The U.S. coal industry, long in decline, is experiencing an unexpected resurgence in 2025. Driven by the surging power demands of artificial intelligence, data centers, and industrial reshoring, coal units once slated for retirement are being reactivated. This shift is not a return to the past, but a strategic response to a capacity crunch that renewables and gas alone cannot fill. With policy pressures momentarily eased, coal plants are finding a new role defined by efficiency, reliability, and return on investment.
Over the past decade, most coal plants operated in “maintenance-only mode,” deferring investment and slipping into lower efficiency. Now, utilities are being asked to do more, operate more efficiently, and run cleaner without significant capital upgrades. This has pushed operators to focus on selective modernization, particularly in areas that provide immediate, measurable benefits.
One of the most effective tools transforming coal economics is fuel chemistry optimization, led by Environmental Energy Services (EES) and its CoalTreat additive program. CoalTreat additives are applied to the fuel and can alter coal ash characteristics during and after combustion, raising fusion temperatures, decreasing fouling, and recovering lost megawatts. In one 750-MW tangential-fired boiler, CoalTreat eliminated reheat-section slagging that had previously caused derates. The unit increased output by 3% and lowered NOx emissions by 0.02 lb/MMBtu. Another 650-MW plant firing high-slag Illinois Basin and Northern Appalachian blends operated five consecutive days at full load—a feat once impossible—after treatment. The economic benefits are equally significant. Switching from premium Central Appalachian to Illinois Basin fuel saved plants $40 per ton while keeping output and compliance intact. At another location, slagging had lowered furnace exit-gas temperatures by 100F, which improved heat rate by 2.5% and increased net annual revenue by an estimated $2.5 million.
Slag formation begins when minerals in coal, such as silicates, iron, sodium, and potassium, are volatilized and/or react during combustion to create high-strength, low-melting point, sometimes glassy deposits that adhere to tube surfaces. CoalTreat works by introducing specially formulated chemical additives that alter ash chemistry, promoting the formation of brittle crystals (high-melting crystalline structures like anorthite and hematite) instead of “sticky” amorphous glass. The result: Fluxing or molten deposits become solid and friable, and are easily removed by sootblowing. Ash fusion temperatures increase by 150F to 200F. Accumulated slag or fouling is weaker, as shown in sintering strength data, becoming increasingly friable and more easily removed by existing equipment. Forced outages and heat transfer losses decrease. Changes in ash chemistry can be observed through high-temperature probe (HTP) testing that simulates tube-surface conditions. Probe accumulations and associated temperature mapping data consistently show reduced slag adhesion and no or reduced “black glass” formation, validating the chemistry’s effectiveness in actual furnace operating conditions. HTP testing, along with furnace infrared photography/thermography conducted during field trials can be used to verify performance in short demonstration programs.
The shift from maintaining the status quo to a renewed focus on maximizing generating capacity and reliability is borne out daily across the U.S. fleet. Utilities that once viewed additive chemistry as a tool of last resort are now actualizing significant operational and financial returns. A case study from a Midwestern public utility demonstrates how a targeted CoalTreat program restored lost megawatts, improved heat rate, and delivered multimillion-dollar gains—all without capital upgrades. The unit avoided more than 9,000 MWh of derate due to fouling and cut forced outages by about 120 hours. Additionally, the unit improved its average heat rate by nearly 200 Btu/kWh and significantly lowered boiler maintenance and sootblower steam consumption. The savings from heat-rate improvement contribute approximately $1.0 million annually to the plant’s bottom line. Recovered power sales generated a net income of about $5 million per year (after fuel costs), based on an average power sale price of $100/MWh. Maintenance savings from reduced boiler cleaning and weld repairs eliminated roughly $100,000 in annual maintenance expenses.
Peak power sales in many regions will continue to rise. For example, PJM peak power prices hit $898/MWh on April 8, 2025, and $1,334/MWh on June 23, 2025. Plants that can increase power sales during peak hours can substantially boost their profitability. For example, at PJM’s June 2025 peak ($1,334