Brian Barton
Coal pollution mitigation refers to a set of strategies and technologies aimed at reducing the negative health and environmental impacts associated with burning coal for energy. The combustion of coal releases harmful substances such as carbon dioxide (CO2), sulfur dioxide, nitrogen oxides, mercury, and other pollutants, contributing to air pollution, acid rain, and greenhouse gas emissions. To address these issues, various policies and technologies have been proposed and implemented. These include pre-combustion techniques such as cleaning coal using physical or chemical methods, and post-combustion approaches like flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction. Additionally, carbon capture and storage (CCS) technologies, tax credits for refined coal production, and stricter emission standards outlined by organizations like the EPA, aim to reduce coal's environmental and health impacts.
| Characteristics | Values |
|---|---|
| Cleaning coal before combustion | Physical cleaning involves gravimetric processes, often with froth flotation, to remove minerals and other non-combustible components. Chemical treatments use acids or bases to remove deleterious components, leaving combustible material. |
| Cleaning coal after mining | The coal industry has found more effective ways of cleaning coal after it is mined. |
| Flue-gas desulfurization | Also known as scrubbers, this equipment reduces the amount of sulfur exiting smokestacks. |
| Selective catalytic reduction | |
| Electrostatic precipitators | |
| Fly ash reduction | U.S. air pollution laws now require most fly ash emissions to be captured by pollution-control devices. |
| Carbon capture and storage (CCS) | CCS technology captures carbon dioxide and stores it permanently underground. |
| Oxy-fuel carbon capture | An example is the Schwarze Pumpe power station in Germany, which captures CO2 and acid rain-producing pollutants, separates them, and compresses the CO2 into a liquid. |
| High-efficiency power plants | New plants could reduce CO2 emissions by 7% as they won't need to burn as much coal to generate the same amount of power. |
| Tax credits for refined coal | Producers of refined coal can qualify for tax credits, intended to reduce emissions. |
| Mercury and Air Toxics Standards (MATS) | The Biden-Harris administration has strengthened these standards, tightening the emissions standard for toxic metals by 67% and reducing mercury emissions by 70%. |
| Water pollution reduction | The Biden-Harris administration has introduced rules to reduce pollutants discharged through wastewater from coal-fired power plants by more than 660 million pounds per year. |
| Safe coal ash management | The Biden-Harris administration has introduced rules to ensure the safe management of coal ash, preventing groundwater contamination. |
| Carbon Pollution Standards | The Biden-Harris administration's Clean Air Act standards limit the amount of carbon pollution covered sources can emit, based on proven and cost-effective control technologies. |
| Bipartisan Infrastructure Law | This law includes funding to advance and deploy CCS technology and infrastructure. |
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What You'll Learn
Carbon capture and storage (CCS)
CCS has been described as a three-step process: capturing the CO2, transporting it, and then permanently storing it deep underground. This process helps to create a "closed loop", where carbon is extracted from the Earth as a fossil fuel and then returned to the Earth as CO2. Most current carbon capture projects use a liquid to chemically remove the CO2 before it exits the smokestack, but several new types of capture processes are also being developed.
CCS has been in operation since 1972 in the United States, where several natural gas plants in Texas have captured and stored more than 200 million tons of CO2 underground. As of 2024, there were 194 large-scale CCS facilities globally, with a CO2 capture capacity of 244 million tons per annum. The oil and gas industry is involved in 90% of CCS capacity worldwide, and CCS projects are currently storing almost 45 million tons of CO2 every year.
While CCS has the potential to significantly reduce CO2 emissions, implementing CCS technologies at coal-fired power plants has proven challenging due to economic viability and other external factors. The effectiveness of CCS in reducing carbon emissions depends on the plant's capture efficiency, the additional energy used for CCS, leakage, and business and technical issues.
There are also related concepts to CCS, such as Carbon Capture Utilisation (CCU or CCUS), which involves reusing the captured CO2 in industrial processes to create products such as plastics, concrete, or biofuel. Enhanced oil recovery (EOR) is the major use of CO2 today, where it is injected into oil wells to help extract more oil. However, there is controversy over whether this truly benefits the climate.
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Clean coal technologies
The development and commercialisation of clean coal technologies are important to maintain market competitiveness and address future energy supply concerns, energy price volatility, and environmental effects. However, clean coal technologies are costly and energy-intensive, and implementing CCS technologies at coal-fired power plants has proven challenging due to economic viability issues.
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Reducing mercury emissions
Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. One of the key pollutants released during coal combustion is mercury. Mercury is a neurotoxin that can cause developmental damage in humans. It is typically trapped underground along with fossil fuels but is released into the atmosphere when coal is burned. Mercury can stay airborne for over a year and travel to remote ecosystems, especially in the Arctic Circle. It can undergo chemical reactions with sunlight and other elements, turning into a type of salt that dissolves in water vapour and falls as rain, contaminating soil and water.
Coal-fired power plants are the largest single anthropogenic source of mercury emissions, with 21% of global emissions, or approximately 2220 tonnes per year, coming from this source. The majority of coal-burning power plants emit 5 kilograms of mercury per year, but there are clusters of lignite-burning plants in North Dakota and Texas that emit over 100 kilograms annually. Mercury exposure is particularly dangerous for children, and people who live near power plants, often low-income communities, are at a higher risk of exposure. A national survey estimated that 19 million people in the United States who ate self-caught fish at least three times a week were exposed to dangerous levels of mercury.
To reduce mercury emissions from coal-fired power plants, equipment that reduces sulfur dioxide, nitrogen oxides, and particulate matter can be used, as this equipment can also reduce mercury emissions from some types of coal. Scientists are also working on new methods to tackle mercury emissions, and research is underway. One method is carbon capture, which separates and recovers CO2 from emissions sources, allowing it to be injected underground for permanent storage. Up to 95% of mercury releases from power plants can be reduced by improving coal and plant performance and optimising control systems for other pollutants.
