Converter operation method

Abstract

To propose an operation method for a converter which bottom-blows oxygen-containing gas.SOLUTION: An operation method for a converter in which at least an oxygen-containing gas is bottom-blown includes a desiliconization treatment in which oxygen gas and an inert gas exceeding 50 vol.% are mixed with hot metal in the initial stage of blowing and supplied from a bottom-blown tuyere. Preferably, the Si concentration in the hot metal is 0.30 mass% or more. A supply flow rate as the oxygen gas supplied from the bottom-blown tuyere is preferably determined from a supply rate of CaO, a slag formation rate of CaO, the desiliconization efficiency, an amount of oxygen required to completely oxidize Si in hot metal stoichiometrically during a predetermined desiliconization treatment period, and a supply flow rate as the oxygen gas supplied from sources other than the bottom-blown tuyere. Oxygen for refining is preferably supplied only from the bottom-blown tuyere.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an operation method of a converter for bottom-blowing an oxygen-containing gas.

Background Art

[0002] Conventionally, in the desiliconization treatment for oxidizing and removing Si in hot metal in a converter, while adding a slag-forming agent to the hot metal in the converter furnace, oxygen is supplied from an upper blowing nozzle or a bottom blowing tuyere, and hot metal stirring is performed by supplying an inert gas from the bottom blowing tuyere as necessary, and blowing is performed while suppressing slopping due to foaming of the slag (for example, Patent Document 1).

[0003] When performing desiliconization treatment by supplying pure oxygen gas from the bottom blowing tuyere, conventionally, the bottom blowing inner pipe pure oxygen gas flow rate that ensures a bottom blowing inner pipe tuyere pressure higher than the hot metal static pressure has been blown in. For example, Non-Patent Document 1 gives the lower limit volume flow rate Q min (Nm 3 / min) of the bottom blowing gas that does not allow hot metal to enter the bottom blowing tuyere by the following formula 1. N in the formula is the number of bottom blowing tuyeres, and ρ g is the gas density (kg / m 3 ), ρ l is the hot metal density (kg / m 3 ), H is the bath depth (m), and d is the tuyere diameter (m).

Equation

Equation

[0004] Techniques for mixing an inert gas with oxygen gas are also disclosed. For example, Patent Document 2 discloses a blowing method for a top-bottom blown converter, in which an inert gas is supplied from a bottom blowing tuyere, and decarburization is carried out by mixing at least one diluent gas of air, nitrogen, argon, and steam with oxygen from a top blowing lance. Patent Document 3 discloses a steel melting method in which atomized water droplets are blown from a tuyere under the molten steel surface together with an oxidizing gas and / or an inert gas. Patent Document 4 discloses a technique in which, when subjecting hot metal subjected to desiliconization and dephosphorization treatment to top-bottom combined refining blowing, a slag-forming agent is added, and in the first half of the blowing, oxygen gas containing an inert gas of substantially 50% by volume or less is bottom-blown.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the above prior art has the following problems. That is, in the technique disclosed in Patent Document 1, increasing the supply rate of the slag-forming agent (CaO source) added in the hot metal desiliconization treatment leads to an increase in the unit consumption of the slag-forming agent, resulting in an increase in the refining cost. Therefore, it becomes an issue to reduce the SiO 2 generation rate.

[0008] Moreover, the techniques disclosed in Patent Documents 2 and 3 are techniques related to the low carbon concentration region at the end of blowing, and there is no disclosure regarding the findings when applied to the desiliconization period at the beginning of blowing. The technique disclosed in Patent Document 4 is for promoting slag formation at the beginning of blowing for hot metal subjected to desiliconization and dephosphorization treatment with a Si concentration of 0.2 mass% or less and a P concentration of 0.1 mass% or less. There is no disclosure regarding suppressing slopping when desiliconizing hot metal containing 0.30 mass% or more of Si. Also, the utilization of secondary combustion during the period of a large amount of CO gas generation at the beginning of decarburization is not mentioned.

[0009] When blowing pure oxygen gas from the bottom blowing tuyere as described in Non-Patent Document 1, the control range is narrow, and Q min / Q max is about 0.58. That is, the flow rate of the pure oxygen gas blown from the bottom can only be reduced to 58% of the maximum value.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to propose a method for suppressing slopping in the operation of a converter that blows at least an oxygen-containing gas from the bottom. At the same time, a method for effectively utilizing secondary combustion at the beginning of decarburization is proposed.

