The University of Utah is involved in an extensive effort to develop predictive simulation capabilities for pulverized oxy-coal flames in order to facilitate the design of next-generation low-carbon-emission utility boilers. This work is being carried out by the Carbon Capture Multidisciplinary Simulation Center (CCMSC), which is a $16M research center funded by the U.S. Department of Energy. A key component of the center is a detailed Validation and Verification effort with coupled Uncertainty Quantification (V&V/UQ). The V&V/UQ work is being carried out using experimental data at multiple scales with the ultimate goal of providing confidence in the predictive capabilities of the code for simulations at a scale where no experimental data exists.
One specific endeavor is the simulation of experimental data obtained in the 1.5 MW oxy-coal furnace (L1500) located at the University of Utah. The quantity of interest (QOI) for the V&V/UQ effort is heat flux, since ability to predict this parameter accurately throughout the boiler was identified by our industrial partner as being the most critical need for designing a next-generation boiler. Predictions of heat flux are highly influenced by the thermal properties of the furnace walls; thus, the values for properties of coal ash deposits on the walls must be carefully selected for the model. Due to the highly variable nature of coal ash, however, there is a great deal of uncertainty and variability in the information available in the literature on these properties. Thus, a study was initiated to provide detailed information on the actual deposits obtained from the furnace walls.
The thermal properties examined in this work are the infrared emissivity and thermal diffusivity of ash deposits. The walls of the furnace are composed of multiple layers of insulation and refractory, which become covered over time by layers of ash deposits. These ash deposits can exhibit significant variability from location to location, especially in comparison with the values for pure refractory. Observations inside the furnace (1.1 x 1.1 m2 internal cross section, 12 m length) showed that the deposits varied greatly in color and structure. Thus, it appeared that previous models, which have used uniform values over the entirety of the furnace, may not have been sufficient. The objective for this study was to evaluate that assumption by charting the differences in the thermal diffusivity and infrared emissivity of the deposits as a function of their location on the interior walls of the furnace.
This paper will present the results of this study and provide recommendations for a suitable approach for addressing the variability of ash deposits in simulations of large-scale boilers and furnaces.
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