Patent Application
20170009311
The present invention relates to a secondary material for steel refining used so as to promote a desulfurization reaction in molten iron.
At present, calcium oxide (lime) is widely used as a desulfurizing agent for molten iron. In addition, a secondary material for steel refining, containing aluminum ash, is used in combination with lime for promoting the desulfurization reaction by lime in molten iron.
Aluminum ash can be obtained, for example, from an oxide layer, etc. produced on the molten metal surface when an aluminum raw material is melted. The oxide layer is called aluminum dross and contains, in terms of mass percentage, approximately from 60 to 70 wt % of metallic aluminum (M.Al). In the case of obtaining aluminum ash from aluminum dross, it is sometimes recovered as residual ash remaining after recovering metallic aluminum by a metallic aluminum recovery process. Here, the aluminum ash as a secondary material for steel refining contains, in terms of mass percentage, about 30 wt % of metallic aluminum so as to effectively promote a desulfurization reaction in molten iron.
Patent Document 1 discloses such aluminum ash.
The aluminum ash disclosed in Patent Document 1 is aluminum ash added to a desulfurizing agent for molten iron and is characterized by containing aluminum oxide and metallic aluminum, in which the sulfur content is 0.05 mass % or less and the chlorine content is 0.5 mass % or less.
Patent Document 1: JP-A-2006-283083
Conventionally, in using aluminum ash as a secondary material for steel refining, it has been considered that a certain content of metallic aluminum is preferably contained and that, for example, when the metallic aluminum content is about 10 wt %, the aluminum ash can be hardly used as a desulfurizing agent. In the aluminum ash disclosed in Patent Document 1 as described above, the metallic aluminum content is therefore supposed to be preferably 20 wt % or more for the purpose of promoting a desulfurization reaction, and about 30 wt % of metallic aluminum remains in general aluminum ash.
That is, originally recoverable metallic aluminum remains in aluminum ash, and this raises a problem that the recovery efficiency in the metallic aluminum recovery process is reduced.
In addition, a conventional aluminum ash containing a large amount of metallic aluminum has a fear of spontaneous combustion during storage and requires paying attention to ensuring safety when it is stored.
The present invention has been made by taking into account the above-described problems, and an object thereof is to provide a secondary material for steel refining, which exerts a desulfurization effect on molten iron and at the same time, carries a low risk of combustion during storage.
In order to attain the above-described object, the present invention employs the following technical means.
The secondary material for steel refining according to the present invention is a secondary material for steel refining, which is to be supplied to a molten iron together with a lime so as to promote a desulfurization reaction in the molten iron, containing aluminum nitride in an amount of 20 wt % or more in terms of weight percentage.
Here, metallic aluminum is preferably contained in an amount of 10 wt % or less.
Here, silicon dioxide is preferably contained in an amount of 2 wt % or less.
The above-described secondary material for steel refining is preferably produced from an aluminum dross processed in an arc furnace.
Furthermore, it is preferred that the metallic aluminum is contained in an amount of 0 wt % or more and 10 wt % or less and an aluminum oxide is contained in an amount of 80 wt % or less.
According to the secondary material for steel refining of the present invention, a desulfurization effect is exerted on molten iron and at the same time, the risk of combustion during storage is reduced.
An embodiment of the present invention is described by referring to the drawings.
The embodiment described below is an example embodying the present invention, and the configuration of the present invention is not limited to the embodied example. Accordingly, the technical scope of the present invention is not limited to the contents disclosed in the present embodiment.
The secondary material for steel refining according to the present embodiment is described below.
The secondary material for steel refining according to the present embodiment is used for a desulfurization treatment in the process of refining molten iron. In the desulfurization treatment of removing sulfur S in molten iron, lime (CaO, calcium oxide) is charged (added) into molten iron. Calcium (Ca) in the lime added binds to sulfur S in the molten iron according to a chemical reaction formula represented by the following Formula (1), whereby sulfur S is recovered (desulfurized) from the molten iron.
