Kiera Jefferson
Coal is an abundant and inexpensive fuel source, but it is also one of the dirtiest. The process of extracting and burning coal has a significant impact on the environment. In the US, surface mines (or strip mines) were the source of about 63% of the coal mined in 2022, and mountaintop removal and valley fill mining have affected large areas of the Appalachian Mountains. As such, the development of clean coal technologies has become increasingly important. Clean coal refers to technologies that aim to reduce the negative environmental impacts of coal combustion, including carbon capture and storage (CCS), which captures and stores carbon dioxide emissions from coal plants, preventing them from being released into the atmosphere. However, critics argue that CCS is expensive and cannot address all of coal's pollutants, such as mercury and nitrogen oxide. While clean coal technologies may help reduce carbon emissions, it is important to also consider the environmental impacts of coal extraction and the potential for water pollution during the cleaning process.
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What You'll Learn
Clean coal technology
One of the most promising CCTs is carbon capture and storage (CCS), which catches and sequesters carbon dioxide (CO2) emissions from power plants. CCS can be achieved through flue-gas separation, which removes CO2 with a solvent, or ocean storage, which involves injecting liquid CO2 into deep waters. However, these technologies are often expensive and can create environmental problems if not carefully managed.
The integrated gasification combined cycle (IGCC) technology is another CCT that offers high efficiency and low environmental impact. IGCC systems convert coal to a fuel gas at high temperatures, removing particulates and sulfur compounds before combustion.
Overall, clean coal technology is important for maintaining the market competitiveness of coal in the face of concerns about future energy supplies, energy price volatility, and environmental effects. However, it is important to note that CCTs do not eliminate all toxic emissions from coal, and the success of these technologies depends on their ability to mitigate environmental issues without creating new ones.
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Carbon capture and storage (CCS)
CCS projects are storing almost 45 million tons of CO2 every year, equivalent to the emissions of about 10 million passenger cars. Capture generally takes place at large stationary sources of CO2, like power plants or industrial plants that make cement, steel, and chemicals. 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 under development.
The captured CO2 gas is compressed and transported to a storage site, generally through a pipeline. Once at the storage site, the CO2 is pumped more than 2,500 feet down wells into geological formations like used-up oil and gas reservoirs, as well as formations that contain unusable, salty water.
There is also a related concept, CCUS (Carbon Capture Utilization or Usage, and Storage), where instead of storing CO2, it could be reused in industrial processes by converting it into plastics, concrete, or biofuel. The main use of CO2 today is enhanced oil recovery, where CO2 is pumped into oil wells to help flush out hard-to-extract oil. However, controversy remains over whether using captured CO2 to extract more oil ultimately benefits the climate.
CCS can be used in combination with bioenergy (BECCS), where biomass (like wood or grasses) removes CO2 from the air through photosynthesis. The biomass is then burned in a power plant, with the resulting CO2 captured and stored, creating "negative emissions". Direct air capture (DAC) is another negative emissions option, where CO2 is removed from the air using a chemical process, but this is currently inefficient and expensive.
According to the Global CCS Institute's 2022 report, there were 194 large-scale CCS facilities globally, with a CO2 capture capacity of 244 million tonnes per annum. However, the effectiveness of CCS in reducing carbon emissions depends on factors such as capture efficiency, additional energy used, leakage, and technical issues. Overall, CCS is a proven technology that has been in safe operation for over 45 years, and it plays a crucial role in reducing carbon dioxide emissions to combat climate change.
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Scrubbers and other pollution control measures
Clean coal technology is moving towards coal gasification, which produces a concentrated and pressurised carbon dioxide stream, followed by its separation and geological storage. This technology has the potential to achieve "zero emissions", or at least extremely low emissions of conventional coal pollutants and engineered carbon dioxide emissions. However, burning coal without adding to global carbon dioxide levels remains a significant technological challenge.
One of the primary strategies for reducing emissions from coal-fired power plants is the installation of scrubbers, which are pollution-control devices that can directly impact human health. Scrubbers, or flue-gas de-sulfurisation scrubbers, work like giant filters that remove over 90% of the flue gases emitted by coal exhaust. They are highly effective in reducing SO2 emissions, which are dominant in the United States and harmful to human health.
The use of scrubbers has been a key feature in the decline of certain types of air pollution in the United States. Coal plants without scrubbers account for a majority of U.S. SO2 emissions. FGD scrubber SO2 removal rates can vary depending on equipment type, age, and the sulfur content of the coal, with new systems achieving up to 98% removal efficiency, according to EPA estimates. Subbituminous coal, with its lower sulfur content, has made plants burning this type of coal less likely to add scrubbers.
