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Xcel Energy's $1.3-billion 750-megawatt Comanche 3 coal-fired unit, shown here in a Jan. 26, 2020, photo, went into operation in 2010. It's the state's largest coal-burning power plant. (Mike Sweeney, Special to The Colorado Sun)

The Colorado Public Utilities Commission on Wednesday launched an investigation into Xcel Energy’s problem-plagued Comanche 3 coal-fired power plant, which has had chronic breakdowns requiring millions of dollars in repairs.

The $1.3 billion plant near Pueblo has been out of service since mid-January. It was idled between January and June for repairs, Xcel said. When the company tried to restart the plant in June, the loss of lubricating oil in a pump caused major damage, keeping the plant off line since. It may not be returned to service this year.

The investigation, approved at the PUC’s weekly meeting, will focus on what has caused the problems, how the unit compares to similar coal-fired plants and the cost to Xcel customers, PUC Deputy Director Gene Camp said.

“The plant has been a dog as far as operations and there has been a pot of capital going in to fix Comanche,” said Joseph Pereira, deputy director of the Colorado Office of Consumer Counsel. “The question is, is this plant viable?”

In a statement, Xcel Energy said “the unit experienced an operating issue as work was being done to bring it back online from a maintenance and repair outage earlier in the year.  Various resources and vendors continue to work to make the repairs needed.”

While no direct action will be taken as a result of the investigation, the findings could be used in evaluating future rate cases and the company’s clean energy and resource plans.

“What we are doing is a bit of public and private review of the utility’s performance,” PUC Chairman Jeffrey Ackermann said.

Comanche 3 is one of the last coal-fired power plants to be built in the West and was outfitted with cleaner burning, supercritical pulverized coal technology and top-of-the-line pollution controls.

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The 750-megawatt unit went into operation on May 14, 2010, about six months behind schedule, and from that date on customers have been paying for the plant.

The unit was plagued by a string of operational and mechanical woes from the beginning.

The initial delay was caused by leaking steam tubes in the boiler, the result of poor welds done by contractor Alstom Power in its workshop in the Czech Republic. Then a damaged boiler feed pump added to the delay.

When the unit was started, it emitted a high-pitched noise that distressed neighbors as far as 5 miles away. In its first full year of operation, 2011, the plant, still dogged by leaking pipes, ran at half its capacity.

The metal alloy Alstom had used in the tubes in the unit’s superheater, it turned out, was prone to exfoliation, where scale builds up in the tubes blocking the flow of steam. That creates a potential for short-term failures and outages.

Comanche 3 suffered 15 outages and was down for 79 days to install a new superheater. In 2015, Xcel replaced all the alloy tubes with stainless steel ones at a cost of $11.7 million.

Xcel sought to recoup that money from customers. The PUC initially rejected the request, but in May the commission “with reluctance” approved adding it to the rates customers pay.

A month later, the severe damage to the pump shutdown the unit, which was not available during peak summer demand months.  Xcel on Oct. 8 delivered a report to the PUC on the causes of the June accident.

Camp said that the investigation will develop a complete chronology of outages. It will look at the cost of replacement power during the outages.

The study will look at what Xcel said the operation and maintenance costs would be when it applied for approval of the plant and compare them to actual costs.

To get an idea of what it costs ratepayers to get electricity from Comanche 3, the study will take all the costs of the plant and divide that by all the megawatt-hours of electricity  the unit has produced. This gives a dollar cost per megawatt-hour. 

The commissioners said the report would also be useful in evaluating the plant in relation to the state’s goal for reducing greenhouse gas emissions. Comanche 3 is the largest single source of carbon dioxide emissions in Colorado – nearly 5 million tons a year between 2017 and 2019.

“Colorado leaders seeking to reduce emissions have to scrutinize the largest emitter in the state,” said Anna McDevitt, a representative of the Sierra Club’s Beyond Coal Campaign.

“The commission’s job is to make sure Coloradans have access to reliable and affordable electricity and when it comes to Comanche 3 they have neither reliable nor affordable electricity,” McDevitt said.

CORRECTION: This story was updated at noon on Oct. 30, 2020, to update how long Comanche 3 has been out of service. The coal-fired plant was taken offline in January for repairs. When Xcel Energy attempted to restart the plant in June, the loss of lubricating oil in a pump caused major damage and the plant may not return to service this year.

Special to The Colorado Sun Twitter: @bymarkjaffe