Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
1999-03-31
2003-01-14
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
Reexamination Certificate
active
06506353
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process and apparatus for producing iron carbide.
BACKGROUND ART
A traditional method for producing steel from iron oxide such as iron ore normally comprises the steps of;
in the first step, producing molten pig iron in such a manner that coke produced at a coke oven, other raw materials and iron oxide are charged into a blast furnace, and thereafter, iron oxide are molten and reduced by combustion heat of carbon contained in coke generated due to blowing of high temperature oxygen and carbon monoxide generated due to combustion of said carbon;
in the second step, charging the molten pig iron into a converter, and converting the molten pig iron by oxygen blowing into steel, wherein a carbon concentration of which is under the demanded value.
Since such traditional steel making process by a blast furnace requires many ancillary facilities such as coke oven, sintering furnace, and air-heating furnace, equipment cost becomes high. Furthermore, this steel making process via a blast furnace requires the expensive coal such as high coking coal and huge site for many facilities and raw materials storage. Therefore, recently, to overcome the above disadvantages of using a blast furnace, new iron making processes, instead of a blast furnace, have been developed and put to practical use.
For example, one of the newly developed processes for producing steel is a method called as iron carbide-electric furnace process. This process comprises the steps of obtaining iron carbide by reacting grainy iron oxide with a reducing agent such as hydrogen and a carburizing agent such as methane gas, and producing steel by smelting said iron carbide at an electric furnace. A fluidized bed reactor is a well known apparatus for producing iron carbide. The laid open publication No. HEI 6-501983, which is the publication of the Japanese translation of International Patent Application No. PCT/US91/05198 discloses an apparatus for producing iron carbide. As shown in
FIG. 8
, said publication shows an apparatus for producing iron carbide, wherein when a grainy iron oxide is charged into fluidized bed reactor
32
via inlet
31
, the grainy iron oxide is reduced under floating and fluidizing due to the high temperature and high pressure gas being introduced from multiple nozzles
33
located in the bottom portion of the reactor. Thereafter, the iron oxide is broken into smaller pieces as a result of the foregoing reaction and moves along with a passage formed by baffle-plates
34
,
35
,
36
,
37
, and is finally discharged as iron carbide from outlet
38
. (Hereinafter, this apparatus is called as prior art.)
By the way, the reaction for converting iron oxide into iron carbide proceeds as shown in the following formulas (1) through (6).
(1) Fe
2
O
3
+3H
2
→2Fe+3H
2
O (FeO
1.5
+1.5H
2
→Fe+1.5H
2
O)
(2) Fe
3
O
4
+4H
2
→3Fe+4H
2
O (FeO
1.3
+1.3H
2
→Fe+1.3H
2
O)
(3) Fe
3
O
4
+H
2
→3FeO+H
2
O
(4) FeO+H
2
→Fe+H
2
O
(5) 3Fe+CH
4
→Fe
3
C+2H
2
(6) 3Fe
2
O
3
+5H
2
+2CH
4
→2Fe
3
C+9H
2
O
As shown in the above formulas (1) through (6), the iron oxide is converted into iron carbide in turn of Fe
2
O
3
, Fe
3
O
4
, FeO, Fe and Fe
3
C, and the volume of the reducing gas H
2
to be used varies according to each stage in the reducing reaction. On the other hand, under some gas temperature or some gas composition, there is such a case that FeO is not generated. As is described below, the prior art has the various problems to be solved.
First, the higher the concentration of methane and carbon monoxide contained in the reducing and carburizing gas becomes, the faster the carburizing reaction proceeds. But when the concentration of methane and carbon monoxide contained in said reaction gas becomes excessively high, a fixed carbon is generated from the reaction gas due to the reaction as shown in the following formulas (7) and/or (8).
As a result, extra reaction gas is uselessly consumed. Furthermore, the fixed carbon has such a bad effect upon the gas circulation loop as to be turned into dust and sticked on a tube of gas heater.
(7) CH
4
→C(fixed carbon)+2H
2
(8) 2CO→C(fixed carbon)+CO
2
At the most vigorous stage of the reaction, the reducing reaction by hydrogen is conducted vigorously as is described above, and the water vapor generated by said reducing reaction prevent the generation of fixed carbon. But, at the final stage of the reaction, since little water vapor for preventing the generation of fixed carbon is generated, the fixed carbon is liable to easily generate. There are two means to prevent the generation of fixed carbon. One is to decrease the concentration of methane and carbon monoxide contained in the reaction gas, and the other is to increase the concentration of water vapor contained in the reaction gas. But those means result in the decline of the reaction speed, namely, the lowering of the productivity.
The higher the gas temperature becomes, the faster the reaction speed becomes. But, when the temperature of the fluidized bed comes to be over about 600° C. (for example, 570° C.~590° C.) due to the excessively high temperature gas, the iron oxide remained in the product of iron carbide is turned into not Fe
3
O
4
whose chemical character is stable, but FeO whose chemical character is unstable.
If the reaction gas temperature is decreased so as to avoid the above disadvantage, it will result in the decline of the reaction speed, namely, the lowering of the productivity.
Furthermore, as the reaction proceeds, the specific gravity of iron oxide becomes lower and the diameter of iron oxide particles become smaller due to its own powdering. Therefore, the iron oxide particles at the stage of the second half of the reaction is liable to fly. The iron oxide particles flown outside the reactor has the low carburization degree because of the short staying time at the reactor. As a result, it brings the lowering of the average carburization degree of the product of iron carbide.
Consequently, it is preferable to regulate the flow velocity of the gas flowing through the fluidized bed according to the proceeding of the reaction. But it is impossible for the prior art to change the flow velocity of the gas, unless applying some complicated works, such as alternating the resistance of the gas blowing nozzle installed at the gas distribution plate.
Furthermore the method for producing iron carbide, which is characterized by that the reducing reaction is partially conducted in a first stage reactor, then the further reducing and carburizing reaction is conducted in a second stage reactor, is known.
But in this method, the control of reduction degree of the ore discharged from the first stage reactor is necessary. It is possible to control the reduction degree by altering the gas flow rate, the gas temperature or the gas composition. Said altering, however, is not easy because the quantity of gas to deal with is so much. As a result, it presents the difficulty in controlling conformably and carefully the reduction degree.
The above-mentioned disadvantages of the prior art for producing iron carbide will be easily overcome by the present invention.
The objective of the present invention is to provide a process and apparatus for producing effectively iron carbide having the chemically stable components.
DISCLOSURE OF THE INVENTION
An object of this invention is to provide a process for producing iron carbide by an apparatus having constitution elements (a) to (e);
(a) a fluidized bed located at an upper part within a fludized bed reactor, and,
(b) a chamber located at a lower part within the reactor to work as a gas header for introducing a reducing and carburizing gas; wherein the fluidized bed and the chamber are separated into upside and downside by a distribution plate on which multiple gas introducing nozzles are installed; and the fluidized bed located at an upper part of the distribution plate is partitioned into
Inoue Eiji
Miyashita Torakatsu
Nakatani Junya
Uchiyama Yoshio
Hendrickson Stuart L.
Kawasaki Jukogyo Kabushiki Kaisha
Oppenheimer Wolff & Donnelly LLP
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