Apex Controls Specialists (ACS) completed a retrofit “Scrubber” project for a major Midwest power generating station.  This facility is a coal-fired station built in 1963 utilizing a variety of discrete and manual control systems.   With the growing maintenance needs of the existing control system, coupled with the number of personnel needed to operate the varied array of equipment in the different locations, management decided to upgrade the station’s Scrubber control system.  Because ACS had previously upgraded the generating station’s ash handling system, ACS was selected to provide the scrubber controls upgrade.

A limestone scrubbing process is utilized at this facility.  This process crushes limestone and mixes the crushed limestone into a water slurry that is sprayed over the rising stack gases.  The limestone slurry neutralizes the acidity of the gases prior to discharge into the environment.  This process requires several remotely located sub-systems, (i.e. conveyors, ball mill, pumping stations, storage, and mixing stations, etc.).  All of the existing sub-system’s remote devices had been wired into a central walk-in marshaling panel located remotely from the main generating station control room.

The ACS project methodology utilized the existing walk-in marshaling panel as a remote PLC and I/O housing.  The existing wiring from the field was left in place while the wiring feeding signals into the discrete controllers and older relay boards were redirected to the new PLC I/O structure.  The basic components of the system are a GE Series 90-70 used for scrubber control with 488 discrete I/O points and 40 analog points, a GE Series 90-30 used for data archiving, one existing GE Series 90-30 used for ash handling, and one new NT based Cimplicity HMI system all tied together with a new interplant Ethernet.   The data archiving system collects and archives data from the scrubber, fly-ash, turbine, and boiler processes.  The HMI was located in the main generating station control room, bringing all control functions into one control room.

Understanding the sensitivity of operators to new technology and their importance to the success of a retrofit project, ACS worked hard to develop a healthy relationship with the operations staff.  By ACS bringing the operators to our Mt. Vernon facility to help in the design of the HMI control screens, a high level of operator buy-in was established.  This buy-in was instrumental in the project success.

Since ACS built the PLC and I/O sub-panels and developed the HMI control screens all in our Mt. Vernon facility, we were able to assure the customer of system functionality prior to shipment and allow for a more compressed installation time.  This project was viewed by the customer as highly successful.