Method for treating the bottom of a metallurgical furnace during cold repair

Abstract

The application belongs to the field of smelting, and particularly relates to a furnace bottom treatment method in a cold repair process of a metallurgical furnace, comprising the following steps: (1) after the metallurgical furnace is shut down and cooled, cracks of working layer refractory bricks of the furnace bottom are found out, and the cracks are filled with polyurethane foam joint filling agent; (2) maintenance is performed; and (3) after the maintenance is completed, sundries on the working layer refractory bricks of the furnace bottom are cleaned. According to the above scheme, the cracks between the working layer refractory bricks of the furnace bottom are filled with the polyurethane foam joint filling agent before the maintenance, the joint filling agent expands after entering the cracks, not only fills the cracks between the furnace bricks, avoids foreign matters from entering the cracks during the maintenance process and affecting the shrinkage of the cracks of the furnace bricks in the subsequent furnace heating process, but also has a certain strength after hardening, and can bear the pressure of treading during the maintenance; more importantly, the joint filling agent does not need to be cleaned after the maintenance is completed, the polyurethane joint filling agent is liquefied, thermally decomposed and completely gasified with the increase of the temperature in the furnace heating process of the smelting furnace, and does not affect the shrinkage of the cracks of the furnace bricks.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, specifically relating to a method for treating the furnace bottom during cold repair of a metallurgical furnace. Background Technology

[0002] After a period of operation, the refractory material of a metallurgical furnace is gradually eroded and loses its protective function due to the erosion and scouring of the high-temperature melt and flue gas. At this time, it is necessary to stop the operation of the furnace and let it cool down so that the severely eroded refractory material can be replaced. This is called the operating cycle of the metallurgical furnace, also known as the furnace life. Depending on the size and metallurgical process of the metallurgical furnace, the furnace life generally ranges from several months to several years.

[0003] A metallurgical furnace structure consists of a furnace top, furnace walls, and furnace bottom. Generally, within an operating cycle, the refractory bricks of the furnace top and walls suffer severe erosion and are typically replaced entirely during offline cold repairs. The erosion rate of the furnace bottom refractory bricks is much lower, and in most cases, replacement is unnecessary or only required in parts. However, during maintenance, the furnace needs to be shut down from its prolonged high-temperature state and rapidly cooled. This cooling process causes cracks of varying lengths and widths to form in the furnace bottom refractory brick layer. Once the furnace enters a cold-state maintenance phase, the construction process generates a large amount of hard foreign matter, some of which inevitably enters the cracks in the furnace bottom. Current technologies, based on various factors and analyses, generally employ the following two solutions:

[0004] Option 1: To avoid improper handling of furnace bottom cracks affecting the thermal expansion recovery of subsequent furnace drying and shrinkage cracks, the entire furnace bottom bricks will be replaced. This involves cutting and removing all residual molten material and the furnace bottom refractory bricks, and then rebuilding with new refractory bricks, putting the entire furnace bottom into operation in a brand-new condition. The drawbacks of this option are: the removal of the metallurgical furnace bottom is difficult, and the removal and subsequent rebuilding operations will consume a significant amount of maintenance time, resulting in a long construction period and a substantial impact on the company's annual production rate. Furthermore, the labor costs for dismantling and installing the furnace bottom refractory bricks, as well as the cost of purchasing new refractory bricks, significantly increase maintenance costs.

[0005] Option 2: The refractory bricks at the furnace bottom are not removed. Insulation cotton is used to plug the surface of the cracks in the furnace bottom to prevent foreign objects from entering. The remaining areas are removed and replaced normally, and the furnace bottom is retained until the next operating period. The drawback of this option is that the insulation cotton or other flexible materials can only cover the surface of the cracks. As construction inside the furnace progresses, the crack covering is trampled and pulled, rendering it ineffective. A large number of hard foreign objects enter the cracks, making later cleaning difficult and affecting the subsequent shrinkage of the cracks during furnace drying. This poses a significant safety hazard of melt penetration and leakage to production. In addition, the furnace bottom is not effectively protected. During construction, a large number of foreign objects will fall off, be transported, and be crushed, which will also damage the refractory bricks of the working layer at the furnace bottom. Summary of the Invention

[0006] The purpose of this invention is to provide a method for treating the furnace bottom during cold repair of a metallurgical furnace, so as to completely solve the problem of hard foreign objects entering the gaps of the refractory bricks in the working layer of the furnace bottom during cold repair of a metallurgical furnace.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for treating the furnace bottom during cold repair of a smelting furnace, characterized by comprising the following steps:

[0008] (1) After the metallurgical furnace is shut down and cooled, the cracks in the refractory bricks of the working layer at the bottom of the furnace are located and the cracks are filled with polyurethane foam sealant.

