JPS621451B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a double tube tuyere for metallurgical furnaces, and in particular to the structure of the bottom double tube tuyere used at the bottom of bottom-blown or top- and bottom-blowing converter furnaces. We propose the structure of an inner pipe into which a ceramic pipe is inserted. Generally, in the tuyere of an oxygen bottom-blown converter, oxygen gas for refining, etc. is passed through the central passage in the inner tube, and hydrocarbon gas for cooling the tuyere is passed through the annular passage, which is the gap between the inner tube and the outer tube. It has a concentric double pipe structure that allows gas etc. to flow through it. Conventionally, metal pipes have been used for the inner and outer tubes of the tuyere. Among these, the inner tube is subject to severe wear because fluxes such as lime powder may flow together with the oxygen gas from the center flow path, so in order to prevent such wear, a ceramic pipe is inserted inside the inner tube. fit (ba)
I have used it before. As such ceramic pipes, alumina or mullite dense ceramics with low porosity have conventionally been used throughout the tuyere inner pipe. However, in the case of this dense ceramic, although it has excellent wear resistance, it has poor thermal shock resistance, so it is more likely to be exposed to the inside of the furnace than the surface of the permanent brick layer at the hearth bottom, which is prone to rapid temperature changes. These parts are prone to significant deterioration and breakage, which causes significant wear and tear on the tuyere and shortens its lifespan. On the other hand, if a porous ceramic with a high porosity is used to improve thermal shock resistance, the wear of the tuyere inner tube becomes severe if lime powder or the like is allowed to flow together in the central channel. When we investigated the phenomenon of large wear damage caused by such injected lime powder, we found that this phenomenon was observed more often on the outside of the furnace than on the permanent bricks at the bottom of the furnace.
This is because the lime powder flowing together with the refining gas or carrier gas first collides with force on the outside of the furnace on the permanently stretched brick layer near the introduction part of the L-shaped pipe connected to the lower end of the tuyere, which causes wear. This is thought to be because it becomes more intense. As a result, wear gradually propagates to the upper part of the ceramic pipe, which is located inside the furnace, gradually shortening its life. This invention focuses on the ceramic pipe for the tuyere inner pipe, which requires excellent properties in both abrasion resistance and thermal shock resistance, and focuses on the areas where each property is required.
The aim is to advantageously overcome the problems of the prior art, and the gist of its construction is that it is buried in the furnace wall located below the surface of the molten steel bath, with one end exposed inside the furnace. In the double-tube tuyere with concentric inner and outer tubes, the inner side of the inner tube is bordered by the area where the permanent tension bricks in the furnace wall are located, and the outer part of the furnace is made of a dense material with excellent wear resistance. While it is composed of
This double-tube tuyere for a metallurgical furnace is characterized by a ceramic pipe made of porous material with excellent thermal shock resistance inserted and fixed in the inner part of the furnace. The details of the configuration will be explained below. Fig. 1 shows a preferred example of a tuyere installed at the bottom of an oxygen bottom-blowing converter. The reference numeral 1 in the figure indicates an inner tube, and the outer tube, which forms a concentric double tube, is shown in Fig. 1. A pipe 2 is located, and ceramic pipes 3a and 3b are fitted and fixed inside the inner pipe 1, and refining gas (O ₂ , Ar) and solids are regulated by each pipe. A central flow path 1e for flowing flux powder and an annular flow path 2e for flowing cooling hydrocarbon gas (propane) as well as carbon dioxide gas and argon gas are formed. The furnace wall is formed by piling up the furnace bottom liner bricks 5 on the inside of the furnace and the permanent furnace bottom liner bricks 6 on the outside where the furnace shell shell 7 is located. Now, Figure 2 shows the material of the ceramic pipe to be inserted inside the inner tube 1 (main component is Al ₂ O ₃ -69%,
SiO ₂ -28% etc.): In particular, the relationship between porosity (%) and wear rate is shown in Figure 3. This was determined from the results of a 230-ton converter-500 charge operation. In addition, in the above experiment, samples were obtained from the part near the steel shell 7 where the wear characteristics are a problem in the case of Fig. 2, that is, the part corresponding to the permanent tension brick 6, and the third
In the case shown in the figure, a sample was obtained and tested at the inside of the furnace where thermal shock characteristics are a problem, that is, at a location equivalent to 5 parts of the lining brick. The reason for conducting such an experiment is that, according to the inventors' findings, the parts of the inner ceramic pipe where wear and tear caused by lime powder, etc. are most likely to occur are located outside the furnace from the 6th part of the permanent bricks at the base of the tuyere. This is the location where the L-shaped pipe 4 connected to the bottom of the pipe is susceptible to collision with lime powder, so wear and tear is significant, so it is necessary to install a material with excellent wear resistance. This is because it was considered necessary. The area affected by this lime powder varies depending on the degree of bending of the L-shaped pipe 4 connected to the lower part, but from the observation results after actual use, it is found that the area is 100 mm to 100 mm from the lower end of the tuyere. This is the area near the 7th part of the 600mm permanent brick. If a porous ceramic pipe with a porosity exceeding 5% is used in this area as shown in FIG. 2, it will not be suitable for practical use because it will easily wear out due to wear and tear caused by lime powder. Therefore, a pipe 3a made of dense ceramics with excellent abrasion resistance and a porosity of 5% or less is effective for the area from the lower end of the tuyere to the area where the permanent bricks 6 are located in the furnace wall. On the other hand, on the inside of the furnace from the permanently stretched bricks 6 above the tuyere, a rapid temperature change occurs due to the refining oxygen gas and the cooling hydrocarbon gas during blowing. Therefore, a material with excellent thermal shock resistance is required. Therefore, it is effective to use a porous ceramic pipe 3b, which has better thermal shock resistance than abrasion resistance, in the upper part of the tuyere. However, as shown in Figure 2, porous ceramics with a porosity exceeding 40% have extremely poor wear resistance, and even the upper part of the tuyere, where the degree of wear damage is relatively slight, is easily worn away by lime powder. Because of this, it cannot withstand actual use. Furthermore, as is clear from FIG. 3, ceramics with a porosity of 5% or less have poor thermal shock resistance and are susceptible to damage due to rapid temperature changes, making them unsuitable for practical use. Therefore, the porosity of the upper part of the tuyere, which is on the inside of the furnace, bordering around the 6th part of the permanent bricks on the furnace wall, is
It is found that 40% porous ceramics are effective. Next, embodiments of the invention will be described. In this example, a 230-ton oxygen bottom-blown converter was used, and a high alumina ceramic pipe containing 69% Al ₂ O _{3 -} 28% SiO ₂ by weight as the main component and a porosity of 1.1% was used. A conventional oxygen bottom-blowing converter tuyere (comparison tuyere A) is inserted over the entire inner surface of the stainless steel inner tube, and a ceramic pipe made of the same material with a porosity of 26.5% is used over the entire inner surface of the inner tube. A tuyere for an oxygen bottom-blown converter (comparison tuyere B) was used, and a ceramic pipe made of the same material with a porosity of 1.1% was used from the bottom end of the tuyere to the permanently tensioned brick part approximately 450 mm.
At the top of it, a ceramic pipe with a porosity of 26.5% is added and integrated into an integrated ceramic pipe, which is inserted into the inside of the inner pipe (cold fit) to form an oxygen bottom-blown converter blade of the present invention. When the mouth (tuyere C of the present invention) was used in a converter and inspected at 800 charges, the following results were obtained.

