Design And Installation Of A Cost-Effective Spar Buoy Flare System

ABSTRACT To meet the requirements of flaring large amounts of gas, a cost effective Spar Buoy Flare (SBF) system was designed, built and installed by IMODCO in less than a year at AGIP Petroleum's Agbara field production platform, offshore Nigeria. The system is designed to withstand the 100 year return storm and is capable of flaring 116,500 m3/Hr of gas at an exit velocity of 150 m/s. This paper presents the system development design, installation, model testing of the Agbara SBF system. INTRODUCTION To meet increasing gas production rates disposal requirements at the Agbara field, Nigeria, a cost effective Spar Buoy Flare (SBF) was designed, constructed and installed within ten months. The Agbara platform was designed originally with an integral flare boom for gas disposal. The increasing production required the need for a system capable of remotely flaring large amounts of gas from the offshore platform. The gas is flared continuously through a 17 inch internal diameter flexible pipe that runs from the production platform to the SBF structure. Compared with other types of remote flaring structures such as bridge and platform, tripod and articulated type the SBF offers the following advantages:SBF's light weight structure is efficient and particularly suited to deep water.SBF is fabricated in cylindrical sections and is designed for easy local assembly.SBF can be installed with light offshore equipment.SBF can be adapted to different sites.An SBF is a cost effective system especially when considered on a turnkey basis.SBF variable ballast allows for maintenance of splash zone and inspection of chain stoppers. The general arrangement of the Agbara SBF is shown in Figures 1 and 2. SBF DESCRIPTION The SBF is an all cylindrical welded steel structure with an upper section that is 21 m long with a 1.6 m diameter, and a lower section that is 45 m long with a 2.25 m diameter. Between the upper and the lower section is a transition cone which is 2 m long. The SBF has eleven watertight compartments. The spacing of the compartments allows for accidental flooding of any one compartment without losing stability. The bottom three compartments are used for permanent and seawater ballasting. The bottom compartment is designed for high density ballast, The SBF structural arrangement and the installed configuration of the SBF are shown in Figures 3 and 4. The major components of the SBF include:SBF pipingChain stoppers interfaceFlare tipWalkway, ladder and boat landingBallast/venting pipingMooring systemCathodic protectionFlexible pipeBallast system The Agbara SBF structural mass is approximately 100 tonnes; total installed displacement is approximately 200 tonnes. Flare Piping The transition piping from the flexible pipe to SBF is provided at approximately 23 m above the SBF keel, The pipe penetrates the decks through seal welded collars that maintain the watertight compartments. Provisions are made to allow the pipe to expand thermally in theaxial direction.