Means for Solving the Problems

[0011] The converter operation method according to the present invention that advantageously solves the above problems is a converter operation method that blows at least an oxygen-containing gas from the bottom, and is characterized in that it includes a desiliconization treatment in which oxygen gas and an inert gas of more than 50% by volume are mixed and supplied from the bottom blowing tuyere to the hot metal at the beginning of blowing.

[0012] In addition, the converter operation method according to the present invention is (a) the Si concentration in the hot metal is 0.30 mass% or more, (b) The supply flow rate Q of oxygen gas supplied from the bottom blowing tuyere B (O 2 ) The upper limit value is determined from the supply rate S of CaO supplied into the furnace, the CaO slagging rate α, the desiliconization efficiency β, and the supply flow rate Q of oxygen gas supplied from sources other than the bottom blowing tuyere U (O 2 ) and perform desiliconization treatment at the initial stage of blowing (c) The lower limit value of the supply flow rate Q of oxygen gas supplied from the bottom blowing tuyere B (O 2 ) is calculated from a predetermined desiliconization treatment time, the amount of oxygen required to chemically oxidize Si in the hot metal completely, and the supply flow rate Q of oxygen gas supplied from sources other than the bottom blowing tuyere U (O 2 ) (d) Supply refining oxygen only from the bottom blowing tuyere etc. can be more preferable solution means

Advantages of the Invention

[0013] According to the converter operation method of the present invention, in the operation of at least a converter that bottom blows an oxygen-containing gas, while blowing a bottom blowing tuyere gas flow rate having a pressure higher than the static pressure of the hot metal in the furnace, diluted oxygen gas is bottom blown. Therefore, in the desiliconization treatment, rapid oxidation of Si can be suppressed, a decrease in slag basicity can be suppressed, and the occurrence of slopping can be suppressed. In addition, the period of a large amount of CO generation at the initial stage of decarburization can be extended, the effective period of secondary combustion heat in the furnace can be extended, and it can be used for melting of the metal at the furnace mouth and the like

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be specifically described. The following embodiments illustrate devices and methods for embodying the technical idea of the present invention, and do not specify the configuration to be the following. That is, various changes can be made to the technical idea of the present invention within the technical scope described in the claims.

[0016] The converter operation method according to this embodiment can be applied when desiliconizing hot metal, when performing desiliconization and dephosphorization treatment, or when performing decarburization refining including desiliconization treatment, using a converter having a function of bottom-blowing an oxygen-containing gas. It may also have a function of blowing top-blown oxygen.

[0017] In this embodiment, after charging hot metal into the converter, an oxygen-containing gas is supplied from the bottom-blowing tuyere to start blowing. The oxygen-containing gas is a mixed gas of oxygen and an inert gas exceeding 50% by volume. As the inert gas, gas species that do not affect refining, such as nitrogen gas, argon gas, and CO 2 gas, can be applied. This diluted blowing is applied, for example, when blowing with pure oxygen during the desiliconization treatment period and the SiO 2 generation rate becomes higher than the slag formation rate of the supplied slag-forming agent. It can also be applied when extending the period of a large amount of CO gas generation at the initial stage of decarburization to utilize the effective use of secondary combustion heat in the furnace. Here, the desiliconization treatment period refers to the period from the start of blowing to the end of desiliconization, that is, until the Si concentration in the hot metal becomes 0.01% by mass. Also, when the slag basicity during the desiliconization treatment, that is, the ratio of the concentration of CaO to the concentration of SiO 2 in the slag on a mass basis (hereinafter abbreviated as C / S) is less than 2.7, slopping is likely to occur due to slag formation. Also, as a condition where the SiO 2 generation rate is high, the case where the Si concentration of the hot metal is 0.30% or more can be mentioned.

[0018] By supplying an oxygen-containing gas mixed with an inert gas exceeding 50% by volume from the bottom-blowing tuyere, as described above, while making the gas pressure in the inner pipe of the tuyere equal to or higher than the static pressure of the hot metal, the supplied oxygen flow rate can be appropriately reduced.

