Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
1999-02-08
2001-12-11
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
C075S444000
Reexamination Certificate
active
06328946
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing iron carbide from an iron-containing feed material. More specifically, the present invention utilizes a two step process to convert iron oxide to metallic iron in the first step and metallic iron to iron carbide in the second step for use in steel-making.
BACKGROUND OF THE INVENTION
The steel industry has relied on a process that has been in use for many years for the conversion of iron ore into steel. The process converts iron ore into pig iron in a blast furnace using coke produced in a coke oven. The process next converts the pig iron or hot metal into steel in an open hearth or basic oxygen furnace.
In recent years, federal and local environmental regulations have caused numerous problems for steel producers using this steel-making process. The blast furnace and coke ovens used in the process are not only energy intensive but also responsible for most environmentally damaging emissions by steel producers. To redesign or modify blast furnaces and coke ovens to comply with pollution standards is expensive. The expense would cause the cost of steel produced by the conventional steel-making process to be non-competitive with steel produced by foreign competitors.
To address these problems, a process was developed for steel production that eliminates the blast furnace and coke oven in the steel-making process. In the process, a bed of iron oxide is fluidized by a single, multiple-component gas stream and directly converted into an iron carbide-containing product, primarily consisting of Fe
3
C. The iron carbide is then added to a basic oxygen or electric arc furnace to produce steel. In the process, reduction and carburization reactions occur together in the same fluidized bed.
Another process has been applied to produce acicular iron carbides having desired magnetic characteristics for use in magnetic recording and as catalysts for converting CO and H
2
into lower aliphatic hydrocarbons. In the process, a bed of the acicular iron oxide is reduced by one gas and a bed of the reduced product is then carburized by another gas to produce acicular iron carbides. The process suffers from slow reaction kinetics and large amounts of impurities (including iron oxide, free carbon and metallic iron) in the acicular iron carbide product.
Other techniques to convert an iron-containing feed material into an iron carbide-containing product are batch processes, require expensive components and/or otherwise raise other operational complications.
It would be advantageous to provide a continuous process to convert iron-containing materials into iron carbide. It would be further advantageous to produce an iron carbide product with environmentally friendly and/or non-hazardous byproducts. It would be a further advantage to optimize the reaction kinetics of chemical reactions to convert iron-containing materials into iron carbide and to produce an iron carbide product that has high purity.
Additionally, it would be advantageous to develop an environmentally friendly, energy efficient and inexpensive process to produce steel. It would be further advantageous to convert, inexpensively and efficiently, iron-containing materials into iron carbide for use in the production of steel. It would be a further advantage to eliminate the blast furnace and coke oven from the steel-making process.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, a two step process for producing iron carbide is provided. In the first step, a first feed material containing iron is contacted with a first gas to produce a first product containing metallic iron. The first gas contains hydrogen. The hydrogen in the first gas can be hydrogen gas, a hydrogen gas precursor, or mixtures thereof.
The first product contains no more than about 49 percent by weight iron carbide. To yield this result, the first gas contains no more than a predetermined amount of reactive carbon. As used herein, “reactive carbon” refers to any carbon-containing compound capable of providing carbon to carburize metallic iron at the temperature, pressure and composition of the reactor atmosphere. For example, reactive carbon can include carbon monoxide, carbon dioxide, and mixtures thereof. Carburization of the first feed material is undesired as it reduces the rate at which the iron oxide is reduced to metallic iron.
It is preferred that iron oxide be at least about 90 mole percent of the feed material in the first step on a water free basis. Preferably a substantial portion, and more preferably a majority, of the iron oxide in the first feed material is converted to metallic iron in the first step. The presence of iron oxides in the first product is not desired since iron oxide will slow the reaction kinetics and lengthen the residence time in the second step.
In a second step, the first product is contacted with a second gas to produce a second product containing iron carbide. To produce a second product containing iron carbide, the second gas includes (a) a first component containing carbon monoxide or a carbon monoxide precursor, carbon dioxide or a carbon dioxide precursor, or mixtures thereof and (b) a second component containing hydrogen gas or a hydrogen gas precursor. The second gas can also include a third component containing methane or a methane precursor. The second product can be fed directly to an appropriate reactor for conversion into steel.
A majority of the second product is preferably iron carbide. It is desired that at least about 90 mole percent, and more preferably 95 mole percent of the iron carbide be in the form of Fe
3
C. Fe
2
C is not desired as it, unlike Fe
3
C, is highly reactive and will oxidize upon exposure to air. The second product should contain no more than about 6 to about 8 mole percent impurities, including metallic iron, free carbon, and iron oxide. Impurities such as metallic iron, free carbon, and iron oxide can cause problems if the second product is converted into steel and the steel processed into useful articles.
In the second gas, the first component is preferably carbon monoxide or a carbon monoxide precursor, carbon dioxide or a carbon dioxide precursor, or mixtures thereof. The first component should be the primary source of carbon in the conversion of metallic iron into iron carbide. Although the methane or methane precursor in the third component contains carbon, the preferred sources of carbon for the carburization of the metallic iron are carbon monoxide or a carbon monoxide precursor, carbon dioxide or a carbon dioxide precursor, or mixtures thereof. Water and not hydrogen gas will be a byproduct of carburization using the preferred compounds.
In the second component, water vapor, a hydrogen gas precursor limits substantially the decomposition of carbon monoxide into free carbon and thereby substantially eliminates free carbon from the second product.
The third component, methane, a methane precursor, or mixtures thereof, prevents hydrogen from reacting with the carbon in iron carbide, a reaction which would convert iron carbide into metallic iron. Metallic iron in the second product can oxidize to form iron oxides which create difficulties in converting the second product into steel.
In one embodiment of the present invention, the process is a continuous process. Preferably, the two process steps are conducted in separate reaction zones to facilitate the continuity of the process. Preferably, in one or both process steps the reaction zone is a fluidized bed.
The present invention has numerous advantages over existing methods and apparatuses. One embodiment of the present invention advantageously provides a continuous process to convert the iron-containing materials into iron carbide. The present invention thereby avoids the increase in operating expenses associated with batch processes.
Another embodiment of the present invention advantageously provides a process with rapid reaction kinetics. The composition of each gas can be selected to optimize the kinetics of the reaction in each process
Hendrickson Stuart L.
Iron Carbide Holdings, Ltd.
Sheridan & Ross P.C.
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