Furnace cover and method for cooling the furnace cover

Abstract

To provide a furnace cover capable of suppressing the generation of heat cracks in an inner wall therein, and a furnace cover cooling method.SOLUTION: A furnace cover covering an opening upper end face of a container comprises: a hollow cooling chamber provided therein; a nozzle provided for injecting cooling water toward an inner wall inside the cooling chamber; and an annular drainage provided over all the circumference of a lower end part of the cooling chamber; and an exhaust port connected to the drainage. In the inner wall side of the drainage, the inner diameter thereof is larger than the opening inner diameter of the container, and the inner wall side of the drainage lower than a position in which the inner diameter is made maximum has a cylindrical shape with the same inner diameter or is diameter-reduced downward. Also provided is a furnace cover cooling method in which cooling water is injected to the inner wall inside the cooling chamber from the nozzle to cool the inner wall, and the cooling water injected to the inner wall is drained from the exhaust port to the outside of the furnace cover via the drainage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a furnace cover for covering the upper end surface of the opening of a vessel such as a ladle refining furnace or an electric furnace, and a method for cooling the furnace cover. [Background technology]

[0002] The lid of a vessel that contains high-temperature molten metal, such as a ladle refining furnace or an electric furnace vessel, may be deformed or melted due to the high heat during refining. To address this issue, a spray-type lid that cools the lid by spraying cooling water into a hollow cooling chamber formed inside is known. The spray-type lid cools the inner wall surface of the lid with a jet of water, and can achieve a large cooling effect with a small flow rate compared to the water-cooled jacket method. However, the spray water does not reach the area below the water level of the drainage water accumulated on the bottom of the lid, and only slow cooling is achieved due to the slow flow rate toward the drain outlet. This may cause heat cracks due to insufficient cooling, leading to water leakage. Water leakage may cause a steam explosion due to contact with the high-temperature molten metal inside the vessel, which is a major safety issue.

[0003] To address this issue, Patent Document 1 discloses a method of providing an outer peripheral drainage ditch and allowing wastewater to fall naturally into the outer peripheral drainage ditch. Patent Document 2 discloses a method of installing a nozzle for accelerating the wastewater flow in the drainage channel. Patent Document 3 discloses a method of using a vacuum pump to suck and discharge wastewater, and a method of installing a water-cooling jacket on the inside lower part of the furnace lid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-260367 [Patent Document 2] Japanese Patent Application Publication No. 10-246576 [Patent Document 3] JP 2017-116186 A Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned conventional techniques have the following problems.

[0006] In the method of Patent Document 1, drainage grooves are provided on the outer periphery of the furnace lid, which prevents wastewater from accumulating on the bottom of the lid and prevents insufficient cooling on the bottom of the lid. However, since the drainage grooves protrude from the outer periphery of the lid, there is a risk of interference with the lid's suspension arm and surrounding equipment. For this reason, it is difficult to provide drainage grooves around the entire periphery of the lid, and insufficient cooling occurs in areas where drainage grooves are not provided.

[0007] In the method of Patent Document 2, a nozzle that accelerates the flow of wastewater is provided to prevent wastewater from accumulating in the drainage channel. However, in order to obtain a sufficiently high flow velocity, a large amount of water is required in addition to the spray water, which inevitably leads to an increase in the size of the wastewater treatment device.

[0008] In the method of sucking and discharging wastewater using a vacuum pump as described in Patent Document 3, the wastewater is sucked and discharged by the vacuum pump, which can prevent the wastewater from accumulating on the bottom surface of the furnace lid. However, the vacuum pump that sucks and discharges such a large amount of wastewater has strict specifications and is expensive.

[0009] In the method of installing a water-cooled jacket at the bottom inside the furnace lid in Patent Document 3, the furnace lid is cooled by the water-cooled jacket, which can eliminate the insufficient cooling at the bottom of the furnace lid. However, when a new small water channel is installed inside the furnace to cover the pooled water at the bottom of the furnace lid, the cooling water needs to be pumped to increase the flow rate in order to obtain a sufficient cooling effect. If the small water channel is damaged during operation due to molten metal splashing, etc., a large amount of cooling water will gush out due to the pressure of the pumping, which poses a safety risk. In the case of spray cooling and pooled water, there is no risk of gushout because the pressure inside the furnace lid is atmospheric pressure.

