Fuel flexibility is a matter of survival for coal-fired power plants, considering the cloudy economics besetting segments of the power industry. What is less understood, however, is that fuel flexibility can also lead to major savings for plant operators.

“Most coal-burning generators were built in an era when coal was cheap, environmental pressures were low, and competition from other generation sources was scant,” said Una Nowling, Fuels Technology Lead for Black & Veatch’s energy business.

Over the last decade, coal plants have faced economic and technological pressures that few were designed to withstand. For a coal power plant to maintain relevance, it will either have to exist in a niche market or adapt and evolve, Nowling said.

“The key to surviving in the new environment means developing a tolerance for fuels well outside the parameters that were laid down on a drawing board decades ago,” she notes.

Fuel flexibility can be defined as the ability of a power plant to safely, efficiently and cost-effectively burn a wide range of fuels with different properties such as coal, natural gas, fuel oil or biomass. “Most coal-fired power plants were designed to operate within a relatively narrow set of quality specifications. Deviations from these specifications can lead to unpleasant consequences in terms of degraded performance or even damage to the equipment,” Nowling said.

Savings Through Wider Fuel Flexibility

What is not always understood, she notes, are the “incredible savings” that can result from being able to use a range of coals. Plant alterations often can be made for a relatively small capital investment. She cites three examples:

• An Eastern utility modified its coal pulverizers, thus allowing the maximum moisture content of the coal to increase to 16 percent from 12 percent. This opened new spot market sources of coal to the plant, resulting in a savings of $4 million in the first year. The mill modifications cost $325,000.
• A Southwestern utility that frequently blended sub-bituminous Powder River Basin (PRB) coal with local coal at a 30:70 ratio modified its mills, thereby enabling a higher blend of PRB coal. Increasing the PRB coal share to 50 percent resulted in a $23 million savings on the utility’s long-term coal contract. The modifications cost about $1 million.
• An Illinois utility reactivated a row of “dead” furnace wall sootblowers above the burner zone, finding that it could now accommodate larger quantities of a higher-ash, higher iron-content coal in its fuel diet. Using the lower quality coal resulted in an estimated savings of $500,000 per year. The cost of the repairs? About $120,000.

The advantages of fuel flexibility go beyond the directly measurable savings, strengthening Adam Smith’s “invisible hand” of the marketplace. Nowling notes that a 2012 Swedish study of fuel switching at European power plants from 1978 to 2004 found that units with multi-fuel ability exerted competitive pressure on coal suppliers that even limited their ability to raise fuel prices for units that were not fuel-flexible.

Upgrading Pulverizers Gleans Benefits

Benefits in terms of unit performance, operations, emissions and maintenance practices can also result from fuel flexibility. She points out that by upgrading the pulverizers, a utility could hold one mill in reserve, rather than having all pulverizers running at capacity, which could result in a significant improvement in the availability factor of the generating unit.

A Black & Veatch study of proposed mill upgrades for a 650-megawatt unit found that the benefit of having a spare mill to accommodate unplanned outages and to improve maintenance scheduling was an increased generation opportunity of 7,200 megawatt hours (MWh) per year (assuming a 65 percent net capacity factor). At a market rate of $35/MWh, this equated to approximately $250,000 of increased revenue per year.

“When the ability to use a broad range of coal quality is combined with the ability to utilize a second primary fuel source, good synergies often result,” she says. The most common example is a coal power plant that has the capability to co-fire with natural gas, but plants that can co-fire with oil and biomass can also see a good result.

For example, by co-firing with gas, lower quality and thus lower cost coals can be purchased with less concern for lost generating capacity. Other potential advantages are that unexpected outages of coal handling equipment can be hedged by having natural gas available to make up the lost load. In addition, coal inventories can be reduced, and supply delays and shortfalls can be better managed. Conversely, should natural gas supply restrictions unexpectedly occur, coal could be increased to maintain generation.

Working Alongside Renewables Increases Fuel Flexibility

Yet another unorthodox method of increasing fuel flexibility exists in improving the relevance of coal-fired assets – by making capital and operations upgrades to support the renewable generation being added to the grid.

The U.S. Department of Energy National Renewable Energy Laboratory, in a 2013 report, outlined the benefits of upgrading coal- and gas-fired power plants to improve operational flexibility through ramp up/down rates, faster startup times, and the ability to operate stably at very low loads that were gleaned in a test case on the Rocky Mountain Power Pool system.

“In my more than two decades of experience, I have learned that the one resource most utilities lack is the freedom to make investments in their own future,” Nowling said. “One can lay blame at many feet – regulatory uncertainty, unregulated competition, or even forces beyond anyone’s control. Whatever the case, by enhancing fuel flexibility, a utility or merchant generator has the potential to improve operations, increase profits and keep generating assets from becoming extinct.”

Published originally on Black & Veatch Solutions.