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Title: Determination of heat conductivity of waste glass feed and its applicability for modeling the batch-to-glass conversion

Abstract

The heat conductivity of reacting melter feed affects the heat transfer and conversion process in the cold cap (the reacting feed floating on molten glass). To investigate it, we simulated the feed conditions and morphology in the cold-cap by preparing “fast-dried slurry blocks”, formed by rapidly evaporating water from feed slurry poured onto a 200°C surface. A heat conductivity meter was used to measure heat conductivity of samples cut from the fast-dried slurry blocks, samples of a cold cap retrieved from a laboratory-scale melter, and loose dry powder feed samples. Our study indicates that the heat conductivity of the feed in the cold cap is significantly higher than that of loose dry powder feed, resulting from the feed solidification during the water evaporation from the feed slurry. To assess the heat transfer at higher temperatures when feed turns into foam, we developed a theoretical model that predicts the foam heat conductivity based on morphology data from in-situ X-ray computed tomography. The implications for the mathematical modeling of the cold cap are discussed.

Authors:
 [1]; ORCiD logo [1];  [1];  [2];  [2];  [2];  [2];  [2];  [3];  [2]
  1. Laboratory of Inorganic Materials, Joint Workplace of the University of Chemistry and Technology Prague and the Institute, Institute of Rock Structure and Mechanics of the ASCR, Prague Czech Republic
  2. Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington
  3. U.S. Department of Energy, Office of River Protection, Richland Washington
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1430436
Report Number(s):
PNNL-SA-127403
Journal ID: ISSN 0002-7820; 830403000
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Ceramic Society; Journal Volume: 100; Journal Issue: 11
Country of Publication:
United States
Language:
English