[Table] As a result, compared to the comparative example, the tuyere C of the present invention has a significantly lower wear rate, and when observed after use, cracks caused by sudden temperature changes in the upper part of the tuyere are significantly reduced. The degree of wear due to the injection of lime powder was not at all similar to that of the comparative example. Regarding comparison tuyere B, since porous ceramics were used throughout the inner tube of the tuyere, wear progressed more rapidly in the area outside the furnace than in the permanently tensioned brick area.
This causes a phenomenon where it spreads to the upper part.
The overall tuyere wear rate appears to be large. As another example, in the same furnace as in the above example, the main components were Al ₂ O ₃ -87% by weight and SiO ₂ -9.
If you insert a ceramic pipe made of alumina ceramics with a porosity of 2.5% by weight on the outside of the furnace and a ceramic pipe of the same composition with a porosity of 15% on the inside of the furnace, the ceramic pipe is inserted into the inner pipe. When inspecting the tuyere after using a 750 charge, the tuyere wear rate was 0.45 mm/charge, the wear rate on the outside of the furnace was 15%, and the chipping rate on the inside of the furnace was 20%. Compared to conventional pipes that are made entirely of dense ceramics, they have a much better lifespan.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of the tuyere for an oxygen bottom-blowing converter according to the present invention, and FIG. 2 is a graph showing the relationship between porosity and wear rate of a ceramic pipe used from the permanent bricks at the bottom of the furnace to the outside of the furnace. FIG. 3 is a graph showing the relationship between the porosity and defect rate of a ceramic pipe used inside the furnace from the permanently stretched bricks at the bottom of the furnace. 1... Tuyere inner pipe, 2... Tuyere outer pipe, 3a... Dense ceramic pipe, 3b... Porous ceramic pipe, 4... L-shaped pipe, 5... Lining brick, 6... Permanent tension brick, 7... Hearth iron skin.

Claims (1)

[Scope of Claims] 1. A double tube tuyere with concentric inner and outer tubes that is buried in the furnace wall located below the surface of the molten steel bath and used with one end exposed in the furnace, On the inside, the area where the permanent bricks in the furnace wall are located is the boundary, while the outside part of the furnace is made of a dense material with excellent wear resistance.
A double pipe tuyere for a metallurgical furnace, characterized in that the inner part of the furnace is a ceramic pipe made of a porous material with excellent thermal shock resistance, which is inserted and fixed.