Design and Validation of a Redundant Nitrogen Backup System for Gas Compressor Dry Gas Seals in an Oil Refinery Facility

Abstract

This paper presents the design of a nitrogen backup system for dry gas seals in the gas compressor of an FCC unit. The VDI 2221 methodology was applied to structure the design process from problem definition to the technical solution, incorporating the Deming cycle (PDCA) as a basis for future improvement. The theoretical calculation determined a total nitrogen volume of 23.8 m3, distributed in four accumulators of 5.95 m3 each, and MATLAB simulation confirmed that this volume is capable of supplying nitrogen to the dry gas seal for an estimated period of 8 hours in the event of a loss of the main supply. It was also identified that the system could prevent an unplanned shutdown of the FCC unit, evaluated using an indicator of USD 30,500 per hour of avoided downtime, and reduce the risk of damage to the dry gas seal, whose replacement cost may range between USD 40,000 and 70,000. Finally, the automatic and manual operating logic was defined for implementation in a Siemens S7-1200 PLC, allowing the activation of nitrogen backup in the event of a pressure drop and enabling recharge when the main line is restored, ensuring safe system switching.