Inert Gas System
The Inert Gas system can be divided into two basic groups:
a) A production plant to produce inert gas and deliver it under pressure, by means of blower(s), to the cargo tanks.
b) A distribution system to control the passage of inert gas into the appropriate cargo tanks at the required time.
The basis of inert gas production in the IG plant is the flue gas generated from the ship’s boiler. The high-temperature gas mixture from the boiler uptake is treated in an inert gas plant which cleans, cools and supplies the inert gas to the individual tanks via PV valves and breakers to ensure the safety of the tank structure and atmosphere.
Boiler uptake gases are drawn to the scrubber unit via flue gas isolating valve(s) to the scrubber unit. In the scrubber unit the gas is cooled, cleaned and dried before being supplied to the tanks. Motor-driven inert gas blowers supply the treated gas from the scrubber tower to the tanks. They are mounted on rubber vibration absorbers and isolated from the piping by rubber expansion bellows.
Regulation of gas quantity delivered to the deck is taken care of by the gas control valves and the deck pressure is managed by the pressure controller. If the deck pressure is lower than the set point the output signal will be raised to open the valve more, and vice versa if the deck pressure is lower than the set-point. These valves will then work in cooperation to keep both the deck pressure/blower pressure at their respective setpoint without starving or overfeeding the circuit.
Also Read: Components of Inert Gas system: 13 Crucial Ones.
Before entering the deck line, the gas passes through the deck water seal which also acts as a non-return valve automatically preventing the back-flow of explosive gases from the cargo tanks. After the deck seal, the inert gas relief is mounted to balance built-up deck water seal pressure when the system is shut down. In case of a failure of both the deck seal and the non-return valve, the relief valve will vent the gases flowing from the cargo tank into the atmosphere.
The oxygen analyser which is fitted after the blower separates the “production” and “distribution” components of the plant and analyzes the oxygen content of the gas and if it is more than 8%, it gives an alarm and shuts down the plant.
Ref: Marine Insight website & Cult of sea website
