Replacing vintage actuators with new "smart" electric drives eliminates high maintenance costs and offers large fuel savings on coal-fired boilers
Warminster, PA, -- Alabama Power has modernized drives for most major air dampers on two, coal-fired generating units -- 90 drives in all. Installations took place at the company's 25-year old, James H. Miller, Jr. plant near West Jefferson, AL. Each unit has a nominal generating capacity of 720 MW.
After a comprehensive engineering study, Alabama Power decided to purchase Intelligent Contrac(TM) electric actuators from ABB. Added to ABB's actuator line in the 1990's, these digital positioners come in a series of models with torque ratings up to 12,000 ft-lbs.
Functions of the 45 drives on each generator are shown in the diagram, indicated by red bars. A central (DCS) computer sends each drive a specific setpoint signal computed to position each damper for optimum boiler operation and combustion efficiency.
High maintenance levels with the old drives, plus growing scarcity of replacement parts, provided plant engineers with ample economic justification to upgrade the actuators. The new drives offer significantly more precise and responsive damper positioning. According to industry research, improving excess O2 control 0.5% with tighter FD/ID fan damper positioning can result in 0.15% heat rate improvement. For the two Alabama Power boilers, that equates to $350,000/yr in fuel savings. The replacements have also drastically reduced maintenance costs for drives at the plant, which have a 10-year service interval.
A separate Power Electronics Unit, panel-mounted in the photograph, provides the intelligence for the Contrac actuator. Microprocessor-based and configurable, this unit receives a DCS setpoint signal (HART communications protocol) in the range of 4 to 20 mA DC, calling for a correct damper opening for optimum plant operation. It feeds back 4-20 mA signals to the DCS, representing actual actuator positions.
With rapid resonse to the setpoint signal, the electronics unit uses advanced frequency converter technology to independently vary the drive's torque or travel speed as it modulates damper position. The actuator's motor is stepless, and increases or decreases the torque smoothly as it moves the damper to a new position with an accuracy of 0.1%.
Additional functions provided by the electronics unit include logging maintenance and service information as well as predictive diagnostics to warn of critical maintenance needs.
ABB (www.abb.com) is a leader in power and automation technologies that enable utility and industry customers to improve their performance while lowering environmental impact. The ABB Group of companies operates in around 100 countries and employs about 107,000 people.
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