JPH01205019A - Smelting reduction method - Google Patents

Abstract

PURPOSE:To execute smelting reduction of ore at good workability and high productivity by charging preheated and pre-reduced ore together with carbonic material and slag making material into a smelting furnace, blowing oxygen into slag layer intensively stirred and reforming exhaust gas from the smelting furnace. CONSTITUTION:The ore preheated and pre-reduced by flowing the exhaust gas from the smelting furnace 10 in a preheating and pre-reducing furnace 30 is charged into the smelting furnace 10 together with the carbonic material and slag making material. To the iron bath 11 and slag layer 12 formed in there, inert gas, CO or process gas is blown and stirred, to execute the smelting reduction. Then, the oxygen for decarbonizing and secondary combustion is blown into the slag layer 12 from a top blowing oxygen lance 21. Further, at least a part of gas from a side blowing tuyere 25 is blown so as to hit to the molten metal part risen with the above gas from a bottom blowing tuyere 26. Oxidizing degree (H2O+CO2)/(H2+H2O+CO+CO2) of the gas generated with this is made to 0.5-1.0 and temp. is made to 400-1,200 deg.C, to improve the heat transfer efficiency. Further, the carbonic material is charged into the preheating and pre-reducing furnace 30, and the oxidizing degree of the introducing gas is reformed into <0.5, to obtain high preheating and pre-reducing ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a smelting reduction method in which iron ore is reduced in a molten state in a converter-type smelting furnace using carbonaceous materials as fuel and reducing material.

[Conventional technology] The smelting reduction method is an alternative to the blast furnace pig iron making method, and has been developed in recent years to overcome the drawbacks of the blast furnace iron making method, such as the high cost of constructing a blast furnace and the need for a large area. It is what was done. In the conventional smelting reduction method, iron ore is pre-reduced with exhaust gas from a smelting furnace and charged into the smelting furnace together with carbonaceous material and slag-forming agent, and oxygen gas or stirring gas is added to the smelting furnace. It is blown into the furnace. In this way, the carbonaceous material is dissolved in the previously charged hot metal, and the carbon in 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 molten pig iron is secondary combusted by the oxygen gas injected in excess and becomes CO2 gas. The sensible heat of this CO2 gas is transferred to the slag or forming iron granules covering the hot metal, and then to the hot metal. In this way, 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 reduced to 60%.
Therefore, the exhaust gas from the smelting furnace uses a large amount of highly reducing gas with a low oxidation degree. (For example, Japanese Patent Publication No. 61-43406) [Problem to be solved by the invention] However, in order to reduce the reduction process in the smelting furnace, the preliminary reduction rate of iron ore before being charged into the smelting furnace is reduced to 30%.
or higher, the oxidation degree of the exhaust gas from the smelting furnace [(H
20+CO2)/(H2+H20+CO+CO2), hereinafter simply abbreviated as OD]. This will inevitably increase the amount of exhaust gas (
For example, Japanese Patent Publication No. 61-43406), this naturally leads to an increase in manufacturing costs. In addition, in order to obtain a high pre-reduction rate, exhaust gas with a low OD is required as described above, and the residence time of the iron ore in the pre-reduction furnace is lengthened, resulting in gA of the pre-reduced iron ore. It is difficult to balance the charging cycle of the hot metal into the furnace and the tapping cycle of the produced hot metal. This inevitably greatly limits the flexibility of the smelting furnace. In addition, in order to improve the reduction processing speed of iron ore and increase the amount of iron ore reduced per unit weight of charged coal material, a method of secondary combustion of CO gas in the furnace and use of the heat has been considered. 02 for secondary combustion from the upper wall of the furnace.
A method of blowing gas is used. However, conventionally 2
Although the exhaust gas temperature increases when the secondary combustion ratio is increased, there is no technology to transfer the sensible heat of the exhaust gas to the molten metal, and as a result, the heat transfer efficiency decreases and high-temperature exhaust gas must be discharged. There is a major problem in that such high-temperature exhaust gas severely wears out the refractories on the furnace inner wall, and the general idea has been that the degree of oxidation of the exhaust gas cannot be increased very much for this reason.

As described in detail later, the present invention succeeded in increasing the degree of oxidation of exhaust gas by promoting the reduction reaction and secondary combustion of iron ore in the smelting furnace. When the exhaust gas is introduced into the preheating pre-reduction furnace, there is a possibility that the iron ore cannot be reduced at a sufficiently high reduction rate for practical use.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide a smelting reduction method with good operability and high productivity, which increases the efficiency of heat transfer to hot metal or slag and provides a high preheating prereduction rate.

