Clean Coal: What Is It, Is It Really ‘Clean’ & Eco Friendly, & Is It Feasible?

Some people may have heard about and looked into clean coal and clean coal technologies

Others may not know a lot about it.

In this guide, we aim to outline and explain some of the key aspects of clean coal, such as:

– What clean coal is, and how the definition may have changed over time

– The range of clean coal methods and technologies that have either been used to date, or, are in development

– Whether clean coal is really ‘clean’ & eco friendly

– How feasible it might be as an energy source, and what it’s future might be


Summary – What Is Clean Coal, Is It ‘Clean’ & Eco Friendly, & Is It Feasible?

What Is Clean Coal?

Clean coal might generally be any method or technology that improves the eco friendliness or sustainability of coal as an energy source

Reducing air pollutants (such as nitrogen dioxide, sulphur dioxide and fine particulate matter), and also reducing carbon emissions might be two of the main examples of this

We explain some of the main developments in the definition of clean coal over time in the guide below


List Of Clean Coal Methods, Devices & Technologies

There are a range of different clean coal methods, devices and technologies.

A summarised list of the ones we outline in the guide below are:

Washing coal and dewatering coal

Electrostatic precipitators and fabric bag filters (and fine particle bag filters)

Flue gas desulfurization

Low-NOx burners

Mercury absorbers

Wet scrubbers

New or advanced coal plant systems or technology

CO2 processing technology and systems, such as CCS

New types of coal plants (such as HELE plants)

The type of coal used at the coal power plant

Ultra clean coal

Retrofitting or upgrading existing coal power plants

Retiring or shutting down old coal plants

Coal station licenses and permits

Coal plant auditing bodies

Regulations and legislation

Taxes, fines and other penalties for older ‘dirty’ plants and polluters

Future developments and future technology

Reusing, treating, managing, or commercialising coal energy waste


Is Clean Coal Actually ‘Clean’, & Is It Eco Friendly?

Some clean coal methods, devices and technologies may have a more significant eco friendly impact than others

Additionally, different methods, devices and technologies impact different sustainability indicators e.g. some impact carbon capture, some impact air pollutant reduction, and so on

In the guide below, we list the potential sustainability benefits of different proposed clean coal solutions

Something else we mention below is that whilst clean coal can be more sustainable than regular coal plants across some sustainability indicators, other energy sources like natural gas (excluding methane leaks at the mining stage), nuclear and renewables may outperform it across some sustainability indicators.


Is Clean Coal Feasible, & Does It Have A Future?

It might be fair to say that some clean coal technology has some significant potential drawbacks.

Some technologies and some projects also have a reported poor record/history in terms of performance and reliability, and being expensive compared to the (lack of) return they provide 

For these reasons, it might be fair to say that some clean coal technology presents issues, and may be speculative and uncertain as an energy source of the future


Potential Pros & Cons Of Clean Coal

Read more about the potential pros and cons of clean coal in this guide.


*A Note About This Guide

This is a generalised guide.

Each type of clean coal method, device or technology may ultimately have it’s own set of variables that determines how clean, feasible they are (relating to effectiveness, efficiency, cost, or reliability, and more)

An individual assessment may be required instead of a generalisation.


What Is Clean Coal Technology?

Clean coal technology might be a general term to describe any method or technology that makes coal energy ‘cleaner’ or more sustainable in some way.

It could be a process or action, a method/technique, a device, a system, a piece of technology, a new design of power plant, a legal regulation, or something else that’s intended to make coal energy more sustainable.


The general definition or description for the phrase ‘clean coal’ has changed over time.

