Conversion of batch to molten glass, I: Volume expansion

Journal of Non-Crystalline Solids

Marcial

2011

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During glass-batch melting, solid silica (quartz) usually dissolves last. The measured rate of dissolution, while the temperature was increasing at a constant rate, was compared with the hypothetical diffusion-controlled volume flux from regularly distributed particles through concentration layers of a uniform thickness. The actual rate was up to two orders of magnitude lower than that of the "ideal" case, revealing a progressive inhibition of silica dissolution. As a measure of this retarded dissolution, we introduced a retardation factor defined as a ratio of the actual and "ideal" dissolution rates measured as the volume flux at the melt-particle interface. The severe inhibition of silica dissolution has been attributed to the irregular spatial distribution of silica particles that is associated with the formation of nearly saturated melt on a portion of their surfaces. Irregular shapes and unequal sizes of particles also contribute to their extended lifetime.

Section: Discussionmentioning

confidence: 99%

“…To obtain concrete shapes of the γ(T) function, we used experimental data for the dissolution of crushed quartz while heating batches formulated for a high-alumina, high-level waste as reported in [1,13,14]. We have selected four batches containing silica particles of 45, 75, 150, and 195 μm.…”

Section: Experimental Datamentioning

confidence: 99%

Dissolution retardation of solid silica during glass-batch melting

Journal of Non-Crystalline Solids

Marcial

2011

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“…20,21 Gas bubbles are produced not only by residual batch gases, creating so-called primary foam, but also by redox reactions in the melt under the cold cap-these are responsible for secondary foam formation. Both foams coalesce into larger cavities 2 that eventually escape into the plenum space.…”

Section: Reaction Kineticsmentioning

confidence: 99%

Experimental Investigation and Mathematical Modeling of Cold Cap Behavior in High‐Level‐Waste Glass Melter

Ceramic Transactions Series

2014

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The cold cap is a layer of reacting melter feed floating on the surface of molten glass in a glass-melting furnace. The cold cap consists of two distinct portions, the upper portion which allows the reaction gases to escape through open pores, and the lower portion which traps the gases within the continuous glass-forming melt, creating foam. The temperature span over the cold cap is ~1000 K. Data needed to simulate the cold cap mathematically include the kinetics of multiple reactions, reaction enthalpies, heat capacity, density, porosity, and heat conductivity as functions of both the temperature and the rate of heating. These data were produced via crucible experiments. The mathematical model has been completed. It relates the cold cap thickness, the rate of melting, the temperature field, and cold cap structure (foaming, dissolution of quartz particles, and formation and subsequent dissolution of crystalline phases, such as spinel) to the cold cap bottom temperature, the fraction of heat flow to the upper cold cap surface, the melt foaminess, and the chemical and physical nature of melter feed materials. To verify the model, cold caps were produced in a laboratory-scale melter and their structure is currently investigated.

“…Then, above 800°C, the density decreased as the bubbly melt turned to foam, reaching a minimum. The density was estimated from the expansion data reported in [13,14].…”

Section: Materials Propertiesmentioning

confidence: 99%

“…This work presents an initial step toward the modeling of a cold cap in a me Iter for high-Ievelwaste glass while taking advantage of the availability of data for the key properties and the reaction kinetics for a high-alumina melter feed [13][14][15][16] considered for the Waste Treatment and Immobilization Plant, currently under construction at the Hanford Site in Washington State, USA. The 1D model is based on the ideas by Hrma [9] and Schill [10,11].…”

Section: Introductionmentioning

confidence: 99%

Nuclear waste vitrification efficiency: Cold cap reactions

Journal of Non-Crystalline Solids

Kruger

Pokorný

2012

The cost and schedule of nuclear waste treatment and immobilization are greatly affected by the rate of glass production. Various factors influence the performance of a waste-glass melter. One of the most significant, and also one of the least understood, is the process of batch melting. Studies are being conducted to gain fundamental understanding of the batch reactions, particularly those that influence the rate of melting, and models are being developed to link batch makeup and melter operation to the melting rate.Batch melting takes place within the cold cap, i.e., a batch layer floating on the surface of molten glass. The conversion of batch to glass consists of various chemical reactions, phase transitions, and diffusion-controlled processes. These include water evaporation (slurry feed contains as high as 60% water), gas evolution, the melting of salts, the formation of borate melt, reactions of borate melt with molten salts and with amorphous oxides (Fe203 and AI 2 0 3 ), the formation of intermediate crystalline phases, the formation of a continuous glass-forming melt, the growth and collapse of primary foam, and the dissolution of residual solids. To this list we also need to add the formation of secondary foam that originates from molten glass but accumulates on the bottom of the cold cap.This study presents relevant data obtained for a high-level-waste melter feed and introduces a one-dimensional (10) mathematical model of the cold cap as a step toward an advanced threedimensional (3D) version for a complete model of the waste glass melter. The 1D model describes the batch-to-glass conversion within the cold cap as it progresses in a vertical direction. With constitutive equations and key parameters based on measured data, and simplified boundary conditions on the cold-cap interfaces with the glass melt and the plenum space of the melter, the model provides sensitivity analysis of the response of the cold cap to the batch makeup and me Iter conditions. The model demonstrates that batch foaming has a decisive influence on the rate of melting. Understanding the dynamics of the foam layer at the bottom of the cold cap and the heat transfer through it appears crucial for a reliable prediction of the rate of melting as a function of the melter-feed makeup and melter operation parameters. Although the study is focused on a batch for waste vitrification, the authors expect that the outcome will also be relevant for commercial glass melting.