JPH0447004B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for melting and reducing iron ore without using a blast furnace process.

(Conventional technology) As a process to obtain molten iron by reducing iron ore,
The most commonly used process is the blast furnace method.

In this blast furnace iron ore reduction process, a large amount of coke is used as a heat source and reducing agent. The coke supplied to the blast furnace is manufactured by carbonizing highly coking coal, as it needs to have enough physical strength to not be destroyed by the load of the contents of the furnace, which can reach tens of meters in height. However, there is a problem in that the supply of strong coking coal is likely to be unstable, since the amount of hard coking coal is small worldwide and the availability is unevenly distributed in different regions. In addition, it requires huge equipment (coke oven) and a great deal of labor to carbonize the coal.

Further, iron ore supplied to the blast furnace is usually sintered and charged into the blast furnace as sintered ore. However, the iron ore sintering process requires a large amount of energy and generates large amounts of sulfur oxides and nitrogen oxides in the process of obtaining sintered ore, which requires high costs to process. There is.

Therefore, a simple iron ore reduction process that does not involve a blast furnace is strongly desired.

Various studies are underway to meet this demand.
For example, there is a method in which iron ore is reduced to metallic iron in a shaft furnace or a retard kiln, and then this metallic iron is melted in an electric furnace. There is a drawback in terms of cost. In our country, electricity is the most expensive energy, and processes that use electricity as the main heat source are extremely disadvantageous.

Therefore, it is important to create a process that uses cheap primary energy such as coal or coke as a heat source.

On the other hand, a smelting reduction process in which iron ore is reduced while being heated and melted has also been studied. In the melting and reduction process, how to protect the refractory material inside the furnace from the highly corrosive molten iron oxide, and
How to supply the large amount of energy necessary for reduction and dissolution is the key to whether or not the process can be carried out.

One of the melting reduction processes is the rotary furnace method disclosed in Japanese Patent Publication No. 13043/1973, for example. Although the rotary furnace method was proposed from the viewpoint of increasing thermal efficiency, it is difficult to increase its size due to the mechanical constraints of rotating a high-temperature reaction vessel.

Further, as one of the melting and reduction processes for metal oxides, there is a method that uses electric power as a heating source. For example, processes using arc furnaces or plasma. These processes that use electricity as a heat source are
Although it has the advantage of being able to heat in a reducing atmosphere, it is disadvantageous in terms of cost because it uses electricity as a heat source.

On the other hand, in the melt reduction process that directly utilizes the heat of combustion of carbonaceous materials such as coal, it is difficult to achieve both the oxidation reaction of burning the carbonaceous materials and the reduction reaction of reducing metal oxides, such as iron ore. can be,
So far, there have been no success stories.

In recent years, with the progress of bottom blowing converter technology, as disclosed in Japanese Patent Publication No. 56-8085, by placing the combustion point in the molten iron bath,
Since it improves heat transfer efficiency and reduces erosion of refractories, it has become a possibility for processing that does not require reduction, such as melting scrap.

However, even with this converter technology,
It has not yet been possible to charge a metal oxide, such as iron ore, into a reaction vessel and perform melt reduction.

The technical issues in the process of melting and reducing metal oxides such as iron ore, which directly utilizes the heat of combustion of coal and other carbonaceous materials, are as follows: Second, how to charge the reducing agent into the smelting reduction furnace. Third, how to input heat into the smelting reduction furnace.

U.S. Pat. No. 3,985,544 discloses that in a fluidized bed, carbonaceous material is gasified by a partial combustion reaction with oxygen and turned into a char, and the gas generated in this reaction is charged together with the carbonaceous material. A process for reducing iron ore is disclosed. In the process disclosed in U.S. Pat. No. 3,985,544, ore pre-reduced by a reaction in a fluidized bed and chars obtained by partial combustion of carbonaceous material are prepared in the form of powder and hollow. The pre-reduced ore is charged into an electric furnace through an arc electrode, and while the pre-reduced ore is melted, a reduction reaction proceeds using the char as a reducing agent.

This prior art is excellent in that it can simultaneously perform preliminary reduction of metal oxides such as iron ore and obtain the char necessary for melt reduction.

However, melting and reduction requires electricity as a heat source, and the process has not moved beyond the realm of electricity-based processes.

