General arrangement of the inert gas system.
The general arrangement of the inert gas system is as follows:
- The inert gas generator-
Exhaust gas from the main boiler or the auxiliary boiler is used.
This is installed to clean and cool the exhaust gas.
Working of scrubber:
The exhaust gas coming out of the boiler enter the scrubber and passes through a water seal in a water tank at the bottom of the unit. The gas then moves upwards and sea water is introduced at the top of the tower for cooling and purification. The sea water is then distributed into the space by means of a sprinkler system.
The water seal at the start is to prevent the inert gas coming out of the cargo tank from entering into the boiler.Its sought of another non return device. Its other function is to cool the high temperature exhaust gas.
This is installed to separate water and solid contained in the inert gas coming from the scrubber sucked by the fan.
Working of demister:
Inert gas containing water and dust is flown into the demister and it is given centrifugal force by a vane at the entrance .the va ne also provides in separating the water and dust .The water and solid separated is exhausted from the drain outlet. The clean inert gas is now sucked by the fan.
- IG fan
This is a single stage centrifugal blower driven by the motor, which draws out the gas coming through the uptake of the boiler and sends it out to the deck seal unit through the scrubber and demister.
Working of inert gas blower:
Blowers are used to deliver the scrubbed gas to the cargo tanks. Ships require at least two blowers which together shall be capable of delivering inert gas to the cargo tanks at a rate of at least of 125% of the maximum rate of discharge capacity of the expressed as a volume.
In some ships there is an additional small capacity blower which is used during topping up of cargo tanks.
- Control valve
This valve adjusts the pressure in the inert gas line in accordance with the pre set pressures.
- Deck seal unit
The inert gas coming from the IG blowers is sent to the individual tanks trough the deck seal unit .The main purpose of the deck seal is to prevent the back flow of HC gas into the IG system and then into the boiler. The deck seal is an additional precaution in case of failure of the non return valve situated after the deck seal and before the IG isolating valve.
- Deck isolating valve
The inert gas coming out of the deck seal unit is distributed to each cargo tank through this valve.
- The scrubber unit
The purpose of the scrubber is to purify the exhaust gas and to remove solid substances and to cool the exhaust gas.