JP2768775B2 - Metal smelting reduction method and smelting reduction furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a smelting reduction method for metal oxides, and more particularly to a smelting reduction method for iron and ferroalloys.

(Prior art) In the smelting reduction method, in order to efficiently and inexpensively supply a large amount of heat consumed in a furnace, the ratio of secondary combustion is increased and the amount of heat generated per unit of coal is increased. Many attempts have been made. In other words, the amount of heat generated when oxidizing carbon to carbon monoxide is about 2200 kcal / kg-C, whereas the amount of heat generated when oxidizing carbon dioxide is about 7800 kcal / kg-C, This is because the amount of heat generated per kg of carbon and per Nm ^{3 of} oxygen is large. In addition, since hydrogen is burned only in secondary combustion, secondary combustion is indispensable in order to effectively use the combustion heat of hydrogen.

For example, as seen in JP-A-62-280311,
There is an operation method aimed at increasing the amount of generated heat of coal and increasing thermal efficiency by obtaining a high secondary combustion rate in a smelting reduction furnace and efficiently transmitting the combustion heat to an iron bath.

However, even if the secondary combustion rate in the smelting reduction furnace is increased, if steam coal with a high volatile content (hereinafter referred to as VM) of 25 to 40% is directly used in the furnace, A practical limit is around 40-50%. Because the VM
It is generally accepted that steam coal containing a large amount of coal has a poor combustion characteristic in a smelting reduction furnace, and that when high secondary combustion rate operation is performed, the heat-charging efficiency is deteriorated.

In this way, in the case of steam coal, in the operation of high secondary combustion, the heating efficiency deteriorates rapidly.If the secondary combustion rate is increased in the smelting reduction furnace using steam coal, the space above the slag in the furnace As a problem in operation, the amount of heat generated per unit volume of the gas increases and the temperature of the gas rises rapidly.

For example, when the secondary combustion rate is 50%, even if the heat efficiency of this secondary combustion is 80% and the operation is relatively good, the gas temperature in the upper part of the furnace becomes 1900 ° C or more, However, the temperature exceeds the service temperature of the brick, and cannot be said to be a method for producing metal at low cost.

In other words, in general, it is essential to reduce the cost of bricks from several hundred yen / T to several thousand yen / T in order to economically manufacture iron and alloyed iron. It is indispensable to use bricks made of relatively inexpensive materials such as magnesium oxide, calcined dolomite, aluminum oxide, silicon oxide and chromium oxide.

However, with these materials, the service temperature is only 1700 to 1800 ° C. under the conditions for the production of iron or alloyed iron, and an increase in the production cost becomes a major problem in smelting reduction.

In other words, a problem in the operation of a high secondary combustion rate in which the secondary combustion rate is 40 to 50% or more in a smelting reduction furnace is that the rate of wear of the furnace wall refractories by a high-temperature and strongly oxidizing gas is large. .

In the operation using steam coal, if the secondary combustion rate is about 50%, the heating efficiency of the secondary combustion is only about 85%, so the gas temperature in the upper space of the furnace becomes 1800 to 2000 ° C.
In addition, a high ratio of H ₂ O and CO ₂ , an oxidizing gas that has a great effect of degrading graphite-containing refractories, is generated from the smelting reduction furnace. Is intense.

In general, there are several operational factors to reduce the wear rate of a refractory, but the most effective method is to lower the temperature of the operating surface of the refractory. In addition, it has been observed that the wear rate of the refractory exposed to the gas increases when exposed to a highly oxidizing gas, and reducing the degree of oxidation of the gas is also effective for protecting the refractory. It is a way.

However, lowering the gas temperature and lowering the degree of oxidation of the gas is inconsistent with increasing the secondary combustion rate, supplying a large amount of heat to the iron bath, and reducing the unit consumption of coal. According to the conventional method, it was difficult to operate the coal with a low unit consumption and a long life of the refractory.

Therefore, considering the service life of bricks, the secondary combustion rate of the smelting reduction method can be increased only to the above-mentioned about 40%, that is, if the operation is performed with low secondary combustion and the smelting reduction of iron, When ore is used without preliminary reduction, the unit consumption of coal increases to 1000 to 1200 kg / T, and an economical method for producing hot metal cannot be performed.

On the other hand, in order to reduce the unit consumption of coal, pre-reduction of the raw material ore is one of the effective methods. In other words, the iron ore used in the production of hot metal is mainly hematite ore (Fe ₂ O ₃ ) or magnetite ore (Fe ₃ O ₄ ), and consumes C for the reduction of these iron oxides and reduces the heat of reduction. There is a problem that it is not possible to reduce the unit consumption of coal due to the huge amount of coal.

However, by pre-reducing the ore, the amount of oxygen in the iron oxide is reduced, the amount of carbon consumed by the reduction can be reduced, and the reduction heat required for the reduction of the iron oxide is reduced. Also, the heat of combustion of coal can be reduced. For these reasons, the pre-reduction of ore is a very effective method for reducing the unit consumption of coal.

The gas generated from the smelting reduction furnace is H ₂ O, H ₂ , CO, CO
₂ , N ₂ , and it is clear that in the smelting reduction method of iron, it is most desirable to effectively use this gas as a method of performing a preliminary reduction of iron ore, and various methods have been proposed. I have.

One method of pre-reduction of the efficient ore, after of H ₂ O to inhibit the reduction of the ore to remove the water by cooling the gas, which also reduces the proportion of CO ₂ to inhibit reduction For the purpose, there is a method of decarbonating the gas to increase the reduction efficiency in the preliminary reduction furnace.

However, in order to perform dehydration and decarboxylation, the gas must be cooled to room temperature, and this gas must be reheated to 800 to 1000 ° C, the temperature required for preliminary reduction, to prereduce ore. is required.

