Among the various furnaces used to produce an iron melt or to melt ferriferous materials, it is known to provide a solid charge constituted by the ferriferous material and a predetermined quantity of carbonaceous material such as coke. The melt is formed at the bottom of this furnace and generally a gas rich in oxygen is caused to pass upwardly through the solid charge bed so that the reaction of the oxygen of the gas with the carbon of the charge in the exothermic production of carbon oxides, generates the heat necessary to melt the charge. It is customary to blow the charge by tuyeres or air or oxygen injectors disposed somewhat above the melt in the furnace and thus generally at a location between the point at which the charge is introduced into the furnace and the point at which the melt is tapped therefrom.
Typical of these furnaces are the cupola melting furnaces. The cupola charge is constituted generally on the one hand by the ferriferous solid materials having a high concentration of metallic iron such as scrap, solidified iron (pig iron) or sponge iron produced in direct reduction furnaces from iron ore. Another part of the charge is generally coke which provides the carbonaceous material and also is present to assure the permeability of the charge to the oxygen containing gases which are injected by the tuyeres.
The quantity of coke which is used must be sufficient not only to ensure the carburization of the iron, i.e. the formation of an iron melt containing a predetermined concentration of carbon, but also to combine with the oxygen for producing the thermal energy required to melt the iron.
In some cases it is necessary to generate the thermal energy by introducing through the tuyeres auxiliary combustible materials such as natural gas or liquid fuels.
While such systems are highly versatile in that they allow selection among the various energy sources or fuels and permit coke or hydrocarbon sources to be selected or utilized interchangeably, the versatility is nevertheless limited by the fact that only fossil fuels or materials can be employed.
In addition, since the heat carrier is a gas formed in situ by a thermal reaction, the quantity of gas which must traverse the charge may exceed the permeability characteristics thereof and may introduce economic difficulties, especially when a closed circulation is desired through the furnace. This is a consequence of the fact that comparatively large volumes of carbon oxides are formed in the reaction and, in the event recirculation is desirable, e.g. as a heat conversing measure, the comparatively large quantities of carbon oxides can pose problems.
Finally, in connection with conventional techniques, it is important to note that they rely upon non-renewable energy sources and hence may be intolerable in locations in the world where renewable energy sources are available but fossil fuels are comparatively expensive or are of only limited availability. It should be noted that, in many cases, environmental concerns militate against the use of non-renewable energy sources when renewable energy sources are available.