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Operation of Inert Gas (IG) Systems on Ships

written by: Ricky • edited by: Lamar Stonecypher • updated: 11/24/2008

This article briefly describes the starting, running and stopping procedures for a typical inert gas (IG) system on board ships. The exact operation may vary with the specific type of plant.

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    In the previous article we saw the drainage arrangements for the IG system on ships and specifications and requirements for designing drainage for scrubber effluents and deck seal water. Having taken a thorough look at various parts of the IG plant, we will now learn about the few basic operating principles of a typical IG plant though exact procedures could vary slightly for different systems.

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    Operation of the IG Plant

    • Since the IG plant uses exhaust gases from the boiler (there are other arrangements but we are limiting ourselves to this common scenario) it is evident that the boiler should be running before inert gas could be generated. The combustion in the boiler should be so adjusted that the oxygen content is around the region of 5% by volume in the flue gases.

    • The operator should next ensure that all the power supplies required for the various components, controls and monitors is available and the pumps required for supplying sea water and deck seal water are running satisfactorily.

    • Various valves in the system should be in their respective open or closed position as desired and the relevant blanks are in place. Then the first valve to be opened should be the flue gas isolating valve (see here for layout of the plant). Then the IG blower should be started after making sure its inlet and outlet valves are correctly opened. The recirculating and regulatory valves should be opened in the same order.

    • After this the oxygen analyzer readings should be checked to ensure that the gas from the plant is actually in the inert condition before supplying it to the cargo spaces.

    • When all the above procedures have been satisfactorily carried out, the tanks should be filled with inert gas until the atmosphere inside the tanks has reached the desired levels after which the plant could be shut down.

    • The regulating valve should be shut down after opening its vent to the atmosphere followed by stopping of the inert gas blower. The blower should then be water washed for a specific time period after shutting inlet and outlet valves but opening the drain valve. The flue gas isolating valve should be the last to be shut down.

    • The scrubber water pump needs to be kept running for a time as recommended by the manufacturer while the deck seal water certainly needs to be running continuously.

    Having learnt about the IG plant operation, its now time to take a look at the actual inerting process of the tanks and several procedures associated with it in our next article.