The J.T. Deely power plant — CPS Energy’s first coal-fired generator — was half-hidden in fog. Its stack stood hundreds of feet tall, red warning lights blinking along its side, but visitors to the Calaveras Lake complex last spring couldn’t see the top because of the clouds.

For 41 years, the 1970s-era facility on San Antonio’s Southeast Side has generated electricity for CPS customers — a lot of electricity.

One megawatt can power about 200 homes on a hot summer day. Running full-tilt, Deely alone, producing 840 megawatts of electricity, can keep the air conditioning running in 168,000 homes.

On New Year’s Eve, however, CPS workers will dump the last load of Wyoming coal into the plant’s furnace and start the long, complicated process of mothballing the facility. The 67 utility employees who’ve kept the plant running, their numbers augmented by contractors, will be assigned to other CPS power generators and operations.

The era of coal plants is ending.

The question for CPS now is: What will it do with the carcass of Deely?

A first for CPS

If the plant’s closing is a sign of coal’s demise — at least as a fuel for generating electricity — Deely’s beginning was part of its rise.

The Deely units were the first of their kind for CPS. Prior to their construction, the city-owned utility built only natural gas-powered plants. But the energy crisis of the 1970s drove the price of natural gas sky high. Coal was cheap by comparison.

Deely began an era of energy diversification for San Antonio, which also included the construction of the South Texas Nuclear Project complex in Matagorda County near the Gulf Coast.

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The trade-off for cheaper power generation was more air pollution. Environmentalists, who fought for decades to close the facility, refer to the plant as “Dirty Deely.”

In 2016, Deely pumped 3 million tons of carbon dioxide, which contributes to global warming, into the atmosphere, according to CPS. It also spewed nearly 1,300 tons of nitrogen oxides, an ingredient of the lung-irritant ozone, and more than 7,600 tons of sulfur dioxide, which can be harmful to asthma sufferers.

“Retiring Deely by the end of 2018 is a boost to cleaning up carbon emissions and ozone precursors like nitrogen oxides in San Antonio, and that deserves a clean-air celebration," said Peter Bella of March for Science-San Antonio, which organizes marches and rallies advocating for evidence-based science.

Deely had been scheduled to be decommissioned by 2033. But then-CPS chief executive Doyle Beneby decided seven years ago to retire the plant by the end of 2018.

Beneby had pushed to expand the utility’s reliance on clean energy — namely, wind- and solar-generated electricity — but his Deely decision had more to do with CPS’ bottom line. It would have cost about $600 million to install scrubbers and other pollution controls to bring the plant into compliance with stricter environmental regulations then looming on the horizon.

Beneby left CPS in 2015. His successor, Paula Gold-Williams, has stuck to the plan — despite President Donald Trump’s rollback of environmental regulations in his attempt to revive the coal industry. On Friday, the administration proposed changes to required cost-benefit analyses that would benefit the owners of coal-burning plants, the New York Times reported.

CPS isn’t alone in moving away from coal. Power company Luminant has shut down three coal-fired plants in Texas this year. Nationwide, 529 coal plants were shuttered between 2007 and 2017 largely because of the expense of meeting tougher air-quality standards — but also because of the low cost of natural gas and the increasing availability of renewables.

This year, CPS coal plants — including Spruce 1 and Spruce 2 units next door to Deely — have generated 18 percent of its electricity, natural gas facilities 46 percent, and wind and solar 22 percent. The South Texas Nuclear Project, which CPS co-owns, produced the rest.

Deely’s retirement will be the first since the utility shut down the last units of the 1950s-era W.B. Tuttle natural gas-fired power plant in 2011. The following year, CPS bought the Rio Nogales natural-gas fired power plant in Seguin for less than $400 million to help offset the expected loss of Deely’s generation.

There’s a chance that CPS’ next power plant could also be fueled by natural gas — and that it could be a resurrected Deely.

Rebirth of a giant?

Deely’s dimensions are enormous.

Its first unit went online in 1977, its sister unit firing up the following year. Combined, they’re made of 26,000 tons of steel, the weight of 62 fully-loaded C-5 Galaxy military transport planes, the largest in the U.S. military. Operating at full capacity, the two units burn more than 500 tons of coal an hour and produce 24 tons of ash, which is then sold as an ingredient in concrete.

