module click on the button to learn more about low salt
at the time of issue of this module the maximum limit for sulfur content
according to MARPOL annex 6 regulations is 4.5% for general use and 1.5% for
special areas these special areas known as sea cars
Sox emission control areas are currently the Baltic Sea area and the North Sea
area with other areas to be identified in the future
due to the rising cost of traditional fuels and the environmental impact of
burning them as well as concerns regarding future supplies much work has
been done with alternate fuels
since these fools may require major modification to
the onboard fuel systems they should be mentioned in this module the two main
alternatives at present are gas from cargo boil off and biodiesel you can
learn more about these when transporting liquefied natural gas
or LNG for short buy a ship it is usual to keep the cargo at boiling point which
is approximately minus 161 degrees Celsius this is achieved by using
specially constructed and insulated cargo tanks even so as heat leaks
through the insulation some of the liquid cargo flashes off as gas if this
is not dealt with then the cargo tanks may become over-pressurized and rupture
there are three possible actions that may be taken vent the gas to atmosphere
this is wasteful and harmful to the environment
we liquefy the gas this requires an expensive complex plant use the boil off
as a fuel to power the ship this is the usual method adopted due to technical
limitations it was easier to adapt boiler combustion systems to gas burning
than diesel engine systems therefore most LNG vessels have been powered by
steam turbines the development of so-called dual fuel systems for diesel
engines has resulted in an increase in the number of diesel engine powered LNG
tankers some new Bills have either diesel or diesel electric propulsion we
will look at dual fuel systems in detail later in the module the current
extensive use of petroleum-based fuels is the cause of great concern first they
due to the rate that oil reserves are being used up and secondly due to the
environmental impact of burning these fuels in an effort to find sustainable
environmentally acceptable alternate fuels a lot of research has gone into
developing so-called biofuels biofuel is usually produced from vegetable matter
such as sugarcane rapeseed or soya beans and the product is mixed with
petroleum-based diesel oil to produce biodiesel biodiesel mixtures containing
less than 20% biofuel can usually be used in a diesel engine without any
modifications to the engine at the time of production of this module the use of
biodiesel in the marine field is mainly limited to the leisure sector although
there are efforts being made to extend this into commercial shipping some large
diesel engines have been successfully tested with by
diesel and a number of shore side installations are being populated on
these fuels however the current high cost and poor availability of biodiesel
mean that it will be a long time before you are likely to have it as the main
fuel for your vessels in this chapter we have looked briefly at the various fuels
available for marine use although alternative fuels are being developed it
is unlikely that they will replace the existing fuels for some time to come
strong environmental pressure has also brought about the development of low
sulfur marine fuels and it is likely that future legislation will not only
reinforce this but also lead to lower limits for sulfur content as we will see
later in the module this has already influenced diesel engine fuel systems
and how we operate the engines