Since the early 1990's, CAER has been actively working with utilities and ash management companies to find new ways to use CCB's. Success requires the cooperation and commitment of everyone involved. A few of the success stories are listed below.
Tampa Electric Co (TECO) operates a unique power plant in Mulberry, FL. Rather than combusting coal, this power plant converts coal to a gas and burns the gas to produce electricity. The result is a much cleaner operating, more efficient power plant. Since the way they use coal is so unique, the by-products they generate are also unique, and there was no way to utilize them.
As a result, over 70,000 tons/year of gasification byproducts (slag) were stored for eventual disposal in landfills. A flowsheet to separate the byproducts into useable products was developed at CAER and a processing plant was constructed by Charah, Inc. in 2002. The processing plant was designed to treat all of the stockpiled slag as well as current production. The process essentially separates the slag into two products, a low carbon vitreous frit and a high carbon fuel. The frit is sold as raw feed for the production of Portland cement and the fuel product is recycled back to the gasifier. By spring 2004, the by-product stockpile was completely eliminated. As a result of this effort, utilization at Polk Station increased from 0% to 100% in 2 years. Currently, all of the slag produced at Polk Station is utilized.
Many utilities produce bottom ash that is porous and suitable for use as lightweight aggregate. Unfortunately, the bottom ash is often contaminated with pyrite from coal pulverizing mills or is not suitably sized for this use. By eliminating contamination through proper management practices and screening to produce a consistent size distribution, it is possible to produce high quality lightweight aggregate from bottom ash. Using this material in concrete blocks makes the blocks much lighter without compromising strength.
Charah, Inc. currently operates lightweight aggregate production facilities at two utility sites, Belews Creek in Walnut Cove, NC and Marshall in Terrell, NC. Working with the CAER, an effective processing flowsheet was developed and a strategy was implemented to separately store pyrite. As a result, Charah currently produces over 100,000 tons/year of marketable lightweight aggregate from bottom ash that would have otherwise been disposed.
When utilities use high sulfur coal, the bottom ash is frequently too dense to be used as lightweight aggregate. Such is the case at E.ON U.S.'s Mill Creek Station in Louisville, KY. Working together, the CAER, Charah, Inc, Flynn Borthers Construction and LG&E Energy developed a plan to utilize processed bottom ash from this site as fill sand for backfilling sewer trenches on a sewer expansion project near the utility site, rather than to use sand dredged from the Ohio River. Before the plan could be implemented, it was first necessary to secure the approval of the Louisville Metropolitan Sewer District (MSD).