3.1.1 A typical arrangement for an inert flue
gas system is shown in figure 6. It consists
of flue gas isolating valves located at the boiler uptake points through
which pass hot, dirty gases to the scrubber and demister. Here the
gas is cooled and cleaned before being piped to blowers which deliver
the gas through the deck water seal, the nonreturn valve, and the
deck isolating valve to the cargo tanks. A gas pressure regulating
valve is fitted downstream of the blowers to regulate the flow of
gases to the cargo tank. A liquid-filled pressure/vacuum breaker is
fitted to prevent excessive pressure or vacuum from causing structural
damage to cargo tanks. A vent is fitted between the deck isolating/nonreturn
valve and the gas pressure regulating valve to vent any leakage when
the plant is shut down.
3.1.2 For delivering inert gas to the cargo tanks
during cargo discharge, deballasting, tank cleaning and for topping
up the pressure of gas in the tank during other phases of the voyage,
an inert gas deck main runs forward from the deck isolating valve
for the length of the cargo deck. From this inert gas main, inert
gas branch lines lead to the top of each cargo tank.