Followings are component of IG plant;
Boiler uptake valve- Provides a take off point for the flue gas, A cleaning arrangement is fitted to prevent soot build up.
Scrubber- Flue gas passes to the scrubber via the uptake valve, here it enters at the bottom via a waterseal 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 2oC 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 inconel or glassfibre to protect against the SO2 .The water seal at the bottom is provided by the weir arrangement fitted to the drain system.
The following alarms are fitted;
- High water level alarm and trip
- Low water level alarm
- Low water level alarm
Fans-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
Shut down of the fans occurs due to;
- High gas temperature after the blowers
- Low scrubber water pressure, high scrubber water lvl.
- Blower failure.
A blank on a stub pipe may be removed to allow the fans to blow fresh air up the I.G. main when gas freeing
Recirculating and regulating valves- 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 recirculating v/v opens thereby reducing the possibility of the fan overheating by passing the gas back to the scrubber tower.
Oxygen monitor- Fitted just upstream of the regulating v/v and initiates an alarm if oxygen content above 8%.
Deck water seal- The inert gas leaving the engine room to deck passes through the deck water 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. The weir 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.
Non-return v/v- Purpose similar to the deck seal
Deck isolating valve- Allows the isolation of the deck system from the engine room system
Pressure/vacuum breaker ( PV)- This is the safety valve for the system and prevents both under and over pressurisation of the tanks. Flame screens are fitted to the PV breaker vent. The PV breaker may be of the mechanical or liquid type. The liquid type is filled with a liquid of the correct specific gravity, such as monoethylene Glycol and water.