In this method, regardless of the secondary combustion rate of the smelting reduction furnace, the degree of gas oxidation of pre-reduction (P _CO2 + P _H2O ) / (P _CO2 + P
_CO + P _H2 + P _H2O )) can be reduced to a ratio appropriate for ore reduction, and the chemical equilibrium and reaction rate of ore reduction can be improved, so that a desirable reduction rate for the smelting reduction furnace can be obtained.

However, in this method, the exhaust heat boiler for cooling the gas generated from the smelting reduction furnace, dust collection equipment, water removal equipment,
It requires enormous equipment costs such as decarbonation equipment, gas holders for preventing fluctuations in supply and demand, gas pressure boosters, and heat exchange equipment for gas heating, which is not an economical preliminary reduction method.

On the other hand, the gas generated from the smelting reduction furnace is not cooled to room temperature, but is cooled to a temperature suitable for preliminary reduction, with the aim of reducing equipment costs without using such a huge facility. There is also a method in which the gas is directly led to a pre-reduction furnace to pre-reduce the ore. In this method, as a gas treatment facility, simple facilities such as a recovery duct for generated gas and a dust remover are required, and there is an effect that facility costs are reduced.

However, on the other hand, in this method, the degree of oxidation of the gas generated from the smelting reduction furnace is determined by the secondary combustion rate of the smelting reduction furnace, and there is a problem that the degree of oxidation cannot be reduced.

In this method, if the operation of the secondary combustion rate is low in the smelting reduction furnace, that is, if the operation is about 20 to 30%, as expected from the chemical equilibrium at the pre-reduction temperature of 800 to 1000 ° C, the iron ore ( Fe ₂ O ₃ ) is partially reduced to metallic iron, and a pre-reduction rate of ore of about 40% is possible.

However, if the preliminary reduction rate is about 40% and the secondary combustion rate of the smelting reduction furnace is about 20%, the unit coal consumption required for operation is 11%.
00kg / T or more,
The operation is much higher than 700-800 kg / T, and this method cannot produce hot metal economically.

By the way, on the other hand, by increasing the secondary combustion rate in the smelting reduction furnace,
By increasing the heat supply per unit weight of coal to the iron bath,
In the operation method that reduces the unit consumption of coal, the heat supply of the smelting reduction furnace is improved. However, the gas oxidation degree of the smelting reduction gas obtained by high secondary combustion of about 40-50% indicates that if this gas is used for direct pre-reduction without water removal or decarbonation, iron ore can be sufficiently reduced. Preliminary reduction is not possible.

Because, when using a gas with such a degree of oxidation,
800-1000 which is the reduction temperature usually used in the preliminary reduction furnace
At ° C, it can only be reduced to Fe ₃ O _{4 in} chemical equilibrium. In other words, hematite ore (Fe ₂ O)
_{In 3} ), the pre-reduction rate is up to about 11%, which means that magnetite ore (Fe ₃ O ₄ ) such as iron sand cannot be reduced at all. In other words, there is a disadvantage that a high pre-reduction rate cannot be obtained because the chemical equilibrium determined by the gas composition after the secondary combustion controls the ore reduction in the pre-reduction furnace.

Therefore, in a smelting reduction furnace that uses steam coal directly,
Even if the secondary combustion rate is improved to 40 to 50%, the preliminary reduction rate of iron ore remains low, so it is not possible to sufficiently reduce the basic unit of coal, and this method reduces the basic unit of coal to about 900 kg / T. I can only do that.

By the way, as described above, it has been found that the secondary combustion rate in the smelting reduction furnace is strongly affected by the average volatile content of the carbonaceous material used.

Inexpensive and high-yielding steam coal typically has a VM of 25-40
Contains%. If hot coal is to be produced at low cost using steam coal, if the steam coal is used directly in the smelting reduction furnace, the secondary combustion rate that can be reached with relatively high thermal efficiency will be
In order to supply the heat required for the smelting reduction of iron ore, it is necessary to reduce the unit consumption of coal by simultaneously increasing the secondary combustion rate and the heating efficiency.

One method for this is to partially distill coal to reduce the VM content. However, the ordinary coal distilling method requires a special coal distilling furnace, and also requires a calorific value for distilling, which requires an additional facility cost.

Therefore, if no special distillation furnace is used and there is no idea of a method that can economically procure the heat of the distillation, the method of distilling the coal can be used for the smelting reduction furnace using the coal that is partially economically distilled. Therefore, hot metal cannot be produced.

In other words, the dry distillation of coal and the reduction of the degree of oxidation of the gas generated from the smelting reduction furnace can be performed at the same time, and the coal dry distillation and gas reforming method makes it possible to reduce coal costs without increasing variable costs and equipment costs. A technology that can reduce the unit has been desired.

In other words, in order to produce hot metal economically, it is necessary to provide a simple and inexpensive facility that can reduce the oxidation of gas generated from the smelting reduction furnace and dry-distill part of coal. .

In addition, coal mining is carried out in large quantities of about 1 million to 5 million T / year. About 10 to 20% are in the form of powder of 2 mm or less.

If the pulverized coal cannot be used effectively, the surplus coal must be disposed of, and there is a problem that disposal facilities and costs are required. Therefore, in order to economically produce hot metal, it is important to effectively use this coal powder.However, when powder coal is charged into the smelting reduction furnace from above, the rising flow of gas generated from the smelting reduction furnace causes However, there was a problem that a portion of the coal powder was scattered and could not be used effectively.

Coal dry distillation and gas reforming (reducing the degree of oxidation of gas) include, for example, smelting reduction furnace or a method of gasifying coke using gas generated from a coal gasifier.
There is a technique as disclosed in Japanese Patent Application Laid-Open No. 62-283190, but in this method, only coke with good air permeability can be used as a carbonaceous material for gasification.

In other words, when coal containing VM is used in such a method, there is a problem in that tar is generated during dry distillation and the tar is liquefied in a portion where the temperature of the gas is low, thereby inhibiting gas aeration. Therefore, it is difficult to dry-distill coal containing powder with this method.