Each unit is 160 feet tall and 140 feet deep. Their boilers share a towering concrete-and-steel stack. It would be just 50 feet below the tip of the antenna on the Tower of the Americas if you could set the two structures side by side. Like the Tower of the Americas, the stack has its own elevator.

Nearly 280 miles of boiler tubes and pipes for water, steam and air snake through the units, enough to stretch to Austin and back — twice. Some workers use three-wheeled bikes or gas-powered carts to travel around the complex, inspecting the units to ensure they’re operating properly.

Walking through the ground floor, heavy equipment and bursts of steam screech overhead, although the noise is muffled by protective earplugs.

When Deely goes quiet on Monday, CPS will monitor and preserve the 41-year-old facility — either for a possible rebirth as a natural gas-fired plant or its eventual dismantling. And while the utility figures out its next move, it’ll pick Deely’s insides clean, selling its coal-processing and burning machinery to coal power plants the world over.

“Even if it’s not a system or component we would use in a gas facility - if we made that choice - other people run coal plants. People buy used equipment — there’s a value,” said Benny Ethridge, CPS vice president of power generation. “That’s an asset that we can turn into money through a resale process. We’re going to preserve it all.”

Both Ethridge and Paula Gold-William have raised the possibility of turning Deely into a natural gas plant — and underscoring that it’ll never run on coal again.

“We need much less infrastructure to manage gas,” Ethridge said, “so, basically, (a conversion) involves removal and bypassing of systems, and then the addition of gas and gas controls. It’s not a terribly complex process.”

The utility will have to decide whether to convert Deely or schedule it for dismantling in the next five years. Otherwise, technological advances could threaten how competitive a reworked Deely plant would be in the Texas energy market, Ethridge said.

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Transforming Deely into a gas-fired plant, Ethridge said, would cost CPS “lots of tens of millions (of dollars).”

Current market conditions could be an obstacle to Deely’s potential return as a natural gas plant.

In July, when a heat wave led to record-breaking electricity demand, the average price was $47.20 per megawatt hour, according to the Electric Reliability Council of Texas, or ERCOT, the state’s grid operator. But even though the prices were more than 50 percent higher than in the summer of 2017, power companies have said that at those levels, it wouldn’t make business sense to build new power plants in the ERCOT system.

Meanwhile, natural gas prices spiked in October to nearly five-year highs, briefly doubling the price compared to what producers charged the year before.

CPS Chief Operating Officer Cris Eugster said in March the utility “will not be building a large base-load power plant again,” and Mayor Ron Nirenberg — a member of the utility’s board of trustees — has said he would oppose building any new fossil-fuel power plant, including a gas-fired facility.

All that coal...

On a visit last spring, visitors were shown the coal yard just south of Deely — tall piles that resembled black waves sitting in the middle of a peninsula that juts into Calaveras Lake. The 360-acre site employs 70 people, and long trains — some 150 train cars in length — surround the site. Some of the cars were empty, and others filled with tons of coal, waiting to be unloaded.

In 2017 alone, 337 coal trains dropped off loads at the Calaveras Lake coal pile. Each train can hold over 18,000 tons of coal.

Every carful of coal comes from Wyoming, the top U.S. coal producer.

The coal mound was almost featureless. Each step around the site stirred up a fine, pitch-black dust that coated the bottoms of shoes and stuck to anything it touched. A large bulldozer clanged rhythmically as it rumbled up a coal pile.

The piles would be reduced by half when J.T. Deely closes, Ethridge said. Employment at the coal yard and related facilities, however, will hold steady — CPS still owns more than 1,000 rail cars that will need maintaining. They’ll be used for future coal shipments for the Spruce power plant at Calaveras.

That facility’s older unit is expected to run until at least 2030, while the newer unit, Spruce 2, is expected to remain in operation till at least 2040.

The coal yard also needs maintenance. Francisco Mata, a retired CPS control-room operator, said the mounds of coal need work to keep them from combusting.

If there were air or water in the coal, the mound could smolder and start a fire, Mata said. Large bulldozers and other machines are used to move the coal and keep it compacted.

In other words, there’s still work to be done on the coal pile next to Deely. It’s a little too early to think of it as a burial mound.

Rye Druzin is a San Antonio-based staff writer covering Texas energy. Read him on our free site, mySA.com, and on our subscriber site, ExpressNews.com. | rdruzin@express-news.net | Twitter: @druz_journo