(Problems to be Solved by the Invention) This invention solves the problem that, when obtaining molten iron from iron ore, a process of carbonizing coal (coke manufacturing process) and a process of converting iron ore into burnt ore, such as in a blast furnace process, are required. The technical challenge is to create a process that does not require electricity and does not require electricity as a heat source.

(Means for Solving the Problems) The gist of the present invention is to charge iron ore, coal, and oxygen-containing gas into a fluidized bed reactor and allow the reaction to proceed to produce a preliminary reduction product of the ore and char. The briquettes obtained by mixing and agglomerating this pre-reduced ore, coal, and coal supplied from another system are charged into a top-bottom blowing converter type reaction vessel, and the pre-reduced ore is melted and reduced. A method for melting and reducing iron ore is characterized by the following.

This invention will be explained in detail below.

In the process of this invention, the pre-reduced ore produced in the fluidized bed reactor is melted and melted after reaching the interface between carbon-containing molten iron and slag in the smelting reduction furnace (top-bottom blown converter type reaction vessel). The key is to react.

Therefore, in this invention, a process of agglomerating the prereduced ore produced in the fluidized bed reactor together with char and other carbon materials is essential.

That is, the important point is how to bring the granular semi-reduced ore pre-reduced in the fluidized bed reactor to the reaction side with carbon in the iron bath. In order to bring the granular semi-reduced ore to the reaction side,
When trying to blow into the iron bath from the bottom blowing tuyere, approximately 1.2 to 1.3 tons of semi-reduced ore must be charged through the bottom blowing tuyere for each ton of molten iron produced, and the charging equipment is It gets complicated. Therefore, the semi-reduced ore is not melted in the slag layer in the smelting reduction furnace, but is made into lumps of a size that allows it to reach the interface between the iron bath and slag, react with carbon in the iron bath, and proceed with reduction. There is a need.

When agglomerating the semi-reduced ore from the fluidized bed reactor, the present inventors mixed the charred coal that had been used for preliminary reduction of iron ore in the fluidized bed reactor, and added it to the smelting reduction furnace. At the same time, we focused on incorporating a portion of the coal to be charged into the briquette, and at the same time making the coal itself function as a binder for agglomerating semi-reduced ore.

Furthermore, in the melting reduction furnace, carbonaceous material is suspended in the slag to promote the reduction reaction and reduce damage to the refractories.

Unlike the conventional technology using an electric furnace, as in the present invention, the heat source for the melting reduction furnace is the combustion of carbonaceous material and gas generated in the furnace, so the slag on the iron bath is exposed to an oxidizing atmosphere. The FeO concentration in the slag increases, which eventually leads to corrosion of the refractories, but in the present invention, this problem is solved by suspending carbonaceous material in the slag.

In the present invention, iron ore pre-reduced in a fluidized bed reactor is agglomerated together with simultaneously obtained char and carbon material supplied from another system, and then charged into a smelting reduction furnace. After this agglomerate is charged into the furnace, it does not melt immediately, but passes through the slag layer and melts when it reaches the interface between the molten iron and slag, where the carbon in the molten iron converts it into iron ore. of the pre-reduced product is reduced. Therefore, even when the pre-reduced ore (iron oxide) supply rate is high, the concentration of FeO in the slag can be kept low, and damage to the refractories of the smelting reduction furnace can be maintained at a low level while maintaining high productivity. It has become possible to perform melt reduction at lower temperatures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in more detail below with reference to the drawings showing an apparatus for carrying out the invention.

In Fig. 1, 1 is an ore preheating furnace, and 2 is a fluidized bed reactor, which pre-reduces granular iron ore and separates the volatile content of granular coal charged at the same time. It functions to make the team more attractive.

3 is an agglomeration device to which, for example, a briquette machine is applied, which kneads and agglomerates the prereduced ore from the fluidized bed reactor, the char, and the carbon material supplied from other systems.

4 is a melting reduction furnace, and in the case of this invention, a top-bottom blowing converter type reaction vessel is applied. The melting reduction furnace 4 includes a lance 5 for top-blowing oxygen, a tuyere 6 for bottom-blowing oxygen and, if necessary, a gas for stirring powdered carbonaceous material, an iron bath, and slag, and agglomerates (briquettes). 17) is provided with a charging device 7 for charging a solid charge such as 17) into the smelting reduction furnace.

