(h)Unit 2 IG System
-
Upload
prem-vikas -
Category
Documents
-
view
23 -
download
1
description
Transcript of (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
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.
DECK DISTRIBUTIONDECK DISTRIBUTION
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.
DECK DISTRIBUTIONDECK DISTRIBUTION
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.
ROLE OF PV / HVV VALVE ROLE OF PV / HVV VALVE WHILE LOADINGWHILE LOADING
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
ROLE OF PV / HVV VALVE ROLE OF PV / HVV VALVE WHILE LOADINGWHILE LOADING
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’