[Designation of Document] SPECIFICATION
[Title of the Invention] SLAG FOAMING DEPRESSANT MATERIAL AND
METHOD FOR DEPRESSING SLAG FOAMING
[Technical Field]
[0001]
The present invention relates to a slag foaming depressant material for depressing a slag that is foaming (generating foams), and a method for depressing slag foaming.
This application claims priority from Japanese Patent Application No. 2008-138320 filed on May 27, 2008, the disclosure of which is incorporated by reference herein. [Background Art]
[0002]
Steelmaking slag (hereinafter, simply referred to as slag) generated in the process of producing molten steel, often undergoes generation of foam (foaming) (that is, expansion of the slag in volume) due to the CO bubbles generated at the interface with the molten iron or inside the slag itself, during a refining treatment or after a refining treatment. In the case where the extent of this generation of foam is severe, there are occasions in which slag undergoes overflowing from refinery facilities such as a converter furnace, a torpedo ladle car and a discharge ladle, or from a transport container for molten iron or slag. Since this slag is at a high temperature of 1300 to 1650°C, the slag damages the facilities when it overflows, and enormous time and effort are required for repair of the facilities.
As a method for avoiding such slag overflow, for example, a method of decreasing the speed of the refining processes, or a method of temporarily stopping the
refining processes may be mentioned. However, these methods have adverse effects on the productivity of molten steel, and are therefore not preferable.
[0003]
The process of generation of CO bubbles as described above occurs in two ways, such as a case where FeO (iron oxide) in the slag and C in the molten iron react at the interface, and a case where, similarly, FeO in the slag and C in the granular iron contained inside the slag react. In all of these cases, gas bubbles that take a longer time (have a longer lifespan) to reach the slag surface and burst are more likely to be retained in the slag. As the bubbles have a smaller diameter, and as the slag components become more viscous, the bubbles are able to exist stably in the slag, and therefore, the lifespan is extended (the bubbles are difficult to burst). From this point of view, in order to suppress expansion of the slag, it is desirable to accelerate the coalescence of minute bubbles to make coarse bubbles.
Also, in the case of both of the two above-described reactions, it is understood that the higher the FeO concentration of the slag, the larger the quantity of CO bubbles that are generated. Therefore, a slag having a higher FeO concentration has particularly strong foamability, and thus is likely to expand rapidly and overflow. Thus, in order to prevent the overflow of a foaming slag, it is necessary to destroy the layer where bubbles stay in the slag (foam layer) to shrink the slag, and to thereby depress the slag. Accordingly, a method of introducing a material which gasifies in the slag, and using the volume expansion energy obtained upon gasification in the destruction of the foam layer, is generally implemented.
As described above, it is clear that a slag which is more viscous or which has a higher FeO concentration is more likely to undergo foaming. Furthermore, as a means to reduce this foaming, a depressant material which depresses foaming through
acceleration of the coalescence of bubbles or destruction of the foam layer, is being commonly used.
[0004]
As an example of such a depressant material, carbon powder is known.
For example, Patent Document 1 as shown below discloses a method of depressing foaming by ejecting carbon powder (wood charcoal) to a foaming slag at a rate of 5 to 100 kg/min.
Patent Document 2, as shown below, also discloses a method of depressing foaming by injecting carbon powders (wood charcoal) having a particle size of 0.1 to 1 mm and 1 to 5 mm from respective independent ejection systems, and setting the amount of ejection at 0.1 kg or more and less than 0.8 kg per ton of hot metal through a single suppression operation, and setting the ejection rate at 5 to 100 kg/min.
[0005]
In recent years, when producing molten steel by refining hot metal, a method of performing a dephosphorization treatment in a converter furnace, subsequently discharging a part of the slag in the furnace to the discharge ladle installed underneath the furnace, and continuously performing decarbonization (multifunctional converter furnace method) has been carried out.
In this method, the dischargeability of the slag is improved by adjusting the ratio of CaO/SiO2 (hereinafter, referred to as basicity) of the slag component in the converter furnace to 0.8 to 1.5, and increasing the viscousness of the slag to thereby facilitate foaming. Since the slag discharged from the converter furnace has bubbles with relatively small diameters, and the slag is highly viscous, the slag is more prone to rapid foaming compared to immediately after being discharged to the discharge ladle.
Furthermore, in the above-described multifunctional converter furnace
method, the FeO concentration of the slag in the converter furnace is increased, and C in the hot metal and in the slag are vigorously reacted at the interface to induce foaming, so as to make the dischargeability of the slag better. In such slag foamed, a large amount of granular iron is entrained, concomitantly with the vigorous generation of CO bubbles at the interface of the slag and the hot metal. Therefore, the slag discharged from the converter furnace is prone to rapid foaming, because FeO in the slag and C in the granular iron that is contained inside the slag react to generate CO bubbles starting immediately after the slag is discharged to the discharge ladle.
Also, though once foaming depressed, the slag will be very likely to foam continuously due to other portions of slag that are discharged one after another.
[0006]
Therefore, in order to discharge such slag from the converter furnace to the discharge ladle in a larger amount in a shorter time, while preventing an overflow of the slag from the discharge ladle, it is important to depress foaming at the discharge ladle, and the effects of the depressant material which suppresses foaming have an important meaning.
Here, if the effects of the depressant material are small, the amount of slag-off should be reduced to avoid an overflow of the slag. In this case, it is likely that an increase in rephosphorization in the decarbonization treatment after slag-off, or occurrence of slopping may result. Furthermore, in order to suppress this rephosphorization and slopping, it is desirable to increase the amount of CaO used, but this causes an increase in the amount of slag generated having a high CaO concentration. Thus, it is not preferable from the viewpoints of not only the refining costs but also of slag treatment.
[0007]
Thus, for example, Patent Document 3 as shown below discloses a solid depressant material for a converter furnace, which includes 50 to 90% of a pulp waste slag having a water content of 20% or less as a material generating gas with the heat of the slag, 5 to 25% of a converter furnace waste as a material adding the mass, and 5 to 25% of a binder such as bentonite.
Patent Document 4 as shown below also discloses a depressant material prepared by mixing less than 40% of thermodecomposable materials such as coal, limestone, plastics and paper as gas-generating materials, with microgranular iron powder and a binder, forming the mixture into briquettes, and adjusting the apparent specific gravity to 2 to 5.
[Patent Documents]
[0008]
[Patent Document 1] Japanese Unexamined Patent Application, First Application No.H4-l 80507
[Patent Document 2] Japanese Unexamined Patent Application, First Application No. H5-287347
[Patent Document 3] Japanese Unexamined Patent Application, First Application No. S54-32116
[Patent Document 4] Japanese Unexamined Patent Application, First Application No. H11-50124 [Disclosure of the Invention] [Problem that the Invention is to solve]
[0009]
However, upon depression of foaming in the discharge ladle, in the case of ejecting carbon powder to the slag surface as described in the Patent Document 1, it is
difficult for the carbon powder to go into the inner part of the slag because of its low specific gravity and small volume. For this reason, the effects of the carbon powder are exhibited only on the surface side of the slag, and the carbon powder is almost ineffective for slag which undergoes fast foaming.
