What Works: New control system implementation reduces response time without outages

The Ripon Cogeneration Plant (Ripon Cogen) in Ripon, California, partnered with Maverick Technologies to perform a DCS migration of an existing proprietary Westinghouse WDPF BOP control system to a non-proprietary control system without any scheduled outage of the facility. A human-machine interface (HMI) for systems outside of the BOP was to be incorporated into the new control system.

The BOP control system is a complex and interdependent control system that involves all of the related areas within the overall Ripon Cogen vicinity including HRSG control, gas compressor, ammonia plant, chiller, and water treatment. This was an entirely brownfield project with all of the inherent problems and constraints: zero impact to production, limited number of shutdown opportunities, limited and unreliable documentation, older and unreliable equipment, physical space limitations, and internal resources with competing production priorities.

Performing logic and wiring conversions at the same time is considered to be an excessive risk. The phased implementation installed and tested the PlantPAx system using simulation software. The customer needed a BOP DCS migration for the following reasons:

decreasing availability of hardware
serviceability issues
proprietary networks
proprietary operating system with no vendor support
failed historian server
no automated report generation
downtime issues.

Maverick’s Westinghouse WDPF engineers analyzed the existing system and developed a functional specification. After taking a fresh look at plant operations with Ripon Cogeneration’s operation and maintenance staff, Maverick developed a new enhanced functional specification for the BOP DCS.

PlantPAx process objects were selected for the BOP development of additional functionality. Once the new applications were proven to function as desired, the Westinghouse WPDF control system will be replaced by the PlantPAx during the shutdown period. The Wonderware HMC applications for the turbine control, chiller, and distillation are also being migrated into the PlantPAx system.

Maverick's engineers analyzed the existing DCS hardware system and developed a low-risk hardware replacement plan. Westinghouse WDPF redundant processor drops were replaced with redundant ControlLogix L73 processors using device level ring (DLR) for I/O communications. Existing Westinghouse Numa-Logic I/O was replaced with 1756 ControlLogix.

The BOP includes the following units:

heat recovery steam generator(HRSG)
de-aerator and feed water system
gas compressor system
compressed air system
water treatment plant.

Non-BOP systems migrated into the PlantPAx DCS include the following units:

turbine control
water distiller plant
ammonia chiller plant.

The new DCS system architecture is as follows:

Westinghouse WDPF drops 1 and 2 were replaced by a redundant Allen-Bradley PlantPAx L73 ControlLogix processor.
Westinghouse WDPF Drop 3 with seven I/O points were eliminated, and the I/O moved to new Drop 1 Allen-Bradley PlantPAx L73 ControlLogix processor.
25% I/O chassis expansion capacity has been provided.
Communications will be redundant Ethernet/IP via DLR for remote I/O.
All analog input and output are HART protocol enabled for enhanced troubleshooting and maintenance of plant process instruments.
FactoryTalk Historian Site Edition (SE) is provided for historical logging with a FactoryTalk enabled OSI PI historical engine (1000 Tag).
FactoryTalk VantagePoint EMI is being provided for trend visualization, production report visualization, and four additional customer-specified reports (total of five reports will be provided).
FactoryTalk View SE redundant HMI servers and screens will help to visualize and control the cogeneration balance of plant.
New control system includes primary domain controller, engineering workstation/historical server, FT VantagePoint reporting, primary HMI server, backup HMI server and two operator workstations.

Metrics that have improved as a result of this DCS project include:

PlantPAx DCS power requirements dropped by 50% compared to the legacy DCS. It was an unexpected positive.
Response to any problem with the BOP DCS went from weeks to 15 minutes with the PlantPAx DCS.
Operators are able to respond to process upsets much more quickly due to the additional information provided by the new DCS system.

Ripon Cogen experienced no unscheduled outages during the migration process, and the facility started up on schedule. The facility ramped to full power on the first day of operation. There have been fewer outages due to the enhanced control and speed of the control system. Future projects with Ripon Cogen include continued plant automation and report improvements.

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