JPS5938318A - Bottom blowing furnace - Google Patents

Abstract

PURPOSE:To prolong the life of a bottom blowing furnace by interposing a refractory having specified heat conductivity and a specified coefft. of thermal expansion between a tuyere of the furnace and tuyere brick to prevent the cracking of the brick and to reduce considerably the wear rate. CONSTITUTION:A refractory 3 is interposed between the outer pipe 1B of a bottom tuyere 1 of an AOD furnace for decarburization refining and tuyere brick 2. The refractory 3 has lower heat conductivity and a lower coefft. of thermal expansion than the brick 2, and mullite (Al2O3-SiO2) is preferably used as the refractory 3. Mullite has much lower heat conductivity and a much lower coefft. of thermal expansion than magnesia-chrome brick.

Description

[Detailed description of the invention]

An example of a bottom blowing furnace FI7 that performs refining by injecting waste into the bottom (bottom blowing furnace FI7 that performs decarburization refining by injecting C-related raw gas) is shown,
Conventionally, a double pipe tuyere of 4'1"X structure as shown in FIG. A large amount of oxygen gas or inert gas 2 necessary for decarburization refining flows through the passage 11vc of the inner pipe 1A, and cooling is carried out in the gap 12 between the outer pipe IB and the inner pipe IA to prevent wear and tear on the inner pipe. Inert gas (Ar
, N2, etc.) or a gas that performs decomposition endotherm such as OnHm (pronone). The outer peripheral portion of the tuyere brick 2 near the furnace inner end surface S is 160
Due to heat conduction from the inner end surface S of the furnace in contact with the steel bath in the furnace at 0°C or higher, the inner peripheral part of the tuyere brick 2 in contact with the outer tube IB reaches a very high temperature (!). However, due to the VC, the temperature is much lower than that of the outer peripheral portion. Therefore, as shown in Figure 2, one point on the inner circumference is opposite to one point on the outer circumference.
Points, a-b, c-d. A large temperature difference occurs between each point e-f and g-h, and due to this temperature difference, the tuyere brick 21 is subjected to a large heat load compared to other bricks that are in contact only with the steel bath, and the heat Cracks 4 (shown in 2nd 1YI) occur due to surface spalling, and the wear rate per charge is high (often a bottleneck in extending the life of the furnace body. Various measures have been taken, such as improving the quality of the bricks and reducing the length of the bricks, but no definitive countermeasures have been taken. By significantly reducing the
The purpose of the present invention is to provide a great advantage in terms of cost, and in a bottom blowing furnace which is fully equipped with tuyeres inserted into the tuyere bricks, the present invention has a structure in which there is a space between the tuyeres and the tuyere bricks, which This is a T-blowing furnace characterized by interposing a refractory material with low thermal conductivity and thermal expansion. The details of the present invention are as follows: Decarburization of stainless steel N'# k1! !
A specific explanation will be given by taking an example of an AOD furnace used for. FIG. 3 shows the A, OD furnace, in which a double front tuyere l is attached to the side wall near the bottom R of the furnace F'. Conventionally, the conventional double front tuyere shown in Fig. 2 was not used, and the outer pipe lB and inner R
The gap 12VC of IA allows an inert gas such as argon to flow between the coolant and I-, and the gap 12 is generally about 11V.
), and stainless steel is used for the outer tube IB, and its wall thickness t is approximately 1. Q mm. The gas flowing through the gap 12 is 60 to 1 ('l ONm"/h) per tuyere.
It is very important. The tuyere brick 2 is generally a maguro brick (Mgo 60-7)%, C! r20320~30
%) is used. As a comparative example to the known example of the present invention described below, the temperature of each measurable part of the tuyere brick 2 was measured using the brick shown here during decarburization refining with a conventional tuyere brick 2 having the configuration shown in FIG. 2. death,
"+c+etg" on the inner periphery of the tuyere brick 2 in contact with the outer pipe IB
points and the outer periphery of the paneled roof tile 2 corresponding to each of these points b, d, f, between points b, that is, between a and b, between C and d, between e and f, between g and h Estimating the respective temperature distributions between the two, the results are as shown by the circles in FIG. In this case, the thickness of the tuyere tiles is 45 m, and the horizontal axis 0 in Fig. 5 is the surface where the bricks and the outer tube are in contact, that is, the inner surface of the bricks, and 45 filK is the thickness of the bricks. It's on the outside. It is clear from this circuit (@ point a on the inner surface near the end surface S of the tuyere brick inside the furnace that comes into contact with the bath, and point b on the outer surface (a-b
), but there is a temperature difference of about 1150°C between point d on the inner surface, which is 5 meters from the furnace inner end surface S, and point d on the outer surface (c-d), and there is a temperature difference of about 1150℃, Approximately 1350℃ between f and approximately ]25 between g and h inside 15mm
It was found that there was a temperature difference of 0°C. Next, a practical example of the present invention will be explained with reference to FIG. FIG. 4 is a cross-sectional view of the tuyere metal housing part of the present invention, in which a refractory 3 with low thermal conductivity and thermal expansion coefficient is interposed between the outer tube IB and the tuyere brick 20. . As this refractory material 3, it is preferable to use Murai F''f'f (AIaO3-S i 02 series), and the mullite material is maguro brick (wJ
It is a refractory with extremely low thermal conductivity and coefficient of thermal expansion. This refractory 3

