U.S. patent application number 09/367300 was filed with the patent office on 2001-11-01 for method for producing iron carbide.
Invention is credited to INOUE, EIJI, MIYASHITA, TORAKATSU, NAKATANI, JUNYA, NAKAZAWA, TERUYUKI, NIO, AKIO, UCHIYAMA, YOSHIO.
Application Number | 20010036436 09/367300 |
Document ID | / |
Family ID | 12726685 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010036436 |
Kind Code |
A1 |
INOUE, EIJI ; et
al. |
November 1, 2001 |
METHOD FOR PRODUCING IRON CARBIDE
Abstract
Provided is a method for producing iron carbide in which free
carbon is generated with difficulty. When iron carbide is produced
by reducing and carburizing iron-containing raw materials for iron
making using a reaction gas mainly containing hydrogen and methane,
steam or carbon dioxide is added into fluidized bed reactor (1)
through line (7) in addition to the reaction gas supplied from line
(2) into reactor (1) corresponding to a quantity of free carbon
generated in reactor (1) which is obtained by means of dust meter
(9). Consequently, the generation of the free carbon can be
controlled.
Inventors: |
INOUE, EIJI; (HYOGO, JP)
; MIYASHITA, TORAKATSU; (HYOGO, JP) ; UCHIYAMA,
YOSHIO; (HYOGO, JP) ; NAKATANI, JUNYA; (HYOGO,
JP) ; NAKAZAWA, TERUYUKI; (TOKYO, JP) ; NIO,
AKIO; (TOKYO, JP) |
Correspondence
Address: |
GARY E LANDE
OPPENHEIMER WOLFF & DONNELLY
2029 CENTURY PARK EAST
SUITE 3800
LOS ANGELES
CA
900673024
|
Family ID: |
12726685 |
Appl. No.: |
09/367300 |
Filed: |
August 10, 1999 |
PCT Filed: |
February 25, 1998 |
PCT NO: |
PCT/JP98/00789 |
Current U.S.
Class: |
423/439 |
Current CPC
Class: |
C21B 13/0033 20130101;
Y02P 10/143 20151101; Y02P 10/134 20151101; Y02P 10/136
20151101 |
Class at
Publication: |
423/439 |
International
Class: |
C01B 031/30 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 1997 |
JP |
HEI 9-045701 |
Claims
1. (cancelled)
2. (amended) A method for producing iron carbide in which free
carbon can be prevented from being generated by thermal
decomposition of carbon monoxide or hydrocarbon when raw materials
for iron making or steel making mainly comprising iron carbide as a
main component is produced by reducing and carburizing
iron-containing raw materials for iron making mainly comprising
iron oxides and iron hydroxides as main components using a reaction
gas mainly containing hydrogen and methane, comprising the steps of
dividing an inside of a reactor into a plurality of compartments,
detecting the free carbon according to a change of a temperature of
a thermometer installed in a latter half of the compartments which
are closer to an outlet port for product, and changing a
composition of the reaction gas corresponding to a quantity of the
detected free carbon.
3. (cancelled)
4. (amended) The method for producing iron carbide of claim 2,
wherein the free carbon is detected according to a result of
detection of a ratio of methane to hydrogen in gas picked up by a
gas pick-up device installed on an upper portion in the latter half
of the compartments.
5. (amended) The method for producing iron carbide of claim 2,
wherein the free carbon is detected by combining two or more of a
process of detecting the free carbon according to a change of a
temperature of a thermometer installed in the latter half of the
compartments, a process of detecting the free carbon by analyzing
dust picked up by a dust pick-up device installed on an upper
portion in the latter half of the compartments and a process of
detecting the free carbon according to a result of detection of a
ratio of methane to hydrogen in gas picked up by a gas pick-up
device installed on the upper portion in the latter half of the
compartments.
6. (cancelled)
7. (amended) The method for producing iron carbide of claim 2,
wherein the composition of the reaction gas in the reactor is
changed by increasing carbon dioxide in the reaction gas
corresponding to the quantity of the detected free carbon.
8. (cancelled)
9. (cancelled)
10. (amended) The method for producing iron carbide of claim 7,
wherein the composition of the reaction gas in the reactor is
changed by controlling the composition of the reaction gas to be
introduced into the reactor.
