Clean Coal Processes: The Fabrication of Value Added Cement Products form Circulating Fluid Bed Combustion Ash

Grants and Contracts Details


The 300 MW Gilbert Circulating Fluidized Bed Combustor (CFBC) operating at East Kentucky Power Cooperatives Spurlock Power Plant in Maysville, Kentucky, is currently the cleanest in the State. It is also one of the most economical. The CFBC burns coal in the presence of a bed of slaked limestone, which effectively absorbs sulfur dioxide (S02) to form anhydrite (CaS04)' It low temperature operation produces much less thermal NOx than pulverized coal combustion (PCC). By its nature CFBC is also fuel flexible, and can burn very high ash and sulfur fuels cleanly and efficiently. This technology does have a drawback however. Because it uses a higher CaiS ratio than a scrubbed PCC system, it consumes more limestone produces more solid waste and C02 than conventional coal plants. The development of added value construction products from the Gilbert CFBC spent bed materials is proposed. These products will replace Portland cement; an energy and C02 intensive product and thus help to mitigate carbon emissions. CFBC produces two kind of spent bed materials, coarse bottom ash (BA) and a much finer fly ash (FA). Both of these products are very high in calcium. The Gilbert BA averages 55% CaO and the fly ash 30% CaO. Conventional fly ash from eastern U.S. coal typically has much less than 5% CaO. Some of the calcium in the CFBC ash is present as anhydrite, but about half of it is present as un-slaked lime. When properly conditioned these materials are capable of acting as hydraulic cements, forming both calcium aluminosulfate minerals, most importantly ettringite, as well as calcium-aluminasilica gels, like that formed from Portland cement. Mortars with strengths ash high as 3,700 psi have been formulated at the CAER laboratory. The research will focus on the creation of two classes of products. A medium strength (2,000 psi to 3,000 psi) material made by pre-hydrating and milling the Gilbert spent bed materials and stabilizing them with conventional fly ash. The second product is formed by heating the spent bed material with other materials to form belite/sulfoaluminate clinker, which, when ground and activated with conventional scrubber sludge, is the base for sulfoaluminate cement (SAC). This material is of high value. It is very rapid and very hard setting and capable of forming very high strength concrete (i.e. 10,000 psi to 12,000 psi). It's performance is as good as, or for some applications better than, that of Portland cement. China currently produces about one million ton per year SAC cement. Research will focus on formulations for both classes of materials that optimize stability. Issues to be addressed include pre-hydration and strength optimization, dimensional stability (e.g. shrinkage and expansion) and durability (e.g. freeze-thaw, chlorination and carbonation resistance).
Effective start/end date7/1/066/30/08


  • KY Office of Energy Policy: $250,466.00


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