The temperature distribution of the refractory and the siding bricks was measured using the same method as in the comparative example above when a mullite refractory with a thickness of - and 5 thick was used. This is indicated by an x in FIG. The temperature distribution shown by this X mark and the temperature distribution of the comparative example (○
The inner surface of the refractory 3 that is in contact with the outside #IB, that is, the point a at Q ram on the horizontal axis. The temperature at point c+erg does not change much. Next 111 Tu'
Object 3 (υ contact surface between the outer periphery and the inner periphery of the tuyere brick 2, i.e. 5 on the horizontal axis)
Regarding #Imσ], the temperature does not change at one point on the innermost side of the furnace, but as it moves further toward the outside of the furnace from point J, point K, and point J, the temperature at each point becomes V in the case of the comparative example. - The temperature has increased by about 100°C, about 150°C, and about 150°C. In addition, because the refractory 3 with a thickness of 5 mm was inserted, the thermal load between the inner and outer periphery of the tuyere brick 2 was approximately 11 mm between c and d in the comparative example.
The temperature difference, which was 50°C, is indicated by the
-d is approximately 350℃, and e-f is approximately ]35
The temperature difference between 0℃ and 600℃ between −f and g−
It was found that the temperature of about 1250'C during the interval was significantly reduced to about 600'C between A and h. On the other hand, the temperature rxtM of the mullite refractory 3 hardly changes between a and i, but it is remarkable at about 800℃ between c and j, about 800℃ between e-, and about 650℃ between g and j. It can be seen from Figure 5 that it is under heat load. However, since the coefficient of thermal expansion of mullite refractories is much lower than that of mag-black bricks, the expansion or distortion caused by thermal load has a small brick area. smaller than in the comparative example where the part is brick. In this example, no cracks as shown at 4 in FIG. 2 were generated. The reason for this is presumed to be that the temperature difference among the bricks is small and the effect of the refractory material on the shoes is small. In the case of mullite refractory 3, no cracks were observed. In the case of the above example, no cracks were observed as described above, but according to the inventor's experiment, It has been found that if the thickness of the refractory is less than iInIn, the effect is small, and if a layer of refractory exceeding 10 mm is provided, cracks may occur in the refractory.As the refractory 3, mullite and other materials may be used. There are various types of refractories, such as cordierite, and the conditions that these refractories must meet are that the thermal conductivity and thermal expansion coefficient are lower than that of bricks, and each value must be less than half of the value of tuyere bricks. It is preferable that the refractory material 3 has a welding resistance against molten steel.The thickness of the refractory material 3 is preferably thicker in order to reduce the temperature difference within the tuyere bricks 2. However, it is preferable to use a mullite-filled hiramic tube as a means to interpose a refractory between the tuyeres and the tuyere bricks. It is preferable to fabricate the tuyere and insert it into the tuyere brick together with the tuyere, or to attach it by spraying a refractory onto the outer periphery of the tuyere, but various other methods are also applicable.In this example, Although we have given an example of a double pipe tuyere as a tuyer, it is also applicable to other types of tuyeres. Table 2 shows the wear rate of the tuyere brick of the embodiment of the present invention in which a refractory of 5 thicknesses made of mullite shown in Table 1 is interposed between the tuyere brick and the conventional example. The wear rate of the sister example of the present invention is 273 of that of the conventional example. This invention was made based on the discovery that the temperature difference between -d, e-f, etc. is large in the vicinity of the outer pipe.According to the present invention, the temperature difference between Since the tuyere brick area is also interposed with a refractory material whose thermal conductivity and thermal expansion coefficient are lower than that of the tuyere bricks, heat removal cooling of the tuyere bricks by the tuyere is suppressed, and the inner and outer peripheries of the tuyere bricks are suppressed. Since the temperature difference between the refractory is made of a material with low heat conduction and low coefficient of thermal expansion, it is possible to ensure a reduction in the temperature difference due to its low heat conduction, and the coefficient of thermal expansion is low. Since it has a low G, it has little effect on the bricks, so there are no cracks in the bricks, and the wear rate is low.Table 1-1 Table 2

[Brief explanation of drawings]

Figure 1 shows a bottom blowing furnace that blows gas from below the surface of the steel bath, Figure 2 shows a combination of a conventional tuyere and tuyere bricks, Figure 3 shows an AOD furnace, and Figure 4 shows an AOD furnace. The figure shows a combination of one blade and tuyere bricks provided in the bottom blowing furnace of the present invention, and Fig. 5 shows the inner and outer circumferential surfaces of the tuyere bricks in the real shaft example of the present invention and the conventional example. It is a graph showing a temperature difference. 1°°・Double pipe tuyere, IA...Inner pipe of tuyere, IB...
- Outer pipe of tuyere, 2... tuyere brick, 3... refractory. Agent: Patent Attorney Masaaki Akizawa, 2 Mitsugai, 11lfl, fF3, Figure 5

Claims (1)

[Scope of Claims] (1) A lower blowing furnace equipped with a tuyere inserted into the tuyere brick is provided, and the said part (2) is provided between the tuyere and the tuyere brick.
2. The bottom blowing furnace according to claim 1, wherein the heat conductivity and thermal expansion coefficient of the refractory are each 1/2 or less of the value of the tuyere brick. (3) The thickness of the refractory is not less than 1Qax and not more than 1Qax (Q lower blowing furnace).