Machines that recover work from the expansion of pressurized process gases — and, frequently, the main product is not the work but the cold: the temperature drop of the near-isentropic expansion is the heart of cryogenic processes (air separation, natural gas processing, LNG).
Usual types
(handbooks per type in Phase 1)
- Turboexpander — high-speed radial, usually in an expander-compressor arrangement (API 617 Part 4): class TE of ISO 14224:2016;
- Piston expander — reciprocating volumetric, small cryogenic capacities;
- Screw expander — rotary volumetric: waste-heat recovery and ORC cycles, tolerates wet vapor.
Reliability: bearings (magnetic or gas in turboexpanders), liquid/hydrate formation across the expansion and axial thrust balance dominate; start-up and trip are the critical transients.