TANKERS ABOVE 30000DWT IS A MUST!!!!!
INERT
GAS SYSTEM/GENERATOR
Inert gas system(IGS) or inert gas
generator(IGG) are only used in tanker ships. This is the most important in
tanker ships. The major function of this system is for safety. Safety for cargo
tanks. For a more clear picture eloborating this will be more specific. In
atmosphere there is 21% of oxygen. Oxygen has its presence in all the place
even in an enclosed cargo tank. So when there is loading or discharging
operation is done in tanker ships with oxygen in it most probably the ship may
explode because of pressure, temperature and air so called the mixture for
combustion. So to overcome this problem IGG & IGS are introduced. The
working principle are quite simple and easy. IGG & IGS both have different
working procedures but the production is the same. The end product is inert
gas. You may think why specificalyy inert gas is used. What is an inert gas?
DEFINITION OF INERT GAS
Inert gas is
a type of gas whichcontains low volume of oxygen and have an excessive amount
of nitrogen and carbon dioxide and also contains sulphur oxide.
So from here we can conclude that
inert gas would help in reducing oxygen content. So to produce this inert gas
there are 2 ways. One is IGG and the other one is IGS. First and foremost i
would like to explain how an IGS works.
HOW AN IGS WORKS?
Inert gas system(IGS) depends on the
boiler. You might think what is the connection betwen IGS and a boiler. There
is an obvious huge connection between them. IGS is operated by the flue gas of
the boiler. Yes. The flue gas produced from the boiler is more less have the
properties of an inert gas. So flue gas is used in IGS. This flue gas from
boiler is not wasted by discharging through funnel but is used as inert gas for
cargo tanks.
This gases are cooled
directly by seawater then is sucked via the uptake valve to the venturi
scrubber by a blower. This cooling process have 2 stages. The first stage, flue
gas is cooled directly by sea water in the venturi scrubber. The second stage,
the gas is cooled by sprayers in the combustion chamber. In the venturi
scrubber the sulphur oxides and particles are washed out, while the content of
nitrogen, carbon dioxide and oxygen remain unchanged. At the end of the cooling
section the water droplets/mist is seperated from the flue gas by a help of
demister. This is to prevent the flue gas that will be supplied to the cargo
tanks is moist. The cooled and clean flue gas is then supplied to blowers or
downstream the generator. The cooling and scrubbing water is dscharged through
a drain line beneath the combustion chamber.
After that the clean flue gas is discharged through the IG
line to deck seal water. The main purpose of the deck seal is to provide
constant pressure and temperature to the gas. The deck seal also helps to clean
any remaining soot or carbon from the flue gas. Then from there the flue gas is
inerted in the cargo tank as an inert gas.
HOW IGG WORKS?
The inert gas generator(IGG) should
be reliable for a good combustion process. The process of an IGG is more less
similar to the IGS after the combustion process. The IGG is fitted with a
burner. The burner system has a specialized design in accordance with the
Aalborg industries’ Inert System Ultramizing Combustion System(ISUCS).
The ISUCS is meant by combustion air
is supplied under pressure to the burner where the fuel is atomized in such a
way where a perfec fuel/air mixture is achieved, so that the behaviour/properties
of the flame will be identical to the gas/air mixture.
The product is a light blue flame
which barely or will not produce any soot. Actually this soot cannot be
tolerated in the IGG neither in the cargo tanks nor piping system. So to prevent
the soot especially during long run of the generator a well balanced and
extremly stable combustion process must occur. We will look into the problem if
there is soot in the system later. The hot inert gas that is produced after the
combustion process contains nitrogen, carbon dioxide, sulphur oxide and a very
low volume of oxygen.
Then this hot combustion gases are
cooled indirectly first by a jacket water cooling in the combustion chamber.
This is called as pre cooling. The main cooling process is taken place during
the cooling/washing section in the combustion chamber where the gases are
cooled directly with seawater and at the same time the sulphur oxides are
washed out. Sulphur is present in the fuel and is oxidized during combustion
and produce as sulphur oxide.
At the end of the cooling process,
the water droplets/mist are seperated from the gas by a demister which then
allows only the flow of gas through it. The required final pressure of the IGG
is achieved by a blower upstream the combustion chamber and a pressure
regulating valve in the IG line. A water loopseal under the cooling section
discharges the water and at the same time maintaining the required pressure and
also prevent the inert gas from escaping.
FUEL TO AIR RATIO/OXYGEN CONTENT
The fuel to air ratio has been set over the whole capacity
range by means of the adjustable screw in the fuel oil regulatiing valve. In
case there is drastic changes in air humidity, temerature or quality, the
oxygen content becomes too high or too low. In this event, the fuel oil
pressure before the fuel oil regulating valve must be incresed or decresed by
means of the pressure control valve in the fuel oil return line.