[Math. 1]
CaO+S→CaS+O Formula (1)
Simultaneously with the addition of lime or in the state of being previously mixed with lime, the secondary material for steel refining is charged (added) into the molten iron so as to promote the desulfurization reaction according to Formula (1). With respect to a conventional secondary material for steel refining, aluminum ash as disclosed in Patent Document 1, containing metallic aluminum in an amount of, for example, about 30 wt % in terms of weight percentage (wt %) is used. The metallic aluminum added eliminates oxygen O from lime (CaO) (deoxidation reaction) according to a chemical reaction formula (desulfurization reaction) represented by the following Formula (2) and promotes binding of calcium Ca to sulfur S (desulfurization) in the molten iron.
[Math. 2]
3CaO+3S+2Al→3CaS+Al2O3 Formula (2)
In this way, a secondary material for steel refining, utilizing a desulfurization reaction of metallic aluminum with lime, has been conventionally used, but the inventors of the present invention have found through studies that at least in molten iron, aluminum nitride (AlN) exercises a deoxidation reaction (deoxidation effect) equivalent to that of metallic aluminum on lime (CaO).
When aluminum nitride is charged (added) as a secondary material for steel refining into molten iron simultaneously with or immediately after the addition of lime to the molten iron, the aluminum nitride added eliminates oxygen O from lime (CaO) (deoxidation) according to a chemical reaction formula represented by the following Formula (3) and promotes binding of calcium Ca to sulfur S (desulfurization) in the molten iron.
[Math. 3]
3CaO+3S+2AlN→3CaS+Al2O3+N2 Formula (3)
As such, aluminum nitride (AlN) can be used as a secondary material for steel refining. With respect to the aluminum nitride as a secondary material for steel refining, it may be preferable to use a reagent having a purity of 100% or nearly 100%, but when a substance containing, in terms of weight percentage, 20 wt % or more of aluminum nitride is used as a secondary material for steel refining, the desulfurization reaction represented by Formula (3) can be sufficiently promoted.
Referring to the graph of
It is understood that when a desulfurizing agent containing the secondary material for steel refining according to the present embodiment is used, the desulfurization reaction rate is promoted for several times higher than in the case of not containing the secondary material for steel refining.
Here, arc furnace ash is described as an example of the secondary material for steel refining containing about tens of wt % of aluminum nitride.
The arc furnace ash is residual ash produced by recovering metallic aluminum from well-known aluminum dross processed, for example, by using an arc furnace 1 that is an electric furnace depicted in
In the arc furnace ash 4, one having a particle diameter suitable for use as a secondary material for steel refining is present, and the particle diameter of the arc furnace ash 4 can be measured by sieving. For example, when being sieved through a sieve having a nominal opening size of 10 mm (metal-made wire sieve, in conformity with JIS8801-1), the arc furnace ash 4 under the sieve, which has passed through the sieve can be defined as arc furnace ash 4 having a particle diameter of 10 mm or less.
In view of desulfurization performance, etc., the particle diameter (particle size) of the arc furnace ash 4 used as the secondary material for steel refining of the present invention is preferably 12 mm or less and more preferably 3.5 mm or less. The results when the arc furnace ash as the secondary material for steel refining is evaluated for the desulfurization performance and ignitability are described below.
A plurality of arc furnace ash differing in the content ratio of components were prepared and evaluated for the desulfurization performance and ignitability. The content ratio of components in the arc furnace ash was analyzed by focusing attention mainly on the total amount WT.Al (wt %) of aluminum (Al) contained in the arc furnace ash, the amount WM.Al (wt %) of metallic aluminum (MAD, the amount of aluminum nitride (AlN), and the amount WAl2O3 (wt %) of aluminum oxide (Al2O3).
First, the total amount WT.Al of aluminum (Al) was measured from the entire arc furnace ash by ICP emission spectrometry. Next, the amount WM.Al (wt %) of metallic aluminum (M.Al) was detected by bromine-methanol decomposition-ICP emission spectrometry. Furthermore, the N content in the residue resulting from bromine-methanol decomposition was measured by using a neutralization titration method, and the amount WN of nitrogen N detected was assumed to be all derived from aluminum nitride (AlN). The value obtained by subtracting the metallic aluminum (M.Al) amount and the Al amount in aluminum nitride (AlN) from the total amount WT.Al of aluminum (Al) was assumed to be the Al amount of aluminum oxide (Al2O3).
The amount WAl2O3 of aluminum oxide (Al2O3) was calculated according to the following Formula (4) based on these assumptions.
WX: the analysis value (wt %) of component X measured by ICP emission spectrometry,
WM.Al: the M.Al amount (wt %) measured by bromine-methanol decomposition-ICP emission spectrometry, and
MX: the atomic weight of element X.
