Melting glass with oxidation control and lowered emissions
AssigneePPG Industries, Inc.
InventorsLeonard A. Knavish, William C. Harrell
Life of this patent
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Abstract
Premature dissociation of fining agent is avoided in a glass melting operation while controlling the final redox state of the product glass by initiating the melting process under relatively oxidizing conditions and subsequently altering the redox conditions to make the glass more reducing. A glass that is more reduced than usual can thereby be produced without sacrificing the ability to adequately fine the glass. For a given redox level, less fining agent need be used, thereby lowering emissions from the melting operation, because dissociation of the fining agent is delayed until a later stage of the process where the redox conditions are changed.
Claims26
A method of making glass so as to control the final valence state of multivalent ions contained in the glass, comprising:
- melting glass batch materials containing a source of the multivalent ion and a fining agent at an upstream zone in which redox conditions in the melting glass are maintained relatively oxidizing as measured by the ratio of ferrous iron to total iron, whereby the batch material is substantially liquefied while avoiding undue premature dissociation of the fining agent and assuring the presence of sufficient fining agent in the molten glass entering a downstream fining zone to provide adequate fining;
- at a downstream zone introducing a reducing agent uniformly throughout the melt to alter the redox conditions to be more reducing as measured by an increase in the ratio of ferrous iron to total iron of at least twenty percent compared to the ratio in the upstream zone, thereby reducing solubility of the fining agent in the melt to induce dissociation of the fining agent to thereby aid in fining, and thereby controlling the final valence state of the multivalent ions in the glass product by inducing a greater proportion of the multivalent ions to be present in their lower valence state.
A method of melting and fining glass wherein dissociation of sulfur compounds is an aid to fining the melting glass, comprising:
- melting glass batch materials including sulfur compounds in an amount sufficient to produce a glass having no more than 0.20 percent sulfur measured as SO.sub.3 ;
- during the initial melting stages maintaining relatively oxidizing conditions as measured by a ratio of ferrous to total iron of no more than 0.3 whereby solubility of sulfur compounds is enhanced;
- after the batch material has been substantially liquefied, altering the redox condition of the liquefied glass to be more reducing as measured by an increase in the ratio of ferrous iron to total iron of at least twenty percent compared to the ratio in the initial melting stages, whereby dissociation of sulfur compounds is enhanced by reduced solubility in the glass.
Dependencies are inferred from the claim text.