In the case of ejecting carbon powder to the inner part of slag as described in the Patent Document 2, the carbon powder is difficult to disperse throughout the entire slag because of its low specific gravity and small volume. For this reason, the effects of the carbon powder are exhibited only in the vicinity of the injected position. Therefore, in order to exert the effects of the carbon powder over the entire slag, the ejecting in must be performed from a number of positions, and workability is deteriorated, while the facility configuration becomes complicated.
[0010]
Furthermore, upon depression of foaming in the discharge ladle, the depressant material described in the Patent Document 3 uses the CO or CO2 gas generated by combustion of the pulp waste slag, and H2O gas from the moisture. However, since the moisture level is as low as 20% or less, the amount of gas generation immediately after introduction is small. Therefore, a large amount of the depressant material should be introduced for slag undergoing rapid foaming.
The depressant material described in the Patent Document 4 utilizes the CO or CO2 gas generated from the thermodecomposable material, but since the ratio of the microgranular iron powder to this thermodecomposable material is high, the amount of generation of the CO or CO2 gas is small. Therefore, similarly to the case of the Patent Document 3, a large amount of the depressant material should be introduced for slag undergoing rapid foaming.
Introduction of a large amount of such a depressant material to slag has a
problem of bringing about: (1) an increase in the refining costs, (2) an increase in the amount of the residue of the depressant materials after gas generation remaining in the slag as impurities, and (3) deterioration of the working environment as a result of an increase in the amount of the residue turned into white smoke and blown off.
[0011]
The invention has been made under such circumstances, and it is an object of the invention to provide a slag foaming depressant material and a slag foaming depressant method whch are capable of rapidly depressing a foaming molten slag using a small amount of the depressant material, and realizing the stable maintenance of productivity by preventing damage to facilities due to an overflow of molten slag. [Means to Solve the Problems]
[0012]
The invention employs the following means in order to achieve the relevant objects by solving the above-described problems. Specifically,
1) A slag foaming depressant material according to the invention includes a mixture containing 20% by mass or more and 40% by mass or less of a carbon powder having a particle size of 0.2 mm or more and 2 mm or less, and 30% by mass or more and 60% by mass or less of moisture; and a container for containing the mixture, formed from a non-water-permeable and flammable material.
2) In the slag foaming depressant material according to the preceding item (1), the mass of the mixture contained in the container may be 1 kg or more and 10 kg or less.
[0013]
(3) A method for depressing slag foaming according to the invention
includes introducing the slag foaming depressant material according to the preceding
item (1), into a foaming molten slag having a basicity of 0.8 or more and 1.5 or less.
4) In the method for depressing slag foaming according to the preceding item (3), the slag foaming depressant material may be introduced at the position of discharge of the molten slag that is discharged from a converter furnace, during the period of 30 seconds after the initiation of discharge of this molten slag.
5) An another method for depressing slag foaming according to the invention includes introducing the slag foaming depressant material according to the preceding item (1) into a discharge ladle and subsequently introducing a molten slag having a basicity of 0.8 or more and 1.5 or less, into the discharge ladle.
[0014]
6) A still another slag foaming depressant material according to the invention includes a mixture containing 30% by mass or more and 60% by mass or less of moisture and 35% by mass or more and 65% by mass or less of a fuel component and a container for containing the mixture, formed from a non-water-permeable organic material.
7) In the slag foaming depressant material according to the preceding item (6), the mass of the mixture contained in the container may be 1 kg or more and 10 kg or less.
[0015]
8) A still another method for depressing slag foaming according to the invention includes introducing the slag foaming depressant according to the preceding item (6), into a foaming molten slag having an iron oxide concentration of 15% by mass or more and 25% by mass or less.
9) In the method for depressing slag foaming according to the preceding item (8), the slag foaming depressant material may be introduced at the position of
discharge of the molten slag that is discharged from a converter furnace, during the period of 30 seconds after the initiation of discharge of this molten slag.
[0016]
The moisture and carbon powder of the mixture constituting the slag foaming depressant material (hereinafter, may be simply referred to as depressant material) are defined as follows.
The moisture is, for example, a material that gasifies when heated at 100°C for 2 hours, and the mass content % is determined from the ratio of mass change before and after heating. In view of the measurement technique, materials having a boiling point lower than that of H2O, such as ethanol, also gasify together with the moisture, but since such low boiling point materials are not often included in large amounts during the production of the depressant material, and even if included in a small amount, the low boiling point materials do not inhibit the contribution of H2O to depression, the invention defines the moisture to include these low boiling point materials.
[0017]
The carbon powder is a material containing carbon as a main component (80% by mass or more), such as coke powder, coal powder or graphite powder. The particle size of this carbon powder is defined by the mesh opening size of the sieve through which the carbon powder can pass. That is, a particle size of 0.2 mm or more and 2 mm or less means a particle which can pass through a sieve having a mesh opening size of 2 mm but cannot pass through a sieve having a mesh opening size of 0.2 mm.
[0018]
The fuel component is a material which burns and gasifies when heated at
815°C for 1 hour under atmospheric conditions, and the mass content % is determined by subtracting the moisture mass content % from the ratio of mass change before and after heating (gasified fraction). This fuel component is formed from solids or a mixture of solids and liquids, and for example, cellulose in pulp waste slag, plastics, tray, waste oil of cooking oil, engine oil and the like, and organic materials such as oil-containing sludge fall in this category.
[0019]
The remaining part other than the moisture and the fuel component in the mixture constituting the slag foaming depressant material is called the ash component, and corresponds to the residue remaining after gas generation. Since this ash component is indispensably included in the mixture in a proportion of at least about 5% by mass, the sum of the moisture and the fuel component is a maximum of 95% by mass.
The relationship between the moisture, the fuel component and the ash component discussed above is as follows.
(Mixture constituting depressant material) = (moisture) + (fuel component) + (ash component) = 100 (% by mass) [Effects of the Invention]
[0020]
In regard to the slag foaming depressant material described in (1) or (6) above and the method for depressing slag foaming described in (3) or (8) above of the invention, the depressant material constituted of a mixture containing a predetermined amount of moisture and carbon powder is contained in a container composed of a non-water-permeable and flammable material, and is introduced into a foaming molten slag. Therefore, it is possible to disperse carbon powder in the molten slag by means of the
explosive volume expansion energy resulting from the gasification of the moisture. As a result, foaming of the molten slag can be efficiently suppressed, and therefore a high depressant effect can be obtained even with a small total amount of the depressant material introduced. Accordingly, cost reduction for the depressant material, improvement of workability due to prevention of the damage to facilities caused by an overflow of the molten slag, and stable maintenance of productivity in the refining process are made possible. [Brief Description of the Drawings] [0021]
[FIG. 1] FIG 1 is a graph showing the relationship between the diameter of bubbles in the molten slag and the lifespan of the bubbles. The horizontal axis represents the diameter of bubbles, and the vertical axis represents the lifespan of bubbles.
[FIG. 2] FIG. 2 is an explanatory diagram of the method for depressing slag foaming according to an embodiment of the invention.
