1. Flue gas system - If available, flue gas from ship boilers can be used for inerting. The flue gas system washes and cools the boiler flue gas, and delivers it to the cargo tanks during cargo unloading and tank washing. As the flue gas already contains less then 5% oxygen, no further treatment is therefore necessary. This system is primarily used on crude oil tankers. The main components are the scrubber unit, inert gas blowers, the deck water seal, the pressure/vacuum breaker, valves, instrumentation and the control system. Surplus gas is automatically circulated back to the scrubber unit. The system can also be preset to deliver fresh air for gas-freeing purposes.
2. Flue gas system with topping up generator - Another solution is flue gas system with topping up generator. This alternative method consists of a flue gas system supplemented by a separate small (500Nm3/h) inert gas generator. The flue gas system covers the bulk of the inerting during cargo unloading, and the generator tops up tank pressures during the sea voyage.
3. Inert gas generator systems - Inert gas generator systems are applied when no existing supply is available. These systems produce and distribute inert gas based on combustion of hydrocarbon fuels and are widely used by ships transporting crude oil and refined products that can tolerate water vapour and carbon dioxide.
Components of the inert gas generator systems for tankers are:
- Inert gas generator.
- Blower units which supply combustion air to the generator.
- Deck water seal which prevents the back flow of hydrocarbon gases to unsafe areas.
- Pressure/vacuum breaker that releases excessive pressure/vacuum from the cargo tanks.
- Deck distribution system.
- Control system.