Schematic outline and miniature model of a cold blast cupola furnace

In order to optimise the efficiency of the cupola furnace, the combustion air may be preheated. 

This principle is used in the hot blast cupola (HBC), i.e. a cupola which uses a preheated blast. 

The advantages of the hot-blast operation may be summarised as follows reduced coke consumption increased metal temperature increased melting rate reduced sulphur pick-up reduced melting losses 

It should be noted that not all these advantages can be attained at the same time. For example, an increase in the proportion of steel scrap in the furnace charge may require an increase in the proportion of coke for recarburisation this in turn will reduce the melting rate and increase the sulphur pick-up. 

Recuperative heating This involves the transfer of the residual ( latent ) heat of the fluegases to the combustion air. The flue-gases are collected at the top of the furnace, mixed with sufficient air and then burned in a post combustion unit. This provokes the exothermic oxidation of CO. The burnt gases are led through a heat-exchanger (recuperator) where the heat is transferred to the combustion air. Typically the blast air is heated at temperatures of 500 to 600 °C. Above these temperatures, problems arise with the sintering of fiimace dust on the surface of the recuperator 

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Figure 2.9 Schematic outline and miniature model of a (cold blast) cupola furnace [44, ETSU, 1993], [237, HUT, 2003]...

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