Metallurgical apparatus – Means for treating ores or for extracting metals – By means applying heat to work – e.g. – furnace
Reexamination Certificate
2002-03-21
2003-11-25
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for treating ores or for extracting metals
By means applying heat to work, e.g., furnace
C266S176000
Reexamination Certificate
active
06652802
ABSTRACT:
The invention relates to the manufacturing of iron and steel and more particularly, to a process for direct iron and steelmaking.
My U.S. Pat. No. 5,542,963 describes a process for direct iron and steelmaking featuring the combination of solid-state iron oxide reduction by pressurized hot reducing gases followed by continuous melting of the hot reduced iron. This invention comprises a modified process extended to be more versatile, including several improvements and additions. This application is a continuation-in-part of co-pending application Ser. No. 08/916395.
There are a large number of known processes and variations thereof for accomplishing solid-state iron oxide reduction, all of which achieve the object of producing direct reduced iron, known as DRI or sponge iron, as the end product. These may conveniently be divided into the following two groups:
Group A: Solid-state reduction processes employing pressurized hot reducing gases percolated through a gravity contact-supported or fluidized columnar moving bed of iron oxide particles, pellets or lumps, wherein the pressurized reducing gases comprise recirculated top gases enriched by externally reformed hydrocarbons and/or directly introduced hydrocarbons and the in-bed pressure of the reducing gases at product discharge is substantial, typically in the range of 1-5 atmospheres; and
Group B: Solid-state reduction processes employing coal or other solid carbonaceous reductant, either mixed with iron oxide pellets or lumps as discrete particles, or as a constituent of agglomerated (pelletized) iron oxides, traversing along elongated and relatively shallow moving beds within rotary kilns or carried upon rotary or traveling hearths, and which include a non-recirculated heating gas phase over the bed, as well as reducing gas phase within the bed generated by in-bed reaction of the coal, and wherein the process gas pressure at product discharge is close to zero relative to ambient atmospheric pressure.
Group A processes for DRI production include, for example, MIDREX, HYL, PUROFER, NIPPON STEEL—DR, and AREX—SBD featuring gravity contact-supported descending moving beds within shaft furnace reactors and the FIOR, FINMET, SPIREX, CIRCORED and CIRCOFER processes in fluidized beds and the iron carbide processes, either with fluidized or gravity contact-supported beds.
Group B processes include SL/RN, DRC, KRUPP—CODIR and ACCAR (with coal) processes employing discrete particle iron-coal mixtures heated within rotary kilns. The FASTMET and INMETCO processes employ pelletized mixtures of fine particulate iron oxide and coal, and COMET alternate layers or iron oxides and a coal/limestone mixture, heated upon. rotary hearths.
An overall object of the present invention is to combine in-process features from known processes in these two groupings within the art of solid-state iron ore reduction together with continuous metal melting, comprising a continuous sequence of process steps to produce liquid iron and steel directly from iron oxides, to realize higher output with improved control of product composition and quality, lower energy requirements, higher metal yield with lower material losses, and lower discharge of environmental pollutants than by currently known processes or combinations of processes.
When considering the solid-state reduction process stage, it is not notable that the ACCAR process, when operated with only natural gas or fuel oil, is an exception outside the two above groupings, because it operates near atmospheric pressure without solid carbonaceous reductant. Between 1967 and 1977, in pilot and demonstration rotary kiln plants operated at near-atmospheric pressures, it was shown that hydrocarbons in the form of natural gas or oil, when injected directly into a hot bed of iron oxide pellets, were reformed into reducing gases (CO+H
2
) within the bed itself, obviating the need for external reforming. This work was summarized in “Direct Reduced Iron-Technology and Economics of Production and Use”, Iron and Steel Society, AIME, 1980, pp. 87-90. Only after about ten or more years was this conceptual breakthrough also applied to Group A processes, for example, AREX technology as an alternative to other shaft furnace technologies which use externally reformed gases for reduction. A wide range of reducing gas makeups are therefore workable, appearing necessary only that approximately suitable temperatures and ratios between H, C and O be maintained in the reducing gas, for sustainable solid-state reduction to metallic iron to proceed. This latitude allows the selection of features for solid-state iron oxide reduction circuits to be more freely focused upon such objects as low process energy requirements, high production rate, low volumes of waste gases containing less particulates and unburned combustibles, improved control of product composition, simplicity and low costs.
The various oxygen converter and electric-arc furnace processes dominate current commercial steelmaking practice, but share a common problem of unburned combustibles CO and H
2
contained in the off-gases. The known bath smelting processes also share this difficulty. The development of post-combustion technology has mitigated this problem, but the post-combustion degree (PCD) continues to vary widely during different stages of each heat of steel and substantial excess oxygen via multiple furnace gas-stream injectors is a typical requisite. The heat transfer efficiency (HTE) of in-furnace utilization of the heat so-generated is also relatively low, mainly because of the batch-wise operating mode, typical EAF or BOF geometric shape, and remoteness of the bath from the gas stream exit. Subsequent utilization, such as for preheating scrap, has been only marginally viable as typically somewhat complex and costly to apply in practice. One object of the invention is to realize consistent and near-complete post-combustion including efficient in-furnace heat transfer to the charge, as characterized by uniformly high PCD and HTE and also efficient utilization within the process system of the remaining sensible heat contained in the off-gases from melting, thereby minimizing overall process energy requirements and discharging into the atmosphere only substantially combustible-free exhaust gases at low temperatures.
These current iron and steelinaking processes almost universally feature lancing or sub-surface injection of high-purity oxygen into the bath, typically at high pressures and high velocities in the sonic range. The chemical combination of some of the oxygen with iron generates iron oxide fume which is exhausted as fine particulates, with the effect of reducing metal yields and polluting the environment. Another object of the present invention is to provide a steelmaking process which does not inherently involve injecting oxygen into the bath, using it only when needed for handling specific process materials and special product requirements. A corollary object is to substantially decrease the generation of iron oxide fumes which are typical of current commercial steelmaking processes. Another corollary object is providing the application for low-pressure oxygen of lower purity, such as generated from air separation by molecular sieves, instead of high-purity, high-pressure oxygen.
Still another object of the invention is to release only a minimum volume of exhaust gases at relatively low temperature which are substantially free of combustibles, thereby carrying less heat losses and pollutants into the atmosphere than other overall iron ore reduction and steelmaking combinations.
A further object is to accomplish transfer and immersion of hot solid reduced iron from the reduction stage into a partially melted metal bath at the melting stage with minimum time, heat loss and contact with the ambient atmosphere, furnace gases and steelmaking slag cover.
A still further object is to distribute the hot solid reduced iron pieces at entry into the partially melted metal bath and disperse them sufficiently to avoid the formation of agglomerated floating isla
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