[0009] (2) Carry out maintenance;

[0010] (3) After the maintenance is completed, clean the debris on the refractory bricks of the working layer at the bottom of the furnace.

[0011] Polyurethane foam sealant is available on the market. It is a single-component, moisture-curing, multi-purpose polyurethane foam filling elastic sealing material. It is a special polyurethane product that fills polyurethane prepolymer, foaming agent, catalyst and other components in a pressure-resistant aerosol can. It is generally used for filling and sealing gaps around building doors and windows, expansion joints of components and holes. The use of this sealant in the technical solution of this invention is quite different. Initially, the crack filling is purely for filling purposes. After maintenance is completed, the sealant is no longer needed and does not need to be removed. Polyurethane foam generally has a melting point of 170–190℃. According to the research on the synthesis and properties of polyester-type polyurethane elastomers (Yuan Feng et al., Institute of Composite Materials and Structures, Harbin Institute of Technology, *Materials Science*, 2016, No. 02), "The temperature range of the first weight loss is 275℃–420℃, and the temperature range of the second weight loss is 420℃–500℃. The first weight loss is caused by the decomposition of the soft segments of polyurethane, and the second weight loss comes from the decomposition of the hard segments of polyurethane." It can be seen that the polyurethane foam sealant has already completely decomposed into small molecules at around 500℃. With continued heating, the small molecules vaporize. By the time the metallurgical furnace reaches approximately 1200℃ at the end of the furnace drying process, the sealant has already completely vaporized, without affecting the shrinkage of cracks in the refractory bricks of the working layer at the bottom of the furnace.

[0012] The above-mentioned solution involves filling the gaps in the refractory bricks of the working layer at the bottom of the furnace with polyurethane foam sealant before maintenance. After the sealant expands into the cracks, it not only fills the cracks between the furnace bricks, preventing foreign objects from entering the cracks during maintenance and affecting the shrinkage of the cracks in the furnace bricks during the subsequent furnace drying process, but also provides a certain strength after hardening, which can withstand the pressure of being stepped on during maintenance. More importantly, after maintenance, the sealant does not need to be cleaned. During the furnace heating and drying process, the polyurethane sealant will liquefy, thermally decompose, and eventually completely vaporize as the temperature rises, without affecting the shrinkage of the cracks in the furnace bricks. Attached Figure Description

[0013] Figure 1 A schematic diagram showing a hard foreign object entering a crack in a furnace brick;

[0014] Figure 2 This is a schematic diagram illustrating the filling and covering of cracks using the solution of this invention. Detailed Implementation

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings.

[0016] A method for treating the furnace bottom during cold repair of a smelting furnace, characterized by comprising the following steps:

[0017] (1) After the metallurgical furnace is shut down and cooled, the cracks 11 of the refractory bricks 10 in the working layer at the bottom of the furnace are located and the cracks are filled with polyurethane foam sealant 20.

[0018] (2) Carry out maintenance;

[0019] (3) After the maintenance is completed, clean the debris on the refractory bricks 10 of the working layer at the bottom of the furnace.

[0020] The furnace bricks in a smelting furnace include a permanent layer of refractory bricks at the bottom and a working layer of refractory bricks above it. The working layer of refractory bricks includes the furnace wall working layer and the furnace bottom working layer. Typically, cold repairs of a smelting furnace require replacement or repair of the furnace top equipment, necessitating the replacement of the furnace wall working layer refractory bricks. However, the furnace bottom working layer refractory bricks do not require replacement. Therefore, after the smelting furnace is shut down and cooled, the furnace bottom working layer refractory bricks need to be protected. If a crack or hard foreign object accidentally enters the crack in the furnace bottom working layer refractory bricks, the crack cannot close properly during subsequent heating and drying processes, leading to cracks in the working layer bricks. During smelting, high-temperature molten metal enters the cracks and seeps downwards, contacting the permanent layer bricks. This not only damages the bricks but, over time, the continuous downward seepage of molten metal eventually damages the entire smelting furnace.

