JPH03140405A - Smelting reduction method of metal - Google Patents

Abstract

PURPOSE:To produce molten iron from iron ore at a low cost by regulating stirring force to the molten iron with gas blowing from bottom blowing tuyeres and oxygen supplying pressure with a top blowing lance to the specific condition at the time of producing the molten iron from iron ore into a converter having the oxygen top blowing lance and the bottom blowing tuyeres. CONSTITUTION:The iron ore and coal as reducing agent are charged into a small quantity of molten iron 11 and molten slag 12 in the converter 1 having the oxygen top blowing lance 2 and plural bottom blowing tuyeres 3, and the gas is blown at the ratio of 70-450Nm<3>/hr per one piece of the bottom blowing tuyere 3 in the normal state conversion to stir the molten iron 11 with the stirring force of 1-6kw/ton of molten iron. Further, the oxygen is injected from the top blowing lance 2 and the iron ore is melted and contained Fe2O3 is reduced into Fe with the coal in the molten slag 12 or C in the molten iron 11 to make the molten iron. In this case, the molten slag 12 quantity on surface of the molten iron 11 is made to >=1500kg/m<2> and height of the lance 2 tip, stirring gas quantity from the tuyeres 3, oxygen supplying rate with the top blowing lance 2 and nozzle shape of the lance, are controlled so as to satisfy the inequality I between thickness L0 of the molten slag 12 and depth L of recessing part 21 in the molten slag 12 with oxygen supplying pressure from the top blowing lance 2 to produce the molten iron from the iron ore with the excellent productivity.

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 ferroalloys.

There is an operating method that utilizes the large amount of slag present in the furnace as a medium for melting and reducing ore, and various developments are underway regarding reactions, heat transfer, and stable operating methods using this method.

For example, Japanese Patent Application Laid-Open No. 61-221322 discloses a technique in which secondary combustion heat is transferred to slag in a converter type vessel, and the slag bath is further stirred with gas to transfer the heat to molten metal. As a stirring method, a technique has been proposed in which gas is blown into the slag and molten metal to promote heat transfer. Furthermore, Japanese Patent Application Laid-Open No. 61-213310 discloses that when performing melt reduction in a converter-type container capable of top-bottom blowing,
■ Slag size is 250 kg/or more, ■ Bottom blown gas amount is 3 to 40% of the total gas amount, ■ Slag MgO + 1V
A technique for improving heat utilization efficiency under the condition of z03≦23% is disclosed.

By the way, ore as the main raw material in smelting reduction is supplied from above or from the bottom of the furnace, and is dissolved in an iron bath or slag, and is dissolved in the slag in the form of iron oxide. This iron oxide is reduced to hot metal by carbon dissolved in the hot metal and carbon material in the form of coke or char mixed in the slag.

A large amount of reduction heat is required when reducing the ore,
For this reason, in the smelting reduction method, oxygen or a gas containing oxygen is supplied into the furnace, and carbon or hydrocarbons such as coal, coke, and petroleum carbonization residue supplied as fuel are burned to compensate for this heat. Operations are carried out. In addition, we have developed a technology to generate a large amount of heat in the furnace through secondary combustion in which CO gas and H2 gas generated from the iron bath are further combusted to CO□ gas and H20 gas, thereby securing the amount of heat necessary for the reduction. is also being actively promoted.

At this time, stirring the hot metal and slag is an effective method for promoting reaction and heat transfer, and various techniques for stirring the hot metal and slag have been adopted as a means to improve thermal efficiency. has been done. This stirring effectively functions to block top-blown oxygen from the iron bath 4, prevent metal reoxidation, and cause a reduction reaction within the slag.

On the other hand, the carbonaceous material suspended in the slag reduces iron oxide dissolved in the slag on its surface and functions as a heat transfer medium for combustion heat. In addition, it also has the function of coalescing the microbubbles of carbon monoxide generated in the slag due to the reduction reaction of iron oxide, suppressing excessive bubbling of the slag due to the generated gas, and causing the slag to boil from the furnace mouth. This function also serves to suppress the phenomenon in which operations cannot be continued (hereinafter referred to as slopping). In order to effectively utilize the functions of such carbonaceous materials, stirring of the slag is an important means for circulating the slag and uniformly distributing the carbonaceous materials within the slag. Methods of stirring the slag include a method of stirring the slag by blowing gas into the iron bath, a method of blowing gas directly into the slag, and a method of stirring the slag with a mechanical rotating body. However, with the method of blowing gas directly into the slag, the gas is supplied from the side wall of the furnace, so although the slag can be agitated near the wall, it has the problem that, especially in large furnaces, it is almost impossible to agitate the slag in the center. There is. In addition, regarding the method of stirring slag with a rotary body, the durability of the rotary body is extremely short because slag from melt reduction is highly erosive to refractories. Attaching a moving object was a major maintenance problem.For this reason, it was far from practical use, and therefore, the conventional method of stirring the slag was by blowing gas into the iron bath. Ta.

