« Clean coal » thermal power plant: ecologic or not?

At the time where climate change occupies all minds, coal, the most polluting fossil fuel wants to rebuild its image. It is under the name of “clean coal” that it does its come back with a capital mission: reducing greenhouse gas emissions. But can coal really be clean? Behind this ecological ambition are hiding new technologies and its share of environmental risks that comes with it.


Coal, a polluting energy but attractive

Coal, this polluting energy that nobody can live without, is the fuel for thermal power plants. They produce electricity from the heat emitted during the combustion, here coal, that make water boil and the water vapor drives the turbine. But some power plants use as raw material fuel oil or natural gas.

Coal is the second most consumed energy. In 2016, its part in the global energetic mix was 28,1% behind oil. It covers around 40% of electricity needs on the global scale. The biggest consumers are USA and China, and generally speaking, countries that have the biggest fossil fuel reserves in their soil such as Russia, Poland or Australia. The part of coal in the Chinese energetic mix is peaking at 64.4% even if the country is on the right track to energetic transition. In the USA, 30% of electrical production comes from coal.

In contrast, coal only holds a 4% part in the French energetic mix. The Climate Plan of the Ecological transition and solidarity Minister, Nicolas Hulot, plans the exit of coal by 2022 with the shutdown of the last thermal power plants.

Abundant, accessible, economic but disastrous for the environment, this fossile fuel isn’t done being talked about. The request for coal is globally increasing of 2% per year and will remain for the next twenty years according to estimations.


© Apphim

While oil reserves are depleting, coal ones can still go for another 150 years of exploitation perhaps 200 years for some countries.

This energy is also 6 times cheaper than natural gas or oil. Therefore it is very attractive in developing countries. Coal threatens to catch up with oil, in terms of consumption, so much that it is competitive. Over a thousand power plants are under project in sixty countries of the world.

In China, a thermal power plant is built every week. But they are “clean” power plants and the most polluting power plants have already been closed. According to experts, China will not be able to let go of coal so easily as it highly depends on it. Although we are talking about reducing coal part to 50% by 2035 and even more by 2050. In developing countries also, coal remains a major energy source almost essential during energetic transition and the exit process from nuclear power. Thus, Germany which decided to give up nuclear energy following the Fukushima shock in 2011, has to use coal while they are developing the green energy park. The country hopes to reach 35% of renewable energies by 2035. In our country (France), which chose nuclear power, only five coal power plants remain in activity, with a few fuel and gas power plants. But these power plants still play a decisive role as they supply energy during consumption peaks and severe cold periods.

Yet, coal is the most polluting fossil fuel source, this on every level of exploitation, since extraction to combustion.

Highly criticized for its large contribution to climate change, coal emits effectively 1.7 times more than carbon dioxide (CO2) than natural gas and 1.3 times more than oil. Its combustion rejects also fine particles in the air, of which is Sulphur dioxide (responsible of acid rains) and nitrogen dioxide. They both are greenhouse gases.


«Clean coal»: two technologies under the same name

Continuing to use coal by suppressing its environmental impact that is the challenge of “clean coal”. We owe this phrase to the coal industry it-self to energy companies and politic sphere. It covers a set of techniques that can be divided in two categories: technologies that improve power plants performances and capture and storage of carbon dioxide technologies called CSC technologies.

Technologies improving the power plants energetic efficiency

A first solution to make coal cleaner is to simply modernize the current production park thanks to new technologies. Indeed, two thirds of the world power plants are around 20 years old and average performance only reaches 29 to 33%.

The last generation power plants or high-performance display ballooned performances. More modern and more efficient they release less CO2 compared to older installations. For example, doubling the power plant performance necessarily drives to reduce by half the greenhouse gas emissions as for a same quantity of used combustible, the energy quantity produced is larger.

Even without having carbon capture units, these power plants are therefore less polluting. That’s why the industry also calls this “clean coal”.

Some of the new technologies include:

  • supercritical” power plants or a supercritical value cycle where water is heated to a temperature and to a pressure superior to traditional power plants conditions, 565 to 585°C for a pressure of 221 bars. The system allows to increase the performance up to 45%. This is the favored technology of China. Industry is speaking of “ultra-supercritical” power plant, with temperature and pressure conditions higher to reach performances of 50% by 2020.
  • Coal gasification, which consist in producing synthetic natural gas from coal by making it reach the gaseous state. After filtration, the gas is “clean” and can be exploited, meaning burned in a gas thermal power plant. The performance of this technology is 55% but the high cost is dissuasive.
  • Polygeneration, that value a unique energy source by making a great variety of products from this source. Power plants properly equipped could produce with coal not only electricity and heat but also petrochemical products and hydrogen.

The CSC technologies of capture and storage of CO2

The second type of technologies called CSC for capture and storage of carbon, aims to remove greenhouse gas emissions from coal combustion in power plants. These technologies work on the basis of entrapment of carbon dioxide then the confinement of this gas in deep geological layers. These storage sites are among other things depleted natural gas and oil fields.