11. (added) A method for producing iron carbide in which free
carbon can be prevented from being generated by thermal
decomposition of carbon monoxide or hydrocarbon when raw materials
for iron making or steel making mainly comprising iron carbide as a
main component is produced by reducing and carburizing
iron-containing raw materials for iron making mainly comprising
iron oxides and iron hydroxides as main components using a reaction
gas mainly containing hydrogen and methane, comprising the steps of
dividing an inside of a reactor into a plurality of compartments,
detecting the free carbon in a latter half of the compartments
which are closer to an outlet port for product, and increasing the
quantity of iron carbide product to be discharged corresponding to
a quantity of the detected free carbon.
12. (added) The method for producing iron carbide of claim 11,
wherein nonreacted iron-containing raw materials are fed into a
latter half of the compartments in place of increase in quantity of
iron carbide product to be discharged.
13. (added) A method for producing iron carbide in which free
carbon can be prevented from being generated by thermal
decomposition of carbon monoxide or hydrocarbon when raw materials
for iron making or steel making mainly comprising iron carbide as a
main component is produced by reducing and carburizing
iron-containing raw materials for iron making mainly comprising
iron oxides and iron hydroxides as main components using a reaction
gas mainly containing hydrogen and methane, comprising the steps of
measuring a quantity of metallic iron contained in iron carbide
product, and changing a composition of the reaction gas in the
reactor corresponding to the quantity of the metallic iron.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing iron
carbide (Fe.sub.3C) suitable for raw materials for iron making or
steel making which comprises iron carbide (Fe.sub.3C) as a main
component, for example, raw materials for steel making which is
used in an electric furnace and the like.
BACKGROUND ART
[0002] 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 converter. 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.sub.3C) 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.
[0003] 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 has
recently attracted special interest.
[0004] 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., a
methane gas and the like) at a predetermined temperature. Thus,
iron oxides (hematite (Fe.sub.2O.sub.3), magnetite
(Fe.sub.3O.sub.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
into a single reactor) as shown in the following reaction formula
((1), (2), (3), (4)).
3Fe.sub.2O.sub.3+H.sub.2.fwdarw.2Fe.sub.3O.sub.4+H.sub.2O (1)
Fe.sub.3O.sub.4+H.sub.2.fwdarw.3FeO+H.sub.2O (2)
FeO+H.sub.2.fwdarw.Fe+H.sub.2O (3)
3Fe+CH.sub.4.fwdarw.Fe.sub.3C+2H.sub.2 (4)
[0005] Furthermore, the formula (1) to (3) may be put together. As
a result, the reaction formula for deciding the progress of
reduction and carburization of iron oxide can be shown by the
following reaction formula (5) and the above-mentioned reaction
formula (4).
Fe.sub.2O.sub.3+3H.sub.2.fwdarw.2Fe+3H.sub.2O (5)
[0006] The prior art related to the field of the present invention
has been described in the publication No. 6-501983 of Japanese
Translation of International Patent Application (PCT/US91/05198),
for example.
[0007] However, free carbon is sometimes generated depending on the
producing conditions such as a gas composition, a reaction
temperature and the like in a fluidized bed reactor. In a case
where the free carbon is mixed with iron carbide, there come out
the following drawbacks.
[0008] (1) There is a possibility that a dust fire or explosion
might be caused by free carbon scattered in a gas exhausted from
the fluidized bed reactor.
[0009] (2) An opening such as an inlet port for raw materials, an
outlet port for product of the fluidized bed reactor is sometimes
blocked by the free carbon.
[0010] (3) CH.sub.4 is consumed with the generation of the free
carbon. For this reason, CH.sub.4 which is necessary for the
generation of iron carbide is additionally required.
[0011] (4) Once the free carbon is generated, the generation of the
free carbon is promoted.
[0012] 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 free carbon is generated
with difficulty.
DISCLOSURE OF THE INVENTION
[0013] In order to accomplish the above-mentioned object, the
present invention can detect free carbon in a latter half of
compartments in a reactor and change a composition of a reaction
gas corresponding to a quantity of the detected free carbon,
thereby controlling the generation of the free carbon.
