My first encounter with what we often call clean coal technology happened long before carbon capture became the center of the conversation.
It was in 2008, when I visited a coal washing plant in Colombia.
There was nothing futuristic about the basic principle.
The objective was straightforward: remove part of the rock, mineral matter and other impurities before the coal reached its final customer. That experience taught me something I still consider fundamental today: Improving how we use coal begins before the coal enters the boiler.
But it also raises a more difficult question. Can coal ever really be called “clean”?
The answer depends on what we mean by clean. Coal washing can reduce impurities.
Higher-efficiency plants can reduce the amount of coal required per MWh.
Advanced pollution controls can reduce particulate matter, SOx and NOx.
Carbon capture can prevent part of the CO₂ from reaching the atmosphere.
But none of those technologies makes the environmental impacts of coal disappear completely.
So perhaps the useful question is not: Is clean coal real?
It is: How much can technology reduce the environmental impact of coal that is still being used?
What does “clean coal technology” actually mean?
There is no single technology called clean coal.
The term has been used broadly to describe technologies applied at different stages of the coal value chain to reduce environmental impacts or improve energy performance.
They can begin before combustion with coal preparation.
They can continue inside the power plant through higher-efficiency steam cycles or gasification.
And they can extend after or around combustion through pollution-control systems and carbon capture, utilisation and storage.
That distinction is important because these technologies solve very different problems.
Removing ash is not the same as reducing NOx.
Reducing SO₂ is not the same as reducing CO₂.
Improving efficiency is not the same as eliminating emissions.
A technically serious discussion about clean coal has to separate them.
1. Coal washing and beneficiation: cleaner fuel before combustion
Coal preparation is probably one of the oldest examples of what has been called clean coal technology.
The U.S. Energy Information Administration defines prepared or cleaned coal as coal that has been processed to reduce impurities and improve its burning characteristics. Coal preparation can include crushing, screening and mechanical cleaning to separate rock, clay and other mineral material from the coal.
This can provide important operational advantages.
Removing part of the mineral matter may improve the heating value of the product on a mass basis, reduce the ash entering the boiler and reduce the amount of material that later has to be handled as fly ash or bottom ash.
It can also improve fuel consistency.
But coal washing has limits.
It does not remove all mineral matter.
It does not eliminate the carbon contained in the coal.
And therefore it does not solve the fundamental CO₂ emissions associated with combustion.
It is a fuel-quality improvement technology, not a decarbonization technology.
That distinction matters.
Can coal be cleaned without water?
Traditional beneficiation often uses water-based processes.
But dry coal beneficiation also exists.
I recently had a conversation about technologies that use air rather than water to separate coal from part of its mineral matter.
This is particularly interesting in areas where water availability is constrained.
Air-dense-medium fluidized-bed and other dry separation technologies have been developed and demonstrated for coal beneficiation, although their suitability depends on characteristics such as particle size, coal properties, separation requirements and project economics.
That does not make wet preparation obsolete.
It gives us another example of how coal-handling technology continues to evolve.
2. Higher efficiency: getting more electricity from the same fuel
Once coal reaches the power plant, another strategy is simple in principle: extract more useful energy from every unit of fuel. Conventional subcritical coal units operate at lower steam temperatures and pressures than supercritical and ultra-supercritical plants.
Increasing steam conditions can improve cycle efficiency.
The consequence is important.
If two plants produce the same amount of electricity but one requires less coal, the more efficient plant generally produces less CO₂ per MWh as well as consuming less fuel.
That is why efficiency matters.
But again, efficiency is not the same as zero emissions.
A more efficient coal plant can have lower CO₂ intensity than a less efficient coal plant while still producing significant absolute greenhouse-gas emissions.
This is one of the most important distinctions in the clean-coal debate: efficiency mitigates the problem; it does not eliminate it.
3. IGCC: changing the way coal is converted into power
Integrated Gasification Combined Cycle — IGCC — approaches coal differently from a conventional pulverized-coal boiler.
Instead of burning coal directly in the traditional way, coal is gasified to produce a combustible gas.
That gas can be cleaned and used in a gas turbine, while heat from the gas-turbine exhaust is recovered to generate steam for a steam turbine.
The result is a combined cycle.
Japan has invested for decades in developing this technology.
And this is where I believe Japan provides one of the most interesting case studies in the world.
Japan: a laboratory for high-efficiency coal technology
Japan is an unusual energy case.
It has very limited domestic fossil-energy resources and therefore depends heavily on imports.
In 2024 Japan imported approximately 166 million tonnes of coal, with import dependency close to 100%.
Coal still represented 24.4% of Japan’s primary energy supply in FY2024, while the latest detailed official generation breakdown available for FY2023 placed coal at 28.3% of electricity generation.
