Image. Coal Creek station, from internet!
Magic Tricks for Coal: How to Boost Energy in Low-Grade Coal
What if the problem isn’t the coal you’re burning, but the energy you’re wasting before it even reaches the boiler?
Coal is frequently judged by its calorific value. The higher the energy content, the better the fuel. The lower the heating value, the worse the coal. At least, that is what many people assume.
But what if low-grade coal is not necessarily a bad fuel?
What if a significant part of the problem lies in the moisture and mineral matter we insist on transporting, pulverizing, heating, and processing alongside the combustible material?
Here is an uncomfortable truth: sometimes, improving coal quality delivers more value than simply searching for a more expensive coal.
And no, this is not magic. It is engineering.
Can We Really Increase the Energy Content of Low-Grade Coal?
Yes. Coal beneficiation and drying can increase the heating value of low-grade coal on an as-received basis by removing noncombustible material, particularly mineral matter and moisture.
However, these processes do not create new chemical energy. Instead, they concentrate the combustible material and reduce the energy wasted during fuel processing and combustion.
Two major components deserve particular attention:
- Ash-forming mineral matter: Noncombustible components that dilute the fuel and contribute to ash handling, deposition, erosion, and other operational problems.
- Moisture: Water that adds mass to the fuel and absorbs heat during combustion, reducing the effective energy available to the boiler.
Controlling these components can change how a coal performs inside an entire power generation system.
The question is not simply how much energy the coal contains.
The question is how much of that energy your power plant can actually convert into electricity.
Coal Washing: Why Pay to Burn Rocks?
Imagine buying coal with 40% ash content.
For every 100 tonnes of fuel delivered to your facility, approximately 40 tonnes will remain as ash after combustion, assuming the ash analysis is expressed on the same mass basis.
You are paying to transport, handle, pulverize, and process a significant amount of material that contributes little or nothing to the coal’s useful heating value.
Does that sound efficient?
Absolutely not.
How Does Coal Washing Improve Calorific Value?
Coal washing is a beneficiation process designed to separate mineral-rich material from coal using differences in physical properties, particularly density.
Conventional techniques include:
- Dense-medium separation.
- Gravity separation and jigs.
- Froth flotation for suitable fine-coal fractions.
By removing part of the mineral matter before combustion, coal washing can increase the calorific value per unit mass of the cleaned coal.
The potential benefits go beyond heating value.
Lower ash content can reduce the burden on fuel handling and pulverizing systems, decrease ash disposal requirements, and potentially reduce erosion and certain mineral-related deposition problems in boilers.
However, the benefits depend on the mineral composition, combustion conditions, and characteristics of the coal.
Can Coal Washing Remove 95% of the Ash?
Under favorable circumstances, exceptionally large reductions in ash content are technically possible.
But presenting a 95% reduction as a normal result would be misleading.
Not every high-ash coal is washable, and not every washable coal can produce a low-ash product at an economically acceptable recovery.
A coal containing 40% ash will not automatically become a 3% ash product simply because it passes through a washing plant.
The outcome depends on mineral liberation, particle size, density distribution, separation efficiency, and the proportion of combustible matter rejected with the mineral material.
This is precisely why washability testing and yield-versus-ash analysis are essential.
The real engineering challenge is not achieving the lowest possible ash content at any cost. It is determining the most profitable balance between recovered coal, calorific value, processing cost, and downstream performance.
And there is another important issue.
Removing mineral matter before combustion does not make it disappear. Washing produces rejects and, depending on the process, wastewater or tailings that must be responsibly managed.
Coal beneficiation can reduce certain downstream impacts, but it is not an environmental free pass.
Coal Drying: Stop Using Your Boiler to Evaporate Water
Now imagine buying coal with 38% moisture content.
A substantial portion of the material entering your power plant is water.
Water does not burn.
Yet the boiler must provide energy to heat and evaporate that water, and the resulting vapor affects flue-gas volume, heat transfer, and plant performance.
Your boiler is designed to generate steam efficiently, not to compensate endlessly for poorly managed fuel moisture.
This is especially relevant for lignite and sub-bituminous coals, which can contain considerable amounts of moisture.
Surface Moisture vs. Inherent Moisture: Why Does It Matter?
Coal moisture can be broadly divided into two categories.
Surface moisture is associated with water on particle surfaces and between particles. Depending on ambient conditions, some of it can be removed by draining or natural drying.