[0014] More specifically, the present invention provides a method
for preventing free carbon from being generated by thermal
decomposition from carbon monoxide or hydrocarbon when raw
materials for iron making or steel making mainly comprising iron
carbide as a main component is produced by reducing and carburizing
iron-containing raw materials for iron making mainly comprising
iron oxides and iron hydroxides as main components using a reaction
gas mainly containing hydrogen and methane, comprising the steps of
dividing an inside of a reactor into a plurality of compartments,
detecting the free carbon in a latter half of the compartments
which are closer to an outlet port for product, and changing a
composition of the reaction gas corresponding to a quantity of the
detected free carbon.
[0015] As a process of detecting free carbon, it is possible to
employ "a process of detecting free carbon based on a change of a
temperature of a thermometer installed in the latter half of the
compartments", "a process of detecting free carbon by analyzing
dust picked up by a dust pick-up device installed on an upper
portion in the latter half of the compartments" or "a process of
detecting free carbon based on a result of detection of a ratio of
methane to hydrogen in gas picked up by a gas pick-up device
installed on an upper portion in the latter half of the
compartments". In addition, these two or more processes can be
combined.
[0016] As a process of changing the composition of the reaction gas
in the reactor, it is possible to employ "a process of increasing
steam in the reaction gas corresponding to the quantity of the
detected free carbon", "a process of increasing carbon dioxide in
the reaction gas corresponding to the quantity of the detected free
carbon" or "a process of decreasing the carbon monoxide or the
hydrocarbon in the reaction gas corresponding to the quantity of
the detected free carbon". In addition, these two or more processes
can be combined.
[0017] The above-mentioned change of the composition of the
reaction gas can be performed by controlling the composition of the
reaction gas to be introduced into the reactor.
[0018] The status of the change of iron-containing raw materials in
the reactor according to the present invention having the
above-mentioned constitution will generally be described. A part of
raw materials in the compartments on the side closer to the inlet
port for raw materials is converted into Fe by mainly reducing
reaction. Then, the residual reducing reaction and the carburizing
reaction into iron carbide (Fe.sub.3C) of the iron-containing raw
materials are performed in the compartments on the side closer to
the outlet port for product. If the carburizing reaction in which
an upper limit of a ratio of conversion into Fe.sub.3C obtained at
a certain H.sub.2O partial pressure is exceeded is carried out,
free carbon is generated. By the following process, the free carbon
is detected. Then, the composition of the reaction gas is changed
by the following process corresponding to the quantity of the
detected free carbon. Consequently, the generation of the free
carbon can be controlled.
[0019] (1) Detection of Free Carbon
[0020] a. Change of Reaction Temperature
[0021] The change of a reaction temperature can be used as means
for indirectly detecting the generation of free carbon. The reason
is as follows. It is supposed that a temperature in a reactor is
generally uniform when reaction steadily progresses in a fluidized
bed reactor. However, deposition of the free carbon which is caused
in the reactor is an endothermic reaction. For this reason, a
temperature is dropped in a portion where the free carbon is
deposited. Therefore, thermometers are installed in a portion where
the free carbon is easily deposited (a portion closer to the outlet
port for product of the reactor) and other portions in the reactor
where the free carbon is deposited with difficulty, and their
measuring temperatures are compared with one another. If it is
apparent that the temperature in the portion closer to the outlet
port for product is clearly lower than the temperatures in the
other portions, it is possible to decide that the free carbon is
deposited.
[0022] b. Analysis of Dust
[0023] By analyzing dust picked up by means of the dust pick-up
device, the free carbon can be directly detected.
[0024] c. Analysis of Gas Composition
[0025] As described above, the free carbon is generated when the
ratio of conversion of Fe into Fe.sub.3C has become equal to or
greater than a constant value. In other words, if a ratio of
CH.sub.4/H.sub.2 in the gas composition is raised to a constant
value or more as shown by the above-mentioned reaction formula (4),
there is a higher possibility that the free carbon might be
generated. Accordingly, the gas composition in the latter half of
the compartments of the reactor is analyzed, and the generation of
the free carbon can be indirectly detected if a value of CH
.sub.4/H.sub.2 in the above gas has been rapidly reduced.
