Results will be presented from a multiyear study (supported by the Department of Energy) in which portland cement was produced at a full-scale cement plant with several 3-day trial burns of various alternative fuels along with coal. The fuels combinations investigated were: 1) coal only, 2) coal and tires, 3) coal, tires, and waste plastics, 4) coal, tires, and broiler litter, 5) coal, tires and switch grass, and 6) coal, tires, and wood chips. Samples of raw materials, fuels, cement kiln dust, clinker, cement, and emissions were collected systematically during each trial burn. Chemical compositions, physical characteristics, and mechanical properties were obtained for the samples. Chemical analyses showed that the primary chemical compounds of the cements exhibited no significant changes during the trial burn periods. Cement and concrete properties for each trial burn showed no significant changes in drying shrinkage development, splitting tensile strength, and permeability. The compressive strength of concrete from waste plastics and broiler litter burns showed an increase relative to the other burns, though it is not possible to attribute this result exclusively to the use of these fuels. The NOx emissions were the lowest for the coal only and broiler litter trial burns. The VOC emissions were the lowest for the coal only and waste plastics burns. The CO emissions of the cement plant were lower for all burns that included alternative fuels.
The trial burns also revealed a number of issues and technologies which are now being addressed to enable the large scale use of alternative solid fuels for cement manufacturing. Among these are alternative fuels handling facilities and best practices and process operation and control limitations that cap the substitution rates.
The burn trials showed that all of the alternative fuels had high potential as a coal substitute because they exhibited minimal impact on product quality and in some cases had positive impact on emissions.