Second-tier systems replace legacy controls

With the old system, all five of the rotary cookers and all four of the pot cookers would have went down, Durant said. “This saved us several thousands of dollars that we definitely would have lost had we still been using our previous software.”

Looking back at how much progress McCall Farms has made, Durant sleeps a bit easier at night, "We don't have crashes any more and we feel a lot more confident that the equipment will be running when we come to work in the morning."

New System Ups Power Plant Performance
St Johns River Power Park (See Figure 3 below), located on a 1900-acre site in northeast Jacksonville, Florida, is a coal-fired generating station owned jointly by Jacksonville Electric Authority (JEA) and Florida Power & Light Co (FPL). It has two 640MW units, each with a Foster Wheeler drum boiler and a General Electric tandem compound steam turbine-generator. The plant uses a variety of domestic and foreign coals, as well as 20% petroleum coke.

	FIGURE 3: BETTER COAL BURNING
	Legacy control systems at Units 1 and 2 at St Johns River Power were both upgraded.

St Johns needed to respond faster to automatic dispatch commands. In addition, they wanted to startup faster and burn myriad fuels without having to re-tune the control system. Finally, it wanted to provide its operators and engineers with better tools to improve day-to-day operations. This required replacing legacy control systems with something more modern.

Replacing two complete control systems is a challenge at any plant of this size. Further, it required that planning, contract award, engineering, testing, installation and commissioning be done in about ten months.

A modernization of this scope usually requires extensive up-front planning to develop project guidelines, requirements and vendor specifications. St Johns management initially considered hiring an architect engineer for this work and to oversee the project, but realized the time involved would preclude startup according to their schedule.

They chose instead to have Metso Automation do a thorough study of the existing systems and propose a solution to meet schedule and performance requirements. Based upon the study, Metso Automation and St Johns personnel decided to modernize the plant with two Metso maxDNA automation systems. Metso Automation provided a turn-key solution, taking prime responsibility for design, installation and commissioning of the new control systems and field equipment.

It was agreed to emulate “hard” control schemes that were familiar to plant operators. Further, St Johns wanted Metso Automation to implement the latest generation of Leeds & Northrup’s original D-E-B coordinated control, which assures parallel control of the boiler and steam turbine generator.

Plant operators were included on the project team. They provided extensive input to the design of operating graphics. The team worked together to determine standards, display layouts and functions. Another goal was to make the transition to the new system as smooth as possible. To that end Metso Automation designed the control strategy configuration to match the existing system wherever possible. Plant Manager Paul Smith said, “for the most part, the control sequences, indicators, alarms, operator response sequences, etc. of the new system were designed to mirror what our unit operators have been familiar with for the last ten or twenty years.”

Data base parameters from the existing system were imported into the new maxDNA system and tuning constants were imported to speed automatic operation on startup.

Unit 2 was upgraded first, during the annual Spring outage. The new maxDNA system, which had already arrived, was installed as the older cabinets, cables and consoles were removed. Within four days of startup, Unit 2 was operating in automatic mode and within two weeks the unit was responding to automatic dispatch commands.

While the new system was being installed, plant operators were being trained four hours per day on a maxDNA-based simulator (See Figure 4 below). The plant-specific simulator included all of the startup and shutdown sequences, plus a variety of situations that could lead to a unit trip, from auxiliary failures to process upsets. “The simulator was one of our cornerstones of success with the project and I would strongly recommend including a simulator with any planned upgrade,” says Smith.

FIGURE 4: ON-SCREEN TRAINING
Operators at St. Johns were trained on a simulator supplied by Metso Automation.

The plant burns coal from Western Kentucky, Columbia, other South American countries and several other sources at times. “We blend in 20% petroleum coke,” explains Smith. “Since the moisture content and BTUs are variable, it is important that our control system detect them and initiate smooth proportional corrections without triggering process upsets. We are definitely sold on Metso Automation’s Heat Release algorithm. Our old D-E-B control system used this algorithm and we wanted to duplicate the success we had with it. It allows us to burn a litany of different fuels without having to make constant tuning adjustments to our critical process loops. As a result we have been able to lower costs by purchasing attractively priced random lots of coal and pet-coke on the spot market.”