[0026] d. Combination of Detecting Process
[0027] If two or more of "change of reaction temperature",
"analysis of dust" and "analysis of gas composition" are combined,
the free carbon can be detected more rapidly.
[0028] (2) Change of Reaction Gas Composition
[0029] a. Addition of Steam (H.sub.2O)
[0030] It is not preferable that a ratio of conversion from
iron-containing raw materials into iron carbide be low (equal to or
lower than about 90%). The reason is that the grade of the iron
carbide having the low conversion ratio is too low to be used as
raw materials for iron making or steel making. On the other hand,
if the ratio of conversion from iron-containing raw materials into
iron carbide is too high (equal to or higher than about 99%), free
carbon is easily deposited. Therefore, if it is hoped that raw
materials for iron making or steel making with high grade is
obtained while controlling the generation of the free carbon, it is
preferable that the ratio of conversion from iron-containing raw
materials into iron carbide should be kept within a constant
range.
[0031] As described above, it is possible to collectively express,
by the following two reaction formula, the reaction where iron
carbide (Fe.sub.3C) is produced from iron-containing raw materials
using a reaction gas mainly containing hydrogen and methane.
Fe.sub.2O.sub.3+3H.sub.2.fwdarw.2Fe+3H.sub.2O (5)
3Fe+CH.sub.4.fwdarw.Fe.sub.3C+2H.sub.2 (4)
[0032] In the last stage of the conversion into Fe.sub.3C (in which
most of the iron-containing raw materials are converted into
Fe.sub.3C), the reaction approaches an equilibrium state. If steam
(H.sub.2O) is added into a reaction system in the equilibrium
state, potentials of hydrogen and oxygen are increased and
potentials of iron and carbon are decreased. More specifically,
when H.sub.2O is added to the reaction system of the reaction
formula (5), a concentration or partial pressure of a molecule on
the right side is raised. For this reason, the reaction progresses
toward the left side to recover the equilibrium state. In other
words, H.sub.2 is increased and Fe is decreased. In the reaction
formula (4), the reaction progresses toward the left side in order
to consume the increase in H.sub.2 and to compensate for the
decrease in Fe. As a result, it is possible to control excessive
conversion from iron-containing raw materials into iron
carbide.
[0033] Thus, by adding the steam to the reaction gas, the
generation of the free carbon can be controlled. In addition, it is
possible to obtain raw materials for iron making or steel making
with high grade in which a ratio of conversion into iron carbide is
kept within a proper range.
[0034] b. Addition of Carbon Dioxide (CO.sub.2)
[0035] In a case where carbon dioxide is added in place of steam,
the following reaction progresses.
CO.sub.2+H.sub.2.fwdarw.CO+H.sub.2O (6)
[0036] More specifically, addition of CO.sub.2 is synonymous with
that of H.sub.2O. By the above-mentioned action, the generation of
free carbon can be controlled.
[0037] c. Decrease in Quantity of Methane (CH.sub.4) to be
Supplied
[0038] A decrease in the quantity of CH.sub.4 to be supplied is
equivalent to the progress of the reaction in the reaction formula
(4) toward the left side or a delay of the progress of the reaction
in the reaction formula (4) toward the right side. As a result,
excessive conversion from iron-containing raw materials into iron
carbide can be controlled. Consequently, the generation of the free
carbon can be controlled. If a quantity of CH.sub.4 to be supplied
is excessively reduced, the generation of the free carbon can be
controlled but a quantity of metallic iron (M--Fe) accumulated in a
product is increased. The metallic iron contained in the product
gradually reacts with oxygen in the air at an ordinary temperature
and is then returned to iron oxide. Accordingly, it is preferable
that the quantity of CH.sub.4 to be supplied should not be reduced
excessively but be reduced to obtain such a gas composition to
approach an equilibrium state with a solid at that time. Referring
to an equilibrium of the gas composition in Fe--CHO reaction
system, in other words, a concentration of CH.sub.4 is reduced to
approach the equilibrium state in order to correct a carbon
potential which is excessively higher than an equilibrium
composition of Fe and Fe.sub.3C. Consequently, the generation of
the free carbon can be controlled.