[0021] In step (1), after filling the cracks, the entire working layer of refractory bricks 11 at the bottom of the furnace is covered with a heat-resistant and wear-resistant blanket 30, and the joints of the heat-resistant and wear-resistant blanket 30 are sewn together with metal thread. Generally, the heat-resistant and wear-resistant blanket 30 (usually felt, etc.) and the thin steel plate have fixed widths, so splicing is required to cover the entire bottom of the furnace.

[0022] A thin steel plate 40 is laid on the heat-resistant and wear-resistant blanket 30, and the joints of the thin steel plate 40 are spot-welded together. The thickness of the thin steel plate 40 is 0.2-4mm. With the cushioning of the underlying felt, the thin steel plate 40 will not be damaged during maintenance and trampling. Moreover, the felt and the thin steel plate are inexpensive and reusable.

[0023] In step (1), after the metallurgical furnace is shut down and cooled, all cracks in the refractory bricks 11 of the working layer at the bottom of the furnace are first identified and marked, and then filled with polyurethane foam sealant 20. This can prevent cracks from being missed.

[0024] In step (2), the overhaul includes replacing or repairing the furnace top equipment and replacing the refractory bricks of the furnace wall working layer. The furnace top equipment and furnace wall refractory bricks are severely damaged and basically need to be replaced every time there is a cold repair. The refractory bricks of the furnace bottom working layer can be used for several operating cycles and replaced with new bricks when they are severely damaged.

[0025] In step (3), after the maintenance is completed and the debris is cleaned, the thin steel plate 40 and the heat-resistant and wear-resistant blanket 30 are removed. All debris in the furnace cavity is cleaned to ensure that no debris enters the crack and affects the crack shrinkage after the sealant decomposes and vaporizes during the furnace baking process.

[0026] The technical solution of the present invention has the following technical effects:

[0027] 1. All cracks are filled with foam adhesive, which is not affected by the location, size, or shape of the cracks and can achieve 100% filling, eliminating the possibility of foreign objects entering the cracks;

[0028] 2. The heat resistance temperature of the foam adhesive is 150℃. No treatment is required after construction. During the subsequent furnace drying process, the foam adhesive is directly burned off and does not affect the expansion and recovery of the cracks in the refractory bricks at the bottom of the furnace.

[0029] 3. The heat-resistant and wear-resistant blanket and thin steel plate covering further prevent foreign objects from entering the furnace bottom. At the same time, it provides very effective protection for the furnace bottom refractory bricks that are not replaced. Even if a large number of heavy objects fall, crush, or move during the construction process, it will not damage the furnace bottom.

[0030] 4. It saves on maintenance costs. For example, with a flash furnace with a capacity of 400,000 tons / year, it can save hundreds of tons of refractory materials.

[0031] 5. Save on overhaul time. Taking a flash furnace with a capacity of 400,000 tons / year as an example, if the furnace body refractory bricks are replaced as a whole, the demolition and reconstruction will save at least 7 days of construction time and a lot of labor costs.

Claims

1. A method for treating the furnace bottom during cold repair of a smelting furnace, characterized in that, Includes the following steps: (1) After the metallurgical furnace is shut down and cooled, the cracks (11) in the refractory bricks (10) of the working layer at the bottom of the furnace are found and filled with polyurethane foam sealant (20); after filling the cracks, the entire refractory bricks (10) of the working layer at the bottom of the furnace are covered with heat-resistant and wear-resistant blanket (30), and the joints of the heat-resistant and wear-resistant blanket (30) are sewn with metal wire; a thin steel plate (40) is laid on the heat-resistant and wear-resistant blanket (30), and the joints of the thin steel plate (40) are spot welded together; (2) Carry out maintenance; maintenance includes replacing or repairing the furnace top equipment and replacing the refractory bricks of the furnace wall working layer; (3) After the maintenance is completed, clean the debris on the refractory bricks of the working layer at the bottom of the furnace, and remove the thin steel plate (40) and the heat-resistant and wear-resistant blanket (30).

2. The method for treating the furnace bottom during cold repair of a smelting furnace according to claim 1, characterized in that: In step (1), after the metallurgical furnace is shut down and cooled, all cracks (11) in the refractory bricks (10) of the working layer at the bottom of the furnace are first identified and marked, and then filled with polyurethane foam sealant (20).

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