[0019] When pure oxygen gas is bottom-blown, the minimum and maximum supply oxygen flow rates (volume flow rates) can be obtained according to the above-mentioned formulas (1) and (2) described in Non-Patent Document 1. The inventors studied the appropriate gas supply amount when supplying a mixed gas in which oxygen is diluted with an inert gas from the bottom-blowing tuyere. As a result, it was found that it should be arranged in terms of mass flow rate. When the mass flow rate of the gas blown into the bottom-blowing tuyere is W M (kg / min), per bottom-blowing tuyere, Q min / N×32 / 22.4≦W M / N≦Q max / N×32 / 22.4 It was found that it is appropriate to satisfy the relationship. Here, N is the number of bottom-blowing tuyeres.

[0020] The above-mentioned minimum oxygen gas supply amount Q min Since the gas flow rate may fluctuate upward or downward from the set value at the timing of blowing the auxiliary raw material from the inner pipe or changing the gas flow rate during the blowing process, it is preferable to set it in consideration of the downward fluctuation. Since it was obtained from the simulation results that the above-mentioned downward fluctuation occurs up to 2%, the corrected minimum oxygen gas flow rate Q’ min =Q min ×1.02 may be set.

[0021] In addition, the lower limit of the ratio of oxygen gas to inert gas in the oxygen-containing gas can be arbitrarily set according to the blowing conditions. For example, the supply flow rate Q B (O 2 ){Nm 3 / (min·t - hot metal)} of the oxygen gas supplied from the bottom-blowing tuyere can be calculated from the predetermined desiliconization treatment time, the amount of oxygen required to oxidize Si in the hot metal stoichiometrically, and the supply flow rate Q U (O 2 ) of the oxygen gas supplied from other than the bottom-blowing tuyere.

[0022] The supply flow rate Q B (O 2 ){Nm 3 / (min·t - hot metal)} is preferably determined as follows. The CaO slagging rate {kg / (min·t - hot metal)} in the slag-forming agent (CaO source) is taken as the CaO input rate {kg / (min·t - hot metal)} in the slag-forming agent × slagging rate α (%) × 0.01. The slag-forming agent may be supplied from the upper part of the converter or from the bottom blowing tuyere. When the slag-forming agent is supplied from the upper part of the converter, the CaO input rate in the slag-forming agent is obtained by dividing the supplied amount of the slag-forming agent by the time required for the slagging rate of CaO to reach a predetermined value after the addition of the slag-forming agent. SiO 2 generation rate {kg / (min·t - hot metal)} is the oxygen gas flow rate Q in the inner pipe of the tuyere B (O 2 ) × deoxidation efficiency β (%) × 0.01 / 22.4 × 60. Also, the supply flow rate of the oxygen gas contributing to the refining supplied from other than the bottom blowing tuyere is Q U (O 2 ){Nm 3 / (min·t - hot metal)}. Here, contributing to the refining means not including the oxygen used for secondary combustion in the furnace. The slagging rate α of CaO can be determined by slag analysis for the CaO other than the CaO remaining as a single solid among the input CaO. The deoxidation efficiency β is the percentage of the oxygen amount contributing to the generation of SiO 2 among the input oxygen amount. Q B (O 2 ) ≤ S × α / β × 22.4 / 60 - Q U (O 2 ) (1)

[0023] This embodiment is preferably applicable when supplying the oxygen-containing gas only from the bottom blowing tuyere.

Example

[0024] An operation example (invention example) of a converter applying this embodiment at the initial stage of blowing using a 340 t-scale oxygen bottom-blown converter is shown in Fig. 1. An example of blowing pure oxygen during the blowing period (conventional example) is shown in Fig. 2. The Si concentration in the hot metal at the time of charging into the converter was 0.35 mass%. It was determined that the desiliconization treatment was completed when the Si concentration in the hot metal fell below 0.01 mass%. The slag-forming agent was pre-charged at a CaO unit of 17.0 kg / t-hot metal, and 2.5 kg / t-hot metal was added 3 minutes after the start of blowing, 5.0 kg / t-hot metal was added 4 minutes later, and 0.4 kg / t-hot metal was added 5 minutes later. The CaO slagification rate α of the slag-forming agent was set to 75%. The desiliconization oxygen efficiency β was set to 50%. The time required for the CaO slagification rate α of the slag-forming agent to reach 75% from the addition of the slag-forming agent was 8.3 minutes, and the CaO input rate in the slag-forming agent was the highest 5 minutes after the start of blowing, at 3.0 {kg / (min·t-hot metal)}. Q obtained from Equation (1) B (O 2 ) has the highest upper limit value 5 minutes after the start of blowing, at 1.68 {Nm 3 / (min·t-hot metal)}.

