JPH05179332A - Cooling and protecting method for oxygen blowing tuyere to underside of molten iron bath surface in converter - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the wear of tuyere by properly supplying cooling propane gas to the tuyere that blows oxygen gas below the surface of the molten iron bath in the converter. [Composition] The tuyere according to the oxygen gas basic unit calculated from the heat load applied to the tuyere 10 due to the progress of refining by the oxygen gas flowing under the bath surface through the central flow path 4 of the tuyere 10. The flow rate of the cooling propane gas flowing through the ten annular flow paths 5 is adjusted stepwise. [Effect] Since the tuyere 10 can be effectively cooled without wasting cooling propane gas, the life of the tuyere can be extended.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling and protecting a tuyere blown with oxygen gas below the surface of a molten iron bath in a converter.

[0002]

2. Description of the Related Art As a method of cooling and protecting bottom blowing or side blowing tuyere of oxygen gas in a converter, N ₂ , Ar, CO, etc. are provided in an outer annular gas line surrounding a central line for supplying oxygen gas.
It is common to supply a cooling protection fluid such as CO ₂ , propane, methanol, water vapor, and liquefied hydrocarbon to prevent combustion and melting damage of the oxygen blowing tuyere.

A bottom blowing converter is a tuyere provided at the bottom of the furnace.
In a horizontal blow converter, an oxidizing gas such as pure oxygen is blown into the steel bath from the tuyere provided on the furnace wall to oxidize and remove carbon, silicon, phosphorus, etc. contained in the steel to produce steel. It is a refining furnace. The main refining reaction in this refining furnace is an oxidation reaction accompanied by heat generation generated by the oxidation of carbon, silicon, phosphorus and the like, and this reaction heats the molten steel around the tuyere to a remarkably high temperature.

At this time, in order to reduce or prevent the tuyere from being consumed and damaged due to high heat, hydrocarbons (chemical formulas CnHm, n, m are used as cooling gas from the periphery of the tuyere pipe line through which the oxidizing gas conventionally passes. Gas such as (integer) is blown into the furnace. When heated, this gas decomposes into C and H ₂ gas,
Since the decomposition is an endothermic reaction, the effect of cooling the tuyere is exerted, and the wear of the tuyere is reduced.

By the way, as described above, the heat received by the tuyere is mainly due to the heat generated by oxidation, but since this heat generation changes with the progress of the blowing process, the heat received by the tuyere also fluctuates moment by moment. According to the conventional method, proportional flow rate control is employed in which the amount of cooling gas is increased / decreased in proportion to the amount of oxygen transport, and the larger the amount of oxygen transport is, the more the cooling gas flow is increased at a constant rate.

According to the blowing method of the bottom blowing converter as described above, the cooling gas flow rate is set so that the flow rate of the cooling gas is set to a sufficiently large amount in consideration of the safety factor with respect to the blowing oxygen flow rate. However, the cooling gas was wasted more than necessary at some point during the blowing process. As described above, when the flow rate of the cooling gas is excessive, not only is the consumption of the cooling gas itself uneconomical, but further, solidified metal that adheres to the tuyere due to excessive cooling (commonly called mushroom) Becomes abnormally large, and due to the abnormal size, it suddenly comes off or peels off. In such a case, the tip of the tuyere is in a bare state, so that the tuyere is considerably worn out, the tuyere periphery recedes in a concave shape, and the life after that is shortened, resulting in an extremely unfavorable state.

Further, due to such excessive cooling, the furnace bottom brick around the tuyere is extremely strongly cooled and a locally large temperature gradient portion is generated. Normally, even if such a temperature gradient occurs in the brick, it can withstand sufficiently if it continues in that state. However, in the case of a brick in the converter, the inside of the furnace will be empty during the waiting time after tapping until the next blowing, and of course, refining oxygen will not flow, so
Cooling gas such as hydrocarbon is not flowed, and only a very small amount of nitrogen gas is flowed to prevent tuyere blockage.

