A utility’s advanced technology power plant byproducts were originally expected to be directly suitable for use in various industry applications. However, upon plant startup, the large quantity of char mixed with the slag made the process byproducts unsuitable for beneficial use. As an interim solution, the slag and remaining carbon byproduct was trucked to a traditional pulverized coal burning station and used as a fuel. This solution recovered the fuel energy content, but resulted in accelerated wear of fuel handling equipment due to the abrasive nature of the slag. Although a number of tons of slag were disposed of in a landfill, long-term on-site or off-site disposal was unacceptable. Because of these issues, a large quantity of slag had accumulated in the on-site temporary storage area.
After four years of use of the high carbon slag as a fuel at the pulverized coal units, the utility decided to halt the use of the byproduct fuel. This decision left disposal at a landfill, at over $30 per ton, as the primary option. According to the facility’s general manager, “we were facing a significant increase in expense to dispose of a material that was expected to be a valuable byproduct.” The challenges were to (1) process the on-site fuel byproduct pile for recycling/beneficial uses and (2) produce processed byproducts directly from continuing operation that could be beneficially used.
The utility established an internal team to enhance the quality of the byproduct slag produced so that disposal quantities could be minimized or eliminated and beneficial use would be maximized. The team included representatives from plant operations, engineering, marketing, and environmental personnel. The scope of their work was to first conduct an in-depth review of the beneficial use opportunities and specifications in light of current slag quality and processing operations. The scope then allowed for permanent fixes to be made rather than short term patches.
Charah was approached by the utility to assist with the growing byproduct slag problem. After an initial analysis of the slag samples, Charah contacted the University of Kentucky Center for Applied Energy Research and asked them to analyze the slag for characteristics that Charah felt were needed to determine if and how the slag could be processed and made into usable products. The resulting collaborative research determined that the slag could be processed and made into usable products.
Charah designed a flow sheet detailing the equipment and processing needed to solve the power plant’s byproduct slag problem. The challenges were met by separating the byproducts into the two constituents, slag and a fuel rich char. Charah was then commissioned to develop an independent system to beneficiate the existing on-site byproducts in December 2001 and immediately produced useful products. As a result, Charah designed and built a processing system which it owned and operated on-site. This patented processing system separates unburned fuel from the slag materials and makes it available for reuse by the power plant process. In addition, Charah identified marketing opportunities for the coarse and fine products that are left behind after fuel recovery is complete.
Processing and Beneficiation of the byproducts enabled the utility to reintroduce the char from the over 100,000 tons of stockpiled byproducts stored on-site into the fuel stream. The slag was sold for beneficial uses. As a result, the plant was able to process, use and market all the stockpiled slag plus all of the slag produced daily for nearly three years with a significant financial savings.
The plant now operates as a closed loop system, where the only byproducts leaving the site are those that are utilized as raw materials for manufacturing. Charah has a patent on this IGCC slag beneficiation process.