Blowing stirring gas into the iron bath has the effect of promoting the movement of substances and heat within the iron bath, making the components and temperature uniform, and also effectively stirring the slag-metal interface. It also has the effect of further improving the reduction reaction rate.

However, in the operation using the conventional technology mentioned above, the technical idea is that it is only necessary to stir the slag well, focusing only on improving heat transfer efficiency and reaction rate, and there is no need for any other methods other than stirring the slag. For example, sufficient research has not been conducted on controlling the bottom blowing agitation within an appropriate range to suppress the amount of dust generated. Also,
The development of conventional smelting reduction methods has been carried out in very small test furnaces of 1 to 10 ton furnaces.
The gas flow rate per tuyere of stirring gas is several tens to 100.
The amount was as small as Nrrf/hr. For this reason, tuyere 1
Regarding the effect of increasing the actual gas flow rate,
This was not fully understood, and the problems associated with the large flow rate of bottom-blown gas injection, which is inevitably carried out in large reactors, remained unresolved.

In other words, if the bottom blowing gas flow rate is increased more than necessary, hot metal is blown up into the slag. As a result, the amount of granular iron in the slag increases, and the amount of iron accompanying the generated gas increases.
If granulated iron is discharged as dust outside the furnace or comes into contact with the oxygen jet ejected from the top blowing lance, serious problems such as iron being blown away by the oxygen jet and increased iron dust loss can occur. Moreover, if a large amount of granulated iron in the slag comes into contact with the oxygen jet, a problem arises in that the secondary combustion rate decreases. In the prior art, no appropriate method of dealing with such problems has been established.

In the conventional operation, the iron dust loss is 60 to 80 kg/t even under good conditions, and sometimes exceeds 100 kg/t depending on the operating conditions. Since a large amount of iron dust loss is generated in this way, the generated dust is collected and
It is necessary to feed this into the furnace again, which requires large-scale equipment for dust recycling. Furthermore, since excess recycled dust is supplied into the furnace, the heat of melting the iron dust increases, leading to a problem in which the thermal efficiency of the entire process decreases. In particular, when the dust loss exceeds 100 kg, the heat balance deteriorates by 5,000~? , 0O
This results in an increase in the amount of coal used as fuel by 30 to 50 kg/t.

As mentioned above, a weight of carbonaceous material is suspended in the slag. However, this carbon material is easily scattered,
In some cases, as much as 15-20% of the coal input is scattered. The scattering of carbonaceous materials not only causes an increase in the basic unit of carbonaceous materials, but also causes problems such as a decrease in the mixing ratio of carbonaceous materials in the slag, resulting in occurrence of slopping. In particular, when there is a large amount of dust loss of carbonaceous materials, the mixing ratio of carbonaceous materials in the slag decreases and slopping occurs.In severe cases, this slopping occurs within 30 to 40 minutes after the start of operation. Operation becomes impossible at this point. For these reasons, methods for reducing the scattering loss of carbonaceous materials have particular problems that have been desired to be solved.

In order to solve this problem, it is important to reduce the scattering rate of carbonaceous materials as much as possible, but there is no suitable method in the conventional method.
It remained unresolved.

<Problems to be Solved by the Invention> When attempting to efficiently and economically carry out melt reduction operations, the following points become technical issues.

The purpose is to maintain the proper stirring state of molten iron and molten slag by adjusting the stirring force within an appropriate range. In other words, (1) the stirring power of the iron bath of the smelting reduction furnace by the bottom-blown stirring gas is set within an appropriate range, and the circulation flow of the slag is kept particularly well, and the interface where heat transfer of secondary combustion and reduction reaction occur; Thermal efficiency and reaction rate are maintained at a good level by ensuring proper levels of mass transfer to the reactor.

(2) Reduce the amount of granulated iron blown up into the slag to suppress the generation of iron dust.

(3) Prevents contact between the granulated iron in the slag and the top-blown oxygen jet, thereby preventing a decrease in the secondary combustion rate.

(4) Reduce the amount of carbon material entrained and scattered by the generated gas.

The present invention provides a melt reduction method that effectively solves the above problems.

Means for Solving the Problems> The present invention was invented as a result of various research studies conducted in a large test reactor that can be applied to actual operations in order to solve the above-mentioned problems in melt reduction. In an iron bath type melting reduction furnace in which oxygen is blown from a top blowing lance and stirring gas is bottom blown from a plurality of tuyeres below the bath surface, the stirring power of the iron bath by the stirring gas is in the range of 1 to 6 kW/t. and the gas flow rate per tuyere is 70 in terms of standard conditions.
It is characterized by controlled operation within the range of ~450 Nr+(/hr).

In addition, in the above operating method, the stirring gas flow rate, the lance height, and the oxygen supply flow rate are adjusted so that the relationship between the concavity depth (L) of top-blown oxygen to the slag and the slag thickness (L0) satisfies the following equation (1). The present invention is characterized in that one or more of the nozzle shapes of the top-blowing lance are controlled.

