Emissions controls at a coal fired power plant

Coal pollution mitigation, sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances, including mercury, lead, sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon dioxide (CO2), contributing to air pollution, acid rain, and greenhouse gas emissions. Methods include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction focusing on reducing the emissions of these harmful substances. These measures aim to reduce coal's impact on human health and the environment.

Description

When coal is burned, various chemicals are released into the air. These chemicals include mercury, lead and other heavy metals, sulfur dioxide, and nitrogen oxides, the primary molecules contributing to the formation of acid rain. Additionally, an abundance of (CO2), the primary greenhouse gas associated with burning fossil fuels, enters the atmosphere, contributing to smog. Finally, the burning of coal can lead to the release of small amounts of radioactive materials occurring naturally within anthracite.[1]

Coal pollution mitigation is a series of systems and technologies that seek to mitigate the Health and environmental impact of the coal industry|health and environmental impact of coal; in particular, air pollution from coal-fired power stations and from coal burnt by heavy industry. Systems of coal pollution mitigation primarily focus on mitigating the release of sulfur dioxide, nitrogen oxides, and particulates comprising chemical smog, which cause visible air pollution, illness, and premature deaths.

Sulfur dioxide can be removed by flue-gas desulfurization and nitrogen oxides by selective catalytic reduction (SCR). Particulates can be removed with electrostatic precipitators. Although perhaps less efficient, wet scrubbers can remove both gasses and particulates. Reducing fly ash reduces emissions of naturally occurring radioactive materials. Mercury emissions can be reduced by up to 95%. Capturing carbon dioxide emissions from coal is a process in which a relatively pure stream of carbon dioxide from industrial sources is separated, treated, and transported to a long-term storage location.: 2221 

Background

Coal becoming a necessity and a problem

The Industrial Revolution was characterized by the use of steam power, the growth of factories, and the mass production of manufactured goods. In this case, coal became a mass necessity, “for it was a cheap and abundant source of energy”[2] used to power steam engines, heat buildings, and generate electricity. With coal becoming a main source of energy, there was an increase in the employment of coal miners. With this increase in demand for labor came humanitarian issues. Notably, “Children were ideal employees because they could be paid less, were often of smaller size so could attend to tasks in tight spaces and were less likely to organize and strike against their pitiable working conditions.”[3]

Environmental impact of coal

Combustion by-products

By-products of coal combustion are compounds that are released into the atmosphere as a result of burning coal. Coal includes contaminants such as sulfur compounds and non-combustible minerals. When coal is burned, the minerals become ash (i.e. particulate matter or PM), and the sulfur forms sulfur dioxide. Since air is mostly nitrogen, the combustion of coal often leads to the production of nitrogen oxides. Sulfur dioxide and nitrogen oxides are the primary causes of acid rain. For many years—before greenhouse gasses were widely understood to be a threat—it was thought that these by-products were the only drawback to using coal. These by-products are still a problem, but they have been greatly diminished in most advanced countries due to clean air regulations. It is possible to remove most of the sulfur dioxide, nitrogen oxides, and particulate matter (PM) emissions from the coal-burning process. For example, various techniques are used in a coal preparation plant to reduce the amount of non-combustible matter (i.e. ash) in the coal before burning. During combustion, fluidized bed combustion is used to reduce sulfur dioxide emissions. After burning, particulate matter (i.e. ash and dust) can be reduced using an electrostatic precipitator, and sulfur dioxide emissions can be further reduced with flue-gas desulfurization. Trace amounts of radionuclides are more difficult to remove.[citation needed

Coal-fired power plants are the largest aggregate source of the toxic heavy metal mercury: 50 tons per year come from coal power plants out of 150 tons emitted nationally in the US and 5000 tons globally. However, according to the United States Geological Survey, the trace amounts of mercury in coal by-products do not pose a threat to public health. A study in 2013 found that mercury found in the fish in the Pacific Ocean could possibly be linked to coal-fired plants in Asia.[citation needed]