[Means and effects for solving the problem] 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 developed a mechanism of smelting reduction and a specific example corresponding thereto. As a result, the following facts were discovered.

■As mentioned above, the basic idea in the past was that it was not possible to significantly increase the secondary combustion ratio due to technical limitations in improving heat transfer efficiency and the wear and tear of refractories. By blowing oxygen into the slag and stirring the slag strongly, heat transfer efficiency can be effectively increased while ensuring high secondary combustion. Due to such high secondary combustion 3fF, high heat transfer efficiency, the temperature of the slag and the iron ore in the slag becomes high, and the reduction rate of the iron ore by 9- (C in the molten metal) expressed as Fe203 +3C-2Fe+3CO increases. can be effectively increased.

(2) In conventional methods, there are examples in which bottom blowing of oxygen is carried out during one period or all nine periods of reduction treatment, but such bottom blowing of oxygen is harmful to 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 strongly stirred.As a result, the molten metal splash reaches the secondary combustion zone, and the C contained in this molten metal splash reacts with oxygen. This inhibits secondary combustion. Therefore, it is necessary to avoid bottom-blowing oxygen during part or all of the reduction period.

Based on this knowledge, the present invention defines the following conditions, thereby making it possible to perform 31-element processing at high processing speed.

(b) By combining bottom blowing and side blowing of stirring gas,
The molten metal is diffused in a region where the iron ore in the slag is present, and the reduction action of the iron ore by C in the molten metal is promoted.

(b) Oxygen for secondary combustion is blown separately from oxygen for decarburization so as to obtain an oxidation degree of a predetermined level or higher. Then, this secondary combustion oxygen is blown into the slag from the top blowing lance to form a secondary combustion region in the slag, and the slag is strongly agitated by the side blowing gas, and the heat generated by the secondary combustion is transferred to the iron ore. heat it up.

(c) 2 due to reduction action by C in the molten metal and top-blown oxygen
In order to prevent the subsequent combustion from being inhibited, CO or an inert gas is used as the side-blown gas and bottom-blown gas, and oxygen is not used.

In addition, the smelting reduction method according to the present invention injects powdered carbonaceous material or steam as a gas reforming material through the tuyere provided in the preheating pre-reduction furnace to reform the gas generated in the furnace. A high preliminary reduction rate can be obtained, and at the same time a significant amount of gas can be recovered. Note that the gas temperature in the smelting furnace is 400°C to 1300°C, but if the temperature is less than 400°C, the effect of preheating will be poor considering the temperature drop until the exhaust gas is introduced into the preheating pre-reduction furnace. Not only cannot be expected, but there is a risk of the tar trouble described below occurring, and if the temperature exceeds 1300°C, problems will arise with the fire resistance of the equipment. That is, in the smelting reduction method according to the present invention, ore that has been preheated and prereduced in a preheating and prereducing furnace is charged into a smelting furnace together with carbonaceous material and a slag-forming agent, and the ore is inertly removed from the bottom blowing tuyere and the side blowing tuyere. This is a smelting reduction method in which gas CO or process gas is blown into the slag layer. 2) At least a 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, and (3) the oxidation degree of the gas in the smelting furnace [= (H20+COz)/(H2+H20+CO+C
O2)] from 0.5 to 1.0 and the temperature from 400℃ to 1.
200° C., and (4) charging a gas reforming material into the preheating pre-reduction furnace to reform the gas introduced into the preheating pre-reduction furnace so that its degree of oxidation is less than 0.5. It is characterized by