[0039] d. Combination of Processes of Changing Reaction Gas
Composition
[0040] If two or more of "addition of steam", "addition of carbon
dioxide" and "decrease in quantity of methane to be supplied" are
combined, the generation of free carbon can be controlled more
effectively.
[0041] (3) Process of Changing Reaction Gas Composition
[0042] By controlling a flow rate of a gas to be exhausted from the
reactor, a gas composition in the reactor can be changed. However,
if this process is carried out, a gas balance within the reactor is
sometimes lost. Therefore, this process is not preferred.
[0043] As compared with the foregoing, a process of increasing a
steam content of the reaction gas to be introduced into the
reactor, adding steam or carbon dioxide to the reaction gas or
decreasing a quantity of methane to be supplied can be easily
performed directly and has no drawbacks which are caused by the
process of controlling the flow rate of the exhaust gas.
[0044] (4) Other Processes of Controlling Generation of Free
Carbon
[0045] Other processes of controlling the generation of free carbon
than the above-mentioned processes are as follows.
[0046] a. Increase in Quantity of Iron-Containing Material to be
Fed and Increase in Quantity of Iron Carbide to be Discharged
[0047] If the quantity of iron carbide to be discharged is
increased, iron carbide in which free carbon is actually deposited
is discharged and iron-containing raw materials having a large
number of nonreacted components is increased in the vicinity of the
outlet port of the reactor. Once the free carbon is deposited, the
generation of the free carbon is promoted. Therefore, it is
preferable that the deposited free carbon should be discharged
quickly. Even if the quantity of iron-containing raw materials to
be fed is increased, the same action can be obtained.
[0048] b. Feeding Nonreacted Iron-Containing Raw Materials in Stage
in Which Reducing Reaction and Carburizing Reaction have Progressed
to Constant Extent or More
[0049] If nonreacted iron-containing raw materials are fed into a
portion in which reducing reaction and carburizing reaction have
progressed to a constant extent or more and a ratio of conversion
into iron carbide is very high (for example, a portion in the
vicinity of the outlet port of the reactor), oxygen potential is
increased in that portion. Therefore, H.sub.2O is generated and
excessive conversion into iron carbide is inhibited in the same
manner as the addition of steam. Consequently, the generation of
the free carbon can be controlled.
[0050] c. Drop in Reaction Temperature
[0051] If a temperature is dropped, a reaction speed is reduced so
that the generation of the free carbon can be controlled.
[0052] (5) Means for Predicting Generation of Free Carbon
[0053] The quantity of metallic iron contained in a product can be
used as means for predicting the generation of free carbon. The
reason is that the ratio of the metallic iron contained in the
product is low in the last stage of the reaction, and iron produced
by reducing residual iron oxide immediately is liable to be
converted into iron carbide. More specifically, very small quantity
of metallic iron (or lack of the metallic iron) indicates excessive
conversion into iron carbide. If a quantity of the metallic iron
contained in the product is known, the generation of the free
carbon can be predicted. A specific method for predicting the
generation of the free carbon is as follows. A gas composition in
the vicinity of the outlet port of the reactor (which has an
equilibrium relationship with the product) is known by a gas
chromatography method, for example, and the quantity of the
metallic iron contained in the product is estimated using the gas
composition as a basis. Thus, the generation of the free carbon can
be predicted.
[0054] According to the present invention described above, the
inside of the reactor is divided into a plurality of compartments,
free carbon is detected in a latter half of the compartments which
are closer to the outlet port for product, and the composition of a
reaction gas is changed corresponding to the quantity of the
detected free carbon. Thus, the generation of the free carbon can
precisely be detected and the generation of the free carbon can be
controlled.
[0055] By employing the above-mentioned process of detecting the
free carbon, the generation of the free carbon can be detected more
surely.
[0056] Furthermore, the above-mentioned process is employed to
change the composition of the reaction gas in the reactor.
Consequently, the generation of the free carbon can be controlled
ffectively. Therefore, it is possible to eliminate drawbacks such
as blocking of the reactor, a dust fire and the like which are
caused by the free carbon. In addition, it is possible to produce
iron carbide as raw materials for iron making or steel making with
high grade to which no carbon sticks. Furthermore, since the
generation of the free carbon can be controlled effectively, it is
possible to prevent wasteful consumption of carbon monoxide or
hydrocarbon which acts as a resource for producing iron
carbide.
