JP2668913B2 - Smelting reduction method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a smelting reduction method for reducing iron ore in a molten state in a converter type smelting furnace using a carbonaceous material as a fuel and a reducing agent.

[Prior Art] The smelting reduction method is an alternative to the blast furnace ironmaking method, and the blast furnace ironmaking method has been developed in recent years to eliminate the drawback that the construction cost of the blast furnace is high and a vast site is required. It was done. In the conventional smelting reduction method, iron ore is preliminarily reduced with exhaust gas from a smelting furnace, charged into a smelting furnace together with carbonaceous material and a slag-making agent, and oxygen gas or stirring gas is supplied to the smelting furnace. Is blown into. In this way, the carbonaceous material is dissolved in the hot metal charged in advance, and C of the carbonaceous material is oxidized by the oxygen gas. The ore is melted by the heat of oxidation at this time, and the iron ore is reduced by C in the carbonaceous material. The CO gas generated from the hot metal is secondarily combusted by the oxygen gas blown excessively to become CO ₂ gas.
The sensible heat of the CO ₂ gas is transferred to the slag or forming granular iron covering the hot metal and then to the hot metal. In this way, the iron ore is reduced to produce hot metal, but in order to reduce the reduction process in the smelting furnace, the preliminary reduction rate of the iron ore before being charged into the smelting furnace is set to 60% to 75%. Therefore, the exhaust gas from the smelting furnace uses a large amount of highly reducing gas with low oxidation degree. (For example, Japanese Patent Publication No. 61-4340
6) [Problems to be solved by the invention] However, in order to reduce the reduction step in the smelting furnace, the preliminary reduction rate of iron ore before being charged into the smelting furnace is 30%.
In the case of the above, the degree of oxidation [(H ₂
O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ ). This inevitably increases the exhaust gas amount (for example, Japanese Patent Publication No. 61-43).
406), which naturally leads to an increase in manufacturing cost. In addition, in order to obtain a high pre-reduction rate, as described above, exhaust gas having a low OD is required, and the residence time of the iron ore in the pre-reduction furnace is prolonged. It is difficult to balance the charging into the smelt and the tapping cycle of the hot metal produced. This inevitably limits the freedom of the smelting furnace. Also, in order to increase the reduction rate of iron ore and increase the amount of iron ore reduction per unit weight of charged carbonaceous material, a method of secondary combustion of CO gas in the furnace and utilizing the heat is considered. Therefore, the method of blowing O ₂ gas for secondary combustion from the upper wall of the furnace has been conventionally used. However, in the related art, although the exhaust gas temperature rises when the secondary combustion ratio is increased, there is no technology for transmitting the sensible heat of the exhaust gas to the molten metal. As a result, the heating efficiency is reduced and the high-temperature exhaust gas must be discharged. Such high-temperature exhaust gas has a serious problem of severely wearing down the refractory on the inner wall of the furnace. Therefore, it has been a general idea that the degree of oxidation of the exhaust gas cannot be increased so much.

According to the present invention, as will be described in detail later, the oxidation degree of exhaust gas has been successfully increased by promoting the reduction reaction and secondary combustion of iron ore in a smelting furnace, but the oxidation degree has been increased. When the exhaust gas is introduced into the preheating pre-reduction furnace,
There is a possibility that iron ore cannot be reduced at a sufficiently high reduction rate for practical use.

The present invention has been made in view of the above circumstances, and provides a smelting reduction method with good operability and high productivity which can improve the heat transfer efficiency to hot metal or slag and can obtain high preheating preliminary reduction. What you want to do.

[Means and Actions for Solving the Problems] Regarding the above-mentioned problem of increasing the heat transfer efficiency in the smelting furnace and promoting the reduction reaction of iron ore, the present inventors have proposed a smelting reduction mechanism and a concrete method corresponding thereto. Investigations have been made repeatedly on the practical means, and as a result, the following facts have been found.

As described above, in the past, the basic idea was that the secondary combustion ratio could not be greatly increased in terms of the technical limit for improving the heating efficiency and the wear of refractories, but the secondary combustion was mainly used. By blowing oxygen and generating strong agitation of the slag so as to generate it in the slag, it is possible to effectively increase the heat-receiving efficiency while ensuring high secondary combustion. Due to such high secondary combustion and high heat deposition efficiency, the temperature of the slag and the iron ore in the slag increases, and the reduction of iron ore by C ( C in the molten metal) represented by Fe ₂ O ₃ +3 C = 2Fe + 3CO. The speed can be effectively increased.