On the other hand, it is known that fine ore is easily mined as compared with lump ore, and its quality can be improved by means such as washing or flotation. Thus, it is important to utilize the fine ore skillfully to produce pig iron at low cost.

Also, if the fine ore can be used for cooling bricks, there is no incremental cost of supplying extra material into the furnace, and there is little thermal disadvantage. The same can be applied to auxiliary materials such as powdered quicklime.

(Problems to be Solved by the Invention) In the present invention, such problems are solved, the equipment is simplified, the iron ore reduction efficiency in the preliminary reduction furnace is increased, and the secondary reduction in the smelting reduction furnace is performed. It is an object of the present invention to provide a technique for producing hot metal which reduces the unit consumption of coal in the smelting reduction method by increasing the combustion rate, has a long refractory life, has low equipment costs, and has a low production cost.

(Means for Solving the Problems) In the present invention, a powdery raw material used for smelting reduction is blown into a combustion gas space at the upper part of the furnace, and the gas temperature is lowered by sensible heat of the raw material and endothermic reaction. . In particular, pulverized coal generated inevitably is blown into the combustion gas space at the top of the furnace,
The coal is distilled and a hydrocarbon-based gas generated when the coal is distilled is reacted with a high-temperature gas containing a large amount of H ₂ O and CO ₂ generated from a smelting reduction furnace. That is, the degree of oxidation of the gas is lowered, and the gas temperature is lowered by the heat of reaction (endothermic reaction).

Therefore, the service life of the brick is extended, and efficient pre-reduction with a gas having a low oxidation degree can be performed. In addition, by supplying the distilled coal to the smelting reduction furnace, an operation with a high secondary combustion rate is performed, and inexpensive hot metal is produced. Further, when using fine ore as a powdery raw material, the fine ore is brought into contact with the high-temperature gas in the furnace and is preheated and partially preliminarily reduced.

 Hereinafter, the present invention will be described in detail.

In the operation of the smelting reduction furnace, the hot metal 13 and the slag 14 are placed at the bottom of the furnace in which the refractory brick lining 8 is provided on the furnace body 1 shown in FIG.
Each form a bath. The hot metal and slag are at a high temperature of about 1400 to 1700 ° C. After supplying ore into the hot metal and melting the iron oxide, the carbon material in the form of coke or char mixed in the slag The molten carbon in the hot metal reduces the molten iron oxide to produce hot metal.

As a method of supplying ore, there are a method of dropping and throwing from an upper hopper of the furnace, a method of spraying from the side wall of the furnace, a method of blowing into slag or hot metal, and FIG. 1 shows a typical example of the furnace. A method for feeding ore from the upper hopper 5 has been described.

Oxygen (also may be oxygen-enriched air or heated air) is supplied from the upper blowing lance 2 to the hot metal in the furnace and the carbon material in the slag to supplement the heat of reduction and the sensible heat of the product. The supplied oxygen burns the dissolved carbon in the coal and hot metal to generate heat. Further, these gases also cause a combustion reaction, and further generate heat. The former combustion is called primary combustion, and the latter combustion is called secondary combustion.

In addition, a gas is supplied from the bottom of the furnace through the tuyere 3 for stirring for the purpose of accelerating the ore dissolution, reduction reaction, and heat transfer. Since this gas is intended for stirring, the gas type is not particularly limited, and generally, hydrocarbons such as nitrogen, argon, oxygen, and propane are used.

Coal is supplied so as to keep the carbon balance in the smelting reduction furnace almost constant. As a supply method, there is a method similar to that of ore, and FIG. 1 shows a method of supplying coal from the hopper 4 above the furnace as a typical example.

During the smelting reduction operation, the ore is continuously supplied from the hopper 5 and the coal is continuously supplied from the hopper 4, and oxygen is also blown from the top-blown lance 2 in the direction of slag and hot metal,
The supplied ore is melted and reduced, and settles as hot metal in the hot metal bath at the bottom of the furnace.

Further, the gas obtained by burning the coal is collected through an exhaust gas duct 12, dust in the gas is removed by a dust collector 9, and used as a reducing gas or a fuel for a preliminary reduction of ore in a preliminary reduction furnace 10. You. At this time, since the gas has a large amount of sensible heat, this sensible heat may be effectively used as heat for generating steam or the like.

Next, as the operation of smelting reduction progresses, hot metal and slag accumulate in the furnace, so that hot metal and slag are periodically discharged.

FIG. 2 shows the results of an investigation on the relationship between the secondary combustion rate of the carbon material used for smelting reduction and the heat transfer efficiency in a 100T bath smelting reduction furnace.

In this experiment, the operation using three types of carbonaceous materials, including coke, semi-anthracite containing 17% VM, and steaming coal containing 31% VM, assuming no VM is shown. As can be seen from Fig. 2, while the coke without VM has a heating efficiency of 90 to 95% up to the secondary combustion rate of 60%,
With semi-anthracite, heat arrival has deteriorated from the secondary combustion rate of 55%.
In addition, it is recognized that the thermal combustion of the thermal coal containing 31% VM has deteriorated from the secondary combustion rate of about 45%.

Furthermore, the present inventors simulated the fluid flow and reaction in a smelting reduction furnace.

 FIG. 3 shows the results.

That is, as a result of performing the same operation under the conditions of this simulation, in a 100T smelting reduction furnace, MgO-Cr ₂ O _A brick consisting of ₃ was attached to the top of the furnace.

According to the test results, the wear rate is very large at 2 to 5 mm / Hr with respect to the operation time of the smelting reduction.

In particular, the gas temperature is the highest at 2000 ° C. or higher near the wall of the upper space of the furnace, and the gas forms an upward flow. Also, the wear rate of the brick is the highest in this region.

The gas flow in the upper space in the furnace is 1 /
It was confirmed that upflow was within 3 and downflow was within 2/3 from the furnace center.

