JPH03277708A - Iron bath smelting reduction method - Google Patents

Abstract

PURPOSE:To stably execute smelting reduction of iron bath at low temp. by constituting a refractory wall at upper part of a smelting furnace with a cooling structural body and also specifying composition of slag and molten iron temp. CONSTITUTION:Into the smelting furnace having the refractory wall at inside of iron shell, iron ore, carbonaceous material, auxiliary material, etc,. are charged and oxygen is blown toward the molten slag 13 from the upper part to execute the smelting reduction to the iron bath 12. Then, in the refractory wall at the upper part of smelting furnace, a brick cooling part 4 for cooling the furnace brick 1 with cooling water and cooling gas and a metal-made cooling plate 3 for passing the cooling water are arranged and connected with gas piping 10 and cooling water piping 11, respectively. Further, blending ratio of the auxiliary material is so adjusted to the gangue content in the ore and ash content in the carbonaceous material in the furnace that the slag composition becomes 1.1-1.4 CaO/SiO2, 15-25wt.% Al2O3 and <13wt.% MgO, and the molten iron temp. is made to <=1420 deg.C. Further, the operation is executed so that the molten slag 13 on the iron bath 12 becomes >=2000kg per unit area (m<2>) of the iron bath. By this method, eroding velocity of the refractory at lower part in the furnace can be restrained to <= about 0.5mm/h.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for melting and reducing metal oxides, and particularly to a method for melting and reducing iron and iron alloy baths.

(Prior art) In the iron bath type smelting reduction method (hereinafter referred to as smelting reduction), hot metal and slag carbonaceous materials are held in a furnace in advance, and raw materials such as iron ore, coal, lime, etc. At the same time, oxygen gas is injected, coal is combusted, and the heat of combustion is used to reduce iron ore to obtain hot metal.

In order to increase productivity in this melting reduction operation,
It is necessary to allow the reduction reaction to proceed smoothly.

For this purpose, a large amount of heat necessary for the reduction reaction must be supplied, and the combustion of the gas in the furnace, that is, the secondary combustion rate ((H2H + 002) / (H2 + H20 + CO +
An operating method is adopted that increases C02) x 100%)) and increases the amount of oxygen, amount of coal, and calorific value per light. Normally, the secondary combustion rate is set at 30 to 7%, and this mode of operation increases productivity and improves oxygen and coal consumption rates. However, since the amount of heat generated is large, the gas temperature rises, resulting in melting and loss of the refractory.

The refractories currently used for melting reduction furnaces are MgO-
Currently, the following problems are encountered with the use of Cr203, Mg0-C, Ag2O3, etc.

Although the operating temperature in the lower part of the furnace (the part immersed in the iron bath or slag bath) is relatively low at around 1500°C, the wear rate is 1 to 4 m due to the large stirring force produced by the bottom blowing gas.
It is about m/h. In the upper part of the furnace (gas combustion part), the secondary combustion rate is high, so the gas temperature is high < 1700 to 200
It is 0°C. It is also subject to slag erosion due to slag splash.

Therefore, the rate of wear is also high, currently 3 to 10 mm. In order to prevent the elution of Mg0-C bricks, it is necessary to bring the MgO4 degree in the slag close to the saturation concentration. High MgO
To increase the concentration, dolomite is generally added during operation, which increases costs, and the high MgO slag absorbs moisture and expands, making it difficult to reuse as a resource.

The target value for the refractory wear rate at which the smelting reduction method can be cost competitive with the current coke-blast furnace method is 0,
It is thought to be 5 to 1 mm/h.

The biggest cause of such wear and tear on refractories is heat-induced melting loss, and one possible way to suppress the melting speed is to lower the operating temperature. Japanese Patent Publication No. 82-230908
The publication states that in order to promote dephosphorization during operation, the C in the pig iron should be >3.5%, and the tapping temperature should be maintained at 200°C or more higher than the liquidus line and 1450°C or lower. Techniques for low temperature operation are disclosed.

