Arizona Electric Power Cooperative
Arizona Electric Power Cooperative, Inc. (AEPCO), is a G&T (generation and transmission) cooperative which owns and operates the Apache Generating Station located about 30 miles east of Benson, Arizona, where its corporate offices are located. The station consists of coal-fired Steam Units 2 and 3, each of which produces 195 megawatts of power for a combined 390 MW, Steam Unit 1 and Gas Turbine Unit 1 operating in combined cycle with a combined output of 86 megawatts, and Gas Turbines 2 (20 MW) and 3 (65 MW) together rated at 85 megawatts. Add the LM6000 PC gas turbine rated at 41 megawatts which went online in 2002 and Apache Generating Station has a total (gross rated) output of 602 MW. Between 1991 and 1993 Steam Units 2 and 3 were converted to dual fuel capability and can burn either coal or natural gas.
Aerial view of the Apache Station
AEPCO celebrated its fiftieth anniversary in the spring of 2011, having been created in 1961 by four of its six Class-A Member systems. The founding Arizona cooperatives include Duncan Valley Electric Cooperative, Inc. in Duncan, Graham County Electric Cooperative, Inc. in Pima, Sulphur Springs Valley Electric Cooperative, Inc. in Willcox and Trico Electric Cooperative, Inc. in Marana. Mohave Electric Cooperative, Inc. in Bullhead City joined in 1973 and Anza Electric Cooperative, Inc. in Anza, California has been a Class-A member since 1979.
Providing power to more than 144,000 customers in Arizona, California and New Mexico, AEPCO and its members serve customers in nine Arizona counties (Cochise, Coconino, Graham, Greenlee, Mohave, Pima, Pinal, Santa Cruz and Yavapai), one county in California (Riverside) and two counties in New Mexico (Hidalgo and Grant).
In 1999, AEPCO restructured into three legally separate cooperatives: AEPCO, Sierra Southwest Cooperative Services, Inc., (Sierra), and Southwest Transmission Cooperative, Inc. (SWTC). Under this restructuring, AEPCO retained the power generation function, SWTC became the transmission and power delivery cooperative, and Sierra became the staffing and service provider, and collectively they are known as Arizona’s G&T Cooperatives.
AEPCO and Arizona’s G&T Cooperatives have a unique relationship to the land where the Apache generating station is located. Their employees created the Apache Station Wildlife Area where, through discharge of well water to the Willcox Playa, approximately 100 acres of wetlands provide a haven for Sandhill Cranes, water birds, and other endemic wildlife. Thousands of Sandhill Cranes roost in the Sulphur Springs Valley during the winter, and Apache Station encourages birders to come the Wildlife Area to view the Cranes and other birds during the roosting season and during the annual Wings over Willcox festival.
AEPCO demonstrates its commitment to the environment through the SunWatts program whereby AEPCO and certain members together promote the use of renewable resources by providing member/customers in Arizona with rebates on qualifying renewable energy systems depending on the type of unit(s) installed. AEPCO has a 25 kilowatt photovoltaic system located at its Benson headquarters and has generated nearly 100,000 kilowatt hours of energy.
Most recent figures show the Apache Generating Station is one of the most reliable coal-burning generators in the country, based on the December 2008 Industry Report released by Electric Light & Power using data for 2007. The report shows the 96.3 percent capacity factor placed it fourth in the nation on a list of the top 20 most reliable coal generators.
TOUCHSTONE ENERGY: As one of a handful of cooperatives across the nation involved in creating the Touchstone Energy brand, AEPCO has served as a regional partner representing the Touchstone Energy members throughout Arizona in addition to Anza Electric Cooperative, Inc. in California.
ORP Probe: Apache Station was the site at which Nalco developed it’s “at-temperature oxidation/reduction potential (ORP) probe”. This ORP probe allows a power station to measure the corrosion potential of the feedwater before it enters the boilers. Monitoring of ORP allows the control system to accurately feed chemicals to the feedwater to minimize migration of copper from the feedwater heaters into the boiler, secondly to also minimize iron oxidation of boiler components. A third benefit is that silica in the water is properly controlled, resulting in reduced unit startup times after a unit trip or hot startup. Apache Station personnel were intimately involved in the day-to-day monitoring and evaluation of the ORP system.
Cooling Tower Replacement: AEPCO recently replaced its two nine-cell Marley wooden cooling towers. Construction was done two cells at a time. The wooden structure from the cells was demolished, and reconstructed with the new fiberglass members. The final step was to install fill, louvers, drift eliminators and exterior casing. The year-long process to rebuild the cooling towers for Steam Units 2 and 3 was mostly complete in December of 2008.
AEPCO Fast Facts
- Total generating capacity: (combined gross rated) 602 MW.
AEPCO/Coal-fired Steam Units 2 and 3
- Electric cable: 3,400,000′ (644 miles)
- Concrete: 43,394 cu. yds. (Equal to 450 miles of sidewalk)
- Coal storage: 160,000 tons (40-day supply)
- Turbine-generators: Made by GE, each unit capable of producing 194,700 KVA
- Steam superheated to 1,000 F
- 3,600 rpm
- 2,400 PSIG
Stack
- Height: 400′
- Width: 69′
- Boilers:Fuel requirements up to 98 tons of coal/hour; up to 48 MCF natural gas/hour per each unit
- Steam generation: 1,355,000 lbs/hour at 1,005 F
- Pressure: 2,620 PSIG at superheater outlet
- Height: 192′
- Structural steel in each boiler unit: 2,400 tons
- Total Class-A member cooperatives: six
Total Employees
- Collectively Arizona’s G&T Cooperatives (which includes AEPCO) employ 280 people