Three of the main developments in the definition of ‘clean coal’ (what it might refer to) over time might have been:


1. Washing Coal

Clean coal might have started out as simply washing coal at the mine site after it has been mined

This has the intended effect of removing contaminants or chemicals like sulfur from the coal

In addition to making the coal cleaner, indicates that (paraphrased) washing the coal can also make it cheaper to transport


2. CCS

The definition of clean coal might have then changed to refer to CCS (carbon capture and storage technology)

This involves capturing the CO2 generated by coal plants, and storing it underground (usually in rock formations and aquifers)


3. Coal Plants With New Designs (such as HELE’s)

Today, the term clean coal might increasingly be used to refer to newly designed coal plants that are either more efficient with the coal they use, are designed to reduce air pollutants (like sulphur dioxide, nitrogen dioxide, and particulate matter), or are designed to reduce carbon emissions

Examples of these newly designed coal plants might include ‘Super Critical Coal Power Plants’, and ‘Ultra Super Critical Coal Power Plants’ – both of which might be categorised as ‘HELE’s’ (High Efficiency Low Emission Coal Power Plants)



The term ‘clean coal’ is increasingly being used for supercritical coal-fired plants without CCS … [on the basis that CO2 emissions are less than for older plants]


What Might Be The Main Goals Of Clean Coal?

Two of the main sustainability goals of clean coal might be:

1. Reducing air pollutants

In terms of air pollutants, there might be a focus on reducing particulates (such as PM2.5 and PM10), as well as both SO2 and NOx.


2. Reducing CO2 emissions from the flue gas that is released out of the smoke stack of a coal power plant


Other goals may or may not include:

– Purifying the coal itself (removing it’s impurities)

– Greater efficiency of converting coal into electricity (and coal combustion) 

– Treating, managing, or reusing coal energy waste (like fly ash)


List Of Clean Coal Methods, Devices & Technologies 

There are a range of different clean coal methods, devices and technologies.

Some have been used for years, whilst others are new or still under development, and might be more speculative or unproven.

They can be used at different stages of the coal energy process – at the mining stage (such as washing coal), at the coal power plant stage (such as capturing air pollutants and carbon), or the waste stage (such as managing, or reusing and commercializing coal waste)

A summarised list of the methods, devices and technologies includes:


– Washing Coal, & Dewatering Coal

Washing coal involves chemically washing it after mining to remove sulfur, and other chemicals or impurities (including rocks and soil).

This essentially ‘purifies’ the coal.

It is intended to help reduce emissions of ash and sulfur dioxide when coal is burned

It may also have the added benefit of making the coal cheaper to transport

Dewatering involves ‘dewatering’ lower ranked coals like brown coal – this may help improve the calorific value and therefore the efficiency of coal in it’s conversion to electricity


– Electrostatic Precipitators & Fabric Bag Filters (& Fine Particle Bag Filters)

Electrostatic precipitators (also referred to as a type of filter – specifically a dry scrubber) use static to remove particles, and soot and ash from combustion fumes indicates that electrostatic precipitators in particular may be ‘… considered best practice for capturing emissions from brown coal’

Fabric bag filters are also intended to help capture/filter, and remove dust or particles from power plant fumes 

Regular fabric bag filters may help reduce PM10 particulates

Fine-particle bag filters may specifically help reduce fine particulates – PM2.5.

Some reports indicate that particles below PM 2.5 may pose the greatest threat to human health, so, they may be a priority to focus on in some instances.


– Flue Gas Desulfurization

Intended to reduce the output of sulfur dioxide during the combustion of coal


– Low-NOx Burners

Intended to reduce nitrogen oxide emissions


– Mercury Absorbers

Intended to absorb mercury emissions, or reduce the concentration of mercury released during coal combustion


– Wet Scrubbers

Apparatus’ that clean he gas passing through the smokestack using ‘wet’ methods/techniques

Some may spray limestone and water on the gas for example


– New Or Advanced Coal Plant Systems Or Technology

Such as Integrated Gasification Combined Cycle (IGCC) and Pressurised Fluidised Bed Combustion (PFBC), which may help increase thermal efficiency mentions that using the ‘… carbonate looping process [helps with post-combustion CO2 capture from power plants]

Other technologies may help treat flue gases to remove air pollutants


– CO2 Processing Technology & Systems, Such As CCS mentions that ‘CO2 processing and processing techniques can include carbon capture storage (in the ground or ocean), flue gas separation, oxy-fuel combustion, or pre-combustion capture’

CCS is a ‘Carbon Capture & Storage System’, that captures and separates carbon emissions during the combustion of coal, and stores it, usually underground (into deep geological strata, and potentially saline aquifers and depleted oil and gas fields) mentions that CCS can include: ‘Pre combustion capture, post combustion capture and oxy fuel combustion’

