JP4329444B2 - Method for producing sponge iron - Google Patents

Description

  The present invention relates to a method for producing sponge iron used as a raw material for production of sintered products such as machine parts and magnetic materials, or reduced iron powder used in powder form.

Sponge iron is generally used in a refractory cylindrical reaction vessel 1 called a sagar as shown in FIG. 1, and iron oxide powder 2 and coke powder such as crushed mill scale and iron ore. The raw material, which is a solid reducing agent 3 such as coal powder, is packed into a concentric cylinder in a batch mode, and the whole container is introduced into a tunnel furnace and the like, and is indirectly processed at a temperature of 1050 to 1200 ° C. And the iron oxide in the container is reduced (Non-Patent Documents 1 and 2).
"Steel Handbook 4th Edition" Page 1363 Fig. 1 "Steel Handbook 3rd Edition" page 457, right column, lines 10-13

In the conventional sponge iron manufacturing technology using a sagar, as shown in FIG. 1, the raw material is filled with iron oxide 2 in a reaction vessel 1 in a cylindrical shape, and around the cylindrical iron oxide 2. The solid reducing agent 3 is filled so as to surround it, and is also filled in the upper and lower sides and the central part thereof. As a result, when the reaction vessel 1 is heated after the raw material is charged, first, carbon in the reducing agent 3 reacts as shown in the following formula (1) in the solid reducing agent deposition layer to generate CO gas.
C + CO ₂ → 2CO (1)
The CO gas generated in this way reaches the powdered iron oxide deposition layer 2 from the three layers of the solid reducing agent, and the following formula (2);
FeO _n + nCO → Fe + nCO ₂ (2)
In this reaction, iron oxide 2 is reduced and CO ₂ gas is generated. Further, the CO ₂ gas diffuses in the iron oxide deposition layer 2 and reaches the layer of the solid reducing agent 3 again, in which carbon is converted into CO gas.
The powdered iron oxide 2 filled in the reaction vessel 1 is all reduced by repeating the above reaction occurring at the contact point between the iron oxide 2 and the solid reducing agent 3 for a certain period of time. Simultaneously with the reaction, sintering of the reduced iron proceeds to form a cylindrical sponge iron.
According to the formula (2), (number of moles of carbon atoms in carbon monoxide / number of moles of oxygen atoms in iron oxide) is 1.0. In other words, (number of moles of carbon atoms in solid reducing agent / number of moles of oxygen atoms in iron oxide) is 1.0. Hereinafter, (number of moles of carbon atoms in solid reducing agent / number of moles of oxygen atoms in iron oxide) is referred to as “molar ratio”.

The feature of the above prior art is that the diffusion of CO gas and CO ₂ gas generated in the reaction vessel 1 into the sponge iron and the solid reducing agent 3 controls the progress of the reduction reaction. However, in the method of taking the filling structure shown in FIG. 1, the layers of powdered iron oxide 2 and powdered solid reducing agent 3 are layered along the paper surface of FIG. 1B, that is, along the axial direction of the cylinder. Since they are separated, the diffusion distance of CO gas and CO ₂ gas increases, and there is a problem that it takes a longer time for reduction. For example, in an industrial production scale manufacturing process that uses a tunnel furnace for heating, reaction efficiency (gas utilization efficiency) is reduced, and it takes several days from filling of raw materials to extraction of sponge iron, leading to a reduction in productivity. In addition, there is a problem that the consumption of heating energy required for the reduction is remarkably increased.
That is, in the cylindrical filling method as shown in FIG. 1, in order to increase the amount of sponge iron to be manufactured, it is necessary to increase the thickness of one layer of iron oxide. Sex is reduced.

  Further, in such a cylindrical filling method, the CO gas generated by the above reaction inevitably flows out of the reaction vessel 1 through the layer of the solid reducing agent 3 which is a low density layer, and this gas. Does not contribute efficiently to the reduction reaction, or the solid layer between the reaction vessel 1 and the iron oxide 2 or inside the cylindrical iron oxide layer so that the iron oxide 2 layer does not collapse as the sintering proceeds. Reducing agent 3 in excess (more than 2.0 in molar ratio) than the amount of oxygen in iron oxide and the amount of carbon in carbon monoxide, that is, the amount of oxygen in iron oxide and the amount of carbon in the solid reducing agent in formula (2). There is also a problem that the basic unit of the solid reducing agent deteriorates because of the tendency to fill.