That dependence has historically encouraged Japan to investigate how to extract more value from imported fuel.
Nakoso IGCC
The history of Nakoso is particularly interesting because there have been different stages.
The original 250 MW-class demonstration facility was later operated commercially as Nakoso Unit 10 and achieved approximately 42.9% net efficiency on an LHV basis.
A new commercial-scale Nakoso IGCC facility began operation in April 2021.
Mitsubishi Power reports efficiency of approximately 48% on an LHV basis for the commercial IGCC configuration.
That is a better example than simply saying that all IGCC plants achieve 47% efficiency.
Efficiency figures always need a basis — particularly HHV versus LHV — and plant configuration matters.
4. Osaki CoolGen: efficiency plus CO₂ capture
The Osaki CoolGen project takes the technology discussion further.
Its first stage demonstrated a 170 MW oxygen-blown IGCC system.
The actual demonstration achieved a net efficiency of 40.8% on an HHV basis.
The project developers estimated that the technology, when scaled to a future commercial plant using a 1,500 °C-class gas turbine, could reach approximately 46% net efficiency on an HHV basis.
This distinction matters.
40.8% was demonstrated.
Approximately 46% was the projected commercial-scale performance.
The project then moved into CO₂ separation and capture and later IGFC demonstration.
Development has continued: Osaki CoolGen reported further CO₂-separation-and-capture IGCC testing related to grid flexibility during FY2025.
That makes Osaki valuable not because it proves that coal has become emission-free.
It shows how efficiency, gasification and carbon capture can be tested as an integrated system.
5. Carbon capture: the most important—and difficult—part of the CO₂ problem
Efficiency can reduce CO₂ emissions per MWh.
But it cannot eliminate them.
If the objective is to continue using fossil carbon while achieving very large reductions in atmospheric CO₂ emissions, carbon capture becomes much more important.
Carbon Capture and Storage — CCS involves separating CO₂ from an industrial or power-generation stream, compressing and transporting it, and permanently storing it in an appropriate geological formation.
If captured CO₂ is used rather than simply stored, we generally speak about CCU or, more broadly, CCUS.
These technologies can substantially reduce emissions from specific processes when appropriately designed.
But they introduce additional equipment, energy consumption, infrastructure and cost.
That is why the existence of CCS technology does not automatically mean that every coal-fired power plant can economically install it.
CCS is real. But deployment remains small.
This is where I think the clean-coal conversation needs more realism.
Carbon capture is not science fiction.
Commercial facilities exist.
But global deployment on coal remains very limited compared with the scale of coal consumption.
The IEA estimated that, as of October 2025, operating CO₂ capture capacity at coal-using facilities globally was around 10 million tonnes per year.
That represented only about 0.06% of total coal-related emissions.
That number tells us two things at the same time.
The technology exists.
And:
we are nowhere near deploying it at the scale required to describe global coal use as low-carbon.
Both statements can be true.
Direct air capture is not the same as coal-plant carbon capture
This distinction is also important.
Direct Air Capture — DAC removes CO₂ directly from ambient air.
It is therefore a carbon-removal technology rather than a conventional point-source capture technology installed on the exhaust of a coal plant.
The IEA explicitly distinguishes DAC from point-source carbon capture.
DAC may eventually complement broader carbon-management strategies.
But it should not be presented as though it were another pollution-control device inside a coal-fired boiler.
Can captured CO₂ become a raw material?
Sometimes.
Captured CO₂ can be used in applications including fuels, chemicals and certain building materials.
This is one reason the broader term Carbon Capture, Utilisation and Storage — CCUS is used.
But “using CO₂” and “permanently avoiding CO₂ emissions” are not automatically the same thing.
The climate benefit depends on where the CO₂ came from, how much energy the conversion requires, what product is created and whether the carbon remains stored or is later released.
That means utilisation projects need to be evaluated through their complete carbon balance rather than simply assuming:
CO₂ became a product, therefore the emissions disappeared.
So is Japan proving that coal can become clean?
I would phrase it differently.
Japan has demonstrated that coal technologies can become more efficient and capable of integrating increasingly sophisticated emissions-control and carbon-management systems.
But Japan’s own energy policy does not assume that unlimited conventional coal generation is the future.
Its Seventh Strategic Energy Plan, adopted in 2025, calls for reducing electricity generation from inefficient coal-fired plants while pursuing decarbonization of thermal generation through technologies including hydrogen, ammonia and CCUS. It also aims to maximize renewable-energy deployment and increase nuclear generation while maintaining energy security.
That is a much more interesting lesson.
Japan is not simply choosing between:
coal or renewables.
It is trying to balance:
energy security, economic efficiency and decarbonization.
What about China and India?
