Barossa Offshore Project FPSO EPCI (MODEC) - Inert Gas System

⁠⁠⁠Scope of Work

Inert gas system shall be designed with suitable capacity and redundancy to meet Class and project requirements. The Inert Gas System utilizing boiler flue gas, shall be dimensioned to produce inert gas at a rate of at least 125% of the maximum offloading rate. The oxygen content in the inert gas supply shall not normally exceed 5% by volume at the supply main, and not exceeding 8% by volume with in a condensate tank. Automatic inert gas control valve shall be used to regulate the flow of inert gas to the condensate and slop tanks. This valve shall be controlled by the inert gas pressure sensed between the deck isolating valve and the condensate and slop tanks and shall be provided with means to indicate whether the valve is opened or closed. Inert gas system shall be designed in compliance with SOLAS Reg. 62.9.1 Condensate and slops tank blanketing and venting systems shall be routed through dedicated headers. A three-header Inert Gas and Vent System shall be provided for the tanks. The system shall comprise the following headers:

•  Dirty IG header (normal operation blanketing when loading, offloading and purging)
•  Clean IG header (IG supply for use in tank purging when taking tanks in/out of service)
•  Vent header Tank blanketing for MEG shall be done by Fuel Gas. Fuel Gas shall be supplied from topsides facilities.
•  Tank venting arrangements shall be led to safe locations in accordance with Classification Society and IMO requirements.

The flue gas from the boiler is passed through the scrubber for cleaning and cooling before entering the cargo tanks. The type of scrubber used is important with regards to efficiency of extraction of soot and SO2. Capacity of the IGG system is expected to be 5625 m3/h.
The package will consist of a scrubber with an outside venturi section equipped with an adjustable venturi ensuring an optimal soot extraction of all the different grades of soot particles during all running conditions.
Scrubber plant:

• 1st stage: Precooler with water injection, to cool the high temperature flue gas.
• 2nd stage: Venturi scrubber to remove the soot particles. It should be possible to manually adjust the venturi pressure drop. After leaving the venturi scrubber the inert gas to be bubbled through a water bed before entering the washing tower.
• 3rd stage: Washing tower cools and effective to remove the SO2 gas. Packed bed sections ensure a large surface contact area between water and gas for maximum extraction of SO2 from the flue gas.

Drop eliminator mounted in top of washing tower to prevent free water entering the inert gas supply piping. High pressure centrifugal blowers positioned downstream flue gas scrubber provide inert gas to cargo tanks. System capacity shall automatically be controlled by deck pressure set-point in software. Pressure Vacuum Breaker to be provided to ensure safe loading and offloading. Deck Water Seal shall be provided to ensure a safe sealing of inert gas and prevent back flow of cargo gases to safe area.

Gas freeing facility to be provided which can be performed by closing the scrubber isolating valves and open the fresh air valve, the system shall also be used to gas free the cargo tanks after inerting. The different modes (IG and fresh air) shall be able to be easily selected in the control panel HMI