Up to now the chemical and physical processes occurring in exhaust gases doped with volatilized matter from the glass melt are only understood in general terms. During transport from the furnace to the stack, the exhaust gases are cooled down from 1800 K to approximately 500 K. During this transportation the exhaust gas flow passes surfaces with lower temperatures. Heat transport from the exhaust gas to these relatively cold surfaces is accompanied by mass transport of gaseous species towards the surface resulting in deposition of exhaust gas components. Recuperation of part of the heat content of the exhaust gases is a procedure generally applied in the glass industry. Heat is transferred from the flue gases to the combustion air by means of regenerators or recuperators. Deposition of several condensing exhaust gas components at the relatively cool surfaces in regenerators may cause blockage of the channels, a decreasing heat transfer and corrosion. Inorganic salts like sodium sulphate, lead sulphate or sodium borates are the main constituents of the deposits in regenerators or recuperators. Alkali, sulphur and occasionally lead, boron, chloride and fluoride components are introduced in the exhaust gas by fuel impurities or, have volatilized from the glass melt. The chemical composition of the exhaust gas is strongly dependent on the temperature. Variants in temperature, result in changing thermodynamic conditions causing chemical conversions in the exhaust gases. Generally, the chemical composition of the bulk exhaust gas is different from the composition of the gaseous phase near a colder surface. This causes diffusion mainly of salt forming elements like sodium, sulphur, lead or boron towards the wall. In this study the deposition behaviour has been investigated for several exhaust gas compositions~under different conditions. Physical models have been developed in this field and applied to calculate the deposition rates and the nature of the deposited product for practical cases. To obtain a better understanding of the processes that cause the entrainment of certain chemical elements in the flue gases of the furnace, a detailed description of the glass melting process is given in chapter 1.
