As the offshore oil and gas industry recovers from a sudden and deep drop in oil prices triggered by the COVID-19 pandemic and subsequent Russia-Saudi Arabia price war, the sector must identify the most effective way to recoup margins and allocate the scarce resources that remain. Graeme Turnbull, System Product Manager at AAF International, reports.
Thanks to a decade of oil price fluctuations and the ever-growing pressure to decarbonise, the offshore industry has become hard-wired to effective change management. Yet, despite this, the recent plunge in energy demand and oil prices has left even the most seasoned executives wondering how best to protect their businesses, during what the International Energy Agency (IEA) has described as “a once in a century event”.
For producers, the need for decisive action is unquestionable. But deciding what course of action to take, how, and when to take it, is altogether more complex. Not least, this is because many factors related to the COVID-19 pandemic remain highly fluid and could lead to differing outcomes for the entire offshore industry.
Maintaining critical business functions
In very basic terms, the production of offshore oil and gas cannot be delivered without gas turbines, which run both the mechanical drive and power generation applications on offshore platforms. Indeed, most would agree that gas turbines are a critical business function, and this is reflected in the industry’s long-term focus on turbine reliability and availability. The rationale being, that an asset performing well in these key areas brings greater prospects of overall efficiency, sustainability and profitability.
At the time of writing, we cannot escape from the fact that some gas turbines will be performing a reduced role if they are located on a rig that’s subject to warm stacking. However, in the medium to long term, the fundamental role gas turbines play at the centre of the offshore oil and gas industry remains unchanged. As a result, they are unlikely to be forgotten by prudent budget holders carving out a new strategy that seeks to achieve maximum value from their assets in 2020 and beyond.
Traditional approaches
From Rotating Equipment Engineers, to Mechanical Engineers, Reliability Engineers and C-suite Executives, all disciplines concerned with maintaining gas turbines have long focused on the importance of maintaining the engine of a gas turbine. However, a critical example that often escapes attention is the fundamental importance of air filtration systems, which have the ability to exponentially enhance gas turbine performance and availability while promoting better compressor cleanliness and long-term part integrity.
Currently, around 85% of offshore gas turbines are protected by small high velocity filtration systems that utilise low efficiency filter bags, which only provide adequate protection against large coarse particles, and fail to capture the majority of sub-micron particles offshore. It is worth noting that this scenario traces its roots back to the 1970s when the National Gas Turbine Establishment (NGTE) located at Pyestock, England, published technical paper 59/1975 for ocean going vessels, later to become known in the offshore industry as the “30 knot aerosol”. The research was taken less than 10 metres above sea level on a Royal Navy frigate. The measuring equipment was also appropriate for the time and concluded 95% of particles are >5 microns, with the majority bigger than 13 microns. In the world of filtration these are very large particles and why smaller filtration systems with low efficiency bags were highly appropriate. However, fast forward to 2017 and recent measurements at platform height (which is often >30 m) with modern measuring equipment tell a different story. It is in complete contrast to the NGTE research with 75% of particles in the North Sea smaller than 0.3 microns and in the Middle East that percentage increases to 97%. This is why low efficiency filter bags are not suitable for this environment, in the onshore environment these bags are now only used as pre-filters to protect intermediate and final filters.
The legacy of this situation has resulted in lost production revenue, unplanned gas turbine shutdowns and costly downtime, reduced component and engine life, premature engine failure, and low turbine compression efficiency as well as high CO2 emissions. All of these impacts are significantly magnified and unwanted given today’s current market dynamics and the low price of oil. What’s more, small high velocity systems are designed to allow water, moisture or fog to coalesce as it passes through the filter bags. This process creates larger droplets which are designed to be captured by a downstream vane after the filter bags. However, vanes are not 100% efficient and some of the water and salt in solution will pass through the vanes. In addition, water will often collect on the floor downstream of the bags and upstream of the final vanes. The salt laden water will evaporate over time, which will allow salt crystals to enter the airstream and hence a proportion of these dry salt crystals will pass through the vanes into the gas turbine.