In addition, as a method to prevent melting of refractories during converter operation, an arbitrary number of slag coating formation panels are attached to the easily melted part of the converter wall, and controlled cooling gas can be injected from the tuyeres. JP-A-60-135512 discloses a technique for significantly extending the life of converter refractories by doing so.

In addition, as an efficient operation method for melt reduction, the operation conditions for stable operation are:
As a result of research on the method of supplying top-blown oxygen and the amount of slag, we determined that the agitation intensity using bottom-blown gas was increased from 1 to 6 kW/t.
, the depth of the depression due to top-blown oxygen is 1/2 Lo -L<35 (a ・q/P), and the amount of slag is 1.500 kg/d or more. The application was filed as No.-280459.

α, Volume change rate of bottom blowing gas (-) q: Gas flow per slat (Nm3/h)
P: Furnace pressure (aim) L: Depth of indentation of top-blown oxygen against slag (m) LO nislag thickness (m) (Problem to be solved by the invention) In normal smelting reduction operation, it is difficult to increase the reduction reaction rate. In order to ensure this, it is carried out at about 150 [1°C]. +5
When operating at 00"c or below, although it is effective for dephosphorization as mentioned above, the slag viscosity increases and slag agitation becomes poor, which worsens the transmission of coal combustion. Also, the reduction reaction As the speed decreases, the concentration of σ iron oxide in the slag increases, which not only causes abnormal slag forming and unstable operation, but also increases the loss of iron oxide contained in the slag during slag discharge. As a result, the iron yield decreases.

Additionally, providing an arbitrary number of slag coating layers is effective in suppressing refractory wear in converters where the secondary combustion rate is low and the time of exposure to high-temperature gas is short. In smelting reduction furnaces, the upper space is not only exposed to extremely high temperatures, but also operates for long periods of time, so the slag coating layer formed during tapping and slag removal melts over time. , the refractory surface was exposed and was not very effective.

The technology proposed for stable operation conditions is based on the premise of improving the reaction rate and suppressing the amount of dust generated at the current operating temperature of about 1500'C in order to ensure stable operation. The overall operating conditions, including the operating temperature, were not optimal.

In this way, many developments have been made on technologies that are considered to be optimal for individual operating conditions, but these are only solutions that focus on one aspect of the problem at hand. However, the problem is not solved as a whole process.

The present invention was made in order to propose not only such economical optimum conditions but also optimum conditions for the entire process, and to achieve high productivity when performing low-temperature operation to suppress wear and tear on refractories. This paper proposes a technology that enables stable operation at low temperatures, which has been difficult with conventional technology, while ensuring the same.

(Means for Solving the Problems) The present invention was invented as a result of various research conducted in a large-scale test furnace applicable to actual operations, in order to solve the above-mentioned problems in smelting reduction. Iron ore or pre-reduced ore, carbonaceous materials, auxiliary materials, etc. are put into a melting furnace that has a refractory wall inside the iron shell, and oxygen is blown into the slag from above the furnace. In the smelting reduction method, the fireproof wall in the upper part of the melting furnace is constituted by a cooling structure, and the slag composition is set to CaO/SiO2:1.1.
~1.4, A, Q 203: 15-25iit%, M
It is characterized by operating at a hot metal temperature of 1420° C. or lower while adjusting the blending ratio of the auxiliary material to the gangue content in the ore and the ash content in the carbonaceous material in the furnace so that g O < 13 vt%.

Further, the above operating method is characterized in that the slag on the iron bath is 2000 kg or more per unit area (rrF) of the iron bath.

(for production) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing a cross section of an operation according to the implementation of the present invention.

1 is the refractory brick of the furnace body, Mg0AΩ O, Cr
Made of highly fire-resistant materials such as 2O3 and carbon. 2 is a bottom blowing tuyere, through which gas is blown for the purpose of stirring the iron bath and the slag bath. Since the main purpose is stirring, the type of gas is not particularly limited, and nitrogen, argon, carbon dioxide, and oxygen are usually used. 5 is a bottom-blown gas pipe.

Reference numeral 4 denotes a brick cooling section, in which the outer surface of the brick is cooled by cooling water through the iron skin, and a through pipe is embedded in the brick to cool the brick by flowing cooling gas.