For this reason, the bottom bricks in the tuyere and its surroundings, which have been cooled by the heat absorption due to the thermal decomposition of hydrocarbons, are rapidly reheated. As a result, the large temperature gradient of the furnace bottom brick around the tuyere, which was caused by overcooling during blowing as described above, suddenly decreases, the brick undergoes a severely severe thermal cycle, and the brick around the tuyere spalls. Peels off and shortens the life of the furnace bottom.

Therefore, in order to suppress the wear of the tuyere and its surrounding refractories, that is, the bottom brick, a solidified metal of appropriate size (hereinafter referred to as mushroom) is formed at the tip of the tuyere, and the wing is thereby formed. It is necessary to protect the tip of the mouth and to properly manage the injection of cooling gas so that the bricks around the tuyere are not subjected to severe heat cycles. by the way,
The cooling protection gas not only cools the tuyere itself to lower the temperature, but also forms a porous mushroom at the tip of the tuyere due to the sensible heat and decomposition heat of the cooling gas, and blows oxygen into the molten iron. Due to radiant heat from the high temperature reaction interface called the fire point generated by reaction with carbon etc. in molten iron to the tuyere tip, melting loss due to molten iron stirring flow, wear, convective heat transfer of molten iron, etc. It protects the refractory surface.

Therefore, oxygen is blown for the purpose of appropriately maintaining the mushrooms formed at the tip of the tuyere to suppress the melting loss of the tuyere, optimizing the flow rate of the cooling protective gas and reducing the usage amount. The following methods have been proposed as a tuyere cooling method. That is, (1) Japanese Patent Laid-Open No. 61-34114;
A method for cooling a tuyere immersed in a bath, in which the temperature of the outer tube is measured by a thermocouple inserted therein, and the flow rate of the cooling protective gas to be circulated according to the temperature variation is adjusted.

(2) Japanese Patent Application 1-
No. 275771; To protect the tuyere of oxygen blown below the molten iron bath surface, decarburization rate and carbon content in molten iron were estimated from the results of continuous measurement of CO and CO ₂ concentrations in converter exhaust gas and the exhaust gas flow rate. , A method of estimating the fire point temperature at the tip of the tuyere from this result and changing the amount of the tuyere cooling fluid. (3) JP-A-56-4407: It is based on the finding that the degree of heat reception around the tuyere does not always increase with the flow rate of oxygen, but rather it is related to the amount of oxygen stored in the slag.
In a blowing method of a bottom-blown converter equipped with a flue device for guiding exhaust gas, a step of analyzing gas components in the exhaust gas at predetermined intervals during blowing, a step of calculating slag storage oxygen from exhaust gas analysis values A step of changing the flow rate of a hydrocarbon-based gas among at least two kinds of gas for cooling the tuyere by interlocking with the amount of change in the slag storage oxygen in the furnace, and the tuyere cooling gas by the operation in the step of the preceding paragraph The method for controlling the cooling gas flow rate through the step of changing the flow rate of the cooling gas other than the hydrocarbon gas so that the total flow rate of the cooling gas does not fall below the minimum flow rate that can prevent the molten steel from entering the cooling gas tuyere.

(4) Japanese Patent Laid-Open No. 57-60008; For blowing a converter of the type in which a refining gas is blown together with a refining gas through a double tube tuyere at the bottom of the furnace, A converter operation method that determines the flow rate of hydrocarbon gas according to the transition of molten steel temperature calculated from the cumulative oxygen usage. (5) JP-A-58-67816; CO ₂ as a tuyere protection fluid
When using a, the cooling effect of the CO ₂ does not involve such a different decomposition reaction wherein the propane, the same heat removal effect and blowing argon or nitrogen only without, according to estimates vs. O ₂ vol%
Since it requires 15 to 17% of CO ₂ gas, and the use of a large amount of CO ₂ is indispensable, there is a drawback that it becomes expensive. Moreover, if a high CO ₂ ratio is blown from the beginning, the CO ₂ of Si in the molten iron
And the oxidation reaction of C with O _2. Si + CO ₂ = SiO ₂ + C C + (1/2) O ₂ = CO These are exothermic reactions, so the temperature near the tuyere Not only rises, but also tar-containing bricks and C of MgO-C bricks
Reacts with to cause deterioration of the refractory.