In the conventional method, there is an example in which the bottom blowing of oxygen is performed during one period or the entire period of the reduction treatment, but such bottom blowing of oxygen is harmful to the secondary combustion. That is, when oxygen is blown from the bottom, a large amount of CO gas is generated in the molten metal and the molten metal is vigorously stirred. As a result, the molten metal splash reaches the secondary combustion zone, and C contained in this molten metal splash reacts with oxygen. This inhibits secondary combustion. Therefore, regardless of part or all of the reduction period, bottom-blowing of oxygen must be avoided.

The present invention defines the following conditions based on such knowledge, thereby enabling reduction processing at a high processing speed.

(B) By combining bottom blowing and side blowing of stirring gas,
The molten metal is positively diffused into the region of the slag where the iron ore is present, thereby promoting the reducing action of iron ore by C in the molten metal.

(B) Injection of secondary combustion oxygen is performed separately from decarburization oxygen so that an oxidation degree equal to or higher than a predetermined level is obtained. Then, this secondary combustion oxygen is blown into the slag from the upper blowing lance to form a secondary combustion region in the slag, and the side blowing gas strongly agitates the slag to heat the heat generated by the secondary combustion to the iron ore. Heat to.

(C) Reduction action by C in molten metal and 2
To prevent the next combustion from being hindered, the side-blown gas and the bottom-blown gas are CO or an inert gas, and oxygen is not used.

In addition to this, the smelting reduction method according to the present invention blows powdery carbonaceous material or steam as a gas reforming material from a tuyere provided in the preheating pre-reduction furnace to reform the generated gas in the furnace, A high pre-reduction rate can be obtained, and at the same time, a gas having a large sensible heat can be recovered. The temperature in the smelting furnace is 400 ° C. to 1300 ° C., but when the temperature is less than 400 ° C., an effect of preheating is expected in consideration of a temperature drop until exhaust gas is introduced into the preheating pre-reduction furnace. Not only is it not possible to do this, but there is a risk of tar troubles to be described later, and if it exceeds 1300 ° C., the problem of fire resistance of the equipment arises. That is, in the smelting reduction method according to the present invention, the ore preheated and pre-reduced by the preheating pre-reduction furnace is charged into the smelting furnace together with the carbonaceous material and the slag smelting agent, and inert from the bottom and side blowing tuyeres. A smelting reduction method in which a gas CO or a process gas is blown, wherein (1) the decarburizing oxygen and the secondary combustion oxygen are blown from an upper blown oxygen lance whose tip is at a level near the upper surface or the lower surface of the slag layer, 2) At least a part of the gas flow from the side blown tuyere hits the molten metal portion raised by the gas blown from the bottom blown tuyere, (3) Oxidation degree of the gas in the smelting furnace [= _{(H 2 O + CO 2)} / (H 2 + H 2 O + CO + CO 2)] 0.5 to the
1.0 The temperature is set to 400 ° C. to 1200 ° C., (4) A gas reforming material is charged into the preheating pre-reduction furnace, the gas introduced into the preheating pre-reduction furnace is reformed, and its oxidation degree is reduced. It is characterized in that it is less than 0.5.