The gas is not particularly limited as long as it is used for cooling purposes, but nitrogen, carbon dioxide, exhaust gas from a smelting-reduction furnace, etc. are usually used.

Alternatively, the cooling gas may be air or water mixed with water. In order to efficiently cool the bricks in this part, for example, Ag2O
It is desirable to use a material with high thermal conductivity such as 3-C or Mg0-C.

3 is a metal cooling plate, and the inner surface may be coated with a refractory material. Pour enough cooling water so that the metal surface does not melt. Cooling plates are usually made of copper, pig iron, or steel, and may also be made of titanium in areas with particularly high heat loads.

The cooling structure parts 4 and 3 are usually installed above the furnace body part which mainly covers the slag, and the brick cooling part 4 and the cooling platen 3 are sometimes installed independently.
Figure 1 shows an example where both are installed together. Also,
In some cases, the cooling plate 3 may be installed below the top surface of the slag.

6 is a belt conveyor for supplying raw materials, and 7 is a chute for inputting raw materials. Although FIG. 1 shows an example in which the raw material is supplied from above, there is also a method in which powdered raw material is sprayed onto the slag or into an iron bath or a slag bath.

8 is a top-blown oxygen lance, and usually a plurality of nozzles, 4 to 20, are used to promote secondary combustion.

Reference numeral 9 denotes a gas duct for collecting exhaust gas, which is usually water-cooled or lined with a refractory material to be heat resistant. In addition, in the case of water cooling, the sensible heat of the exhaust gas may be recovered as steam or the like.

10 is a gas pipe for cooling the bricks, and 11 is a cooling water pipe for cooling the bricks and cooling platen.

12 is an iron bath, iron contains a large amount of carbon, and usually 2
%, it is in a state of carbon saturation. Reference numeral 13 denotes a slag bath, which is bubbling due to the passage of the stirring gas of the iron bath and carbon monoxide gas generated during reduction of iron oxide, and is swollen to 1.5 to 3 times its size at rest.

First, low temperature operation, which is one of the main features of the present invention, will be explained.

By maintaining the iron bath temperature at a low temperature, the following effects can be expected.

■Since the temperature of hot metal and slag is low, the rate of wear of refractories in the parts that are in contact with hot metal and slag is reduced.

■As hot metal sensible heat, slag sensible heat, and exhaust gas sensible heat decrease, the heat generated in the furnace is effectively used for reduction, and the amount of heat carried out of the system as exhaust gas sensible heat decreases, improving heat balance. be done.

As a result, coal and oxygen consumption rates can be reduced, and productivity can also be improved.

■As the exhaust gas temperature decreases, the heat load on the exhaust gas recovery device decreases, reducing the amount of cooling water required.
The lifespan of cooling water piping and exhaust gas recovery equipment will be extended.

(2) By lowering the temperature of the hot metal and slag, the distribution ratio of P and Mn to the slag phase increases thermodynamically, making it easier to remove impurities in the hot metal. Therefore, manufacturing of high-purity steel becomes easier, and the cost of refining treatment for removing P and Mn can be reduced.

■If the slag generated during melt reduction is to be reused as a resource, it can be used as a raw material for cement or as a roadbed material, similar to blast furnace slag.

In this case, if the MgO concentration in the slag is high, MgO will
Since the gO phase is precipitated and expands due to absorption of moisture in the air, the upper limit of Mg04 degree for utilization is said to be 13%. When using MgO bricks for the lining,
In order to suppress the elution of bricks, operations are generally carried out in which MgO is added to slag. In the case of low-temperature operation, the MgO saturation solubility in the slag decreases, and it becomes easy to suppress the MgO saturation of the slag to 13% or less.

Figure 2 shows how the rate of wear of the refractories in the lower part of the furnace decreased.

