Refrigeration Compressor Dry Gas Seal Panel Vent Header Design Consideration

LyondellBasell’s Corpus Christi Olefins plant recently underwent a debottleneck which included a new gas seal package for the refrigeration compressors. As is typical, the primary vent (normally >95% nitrogen) was routed to the flare header. Issues with potential back pressure during heavy flaring events were identified early in the design process, so the decision was made to route a bypass to atmosphere with a rupture disk used for containment. During the subsequent plant startup, high backpressure occurred but the rupture disk did not rupture per design. Inspection revealed a partially burst disk that held backpressure yet was unable to fully burst. Investigation and modeling revealed a unique design requirement for low pressure rupture disks. A modified rupture disk configuration, testing of the configuration and the final solution for the dry gas seal panel will be reviewed. We will also discuss the hazards associated with gas seal pressure reversal and methods of monitoring.