Patent Application
20240068060
The present invention is related to a refining method of molten iron in a converter and a manufacturing method of molten steel using the same.
A method required to reduce the amount of CO2 generated from iron and steel processing includes increasing the amount of scrap (scrap iron) used in a converter to lower the blending ratio of molten pig iron (“hot metal ratio”) that contains approximately 4.5 mass % C. Increasing the amount of scrap causes the heat of the molten pig iron to be consumed in heating and dissolving the scrap, which results in a temporary decrease in the temperature of the molten pig iron. Consequently, the following two problems arise.
(1) A decrease in the scrap dissolution rate:
There will be a decrease in the scrap dissolution rate because one or both of carburization of and heat conduction to the scrap is reduced, for the reason that the molten pig iron in contact with the scrap surfaces becomes solidified due to the lower temperature and hinders the carburization or that the difference (ΔT) becomes smaller between the molten pig iron temperature and the liquidus temperature of a melting point depression phase formed in the scrap due to carburization from the molten pig iron.
(2) A clog in a bottom-blowing nozzle:
In conjunction with the scrap dissolution, when the molten pig iron temperature becomes equal to or lower than “60° C.+a molten pig iron liquid phase linear temperature” determined in accordance with the concentration of C in the molten pig iron, the molten pig iron immediately above the bottom-blowing nozzle becomes solidified and makes the bottom-blowing nozzle clogged. That causes the deterioration of agitation/blending characteristics of the molten pig iron to inhibit the carburization from the molten pig iron into the scrap, leading not only to a decrease in the dissolution rate of the scrap but also to a decrease in the efficiency of refining processes such as dephosphorization, for example, which will result in a large cost increase.
To solve the problems described in (1) and (2) above, conventionally a heating material such as ferrosilicon, earthy graphite, and/or silicon carbide is charged into a converter to increase the molten pig iron temperature with the heat generated from an exothermic reaction between Si/C contained in each heating material and oxygen for blowing into a converter. However, the use of ferrosilicon causes an increase in the Si concentration in the molten pig iron, for which it is necessary to add a CaO content represented by calcium oxide, for example, to the inside of the furnace to prevent the basicity of slag (=Ca concentration in the slag (mass %)/SiO concentration in the slag (mass %)) to remove impurities such as P from becoming lower, thus increasing refining costs. In contrast, earthy graphite and silicon carbide contain carbon and are therefore not suitable for use, in view of the endeavor to reduce the amount of generated CO2.
Further, methods not using the abovementioned heating material have been proposed (see Patent Literature 1 and Patent Literature 2) by which heated powder particles serving as a heat transfer medium are blown onto molten pig iron or molten steel from a top-blowing lance having a burner function.
Patent Literature 1: JP-2019-119906A
Patent Literature 2: JP-2014-159632A
However, in both methods described in Patent Literatures 1 and 2, the top-blowing lance having the burner function is integrated with a top-blowing lance for blowing. For this reason, when the lance height is raised to prioritize heat transfer (to prolong an in-flame staying time period of powder), there is no choice but to perform a so-called “soft-blow operation”, which denotes an increase in the concentration of iron oxide in the slag. That frequently causes a phenomenon called slopping where the slag in the converter expands and overflows to the outside of the furnace due to generated gas, significantly deteriorating the stability of the blowing process. Lowering the lance height in order to avoid slopping decreases the amount of heat transfer also. Consequently, this method is not considered practical because there would be large costs due to an increase in the lance weight caused by an intricate lance structure, as well as re-designing and strengthening of equipment or the like to support the weight, in comparison to a reduction in the hot metal ratio achieved without using the heating material.
The present invention is made in view of such circumstances as above and proposes a refining method of molten iron that solve the problems in the conventional refining methods based on the use of the integrated lance and a manufacturing method of molten steel using the same.
The inventors have conducted various experiments to solve the abovementioned problems and studied subjects in refining methods using existing-type integrated lances. As a result, we discovered a molten iron refining method and a molten steel manufacturing method using the same that are novel and capable of solving the existing problems. The present invention is based on this discovery, and the gist thereof is presented below.