Subsequently, the desulfurization performance was evaluated by using, as the secondary material for steel refining (secondary material) according to the present embodiment, five kinds of arc furnace ashes shown in Example 1 to Example 7 and an AlN reagent shown in Example 8. As well as Examples 1 to 8, the desulfurization performance was evaluated also on Comparative Examples 1 to 4, and the obtained evaluation results are shown in Table 1 below.
The particle diameter (particle size) of the secondary materials used in Examples 1 to 8 below is 3.35 mm or less in both the arc furnace ash and the aluminum ash.
The secondary materials for steel refining of Example 1 to Example 8 are ones in which the amount of aluminum nitride (AlN) contained is adjusted to 20 wt % or more. In particular, the secondary materials for steel refining of Example 1 to Example 7 are arc furnace ashes in which the amount of aluminum nitride contained is 20 wt % or more and 50 wt % or less, and the secondary material for steel refining of Example 8 is an AlN reagent in which the amount of aluminum nitride contained is 100 wt %.
In the secondary materials for steel refining of Example 1 to Example 8, the amount of metallic aluminum (M.Al) contained is adjusted to a range of substantially 0 wt % or more and 10 wt % or less. The amount of aluminum oxide (Al2O3) contained is preferably from 30 wt % or more and 80 wt % or less, but in the secondary materials for steel refining of Example 1 to Example 7, it is adjusted to take a value of substantially from 40 wt % to 50 wt %.
In the present invention, it is sufficient if 20 wt % or more of AlN is contained. Therefore, although 100 wt % of AlN may be used, AlN may be used by adjusting the AlN content to 20 wt % or more based on a normal secondary material. A normal secondary material mainly contains 90 wt % or more of Al2O3: from 20 to 80 wt %, M.Al: from 10 to 50 wt %, AlN: less than 20 wt %, SiO2: 10 wt % or less, and MgO: 15 wt % or less and in addition, unavoidably contains a slight amount of MnO, K2O, Na2O, etc.
The evaluation shown in Table 1 was performed under the following conditions. In a melting furnace, 300 kg of molten iron having a carbon concentration [C]=from 4.2 to 4.6 wt %, a silicon concentration [Si]=from 0.3 to 0.8 wt %, a manganese concentration [Mn]=from 0.1 to 0.4 wt %, a phosphorus concentration [P]=from 0.1 to 0.2 wt %, and a sulfur concentration [S]=from 0.025 to 0.035 wt % was melted, and thereinto was charged 3.0 kg (10 kg/ton of molten iron) of a desulfurizing agent obtained by mixing lime (CaO) with the secondary material for steel refining according to the present embodiment containing components of secondary material (Al2O3, AlN, M.Al) shown in Examples 1 to 7 of Table 1. Here, the blending proportions of lime and the secondary material are as in the blending percentage shown in Examples 1 to 7 of Table 1.
After charging the desulfurizing agent into the molten iron, desulfurization was started by a mechanical stirring method using a stirring blade disclosed, for example, in patent publication of JP-A-2011-256445, and the sulfur concentration [S] in the molten iron after treatment at 1,350° C. for 10 minutes was sampled.
In Table 1, the results of evaluation based on whether or not the sampling result of sulfur concentration [S] indicates a concentration of less than 20 ppm are shown together.
The evaluation results shown in Table 1 are discussed below.
In the secondary material for steel refining (arc furnace ash) according to the present embodiment shown in Examples 1 to 7, when compared with a conventional secondary material for steel refining (aluminum ash) shown in Comparative Example 1, the sampling result of sulfur concentration [S] shown as S after Treatment in Table 1 was less than 20 ppm in all cases, and a desulfurization effect equivalent to or greater than that of aluminum ash was exerted. That is, since it is apparent that a desulfurization performance is brought out even when MN and M.Al are present as a mixed state, arc furnace ash and aluminum ash can also be used as a mixture.
In all of Examples 1 to 3, the amount of aluminum nitride (AlN) was set to 20 wt % or more, though it was different from each other and varied. In this way, when a sufficient amount of aluminum nitride (AlN) was contained, all of the sampling results of sulfur concentration [S] shown in Table 1 were less than 20 ppm, and the arc furnace ash thus exerted an effective desulfurization effect.
