Browsing by Author "Beerkens, Ruud G. C."
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- ItemAmber chromophore formation in sulphur- and iron-containing soda-lime-silica glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Beerkens, Ruud G. C.During cooling of reduced soda-lime-silica glass melts, doped with iron oxides and sulphur species, ferrous iron (Fe2+) reacts with sulphite (SO3 2-), and the Fe3+ (ferric iron) and also the S2- (sulphide) concentration will increase. The sulphite concentration in the amber glass melt after fining is sufficient to produce ferric iron and sulphide, required for amber chromophore formation during the cooling process. The product of the concentrations of Fe3+ and sulphide will strongly increase during coohng below about 1000 K. This mechanism implies that a necessary condition for amber formation is the availability of sufficiently large iron concentrations in the presence of a sufficient sulphite content in the high-temperature glass melt. The formation of a chromophore, based on Fe3+ - S2- - 3O2- - nNa+ complexes in the silicate glass will lead to amber colouring. Α strong dependency of the amber intensity of the glass on the maximum temperature of melting, the alkali concentration of the glass, the total iron concentration and on the oxidation-state of the melt has been found experimentally. The charge of the networkmodifying alkali ions stabilizes the ferric iron-sulphide-oxide-alkali chromophores. In strongly reduced melts, hardly any sulphite can be formed and during cooling, the amber chromophore formation is limited. Experiments show a decrease in ferric iron concentrations and in the amber intensity when over-reducing glasses. Α decrease in the amber intensity of amber glasses with increasing water content is probably caused by lower sulphite retention after fining of waterrich melts.
- ItemGlass industry in the Netherlands(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Beerkens, Ruud G. C.; Sturm, Mart[no abstract available]
- ItemImpact of furnace atmosphere and organic contamination of recycled cullet on redox State and fining of glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Beerkens, Ruud G. C.; Zaman, Laurens; Laimböck, Paul; Kobayashi, ShoThe onset temperature of fming and the quantity of fming gases is not only determined by the amount of fming agents in sodalime- silica batches, but also by the level of organic contaminants in the cullet or normal batch and the water vapor pressure in the furnace atmosphere. These conditions will also determine the redox State of the glass and residual sulfate or sulfide concentrations in the glass. Organic contaminants will form char during headng of the batch. This char partly reacts with CO₂ Coming from the decomposition of the soda, limestone or dolomite forming carbon monoxide. Stable types of char or cokes or cuUet-rich batches with only small amounts of carbonates will result in some carbon residues after the CO₂ evolution. This carbon partly reduces Sulfates and ferric iron in the fresh melts. This results in sulfide and ferrous iron formation in these glass melts. At increasing temperatures in the melt, the sulfides and Sulfates react together forming sulfur-containing gases between 1000 to 1250°C. The Sulfate retention decreases, finally the glass even may contain sulfur only in the sulfide form under very reduced conditions. In batches without reducing agents, Sulfates in the melt Start to decompose at temperatures exceeding 1400 °C. Small amounts of carbon and water vapor reduce the fining onset temperature. Water vapor from the furnace atmosphere predominantly Infiltrates the batch blanket during melting and foaming. The water will enhance the bubble and seed growth during fining. Water in the melt will influence the redox State of the final glass. Only in batches containing coarse raw materials or cullet, reducing or oxidizing gases from the furnace atmosphere Infiltrate the batch blanket and these gases will respectively reduce and oxidize components like iron oxides, sulfate/sulfide or chromium oxides in the batch blanket interior.
- ItemModelling of sand grain dissolution in industrial glass melting tanks(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Beerkens, Ruud G. C.; Muijsenberg, Hendricus P. H.; van der Heijden, TomA combinadon of two models, deseribing dissoludon of sand grains in bateh blankets or in the molten glass, is presented: a microscale and a macroscale model. The macroscale model is based on a 3-dimensional calculation procedure to determine the temperature distributions and the flows in industrial glass melting tanks. By means of microscale models, using mass transfer relations for diffusional transport, the dissolution rate of single sand grains can be calculated. The dissolution of the sand is determined by following a large number of single grains during their trajectories through the batch blanket and the molten glass in the glass melting tanks. The dissolution rate of a sand grain is calculated for the temperatures and flow conditions i n every volume element in the tank through which the grain proceeds. The dissolution rate in the batch blanket depends strongly on temperature and the stage of the dissolution process. Initially the very fast shrinkage rate of the grains as temperatures exceed 1200°C results within 10 min in the dissolution of more than 50 % of the sand in the blanket. Forced and free convection in the glass melt leads to increases in the dissolution rate, up to a factor 5 compared to motion-free conditions. Forced bubbling for instance results locally in extremely high mass transfer rates and often improves the melting performance of industrial glass furnaces.
- ItemThe role of gases in glass melting processes(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Beerkens, Ruud G. C.The formation of gases and vapors during glass melting and the interaction between furnace atmospheres and industrial glass melts have an important impact on the emissions of glass furnaces, the glass properties and the quality of the glass products. Degassing or fining of glass melts is necessary to obtain a glass without gaseous inclusions. A simulation model has been developed which describes the behavior of gas bubbles in glass melts, depending on the process conditions. This model can be used to optimize the fining process in industrial furnaces. Foam formation on top of glass melts blocks the radiation from the combustion chamber of glass furnaces into the melt. Laboratory tests are used to find practical ways to reduce foaming during melting of sulfate-containing glasses. These tests show the importance of the furnace atmosphere on foam behavior in glass meldng tanks. Volatilization is the major source of particulate emissions in most glass furnaces. Volatilization rates from glass melts can be reduced by lowering the hot-spot temperatures and local gas velocities directly above the melt. One of the most important issues for glass makers today is the NOₓ formation of fossil fuel-fired furnaces. Results from West European glass producers show the possibility to decrease the formation levels of NOₓ by delayed mixing of the fuel and the oxidant and by intelHgent combustion control. Increased levels of water vapor in the glass furnace atmosphere will give higher water concentrations in the glass melt. In water rich glass melts, the sulfate retention will be often much less than in glasses molten in dry atmospheres. The water vapor effects the viscosity, radiative properties and the redox state of the melt. Because of these effects, the color of glasses molten in oxy-fuelfired furnaces, with high water vapor concentrations, may be different from glass molten in air-fired furnaces, using the same batch composition.
- ItemUpgrading glass melting technology by model-based processing(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Beerkens, Ruud G. C.; Faber, Anne-Jans; Muysenberg, Erik; Simonis, Frank[no abstract available]