Figure 2 shows the temperature of hot metal in a 100T iron bath furnace.
This is the knowledge obtained through test operation at 0 to 1600° C., and the values set were the same as the equipment configuration shown in FIG. 1, in which all raw materials were introduced from above, and the entire amount of oxygen was blown from an upper lance. Bottom-blowing stirring was performed by blowing in nitrogen gas. The stirring force was determined by the following formula and was in the range of 2 to 6 kl//l per weight of the iron bath.

ε=(6,18・Q-T/WT)ρn(1+h.

/1.46 X 103) Q: Bottom blowing gas flow rate □Jm3
/m1n) T: Bath temperature (K) WT: Hot metal amount (1) h, Bath depth (rn) ε: Stirring energy (Watt/t) The operating conditions are that the secondary combustion rate is 40 to 45%, and the slag The composition is C
a O/S i 021.2~1.35, 8Ω
20314-17% and MgO<13%.

The brick is Mg0-C. The amount of slag is 1200kg
/I am.

○ in the figure is the brick wear rate in the iron bath (furnace bottom).
・ is the brick wear rate in the slag bath (furnace wall).

It can be seen that the wear rate of the bricks in both the iron bath part and the slag bath part decreases as the hot metal temperature decreases, and if it is below 1420°C, the above-mentioned target value of 0.5 mm/h is achieved.

However, because the temperature is low, the reduction reaction rate constant becomes small, resulting in the problem that a high reduction reaction rate cannot be obtained. Therefore,
As a method to solve this problem, the inventors conducted operational experiments under various conditions and found that a high reduction reaction rate constant could be obtained by increasing the amount of slag.

FIG. 3 shows the results of investigating the apparent reaction rate constant at each hot metal temperature under the same operating conditions as in FIG. 2, with a slag amount of 1200 kg/rrf. The reduction reaction equation for iron is generally expressed by the following equation, and by normalizing the operating conditions, the reduction reaction rate is R-k (%T, Fe) R1 reduction reaction rate (kmoN ・02/rr? ・m
1n) (%T, Pe) Total iron weight % in Nisslag (%)k: Apparent reduction reaction rate constant (kmoN ・02/rrr -min(%T
, Fe)) in the slab per unit area for comparison.
T.

Fe) Find the apparent reaction rate constant k per 1%,
Plotted against hot metal temperature. As is clear from FIG. 3, the reduction reaction rate constant decreases as the hot metal temperature decreases.

Therefore, the present inventors set the hot metal temperature to 1360°C to 142°C.
A test was conducted in which the amount of slag was increased during operation maintained at 0°C.

FIG. 4 is a diagram showing the relationship between the apparent reduction reaction rate constant and the amount of slag.

It can be seen that as the slag amount increases, the apparent reduction reaction rate also increases, and the slag amount increases rapidly at 2000 kg/kg or more.

The productivity in the blast furnace method is approximately 1.007 per hearth area.
/r&・D, and compared to this value, in order to achieve the same level of productivity when operating smelting reduction on a commercial scale, the apparent reduction reaction rate is 0.091vol.
Must be greater than or equal to O,,/rn''-win(T, Fe).

As shown in FIG. 4, it was found that it was possible to increase the slag amount to 0.09 or more by increasing the slag amount to 2000 kg#rf or more. Slag amount is 1500kg/
rrr to 2000kg/rr? The reason for the sudden increase in the apparent reduction reaction rate is that the thickness of the slag layer increases, and the slag thickness becomes larger than the size of the depression in the slag layer caused by top-blown oxygen. This is because re-oxidation of the iron bath due to oxygen could be prevented.

Next, the slag composition will be described.

As mentioned above, it was shown that high productivity can be obtained by increasing the amount of slag even at hot metal temperatures below 1420°C, and this is possible by maintaining a fluid slag composition even at low temperatures.

As mentioned above, when considering the reuse of slag as raw material for cement or roadbed material, the MgO concentration must be kept below 10%, or the saturated solubility of MgO in slag will decrease by lowering the temperature. , lowering the temperature is effective for adjusting MgO in slag.

The composition that can ensure slag fluidity even below 1420°C under the condition of MgO concentration of 13% or less is the so-called Me
lNjte phase, CaO/5iO2-0,8~1,
4 and Ag203<25%.