[0010] Another known method is to expand the outer diameter of the furnace lid to widen the drainage channel in order to lower the drainage water level, but this causes interference with surrounding equipment, and the weight of the furnace lid increases significantly, requiring a large lifting device for the lid, which increases the cost of equipment.

[0011] Therefore, an object of the present invention is to provide a spray-cooled furnace cover that suppresses the occurrence of heat cracks in the inner wall of the furnace cover, and a method for cooling the furnace cover. [Means for solving the problem]

[0012] The furnace cover according to the present invention, which advantageously solves the above problems, is configured as follows.

[0013] [1] A furnace cover comprising a hollow cooling chamber provided within a furnace lid covering the upper end surface of a vessel opening, nozzles provided within the cooling chamber for spraying cooling water toward the inner wall, an annular drainage channel provided circumferentially at the lower end of the cooling chamber, and a drain outlet connected to the drainage channel, wherein the inner diameter of the inner wall side of the drainage channel is larger than the inner diameter of the vessel opening, and the inner wall side of the drainage channel below the position where the inner diameter of the inner wall side is maximum is cylindrical with the same inner diameter or narrows downward. [2] In the above [1], the inner wall side of the drainage channel above the point where the inner diameter of the inner wall side is at its maximum is a furnace cover that has an inclined surface whose inner diameter increases downward. [3] In the above [1] or [2], the position where the inner diameter of the inner wall of the drainage channel is maximum is a furnace cover that is below the water level of the maximum water level of the cooling water present in the drainage channel. [4] In any of [1] to [3] above, the furnace cover further has an outer peripheral drainage groove connected to the branching portion of the drainage channel and positioned outside and lower than the drainage channel, and the inner diameter of at least the inner wall side other than the branching portion of the drainage channel is larger than the inner diameter of the opening of the vessel. [5] In any of the above [1] to [4], the maximum inner diameter of the inner wall of the drainage channel is a furnace cover that is set based on the water level position of the maximum water level of the cooling water present in the drainage channel. [6] In the above [5], when the furnace cover is attached to the vessel containing molten metal, the setback of the inner wall of the furnace cover satisfies the formula (1). (Setback amount) / (Height of molten metal surface)>0.10...Equation (1) Here, in the above formula (1), the setback amount refers to the outward displacement of the lower end of the inner wall side of the drainage channel relative to the upper end of the container opening, and the height of the molten metal surface refers to the distance from the upper end surface of the container opening to the molten metal surface.

[0014] The method for cooling a furnace roof according to the present invention, which advantageously solves the above problems, is configured as follows. [7] A method for cooling a furnace lid, comprising using a furnace lid described in any one of [1] to [6] above, cooling the inner wall of the cooling chamber by spraying cooling water from the nozzle onto the inner wall, and discharging the cooling water sprayed onto the inner wall through a drainage channel and out of the furnace lid from a drain outlet. Effect of the Invention

[0015] In the present invention, when attaching the furnace lid to the upper end surface of the vessel opening, the inner wall side of the annular drainage channel provided at the lower end of the hollow cooling chamber is shifted to the outside of the vessel opening, i.e., the inner diameter of the inner wall side of the drainage channel is made larger than the inner diameter of the vessel opening, and further the inner wall side of the drainage channel below the position where the inner diameter is maximum is made cylindrical or narrowed toward the inside of the vessel, thereby reducing the water level of the accumulated drainage water, and thereby suppressing heat cracks by reducing the thermal load. In addition, the present invention does not require a vacuum pump or a large amount of wastewater treatment equipment, so equipment costs are reduced, and it is safe because there is no cooling water pressure delivery section from which molten metal may splash. [Brief description of the drawings]

