The Evolution of Inert-Gas Systems on SBM FPSOs: The Problem of Venting and a Straightforward Solution
- Dirk de Vos (Single Buoy Moorings Inc.) | Michael Duddy (Single Buoy Moorings Inc.) | Jos Bronneburg (Gusto MSC)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- June 2007
- Document Type
- Journal Paper
- 1 - 11
- 2007. Society of Petroleum Engineers
- 4.5.3 Floating Production Systems, 4.5 Offshore Facilities and Subsea Systems, 6.3.7 Safety Risk Management, 6.1.5 Human Resources, Competence and Training, 5.4.2 Gas Injection Methods, 4.6 Natural Gas, 4.1.4 Gas Processing, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 4.2.3 Materials and Corrosion, 4.1.3 Dehydration, 4.1.6 Compressors, Engines and Turbines
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As a floating production, storage, and offloading vessel (FPSO) continually loads stabilized crude oil to the cargo tanks, the inert-gas (IG) blanket within the tanks is compressed. At a certain pressure, below that which could cause damage to the vessel structure, this mixture of now IG and volatile organic compounds (VOCs), emanated from the loaded crude, must be vented safely to atmosphere by some means.
From the very first FPSO that Single Buoy Moorings (SBM) operated, the FPSO II in 1980, errant gas (IG) has resulted in a number of emergency shutdowns (ESDs) while venting the cargo tanks during calm weather. With no wind to disperse the heavier-than-air gas, the result is the mixture falling onto the vessel main deck or the process modules, triggering the FPSO gas-detection system and subsequently causing an ESD. The cost can quickly become considerable because of loss or delay of production in this manner.
More importantly, while venting the cargo tanks, personnel are relocated to a safe area to ensure their safety, and any hot-work being undertaken is postponed. Crane and helicopter operations also are suspended. There is, of course, a cost associated with the loss of personnel productivity during these events.
To prevent reoccurrence of IG venting-related incidents, a number of operational measures are used.
As a high concentration is attained [usually approximately 40% of the lower-explosive limit (LEL)], venting is stopped until the gas has been dispersed. Typically, the alarm is activated at 20% LEL, and the executive action (in this case, an ESD) is set at 60% LEL.
With FPSOs becoming larger, and production rates correspondingly so (sometimes more than 300 000 B/D), the financial penalties resulting from an unplanned shutdown are even more significant. Although using operational means can be a successful way of mitigating both the safety and production risks associated with IG venting, a system that would obviate the need for such procedures has been sought by SBM since their first operating FPSO, more than 25 years ago.
This paper describes the evolution of the IG arrangements on board SBM's units, past and present systems that have been used with varying degrees of success and the recent (July 2005) retrofit of an IG eductor to 2 SBM FPSOs operating west of Africa. The details of the patented IG eductor, from conception, design, safety studies, construction, installation, and operational success, are also presented.
|File Size||2 MB||Number of Pages||11|
Advanced Production andLoading. Volatile Organic CompoundsReturn System.http://www.apl.no(accessed 22 May 2007).
Cargo Vent Gas BlowerEvaluation. Memo. Gusto MSCES2388-IM-001, September 2003.
Corrosion Rates. Memo. Gusto MSC ES2388-IM-003, November2003.
Cost Estimate. Gusto MSC ES2338, December 2003.
FPSO ‘A' Topsides Eductor P&ID. SBM-Imodco ES47110DTT27015 X1, July 2005.
FPSO ‘A' Topsides Eductor Process Data Sheet. SBM-ImodcoES47110 STT92411 A1, March 2005.
FPSO ‘A' Vessel Inert Gas System PFD. SBM-Imodco ES47110DFV92051 X1, July 2005.
FPSO ‘B' Topsides Eductor P&ID. SBM Imodco IR38136DTT27015 X1, August 2005.
FPSO ‘B' Vent Eductor Operating Procedures, 210792053Issue 01 Revision 02. SBM-Imodco, September 2005.
FPSO ‘B' Vessel Inert Gas System PFD. Gusto MSC HI39230DFV92051 A1, November 2002.
FPSO Capixaba Vessel Inert Gas System PFD. Gusto MSC HI39350DKF27001 A1, September 2005.
FPSO Kuito Vessel Conversion Inert Gas Piping SystemP&ID. Gusto MSC HI39120 DPF05004 A5, June 1999.
FPSO Smoke and Vent GasDispersion. Study Report. GustoMSC/WS Atkins HI39230 RHF36042 A1, October 2002.
Topsides Cargo Vent Eductor ProcessFunctional Specification. Gusto MSCES2388 STT27201 C1, December 2003.
Topsides Vent Gas BlowerSpecification. Gusto MSC ES2388SKT27001 C4, August 2003.
Topsides Vent Gas EductorP&ID, Gusto MSC ES2388DTT27001C4. February 2004.