Ending Coal Pollution: Strategies For A Cleaner Future

Coal pollution is a pressing issue that has devastating effects on both human health and the environment. Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. The combustion of coal releases diverse chemicals into the air, with the main by-products being water and carbon dioxide. To combat this, there are a series of systems and technologies that can be implemented to mitigate the impact of coal burning. These include pre-combustion approaches, such as cleaning coal, and post-combustion approaches, such as flue-gas desulfurization and selective catalytic reduction. Additionally, organisations like Bloomberg Philanthropies are working to stop coal and air pollution globally, and the Environmental Protection Agency is proposing new regulations to address air pollution and coal ash.

Cleaning coal before it is burned

Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. One way to mitigate this is to clean the coal before it is burned. This is known as a precombustion approach.

Cleaning coal involves removing impurities such as sulphur, mercury, and other trace elements. This can be done through physical or chemical processes. Physical cleaning methods include crushing, screening, and gravity separation, which remove larger impurities such as rocks and minerals. Chemical cleaning methods, on the other hand, use reagents to remove specific impurities. For example, limestone can be used to remove sulphur, while sodium hydroxide can be used to remove mercury.

Another precombustion approach is carbon capture and storage (CCS) technologies. This involves capturing the carbon dioxide produced during the burning of coal and storing it underground instead of releasing it into the atmosphere. CCS technologies can significantly reduce greenhouse gas emissions and have been supported by politicians such as former US President George W. Bush and Barack Obama.

By cleaning coal and implementing CCS technologies, we can reduce the negative impact of coal on human health and the environment. These precombustion approaches are an important part of coal pollution mitigation and can help create a cleaner and healthier future for our communities.

Flue-gas desulfurization

A new, emerging flue gas desulfurization technology has been described by the IAEA. It is a radiation technology where an intense beam of electrons is fired into the flue gas at the same time as ammonia is added to the gas.

Selective catalytic reduction

Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. One way to reduce coal pollution is through selective catalytic reduction (SCR). SCR is a post-combustion approach that involves the injection of a liquid reductant into the flue gas stream of a coal-fired boiler. The reductant, typically ammonia or urea, reacts with nitrogen oxides (NOx) in the flue gas to form harmless nitrogen gas (N2) and water vapour (H2O). This process significantly reduces the amount of NOx emitted into the atmosphere, which is beneficial as NOx is a major contributor to smog and acid rain formation.

SCR technology is highly effective in reducing NOx emissions and can achieve up to 90% reduction rates. It is widely used in coal-fired power plants and industrial boilers due to its ability to handle high flue gas temperatures and flow rates. The process is also flexible and can be customised to meet specific emission reduction goals.

The SCR system consists of several key components, including an ammonia injection grid, a catalyst, and a reactor. The ammonia injection grid introduces the liquid reductant into the flue gas stream, where it vaporises and mixes with the gas. The catalyst, typically made of titanium dioxide or vanadium pentoxide, provides a surface for the chemical reaction between the reductant and NOx to occur. The reactor, or reaction chamber, provides the necessary residence time and temperature conditions for the reaction to take place efficiently.

To ensure the effectiveness of the SCR system, proper maintenance and operation are crucial. Regular inspections and cleaning of the catalyst are necessary to remove any accumulated dust or debris that may impede the reaction. Additionally, the ammonia injection system requires careful monitoring to maintain the correct dosage and distribution of the reductant. By following these practices, the SCR system can consistently achieve the desired NOx reduction levels and contribute to the overall reduction of coal pollution.

Electrostatic precipitators

The working principle of the electrostatic precipitator is moderately simple. It consists of two sets of electrodes: positive and negative. The negative electrodes are in the form of a wire mesh, and the positive electrodes are plates. These electrodes are vertically placed and are alternate to each other. The gas-borne particles such as ash are ionised by the high-voltage discharge electrode by the corona effect. These particles are ionised to a negative charge and are attracted to positively charged collector plates. The treated air then passes out of the precipitator and through a stack to the atmosphere.

When enough particles have accumulated on the collection devices, they are shaken off the collectors by mechanical rappers. The particulates, which can be either wet or dry, fall into a hopper at the bottom of the unit, and a conveyor system transports them away for disposal or recycling. Precipitators are often deployed with denitrification units that remove nitrogen oxides and scrubbers or other devices that remove sulphur dioxide.

Fly ash reduction

Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. Mitigation includes pre-combustion approaches, such as cleaning coal, and post-combustion approaches, including flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction.

Fly ash is a fine powder-like particulate matter that is a byproduct of burning coal. It is made up of inorganic minerals and trace amounts of heavy metals, which can be toxic to humans and the environment. Fly ash reduction is an important strategy to mitigate the health and environmental impacts of coal combustion.

There are several ways to reduce fly ash emissions:

• Electrostatic precipitators: These devices use electrostatic forces to remove fly ash particles from the flue gas stream before it is released into the atmosphere. They are highly effective in removing fine particulate matter, including fly ash.
• Baghouses: Baghouses are fabric filters that can capture fly ash particles. They work by filtering the flue gas through a series of bags or tubes, which trap the fly ash particles. Baghouses are highly efficient and can remove up to 99% of fly ash.
• Wet scrubbers: Wet scrubbers use a liquid, usually water, to remove fly ash particles from the flue gas. The flue gas is passed through a liquid spray or a pool of liquid, which captures the fly ash particles. Wet scrubbers can also help to remove other pollutants, such as sulphur dioxide and nitrogen oxides.
• Carbon capture and storage (CCS): CCS technologies can be used to capture carbon dioxide and other pollutants, including fly ash, before they are released into the atmosphere. CCS involves capturing the carbon dioxide and fly ash, transporting them to a storage site, and sequestering them underground.

By implementing these technologies and strategies, fly ash emissions can be significantly reduced, improving air quality and mitigating the health and environmental impacts of coal combustion.

Frequently asked questions