However, in the case of cooling using this CO ₂ , if a large amount of C is present in the molten steel, it is predicted that it reacts with the C and absorbs heat and the vicinity of the tuyere can be cooled by the reaction heat. .. Therefore, the prior art of this publication was made based on the above-mentioned knowledge that the C concentration in the steel bath mainly contributes, and CO ₂ introduced from the annular passage of the tuyere outer tube for cooling. There has been proposed a converter tuyere cooling method in which effective tuyere cooling is achieved by controlling the blowing amount of carbon dioxide according to the C concentration in the steel bath according to the transition of the refining stage.

[0014]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method according to Japanese Patent Publication No. 34114-has the following problems. That is, even if there is a cooling action of the cooling protective gas, the wear of the tuyere cannot actually be zero.Therefore, a temperature sensor such as a thermocouple inserted in the tuyere may contact the molten iron when the tuyere is worn. Since the wire will be broken, it is necessary to insert multiple points in the length direction of the tuyere. Therefore, the structure of the tuyere is complicated,
In addition to being expensive, measurement becomes difficult when the number of tuyere increases, and the cost of the temperature sensor is high, so that it cannot withstand long-term process use.

In the technique of Japanese Patent Application No. 1-275771 of the above (2), it is low in accuracy to estimate the decarburization rate and the carbon content in molten iron from the exhaust gas flow rate generated by refining and the exhaust gas component analysis value. There was a problem of poor practicality. This problem is that the decarburization amount and the secondary combustion amount are estimated by using the exhaust gas component analysis value and the exhaust gas flow rate, and the stored oxygen amount in the slag is calculated by the above method (3). This is a problem inherent in the method disclosed in the publication. In addition, the method (3) has a problem in practical use because not only the measurement accuracy is low, but also the calculation of oxygen stored in the slag is complicated and there is a time delay.

The method according to JP-A-57-60008 of the above (4) is based on the premise that the molten steel temperature rises with the cumulative amount of oxygen used for blowing and the functional relationship is almost linear. However, the actual molten steel temperature depends on the operating conditions of the converter, the molten iron composition, the molten iron charging ratio (or scrap charging ratio), the amount and timing of addition of the slag-making agent, the secondary combustion rate and the secondary combustion heat deposition. Due to the complicated influence of various factors such as heat ratio, the functional relation cannot be said to be direct.

In particular, the oxidation reaction of various components (C, Fe, Mn, P, etc.) in the low carbon region at the early stage of blowing and the final stage of blowing is difficult to divide based on the above premise, and At these times, the decarburization reaction rate is low and the CO stirring in the steel bath is weak, so the temperature of the fire point near the tuyere tip is more localized than at other times, and the cumulative oxygen It is not possible to estimate the temperature of the steel bath linearly according to the amount used, considering the thermal effect on the tip of the tuyere.

The method (5) according to Japanese Patent Laid-Open No. 58-67816 is particularly effective when CO ₂ is used as a cooling protective gas, but the C concentration in the molten steel can be accurately measured continuously or intermittently. It is difficult to measure or estimate well. Furthermore, in the low carbon region at the end of decarburization, if a large amount of CO ₂ gas is flown, the CO ₂ gas leaks to the brick joints around the tuyere and reacts with C of the MgO-C brick, leading to deterioration of the brick. It has the disadvantage of reducing the life of the bricks around the mouth and the life of the tuyere.

In view of the problems of the prior art as described above, the present invention determines the optimum cooling protection fluid flow rate based on detailed model calculation effects such as the hot spot temperature in the iron bath and the convective heat transfer of molten iron. Wear rate of tuyere and furnace bottom refractories without patterning and directly measuring tuyere temperature, exhaust gas analysis value, and exhaust gas flow rate, and without continuous or intermittent measurement of C concentration in molten iron The object of the present invention is to provide a cooling protection method for an oxygen blowing tuyere below the surface of the molten iron bath in the converter so as to improve the above.

