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Title: Effect of melter feed foaming on heat flux to the cold cap

Abstract

The glass production rate, which is crucial for the nuclear waste cleanup lifecycle, is influenced by the chemical and mineralogical nature of melter feed constituents. The choice of feed materials affects both the conversion heat and the thickness of the foam layer that forms at the bottom of the cold cap and controls the heat flow from molten glass. We demonstrate this by varying the alumina source, namely, substituting boehmite or corundum for gibbsite, in a high-alumina high-level-waste melter feed. The extent of foaming was determined using the volume expansion test and the conversion heat with differential scanning calorimetry. Evolved gas analysis was used to identify gases responsible for the formation of primary and secondary foam. The foam thickness, a critical factor in the rate of melting, was estimated using known values of heat conductivities and melting rates. The result was in reasonable agreement with the foam thickness experimentally observed in the laboratory-scale melter.

Authors:
; ; ; ; ; ; ; ORCiD logo; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1416685
Report Number(s):
PNNL-SA-124642
Journal ID: ISSN 0022-3115; 830403000
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials; Journal Volume: 496; Journal Issue: C
Country of Publication:
United States
Language:
English

Citation Formats

Lee, SeungMin, Hrma, Pavel, Pokorny, Richard, Klouzek, Jaroslav, VanderVeer, Bradley J., Dixon, Derek R., Luksic, Steven A., Rodriguez, Carmen P., Chun, Jaehun, Schweiger, Michael J., and Kruger, Albert A.. Effect of melter feed foaming on heat flux to the cold cap. United States: N. p., 2017. Web. doi:10.1016/j.jnucmat.2017.09.016.
Lee, SeungMin, Hrma, Pavel, Pokorny, Richard, Klouzek, Jaroslav, VanderVeer, Bradley J., Dixon, Derek R., Luksic, Steven A., Rodriguez, Carmen P., Chun, Jaehun, Schweiger, Michael J., & Kruger, Albert A.. Effect of melter feed foaming on heat flux to the cold cap. United States. doi:10.1016/j.jnucmat.2017.09.016.
Lee, SeungMin, Hrma, Pavel, Pokorny, Richard, Klouzek, Jaroslav, VanderVeer, Bradley J., Dixon, Derek R., Luksic, Steven A., Rodriguez, Carmen P., Chun, Jaehun, Schweiger, Michael J., and Kruger, Albert A.. 2017. "Effect of melter feed foaming on heat flux to the cold cap". United States. doi:10.1016/j.jnucmat.2017.09.016.
@article{osti_1416685,
title = {Effect of melter feed foaming on heat flux to the cold cap},
author = {Lee, SeungMin and Hrma, Pavel and Pokorny, Richard and Klouzek, Jaroslav and VanderVeer, Bradley J. and Dixon, Derek R. and Luksic, Steven A. and Rodriguez, Carmen P. and Chun, Jaehun and Schweiger, Michael J. and Kruger, Albert A.},
abstractNote = {The glass production rate, which is crucial for the nuclear waste cleanup lifecycle, is influenced by the chemical and mineralogical nature of melter feed constituents. The choice of feed materials affects both the conversion heat and the thickness of the foam layer that forms at the bottom of the cold cap and controls the heat flow from molten glass. We demonstrate this by varying the alumina source, namely, substituting boehmite or corundum for gibbsite, in a high-alumina high-level-waste melter feed. The extent of foaming was determined using the volume expansion test and the conversion heat with differential scanning calorimetry. Evolved gas analysis was used to identify gases responsible for the formation of primary and secondary foam. The foam thickness, a critical factor in the rate of melting, was estimated using known values of heat conductivities and melting rates. The result was in reasonable agreement with the foam thickness experimentally observed in the laboratory-scale melter.},
doi = {10.1016/j.jnucmat.2017.09.016},
journal = {Journal of Nuclear Materials},
number = C,
volume = 496,
place = {United States},
year = 2017,
month =
}
  • As the nuclear waste glass melter feed is converted to molten glass, the feed eventually becomes a continuous glass-forming melt in which dissolving refractory constituents are suspended together with numerous gas bubbles. Knowledge of mechanical properties of the melter feed is crucial for understanding the feed-to-glass conversion as it occurs in the cold cap. We measured the viscosity during heating of the feed and correlated it with the independently determined volume fractions of dissolving quartz particles and the gas phase. The measurement was performed with a rotating spindle rheometer on the melter feed heated at 5 K/min starting at severalmore » different temperatures. The effect of quartz particles, gas bubbles, and compositional inhomogeneity on the glass-forming melt viscosity was determined by fitting a linear relationship between log viscosity and volume fractions of suspended phases to data.« less
  • 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
  • As the nuclear waste glass melter feed is converted to molten glass, the feed becomes a continuous glass-forming melt where dissolving refractory constituents are suspended together with numerous gas bubbles. Knowledge of mechanical properties of the reacting melter feed is crucial for understanding the feed-to-glass conversion as it occurs during melting. We studied the melter feed viscosity during heating and correlated it with volume fractions of dissolving quartz particles and gas phase. The measurements were performed with a rotating spindle rheometer on the melter feed heated at 5 K/min, starting at several different temperatures. The effects of undissolved quartz particles,more » gas bubbles, and compositional inhomogeneity on the melter feed viscosity were determined by fitting a linear relationship between log viscosity and volume fractions of suspended phases.« less
  • The development of advanced glass formulations are a part of the plan for reducing the cost and time for treatment and vitrification of the 210,000 m3 of nuclear waste at the Hanford Site in southeastern Washington State. One property of interest in this development is melt viscosity, which has a decisive influence on the rate of glass production. In an electric melter, the conversion process from feed-to-glass above the melt pool occurs in the cold cap. At the final stage of conversion when the glass-forming melt becomes connected, gas evolving reactions cause foaming. The melt viscosity affects foam stability. Threemore » glasses were formulated with viscosities of 1.5, 3.5, and 9.5 Pa s at 1150°C by varying the SiO2 content at the expense of B2O3, Li2O, and Na2O kept at constant proportions. Cold caps were produced by charging simulated high-alumina, high-level waste feeds in a laboratory-scale melter (LSM). The spread of the feed on the cold cap during charging and the cross-sectional structure of the final cold caps were compared. The amount of the foam and the size of the bubbles increased as the viscosity increased.« less