Therefore, in the present invention, the powdery raw material is blown into the in-furnace gas upward flow within 1/3 of the center direction from the furnace wall.

In FIG. 3, the left indicates the temperature (° C.), the right indicates the gas flow rate (m / sec), − indicates an upward flow, and + indicates a downward flow.

In the smelting reduction furnace, char (a dry matter of coal) manufactured by the method described below is mixed with coal to lower the average VM of the carbon material used, and to operate at a high secondary combustion rate. In this case, the secondary combustion rate is desirably 40 to 50%, but is preferably 50%.
Implementation is possible with the above.

Here, since the secondary combustion rate is high, the gas temperature in the upper part of the smelting reduction furnace becomes 2000 ° C. or higher. In order to make effective use of the sensible heat of this high-temperature gas, a powder injection nozzle 7
, A powdered raw material such as fine coal, fine ore, fine limestone, etc., is blown into the raw material, and the raw material is heated and reacted by a high-temperature gas. This allows for cooling of the gas.

Further, when the pulverized raw material is pulverized coal, the effect is large,
By contact with the high-temperature gas, the pulverized coal carbonizes and reforms the gas, and the reaction at this time can significantly lower the gas temperature.

 A description will be given below by taking pulverized coal injection as an example.

 FIG. 4 is a partially enlarged view of FIG.

The blowing nozzle is schematically shown in FIG. Arrows in the figure indicate the direction in which coal is discharged. 7 is a blowing nozzle, and 16 is an ejection port.

Incidentally, the angle θ shown in FIG. 4, a angle formed by the parallel lines x ₂ to the center line x ₁ and the furnace wall of the spout 16, which represents the injection direction of the pulverized coal with respect to the furnace wall.

The pulverized coal is rapidly heated by the high-temperature gas and quickly generates VM of the coal. The generation rate of this VM depends on the particle size of the coal. However, in the case of pulverized coal having a certain particle size or less, the speed of VM separation is high because heat transfer is fast, and the
VM separation is completed in a short time of about seconds. The reason for limiting the particle size of the pulverized coal will be described later.

Further, the form in which VM is released is a gas composed of hydrocarbons, carbon monoxide and hydrogen, but at a high temperature of 2000 ° C. or higher as in the smelting reduction furnace of the present invention, coal dry distillation in a coke oven or the like is performed. Unlike the furnace, tar production is hardly recognized, and the operation of the present invention has an advantage that tar treatment is unnecessary. Immediately after this VM has been released from the coal, the gas has a relatively high degree of oxidation from the furnace,
Reacts with hot gases. Among the gas generated from coal, the gas species that reacts with the gas from the smelting reduction furnace is hydrocarbon, and the hydrocarbon undergoes a reforming reaction with the carbon dioxide and steam of the generated gas, and is decomposed into hydrogen and carbon monoxide. You.

This reaction is an endothermic reaction as shown in the example of the following formula, and since this reaction occurs, the average temperature of the gas in the furnace decreases.

CH ₄ + CO ₂ → 2CO + 2H _{2 In other} words, the reaction between coal dry distillation and gas reforming can be performed using the sensible heat of the gas generated from the smelting reduction furnace, and the gas is cooled while performing exhaust heat recovery be able to.

Next, an example of operation in a 100T iron bath smelting reduction furnace according to the present invention will be described.

First, to the smelting reduction furnace, a preliminary reduced ore as an iron source, and a mixture of general coal and char obtained by distilling the general coal are continuously supplied. In addition, quick lime is also mixed and supplied with the preliminary reduced ore as an auxiliary raw material for adjusting the components of the slag.
The entire amount of oxygen is blown from a top blowing lance, and nitrogen gas is supplied from a tuyere at the bottom of the furnace for stirring the iron bath and the slag bath.

In the operation of the smelting reduction furnace, the operation of relatively high secondary combustion was performed, the secondary combustion rate was 47.6%, and the generated gas flow rate at this time was 57900 Nm ³ / H. Pulverized coal was blown into the furnace from a powder supply tank 6 using a blowing nozzle 7. Eight blowing nozzles 7 were equally arranged in the circumferential direction at a height of about 1 m from the slag surface.

These blowing nozzles 7 have the shape shown in FIG. 5 (b), and based on the analysis result of the gas flow distribution diagram in the furnace described above, the furnace wall is made to be easily scattered. , Ie, the angle θ was set to zero, and the air was blown in a semicircular fan shape vertically above.

The injected pulverized coal was adjusted to 2 mm or less, which is smaller than the particle size of the coal scattered under these operating conditions. Pulverized coal was dried in the furnace and exhaust gas duct, and its VM was greatly reduced. As shown in Table 2, it was found that the carbon-based duct collected by the dust collector at the outlet of the exhaust gas duct contained almost no VM. In other words, the pulverized coal was sufficiently dry-dried and turned into char-like charcoal containing almost no VM.

In addition, the effect of gas reforming by VM by injecting the pulverized coal was obtained by comparing the sampling gas in the furnace with the gas component at the outlet of the exhaust gas duct. The results are shown in the following table.
3 is shown.

The oxidation degree of the gas in the furnace was 0.476, but the VM of pulverized coal
As a result of reacting with the carbon dioxide and water vapor of the gas, the gas was reduced to 0.345 at the outlet of the exhaust gas duct, indicating that the generated gas was reformed to an oxidation degree suitable for pre-reduction of the ore. In addition, hydrocarbons such as methane and ethane were not detected in the gas collected at the outlet of the exhaust gas duct.
From this, it was found that the reaction between the exhaust gas and the VM was almost completely completed in the exhaust gas duct.

Measurements were also made of the gas temperature during this operation. The gas temperature around the brick wall above the furnace and the temperature at the outlet of the exhaust gas duct were measured. For comparison, Table 1 also shows the measurement results obtained by operating the smelting reduction furnace, which was almost the same, and operating by the conventional method without pulverized coal injection.