Coal pollution produces smog

A visibly persistent example of the effects of pollution from burning coal is the “smog and soot which had serious health impacts on residents of growing urban centers.”[4] Smog is a colloid that is formed when sunlight reacts with gaseous nitrogen oxides and at least one volatile organic compound (VOC) latent within the atmosphere. Smog is often visible to the naked human eye, and exists as a hazy, white smoke sometimes causing acute irritation of the eyes, nose, and respiratory system.[5] The two main sources that cause smog are primary and secondary pollution. Primary pollution is emitted directly from a source, such as driving a car, burning coal, burning fossil fuels, etc., whereas secondary pollution is formed in the atmosphere, such as natural chemical reactions between sunlight and ozone. According from the Water and Air Pollution "The great smog of 1952 was caused by the mass production of burning coal, killing 4,000 people in londonWater and Air Pollution,[4] and in “1948 there was severe industrial air pollution created deadly smog that asphyxiated 20 people in Donora Pennsylvania and made 7,000 more people sick.” [4]

Measurement of pollution and availability of pollution data

In some countries, such as the EU, smokestack measurements from individual power plants must be published. Meanwhile, in some countries, such as Turkey, they are only reported to the government, not the public. However, since the late 2010s satellite measurements of some pollutants have been available.

Greenhouse gasses

As coal is mostly carbon, burning it produces a lot of carbon dioxide. The IEA said in 2022 that ‘achieving a swift reduction in global coal emissions is the central challenge for reaching international climate targets’.[6]

Carbon sequestration technology, to remove significant quantities of carbon dioxide from the air, has yet to be tested on a large scale and may not be safe or successful. Sequestered CO2 may eventually leak up through the ground, may lead to unexpected geological instability or may cause contamination of aquifers used for drinking water supplies.[citation needed] Carbon capture and storage is applied at large point emitters of carbon dioxide with the objective of preventing it from entering the atmosphere.

As approximately 37% of the world energy consumption in 2022 was from coal, reaching the carbon dioxide reduction targets of the Paris Agreement will require modifications to how coal is used.[7]

Clean coal and the environment

Further information: Health and environmental impact of the coal industry

In conjunction with enhanced oil recovery and other applications, commercial-scale CCS is currently being tested in the U.S. and other countries.[by whom?] Proposed CCS sites are subjected to extensive investigation and monitoring to avoid potential hazards, which could include leakage of sequestered CO2 to the atmosphere, induced geological instability, or contamination of water sources such as oceans and aquifers used for drinking water supplies. As of 2021, the only demonstrator for CCS on a coal plant that stores the gas underground is part of the Boundary Dam Power Station.

The Great Plains Synfuels plant supports the technical feasibility of carbon dioxide sequestration. Carbon dioxide from the coal gasification is shipped to Canada, where it is injected into the ground to aid in oil recovery. A drawback of the carbon sequestration process is that it is expensive compared to traditional processes.

Technology

Flue-gas desulfurization

SO2 can be removed by flue-gas desulfurization.

Selective catalytic reduction

NO2 can be removed by selective catalytic reduction (SCR).

Electrostatic precipitation

Particulates can be removed with electrostatic precipitators.

Scrubbers

Wet scrubbers

Although perhaps less efficient than desulfurization, SCR, and electrostatic precipitation, wet scrubbers can remove both gases and particulates.

Mercury removal

Mercury emissions can be reduced by up to 95%.[8]

Fly ash reduction

Reducing fly ash reduces emissions of radioactive materials.

Carbon capture

Several different technological methods are available for carbon capture as demanded by the clean coal concept:

  • Pre-combustion capture – This involves the gasification of a feedstock (such as coal) to form synthesis gas, which may be shifted to produce an H2 and CO2-rich gas mixture, from which the CO2 can be efficiently captured and separated, transported, and ultimately sequestered,[9] This technology is usually associated with Integrated Gasification Combined Cycle process configurations.[10]
  • Post-combustion capture – This refers to capture of CO2 from exhaust gases of combustion processes.
  • Oxy-fuel combustion – Fossil fuels such as coal are burned in a mixture of recirculated flue gas and oxygen, rather than in air, which largely eliminates nitrogen from the flue gas enabling efficient, low-cost CO2 capture.[11]

The Kemper County IGCC Project, a proposed 582 MW coal gasification-based power plant, was expected to use pre-combustion capture of CO2 to capture 65% of the CO2 the plant produces, which would have been utilized and geologically sequestered in enhanced oil recovery operations.[12] However, after many delays and a cost runup to $7.5 billion (triple the initial budget),[13] the coal gasification project was abandoned and as of late 2017, Kemper is under construction as a cheaper natural gas power plant.[14]

The Saskatchewan Government's Boundary Dam Integrated Carbon Capture and Sequestration Demonstration Project will use post-combustion, amine-based scrubber technology to capture 90% of the CO2 emitted by Unit 3 of the power plant; this CO2 will be pipelined to and utilized for enhanced oil recovery in the Weyburn oil fields.[15]

