Chemistry of inorganic compounds – Carbon or compound thereof – Binary compound
Reexamination Certificate
1999-08-24
2001-07-24
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Binary compound
Reexamination Certificate
active
06264911
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a method for producing iron carbide suitable for raw materials for iron making and steel making which comprises iron crabide (Fe
3
C) as a main component, for example, raw materials for steel making which is used in an electric furnace and the like.
2. Background Art
The production of steel normally comprises the steps of converting iron ore into pig iron using a blast furnace, and then converting the pig iron into steel using an open hearth furnace or a convertor. Such a traditional method requires large amounts of energy and large-scale equipment, and has a high cost. Therefore, for a small-scale steel making, a method comprising the steps of directly converting iron ore into raw materials to be used in a steel-making furnace, and converting the raw materials into steel using an electric furnace and the like has been used. With respect to this direct steel making process, a direct reduction process has been used to convert iron ore into reduced iron. However, the reduced iron produced by the direct reduction process is highly reactive and reacts with oxygen in the air to generate heat. Therefore, it is necessary to seal the reduced iron with an inert gas or by some other measures during transportation and storage of the reduced iron. Accordingly, iron carbide (Fe
3
C) containing a comparatively high iron (Fe) content, and which has a low reaction activity and can be easily transported and stored, has recently been used as the raw materials for steel making in an electric furnace and the like.
Furthermore, raw materials for iron making or steel making containing iron carbide as a main component is not only easy to be transported and stored, but also has the advantage that carbon element combined with iron element can be used as a source of fuel in an iron making or steel making furnace, and can be used as a source to generate microbubbles which accelerates a reaction in the steel making furnace. Therefore, raw materials for iron making or steel making containing iron carbide as a main component have recently attracted special interest.
According to a conventional method for producing iron carbide, iron ore fines are fed into a fluidized bed reactor or the like, and are caused to react with a gas mixture comprising a reducing gas (e. g., hydrogen gas) and a carburizing gas (e. g., methane gas and the like) at a predetermined temperature. Thus, iron oxides (e.g., hematite (Fe
2
O
3
), magnetite (Fe
3
O
4
), wustite (FeO)) contained in iron ore are reduced and carburized in a single process (which means a process performed by simultaneously introducing a reducing gas and a carburizing gas to a single reator). This reaction is performed by the following overall reaction formula (1).
3Fe
2
O
3
+5H
2
+2CH
4→2
Fe
3
C+9H
2
O (1)
The prior art related to the field of the present invention has been described, for example, in the publication No. 6-501983 of Japanese translation of International Application (PCT/US91/05198).
In order to easily understand the present invention, an example of an apparatus for producing iron carbide according to the prior art will be described below. For example, an apparatus shown in
FIG. 3
has been known. With reference to
FIG. 3
, the reference number
1
denotes a reactor. Iron-containing raw materials are fed into reactor
1
through feeding port
2
and iron carbide is discharged from exhaust port
3
. The reference number
4
,
5
and
6
indicate a dehumidifier, a compressor, a tube-shaped heater respectively. Reactor
1
, dehumidifier
4
, compressor
5
, and heater
6
form a circulating loop
7
. The reference number
8
is a line for supplying natural gas containing methane as a main component. Line
8
diverges into line
9
and line
10
, and line
9
is connected to circulating loop
7
in the rear of compressor
5
. Line
10
is connected to circulating loop
7
via steam reformer
11
, shift-converter
12
, and decarbonator
13
. An example of method for producing iron carbide using the above apparatus will be described below.
When iron-containing raw materials for iron making are fed into reactor
1
through feeding port
2
, iron-containing raw materials are reduced and carburized in reactor
1
to be converted into iron carbide in accordance with the above reaction formula (1). In this reaction, since hydrogen is consumed to perform a reducing reaction and methane is consumed to perform a carburizing reaction, it is necessary to supply reactor
1
with reducing gas component and carburizing gas component. So, natural gas containing methane as the main component is supplied as carburizing gas component to circulating loop
7
through line
9
.
Natural gas flowing through line
10
is steam-reformed according to the following reaction formula (2) at steam reformer
11
.
CH
4
+H
2
O→3H
2
+CO
2
(2)
Carbon monoxide contained in steam-reformed gas is converted into hydrogen and carbon dioxide at shift converter
12
in accordance with the following reaction formula (3)
CO+H
2
OH
2
+CO
2
(3)
Carbon dioxide obtained by the reaction at shift converter
12
is eliminated from the gas at decarbonator
13
. Thus, hydrogen is supplied from line
10
to circulating loop
7
.
As described above, hydrogen and methane supplied to circulating loop
7
are heated at tube-shaped heater
6
to a temperature of 650~700° C. with circulation gas circulating through loop
7
. But, if gas containing hydrogen and methane is heated to such a high temperature, hydrocarbon (C
n
H
m
) comprising methane as the main component is thermal-decomposed and active carbon is generated according to the following reaction formula (4). As shown in the following reaction formula (5), this active carbon is reacted with metallic component (M), such as Nickel and the like, which is material for heating tube to be a constituent component of heater. As a result, metallic carbide (M
x
C) is formed.
C
n
H
m
→nC+(m/2)H
2
(4)
C+
x
M→M
x
C (5)
FIG. 5
shows a cementation speed of 20Cr—12Ni steel as an example of cementation of metal under the conditions of temperature of 750° C., pressure of 4~6 atm., and reaction gas comprising a mixture of CH
4
, CO, CO
2
, H
2
and H
2
O. In
FIG. 5
, line A of the graph denotes the case in which CH
4
accounts for 60 volume percent in the mixture of the above gases, and line B of the graph denotes the case in which CH
4
accounts for 65 volume percent in the mixture of the above gases. As shown in
FIG. 5
, a cementation speed is in the range from about 2.1 to 6.0 mg/cm
2
.60 hr.
However, if the formation of metallic carbide becomes a supersaturated condition, carbon is separated from metallic carbide as shown in the following reaction formula (6). At this time, the metallic component on the inside of heating tube
14
shown in
FIG. 4
exfoliates and it is possible that phenomena such as the decrease in thickness of heating tube or pitting will occur.
M
x
C→xM+C (6)
In consideration of the above-mentioned problems of the prior art, it is an object of the present invention to provide a method for producing iron carbide in which metallic carbide is difficult to be formed on the inside of heating tube of a tube-shaped heater which heats reducing gas and carburizing gas for supplying to a reactor.
DISCLOSURE OF INVENTION
In order to accomplish the above-mentioned object, the present invention is characterized by that carburizing gas is heated separately from reducing gas or circulating gas and heated to lower temperature than reducing gas or circulating gas. As a result, in accordance with the present invention, it is possible to control the formation of active carbon in a tube-shaped heater and decrease exfoliation of metallic component of heating tube due to separation of carbon.
A first aspect of the present invention is directed to a method for producing iron carbide comprising the steps of heating hydrocarbon gas, hydrogen gas, which have bee
Inoue Eiji
Miyashita Torakatsu
Nakatani Junya
Nakazawa Teruyuki
Nio Akio
Griffin Steven P.
Kawasaki Jukogyo Kabushiki Kaisha
Nave Eileen E.
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