Contribution to the melting characteristics of the cokeless, natural gas fired cupola furnace: the cokeless cupola furnace uses natural gas to a much better extent than the coke cupola furnace uses coke. Therefore, the necessary quantity of heat for running the cokeless furnace is only half the amount as for a coke cupola of the same capacity.

Almost the whole production of cast iron with flake and nodular graphite is distributed between cupola (some two thirds) and electric induction furnaces (one third) (1). A new kind of cupola furnace is the cokeless, natural gas fired cupola. This has many advantages, especially for production

During 15 years of successful practice and development, several research projects have been initiated, promoted by Germany's Federal Ministry for Education, Science, Research and Technology (BMBF), to measure the metallurgical and engineering processes as comprehensively as possible.

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Description of cokeless melting

The cokeless, natural gas fired cupola furnace (CLCF), is a refractory lined shaft furnace divided by a water cooled grate into the furnace shaft and the firing hearth. Fig. 1 shows a schematic cut through a CLCF. After the ceramic bedding has been fed onto the water cooled grate, the empty furnace will be preheated for about 40 minutes. The cokeless cupola furnace will then be loaded with metallic charge composed of returns, cast iron scrap, pig iron and steel scrap (some 30%) and the slag forming constituents.

In contrast to the coke fired cupola, the energy is brought in by a separate controllable natural gas burner below the water cooled grate. The hot flue gas of the burner flows through and overheats the layer of ceramic spheres and ensures that the charge column is thoroughly preheated. The charge material melts, is overheated while it is in contact with the ceramic bedding and drips into the melting bath. The slag and iron are separated in the syphon slag.

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Slag composition

Full combustion of natural gas (45-53[Nm.sup.3]/[t.sub.Fe]) with formation of C[O.sub.2] and [H.sub.2]O and an excess of [O.sub.2] forms an oxidising atmosphere that oxidises the metal components with evolution of CO and [H.sub.2] with a lesser heat effect in comparison with the combustion reactions (2).

Oxidation (burn off) of Si, Mn and Fe, and the producing oxides Si[O.sub.2], MnO and FeO form with the fluxes (limestone and dolomite) the primary slag. Over the grate, formed primary slag flows or drops together with molten iron into the furnace well. Part is blown out to the sides of the furnace with a jet of combustion products from the burners, flowing along the lining downward in the slag. The slag reacts with iron drops before it is collected in the furnace well as so called 'end slag' (fig. 2).