(Operation) Next, the operation when melting and reducing iron ore using the apparatus shown in FIG. 1 will be explained.

Iron ore 11 and limestone 12 are stored in ore preheating furnace 1
In the step, the limestone (CaCO ₃ ) is heated by the heat of combustion reaction between the coal 13 and the air 21 and is supplied to the fluidized bed reactor 1 as quicklime (CaO).
Note that lime-containing minerals such as dolomite can also be used instead of limestone. In particular, when a magnesia-based furnace material is used in the smelting reduction furnace described later, magnesia-containing minerals such as dolomite are reasonable.

In the fluidized bed reactor 2, coal 13 and oxygen or oxygen-containing gas 22 are blown into the preliminary ore and quicklime in a fluidized state.

Then, the injected coal 13 is thermally decomposed by partial combustion due to heat exchange with the preheated ore and reaction with oxygen, generating reducing gas and becoming coal 15.

The amount of char produced is determined by the fluidized bed reactor (pre-reduction furnace).
From the perspective of preventing sintering trouble in
Although ~10% is appropriate, it can be increased to about 60% when a chia is used as the heat source of the melting reduction furnace. The amount of chir produced in excess of 60% is undesirable because it increases the heat load in the fluidized bed reactor.

On the other hand, in the fluidized bed reactor 2, the gas generated in the smelting reduction furnace 4 or the reducing gas 23 obtained by decarbonizing this gas is exchanged with the fuel gas 24 from the fluidized bed reactor 2. The temperature is raised to 700 to 900°C by a gas pump and then blown into the tank.

The reducing gas 23 blown into the fluidized bed reactor 2 is
It is mixed with reducing gas generated by thermal decomposition of coal 13 to reduce the high temperature granular iron ore in a fluidized state to produce pre-reduced ore (semi-reduced ore) 14.

The preliminary reduction rate of iron ore is selected in the range of 0.5 to 0.8, which is advantageous for the reaction efficiency in the fluidized bed reactor (pre-reduction furnace) and the fuel utilization rate of the entire smelting reduction system of the present invention. Preferably, it is in the range of 0.6 to 0.7.

In addition, quicklime 1 generated in the ore preheating furnace 1
6 is charged into the fluidized bed reactor 2 together with the preheated ore, and after desulfurizing the gas in the fluidized bed reaction 2, it is discharged from the fluidized bed reducing furnace 2 together with the semi-reduced ore 14 and the chia 15.

The amount of quicklime is determined by the slag basicity (CaO/
SiO ₂ ) is determined to be 1.1 to 1.7, taking into account gangue components and amounts in iron ore and carbonaceous materials.

The thus obtained semi-reduced ore 14, char 15 and quicklime 16 are mixed with carbonaceous materials from outside the system such as coal and coke necessary for thermal calculation in the smelting reduction furnace 4, and are then kneaded into agglomerates. After being molded into briquettes 17 by a briquetting device 3, for example, a briquetting machine, the briquettes are charged into a smelting reduction furnace 4 by a charging device 7.

In the melting reduction furnace 4, oxygen 2 is supplied from the top blowing lance 5.
2 is blown toward the bath, and at the same time, oxygen and a carbonaceous material such as coal are blown into the bath from the bottom blowing tuyere 6. Then, the carbon material contained in the supplied briquette 17, the carbon material blown together with oxygen from the bottom blowing tuyere 6, or the carbon material such as coke 18 supplied from the charging device 7, and the top blowing lance 5. A large amount of heat is generated by the reaction with oxygen supplied by the gas.
This large amount of heat melts the semi-reduced ore 14 in the briquette 17, and the reduction progresses to form molten iron 19.

On the other hand, the gangue in the semi-reduced ore 14 reacts with the carbonaceous material and the quicklime 16 to generate slag 20, which is stored in the smelting reduction furnace 4. Since the slag 20 thus increases in the melting reduction furnace 4 over time, it is discharged out of the furnace intermittently or continuously.