[FIG 3] FIG. 3 is a graph showing an example of changes over time of the rate of gas generation per kg of the slag foaming depressant material. The horizontal axis represents the time after the introduction of the depressant material, and the vertical axis represents the rate of gas generation per kg of the depressant material. [Description of Reference Numerals and Signs] [0022]
10 Converter furnace
11 Discharge ladle
12 Depressant material
13 Worktable
14 Mobile carriage
51 Molten slag in converter furnace
52 Molten slag discharged to discharge ladle P Hot metal
[Embodiments of the Invention]
[0023]
The slag foaming depressant material and the method for depressing slag foaming according to embodiments of the invention will be described below with reference to the attached drawings. [First Embodiment]
FIG. 1 is a graph showing the relationship between the diameter of bubbles in the molten slag and the lifespan of the bubbles, where the horizontal axis represents the diameter of bubbles, and the vertical axis represents the lifespan of bubbles. FIG. 2 is an explanatory diagram for the method for depressing slag foaming according to the present embodiment.
[0024]
The slag foaming depressant material (hereinafter, may be simply referred to as depressant material) according to the present embodiment is such that a mixture having carbon powder and moisture is contained in a container composed of a non-water-permeable, flammable material. Hereinafter, the depressant material will be described in detail.
[0025]
Since carbon powder has poor wettability with respect to molten slag, carbon powder has an effect of repelling the molten slag at the surface. Thus, when this carbon powder enters into the slag liquid film present between a bubble and another
bubble, the slag liquid film is cleared off, and the bubbles coalesce. Here, the relationship between the diameter of bubbles and the lifespan of bubbles will be explained, while referring to FIG. 1.
As is obvious from FIG. 1, there is a tendency that the lifespan of bubbles is shortened, concomitantly with an increase in the diameter of bubbles, and thus the bubbles are likely to burst at the surface of the molten slag. Particularly, bubbles having a bubble diameter of greater than 2 mm (2.0 mm) do not show conspicuous differences in lifespan, that is, the time taken until bursting, and the lifespan was about 4 seconds.
Therefore, when causing bubbles having a bubble diameter exceeding 2 mm to coalesce by means of carbon powder, it was found that since the order of decrease in the lifespan of bubbles is small, a large foaming suppressive effect is difficult to obtain. On the other hand, in the case of causing bubbles having a bubble diameter of less than 2 mm to coalesce, it was found that since the order of decrease in the lifespan is large, a foaming suppressive effect is easily obtained.
[0026]
The present inventors also collected molten slag respectively from the torpedo ladle car, the converter furnace and the discharge ladle, and investigated the diameter of bubbles remaining in the slag, and the inventors obtained a finding that the bubble diameters were 0.2 to 5 mm. From this finding, it is presumed that bubbles having a bubble diameter of less than 0.2 mm do not exist, or if they do exist, the number is small. Thus, the influence of such bubbles on foaming is considered to be small.
Here, regarding the bubbles having a bubble diameter exceeding 2 mm, since the bubbles readily burst at the surface of the molten slag even though a depressant material is not introduced, for the reason described above, the influence of the bubbles
on foaming is considered to be small.
[0027]
From these findings, it was found that if it was possible to accelerate coalescence of bubbles having a bubble diameter of 0.2 mm or more and 2 mm or less by the action of carbon powder, and to increase the bubble diameter to more than 2 mm, the lifespan of bubbles would be greatly reduced, and foaming could be suppressed.
However, if it is desired to reliably depress slag foaming using a small amount of a depressant material, it is necessary to disperse carbon powder in the molten slag. This is because when the carbon powder is uniformly dispersed in the molten slag, rather than being localized, the bubbles coalesce throughout the entire molten slag, and the foaming suppressive effect is augmented.
Thus, the present inventors thought of using the volume expansion energy obtained when a gas generating material gasifies, as a means to disperse the carbon powder in the molten slag, and carried out the following test.
[0028]
First, mixtures prepared by using water, pulp waste slag, cooking oil and waste plastics that are available at low cost, as gas generating materials, and by mixing these with widely varying amount of carbon powder, was put in a plastic bag to produce a depressant material. Thus, a test was carried out regarding the introduction of this depressant material into a molten slag which was foaming during slag-off using actual equipment.
As a result, when the amount of introduction of the depressant material was a small amount such as about 1% by mass of the amount of discharged molten slag, there were obtained slag foaming depressant materials that showed a foaming suppressive effect, and slag foaming depressant materials that did not show a suppressive effect.
From these results, the following was found with regard to the suitable scope of the slag foaming depressant material.
[0029]
First, the amount of moisture in the mixture is 30% by mass or more and 60% by mass or less.
Here, if the amount of moisture is less than 30% by mass, the gas generated (steam) is insufficient, and the volume expansion energy is insufficient, so that it is difficult for the carbon powder to be dispersed in the molten slag. On the other hand, if the amount of moisture is greater than 60% by mass, the effect of dispersing the carbon powder is saturated, and also too much steam is generated, so that the molten slag is easily scattered outside the discharge ladle. In that case, there is a possibility that the scattered molten slag will cause damage to the facilities.
As discussed above, the amount of moisture in the mixture was set at 30% by mass or more and 60% by mass or less, but it is preferable to set the lower limit at 35% by mass, and more preferably 40% by mass, and to set the upper limit at 55% by mass, and more preferably 50% by mass.
[0030]
The diameter (particle size) of the carbon powder is 0.2 mm or more and 2 mm or less.
As previously described, the diameter of bubbles that are subject to coarsening is 0.2 mm or more and 2 mm or less. In order for the carbon powder to accomplish the action of entering into the slag liquid film between bubbles and to make the bubbles coalesce, it is required to set the diameter of the carbon powder must be set to be equal to or less than the diameter of bubbles.
Here, if the particle size of the carbon powder is excessively larger than the
diameter of bubbles, it is likely to have a form in which the carbon powder grains are interposed between bubbles, and thus coalescence is rather unlikely to occur. Furthermore, a carbon powder grain having a large particle size easily floats at the surface of molten slag, and is difficult to disperse in the molten slag. Accordingly, a foaming suppressive effect is difficult to obtain.
[0031]
On the other hand, if the diameter of the carbon powder is excessively smaller than the diameter of bubbles, the amount of the slag liquid film eliminated is small, and it is difficult for the carbon powder to accelerate the coalescence of bubbles. Furthermore, since a carbon powder grain having a small particle size has a large surface area, the carbon powder easily reacts with FeO in the molten slag, and generates relatively small CO bubbles. Therefore, such carbon powder is rather prone to promote foaming, and thus a foaming suppressive effect is difficult to obtain.
From the reasons described above, the diameter of the carbon powder was defined to be 0.2 mm or more and 2 mm or less, which is equivalent to the diameter of bubbles that are subject to coarsening, but a carbon powder having a diameter of less than 0.2 mm, and a carbon powder having a diameter of larger than 2 mm may also be included in small amounts (for example, about 20% by mass or less). Furthermore, if the carbon powder includes 65% by mass or more of grains having a size of 0.2 mm or more and 2 mm or less, the above-mentioned foaming suppressive effect is obtained.
[0032]
The amount of the carbon powder having a particle size of 0.2 mm or more and 2 mm or less that is included in the mixture, is 20% by mass or more and 40% by mass or less.
Here, if the amount of the carbon powder having a particle size of 0.2 mm or
more and 2 mm or less in the mixture is less than 20% by mass, the proportion of the carbon powder occupying the mixture is too small, and thus insufficient coalescence of bubbles occurs, making it difficult to suppress foaming. On the other hand, from the results of the aforementioned test, if the amount of the carbon powder having a particle size of 0.2 mm or more and 2 mm or less exceeds 40% by mass, a marked increase in the foaming suppressive effect is not recognized, and it is presumed that the effect is saturated.
