Chloride emission from glass melting furnaces

Abstract

By means of chloride measurements in input and output flows of glass melting furnaces, chloride balances have been established. The measurements were carried out on industrial container and flat glass furnaces. The balances show a good consistence. It has been found that from the chloride in the feed of the furnace roughly the first 110 mg Cl-/kg molten glass wih be incorporated into the glass. The rest will be divided between flue gas and glass (50 %/50 %), however, this depends slightly on the concentration of chloride in the feed, the amount of recycled cullet and the Na2O content in the glass composition. By formulating a model with the three mentioned factors the amount of incorporated chloride can be accurately predicted. The model presented is an empirical one and is applicable to soda-lime-silica glasses. It is valid between the limits: chloride in the feed 160 to 560 mg Cl-/kg molten glass, 0.15 to 0.80 kg cullet/kg molten glass and 0.11 to 0.16 kg Na2O/kg molten glass. The chloride concentration in the flue gas is given by the difference between the chloride content in the feed and in the glass divided by the gas volume per quantity of molten glass. This volume depends on the energy economy of the furnace, the raw materials and the amount of recycled glass used. European emission standards for HCl are expressed per volume of flue gas and, therefore, do not stimulate a more efficient use of energy and of recycled raw materials. This can be changed by providing emission standards which are basded on the quantity of molten glass rather than on the released flue gas volume.