Storage refers to sequestration. ‘Sequestration’ might specifically refer to the disposal and storage of liquid CO2 underground, or in the ocean

Capture and use of carbon might refer to carbon use for oil enhancement 

CCUS stands for ‘Carbon Capture Utilisation & Storage’


– New Types Of Coal Plants (Such As ‘HELE’ Plants)

Includes high efficiency low emissions plants, such as new supercritical and ultra-supercritical coal-fired plants

They are intended to reduce emissions, but may also reduce fuel costs as an added benefit

Some new coal plant designs increase thermal efficiency, and help new plants emit less per kWh of electricity produced

Other new capabilities or operations may include HELE plants using pulverized coal combustion, super critical and ultra critical coal plants having a difference in the steam cycle or stream pressure within the boiler, and more


– The Type Of Coal Used At The Coal Power Plant

The type of coal used can impact how clean the coal burning process is in different ways:

Coal from different mines or different parts of the world can contain slightly different amounts of sulfur and nitrogen 

Brown coal can be less efficient than black coal and lower ranked coal can have higher emissions than higher ranked coal 


– Ultra Clean Coal

Might be still under development, but is intended to reduce ash and sulfur


Ultra-clean coal (UCC) from new processing technologies … reduce ash [and] sulfur [and mean that] pulverised coal might be used as fuel for very large marine engines, in place of heavy fuel oil [but, technologies are still under development … and wastes from UCC are likely to be a problem] (


– Retrofitting Or Upgrading Existing Coal Power Plants

Existing coal power plants might be retrofitted and upgraded in a wide range of ways

Some existing coal power plants may be retrofitted with technology like Carbonate Looping Process technology, just as one example


– Retiring Or Shutting Down Old Coal Plants

Some existing older coal plants may simply be retired or shut down without replacing them with another coal plant

New supercritical and ultra-supercritical coal-fired plants may sometimes be built in their place


– Coal Station Licenses & Permits

These licenses and permits may have the intended effects of controlling and reducing emissions, and requiring more accurate reporting by coal plants.


– Coal Plant Auditing Bodies 

In some countries, coal plants are audited and assessed for their emissions and environmental impact by auditing bodies


– Regulations & Legislation

Some countries also have legislation or regulations relating to coal plant environmental impact requirements.


– Taxes, Fines, & Other Penalties For Older ‘Dirty’ Plants & Polluters

An example of taxes is carbon taxes, which are intended to penalise and discourage high carbon emitters

There may be other fines and penalties for air pollution, coal waste pollution, and so on


– Future Developments & Future Technology

One example might be the gasification of coal

However, these technologies can be unproven and speculative



The clean coal technology field is moving in the direction of coal gasification with a second stage so as to produce a concentrated and pressurised carbon dioxide stream followed by its separation and geological storage.

This technology has the potential to provide [what in reality would aim to become] extremely low emissions of the conventional coal pollutants, and as low-as-engineered carbon dioxide emissions


– Reusing, Treating, Managing, Or Commercialising Coal Waste

Although managing and treating, or reusing and commercialising coal waste such as fly ash isn’t traditionally seen as part of the clean coal space, we have written about it in our guide on the pros and cons of coal energy.

It may help add to the sustainability of coal energy in some ways.


Is Clean Coal Really ‘Clean’, & Is It Eco Friendly?

Compared To Regular Coal

Some reports indicate that coal power plants fitted with clean coal technology and devices, and also new coal power plants (like HELE’s), may emit less carbon or some types of air pollutants than old coal power plants, or power plants without certain clean coal technology


Compared To Other Energy Sources

Some reports indicate that coal power plants, both with and without clean coal technology, may not be as sustainable or eco friendly as other energy sources like natural gas, nuclear and renewables in some ways

An exception to this might be natural gas – when methane leaks at the mining stage and also the transport of gas as LNG are factored in, electricity from natural gas may be on par with electricity from coal fired plants according to some assessments


Potential Eco Or Sustainability Benefits Of The Individual Clean Coal Technologies

Below is generalised numbers and data only.

The actual sustainability of clean coal depends on the variables of the individual clean coal solutions used.

So, it can differ.