[0020]

[Means for Solving the Problems] The first aspect of the present invention for attaining the above object is to allow molten oxygen to flow through a central passage of an oxygen blowing tuyere installed below a molten iron bath surface in a converter. When oxygen gas is blown into the inside and a cooling protective fluid is circulated in the annular flow path outside the central flow passage to cool and protect the oxygen blowing tuyere, the molten iron bath surface is passed through the central flow passage of the tuyere Shown in Table 3 below (1), which is calculated from the desiliconization oxygen efficiency and decarbonation efficiency with the progress of refining by the oxygen gas blown below.
Corresponding to the refining stage of refining oxygen amount basic unit [Nm ³ / t molten iron] in (2), (3), (4) and (5), the flow rate of the cooling protection fluid flowing through the annular flow path is standard. It is cooled protection method of an oxygen blowing tuyere to the converter in the molten iron bath surface underneath, characterized in that by the flow rate F _S based stepwise adjusted in a range of street 1.0F _S ~ 2.0F _S below ..

[0021]

[Table 3]

A second aspect of the present invention for attaining the above object is the desiliconization oxygen efficiency and decarbonation rate as refining is progressed by the oxygen gas flowing through the central channel of the tuyere and blown below the surface of the molten iron bath. (1), (2) shown in Table 1 calculated from the efficiency,
Corresponding to the refining stage of refining oxygen unit [Nm ³ / t molten iron] in (3), (4) and (5), the flow rate of the cooling protection fluid flowing through the annular flow path is based on the standard flow rate Fs. Instead of adjusting the cooling protection fluid in accordance with the standard refining model, the cooling protection fluid flowing through the annular flow path corresponding to the refining stages (1), (2), (3) and (4) shown in Table 4 is used. A method for cooling and protecting an oxygen blowing tuyere below the surface of a molten iron bath in a converter according to the first aspect of the invention, characterized in that the flow rate is adjusted while continuously varying based on the standard flow rate Fs.

[0023]

[Table 4]

[0024]

FIG. 3 is a sectional view conceptually showing the thermal environment in the vicinity of the tuyere of oxygen gas blowing in the bottom blowing converter. In the oxygen blowing tuyere 10 of FIG. 3, a refractory sleeve 3 is fitted to the inner surface of the inner tube 1 to prevent abrasion due to powder or the like, and forms a central flow path 4. In this way, the outer pipe 2 is concentrically provided outside the inner pipe 1 forming the central flow passage 4, and the annular flow passage 5 is formed. Reference numeral 6 is a refractory material laid around the tuyere 10. Further, 7 is a porous solidified iron called a mushroom formed on the upper end portion of the tuyere 10. This mushroom is generated to cool and protect the tuyere 10 and reduce its wear.

O ₂ blown into the molten iron from the inner tube 1 of the tuyere 10
The gas jet mainly causes the following reactions near the tuyere. Fe + (1/2) O ₂ → FeO + Q ₁ (1) FeO + C → Fe + CO-Q ₂ (2) Here, the equation (1) is an exothermic reaction and the equation (2) is an endothermic reaction. Since the heat generation amount Q ₁ is larger than the heat absorption amount Q _{2, the} equations (1) and (2) are combined to generate an exothermic reaction and generate heat of reaction at the flash point. And the annular flow path 5 of the tuyere 10
The following three types of heat are transmitted to the mushroom 7 formed by the cooling action of the cooling protective gas that flows through and flows into the molten iron.