[Example] Embodiments of the invention will be described with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram of the process used in the melt reduction method of the present invention. Inside the smelting furnace 10 there is an iron bath 11 and a slag layer 1.
A first chute 13 is provided at the top of the smelting furnace, and a first chute 13 is provided at the top of the smelting furnace, and a top-blowing oxygen lance 21 is inserted vertically into the furnace. be done. The lance has a nozzle 22°2 that spouts oxygen for decarburization (DCO2) and oxygen for secondary combustion (PCO2), respectively.
Further, a side blowing tuyere 25 and a bottom blowing tuyere 26 are provided on the side wall or the bottom of the smelting furnace, respectively, for blowing inert gas, CO, or process gas as a stirring gas. Above the smelting furnace IO is the raw material iron ore,
The auxiliary raw materials, such as carbonaceous materials and slag-forming agents, are charged into the smelting furnace by falling naturally from a well-known ordinary raw material supply device (not particularly shown for WJ Ming) or from a preheating pre-reduction furnace 30, which will be explained later. A second chute 14 is provided to discharge the exhaust gas from the smelting furnace, and a flue gas conduit 15 is provided to discharge the flue gas from the smelting furnace. A preheating pre-reducing furnace 30 into which exhaust gas from the furnace is introduced to preheat the iron ore, and a separation device W which receives this exhaust gas and removes fine particles of iron ore contained therein.
35 are provided. A charging port 29 for reforming material is provided in the upper part of the preheating pre-reducing furnace 30 to reform the exhaust gas introduced therein. The iron ore fine grains or powder separated from the separator 35 are mixed with a carrier gas such as Ar or N2, and are pressurized to form the side blowing tuyere 2.
5. In order to blow from the bottom blowing tuyere 26, a pressurizing device 27 is provided as a mixing and pressure feeding means. A melt reduction method using the melt reduction apparatus configured as described above will be explained. Iron ore, which is a raw material, enters the preheating pre-reducing furnace 30 from the above-mentioned supply device, is preheated here, and then is charged into the smelting furnace 10 by falling by gravity from the second chute 14. The carbon material and the slag forming agent are charged into the smelting furnace 10 by falling by gravity from the first chute 13 . In the smelting furnace 10, an iron bath 11 made of molten metal and a slag layer 12 are formed, and the degree of oxidation of the gas generated here is increased by an in-furnace reaction 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 part of the preheating pre-reduction furnace 30 and reformed. questioned. In this case, if the modifying material is carbonaceous material and it is in the form of lumps or granules, it is charged by falling by gravity. In addition, when the carbonaceous material is in powder form, a method of charging it together with a carrier gas is effective because the powdery carbonaceous material is well dispersed and the oxidation degree OD of the gas in the preheating pre-reduction furnace is lowered. When steam is used as a reforming material, it is charged together with heavy or powdered carbon material. In addition, in order to avoid tar problems due to the charged carbon material, the temperature near the carbon material charging port 29 must be 300°C or higher, and depending on the brand of carbon material, the temperature may be 500'C or higher. 1200
If the temperature exceeds ℃, problems arise due to the heat resistance of the preheating pre-reduction furnace. In order to avoid the above-mentioned tar trouble, it may be possible to use char obtained by dry distilling coal to remove its volatile content, but this method increases the carbon material consumption rate and the amount of gas generated, increases the equipment cost for char production, Alternatively, this is not a desirable method because it causes excessive sensible heat in the recovered gas.As mentioned above, the in-furnace gas which has a high oxidation degree due to the in-furnace reaction has an oxidation degree of less than 0.5 in the preheating pre-reduction furnace due to the reforming. The iron ore is efficiently preheated and pre-reduced here. This iron ore is introduced into the smelting furnace through the second chute 14, while the exhaust gas enters the separator 35 where fine or powdered iron ore is separated and then discharged through a normal exhaust gas treatment device. Alternatively, it can be used as a process gas, as a stirring gas blown in through the tuyere 25, 26, or as a carrier gas for powder blowing. Furthermore, this exhaust gas is introduced into the gas conduit 15 and mixed with the exhaust gas from the smelting furnace, and can also be used to adjust the temperature of the gas introduced into the dust removal device 31. The fine grained or powdered iron ore separated by the separator 35 is mixed with plain or powdered coal material and sent to the pressurizer 27, where it is mixed with a carrier gas and then pressurized to form a tuyere. Next, the relationship between the gas blown into the smelting furnace from the tuyere 25 or the tuyere 26 and the reaction within the furnace will be explained in detail with reference to FIGS. 2 to 6. FIG. 2 schematically shows the behavior of the blown gas in FIG. 1. During the reduction process, from the initial stage to the final stage, the top blow lance 21,
Gas is blown into the 0 tuyeres 25 and 26 through the side blowing tuyere 25 and the bottom blowing tuyere 26, and the molten metal is diffused into the slag by the cooperative action of the two, dramatically increasing the reduction rate. As mentioned above, it has the effect of increasing
The present inventors have elucidated the fact that the reduction of iron ore in the slag layer 12 proceeds mostly with C in the molten metal as the reducing substance, and based on this, the molten metal is strongly stirred and the slag N (iron ore is suspended) The idea is to actively diffuse it into the surrounding area) to increase the rate of reduction.

