This article mainly analyzes the practical application of converter slag-less smelting technology and discusses the practical process of converter slag-less smelting and slag thermal recycling. Specifically, it can be divided into two links, decarburization and slag retention in steel tapping, and mid-smelting dephosphorization and slag retention, as well as decarburization and tapping slag retention are carried out simultaneously. The smelting process of decarburization and slag retention mainly refers to controlling the slag pouring and slag adjustment processes after tapping, so as to suppress the early blowing splash caused by the slag retention.
Keywords: converter steelmaking; slag-less smelting technology; practical research
For steelmaking plants, achieving high efficiency, low cost and low emissions of related steelmaking technologies are their main development goals. With the rapid development of science and technology, converter slag-less smelting technology has also been proposed, which is also the slag-less steelmaking process technology. In the past, slag-less smelting technology mainly referred to the application of three-removal technology through molten iron pretreatment, thereby removing the load of harmful substances and reducing the amount of converter slag. The low-slag smelting technology described in this article is also obviously different. From a thermodynamic perspective, there is a certain contradiction between dephosphorization and decarburization.
Basic technical ideas
Meishan Iron and Steel does not have the dephosphorization function without molten iron pretreatment, and its main dephosphorization task is concentrated in the converter. According to the degree of difficulty, the slag-less smelting technology can be divided into two links. The first is slag-retaining smelting, which can effectively realize the function of the series decarburization furnace and utilize the remaining beneficial slag iron. In the second stage, it is a “slag + double slag” smelting process. The slag remaining steel from the dephosphorization furnace and the decarburization furnace can be effectively utilized at different times in the same furnace. In this process, the focus is to effectively improve the dephosphorization rate and early slag discharge rate before the converter, while also reducing splashing during the process. The phosphorus content in Mei’s steel water can reach 0.12% to 0.16%. Before low-slag smelting, the average lime consumption is mainly per ton of steel, its weight is 55.8kg, and the amount of slag per ton of steel is about 125kg. During the slag-retaining smelting process, the consumption of lime per ton of steel can be reduced by 28.6%. During the “retaining slag + double slag” test process, the alkalinity and total iron of the slag before the converter can be controlled, and the appropriate pouring point and temperature of the dephosphorized slag can be selected to effectively ensure the dephosphorization of the early slag. and foaming. When the dephosphorization rate of the former is greater than 60%, its slag discharge rate will be greater than 50%. Therefore, by applying the “slag retention + double slag” technology, the consumption of lime per ton of steel can be effectively reduced.
Experiments
Retaining slag smelting
The specific process of converter slag smelting is mainly as follows: pouring slag after tapping, protecting the furnace from splashing slag, and then carrying out slag adjustment treatment, then adding scrap steel and molten iron to it, and blowing down the gun before tapping. Refining. The smelting process of slag retention requires the utilization of decarburized slag, which is mainly iron oxide and calcium oxide from the previous furnace, which can reduce the consumption of steel materials and auxiliary materials. At the same time, it can also promote the rapid formation of early stage slag in the next furnace, thereby realizing the early stage dephosphorization process. However, during this process, it is necessary to control the oxidation, temperature and flow state of the slag before adding iron, otherwise it will easily cause splashing. Starting from the perspective of enterprise experience and combining with production practice, the operation process of slag retention can be clarified, which can achieve safe iron mixing and prevent the splash and amount of slag retention in the converter that occurs in the early stage of the converter due to slag retention under the current conditions. and effectively resolve related issues.
When pouring slag after tapping, it is necessary to add corresponding weighing equipment to the steel slag tank. At the same time, it is also necessary to set up a corresponding slag tube weight indicator on the converter shaking table to take advantage of the good fluidity of the converter final slag. , so that 30% to 50% of the total slag amount can be accurately removed, and the remaining slag needs to be left in the converter. At the same time, the converter material and heat balance can also be accurately calculated, thereby providing a basis for the converter smelting control process. During the slag retention test phase, it is necessary to carry out slag adjustment work. At the end of the slag splashing and furnace protection operation, relevant limestone slag adjustment is added to the converter, and a slag splashing gun is used for stirring, so that it can be mixed with the remaining slag. The waste heat of the slag can effectively roast limestone or raw dolomite, thereby reducing the slag temperature and thickening the slag. It can also play a role in solidifying the slag, thereby reducing the use of related reducing substances, and there is no need to carry out specific modifications to the slag. sexual processing.