Lo L < 35 ((r ・q/p) 1/2
(1) However, q: Gas flow rate per tuyere (Nr
rf/hr) α: Rate of change in gas volume due to reaction of stirred gas in the iron bath (-) p: Furnace pressure (ata,) Furthermore, in the above operating method, the change rate per bath area in the smelting reduction furnace It is characterized by operating with a slag amount of 1500 kg/rrf or more.

<Function> As mentioned above, in smelting reduction, it is important to efficiently stir the hot metal and molten slag and to suspend an appropriate amount of carbonaceous material in the slag to improve thermal efficiency and reaction rate. , is an important operating condition that governs productivity.

The present inventors have developed various methods for reducing the amount of dust generated and preventing a decrease in the secondary combustion rate, which were mentioned as problems while satisfying these operating conditions, in a large-scale test furnace that can be applied to actual operations. As a result of repeated experimental research, we discovered the following facts.

First, in order to analyze the mechanism of iron dust generation, we investigated the distribution of granular iron in the slag, which has the most significant effect on the generation of iron dust, by measuring the material distribution within the slag.

In this example, the measurements were carried out under the following operating conditions using a melting reduction furnace with a maximum bath capacity of 120T.

Furnace capacity of test furnace Max. 120T bath Furnace bath area 22 bowls Iron bath amount Slag amount Carbon material in slag Ore charging speed Coal charging speed Top-blown oxygen flow rate Hot metal temperature Number of tuyeres Stirring gas species Stirring gas flow rate Furnace internal volume 131rr' r 70-110T 21-45T 5-22T Approx. 41T/hr Approx. 27T/hr 20,000 N rri/hr 1500°C 1-6 N2. Co
A special sublance probe was used in which four sample chambers were installed at 300-500 W intervals. Molten materials such as slag and molten iron flow into the sample chamber and are sampled, but the entrance of each sample chamber is closed with cardboard.
The structure is such that a molten material such as slag that burns after a predetermined period of time after coming into contact with the molten material flows into the pipe.

Then, a sublance equipped with this probe is inserted into the slag during operation to collect a sample of the slag layer, and this sample is cooled to separate the slag and iron so that they are not mixed in the slag. The ratio of grained iron present can be determined. Figure 3 shows an example of the measurement results during operation while varying the N2 flow rate and number of tuyeres mentioned above.
The horizontal axis is the N2 flow rate per tuyere, and the vertical axis is the granular iron ratio in the slag. The measurement position was 1.5 m above the iron bath port, where O was operating two tuyeres, and .
This was normal operation, and the slag thickness at this time was 3 to 4 m.

In addition, the secondary combustion rate, the heat transfer efficiency of the secondary combustion, and the amount of dust in the exhaust gas were also investigated by changing the flow rate of N and the number of tuyeres. Figures 4 and 5 show examples of the investigation results, and Figure 4 shows the investigation results for operation with four tuyeres, and the stirring gas flow rate was 300 N rrr /hr/
This figure shows the vertical distribution of iron particles in the slag. As is clear from FIG. 4, the amount of granulated iron in the slag increases rapidly from a certain point down. In other words, it was found that a large amount of iron was mixed in the lower part of the slag layer due to the shaking of the iron bath surface and the blowing up of granulated iron. Also, Figure 5 shows
This figure shows an example of the results of investigating the amount of iron dust generated when the gas flow rate per tuyere was changed. As can be seen from Fig. 5, if it is less than 450 Nrrf/hr/piece, there is less iron dust;
/hr/ As you go beyond the book, the amount of iron dust increases.

As a result of analyzing the relationship between the amount of iron dust in the exhaust gas and the flow rate of stirring gas using various factors as described above, it was found that the gas flow rate per tuyere has the greatest influence on the amount of iron dust.

In addition, from Figure 3, which investigated the relationship between the stirring gas flow rate per tuyere and the amount of granulated iron in the slag, it is clear that when the stirring gas flow rate exceeds 450 Nnf/hr/tuyere, the granulated iron in the upper slag It was also found that the amount increased dramatically. Furthermore, a similar tendency was observed in the amount of iron dust generated as shown in FIG. 5 and the ratio of iron particles in the slag shown in FIG. 3.

The present inventors have discovered that reducing the amount of iron particles in the upper slag is one of the important conditions for reducing iron dust. In other words, it has been found from the various research results mentioned above that when the amount of iron particles in the slag increases, the amount of iron blown away by oxygen jets and generated gas decreases, resulting in a decrease in iron dust. Specifically, by setting the stirring gas flow rate per tuyere to an appropriate range of 4 50 Nn (/hr/piece or less), operation with a low ratio of iron particles in the slag can be achieved, and the amount of iron dust generated can be reduced. We found that it is possible to reduce the

However, if a gas species that reacts in the iron bath, such as carbon dioxide (CO2) or oxygen (0□), is used as the stirring gas, the volume of the gas will increase due to the reaction.
Even at a flow rate of 450 Nrrf/hr/unit or less, a phenomenon in which a large amount of iron dust is generated occurs. However, this phenomenon can be corrected in the same manner as inert Nz, Ar, etc. by multiplying it by a coefficient that takes into account the rate at which the stirred gas reacts in the iron bath and changes its volume. (However, the furnace pressure is 1 ata.

