To prevent blowouts in converter steelmaking, the carbon-oxygen reaction in the furnace must be controlled first. During the blowing process, the oxygen supply intensity and gun position must be accurately controlled to avoid overly violent reactions. At the same time, close attention must be paid to the foamy slag in the furnace to prevent excessive slag and excessive foaming from causing blowouts. In addition, the raw materials must be prepared well to ensure the quality of the raw materials entering the furnace is stable and to avoid abnormal reactions caused by fluctuations in composition. The combined use of these measures can effectively reduce the risk of blowouts in converter steelmaking.
Factors that lead to large explosions in front of the furnace.
Splashing during blowing
Explosive splashing:
Explosive splashing:
It often occurs when batches of materials are added when the temperature of the molten pool is lowered, or when too much ore is added to the second or third batches.
Due to the decrease in the temperature of the molten pool, the decarburization reaction is suppressed, but the oxygen supply continues, and a large amount of iron oxide accumulates in the molten pool. Once the temperature rises, a violent carbon-oxygen reaction will occur, resulting in explosive splashing, that is, large spraying.
The explosive carbon-oxygen reaction is caused by the long hanging and blowing time, and then the gun is suddenly lowered; or because the amount of slag is too large, the slag foams, the furnace space is too small, and the CO gas discharge is blocked, which will form a large spray when it reaches a certain level.
In addition, when the furnace is small, the furnace temperature is low, and there is a lot of FeO in the slag when the furnace is new, it is easy to produce large spraying.
Metal splashing:
Metal splashing:
The slag is not well melted in the early stage, the second batch of materials is added too late and the slag is not melted or it dries up in the middle stage, which makes the slag unable to cover the metal liquid surface well. The oxygen flow pushes the slag to the furnace wall, and the stream directly impacts the metal liquid, causing part of the metal to be broken. In addition, the reflected airflow and CO gas push the metal splashing.
Sometimes, because the slag is too sticky and foamy, there are more metal droplets in the slag, and the slag is close to the furnace mouth. When a fierce carbon-oxygen reaction occurs, the metal droplets may be brought out of the furnace mouth, which will also cause metal splashing.
Foamy slag splashing:
Foamy slag splashing:
During the early stage of blowing, due to the low temperature of the molten pool, high FeO and acidic oxides (SiO2, P2O5) in the slag, and high slag viscosity, a large amount of foamy slag is easily formed to fill the entire furnace.
If the slag foams severely and the slag surface is close to the furnace mouth, the decarburization speed will increase slightly at this time, which may push the slag out of the furnace, causing foamy slag splashing.
Analysis shows that the explosive carbon-oxygen reaction in the molten pool and the instantaneous generation of a large amount of CO gas are the root cause of spattering.
The reason for the big explosion when adding iron or scrap steel
Reasons for large blowouts during iron addition:
The large blowouts during iron addition only occur during slag retention, because the carbon content in the steel is low at the end of converter blowing, which makes the oxygen content in the steel and slag oxidation high. During slag retention, more slag and a small amount of molten steel remain in the furnace. If the conditions remain unchanged, the carbon and oxygen in the steel are basically in equilibrium, and no violent carbon-oxygen reaction will occur.
If iron is added, the conditions in the furnace will change fundamentally. On the one hand, the iron will bring a lot of carbon, and on the other hand, the temperature of the iron will be low, which will cause the temperature of the residual slag and molten steel in the furnace to drop suddenly. These two conditions promote the violent carbon-oxygen reaction, and the furnace will boil violently, which will cause “explosive” blowouts.
Reasons for the final furnace blowout:
① The post-blowing time is long or due to improper operation, the furnace is still reacting violently, causing a large amount of slag to surge out and form splashes.
② The filling charge is not firmly bonded, and it suddenly collapses when the furnace is tilted, causing violent outflow and splashing of slag.
③ The furnace lining collapses in a large area during steel tapping or iron addition.
Reasons for the large steel spray during return to the furnace:
Residual steel is commonly returned to the furnace in the steelmaking system, but if it is not done properly, it will cause a large splash, posing a huge threat to personal safety. Therefore, it is necessary to explore its causes:
After steel is tapped, when the molten steel composition or temperature is unqualified or it cannot be poured due to equipment failure, the molten steel will be returned to the furnace for re-smelting, which is a return accident.
From the perspective of the process system, the amount of molten steel returned to the furnace is generally less than 1/2 of the total loading amount. At the same time, the oxygen in the returned molten steel reacts with the carbon in the molten iron, and the molten iron (steel) is added to the furnace to stir, which can easily cause a violent reaction of C-O and cause splashing accidents. Therefore, when returning to the furnace, the molten steel (iron) should be added slowly, or the returned molten steel should be deoxidized and then slowly added.
Countermeasures to prevent converter splash damage:
Based on the analysis of typical accidents and the causes of large blowouts in the converter system, the following measures to prevent injuries from large blowouts are established.
Prevention of large blowout injuries during blowing: Improving operating standards and reducing the probability of large blowouts during blowing are the fundamental ways to prevent large blowout injuries.
Control the temperature of the molten pool
The temperature in the early stage should not be too low, and the temperature in the middle and late stages should not be too high, so as to prevent the temperature of the molten pool from dropping suddenly, ensure that the decarburization reaction can proceed evenly, and eliminate the explosive decarburization reaction.
Control the iron oxide in the slag
In the early stage, the iron oxide content in the slag should not be too high. In this way, it should not be operated too early, otherwise, due to the gun being raised too high, the iron oxide in the slag will accumulate too much, the slag will foam, and once the temperature rises, the decarburization reaction will accelerate, which will inevitably cause a large explosion. When the slag has melted, the gun must be lowered to reduce the iron oxide in the slag. In the middle stage, it is necessary to prevent the gun from being lowered too low to cause the slag to dry out and cause metal splashing.
When the slag is not melted and the gun is lifted to melt the slag, do not blow oxygen at the high gun position for a long time, otherwise, once the slag is melted, the iron oxide will increase greatly, causing splashing. Once splashing occurs, the gun cannot be lowered immediately. If the gun is lowered at this time, the decarburization reaction will be more intense, which will intensify the splashing. At this time, the gun can be properly raised. On the one hand, it will slow down the decarburization reaction. On the other hand, the mechanical impact force of the oxygen stream will impact the slag, so that the gas will be discharged and the degree of slag foaming will be reduced.
If it is metal splashing, the gun can be properly raised to increase the iron oxide in the slag, and an appropriate amount of fluorite can be added to make the slag melt quickly and cover the steel liquid surface.
It is strictly forbidden to work under the furnace during the refining process.
During the blowing process, the fire-blocking door should be closed, the steel outlet should be blocked, and no people are allowed to pass in front of or behind the furnace.