(1) Radiant heat from a high temperature flame Q _F due to the reactions of the equations (1) and (2) Q _F (2) Convective heat from molten steel Q _M (3) Endothermic heat from a cooling protective fluid Q _C Mushroom 7 In order to make the size of the mushroom 7 constant assuming that the solidified iron component of the surface part of is constant, (Q _F + Q _M ) × (mushroom surface area) = Q _C It is sufficient to supply the cooling fluid amount. Here, propane gas is selected as the cooling protection fluid, detailed heat calculation is performed as oxygen blowing proceeds, and the ratio of the optimum cooling fluid flow rate to the base flow rate (propane flow rate index) is obtained.
Shown in. As shown in Fig. 2, when the carbon content in the steel is around 2.1 wt%, the required flow rate of the cooling protection fluid, that is, the propane flow rate index shows a peak. As shown in Fig. 4, when decarburization and increase in steel bath temperature proceed with the progress of oxygen blowing, the steel bath temperature higher than that in the liquid phase is reached when the carbon content in the steel reaches 2.1 wt%. Surface area of mushrooms Fe Fe of solidified iron
The temperature difference from the solidus temperature of the C system becomes the maximum, that is, the cooling temperature difference that the temperature of the mushroom surface must be lowered from the steel bath temperature in order to maintain the size of the mushroom. It means that Therefore, the required amount of cooling fluid reaches a peak near a carbon content of 2.1 wt%.

Further, in the final stage of refining when the carbon content is 0.04 wt% or less, only the formula (1) which is an exothermic reaction among the above-mentioned reaction formulas (1) and (2) is deficient due to lack of carbon amount in the steel. Equation (2), which is accelerated and is an endothermic reaction, does not proceed so much. As a result, the amount of heat transferred to the mushrooms increases rapidly and the amount of cooling fluid required also increases rapidly. Note that in the non-desiliconization dephosphorization pig (high Si pig) blowing process in the initial stage of refining, the mushrooms are exposed to high temperature due to the exothermic reaction of Si + O ₂ → SiO ₂ + Q ₃ (3). In refining with phosphorous pig iron (Si content 0.02% or more), it is desirable to increase the cooling fluid amount until the Si oxidation reaction is completed.

The heat calculation results as described above are shown in FIG. 2 as a model in the case of standard refining using propane as the cooling protection fluid. It was found that the required cooling fluid flow rate has a maximum value in the initial stage of refining, around 20 Nm ³ / t of refining oxygen intensity that makes C 2.1% in hot metal, and in the final stage of refining. The refining oxygen intensity on the horizontal axis is a standard value only, and varies by about ± 20% depending on the hot metal composition and operating conditions of the converter. This variation is the decarbonation efficiency index η _C (0.8 to 1.2)
It is expressed using. However, in actual refining, it is complicated to continuously change the flow rate of the cooling protection fluid as shown in FIG. 2. Therefore, as shown in FIG. To do.
The start and end of each step of the propane flow rate index in FIG. 1 are set so that the total amount of cooling fluid is almost equal to that in FIG. It should be noted that although the actual refining involves some complexity, it is also possible to continuously change the flow rate of the cooling protection fluid according to FIG. 2, and more detailed refining can be achieved.

[0029]

[Example] Example 1 [C] ≈4.5wt%, [Si] ≈0.5wt% level of hot metal 10t
Using a laboratory total oxygen bottom blowing converter, the refining oxygen unit rate [Nm ^{3 is} determined by the desiliconization oxygen efficiency (η _Si ) and decarbonation efficiency (η _C ) as the refining progresses as shown in Fig. 1. / T molten iron], the experimental operation was continuously carried out over a number of heats in a flow index pattern in which the cooling propane gas flowing through the annular passage of the tuyere was adjusted corresponding to the refining stage. The refining stage of the present invention is described below. For comparison, when the propane gas flow rate was kept constant as the standard flow rate over the entire conventional refining period, that is, the experimental operation of a comparative example of multiple heats was performed with the base propane flow rate index = 1.0 in FIG.

Refining stage 1 of the present invention From the start of refining until the refining oxygen amount basic unit reaches 2 [Nm ³ / t molten iron], the standard flow rate of propane gas for cooling F _S = 0.75
Nm ³ / minute hand, was 1.3F _S. Here, the refining stage 1 was set until the refining oxygen amount basic unit became 2 [Nm ³ / t molten iron], the desiliconization oxygen efficiency η _Si = 0.5, the molten pig iron [Si] = 0.5 wt.
% From Table 1 as 7.97 x η _Si x hot metal [Si] wt% = 7.97
This is because x 0.5 x 0.5 ≈ 2 [Nm ³ / t molten iron].