A molten iron refining method of the present invention capable of advantageously solving the abovementioned problems is a molten iron refining method for refining molten iron by adding an auxiliary raw material and supplying oxidizing gas to molten iron contained in a converter-type vessel, and is characterized by including: inserting, as far as to a position lower than an upper end inside the converter-type vessel, a blowing-purpose oxygen-blowing lance that supplies the oxidizing gas and that is capable of ascending and descending and at least one burner lance capable of ascending and descending independently of the blowing-purpose oxygen-blowing lance; blowing, onto the molten iron, either oxidizing gas or oxidizing gas and CaO-containing refining agent from the blowing-purpose oxygen-blowing lance; forming a flame by causing the burner lance to discharge fuel gas and combustion-supporting gas, and causing powder particles discharged from the burner lance to pass through the flame and to be blown onto the molten iron in a heat-transferred state, to achieve thermal compensation of the molten iron.
The first process of a molten steel manufacturing method according to the present invention includes:
The second process of a molten steel manufacturing method according to the present invention includes:
A third process of a molten steel manufacturing method according to the present invention includes: a raw material charging step of charging a cold iron source and molten pig iron to a converter-type vessel to form molten iron;
The present invention configured as described above can secure an in-flame staying period of the heat transfer medium without being affected by the height adjustments of the blowing-purpose oxygen-blowing lance, achieving heat transfer to the molten iron or to the molten steel without inhibiting the stability of the blowing processes, which has hitherto been a problem. This achievement contributes to the production of a thermal margin for dissolving carbon steel (SC).
<Explanations of a Process in a Molten Iron Refining Method of the Present Invention>
According to the molten iron refining method in the present embodiment, at first, in the converter-type vessel 1 having the molten iron 2 contained therein, the blowing-purpose oxygen-blowing lance 3 capable of ascending and descending in the converter-type vessel 1 and the burner lance 4 capable of ascending and descending independently of the blowing-purpose oxygen-blowing lance 3 are inserted, as far as to a position lower than the upper end inside the converter-type vessel 1. Subsequently, from the blowing-purpose oxygen-blowing lance 3, either oxidizing gas or oxidizing gas and a CaO-containing refining agent are blown onto the molten iron 2. At the same time, the flame 5 is formed by causing the burner lance 4 to discharge the fuel gas and the combustion supporting gas. The powder particles 6 discharged from the burner lance 4 and serving as a heat transfer medium are caused to pass through the flame 5 and to be blown onto the molten iron 2 in a heat-transferred state, so that the molten iron 2 is thermally compensated. The quantity of the burner lance 4 is not limited to one, and even the use of two or more burner lances can achieve similar operation effects as with a single burner lance, by controlling the discharged amounts of the fuel gas, the combustion supporting gas, and the powder particles 6. The oxidizing gas included pure oxygen or a gas mixture of oxygen and carbon dioxide or inert gas. Further, the combustion-supporting gas includes air, oxygen-enriched air, or oxidizing gas.
The molten iron refining method described above is characterized in that the blowing-purpose oxygen-blowing lance 3 and the burner lance 4 can ascend and descend independently of each other, so that the insertion positions of the blowing-purpose oxygen-blowing lance 3 and the burner lance 4 can be arranged mutually different in the converter-type vessel 1. Thus, the in-flame staying time period of the powder particles 6 serving as the heat transfer medium can be obtained by not inserting the burner lance 4 as deep as the blowing-purpose oxygen-blowing lance 3 in the converter-type vessel 1 without being affected by the height adjustments of the blowing-purpose oxygen-blowing lance 3.