[0025] During the dilution blowing of the invention example, the oxygen supply amount from the bottom blowing tuyere was Q B (O 2 ) = 1.04 {Nm 3 / (min·t-hot metal)}, and the nitrogen supply amount as the inert gas was Q B (N 2 ) = 1.38 {Nm 3 / (min·t-hot metal)}. During the blowing of the conventional example, the oxygen supply amount from the bottom blowing tuyere was Q B (O 2 ) = 2.21 {Nm 3 / (min·t-hot metal)}. In the case of this bottom-blown converter, the bottom blowing gas was the mass flow rate per bottom blowing tuyere, and 45.9 ≦ W M / N ≦ 79.5 {kg / (min·unit)} was appropriate.

[0026] In the invention example shown in Fig. 1, the desiliconization treatment period is about 7 and a half minutes. By reducing the oxygen supply amount at the initial stage of blowing, SiO 2The production rate could be reduced, and the rate of decrease in slag basicity could also be reduced. Along with this, the change in slag basicity C / S during the desiliconization treatment period did not fall below 2.7. Therefore, desiliconization treatment can be carried out without concern about slopping occurring at the initial stage of blowing.

[0027] In the conventional example shown in Figure 2, the desiliconization treatment period is about 4 minutes. At the initial stage of blowing, the generation rate of SiO 2 is high, and the slag basicity fell below 2.7 at 2 to 3 minutes after the start of blowing. Therefore, there is concern about the occurrence of slopping.

[0028] In this specification, the unit of mass "t" represents 10 3 kg. The symbol "N" attached to the unit of volume represents the standard state, that is, the state at a temperature of 0°C and a pressure of 101325 Pa.

Industrial Applicability

[0029] According to the method for operating a converter of the present invention, when blowing an oxygen-containing gas from the bottom, an appropriate oxygen supply amount can be set at the initial stage of blowing, so slopping can be prevented and the heat of secondary combustion can be effectively utilized. Therefore, the stability of the operation can be achieved and the productivity can be improved, which is industrially useful.

Claims

1. An operation method for a converter that blows at least an oxygen-containing gas from the bottom, comprising a desiliconization treatment in which, with respect to hot metal, an oxygen gas and an inert gas exceeding 50% by volume are mixed from the start of blowing to the end of desiliconization and supplied from a bottom blowing tuyere. The lower limit value of the supply flow rate QB(O2) of the oxygen gas supplied from the bottom blowing tuyere is calculated from a predetermined desiliconization treatment time, the amount of oxygen required to oxidize Si in the hot metal stoichiometrically, and the supply flow rate QU(O2) of the oxygen gas supplied from other than the bottom blowing tuyere. An operation method for a converter.

2. The operation method for a converter according to claim 1, wherein the Si concentration in the hot metal is 0.30% by mass or more.

3. The supply flow rate Q of oxygen gas supplied from the bottom blowing tuyere Ｂ (O ２ ) the upper limit value of is calculated from the supply rate S of CaO supplied into the furnace, the CaO slagging rate α, the de-siliconization efficiency β, and the supply flow rate Q Ｕ (O ２ ) of oxygen gas supplied from other than the bottom blowing tuyere by S×α / β×22.4 / 60 - Q U (O2), and the de-siliconization treatment from the start of blowing to the end of de-siliconization is performed. The method for operating a converter according to claim 2 However, QB(O2) and QU(O2) respectively represent the supply flow rate of the oxygen gas supplied from the bottom blowing tuyere and from other than the bottom blowing tuyere in Nm3 / (min·t-hot metal), S represents the CaO input rate in the slag-forming agent in kg / (min·t-hot metal), α represents the slag formation rate expressed as a percentage, and β represents the desiliconization oxygen efficiency expressed as a percentage.

4. The operation method for a converter according to any one of claims 1 to 3, wherein refining oxygen is supplied only from the bottom blowing tuyere.

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