An oxyfuel CCS power plant operation processes the exhaust gases so as to separate the CO2 so that it may be stored or sequestered

An early example of a coal-based plant using (oxy-fuel) carbon-capture technology is Swedish company Vattenfall’s Schwarze Pumpe power station located in Spremberg, Germany, built by German firm Siemens, which went on-line in September 2008.[16][17] The facility captures CO2 and acid rain producing pollutants, separates them, and compresses the CO2 into a liquid. Plans are to inject the CO2 into depleted natural gas fields or other geological formations. Vattenfall opines that this technology is considered not to be a final solution for CO2 reduction in the atmosphere, but provides an achievable solution in the near term while more desirable alternative solutions to power generation can be made economically practical.[17]

Other examples of oxy-combustion carbon capture are in progress. Callide Power Station has retrofitted a 30-MWth existing PC-fired power plant to operate in oxy-fuel mode; in Ciuden, Spain, Endesa has a newly built 30-MWth oxy-fuel plant using circulating fluidized bed combustion (CFBC) technology.[18] Babcock-ThermoEnergy's Zero Emission Boiler System (ZEBS) is oxy-combustion-based; this system features near 100% carbon-capture and according to company information virtually no air-emissions.[19]

Other carbon capture and storage technologies include those that dewater low-rank coals. Low-rank coals often contain a higher level of moisture content which contains a lower energy content per tonne. This causes a reduced burning efficiency and an increased emissions output. Reduction of moisture from the coal prior to combustion can reduce emissions by up to 50 percent.[20]

Potential financial impact

Whether carbon capture and storage technology is adopted worldwide will "...depend less on science than on economics. Cleaning coal is very expensive."[21]

Cost of converting a single coal-fired power plant

Conversion of a conventional coal-fired power plant is done by injecting the CO2 into ammonium carbonate after which it is then transported and deposited underground (preferably in soil beneath the sea).[22] This injection process however is by far the most expensive. Besides the cost of the equipment and the ammonium carbonate, the coal-fired power plant also needs to use 30% of its generated heat to do the injection (parasitic load). A test-setup has been done in the American Electric Power Mountaineer coal-burning power plant.

One solution to reduce this thermal loss/parasitic load is to burn the pulverised load with pure oxygen instead of air.[22]

Cost implications for new coal-fired power plants

Newly built coal-fired power plants can be made to immediately use gasification of the coal prior to combustion. This makes it much easier to separate off the CO2 from the exhaust fumes, making the process cheaper. This gasification process is done in new coal-burning power plants such as the coal-burning power plant at Tianjin, called "GreenGen".

Costs for China

As of 2019 costs of retrofitting CCS are unclear and the economics depends partly on how the Chinese national carbon trading scheme progresses.[23]

Costs for India

Pollution led to more than 2.3 million premature deaths in India in 2019, according to a new Lancet study. Nearly 1.6 million deaths were due to air pollution alone, and more than 500,000 were caused by water pollution. India has developed instruments and regulatory powers to mitigate pollution sources but there is no centralized system to drive pollution control efforts and achieve substantial improvements," the study said adding that in 93% of the country, the amount of pollution remains well above the World Health Organization (WHO) guidelines.[24]

Politics

Australia

In Australia, carbon capture and storage was often referred to by then Prime Minister Kevin Rudd as a possible way to reduce greenhouse gas emissions. (The previous Prime Minister John Howard had stated that nuclear power was a better alternative, as CCS technology may not prove to be economically feasible.)

Canada

In 2014 SaskPower a provincial-owned electric utility finished renovations on Boundary Dam's boiler number 3 making it the world's first post-combustion carbon capture storage facility.[25] The renovation project ended up costing a little over $1.2 billion and can scrub out CO2 and toxins from up to 90 percent of the flue gas that it emits.[25]

China

Since 2006, China releases more CO2 than any other country.[26][27][28][29][30] Researchers in China are focusing on increasing efficiency of burning coal so they can get more power out of less coal.[31] It is estimated that new high efficiency power plants could reduce CO2 emission by 7% because they won't have to burn as much coal to get the same amount of power.[31]

India

Japan

Following the catastrophic failure of the Fukushima I Nuclear Power Plant in Japan that resulted from the 2011 Tōhoku earthquake and tsunami, and the subsequent widespread public opposition against nuclear power, high energy, lower emission (HELE) coal power plants were increasingly favored by the Shinzō Abe-led government to recoup lost energy capacity from the partial shutdown of nuclear power plants in Japan and to replace aging coal and oil-fired power plants, while meeting 2030 emission targets of the Paris Agreement. 45 HELE power plants have been planned, purportedly to employ integrated gasification fuel cell cycle, a further development of integrated gasification combined cycle.[32][33]

Japan had adopted prior pilot projects on IGCC coal power plants in the early-1990s and late-2000s.

