C340 Tail Gas Compressor


Implement a safety control system using Triconex controller and Citect HMI to control a hydrogen screw compressor. The compressor was designed as an upgrade to the tail gas system, to run in the refinery’s hydro-cracker unit for the production of off-road low sulfur diesel.

  • Hydrogen gas screw compressor, lube oil system and seal gas system.
  • Triconex Trident Triple Modular Redundant (TMR) controller, with redundant communication modules.
  • Bently Nevada 3500 Series Vibration and Temperature Monitoring System.
  • Two redundant Citect HMI v5.41 nodes to communicate with equipment processors over Ethernet via Triconex DDE Server v4.0.
  • One Microsoft Access database for data storage.
  • One free standing NEMA 4X stainless steel purge cabinet to house equipment.

A Triconex Trident controller was employed as the controls platform for the control system and Emergency Shutdown System (ESD). The control features include: alarm processing, shutdown management, startup sequencing, lube oil system control, and seal gas system control.

The system is designed to be configured via the Citect HMI (Human Machine Interface) in order to limit custom programming. All control and setup parameters (analog ranges, setpoints, etc.) are entered through the Citect HMI. The Citect HMI allows an operator with the proper password clearance to modify virtually all control parameters without the need to modify logic in the controller. This powerful tool enables efficient commissioning and start-up and will allow future modifications to be handled with limited down time.

The Citect HMI functionality also allows for custom trending and logging (field configurable) of user defined events to aid in long term troubleshooting and optimization. Additionally, a Bently Nevada Vibration and Temperature Monitoring System interfaces with the Citect HMI via Modbus over TCPIP, and shutdown data is interfaced with the Trident controller.

The system incorporates an Access database to store all control parameters. The Trident controller restores the initial value assigned to variable tags such as setpoints, instrument ranges and loop tuning parameters on the first scan after a reboot. An operator with the correct security access can edit the live values in the PLC; these changes are also saved to the Access database as stored data. The end user does not have the ability to edit and download changes to the Trident controller initial value property. Therefore, any online edits would be lost on reboot of the processor. The Citect HMI uses a SQL/ODBC connection to download the stored data to the Trident. The live data in the controller can also be uploaded into the database.

Full system documentation and testing was provided for this system including a Functional Specification, Factory Acceptance Test, and Site Acceptance Test. Onsite commissioning support was also provided


The control system was staged in our facility and tested prior to shipment to the field. ACE continued working as part of the project team during the installation and start up of the compressor station to help ensure a smooth system commissioning.