) Q = α Nbo/hr) Here, α differs depending on the gas type, but for example, carbon dioxide is CO□10C→
Because the 2GO reaction doubles the gas volume,
α becomes 2.

In addition, when pressurizing the inside of the furnace for various reasons, the pressure inside the furnace compresses the gas and reduces the effective volume.
The stirring gas flow rate is the limit value 450, which generates less iron dust.
Although it may exceed Nnf/hr/unit, if the flow rate of the stirring gas is corrected by the furnace pressure, it can be summarized by the following formula.

In other words, Q=αXqX (po /p)
・(3) Po: Atmospheric pressure (ATA,) p: Furnace pressure (ATA,).

However, since the atmospheric pressure here is 1 ata, the above equation (3) can be rewritten into the following equation (4).

Q = αX q / p (4) Therefore, in order to evaluate the flow rate of stirring gas in an iron bath where less iron dust is generated, the gas flow rate (Q) converted using equation (4)
It was discovered that the situation inside the reactor could be expressed in a unified manner.

For the above reasons, the present inventors have found that it is desirable to correct the stirring gas flow rate using the above equation (4) and control the operation using a value converted to the standard state.

In addition, even if the bottom-blown gas flow rate is 450 N rrf/hr/unit or less, if the number of tuyeres is increased and the stirring power of the iron bath exceeds 6 kW/L, the amount of dust generated will increase. It was also recognized that It turned out that this was because, as a result of increasing the number of tuyeres to ensure stirring power, the amount of granulated iron blown up increased due to increased interference between the tuyeres. Figure 6 shows an example of the results of investigating the relationship between the stirring force of the iron bath and the amount of dust generated, and the relationship between the stirring force of the iron bath and the heat transfer efficiency, under conditions where the stirring gas flow rate is 500 Nrrf/hr/unit or less. It shows. The horizontal axis is the stirring force, and the vertical axis is the amount of iron dust generated and heat transfer efficiency. Also, * is the heat transfer efficiency, and O is the amount of iron dust generated. The amount of iron dust generated is determined by stirring power of 6 kW/
The amount of iron dust increases sharply after t, indicating that the amount of iron dust increases if the stirring force is too strong. Regarding the heat transfer efficiency, it was observed that a stirring power of less than 1 kW/W decreased the heat transfer efficiency, and in some cases the heat transfer efficiency reached 60 to 70%, resulting in an increase in the temperature of the generated gas. Note that the stirring force used was a value calculated from the following equation (5).

t Here, ε: Stirring power (kW/t-metal) W:
Weight of hot metal (1) ρ: Density of hot metal (kg/rrf) d: Depth of hot metal bath (m) Lo: Atmospheric temperature (K) t: Iron bath temperature (K) As can be seen from this Figure 6, stirring power It was found that the amount of iron dust generated increased as the amount of power increased, and that the amount of iron dust increased significantly when the power exceeded 6 kW/t. In the present invention, the upper limit of the stirring power of the iron bath is set to 6 kW/t for the reason described above.

Next, various studies were conducted on the relationship between the above-mentioned survey results of the distribution of iron particles in the slag and the oxygen jet from the top blowing lance.

As can be seen from FIG. 4, which shows the vertical distribution of iron particles in the slag using the sub-lance probe described above, there is a large amount of iron particles blown up by the stirring gas in the lower part of the slag. In addition, the thickness of the layer with a lot of granular iron is most influenced by the gas flow rate per tuyere. The thickness T of the layer with a high mixing ratio of granular iron is shown in FIG. Figure 7 shows the relationship between the stirring gas flow rate and the thickness of the layer with a lot of granulated iron at the bottom of the slag layer, which was determined based on the survey results in Figure 4. It can be seen that this is strongly influenced by the stirring gas flow rate. When the above relationship was determined from FIG. 7, the following relational expression was obtained.

Thickness: T=35Q1/2 (or 35(αX Q
/ I)) + / Z (6) Q: Bottom-blown gas flow rate per tuyere defined by the above equation (4) Also, to investigate the influence of the interaction between the oxygen jet and the layer with a lot of granular iron. A test was conducted in which the top-blowing lance was moved up and down to change the dent (L) in the slag caused by the top-blowing oxygen jet. In addition, the following formula was used to calculate L, which was converted by the physical property value of slag based on the report by Segawa et al.

h,=36. O(k −F/D)'' L=ho exp (0,'78h/ho) ・
(ρ8/ρ3)−・−・・−・・−(7) However, k: Nozzle coefficient (−)...See Figure 10 F:
Top-blown oxygen flow 1t (N/hr) D: Lance nozzle diameter (Peng) h: Lance-slug upper surface distance ([lll11) ρi:
Hot metal density (T/rrr) ρ, Nisslag density (T/bo) The nozzle coefficient was determined from the relationship between the nozzle angle of the top blowing lance shown in FIG. 10 and the number of nozzle holes as reported by Segawa et al.