BRIEF DESCRIPTION OF DRAWINGS
[0057] FIG. 1 is a schematic diagram showing an example of an
apparatus for producing iron carbide according to the prior
art;
[0058] FIG. 2 is a chart representing a transition of each of
weight ratios of iron carbide (Fe.sub.3C), iron (Fe) and carbon (C)
(observed values and theoretical values) in a product which is
obtained in the case where iron carbide is produced by reducing and
carburizing iron-containing raw materials for iron making;
[0059] FIG. 3 is a schematic diagram showing an example of an
apparatus for producing iron carbide according to the present
invention;
[0060] FIG. 4 is a schematic diagram showing another example of the
apparatus for producing iron carbide according to the present
invention;
[0061] FIG. 5 is a schematic diagram showing yet another example of
the apparatus for producing iron carbide according to the present
invention;
[0062] FIG. 6 is a chart representing a relationship between
precent by volume of H.sub.2O in a fluidized bed reactor and
percent by weight of Fe.sub.3C in a product, which is exerted on
the generation of free carbon; and
[0063] FIG. 7 is a chart representing a relationship between
percent by volume of H.sub.2O in a fluidized bed reactor and
percent by weight of metallic iron (M--Fe) in a product, which is
exerted on the generation of the free carbon.
BEST MODE FOR CARRYING OUT THE INVENTION
[0064] First of all, a convention method for producing iron carbide
will be described. Next, description will be given to a method for
controlling the generation of free carbon when producing iron
carbide by reducing and carburizing iron-containing raw materials
for iron making according to the method of the present
invention.
[0065] A. Conventional Method for Producing Iron Carbide
[0066] In accordance with a conventional method, description will
be given to conditions for conversion of iron ore mainly comprising
hematite (Fe.sub.2O.sub.3) into iron carbide (Fe.sub.3C), the
schematic structure of a reactor and results thereof.
[0067] (1) Condition
[0068] The composition and particle size of iron ore used as raw
materials, the composition of a reaction gas, a reaction
temperature and a reaction pressure are as follows.
[0069] I . Composition of Iron Ore
[0070] 65.3% by weight of Fe, 1.67% by weight of Al.sub.2O.sub.3,
3.02% by weight of SiO.sub.2, 0.080% by weight of P
[0071] II. Particle Size of Iron Ore
[0072] fines having a particle size of 1.0 mm or less (a particle
size of 0.1 mm to 1.0 mm : 80% by weight or more, a particle size
of 0.068 mm or less: 13.4% by weight)
[0073] III. Composition of Reaction Gas (Percent by Volume)
[0074] CH.sub.4:35 to 56%, H.sub.2:33 to 45%, CO: 2.5 to 10%,
CO.sub.2:1.2 to 8%, N.sub.2:2.8 to 9.2%, H.sub.2O :0.6 to 1.5%, The
total is 100%.
1 IV. Reaction temperature 590.degree. C. to 650.degree. C. V.
Reaction pressure 3 kgf/cm.sup.2 G("G" represents a gauge
pressure)
[0075] (2) Schematic Structure of Reactor
[0076] As shown in FIG. 1, line 2 for supplying a reaction gas is
connected to a bottom part of fluidized bed reactor 1, and line 3
for exhausting the reaction gas is connected to a top part of the
reactor 1. Iron ore is fed into fluidized bed reactor 1 from hopper
4 through line 5, and iron carbide product is discharged from line
6.
[0077] (3) Result
[0078] By the above-mentioned conditions, iron carbide was produced
using the reactor shown in FIG. 1. As a result, iron ore was
converted into iron carbide (Fe.sub.3C) with a transition as shown
in FIG. 2. In FIG. 2, an ordinate on the left side represents
percent by weight of Fe and Fe.sub.3C, an ordinate on the right
side represents percent by weight of an observed value and a
theoretical value of carbon, and an abscissa represents a reaction
time (hr). As is apparent from FIG. 2, a time taken for obtaining a
ratio of conversion into 93% by weight or more of iron carbide
which is preferable for raw materials for iron making or steel
making was about 6 hours.