[0016] [Figure 1]FIG. 1 is a schematic horizontal cross-sectional view showing one embodiment of a furnace cover of the present invention. [Diagram 2] 1A is a schematic vertical cross-sectional view of the outer periphery showing one embodiment of the furnace cover of the present invention, (a) is a cross-sectional view taken along line AA in FIG. 1, (b) is a cross-sectional view taken along line BB in FIG. 1, and (c) is a cross-sectional view taken along line CC in FIG. 1. [Diagram 3] 1A and 1B are schematic horizontal and vertical sectional views of a conventional furnace cover. [Figure 4] FIG. 1 is a schematic diagram illustrating the relationship between the setback of the inner wall and the molten steel surface (molten metal surface) visible from the water level in the drainage channel. [Diagram 5] 1 is a graph showing the relationship between the amount of setback / height of the molten steel surface (molten metal surface) and the ratio of the visible molten steel area and the drainage water level. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The furnace lid according to the embodiment of the present invention is for covering the upper end surface of the opening of a vessel such as a ladle refining furnace or an electric furnace. The vessel contains molten steel, which is an example of molten metal. An example of the furnace lid according to the present embodiment is shown in Figs. 1 and 2. The furnace lid of the present embodiment forms a hollow cooling chamber, and the cooling chamber has a structure including a cooling function using cooling water, a drainage function for draining the cooling water, and a radiation heat reduction function for reducing the radiation heat of the molten steel. An example of a conventional furnace lid is shown in Fig. 3. In the cooling chamber of the conventional furnace lid, the cooling water sprayed onto the inner wall 7 is collected as drainage through the drainage channel 1 into one drain outlet 1A. The inner wall side of the drainage channel 1 has a cylindrical shape with the same inner diameter, and the inner diameter coincides with the inner diameter of the upper end of the opening of the vessel 20. A furnace lid lifting arm 3 is provided on the outer periphery of the furnace lid. The furnace lid lifting arm 3 is used when lifting the furnace lid, and four furnace lid lifting arms 3 protrude from each of the four sides of the furnace lid. In the example shown in FIG. 1, only two of the four furnace cover lifting arms 3 are shown.

[0018] <Cooling function> As shown in Fig. 2(c), the furnace cover of this embodiment forms a hollow cooling chamber surrounded by an inner wall 7, an outer wall 8, and a bottom wall 11. A plurality of nozzles 13 are provided in the cooling chamber. A pipe for supplying cooling water is connected to the nozzles 13, and cooling water is sprayed from the nozzles 13 toward the inner wall 7 in the cooling chamber to cool the inner wall 7.

[0019] <Drainage function> As shown in Figures 1 and 2(b), the lower end of the cooling chamber, which is the bottom surface of the furnace lid (the portion surrounded by the inner wall 7, the outer wall 8, and the bottom wall 11), is annular drainage channel 1 around the entire periphery. Cooling water sprayed from nozzles 13 to the inner wall 7 is accumulated therein. Cooling water 15 accumulated in drainage channel 1 flows through drainage channel 1 to drain outlet 1A connected to drainage channel 1, and is drained from drain outlet 1A to the outside of the furnace lid.

[0020] In addition, as shown in Figures 1 and 2(a), it is preferable that the drainage channel 1 formed at the lower end of the cooling chamber is partially connected to the peripheral drainage groove 2. That is, the drainage channel 1 has a branched section 4 to which the peripheral drainage groove 2 is connected, and a non-branched section 5 to which the peripheral drainage groove 2 is not connected. The peripheral drainage groove 2 is provided outside the drainage channel 1 and at a lower position than the drainage channel 1. In this way, by providing the peripheral drainage groove 2, the water level in the drainage channel 1 of the furnace cover can be lowered. This improves the cooling effect of the inner wall 7 of the furnace cover.

[0021] As one example of this embodiment, it is preferable to form the peripheral drainage groove 2 only on the side of the furnace lid opposite to the side where the container is attached and detached. In the example shown in Fig. 1, the peripheral drainage groove 2 is formed only on the left half of the furnace lid. This makes it possible to prevent the peripheral drainage groove 2 from interfering with the container and damaging it when the container (ladle) is moved from the right side to the left side of the furnace lid and the furnace lid is attached to the container.

[0022] <Radiant heat reduction function> 2(b) and (c), an expanded diameter section 9 is formed on the inner wall 7 side of the drainage channel 1 of the furnace lid. The inside diameter of this expanded diameter section 9 is larger than the inside diameter of the opening of the vessel 20, and below the position 10B where the inside diameter is maximum (i.e., the lower part 10 of the expanded diameter section) the inside diameter on the inner wall 7 side of the drainage channel 1 is cylindrical with the same inside diameter, or the inside diameter on the inner wall 7 side of the drainage channel 1 becomes smaller toward the bottom, tapering. If the lower part 10 is cylindrical with the same inside diameter, its upper end is the position 10B where the inside diameter is maximum.

