Enhancing Oil and Gas Production Through Improvements in Gas Turbine Cleanliness
a report by James Kenneth Ross Aftermarket Manager, AAF Power & Industrial, Cramlington
Business Challenge
The oil and gas industry relies heavily on the reliable operation of thousands of gas turbines (GTs) worldwide. GTs are employed in various configurations to support gas gathering, transmission, storage, withdrawal and lift, as well as for power generation for offshore platforms, floating production offloading systems and facility electricity cogeneration. When used for mechanical drive, units provide a compact solution for operating centrifugal compressors for air, process and refrigeration and horsepower for driving pumps for crude oil transportation. Therefore, it follows that maximising the availability, useful life and reliability of these critical machines is of paramount importance if operators are to realise their greatest production yields.
Coastal, fixed and floating offshore facilities present some of the toughest conditions for the continuous operation of turbine engines. A GT consumes vast amounts of atmospheric air heavily contaminated by natural pollutants, such as salt and seawater spray, plus those self-generated by flaring, drilling, shot-blasting and re-ingestion of engine exhaust fumes. As an accumulated mass in fluctuating humidity, these pollutants seriously affect the performance and operating efficiency of a precision GT engine. To protect the turbine from these pollutants, the majority of GT original equipment manufacturer (OEM) specifications, past and present, require air inlet filtration with a final ‘fine’ filter with a classification of F9 (98 Grade Efficiency) or less. High-efficiency particulate air (HEPA) filtration systems, which in the future will be known as EPA, were originally developed for clean room and pharmaceutical applications. With an efficiency level thousands of times greater than the F9 classification, HEPA H12 filters are increasingly being used to protect GTs. The driving force for selecting H-class filters has been to maintain a very high level of cleanliness for the turbine compressor blades and therefore remove the requirement for offline water wash and, consequently, production downtime.
AAF has carried out long-term studies of 30 GTs with and without HEPA filtration, totalling hundreds of thousands of operating hours. This work has led to the counterintuitive conclusion that more power is obtained with HEPA filters than with only fine filters. The consistent finding is that initial power lost due to increased differential pressure is more than offset by the maintenance of a clean condition during the first initial weeks of operation. In other words, the energy payback period of HEPA filtration can be measured in days.
James Kenneth Ross is the Aftermarket Manager at AAF Power & Industrial. His main area of interest is the development of high-technology high-efficiency particulate air filtration technology for offshore marine environments, and leads the engineering division responsible for the work in the field of engine performance optimisation and compressor efficiency. Mr Ross has a degree in business and finance and diplomas in both mechanical engineering and industrial acoustics.
E:
James.Ross@aafgb.com
High-efficiency Particulate Air Potential
Turbine availability, operational performance and component life can be considered as direct functions of the total mass of ingested contaminants. These deposits decrease the air-flow performance of the inlet compressor due to degradation in the blade shape and the surface finish. Ultimately, the overall performance of the turbine is greatly affected.
HEPA filtration provides the critical efficiency required to remove submicron-sized contaminants resulting in laboratory clean air being achieved for engine combustion. The primary technical benefits derived from enhanced filtration technology include:
• •
greater machine availability and reliability; high initial power output is maintained;
• increased fuel efficiency; • longer hot-end component life; •
• lower emissions. The potential commercial upside considers:
• increased plant revenue; • •
greater production yield (i.e. oil and gas, steam); lower fuel and labour costs;
• lower component spend; and • greener technology use.
Up until ten years ago, HEPA filter technology was employed offshore to a very limited extent only. However, its success has resulted in increased use worldwide in a variety of filter configurations operating in demanding environments. This increased utilisation has provided a greater sample which to study and it is now possible to establish whether this achievement of increased performance provides a blueprint for mandatory air quality and efficiency of filters to meet future challenges. If this is the case, results will show that reliable machine availability is matched with consistent machine output and efficiency.
Reduced Productive Hours
Pollutants that are Figures 1 and 2. Water-wash is typically performed using detergents and fresh water.
60 © TOUCH BRIEFINGS 2010 reduction or elimination of the need for water wash; and
Engineering & Construction
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