As can be seen from Table 1, the operation conditions of the smelting reduction furnace are almost the same as those of the conventional method, but there are differences in the gas temperature in the furnace and at the outlet of the exhaust gas duct. In the operation method of the present invention, the average gas temperature in the furnace is reduced by about 110 ° C., and the gas temperature at the exhaust gas duct outlet is reduced by about 160 ° C.

That is, as a result of performing gas reforming by pulverized coal injection and dry distillation of coal, it is shown that the sensible heat of the gas can be effectively used for heat absorption of the dry distillation apparatus and gas reforming.

Next, it is important in the operation of the present invention that coal is efficiently dry-distilled.
It was also clarified that the reaction rate of coal was strongly affected by coal particle size. Regarding the particle size of coal used for gas reforming, as conditions that can be effectively used in the present invention, first, in order to ensure the contact time between gas and pulverized coal, pulverized coal is accompanied by the generated gas, It is desirable that the gas is scattered from the furnace to the exhaust gas duct. In the example, the operation was performed with the coal particle size and the blowing condition satisfying these conditions.

In other words, by injecting coal of a particle size that accompanies the gas by the upward flow of the generated gas, the pulverized coal moves in the exhaust gas duct together with the hot gas, so the contact time between the coal and the hot gas increases. Then, the pulverized coal is easily dried.

First, the present inventors have found that there is a relationship between the coal particle size and the gas reforming effect. In addition, in experiments with high gas reforming efficiency, the fact that more dusty char was mixed into the duct in the exhaust gas was ascertained, and a comparative test of dusting of coal dust and gas reforming was conducted. Table 4 shows the results.

In other words, the fact that gas reforming was performed more efficiently with coal having a small particle size with a high dusting rate was clarified.

Here, the present inventors have compared the upward force and the gravity received in the coal gas in order to predict the scattering rate of the coal, and found that the following relationship holds.

The particle size of the pulverized coal is the particle size determined by the following formula (1), that is, the particle speed of the exhaust gas in the exhaust gas duct is equal to the terminal sedimentation velocity of the coal (the falling velocity after infinite time when the coal falls freely in the gas). It has been found that smaller than the diameter is desirable.

_{^{u = (4g 2 (ρ p}} -ρ g) 2 Dp 3 / 225μρ) 1/2 ...... (1) where, u: terminal settling velocity, mu: viscosity of gas, Dp: particle size, [rho _g: Gas Density, ρ _n : Coal density, In the case of coal, the apparent density is 1.3 to 1.6,
The value of the expression (2) in which this numerical value is substituted into the expression (1) is a condition. Also, when Dp is calculated using the physical properties of the gas at the furnace port at a temperature of 1800 ° C., Dp = 0.47 · V ^2/3 (mm) (2) (V: gas flow velocity in the exhaust gas duct ( m / sec)), and if coal with a particle size smaller than Dp is injected, the coal is entrained with gas from the furnace into the exhaust gas duct,
Dry distillation and gas reforming are performed effectively.

By applying the experimental conditions in Table 4 to this relational expression, V =
4.0m / s and Dp is 1.2mm. That is, test-A
In Test B, it was found that the test conditions were such that the powdered coal was difficult to be scattered, whereas the test conditions were such that the powdered coal was scattered. This is reflected in the difference in the scattering rate of pulverized coal.

In addition, the reaction between the dry distillation of coal and the gas needs to be completed in the exhaust gas duct where the gas is at a high temperature, but the exhaust gas duct for the generated gas treatment is usually designed to be 15 to 30 m, and the gas flow rate Since the design conditions are 10 to 20 m / s, the residence time of the coal together with the gas in the exhaust gas duct is 1 to 2 seconds, and the particle size of the coal specified in the present invention is the dry distillation of coal in the exhaust gas duct. Must meet the conditions to be able to finish completely. That is, since the contact time between the gas and the coal powder between the furnace and the outlet of the exhaust gas duct is about 2 seconds, the dry distillation of the coal powder must be completed within this time.

On the other hand, the present inventors have clarified in research that the distillation time of coal strongly depends on the particle size. That is, a dry distillation experiment in a high-temperature gas was performed in order to obtain a coal particle size for completing the dry distillation in the exhaust gas duct. The results are shown in Table-5.

Since the heat transfer is rate-limiting in the coal distillation, the pulverized coal, which is easily heated to the inside, has a shorter distillation time. As a result, it was clarified that the particle diameter of the coal should be 2 mm or less in order for the residual VM to be 2% in about 2 seconds.

From the above facts, the present inventors have found that, in order to effectively utilize pulverized coal for gas reforming, first, pulverized coal should accompany the gas and rise in the exhaust gas duct, the particle size of the pulverized coal is It has been clarified that two points, which are so small that the reaction is completed in the exhaust gas duct, are important requirements of the present invention.

Also, in order for the coal powder blown into the smelting reduction furnace to have the effect of protecting the refractory, the coal powder must be blown into the furnace, and must be blown into the rising portion of the gas in the furnace. That is, it has been found that the particle size, the injection position, and the injection direction of the coal are important for obtaining the gas reforming effect.

In other words, considering the analysis results of the gas flow in the furnace based on the analysis results, in the operation of the present invention in which fine coal is accompanied by generated gas and dry distillation is performed using the sensible heat of the gas, Must be blown in at an appropriate particle size.

Gas reforming is performed under the following three conditions: pulverized coal is scattered in the exhaust gas duct, and pulverized coal is entrained in the gas in the exhaust gas duct. The results of comparing the effects are shown in Examples of Table-6.

In Example 1 of Table 6, under the blowing conditions in which the pulverized coal is entrained by the upward flow of gas, and using a coal having a particle diameter of 1.2 mm or less, the terminal speed of which is lower than the flow rate of the exhaust gas, Further, in Comparative Example 2, the same nozzle was used, the particle size of the coal was set to 1.5 to 2 mm, and coal which was larger than Dp and hardly scattered was used.

