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DCS Upgrade & Expansion
The existing DCS was a Metso Automation system installed in 1996 as part of a controls' modernization project. It had nine operator stations (CRT) and an engineer's station for each unit, with a data highway connecting the HMI with 19 pairs of redundant controllers (DPUs). Most of the DCS equipment was centrally located in the control complex. Before the project, there were approximately 3,500 hardwired I/O points per unit, plus six data links to other plant I&C systems. At the time of the controls' modernization, the plant was converted to all-soft control using DCS graphic displays as the primary operator interface for as much plant equipment as possible.
This project upgraded the HMI equipment to Metso's maxDNA, including contemporary MS Windows based workstations for both operator and engineer stations. The older operator CRTs and computers were replaced with maxVUE operator workstations. Additionally, two new maxVUE operator workstations were installed in the Control Room, and three were installed at satellite locations at the plant site. Three pairs of redundant controllers were added to the system to support the SCR, the ID Booster Fans, and the Ammonia Processing Facility.
Redundant controllers were added to a new satellite location at the ammonia processing facility 1,450 feet away from the main control complex. The new maxSTATION and controllers with their 150 I/O points were tied into the existing DCS by extending the 100 Mbps dual redundant fiber optic maxNET to the ammonia processing facility.
Remote I/O at the SCR 1,050 feet away, and ID Booster Fans 1,300 feet away, extended the DCS reach throughout the plant site. There are about 260 I/O points at the ID Fan and 410 I/O points at the SCR, with room for future expansion. I/O Bus Extender Modules (BEMs) and redundant fiber optic cables were used to connect the remote I/O to the new controllers in the main control complex. Remote I/O saved time and money as it reduced the amount of instrument wiring that needed to be run to these locations. maxNET connections at the SCR and ID fan control allows an engineer or technician to plug in a laptop computer running the DCS engineering software to routinely verify instrument calibration at the process.
Other features added to the DCS include serial links to the ID Fan Vibration Monitoring System and Dry Fly Ash and Precipitator controls. A new OPC interface connects the new HMI to the plant's existing performance monitoring system and various plant information systems. The DCS was connected to PPL's wide area network to allow engineers access to the DCS from the central engineering office 50 miles away.
The new DCS equipment was staged at Metso Automation's Lansdale, Pa., factory for integrated testing with the complete database as well as the graphics for both the old and new parts of the DCS. The operators designed the new displays and Metso configured them. Each of the displays built for Unit 2 were replicated for use on Unit 1, linked to the database via the process hierarchy.
Plant Control
The twin reactors process control loops ranged from single-loop control to complex three-element, dual mode, control of ammonia flow. The 10 most critical loops are:
Dilution Air Temperature (A side, B side)
Dilution Air Flow (A side, B side)
Seal Air Temperature (A side, B side)
Seal Air Pressure (A side, B side)
Ammonia Flow control (A side, B side)