  Furthermore, in the conventional method for producing sponge iron, iron oxide is filled in a cylindrical shape. Therefore, if the thickness of the iron oxide is reduced in order to shorten the reduction time, the sponge iron that can be produced in the reaction vessel 1 is used. There was a problem that the amount would decrease, and it did not necessarily lead to reduction of reduction time and improvement of production volume, and the filled iron oxide swelled at the bottom due to the load of iron oxide, and within the planned reduction time There was also a problem that the reduction of iron oxide did not proceed and an unreacted part remained.

  Therefore, the object of the present invention can advantageously solve the above-mentioned problems of the prior art. That is, it is to propose a method for producing sponge iron having high reduction reaction efficiency and high productivity.

In order to overcome the above-mentioned problems, the inventors have conducted many experiments regarding shortening the diffusion time of CO gas and CO ₂ gas. As a result, the inventors have found that the above object can be achieved advantageously by devising the form of filling of the iron oxide and the solid reducing agent into the reaction vessel, and preferably the molar ratio, and have arrived at the present invention.
That is, the present invention provides a method for producing sponge iron by filling iron oxide and a solid reducing agent in a reaction vessel and heating to reduce the iron oxide, whereby the iron oxide and the solid reducing agent are alternately horizontal. a method for producing sponge iron, wherein the filling to deposit the layer shape.

According to the present invention, the iron oxide and the solid reductant, by alternately filling the horizontal layer form, so it is possible to produce the sponge iron for high purity (≧ 97mass%) while ensuring high productivity Become.

The production method according to the present invention is characterized in that the method of filling the raw materials (iron oxide and solid reducing agent) into the reaction vessel is devised, and by adopting such a filling type, high productivity is achieved. This is because it can be secured. That is, the present invention is a conventional method as shown in FIG. 1, for example, in a vertical cylindrical refractory reaction vessel, iron oxide and a solid reducing agent are placed in a concentric cylinder along the axial direction (cylindrical). Alternatively, instead of the method of filling in a columnar shape, iron oxide and a solid reducing agent are alternately deposited in a horizontal layer form. As shown in FIG. 3, the iron oxide deposition layer 12 and the solid reducing agent deposition layer 13 A method of filling in a spirally entangled state (hereinafter referred to as “alternate filling” method) is employed.
In addition, when filling in the state where it is intertwined in a spiral shape, the angle between the normal direction of the layer formed by the iron oxide and the solid reducing agent and the vertical direction (gravity direction) is preferably 45 ° or less. The reason is that when the layer is formed in the reaction vessel, the iron oxide or solid reducing agent constituting the forming layer can be prevented from sliding down due to gravity or the like, and a uniform layer can be formed efficiently. It is. On the other hand, if productivity is considered, it is good to set it as 3 degrees or more.
In addition, when filling in a layered manner, it is a (horizontal) layer perpendicular to the axial direction of the container as shown in FIG. Here, “horizontal” means that the normal line of a layer formed of iron oxide and a solid reducing agent is “substantially parallel” to the vertical direction (gravity direction). Further, “substantially horizontal” here means that the angle between the normal and the vertical direction is within 10 °. The reason why it is horizontal is that when the layer is formed in the reaction vessel, the iron oxide or solid lubricant constituting the forming layer is prevented from sliding off due to gravity or the like, and a uniform layer is efficiently formed. Because it can.

  In such an alternate filling method of iron oxide and solid reducing agent, when filling iron oxide and solid reducing agent, the absolute value of the iron oxide layer thickness and the solid reducing layer thickness and the ratio of the iron oxide layer thickness to the solid reducing layer thickness are arbitrarily set. Moreover, it can be changed at any time.

  In filling the raw material into the reaction vessel, the ratio of the amount of iron oxide and the amount of solid reducing agent when performing the above-described alternate filling, particularly the ratio of the necessary reducing agent amount (carbon amount) to iron oxide (oxygen amount) is as described above. As described with the formula (2), the reduction reaction of iron oxide is determined as a reaction of one C atom in the reducing agent and one O atom in the iron oxide (molar ratio 1.0). . In general, the amount of carbon greater than the amount of oxygen in iron oxide is required as a reducing agent. In the conventional method, as described above, the reducing agent is excessively charged, and the reducing agent (molar ratio) is 2.0 to 2.5 times. 2.0 ~ 2.5).

