What are the design and operational principle of the Inert Gas Generator?
Inert Gas Generator was originally developed to supplement CO2 flooding systems. Since if a fire occurred on board a ship at sea and the fire was extinguished by using all the CO2 available and a further outbreak occurred then a backup was available. In a compartment wherein there is an outbreak of fire the minimum percentage of oxygen in the atmosphere in the compartment which will allow combustion to proceed varies with different materials. Between 12 to 16 percent approximately. Hence if the oxygen content of the compartment can be reduced below 12 percent then insufficient oxygen would be present to allow combustion to continue. This reduction in oxygen content can be achieved by employing a generator which will supply inert gas which is heavier than air so displacing the atmosphere in the compartment.
Inert Gas Generator widely used on board tankers for tank inerting purposes.
The generator consists of a horizontally arranged brick-lined furnace cylindrically shaped and surrounded by a water jacket. This is connected to a vertical combustion chamber in which water spray units and lessing rings (Cylinders of galvanized metal arranged to baffle the gas flow) are fitted. A water-cooled diesel engine may be fitted alongside the generator to drive a fuel pump, a constant volume air blower and an electric generator. The electric generator supplies current to an electric motor which in turn drives the cooling water pump. Motor and pump are usually situated at the forward end of the shaft tunnel. By fitting the cooling water pump in the tunnel and having it connected to the wash deck line this pump can also be used as an emergency fire pump. Cooling water for the gas generator can also be supplied by the ballast and general service pumps.
The oil fuel burner is initially lighted by means of high tension electrodes, the electrical supply being through a small transformer. A constant pressure regulator is fitted to the oil supply line to the burner along with a control valve.
A control panel for the gas generator incorporates a CO2 recorder, water and oil fuel alarms and pressure gauges. In the gas piping system leading from the combustion chamber condensate traps and drains are fitted.
The following is an approximate content of the as generated:
- Oxygen: 0-1 %
- Carbon monoxide : Nil
- Carbon dioxide : 14-15%
- Nitrogen: 85%
- Remainder: unburnt hydrocarbons and oxides of Nitrogen.