As described above, the amount of the carbon powder in the mixture is defined to be 20% by mass or more and 40% by mass or less, but it is preferable to set the lower limit at 21% by mass, and to set the upper limit at 35% by mass, and more preferably 30% by mass.
[0033]
The remaining part, other than the moisture and the carbon powder in the mixture constituting the depressant material described above, is not particularly limited, but it is more preferable to use a thermodecomposable material, since the volume expansion energy obtained when gas is generated in the molten slag can be used in dispersion of the carbon powder. Examples of the thermodecomposable material as used herein include, for example, organic materials such as pulp waste slag, waste plastics, cooking oil, and waste oil; carbonates such as CaCO3; and hydroxides such as Ca(OH)2.
[0034]
As discussed above, since the mixture contains a lot of moisture, the mixture has low compressive strength even if compression molded, and is likely to collapse when subject to vibration or impact at the time of transportation or the like. Thus, in order to make certain that the mixture penetrates into the molten slag, the mixture is
contained in a container formed from a non-water-permeable and flammable material.
Here, making the container non-water-permeable is to prevent a decrease in the amount of moisture during the period between the time point of producing the slag foaming depressant material and the time point of introducing the depressant material. Also, making the container from a flammable material allows the container to gasify early in the molten slag, and thereby makes the container disappear, so that the carbon powder contained in the slag foaming depressant material can be rapidly dispersed in the molten slag easily, and foaming can be suppressed more efficiently and easily. As for such a container, for example, a slightly hard container such as a PET bottle shows good workability upon transportation or introduction, and thus is preferable. However, a plastic bag or the like may also be used.
[0035]
The mass of the mixture charged in this container is preferably 1 kg or more and 10 kg or less.
If the slag foaming depressant material is too light, penetration into the molten slag will be insufficiently achieved, and it will be difficult to obtain a depressant effect. On the other hand, if the slag foaming depressant material is too heavy, it will be difficult to handle at the time of production or transportation of the slag foaming depressant material.
Therefore, from the viewpoint of balancing these factors, the mass of the mixture is defined to be 1 kg or more and 10 kg or less, but it is preferable to set the lower limit at 2 kg, and more preferably 3 kg, and to set the upper limit at 8 kg, and more preferably 7 kg.
[0036]
Furthermore, the method for depressing slag foaming according to the present
embodiment will be explained. As previously described, a molten slag having lower basicity has stronger foaming properties, but the slag foaming depressant material of the present embodiment allows a high depressant effect to be obtained even with such a molten slag.
Hereinafter, the instance of using a multifunction converter furnace method will be explained as an example, by referring to the FIG. 2.
[0037]
In the multifunctional converter furnace method, a hot metal P is dephosphorized in a converter furnace 10, and then this molten slag S1 in the converter furnace 10 is discharged to a discharge ladle 11 installed underneath the furnace. Here, since 10 to 15 tons of the molten slag S1 is discharged within a short time of about 3 minutes, the slag-off properties are improved by adjusting the basicity of the molten slag S1 in the converter furnace 10 to 0.8 or more and 1.5 or less (preferably, to a lower limit of 0.9, and to an upper limit of 1.3) during the dephosphorization treatment, and causing the molten slag S1 to foam (generate bubbles). Here, if the basicity is less than 0.8, the dephosphorization ability of the molten slag S1 is reduced due to a low CaO concentration, and if the basicity is greater than 1.5, the low viscousness of the molten slag S1 makes foaming difficult, and thus the slag-off properties are lowered.
[0038]
As such, in the molten slag S2 discharged from the converter furnace 10 and supplied to the discharge ladle 11, FeO in the slag and C in the granular iron included in the slag react to generate CO bubbles, and foaming is likely to occur rapidly and continuously. A depressant material (slag foaming depressant material) 12 used for such molten slag S2 is required to have characteristics of decreasing the lifespan of
bubbles staying at the surface of the molten slag S2 to thereby suppress foaming.
Since the depressant material 12 of the present embodiment makes it possible to uniformly disperse a carbon powder having a bubble coalescing action and a bubble enlarging action, in the molten slag S2 by means of the volume expansion energy obtained when moisture gasifies, it is easy to obtain the effect of carbon powder over the entire molten slag S2. This effect can be obtained even with a highly viscous slag with low basicity in which the lifespan of bubbles is prone to be lengthened, and when compared with the prior art technologies, the difference in effects is even more conspicuous.
[0039]
Therefore, it is preferable to introduce the depressant material 12 into the discharge ladle 11 prior to the initiation of slag-off, and the position of introduction is preferably set at the discharge position of the molten slag S1 to the discharge ladle 11, that is, the position where the molten slag S1 discharged from the converter furnace 10 arrives at the discharge ladle 11. Since stirring of the molten slag S2 in the discharge ladle 11, which is concomitant with discharge, is particularly vigorous immediately after the initiation of slag-off, the carbon powder can be dispersed uniformly in the molten slag S2 using the stirring energy. Here, the amount of the depressant material introduced before the initiation of slag-off is more preferably set at 30 kg or more. Alternatively, the depressant material 12 may be introduced at the position of discharge of the molten slag S1 to the discharge ladle 11 intensively (for example, at once, continuously, or in several divided times) for a period of 30 seconds from the initiation of slag-off of the molten slag S1. The reason is similar to the case of slag-off as described above, and the amount of the depressant material 12 introduced for 30 seconds from the initiation of slag-off is more preferably set at 30 kg or more.
[0040]
In all the introduction methods described above, the depressant material 12 may be further introduced depending on the conditions of foaming, after a lapse of 30 seconds from the initiation of slag-off of the molten slag S1. In this case, the depressant material 12 may be used in combination with a conventionally known depressant material.
It is preferable to carry out the introduction of the depressant material 12 during the period of 30 seconds from the initiation of slag-off of the molten slag S1
(first half), and after a lapse of 30 seconds from the initiation of slag-off (second half), uniformly per unit time. At this time, the amount of the depressant material 12 introduced per unit time in the first half is preferably double or more and triple or less of the amount of the depressant material 12 introduced in the second half.
Furthermore, reference numeral 13 in FIG. 2 indicates a worktable, and reference numeral 14 indicates a mobile carriage. [EXAMPLES]
[0041]
Next, an Example carried out to check the operating effects of the invention will be described.
A depressant material was produced by filling a container such as a plastic bag (volume: 13500 cm3, thickness: 0.5 mm), aplastic bottle (volume:12000 cm3, thickness: 1.5 mm), or a paper bag (volume: 13500 cm3, thickness: 0.5 mm), with a mixture prepared by mixing a pulp waste slag having a moisture content of 60% by mass, coke powder and graphite powder, and according to necessity, adding waste plastics (PET bottles crushed into a flake form) and water for moisture adjustment. The raw material mixing ratio of the mixture of this depressant material is presented in
Table 1. The particle size (particle diameter) of the carbon powder in Table 2 is the particle size of the mixture of coke powder and graphite powder in the Table 1, and the particle size is presented in three distinct classes of smaller than 0.2 mm, 0.2 mm to 2 mm, and larger than 2 mm. Furthermore, the Table 2 also indicates the mass per pack of depressant material, but since the container is a plastic bag, a plastic bottle or a bag, and the mass is negligible compared to the mass of the mixture, the mass of one pack of depressant material is the amount of one mixture per pack of the depressant material.