In an example where the tip end of an existing-type integrated blowing-purpose oxygen-blowing lance 3 is required to be positioned 2 m to 3 m away from the molten iron surface of the molten iron 2, the present embodiment allows the tip end of the burner lance 4 to be positioned 3 m to 4 m away from the molten iron surface of the molten iron 2 while maintaining the tip end of the blowing-purpose oxygen-blowing lance 3 at a position 2 m to 3 m away from the molten iron surface of the molten iron 2. In other words, in the conventional example, the tip end of the burner lance 4 needs to be positioned 2 m to 3 m away from the molten iron surface of the molten iron 2, while, in the present embodiment, the tip end of the burner lance 4 can be arranged 3 m to 4 m away from the molten iron surface of the molten iron 2, which is farther away from the molten iron surface of the molten iron 2. That can prolong the staying time period in the flame 5 of the powder particles 6 discharged from the burner lance 4 and serving as a heat transfer medium, for example, from the range of 0.01 s to 0.05 s in the conventional example (where the height lh from the tip end of the lance 4 to the molten iron surface of the molten iron 2=2 m to 3 m) to the range of 0.05 s to 0.5 s (where lh=3 m to 4 m). When defined as a ratio of the amount of heat transferred from the actual temperature increase of the molten iron to the amount of heat supplied by the burner lance, a heat transfer efficiency (%) can improve by approximately 20% at a maximum with respect to the same particle diameter dp (μm) of the powder particles 6, as shown in
Next, a molten steel manufacturing method using the molten iron refining method described above will be explained, with reference to
<The First Process of a Molten Steel Manufacturing Method>
The first process of the molten steel manufacturing method described above involves performing the above-mentioned molten iron refining method in at least one step selected from the desiliconization blowing step (step 2), the dephosphorization blowing step (step 4), and the decarburization blowing step (step 7), That can achieve heat transfer to the molten iron or the molten steel without inhibiting the stability of the blowing processes, which has hitherto been a problem, thus producing a thermal margin for dissolving the carbon steel (SC) serving as the cold iron source.
<The Second Process of the Molten Steel Manufacturing Method>
The second process of the molten steel manufacturing method described above involves performing the above-mentioned molten iron refining method in at least one step selected from the desiliconization and dephosphorization blowing step (step 2) and the decarburization blowing step (step 4). That can achieve heat transfer to the molten iron or to the molten steel without inhibiting stability of the blowing processes, which has hitherto been a problem, thus producing a thermal margin for dissolving the carbon steel (SC) serving as the cold iron source.
<The Third Process of the Molten Steel Manufacturing Method>
The third process of the molten steel manufacturing method described above involves performing the abovementioned molten iron refining method in the blowing step (step 3). That can achieve heat transfer to the molten iron or the molten steel without inhibiting the stability of the blowing processes, which has hitherto been a problem, producing a thermal margin for dissolving the carbon steel (SC) serving as the cold iron source.
Molten steel was manufactured by using the first to the third processes of the molten steel manufacturing method described above, with the same operation patterns (an oxygen blowing rate, a bottom blowing rate, and the like) under the conditions of the same ingredients, a pre-treatment temperature, treatment time, and the like. Further, a Hot Metal Ratio (HMR) was measured in each example to compare.
As shown in Table 1, for the first process, molten steel was manufactured with respect to the following: Treatment Nos. 1 and 2 without using a burner lance; Treatment Nos. 3 to 5 using a burner lance integrated with a blowing-purpose oxygen-blowing lance (the distance between the tip end and the molten iron surface: 2.5 m); and Treatment Nos. 6 to 8 using a burner lance capable of ascending and descending independently of a blowing-purpose oxygen-blowing lance (the distance between the tip end of the blowing-purpose oxygen-blowing lance and the molten iron surface: 2.5 m; the distance between the tip end of the burner lance and the molten iron surface: 3.5 m), and a hot metal ratio (HMR) reduction percentages as compared to a base condition (Treatment No. 1) were calculated.
