Today’s ethylene plants incorporate Turboexpander Systems to optimize cryogenicrecovery and reduce the energy demand. The molecular weight and flow rate of theresidue gas depend directly on the selected upstream feedstock gas composition,conversion, and feedrates. Various recent ethylene units have generated residue gasvolumetric flow ranges from approximately 100-200%. Hence, the Turboexpandersystem is designed and manufactured accordingly.As we are aware, the typical naphtha cracker produces a methane rich residue gas(bulk hydrogen is recovered, treated, and delivered as a high pressure co-product). Onthe other hand, the typical ethane or E/P cracker produces a very high hydrogencontent residue gas. Current designs and revamps require a wider range of feedstocks,and hence, a correspondingly wide range of residue gas composition and quantity.In order to meet the above demands, the Turboexpander solution must be flexible. Asan overview, we will discuss the typical performance of one- and two-stageTurboexpander solutions for the expansion and recompression of the residue gas. Keymechanical design recommendations (e.g., magnetic bearings, variable nozzles,multistage control, high head wheels) will be outlined. Based on the demand from thedifferent feedstocks and the industry requirements for feedstock flexibility, we will thendiscuss the technology and mechanical solutions. This presentation will also includerelated design improvements that have been successfully utilized in otherTurboexpander applications.
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