FPSO reliability and filtration

While floating production storage and offloading (FPSO) deployment is rising to become a major element of the offshore oil and gas production asset base there is no less emphasis on the must-run nature of key equipment onboard. For the gas turbines that provide electrical power as well as key equipment mechanical drive, the critical denominator of performance and reliability is effective combustion air intake filtration.

Oil and gas exploration and production increasingly rely on FPSO vessels that allow hydrocarbon production in remote, deep-water areas that would be uneconomic to develop using conventional tension leg or fixed pile structures. The changing economics of oil and gas production has led to sharp growth in the deployment of FPSO vessels. Today, they tend to dominate the space in place of more permanent platforms and structures that have previously been the preferred choice. A key benefit of FPSO technology is its flexibility, allowing expensive production assets to be relatively easily relocated in response to changing reserve economics. It is also typically easier to obtain permitting and licensing for structures that are not permanent. As a result, today FPSOs are commonly found working oil and gas reserves in regions such as the east of Brazil and offshore of West Africa.

Typically located far offshore, like their fixed forebears these must-run applications demand the highest reliability to keep production running at full capacity no matter how harsh the environment.

One of the most important pieces of production equipment for FPSO vessels are the gas turbines which provide electrical power as well as mechanical drive for various critical processes.

Like any gas turbine, efficiency, performance, and operational longevity are all directly affected by contamination and potential erosion or corrosion of turbine internals. However, even though FPSOs are slightly less challenged from a filtration perspective than on older generations of fixed platforms – they typically flare less for example – the marine environment hasn’t changed and is particularly unforgiving when considering precision equipment like an advanced gas turbine. A critical consideration then is to prevent corrosive materials and other contaminants from entering the machine at all and that places huge emphasis on effective filtration of the intake air.

Clean air and the challenge of the marine environment

Operating gas turbines consume huge volumes of air, making airborne contaminants a significant issue. Any materials entering the turbine can adhere to the blades of the machine where even a modest coating can have a substantial negative impact on aerodynamic efficiency. Any loss of efficiency has a cost implication but for demanding FPSO applications this can have much more serious consequences. One of the responses to turbine contamination is to execute an offline wash cycle. While this can restore some of the lost performance associated with contamination it also necessitates shutting down the turbine with a potential loss of production that could be worth millions of dollars. Even more significant is the threat of erosion or corrosion of the turbine internals. Accelerated wear can be catastrophic. It not only affects the compressor section as contaminants can be ingested deep within the machine and can therefore also affect components in the hot gas path such as combustors, bearings and the turbine section. Repairing worn components can be a lengthy and costly procedure, especially if, as in the case of an FPSO, the asset is typically located far out to sea. As with offline washes, turbine downtime also likely represents an extremely costly loss of production capability.

While the challenges of air intake filtration are broadly understood, FPSO installations face additional challenges associated with the harsh offshore environment such as bad weather and water coming from sources like rain, mist, fog and sea spray. They must also manage constraints that do not apply to nearly the same degree when considering their terrestrial equivalents. Principally this is a lack of space on board a marine production vessel. Consequently, not only are turbine islands for these applications designed to be as compact as possible, but this also applies to all the related ancillaries, including the air intake filtration system.

Compact and fast is key

Given the extreme limitations of available space onboard FPSOs, gas turbine and compressor package OEMs have dedicated considerable resources to making high-performance systems that still deliver appropriate air quality for the turbine intake, but without the footprint commonly associated with terrestrial GT intake filtration. The Baker Hughes SeaSmart offshore package^TM solution is one such advance.

Achieving this performance within a reduced and compact footprint has led to the development of filtration systems which are very high velocity (compact) but have also relied on technical breakthroughs to ensure that the high velocities do not result in excessive pressure differentials across the required filtration components. To do so would impart significant performance losses. Parker, for example, offers several product ranges that support this compact high-velocity high-performance requirement.

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