This invention agglomerates the product of the preliminary reduction process in the fluidized bed reactor 2, and melts and reacts it preferentially at or near the interface between the molten iron 19 and the slag 20 in the smelting reduction furnace 4. This method is characterized by achieving an unprecedentedly high production rate and allowing both the oxidation reaction of the carbonaceous material and the reduction reaction of the semi-reduced ore 14 to proceed, and this point will be further explained.

The present inventors melted and reduced iron oxide in a melting furnace containing molten iron containing carbon and slag in which coke was suspended above the molten iron, as described later in the embodiment section of the present invention. In this process, it has been found that the reduction rate is higher when iron oxide is supplied in an agglomerated state than in granular form as the form of supply of iron oxide to the smelting reduction furnace.

As a result of research involving experiments, it was found that the lumpy iron oxide supplied from the top of the slag in the smelting reduction furnace reached the interface between the slag and molten iron without dissolving into the slag.

The reduction reaction of molten iron oxide with carbon usually involves 2
A possible case is a street.

FeOx + XCsolid = Fe + XCO ... (1) FeOx + XCiron = Fe + It shows reduction due to contained carbon.

FIG. 2 shows the progress of reduction of molten iron oxide by solid carbon and carbon in molten iron.

In Figure 2, curve A shows the progress of reduction of iron oxide by graphite, that is, solid carbon, which constitutes the crucible, and curve B shows the progress of reduction of iron oxide by carbon-saturated molten iron. It shows.

From Figure 2, in the case of the reduction reaction of iron oxide with solid carbon (curve A), the initial reduction rate is much slower than in the case of the reduction reaction of iron oxide with carbon-saturated molten iron (curve B). It can be seen that after a certain amount of time has elapsed, the iron oxide is reduced to produce molten iron, and the reduction rate becomes faster as it approaches the state of curve B, where reduction by carbon-saturated molten iron progresses.

In this way, the melting reduction rate of iron oxide is often due to the carbon in the molten iron, so in order to improve the productivity of the reactor, it is advantageous to have a process in which iron oxide and molten iron containing carbon are brought into direct contact. It is clear that

On the other hand, when reduced iron pellets are fed into molten slag and melted, the temperature of the fed pellets is low, so a solidified film of slag is formed on the surface.
After a certain amount of time passes and the solidified slag film re-dissolves, the pellet itself begins to dissolve.

Figure 3 shows the change over time in the thickness of the solidified slag film when reduced pellets with a diameter of about 20 mm were immersed in molten slag at 1400°C.

In the case of Figure 3, the solidified film of slag on the surface of the pellet disappears, and it takes about 30 minutes for the pellet to start dissolving.
It turns out that it takes a minute.

In the iron ore smelting reduction process of this invention, 200 to 300 kg of slag is produced per ton of molten iron produced, and this slag is mainly composed of SiO ₂ -Al ₂ O ₃
- Consists of CaO.

Generally, the reaction rate of slag components is proportional to the concentration of the components involved in the reaction.

When the iron ore supplied to the smelting reduction furnace is dissolved into slag, the iron content is diluted into the slag, which is disadvantageous in terms of reaction rate.

The present invention utilizes the fact that the smaller the specific surface area of iron ore agglomerated with chir etc., the longer it takes to dissolve into slag.
The iron ore supplied to the smelting reduction furnace reaches the interface of the slag molten iron without being dissolved in the slag, where it comes into contact with the iron bath and melts and reacts, resulting in a second
The high reaction rate shown in the figure is achieved.

In order to create such a state, it is necessary to control the sedimentation property of the agglomerated charge in the slag in the smelting reduction furnace and the time at which it starts dissolving into the slag. Therefore, when agglomerating the semi-reduced ore 14, the coal 15, and the coal 13, the conditions must be determined with the following points in mind.

In order for the agglomerates (referred to as briquettes for simplicity) thrown into the slag being stirred by gas blowing from the bottom blowing tuyere 6 to settle without floating in the slag, it is necessary to It must have specific gravity. The lower limit of the size of the briquette 17 is regulated from the viewpoints of reducing the specific surface area of the briquette 17 and controlling the rate of dissolution of the briquette into the slag 20, which has formed a solidified slag film due to the temperature difference with the molten slag.

Furthermore, since the rate of reduction of iron oxide is more advantageous in the molten state, increasing the briquette size too much is disadvantageous because it lengthens the melting time. Therefore, an upper limit is defined from this aspect.

