Practical experience with raw-material preheating on glass melting furnaces

Abstract

By preheating the raw materials using the energy of the flue gases after leaving the air-preheating system energy savings of about 20 to 25 % are possible on glass melting furnaces. At the same time, the flue gases are cooled down to temperatures, which are necessary for the cleaning process that follows in the electrostatic precipitator. The preheating of the raw materials has been often discussed in the past, but that time at no suitable heat exchanger was available. Furthermore, there also were many other possibilities to improve the thermal performance of glass melting furnaces, for example better air preheaters, a better insulation of the installation of better burner systems. Nienburger Glas GmbH has been working in the field of batch preheating since about ten years. The preheater, which was developed, works with direct contact of flue gas and batch in a cross-counter flow; the flue-gas ducts are set up by angle irons with the corner at the top side. During the preheating process also most of the acidic components, for example sulphur oxides, chlorine and fluorine, are removed out of the flue gases. After beginning with a small experimental setup a batch preheater for a cross-fired green glas furnace with a pull rate of about 300 t glass/d was designed and built in cooperation with GEA Energietechnik GmbH, Bochum (FRG). This batch preheater has been operated since about 4 years with a cullet content of about 80 to 90 %. The next step in developing this new technique was the installation of a batch preheater on a cross-fired furnace with a capacity of about 350 t glass/d, which is used for the production of white glass with a cullet content of 30 to 50%. Moreover, the first batch preheater for an end-fired furnace has recently been taken into operation. This paper will report about practical experiences with the existing batch-preheating systems. The energy consumption will be treated as well as the emission of sulphur oxides, chlorine and fluorine, the preheating temperatures, the melting behaviour of the furnace, the carry over of dust to the regenerators and the quality of the produced glass.