As a result, the dents (L) in the slag appear in the slag layer 1 with a large amount of iron particles.
When reaching the thickness (T) region of 3 (Fig. 2), an increase in iron dust loss was observed even under conditions where the stirring gas flow rate was 450 Nrrf/hr/unit or less. The depression of the oxygen jet (L) and the thickness of the slag layer 13 containing a lot of iron particles (T
) A schematic diagram is shown in Figure 2 to make it easier to understand the relationship. FIG. 2 is a detailed view of the inside of the furnace during smelting and reduction. Iron pig 11 is present at the bottom of the furnace, and a molten slag layer 12 is present above it, and stirring passes through the slag layer. Foaming occurs due to gas. At the bottom of this molten slag layer 12 is a slag layer 1 containing a lot of granular iron blown up by the bottom blowing gas.
3 is formed, this thickness is expressed as T, and the total thickness of the molten slag layer 12 and the slag layer 13 containing a large amount of granular iron is expressed as Lo. A small amount of granular iron and a relatively large amount of carbonaceous material are mixed in the upper part of the slag, and the molten slag circulates and flows due to stirring by bottom blowing gas and carbon monoxide gas generated when reducing ore. Top-blown oxygen is from lance 2 and slag 1
2, the oxygen forms a supersonic or subsonic jet, displacing the slag and creating a depression with a depth L.

In addition, under these operating conditions, due to the contact between top-blown oxygen and a large amount of granulated iron, carbon dioxide and water vapor produced by combustion due to oxygen react with carbon in the hot metal, producing -carbon oxide and hydrogen. Admitted. In other words, it was found that the secondary combustion rate decreases, which in turn decreases the amount of heat supplied to the furnace, resulting in a decrease in productivity.

Therefore, in order to further reduce iron dust and keep the secondary combustion rate at a high level, in addition to the conditions of the stirring gas flow rate, the concave depth (L) of the top-blown oxygen jet must be adjusted to It is desirable not to reach the region of thickness (T).

, LO-L and (T), the amount of iron dust generated, and the secondary combustion rate are shown in Figure 8. In operation,
It was found that the amount of dust was large and the secondary combustion rate was low.

The slag thickness in this operation was 2,800 mm, and the thickness of the layer containing a lot of granular iron at the bottom of the slag was 600 mm.

This relationship is expressed as the depression depth (L) of top-blown oxygen against the slag.
If expressed in terms of the slag layer thickness (L0) and the bottom blowing gas flow rate, the equation (1) mentioned above, that is, Lo L < 35 (α
X q / p) ''' -----------1・-(1).

That is, L, -L<35 (αX q / p)
Operating under top-blown oxygen and stirring gas supply conditions that satisfy the I/2 relationship is important in order to reduce iron dust and maintain a high secondary combustion rate. The present inventors have discovered that it is possible to carry out operations with good coal consumption and iron yield.

Next, we investigated the relationship between the stirring power of the iron bath and the heat transfer efficiency of secondary combustion, and found that when the stirring power was low, the heat transfer efficiency of secondary combustion decreased.

FIG. 6 shows the results of investigating the relationship between the stirring force of the iron bath defined by the above equation (5) and the heat transfer efficiency. The stirring power of the iron bath is 1
It is recognized that when the power is less than 1 kW/, the heat transfer efficiency of secondary combustion deteriorates. A phenomenon occurred in which the unit consumption rate deteriorated, and good operations could not be carried out.

In other words, the stirring power of the iron bath is preferably 1kW/or more.
Based on the above-mentioned survey results on the amount of iron dust generated, the upper limit is kW.
/ Since the following is desirable, the stirring power of bottom blowing should be 1~
The present inventors have discovered that operation at 6 kW/t is necessary for efficient melt reduction operation.

Here, the flow rate of the stirring gas to make the stirring power of the iron bath 1 kW/t was determined. Average iron bath temperature in smelting reduction: 150
0°C and the depth of the iron bath at which the jet of stirring gas can stably stir the iron bath without causing blow-through, is 700 to 100°C.
In the case of 0mm, 7ONn(/hr(
Inert gas, latm, conversion). On the other hand, when constructing tuyeres for stirring gas, the tuyeres and the support bricks around them are large deformed bricks, and there is a problem in that the interval between the tuyeres cannot be made extremely small. In addition, it is known that due to the reduction in the bottom striking of the blown gas, the rate of erosion of the tuyere is higher than that of the surrounding bricks, and that only the tuyere undergoes preliminary erosion in the form of a dovetail. If the distance between adjacent tuyeres is small, the areas with high melting damage will be connected, causing the problem that the entire bottom brick will be worn away. However, it is usually desirable to set the spacing between the tuyeres to 1 m or more, which means that the ratio of tuyeres is approximately one per 1 m, so the minimum flow rate per tuyere is 7.
ONrd/hr.