[0042]
Table 1
(Table Removed)
[0043] Table 2
(Table Removed)
[0044]
The respective depressant materials (materials A to S) of Examples 1 to 12 and Comparative Examples 1 to 7 shown in these Tables 1 and 2 were introduced into the discharge ladle at the time of slag-off in the multifunctional converter furnace method, and the results are presented in Table 3. Here, an investigation was made for two conditions such as: (1) in the case of providing the depressant material in a discharge ladle having a height of 4 m, which was installed in the lower part of the furnace body, prior to the initiation of slag-off of the molten slag, and (2) in the case of
introducing the depressant material at the position of discharge of the molten slag to the discharge ladle during the period of 30 seconds after the initiation of slag-off. In the case of introducing the depressant material during the period of 30 seconds after the initiation of slag-off, when the molten slag was discharged from the opening of the converter furnace to the discharge ladle by performing dephosphorization, and then tilting the converter furnace while the molten iron was retained in the furnace, the depressant material was introduced via a shoot from the time point of immediately after the initiation of slag-off to the time point of the completion of slag-off. Thereby, depression of the molten slag foaming in the discharge ladle was attempted. The discharge time of this molten slag was set at 3 minutes for all cases. In addition, the mass of the molten slag during slag-off was measured with a weighing instrument carried by the mobile carriage where the discharge ladle was installed.
[0045]
Table 3
(Table Removed)
[0046]
In Examples 1 to 12, depressant materials (materials A to L) formed from a mixture including 30% by mass or more and 60% by mass or less of moisture and 20% by mass or more and 40% by mass or less of a carbon powder having a particle size of 0.2 to 2 mm, contained in a container composed of a non-water-permeable and flammable material, were used in all cases. As a result, foaming could be depressed by introducing 120 kg of these depressant materials, and 10 tons (target value) or more of molten slag could be discharged. Particularly, in Example 1, upon discharging a molten slag having a basicity of 1.1, 40 kg of the depressant material (material A) was disposed in the discharge ladle before the initiation of slag-off, and 80 kg of the depressant material (material A) was further introduced at the position of slag-off of the molten slag from 30 seconds after the initiation of slag-off. There, the effect of depression was significant, and 14 tons of the molten slag could be discharged. In Example 2 in which 40 kg of the depressant material (material B) was introduced during a period of 30 seconds from the initiation of slag-off of the molten slag, similar results were obtained.
[0047]
In Example 3, in regard to the carbon powder used, the proportion of grains having a particle size of less than 0.2 mm relative to the total amount of the carbon powder was high. Therefore, the effect of accelerating coalescence of bubbles in the molten slag was smaller when compared to Example 2, and it was difficult to obtain a foaming suppressive effect due to the generation of relatively small CO bubbles. Thus, the amount of discharge of the molten slag was 11.5 tons.
On the other hand, in Example 4, in regard to the carbon powder used, the proportion of grains having a particle size of more than 2 mm relative to the total amount of the carbon powder was high. Therefore, the effect of accelerating
coalescence of bubbles in the molten slag was smaller when compared to Example 2, and it was difficult to obtain a foaming suppressive effect since the carbon powder is difficult to disperse in the molten slag. Thus, the amount of discharge of the molten slag was 11.5 tons.
[0048]
In Example 5, a depressant material (material E) of which the mass of the mixture filled in a plastic bag was 0.8 kg (less than 1 kg), was used, and thus penetration into the molten slag was insufficient when compared to Example 2. The amount of discharge of the molten slag was 11 tons.
On the other hand, in Example 6, a depressant material (material F) in which the mass of the mixture filled in a plastic bottle was 12 kg (more than 10 kg), was used. Therefore, penetration into the molten slag was sufficient, and 14 tons of the molten slag could be discharged as in the case of Example 2. However, because the mass of the depressant material was too heavy, workability in the production, transportation and the like was poorer than that of Example 2.
[0049]
In Example 7, the depressant material was introduced near an end of the discharge ladle, and thus it was difficult for the depressant material (material G) to penetrate into the molten slag, when compared to Example 2. Thus, the amount of discharge of the molten slag was 10.5 tons.
In Example 8, the amount of the depressant material (material H) introduced from the initiation of slag-off to 30 seconds thereafter, was retained at 24 kg, which was smaller than the amount used in Example 2. Thus, the amount of the molten slag discharged was 11 tons.
[0050]
In Example 9, a depressant material (material I) in which the amount of moisture in the mixture constituting the depressant material was lower than that for the depressant material of Example 2, and thus steam generated therefrom was insufficient, making the carbon powder difficult to disperse in the molten slag. Thus, the amount of the molten slag discharged was 10.5 tons.
In Example 10, a depressant material (material J), in which the amount of moisture and the amount of the carbon powder having a particle size of 0.2 mm to 2 mm in the mixture constituting the depressant material, were smaller than those of the depressant material of Example 2 (the amount of moisture was equal to that of Example 9), was used. Therefore, in addition to the phenomenon of Example 9, it became more difficult to suppress foaming, and 10 tons of the molten slag, which was less than the amount in Example 9, could be discharged.
[0051]
In Example 11, a depressant material (material K), in which the amount of moisture in the mixture constituting the depressant material was lower than that of the depressant material of Example 2, was used. However, since the amount of the carbon powder having a particle size of 0.2 mm to 2 mm was larger than that of the depressant material of Example 2, the amount of the molten slag discharged was 11 tons.
In Example 12, a depressant material (material L), in which the amount of moisture in the mixture constituting the depressant material was larger than that of the depressant material of Example 2, was used. However, since the amount of the carbon powder having a particle size of 0.2 mm to 2 mm was smaller than that of the depressant material of Example 2, the amount of the molten slag discharged was 10.5 tons.
Examples 1 to 12 discussed above relate to results obtained using molten slag having basicity in the range of 0.8 or more and 1.5 or less, but satisfactory results were obtained in all cases.
[0052]
On the other hand, in Comparative Examples 1 and 2, the amount of moisture in the mixture constituting the depressant material (materials M and N) was less than 30% by mass, and moisture was insufficient. Thus, dispersion of the carbon powder in the molten slag was insufficient, and in all cases, foaming could not be suppressed using the same amount of introduction as in Examples 1 to 12, while it was necessary to introduce about one and a half times the amount of depressant material.
Particularly, in Comparative Example 2, even though the amount of the carbon powder having a particle size of 0.2 mm to 2 mm in the mixture was larger than that of the depressant materials of Examples 1 to 12 (exceeding 40% by mass), it was necessary to introduce the depressant material in excess.
[0053]
In Comparative Examples 3 and 4, the amount of the carbon powder having a particle size of 0.2 mm to 2 mm in the mixture constituting the depressant material (materials O and P) was less than 20% by mass, and the carbon powder was insufficient. Thus, the amount of enlarged bubbles was insufficient, and in all cases, foaming could not be suppressed using the same amount of introduction as in Examples 1 to 12, and it was necessary to introduce about one and a half times the amount of depressant material.
