Integrated machinery systems for cryogenic processes consisting of turboexpander, compressor, high-frequency motor and generator with magnetic bearings

The coupling of the power of a turboexpander/compressor unit has a reciprocally negative effect on efficiency, when process conditions deviate from the nominal conditions and, as a consequence, the speed of the unit is variable. The advantage of constant speed, independent of the power scale, can be achieved for conventional designs using coupled systems of turboexpander and compressor by integrating an electrical machine combined with gears. Here the electrical machine, which may be a generator as well as motor, offers the required power balance in a power decoupled arrangement. Such a solution entails a high degree of flexibility and efficiency but with the following drawbacks: the speeds are stable, but they may not be changed and when kept at a stable level the considerable transmission losses in the gears impairs the energy balance. Turboexpander/compressor units with the rotor fixed in its position by active magnetic bearings have been in industrial operation since 1984. In 1989, the development of a prototype for a hybrid unit consisting of a turboexpander and an integral high speed frequency generator both suspended in active magnetic bearings started. The characteristic feature of this design is that the center of the turboexpander shaft forms the rotor of a generator. All design characteristics required for the construction of a high frequency motor are included in the high frequency generator. This paper is the description of the development process which provided a turboexpander/compressor integrated with a high frequency motor/generator and active magnetic bearings for adjustable speed operation.