JPS5867816A - Cooling method for converter-tuyere - Google Patents

Abstract

PURPOSE:To cool a tuyere effectively and to prevent the damage for converter bottom- refractries by controlling the blowing amount of CO2 gas introduced for cooling from the annular path of a tuyere-outside tube in combination with the C concentration in the molten steel corresponding to the change of refining stage. CONSTITUTION:When the double tubes-tuyere causing O2 gas for refinning to flow from a central flow-path equipped under the surface of molten steel-bath is cooled, CO2 gas blown into the molten steel from the outside annular flow path is controlled by following. That is to say, when C concentration in the molten steel in the beginning period of blow-refining is larger, CO2 ratio is caused to become small. In the finishing period where the molten steel contains low C concentration, as the tuyere is cooled by almost only sensible heat of CO2 gas, the refining is carried out by keeping CO2 ratio high to some extent. Thus, the blowing amount of CO2 gas is controlled in combination with C content in the molten steel corresponding to each refining stage. Consequently, as shown in the figure, the tuyere-temperature becomes constant in total refining period, so CO2 consumption is reduced, and simultaneously the expansion and contraction for the refractories adjacent to the tuyere by thermal hysteresis is reduced. Additionally, the refractory-life is prolonged by preventing the loss of C source in the refractory.

Description

[Detailed Description of the Invention] The present invention relates to a method for cooling a converter tuyere, and in particular to a method for cooling a converter tuyere,
C as a cooling gas to protect the bottom tuyeres of top-bottom blowing converters.
In the tuyere cooling method using 02 gas, by changing the flow of CO2 gas according to [%O] in the whole steel bath, it is an advantageous method to reduce the amount of CO2 gas and prevent wear and tear on large parts at the bottom of the furnace. I would like to make a proposal.

Oxygen bottom-blown converters have advantages over LD converters in terms of better agitation and mixing, shorter steelmaking time, improved alloy yield, and improved iron yield. However, since the tuyere is located below the bath surface, it is difficult to cool the tuyere itself, and the conventional method generally used is to use concentric λ-layered pipe siding, and the outer annular flow is A hydrocarbon gas such as propane is passed through the tuyeres, and the tuyere is cooled and protected by absorbing heat due to the decomposition of the hydrocarbon gas. The disadvantage of this prior art is that hydrogen remains in the steel after decomposition of the hydrocarbons, resulting in a 2-s ppm higher hydrogen content in the steel than in an LD converter.

There is also a technique that uses CO2 as a siding protection fluid.

However, unlike the propane mentioned above, the cooling effect of 002 does not involve a decomposition reaction, so it only has a heat removal effect similar to the blowing of argon or nitrogen, and according to the inventors' calculations, it has a cooling effect of 0.
Since 002 gas of 2 volume %/J~17% is required and the use of a large amount of CO8 is essential, it has the disadvantage of being expensive. Moreover, if it is blown in at a high 002 ratio from the beginning, it will react with the 0 of the impregnated bricks and MgO-Cj bricks, leading to deterioration of the refractories.

However, this 00. In the case of cooling using C, it is predicted that if C is present in many sources in the molten steel, it will react with the C, absorb heat, and cool the area near the surface by the heat of reaction.

This invention is a method developed based on the above-mentioned knowledge that the C concentration in the steel bath contributes. The feature is that effective slat cooling is achieved by controlling the C concentration in the steel bath according to the progress of the refining stage.

In short, the cooling capacity of CO3 is C'flI in the hot bath inside the converter.
It was found that it strongly depends on the 4th degree. Therefore, the present inventors conducted a thermodynamic study on the reaction heat and sensible heat when 002 reacts with O and Fe in steel. The results are shown in Table 1. Further, when similar calculations were made for propane, which has conventionally been widely used as a cooling gas, the cooling capacity of propane was 79.0a17mo1. Therefore, the following calculations were made regarding the OO2 cooling capacity based on the propane cooling capacity described above. In other words, now B
When the CO2 scum of ``C'' rises to 1600°C, the heat that the CO2 takes away from the surroundings - sensible heat is (ΔH).