Refining stage 2 The propane gas for cooling is set to have a base propane gas flow index of 1.0 and its flow rate is 1.0 F _S until the refining oxygen amount basic unit exceeds 2 to 10 [Nm ³ / t molten iron]. Here, the refining oxygen amount basic unit is set to 10 [Nm ³ / t molten iron], and the decarbonation efficiency is η _C = 0.83. From Table 1, 12.0 × η _C ≈10 [Nm ³
/ T molten iron].

Refining stage 3 The propane gas flow rate index for cooling is 1.3 and the flow rate is 1.3 F _S until the refining oxygen basic unit exceeds 10 to 25 [Nm ³ / t molten iron]. Here, the basic unit of the amount of refined oxygen is 10 [N
m ³ / t molten iron] is because decarbonation efficiency η _C = 0.93 yields 27.0 × η _C ≈25 [Nm ³ / t molten iron] from Table 1.

Refining stage 4 The propane gas flow rate index for cooling is 1.0 and the flow rate is 1.0 F _S until the refining oxygen amount basic unit exceeds 25 to 30 [Nm ³ / t molten iron]. Here, the refining oxygen amount basic unit is 30
[Nm ³ / t molten iron] is because η _C = 0.86 and 35 × η _C ≈30 [Nm ³ / t molten iron] from Table 1 is obtained.

Refining stage 5 Refining oxygen amount basic unit exceeds 30 to 34 [Nm ³ / t molten iron] and is refined and blown off to the target component, but the flow rate index for cooling propane gas at this stage is 2.0 and the flow rate is 2.0. _Let F _S. FIG. 5 shows the wear index of tuyere according to the example of the present invention and the comparative example in correspondence with the number of charges. The tuyere wear index = tuyere wear rate (experimental charge) [mm / ch] / tuyere wear rate (reference value) [mm / ch].

As shown in FIG. 5, the tuyere length was measured every about 30 charges and the change in the wear rate was investigated. As a result, blowing was carried out according to the propane flow rate index pattern of FIG. 1 of the embodiment of the present invention. It can be seen that the wear rate is reduced by about 5% as compared with the conventional example during the different period. This is evidence that the practice of the present invention keeps the mushrooms healthy and that the present invention is effective for tuyere protection.

Example 2 Similar to Example 1, [C] ≈4.5 wt%, [Si] ≈0.5 wt%
A standard refining model as shown in Fig. 2 is used for 10 tons of hot metal in an experimental total oxygen bottom blowing converter, that is, the refining oxygen source of C2.1 wt% in molten iron at the initial stage of refining with desiliconization. unit
Corresponding to the refining stage of the basic unit of oxygen amount [Nm ³ / t molten iron] of the refining by the refining model where the required cooling fluid flow rate reaches a maximum value at around 20 Nm ³ / t and C 0.38 wt% in molten iron. The experimental operation was performed continuously over a number of heats in a flow index pattern in which the cooling propane gas flowing through the annular flow path of the tuyere was continuously varied and adjusted.

The flow rate of the cooling propane gas is calculated using a computer 12 as shown in FIG. 6, and the opening of the flow rate control valve 11 arranged in the propane gas supply pipe 9 is automatically calculated based on the calculated value. The required amount of propane gas is supplied to the tuyere 10 while being continuously and continuously varied. A flow rate control valve 11 is also provided in the oxygen gas supply pipe 8, and the opening of the flow rate control valve 11 is controlled so that the oxygen gas amount calculated by the computer 12 is obtained. The amount of propane gas and oxygen gas used (Nm ³ ) is measured by the flow meter 14 and the total is calculated by the computer 12.

