The damage to the converter lining is aggravated due to the physical impact, temperature difference change, chemical reaction and other reasons in the production and operation of the converter. In order to ensure the safety and stability of the converter refractory material during the whole furnace service, and avoid the rapid damage of the partial furnace lining and the short life board, the daily monitoring and repair of the converter refractory material should be strengthened, especially the daily monitoring of the weak parts such as the furnace lining which is seriously damaged. And repair, in order to make the damage degree of the furnace lining as balanced as possible and prolong the service life of the converter. Furnace lining maintenance methods traditionally use brick tiling, gunning, slag splashing, material replenishment, slag replenishment, etc., but the premise is that the converter needs to be shut down and sufficient sintering time is guaranteed, which will affect the cost and production efficiency. The use of comprehensive lining maintenance technology can effectively reduce the rate of lining erosion, improve productivity and reduce production costs.
Related Product: Magensia carbon bricks
1. Balanced design of molten pool structure
During the blowing process, extremely complex redox reactions are carried out in the converter, and there is a high-speed flow field movement. During the whole furnace operation, various parts of the furnace lining are subjected to different physical and chemical effects and mechanical impacts, and the degree of erosion and damage is different, resulting in large differences in the life of the furnace lining in different parts. In view of this, on the basis of the original comprehensive furnace building technology, combined with the specific situation of the erosion of various parts of the converter lining, a forward-looking design and adoption of a special converter lining structure for steelmaking was adopted.
The working layer of the converter is made of multi-layer magnesia-carbon bricks, and the design and masonry method of gradual transition thickening are adopted in the lower molten pool: the length of the multi-layer annular magnesia-carbon bricks is gradually changed from the upper layer to the lower layer in the height direction. Long, that is, the thickness of the molten pool bricks of the working layer gradually becomes thicker from the upper layer to the lower layer, and the diameter of the inner cavity of the converter gradually decreases from the upper layer to the lower layer. The overall structure of the molten pool for each layer (see Figure 1).
During the production and operation of the converter, especially during the oxygen blowing smelting, the molten pool and the slag line at the bottom of the converter are relatively seriously eroded, which has led to the fact that this part has always been a weak part in the later stage of the furnace operation, and it is also a key safety concern. As can be seen from the above figure, this special furnace lining design structure, in which the molten pool formed by the superposition of the multi-layer annular magnesia-carbon bricks into a large upper and lower small approximately conical shape, prospectively solves the problem of fast erosion in the weak part of the converter molten pool. , which ensures the maintenance cost economy in the entire furnace life cycle, improves the safety and stability of use, effectively balances the comprehensive life of each part of the furnace lining during the entire furnace operation, and improves the furnace age and comprehensive economic benefits.
2. Innovative slag splashing furnace protection technology
Optimize and innovate the slag splashing protection process, and innovatively adopt a maintenance method for the converter lining: during the slag splashing protection operation, the oxygen lance changes from the traditional continuous opening of nitrogen to intermittently depositing liquid slag in the converter. Blowing compressed nitrogen, the liquid slag will generate waves and spread outward under the action of high-pressure nitrogen, “surge” to the lining of the converter, and repeatedly contact, slag, bond and solidify with the surface of the lining. The converter final slag with high viscosity and refractoriness is repeatedly sprayed onto the furnace lining under the action of nitrogen gas with high pressure, large flow rate and large impact on the slag at the moment of valve opening, which significantly improves the effect of slag splashing to protect the furnace.
Under the premise of not adding special equipment, prolonging auxiliary time, increasing labor intensity and gunning material cost, and not affecting the rhythm of steelmaking production, this process optimizes the slag splashing furnace protection process, improves the slag splashing furnace protection effect, and effectively Slow down the erosion rate of the molten pool.
3. Explore iron slag filling technology
The commonly used repair methods of large converters basically adopt “slag repair” and “material repair”. Material replenishment will increase the consumption of filling materials, and the falling off of the filling materials will easily lead to the increase of inclusions in molten steel, making it difficult to slag slag, and affecting the quality of molten steel; slag replenishment is to leave the final slag in the furnace, requiring sufficient time to cool and solidify, which directly affects the quality of molten steel. Converter production efficiency. The iron block slag repair technology uses the rapid heat exchange and temperature gradient between the iron block and the high-temperature liquid slag to achieve high-efficiency cold solidification and bonding, and locally repairs and maintains the weak parts of the specific furnace lining, thereby saving the consumption of charging materials and prolonging the life of the furnace lining. The iron block slag filling is suitable for slag filling and pouring the slag surface. It is required to control the appropriate slag basicity and composition in the previous furnace. The iron blocks (2-3t) prepared in advance are evenly poured into the predetermined position with a scrap hopper, and shaken repeatedly for several times. In the second furnace, the iron blocks are completely immersed in the slag, and the temperature is lowered by the rapid heat exchange between the pig iron blocks and the high-temperature liquid slag. The iron block is cooled and solidified and wrapped and adhered to the furnace lining, so as to achieve the purpose of fast maintenance of the furnace lining.
4. Improve the slag retention operation of the converter
The slag retention operation of the converter means that after the slag splashing, not all slag is poured out, but a part of the slag with high temperature, high basicity and certain (FeO) content is reserved for the next furnace, which is conducive to the rapid slag formation of the next furnace and improves the effect and efficiency of the slag. , which is conducive to improving thermal efficiency, reducing slag-forming material consumption, reducing metal loss and slowing down the erosion of furnace lining. With the optimization of the slag splashing protection technology and the optimization and improvement of the top and bottom double blowing converter equipment, through the analysis of the root cause of the slag splashing, and the continuous exploration and improvement of preventive measures, the slag retention operation process has been gradually optimized and improved.
The final slag of the converter contains a certain ∑(FeO). When the slag is added to the molten iron in the next furnace, it will react with [C] in the molten iron, see equations (1) and (2); When the slag has a high oxidizing property and the content of FeO in the slag is greater than 20%, the two formulas may react at the same time, and the amount of gas generated increases instantaneously, and the operation control is difficult to cause an explosive splash accident.
(FeO)+[C]=[Fe]+CO
2(FeO)+[C]=2[Fe]+CO2
It can be seen from the above analysis that to control the instantaneous accumulation of gas in the furnace and slow down the reaction speed, the reactants in the formula, namely (FeO) and [C] contents, must be reduced. However, the content of [C] in the molten iron changed little, only the content of (FeO) in the slag was controlled when adding molten iron. Preventive measures: one is to reduce the final slag (FeO) content by controlling the time of the blowing end point of the gun, the timing of carbon pulling, increasing the bottom blowing flow, and reducing the oxidation of the slag [5]; the other is to add 1000 FeO before adding molten iron. ～1500kg lime is used to dilute and cool the final slag; at the same time, it is required that the total slag amount of the slag-retaining furnaces should not be too large, so as to avoid excessively high and fluctuating terminal temperature, reduce the content of final slag (FeO), and avoid or slow down formula (1), Equation (2) reacts at the same time to cause splashing.