Inert Gas System

                                  Inert Gas System

Introduction

Oil Tankers carry different grades of oil, having the property to produce flammable gases even if the hold is empty, still there can be harmful flammable gases .when these vapour of oil mixes with air at a suitable range then explosion can occur. to protect this situation inert gas is used.

What is Inert Gas ?

Inert gas contains insufficient oxygen ( normally less than 8% volume) to suppress combustion of flammable hydrocarbon gases 

Inert gas system spreads the inert gas over the hydrocarbon mixture which increases the LEL and decreases the HEL ,when the concentration of inert gas reaches 10% an atmosphere is created in tank which hydrocarbon cannot burn.

                         Components & Description 

Exhaust Gas Source:  

Inert gas is taken from exhaust uptakes of boiler or main engine as flue gas contains in it. or it is produced by separate inert gas system.

Inert gas Isolating valve:

Supply valve between uptake and rest of the system .when not in use isolates both system.

Scrubber Tower:

Flue gas enters from the bottom and passes through a series of water spray and baffle plates to cool, clean and moist the gases . the SO2 level decreases up to 90% and becomes clear.

Demister :

Normally made of polypropylene used to absorb moisture and water from the gases.

Gas Blower :

Two types of blowers are used in inert gas system 

1) Stem driven turbine blower for IG operation

2) Electrically driven blower for topping up purpose

IG Pressure regulating valve:

The pressure in the tank varies due to property of oil or atmosphere. To prevent this variation and to prevent overheating of blowers a regulating valve is given after the blowers which sends the excess pressure back to the scrubber tower 

Deck Seal:

Purpose is to stop the gases to return back which are coming from blowers to cargo tanks normally wet type deck seal is used.

Mechanical non return valve:

Addition non return valve inline with deck seal.

Deck Isolation valve:

Engine room system can be isolated fully with the valve

PV breaker:

helps to control over & under pressurization of tanks.

Cargo Tanks Isolation Valve :

A vessel has number of cargo holds and each hold is provided with isolating valve to control the flow of inert gas in hold. 

Mast Riser :

Used to maintain a positive pressure of inert gas at the time of loading of cargo and during loading time it is kept open to avoid pressurization of tank.

Safety & Alarm system :

1) Power failure alarm leads to alarm and shut down of blower and scrubber tower,

2) Emergency stop leads to alarm and shut down of blower and scrubber tower

3) High level in scrubber leads to alarm and shut down of blower and scrubber tower.

4) Low pressure sea water supply in scrubber leads to alarm and shut down of blower.

5) high oxygen content leads to alarm and shutdown ,

6) low level in deck seal leads to alarm and shut down of gas delivery.

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