Supercritical Ethylene – Pump Versus Compressor

Some ethylene plants require the product delivery at supercritical conditions. This can be achieved in two ways: Pumping of liquid ethylene or compression of vapour ethylene.

The trans-critical product compression can be combined with the open loop subcritical refrigeration cycle resulting in one ethylene compressor serving multiple tasks. However, the combination of the different tasks in one machine results in fundamental design issues particularly induced by physical properties of trans-critical ethylene.

This paper outlines the principal compressor design features to be considered, describes the selection of an adequate control scheme and finally addresses the verification process for transient operation to assure highest level of system safety and reliability.

The process design for trans-critical ethylene product compression is further compared to pumping of liquid ethylene considering costs and other constraints including operability, possible liquefaction requirements and intermediate BL pressure specifications.