Industrial electric heating furnaces – Arc furnace device – Charging or discharging
Patent
1998-02-06
1999-08-31
Hoang, Tu Ba
Industrial electric heating furnaces
Arc furnace device
Charging or discharging
373 1, 373 85, F27D 1300
Patent
active
059463406
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for smelting metallic raw materials in a shaft furnace, in which coke is burnt with preheated air and largely pure oxygen and the flue gases heat the metallic charge in countercurrent, and in which the melt is superheated and carburized in the coke bed.
Metallic and non-metallic materials, such as iron and non-ferrous metals, basalt and greenstone, are still smelted in coke-heated shaft furnaces in spite of the development of electrical and flame-heated smelting processes. Thus, about 60% of all iron materials are nowadays still produced in cupola furnaces.
The reason for this high market share of the cupola furnace is the continuous further development, with the development of the hot-blast cupola furnace and the use of oxygen amongst the large number of known process modifications being of importance.
Thus, for example, the process engineering disadvantages and metallurgical disadvantages of the cold-blast cupola furnace, such as furnace.
Similar improvements are achieved by the use of oxygen, the oxygen being blown into the cupola furnace either by enriching the cupola furnace blast up to a maximum of 25% or by direct injection at subsonic velocity. Owing to the high operating costs, however, oxygen is employed only discontinuously, for example for rapid starting of the cold furnace or for raising the iron temperature for a limited period. The possibility of increasing the output, i.e. continuous use of oxygen, is exploited only in exceptional cases.
In spite of the introduction of these process modifications, it is still possible for point.
The relationship between melting output and blast rate as well as the rate of addition of oxygen is described by the known Jungbluth equation. This equation results from a generation of mass and energy, with the coke charge and the combustion ratio having to be determined empirically for every cupola furnace.
Linking the active parameters, namely blast rate, coke charge and combustion ratio, to the target parameters results in the smelting output diagram, FIG. 1, with curves of equal coke charge and equal blast rate.
This smelting output diagram, known as the Jungbluth diagram,must be determined empirically for every cupola furnace. A transfer to other cupola furnaces is not possible, since the operating behavior changes immediately when the conditions such as lumpiness of the coke, reactivity of the coke, charge composition, blast velocity, furnace pressure, temperature etc. are altered.
The heat losses are lowest at the temperature maximum. At unduly high blast rates, i.e. high flow velocity, the furnace is overblown. At unduly small air rates, i.e. unduly low flow velocity, the furnace is underblown. In both cases, the combustion temperature is lowered, since, on the one hand, the additional N.sub.2 ballast must also be heated and, on the other hand, heat is removed by the additional formation of CO. Furthermore, the elements accompanying the iron are more thoroughly oxidized in overblowing.
By using oxygen up to, for example, 24% by volume in the blast, the net line is shifted towards the top right, i.e. to higher temperatures and to higher iron throughputs. The temperature maximum flattens, and the furnace becomes insensitive to underblowing or overblowing.
A reduction in the coke charge at constant iron throughputs and reduced blast rate is not possible even with continuous addition of oxygen, since the iron temperature then falls and additional metallurgical and process engineering problems, such as
Since, from the point of view of combustion technology, a large excess of coke is present, a reduction in the quantity of coke at constant smelting output is of great interest for reason of economics, since the manufacturing costs of molten iron are affected essentially by the remelting costs and the raw material costs.
Furthermore, it has been known for a long time that, especially in the case of cupola furnaces having large frame diameters, the so-called "dead man" remains standing in the center of
REFERENCES:
patent: 3964897 (1976-06-01), Langhammer
patent: 4547150 (1985-10-01), Vereecke
patent: 4851039 (1989-07-01), Papst et al.
patent: 5060913 (1991-10-01), Reid
patent: 5513206 (1996-04-01), Mori et al.
Koperek Albert
Ramthun Josef
Georg Fischer Disa Engineering AG
Hoang Tu Ba
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