“Retaining slag + double slag” smelting
The specific steps of the “slag-retaining + double-slag” smelting process of Meishan Iron and Steel’s converter are: first, slag-retaining treatment is required, and then relevant scrap steel is added and mixed with molten iron. After desiliconization and dephosphorization treatment in the converter, slag can be discharged. After decarburization and heating up, the converter can be tapped, and then the converter slag smelting process can be repeated to form a cycle so that the decarburization slag and dephosphorization slag can be fully utilized. In the specific smelting process, excess phosphorus in the molten steel can be removed first through blowing, and semi-steel with lower phosphorus content can be obtained after slag pouring. In the second stage of blowing, the pressure is reduced during dephosphorization, which can better achieve the goal of smelting with less slag volume. For this reason, relevant test personnel need to increase the dephosphorization rate in the first stage, select the appropriate time to carry out furnace slag discharge, and effectively control the slag discharge rate, thereby further ensuring the slag amount during the decarburization period. During the early stage of smelting in the converter, smelting treatments such as desiliconization and dephosphorization are required. For the control of gun positions, it is usually necessary to maintain the order of gun positions from high to low, and then from low to high. The oxygen supply during desiliconization and dephosphorization needs to be controlled to 30% of the total oxygen supply for the smelting furnace. At the same time, it is also necessary to control the initial slag alkalinity, iron oxide content, and temperature at the end of the dephosphorization stage. Through specific production practice, it can be found that by effectively controlling the composition and temperature of the slag in the early stage, the dephosphorization rate of the slag can be further guaranteed to reach more than 60%. When selecting the furnace downturn point, it is necessary to control the oxygen supply for desiliconization and dephosphorization to keep it within the range of 26% to 34% of the total oxygen supply for the smelting heat. This is mainly calculated based on relevant requirements. the resulting range. When the blowing time is relatively short, the relevant requirements for dephosphorization rate cannot be effectively met. When the blowing time is extended, the temperature of the molten pool will increase, which will affect the early dephosphorization rate. At the same time, when the furnace is turned over and slag discharged, violent boiling will occur in the furnace, which will increase the amount of iron in the slag. During the early slag discharge process, the furnace should be shaken in front of the converter during the desiliconization and dephosphorization smelting period, and the foaming status of the slag should be observed. If the slag is in good foaming condition, it can be directly discharged. But if the foaming situation is relatively poor, a foaming agent should be added to it.
Test results
In the specific steelmaking process, advanced technology has been effectively applied, the dephosphorization furnace and the decarburization furnace have been effectively separated, and the main task characteristics of the converter smelting have been controlled, which allows the original converter smelting to pass The two converters are operated in series. The dephosphorization furnace semi-steel is used for secondary use in the decarburization furnace, and the slag produced by the decarburization furnace can be used in the dephosphorization furnace to achieve the realization of molten steel and slag. to the transfer process, thereby making the division of labor more efficient and refined. In the converter staged smelting process, manganese ore and other related substances can be used in specific decarburization converter operations, thereby reducing alloy consumption and saving production costs. Decarburized converter slag can also be used as a specific dephosphorization agent, thereby reducing production costs and ensuring rational use of resources.