Citation Formats

Hujova, Miroslava, Pokorny, Richard, Klouzek, Jaroslav, Dixon, Derek R., Cutforth, Derek A., Lee, Seungmin, McCarthy, Benjamin P., Schweiger, Michael J., Kruger, Albert A., and Hrma, Pavel. Determination of heat conductivity of waste glass feed and its applicability for modeling the batch-to-glass conversion. United States: N. p., 2017. Web. doi:10.1111/jace.15052.
Hujova, Miroslava, Pokorny, Richard, Klouzek, Jaroslav, Dixon, Derek R., Cutforth, Derek A., Lee, Seungmin, McCarthy, Benjamin P., Schweiger, Michael J., Kruger, Albert A., & Hrma, Pavel. Determination of heat conductivity of waste glass feed and its applicability for modeling the batch-to-glass conversion. United States. doi:10.1111/jace.15052.
Hujova, Miroslava, Pokorny, Richard, Klouzek, Jaroslav, Dixon, Derek R., Cutforth, Derek A., Lee, Seungmin, McCarthy, Benjamin P., Schweiger, Michael J., Kruger, Albert A., and Hrma, Pavel. Mon . "Determination of heat conductivity of waste glass feed and its applicability for modeling the batch-to-glass conversion". United States. doi:10.1111/jace.15052.
@article{osti_1430436,
title = {Determination of heat conductivity of waste glass feed and its applicability for modeling the batch-to-glass conversion},
author = {Hujova, Miroslava and Pokorny, Richard and Klouzek, Jaroslav and Dixon, Derek R. and Cutforth, Derek A. and Lee, Seungmin and McCarthy, Benjamin P. and Schweiger, Michael J. and Kruger, Albert A. and Hrma, Pavel},
abstractNote = {The heat conductivity of reacting melter feed affects the heat transfer and conversion process in the cold cap (the reacting feed floating on molten glass). To investigate it, we simulated the feed conditions and morphology in the cold-cap by preparing “fast-dried slurry blocks”, formed by rapidly evaporating water from feed slurry poured onto a 200°C surface. A heat conductivity meter was used to measure heat conductivity of samples cut from the fast-dried slurry blocks, samples of a cold cap retrieved from a laboratory-scale melter, and loose dry powder feed samples. Our study indicates that the heat conductivity of the feed in the cold cap is significantly higher than that of loose dry powder feed, resulting from the feed solidification during the water evaporation from the feed slurry. To assess the heat transfer at higher temperatures when feed turns into foam, we developed a theoretical model that predicts the foam heat conductivity based on morphology data from in-situ X-ray computed tomography. The implications for the mathematical modeling of the cold cap are discussed.},
doi = {10.1111/jace.15052},
journal = {Journal of the American Ceramic Society},
number = 11,
volume = 100,
place = {United States},
year = {Mon Jul 10 00:00:00 EDT 2017},
month = {Mon Jul 10 00:00:00 EDT 2017}
}
  • The cold cap is a layer of reacting glass batch floating on the surface of melt in an all-electric continuous glass melter. The heat needed for the conversion of the melter feed to molten glass must be transferred to and through the cold cap. Since the heat flux into the cold cap determines the rate of melting, the heat conductivity is a key property of the reacting feed. We designed an experimental setup consisting of a large cylindrical crucible with an assembly of thermocouples that monitors the evolution of the temperature field while the crucible is heated at a constantmore » rate. Then we used two methods to calculate the heat conductivity and thermal diffusivity of the reacting feed: the approximation of the temperature field by polynomial functions and the finite-volume method coupled with least-squares analysis. Up to 680°C, the heat conductivity of the reacting melter feed was represented by a linear function of temperature.« less
  • The heat conductivity ({lambda}) and the thermal diffusivity (a) of reacting glass batch, or melter feed, control the heat flux into and within the cold cap, a layer of reacting material floating on the pool of molten glass in an all-electric continuous waste glass melter. After previously estimating {lambda} of melter feed at temperatures up to 680 deg C, we focus in this work on the {lambda}(T) function at T > 680 deg C, at which the feed material becomes foamy. We used a customized experimental setup consisting of a large cylindrical crucible with an assembly of thermocouples, which monitoredmore » the evolution of the temperature field while the crucible with feed was heated at a constant rate from room temperature up to 1100°C. Approximating measured temperature profiles by polynomial functions, we used the heat transfer equation to estimate the {lambda}(T) approximation function, which we subsequently optimized using the finite-volume method combined with least-squares analysis. The heat conductivity increased as the temperature increased until the feed began to expand into foam, at which point the conductivity dropped. It began to increase again as the foam turned into a bubble-free glass melt. We discuss the implications of this behavior for the mathematical modeling of the cold cap.« less
  • During nuclear waste vitrification, a melter feed (generally a slurry-like mixture of a nuclear waste and various glass forming and modifying additives) is charged into the melter where undissolved refractory constituents are suspended together with evolved gas bubbles from complex reactions. Knowledge of flow properties of various reacting melter feeds is necessary to understand their unique feed-to-glass conversion processes occurring within a floating layer of melter feed called a cold cap. The viscosity of two low-activity waste (LAW) melter feeds were studied during heating and correlated with volume fractions of undissolved solid phase and gas phase. In contrast to themore » high-level waste (HLW) melter feed, the effects of undissolved solid and gas phases play comparable roles and are required to represent the viscosity of LAW melter feeds. This study can help bring physical insights to feed viscosity of reacting melter feeds with different compositions and foaming behavior in nuclear waste vitrification.« less
  • The rate of batch-to-glass conversion is a primary concern for the vitrification of nuclear waste, as it directly influences the life cycle of the cleanup process. This study describes the development of an advanced model of the cold cap, which augments the previous model by further developments on the structure and the dynamics of the foam layer. The foam layer on the bottom of the cold cap consists of the primary foam, cavities, and the secondary foam, and forms an interface through which the heat is transferred to the cold cap. Other model enhancements include the behavior of intermediate crystallinemore » phases and the dissolution of quartz particles. The model relates the melting rate to feed properties and melter conditions, such as the molten glass temperature, foaminess of the feed, or the heat fraction supplied to the cold cap from the plenum space. The model correctly predicts a 25% increase in melting rate when changing the alumina source in the melter feed from Al(OH)3 to AlO(OH). It is expected that this model will be incorporated in the full glass melter model as its integral component.« less