United States

In the United States, clean coal was mentioned by former President George W. Bush on several occasions, including his 2007 State of the Union Address. Bush's position was that carbon capture and storage technologies should be encouraged as one means to reduce the country's dependence on foreign oil.

During the US Presidential campaign for 2008, both candidates John McCain and Barack Obama expressed interest in the development of CCS technologies as part of an overall comprehensive energy plan. The development of pollution mitigation technologies could also create export business for the United States or any other country working on it.

The American Reinvestment and Recovery Act, signed in 2009 by President Obama, allocated $3.4 billion for advanced carbon capture and storage technologies, including demonstration projects.

Former Secretary of State Hillary Clinton has said that "we should strive to have new electricity generation come from other sources, such as clean coal and renewables", and former Energy Secretary Dr. Steven Chu has said that "It is absolutely worthwhile to invest in carbon capture and storage", noting that even if the U.S. and Europe turned their backs on coal, developing nations like India and China would likely not.

During the first 2012 United States presidential election debate, Mitt Romney expressed his support for clean coal, and claimed that current federal policies were hampering the coal industry.[34]

During the Trump administration, an Office of Clean Coal and Carbon Management was set up within the United States Department of Energy, but was abolished in the Biden administration.

Regulations

Criticism of the approach

Environmentalists such as Dan Becker, director of the Sierra Club's Global Warming and Energy Program, believes that the term clean coal is misleading: "There is no such thing as clean coal and there never will be. It's an oxymoron." The Sierra Club's Coal Campaign has launched a site refuting the clean coal statements and advertising of the coal industry.

Complaints focus on the environmental impacts of coal extraction, high costs to sequester carbon, and uncertainty of how to manage result pollutants and radionuclides. In reference to sequestration of carbon, concerns exist about whether geologic storage of CO2 in reservoirs, aquifers, etc., is indefinite/permanent.

The palaeontologist and influential environmental activist Tim Flannery made the assertion that the concept of clean coal might not be viable for all geographical locations.

Critics also believe that the continuing construction of coal-powered plants (whether or not they use carbon sequestration techniques) encourages unsustainable mining practices for coal, which can strip away mountains, hillsides, and natural areas. They also point out that there can be a large amount of energy required and pollution emitted in transporting the coal to the power plants.

The Reality Coalition, a US non-profit climate organization composed of the Alliance for Climate Protection, the Sierra Club, the National Wildlife Federation, the Natural Resources Defense Council, and the League of Conservation Voters, ran a series of television commercials in 2008 and 2009. The commercials were highly critical of attempts to mitigate coal's pollution, stating that without capturing CO2 emissions and storing it safely that it cannot be called clean coal.

Greenpeace is a major opponent of the concept, because they view emissions and wastes as not being avoided but instead transferred from one waste stream to another. According to Greenpeace USA's Executive Director Phil Radford speaking in 2012, "even the industry figures it will take 10 or 20 years to arrive, and we need solutions sooner than that. We need to scale up renewable energy; 'clean coal' is a distraction from that."

Demonstration projects

Projects in the United States

In the late 1980s and early 1990s, the U.S. Department of Energy (DOE) began conducting a joint program with the industry and State agencies to demonstrate clean coal technologies large enough for commercial use. The program, called the Clean Coal Technology & Clean Coal Power Initiative (CCPI), has had a number of successes that have reduced emissions and waste from coal-based electricity generation.[35] By 2000, the EPA and DOE made many basic systems required. The National Energy Technology Laboratory has administered three rounds of CCPI funding and the following projects were selected during each round:[36]

