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Converter steelmaking process control and slagging system optimization

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Converter steelmaking is an efficient steelmaking technology commonly used by steel companies. This article will comprehensively elaborate on the optimization strategy of converter steelmaking process control and slagging system.

Keywords: converter steelmaking; process control; slagging system; optimization strategy

In recent years, the domestic steel trading market has been extremely hot, and the demand for steel products in various fields of society has been increasing day by day. At the same time, the state and relevant industry departments have increasingly higher requirements for energy conservation and environmental protection in the steelmaking production process. If we use steelmaking process information to optimize various technical indicators and slagging systems of the entire smelting process, so that product quality meets standard requirements and complete ecological benefit indicators, it has become an urgent problem that steel production enterprises need to face and solve.

Automatic control system for converter steelmaking

According to statistical data, more than 80% of my country’s steel products come from the converter steelmaking production process, and this data is constantly being refreshed. It can be seen that converter steelmaking has become a leading technology in the field of steel production. With the improvement of converter steelmaking automation technology, the process control methods used in some large-tonnage converters of my country’s steel companies have all realized automatic control. From the perspective of system structure, converter steelmaking includes the converter body, one-time dust removal device, bulk materials, argon blowing station, circulating water pump room, secondary dust removal device, etc. The technical principle of the production process is: when the oxygen blowing temperature reaches 1700°C, molten steel will flow out of the ladle after the converter, and then nitrogen will be blown into the converter. After the molten steel is poured into the ladle, alloy elements are used to adjust the composition of the molten steel. At this time, the converter flue gas is discharged through two dust removal systems. The primary dust removal system draws air from the converter hood with the help of a high-pressure fan. The secondary dust removal system draws out the flue gas poured into the molten steel from the converter by the crane under the action of the high-pressure fan.

The automatic control system can monitor the entire process of steelmaking and ironmaking, and accurately locate, record, analyze, and detect various data indicators in the production process, which greatly reduces manual operations. The automatic control system mainly consists of process control computers, microcomputers, automatic detectors, electronic weighing devices, etc., while the auxiliary systems include oxygen supply systems, raw material systems, and gas recovery systems. These systems and devices are managed and controlled by computers.

Converter steelmaking process control method

The working principle of the converter steelmaking automatic control system is relatively complex, and dynamic detection methods also include many types. The most common ones are the secondary gun detection method, furnace gas analysis and audio slag detection method. Through dynamic detection, accurate data is obtained, and the computer system analyzes, compares and filters these data. It is displayed in the computer system in the form of a mathematical model, and then the mathematical model is simulated according to the designed program instructions, and the most optimized control method is determined and selected through the simulated image.

At present, converter steelmaking process control mainly includes two methods: fixed-point control and full-process control. Fixed-point control mainly selects a certain moment before reaching the blowing point, and uses detection equipment to detect the composition and temperature of molten steel in the molten pool. Then the test results are compared with the target composition and temperature of the molten steel at the end of blowing, and the steelmaking production process is adjusted to promote the improvement of production efficiency. Compared with fixed-point control, the full-process control law is more efficient and practical. This method mainly uses the feedback information of the system to analyze and calculate, and then optimizes and adjusts the production process based on the calculation result data. Through full-process control, technicians can obtain data indicators for each production link of steelmaking production and master data information on every change process of molten steel. Then formulate the most optimized rectification plan, which will help improve product quality and will also play a positive role in promoting the company’s goal of maximizing economic benefits.

Converter steelmaking process control optimization strategy

When steel products are smelted using the converter steelmaking process, there are many uncontrollable variables in the production process. For example, oxygen flow, oxygen gun position, input method of auxiliary materials, etc. These variables can easily have an adverse impact on the automatic control effect. When applying one-click steelmaking automation control technology, some data indicators of the steelmaking process are easy to change. , thereby reducing product quality and affecting production efficiency per unit time. Therefore, effective optimization measures should be taken for the variables existing in process control to achieve the purpose of maintaining quality, quantity, and efficiency.

(1) Optimization strategy of oxygen flow

During the operation of the converter equipment, sufficient oxygen needs to be blown into the converter, but the demand for oxygen in each steelmaking process is quite different. For example, in the decarburization, desulfurization, and dephosphorization processes of molten steel, due to the complexity of the process and the long time required, a large amount of oxygen needs to be supplied so that the oxygen can effectively remove impurities in the molten steel. If oxygen is supplied blindly and the oxygen supply exceeds the standard range, the excess oxygen will react chemically with the precious metal alloy in the molten steel, thereby reducing the quality of the product. Therefore, when controlling the oxygen flow, two aspects should be considered comprehensively. One is to make full use of oxygen and try to ensure that there is no remaining oxygen. The second is to reduce the oxidation loss of precious metals to ensure product quality and achieve cost savings.

2) Accurately control the oxygen gun position

The height of the oxygen lance directly determines the quality of the product. Different heights will also have different effects on the molten steel. Although many steel companies attach great importance to this issue and have developed standard operating modes, many problems are still exposed in practical applications depending on the uncertainty of location. For example, in actual operation, the gun positions of oxygen lances are usually divided into high-low-high, high-low-high-low, low-high-low-high-low and other modes. Which gun position a steel company chooses depends on The smelting requirements of the converter are directly related to the oxygen demand at different stages. Therefore, steel companies should reasonably adjust the height of the oxygen lance based on the actual production. In order to effectively control the position of the oxygen lance, a furnace condition information collector can be installed on the oxygen lance. Technicians use the data information collected by the collector to compare it with the standard values in the database, and then formulate scientific optimization and adjustment plans based on the comparison results so that the gun position of the oxygen gun is always in the standard position.

