(h)unit 2 ig system

OXYGEN CONTROLOXYGEN CONTROL

Theoretically any mixture with less

than 11.5% oxygen will not support

combustion, However, for safety

the level is reduced to 8% vol.

HOW TO CONTROL ? ?HOW TO CONTROL ? ?

INERT GAS

INERT GASINERT GAS

• ARGON

• KRYPTON

• NEON

• HELIUM

ARE WE REFERRING TO ELEMENTS IN

PERIODIC TABLE ?

INERT GASINERT GAS

INERT GAS IS A GAS ( or )

COMPOSITION OF GASES WHICH

HAS INSUFFICIENT OXYGEN TO

SUPPORT COMBUSTION

INERT GAS ON BOARD THE SHIP

CAN BE OBTAINED FROM THE INERT GAS

SYSTEM

INERT GAS SYSTEM

BOILER UPTAKE

INERT GAS GENERATOR

INERT GAS PLANTINERT GAS PLANT

This is a system specially

designed to supply cool, clean,

pressurised, monitored and

controlled inert gas.

INERT GASINERT GAS DISTRIBUTION SYSTEM DISTRIBUTION SYSTEM

INERT GAS DISTRIBUTION SYSTEM

MEANS ALL PIPING , VALVES AND

ASSOCIATED FITTINGS TO

DISTRIBUTE INERT GAS FROM INERT

GAS PLANT TO CARGO TANKS

INERT CONDITIONINERT CONDITION

OXYGEN CONTENT THROUGHOUT

THE ATMOSPHERE OF THE TANK

HAS BEEN REDUCED TO <8% BY

VOLUME

INERT GAS SYSTEMINERT GAS SYSTEM

BOILER UPTAKE VALVEBOILER UPTAKE VALVE

Provides a take off point for the

flue gas, A cleaning arrangement

is fitted to prevent soot build up.

SCRUBBERSCRUBBER Flue gas passes to the scrubber via the uptake valve, here it enters at the bottom via a water seal and passes up through a series of sea water sprays and baffle plates being cooled and cleaned before exiting via a demister The water is supplied via the Scrubber pump, the sprays reduce the temperature to within 2*C of the sea water temperature, the Sulphur dioxide content is reduced 90%, and the gas is clear of soot. The tower is rubber lined and other parts are made of glass fiber to protect against the SO2 . The water seal at the bottom is provided by the weir arrangement fitted to the drain system.

BLOWERSBLOWERS

Two types of fans are fitted, a steam turbine driven one of sufficient capacity to supply I.G requirements during cargo ops, and an electrically driven unit with sufficient capacity for topping up only

BLOWERSBLOWERS

• CAPACITY = > 125 % OF THE MAX

DISCH RATE

• MAY BE 2 BLOWERS (or) 1 BLOWER TO MEET THE CRITERIA

REGULATING VALVEREGULATING VALVE

The pressure within the tanks is controlled by automatic or manual operation of the regulating v/v, if the demand is low and the regulating v/v nearly closed then the re-circulating v/v opens thereby reducing the possibility of the fan overheating by passing the gas back to the scrubber tower

DECK SEALDECK SEAL

The Inert gas leaving the engine room to deck passes through the Deck Seal whose purpose is to prevent gases from passing back to the engine room from the cargo tanks. A demister is fitted on the outlet side. The seal is internally rubber lined and a heating coil fitted to allow use in low temperatures.

DECK SEALDECK SEAL

The controlled water level has a low level alarm fitted. As the seal is a primary safety feature it is supplied from the general salt water system when the scrubber pump is not in use. Checks are made on the pipe from the seal to the regulating v/v to ensure no HC prescience which would indicate corrosion damage.

DECK SEAL DECK SEAL - - TYPESTYPES

DECK SEAL

WET TYPE SEMI-DRY TYPE DRY TYPE

FOUND ON SOME SHIPS + NOT HIGHLY PREFERRED

SLUGGISH IN RESPONSE +

NOTPREFERRED

PREDOMINANTLY FOUND + HIGHLY

EFFECTIVE

DECK SEAL DECK SEAL –– WET TYPEWET TYPE

DECK SEAL DECK SEAL –– SEMI DRY TYPESEMI DRY TYPE

DECK SEAL DECK SEAL –– DRY TYPEDRY TYPE

NON – RETURN VALVENON – RETURN VALVE

As an additional safeguard to prevent

the backflow of gas from the cargo

tanks, one or more mechanical non-

return valves are installed on the cargo

tank side and in series with the deck

water seal.

DECK ISOLATION VALVEDECK ISOLATION VALVE This valve is used to isolate the inert

gas plant from the deck distribution subsystem and the cargo tanks; it therefore constitutes the “First" barrier to any reverse flow of cargo tank gas when the IGS is started, tested, or secured. A second valve is necessary unless the deck mechanical non-return valve has a positive means of closure.

DECK DISTRIBUTIONDECK DISTRIBUTION

This subsystem consists of a single inert gas

main running the entire length of the cargo deck,

starting at the deck isolating valve aft and ending

at the vent valve forward. One or more

pressure/vacuum devices are fitted to the inert

gas main to prevent the cargo tanks from being

over or under-pressurized.


The inert gas main contains a means for

receiving an outside source of inert gas

when the IGS is not functioning. From the

inert gas main, individual branch lines run to

the cargo tanks. Stop valves or equivalent

closures are fitted at each branch line, so

that each cargo tank can be isolated from the

inert gas system.

PRESSURE – VACCUM PRESSURE – VACCUM VALVESVALVES

• EACH TANK FITTED

• SECONDARY VALVE FITTED IF NO PRESSURE MONITORING DEVICE

• PREVENT OVER AND UNDER PRESSURISATION OF TANKS

PRESSURE – VACCUM PRESSURE – VACCUM VALVEVALVE

PRESSURE SIDE – LIFTSOFF WHEN TANK

PRESSURE EXCEEDSTHE SET LIMITS

VACCUM SIDE – LIFTS OFF WHEN TANK

RUNS INTO VACCUMAND ATMO IS

LET IN

ROLE OF PV / HVV VALVE ROLE OF PV / HVV VALVE WHILE LOADINGWHILE LOADING

When loading cargo tanks at high rates,

steps must be taken to avoid pressure

build up which can cause structural

damage. This requires the release of the

vapours from the tank. This could be by

pipes led up the mast with a release point

via a flame trap.


An alternative as shown provides a high velocity release which carries the gas well clear of the ship. Depending on the pressure, the area between the fixed cone and the orifice plate will change allowing the velocity to be maintained. At high pressures the orifice is forced upwards against the bellows force, thus increasing the flow area. At low pressure the counterweight pulls the orifce downwards thereby reducing the flow area and maintaining the gas velocity

INERT GAS GENERATORSINERT GAS GENERATORS

PREDOMINANTLY FOUND ON PRODUCT TANKERSAND DEDICATED CHEMICAL TANKERS.

THE UNDERLYING PRINCIPLE IS SAMEEXCEPT THAT THE BOILER FLUE GAS IS NOT USED.

A SEPARATE COMBUSTIONCHAMBER IS MADE USEOF FOR GENERATINGINERT GAS

BENEFITSBENEFITS

REDUCED FIRE HAZARD

REDUCED CARGO DISCHARGE TIMES

THANK ‘U’THANK ‘U’

(h)unit 2 ig system

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