[0023] Specifically, the enlarged diameter section 9 is divided into an "upper section" 10A above the position where the inner diameter is maximum, and a "lower section" 10 below the position 10B where the inner diameter is maximum. The upper section 10A of the enlarged diameter section has an inner diameter on the inner wall 7 side of the drainage channel 1 that increases toward the bottom, and has an inclined surface (approximately a truncated cone surface). On the other hand, the lower section 10 of the enlarged diameter section is a cylinder (vertical surface) with the same inner diameter on the inner wall 7 side of the drainage channel 1 in the examples of Figures 2(b) and (c). Note that the position 10B where the inner diameter on the inner wall 7 side of the drainage channel 1 is maximum is preferably below the water level of the maximum water level of the cooling water (drainage) 15 that accumulates in the drainage channel 1. Furthermore, it is more preferable that it is above the water level of the minimum water level of the cooling water 15 that accumulates in the drainage channel 1.

[0024] The lower part 10 of the enlarged diameter portion may not be cylindrical with the same inner diameter on the inner wall 7 side of the drainage channel 1, but may be an inclined surface (approximately a truncated cone surface) in which the inner diameter on the inner wall 7 side of the drainage channel 1 decreases as it extends downward. Also, the upper part 10A of the enlarged diameter portion is not limited to an inclined surface as long as it has a shape such that the inner diameter of the furnace cover increases as it extends downward, and may be a shape having a step, for example.

[0025] By making the upper part 10A of the enlarged diameter portion an inclined surface, the angle of the inner wall 7 can be made nearly perpendicular to the angle of the nozzle 13 (the angle of the cooling water sprayed from the nozzle 13), thereby improving the efficiency of heat extraction. Also, by making the upper part 10A of the enlarged diameter portion an inclined surface, it is possible to suppress accumulation of wastewater (cooling water) compared to when the upper part 10A is in a stepped shape.

[0026] In this embodiment, the above-mentioned enlarged diameter portion 9 is formed on the entire circumference of the inner wall 7 side of the drainage channel 1, that is, on both the branched portion 4 and the non-branched portion 5. However, since the non-branched portion 5 where the outer peripheral drain groove 2 is not provided is where the wastewater is likely to accumulate, the enlarged diameter portion 9 may be formed at least on the inner wall 7 facing the non-branched portion 5 of the drainage channel 1. In other words, the outer peripheral drain groove 2 may be connected to the branched portion 4 of the drainage channel 1, and the inner wall 7 side of the branched portion 4 of the drainage channel 1 may be cylindrical with a radius equal to the inner diameter of the opening of the vessel. By making the inner wall 7 side of the branched portion 4 where the outer peripheral drain groove 2 is provided cylindrical with a radius equal to the inner diameter of the upper end of the opening of the vessel, the manufacture and repair of the furnace cover are facilitated. In addition, since the overlap between the upper end surface of the opening of the vessel and the bottom wall 11 of the furnace cover is large, the barrier between the molten steel and the outside air can be improved.

[0027] In this embodiment, particularly in the non-branched portion 5 of the drainage channel 1 where the outer peripheral drainage groove 2 is not provided, the lower end of the drainage channel 1 on the inner wall 7 side is shifted outward from the container to form an expanded diameter portion 9, as shown in Fig. 4. Here, in the following description, the outward shift of the lower end of the drainage channel 1 on the inner wall 7 side relative to the upper end of the container opening is referred to as setback 12. Due to this setback 12, when the furnace cover is attached to the vessel 20, part of the radiant heat emitted from the molten steel surface (molten metal surface) 14 is blocked by the upper edge of the opening of the vessel 20 and does not reach the inner wall 7 of the drainage channel 1. This effect becomes more noticeable at the lower part.

[0028] In addition, in the inner wall 7 of the furnace roof of this embodiment, the portion above the water level 18 of the cooling water 15 (sump water) that accumulates in the drainage channel 1 is strongly cooled by the spray of cooling water, so heat cracks are unlikely to occur. On the other hand, in the portion below the water level 18 of the sump water, the effect of blocking the radiant heat emitted from the molten steel surface (molten metal surface) 14 becomes more pronounced. Therefore, from the standpoint of cooling and heat load, heat cracks are most likely to occur in the inner wall 7 (iron shell) portion at the water level 18 of the drainage sump water in the drainage channel 1, and it is important to lower the water level.