The global coal story cannot be understood without Asia.
Coal remains the world’s largest source of electricity generation.
In 2024, coal generated approximately 35% of global electricity, even though its share of the power mix continued to decline.
China in particular has developed one of the world’s largest fleets of high-efficiency coal generation, including extensive deployment of ultra-supercritical technology.
That does not make the emissions issue disappear.
It means the future of existing coal assets is simultaneously an efficiency problem and a decarbonization problem.
Improving the former without addressing the latter is not enough for a net-zero pathway.
What does this mean for Colombia?
Colombia presents a different situation.
Its electricity system has historically relied heavily on hydropower, but thermal generation becomes particularly important when hydrological conditions deteriorate.
At the same time, the country has strengthened its climate commitments.
Colombia’s NDC 3.0, approved in 2025, reaffirmed a maximum national emissions level of 169.44 MtCO₂e in 2030 and added a 2035 target of between 155 and 161 MtCO₂e.
That creates an important engineering question.
When coal or other fossil generation is needed for reliability, how efficiently should those assets operate while the energy system evolves?
My answer is simple: As efficiently as technically and economically possible.
That means better fuel characterization.
Better coal handling.
Better combustion.
Lower heat losses.
Higher boiler efficiency.
Better plant heat rate.
Appropriate pollution-control systems.
And, where technically and economically justified, carbon-management technologies.
Is “clean coal” a misleading term?
It can be.
The word clean easily suggests that environmental impacts have disappeared.
They have not.
Coal mining affects land and ecosystems.
Coal preparation can create waste streams and water-management challenges.
Combustion creates CO₂.
Pollution-control systems create their own by-products.
Carbon capture requires additional energy and infrastructure.
For that reason, I prefer increasingly to talk about specific technologies instead of treating “clean coal” as one homogeneous solution.
Say what you mean:
washed coal.
high-efficiency coal generation.
ultra-supercritical technology.
IGCC.
low-NOx combustion.
flue-gas desulfurization.
particulate control.
CCS.
Each technology has a job.
And each has limits.
Frequently asked questions about clean coal technology
What is clean coal technology?
Clean coal technology is a broad term used for technologies that improve coal quality, increase conversion efficiency or reduce environmental impacts associated with coal use. It can include coal preparation, high-efficiency generation, gasification, pollution controls and carbon capture.
Does washing coal reduce CO₂ emissions?
Coal washing primarily removes part of the mineral matter and other impurities. It can improve fuel quality and may indirectly reduce emissions per unit of useful energy under some conditions, but it does not remove the carbon that creates CO₂ during combustion.
What is IGCC?
Integrated Gasification Combined Cycle converts coal into a combustible gas, cleans that gas and uses it in a gas turbine combined with a steam cycle. The configuration can achieve higher efficiency than many conventional coal technologies and can facilitate pre-combustion CO₂ separation in certain designs.
Can CCS remove all emissions from a coal plant?
No.
CCS can capture a substantial fraction of CO₂ under appropriate designs, but capture is not normally 100%, it requires additional energy, and other environmental impacts associated with coal remain.
Is CCS commercially available?
Yes, carbon capture operates commercially in several applications. However, deployment at coal-using facilities remains very small relative to total coal emissions.
Is direct air capture a clean coal technology?
Not specifically.
DAC removes CO₂ from ambient air and can theoretically offset emissions from many sources. It is different from capturing CO₂ directly at a coal-fired power plant.
So, is clean coal the future—or an impossible dream?
Neither answer is completely satisfactory.
“Clean coal” is not a magic technology that makes the consequences of coal disappear.
But neither are technologies such as coal beneficiation, ultra-supercritical generation, IGCC and carbon capture imaginary.
They exist.
Some are mature.
Some are commercially deployed.
Others remain expensive or limited in scale.
The useful discussion is therefore not whether coal deserves the adjective clean.
The useful discussion is:
For every tonne of coal that the world continues to use, how much useful energy can we extract from it, how much pollution can we prevent, and how much CO₂ can realistically be avoided?
That is an engineering question.
And it is much more useful than turning coal into either a hero or a villain.
Coal still provided around 35% of global electricity in 2024.
As long as large quantities continue to be consumed, improving the efficiency and environmental performance of that consumption has value.
But improving coal use should not be confused with eliminating its climate impact.
Efficiency matters.
Emission control matters.
Carbon capture matters.
And knowing exactly what each technology can—and cannot—accomplish matters even more.
If you are curious about how coal can be used more efficiently, I explore this discussion further in my book, particularly in the chapters “USANDO CARBÓN LIMPIO” and “ACABANDO CON LA NUBE DE LA MUERTE.”
Because the future of coal should not be built on slogans.
It should be built on engineering, measurement and evidence.