[Document Type]
SPECIFICATION
[Title of the Invention] IRON BATH TYPE SMELTING REDUCTION FURNACE
[Technical Field]
[0001]
The present invention relates to an iron bath type smelting reduction furnace that is used to reduce and melt an iron oxide and an iron material containing an iron oxide.
The present application is filed on the basis of Japanese Patent Application No. 2007-220227, the entire contents of which are incorporated herein by reference. [Background Art]
[0002]
In an iron bath type smelting reduction furnace that is used to reduce and melt an iron oxide and an iron material containing an iron oxide, an MgO-C brick, an MgO-Cr2O3 brick, or the like has been mainly used as a refractory lining. For example, the following Patent Document 1 has disclosed an iron bath type smelting reduction furnace of which the liner is formed of a MgO-C brick that is a lining brick of a steelmaking converter and has a C content of 15 mass% to 18 mass%. Further, the following Patent Documents 2 and 3 have disclosed a method of controlling the damage of a refractory by a cooling effect that is obtained by blowing gas into a gas supply pipe provided in a brick.
[0003]
However, the MgO-C brick, which is the lining brick of the steelmaking converter disclosed in Patent Document 1 and has a C content of 15 mass% to 18 mass%, has a ratio between CaO and SiO2 (CaO/SiO2), which are generated during the operation of the iron bath type smelting reduction furnace, in the range of 1.0 to 1.7, and does not have sufficient durability against the slag that contains an iron oxide caused by the iron

oxide raw material to be fed.
[0004]
Further, a cooling pipe is provided in the brick in the method of controlling the damage of the refractory by the cooling effect, which is obtained by gas blowing, disclosed in Patent Documents 2 and 3. Therefore, there have been problems in that the manufacturing cost of the brick increases and the structure of the brick becomes complicated.
[0005]
In contrast, a top-maintenance method of blowing off slag in the form of a splash by using an upper main lance to coat the slag has been disclosed in Patent Documents 4 and 5 as a method of controlling the damage of a refractory that does not require time and efforts and also does not use gas blowing and a brick. However, the method disclosed in Patent Documents 4 and 5 has the following problems. That is, it is difficult to uniformly attach slag, which has a ratio of CaO/SiO2 generated during the operation in the iron bath type smelting reduction furnace in the range of 1.0 to 1.7 and has a small viscosity, to the entire inner surface of the furnace, and it is not possible to sufficiently control the damage of a refractory.
[0006]
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. HO 1-252706
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. S63-39147
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. S63-90562
[Patent Document 4] Japanese Unexamined Patent Application, First Publication
No. S61-56223
[Patent Document 5] Japanese Unexamined Patent Application, First Publication No. S62-17112 [Disclosure of the Invention] [Problems to be Solved by the Invention]
[0007]
The present invention has been made to solve the above-mentioned problems in the related art about an iron bath type smelting reduction furnace that is used to reduce and melt an iron oxide and an iron material containing an iron oxide, and an object of the present invention is to provide an iron bath type smelting reduction furnace that includes a refractory lining having excellent durability. [Means for Solving the Problem]
[0008]
The present inventors employed the following construction in consideration of the above-mentioned situation. In an iron bath type smelting reduction furnace that was used to reduce and melt an iron oxide and an iron material containing an iron oxide, an MgO-C brick of which the C content was in a specific range was mainly used as a lining brick, and the thermal stress generated in a lining was controlled for the purpose of the stability of the lining. As a result, it was possible to provide a refractory lining that was excellent in durability. The gist of the present invention will be described below.
(1) An iron bath type smelting reduction furnace according to the present invention includes a side wall lining that is formed of a plurality of refractories, and the refractory is an MgO-C brick of which the carbon content is 1 mass% or more and less than 5 mass%.
(2) In the iron bath type smelting reduction furnace disclosed in the above (1),
assuming that the bending strength of the refractory is represented by B (MPa) and the thermal stress generated in the side wall lining and calculated by the following Equation (1) is represented by L (MPa), 3≤B/L≤6 may be satisfied.
(Equation Removed)
where
E: Elastic modulus (GPa) of the refractory to be used,
a: Coefficient of thermal expansion (/°C) of the refractory to be used,
T: surface temperature (°C) of the lining
L: length (m) of the lining, and
A: expansion allowance (m) in the lining. [Effects of the Invention]
[0009]
According to the present invention, in the iron bath type smelting reduction furnace that is used to melt and reduce an iron oxide and an iron material containing an iron oxide, an MgO-C brick of which the C content is in a specific range is mainly used as the lining brick of a side wall, and the thermal stress generated in the lining is controlled for the purpose of the stability of the lining. Therefore, it is possible to obtain an industrial applicability, that is, to provide an iron bath type smelting reduction furnace including a refractory lining that is excellent in durability.