It also depends on the sustainability indicator being measured e.g. carbon emissions, air pollutants, and others.

What we see below is that each individual type of clean coal technology may have a different impact on different aspects of sustainability, such as reducing air pollutants, reducing fly ash, capturing and reducing carbon, and so on.

The claimed eco or sustainability benefits of the different clean coal options might be:


– Coal Washing

Coal washing may be significantly more sustainable when measuring air pollution.


[Some Chinese estimates indicate] Coal washing can remove 50%-80% of ash and 30%-40% of total sulfur (or 60%~80% of inorganic sulfur) in coal (


– Electrostatic Precipitators, & Also Fabric Bag Filters

Electrostatic precipitators and fabric bag filters may be significantly more sustainable when measuring air pollution, and perhaps coal waste.


… fabric filters [together with electrostatic precipitators] can remove 99% of the fly ash from the flue gases (



Power stations … that haven’t fitted fine-particle bag filters … jump off the charts in terms of fine particle pollution

But bag filters are less effective for PM 2.5 [which is] particulate matter smaller than 2.5 microns


– Flue Gas Desulfurization

Flue gas desulfurization may be significantly more sustainable when measuring air pollution.


[Flue gas desulfurization] … reduces the output of sulfur dioxide to the atmosphere by up to 97% … depending on the level of sulfur in the coal and the extent of the reduction (


– Low-NOx burners

Low-NOx burners may be significantly more sustainable when measuring air pollution.



[Low-NOx burners] … allow coal-fired plants to reduce nitrogen oxide emissions by up to 40%.

Coupled with re-burning techniques NOx can be reduced 70% and selective catalytic reduction can clean up 90% of NOx emissions 


– New Or Advanced Coal Plant Systems Or Technology

Some new or advanced coal plant systems and technology may be significantly more sustainable when measuring efficiency.


Advanced technologies such as Integrated Gasification Combined Cycle (IGCC) and Pressurised Fluidised Bed Combustion (PFBC) enable higher thermal efficiencies still – up to 50% in the future (


– CCS, CCU, & Other Carbon Capture Technology

CCS may only be mildly more sustainable when measuring carbon emissions, and may in some cases increase certain pollutants.

The Carbonate Looping Process may be significantly more sustainable when measuring CO2 reductions.



… as much as a 12 percent reduction in carbon emissions can be achieved by 2050 through CCS.

… [But,] while CCS may have an overall positive effect on air pollution, emissions of some pollutants may increase


The Carbonate Looping Process can be used to separate more than 90 per cent of the CO2 released during the combustion of fossil fuels (


– New Types Of Coal Plants (Such As ‘HELE’ Plants)

Compared to older plants, HELE plants may in some cases lead to a significant increase in thermal efficiency, reductions in air pollutants, and may lead to fuel cost savings too.

However, in some countries, old coal plants may be less emissions intensive than new coal plants.



[The] Increased efficiency of [plants is] up to 46% thermal efficiency now (and 50% expected in future) means that newer plants create less emissions per kWh than older ones

Ultra-supercritical (USC) HELE technology … reduces emissions and fuel costs to about 75% of subcritical plants


From (in regards to thermal efficiency):

A typical new subcritical plant will have a thermal efficiency of 38 per cent, meaning that 38 per cent of the thermal energy contained in the fuel is converted into electrical energy fed into the grid.

A supercritical plant will have an efficiency of maybe 42 per cent and a typical ultra-supercritical plant will achieve around 44 per cent (designs going up to 47 per cent are being developed).


Also from (in regards to flue gas emitted, and potential air pollutant reductions):

The difference between subcritical and ultra-supercritical technology is that the total amount of flue gas emitted from the ultra-supercritical plant is about 14 per cent smaller, and hence the capacity of the SO2 control device can be about 14 per cent lower, resulting in savings in investment and operating costs [as well as SO2 emissions that are about 14 per cent lower]

The same logic applies to the emissions nitrogen oxide (NOx), particulate matter (PM), mercury and other heavy metals.


[Super critical brown coal plants in Australia … [might] still be more emissions intensive than the majority of Australia’s existing coal plants] (


You can read more about the different types of new coal plants and their efficiency rates at, and also


– Ultra Clean Coal

The reductions of some air pollutants and coal ash may be significant.


