High Carbon Fly Ash Treatment

NETL Collaborators Invent Method for Treating High Carbon Fly Ash

The U.S. Patent and Trademark Office has assigned Patent No. 8,440,015 to researchers from Waynesburg University and the National Energy Technology Laboratory (NETL) for a thermal method that retains yet passivates carbon and/or other components in fly ash. John Baltrus, a research chemist at NETL, along with Professor Robert LaCount and Douglas Kern of Waynesburg University cooperated on the invention. The research resulted from a project sponsored by the Combustion Byproducts Recycling Consortium (CBRC), which is funded by NETL.

Fly ash is the finely divided residue resulting from the combustion of ground or powdered coal and is a major by-product of coal-fired electric generating plants. Finding alternate uses for this byproduct benefits the environment by diverting it from landfills. Fly ash is most popularly used as a component of concrete. Approximately 30 percent of U.S. fly ash is recycled this way, replacing a portion of the portland cement normally required. In addition to the direct environmental advantage of utilizing a potential waste stream to substitute for an ingredient that would otherwise have to be produced through an energy-intensive process, incorporation of fly ash improves concrete performance and quality.

Some fly ash is not suitable for use in concrete because its chemical composition, including high carbon content, would require excessive amounts of air entrainment agents–surfactants used to increase the workability of a concrete mixture and its durability through freeze-thaw cycles when cured.

The invention titled, “Fly Ash Carbon Passivation,” provides a means whereby a greater percentage of U.S. fly ash can be recycled by incorporation into concrete mixtures. The patent describes a thermal method for inactivating the carbon and/or other components in fly ash while retaining them in the fly ash. The process, which involves heating the fly ash to between 400°C and 800°C under an inert gas containing up to 10 percent oxygen, results in sharply decreased amounts of surfactants that need to be added to the fly ash even though most of the carbon remains in the fly ash.

The patented method has several advantages. High-carbon fly ash, typically the result of using low-NOx burners, can now be repurposed for concrete, including conductive concrete, as opposed to being sent to a landfill. To avoid landfilling, high-carbon fly ash would otherwise need treatment at temperatures greater than 800°C under an oxygen-rich atmosphere to burn the carbon out of the fly ash before it can be used in concrete. The patented method reduces that temperature requirement and the need for carbon burnout, both resulting in lower greenhouse gas emissions. The research leading to the patent has been described in several peer-reviewed journal articles and presentations.

Contact: John Baltrus, 412-386-4570

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