Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1980-10-29
1982-11-23
Andrews, M. J.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 26, 75 36, C21B 1306
Patent
active
043603785
DESCRIPTION:
BRIEF SUMMARY
Strong efforts are made today for the development of methods for the production of raw iron or so-called metallized iron ore. The raw iron can be converted further in direct connection with the reduction process or be shipped as raw material for further conversion at steel mills at other locations. Such processes are described e.g. in the Swedish patent publications Nos. 363161, 384225 and 387366.
In these known processes the reduction is carried out at a temperature which is lower than the melting point of the iron and the iron containing material as well as the reduction agent are present in a finely divided state. The reduction agent is a fossil fuel, e.g. anthracite, coal, lignite, oil natural gas, etc. These fuels coke to a varying degree to solid carbon containing material which is present in intimate mixture with the iron containing material.
These known processes are carried out in several steps in different process systems containing rotating furnaces, fluidized beds, etc. The Swedish patent publication No. 384225 describes e.g. a procedure which relies on so-called circulating fluidized beds.
The Swedish patent publication No. 395017 describes another method for the production of a prereduced product whereby the iron containing material is reduced while it is falling through a shaft whereby the material is melted.
Quite generally a raw iron process should meet the following requirements among others:
(1) The degree of reduction should be high, preferably exceeding about 90-95%.
(2) The reduction agent should not deliver impurities to the raw iron which then have to be eliminated.
(3) As much of the reduction agent as possible should be utilized for reduction work.
(4) The raw iron should have suitable properties for subsequent processing, in particular a large specific surface, good general properties for materials handling, small tendency for reoxidation, etc.
(5) The process system should contain as few system parts as possible to cut down the capital investment and improve the reliability of the operation.
(6) The reduction agent should be generally available at predictable costs in order to insure operation of the process system during its physical life.
The temperature is a key parameter for the different raw iron processes, another key parameter is the composition of the reduction gas in different steps of the process. The major problem with processes which operate with the material in its solid state of aggregation the whole time is the so-called cladding which easily takes place at temperatures above 700.degree.-750.degree. C. Lower temperatures give a lower reduction velocity as is well known. The equilibria for the different process steps are also strongly influenced by the temperature and is described in the Swedish patent publication No. 222512.
The rate of the reduction process in particular the final reduction to metallic iron depends on the particle size of the iron containing material as well as on the reactivity of the reduction agent. The so far preferred fossil fuels, in first hand cheap dust coal, require comparatively high temperatures for sufficiently fast pyrolysis and gasification reactions, which generate the reducing gases which then react with the iron containing material.
The present invention relies on a reduction fuel that has been of limited application in this connection, i.e. biofuel, in a new way. The invention seems to satisfy very well the requirements that have been claimed above. In several of the cases, e.g. the requirement (6), this is a consequence of the property of this fuel to be renewable and available all over the world. The advantages of the new raw iron process and its surprising effects can be derived from the utilization and the special properties of the biofuel which characterizes this invention. The invention thus comprises a procedure for the reduction of iron containing material in a finely divided state in three steps which may be continuously following each other or running simultaneously, i.e. preheat, prereduction and final reduction which
REFERENCES:
patent: 2014873 (1935-09-01), Wildman
patent: 2864686 (1958-12-01), Agarwal
Sandviken Handbook pp. 20 and 29.
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