Therefore, in the present invention, stirring gas is supplied from the bottom blowing tuyere 26 to form the raised portion (A) on the molten metal surface, and at the same time, at least a part of the gas flow from the side blowing tuyere 25 is directed to the raised portion of the molten metal. (A>), and this side-blown gas scatters the molten metal in the molten metal protrusion (A) into the slag.The apparent specific gravity of the slag is usually 0.1. ~0.5, while the bulk specific gravity of iron ore is 1-3
Therefore, the iron ore in the slag is concentrated and suspended in the lower region of the slag. When the molten metal protrusions are scattered by side-blown gas as described above, the scattered molten metal diffuses into the lower region of the slag layer 12 where iron ore exists, and the carbon in this diffused molten metal reduces the iron ore, resulting in high The rate of reduction is obtained.

In order to obtain such an effect, it is preferable that the side-blown gas hits the molten metal protrusion (A) as accurately as possible in the vertical and horizontal directions of the smelting furnace. It is preferable to provide the tuyeres 25, 26 in the positional relationship shown in a) and (b).

In addition, it goes without saying that both bottom blowing and side blowing require blowing a relatively large amount of gas and strong stirring.
The amount of blown gas is determined depending on the amount of molten metal, the depth of molten metal, etc. In addition to the above-mentioned molten metal diffusion effect, the side-blown gas also has the effect of stirring the slag in which the secondary combustion region is formed, which will be described later. The side-blown gas and bottom-blown gas used in the present invention are inert gas (N
2, Ar, etc.), CO or process gas,
02 is not used.

This is due to the following reasons. First, when oxygen is used as side blowing gas, C in the molten metal scattered to reduce iron ore is
The basic problem is that it inhibits the reducing action of In addition, when oxygen is used, the temperature of the refractory increases, causing the problem of wear and tear of the refractory. In addition, when oxygen is used as the bottom blowing gas, a large amount of C is generated in the molten metal as mentioned above.
O gas is generated and the molten metal is stirred too strongly, and as a result, the splash of the molten metal reaches the secondary combustion region (see Figure 2), and the C in the molten metal reacts with the oxygen for secondary combustion described later, resulting in secondary combustion. Combustion will be inhibited. In addition, when oxygen is used, the temperature of bottom-blown tuyeres and refractories rises too much, so cooling gas (
It is necessary to add C3H8), which also increases the amount of bottom-blown gas and excessively promotes the occurrence of strong stirring→molten metal splash. Figure 4 shows the set OD[=PCO□/(DCO2+02
+ 02 in carbon material + water adhering to the raw material + 02 in carbon material + (1/2) hydrogen in carbon material)] This shows the results of actually measuring OD for 02 + water adhering to the raw material + (1/2) hydrogen in carbon material), and shows that secondary combustion is inhibited by bottom blowing in 02. It has been shown that Note that stirring gas such as CO and N2. Inert gases such as Ar can be used alone or in combination.

In the present invention, high secondary combustion is realized while forming the secondary combustion region mainly within the slag.In this way, the secondary combustion region is formed within the slag and the slag is strongly agitated by the side-blown gas. By doing so, it is possible to obtain high heat transfer efficiency while ensuring high secondary combustion. Therefore, the secondary combustion oxygen needs to be blown into the slag so that a secondary combustion region is primarily formed within the slag. Specifically, the height of the top blowing lance must be set at an appropriate level relative to the slag and molten metal levels. That is, the nozzle hole height of the top blowing lance 21 can be set above the slag surface or below the slag surface.
If the height is too high, there is a problem that a secondary combustion region is not formed in the slag and the heat transfer efficiency decreases.
Furthermore, if the lance height is too low, the secondary combustion region will not be formed properly. Figure 5 shows the relationship between the height of the lance tip from the slag surface (ohmink level) and heat transfer efficiency, and shows that if the lance height is too high relative to the slag surface, good heat transfer efficiency cannot be obtained. has been done. In addition, Figure 6 shows the relationship between the amount of side-blown gas and heat transfer efficiency, and it can be seen that good heat transfer efficiency can be obtained by blowing a large amount of side-blown gas and stirring the slag layer strongly. . The operating conditions when Figures 5 and 6 were obtained were a capacity of 50
t smelting furnace, the production rate of hot metal is 28 t/hr.
In the present invention, a high heat transfer efficiency can be obtained, so a high reduction rate can be obtained by increasing the OD as described above, but in addition to this, by increasing the OD, the amount of carbon material (mainly coke) added can be kept low. As a result, it is possible to reduce the unit consumption of carbonaceous material, and since most of the P component in the molten metal is brought in by the carbonaceous material, it is possible to reduce the amount of P in the molten metal. Furthermore, when the OD increases, the vaporization desulfurization phenomenon becomes active, and S in the molten metal also decreases. Also from this point of view, in the present invention, the OD is set to 0.5 or more. The upper limit of OD is 1.0, but the higher the OD, the more desirable it is.As described above, the gas with a high OD, that is, low calorie, is passed through the tuyere provided at the upper part of the preheating pre-reduction furnace 30. Charcoal material is charged from No. 29, the gas in the preheating pre-reduction furnace is reformed, and the OD of this gas is reduced to 0.5.
iron ore can be efficiently pre-reduced.