In Example 1, the gas reforming effect was large at a coal scatter rate of 90% or more, whereas in Comparative Example 2, the coal scatter rate was only half and the gas reforming effect was only about 50%.
It turns out that coal distillation and gas reforming could not be carried out efficiently.

In the present invention, the particle size of the pulverized coal to be blown is 2 mm or
The reason why the diameter is smaller than any of the particle diameters blown off by the gas flow velocity in the gas recovery device is as described above.

Next, the blowing position and blowing conditions of the pulverized coal are also important requirements in the present invention.

As shown in FIG. 3 shown above, the gas flow in the furnace is not uniform, and the center of the furnace has a downward flow under the influence of the oxygen gas jet blown from the upper blowing lance. The generated gas rises near the wall.

As can be seen in FIG. 3, the periphery of the furnace wall, and 2/3 from the center of the furnace, is the boundary between the upward flow and the downward flow. Further, such ascending flow and descending flow are generated only in the furnace, and particularly, the strong ascending flow of -10 m / s or more is based on the upper surface 14a of the slag (FIG. 1). Then
The height is up to about 1.5 times the furnace radius.

Reflecting the result of this gas flow simulation,
When viewed from the center of the furnace in which the upward flow of -10 m / s or more is generated, pulverized coal is blown by a nozzle that blows toward the furnace wall side more than 2/3 and a nozzle that blows toward the center side of the furnace from this range. A blowing comparison test was performed.

Example 1 in Table 6 has the shape of the blowing nozzle 7a shown in FIG.
430m from the wall of the furnace port using a blow nozzle (hereinafter referred to as blow nozzle A).
In this case, pulverized coal was blown up to m, and the inside diameter of the furnace opening was 3 m, which satisfies the above-mentioned condition for blowing into the upward flow.

Next, in the second embodiment, a blow nozzle having the shape of the blow nozzle 7b shown in FIG. Using a nozzle B), pulverized coal is blown in a fan shape parallel to the furnace wall at a position 100 mm from the wall of the furnace opening and at an angle of 180 ° upward.

This embodiment also satisfies the blowing condition of the present invention as in the first embodiment.

On the other hand, Comparative Example 1 has a shape of the blowing nozzle 7c shown in FIG. 5 (c), in which the angle θ with respect to the furnace wall was set to 18 ° so that the blowing nozzle could be blown 800 mm from the wall of the furnace opening. (Hereinafter, the nozzle under this blowing condition is referred to as blowing nozzle C). In Comparative Example 1, the condition of the position 1/3 from the furnace wall was not satisfied.

As shown in Table 6, according to the results of this comparative test, when the blowing nozzles A and B were used, the ratio of dust coal collected by the dust collector after the exhaust gas duct was 90% or more. In the case of Comparative Example 1 in which the gas was used, it was as low as about 70%, and it was found that the gas was not sufficiently reformed.

In the present invention, pulverized coal is blown in the direction from the furnace wall until the pulverized coal is discharged from the furnace. For that reason.

Next, Comparative Example 3 shows the result of a comparative test in which pulverized coal having a particle size that does not end the reaction in the exhaust gas duct is blown while the pulverized coal is scattered.

In Comparative Example 3, an experiment was performed under the condition that the gas flow rate in the exhaust gas duct was increased and powdered coal having a particle size that did not end the reaction in the exhaust gas duct was also scattered. As a result, pulverized coal was scattered, but the gas reforming reaction did not proceed sufficiently, and the gas reforming effect was only about 70%.

In addition, the present inventors have studied various types of pulverized coal nozzle shapes other than Examples 1 and 2, but if the pulverized coal is scattered under the above-mentioned conditions, the gas reforming effect is not so different. It was found that there was no
Although a furnace without a cone at the upper part of the furnace as shown in the figure was carried out, it was also clarified that the gas reforming could be carried out sufficiently efficiently if the conditions of the present invention were satisfied.

When the iron ore was preliminarily reduced in a one-stage fluidized bed prereduction furnace using the gas obtained according to the present invention, the degree of oxidation of the gas was reduced, so that highly efficient operation was possible.
The results are shown in Table 7, where the pre-reduction rate in the high secondary combustion operation of the conventional method 2 is 9%, while in the operation example of the present invention, the high reduction operation is similarly performed in the smelting reduction furnace. Pre-reduction is improved up to 40% in spite of subsequent combustion.

Since the gas obtained by the gas reforming according to the present invention is usually at 1100 to 1300 ° C., the gas temperature required at the inlet of the pre-reduction furnace is about 1000 ° C. or more. With a simple operation of mixing a small amount of cooling gas, there is no need to reheat the gas.

In other words, in performing the pre-reduction according to the present invention, a huge amount of gas cooling and re-heating equipment can be eliminated, and even if the pre-reduction furnace and the smelting reduction furnace are directly connected with a hot gas, a highly efficient pre-reduction method, The smelting reduction method with high secondary combustion rate was compatible.

Next, a case where a powdery raw material other than coal is blown will be described.

First, the operation of injecting fine ore will be described. When the fine ore was blown using the blowing nozzle 7a shown in FIG. 5 (a), it flowed along the furnace wall and cut off the radiant light from the furnace gas to the furnace wall. It was found to be lower. Then, the fine ore was placed in parallel with the furnace wall from the
While blowing under the min conditions, a heat flux meter was embedded in the furnace wall brick to measure the amount of heat input to the furnace wall.

As a result, the heat input before the injection of fine ore was 19,600 kcal
/ m whereas ^2-was hr, after included fine ore blown in 11,000k
Cal / m ² · hr was greatly reduced. In addition, as shown in Table 8, the gas temperature near the furnace wall was 11 times higher than before the injection of fine ore.
It was confirmed that the temperature had dropped by 5 ° C. The excellent effect was observed such that the wear rate of the refractory brick when such an operation was performed was reduced to about half by the injection of fine ore.