By contrast, high Efficiency Particulate Air Filter (EPA) E12 technology captures 99.95% of 0.3-micron particles, compared with low efficiency filter bags which only capture 5% of particles at this size. This significantly protects and enhances the performance of expensive gas turbine components. As offshore operators have become aware of the benefits of EPA E12 air intake filtration, there has been a push to upgrade existing high velocity units installed offshore. However, traditional EPA E12 filtration technologies – with much larger equipment envelopes – have necessitated that the air intake filter system is replaced in its entirety. This increases foundation loads and incurs significant costs and downtime. However, there is another route, using a new revolutionary EPA E12 system which provides all the associated benefits of EPA E12 air filtration, but can be quickly and seamlessly installed within the existing high velocity air intake filtration system.
BP Clair
BP’s Clair platform in the North Sea, demonstrates the optimum role air filtration systems can play in unlocking considerable financial, operational and environmental benefits.
The BP Clair platform operates three Titan 130 gas turbines (GTs 1, 2 & 3) employed in power generation application to provide power to the asset. Each gas turbine was experiencing compressor blade fouling, corrosion and erosion, as well as turbine section hot gas path corrosion. Operationally, this resulted in poor engine reliability, reduced availability and premature engine overhaul and/or replacement. All of which severely impeded the long-term strategic planning for the platform for both production and maintenance.
Eventually, the poor filtration provided by the high velocity bag system resulted in a catastrophic failure of GT2 after 12,000 operating hours, which equated to only a 1/3 of the engine design life. The root cause of the failure being inlet guide vane seizure and in turn compressor section imbalance and ultimately blade liberation. This resulted in irreparable damage and a new replacement engine was required, incurring unplanned long-term shutdown and significant unbudgeted costs.
BP was aware that AAF International was in the final stages of developing a new EPA E12 high velocity filtration solution. Critically, this new design could be installed within an existing high velocity housing with no penalty in differential pressure (dP), therefore negating the need for a larger housing replacement. As a consequence of this failure on GT2, BP was expediting the GT OEM (Original Equipment Manufacturer) for fast-track delivery of a replacement engine and approached AAF to determine if this new technology (N-hance® Performance Filtration) could be urgently deployed in a field trial as a technology collaboration initiative.
Thanks to a longstanding previous relationship between the two companies, BP was able and confident to pilot AAF’s N-hance technology. The N-hance filters and conversion parts were delivered to BP within 5 weeks and commissioned along with the new GT2 engine on BP Clair in February 2017.
The pilot delivered excellent results. There was a significant increase in engine availability resulting from a reduction in unplanned downtime and shortened shutdown periods. There was also a decrease in CO2 emissions improving sustainability, as well as retained power output (compressor efficiency) and heat rate. Critically, BP has also eliminated the risk of potential GT failure due to corrosion at just a 1/3 of design life.
Commenting on the project, BP’s asset team said: “The upgrade project has enabled improved reliability, cost savings and will feed into the reformation of outdated air filtration standards as well as playing a part in helping to achieve offshore asset efficiency of 90%.”
Seizing a unique opportunity for change
In today’s offshore oil and gas industry, market conditions will undoubtably influence the purchasing decisions of asset owners and managers. However, when making decisive decisions amid unprecedented uncertainly, business leaders also face a new dynamic: the growing call for a fresh approach that seizes current circumstances as an unparalleled opportunity for long-term positive change.
In the past, when oil prices peaked, there was more capex to spend on technologies that drove efficiency. Today, the reality is that many asset owners may be considering cheaper, faster solutions. By harnessing revolutionary new EPA E12 technology for offshore high velocity applications, asset owners and managers can build further resilience, increasingly energy security through a reduction in unplanned downtime and shortening shutdown periods, all while significantly reducing the risk of catastrophic failure. EPA E12 gas turbine filtration in small high velocity systems is now operating around the world with great effect, such proven technology is part of the solution to a secure long-term future for the offshore oil and gas industry.