Nowadays, the process of less-slag smelting technology has been simplified again, and the relevant single-furnace slag circulation method has been adopted. The dephosphorization and decarburization processes can be connected in series in the same converter, while the molten steel and slag do not have any substances to transfer. However, The composition and amount of slag need to be precisely controlled, which can reduce the investment in series equipment. Based on the single-furnace slag circulation method, the less-slag steelmaking technology has the related characteristics of low blowing damage and low consumption of low-level slag, which can effectively reduce costs. The “retaining slag + double slag” smelting on the converter can specifically divide the smelting of one furnace of steel into two blowing stages. In the first stage, desiliconization and dephosphorization are mainly carried out, while in the second stage, desiliconization and dephosphorization are mainly carried out. Carbon heats up. After the desiliconization and dephosphorization period is completed, the silica containing higher content can be poured out to achieve the dephosphorization effect. For the remaining early slag and decarburization stage in the furnace, relevant auxiliary materials can be added to form a specific decarburization slag. When steel tapping is completed, the decarburized slag can be left in the furnace to be used in the decarburization and dephosphorization steps of the next furnace, allowing the converter slag to be recycled and reduce the consumption of auxiliary materials.
Smelting effect of slag retention
At the specific relevant stage, it is necessary to make a specific comparison between the relevant index parameters of slag-retaining smelting and conventional smelting heats. In the slag-retaining smelting of the Meishan Iron and Steel converter in this article, phenomena such as iron splashing did not occur. Compared with the conventional smelting process, the consumption of lime, steel materials, etc. per ton of steel in the slag-retaining smelting process has been reduced, and the consumption of lime and steel materials per ton of steel in the slag-retaining smelting process has been reduced. There is no significant difference in the oxygen consumption of steel. During the converter end point control process, the levels of related indicators such as alkalinity are basically consistent. When reducing the amount of converter auxiliary materials, the dephosphorization rate did not change, which shows that the utilization rate of converter lime has been effectively improved when slag-retaining smelting reduced lime consumption. At the same time, smelting with slag retention can also reduce the consumption of auxiliary materials, but in fact, when smelting alone, the total slag amount does not show a downward trend.
“Retaining slag + double slag” smelting effect
Select a certain time period and compare some indicators of the “slag + double slag” smelting heat with conventional smelting heats. According to the comparison results, it can be found that “retaining slag + double slag” can reduce the consumption of lime when smelting tons of steel. During the converter end point control process, the levels of alkalinity and other indicators remain basically the same, but “retaining slag + The “double slag” process will have a corresponding impact on the control of residual manganese in molten steel, which will be lower than the normal process. When the “retaining slag + double slag” smelting process reduces converter auxiliary materials, the downward trend in steel material consumption is not obvious. This is mainly due to the occurrence of splashing during the specific process. The smelting splash rate of “retaining slag + double slag” is relatively large, and when analyzed from the perspective of auxiliary material consumption, it can truly achieve the goal of less slag smelting, and by controlling the consumption of steel materials and the smelting ratio, it can further Improve economic efficiency.
Conclusion
(1) The slag-less smelting process is in the process of specific practical exploration. It has mainly experienced two periods: slag-retaining smelting and “slag-retaining + double slag” smelting. At present, relevant enterprises are working hard to increase the proportion of “retained slag + double slag” smelting, which accounts for about 30%.
(2) Slag-retaining smelting can effectively control related processes such as slag pouring, slag adjustment, and smelting, thereby further ensuring the safety of the slag-retaining iron mixing process and effectively reducing the consumption of converter auxiliary materials and steel materials.
(3) “Slag retention + double slag” smelting can control the early smelting of the converter, the selection of the furnace turning point, and the early slag discharge and other related processes, thereby effectively improving the early dephosphorization rate and enabling the slag discharge rate to reach more than 50%, and This greatly reduces the consumption of converter auxiliary materials and effectively reduces the consumption of related steel materials.
(4) “Retaining slag + double slag” smelting has achieved preliminary results in specific practice, but it is necessary to effectively explore related issues such as splashing during the smelting process, low residual manganese content in the molten steel, and the easy foaming of early slag in the slag tank. , thereby effectively increasing the smelting ratio and recycling rate, further enhancing the economic benefits of the enterprise.