In Examples 1, 4 and 5, arc furnace ash having the same components (Al2O3, AlN and M.Al) of secondary material was used and the blending ratio of lime and arc furnace ash was changed to 95:5, 92.5:7.5 and 97.5:2.5. Even when the blending ratio of lime and arc furnace ash was thus changed, all of the sampling results of sulfur concentration [S] shown in Table 1 were less than 20 ppm, and the arc furnace ash thus exerted an effective desulfurization effect.
In Example 8, an AlN reagent having an aluminum nitride content of 100 wt % was used. Even when an AlN reagent not containing aluminum oxide (Al2O3) and metallic aluminum (M.Al) was used, the sampling result of sulfur concentration [S] was 5 ppm, and the MN reagent exerted a desulfurization effect greater than that of arc furnace ash. As seen also from this, the AlN concentration is preferably as high as possible.
In Comparative Examples 2 to 4, the secondary material components are greatly different from those in Examples 1 to 7. In Comparative Example 2, since a secondary material containing aluminum oxide in an amount of 100 wt % and not containing aluminum nitride (AlN) and metallic aluminum (M.Al) was used, the sampling result of sulfur concentration [S] was 51 ppm, and thus a desulfurization effect was not exerted.
The secondary material of Comparative Example 3 contained 5 wt % of metallic aluminum (M.Al) and the secondary material of Comparative Example 4 contained 15 wt % of aluminum nitride (AlN). In both of them, the sampling result of sulfur concentration [S] exceeded 30 ppm, and thus a desulfurization effect was not sufficiently exerted. The reason therefor is considered to be that the amount of metallic aluminum (M.Al) or aluminum nitride (MN) contained was not sufficient. Since the arc furnace ash is heat-treated in the air as described above, aluminum oxide as well as aluminum nitride are therefore produced. The results above reveal that in view of desulfurization performance, the amount of aluminum oxide needs to be 80 wt % or less.
Furthermore, the amount of silicon dioxide (SiO2) in the desulfurizing agent is preferably as small as possible. Since SiO2 reacts with CaO to form a reaction phase having a high melting point, such as 2CaO.SiO2, which inhibits a desulfurization reaction, the SiO2 concentration is preferably as low as possible. It is seen that in Example 7, the amount of SiO2 contained exceeds 2 wt % and the desulfurization performance is reduced as compared with Examples 1 to 6. For this reason, the content of SiO2 in the secondary material is preferably 2 wt % or less.
Next, the ignitability (ignition quality) was evaluated by using four kinds of arc furnace ashes shown in Example 9 to Example 12 as the secondary material for steel refining (secondary material) according to the present embodiment. As well as Examples 9 to 12, the ignitability was evaluated also on Comparative Example 5, and the obtained evaluation results are shown in Table 2 below.
In Table 2, Example 9 shows the results on arc furnace ash having equivalent components of secondary material as in Example 1 of Table 1. Similarly, Example 10, Example 11 and Example 12 show the results on arc furnace ash having equivalent components of secondary material as in Example 2, Example 3 and Example 6, respectively. Comparative Example 5 shows the results on aluminum ash having equivalent components of secondary material as in Comparative Example 1.
The evaluation shown in Table 2 was performed under the following conditions.
The aluminum ash and the arc furnace ash were evaluated for the ignitability by using the minimum ignition energy MIE (Minimum Ignition Energy) that is one indicator of the ignitability of powder. In the MIE measurement, a blowup type ignition testing apparatus (Hartmann method, MIKE-3) in conformity with IEC Standards, which is normally used at home and abroad, was used.
In this apparatus, compressed air (0.7 bar) in a receiver tank (1.28 L) blows up dust placed at the bottom of a glass-made explosion vessel (1.2 L) upon opening a solenoid valve and forms a uniform dust cloud inside the explosion vessel. A capacitor of 20 pF to 20 nF is charged from a direct-current high-voltage power source of 15 kV at a maximum to create a predetermined discharge energy, and this discharge energy is applied to the dust cloud, whereby the ignitability was evaluated. When flame of 50 mm or more was propagated in the explosion vessel, the sample was judged to be ignited, and the minimum ignition energy was measured for each case.
