Hot blast cupola furnace

In this section, techniques concerning melting practices and furnace operation will be discussed. These techniques may apply either to cold or hot blast operation, or to both. Flue-gas related techniques, such as post combustion and flue-gas cleaning, are discussed in Section 4.5.2. That section also discusses the conversion of cold blast to hot blast cupola furnaces. 

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

Figure 4.11 gives a comparison of the operational conditions for hot blast cupola furnaces with a wet and dry dedusting system. The main differences are the temperature profile of the flue-gas... 

Table 4.37 Operational data of hot blast cupola furnaces using a bag filter and a disintegrator for dust capture...

Wet scrubbers are applied where large voliunes of waste gas containing relatively high concentrations of organic substances are generated (waste gas from core-making) or where high flue-gas temperatures occur (flue-gas from hot-blast cupola furnaces). 

Ferrous foundries consist of two types steel foundries in which electric furnaces (EAF and induction) are used, and iron foundries in which hot-blast cupolas and/or electric furnaces are used. Electric furnaces use virtually 100% scrap charges. Cupolas are shaft furnaces which use preheated air, coke, fluxes, and metallic charges. Scrap is over 90% of the metallic charge. Cupolas accounted for about 64% of total iron foundry scrap consumption in 1994 and electric furnaces accounted for about 34%. The balance was consumed by other furnaces, such as air furnaces. Iron foundry products have a high carbon content and the scrap charge usually contains a high percentage of cast iron or is used in combination with pig iron. 

High conductivity coppers These are used mainly for their high electrical and thermal conductivities. Applications include tuyeres for blast furnaces and hot blast cupolas, water-cooled electrode clamps, switchgear, etc. 

In ferrous metal foundries, the channel induction furnace is mainly used as a holding furnace. It is the furnace of choice for duplex operation with the hot blast cupola. In this case, its function is either to hold or to homogenise the chemical composition of the metal, or to serve as a reservoir of the melted metal for the casting. The furnace s role is not to increase the metal temperature, but rather to prevent unwanted cooling. 

CBC Cold blast cupola HBC hot blast cupola RF rotary furnace IF induction furnace EAF electric arc furnace ... 

The data show that the average, the standard deviation and the range of values are similar for both cold blast and hot blast furnaces. The median value for hot blast is lower than for cold blast furnaces. This confirms the statement from [224, Helber, et al., 2000] that there is no statistical difference between dioxin emissions for hot and cold blast cupola furnaces. The high standard deviation shows that the data should be interpreted on a plant-by-plant basis rather than on an averaged basis. 

To y, almost all European hot blast cupolas inject oxygen through the tuyeres. For cold blast furnaces, the use of oxygen enrichment can be considered as the standard technique. In this case, enrichment of the blast supply is usually applied. The oxygen level of the oxidising air mixture is usually between 22 and 25 % (i.e. an enrichment of 1 % to 4 %). 

The effect and use of the oxygas burner depends on the cupola concerned. In cold blast cupola furnaces, the technique is used to ensure easy restarts or to reduce the proportion of coke. In hot blast operation, the technique is used to increase the furnace capacity without modifying the melting bed. The replacement of part of the coke with CH4 results in a reduction in flue-gas voliune. This is used as a means of increasing the furnace capacity, without over-saturating the installed flue-gas cleaning system. 

The technique may be applied on both cold blast and hot blast cupolas in both new and existing installations. The advantages drawn from the application (increased flexibility, economical benefit, reduced flue-gas volume, increased capacity) will depend on the specific melting conditions of the installation under consideration. The technique has been reported to cause difficulties for controlling the process and also increases the complication of the furnace shell required. 

Table 4.37 gives economic data for the example plants. For foundry G, the investment costs for a hot blast cupola with bag filter and extensive heat recovery are given. The operational costs for 1994 (after refurbishment of the melting shop) were 25 % lower than those for 1985, i.e. with the old melting furnace. For foundry H, investment costs for 1980 - 1981 are given. After refurbishment, the operational costs went down by 2 %/tonne of liquid iron. 

For economic reasons, the application of post combustion has mainly been related to hot blast cupolas. However, recently, a post combustion system for cold blast furnaces, without the complexity of a hot blast installation, has also been developed. This system is currently in operation in France. In-shaff post combustion therefore applies to both hot blast and cold blast cupola operation. 

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... 

HBI has been successfully melted in cupolas (hot or cold blast), induction furnaces (coreless or channel), and electric arc furnaces. It can be a valuable charge material for ductile and malleable irons as well as steel. It is of particular value in making ductile iron castings because of its very low residual element content. 

Cupola furnaces In cupola furnaces, a massive surplus of chlorine is always present from coke. Enough carbon is present from coke too, but an additional input of carbon may be needed the event of caused by poor scrap qualities. Under specific operational conditions, the conditions for dioxin formation could occur. Since de novo synthesis mainly occurs during cooling of the flue-gas, this applies to both hot blast and cold blast cupolas. In Table 3.34, the result of a statistical analysis of all the measurement data from Table 3.33 for CBC and HBC is given. Whereas Table 3.33 presents average values per plant, for Table 3.34 individual measurements were used to perform an overall analysis. 

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. 

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). 

Installing post combustion on cold blast cupolas can be combined with a full retrofit to hot blast operation. In general, this choice is based on operational considerations. The characteristics of hot blast and long campaign furnaces are discussed in Section 2.4.1. 

UK Environment Agency (2002). "DRAFT Process Guidance Note Hot and cold blast cupolas and rotary furnaces", UK Environment Agency, 163. 

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

Fractions with high calorific values can be used in cupola or blast fiunaces in production or processing of iron. Cupola furnaces are used mainly to melt scrap metal with coke. In blast furnaces, metallic iron is melted in iron ore reduction. For this purpose, along with the coke highly sulfurous heavy oil or coal is injected and gasified with the hot blast. Plastic material can substitute the heavy oil to a certain extent [19]. Use of plastics in blast furnaces require prior comminution to a diameter of max. 5 mm, since this granulate is introduced into the lower section of the blast furnace out of a pressurized container at 0.4—0.5 MPa through a lance. 

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