These briquette size conditions are also related to heating properties such as heat capacity and thermal conductivity, so
It also depends on the ingredients of the briquette and the packing density.

On the other hand, the conditions on the slag side in the smelting reduction furnace include the temperature, other physical properties related to heat transfer characteristics such as the melting point and heat capacity of the slag, and more important factors such as the thickness of the slag layer and the reaction process. There are factors related to the settleability of briquettes, such as the apparent density, which is reduced due to air bubbles generated in the briquette, and the intensity of agitation.

As described above, it is difficult to generalize the conditions for allowing the briquettes to reach the slag-metal interface without melting in the smelting reduction furnace. The briquette size is determined based on the production rate of molten iron, the required amount of gas to be generated from the smelting reduction furnace, the preliminary reduction rate of iron ore determined from the heat balance in the fluidized bed reactor, and the required amount of carbon material. Determine the composition (amount of iron ore, amount of carbonaceous material, amount of quicklime), and further consider the amount of bottom-blown oxygen, the stirring strength determined by the amount of stirring gas, and the thickness of the slag layer.

As a guideline for briquette size, use Stokes' terminal velocity equation for particles in a fluid. where: s: Viscosity of slag [Kg/m・sec] u _n : Speed of slag being stirred [m/sec] 〓g: Density of briquette [Kg/m ³ ] 〓s: Viscosity of slag during forming Apparent density [Kg/m ³ ] Dp: Limit size of briquette that flows equally as slag [m] Since the size of briquette that flows equally as slag is determined, it is sufficient to select a particle size larger than this. .

According to the experience of the present inventors, a briquette size of 10 to 50 mm in diameter gave good results.

In actual operation, a part of the iron ore is dissolved into slag, and the FeO concentration in the slag becomes high, especially when the charging speed of the briquettes to the smelting reduction furnace is high. In such a case, the FeO concentration is lowered by suspending coke or char produced in a fluidized bed reactor in slag and proceeding reduction with solid carbon in parallel.

On the other hand, carbon may be supplied to the iron bath by charging carbon material from the top, but an effective method is to blow it into the iron bath along with oxygen from the bottom blowing tuyere.

FIG. 4 shows the carbon dissolution rate versus the coke injection rate when coke is blown into the iron bath from the bottom blowing tuyere. As is clear from this figure, sufficient carbon can be supplied by blowing coke from the bottom blowing tuyere.

(Example) Using a high frequency melting furnace with a rated amount of molten metal of 100 kg,
Three types of raw materials were melted and reduced: iron oxide powder, iron oxide pellets, semi-reduced ore obtained from the fluidized bed reactor shown in FIG. 1, char, and briquettes obtained by agglomerating quicklime.

For melt reduction using iron oxide powder (iron ore powder) as a raw material, 60 kg of carbon-saturated iron is heated in the aforementioned high-frequency melting furnace.
CaO: 45%, SiO ₂ : 35%, Al ₂ O ₃ : 10%,
Melting reduction proceeded in the presence of a slag consisting of 10% MgO. The thickness of the slag layer when left still was 40 mm. Coke grains (particle size: approx. 10 mm) are put into the slurlag, and when the temperature reaches 1500℃, iron ore (particle size:
0.075 to 2 mm) to increase the iron concentration in the slag.
It was set to 10%.

The slag was sampled at predetermined time intervals while maintaining a constant temperature, and iron was analyzed to investigate the decrease in iron concentration in the slag as the reduction progressed, thereby determining the reaction rate.

In FIG. 5, the reaction rate constants are shown as a function of the amount of coke present in the slag.

Figure 5 shows that the reduction rate increases as the amount of coke increases, and that the reaction proceeds at a considerable rate even when the amount of coke is zero, indicating that the reduction reaction is carried out by the carbon in the iron bath. I understand that.

The reaction rate when iron oxide (iron ore powder) pellets are used as a raw material in melt reduction is also shown in broken lines in FIG.

As is clear from FIG. 5, when iron oxide pellets are used as the raw material for melt reduction, the reaction rate is much higher than when iron oxide powder is used as the raw material.