Treatment No. 1 without using a burner lance serves as the base condition of the first process. Treatment No. 2 had the same ingredients and pre-treatment temperature as Treatment No. 1 but had increased [Si] in the molten iron due to the charging of FeSi as a heating material, and had a longer treatment time than Treatment No. 1 by 0.35 minutes. Treatment No. 3 had the same ingredients, pre-treatment temperature, and treatment time as Treatment No. 1. Treatment No. 4 had the same ingredients and pre-treatment temperature as Treatment No. 1, but had a significantly prolonged treatment time because the dephosphorization treatment blowing period was temporarily suspended due to occurrence of slopping. Treatment No. 5 had the same ingredients, treatment temperature, and treatment time as Treatment No. 1. Treatment Nos. 6, 7, and 8 each had the same ingredients, treatment temperature, and treatment time as Treatment No. 1.
As shown in Table 2, for the second process, molten steel was manufactured with respect to the following: Treatment Nos. 9 and 10 without using a burner lance; Treatment Nos. 11 and 12 using a burner lance integrated with a blowing-purpose oxygen-blowing lance (the distance between the tip end and the molten iron surface: 2.5 m); and Treatment Nos. 13 and 14 using a burner lance capable of ascending and descending independently of a blowing-purpose oxygen-blowing lance (the distance between the tip end of the blowing-purpose oxygen-blowing lance and the molten iron surface: 2.5 m; the distance between the tip end of the burner lance and the molten iron surface: 3.5 m), and a hot metal ratio (HMR) reduction percentages as compared to a base condition (Treatment No. 9) were calculated.
Treatment No. 9 without using a burner lance serves as the base condition of the second process. Treatment No. 10 had the same ingredients and pre-treatment temperature as Treatment No. 9, but had increased [Si] in the molten iron due to the charging of FeSi as a heating material, and had a longer treatment time than Treatment No. 9 by 0.4 minutes. Treatment No. 11 had the same ingredients and pre-treatment temperature as Treatment No. 9, but had a prolonged treatment time than Treatment No. 9 by 1 minute because the oxygen blowing rate was decreased due to occurrence of slopping in the desiliconization and dephosphorization blowing process. Treatment No. 12 had the same ingredients, pre-treatment temperature, and treatment time as Treatment No. 9, Treatment Nos. 13 and 14 each had the same ingredients, pre-treatment temperature, and treatment time as Treatment No. 9.
As shown in Table 3, for the third process, molten steel was manufactured with respect to the following: Treatment Nos. 15 and 16 without using a burner lance; Treatment Nos. 17 using a burner lance integrated with a blowing-purpose oxygen-blowing lance (the distance between the tip end and the molten iron surface: 2.5 m); and Treatment No. 18 using a burner lance capable of ascending and descending independently of a blowing-purpose oxygen-blowing lance (the distance between the tip end of the blowing-purpose oxygen-blowing lance and the molten iron surface: 2.5 m; the distance between the tip end of the burner lance and the molten iron surface: 3.5 m), and a hot metal ratio (HMR) reduction percentages as compared to a base condition (Treatment No. 15) were calculated.
Treatment No. 15 without using a burner lance serves as the base condition of the third process. Treatment No. 16 had the same ingredients and pre-treatment temperature as Treatment No. 15, but had increased [Si] in the molten iron due to the charging of FeSi as a heating material, and had a prolonged treatment time than Treatment No. 15 by 0.4 minutes. Treatment No. 17 had the same ingredients and pre-treatment temperature as Treatment No. 15, but had a significantly prolonged treatment time because the blowing was temporarily suspended due to slopping that occurred when the degree of progress in the blowing was 20%. Treatment No. 18 had the same ingredients, pre-treatment temperature, and treatment time as Treatment No. 15.
Tables 1 to 3 below show the results of the examples.
The results presented in Tables 1 to 3 and
The molten iron refining method of the present invention can be used not only in any of the decarburization blowing, dephosphorization blowing, and desiliconization blowing processes as described above, but is also applicable to any refining process as long as a lance nozzle is employed, including a refining process in an electric furnace, for example, and therefore it is very useful.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-014513 | Feb 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/045253 | 12/9/2021 | WO |