In Table 2, the measurement results are shown and at the same time, the ignitability is evaluated by judging that the ignitability (ignition quality) is low when the obtained minimum ignition energy is 50 mV or more, and assigning a rating “A”; judging that the ignitability cannot be said to be very low when 10 mV or more and less than 50 mV, and assigning a rating “B”; and judging that the ignitability is very high when less than 10 mV, and assigning a rating “C”.
The evaluation results shown in Table 2 are discussed below.
In the secondary material for steel refining (arc furnace ash) according to the present embodiment shown in Examples 9 to 11, the minimum ignition energy is 50 mV or more, and compared with the minimum ignition energy 4 mV of Comparative Example 5, the ignitability can be judged to be very low. The reason therefor is considered to be that the amount of metallic aluminum (M.Al) contained in the secondary material for steel refining is less than 10 wt % and falls much below 30.4 wt %, i.e., the amount of metallic aluminum (M.Al) in Comparative Example 5.
In Example 12, compared with Examples 9 to 11, the amount of metallic aluminum (M.Al) is slightly increased and is contained in an amount of more than 10 wt %. In Example 12, with an increase in the amount of metallic aluminum (M.Al), the minimum ignition energy is reduced to 23 mV, i.e., 50 mV or less. That is, when the amount of metallic aluminum (M.Al) exceeds 10 wt %, the sample is slightly susceptible to combustion, compared with Examples 9 to 11, and the ignitability cannot be said to be very low. In view of ignition quality, the amount of metallic aluminum (M.Al) is preferably 10 wt % or less.
The aluminum ash of Comparative Example 5 contains 30 wt % or more of metallic aluminum (M.Al), and the minimum ignition energy is 4 mV. As described above, the aluminum ash is a secondary material very susceptible to combustion without comparing to the arc furnace ash of Examples 9 to 12 and requires careful handling.
Consequently, it can be said that the arc furnace ash as the secondary material for steel refining according to the present embodiment exerts, by virtue of containing aluminum nitride (AlN), a desulfurization performance comparable to aluminum ash that is a conventional secondary material for steel refining, and in terms of ignitability, is less susceptible to ignition (combustion) than aluminum ash, excellent in the safety, and easy to store.
Next, with respect to aluminum ash and arc furnace ash, the desulfurization performance and the handleability (low likelihood of combustion) are compared and shown together in Table 3. It can be confirmed that in comparison to the aluminum ash, the arc furnace ash provides excellent handleability while exerting comparable desulfurization performance.
In addition, the advantage of use of arc furnace ash includes the following points. The aluminum ash has a fear that since metallic aluminum is oxidized by the air during storage, the metallic aluminum has promoted a deoxidation reaction prior to being charged into high-temperature molten iron and the desulfurization performance is reduced. On the other hand, aluminum nitride of the arc furnace ash is stable in the air and since a deoxidation reaction proceeds only when the arc furnace ash is charged into a high-temperature molten iron, reduction in the desulfurization performance during storage need not be feared.
The embodiments disclosed here are to be considered illustrative and not restrictive in all respects. In particular, for the matters not specifically disclosed in the embodiments disclosed here, such as operating condition or manipulating condition, various parameters, and dimensions, weights, volumes, etc. of components, a value that does not depart from the scope ordinarily implemented by one skilled in the art and can be easily anticipated by one skilled in the art, is adopted.
For example, in the secondary material for steel refining according to the above-described embodiment, aluminum nitride (AlN) is contained as the substance for promoting a desulfurization reaction through a deoxidation reaction but, for example, an aluminum compound capable of decomposing at a relatively low temperature in regard to the temperature of molten iron, such as aluminum bromide (AlBr3) or aluminum chloride (AlCl3), can be used in place of the aluminum nitride (AlN). Even with a secondary material for steel refining which uses aluminum bromide (AlBr3) or aluminum chloride (AlCl3), a desulfurization reaction can be promoted through a deoxidation reaction by substantially the same mechanism as in the desulfurization reaction of Formula (3) already described above.
The present application is based on Japanese Patent Application (Application No. 2014-021555) filed on Feb. 6, 2014, and the contents thereof are incorporated herein by reference.
The secondary material for steel refining of the present invention not only provides a desulfurization effect equivalent to or greater than that of conventional aluminum ash but also carries a low risk of combustion during storage and is useful for use in refining equipment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-021555 | Feb 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/053228 | 2/5/2015 | WO | 00 |
