Gas Disposal Aboard A Floating Production Facility

Abstract The Cadlao Floating Production, Storage and Offloading (FPSO) Facility has on board equipment to separate the oil, water and gas produced from two subsea wells. The produced natural gas is used to fire the original ship's steam boilers and excess gas is disposed of through an enclosed vertical flare. The Cadlao produced gas contains up to 6000 ppm H2S and added safeguards were necessary for burning the sour gas in the boilers and in the flare stack. Gas compression equipment installed to allow gas injection into the well-streams to reduce the hydrostatic head of the produced fluid column has not yet been used. BOILER FUEL The converted tanker was equipped with two 50000 kg/hour standard marine boilers. The boiler room equipment was completely redundant to insure steam for vessel maneuverability at all times. The converted vessel does not require steam for maneuverability and with a 750 kw diesel standby generator, and a 330 kw emergency diesel generator in addition to the two original 700 kw steam-driven generators can be without steam power to extended periods of time. The FPSO boilers operate in two modes:producing operations where the distillation plant and one 750 kw steam-turbine generator are in use oroffloading when the steam-driven cargo and stripping pumps ore also added to the boiler load. Either boiler has adequate capacity for both load conditions, and only one boiler is fired at a time. The boiler not in use is alternated each month to assure continued proper operation of both boiler systems. All fuel gas lines are made up of concentric piping up to the individual boiler face. At the boiler face, the fuel gas controls and piping are enclosed in an exhaust hood which will exhaust any sour fuel gas leaked from the boiler face piping/controls (see Figure 2). The pressure reduction from the exhaust fans at this location is sufficient to overcome the tendency of H2S gases to sink to the lower levels of the engine room. The exhaust fan failure and HAS and explosive level located in the exhaust hood are interlocked with the boiler fail-safe shut-dawn system. Other H2S sensors are strategically placed about the engine room. p. 11–61 p. 11–61