Prospects and physical limits of processes and technologies in glass melting

The paper is devoted to the physics of continuously operating fuel-fired glass furnaces with supplementary electrical boosting. Furnaces are treated in their basic function as heat exchangers and chemical reactors. First, as an expression of the 1(st) law of thermodynamics, a general heat balance is elaborated in detail. The function as heat exchanger is characterized by three dimensionless key indicators: the temperature efficiency (comprising adiabatic flame, glass exit, and environmental temperature), the heat capacity flow match of hot and cold stream, and the number of heat transfer units. A 2(nd) law treatment reveals the bottle neck of furnace optimization between two conflicting objectives. i.e., high production rates and high energy efficiency. Based on this treatment, an evaluation procedure for furnace performance is presented. It rests on a retrospective analysis of furnace operation data and allows one to quantitatively compare furnaces of different sizes and production capacities as well as the effect of different batches used in the same furnace. A number of industrial case studies demonstrate the usefulness and reliability of the approach. Finally, an expression for the ultimate physical limit of energy utilization efficiency of a fuel fired furnace in general is derived.