Maximizing Coal Resources by Recycling Byproducts and Reducing Waste
Coal still fuels over a third of the world’s electricity. Reusing coal ash and repurposing coal waste can boost the benefits of a fossil fuel that is slowly being replaced by renewable energy sources.
The shift to clean energy is a complex process that depends on carefully transitioning from fossil fuels to renewable energy sources. So while pioneering cutting-edge innovations in clean energy are critical, it is just as important for engineers to keep pursuing creative solutions to minimize the environmental impact caused by energy sources like coal.
Carbon fibers made from coal waste. Image used courtesy of University of Kentucky
Coal is still an abundant fuel source that currently supplies over 30 percent of the world’s electricity, according to the International Energy Agency (IEA). There is no proverbial switch to throw that can install new green technologies overnight. One way to capitalize on the benefits of the remaining coal resources is to use coal byproducts rather than dispose of them as waste.
Repurposing Coal Byproducts
There are currently 6,565 coal-fired power stations operating across the globe, which inevitably produce ash as the coal is burnt. Waste products result from this burning, and one byproduct called pulverized fuel ash (PFA) is a known hazard.
Historically, PFA was simply released into the atmosphere as the coal-fired power station operated, but to comply with stricter air quality regulations, this byproduct is no longer discharged into the air. It is now captured and put into landfills.
Coal ash added to concrete. Image used courtesy of Federal Highway Association.
However, researchers found that PFA can be combined with Portland cement to help meet the worldwide demand for concrete. This demand is substantial, with approximately 3.5 billion metric tons of Portland cement produced every year, and it is used not only for concrete but stucco and mortar as well.
Additionally, using PFA for concrete is advantageous because it prevents waste and reduces costs associated with concrete production, which typically uses natural resources and contributes to carbon emissions. This repurposing of PFA reroutes it from the landfill into another cost-effective role. From a material engineering perspective, PFA can actually increase the performance and durability of cement when used as an ingredient.
Total fly ash production and use in metric tons. Image used courtesy of the ACAA
Because of a general push to reduce coal use, the production of coal byproducts like PFA has gradually declined, but there is still a gap that can be closed so that more is responsibly recycled.
Waste Coal and Carbon Fiber Production
Recycling coal byproducts is one effective way to harness the benefits of coal still being used as a fuel source, but researchers have also discovered a productive use for coal that has never been burned.
Waste coal is the term used to describe coal that has already been mined but is deemed unusable.
Researchers at the University of Kentucky Center for Applied Energy Research (CAER) have been investigating how Kentucky can use waste coal. Kentucky alone has over 4 billion tons of waste coal, so the payoff is significant if they can prevent it from being nothing more than a financial loss and environmental liability.
The UK CAER team created a multistep process to ultimately transform waste coal into a liquid crystal material that can be subsequently used in the production of carbon fibers and graphite powders. This process begins by first transforming solid coal into a filtered liquid by exposing the coal to hydrogen at both high temperatures and high pressures. This liquid is subsequently used to create mesophase pitch, which is the building block of the crystal material used for the carbon fibers and graphite powder.
Both carbon fibers and graphite powders have a multitude of uses, as carbon fibers can be shaped into grid sensors to monitor building deformation and graphite powders are utilized in the production of the anode component of lithium-ion batteries (LIBs). Given such utility, the waste coal is now becoming a supply source for two commercially viable resources.
Recycling coal byproducts like PFA and using waste coal to create valuable resources are two methods that help maximize the benefits of coal while the world continues its clean energy transformation.