As mentioned above, when iron oxide pellets are used as a raw material, the pellets dissolve near the interface between the iron bath and the slag due to the difference in sedimentation and dissolution rate with respect to the slag, and this area locally becomes iron oxide. This is because the part has a high concentration and is advantageous for the reduction reaction. Moreover, since the above-mentioned areas with high iron oxide concentration were localized, there was no adverse effect on the furnace wall refractory material.

Next, semi-reduced ore obtained from the fluidized bed reactor shown in Fig. 1, char (mixing ratio 10% by weight), quicklime,
The relationship between the reaction rate constant and the amount of coke in the slag when coal kneaded and agglomerated at high temperature is used as a raw material in melt reduction is also shown as point A in FIG.

It can be seen that the reducing property is further improved due to the reaction promoting effect of incorporating carbonaceous material into the raw material briquette.

In the process of the present invention, the semi-reduced ore and char obtained from the fluidized bed reactor are
Because the temperature is ~800°C, it is possible to mix materials that exhibit fluidity at high temperatures, such as coal, as a binder and agglomerate them in hot water.In this case, there is no need to add a binder separately, which reduces costs. It is not only advantageous in terms of energy efficiency but also in terms of energy utilization efficiency from the perspective of utilizing the sensible heat of semi-reduced ore.

In this example, when agglomerating the raw materials, the mixing ratio of chir was 10% by weight.
In order to ensure reaction and melting in a smelting reduction furnace, for example, if the type of coal has a volatile component of about 30%, about 500 kg of additional coal is required as a reducing agent and heat source.

In a smelting reduction furnace, if powdered coal is fed from the top, it will scatter due to the gas generated in the furnace, making it extremely difficult to charge it into the furnace, but it can be obtained from a fluidized bed reactor. If it is agglomerated together with semi-reduced ore and char and charged as briquettes, charging becomes extremely easy.

When agglomerating the raw material charged to the smelting reduction furnace,
Although the amount of chir was set at 10% by weight to prevent sintering in the fluidized bed reactor and for other reasons, from the standpoint of heat balance in the smelting reduction furnace, an increase in the amount of chir leads to a decrease in the amount of coal required. Since chir is advantageous in terms of reaction, the amount of chir should be as large as possible within the allowable range of briquette moldability and cost for forming chir.

(Effects of the Invention) Since the present invention is configured and operated as described above, the present invention can be used in a coal carbonization process for coke production, a process for sintering iron ore,
Furthermore, molten iron can be produced from iron ore and coal with extremely compact equipment and with high equipment productivity and labor productivity without requiring heating power.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram showing the overall picture of the smelting reduction method of the present invention, Figure 2 is a diagram showing the transition of iron oxide melting and reduction by solid carbon and carbon in molten iron, and Figure 3 is a diagram showing the transition of iron oxide immersed in molten slag. Figure 4 shows the relationship between the dissolution rate of carbon in molten iron and the coke injection rate when coke is bottom-blown, and Figure 5 shows the relationship between the melting rate of carbon and the coke injection rate when coke is bottom blown. FIG. 3 is a diagram showing changes in the reduction rate when the stone supply format is changed to powder, pellet, and briquette with carbonaceous material. 1...Ore preheating furnace, 2...Fluidized bed reactor, 3...
...Agglomeration equipment, 4...Smelting reduction furnace (top-bottom blown converter type reaction vessel), 5...Top-blowing lance, 6...Bottom-blowing tuyere, 7...Charging device, 11...Iron ore , 12...
Limestone, 13... Coal, 14... Pre-reduced ore (semi-reduced ore), 15... Cheer, 16... Quicklime, 17... Agglomerate (briquette), 18...
Coke, 19...molten iron, 20...slag, 21
...Air, 2...Oxygen-containing gas, 23...Reducing gas, 24...Fuel gas.

Claims (1)

[Claims] 1 Iron ore, coal, and oxygen-containing gas are charged into a fluidized bed reactor and the reaction proceeds to obtain a pre-reduced product of iron ore and char, which is supplied from the pre-reduced ore and char as well as from another system. A method for melting and reducing iron ore, which comprises charging briquettes obtained by mixing and agglomerating iron ore with coal into a top-bottom blowing converter type reaction vessel, and melting and reducing the pre-reduced ore.