In addition, even in operations where powdered limestone is blown in as a powdered raw material other than pulverized coal and ore, about 150 kg /
When min was blown, the same effect as that of the above-described fine ore blowing was obtained.

Next, a blowing nozzle for efficiently blowing the powdery raw material under the above-described conditions will be described.

The blowing nozzle is used under extremely severe conditions, such as being exposed to the high-temperature gas in the furnace while being severely worn by the powder. For this reason, it is worn out in a short period of time and has to be replaced.

In the replacement of the blowing nozzle, refractories around the blowing nozzle are often damaged, and it is necessary to cool down the furnace for replacement. Was.

Thus, in the present invention, as shown in FIG. 6, an opening 21 is provided in the refractory brick 8 of the furnace body 1, that is, an upper part of the furnace wall, and the above-described blowing nozzle 7 is attached to the opening 21 so as to be able to advance and retreat. This effectively solved the problem.

To move the blowing nozzle 7 forward and backward, for example, the opening 21
Bogie that runs freely on a gantry 22 arranged in close proximity to
23 holds the blowing nozzle 7 and
In addition, a mechanism in which a traveling drive device 24 such as a hydraulic, pneumatic or electric drive type cylinder device, or an electric motor is connected is used. Numeral 30 is a flexible hose for supplying the raw material.

Further, the refractory brick 80 around the opening 21 where the blowing nozzle 7 advances and retreats may be, for example, a cooling plate 81 through which a cooling medium such as water, a gas-liquid mixture, or a compressed gas flows, or a cooling pipe (not shown). Although not shown, the furnace body (steel shell) 1 near the refractory brick 80 was made to have a water-cooled structure, and a cooling structure mechanism for cooling the refractory brick 80 was provided.

With such a structure, the blowing nozzle 7 can be attached to the furnace body 1 only during operation, and can stand by at a distance from the high-temperature furnace body 1 during non-operation. Further, the worn-out blowing nozzle 7 can be replaced without cooling the furnace, and the service life of the refractory brick 80 can be greatly extended, so that the operation rate can be significantly increased.

As the cooling structure mechanism, for example, as shown in FIG. 7, a structure in which a plurality of cooling medium ejection pipes 82 having an opening surface 82a are buried inside the furnace has a more excellent function as described later. Demonstrate.

That is, by blowing the cooling medium from the opening surface 82a located inside the furnace of the blowing pipe 82 via the header portion 83, the refractory brick 80 near the blowing nozzle 7 can be more strongly cooled.

In addition, if oxygen gas is added to the cooling medium, the opening 21
A secondary effect of suppressing adhesion of slag and the like to the vicinity can also be obtained. In this case, as the cooling medium, nitrogen gas, carbon dioxide gas, which is produced by cooling the gas generated from the smelting reduction furnace since it is jetted into the furnace, steam-water obtained by adding an appropriate amount of water to a compressed gas, or the like can be used. .

(Example) The present invention was implemented in an integrated plant in which a smelting reduction furnace and a preliminary reduction furnace were directly connected.

In the operation using pulverized coal, as shown in Fig. 1, in the smelting reduction furnace, the ore obtained by partially reducing the iron oxide in the preliminary reduction furnace is used as the source of iron to be reduced. A mixture of coal char is used as the carbonaceous material. The gas generated from the smelting reduction furnace is reformed with pulverized coal, and this is led to a fluidized bed type pre-reduction furnace at a high temperature to partially reduce the ore.

Examples are the results of producing molten iron by smelting and reducing iron ore using a smelting reduction facility with a 100T bath, and operating conditions were the same for all three cases using the same brand of ore and coal.
Hot metal temperature-1500 ° C, hot carbon is saturated, slag basicity-
It is the result of operating under the conditions of 1.2 to 1.3.

In order to carry out economical operations, the smelting reduction furnace uses coal that contains almost no VM generated during gas reforming in coal and uses it by dry distillation and gas reforming of pulverized coal.
The upper limit of the secondary combustion rate that can suppress the wear of refractory bricks is about
This gas was operated at 50% and the degree of oxidation and the temperature of this gas was reduced with pulverized coal for gas reforming, and efficient pre-reduction was performed.

Two examples of a high secondary combustion rate operation and a low secondary combustion rate operation are shown as comparative examples of the conventional operation without gas reforming using pulverized coal.

In the operation of the conventional method 1, since the smelting reduction furnace operates at a low secondary combustion rate, the gas temperature in the smelting reduction furnace remains at about 1720 ° C., and the brick wear rate is low. Also, the low degree of gas oxidation at the inlet of the pre-reduction furnace enabled the pre-reduction rate of ore to be as high as 41%.

However, in this operation, since the preliminary reduction rate is high but the secondary combustion rate is low, the amount of heat generated in the smelting reduction furnace is small, the productivity is low, and the unit consumption of coal and the unit consumption of oxygen are increased. It is clear that this is not an economical hot metal production method.

Further, in the conventional method 2, the gas temperature in the furnace is as high as about 1910 ° C. because of the high secondary combustion rate operation. As a result, the wear rate of the brick at the top of the furnace was 3.2 mm / Hr, which was about 4 times larger than other operations, and the basic unit of brick was 5.7k.
Due to poor g / T, the cost of hot metal production increased, and there was a problem of a decrease in equipment operation rate and an increase in maintenance costs due to an increase in repair of bricks.

Furthermore, since the secondary combustion rate is high, the degree of gas oxidation at the inlet of the pre-reduction furnace is high, and the pre-reduction rate of the ore is as low as 9%. As described above, although the secondary combustion rate is high and heat is generated in the smelting reduction furnace much, productivity is not improved much because of the low pre-reduction rate of ore. The results are relatively large.