However, if A1)20a is less than 15%, the melting point of the slag will rise, so in order to operate at 1420℃ or less, A
I 20 a "" is preferably in the range of 1.5 to 25%.

In melt reduction, the reduction reaction rate is
Since it strongly depends on SiO2 and impurities such as PuMn are difficult to remove if CaO/SIO2 is low, it is desirable that CaO/5IO2 be 1.1 or more.

From the above, the range of slag composition is CaO
/ SiO2 = l, l ~ l, 4, MgO
It is necessary to adjust the supply amount of the auxiliary material to the gangue content in the supplied ore and the ash content in the carbonaceous material so that it is in the range of <13%, Ag203-15 to 25% (weight% in slag). be. The auxiliary materials to be supplied include lime, dolomite, silica or alumina.

Next, let's talk about refractories.

The materials currently used for refractories include MgO, Al1203, CaO, and 5i.
There are 02 series, Cr2O3 series, and Z r O2 series. CaO
Under the above-mentioned slag composition conditions, the brick wear rate is too high for the 5102 series and the 5102 series, so there are problems with durability. Cr
In the case of 2O3 type, it is better to avoid using it because the Cr in the brick will dissolve into the molten iron due to the erosion of the refractory, increasing the Cra level. In the Z r 02 system, when Z r 02 is mixed into the slag layer, the viscosity of the slag increases, which deteriorates the fluidity of the slag.

From the above, MgO type or A refractories are recommended.
It is preferable to use something from the g203 series.

Finally, we will discuss the cooling structure of the refractory wall at the top of the melting furnace.

In smelting reduction, heat of reduction is supplied, which causes secondary combustion in the upper space of the furnace, so the gas temperature in the upper space becomes extremely high. In addition, the surface of the furnace inner wall is constantly leaking due to scattered slag, which easily causes slag wetting into the brick matrix and elution of the brick base material.
As the bricks wear out, MgO and Ag2O3 are added to the slag.
mixed in with the slag, resulting in a change in the slag composition.

That is, in order to maintain the above-mentioned slag composition over the entire period of operation, a large amount of auxiliary material must be supplied during operation.

Therefore, we proposed cooling the refractory wall above the slag surface, or creating a cooling plate structure in which the majority of the wall is not lined with refractory material.

Cooling methods for fireproof walls include water cooling from the outside of the furnace (shell side), cooling by blowing air water, and cooling from one to multiple through pipes inside the bricks from the steel shell side to the inside of the furnace. Co2. N2. Alternatively, exhaust gas generated from the furnace can be used. Furthermore, by using air water obtained by adding water to these cooling gases, the cooling capacity is increased.

Alternatively, there is a method of directly spraying a cooling medium such as gas, water, or powder from inside the furnace, but any method may be used.

In this case, it is better to widen the range of cooling and increase the cooling intensity, or to minimize it, as excessive implementation will lead to increases in construction and operating costs. According to the inventors' experience, the cooling intensity is 20,000 kcai)
/rr?・For more than h, the cooling area must be at least the area of the lower half from the top surface of the slag to the furnace mouth.

As for the cooling panel structure that does not use refractories, any structure can be used as long as the cooling strength is large, such as the stave type used in blast furnaces or the water-cooled panel type used in electric furnaces, which can be easily constructed. can. Materials include cast iron, copper, titanium, etc., and any material may be used.

The present invention is characterized by stable operation at a low temperature. However, if the temperature of the produced hot metal is low and problems arise in handling in downstream processes after tapping, After producing a predetermined amount of hot metal through a smelting reduction operation, a method may be used in which only the supply of ore is reduced or stopped and the hot metal is raised to the required temperature.

(Example) The present invention was carried out using a melting reduction furnace with a 100T bath as shown in FIG. Table 1 shows the materials and structure of the refractories used during the implementation, and Table 2 shows the common operating conditions throughout the period.

/ No. 2 table Table 3 shows the operation results for each period.

The operation results will be explained below.

