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100t electric arc furnace lining refractory damage and measures to improve service life

  1. Furnace type and refractory material for each part

The 100t ultra-high power electric arc furnace shown in this paper is the eccentric bottom tapping form. The furnace shell is split, the upper furnace shell has a water-cooled plate frame structure; the lower furnace shell has a butterfly bottom form with a vertical periphery, and the internal masonry refractory material forms a molten pool. The furnace shell is used for one, and the furnace shell is replaced as a whole after the furnace service life expires, and the off-line masonry is rebuilt for standby. The refractory materials used in the main parts of the furnace lining are shown in Table 1.

 

Performance index of refractory material for lining of electric arc furnace

Table 1 Performance index of refractory material for the lining of electric arc furnace

 

  1. Erosion Mechanism of Refractory for Furnace Lining

After the refurbishment of the electric furnace, the service life of the furnace lining of the first furnace was 300 furnaces, and the output was about 30,000 tons. During the use of the furnace, wet spraying of the furnace wall and magnesia ramming material pad were adopted to protect the furnace slope. The consumption of feeding material is 1.7kg/t, the consumption of ramming material is 2.3kg/t, and the cost of refractory material is 45 yuan/t, which has not reached the ideal service life. The anatomical measurement of the erosion of the furnace lining refractory material in the lower line is carried out, and the erosion of each part is shown in Table 2.

 

Measurement-of-erosion-thickness-of-main-parts-of-furnace-lining.

Table 2 Measurement of erosion thickness of main parts of furnace lining

 

The lining refractory is subjected to the physical impact of the scrap steel charge, the radiation and reflection of the electrode arc, and the chemical erosion of the molten steel and slag. Especially at the interface of steel and slag, it is subject to physical penetration and chemical erosion of slag with high oxidation (FeO content of 25% to 30%), causing the graphite on the working surface of magnesia-carbon brick to be oxidized to form a loose decarburized structure. The continuous and repeated action of oxidation, decarburization, and erosion will eventually be lost in the molten state and flake-like spalling state under heat and steel slag erosion. The furnace lining in the hot zone of the electrode is radiated by the high-temperature arc light, and the furnace lining in the furnace wall cluster oxygen lance area is corroded by the local slag steel circulation, which makes the corrosion and damage of the furnace lining in these two areas more serious. The furnace bottom and furnace slope are knotted with magnesia ramming material. In the early stage, the knotting of the furnace is not compact and the sintering of the oven is not good. The loose defects of the magnesia working layer exist. Under the action of bottom blowing and stirring, the slag penetrates into the magnesia The reaction forms iron-rich magnesia finite, which reduces the melting point of magnesia and accelerates the dissolution of magnesia. At the same time, when the sintering in the early stage of the furnace is insufficient, it is subjected to the collision, vibration, and impact of the charging material, forming local pits in the bottom of the furnace, resulting in excessive damage to the local area.

 

  1. Measures to improve the service life of the furnace lining

3.1 Strictly tie the working layer of the furnace lining and the furnace slope

The working layer of the furnace wall is dry-laid with magnesia-carbon bricks, stacked in a staggered manner, and the brick joints should be less than 1mm. When building, it is necessary to prevent internal cracks caused by impact, and fractures and blocks will occur during use, which will affect the service life. The furnace bottom and furnace slope working layers are knotted with magnesia ramming material, the first layer of magnesia is appropriately thickened (about 40% of the total thickness), and rammed from the furnace edge to the center with a pressure vibrating hammer, and then The center is rammed radially to the edge, and each layer is rammed 3 times so that the hammers are interlocked and the joints between the layers are occluded. Compressed air vibrating fork is used for furnace slope ramming, relying on vibration to fully discharge the air in the magnesia ramming material, so as to achieve smooth ramming, high density, and strong integrity. Furnace slope inclination control <45°, which is convenient for later maintenance. When a new furnace is opened, the qualified furnace lining should be covered with thin steel plates to prevent the impact damage of the charging on the furnace bottom. At the same time, after the offline masonry is qualified, moisture-proof measures should be taken.