Embodiment An embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an explanatory view of a process used in the smelting reduction method of the present invention. Inside the smelting furnace 10, there is an iron bath 11 and a slag layer 12.
Is formed, and a first chute 13 into which a carbonaceous material and a slag-making agent as auxiliary materials are charged is provided at an upper portion of the smelting furnace, and an upper-blown oxygen lance 21 is vertically charged into the furnace. Is done. Oxygen for decarburization (DCO ₂ ) and oxygen for secondary combustion (PC
Nozzles 22 and 23 for jetting O ₂ ) are respectively provided, and an inert gas,
A horizontal blowing tuyere 25 and a bottom blowing tuyere 26 for blowing CO or a process gas as a stirring gas are provided. In the upper part of the smelting furnace 10, a raw material supply device (not particularly shown for simplicity) or a preheating device, which is well-known, contains iron ore as a raw material, carbonaceous material as a secondary raw material, and slag-making agent. Preliminary reduction furnace 30
2nd chute charged to smelting furnace by natural fall
An exhaust gas conduit 15 for discharging exhaust gas from the smelting furnace is provided. Further, a dust remover 31 for introducing the exhaust gas and removing the dust at a high temperature, and a preheating pre-reduction furnace 30 for introducing the exhaust gas from the dust remover and preheating the iron ore,
And a separator 35 for receiving the exhaust gas and removing fine particles of iron ore contained therein. At the upper part of the preheating preliminary reduction furnace 30, a charging port 29 for modifying the exhaust gas introduced therein is provided. The fines or powder of iron ore separated from the separator 35, and mixed Ar, together with a carrier gas such as N _2, and pressurized lateral tuyeres 2
5. Since the air is blown from the bottom blowing tuyere 26, a pressure device 27 is provided as a means for mixing and pressure feeding. A smelting reduction method using the smelting reduction apparatus configured as described above will be described. Iron ore, which is a raw material, enters the preheating pre-reduction furnace 30 from the above-described supply device, is preheated here, and is charged into the smelting furnace 10 by gravity falling from the second chute 14. The carbonaceous material and the slag forming agent are charged into the smelting furnace 10 by gravity falling from the first chute 13. Inside the smelting furnace 10, the iron bath 11 and the slag layer made of molten metal
12 is formed, and the degree of oxidation of the gas generated here is increased by the reaction in the furnace which will be described in detail later. This gas enters the preheating pre-reduction furnace 30 from the exhaust gas conduit 15 through the dust remover 31, but is mixed with the reforming material charged from the charging port 29 provided at the upper portion of the preheating pre-reduction furnace 30 and modified. Quality. in this case,
When the modifier is carbonaceous material, and when it is lumpy or granular, it is charged by gravity falling. When this is powdery, the method of charging together with the carrier gas is such that the powdery carbon material is well dispersed and the oxidation degree OD of the gas in the preheating pre-reduction furnace is
Is effective for lowering. When steam is used as the reforming material, it is charged together with plain or powdery carbonaceous material. Also, in order to avoid tar troubles due to the charged carbonaceous material, the temperature in the vicinity of the carbonaceous material inlet 29 must be 300 ° C or higher,
Depending on the brand of carbonaceous material, it may be necessary to exceed 500 ° C. 1200
If the temperature exceeds ℃, a problem occurs due to the heat resistance of the preheating pre-reduction furnace. In order to avoid the above-mentioned tar trouble, it is conceivable to use char whose dry matter has been removed by dry distillation of coal.However, this method increases the unit consumption of carbon material and the amount of generated gas, and increases the equipment cost for producing char. Or, it causes excessive sensible heat of the recovered gas, which is not a desirable method. As described above, the in-furnace gas having a high degree of oxidation due to the in-furnace reaction is reduced to a degree of oxidation of less than 0.5 in the preheating pre-reduction furnace by the reforming, and the iron ore is efficiently preheated and pre-reduced here. . The iron ore is introduced into the smelting furnace from the second chute 14, while the exhaust gas enters the separation device 35, where fine or fine iron ore is separated and discharged through the usual exhaust gas treatment device. It is used as a stirring gas blown from the tuyere 25, 26 as a process gas, or as a carrier gas for blowing powder. Further, the exhaust gas is introduced into the gas conduit 15 and mixed with the exhaust gas from the smelting furnace, and can be used for controlling the temperature of the gas introduced into the dust removing device 31. The fine or powdery iron ore separated by the separating device 35 is mixed with a plain or powdered carbonaceous material and a pressurizing device.
27, where it is mixed with a carrier gas and then pressurized and blown into the smelting furnace from the tuyere 25 or tuyere 26.
Next, the relationship between the gas blowing into the smelting furnace and the reaction in the furnace will be described in detail with reference to FIGS. FIG. 2 schematically shows the behavior of the blown gas in FIG. During the reduction process, gas is blown from the upper blowing lance 21, the side blowing tuyere 25, and the bottom blowing tuyere 26 from the beginning to the end. The gas blowing from the tuyeres 25, 26 has the effect of diffusing the molten metal into the slag by the cooperation of the two, and dramatically increasing the reduction rate. As described above, the present inventors have elucidated the fact that the reduction of iron ore in the slag layer 12 mostly proceeds with C in the molten metal as a reducing substance. The area is where iron ore floats) and is actively diffused in order to increase the reduction rate.

Therefore, according to the present invention, the agitating gas is supplied from the bottom blowing tuyere 26 to form a bulge (A) on the molten metal surface, and at the same time, at least a part of the gas flow from the horizontal blowing tuyere 25 causes the molten bulge ( Agitating gas is supplied so as to hit A), and the molten metal in the molten metal bulge (A) is scattered into the slag by the laterally blown gas. The apparent specific gravity of the slag is usually 0.1 to 0.5, while the bulk specific gravity of the iron ore is 1 to 3, and thus the iron ore in the slag is concentrated and suspended in the lower region of the slag. When the molten metal ridge is scattered by the side-blown gas as described above, the scattered molten metal diffuses into the lower region of the slag layer 12 where the iron ore is present, and C in the diffused molten metal reduces the iron ore and is high. A reduction rate is obtained.