As described above, the present inventors have elucidated the stirring conditions for the iron bath and slag using stirring gas that achieve better operating conditions than conventional methods in terms of secondary combustion, heat transfer efficiency, and amount of iron dust generated.

Furthermore, in the operation of smelting and reduction, reducing the scattering loss of carbonaceous materials is a very important operational element, as mentioned above, and therefore, the present inventors are actively developing methods for reducing the scattering loss of carbonaceous materials. conducted research.

Figure 9 shows an example of the results of investigating the relationship between slag amount and carbonaceous dust retention under various operating conditions.
As the amount of slag or the amount of slag per iron bath area increases, the amount of carbonaceous material scattering (charcoalwood dust) decreases, and when the slag amount is 1500 kg/rrf or more, the carbonaceous material scattering loss has been shown to be reduced. In other words, it was found that increasing the amount of molten slag in the furnace is important as the operational factor that has the strongest effect on the scattering loss of carbonaceous materials.

Therefore, in order to elucidate this factor, the present inventors measured the swelling state of the molten slag in the furnace during the smelting reduction operation, and found that the slag in the furnace is normal because the generated gas passes through the slag. It was found that the swelling was three to four times larger than when it was sedated. In other words, if you convert the apparent slag into specific gravity based on this swelling ratio, the apparent specific gravity of the swollen slag is 0.5 to 0.
．． It was found that the speed was 7T/rrr. The value of this slag specific gravity indicates that the apparent carbonaceous material (in the form of char) suspended in the slag is 0.7 to 0.0% of the specific gravity. BT/rr
Almost equal to f. Since the apparent specific gravity of carbonaceous material is the same as that of slag, carbonaceous material has the ability to mix well with the rapidly flowing slag, and by increasing the amount of slag, the effect of slag covering the carbonaceous material increases. It was revealed that the cause was a decrease in the transfer ratio to gas in the furnace.

Therefore, by increasing the amount of slag in the furnace and increasing the thickness of the slag, the slag can sufficiently cover the carbonaceous material.Since the covering effect of this slag is determined by the thickness of the slag, the amount of slag can be increased. It was found that the evaluation should be based on the area of the iron bath.

FIG. 9 shows that as the amount of slag increases, the amount of scattering loss of carbon material decreases.

It has been found that with this equipment, if the slag amount is 30 or 337 or more, that is, if the slag amount per bath area is 1500 kg/n or more, the scattering loss of carbon material is reduced to 10% or less.

<Example> The present invention was carried out in a melting reduction furnace shown in FIG.

In FIG. 1, reference numeral 1 denotes a furnace body lined with refractory bricks, and in the lower part of this furnace body 1, hot metal 11 and molten slag 12 each form a bath. The hot metal 11 and molten slag 12 are at a high temperature of about 1400 to 1700°C, and after ore is fed into these and iron oxide is melted, the coke or char mixed in the slag is removed. This molten iron oxide is reduced by the carbonaceous materials in the molten metal and the dissolved carbon in the hot metal, and hot metal is produced. The hot metal 11 and slag 12 are used to compensate for the heat of reduction and the sensible heat of the product.
Oxygen (oxygen-enriched air, or even heated air) is supplied from the top-blowing lance 2 to the carbonaceous material inside.

The supplied oxygen burns dissolved carbon in the coal and hot metal to generate CO and H2 and generate combustion heat. In addition, combustion reactions occur with these generated gases, resulting in CO
t and H2O, and also generates combustion heat. The former combustion is called primary combustion, and the latter combustion is called secondary combustion.

Further, stirring gas is supplied through the tuyeres 3 below the bath surface for the purpose of promoting ore dissolution, reduction reaction, and heat transfer.

Since this stirring gas is intended for stirring, the type of gas is not particularly limited, and generally hydrocarbons such as nitrogen, argon, oxygen, and propane are used. However, when operating with the goal of maintaining a high secondary combustion rate, gases such as oxygen and carbon dioxide that consume carbon in the iron bath are undesirable. In other words, when these oxidizing gases are bottom blown, even if the gas reacts with dissolved carbon in the iron bath, thermodynamically it will only produce carbon monoxide, and the proportion of carbon dioxide in the generated gas, that is, the secondary This is because it results in a reduction in the combustion rate.

There are several ways to supply ore, such as dropping it from the hopper at the top of the furnace, blowing it from the side wall of the furnace, and blowing it into the slag or molten iron bath.
The illustrated embodiment shows a method of feeding ore from a hopper 5 above the furnace.

Coal is supplied so as to keep the carbon balance within the smelting reduction furnace approximately constant. As with ore, there are several feeding methods, such as charging from above, blowing, and blowing into the molten iron or slag bath. In the embodiment shown in FIG. 1, coal is fed from the hopper 4 above the furnace. Showed how to supply.

