7 research outputs found
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Impact of furnace atmosphere and organic contamination of recycled cullet on redox State and fining of glass melts
The 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
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Upgrading glass melting technology by model-based processing
[no abstract available
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Fouling of heat exchanger surfaces by dust particles from flue gases of glass furnaces
Fouling by dust particles generally leads to a reduction of the heat transfer and causes corrosion of secondary heat exchangers. Α deposition model, including thermodynamic equilibrium calculations, has been derived and applied to describe the deposition (i.e. fouling) process and the nature of the deposition products in a secondary heat exchanger. The deposition model has been verified by means of laboratory experiments, for the case of flue gases from soda-lime glass furnaces. Corrosion of iron-containing metallic materials, caused by the deposition products, has been briefly investigated with the same equipment.
There is a close similarity between the experimental results and model calculations. The largest deposition rates from flue gases on cylindrical tubes in cross-flow configuration, are predicted and measured at the upstream stagnation point. The lowest deposition rates are determined at downstream stagnation point locations. At tube surface temperatures of approximately 520 to 550 K, the fouling rate on the tube reaches a maximum. In this temperature region NaHSO4 is the most important deposition product. This component is mainly formed at temperatures from 470 up to 540 K. The compound Na3H(SO4)2 seems to be stable up to 570 K, for even higher temperatures Na2SO4 has been found. These deposition products react with iron, SO3, oxygen and water vapour forming the complex corrosion product Na3Fe(SO4)3. NaHSO4, which is formed at tube surface temperatures below 540 K, causes more severe corrosion of iron-containing materials than Na2SO4. Maintaining temperatures of the heat exchanger surfaces above 550 to 600 Κ reduces the fouling tendency and corrosion in case of flue gases from oil-fired soda-lime glass furnaces
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Modelling of sand grain dissolution in industrial glass melting tanks
A 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
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Energy efficiency benchmarking of glass furnaces
Α method for a comparison of data on the specific energy consumption of a large set of glass melting furnaces is presented. This benchmarking of the energy efficiency levels takes the effect of the cullet fraction in the batch into account. The investigated energy consumption data, including electric boosting and oxygen consumption, are normalized to the primary energy equivalent (primary energy consumption of electricity and oxygen generation). Α ranking of the energy efficiency of about 130 container glass furnaces has been derived. The difference in the specific energy consumption of the most energy efficient container glass furnaces and the furnace ranking the position 50 % is only about 20 to 25 %. The effect of furnace age, specific pull, total pull rate, type of furnace, cullet fraction and glass colour on energy consumption levels of container glass furnaces has been derived from a set of energy consumption data of more than 130 furnaces. From these data, the most energy efficient container glass furnace has been identified and a typical energy balance for such a furnace is given. Based on primary energy equivalent and 50 % cullet in the glass forming batch, the most energy efficient container glass furnaces show energy consumption levels close to 3.8 MJ/kg of molten glass. Results of a benchmarking analysis of the specific energy consumption of float glass furnaces are also presented. The energy consumption levels of these furnaces depend strongly on the size of the furnace, pull rate and furnace age, correlations for these factors have been derived