Carbon dioxide is captured in the power plant. It flows in the form of compressed gas in the pipes until its dedicated storage place where it is injected very deeply in the ground. The gas becomes liquid in these temperature and pressure conditions which is a secured storage means and avoid polluting the atmosphere. As a reminder, the oceans, trees or bogs naturally store CO2. The storage in deep geological layers could reduce global CO2 emissions of 4 billiard tonnes by 2050. This represents a 10% reduction promised by the international agreements. The price to pay for this prowess, or 900 billiard euros is however prohibitive.

The CSC technologies show three methods:

  • Carbon entrapment contained in smokes thanks to a liquid. Once this liquid is heated it releases the gas that can be captured and stored.
  • CO2 capture before coal combustion by gasification. We have a monoxide carbon gas and hydrogene. By treating this gas with water vapor, we can retrieve the carbon dioxide.
  • Oxycombustion, which is coal combustion with oxygen instead of air. This product is a gaseous mix of water vapor and CO2 that we know how to separate by cooling and gas compression.

These technologies affect thermal power plants using coal but also the one using natural gas and biomass. They can reduce polluting gas emissions in varied sectors such as concrete industry, oil and steel.

Projects and difficulties

Processes covered by “clean coal” are complex but working. They were proved by pilot project, at small scale. The industry has to reproduce them at larger scale which will require huge investments. These technologies should reach maturity by 2020. The modules and carbon capture units will be installed on existing power plants and other plants.

We count around twenty ongoing projects worldwide that will allow to evaluate the impact of “clean carbon”. For CSC technologies for example, the surveillance of CO2 injected in deep layers has a crucial importance.

On the European side, Total is leading a CSC project in France, nearby the Lacq field in New-Aquitaine. 50 000 tonnes of CO2 were injected in the soil the last few years and are now being monitored for any evolution. In the UK, the White Rose project consists in capturing 90% of emissions of the Drax power plant located in the Yorkshire. The gas storage sites are out at sea in the North Sea.

Germany chose the Schwarze Pumpe power plant in the Brandebourg, to be the first pilot power plant to use the oxycombustion process. The plant, operated by Vattenfall, uses lignite, a type of coal specially rich in carbon (65 to 75% of carbon) and that is even more polluting than carbon. The smokes produced are full of CO2 which helps capturing the gas.

On American territory, a unique power plant with CSC technology is fully working. This is the Petra Nova plant in Texas. The captured gas is injected in the neighboring oil fields still operated. This process facilitates the black gold extraction by pushing it towards a direction where it is easy to retrieve it.

The Weyburn project in North Dakota is a CSC plant with coal gasification. The gas is transported across the Canadian border to be injected in Saskatchewan’s oil fields.

Another ultra-modern and productive plant but without CSC technology is fully working in Arkansas. However, it is very costly.

In Canada, in the Saskatchewan province, is since 2014 the Boundary Dam thermal power plant. The company Saskpower who is in chrge of its operation claims that this CSC technology power plant emits almost no carbon dioxide. The gas is captured in the smokes generated by combustion before they go through the chimneys. The Saskpower company claims having a reduction of CO2 emissions of one million tonnes per year.


The Boundary Dam coal power plant of SaskPower, in 2008. Own work (Original text: I (Wtshymanski (talk)) created this work entirely by myself.)
© Wtshymanski

China, very active in the “clean coal” sector is at the state-of-the-art of technologies. These efforts acknowledged by the international energy Agency and by companies that are numerous to start development projects in the country.

French company Alstom opened a boiler fabrication plant for thermal power plants in Wuhan. This technology helps increasing by 50% the electricity volume produced with a same quantity of coal, reducing the greenhouse gas emissions as a consequence.

American company, General Electric and Chinese giant company Shenhua made an alliance to work on coal gasification techniques as well as carbon capture.

The implementation of “clean coal” technologies has two major handicaps: a cost too high and an energy overconsumption. A power plant with CSC technologies is 75% more expensive than a traditional power plant. Likewise, the megawatt electricity price per hour – 40 to 60% more expensive – penalizes consumers as much as the supplier.

Several projects were terminated because of budget overspending such as FutureGen and Kemper County Energy Facility while billions of dollars were invested. The power plant of Kemper in Mississipi, operated by Southern Company provided great hopes though. The project initiated in 2010 was to find the feasibility of “clean coal”. It was the future of electric production in the USA.

It was initially built to try out the coal gasification process and especially the lignite. The greenhouse gas emissions were to be reduced by 65% which would have make the coal operation as clean as natural gas. In the end, the project turned out to be a failure. Kemper was transformed in a classic natural gas thermal power plant to avoid any more loss.

Furthermore, the CSC technologies consume a lot more energy. Between 20 to 40% of produced electricity by a power plant power the capture units of which it is equipped. Regarding the Canadian power plant of Boundary Dam, a third of energy produced there is used for carbon dioxide capture. In addition, the transportation of compressed gas to storage sites is also very complex and energy consuming.

clean coal” technologies are not yet competitive and lack of financial support from governmental institutions.

For example, the European Commission does not follow the sector evolution and is growing demand of financing.

To incite industries to invest in “clean coal”, a reform of the CO2 emissions market is needed with the instalment of a carbon tax to punish the biggest CO2 emitters or climate directives. Such actions are still non-existent in the USA yet biggest coal consumer.