[0029] The water level 18 of the sump water in the drainage channel 1 is determined by the flow velocity at which the sump water flows out to the branch point 4 where the outer drainage ditch 2 is located (an area where almost no sump water accumulates). This corresponds to a square weir, and according to Torricelli's theorem, the deeper the water level, the greater the outflow flow velocity. For this reason, if the lower portion 10 of the enlarged diameter portion 9 of the inner wall 7 of the furnace cover is inclined outward, that is, if the inner diameter is increased downward, the horizontal area at the deep water level where the outflow flow rate becomes faster becomes small, and as a result, the water level becomes higher for the same outflow volume. In contrast, the water level can be lowered by leaving the inner diameter of the lower part 10 of the expanded section 9 of the inner wall 7 of the furnace cover unchanged, i.e., moving vertically downward, or by making the inner diameter smaller, i.e., by sloping it toward the inside of the vessel 20, and increasing the horizontal area as the water level increases.

[0030] In this embodiment, the position 10B where the inner diameter of the enlarged diameter portion 9 is maximum (the position of the maximum inner diameter) is set based on the maximum water level 18 of the cooling water 15 (drainage sump water) accumulated in the drainage channel 1. If the position of the outer wall 8 of the furnace cover is constant, the larger the inner diameter of the inner wall 7, the greater the effect of reducing the heat load on the inner wall 7, i.e., the effect of increasing the area 17 where the molten steel surface 14 is blocked by the edge of the vessel. On the other hand, the flow path of the drainage channel 1 becomes narrower, and the water level becomes higher. Therefore, there is an optimal value for the position of the inner wall 7. Also, there is a correlation between the setback 12 amount of the inner wall 7 and the height of the molten steel surface (molten metal surface) 14 (the distance 19 from the upper end surface of the opening of the vessel to the molten steel surface (molten metal surface) 14).

[0031] FIG. 5 shows the relationship between the value obtained by dividing the setback amount 12 by the height of the molten metal surface (distance 19), the ratio of the visible molten steel area 16, which is the surface area of ​​the molten steel (molten metal) that is visible from the water level of the drainage sump water to the surface area of ​​the molten steel surface (molten metal surface) 14 of the vessel, and the water level height 18 (drainage water level) of the drainage sump water, in a case where an outer peripheral drain groove 2 is provided (FIG. 1) and a case where a conventional drainage channel 1 is provided (FIG. 3). Here, the setback amount 12 refers to the outward shift of the lower end of the drainage channel 1 on the inner wall 7 side relative to the upper end of the opening of the vessel 20, that is, the distance between the inner diameter of the opening of the vessel 20 and the maximum inner diameter 10B of the enlarged diameter portion 9 (radius difference) (FIG. 2(c) and FIG. 4). In either case, the ratio of the visible molten steel area 16 decreases as the (setback amount 12) / (distance 19) increases to 0.20. However, since the water level 18 of the drainage sump water rises accordingly, if (setback 12 amount) / (distance 19) exceeds 0.20, the visible molten steel area 16 will rather increase. For this reason, in Figure 5, the optimal value for (setback 12 amount) / (distance 19) is 0.20. From the viewpoint of reducing the thermal load on the inner wall, it is preferable that the visible molten steel area 16 is 90% or less, and in Fig. 5, in a furnace cover having a conventional drainage channel 1 (Fig. 3), the visible molten steel area 16 is 90% when (setback 12 amount) / (distance 19) is 0.10. Therefore, in order to reduce the thermal load on the inner wall, the setback when attaching a furnace cover to a vessel containing molten metal is set within a range that satisfies the following formula (1). (Setback amount) / (Height of molten metal surface)>0.10...Equation (1)

[0032] Furthermore, when the peripheral drainage groove 2 is installed, the water level height 18 of the accumulated water in the drainage channel 1 is lower, so the proportion of the visible molten steel area 16 can be made lower when the peripheral drainage groove 2 is installed. EXAMPLES

