Abstract :
Reliable automatic bottom temperature control of a glass furnace is difficult because of the large time delay present between heat being input at the surface and that heat input affecting the temperature of the bottom glass. This delay is typically of the order of several hours although the exact time delay does alter with varying furnace conditions such as the furnace throughput (pull) and the amount of floating unmelted raw material (batch cover). Such conditions can be considered as unmonitored process disturbances. Because the temperature of the bottom glass of the furnace is an important factor relating to the quality of the glass produced, many furnaces operate with additional heating entered directly into the bottom of the furnace by means of passing an electric current through the bottom layer of glass. Whilst this has proved to be effective, it is very expensive with regard to running costs. When a furnace is operated beyond its design capacity such electric heating is often the only way to achieve higher output whilst maintaining acceptable bottom glass temperatures. The project described deals with a furnace operating within design capacity but with a bottom glass temperature that is difficult to hold stable in the presence of considerable process disturbances