During the smelting reduction operation, ore was continuously supplied from hopper No. 5, coal from hopper No. 4, and oxygen was also supplied by blowing from a top-blown lance toward the slag and hot metal. The ore is melted, reduced, and settled as hot metal in the hot metal bath at the bottom of the furnace. Furthermore, the gas from the combustion of coal is recovered via the exhaust gas duct 7, and the dust in the gas is removed by the dust collector 8, and is used as reducing gas for preliminary reduction of ore in the preliminary reduction furnace or as fuel. Ru. At this time, since the gas has a large amount of sensible heat, this sensible heat may be effectively used as heat for steam generation, etc.

In order to control the operation, it is necessary to measure the conditions inside the furnace, so samples of the hot metal and slag are collected using the sublance 6, and the heights of the top surfaces of the slag and hot metal are also measured. Further, an exhaust gas analyzer 10 is also installed for purposes such as measuring the secondary combustion rate.

As the smelting reduction operation progresses, hot metal and slag accumulate in the furnace, so the hot metal and slag are periodically discharged.

Hot metal was produced in the smelting reduction furnace described above under the conditions shown in Table 1. In Table 1, in the examples according to the present invention, each of the bottom-blown gas flow rate, stirring power, comparison of the dent depth of the slag due to the top-blown oxygen jet and the thickness of the slag layer containing a lot of granular iron, and the slag amount specified in the present invention were These are the results of operation under the conditions of the present invention.

In Example 1, nitrogen gas that does not react in the iron bath is blown from the bottom,
This is a standard operation in which the pressure inside the furnace is atmospheric pressure. Further, in Example 2, the operation was performed with the furnace pressure at 2 atmospheres. The stirring gas flow rate at this time is displayed in normal conversion (Nrr
f/hr) exceeds the upper limit of the bottom-blown gas flow rate per tuyere defined in the present invention, but the flow rate corrected for the furnace pressure (converted to standard conditions: Q) is within the operating conditions of the present invention. This is a new operation. Example 3 shows the operation results when carbon dioxide gas, which reacts with carbon in the iron bath to become carbon monoxide and doubles in volume, is blown in as a stirring gas.

In all of these examples, the secondary combustion rate was 43 to 46%.
This is relatively high, and the heat transfer efficiency is also over 90%. The amount of iron dust generated is less than 3% per produced hot metal, and the amount of carbonaceous dust generated remains at a low level of about 5 to 7%. In this way, we were able to conduct a good operation in terms of secondary combustion and dust generation, and the coal consumption rate was reduced to 1000.
kg/ is below.

On the other hand, in Comparative Example 1, which is operated by the conventional method,
Since the stirring gas flow rate per tuyere is as high as 65ON/hr, the amount of iron dust is as high as 85.4kg/t, and as the iron yield is poor, the coal consumption rate is also 1000k.
exceeding g/t.

In addition, Comparative Example 2 is the result of operation in which the furnace pressure was increased to 2 atmospheres, and even if the pressure is corrected, the gas flow rate (Q) per tuyere converted to the standard state is still lower than that of the present invention. Since it exceeded the range of 450 N rrr/hr, the amount of iron dust generated was large at 98.7 kg, and the coal consumption rate was also poor.

Next, in Comparative Example 3, in which carbon dioxide gas is blown in, which reacts in the iron bath and doubles its volume, if the reaction in the iron bath is not taken into account, the amount of gas per tuyere is Although the flow rate falls within the range of the present invention, when the reaction is taken into consideration, the results are shown in an operation where Q exceeds the upper limit. In the operation of Comparative Example 3 as well, the amount of iron dust was as large as 100 kg or more, and the coal consumption rate was also 1100 kg or more. These operational results show that the upper limit of the bottom-blown gas flow rate must take into account the change in volume due to the reaction within the iron bath.

Next, Comparative Example 4 will be shown as an operation in which the stirring force was weak and the heat transfer efficiency of secondary combustion was deteriorated. In this test operation, the stirring power of the iron bath was weak at 0.8 kW/t, and in the comparative example, which was less than 1 kW/t, which is the operating range of the present invention, the heat transfer efficiency was 79%. As a result, the coal consumption rate was 1295kg compared to other operation examples.
/t, which was a very large amount, and could not be said to be an economical hot metal production method.

In Comparative Example 5, the gas flow rate per tuyere satisfied the conditions of the present invention, but since the number of tuyeres was as large as 6, the stirring power of the iron bath exceeded 6 kW/. As a result, the amount of iron dust generated was approximately 120 kg/t, resulting in a large operation.

In Comparative Example 6, the dent in the slag formed by the top-blown oxygen jet reached the thickness (T) of the layer containing a lot of iron particles at the bottom of the slag, which was formed by the bottom-blown gas blown for stirring. This is an example of a similar operation. In this operation, oxygen and granulated iron come into contact, and the granulated iron is blown away into the generated gas. At the same time, the top-blown oxygen and carbon monoxide gas generated from the iron bath are combusted, resulting in carbon dioxide and carbon dioxide in the granulated iron. The carbon reacted and returned to -carbon oxide. As a result, the amount of iron dust generated was large, and the secondary combustion rate was decreased, and the amount of iron dust generated was about 100 kg/t, and the coal consumption rate was also high at 1251 kg/t.