The refining step of the present invention will be described with reference to FIG. 2 and Table 4. Refining stage 1 of the present invention From the start of refining to the end of desiliconization when the refining oxygen amount basic unit becomes 4 [Nm ³ / t molten iron], the standard flow rate F _s of cooling propane gas
= 0.75 Nm ³ / min was gradually reduced while changing from 1.3 F _s to 1.0 F _s respect. Refining stage 2 of the present invention Refining oxygen amount basic unit 4 [Nm ³ / t molten iron] From over C 2.10.
Up to 20 [Nm ³ / t] to be decarburized to 1.3 from 1.0F _s
The value was gradually changed to F _s and increased. Refining Stage 3 Refining oxygen intensity from 20 [Nm ³ / t molten iron] to over 0.3 [Nm ³ / t molten iron] decarburized to C0.38 in steel from 1.3 F _s to 1.0
It was gradually changed to F _s and decreased. Refining stage 4 From refining oxygen intensity 30 [Nm ³ / t molten iron] to the end of refining
From 1.0F _s up to 5.3F _s was soaring while changing.

Also in the case of the second embodiment of the present invention, the same tuyere wear reduction as in the case of the first embodiment can be obtained, and good results can be achieved.

[0040]

As described above, according to the present invention, it is possible to optimally cool an oxygen gas blown tuyere without using a special measurement and analysis device such as tuyere temperature measurement or exhaust gas analysis or a control device. The amount of fluid can be controlled, and the tuyere wear rate is significantly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a propane gas flow rate index pattern corresponding to a refining oxygen amount basic unit [Nm ³ / t molten iron] and a carbon amount in steel [wt%] according to the progress of refining according to the present invention. ..

FIG. 2 is a relationship between a propane gas flow rate index pattern and a carbon amount in steel [wt%] corresponding to a refining oxygen amount basic unit [Nm ³ / t molten iron] with progress of refining which is the basis of FIG. 1 according to the present invention. FIG.

FIG. 3 is an explanatory diagram showing, in a schematic cross-section, the state of heat balance around the tuyere, which is a model for heat calculation according to the present invention.

FIG. 4 is a diagram showing changes in solid phase temperature of molten mushroom and molten steel temperature with progress of decarburization.

FIG. 5 is a diagram showing indices of tuyere wear measurement results of an example of the present invention and a comparative example.

FIG. 6 is a schematic explanatory view of an apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Inner pipe 2 Outer pipe 3 Fireproof sleeve 4 Central flow passage 5 Annular flow passage 6 Refractory material 7 Mushroom 8 Oxygen gas supply pipe 9 Propane gas supply pipe 10 Tuyere 11 Flow control valve 12 Computer 13 Converter 14 Flowmeter

Claims (2)

[Claims] 1. An oxygen gas is circulated through a central passage of an oxygen blowing tuyere installed below the surface of the molten iron in the converter to blow the oxygen gas into the molten iron and cool the annular passage outside the central passage. When cooling the oxygen blowing tuyere by circulating a protective fluid,
Shown in Table 1 below (1), which is calculated from desiliconization oxygen efficiency and decarbonation efficiency with the progress of refining by oxygen gas flowing under the surface of the molten iron flowing through the central passage of the tuyere.
Corresponding to the refining stage of refining oxygen amount basic unit [Nm ³ / t molten iron] in (2), (3), (4) and (5), the flow rate of the cooling protection fluid flowing through the annular flow path is standard. cooling method of protecting oxygen blowing tuyere to the converter in the molten iron bath surface underneath, characterized in that by the flow rate F _S based stepwise adjustable from street 1.0F _S ~ 2.0F _S below. [Table 1] 2. Table 1 calculated from the desiliconization oxygen efficiency and decarboxylation efficiency with the progress of refining by oxygen gas flowing under the molten surface flowing through the central passage of the tuyere (1). ,
Refining oxygen intensity of [2], (3), (4) and (5) [N
m ³ / t molten iron], instead of stepwise adjusting the flow rate of the cooling protection fluid flowing through the annular flow path based on the standard flow rate F _S , according to the standard refining model, see Table 2 below. Corresponding to the refining stages (1), (2), (3) and (4) shown, while continuously varying the flow rate of the cooling protection fluid flowing through the annular flow path with reference to the standard flow rate F _s. The method for cooling and protecting the tuyere of oxygen blown below the surface of the molten iron bath in the converter according to claim 1, characterized in that it is adjusted. [Table 2]