In order to obtain such an effect, it is preferable that the cross-blown gas hit the molten metal ridge (A) as accurately as possible in the vertical and horizontal directions of the smelting furnace. The tuyeres 25, 26 are preferably provided in a positional relationship as shown in a) and (b).

Needless to say, it is necessary to blow a relatively large amount of gas for both bottom blowing and side blowing to perform strong stirring, but the amount of blowing gas is determined according to the molten metal amount, the molten metal depth, and the like. The side-blown gas performs the function of stirring the slag forming the secondary combustion region in addition to the function of diffusing the molten metal as described above, which will be described later. The side-blown gas and bottom-blown gas used in the present invention are limited to inert gas (N ₂ , Ar, etc.), CO or process gas, and O ₂
Is not used.

This is for the following reasons. First, when oxygen is used as the side-blown gas, there is a basic problem that the reducing action by C in the molten metal scattered for reducing the iron ore is hindered. In addition, when oxygen is used, the temperature of the refractory material rises, causing a problem of wear of the refractory material. In addition, when oxygen is used as the bottom blown gas, a large amount of
CO gas is generated, and the molten metal is agitated excessively. As a result, the splash of the molten metal reaches the secondary combustion region (see FIG. 2), and C in the molten metal reacts with oxygen for secondary combustion to be described later to form secondary gas. Combustion is hindered. In addition, when using oxygen,
Cooling gas (C ₃ H ₈ ) needs to be added because the temperature of refractory such as bottom blowing tuyere rises too much, which also increases the amount of bottom blowing gas and strongly promotes the generation of strong stirring → molten metal splash. Will be. FIG. 4 shows the set OD [= PCO ₂ / (DCO ₂ + O _{2 in} ore + O in carbonaceous material) for the present invention in which N ₂ bottom blowing and the comparative example in which O _{2 was} blown instead of N _{2. 2} + raw material adhering water + O _{2 in} carbon material + (1/2) hydrogen in carbon material)] shows the results of an investigation of the actually measured OD. Secondary combustion is inhibited by O ₂ bottom blowing It is shown that it is. The inert gas such as CO, N ₂ or Ar that is a stirring gas can be used alone or in combination.

In the present invention, high secondary combustion is realized while forming the secondary combustion region mainly in the slag, and thus the secondary combustion region is formed in the slag and the slag is strongly stirred by the side-blown gas. This makes it possible to obtain high heat-receiving efficiency while ensuring high secondary combustion. Therefore,
The oxygen for secondary combustion needs to be blown into the slag so that a secondary combustion region is mainly formed in the slag. Specifically, it is necessary that the height of the upper blowing lance is set to an appropriate level with respect to the slag and the molten metal level. That is, the upper blowing lance 21 can have its nozzle hole height above the slag surface or below the slag surface.
If the height is too high, the secondary combustion region is not formed in the slag, and there is a problem that the heat transfer efficiency is reduced.
If the lance height is too low, the secondary combustion region will not be properly formed. FIG. 5 shows the relationship between the height of the lance tip from the slag surface (forming level) and the heat transfer efficiency. It is shown that if the lance height is too high relative to the slag surface, good heat transfer efficiency cannot be obtained. I have. Further, FIG. 6 shows the relationship between the amount of laterally blown gas and the heat transfer efficiency. It can be seen that good heat transfer efficiency can be obtained by blowing in a large amount of horizontally blown gas and strongly stirring the slag layer. . 5 and 6, the operating condition is 50 capacity.
In the smelting furnace of t, the production rate of hot metal is 28t / hr. In the present invention, since a high heat transfer efficiency is obtained, a high reduction rate can be obtained by increasing the OD as described above. In addition, by increasing the OD, the addition amount of the carbonaceous material (mainly coke) is suppressed low. As a result, the basic unit of the carbon material can be reduced, and most of the P component in the molten metal is carried by the carbon material.
Can be reduced. Further, when the OD becomes high, the vapor desulfurization phenomenon becomes active and the S in the molten metal also decreases. From such a viewpoint, OD is set to 0.5 or more in the present invention. The upper limit of OD is 1.0, but the higher the OD, the more desirable. As described above, a gas with a high OD, that is, a low-calorie gas, is charged with carbonaceous material from the tuyere 29 provided at the upper portion of the preheating preliminary reduction furnace 30, and the gas in the preheating preliminary reduction furnace is charged. To reduce the OD of this gas to less than 0.5 and efficiently pre-reduce iron ore.

