Pumps and compressors are critical for handling liquid and gas throughout the industry. To ensure they are operating with utmost efficiency, engineers are reviewing their entire drive chain, from the mechanical components, including electric motors, gearboxes and drives, generators to the control and automation components.
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Electric motors play a key role in the upstream side of the oil and gas industry and are widely used to drive equipment such as pump and compressor systems.
Motors
Electric motors are the largest individual source of energy use, accounting for 45% of the world’s electricity consumption, and over half of this energy demand originates from motors used in pumps and compressors.
Electric motors play a key role in the upstream side of the oil and gas industry and are widely used to drive equipment such as pump and compressor systems. Yet, they can have a dramatic impact on energy consumption. For example, they can demand up to 80% of the energy produced by a typical offshore platform main generation system with 100MVA capacity.
Over the last 50 years, global motor manufacturers put significant effort into research and development, achieving major advancements in energy efficiency. For example, 45kW four-pole induction motors – which are commonly used in oil and gas applications - have evolved from 88% to 95.8% efficiency, resulting in a 68% reduction in energy losses. However, old-fashioned and inefficient motor technologies are still widely used across the oil and gas industry.
With the need to limit CO2 emissions and new environmental regulations coming into force in recent years, oil and gas businesses are becoming more aware of the importance of choosing energy-efficient motors. For example, in the EU, the 2005/32/EC Ecodesign Directive now stipulates that motors with a rated output of 7,5-375 kW shall not be less efficient than the IE3 or meet the IE2 efficiency and be equipped with a variable speed drive (VSD). Other countries, including the USA, Brazil and Mexico - to mention but a few – are also moving towards more demanding energy-efficiency regulations.
While the legislation is yet to affect motor equipment used in hazardous areas, it is setting new international benchmarks in terms of energy efficiency, raising awareness of the significant difference that the latest motor technology can make in terms of energy consumption. As a result – regardless of actual legislation requirements - growing numbers of oil and gas operators are starting to request the most energy efficient equipment available on the market, some which already exceed current regulations, reaching IE4 or even IE5 levels of efficiency.
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WEG has specifically adapted its MGF 560 motors to drive triple-plunger high-pressure hydraulic pumps on Petrobras' FPSOs.
Motors have to meet health and safety certification requirements for equipment installed in hazardous areas, including European ATEX and International IECEx standards. For example, the ATEX Directive 94/9/EC stipulates that all motors used in upstream oil and gas applications need to be suitable for use in hazardous area defined as Zone 1 - Gases and Vapours (G), and Zone 21 – Gases, Vapours and Dust (GD).
With this in mind, selecting motors that have been designed with both energy efficiency and safety as a priority, such as WEG’s ATEX/IECEx certified W22Xd Super Premium Efficiency hazardous area motors – the most energy-efficient flameproof motors available on the market (exceeding IE4 standards) - is key to achieving energy savings while complying with new regulations.
It is also crucial to choose motors that are designed to endure the most severe applications. For example, oil production in areas such as deep-sea fields off the Brazilian coast is especially demanding. This is because oil is not only located over 1,000 metres below sea level, but also covered by a salt layer up to 2,000 metres thick.
To meet such challenges, WEG has specifically adapted its MGF 560 motors to drive triple-plunger high-pressure hydraulic pumps on Petrobras’ P66 to P71 FPSOs operating in that region. The units are explosion-proof for Zone 2 (group IIA, thermal class T3) and designed for an ambient temperature range of -45 to +45°C. The starting current is limited to six times the rated current and, due to the aggressive ambient conditions, heat exchangers, fasteners and motor fans are made from stainless steel to provide enhanced corrosion resistance. Additionally, motor windings are protected against voltage surges by capacitors and integrated surge protectors. All these special features make these motors fully compliant with INMETRO certifications for use in explosion hazard areas and by BV Bureau Veritas for shipboard use.