Inherent moisture is associated with water retained within the coal’s pore structure. Its removal generally requires more controlled thermal or mechanical processing.
Natural air drying is limited by environmental equilibrium conditions, particle characteristics, pile configuration, and weather.
When moisture content remains high, industrial drying technologies can offer an alternative.
But there is a catch.
Drying coal consumes energy, and using valuable high-temperature energy simply to remove moisture may undermine the economic benefit.
That is why low-temperature drying integrated with waste heat recovery deserves particular attention.
Coal Creek Station: The Power Plant That Refused to Accept Poor Fuel Quality
<em>Image recommendation: Coal Creek Station, North Dakota, USA. Use an authorized photograph with attribution to its original source.</em>
By the year 2000, Coal Creek Station in North Dakota was facing a serious fuel-quality problem.
The facility consisted of two approximately 600 MW coal-fired generating units designed to operate with lignite.
Over time, however, the quality of the supplied fuel had deteriorated.
Its heating value had fallen from approximately 6,800 Btu/lb to 6,200 Btu/lb, while moisture content had increased from its original design value of 29% to more than 38%.
The consequences were not theoretical.
More coal was required to supply the same thermal input. More fuel had to be pulverized, and additional flue gas had to be handled.
All eight pulverizers were operating continuously, leaving no spare milling capacity.
When a pulverizer required maintenance, generating capacity could be restricted.
The plant was trapped between deteriorating coal quality and equipment designed for different fuel specifications.
A familiar situation for many coal-fired power plants.
And what happens when the equipment reaches its limits?
Some managers begin thinking about replacing equipment.
Others accept reduced performance as unavoidable.
But the engineers at Coal Creek asked a different question.
What if we improve the fuel before it reaches the pulverizers instead of continuously adapting the entire plant to inferior fuel quality?
DryFining Technology: Turning Waste Heat into Better Coal
Great River Energy developed a low-temperature coal drying and beneficiation process known as DryFining™.
The idea was relatively straightforward: use low-grade waste heat from the power plant to remove part of the moisture before the coal entered the combustion system.
The technology employed fluidized-bed drying equipment and also incorporated separation of certain dense, mineral-rich particles.
Development and demonstration activities took place during the 2000s. After successful testing, the technology was implemented commercially at both Coal Creek units in December 2009.
This was not about changing the fundamental nature of lignite.
It was about eliminating part of the burden that moisture and mineral matter imposed on the entire power generation process.
What Happened When Coal Moisture Fell from 38% to 29%?
The published operating experience provides a remarkable engineering case study.
| Performance indicator | Reported result |
|---|---|
| Coal moisture | Approximately 38% reduced to 29% |
| Heating value | Approximately 6,200 to over 7,000 Btu/lb |
| Raw fuel purchasing | Approximately 4% reduction |
| Flue gas volume | Approximately 16% reduction |
| Net unit heat rate | Approximately 4% improvement reported in the 2017 account |
| Annual operational savings | More than USD 18 million |
| Sulfur dioxide and mercury emissions | Approximately 40% reduction |
| Nitrogen oxides emissions | Approximately 20% reduction |
| Carbon dioxide emissions | Approximately 4% reduction |
Results are historical figures reported for Coal Creek, principally in Great River Energy’s 2017 operating account. They are not guaranteed outcomes for other plants. Different publications report somewhat different performance figures depending on the test period and measurement boundaries.
Think about what those numbers mean.
By removing water before combustion, the plant reduced the amount of material processed and the energy penalty associated with fuel moisture.
The decrease in flue-gas volume also reduced the burden on downstream equipment.
Meanwhile, separating some mineral-rich particles contributed to reducing specific pollutants.
And all of this was achieved without replacing the entire boiler.
More than USD 18 million in annual savings from improving the fuel before burning it.
Now tell me again that energy efficiency is just an operational expense.
The Hidden Financial Cost of Burning Low-Quality Coal
Coal purchasing decisions are too often dominated by one variable: price per tonne.
But the cheapest tonne of coal is not necessarily the cheapest source of electricity.
A fuel with a low purchasing price can become expensive when its moisture, ash content, grindability, or other properties increase the operating burden of a power plant.
Consider the possible consequences:
- Higher fuel consumption to maintain thermal input.
- Increased auxiliary power demand.
- Reduced pulverizer capacity and availability.
- Higher ash handling and disposal costs.
- More difficult combustion optimization.
- Increased maintenance and potentially higher emissions-control costs.
