The Utilization of Alternative Fuels in the Production of Portland Cement
Type of DegreeThesis
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The production of portland cement converts many different raw materials into clinker, in the presence of temperatures on the order of 1,500 degrees Celsius. Historically, nonrenewable fossil fuels have been used to maintain these temperatures; however, the cement industry has started to explore options to supplement nonrenewable fuels with alternative sources. These alternative fuels are generally derived from waste, and their disposal in a cement kiln could benefit the cement industry as well as the environment. The cement for this study was produced in a full-scale, operational, cement plant, where three different 3-day test burns were conducted using various combinations of alternative fuels. The fuels used in each burn period were: Coal Only; Coal plus Tires; and Coal, Tires, and Plastics. One objective of this study was to determine if the alternative fuels selected could be successfully burned while maintaining production at the cement plant. Although some minor problems did occur, the energy content, availability, cost, and overall compatibility made both tires and specific waste plastics viable options. Another objective was to determine if the chemical composition of the fuels directly impacted the chemical composition of the clinker and/or cement. The primary chemical compounds; Al2O3, CaO, Fe2O3, and SiO2 showed no practically significant changes. Some changes did occur in other compounds, but based on this study it was not possible to conclude that these changes were a direct result of the fuels that were burned. The main objective of this study was to determine if the fuels had a direct impact on the properties of the cement and/or concrete produced from the cement. Although the results could not be attributed directly to the fuels, some significantly different results were found relative to the baseline burn, which used Coal plus Tires as fuel. Tests of drying shrinkage development, splitting tensile strength of concrete, and concrete permeability all showed no significant changes. Paste setting times showed an acceleration of 27 percent in the Coal, Tires, and Plastics Burn, and concrete setting times showed a retardation of 40 percent in the Coal Only Burn. Additionally, the compressive strength of concrete made from the Coal Only burn period showed a decrease of as much as 20 percent. The final objective of this study was to determine if the fuels directly affected the emissions. Based on the averages, the Coal plus Tires burn was the highest, and the Coal Only was the lowest in NOx, SO2, and VOC. The CO emissions emitted by the cement plant were the highest for the Coal Only burn. The use of tires and waste plastics appear to be feasible alternative fuels for cement production and their use should be further explored.