The installation of scrubbers can also help address health issues related to coal-burning, such as hospitalisations for Ischemic Heart Disease (IHD) among older individuals. By capturing waste products, scrubbers can also enable the production of materials like cement and synthetic gypsum for wallboard.
While scrubbers are effective in reducing SO2 emissions, other measures are also necessary to address NOx emissions. The refined coal subsidy, adopted as part of the American Jobs Creation Act of 2004, aimed to reduce NOx emissions, but there is little evidence of its success. Power plants can purchase tradable pollution credits through the U.S. cap-and-trade system, which sets an overall limit on pollution and allows plants to earn credits by reducing pollution. However, this system has been associated with increased NOx emissions at some power plants, as it can be more cost-effective to buy credits than run pollution control equipment continuously.
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The cost of capture and storage technology
Clean coal technologies, such as carbon capture and sequestration (CCS) or carbon capture, use and storage (CCUS), are crucial for transitioning to clean energy. However, the high costs associated with capture and storage technology pose significant challenges to its widespread adoption.
The Global CCS Institute estimates that a total investment of $650 billion to $1.2 trillion will be necessary to meet the 2050 climate goals. While CCUS can be retrofitted to power and industrial plants, reducing future emissions, the high costs of the technology have slowed its deployment. There are only about 20 commercial CCUS operations worldwide, with commentators citing the expense as a significant barrier. The cost of carbon capture varies depending on the CO2 source, ranging from $15-25/t CO2 for "pure" CO2 streams to $40-120/t CO2 for "dilute" gas streams. Capturing CO2 directly from the air is currently the most expensive method.
The energy penalty associated with CCS is estimated to be 20-30% of electrical output, impacting the economics of burning coal. However, CCUS-equipped power plants can provide on-demand capacity and supply electricity regardless of renewable energy availability. Additionally, CCUS can be a cost-efficient strategy for existing coal- and gas-fired power plants to reduce emissions without incurring the cost of plant closure and retrofitting.
In conclusion, while capture and storage technology is essential for achieving clean coal, the high costs of implementation, operation, and energy efficiency loss pose significant challenges to its widespread adoption. Lowering the cost of carbon capture and advancing the commercial deployment of CCUS technologies are crucial for making clean coal a viable option in the transition to clean energy.
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Environmental impact of coal mining
Coal is the most abundant and inexpensive fossil fuel, accounting for almost 40% of total worldwide power generation. However, coal mining and use have significant environmental impacts.
Surface mines, which remove the soil and rock above coal deposits, were the source of about 63% of coal mined in the United States in 2022. Mountaintop removal and valley fill mining have severely impacted the Appalachian Mountains in West Virginia and Kentucky. This technique changes the landscape and can contaminate downstream aquatic wildlife.
Surface mining also involves clearing forests, which fragments and displaces wildlife habitats. It can also cause erosion, as precipitation carries away loose topsoil into nearby waterways, disrupting their natural flow and decreasing aquatic habitats. Additionally, valley fills permanently bury headwater streams, causing losses in clean water sources and natural benefits like nutrient regulation and flood control.
Water contamination from coal mining has devastating effects on wildlife. Selenium pollution in water from coal mining is associated with the decline and deformities in fish and bird populations. Coal mine workers also face health risks, including lung disease from prolonged exposure to coal dust.
Coal mining and combustion contribute to air pollution and climate change. Coal combustion emits fly ash particles and gaseous byproducts like carbon dioxide, nitrogen oxide, sulfur dioxide, and methane gas, which contribute to global warming.
Efforts to reduce the environmental impacts of coal include land reclamation, carbon capture and sequestration technologies, and the use of scrubbers to reduce emissions from power plants. While "clean coal" technologies aim for zero emissions, challenges remain in bringing down the cost of capture and storage technology.
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Frequently asked questions
No, clean coal is not entirely pollution-free. While technologies like carbon capture and storage (CCS) can effectively capture carbon dioxide (CO2) produced at power plants, coal contains various other pollutants, including mercury and nitrogen oxide.
One significant challenge is the cost of capture and storage technology, which needs to be sufficiently low for clean coal to be a competitive energy source. Additionally, there are concerns about the effectiveness of clean coal in reducing certain emissions, such as NOx.
Alternatives to clean coal technology include the use of natural gas, renewables such as wind and solar power, and nuclear power.
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