The Biden administration issued regulations in 2024 that tightened limits on mercury emissions from coal-burning power plants, lowering allowable emissions from lignite coal-burning plants by 70%. However, the Trump administration has allowed many coal-fired power plants to bypass these air pollution limits, and the development and implementation of carbon capture technologies have faced challenges due to economic viability and external factors. Nevertheless, tax credits have been offered to producers of refined coal, which involves mixing chemical additives with conventional coal to reduce emissions when burned.
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Regulations and standards
Air Pollution Control Regulations:
- The Clean Air Act: The Clean Air Act, as mentioned in the context of the US, mandates the reduction of pollutants released into the air by industries, specifically targeting toxic metals and mercury emissions from coal-fired power plants.
- Emission Standards: Governments have implemented stringent emission standards to limit the amount of carbon pollution and other toxic emissions that coal-fired power plants can release. These standards are based on proven and cost-effective control technologies. For example, the Biden-Harris Administration in the US tightened emission standards, aiming for a 67% reduction in toxic metal emissions and a 70% reduction in mercury emissions.
- Paris Agreement: The Paris Agreement of 2015 highlighted the urgency of achieving carbon neutrality and net-zero emissions globally. While there has been some progress, further delays in implementing national policies could have significant consequences on global warming.
Water Pollution Regulations:
- The Clean Water Act: The Clean Water Act requires industries to reduce pollutants discharged into water bodies. This includes addressing coal-fired power plants' wastewater pollutants and ensuring the safe management of coal ash to prevent groundwater contamination.
- Wastewater Discharge Standards: Regulations are in place to reduce pollutants discharged through wastewater from coal-fired power plants, aiming to ensure cleaner water for affected communities, especially those with environmental justice concerns.
Mining and Land Reclamation Regulations:
- Mountaintop Removal Restrictions: Mountaintop removal mining has significantly impacted the Appalachian Mountains in the US. Regulations now require controlling dust and water runoff from coal mining operations and reclaiming the land to restore it to its original condition.
- Land Reclamation for Airports, Landfills, and Golf Courses: Reclaiming land previously used for coal mining can mitigate environmental impacts and provide new purposes, such as airports, landfills, and golf courses.
Carbon Capture and Storage (CCS) Standards:
- CCS Technology Implementation: CCS technology captures carbon dioxide from coal-fired power plants and stores it permanently underground. While there have been challenges and economic viability concerns, advancements and investments are being made to improve CCS technology and infrastructure.
- Oxy-combustion Carbon Capture: This method, demonstrated by Vattenfall's Schwarze Pumpe power station in Germany, captures CO2 and acid rain-producing pollutants, separates them, and compresses the CO2 into a liquid for underground injection.
Tax Credits and Incentives:
- Tax Credits for Refined Coal: In certain countries, the production of refined coal, which involves mixing chemical additives to reduce pollution during burning, can qualify producers for tax credits. However, there have been concerns about the effectiveness of this approach in reducing emissions.
- Biden's Inflation Reduction Act: President Biden's Inflation Reduction Act provides tax incentives for companies adopting CCS technology, helping to offset the costs and improve emissions control.
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Cleaning coal pre-combustion
Coal pollution mitigation involves a range of technologies and systems that aim to reduce the negative health and environmental impacts of burning coal for energy. Cleaning coal pre-combustion is one such approach, which can be achieved through physical and chemical means.
One physical cleaning method is the gravimetric process, often used in conjunction with froth flotation. This method removes minerals and other non-combustible components from coal by exploiting their greater density compared to coal. Froth flotation is a widely practised technology for coal cleaning. Another physical cleaning method is the use of a modified air table, as seen in a study on Turkish coal, which employs a dry cleaning approach.
Chemical cleaning treatments involve using acids or bases to treat crushed coal, removing deleterious components while leaving combustible material behind. This technology is generally expensive and has rarely progressed beyond the demonstration phase. However, during World War II, German industry successfully employed hydrofluoric acid treatments to remove ash from coal.
Coal washing is another coal preparation technique that falls under chemical cleaning. It involves mixing crushed coal with a liquid, allowing unwanted minerals to separate and settle. This process helps minimize emissions of sulfur dioxide, nitrogen oxides, and particulates.
Additionally, enzymology has been applied to clean coal technology. This involves using hydrophilic oxidative enzymes in reverse micelles within an organic solvent to remove organic sulfur from coal. The enzymes oxidize the sulfur groups, breaking the C-S bonds and releasing sulfur as sulfuric acid.
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Frequently asked questions
Coal pollution mitigation is a series of systems and technologies that aim to reduce the negative health and environmental impacts of burning coal for energy.
Coal can be cleaned by physical and chemical means. Physical cleaning involves gravimetric processes, often in conjunction with froth flotation, to remove non-combustible components. Chemical cleaning uses acids or bases to treat crushed coal and remove deleterious components.
Post-combustion approaches include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction. These methods aim to reduce harmful emissions from coal combustion, such as sulfur dioxide, nitrogen oxides, and particulate matter.
The Clean Air Act and The Clean Water Act in the United States require industries to reduce pollutants released into the air and water. The Biden-Harris administration has also finalized stronger Carbon Pollution Standards for existing coal-fired and new natural gas-fired power plants to limit carbon pollution.
Carbon Capture and Storage (CCS) technology captures carbon dioxide from coal-fired power plants and stores it permanently underground. Oxy-combustion carbon capture is another approach, as seen at the Schwarze Pumpe power station in Germany, which captures and separates CO2 and acid rain-producing pollutants.
