Melting and Fining
Industrial glass melting in tank furnaces involves transfer of heat required for the fusion of the batch materials and to obtain a low-viscous melt. The heat transfer process to the melt, in fossil-fuel-fired furnaces, is dominated by the radiation from t
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2.1 Modeling of the Melting Process in Industrial Glass Furnaces Ruud G. C. Beerkens Introduction Industrial glass melting in tank furnaces involves transfer of heat required for the fusion of the batch materials and to obtain a low-viscous melt. The heat transfer process to the melt, in fossil-fuel-fired furnaces, is dominated by the radiation from the combustion chamber to the batch blanket and to the glass-melt surface. Another possible source of energy is an electrode system immersed in the melt. Temperature differences will cause density gradients, driving free convection flows in the melt tank. The convection of mass in the melt is essential for mixing and heat transport, particularly for melts with low heat transmission. The mass and heattransfer processes have been described in the last two decades of the 20th century by several models based on fluid-dynamic laws. From the calculated temperature field and flow conditions, residence-time distribution and chemical conversions can be derived. Melting kinetics and the removal of gaseous inclusions are the most critical processes in a melting tank, depending on temperature, velocity gradients, and glass-melt or batch composition. Today, there exist models, describing the kinetics of sand-grain or aluminum-oxidegrain dissolution and the exchange of gases between melts and bubbles. In this chapter we describe the use of CFD models and post-process melting and fining models for simulating glass-melt processes. The combustion process and the heat radiation are briefly discussed and additional models for predicting evaporation and superstructure corrosion by alkali vapors are shown. Simulation models offer the possibility of optimizing furnace design and operating conditions, and, in the near future, fast dynamic modeling will be applied for so-called model-based control of glass-furnace operations. Simulation of the most essential processes in glass-melting furnaces is a valuable tool that becomes increasingly important for the: • design of glass furnaces, • optimization of the process operation parameters, H. Loch et al. (eds.), Mathematical Simulation in Glass Technology © Springer-Verlag Berlin Heidelberg 2002
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2. Melting and Fining
• understanding of the physics and chemistry of glass melting and combustion, • controlling of glass-melting operations. The first section addresses the possible application of simulation models, mainly based on computational fluid dynamics, in the glass industry and the development of such models over the last decades. Section 2.1.2 discusses the modeling of heat transfer in the melt and combustion space and the modeling of glass-melt flows in melting tanks of glass furnaces. Illustrative examples of the application of such modeling will be presented. Section 2.1.3 describes the submodels on sand-grain dissolution and gas-bubble removal, often used to model the melting and fining kinetics of glass-melting furnaces. We will also demonstrate the use of so-called quality-index calculations to characterize the fining or melting qua
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