Technologically required time and energy for glass elaboration

Abstract

As is known, using different kinds of markers it has been shown that a batch portion, introduced in a glass melting tank furnace, leaves it gradually, after times varying between 7 and 130 h, depending on its construction and working conditions. A mean duration may be assessed, having, for different furnaces, values between 25 and 60 h, called retention time ( t rm). On the other hand, the available data concerning the melting time, the refining time and the conditioning time, resulted in a total of about 8 h. This minimum time required to obtain glass of a given quality from a certain batch was named technologically necessary time ( t tn). Obviously this time is much smaller than the retention time. The ratio t rm t tn has, for the majority of continuous glass melting tank furnaces, values greater than 3, for some glass portions even exceeding 10. The processes taking place by glass melting may be grouped in two categories: energy consuming essentially independent of time, related to transformations and reactions in raw materials and, on the other hand, consuming energy in time, in order to obtain the desired glass melt quality. Using a new indicator - hourly specific energy consumption - it becomes possible to estimate the energy consumption for processes from the second group and, in general, for the time the glass stays at high temperatures in a given furnace. It results that for some furnaces, the energy consumed in the additional retention time ( t rm − t tn, when glass flows useless through the furnace, may represent even 50% of the total energy consumption. The presented diagrams allow to visualise the amount of energy consumption for different processes and the possibilities of intervention in order to diminish it.