[0033] The inner wall surface of the furnace cover was cooled in a conventional furnace cover and in the furnace cover of the above embodiment, and the effect was confirmed. (1) Conventional furnace cover (Fig. 3) The heat transfer coefficient on the inner wall of the furnace roof is 6,000 to 7,500 W / m 2 ·K, the heat transfer coefficient in the drainage basin is 600~2,500W / m 2 ·K, and spray cooling with cooling water has a higher cooling capacity than stagnant water in a drainage channel. The maximum water level h of the pool in the drainage channel was calculated as follows:

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[0034] (2) The furnace cover of the above embodiment (FIGS. 1 and 2) Nozzles were installed in the hollow part of the furnace lid to spray cooling water, an outer peripheral drainage groove was installed, and an expanded diameter part was formed at the bottom end of the inner wall (the inner wall side of the drainage channel), expanding the inner diameter of the furnace lid, the upper part of the expanded diameter part was a downwardly inclined surface, and the lower part 10 of the expanded diameter part was cylindrical, and cooling was performed with cooling water using a furnace lid with a constant inner diameter. (Setback amount) / (height of molten metal surface) was 0.20. As a result, the drainage water level was 120.0 mm, and the ratio of visible molten steel area was evaluated to be 76%. No heat cracks occurred on the inner wall of the furnace roof. [Explanation of symbols]

[0035] 1 Drainage channel 1A Drain port 2 Periphery drainage ditch 3 Furnace Lifting Arm 4 Branching section 5 Non-branched section 7 Inner wall 8. Exterior Walls 9 Expanded diameter part 10 Lower part of enlarged diameter section 10A Upper part of the expansion 10B Position where the inner diameter of the expansion section is maximum 11 Bottom wall 12 Setback 13 Nozzle 14 Molten steel surface (molten metal surface) 15 Cooling water accumulating in drains (sump water) 16 Surface area of ​​molten steel (molten metal) visible from the water surface height of the drainage sump: Visible molten steel area 17 The area of ​​molten steel (molten metal surface) obstructed by the edge of a vessel 18 Water level in drainage basin 19 Distance from the top of the vessel opening to the molten steel surface (molten metal surface) 20 containers

Claims

1. a hollow cooling chamber provided within a furnace cover covering an upper end surface of an opening of the vessel; A nozzle provided in the cooling chamber for spraying cooling water toward an inner wall; a ring-shaped drainage channel provided in a circumferential direction at a lower end of the cooling chamber; A drain outlet connected to the drainage channel; Equipped with The inner diameter of the inner wall of the drainage channel is larger than the inner diameter of the opening of the container, and the inner wall of the drainage channel below the position where the inner diameter of the inner wall is maximum is cylindrical with the same inner diameter or is tapered downward; A furnace cover in which the inner wall side of the drainage channel above the position where the inner diameter of the inner wall side is maximum is an inclined surface whose inner diameter increases downward.

2. 2. The furnace cover according to claim 1, wherein the position at which the inner diameter of the inner wall side of the drainage channel is maximum is below the maximum water level of the cooling water present in the drainage channel.

3. A furnace cover as described in claim 1 or 2, further comprising an outer peripheral drainage groove connected to a branching portion of the drainage channel and positioned outside and lower than the drainage channel, and at least the inner diameter of the inner wall side other than the branching portion of the drainage channel is larger than the inner diameter of the opening of the container.

4. The maximum inner diameter of the drainage channel on the inner wall side is the water surface position of the maximum water level of the cooling water present in the drainage channel. The furnace cover according to any one of claims 1 to 3, which is set based on the above.

5. 5. The furnace cover according to claim 4, wherein when the furnace cover is attached to the vessel containing molten metal, the setback of the inner wall of the furnace cover satisfies formula (1). (Setback amount) / (height of molten metal surface)>0.10...Equation (1) Here, in the above formula (1), the setback amount refers to the amount of outward displacement of the lower end of the inner wall side of the drainage channel relative to the upper end of the container opening, and the height of the molten metal surface refers to the distance from the upper end surface of the container opening to the molten metal surface.

6. A method for cooling a furnace lid, comprising: using the furnace lid described in any one of claims 1 to 5; cooling the inner wall by spraying cooling water from the nozzle onto the inner wall in the cooling chamber; and draining the cooling water sprayed onto the inner wall through a drainage channel and out of the furnace lid from a drain outlet.

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