FIG. 4 shows a state in which reduction is performed by changing the amount of carbon (molar ratio) with respect to the amount of oxygen in iron oxide and the thickness of the amount of iron oxide when alternating filling (layered) and cylindrical filling are performed. It is a graph which shows transition of reduction time to obtain sponge iron of mass% iron.
In FIG. 4, an example of the result of the conventional cylindrical filling (FIG. 1) is indicated by ●. In this conventional method, when the thickness of the iron oxide layer was 55 mm and the amount of carbon / oxygen (molar ratio) was 2.2, the reduction time took 53 hours.
On the other hand, in the example of conformity with the present invention, reduction experiments were carried out in the case where the thickness of the iron oxide layer was 15 mm, 20 mm, 30 mm, and 50 mm by laminar alternating filling (FIG. 2). As a result, the reduction time was shortened by reducing the thickness. At a thickness of 20 mm or more, the reduction time became almost constant when the molar ratio was 1.2 or more, but when it was less than 1.2, the reduction time became longer. It was also found that when the thickness of the iron oxide layer was 15 mm, the reduction time was almost constant at a molar ratio of 1.6 or more.
As a result of repeated experiments, it was also found that the following relationship was established when the thickness of oxygen iron was less than 20 mm.
Molar ratio x iron oxide layer thickness (mm) = 2.3 to 2.5 (3)
If the thickness of the iron oxide layer is less than 20 mm, filling is performed to satisfy the above equation (3). If the thickness of the iron oxide layer is determined, the reduction time is uniquely determined and the operation is stabilized. The quality of the sponge iron that is produced is also stable.

  In the alternate filling of the raw material into the reaction vessel, iron oxide 12 and solid reducing agent 13 are alternately placed in a reaction vessel 11 made of a cylindrical refractory (such as SiC) called sagar as shown in FIG. It fills up in layers or, as shown in FIG. 3A, alternately fills up so as to be intertwined spirally using a raw material charging machine 14. In addition, the raw material charging machine 14 for filling in this spiral shape is divided into two in the axial direction of the cylindrical main body by the partition wall 14a, and the partitioned rooms (accommodating portions) 17 and 18 are oxidized. Mainly composed of a rotary charging cylinder 14b in which iron 12 or solid reducing agent 13 can be charged and the lower end portion is provided with cutout openings 15 and 16 capable of adjusting gaps through a slide gate (not shown). Has been. If it cuts out simultaneously from the openings 15 and 16, it becomes spiral alternate filling, and if it cuts out from only one side of the opening, horizontal layer-like alternating filling can be performed.

  In order to alternately fill the raw material spirally using such a raw material charging machine 14, the rotary charging tube 14b is first inserted into the reaction vessel 11 from above, and the openings 15, 16 By adjusting the opening area and increasing it at a constant speed while rotating, it is alternately packed so that the iron oxide layer thickness and the solid reducing agent layer thickness are in a constant ratio and entangle in a spiral shape. Thus, a packed bed in which the iron oxide and the solid reducing agent are alternately deposited in a spiral manner is formed in the reaction vessel 11 in this manner.

In the present invention, in such horizontal layered or spiral alternating filling, the thickness and the layer thickness ratio of each of the deposited layers of the iron oxide deposited layer 12 and the solid reducing agent deposited layer 13 are changed continuously or intermittently. It is possible to continue. This means that the layer thickness ratio is changed in the height direction of the vertical reaction vessel 11, for example, near the bottom, middle, and top, in addition to the case where the layer thickness ratio is controlled to be constant.
In addition, each layer thickness variable filling as described above adjusts at least one of the rotational speed of the rotary charging cylinder 14b, its rising speed (push-up speed), and the size of the openings 15 and 16. Can be realized. In particular, it is preferable that the size of the openings 15 and 16 is controlled through gate opening / closing control because it can be realized while ensuring stable operation without incurring diffusion resistance of gas, extension of reduction time, and generation of unreacted parts. .

  In the method for producing sponge iron according to the present invention, at least iron oxide and a solid reducing agent are required as raw materials to be filled in the reaction vessel, and the iron oxide 12 is generated in an iron ore or a hot rolling process. It is preferable to use iron oxide powder (particle size: 0.05 to 10 mm) such as mill scale. Moreover, as the solid reducing agent 13, it is preferable to use carbonaceous powders such as coke powder, char, and caking coal powder. It is to be noted that there is no problem even if this solid reducing agent is used by further adding limestone or calcined lime powder as a part of the solid reducing agent layer as necessary.

