Turboexpander labyrinth seal

A turboexpander having a labyrinth seal for reducing gas losses around a rotating shaft, comprising:

• a rotating shaft defining a longitudinal axis of rotation and having a series of external teeth thereon along an axial segment;
• a compressor wheel fixed to a first end of the shaft;
• a bearing housing having bearings that supports the shaft, the axial segment having teeth being located between the bearings and compressor wheel;
• and
• a stationary labyrinth seal surrounding the axial segment of the shaft having teeth, the labyrinth seal having an inner lumen in contact with the teeth and having a plurality of sets of inner openings in fluid communication with the axial segment, each set of inner openings surrounding the shaft at a particular axial position, wherein the sets of openings extend in series from a first set of inner openings at a high pressure end of the axial segment adjacent the compressor wheel to a last set of inner openings at a low pressure end of the axial segment adjacent the bearings, each set of inner openings leading to a flow channel common to those inner openings, and each flow channel being ported to a location separate from the other flow channels, wherein
• high pressure gas at the high pressure end of the axial segment that leaks between the inner lumen of the labyrinth seal and the teeth reaches the first set of inner openings whereby the high pressure gas is ported to a first recovery location, and medium pressure gas that leaks between the inner lumen of the labyrinth seal and the teeth to reach a second set of inner openings in series with the first set of inner openings is ported to a second recovery location, with the process continuing to the last set of inner openings whereby low pressure gas is ported to the atmosphere.