DETAILED PROCESS DESCRIPTION OF IGS
FLUE GAS/AIR
SUPPLY
·
Have
2 blowers each with 100% capacity
·
Casing
of blowers have internal lining and inspection openings
·
There
is a rinsing and drain connection for the cleaning of blowers.
·
Rinsing
should be done manually during run down of the blowers at normal stop of the unit
BOILER
UPTAKE VALVE
·
This
valve situated in between the boiler and
the venturi scrubber.
·
Normally
in closed postion
·
The
valve operated automatically
·
This
valve is controlled by the limit switch
·
The
uptake valve will have some leakage when in closed position, so in preventing
the leakage a high performance valve is installed behind this valve
·
This
high performance valve do not have leakage because there is a sealing air
connection after the uptake valve.
·
In
this case, when theuptakevalve is closed th high performance valve also will be
in close position
VENTURI
SCRUBBER
·
The flue gases(400oC) coming fromthe
boiler, enters the venturi scrubber via a flexible joint.
·
Designed
to ensure high efficiency in removal of sulphur and soot particles from the
flue gas
·
Also
precools the flue gas at the same time
·
The
velocity inside is over 50m/s
·
Water
supply fixed by the orifice
·
The
gas speed atomizes the injected water and the fine droplets catches the soot
and also other small particles/impurities that is found in the flue gas.
DETAILED DESCRIPTION OF IGG
COMBUSTION
AIR SUPPLY
·
Combustion
air is supplied to the main burner with required pressure by the blower
·
The
oil pressure must be adjusted in such a way, that the oxygen content of the
inert gas is produced, will be between its limit.
PILOT BURNER
·
Certain
interval of ignition sequence, pilot burner is supplied with fuel oil with
16bar pressure and instrument air for atomization and combustion; adjusted by a
pressure regulator(approx.1.4bar)
·
Ignition
occurs with help of an ignition transformer and a spark plug
·
The
burning of the flame is monitored by an UV-flame detecter, in conjunction with
the flame safeguard relay in the electric system.
MAIN BURNER
·
The
main burner is ignited by the pilot burner
·
Fuel
oil is atomized in 2 steps:
1. The fuel oil is dispersed by a spray
nozzle
2. It is subjected to a tangential
impulse flow of combustion air which, added to the mainly axially orientated
impulse flow of the liquid itself, results in an ultrafine dispersion of the
liquid.
·
The
tangential impulse flow is created by supplying the air through slots in a ring
fitted around the spray nozzle.
·
An
optimal atomization of the fuel oil is achieved if the differetial pressure
over the slots of the atomizing ring approximately 0.1bar
·
At
a lower atomizing pressure, the quality of combustion will grow worse and the
possibilty of soot being form will be greater
COMBUSTION
CHAMBER AND SCRUBBING TOWER
·
Main
and pilot burners are mounted on the combustion chamber.
·
The
combustion chamber is surrounded by a cooling water jacket to discharge the
generated heat as much as possible.
·
The
cooling water jacket is spiral, so the cooling water flows around the
combustion chamber wall and an optimum cooling effect is achieved
·
Hot
inert gas flows through the cooling tower, where they are cooled directly with
seawater and at the same time sulphur oxides are washed out from the inert gas
·
Seawater
is supplied by the orifice to the sprayer and the combustion chamber jacket
·
Seawater
leaving sprayers flows out via the waterseal
·
Sufficient
cooling is needed for the combustion chamber
These are the working principle and detailed description of
each parts of the IGS and IGG. There might be some questions regarding the
oxygen content in the inertgas produced. Some might ask if an inert gas contain
oxygen how it can it be considered as safety.
In a cargo tank if the oxygen content is more than 8% itis
considered dangerous and can cause explosion if correct method is not used. IGS
or IGG that produces inert gas can have an oxygen content of 3-5%. If the
oxygen content is more than that an alarm will be rang and a safety
interlocking device will open the purge valve and closes the main delivery
valve. This is to reduce the oxygen content in the inert gas.
The inert gas will be blown off at the begining stage of
combustion for 5 minutes. This is to ensure that the oxygen level inside the
combustion chamber reduces. After 5 minutes if there is still footage of oxygen
can be detected the fuel to air ratio should be checked and set back to
required ratio.
This IGS and IGG can only be found in ship more than
30000DWT. Some ships which sail to America or similar countries only should
have IGG. IGS is considered less safety in such countries so they banned the
usage of IGS in ships that sail to this countries.
I will be posting the working principles of each component of IGG and IGS next week.... for more detail description of IGG and IGS stay tuned in www.mksince10.blogspot.com
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| IGG |
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| Blower: Deliver IG to Cargo Tank |
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