  • Round 1 CCPI Projects
    • Advanced Multi-Product Coal Utilization By-Product Processing Plant
    • Demonstration of Integrated Optimization Software at the Baldwin Energy Complex
    • Gilberton Coal-to-Clean Fuels and Power Co-Production Project
    • Increasing Power Plant Efficiency: Lignite Fuel Enhancement
    • TOXECON Retrofit for Mercury and Multi-Pollutant Control on Three 90-MW Coal-Fired Boilers
    • Western Greenbrier Co-Production Demonstration Project
    • Commercial Demonstration of the Airborne Process
    • Integration of Advanced Emission Controls to Produce Next-Generation Circulating Fluid Bed Coal Generating Unit
  • Round 2 CCPI Projects
    • Airborne Process Commercial Scale Demonstration Program
    • Demonstration of a Coal-Based Transport Gasifier
    • Mercury Species and Multi-Pollutant Control Project
    • Mesaba Energy Project
  • Round 3 CCPI Projects

These programs have helped to meet regulatory challenges by incorporating pollution control technologies into a portfolio of cost-effective regulatory compliance options for conventional and developmental coal-fired power plants. This portfolio has positioned the U.S. as a top exporter of technologies such as those used for coal and mercury, and more recently for carbon capture, consistent with a goal of deploying advanced coal-based power systems in commercial service. The DOE continues its programs and initiatives through regional sequestration partnerships, a carbon sequestration leadership forum and the Carbon Sequestration Core Program, a CCS research and development program.[37]

According to a 1999 report by the assistant secretary for fossil energy at the U.S. Department of Energy, clean coal technology has paid measurable dividends. Technological innovation introduced through the CCT Program now provides consumers cost-effective, clean, coal-based energy.[38] By 2015, the estimated emissions per coal plant went down by 22%.

Proposed CCS sites are subjected to extensive investigation and monitoring to avoid potential hazards, which could include leakage of sequestered CO2 to the atmosphere, induced geological instability, or contamination of water sources such as oceans and aquifers used for drinking water supplies.[39][40][41] As of 2021 the only demonstrator for CCS on a coal plant that stores the gas underground is part of the Boundary Dam Power Station.[42]