Next, specific numerical values based on this example are listed in Table 1.

This table was obtained under the same operating conditions as in FIGS. 5 and 6, and compares cases where the exhaust gas was reformed and cases where the exhaust gas was not reformed. As shown in this table, it can be seen that when gas reforming is carried out, the OD of the exhaust gas is lower and the temperature thereof is lower than when it is not carried out.

Table 1 [Effects of the Invention] According to the present invention, oxygen is blown directly into the slag layer from the oxygen nozzle for decarburization and secondary combustion of the top-blowing oxygen lance, and the furnace wall of the smelting furnace is Then, gas is blown into the tuyere provided at the bottom of the furnace for strong stirring, the degree of oxidation of the gas generated in the smelting furnace is adjusted to 0.5 to 1.0, and the temperature of the gas is brought to 400°C.
By charging the preheating pre-reduction furnace with steam or carbonaceous material, it is possible to improve the heat transfer efficiency and iron productivity of the smelting reduction equipment and obtain a high pre-reduction rate. Since the degree of oxidation of the gas supplied to the reduction furnace can be adjusted independently of the operational status of the smelting furnace, the degree of freedom in the operation of the smelting furnace is greatly improved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the process of the smelting reduction apparatus used in the smelting reduction method of the present invention, Fig. 2 is a schematic diagram showing the gas flow in the smelting furnace in Fig. 1, and Fig. 3 is a side blowing tuyere. Fig. 4 is a graph showing the measured OD against the set OD, Fig. 5 is a graph showing the relationship between lance height and heat transfer efficiency, and Fig. 6 is a graph showing the relationship between the lance height and the heat transfer efficiency. FIG. 3 is a graph diagram showing the relationship between gas amount and heat transfer efficiency. DESCRIPTION OF SYMBOLS 10... Smelting furnace, 11... Iron bath, 12... Slag layer, 13... First chute, 14... Second chute, 15... Gas conduit, 21...・Oxygen lance, 2
2.23... Nozzle, 25.26... Tuyere, 27.
... Pressure device, 29 ... Charging port, 30 ... Preheater a
Reduction furnace, 31... Dust remover, 35... Separation device, 41
...Switching valve, 42...Closing valve.

Claims (1)

[Scope of Claims] 1) The ore that has been preheated and prereduced in the preheating prereduction furnace is charged into the smelting furnace together with carbon material and slag forming agent, and inert gas is poured from the bottom blowing tuyeres and side blowing tuyeres. This is a smelting reduction method in which , CO, or a process gas is blown into the slag layer. 2) At least a 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, and (3) the oxidation degree of the gas in the smelting furnace [= (H_2O+CO_2)/(H_2+H_2O+C
O+CO_2)] from 0.5 to 1.0 and the temperature to 400
℃ to 1300℃, and (4) charge a gas reforming material into the preheating pre-reduction furnace to reform the gas introduced into the preheating pre-reduction furnace so that its degree of oxidation is less than 0.5. A melt reduction method characterized by the following. 2) The smelting reduction method according to claim 1, wherein the gas reforming material charged into the preheating pre-reduction furnace is lumpy or granular carbonaceous material. 3) The smelting reduction method according to claim 1 or 2, wherein the gas reforming material charged into the preheating pre-reduction furnace is a powdered carbonaceous material. 4) A claim characterized in that the gas reforming material charged into the preheating preliminary reduction furnace is carbonaceous material, and the temperature near the carbonaceous material charging port provided in the preheating preliminary reduction furnace is 300°C to 1200°C. The melting reduction method according to any one of Items 1 to 3. 5) An oxygen-containing gas, an inert gas, or a process gas is blown from a nozzle provided at or near the carbon material charging port when the carbon material is supplied. Melting reduction method.