Optimizing Turboexpander Selection: Guidelines for Process Design and Operation

Cryogenic turboexpanders have been used in the separation section of ethylene processes since the 1960's to produce the low temperatures that drive efficient separation. Today, turboexpanders are used in new world scale plants as well as for debottlenecking duty in existing plants. It is useful to understand the current state-of-the-art in turboexpander performance, installation, and operation. Advantages and limitations of magnetic bearing technology should be considered for any turboexpander in ethylene plant service. Multi-stage designs (up to four in series) allow efficient cold production from high enthalpy drop duty. Two million tpa production can be handled in a single turboexpander processing train. Auxiliary systems must be designed for high reliability, including seal gas systems, instrumentation, control, and monitoring systems. Process integration considerations include start-up, normal operation, shutdown, and servicing provisions. Availability over 99% is commonly achieved in modern installations.