When this 002 reacts with C in the molten steel around tomorrow, OO2
+ C Negc.

This reaction heat! ! ,! Koal/h+ol, and this amount of heat is taken away from the surroundings. On the other hand, when this co2 decreases and reacts with Fe, the reaction 00, + Fe -FeO+ 00 occurs, and the heat of reaction is r, lr Kcal/m
ol, so if aO, remains unreacted, then 1. -3, 350 Kc
al/mo100! ! When reacts with O, 18.350
+33.5-51.8 KOal/UD100, is F
When reacting with 6, 18.350+8.8-27. IK
Oal/ffI)1. The results are shown in Table 2.

Table 1 On the other hand, 002 concentration constant operation: that is, 0 as in the conventional method.
The thermal cover history of the tuyere during blowing with a constant ratio of 002 to It can be seen that the mouth temperature is low and cooling is excessive. On the other hand, at the halfway point of blowing, the amount of 0 in the steel bath decreases and the temperature of the steel bath itself increases. Therefore, in the later stages of blowing, the heat received by the siding increases, and the cooling effect of CO2 on the siding weakens. 0 from numerous experiments. , 1% or less, and the steel bath temperature was /60α°C or higher, it was found that the surface protection effect deteriorated.

In contrast, FIG. 2 shows the results of an operation in which the ratio of co to oxygen was varied according to the C concentration in the steel bath based on the method of the present invention. In the cooling method of the present invention, if (0)% is sufficiently present in the steel bath at the initial stage of blowing, CO2
In addition, at the end of the blowing process when ((3)% decreases, it is necessary to cool the siding with only CO2 sensible heat, so a large amount of blowing is required, and the CO2 ratio is set high. By controlling this CO2 injection flow rate according to the CIIIt in the bath by increasing the CO2 injection flow rate by one sip at each refining stage, as shown in Fig. 2, the entire blowing process was Since the tuyere temperature remains constant over a period of time, the amount of CO2 used can be reduced, and the expansion and contraction due to the thermal history of the adjacent refractories is alleviated, and the C# in the refractories disappears, making the fire resistant. Product life is improved.

Next, examples of the present invention will be described.

A blowing experiment was conducted using a test converter.

(1) Melting equipment + 5.2t (2) Hot metal component (%): 0/4.5 8j710.3
2Mn10. aa”10.u4 S10,024(3
) Oxidation rate' 12-5 Nm3/min C total 11
1 blow) (4) CO2 gas ratio setting to flow into the outer tube annular flow path C> 7% of CO2 in the light of 1.0 0.3<O (10% of CO2 in the middle of 1,0 Q (0
In the latter half of 3, C02 is 15% (5) target: Q
= 0.02%, Temp -1650°C (6) Number of hearth bottom tuyeres: 4 (7) Hot metal temperature: The results of blowing under conditions of 1222°C or higher are as shown in Table 3.

As described above, in the method of the present invention, the solidified iron adhering to the siding is also normal, and depending on the C setting bell in the steel bath, the C
By changing the O2 injection flow rate, it was possible to reduce the 00□ haze and also to extend the life of the furnace bottom, and the method of the present invention was able to reduce the steel manufacturing cost.

[Brief explanation of the drawing]

Figure 1 is a graph showing the tuyere temperature transition during blowing in a conventional method with a constant C02 amount, and Figure 2 is a graph showing the tuyere temperature transition during blowing and door blowing in the present invention method in which oo2m is varied depending on the O amount in the bath. This is a graph showing.

Claims (1)

[Scope of Claims] L For cooling the concentric double pipe tuyeres through which refining oxygen gas flows from the center channel installed below the surface of the molten steel bath in a bottom blowing converter or a top and bottom blowing converter, In a method of cooling the tuyere by flowing cooling C02 gas through an annular flow path outside the flow path, the blowing amount of the cooling C02 is adjusted according to the carbon concentration in the steel bath, which changes depending on the progress of the refining stage. A method for cooling a converter tuyere characterized by controlling the tuyere of a converter.