(17d) Technology and Rotating Contributions / Combinations . TurboExpander - Recompressors

Today's ethylene plants incorporate Turboexpander Systems in order to optimize cryogenic recovery and energy demand. The related residue gas molecular weight and flow rates depend directly upon the selected upstream feedstock gas composition, conversion, and feedrates. Various recent ethylene units have generated residue gas volumetric flow ranges from approximately 100-200%. Hence, the Turboexpander system 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 high pressure co-product). On the other hand, the typical ethane or E/P cracker produces a very high hydrogen content residue gas. Current designs and revamps require wider range of feedstocks, hence corresponding wide range of residue gas composition and quantity.

In order to meet the above demands, the Turboexpander solution must also be flexible. As an overview, we will discuss the typical performance of one- or two-stage Turboexpander solutions for the residue gas expansion and recompression. Key mechanical design recommendations (e.g. magnetic bearings, variable nozzles, multistage control, high head wheels) will be outlined. Based on the demand from the different feedstocks and the industry requirements for feedstock flexibility, we will then discuss the technology and mechanical solutions. This presentation will also include related design improvements that have been successfully utilized in other Turboexpander applications.