(3) Material delivery control

Material placement is a key process in the steelmaking production process. First of all, the material ratio should be considered. If the ratio is unbalanced, the quality of molten steel will be seriously affected. Secondly, when materials are put in, the amount of material discharged from the initial silo and the amount of slag-forming agent should be effectively controlled, and the monitoring device should be used to monitor the slag condition information in the converter in real time. Before placing materials, operators should refer to standard requirements so that the materials placed can reach the optimal value, so as to ensure that the quality of molten steel is not affected. Finally, when placing the slag-forming agent, the amount and time of the slag-forming agent should be reasonably controlled. During this period, the operator should use the feedback information from the monitoring system to compare it with the mathematical model formed by the system, and adjust the feeding time and dosage based on the comparison results.

Optimization strategy of slagging system

(1) Reduce the amount of slagging materials used

In order to improve the slag retention rate in the furnace, some large domestic steel production companies have successively adopted a series of optimization strategies for the slagging system. One of the most commonly used optimization methods is to reduce the use of slag-making materials. This method can not only reduce production costs and ensure the slag retention rate, but also speed up desulfurization, decarburization, and dephosphorization, which can have a positive effect on improving the quality of molten steel. According to field experimental data, by reducing the use of slagging materials, the phosphorus element content in the molten steel is far less than 0.035%, accounting for more than 95%, so this method has attracted relatively high attention.

(2) Optimize slag formation conditions and formulate safe operating procedures

In order to increase the amount of slag retained, steel production enterprises can optimize the slag forming conditions, formulate standardized and normalized slag retaining operation processes and a complete slag making system. In order to standardize the personal behavior of workers and enable workers to establish a high degree of owner responsibility and safety awareness, steel companies can formulate highly targeted and practical safety operating procedures based on every link and operation step of steelmaking production. Prevent operators from making human errors during actual operations. When formulating the slag-making system, technical personnel should participate in the system preparation process and combine their own work experience and professional and technical standards to establish a slag retention rate target that is consistent with the actual development of the enterprise. For example, some companies set the target of slag retention rate at more than 60%. In steelmaking production, all employees can combine this target and strictly abide by the operating specifications.

In addition, technicians should be proficient in the internal structure of the converter equipment and various functions of the automatic control system, and improve the oxygen lance nozzle based on the structural characteristics of the converter. To reduce the oxygen supply intensity in the converter and expand the contact area of oxygen in the furnace, this can effectively prevent the occurrence of splashing and back-drying. This new oxygen supply method can not only improve the decarbonization and desulfurization efficiency of molten steel, but also reduce the consumption of precious metals in molten steel, thus saving a lot of production costs for enterprises.

(3) Use solid granular slag

In order to further optimize the converter slag-making process, steel companies can use solid granular slag to increase the early slag-making speed. After this solid granular slag enters the furnace, it can effectively adjust the temperature in the furnace to meet the needs of steelmaking production. The specific operation process is: during the production process, approximately 200kg of solid granular slag is first blown into the converter for 3-5 minutes. It should be noted that converters with different volumes have different amounts of additives. These solid granular slags can be used as return slag after entering the furnace body, which can promote the rapid formation of early slag. In the middle and late stages of steelmaking production, adding an appropriate amount of solid granular slag into the furnace can adjust the temperature of the molten steel in the furnace and save a large amount of raw ore materials and auxiliary materials such as lime. In addition, in order to prevent the occurrence of molten steel splashing accidents, operators need to control the end temperature during slag making.

(4) Increase follow-up inspection efforts

Although steelmaking production automation control technology has become increasingly sophisticated, in order to prevent accidents during the production process, technicians should clarify their management and supervision responsibilities, regularly inspect smelting raw materials, and control the slag results from the source. For example, when solid granulated slag agents and lime slag agents are added to the furnace, technicians should carefully check the quality of these slag agents, track and investigate the source of the slag agents, and record the usage of the slag agents. When testing whether the quality of lime slag agent is qualified, the hydration test method can be used to determine the quality of lime. If it is found that the quality curve fluctuates greatly, the test results should be fed back to the superior leader in a timely manner, and the relevant responsible persons should be dealt with seriously. In addition, in order to improve the professional and technical level of technicians and make them proficient in the principles of slag making and converter working principles. Iron and steel enterprises should establish and improve internal education and training systems, and formulate timely and feasible monthly, quarterly, and annual training plans. Through training, they can enhance the sense of responsibility of managers at all levels and field operators to create more economic benefits for the enterprise.

Conclusion

Optimizing the converter steelmaking process control and slagging system is an important measure for steel companies to standardize management and operate efficiently, and it is also an effective path for companies to achieve economic benefit indicators. As the market competition situation becomes increasingly severe, steel production enterprises should take precautions, prepare ahead of time, and promote the long-term development of enterprises by formulating scientific and accurate process control and slagging system optimization strategies.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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