Particularly, in Comparative Example 3, even though the amount of moisture in the mixture constituting the depressant material was larger than that of the depressant materials of Examples 1 to 12 (exceeding 60% by mass), it was necessary
to introduce the depressant material in excess.
[0054]
In Comparative Example 5, the mixture was used without being filled in a container, and therefore less penetration of the depressant material (material Q) into the foaming molten slag occurred, with a small depressive effect. For this reason, it was necessary to suppress the rate of discharge of the molten slag for the purpose of preventing an overflow of the molten slag, and the amount of discharge of the molten slag was only 7.5 tons (less than 10 tons).
In Comparative Example 6, since the mixture was filled in a water-permeable paper bag, the amount of moisture was decreased down to 24% by mass before the depressant material (material R) was introduced into the molten slag. For this reason, it was necessary to suppress the rate of discharge of the molten slag for the purpose of preventing an overflow of the molten slag, and the amount of discharge of the molten slag was only 9 tons (less than 10 tons).
[0055]
In Comparative Example 7, the basicity of the molten slag was as low as 0.7 (less than 0.8). Thus, the molten slag had fairly strong foamability, and the amount of discharge of the molten slag was only 9.5 tons.
From the above results, it was confirmed that when the slag foaming depressant material and the method for depressing slag foaming of the invention are used, a foaming molten slag can be rapidly depressed with a small amount of use of the depressant material, damage to facilities due to an overflow of the molten slag can be prevented, and stable maintenance of productivity can be realized.
[0056]
In the above-described embodiment, a method for depressing slag foaming at
the time of slag-off in a multifunctional converter furnace method using the slag foaming depressant material according to an embodiment of the invention, was explained, but the invention is not to be limited to this. The invention is also applicable to, for example, the depression of slag foaming occurring during refining in a torpedo ladle car or a converter furnace, and similar effects are exhibited.
[0057]
[Second Embodiment]
In continuation, a second embodiment of the slag foaming depressant material and the method for depressing slag foaming of the invention will be described below, while referring to the attached drawings. FIG. 3 is a graph showing an example of changes over time in the rate of gas generated per kg of the slag foaming depressant material. The horizontal axis represents the time after introduction of the depressant material, and the vertical axis represents the rate of gas generated per kg of the depressant material.
[0058]
The slag foaming depressant material (hereinafter, may be simply referred to as depressant material) according to the present embodiment is a mixture having moisture and a fuel component, contained in a container composed of a non-water-permeable organic material. Hereinafter, a detailed explanation will be given.
In order to ensure foaming depression of a molten slag with a small amount of the depressant material, it is required, as a condition for this depressant material, that rapid gas generation occur in a foaming molten slag, and the gas generation be sustained to a certain extent.
Thus, the present inventors performed various experiments to make clear the rapidity and sustainability of gas generation induced by various materials.
[0059]
First, 1 kg of water was placed in a PET bottle, and this was introduced into 10 tons of foaming molten slag. As a result, gas was generated immediately after the introduction of water into the molten slag, and gas generation was completed in about 1 second after the introduction.
From this, it was found that moisture was suitable to satisfy the rapidity of gas generation. This is conceived to be because the water introduced to the molten slag gasified in an explosive manner due to the heat of this molten slag.
[0060]
Furthermore, 1 kg of a pulp waste slag which had been dried to have a moisture content of 5% by mass or less, was placed in a PET bottle, and this was introduced into 10 tons of a foaming molten slag. The main component of this pulp waste slag was cellulose, a fuel component. As a result, gas was generated from about 1 second after the introduction of the pulp waste slag into the molten slag, and gas generation was sustained to 5 seconds after the introduction. The same experiment was carried out for other fuel components such as cooking oil, waste oil, plastics (dried to have a moisture content of 5% by mass or less), or a kneaded mixture of these organic materials, and similar results as in the case of pulp waste slag were obtained.
From these results, it was found that the fuel component was suitable for satisfying the sustainability of gas generation. This is conceived to be because the fuel component underwent an oxidation reaction (combustion) with FeO in the molten slag to generate gases such as CO, CO2 and H2O.
[0061]
Next, a test was carried out regarding preparing depressant materials having
mixtures which varied in the moisture content and the amount of fuel component, and introducing these depressant materials into a molten slag which was foaming during slag-off in actual equipment. As a result, when the amount of the depressant material introduced was a small amount such as about 1% by mass of the amount of the molten slag discharged, there were obtained slag foaming depressant materials that showed a foaming suppressive effect, and slag foaming depressant materials that did not show a suppressive effect. Thus, the following measurement was carried out for several depressant materials that showed a foaming suppressive effect.
This measurement was carried out in the laboratory, by melting 10 kg of slag in the crucible in an electric furnace, attaching a flow meter to a glass tube connected to the crucible, introducing 5 g of a depressant material into the slag, and continuously measuring the changes over time in the volume of gas generated. An example of the results is presented in FIG. 3. Here, FIG. 3 shows the results obtained in the case where the amount of moisture in the mixture constituting the depressant material was 45% by mass, and the amount of the fuel component was 35% by mass. From FIG. 3, it was found that the rate of gas generation normalized with respect to 1 kg of the depressant material, reached 2.0 m /(second-kg) or more immediately after the introduction of the depressant material, and the rate was sustained for 5 seconds or more.
[0062]
The present inventors continued a test for clarifying the suitable ranges of the amount of moisture and the amount of fuel component in the mixture. As a result, it was found that the amount of moisture in the mixture needs to be 30% by mass or more and 60% by mass or less.
If the amount of moisture in the mixture was less than 30% by mass, the rate
of gas generation per kg of depressant material during one second after the introduction of depressant material is less than 2.0 m /(second-kg), and rapid gas generation is difficult. On the other hand, if the amount of moisture is more than 60% by mass, the rate of gas generation per kg of depressant material during one second after the introduction of depressant material can be brought to 2.0 m /(second-kg) or more, but the amount of the fuel component that will be described later falls out of an appropriate range, and it is speculated that continuous gas generation is difficult. Furthermore, if the amount of moisture in the mixture is too large, there is a risk of steam explosion damaging the surrounding facilities, and thus it is desirable to maintain the amount of moisture within the scope of the invention. From the above results, the amount of moisture in the mixture was defined to be 30% by mass or more and 60% by mass or less, but it is preferable to set the lower limit at 35% by mass, and more preferably 40% by mass, and to set the upper limit at 55% by mass, and more preferably 50% by mass.
[0063]
It was also determined that the amount of the fuel component in the mixture needs to be 35% by mass or more and 65% by mass or less.
If the amount of the fuel component in the mixture is less than 35% by mass, the rate of gas generation per kg of depressant material during the period of 1 second to 5 seconds after the introduction of depressant material is less than 2.0 m3/(second-kg), and continuous gas generation is difficult. On the other hand, if the amount of the fuel component is more than 65% by mass, the amount of moisture mentioned above falls out of an appropriate range, and it is speculated that rapid gas generation is difficult.
From the above results, the amount of the fuel component in the mixture was
defined to be 35% by mass or more and 65% by mass or less, but it is preferable to set the lower limit at 38% by mass, and to set the upper limit at 55% by mass, and more preferably 50% by mass. Additionally, in regard to the fuel component, any one or two or more of the aforementioned cellulose in pulp waste slag, plastics, tray, cooking oil, waste oil (for example, engine oil) and organic materials (for example, oil-containing sludge) can be used.
