The Trump administration’s Affordable Clean Energy (ACE) rule announced August 21 calls for coal-fired power plants to meet state-designed performance standards, most notably focused on increases in heat rate and overall efficiency for individual generating stations.
Energy experts speaking at the MEGA Symposium in Baltimore, Maryland, on August 22 agreed it’s a goal worth pursuing. They also said it will be difficult to achieve due to the evolving nature of U.S. power generation.
The rise of natural gas, which today accounts for the largest percentage of the nation’s electricity production, along with the addition of renewable sources such as wind and solar power to the grid, has lessened the amount of coal-fired generation across the country. It has decreased coal’s capacity factor—the average power generated by a particular energy source, divided by the rated peak power of that source—to just above 50%, behind natural gas, and well below the 73% capacity factor for coal as recently as 2008, according to the U.S. Energy Information Administration.
It’s a trend the coal industry wants to slow. And that presents a major challenge for coal plant operators.
“The capacity factor for coal plants falls in direct correlation with the fall in the price of natural gas,” said Tony Licata, a partner with Yonkers, New York-based Licata Energy & Environmental Consultants, who noted the rise in gas-fired generation coincided with low prices for natural gas and increased regulation, such as the Mercury and Air Toxics Standards rule, on the U.S. coal fleet. “A decrease in plant efficiency is in direct correlation to a drop in the capacity factor. EPA [Environmental Protection Agency] wants to increase heat-rate efficiency, but they’re not going to get that with drops in capacity factors.”
“Only gas and coal can make up for reliability and intermittency on the grid,” said Sheila Glesmann of Emission Strategies Inc., a division of Colorado-based ADA-ES. Glesmann moderated the panel on the “Integration of Diverse Generation Sources and Effects of Variable Load on Pollution Control Equipment” and noted the importance of fossil fuel-fired generation to backup wind and solar power. But Licata said that even in that instance gas has an advantage, as gas turbines can ramp quickly to provide power during periods of peak demand, as he showed a slide of how the use of gas turbines increases as wind power declines.
Small-Scale Modular Coal Units
Angelos Kokkinos, director of Advanced Fossil Technology Systems at the U.S. Department of Energy (DOE), said his office’s research and development (R&D) is focused on “advancing small-scale modular coal plants of the future, which are highly efficient and flexible, with near-zero emissions. They must be small, nimble units located close to the source of renewable energy. Renewable energy is not a fad, it’s not going away. We have to adapt to that. We need coal plants that are available all the time [to provide power].”
Kokkinos said those plants must be able to provide backup power at times of peak demand, and help balance the grid as more intermittent, renewable sources of power come online. The balancing act is among the challenges faced by coal plant operators.
“Cycling costs are pretty high,” said Doug Campbell, senior technical advisor for Nova Scotia Power, who said cycling coal units has negative impacts both financially and environmentally.
Campbell cited his utility’s Lingan Generating Station, which has four 150-MW coal-fired units. He noted that a drop from full load to minimum load (about 70 MW) in an individual unit results in a heat rate increase from 10,300 Btu/kWh to 11,400 Btu/kWh, or about a 10% rise. He said that change also results in a 10% increase in fuel cost, and a 10% increase in greenhouse gas emissions.
“The NOxintensity increases per megawatt,” Campbell said. “SOxstays the same, and CO2intensity increases as a function of heat rate. There are higher per-megawatt emissions at lower load. Total emissions are reduced by increased use of renewables,” but as he and the other panelists noted, coal plants are not designed to ramp up and down as a backup or peaking source of power.
“More cycling leads to less-economic units, lower efficiency, and more stress on equipment, shortening expected plant life,” said Kokkinos. “[Coal] plants have dropped from an 80% capacity factor to about 50%, increasing time spent in cycling mode.”
“Coal-fired power plants are being challenged to run at lower loads, at lower temperatures,” said Mike Mattes, president and CEO of Cormetech, a selective catalytic reduction (SCR) catalyst manufacturer and management provider. “Low load operation typically has a negative impact on SCR performance.”
Mattes likened a coal plant to a Mack truck, designed to operate full-out at a constant speed. “Now we’re asking plants to run like Ferraris,” he said.
DOE Touts Coal Program
Kokkinos pointed to his DOE office’s Advanced Coal Energy program—“The White House stole my acronym,” he joked, referring to the ACE rule—as critical for the future of coal-fired plants.
“We are all about improving the existing and future coal fleet,” Kokkinos said. “We need to improve the cost of carbon capture utilization and sequestration (CCUS) technology. The cost of carbon capture has dropped from about $100 per ton to about $40 a ton, and our goal is to get to about $30 a ton.” Kokkinos said costs at the Petra Nova plant in Texas, the world’s largest post-combustion carbon capture system and located at NRG’s W.A. Parish coal-fired plant near Houston, are at about $60/ton. Petra Nova, honored as POWER’s Plant of the Year in 2017, captured more than 1 million tons of CO2last year for use in enhanced oil recovery.
Kokkinos said the current coal fleet “operates at about 31% or 32% efficiency. At 40% efficiency, we would reduce emissions by 25% to 30%.” As part of improving efficiency, “we need to develop systems and controls that will help us predict [when] maintenance [is] needed. Our emphasis in on ‘predictive fail,’ coming up with sensors that help with [predictive maintenance]. We need to come up with sensors that compile data for operators so they can help units run at maximum efficiency,” and with limited downtime.
Asked how a new regulatory regime is part of the picture, Kokkinos didn’t hesitate with his answer.
“All of our R&D cannot happen without some reform of New Source Review (NSR),” he said, referring to the EPA’s permitting program for power plant new-builds and upgrades. The NSR has been criticized for adding increased costs and delays for improvement projects. On that score, the panelists agreed the Trump administration’s new ACE rule could help, as it would give individual states leeway to decide on the permitting process for plant upgrades or expansions, meaning improvement and expansion projects could likely move forward more quickly.
—Darrell Proctor is a POWER associate editor (@DarrellProctor1, @POWERmagazine).