Meanwhile, an iron bath type reduction furnace has characteristics where (a) molten metal always exists in a furnace, and (b) secondary burning for smelting a cooling member containing iron is large and the amount of generated heat is large. Due to the characteristics, there has been a problem in that it is difficult to coat slag. In contrast, according to the present invention, it is possible to coat slag, which is difficult in the related art, by employing a low-carbon MgO-C brick of which the C content is 1 mass%
or more and less than 5 mass%.
Further, since the viscosity of molten iron is lower than that of molten steel, molten metal is easily fed to joints of linings. In contrast, as a result of repetition of experiments, the present inventors found out that this problem was prevented by satisfying 3≤B/L≤6 as described in the above (2). [Brief Description of the Drawings]
[0010]
[FIG. 1 A] FIG. 1A is a view showing an example of an iron bath type smelting reduction furnace, and is a vertical sectional view thereof before a refractory is damaged.
[FIG. 1B] FIG. 1B is a vertical sectional view of the iron bath type smelting reduction furnace when the refractory is damaged.
[FIG. 2] FIG. 2 is a vertical sectional view of an iron bath type smelting reduction furnace according to an embodiment of the present invention.
[FIG. 3] FIG. 3 is a vertical sectional view of an iron bath type smelting reduction furnace according to another embodiment of the present invention. [Description of Reference Numerals and Signs]
[0011]
1: smelting reduction furnace
2: bottom-blown tuyere
3: oxygen lance for blowing
4: molten iron
5: molten slag
6: portion where refractory is damaged
7: refractory
8: portion where MgO-C brick having C content of 1 to 5 mass % is applied
9: portion where MgO-C brick having C content of 15 to 18 mass % is applied [Best Mode for Carrying Out the Invention]
[0012]
An iron bath type smelting reduction furnace according to an embodiment of the present invention will be described in detail below with reference to FIGS. 1A to 3.
[0013]
As shown in FIG. 1 A, an iron bath type smelting reduction furnace 1 according to the present embodiment has the shape of a converter, and includes bottom-blown tuyeres 2 at the lower portion thereof. Further, agitation gas (for example, N2 gas), O2 gas, CO2 gas, powdered coal, iron oxide, or the like is blown into the iron bath type smelting reduction furnace 1 in order to agitate molten iron and molten slag so that a reaction is facilitated. In FIG. 1 A, reference numeral 1 indicates the iron bath type smelting reduction furnace, reference numeral 2 indicates a bottom-blown tuyere, reference numeral 3 indicates an oxygen lance for blowing, reference numeral 4 indicates molten iron, reference numeral 5 indicates molten slag, and reference numeral 7 indicates a refractory.
[0014]
In the iron bath type smelting reduction furnace 1, an iron oxide or an iron material containing an iron oxide, and a carbonaceous material are continuously or intermittently added to a molten material that is composed of molten iron and molten slag. In addition, oxygen is blown from the oxygen lance 3 for blowing in order to reduce the iron oxide to the iron, so that the amount of the molten iron is increased. If the amount of the molten iron reaches a predetermined amount, the molten iron is tapped off. That is, an iron oxide or an iron material containing an iron oxide is supplied to the molten iron, which is provide into the iron bath type smelting reduction furnace 1 and has a
temperature of 1380 to 1415°C and a C concentration of 4.2 mass% to 4.3 mass%. Further, oxygen is blown from the upper oxygen lance 3 at a speed of 7000 Nm /h or more, and a carbonaceous material is supplied from above or below. The supplied iron oxide or the supplied iron material containing an iron oxide is melted and reduced until the amount of molten iron is changed from 50 ton to 80 ton, and the molten iron of 30 ton is tapped off to a pan (not shown) from the iron bath type smelting reduction furnace 1 after the completion of the melting.
[0015]
The slag generated in this case has a low ratio of CaO/SiO2 = 1.0 to 1.7, and causes a severe damages on a refractory lining due to the influence by the iron oxide contained in the slag or an iron oxide provide as a raw material. In particular, as shown in FIG. 1B, the refractory 7, which forms a side wall being in direct contact with the molten slag and the iron oxide during the melting and reduction, is severely damaged. Meanwhile, reference numeral 6 in FIG. 1B indicates a portion where the refractory 7 is damaged.
