Inert gas means a gas or a mixture of gases, such as flue gas, containing insufficient oxygen to support the combustion of hydrocarbons.
The oxygen content of the Inert Gas supplied to cargo tanks should be 5% or less. However, it is to be noted that too less content of oxygen in the IG would introduce other impurities into the cargo tanks.
After efficient scrubbing of the inert gas, the typical constituents of a flue gas are :
- Nitrogen (N)- 83%
- Carbon Dioxide (CO2)- 12-14%
- Oxygen( O2) 2-4%
- Sulphur Dioxide (SO2) 50 ppm
- Carbon Monoxide (CO) Trace
- Nitrogen Oxides ( NOx ) 300 ppm
- Water Vapour (H2O) Trace (hIGh, if not effectively dried)
- Ash and Soot C Traces
- Density 1.044 (heavier than air)
Inert condition means a condition in which the oxygen content throughout the atmosphere of a tank has been reduced to 8% or less by volume by addition of inert gas .
Points to pounder for inert gas :
Inert gas systems on ships Inert gas is produced on board of mainly crude of oil carriers, gas carriers and Chemical carriers, and in Bulk carriers when carrying fish flower, and in refrIGerating ships when carrying fruit products, by using either a flue gas system or by burning Marine Diesel Oil ( MDO or MGO) in a dedicated inert gas generator, or produced clean Nitrogen by an dedicated Nitrogen Generator.
IG keeps the oxygen content of the tank/cargo hold atmosphere below 8%, thus making any air/hydrocarbon gas mixture in the tank too lean to IGnite. IG is most important during discharging of cargo on tankers and during the ballast voyage when more cargo and/or hydrocarbon vapour is likely to be present in the tank atmosphere.
Inert gas can also be used to purge the tank of the volatile atmosphere in preparation for gas freeing – replacing the atmosphere with breathable air – or vice versa. Inert Gas can also be used for emptying cargo lines or Cargo pumps.
Sources of inert gas on tankers including combination carriers are:
- The uptake from the ships main or auxiliary boilers
- An independent inert gas generator, or
- A gas turbine plant when equipped with an afterburner.
Different types of Inert Gas:
Inert Gas for ship’s can be one of the following gas and the choice of this gasses is depending on the product being carried and the capacity required.
- Inert Gas is generated by burning MDO ( marine diesel oil) in a furnace and the exhaust gas is blown by ordinary blowers via a scrubber/filter unit for cleaning out the sulphur, towards the Cargo tanks; ( This unit making the Inert gas is often called Inert Gas Generator)
- Flue Gas:- This Gas is exhaust gas from the steam generating boilers or occasionally from the main engine and blown by a blower via a scrubber/filter unit for cleaning and cleaning out the sulphur towards the cargo tanks.
- Nitrogen, which is made by blowing compressed air from the booster compressor through a small fibre tube, like a Filter material, or via an absorbtion filtering system, by which the air and its gasses will be separated and finally N2 will be forwarded to the Cargo tank by means of the overpressure caused by the booster compressor.
- Pressure is up to 11,5 bar depending on installation.
- Gas composite (up to 99,9 % N2)
- Dew point down to minus 70 Celsius.
- This gas can be used for all Cargoes as the purity of the N2 is very hIGh and no water content or Hydrocarbons are present.
- For pipeline stripping a separate pipeline with buffer tank pressurised up to 11 bar can be used.