Abstract
The aim of the paper is to present the results of research on the carbonation process kinetics of coal combustion ashes originating from fluidized bed boilers used in power plants. Based on the thermogravimetric analysis (TGA), the hypothesis that carbon dioxide is bounded by the mineral substances (calcium compounds) in the fly ashes was confirmed. Determining the kinetic parameters of the carbonation of fly ashes requires simultaneously taking into consideration the kinetics of the drying process of the sample. The drying process of the sample masks the effect of the reaction of CO2 with calcium compound. Unlike the ashes generated in pulverized fuel boilers, fly ashes contain irregular amorphic mineral components or poorly crystalized products of complete or partial dehydroxylation of claystone substance present in shale formations constituting the gangue as well as anhydrite (CaSO4), a desulfurization product. The content of free calcium oxide (CaO) in such ashes ranges from a few to several percent, which is a significant obstacle considering their use in cement and concrete production as type II admixtures understood to be inorganic grained materials of pozzolanic or latent hydraulic properties. The paper presents effective mechanisms which reduce the content of free CaO in ashes from Fluidized Bed Combustion (FBC) boilers to a level that allows their commercial utilization in the cement industry.
Highlights
The interest in circulating fluidized bed (CFB) boilers, including atmospheric circulating fluidized bed (ACFB) and pressurized circulating fluidized bed (PCFB) biolers, has been growing steadily due to their increasing combustion efficiency and considerably lower emissions of NOx and SO2
The aim of this paper is to present the results of research on the kinetics of carbonation process of coal combustion ashes from fluidized bed boilers used in power plants
The content of free calcium oxide in coal fly ash (CFA) was determined as a function of time
Summary
The interest in circulating fluidized bed (CFB) boilers, including atmospheric circulating fluidized bed (ACFB) and pressurized circulating fluidized bed (PCFB) biolers, has been growing steadily due to their increasing combustion efficiency and considerably lower emissions of NOx and SO2. The CFA generated in pulverized fuel boilers is characterized by irregular amorphic mineral components or poorly crystalized products of complete or partial dehydroxylation of claystone substance present in shale formations constituting the gangue in addition to anhydrite (CaSO4 ), which is a desulfurization product. They contain unreacted calcite (CaCO3 ), free CaO and Ca(OH)2 —the product of its hydration as well as unreacted coal. The application of the CFAs in cement and concrete production such as type II admixtures, understood as inorganic grained materials of pozzolanic or latent hydraulic properties, must comply with the European Standard EN 450-1:2005 [6] which specifies that they should not contain more than
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