Environmental risks: health, ecosystems and climate

« Clean coal » as a modernized power plant emitting less greenhouse gas or as a CSC technology power plant is still more polluting than renewable energies and nuclear. Adopting it would encourage continuing the use of this fossil fuel which is polluting from its extraction.

Coal mines pollute rivers and air with dust and heavy metals such as selenium and manganese which are toxic. These particles are responsible for many diseases of which lung cancers, heart diseases or respiratory diseases such as asthma. Needless to say that mines destroy, literally, the environment. In the Apalachees for example, mines are opened by exploding mountains’ summit. Rock debris are spilled in the surrounding valleys and rivers.

clean coal-

Open pit coal mine in Hunter Valley, New South Wales, Australia, in 2011. https://www.flickr.com/photos/beyondcoalandgas/9304143669
Credit: Max Phillips (Jeremy Buckingham MLC)

If « clean coal » power plants reduce carbon dioxide emissions they do not eliminate them completely. We often talk about a 50% reduction. In addition, CSC technologies only capture carbon in general but not the other polluting gases and greenhouse gases.

The air pollution risks still exists with consequences on health or environment: acid rain, atmospheric pollution, etc. In 2014, the pollution emitted by the thermal power plant is supposedly responsible for 7 500 premature deaths according to the Clean Air Task Force organization.

The carbon entrapment and confinement techniques raise many more concerns. On the one hand, the practice consisting in reinjecting CO2 in oil fields to ease its extraction cancels all environmental benefits of these technologies.

Otherwise we fear carbon dioxide leaks in the grounds, groundwaters and on the surface. Because if the permanent storage sites are old fossil fuel reserves they were dotted of holes and wells for their exploitation needs.

Such leaks could alter the ecosystem on surface or in the close underground of the surface and put at risk plants, animals and humans. Carbon dioxide, stored as a liquid, can infiltrate ground waters leading to their acidification. Heavy metals present in the soil, degraded by acidity could also contaminate the water.

Gas emissions on surface can make a terrible sanitary catastrophy as the gas is toxic and can be deadly. As proof, in 1986, a bubble of carbon dioxide freed after a volcanic eruption in Nyos, Cameroun took the lives of 1 700 people and killed thousands of animals within a 25 km radius.

If the gas was to escape to the surface and go in the atmosphere, it would participate to climate change. What “clean coal” technologies claimed to avoid. That is why the GIEC, inevitable instance on climatic matters, asks for a better evaluation of “clean coal” techniques impacts.

Another fear is on carbon dioxide confinement mode. As the gas is stored in deep geological layers under the liquid state, it can potentially provoke earthquakes.

Indeed, according to a study from the OFEN (Swiss Federal Office of Energie/Office fédérale de l’énergie Suisse), the seismic risk is enhanced because this process changes the pressure conditions. It happened in several American states after the injection in the ground of used water from the oil and gas industry.

Lastly, we need to think about the CSC technologies risks at long-term. As, the challenge to limit the coal impact on climate consists in trapping carbon dioxide in the soil on a very long period of time. The safety of this storage has to be guaranteed for several centuries! This responsibility will be a heritage for future generations.

This latest matter is somewhat reminiscent of the controversial storage of highly radioactive waste in deep geological layers in the CIGEO project. For this particular site, we are talking of a 100 000 years commitment.

Does « clean coal » really have a spot in the energetic transition?

Opinion is divided. For some ecologists, coal would be the price to pay to end the nuclear as Germany has done it. It would also be necessary during the time where countries prepare for energetic transition. The world has a too strong dependence on coal and other fossil fuel energies to do without it overnight.

It is estimated that the energetic transition could take several decades. In the meantime, “clean coal” technologies offer the possibility of reducing the impact of this energy source on climate. Except they are not developed fast enough. It would take 130 projects of CSC technologies power plants in operations in 2020 to stay below the 2°C of global warming goal mentioned by the Paris agreements. But we are far from it…

For other ecologists, on the contrary, “clean coal” diverts investments from renewable energy which, remains to be developed especially on the performance side. After having noted that “clean coal” is struggling to be implemented and that it presents risks for the environment, Greenpeace announced in 2008 in a report called “False hope” that this technology, questionable, would not be developed on time to save the climate.

clean coal

© Linh Do

With alternatives that are more ecological such as natural gas and renewable energies, coal, as clean as it can be, cannot compete. Natural gas has the advantage of being less polluting and a lot cheaper than CSC technologies.

Thus, the thermal power plant using coal of Bouchain in France was replaced by a power plant using natural gas. Inaugurated in 2016 by EDF and General Electrics, this powerplant with the combined gas cycle technology has a performance of 62% for a reduction of 55% of CO2 emissions.

The USA chose another alternative: shale gas. Since they turned to this energy source, the coal part in their energetic mix has strongly reduced. But the shale gas exploitation is very controversial, specially because of seismic risks.

Finally, the future belongs to renewable energies that are more capable of preserving our climate. The research and development in this sector are well under way. These energy sources will soon be more attractive than coal on the market which will ease the energetic transition.