Adequate stirring of the converter can provide good molten pool dynamic conditions, thereby increasing the speed and area of gas stirring of molten steel, reducing weak flow areas, and shortening the mixing time of the converter molten pool.
The blowing method and bottom blowing process of the converter have an impact on the gas flow speed, blowing area, and mixing time.
Study on the Effect of Spraying Method on the Flow Characteristics of Molten Pool
The blowing methods of the converter include top blowing, bottom blowing, top and bottom combined blowing, and top and bottom combined blowing plus side blowing. Different blowing methods have different molten pool mixing effects.
In the study of a 300 t top and bottom combined blowing converter in a steel plant, only the structure of the top blowing oxygen gun was optimized by mathematical formula calculation, and the mixing time of the molten pool can be reduced by up to 6 s, and the mixing time of the pure top blowing converter is 108~126 s;
On the basis of top blowing, after increasing the flow rate of bottom blowing from 0.04 m2/(t.min) to 0.2m3/(t.min), the mixing time of the molten pool can be reduced by nearly 50 s, and the mixing time after top and bottom combined blowing is 37~88s.
The study of the 80t top and bottom combined blowing converter shows that the mixing time of the molten pool of the top and bottom combined blowing converter is 25s shorter than that of the pure top blowing converter.
Physical simulation shows that when the 200 t converter has only pure bottom blowing, the mixing time of the converter is as low as about 27s by optimizing the bottom blowing process, while the mixing time of the converter can be reduced to about 22s when the top and bottom combined blowing is used.
It can be seen that bottom blowing has a more obvious effect on shortening the mixing time of the molten pool, but since the bottom blowing nozzle is affected by high pressure, high temperature and high impact force, improving the life of the bottom blowing nozzle is one of the problems that the converter urgently needs to solve.
After adding a side blowing gun to the simulated 30 and 100 t top and bottom combined blowing converters, the mixing time of the molten pool is reduced by an average of 60% compared with the original top and bottom combined blowing converter. Through the water simulation test method, after adding a side gun to the top and bottom combined blowing converter for side blowing, the mixing time of the molten pool was reduced by 15~18 s.
Study on the Effect of Oxygen Lance Structure and Oxygen Supply System on the Flow Characteristics of Molten Pool
The top blowing of the converter is that oxygen passes through the oxygen lance and impacts the surface of the molten pool, causing the molten pool to move and forming a molten pool pit with a certain depth and diameter. Since the oxygen lance of the Laval nozzle has the advantages of fast jet speed, stable jet and strong penetration ability, the molten pool is stirred well, the oxygen lance of the general converter uses the Laval nozzle. Its structure and oxygen supply system have an important influence on the stirring effect, impact depth and impact diameter of the molten pool.
Literature research shows that the mixing time is proportional to the top blowing flow rate and inversely proportional to the oxygen lance position, but both have critical values.
Water model research on combined-blowing converters shows that the flow rate of top-blowing gas has the greatest impact on the mixing time.
Research on combined-blowing converters shows that the critical value of the top-blowing flow rate on the mixing time of the molten pool is 78.94 m3/h. After exceeding the critical value, as the top-blowing flow rate increases, the mixing time of the molten pool decreases slowly.
Water simulation tests on 100 t converters show that when the lance position is 1.7 m, the minimum mixing time of the molten pool is about 23 s.
In addition, when the number of oxygen lances increases from 4 to 5, the mixing time of the molten pool increases by about 30 s.
Research on 300 t combined-blowing converters shows that when the Mach number of the oxygen lance is 2.10, the impact radius and impact area of the oxygen jet on the molten pool are the largest.
In recent years, some scholars have studied the dual-structure oxygen lance, staggered the oxygen lances on different circumferences, and designed the two groups of nozzles with different inclination angles, throat diameters and outlet diameters.
The study of the dual-structure oxygen lance structure of the 260 t combined blowing converter shows that with the same nozzle flow rate, the impact depth of the dual-oxygen lance structure is increased by up to 17.5% compared with the traditional oxygen lance, and the width of the impact pit is increased by at least 1.6%;
Research on the effect of bottom blowing process on the flow characteristics of the molten pool
In order to optimize the dynamic conditions of the converter molten pool, many scholars have studied the influence of the converter bottom blowing process on the converter flow characteristics.
Bottom blowing flow rate.
The bottom blowing flow rate is inversely proportional to the mixing time of the molten pool, but if the bottom blowing flow rate is too large, the energy carried by the bottom blowing gas will shake the molten pool and produce liquid splashing. Therefore, reasonable energy input is an important condition for achieving stable and efficient smelting in the converter. The range of the bottom blowing flow rate studied is generally: 0.02 ~ 0.35m2/<t. min).
Bottom blowing gas supply method.
There are two types of bottom blowing gas supply methods: uniform and non-uniform. Studies have shown that adopting a non-uniform gas supply mode can effectively avoid the deterioration of the converter dynamic conditions caused by the blockage of some bottom blowing components. The research results show that the mixing time of non-uniform gas supply can be reduced by up to 51.5%.
Number of bottom blowing elements.
Some researchers believe that more bottom blowing elements can reduce the mixing time of the molten pool. For example, in the study of a 200 t combined blowing converter, the mixing time of 8 to 12 bottom blowing elements was 6 to 11 seconds less than that of 4 bottom blowing elements, and the mixing time of pure bottom blowing in physical simulation was 14 to 49 seconds.
Some scholars conducted water simulation tests and showed that when a 300 t converter uses 8 bottom blowing elements, the shortest mixing time of the molten pool is about 23 seconds. Some scholars believe that a small number of bottom blowing elements can increase the flow rate of a single bottom blowing element, thereby promoting faster mixing of the converter molten pool.
Layout of bottom blowing elements.
The layout of bottom blowing elements includes layout radius, angle and arrangement. Literature shows that the layout of bottom blowing elements of converters of different tonnages is: radius within 0.30D~0.55D, angle 25°~60°, and arrangement is asymmetric and symmetric.
Studies have shown that the mixing effect of asymmetric arrangement is better than that of circular symmetric arrangement.
From the above analysis, it can be seen that the bottom blowing of the converter has a good stirring effect. In addition to being able to couple with the bottom blowing to form an obvious horizontal flow to optimize the flow field of the molten pool, the top blowing oxygen also has a better slag-removing ability, so the advantages of the top and bottom combined blowing converter in smelting high-quality steel are more obvious.
However, the nozzle of the bottom blowing element of the converter has a low lifespan. It is necessary to develop a bottom blowing nozzle material that is resistant to high temperature, corrosion, and impact, to provide technical guidance for further improving the bottom blowing efficiency of the converter.