[0064]
As discussed above, since the mixture contains much moisture, the mixture has low compressive strength even if compression molded, and is likely to collapse when subject to vibration or impact at the time of transportation or the like. Thus, in order to make certain that the mixture penetrates into the molten slag and generate gas in the molten slag, the mixture is contained in a container formed from a non-water-permeable organic material.
Here, making the container non-water-permeable is to prevent a decrease in the amount of moisture during the period between the time point of producing a depressant material and the time point of introducing the depressant material. Also, making the container from an organic material allows the container to gasify early in the molten slag and thereby make the container disappear, so as to make gas generation easy from immediately after the introduction of the depressant material into the molten slag and to make destruction of the foam layer easy and more efficient. As for such a container, for example, a PET bottle, a plastic bag or the like may be used.
[0065]
The mass of the mixture contained in this container is preferably 1 kg or more and 10 kg or less.
If the depressant material is too light, the depressant material insufficiently
penetrates into the molten slag, and it is difficult to obtain a depressive effect. On the other hand, if the depressant material is too heavy, it is difficult to handle the depressant material at the time of production or transportation.
Therefore, from the viewpoint of balancing these factors, the mass of the mixture is defined to be 1 kg or more and 10 kg or less, but it is preferable to set the lower limit at 2 kg, and more preferably 3 kg, and to set the upper limit at 8 kg, and more preferably 7 kg.
[0066]
In continuation, the case of using the method for depressing slag foaming according to the present embodiment in a multifunctional converter furnace method, will be explained while referring to FIG. 2 that was used in the first embodiment.
First, a hot metal P is dephosphorized in a converter furnace 10, and then this molten slag S1 in the converter furnace 10 is discharged to a discharge ladle 11 installed underneath the furnace. Here, since 10 to 15 tons of the molten slag S1 is discharged within a short time of about 3 minutes, the slag-off properties are improved by increasing the concentration of FeO (iron oxide) in the molten slag S1 in the converter furnace 10 to a value in the range of 15% by mass or more and 25% by mass or less, and causing the molten slag S1 to foam (generate bubbles).
[0067]
As such, in the molten slag S2 discharged from the converter furnace 10 to the discharge ladle 11, FeO in the slag and C in the granular iron included in the slag react to generate CO bubbles, and foaming is likely to occur rapidly and continuously. It is preferable that a depressant material 12 used for such molten slag S2 have characteristics of generating gas instantaneously from the inside of the molten slag S2 toward the outside, thereby making it easy to form open holes for which the gas
staying in the molten slag S2 can be escaped.
For a depressant material 12 having such characteristics, the depressant material according to the present embodiment is used. Since this depressant material enables rapid gas generation immediately after introduction due to moisture, it is easy to form open holes for which CO gas can be escaped. Additionally, since the fuel component contained in the depressant material causes an oxidation reaction (combustion) with FeO that is contained in a large amount in the molten slag, and generates gas, it is advantageous that the effect is easily obtained in slags having high concentrations of FeO.
[0068]
Therefore, when the above-described depressant material is used, moisture gasifies rapidly and forms open holes for CO gas, and subsequently, the fuel component reacts with FeO in the molten slag to continuously generate gas. Therefore, even in a molten slag having a high FeO concentration and having strong foamability, efficient depression is made possible.
As such, when the above-described depressant material is introduced into a molten slag having a FeO concentration of 15% by mass or more and 25% by mass or less, the effect of the depressant material is more remarkably exhibited.
[0069]
During the period of 30 seconds after the initiation of slag-off of the molten slag SI, stirring of the molten slag S2 in the discharge ladle 11, which is concomitant with discharge, is particularly vigorous, and a large amount of CO bubbles are generated from the molten slag S2 to cause foaming. Therefore, the depressant material 12 is preferably introduced intensively (for example, at once, continuously, or in several divided times) during the period of 30 seconds after the initiation of slag-off,
and it is preferable to set the position of introduction to be the position of discharge of the molten slag S1 to the discharge ladle 11.
Thereby, the depressant material 12 can be made to easily penetrate the molten slag S2 more reliably. It is more preferable to adjust the amount of the depressant material 12 introduced to 30kg or more during the period of 30 seconds after the initiation of slag-off, and after a lapse of 30 seconds, the depressant material 12 may be further introduced depending on the condition of foaming.
[0070]
Next, an Example carried out to check the operating effects of the invention will be described.
A depressant material was produced by filling a container, such as a plastic bag or a plastic bottle, with a mixture prepared by mixing a pulp waste slag having a moisture content of 60% by mass, and waste plastics (PET bottles crushed into a flake form), and according to necessity, adding salad oil, steelmaking slag (average particle size: 0.5 mm) and water for moisture adjustment. The raw material mixing ratio of the mixture of this depressant material is presented in Table 4. Table 4 also describes the composition of the mixtures obtained by converting the respective raw material mixing ratios relative to the moisture, fuel component and ash component. The Table 4 also indicates the mass per one pack of depressant material, but since the container is a plastic bag or a plastic bottle, and the mass is negligible compared to the mass of the mixture, the mass of one pack of depressant material is the amount of mixture per pack of the depressant material.
[0071]
Table 4
(Table Removed)
[0072]
The results obtained by introducing the respective depressant materials of Examples 21 to 29 and Comparative Examples 21 to 26 shown in this Table 4 into the discharge ladle at the time of slag-off in a multifunctional converter furnace method, are presented in Table 5. Here, from the time point of immediately after the initiation of slag-off to the time point of the completion of slag-off, the depressant material was introduced via a chute when the molten slag was discharged from the opening of the converter furnace to the discharge ladle which has a height of 4 m and is installed below the furnace, by tilting the converter furnace while the hot metal was remained in the furnace after performing dephosphorization. Thereby, depression of the molten slag foaming in the discharge ladle was attempted. The discharge time of this molten slag was set at 3 minutes for all cases. In addition, the mass of the molten slag during slag-off was measured with a weighing instrument carried by the mobile carriage where the discharge ladle was installed.
[0073]
Table 5
(Table Removed)
[0074]
In Examples 21 to 29, depressant materials formed from a mixture including 30% by mass or more and 60% by mass or less of moisture and 35% by mass or more and 65% by mass or less of a fuel component, contained in a container composed of a non-water-permeable organic material, were used in all cases. As a result, foaming could be depressed by introducing 120 kg of these depressant materials, and 10 tons (target value) or more of molten slag could be discharged. Particularly, in Example 21, upon discharging a molten slag having an FeO concentration of 18% by mass, 40 kg of depressant material contained in plastic bags each having 5 kg of the mixture, was introduced at the position of slag-off, at 30 seconds after the initiation of slag-off, and 80 kg of the depressant material was further introduced over a period from 30 seconds up to 3 minutes after the initiation of slag-off. There, the effect of depression was significant, and 14 tons of the molten slag could be discharged.
[0075]
In Example 22, a depressant material in which the mass of the mixture contained in a plastic bag was 0.8 kg (less than 1 kg) was used, and thus penetration of the depressant material into the molten slag was slightly reduced when compared to Example 21, and the amount of the molten slag discharged was 10 tons.
