Cokeless cupola furnace

In the cokeless cupola, the metal charge is heated by the combustion of natural gas. Instead of the traditional coke bed, a bed of refractory spheres on a water-cooled grid supports the metal charge. The molten metal droplets run through this bed and are collected in the well at the bottom of the furnace. The life of the spheres exposed to the superfieating temperatures of the metal is limited. A cokeless cupola is therefore run at a reduced temperature (1400 C instead of 1500 C) and superheating of the liquid metal is done in an attached gas-fired or induction furnace (duplex operation). 

The oxidising atmosphere and relatively low flame temperature cause increased oxidation losses. This limits the possibility to feed in steel. A maximum amount of 35 % of steel is used in the production of nodular iron, though 20 % can be considered general practice. The quality of the feed needs to be well controlled since the cokeless cupola is more susceptible to bridging than the coke-fired cupola. 

In the production of nodular iron, an important advantage of the cokeless cupola is that there is no resulphurisation, so the melt may be used immediately after recarburisation. 

Besides a higher thermal efficiency, this furnace has other environmental advantages, combustion of natural gas instead of cokes has the following consequences for the flue-gas  

The use of cokeless cupola melting necessitates duplex operation, in order to allow superheating of the iron. For superheating in an induction furnace, there is an increased need for electrical power compared to the hot blast operation. 

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Table 4.7 Typical operational data for a cokeless cupola furnace [202, TWG, 2002]...

Emission data for cokeless and hot blast cupola furnaces are compared in Table 4.8. These apply for the following configurations ... 

Calculation of the heat balance results in the stated heat transfer efficiencies. The cold blast cupola shows an efficiency of <30 %. The application of oxygen or secondary air increases the efficiency to 37 - 40 %. The hot blast cupola shows a further increased efficiency, providing the furnace wall is refractory lined. In liningless operation, the efficiency drops below 40 %, which may be somewhat compensated for by adding oxygen. The cokeless cupola with inductive superheating results in a very high efficiency, close to 60 %. 

Units Melting device Cold blast cnpola Hot blast cnpola Cokeless cnpola Indnction furnace Hot blast cupola Cokeless cupola Induction furnace... 

CTIF induction furnace, hot blast, cold blast, cokeless cupola Neumann cokeless, hot blast, cold blast cupola Nodular base cast iron... 

Due to the absence of cokes (and CO), no latent heat is lost from the cokeless furnace system. Full heat recuperation from the flue-gas occurs in the shaft. In duplex configurations (for example in conjunction with an induction furnace), efficiencies in the range of 40 to 60 % may be obtained. Thermal efficiencies for coke fired cupolas vary between 25 % (cold blast) and 45 % (hot blast, long campaign). 

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