Turboexpanders with Active Magnetic Bearings: History and Looking Ahead

Turboexpanders are important machines in industries where gas expansion to generate refrigeration can be utilized such as ethylene processing and natural gas processing. In many turboexpander applications, oil-free support systems are attractive to avoid process contamination, making turboexpanders with active magnetic bearings valuable. On top of eliminating the risk of oil contaminating the industrial process, active magnetic bearings provide benefits such as increased reliability compared with oil bearings and a smaller footprint. In addition to traditional gas and hydrocarbon processing, new opportunities are under investigation for turboexpanders. To enable active magnetic bearings to thrive supporting turboexpanders in these new opportunities, innovation with the new applications in mind will be necessary for turboexpanders with active magnetic bearings to be a competitive option. In this paper, turboexpander history, a few key case studies, and the authors' experience are used to identify areas that benefit from active magnetic bearings development. The recommendations include ideas for the actuator, the auxiliary bearings, the controller, and industrial specifications and standards. Inspiration is derived from technology in public literature and the applicability to turboexpanders and potential applications are highlighted. Ultimately, with cooperation between industry engineers, academic researchers, and other contributors, active magnetic bearings and turboexpanders can continue working together in novel applications.