The iron oxide 12 and the solid reducing agent 13 are filled in the reaction vessel 11 by the raw material charging machine 14 shown in FIG. For example, a cylindrical SiC reaction vessel 11 called a sagar is alternately filled in a spiral shape.
Then, the reaction vessel 11 filled with iron oxide 12, solid reducing agent 13 and limestone used as necessary is then charged in a state where it is loaded on a cart in a firing furnace such as a tunnel furnace. For a predetermined time. The heating temperature for this reduction is preferably about 1000 to 1300 ° C. When the heating temperature is less than 1000 ° C., the reduction of the iron oxide 12 does not proceed sufficiently. on the other hand. If the temperature exceeds 1300 ° C, the sponge iron, which progresses simultaneously with the reduction, is excessively hardened and hardened, resulting in an increase in power consumption during subsequent grinding and an increase in manufacturing costs due to wear of the grinding tool. There is a fear. Therefore, the heating temperature is preferably in the range of 1000 to 1300 ° C.
By this reduction reaction by heating, the iron oxide 12 is reduced by the solid reducing agent 13 to produce sponge iron.

  After heating for reduction, the produced sponge iron is separated from the reaction vessel 11 and taken out from the solid reducing agent 13. The sponge iron taken out from the reaction vessel 11 is then pulverized to a particle size of about 150 μm or less, subjected to finish reduction, and further pulverized to obtain reduced iron powder.

  In the reduction treatment step, the iron oxide in the reaction vessel 11 moving while being placed on a carriage in the furnace is first heated and held in a preheating zone of about 200 to 900 ° C. for about 24 hours, and then 1000 to 1300. It is held in the baking zone at 36 ° C. for 36 hours or more. Thereafter, after passing through a cooling region of about 200 to 900 ° C., a sponge having a ratio of iron of 97 mass% or more and the height (total thickness) of the agglomerate formed in a columnar shape in the reaction vessel 11 is about 2000 mm or less. You can get iron.

Example 11 (Method of FIG. 2): The filling schedule in this example is that the raw material feeder 14 is used to fill the bottom of the reaction vessel 11 with the powder reducing agent 13 to a thickness of 50 mm, and then Powdered iron oxide (mill scale) 12 was cut and deposited to a thickness of 40 mm on the top, and repeatedly filled up to the upper end of the reaction vessel 11 in such a filling schedule. The upper end of the reaction vessel 11 is filled with a powder reducing agent (coke powder) 13. In this filling, the molar ratio of the amount of carbon in the reducing agent and the amount of oxygen in the iron oxide was 1.6.
Reference Example 12 (Method of FIG. 3): This example is an example in which the spiral filling shown in FIG. 3 is performed. A powdery reducing agent (coke powder) 13 is deposited on the bottom of the reaction vessel 11, and a cylindrical charging cylinder 14 b having an iron oxide opening 15 and a reducing agent opening 16 is rotated on the powder reducing agent (coke powder) 13. By raising, powdered iron oxide (mill case) 12 and powdery reducing agent 13 are continuously and spirally filled in the reaction vessel.

  Next, the refractory reaction vessel 11 filled with the raw material was placed on a carriage and passed through a tunnel furnace, whereby the iron oxide 12 was heated and reduced. The tunnel furnace used had a total length of 100 m, and the area of the center 40 m was adjusted to an atmospheric temperature of 1150 ° C. Table 1 summarizes the results of operations for producing sponge iron with an iron ratio of 97 mass% under such conditions.

  As is apparent from Table 1, in the embodiment of the present invention, the carriage speed is 18% faster than the conventional example (method of FIG. 1) of 1.1 m / hr, 1.3 m / hr. The amount of mill scale filled is 16% larger than the conventional example of 220 kg / container, 256 kg / container. As a result, productivity was improved by 38%. As a result, the amount of heat per unit of sponge iron required for heating was reduced by approximately 30% from 11470 MJ / ton to 8820 MJ / ton.

  The present invention is a raw material for production of sintered products such as machine parts and magnetic materials, or reduced iron powder used as a powder.

It is sectional drawing explaining the conventional iron oxide and a solid reducing agent filling method. It is sectional drawing explaining the iron oxide and solid reducing agent filling method which concern on this invention. It is sectional drawing explaining the iron oxide and the solid reducing agent filling method in the other example of this invention. It is a figure explaining the relationship between molar ratio and reduction time in implementation of this invention.

Explanation of symbols

1, 11 Reaction vessel 2, 12 Iron oxide 3, 13 Solid reducing agent 14 Raw material charging machine
14a Partition wall
14b Rotating charging cylinders 15 and 16 Opening 17 Iron oxide accommodating portion 18 Solid reducing agent accommodating portion

Claims (1)

In a method for producing sponge iron by filling iron oxide and a solid reducing agent in a reaction vessel and reducing iron oxide by heating, the iron oxide and the solid reducing agent are alternately deposited in a horizontal layer. A method for producing sponge iron, comprising filling.

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