 

3.2 Do the baking and sintering of the new furnace lining

A high-quality furnace lining should have sufficient strength after baking and sintering, and the entire furnace lining should be integrated. The first three smelting furnaces of the new furnace are mainly to bake the furnace lining, and all scrap steel is smelted to prevent the impact damage of the molten iron to the furnace lining. shock. It adopts a short arc low power supply, the secondary voltage is controlled at 45-650V, and the secondary current is controlled at 40-45KA. The cluster oxygen lance on the furnace wall uses the burner mode to blow oxygen to assist in melting, and the oxygen flow of each lance is controlled below 750Nm³/hr to reduce the impact of the high-speed cluster oxygen flow on the furnace bottom. After each batch of materials passes through the well and melts to form a molten pool, the power is cut off to “simmer” the furnace for 30 minutes, and the temperature of the molten steel is used to ensure the low-temperature sintering and compact performance of the furnace lining.

 

3.3 Optimize the operation process and reduce the erosion of the furnace lining due to improper operation

Reasonable loading and distribution of materials, with light and thin materials as the base to prevent the impact of heavy materials on the bottom and slope of the furnace to produce pits and accelerate the damage of refractory materials. After the basic molten pool is formed during the smelting and melting period, it is necessary to spray or add carbon powder to the molten pool through the furnace wall carbon powder spray gun or the fourth feeding hole in time. Adjust the ratio of the oxygen flow rate of the three furnace wall oxygen lances to promote the C-O reaction to generate CO gas, increase the lasting foaming height of the molten pool slag, quickly realize the submerged arc operation of the foamed slag, and reduce the arc light and high-temperature molten steel erosion on the furnace lining. At the end of smelting, with the weakening of the C-O reaction, the foamed slag gradually becomes thinner. After the slag flows automatically from the furnace door, slag material and lightly burned dolomite should be added in time to ensure that the basicity of the slag is always controlled at 2.0-2.5 and the original ( The content of MgO) is 5% to 8%, which reduces the erosion rate of the furnace lining. Promote the operation of retaining steel and slag to ensure that 15-20t of steel is retained in the furnace. After tapping, add 500kg of lime to thicken the retained slag, which not only reduces the impact of the charging on the furnace lining but also facilitates the early production of the next furnace. The slag with certain basicity reduces the reaction of SiO₂, P₂O5, Fe₂O₃, and other oxides in the slag in the free state with MgO in the refractory material, reducing the melting point of the surface of the refractory lining and aggravating the damage of the lining.

 

3.4 Strengthen the maintenance of the furnace lining in the later stage

The maintenance of the main parts of the furnace lining in the later stage plays an important role in prolonging the service life. In the lower area of the oxygen lance on the furnace wall and the “hot spot” area of the electrode, measures should be taken to strengthen the gunning and make good use of the tapping time and the temperature in the furnace for high-temperature rapid repair. , Thin fill, the gunning thickness is controlled at 10 ~ 20mm, in order to improve the gunning material adhesion rate and rapid high-temperature sintering effect. In the later period of use, pay attention to observing the erosion of the furnace slope, and use ramming material to make up the furnace slope in time to ensure that the angle of the furnace slope is always maintained at about 45° to prevent serious deformation of the furnace slope. At the same time, it is necessary to prevent the furnace slope from rising due to improper shimming, reduce the volume of the molten pool, and increase the molten steel surface, which affects the stability of the operation.

 

  1. Improved usage

The life of the furnace lining is damaged by erosion due to mechanical action, high-temperature action, chemical erosion, and the influence of operating processes during use. By improving the masonry quality of the furnace lining, improving the operation process and strengthening the maintenance of the later stage of the furnace service, the furnace age has been gradually increased, from 300 furnaces to about 500 furnaces, and maintained continuous stability, and the cost of refractory per ton of steel has been reduced from 45 yuan. to the current 22 yuan. The prolongation of furnace service life and stable use has improved the production operation rate, stabilized the production order, and achieved good results.

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