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Electric motors are the largest individual source of energy use, accounting for 45% of the world’s electricity consumption.
Drives
Selecting the right motor is key to improving reliability and energy-efficiency, but there are also other ways in which the need for reducing energy consumption and maintenance costs can be met throughout the drive chain. In offshore pump and compressor applications, variable speed drives (VSDs) – also known as inverters - can also play a major role in enhancing efficiency while ensuring reliable performance and reducing maintenance costs.
Traditional pumping and compression systems use mechanical valves to control the flow, with the electric motors that drive them always operating in nominal speed. This means that a significant amount of electrical power inevitably goes to waste. This problem is even more acute in offshore applications, where on-site power generation is needed and thus limiting energy consumption is vital. When variable speed drives are used to feed electric motors, the output power is proportional to the flow required by the application, which translates into energy savings of between typically 40% and 60%.
Bearing in mind that the typical electric motor lifecycle cost is 2.5% for acquisition, 1.5% for maintenance and a staggering 96% for power consumption, it is easy to understand how important it is to operate energy efficient electric motors. Investing in highly-efficient electric motors combined with variable speed drives can translate in operational savings as large as 20%. This means that the return of investment of replacing old-fashioned products with energy efficient ones can be a matter of months rather than years.
Generators
If it is true that motors and drives can play a key role in improving energy efficiency and reliability, choosing the right power generation system is also key to ensuring smooth running and reducing maintenance costs in upstream applications. Thus, it is vital to select generators which offer high quality and reliability along with low maintenance and long life, meeting international industry standards such as API 546. Power generation systems should also be robust and able to withstand harsh environmental conditions as well as being suitable for hazardous environments.
Especially when it comes to oilfields that are located in remote desert areas, it is essential to choose generators which are resistant to extreme temperature ranges as well as sandstorms. Formation of sand deposits in the generator need to be prevented and fine sand particles, which can penetrate even the smallest cracks, should be removed immediately to prevent damage. Additionally, in such remote locations, spare parts may not readily available and thus selecting reliable and durable equipment is a top priority.
For example, Wintershall, Germany’s largest global petroleum and natural gas producer, chose WEG’s robust and reliable generators to supply electricity to one of its oilfield facilities in the Libyan Desert. With a capacity of 10.2 MVA, WEG’s synchronous generator runs autonomously and has already totalled more than 20,000 hours in continuous duty. A custom model, the generator took approximately one year to build and one of its special features is air cooling with a top-mounted air/air heat exchanger and external fans. The air filter is designed to prevent sand accumulation, with all sand particles fed out directly through slits. Additionally, the four-pole generator – with IP55 protection rating - is designed for a voltage of 6,000 V at a frequency of 50 Hz and for temperatures of up to 55°C and is painted white to minimise heat absorption.
In another application, WEG supplied six two-pole generators to US energy corporation Chevron for two of its large offshore floating platform projects operating in the Gulf of Mexico. Built according to stringent API 546 standards and certified by American Bureau of Shipping (ABS) on behalf of the US Coast Guard, the generators are driven by GE LM2500 gas turbines and provide the main power onboard the platforms. The 3180 turbo generators are able to develop 30,500 KW and 13,800 volts at 60 Hz each, providing high quality and reliability along with low maintenance and extended service life. They offer brushless excitation, EM Duraguard™ class F VPI insulation, low vibration levels and bracket (end shield) bearing construction.
Conclusion
Ultimately, there is no one-size fits all solution and liaising with experts to determine the most appropriate solution will enable users in the oil and gas industry to gain the most benefits. Energy-efficient and safe motor equipment as well as drives can play a key role in enhancing operational efficiencies and improving bottom-line results in a variety of oil and gas pump and compressor applications where power generation is needed. Yet, generators can also provide a major contribution in terms of ensuring reliability and reducing maintenance costs in the most arduous applications and environment, regardless of the location: from the coldest regions and the deepest oceans of the world, to the hottest deserts.
