Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1999-03-17
2001-05-01
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S451000, C075S488000, C075S505000, C266S172000
Reexamination Certificate
active
06224649
ABSTRACT:
FIELD OF THE INVENTION
The present invention describes a method and apparatus for the production of reduced iron ore, sponge iron (more commonly now referred to as Direct Reduced Iron or merely DRI), or the like, in an ironmaking plant wherein the charge of iron-oxide-containing particles fed to the reduction reactor can be in a form at least inclusive of fines. The invention in a preferred aspect particularly provides process and apparatus which has the ability to produce DRI, utilizing iron ore particles having a broad range of sizes (or the flexibility to handle any sub-range therein) without the necessity of prior screening, separate processing, and/or excessive equipment with poor performance typical of prior art attempts to handle both normal size pellets or lumps together with significant amounts of fines (which were subject to uneven reduction, loss of product fines, need for excessive capital structures or the like). These new methods and apparatus according to the present invention are particularly suitable for friable iron ore of the type which has a significant tendency to break apart and degrade during the reduction stage, causing clogging in the bed of particles in a moving bed reactor, resulting in disrupted gas flow patterns and consequent uneven reduction.
BACKGROUND OF THE INVENTION
Direct reduction plants for producing direct reduced iron, known as DRI or sponge iron, hot briquetted iron, or the like, (in general pre-reduced materials useful as feedstocks for iron and steelmaking), currently produce DRI by reacting a reducing gas, composed principally of hydrogen and carbon monoxide, at temperatures in the range of 750 to 1050° C., with a bed of particulate iron-containing material. Since the handling of feed materials produce variable quantities of iron ore fines, there has been a constant search for methods and apparatus which avoid the problems of processing fines in a conventional reactor shaft. The most common solution in the past has been to pelletize the fines to give a relatively easily handled particulate charge of quite uniform size (on the order of ⅜ths of an inch). However, such pelletization adds to the cost of the overall process for the production of DRI. Also even pelletized ores include fines that are generated by the ordinary process handling of the pellets. If the pelletizing step could be eliminated (and instead use just ore lumps) without causing more problems than it solves, this would be very desirable.
DESCRIPTION OF THE PRIOR ART
The prior art discloses methods and apparatus for reducing iron ore in the form of pellets and/or lumps in a single reactor usually a vertical shaft furnace. These particles form a bed of iron-containing material which may be static (fixed bed) or may be descending by gravity (moving bed) within a reduction reactor. Examples of such processes are described in U.S. Pat. Nos. 3,749,386; 3,764,123; 3,816,101; 4,002,422; 4,046,557; 4,336,063; 4,375,983; 4,428,072; 4,556,417; 5,078,787; and 5,858,057. These and the other patents or patent applications cited in this application and their content are incorporated by reference.
It is well known to those skilled in the art that fines cause several problems when introduced into or produced in a moving bed reactor. Some of these problems are discussed in the patents described below.
U.S. Pat. No. 5,435,831 to Meissner shows a process capable of producing direct reduced iron from pellets, lumps and fines of iron oxide. However, this patent addresses the problem of fines in the DRI raw material merely by the previous separation of fines present in the feedstock from its coarser constituents (usually by means of a screen), followed by independent processing with the fines being reduced in a series of fluidized bed reactors, while the coarse particles are independently reduced in a conventional moving bed reactor. Even though this process can reduce lumps and pellets, as well as fines, it involves the combination of two separate systems using two types of separate reactors. Fines of the feedstock are separated by means of a screen.
This U.S. Pat. No. 5,435,831 discloses that if fines are introduced directly to the shaft reduction furnace, the fines would be blown out into the scrubber for separation from the gas stream (and thus not only be lost as a product but also become a pollution disposal problem). Thus, this patent contemplates the very condition addressed by the present invention, but teaches away from the present invention and does not even mention the desired reduction of said fines within said shaft furnace.
U.S. Pat. No. 4,886,246 to Maeda et al. describes a largely fluidized bed pre-reduction reactor for achieving, for example, only a quite low 30% reduction of iron ore particles which have a broad range of sizes with a content of from about 20% of coarse material (larger than 5 mm) and about 49% of fines (smaller than 0.5 mm). The final reduction and melting to metallic iron is completed in a separate melter-gasifier. A relatively low grade reducing gas, produced in the melter-gasifier and having a composition for example of H
2
:14%; CO:39%; CO
2
:21%; H
2
O:12% and N
2
:14%, is fed to the pre-reduction reactor through a distributor inclined at greater than the particulate angle of repose at the bottom of said pre-reduction reactor. The velocity of the reducing gas and the shape of the reactor are such that from the full charge of particles fed to the upper portion of the reactor, the fluidized medium sized and the non-fluidized coarsest particles both settle downwardly through a fluidized zone, countercurrent to the upflowing reducing gas, to be withdrawn through preferably one conduit at the bottom of said pre-reduction reactor. The fines are carried over in the partially-spent reducing gas from the top of the reactor into a cyclone separator, which recycles enough of the fines to the reactor to assure sufficient reduction and draws off a portion of the fines for delivery eventually, for example, of 97% of the fines to the melter-gasifier separate from the medium sized and the coarsest particles to the same melter-gasifier.
U.S. Pat. No. 5,762,681 to Lee et al. teaches a method and apparatus for reducing a relatively wide variety of sizes of iron ore fines into metallic iron, which includes a drying/preheating furnace, a primary reduction furnace and two secondary reduction furnaces (one being a high-gas-velocity rector for handling the heavier fines, and the other being a low-gas-velocity rector for handling the lighter fines). This process does not teach use of a moving bed reactor.
U.S. Pat. No. 5,529,291 to Meissner describes a system to process fines as feed material. Meissner shows multiple circulating fluidized beds connected in series capable of reducing iron oxides in the form of fines to metallic iron. No reference was found in this patent's teaching of the processing of fines and coarse particles in a single continuous reactor.
U.S. Pat. No. 5,545,251 to Knop describes the large prevalence of large quantities in the world of fine-particle ores and concentrates and the need for technology for effectively handling these (especially in the poorer ores more widely available). Knop teaches a system of processing fines (but not the coarser particles of 1.0 mm and larger) in a fluidized bed horizontal reactor. In this system, the iron ore fines are blown into the reactor and heated therein by means of coil heat exchangers, passing through successive sections forming fluidized beds separated by partial partitions with intercommunications at the top of the horizontal reactor. The fines overflow the partitions passing from one section to another and finally over the last partition, which defines the sponge iron collecting section. This system assertedly represents an improvement in gas utilization and temperature control of each section forming the horizontal reactor. When particles larger than the range of design are fed into the reactor, said particles cannot overflow from one section to another with the same rate of reducing gas supplied,
Andrews Melvyn
Frommer & Lawrence & Haug LLP
Hylsa, S.A. De C.V.
S. Safford A. Thomas
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