Abstract

In an effort to improve the reliability of high pressure centrifugalcompression equipment. NOVA, AN ALBERTA CORPORATION began a program in theearly 1970's to find alternatives to lube and seal oil systems. This programwas successful, resulting in the application, testing and utilization ofmechanical dry gas seals and active magnetic bearings in NOVA's gastransmission system.

This paper covers the development history of dry seals and magnetic bearingsfor centrifugal compressors in high pressure natural gas service. The operatingprinciples, experiences and advantages of mechanical dry seals and activemagnetic bearings are also discussed.

HISTORY

NOVA, AN ALBERTA CORPORATION has over 25 years of experience with pipeline andcompressor equipment associated with the planning, design, construction, operation and maintenance of a l4,OOO kilometre natural gas transportationsystem. This system includes 38 compressor stations totalling over 406 MW, morethan 750 receipt and delivery stations and handles about 75% of marketed Canadian natural gas production.

Centrifugal compressors inherently present operating problems associated withmaintenance, reliability, and safety. As an operator of 63 gas turbinecompressor unit, NOVA has always been concerned with these operating problems.Internal studies conducted in the early 1970's indicated that over 80% of thedowntime on NOVA's centrifugal compressor's was related to problems with theseal or lube oil systems. This prompted NOVA to initiate a program aimed at theelimination o~ these oil systems.

In 1976, NOVA entered into a joint development program for a mechanical dry gasseal with John Crane Houdaille Inc. By 1978, a dry seal was available whichreliably replaced the conventional seal oil system in centrifugalcompressors.

Dry seal development and enhancement continues. NOVA is also working withPacific Weitz, a German seal manufacturer, on the application of an alternativedesign of a mechanical dry seal.

In 1982, NOVA became aware of a new device developed by a French manufacturer(Sociate de Mecanique Magnetique - S2M) which could be the key to completelyeliminating the oil system in centrifugal compressors. This device was anactive magnetic bearing system. A prototype was installed in one of NOVA'soperating compressors which had already been retrofitted with mechanical dryseals. NOVA was pleased with the results on the prototype installation, and hasbeen engaged in a product enhancement and retrofit program since thattime.

The first magnetic bearing installation took place in October.,1985. It yieldedthe world's first oil free mainline compressor unit. This unit is an Ingersoll Rand COP 230, 15,000 HP ISO compressor with a 3,500 pound shaft and a 12,000pound thrust load. There are currently over 5,000 operating hours on thiscombined mechanical seal/magnetic bearing installation.

MECHANICAL DRY GAS SEAL OPERATING PRINCIPLE

The mechanical day seal design is based on technology originally developed forair bearings. The application of this technology to sales has resulted in astudy and versatile design.

The seal is comprised of two sealing rings. One ring with spiral grooves etchedin the seal face rotates with the shaft.

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