World Pumps

Bearing installations stand the test of time

In the mid-1990s NAM set out to find the most cost-effective way to extract gas from Europe’s largest natural gas field. This article explains why Waukesha Magnetic Bearings was chosen to provide the magnetic bearings for every motor-compressor string in the project.

Project overview
Groningen, Europe’s largest natural gas field, located in the Netherlands, was discovered in 1959. Production began in 1963 and by the end of the decade, nearly 50% of the field’s reserves were depleted. Nederlandse Aardolie Maatschappij (NAM), a joint venture between Royal Dutch Shell and ExxonMobil, was created in the mid-1990s to find the most cost-effective way to extract gas from the field and extend the life of its reserves, ensuring the field could continue to supply the region.

By upgrading the field’s equipment, including installation of motors and compressors, the field could supply gas to all of the Netherlands, Germany and Belgium for an additional 40 years. The challenge was to provide at least 87% availability and a low total cost of ownership.

Bearing installations 1

Motor during factory test.

Solving the challenge
When Waukesha Magnetic Bearings (WMB) joined the project, it utilized its latest technology expertise to solve a problem that other industry leaders had deemed impossible due to the wide speed range involving several critical rotor speeds. In fact, it is claimed that NAM was told “It can’t be done” by the other manufacturers it approached.

WMB partnered with Siemens to install three radial active magnetic bearings for the motor, two radial and one thrust active magnetic bearing on the compressor, and a digital controller with analog amplifiers. The system allows for remote monitoring and diagnostics and frequent fully automated remote start-ups. Robust bushing-style auxiliary bearings were selected for their high investment protection and ability to provide remote condition observability.

The controller and auxiliary bearings were fully qualified before product delivery on WMB’s magnetic bearing and auxiliary bearing test rig. Featuring a rotor mass of 1.5 tons, the test rig is comparable in scale to the large turbomachinery typically used in the oil & gas industry.

In addition to handling the wide compressor speed range with minimal vibration and noise, the AMB system met user requirements for high reliability, high energy efficiency, low maintenance and low investment cost. Using magnetic bearings instead of traditional fluid film bearings eliminated the need for additional building construction to house a lubrication system. This reduced costs and provided a simpler, cleaner, more efficient design to lessen the environmental footprint.

There are a total of 20 magnetic bearing-equipped motor-compressor strings at the Groningen field, and magnetic bearings from WMB were installed in each of them. The machines varied significantly in the number of stages, hence the dynamics of the rotor, but WMB was able to adjust for the different rotor dynamics through soft-ware changes in the controllers.

Bearing installations 1

Waukesha Magnetic Bearings test rig, the largest test rig of its type in the world.

Performance counts
NAM’s original goal was to provide 87% availability with the lowest total cost of ownership. Analyzing the results after 17 years, the magnetic bearings from WMB exceeded expectations, providing over 99.9% availability and an investment cost savings of 35%, all while saving on energy costs. “In the end it is the performance that counts and when I look at the performance, it is amazing,” said Wim de Groot, retired rotating equipment engineer, NAM GLT.

Bearing installations 3

NAM motor (right) and compressor bundle (left) being installed at the Groningen site.

Versatility with magnetic bearings
Magnetic bearing systems are able to accommodate a wide variety of rotating equipment, so applications other than large natural gas fields can reap the benefits of magnetic bearing technology. Magnetic bearings have achieved high availability, cost savings and environmentally responsible operation in steam turbines, generators, turbo-expanders, pumps, blowers, compressors and motors in natural gas production and pipelines, oil fields, the chemical industry, the refrigeration industry and more.