[0079] As shown in FIG. 2, while the weight ratio of carbon had a
theoretical value of about 6.6% by weight in case of a ratio of
conversion into iron carbide of 100%, an observed value of 8% by
weight was obtained. It is supposed that a difference of "1.4% by
weight" was caused by free carbon.
[0080] B. Method for Producing Iron Carbide According to the
Present Invention
[0081] Description will be given to the schematic structure of a
reactor which is suitable for carrying out the method of the
present invention and the result of investigations related to
effects of reaction conditions which are exerted on the generation
of free carbon.
[0082] (1) Schematic Structure of Reactor
[0083] I. Addition of Steam (H.sub.2O) or Carbon Dioxide (CO.sub.2)
to Reaction Gas
[0084] As shown in FIG. 3, line 7 for supplying H.sub.2O or
CO.sub.2 is connected to a bottom part of fluidized bed reactor 1.
An opening of valve 11 is regulated by means of indicator 10
according to a quantity of free carbon detected by dust meter 9 for
detecting free carbon which is installed on an upper portion in a
latter half of five compartments 8 in the reactor 1 partitioned by
partition wall 8a that is closer to an outlet port for product.
Thus, a proper quantity of H.sub.2O or CO.sub.2 is supplied into
fluidized bed reactor 1. The operation of increasing water content
in line 2 for supplying the reaction gas is performed by means of
humidifier 18. Alternatively, line 7 is connected to the latter
half of the compartments of the reactor in which free carbon is
easily generated. Thus, a small quantity of H.sub.2O or CO.sub.2 is
supplied to reactor 1 through line 7.
[0085] As a result, the generation of the free carbon can be
controlled by the above-mentioned mechanism.
[0086] II. Decrease in Quantity of Methane to be Supplied to
Reaction Gas
[0087] As shown in FIG. 4, line 12 for supplying natural gas is
connected to line 2 for supplying the reaction gas to the bottom
part of fluidized bed reactor 1. An opening of valve 13 is
regulated by means of indicator 10 according to a quantity of free
carbon which is detected by dust meter 9. Thus, a flow rate of the
natural gas to be supplied from line 12 to line 2 is regulated.
Natural gas is a lower paraffin based hydrocarbon
(C.sub.nH.sub.2n+2) containing methane as a main component and
necessary for carburizing reaction. In order to promote the
carburization, the natural gas is added to the reaction gas in line
2 if necessary. If the free carbon is generated in fluidized bed
reactor 1, the opening of valve 13 is regulated to reduce the
quantity of the natural gas to be supplied into reactor 1. Thus,
the generation of the free carbon is controlled. In this case, a
line (not shown) for supplying hydrogen may be connected to line 2,
and hydrogen may be supplied from the hydrogen supply line to line
2 according to the quantity of the free carbon which has been
detected by dust meter 9. Thus, a concentration of methane
contained in the reaction gas is relatively reduced. Consequently,
the generation of the free carbon can be controlled.
[0088] In place of the above-mentioned dust meter 9, a gas pick-up
device may be installed. A ratio of methane to hydrogen in the gas
picked up by the gas pick-up device may be detected by a gas
chromatography method or the like. If the ratio of methane has been
rapidly reduced, the generation of the free carbon can be
predicted.
[0089] III. Drop in Reaction Temperature in Fluidized Bed
Reactor
[0090] If a reaction temperature is dropped, a reaction speed is
relatively reduced so that the generation of free carbon can be
controlled. For example, as shown in FIG. 5, thermometers 14, 15
and 16 are inserted into the compartments in the vicinity of an
inlet port for iron ore, a central portion and the vicinity of an
outlet port for product of fluidized bed reactor 1, respectively.
Thus, the temperatures are monitored by means of instrument 17. In
a case where a reaction in fluidized bed reactor 1 progresses in a
steady state, the temperatures measured by the thermometers 14, 15
and 16 are almost equal to one another. However, in a case where
free carbon has been generated in reactor 1, the temperature in
that portion is lower than the temperatures in other portions
because the generation of the free carbon is endothermic reaction.