[0016]
In the iron bath type smelting reduction furnace 1 of according to the present embodiment, an MgO-C brick of which the C content is 1 mass% or more and less than 5 mass% is used as the lining brick 7 that is a side wall lining.
[0017]
If the C content of the MgO-C brick used as the side wall lining is less than 1 mass%, the slag is significantly infiltrated into the MgO-C brick. As a result, the durability of the MgO-C brick deteriorates. Further, the C content of the MgO-C brick is 5 mass% or more, the effect of the coating on the surface of the MgO-C brick is significantly decreased. As a result, the durability of the MgO-C brick deteriorates.
The reason for this is that the slag coating is suppressed due to the increase of a ratio of the area of carbon exposed to the surface of the MgO-C brick. If the C content of the MgO-C brick is less than 5 mass%, a coating property is very excellent even though a ratio of CaO/Si02 is low (1.0 to 1.7) and slag contains an iron oxide provided as a raw material and has low viscosity. Accordingly, a specific slag coating method, such as a method of blowing off the slag in the form of a splash by using the upper main lance to coat the slag, is not required, which is preferable.
[0018]
The most preferable C content is in the range of 3 mass% to 4 mass%, and the MgO-C brick having this C content is particularly excellent in coating property.
[0019]
The MgO-C brick used in the present embodiment is composed of magnesia particles, carbon, and an antioxidant such as an Al alloy or a B compound. It is preferable that the magnesia particles be sintered magnesia or fused magnesia having 95 mass% or more of MgO. The carbon includes flake graphite, earthy graphite, artificial graphite, expanded graphite, pitch, carbon black, a phenol resin, and anthracite coal.
[0020]
It is preferable that an Al alloy, such as Al and Al-Mg, or a B compound such as CaB6 or B4C be used as the antioxidant.
[0021]
In FIG. 2, reference numeral 8 indicates a portion where an MgO-C brick having a C content of 1 mass% to 5 mass% is applied. Further, in FIG. 2, reference numeral 9 indicates a portion where an MgO-C brick having a C content of 15 mass% to 18 mass% is applied.
[0022]
The MgO-C brick used in this embodiment has an extremely low C content as compared to a MgO-C brick that is used as a lining brick of a steelmaking converter and has a C content of 15 mass% to 18 mass%. Therefore, the thermal expansion of the MgO-C brick used in this embodiment becomes large. For this reason, it is preferable to prevent cracks and flaking, which are generated in the MgO-C brick by thermal stress generated under high temperature environment during the operation, from being generated.
[0023]
As a result of repetition of experiments, the present inventors found out that the lining is stabilized without generating cracks and flaking in the MgO-C brick if a ratio B/L between the bending strength B (MPa) of a refractory and the thermal stress L (MPa) that was generated in the side wall lining and calculated by the following Equation (1) was controlled in the range of 3≤B/L≤6.
(Equation Removed)
where
E: Elastic modulus (GPa) of the refractory to be used,
a: Coefficient of thermal expansion (/°C) of the refractory to be used,
T: surface temperature (°C) of the lining
L: length (m) of the lining, and
A: expansion allowance (m) in the lining.
[0024]
That is, cracks are generated in the MgO-C brick and a part of the MgO-C brick flakes under a condition where B/L is less than 3, so that the stability of the lining significantly deteriorates. When a lining is cooled under a condition where B/L exceeds 6, joint openings are generated in the MgO-C brick and the MgO-C brick is
separated due to the generation of the losses of joints or the decrease of the force for binding the lining.
[0025]
Meanwhile, the length L of the lining of this embodiment means the length of the lining, that is, the MgO-C brick in a horizontal direction, and the expansion allowance A in the lining also means a gap between joints of the MgO-C brick in the horizontal direction. Since the lining is weakly bound by an outer steel shell in a vertical direction as compared to the horizontal direction, a condition of B/L is not particularly specified.
[0026]
In the present embodiment, a method of controlling B/L SO as to be 3 or more is performed by setting the expansion allowance A in the lining. A method of setting the expansion allowance A in the lining is not particularly limited. However, a method of inserting a member such as a cardboard, which is burned and then disappears by heating, into a joint part, or a method of applying a coating material, which is volatilized or burned by heating, on the surface of a brick may be preferably used in terms of easy control.
