This article introduces the main process parameters of the slag splashing and furnace protection technology for steelmaking converters and the problems encountered in practical applications in steel rolling mills. In order to stabilize the operation status of nitrogen splashing and improve the use accuracy, we independently innovated the slag splashing nitrogen intelligent management system technology, optimized the slag splashing process, shortened the slag splashing time, and reduced the slag splashing nitrogen consumption, reaching the domestic advanced level.
Keywords: slag splashing; furnace lining; nitrogen; slag hanging
Introduction
Converter slag splashing protection technology is a technology that has been used for many years to protect the converter and improve its age. Since the 1990s, my country has begun to develop converter slag splashing and furnace protection technology that adapts to national conditions. The slag splashing furnace protection technology is to spray high-pressure nitrogen through a spray gun, and the slag is sprayed through the outside of the holes in the injection impact area, and is adsorbed to the converter lining to form a slag layer. This can protect the furnace lining for the next furnace smelting. The final converter slag can not only meet the requirements of the smelting process, but also meet the conditions for slag splashing and furnace protection. That is to say, the slag should be easy to splash onto the furnace lining, and the slag splashed onto the furnace lining can be well combined with it. The splashed slag should have certain fire resistance and high temperature corrosion resistance. These three conditions are not only related to the main components of the slag, but also to the kinetic conditions of slag splashing. The slag splash layer formed by slag splashing has good corrosion resistance, can effectively inhibit the oxidation and decarburization of the furnace lining brick surface, and reduces the erosion and erosion of the furnace lining bricks by high-temperature slag to a certain extent, thus achieving the function of protecting the furnace lining bricks. Reduce the loss rate of refractory materials, reduce the consumption of gunning materials, reduce the labor intensity of workers, increase the service life of the furnace lining, improve the converter operation rate, and reduce production costs.
Important process parameters for slag splashing
Slag composition
Converters generally use magnesia carbon bricks as their linings. The key to reducing lining erosion is to increase the magnesium oxide content in the slag. When the magnesium oxide content in the slag is close to saturation, the dissolved amount of magnesium oxide in the furnace lining is very small, which increases the life of the furnace lining. The alkalinity of the slag is also an important factor affecting the magnesium oxide content in the slag. If the alkalinity of the final slag is about three, the magnesium oxide content can reach saturation at about eight percent. Therefore, the magnesium oxide content of various domestic external converter slag splashes is generally controlled at 8 to 14 percent.
The level of iron oxide content in the slag seriously affects the lining erosion and slag splashing effects. Most of the iron oxide minerals in the slag are low-melting-point ferrites, whose melting points are far lower than the tapping temperature. The higher the iron oxide content, the more ferrites there will be, and the better the fluidity of the slag will be. This results in increased corrosion of the furnace lining and difficulty in adhering to the furnace lining. If the iron oxide content in the slag is too low, it will be difficult to make slag in the converter and remove phosphorus and sulfur. Therefore, it is particularly important to strictly control the iron oxide content in the slag during operation.
Slag viscosity
If the slag viscosity is large, the slag will be thick and difficult to splash, and the amount of slag splashing will decrease. In order to maintain a sufficient amount of slag splashing, more impact energy must be consumed. In addition, thick slag has poor adhesion ability on the furnace lining, low viscosity and thin slag. Although it is easier to cover with splashed slag, the covering layer is relatively thin. Shaking furnaces will cause slag to fall off, and slag material should be added to adjust to ensure that the viscosity of the slag is moderate.
Slag adjusting agent
One of the important factors in the furnace protection effect is the corrosion resistance of the slag splash layer. If the corrosion resistance is poor, slag splashing operation needs to be performed in each furnace, which will not only increase the amount of nitrogen but also prolong the smelting cycle. Therefore, it is necessary to increase the melting temperature of slag to better improve the protective effect. For this reason, we add a slag conditioning agent to the slag to change the quality of the slag to meet the need to increase the melting temperature of the slag. The slag-adjusting agent can not only increase the melting point of slag splashing, but also make it easier to splash slag, thereby improving the dynamic conditions of slag splashing. The slag-conditioning agent can also produce dispersed solid particles in the slag to improve the bonding ability between the slag and the furnace lining.