That is why coal procurement and plant performance engineering should never operate as isolated functions.
How Should We Evaluate the Real Value of Coal?
A meaningful technical and economic assessment must consider more than the quoted fuel price or laboratory heating value.
It should evaluate as-received heating value, total moisture, ash content, sulfur, grindability, fuel handling limitations, combustion performance, boiler efficiency, auxiliary consumption, emissions, and the resulting cost of generation.
It must also account for the capital and operating costs of any washing or drying technology, material losses, and the additional energy consumed by the treatment process.
The objective is not to produce the cleanest-looking coal sample. It is to maximize useful energy and economic value throughout the complete system.
A coal with a higher heating value may still be the wrong choice if other properties compromise plant operation.
Likewise, low-rank coal should not automatically be dismissed when there are technically and economically viable methods to improve its performance.
Does Coal Beneficiation Make Coal Clean?
No.
And we should not pretend otherwise.
Coal washing and drying do not eliminate the carbon dioxide generated by oxidizing the carbon in coal. Nor do they remove every pollutant associated with coal combustion.
Even when a drying project reduces CO₂ emissions per MWh, the power plant remains a fossil-fuel-based generating facility.
However, that does not make efficiency improvements irrelevant.
Quite the opposite.
If a coal-fired power plant is going to operate, allowing it to waste more fuel than necessary is neither an environmental achievement nor a sound engineering decision.
Efficiency, emissions control, and long-term energy transition planning are different challenges. They should not be confused or used as excuses to ignore one another.
Reducing avoidable losses in an operating plant can deliver measurable financial and environmental benefits.
Coal Creek demonstrated that improving fuel quality can be one way to achieve those benefits.
Frequently Asked Questions About Low-Grade Coal Upgrading
What Is the Best Way to Improve Low-Grade Coal?
There is no universal solution. Coal washing is appropriate when mineral matter can be separated economically, while coal drying can be beneficial when excessive moisture limits heating value and power plant performance. A coal characterization and techno-economic assessment should determine the best option.
Does Coal Drying Increase the Heating Value?
Yes, on an as-received mass basis. Removing moisture concentrates the combustible material in each kilogram or pound of fuel. The total chemical energy of the original combustible solids is not created or increased by drying alone.
Can Coal Washing Improve Boiler Efficiency?
It can improve overall plant performance under suitable conditions by reducing mineral matter and associated operational burdens. However, improved fuel heating value does not automatically imply the same percentage increase in boiler thermal efficiency. Plant-specific performance testing is required.
What Is DryFining Technology?
DryFining is a low-temperature lignite drying and beneficiation technology developed by Great River Energy. It uses recovered low-grade heat and fluidized-bed processing to reduce fuel moisture and separate certain mineral-rich materials before combustion.
Is Coal Drying Economically Worthwhile?
It can be, particularly in high-moisture coal applications where waste heat is available and reduced fuel handling, auxiliary power, maintenance, or emissions-control costs justify the investment. Coal Creek is a documented example, but each plant requires an independent evaluation.
Conclusion: The Real Magic Is Engineering, Not Coal
Coal does not become a better fuel simply because we wish it had more energy.
And no engineer can create energy out of nothing.
But we can stop wasting energy unnecessarily.
We can remove mineral matter before combustion when it makes technical and economic sense.
We can dry high-moisture coal using otherwise underutilized heat.
We can improve the performance of the entire system instead of forcing the boiler to compensate for every weakness in fuel quality.
Coal Creek proved that this approach can deliver millions of dollars in annual operational savings.
So perhaps the real question is not whether low-grade coal can be improved.
The real question is: how much money are you willing to keep burning before you decide to improve it?
Burn your fuel, not your money.
References
ASTM D4371/D4371M. Standard Test Method for Determining the Washability Characteristics of Coal.
Sarunac, N., Bullinger, C. W., & Ness, M. (2015). Four Years of Operating Experience with DryFining™ Fuel Enhancement Process at Coal Creek Generating Station. Journal of Energy and Power Engineering. DOI: 10.17265/1934-8975/2015.06.003.
Broekema, S. (2017). Innovative Coal Drying Process Benefits Power Plant. Processing Magazine. Read article.
U.S. Department of Energy (2011). DOE Receives First Repayment from Successful DryFining Clean Coal Power Initiative Project. Read source.
Lehigh University, Energy Research Center. Coal Drying. Read technical overview.