Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
2000-03-22
2002-08-06
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
Reexamination Certificate
active
06428763
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 of the form Fe
5
C
2
. The process suffers from slow reaction kinetics, large amounts of impurities (including iron oxide, free carbon and metallic iron) in the acicular iron carbide product, and poor gas efficiency (i.e., poor utilization of reactants in gas). The product, Fe
5
C
2
, is quite unstable and requires more carbon reagent to form than Fe
3
C (and is therefore more expensive to produce).
Other techniques to convert an iron-containing feed material into an iron carbide-containing product require expensive components, suffer from poor gas efficiency, and/or raise other operational complications.
It would be advantageous to provide a process to convert iron-containing materials into iron carbide that has a high gas utilization. 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 and low residual iron oxide.
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.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, a two step process for producing iron carbide from an iron oxide-containing feed material is provided. As used herein, “iron carbide” preferably includes Fe
2
C and Fe
3
C, and “iron oxide” preferably includes FeO, Fe
2
O
3
, and Fe
3
O
4
. In the first (reduction) step, a feed material containing iron oxide is converted to an intermediate product by contacting the feed material with a reducing gas to reduce the iron oxide to metallic iron, and in a second (carburization) step the metallic iron is converted into an iron carbide product.
The reducing gas preferably contains sufficient hydrogen gas, the primary reducing agent, to perform substantially complete reduction of the iron oxides in the feed material to metallic iron. Typically, the reducing step is a closed circuit process so that virtually all of the reducing reagent is utilized by the process to remove oxygen from the feed material. Preferably, the predominant component of the reducing gas is hydrogen gas, and more preferably the reducing gas contains at least about 80 mole % hydrogen gas. Water, the byproduct of the reduction reaction, is easily removed from the first step off-gas by suitable techniques.
At least most of the iron in the intermediate product is in the form of metallic iron. Preferably, at least about 70 and more preferably at least about 90 mole % of the iron in the intermediate product is in the form of metallic iron. The intermediate product typically contains no more than about 35 mole percent iron carbide, more typically no more than about 25 mole percent, and more typically no more than about 10 mole percent iron carbide.
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 at least most, of the iron oxide in the feed material is converted to metallic iron in the first (reduction) step. The presence of iron oxides in the intermediate product is not desired since iron oxide can slow the reaction kinetics in the carburizing step and lengthen the necessary residence time of the material in the carburizing step for a desired degree of carburization.
In the carburization step, the intermediate product is contacted with a carburizing gas to produce an iron carbide product. The carburizing gas includes carbon monoxide and hydrogen gas. Preferably, the carburizing gas contains at least about 5 and more preferably at least about 15 mole % carbon monoxide and at least about 80 mole % hydrogen gas.
The carburizing gas can also include other components such as carbon dioxide, methane, water vapor and a diluent such as nitrogen or another inert gas. Preferably, the carburizing gas includes no more than about 5, more preferably no more than about 3, and more preferably no more than about 1 mole % carbon dioxide; preferably no more than about 15, more preferably no more than about 10, and more preferably no more than about 5 mole % methane; preferably no more than about 10, more preferably no more than about 1, and more preferably no more than about 0.5 mole % water vapor; and no more than about 10 mole % inert gases.
As will be appreciated, the temperatures of the carburizing gas and of the bed of the intermediate product during carburization are important to the reaction kinetics. Preferably, the carburizing gas has a gas temperature of at least about 550° C. and the intermediate product a bed temperature of at least about 500° C.
Because of the high concentration of carbon monoxide in the carburizing gas and the fact that the carbon monoxide directly converts metallic iron into iron carbide, less gas is required for complete carburization than in suitable two-step processes and the rate of the carburization reaction is relatively high. Compared to other two-step processes, the process of the present invention requires lower capacity components for a given throughput of feed material. The reduced capacity components significantly reduce capital and operating costs and water consumption.
At least most of the carbon monoxide in the carburizing gas is passed through the intermediate product only once (i.e., the carburizing step is preferably an open circuit while the reducing step is preferably a closed circuit). As used herein, a closed circuit means that at least most and more typically at least about 90 mole % of the reducing off-gas is recycled to the reducing step, and an open circuit mean
Hager John P.
Hogsett Robert F.
Stephens Frank A.
Stephens, Jr. Frank M.
Hendrickson Stuart L.
Iron Carbide Holdings, Ltd.
Sheridan & Ross P.C.
LandOfFree
Process for the production of iron carbide from iron oxide... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the production of iron carbide from iron oxide..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the production of iron carbide from iron oxide... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2893046