From a formal point of view, a glass furnace is a heat exchanger comprising a hot stream passing through the combustion space and a cold stream passing through the tank. While the hot stream may be treated as a one-phase flow, the cold stream also involves phase transformations and latent heat storage. Such a set-up is subject to several constraints: a combined area-volume constraint, and a time constraint for both heat transfer and phase transformations. This rather abstract concept is most helpful in assessing the efficiency limits of glass melting. From a practical point of view, it is essential to know if the efficiency of an individual furnace is limited by heat transfer, or rather by the batch-to-melt conversion rate. Consequently, measures aiming at enhancing the operation efficiency must match the individual situation. This principle is demonstrated for campaigns with industrial furnaces. In many cases, the use of low-enthalpy batches and fast conversion batches is an efficient way to improve glass melting.
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