See also

References

  1. ↑ "Radioactive Wastes in Coal-Fired Power Plants". EPA. 2023-06-15. Retrieved 2023-12-27.
  2. ↑ "Industrial Revolution Linked to Early Signs of Climate Change". HISTORY. 2023-04-18. Retrieved 2023-11-28.
  3. ↑ Moehling, Carolyn M. (January 1999). "State Child Labor Laws and the Decline of Child Labor". Explorations in Economic History. 36 (1): 72–106. doi:10.1006/exeh.1998.0712. ISSN 0014-4983.
  4. 1 2 3 "Water and Air Pollution". HISTORY. 2020-03-30. Retrieved 2023-11-28.
  5. ↑ "Smog". education.nationalgeographic.org. Retrieved 2023-11-28.
  6. ↑ "Achieving a swift reduction in global coal emissions is the central challenge for reaching international climate targets - News". IEA. Retrieved 2023-12-29.
  7. ↑ "Coal". IEA - International Energy Agency. Retrieved 28 Dec 2023.
  8. ↑ "Mercury control from coal combustion". UNEP. Archived from the original on August 17, 2018.
  9. ↑ "Pre-combustion Carbon Capture Research". Energy.gov. Office of Fossil Energy, U.S. Department of Energy. Retrieved 22 July 2014.
  10. ↑ "Picking a Winner in Clean-Coal Technology".
  11. ↑ "R&D Facts - Oxy-Fuel Combustion" (PDF). National Energy Technology Laboratory, U.S. Department of Energy. Archived from the original (PDF) on 31 October 2014. Retrieved 22 July 2014.
  12. ↑ "IGCC Project Examples - Kemper County IGCC Project". Gasifipedia. National Energy Technology Laboratory, U.S. Department of Energy. Archived from the original on 17 March 2014. Retrieved 22 July 2014.
  13. ↑ Urbina, Ian (2016-07-05). "Piles of Dirty Secrets Behind a Model 'Clean Coal' Project (Published 2016)". The New York Times. ISSN 0362-4331. Retrieved 2021-02-03.
  14. ↑ Geuss, Megan (2017-06-29). "$7.5 billion Kemper power plant suspends coal gasification". Ars Technica. Retrieved 2017-07-01.
  15. ↑ "Boundary Dam Integrated Carbon Capture and Sequestration Demonstration Project". Global CCS Institute. Archived from the original on 10 August 2014. Retrieved 22 July 2014.
  16. ↑ "Vattenfall's Project on CSS". Vattenfall. Archived from the original on 2010-10-26.
  17. 1 2 http://discovermagazine.com/2009/feb/25-can-clean-coal-actually-work/?searchterm=clean%20coal "Can Clean Coal Actually Work?" article in Feb. 2009 issue, p. 18, Retrieved 2009-05-11
  18. ↑ "Overview of Oxy-fuel Combustion Technology for CO2 Capture". Cornerstone Magazine. World Coal Association. Retrieved 22 July 2014.
  19. ↑ [leads nowhere previously cited - http://ww25.thermoenergy.com/Zm9yY2VTUg]
  20. ↑ Ge, Lichao; Zhang, Yanwei; Xu, Chang; Wang, Zhihua; Zhou, Junhu; Cen, Kefa (2015-11-05). "Influence of the hydrothermal dewatering on the combustion characteristics of Chinese low-rank coals". Applied Thermal Engineering. 90: 174–181. doi:10.1016/j.applthermaleng.2015.07.015. ISSN 1359-4311.
  21. ↑ Ball, Jeffrey (2009-03-20). "Coal Hard Facts: Cleaning It Won't Be Dirt Cheap". The Wall Street Journal.
  22. 1 2 Nijhuis, Michelle (April 2014). "Can Coal Ever Be Clean?". National Geographic. Archived from the original on March 16, 2014.
  23. ↑ "Carbon Capture, Storage and Utilization to the Rescue of Coal? Global Perspectives and Focus on China and the United States". www.ifri.org. Retrieved 2020-01-25.
  24. ↑ "Carbon capture and coal gasification can be a game changer for India - Opinion by Atanu Mukherjee | ET EnergyWorld". ETEnergyworld.com. Retrieved 2020-01-25.
  25. 1 2 Danko, Pete (2014-10-02). "World's First Full-Scale 'Clean' Coal Plant Opens in Canada". National Geographic Society. Archived from the original on January 12, 2019. Retrieved 2017-04-27.
  26. ↑ "China's Emissions: More Than U.S. Plus Europe, and Still Rising". The New York Times. 2018-01-25.
  27. ↑ "Chinese coal fuels rise in global carbon emissions". The Times. 2017-11-14.
  28. ↑ "Yes, The U.S. Leads All Countries In Reducing Carbon Emissions". Forbes. 2017-10-24.
  29. ↑ "World carbon dioxide emissions data by country: China speeds ahead of the rest". The Guardian. 2011-01-31.
  30. ↑ "China now no. 1 in CO2 emissions; USA in second position". PBL Netherlands Environmental Assessment Agency. 19 June 2007. Archived from the original on 2019-07-09. Retrieved 2018-03-20.
  31. 1 2 "China's drive to clean up its coal power, one plant at a time". New Scientist. Retrieved 2017-05-04.
  32. ↑ McHugh, Babs (2017-02-23). "Japanese government planning to build 45 new coal fired power stations to diversify supply". ABC Online. Retrieved 2017-02-23.
  33. ↑ Watanabe, Chisaki (2015-11-10). "Want to Burn Coal and Save the Planet? Japan Touts a Solution". Bloomberg. Retrieved 2017-02-23.
  34. ↑ "Transcript And Audio: First Obama-Romney Debate". NPR. Federal News Service. 2012-10-03. Retrieved 2013-05-24.
  35. ↑ "Clean Coal Technology & The Clean Coal Power Initiative". U.S. Department of Energy.
  36. ↑ "Major Demonstrations: Clean Coal Power Initiative (CCPI)". NETL. Archived from the original on September 24, 2006. Retrieved 1 May 2012.
  37. ↑ "Carbon Sequestration". U.S. Department of Energy.
  38. ↑ "Clean Coal Technology: The Investment Pays Off" (PDF). U.S. Department of Energy.
  39. ↑ "AWWA warns Congress about CO2 injection concerns". American Water Works Association. July 29, 2008. Archived from the original on March 2, 2009. Retrieved 2008-08-27.
  40. ↑ "'Clean coal' push concerns environmental activists". Ohio Valley Environmental Coalition. October 16, 2005. Retrieved 2008-08-09.
  41. ↑ "What is clean coal technology?". HowStuffWorks. 2007-07-18. Retrieved 2018-05-10.
  42. ↑ Dyke, James; Watson, Robert; Knorr, Wolfgang (22 April 2021). "Climate scientists: concept of net zero is a dangerous trap". The Conversation. Retrieved 2021-10-23.

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