Ultra-clean coal (UCC) from new processing technologies … reduce ash below 0.25% and sulfur to very low levels … (


– Retrofitting Or Upgrading Existing Coal Power Plants

Sustainability benefits of coal plant retrofitting and upgrading may depend on the what exactly is being done.

There may be low to moderate efficiency increases, but significant emissions reductions available for some upgrades and updates.


… if existing coal plants were upgraded to high-efficiency, at least 19 percent of total emissions can be reduced on an annual basis (


… [if] power stations in Australia [are] updated with emission control technology [they] could reduce the release of toxins by up to 90% (


– Retiring Or Shutting Down Old Coal Plants

Air pollution may be reduced when some old coal plants are shut down.

But, it may depend on whether they are replaced with another coal plant or energy generation project.



… when old high emitting plants [are] shut down … the data should show a really significant reduction in the toxic pollutant levels.


*Different Sustainability Indicators That Can Be Assessed

A list of the sustainability indicators that might be assessed throughout coal’s lifecycle might be:

– The impact of the coal mining stage

– How coal is transported and processed

– Carbon emissions (and what happens to captured carbon i.e. how it’s used or stored)

– Individual air pollutants

– How flue gas from the smokestack is managed in general

– What happens to coal waste and coal waste by-products


What Might Be The Future Of Clean Coal?

Instead of providing a definitive answer on what the future of clean coal might be, we will instead provide what might be some of the key points both in support of, and in criticism of using clean coal in the future.


Some Individual Clean Coal Solutions Might Be Better Than Others

Some individual clean coal solutions may be better than others

Some clean coal solutions for example may be cheaper, more effective at providing sustainability improvements, and more reliable in terms of performance

It might be fair to say these solutions have a better future, and might be more practical and feasible to use than solutions that are expensive/costly, ineffective, don’t provide a good return for investment, and are unreliable and unproven (or more speculative)

As just one example, a bag filter or similar device might be cheaper, more effective and more reliable, compared to some costly or unreliable CCS systems 

Each type of clean coal technology might do something different, and has different pros and cons across all aspects of its potential use. to consider.


Potential Support For Clean Coal (In General)

There may be some outright support for specific clean coal technologies.

And, there may be some comparisons to other energy sources that show clean coal as being a worthwhile part of the future of the energy sector. notes that (paraphrased) groups like the IPCC and IEA may think that CCS is important in meeting future global carbon targets explains how clean coal with gasification with a second stage might be part of the future for clean coal as a technology:

The clean coal technology field is moving in the direction of coal gasification with a second stage so as to produce a concentrated and pressurised carbon dioxide stream followed by its separation and geological storage.

This technology has the potential to provide … extremely low emissions of the conventional coal pollutants, and as low-as-engineered carbon dioxide emissions.

This has come about as a result of the realisation that efficiency improvements, together with the use of natural gas and renewables such as wind will not provide the deep cuts in greenhouse gas emissions necessary to meet future national targets.


Also from (comparing specifically natural gas to clean coal for electricity):

There are many advocates for the use of natural gas as an alternative to coal for electricity generation, on the grounds that it emits much less CO2 per kWh generated.

[But, leakage of natural gas, and the CO2 in transporting it as LNG could bring it on par with coal-fired electricity in terms of global warming effect]


Gasification may help produce electricity from coal more efficiently compared to the alternative of pulverising coal, so, emissions aren’t reduced per tonne of coal, but less coal might be used in total and there might be less emissions in total


Potential Criticism Of Clean Coal (In General)

Some reports are very critical of the issues that have faced clean coal up until this point in time

In general, they might point to the cost of clean coal, the impact it might have on electricity prices, how energy intensive it can be, and how unreliable or unsuccessful some projects have been in the past

There’s been specific criticism of CCS, and new clean coal plant designs (i.e. the high efficiency, low emissions plants)

Other reports indicate that even gasification for clean coal might not yet be a proven technology yet, and may have some uncertainties (and be speculative, and unproven)

It might also still take time to develop gasification and to be able to use it at scale

Additionally, gasification of coal might still need to prove that is can produce similar or better results than other forms of energy like natural gas, nuclear and renewables.

