Scrap melting process

Details Scrap melting process Scrap melting process

1997-08-11

2000-04-25

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

75575, 75577, 75581, C21B 1102

Patent

active

060539623

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a scrap melting process designed for the production of molten iron from scrap as well as high-calorie exhaust gas valuable as fuel gas from pulverized coal (serving also as the major heat source) and waste plastics (serving also as the secondary heat source).


BACKGROUND ART

The recent ever-increasing supply of scrap iron and steel has posed an important problem with its recycling for the effective use of resources. This has stimulated the development of a new technology for the efficient, economical production of molten iron from scrap.
It has been common practice to use an electric furnace for the production of molten iron from scrap. This process is uneconomical because of heavy consumption of electric energy.
Another way of producing molten iron (for foundry) is by the cupola process. This process suffers the disadvantage of requiring high-quality foundry lump coke as fuel, which is about four times as expensive as blast furnace coke, and hence is not in general use. The necessity for special foundry coke (which is coarser and less reactive and combustible than blast furnace coke) is due to the fact that combustion to promote the smooth melting of scrap in the cupola furnace should take place such that oxygen in the hot air blown from the tuyere is not rapidly cooled by coke at the raceway but is consumed near the scrap melting zone above the coke bed where the temperature reaches a maximum.
As a substitute for the conventional electric furnace process or cupola process mentioned above, there has been proposed a scrap melting process in "Tetsu-to-Hagane", vol. 79, No. 2, pp.139-146. According to this process, scrap melting is accomplished in a shaft furnace charged with scrap (as an iron source) and blast furnace coke which is burned by oxygen-enriched air (at normal temperature) blown together with pulverized coal through the tuyere. The resulting combustion gas produces sensible heat necessary for scrap melting, and scrap melting is promoted by the secondary combustion of the combustion gas which is induced by air blown through the shaft.
There is another scrap melting process as disclosed in Japanese Patent Laid-open No. 195225/1989. This process resorts to a shaft furnace and a separate combustion furnace in which a large amount of pulverized coal is burned. The resulting hot combustion gas is introduced into the shaft furnace charged with scrap and coke. At the same time, an oxygen-containing gas is supplied for the secondary combustion of the combustion gas which generates sensible heat necessary for scrap melting.
The foregoing two scrap melting processes are likely to be economical because they employ pulverized coal (as part of heat source) and inexpensive blast furnace coke to be charged into the furnace.
However, they are merely intended to save energy by reducing the fuel ratio (below 300 kg/t-pig). This object is achieved by blowing air (or oxygen-containing gas) into the combustion gas resulting from the combustion of pulverized coal so as to bring about the secondary combustion. In other words, their aim is a cost reduction through the reduction of fuel ratio and the use of pulverized coal as part of heat source. In fact, their aim differs from that of operating at a high fuel ratio with a large amount of pulverized coal to be intentionally converted into a large amount of combustion gas (or exhaust gas). They are not designed for operation under such conditions.
In addition, although the above-mentioned scrap melting processes employ pulverized coal as part of heat source for cost reduction, they do not fully achieve this object in view of the fact the fuel ratio is low but the coke ratio is high. It should be noted that the ratio (by weight) of pulverized coal to coke is lower than 1.0 (or 0.9 at the highest).
Another disadvantage of these conventional scrap melting processes is that the exhaust gas inevitably contains a large amount of nitrogen and carbon dioxide because air (as an oxygen-containing gas) is blown to effect the second

REFERENCES:
patent: 4556418 (1985-12-01), Syska
patent: 5244490 (1993-09-01), Agarwal
patent: 5772727 (1998-06-01), De Haas et al.

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