In general, iron ore has a high ratio of conversion into iron
carbide in the vicinity of the outlet port for product. In this
portion, free carbon is easily generated. By comparing the
temperature measured by thermometer 16 with the temperatures in
other portions, the generation of the free carbon can be indirectly
known. For example, if a temperature T.sub.0 measured by
thermometer 16 is lower than each of temperatures T.sub.1a and
T.sub.2a measured by thermometers 14 and 15 by a temperature of 30
to 50.degree. C., it is supposed that the free carbon has been
generated. If the operation is carried out in such a manner that
each of temperatures T.sub.1b and T.sub.2b measured by thermometers
14 and 15 is lower than each of the temperatures T.sub.1a and
T.sub.2a in order to make a conversion ratio into iron carbide less
than the conversion ratio based on the conditions in fluidized bed
reactor 1 (the temperatures T.sub.1a, T.sub.2a T.sub.0 and the
ratio of conversion into iron carbide) at that time, the generation
of free carbon can be controlled.
[0091] (2) Effect of Reaction Condition Exerted on Generation of
Free Carbon
[0092] I. Effect of Steam (H.sub.2O)
[0093] FIG. 6 is a chart representing the effect of percent by
volume of H.sub.2O which is exerted on the generation of free
carbon in the case where iron ore having the above-mentioned
composition and particle size has been converted into iron carbide
(Fe.sub.3C) using a reaction gas having the above-mentioned
composition at a temperature of 590 to 650.degree. C. and a
pressure of 3 to 4 kgf/cm.sup.2 G in the fluidized bed reactor 1.
In FIG. 6, mark `.largecircle.` indicates a case where the free
carbon has been not generated, and mark `.tangle-solidup.`
indicates a case where the free carbon has been generated. As is
apparent from FIG. 6, if percent by volume of H.sub.2O is
increased, a region where the free carbon is not generated (a right
region of a line connecting marks `.largecircle.` in FIG. 6 is the
region where the free carbon is not generated) is increased. More
specifically, if steam is added, the free carbon is generated with
difficulty even if the ratio of conversion into the iron carbide
has been increased.
[0094] II. Influence of Metallic Iron
[0095] FIG. 7 is a chart representing a relationship among metallic
iron (M--Fe) in a product, percent by volume of H.sub.2O and the
status of generation of free carbon, in the case where iron ore
having the above-mentioned composition and particle size has been
converted into iron carbide (Fe.sub.3C) using a reaction gas having
the above-mentioned composition at a temperature of 590 to
650.degree. C. and a pressure of 3 to 4 kgf/cm.sup.2 G in fluidized
bed reactor 1. In FIG. 7, mark `.largecircle.` and mark
`.tangle-solidup.` have the same meanings as in FIG. 6. As is
apparent from FIG. 7, if the ratio of metallic iron (M--Fe) is
reduced with the same percent by volume of H.sub.2O, the free
carbon is easily generated. The reason is that the ratio of the
metallic iron contained in the product is very small in the last
stage of the reaction and metallic iron obtained by reducing
residual iron oxide in the iron ore immediately easily tends to be
converted into iron carbide. Thus, the ratio of conversion into
iron carbide is excessive in the last stage of the reaction. As a
result, the free carbon is easily generated. Thus, lack of the
metallic iron causes the generation of the free carbon. Therefore,
if the quantity of the metallic iron contained in the product can
be obtained by analyzing the component of the product, the
generation of the free carbon can be predicted. A gas in the
vicinity of the outlet port of the fluidized bed reactor has an
equilibrium relationship with a product (raw material for iron
making and steel making mainly comprising iron carbide) to be
discharged from the outlet port. Therefore, a gas composition in
the vicinity of the outlet port is detected by a gas chromatography
method, for example, thereby estimating the quantity of the
metallic iron contained in the product. Thus, the generation of the
free carbon can be predicted and a precise countermeasure for
controlling the generation of the free carbon can be taken.
INDUSTRIAL APPLICABILITY
[0096] Since the present invention has the above-mentioned
constitution, the apparatus according to the present invention is
suitable for an apparatus for producing iron carbide in which free
carbon is generated with difficulty.
* * * * *