Marine Fuel
Marine Heavy Fuel Oil History
During the early 19th Century, the cargo ships, which
used sails harnessing wind energy, started getting replaced by
steamships. Later, around the second half of the 20th century, motor
ships using IC engines were mainly used as commercial vessels to carry
cargo. The first four-stroke marine engine using heavy fuel was made
operational in the 1930s. With time, shipping companies started
investing more in R&D and the two-stroke engine became bigger,
powerful and famous.
The use of marine heavy fuel oil became more popular
in the 1950s because of the introduction of high alkaline cylinder
lubrication, which was able to neutralize the acids generated by high
Sulfur content in the heavy fuel oil. In the 1960s, ships with marine
engine burning heavy fuel oil became more popular and increased in
number as compared to the steamships. Eventually, in the 21st century,
motor ships replaced almost all steamships and acquired 98% of the world
fleet.
Marine Heavy Fuel Oil (HFO)
The basic requirement for any marine engine is to
propel a ship or to generate power on-board by using the energy obtained
from burning of fuel oil. HFO or heavy fuel oil is the most widely used
type of fuels for commercial vessels. The fuel oil releases energy to
rotate the ship propeller or the alternator by burning fuel inside the
combustion chamber of the engine or to generate steam inside the boiler.
The amount of heat energy thus released is the
specific energy of a fuel and is measured in MJ/kg.
Under MARPOL Annex 1, the definition of Heavy Grade
Oil is given as:
- Crude oils having a density at 15℃ higher than 900 kg/m3;
- Fuel oils having either a density at 15℃ higher than 900 kg/ m3 or
a kinematic viscosity at 50℃ higher than 180mm2/s; and
- Bitumen, tar, and their emulsions
Class C1 and C2 fuels are kerosene-type fuels. C1 is
for use in flue-less appliances (e.g. lamps). C2 is for vaporizing or
atomizing burners in appliances connected to flues.
Class A2 fuel is suitable for mobile, off-road
applications that are required to use a Sulfur-free fuel. Class D fuel
is similar to Class A2 and is suitable for use in stationary
applications, such as domestic, commercial, and industrial heating. The
BS 2869 standard permits Class A2 and Class D fuel to contain up to 7%
(V/V) biodiesel (fatty acid methyl ester, FAME), provided the FAME
content meets the requirements of the BS EN 14214 standard.
Classes E to H are residual oils for atomizing
burners serving boilers or, except for Class H, certain types of larger
combustion engines. Classes F to H invariably require heating prior to
use; Class E fuel may require preheating, depending on ambient
conditions.
Mazut is a residual fuel oil often derived from
Russian petroleum sources and is either blended with lighter petroleum
fractions or burned directly in specialized boilers and furnaces. It is
also used as a petrochemical feed-stock. In the Russian practice,
though, "mazut" is an umbrella term roughly synonymous with the fuel oil
in general, that covers most of the types mentioned above, except US
grades 1 and 2/3, for which separate terms exist (kerosene and diesel
fuel/solar oil respectively. Russian Federation practice doesn't
differentiate between diesel fuel and heating oil). This is further
separated in two grades, "naval mazut" being analogous to US grades 4
and 5, and "furnace mazut", a heaviest residual fraction of the crude,
almost exactly corresponding to US Number 6 fuel oil and further graded
by viscosity and Sulfur content.
Maritime Fuel Classification
In the maritime field another type of classification
is used for fuel oils:
- MGO (Marine gas oil) -
roughly equivalent to No. 2 fuel oil, made from distillate only
- MDO
(Marine diesel oil) - A blend of heavy gas-oil that may contain very
small amounts of black refinery feed stocks, but has a low viscosity
up to 12 centistoke (a centimeter-gram-second unit of kinematic
viscosity, equal to 1/100 (0.01)stoke, abbreviated, cSt) so it need
not be heated for use in internal combustion engines
- IFO
(Intermediate fuel oil) A blend of gas-oil and heavy fuel oil, with
less gas-oil than marine diesel oil
- MFO
(Marine fuel oil) - same as HFO (just another "naming")
- HFO
(Heavy fuel oil) - Pure or nearly pure residual oil, roughly
equivalent to No. 6 fuel oil
Marine diesel oil contains some heavy fuel oil,
unlike regular diesels.