Next, Table 1 shows specific numerical values based on this embodiment. This table was obtained under the same operating conditions as when the above-mentioned FIGS. 5 and 6 were obtained, and compares the case where the exhaust gas is reformed and the case where the exhaust gas is not reformed. As shown in this table, when gas reforming was performed, the OD of the exhaust gas was lower and the temperature was lower than when gas reforming was not performed.

EFFECTS OF THE INVENTION According to the present invention, oxygen is blown directly into the slag layer from the oxygen nozzle for decarburization of the top-blown oxygen lance and for secondary combustion, and also to the furnace wall and bottom of the smelting furnace. Gas was blown in from the provided tuyere and vigorously stirred, and the oxidation degree of the gas generated in the smelting furnace was adjusted to 0.5 to 1.0 to raise the temperature of the gas to 400 ° C to 130 ° C.
Since the temperature is set to 0 ° C. and steam or carbonaceous material is charged into the preheating pre-reduction furnace, it is possible to improve the heat deposition efficiency of the smelting reduction apparatus, iron productivity, and obtain high pre-reduction. Since the degree of oxidation of the gas supplied to the smelting furnace can be adjusted independently of the operating state of the smelting furnace, the degree of freedom in operating the smelting furnace is greatly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a process of a smelting reduction apparatus used in the smelting reduction method of the present invention, FIG. 2 is a schematic diagram showing a gas flow in a smelting furnace in FIG. 1, and FIG. Explanatory diagram showing the positional relationship between the mouth and the bottom blowing tuyere, FIG. 4 is a graph showing the measured OD with respect to the set OD, FIG. 5 is a graph showing the relationship between the lance height and the heat transfer efficiency, and FIG. It is a graph which shows the relationship between the amount of blown gas, and the heat deposition efficiency. 10 ... Smelting furnace, 11 ... Iron bath, 12 ... Slag layer, 13 ... First chute, 14 ... Second chute, 15 ... Gas conduit, 21 ... Oxygen lance, 22,23 ...... Nozzle, 25, 26 ...... Tuyere, 27 ...... Pressurizer, 29 …… Inlet, 30 …… Preheating pre-reduction furnace, 31 …… Dust remover, 35 …… Separator, 41 …… Switching valve , 42… .Close valve.

 ─────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Kawakami 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Osamu Terada 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Takeshi Inoue, Inspector, Inc.

Claims (5)

(57) [Claims] An ore preheated and pre-reduced by a preheating pre-reduction furnace is charged into a smelting furnace together with a carbon material and a slag-making agent.
A smelting reduction method in which an inert gas, CO, or process gas is blown from the bottom-blown tuyeres and side-blown tuyeres. (1) The tip is removed from the top-blown oxygen lance at the level near the upper surface or the lower surface of the slag layer. Blowing oxygen for charcoal and oxygen for secondary combustion, (2) at least part of the gas flow from the side blowing tuyere hits the molten metal portion raised by the gas blown from the bottom blowing tuyere, 3) The oxidation degree of the gas in the smelting furnace [= (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ )] is from 0.5 to
1.0 The temperature is set to 400 ° C. to 1300 ° C., (4) A gas reforming material is charged into the preheating pre-reduction furnace, the gas introduced into the preheating pre-reduction furnace is reformed, and the degree of oxidation is reduced. A smelting reduction method characterized in that it is less than 0.5. 2. The smelting reduction method according to claim 1, wherein the gas modifying material charged into the preheating pre-reduction furnace is a lump or granular carbon material. 3. The gas reforming material to be charged into the preheating pre-reduction furnace is a carbonaceous material in powder form.
The smelting reduction method according to 1. 4. A gas reforming material to be charged into the preheating pre-reduction furnace is a carbonaceous material, and a temperature near a carbon material inlet provided in the preheating pre-reduction furnace is set at 300 ° C. to 1200 ° C. The smelting reduction method according to any one of claims 1 to 3. 5. The method according to claim 1, wherein an oxygen-containing gas, an inert gas, or a process gas is blown from a nozzle provided at or near the carbon material charging inlet when the carbon material is supplied. The smelting reduction method described in.