Comparative Example 7 is an example of operation with a small amount of slag. In this operation, secondary combustion and iron dust were good, but the amount of slag was 1200 kg/rrf, which was less than the lower limit of 1500 kg/rd of the scope of the present invention, so the amount of carbonaceous dust generated was low. This amounted to 15% of the input coal, resulting in a large loss of coal, and the coal consumption rate was as high as 1150 kg/t. In addition to the deterioration of the coal consumption rate, the amount of carbon suspended in the slag decreased due to scattering loss, which caused slag slopping due to abnormal forming, making it impossible to continue operations.

As described above, in any operation that deviates from the operating range shown in the present invention, operating costs such as a decrease in the secondary combustion rate, a decrease in heat transfer efficiency, an increase in iron dust, and an increase in carbonaceous dust are incurred. However, in Examples 1 to 3, which are within the operational range of the present invention, the amount of iron and carbonaceous dust generated was small ( In addition, we were able to operate an efficient smelting reduction method with good secondary combustion rate and heat transfer efficiency.

〔Effect of the invention〕

By implementing the present invention, it is possible to reduce the amount of iron dust and carbonaceous dust generated in the generated gas during smelting reduction operation, and to perform operation with high secondary combustion rate and heat transfer efficiency. In addition to good yields, it is possible to operate with low coal consumption and oxygen consumption, and in addition to being able to produce hot metal at a low production cost, productivity can also be improved.

[Brief explanation of the drawing]

Fig. 1 is for explaining the operation of the smelting reduction method based on the present invention, and is a block diagram of a well-known iron bath type smelting reduction furnace, and Fig. 2 is a detailed diagram of the inside of the smelting reduction furnace. , A diagram showing the relationship between slag thickness, slag depression caused by oxygen jet, and a slag layer with a large amount of granular iron. Figure 3 is an example of the results of an investigation of the relationship between the weight ratio of granular iron in slag to slag in the operation of the smelting reduction method. Figure 4 shows an example of the investigation results of the vertical distribution of iron particles in the slag, and Figure 5 shows the investigation results of the relationship between the gas flow rate per tuyere and the amount of iron dust generated. Figure 6 shows an example of the relationship between the stirring force of the iron bath and the amount of iron dust generated, and the relationship between the stirring force of the iron bath and heat transfer efficiency. Figure 8 shows an example of the relationship between the bottom blowing gas flow rate per jet and the thickness of the layer with a lot of iron particles at the bottom of the slag layer. Figure 9 shows an example of the results of a study on the relationship between the slag weight and the amount of dust generated from carbonaceous material. Figure 10 shows the height reached by the top-blown oxygen jet. FIG. 3 is a diagram showing the relationship between the nozzle coefficient (k), the nozzle angle, and the number of holes in the lance used for calculation of the distance. Fig. 1 Fig. 3 0 50 00 Z evening 0 per drop a) /v7 journey, amount (Nm'-rei) Fig. 5 470°/QUXd of main come... (Nm3/hr) Fig. 4 / Friend L4 Ij Okazuuno Junsuko (771) Fig. 6 4 Large bath thirst t, partner force (kw/t-metal) Fig. 7 O 25θ 00 7δO Bottom of each feather Amount of slab (t/ynz) of ゛叉2t (1m shiheha Figure 9 bath area t-) 0 0 0 Slab amount (1> Figure 8・Koni; XJζafi 251; ehio: 4 Husband guest occurrence 4L Fig. 10 0/S 0 S ) People's traffic level (°)

Claims (3)

[Claims] (1) In an iron bath-type melting reduction furnace that blows oxygen from a top blowing lance and bottom blows stirring gas from multiple tuyeres below the bath surface,
The stirring power of the iron bath by the stirring gas is set in the range of 1 to 6 kW/t, and the gas flow rate per tuyere is controlled in the range of 70 to 450 Nm^3/hr in terms of standard conditions. A metal smelting reduction method characterized by (2) So that the relationship between the depth of the top-blown oxygen dent in the slag (L) and the slag thickness (L_0) satisfies the following formula:
2. The metal smelting reduction method according to claim 1, wherein any one or more of the stirring gas flow rate, the lance height, the oxygen supply flow rate, and the nozzle shape of the top blowing lance is controlled. L_0-L<35(α・q/p)^1^/^2 However,
q: Gas flow rate per tuyere (Nm^3/hr) α: Rate of change in gas volume due to reaction of stirred gas in the iron bath (-) p: Furnace pressure (ata.) (3) Reduce the amount of slag per bath area in the smelting reduction furnace to 1500
The method for melting and reducing metals according to claim 1 or 2, characterized in that it is operated at a rate of kg/m^3 or more.