With all these points in mind, some groups may suggest that investing resources in other sources of energy such as natural gas, nuclear and renewable energy might be better

Any clean coal solutions might ultimately need a cost benefit analysis of the eco, social and economic (for consumers, investors and suppliers) impact they have throughout the entire coal lifecycle to get an accurate assessment of it’s future


*A Note About The Mining Of Coal

Another potential asterisk on clean coal technology is that it mostly focusses on the handling of coal, the purity of the coal, and the combustion of coal.

It doesn’t focus on the mining of coal, and therefore doesn’t impact the mining of coal.

No amount of clean coal technology can reduce the potential negative impacts of coal mining if there are any.

Although, other sources of energy like wind and solar need mining too – for material for solar panels, wind turbines, energy storage batteries, and so on.


*A Note About The Potential Continued Importance Of Regular Coal

Although regular coal has potential drawbacks, it’s also important to society in a number of ways.

For example, even though there may be pollution and carbon emissions to consider, it may be a cheap, accessible, well developed and reliable source of energy

It also provides a backup and supplemental source of energy to variable renewable energy where nuclear and natural gas aren’t feasible or practical in some instances


More Information About New ‘Clean Coal’ Power Plants

Some of the more important points about new ‘clean coal’ power plants might be that they:


– Include subcritical, super critical and ultra critical coal plants

Although, mentions that HELE plants don’t include sub critical plants

So, subcritical, super critical and ultra critical coal plants may be more efficient or sustainable than regular coal plants in some ways, but only super critical and ultra critical coal plants might be classified as HELE plants


– Are claimed to have lower emissions and higher efficiency compared to non HELE plants


– Use pulverized coal combustion technology like regular or older coal plants


– Have a difference in the steam cycle or the steam pressure within the boiler compared to older coal plants mentions this about steam cycles and their impact:

[The] type of steam cycle [that] is used has no impact on the emissions per tonne of coal burned

The only difference between different steam cycles in terms of emissions is how much power they can generate from one tonne of coal

Emissions per tonne of coal depend solely on the amount of sulphur contained in the coal


Read more about the differences in these plants in the and reports


Potential Variables That Might Change The Impact Of Coal Plants & Coal Energy

Some of the key variables that might change the impact that coal plants have might include:

– The type of power plant

Specifically, whether it’s an old power plant, whether it’s an old power plant that’s been retrofitted with clean coal technology, or whether it’s a new power plant

For example, is it a subcritical, super critical, or ultra supercritical plants (HELE plants)?


– The type of coal, or the form of coal fuel being used

Such as black coal or brown coal

And, also whether coal is pulverised, gasified, and so on


– The type of clean coal methods, devices and technology that have been used throughout the coal energy lifecycle

It matters how many and what types of clean coal solutions are installed on a power plant, such as bag filters, carbon capture devices, and so on

The coal might also have been washed prior to getting to the power plant (so, the handling of the coal matters), and coal waste might be treated and managed after the coal combustion process

But, the what happens to the coal at each stage of the lifecycle should be considered too, such as the mining stage, the transport stage, the processing stage, the power plant and combustion stage, the waste management stage, and so on


*Other Factors

– Total Amount Of Coal Being Used & Combusted

Separate to the clean coal solutions that are used, the total amount of coal (in tonnes) that is used or combusted can impact the total amount of emissions from coal energy in a given year


– Total Number Of Coal Plants In Operation

Separate to the clean coal solutions that are used, the total number of coal plants in operation can impact the total amount of emissions from coal energy in a given year


– Coal Efficiency

A factor like increasing plant efficiency won’t decrease the rate of pollution or emissions per unit of coal burned, but can decrease overall coal used to generate the same amount of electricity (which may be a benefit for the sustainable use of coal as a resource, and how much coal we are using and have left)

It can also contribute to lower total pollution or emission amounts for that same amount of electricity.


– Indirect Factors

Other factors may be more indirect 

Examples of these factors might include coal energy regulations, conditions of new coal plant licenses, and carbon taxes and penalties for coal pollution









6. Various ‘Better Meets Reality’ guides










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