In contrast to the conventional operation, in the embodiment of the present invention,
Since gas reforming is performed in the smelting reduction furnace and in the exhaust gas duct that sends the gas to the smelting reduction furnace and the pre-reduction furnace, high secondary combustion and high pre-reduction can be achieved at the same time. Therefore, it is possible to efficiently dry-distill pulverized coal and effectively utilize the sensible heat of the high-temperature gas generated from the smelting reduction furnace.

In addition, since the heat required for coal dry distillation and gas reforming can be utilized by the sensible heat of the high-temperature gas discharged from the smelting reduction furnace, equipment costs can be reduced and energy is advantageous. .

According to the operation results according to the present invention, as shown in the examples, a high pre-reduction rate of about 40% was realized in the pre-reduction furnace, and about 20% of the coal was distilled off, and the generated char was subjected to the smelting reduction furnace. Since it is used by mixing with coal, the VM of the carbonaceous material disadvantageous to the secondary combustion was reduced, and the heat-reduction efficiency was improved even at a high secondary combustion rate in the smelting reduction furnace.

In addition, coal is blown into the gas combustion section at the top of the furnace with the highest gas temperature in the smelting reduction furnace to perform dry distillation and gas reforming, which lowers the gas temperature and increases the Was able to keep the wear rate low.

As a result, the use of high pre-reduced ore reduces the amount of heat consumed per ton of hot metal in the smelting reduction furnace, and increases the amount of heat generated per unit amount of oxygen and coal by operating at a high secondary combustion rate. Also, the productivity is about 27% higher than that of the conventional method, and both oxygen consumption and coal consumption are significantly reduced.

In addition, the gas temperature in the furnace was about 1730
Because of the temperature in ° C, the wear rate of the refractory bricks could be reduced to almost the same level as the low secondary burning rate operation of the conventional method, the basic unit of brick was 2.0 kg / T, and there was no problem with brick life.

The operation was then carried out using fine ore instead of fine coal. The fine ore was blown from the powder supply tank 6b through the blowing nozzle 7 into a portion 100 mm from the wall of the furnace port.

As the fine ore, fine ore for sintering usually called sinter feed was used. During this operation, the gas temperature at a point 200 mm from the inner wall of the furnace was measured.
A 5 ° C temperature drop was observed. In addition, as a result of collecting and analyzing the flying ore in the generated gas, it was found that the ore was reduced by about 6%, and it was confirmed that the heat load on the furnace wall could be reduced.

(Effect of the Invention) In the smelting reduction operation according to the present invention, the method of injecting pulverized coal does not require complicated and huge facilities such as generated gas cooling, decarbonation, and gas reheating, and performs gas reforming in the exhaust gas duct. As a result, it is possible to perform high-preliminary reduction with low equipment cost and operating cost and high secondary combustion operation.

In addition, increasing the amount of heat generated in the furnace by high secondary combustion in the smelting reduction furnace, which could not be solved by the method of directly connecting the gas generated from the smelting reduction furnace to the By reducing the amount of heat consumed by the smelting reduction furnace, it became possible to reduce the heat consumption of the smelting reduction furnace and reduce the unit consumption of coal to the same level as in the coke oven-blast furnace method.

In the smelting reduction method, it is possible to use inexpensive steam coal that cannot be used in the coke oven and blast furnace methods, and because there is no need for pre-treatment of ore and coal, the unit consumption of coal is made equal to that in the blast furnace method to reduce hot metal. The production cost was reduced by about 10 to 20% compared to the blast furnace method.

Also, since the gas temperature of the smelting reduction furnace was lowered,
The service life of the bricks has been prolonged and the brick costs have been reduced, and the repair cycle of the furnace has also been prolonged. The above continuous operation has become possible, and the operation rate of the equipment has been improved by more than 20%, and the repair cost has been reduced.

Further, also in the method of injecting fine ore, the gas temperature around the furnace wall could be lowered, and the service life of the refractory brick could be greatly extended. In addition, the unit consumption of coal and oxygen was improved due to the partial reduction of fine ore.

[Brief description of the drawings]

FIG. 1 is an overall explanatory view of the present invention, FIG. 2 is a chart of heat-releasing efficiency and secondary combustion rate, FIG. 3 is a partial analysis diagram of the smelting reduction furnace of the present invention, and FIG. 5 (a), 5 (b) and 5 (c) are schematic views of a pipe for pulverized coal of the present invention, wherein (a) is a side view, (b) is a front view, and FIG. FIG. 7 is a cross-sectional view showing one embodiment of a cooling structure mechanism of a refractory brick near the blowing nozzle.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiromitsu Moridera 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu-city, Fukuoka Prefecture Inside Nippon Steel Corporation Equipment Engineering Division (56) References JP-A 1-147009 (JP) JP-A-63-140014 (JP, A) JP-A-1-191719 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21B 11/00-13/14

Claims (4)

(57) [Claims] 1. An iron bath type smelting reduction furnace in which at least a portion of oxygen is blown from above using ore and coal. A smelting reduction method for metals, wherein when blowing a powdery raw material into an ascending gas stream, the coal (Dp) to be blown is set to 2 mm or less, whichever is smaller, which is determined by the following equation. Dp = 0.47 · V ^2/3 (mm) (V: gas flow velocity in exhaust gas duct (m / sec)) 2. The method according to claim 1, wherein the generated gas obtained from the smelting reduction furnace is led to an ore pre-reducing furnace without cooling to room temperature. 3. An iron-bath smelting reduction furnace in which at least a part of oxygen is blown from above using ore and coal, a blowing nozzle for powdery raw material is mounted on the upper part of the furnace wall so as to be able to advance and retreat, and the periphery of the nozzle is provided. A smelting reduction furnace for a metal, characterized in that the refractory brick of (1) is provided with a cooling structure mechanism. 4. The metal according to claim 3, wherein the cooling structure mechanism of the refractory brick around the nozzle is constituted by burying a plurality of cooling medium ejection pipes having an opening surface inside the furnace. Smelting reduction furnace.