Nitrogen pressure and flow
High-pressure nitrogen is the driving force for slag splashing, and its pressure and flow rate directly affect the slag splashing effect. Generally, better results can be achieved when the nitrogen pressure is close to the oxygen pressure. Since the nominal capacity of the converter is different, the nitrogen pressure and flow rate of slag splashing are different.
Slag splashing time
The slag splashing time is generally based on comprehensive considerations such as the furnace slag condition, the amount of slag in the furnace, tonnage, gas supply volume and production rhythm. The nitrogen blowing time of domestic steel plants is generally three to five minutes. The main purpose of blowing nitrogen is to provide power for slag splashing, and also to cool the slag for protection. The first two minutes of nitrogen blowing are mainly to cool the slag, because the slag is relatively thin during this period, and even if the filter slag is splashed on the furnace wall, the adhesion effect is not good. After blowing nitrogen for two minutes, a large amount of slag began to splash, and the splash level could reach the furnace cap. The slag hanging on the furnace lining was in good condition. In practice, we have found that the longer the slag splashing time is, the more slag will be stuck on the furnace lining. If the time is too long, too much slag will be stuck on both the furnace bottom and the molten pool wall, causing the furnace bottom to rise. Excessive slag splashing time will also affect the production rhythm and increase production costs. The slag splashing time must be finally determined based on actual production conditions.
Overview of production status
There are two 150t converters in the 150t furnace area of the steel rolling mill. Each converter adopts the technology of oxygen lance blowing nitrogen and slag splashing to protect the furnace. The slag splashing furnace protection technology is to retain part of the final slag in the furnace after tapping, and blow nitrogen into the furnace at high speed through the oxygen lance to splash the slag onto the furnace lining. The slag covers the furnace lining and forms an effective protective layer after cooling and solidification, thereby greatly reducing the use of gunning materials and increasing the age of the converter. The main functions of nitrogen in steelmaking production include slag splashing to protect the furnace, use as protective gas and gas source for pneumatic regulating valves, etc. Among them, slag splashing and furnace protection consumes the largest amount. The nitrogen consumption of each furnace for slag splashing is obtained by observing the on-site display instrument at the post to record the cumulative flow difference of oxygen lance nitrogen before and after slag splashing. It relies on manual recording and statistics at the post, and the accuracy is not high. The plant uses a database to record the nitrogen consumption of each furnace for slag splashing, and uses a program to automatically generate a production report including the start time of slag splashing, the duration of slag splashing and the consumption of slag splashing immediately after the end of each furnace to ensure the real-time nature of the data. , helps to strengthen nitrogen energy consumption management, collect the switching status of the nitrogen cut-off valve into the converter secondary system, determine the moment when the status of the cut-off valve changes through the converter secondary data acquisition program, and use this moment as the start/end of slag splashing Write to the database all the time. When the cut-off valve is opened, the cut-off valve status label changes from 0 to 1, and the system program records this moment as the start time of slag splashing; when the cut-off valve is closed, the cut-off valve status label changes from 1 to 0, and the system records this moment as the end of slag splashing. time. Rely on the secondary system of the converter to correlate the slag splashing event with the furnace smelting number based on the slag splashing time and the converter status at this time. Through the communication between the converter secondary system and the comprehensive secondary system, the slag splashing nitrogen blowing time and slag splashing nitrogen blowing amount of each heat are finally reflected in the heat report, realizing real-time monitoring and precise control of the converter slag splashing.
Conclusion
The steel rolling mill uses a slag splashing nitrogen intelligent management system. After the slag splashing is completed, the post personnel can query the slag splashing time and nitrogen consumption of the furnace. They can summarize the slag splashing process in a timely manner based on the data, which facilitates the post operators to improve the slag splashing process. The operation level has been optimized, the slag splashing process has been optimized, the slag splashing time has been shortened, and the nitrogen consumption of slag splashing has reached the domestic advanced level.