Tucson Electric Power is replacing two 60-year-old coal-fired units at its largest local plant with 10 natural gas-fired internal combustion engines which average about 19 MW each.
TEP is planning to replace two 1950s-era coal-fired units with the gas engines at its Irvington/H. Wilson Sundt Generating Station. The project is expected to cost about more than $200 million, according to previous news reports.
A press release from the Pima County (Arizona) Department of Environmental Quality indicated it was granting an air permit to TEP allowing the changeover to run its course. The permit, which still has comment and potential appeals periods, would allow the utility to meet peak load needs while continuing to transition its fleet away from coal.
TEP plans to install the gas-fired combustion units in two phases, the first in 2019 and the remainder two years later, according to reports.
Three years ago, TEP allowed the last remaining chunks of coal stacked at H. Wilson Sundt Generating Station to be pulverized and fed into the boiler of Unit 4 for the final time. TEP then announced it was letting the coal inventory deplete to nil at a plant which had shifted back and forth in fuel diversity over the years.
The onetime multi-fuel Unit 4 now burns natural gas, supplemented by renewable landfill gas and a “solar boost” system, according to the company release.
“Eliminating the local use of coal is an important part of our plan to build a cleaner, more diverse energy portfolio,” David G. Hutchens, TEP’s President and Chief Executive Officer, said in a statement at the time. “With the current low cost of natural gas, ending our use of coal at the Sundt Generating Station is a cost-effective way to improve our environmental performance while preserving the reliability of our local electric service.”
The Sundt plant has been here before, in reverse. In 1982, all four gas-fired units were compelled to begin burning coal due to a U.S. Department of Energy edict designed to conserve natural gas during the energy crisis of the late 1970s. The so-called Power Plant and Industrial Fuel Use Act of 1978 was repealed by 1987 although TEP had already converted Unit 4 to coal power.
Fast-forward nearly three decades and TEP forged an agreement with the U.S. Environmental Protection Agency to reduce coal use. In fact, the utility eliminated its coal feed more than two years ahead of the deadline in the 2017 deal with the EPA, according to the company release.
The utility committed to cutting its coal-fired generating capacity by more than 30 percent over five years.
TEP typically fueled Unit 4 with coal when natural gas prices were higher years ago. An April report by the Energy Information Administration, however, that natural gas fuel costs were below coal, while operations of the former were half as expensive as the latter. Gas also has half the carbon emissions of coal, according to reports.
TEP provides electric service to more than 414,000 customers in southern Arizona.
(The latest in gas-fired and coal steam turbine technologies will be featured at the POWER-GEN International conference happening December 4-6 in Orlando.)