[0027]
More preferably, as shown in FIG. 3, a MgO-C brick 9, which is a lining brick of a steelmaking converter and has a C content of 15 mass% to 18 mass%, is also used at a portion of a side wall refractory that is not in contact with the slag during the melting and reduction. The portion of the refractory, which is not in contact with the slag, is mainly corroded by the molten iron, and the corrosion thereof is very little as compared to the portion that is in contact with the slag. For this reason, B/L does not need to be controlled to be 3 or more in the lining where the MgO-C brick having a C content of 15
mass% to 18 mass% is used. In FIG. 3, reference numeral 1 indicates an iron bath type smelting reduction furnace, reference numeral 2 indicates a bottom-blown tuyere, reference numeral 3 indicates an oxygen lance for blowing, reference numeral 4 indicates molten iron, reference numeral 5 indicates molten slag, reference numeral 6 indicates a portion where the refractory is damaged, and reference numeral 8 indicates a portion where an MgO-C brick of which the C content is 1 mass% or more and less than 5 mass% is applied. [Example]
[0028]
An example of the present invention will be shown below.
[0029]
Test results obtained by applying various MgO-C bricks to a side wall lining of an iron bath type smelting reduction furnace according to this example (a portion shown in FIG. 3 by reference numeral 8) are shown below.
In the MgO-C brick, fused magnesia having a purity of 98% or more was used as magnesia particles, flake graphite and a phenol resin were used as carbon, and Al and B4C were used as an antioxidant. An MgO-C brick having a C content of 15 mass% was used in the portion shown in FIG. 3 by reference numeral 9. B/OL was adjusted by setting the expansion allowance A in the lining (a gap between joints of the brick in the horizontal direction). The iron bath type smelting reduction furnace 1 to which a lining shown in Table 1 was applied was prepared in the portion shown in FIG. 3 by reference numeral 8. Further, melting and reduction were performed with the slag composition shown in Table 1, and the state of the slag coating of the MgO-C brick and the state of the damage of the MgO-C brick were evaluated.
[0030]
Table 1
(Table Removed)
[0031]
An index of a coating property shown in Table 1 is obtained by creating an index that corresponds to the thickness of slag attached to the surface of the MgO-C brick, and is excellent as much as the numerical value is large. Further, an index of a damage rate is obtained by creating an index that corresponds to the damage rate (mm/heat) of the MgO-C brick, and is excellent as much as the numerical value is small. In addition, the index of the coating property and the index of the damage rate are obtained by creating indexes when 100 is referred to as results corresponding to the conditions shown in a left column of Table 2 of a comparative example.
[0032] (Comparative example)
Test results obtained by using an MgO-C brick, which is a magnesite chrome direct bonded brick having a C content of 5 mass% or more, in a side wall lining of a furnace used as a comparative example are shown in Table 2. Other conditions of this example are the same as those of Table 1. In the MgO-C brick, like the above-mentioned example, fused magnesia having a purity of 98% or more was used as magnesia particles, flake graphite and a phenol resin were used as carbon, and Al and
B4C were used as an antioxidant. [0033]
Table 2
(Table Removed)
[0034]
As apparent from the test results of these Tables 1 and 2, the example was superior to the comparative example in terms of the index of a coating property and the index of a damage rate. Therefore, it was possible to confirm the superiority of the present invention. [Industrial Applicability]
[0035]
According to the present invention, in the iron bath type smelting reduction furnace that is used to melt and reduce an iron oxide and an iron material containing an iron oxide, an MgO-C brick of which the C content is in a specific range is mainly used as the lining brick of a side wall, and the thermal stress generated in a lining is controlled in a specific range for the purpose of the stability of the lining. Therefore, it is possible to obtain an industrial applicability, that is, to provide an iron bath type smelting reduction furnace including a refractory lining that is excellent in durability.

[Document Type]
CLAIMS
[Claim 1]
An iron bath type smelting reduction furnace comprising:
a side wall lining that is formed of a plurality of refractories,
wherein the refractory is an MgO-C brick of which the carbon content is 1
mass% or more and less than 5 mass%.
[Claim 2]
The iron bath type smelting reduction furnace according to claim 1, wherein assuming that the bending strength of the refractory is represented by
B (MPa) and the thermal stress generated in the side wall lining and calculated by the
following Equation (1) is represented by L (MPa), 3≤B/L≤6 is satisfied.
(Equation Removed)
where
E: Elastic modulus (GPa) of the refractory to be used, a: Coefficient of thermal expansion (/°C) of the refractory to be used, T: surface temperature (°C) of the lining L: length (m) of the lining, and A: expansion allowance (m) in the lining.