Marine Standards and Classification
CCAI and CII are two indexes which describe the
ignition quality of residual fuel oil, and CCAI is especially often
calculated for marine fuels. Despite this, marine fuels are still quoted
on the international bunker markets with their maximum viscosity (which
is set by the ISO 8217 standard - see below) due to the fact that marine
engines are designed to use different viscosity of fuel. The unit of
viscosity used is the centistoke (cSt) and the fuels most frequently
quoted are listed below in order of cost, the least expensive first.
- IFO 380 - Intermediate fuel oil with a maximum viscosity of 380
centistokes (<3.5% Sulfur)
- IFO
180 - Intermediate fuel oil with a maximum viscosity of 180
centistokes (<3.5% Sulfur)
- LS
380 - Low-Sulfur (<1.0%) intermediate fuel oil with a maximum
viscosity of 380 centistokes
- LS
180 - Low-Sulfur (<1.0%) intermediate fuel oil with a maximum
viscosity of 180 centistokes
- MDO
- Marine diesel oil.
- MGO
- Marine gas-oil.
- LSMGO - Low-Sulfur
(<0.1%) Marine Gas Oil - The fuel is to be used in EU Ports and
Anchorages. EU Sulfur directive 2005/33/EC
- ULSMGO - Ultra-Low-Sulfur Marine Gas Oil - referred to as
Ultra-Low-Sulfur Diesel (Sulfur 0.0015% max) in the US and Auto Gas
Oil (Sulfur 0.001% max) in the EU. Maximum Sulfur allowable in US
territories and territorial waters (inland, marine and automotive) and
in the EU for inland use. The density is also an important parameter
for fuel oils since marine fuels are purified before use to remove
water and dirt from the oil. Since the purifiers use centrifugal
force, the oil must have a density which is sufficiently different
from water. Older purifiers work with a fuel having a maximum of 991
kg/m3; with modern purifiers it is also possible to purify oil with a
density of 1010 kg/m3.
- IFO380 & IFO180 are Max 3.5% Sulfur Bunkers (RME, RMF, RMG, RMH,
RMK)
- LS380 & LS180 are Max 1.0% Sulfur Bunkers
- ULSFO is Max 0.10% Sulfur Fuel Oil for Compliance with 2015 ECA
Regulations
- MGO is, unless otherwise specified, a Max 1.50% Sulfur "Clear and
Bright" Distillate (DMA, DMZ)
- LSMGO is Max 0.10% Sulfur Distillate (DMA, DMZ) for Compliance with
2015 ECA Regulations
- MDO is Max 1.50% Sulfur Distillate (DMB)
Treatment Methods of Marine Heavy Fuel Oil Used On-board
Ship
It is impossible to use the heavy fuel oil directly from the bunker tank
without treating it. There are different methods used on a ship to treat
the fuel before using it for combustion. Some of the most used methods
are:
Heating
& Draining: The fuel delivered to the ship is stored in the bunker
tank where it is heated by supplying steam to the coils installed in the
bunker tanks. Heating is an essential process, which makes it an integral
part of fuel oil treatment. The average temperature maintained for heavy
fuel oil bunker tanks is around 40℃. After transferring it to a settling
tank, the fuel is further heated to ensure it is at an appropriate
temperature to enter the separators. Once the fuel is transferred to the
service tank from the separator, the oil temperature is >80℃. The main
intention is to ensure the smooth pump-ability of the fuel oil at
different processes and to separate the maximum quantity of water from
fuel by draining the settling and service tanks and using purifiers.
Purifiers:
For removal of water and sludge from the heavy grade oil, fuel oil
purifiers are used. Depending upon the owner's choice, either conventional
or modern purifiers (computer driven fuel cleaning systems) can be
installed on a ship. The oil flow remains continuous even during the
sludge discharge process. Purification of heavy fuel oil is the most
critical treatment process and is carried out on all commercial ships.
Filtration:
Heating and purification process is used to separate water from the fuel.
However, the solid impurities such as fine metal particles which can cause
abrasion wear in the fuel system must also be removed. A fine filter is
placed in the fuel oil supply line, which blocks the fine metal particles.
These are full-flow units and the substance used inside the filters is
usually natural, or synthetic fibrous woolen felt material.
Chemical treatment: Just like the automotive industry where fuel additives are
popular, the maritime industry also uses chemicals in fuels for different
jobs; However, this process is not much popular. The main types of
residual fuel additives for marine heavy fuel oil are:
- per-combustion
additives such as d emulsifies, dispersants
- combustion
improvers
- ash
modifiers