On the other hand, in Example 23, a depressant material in which the mass of the mixture contained in a plastic bag was 12 kg (more than 10 kg) was used, and thus penetration of the depressant material into the molten slag was sufficient. Therefore, penetration of the molten slag was sufficient, and 14 tons of the molten slag could be discharged as in the case of Example 21. However, because the mass of the depressant material was too heavy, workability in the production, transportation and the like was poorer than that of Example 21.
[0076]
In Example 24, since the FeO concentration in the molten slag was as high as 26% by mass (exceeding 25% by mass), foamability was fairly strong, and the amount of molten slag discharged was 11.5 tons.
In Example 25, the depressant material was introduced near an end of the discharge ladle, and thus it was difficult for the depressant material to penetrate into the molten slag, when compared to Example 21. Thus, the amount of discharge of the molten slag was 10 tons. In Example 26, the amount of the depressant material introduced from the initiation of slag-off to 30 seconds thereafter, was retained at 24 kg, which was smaller than the amount used in Examples 21 to 25. Thus, the amount of the molten slag discharged was 11 tons.
[0077]
In Example 27, a depressant material in which the amount of moisture in the mixture constituting the depressant material was lower than that for the depressant material of Examples 21 to 26 was used, and thus the rate of gas generation immediately after introduction of the depressant material into the molten slag was decreased. Thus, the amount of the molten slag discharged was 11 tons.
On the other hand, in Example 28, a depressant material in which the amount of fuel component in the mixture constituting the depressant material was higher than that of the depressant material of Example 27 was used, and thus the effect of sustaining gas generation could be enhanced. Thus, 12 tons of molten slag, which was larger than the amount of Example 27, could be discharged.
In Example 29, a depressant material in which the amount of moisture in the mixture constituting the depressant material was higher than the amount in the depressant materials of Examples 21 to 26 was used, but because a depressant material
which had a smaller amount of fuel component than that of the depressant materials of Examples 21 to 26 was used, the amount of the molten slag discharged was 13 tons, which was close to the amount of Example 21.
[0078]
On the other hand, in Comparative Examples 21 and 22, the amount of moisture in the mixture constituting the depressant material was less than 30% by mass, and the depressant materials lacked moisture. Thus, the rate of gas generation immediately after the introduction of the depressant material into the molten slag was insufficient, and thus foaming could not be suppressed using the same amount of introducted depressant material as that used in Examples 21 to 29, while about one and a half times the amount of depressant material had to be introduced. Furthermore, in Comparative Example 22, even though the amount of the fuel component in the mixture constituting the depressant material was larger than that in the depressant materials of Examples 21 to 29 (exceeding 65% by mass), it was necessary to introduce the depressant material in excess.
In Comparative Examples 23 and 24, the amount of the fuel component in the mixture constituting the depressant material was less than 35% by mass, and the depressant materials lacked a fuel component. Thus, sustainability of gas generation was insufficient, and thus foaming could not be suppressed when the same amount of introducted depressant material as that used in Examples 21 to 29 is used. Then, about one and a half times the amount of depressant material had to be introduced. Furthermore, in Comparative Example 23, even though the amount of moisture in the mixture constituting the depressant material was larger than that in the depressant materials of Examples 21 to 29 (exceeding 60% by mass), it was necessary to introduce the depressant material in excess.
[0079]
In Comparative Example 25, because the mixture was used without being filled in a container, less penetration of the depressant material into the foaming molten slag occurred, and the depressive effect was small. For this reason, it was necessary to suppress the rate of discharge of the molten slag for the purpose of preventing an overflow of the molten slag, and the amount of discharge of the molten slag was only 7.5 tons (less than 10 tons).
In Comparative Example 26, since the mixture was filled in a water-permeable paper bag, the amount of moisture was decreased down to 24% by mass before the depressant material (material R) was introduced into the molten slag. For this reason, it was necessary to suppress the rate of discharge of the molten slag for the purpose of preventing an overflow of the molten slag, and the amount of discharge of the molten slag was only 9 tons (less than 10 tons).
From the above results, it was confirmed that when the slag foaming depressant material and the method for depressing slag foaming of the invention are used, a foaming molten slag can be rapidly and certainly depressed with a small use amount of the depressant material, damage to facilities due to an overflow of the molten slag can be prevented, and stable maintenance of the productivity can be realized.
[0080]
As such, the respective embodiments of the invention have been explained, but the invention is not intended to be limited to these embodiments, and includes other embodiments or modifications that are considered to be within the scope of the matters described in the claims. For example, even an instance of constituting the slag foaming depressant material and method for depressing slag foaming of the
invention by combining a part or the entirety of the respective embodiments or modifications thereof, is also included in the scope of the invention.
In the above-described embodiment, a method for depressing slag foaming at the time of slag-off in a multifunctional converter furnace method using a slag foaming depressant material, was explained, but the use of the slag foaming depressant material is not to be limited to this. The invention can be used in, for example, the depression of slag foaming occurring during refining in a torpedo ladle car or a converter furnace, and in that case, similar effects are exhibited. [Industrial Applicability]
[0081]
According to the slag foaming depressant material and method for depressing slag foaming of the invention, the foaming of the molten slag can be efficiently suppressed, and therefore a high depressant effect can be obtained even with a small total amount of the depressant material introduced. Accordingly, cost reduction for the depressant material, improvement of workability due to prevention of the damage to facilities caused by an overflow of the molten slag, and stable maintenance of productivity in the refining process are made possible.

[Designation of Document] CLAIMS
[Claim 1]
A slag foaming depressant material comprising:
a mixture containing 20% by mass or more and 40% by mass or less of a carbon powder having a particle size of 0.2 mm or more and 2 mm or less, and 30% by mass or more and 60% by mass or less of moisture; and
a container for containing the mixture, formed from a non-water-permeable and flammable material. [Claim 2]
The slag foaming depressant material according to claim 1, wherein the mass of the mixture contained in the container is 1 kg or more and 10 kg or less. [Claim 3]
A method for depressing slag foaming, comprising introducing the slag foaming depressant material according to claim 1, into a foaming molten slag having a basicity of 0.8 or more and 1.5 or less. [Claim 4]
The method for depressing slag foaming according to claim 3, wherein the slag foaming depressant material is introduced at the position of discharge of the molten slag that is discharged from a converter furnace, during period of 30 seconds after the initiation of discharge of this molten slag. [Claim 5]
A method for depressing slag foaming, comprising:
introducing the slag foaming depressant material according to claim 1 into a discharge ladle; and
subsequently introducing a molten slag having a basicity of 0.8 or more and
1.5 or less, into the discharge ladle. [Claim 6]
A slag foaming depressant material comprising:
a mixture containing 30% by mass or more and 60% by mass or less of moisture and 35% by mass or more and 65% by mass or less of a fuel component; and
a container for containing the mixture, formed from a non-water-permeable organic material. [Claim 7]
The slag foaming depressant material according to claim 6, wherein the mass of the mixture contained in the container is 1 kg or more and 10 kg or less. [Claim 8]
A method for depressing slag foaming, comprising introducing the slag foaming depressant according to claim 6, into a foaming molten slag having an iron oxide concentration of 15% by mass or more and 25% by mass or less. [Claim 9]
The method for depressing slag foaming according to claim 8, wherein the slag foaming depressant material is introduced at the position of discharge of the molten slag that is discharged from a converter furnace, during period of 30 seconds after the initiation of discharge of this molten slag.