In Comparative Example 1, there was no cooling of the bricks and 150
The operation is carried out at a high temperature of 0℃, the rate of wear of the bricks is high, the amount of MgO eluted from the bricks is large, and the MgO in the slag is
The concentration is as high as 19.3%, so it cannot be used as a raw material for cement. In addition, the heat balance has deteriorated, and the coal consumption rate and productivity have also deteriorated.

In Comparative Example 2, the bricks were not cooled or the operation was carried out at a low temperature of 1395° C. of hot metal.

Since the bricks are not cooled, the refractories in the upper part of the furnace are significantly worn out despite the low temperature, and the MgO content in the slag has increased, making it impossible to use this slag as a raw material for cement. In addition, since the amount of slag is small, a large amount of iron dust is generated due to contact between the top-blown oxygen and the metal, and the apparent reaction rate constant is low, and the content (T, Fe) in the slag is high, causing slopping, which makes operations difficult. I couldn't continue.

Comparative Example 3 is the result of operation using a furnace body in which the upper part of the furnace is externally cooled from the iron shell and has a cooling structure using a through pipe.

As for the structure of the penetrating pipe, carbon steel and stainless steel with an inner diameter of 2 and 4.6+ om were buried separately for each part, and the effects of each were confirmed. It was found that the cooling effect of the penetrating pipe can be estimated by calculation using a simple heat transfer model that takes into account the buried density of the vibrator, gas flow rate, brick material, and gas material. As for the operation results, it was operated at a low temperature of 1405℃, CaO/
Since SiO2 was as high as 1.45, the same phase was generated in the slag and the viscosity of the slag increased, resulting in poor fluidity, which caused slopping and made stable operation over a long period of time impossible.

Examples 1 and 2 are both results of operations based on the present invention, and the wear rate of the refractory is small, and the Mg in the slag is low.
0ia degree is also kept low. Stable operation at low temperatures was achieved for a long period of time, and good results were obtained in terms of productivity and coal consumption.

In particular, regarding the refractories in the upper part of the furnace, in Comparative Examples 1 and 2 carried out during test period 1, the amount of wear was at a level that could be visually confirmed, but in Examples 1, 2 and Comparative Example 3, there was almost no amount of wear. It was hard to understand.

(Effects of the invention) By implementing the present invention, stable operation at low temperatures of 1420°C or less can be realized, and the erosion rate of refractories in the lower part of the furnace can be reduced by 0.5 mm.
Not only was it possible to suppress the reduction reaction rate to less than /h, but also a high reduction reaction rate constant, which could only be obtained at temperatures above 1500° C. with the prior art, was achieved.

In addition, the generation of iron dust was suppressed, the heat balance was also improved, and good results were obtained in terms of productivity and coal consumption. The slag generated during operation can also be reused as raw material for cement or roadbed material, making it possible to significantly reduce the total cost of hot metal production compared to conventional technology.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a cross-section of the operation according to the present invention, Fig. 2 is a chart showing the relationship between hot metal temperature and brick wear rate in the lower part of the furnace, and Fig. 3 is a diagram showing the relationship between hot metal temperature and apparent reduction reaction rate. Figure 4 is a diagram showing the relationship between the amount of slag and the apparent reduction reaction rate constant. agent

Claims (1)

[Claims] 1. Iron ore or pre-reduced ore, carbonaceous materials, auxiliary materials, etc. are charged into a melting furnace that has a refractory wall inside the iron shell, and oxygen is blown toward the slag from above the furnace. In the iron bath type smelting reduction method, the refractory wall in the upper part of the melting furnace is composed of a cooling structure, and the slag composition is CaO/SiO_2:1.
．． 1-1.4, Al_2O_3:15-25wt%, M
An iron bath type iron bath method characterized by operating at a hot metal temperature of 1420°C or less while adjusting the blending ratio of the auxiliary material to the gangue content in the ore and the ash content in the carbonaceous material in the furnace so that gO < 13 wt%. Melting reduction method. 2. The iron bath type smelting reduction method according to claim 1, wherein the slag on the iron bath is operated at a weight of 2000 kg or more per unit area (m^2) of the iron bath.