The system is designed on the assumption that the boiler exhaust gas having the following composition is supplied:
1) Oxigen (O2) 3.0 % Vol.
2) Carbon dioxide (CO2) around 13.0 % Vol.
3) Sulfur dioxide (SO2) around 0.3 % Vol. (Max)
4) Nitrogen (N2) remainder
5) Water vapour (H2O) around 5% Vol. (MAX)
6) Solid particles around 250 mg/Nm
The flue gas are allowed to pass through the scrubber at inlet temperature of 400 C and are designed to be inert gas having the following composition.
1) Oxigen (O2) around 3.0% Vol.
2) Carbon dioxide (CO2) around 13.0% Vol.
3) Sulfur dioxide (SO2) around 0.03% Vol.
4) Nitrogen (N2) reminder.
5) Water vapour (H2O) saturated condition.
6) Solid particles 7.5 mg/Nm (for the particles larger than one micron)
7) Water (H2O) 0.125% weight.(max)
INERT GAS SISTEM
Inert gas system in tanker ship is to provides a clean inert gas for cargo oil tanks to maintain a non explosive atmosphere. It is a device to displace and eliminate air from the cargo oil tanks have so low an oxygen content that the combustion can not take place.
A further advantage is that it cuts down cargo discharge time as the pressure of inert gas above crude oil substantially reduce discharging time.
The inert gas is drawn from the boiler up takes through of scrubber by means of blowers which is then distributed to the cargo tanks .
The scrubber uses sea water to cool the hot gas and washes out nearly all the sulphur compounds and carbon particles normally contained in the gas.
1) Rule: DNV and SOLAS 1974 (amend 1981)
2) O2 content less than 5%.
3) Gas temperature max 400C at boiler up take and max 65C at inert gas main line.
4) Deck main gas maximum 1400mm H2O and minimum 100mm H2O.
5) Gas composition O2= 3% , CO2 = 13.0% , SO2 = 0.3% , solid particles 250 mg/Nm
DECK WATER SEAL
Deck water seal prevents the flow of hydrocarbon vapour in the cargo oil tank back in to the engine room. This unit consists of a seal pipe , seal water pot, demister pad etc. and a steam heating coil which prevents sea water from freezing.
INERT GAS FAN
Two blowers unit are provided to blow the inert gas in to cargo oil tanks. Inert gas is cleaned in the scrubber but a small amount of remaining solid deposited on the fan and impeller may cause abnormal vibration an impeller cleaning device is installed to prevent the vibration.
VALVES
Necessary valves and fittings are provided in the system. Butterfly valves are generally used for inert gas line.
O2 ANALYZERS SYSTEM EQUIPMENT
Oxygen concentrations in the inert gas system is detected by an oxygen analyzer , it incorporates an indications gauge. Oxygen is sampled at fan outlet. This equipment is equipped with sampling unit.
PRESSURE VACUUM BREAKER
The pressure vacuum breaker is fitted to the inert gas main line on the deck to protect the cargo oil tanks from abnormal rise and drop of pressure in the tanks caused by miss operation during cargo handling.
CONTROL AND SAFETY DEVICES
Main control panel is installed in the cargo control room and sub panel are installed in the wheel house and engine room.
SPARE AND TOOLS
Necessary spares and tools are supplied in a steel box as manufacturers standard specifications, un less other wise specified.
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