This article introduces the principles, classification and industrial application research progress of converter secondary combustion oxygen lance, and conducts in-depth research on secondary combustion oxygen lance technology. The research results show that when the scrap ratio of a single converter using secondary combustion oxygen lance and heat supplement reaches 41.6%, the end temperature of the converter can reach 1598°C, and the dephosphorization rate is 92.9%; compared with the dual-channel secondary combustion oxygen lance, In comparison, the single-channel secondary combustion oxygen lance only needs to replace the ordinary oxygen lance nozzle with the secondary combustion oxygen lance nozzle. There is no need to modify the original gun body. It has the advantages of simple structure, low investment and quick results, and is suitable for large-scale use. Production promotion and application.
Keywords: converter; secondary combustion oxygen lance; scrap ratio
As one of the raw materials for steelmaking, scrap steel is a green energy-carrying resource that can be recycled indefinitely. The scrap ratio of steelmaking in my country is still far behind that of developed countries. With the advancement of my country’s carbon peak work, major steel companies are vigorously increasing the scrap ratio. At present, the proportion of electric furnace steel in my country is less than 10%. The converter process is still the main process of steel production in China, and the cost advantage of adding scrap steel in the converter process is obviously ahead of the electric furnace. The methods commonly used in the converter to increase the scrap ratio mainly include scrap preheating (ladle preheating, preheating before and after the converter, alloy preheating, etc.) and adding heat supplements to the converter (coke, coke, FeSi, SiC, etc. ), but both technologies have certain shortcomings: the former requires specialized heating equipment, and the latter often comes at the expense of the quality of molten steel. Therefore, it is necessary to develop efficient and clean converter processes to improve the scrap ratio technology.
The converter secondary combustion oxygen lance technology is a clean heat compensation technology that replenishes heat without polluting the molten steel. In 1970, Shepherd first proposed the concept of a dual-flow channel secondary combustion oxygen lance. In 1978, Luxembourg-based ARBED completed the first industrial application test study of a dual-channel secondary combustion oxygen lance. In 1983, the Iron and Steel Research Institute was the first in China to conduct a thermal simulation test of a dual-channel secondary combustion oxygen lance. Since then, Shougang, Panzhihua Iron and Steel, Anshan Iron and Steel and Nanjing Steel Works have cooperated with scientific research institutions and colleges and universities to carry out secondary combustion oxygen lance testing. Extensive research was conducted. Although a lot of research has been conducted on converter secondary combustion oxygen lance technology at home and abroad, and some have reached the level of industrial application, there are currently few reports on the large-scale application of this technology in large-scale industrial production. This article elaborates on the principles, classification and industrial application research progress of converter secondary combustion oxygen lances, conducts in-depth research on secondary combustion oxygen lance technology, and provides a theoretical basis for the large-scale application of this technology in large-scale production.
Principle and classification of converter secondary combustion oxygen lance
Principle of converter secondary combustion oxygen lance
The converter secondary combustion oxygen lance is based on the traditional steelmaking oxygen lance. Through reasonably designed auxiliary holes, the oxygen jet ejected from the main hole undergoes a decarburization reaction. The oxygen jet ejected from the auxiliary hole is used to burn a large amount of carbon monoxide in the furnace to produce a large amount of carbon monoxide. The heat of the converter can be fully utilized, thereby increasing the scrap ratio of the converter. The secondary combustion in the converter is a complex unsteady multi-phase reaction, which is related to the shape of the oxygen stream, the decarbonization reaction and the balance of the combustion of carbon monoxide into carbon dioxide. Figure 1 is a schematic diagram of the secondary combustion oxygen lance principle.
Fig. 1 Principle Schematic Diagram forSecondary Combustion Oxygen Lance
Classification of converter secondary combustion oxygen lances
The converter secondary combustion oxygen lance is divided into two types: double flow channel and single flow channel oxygen lance.
Double-channel secondary combustion oxygen lance
The characteristic of the double-channel secondary combustion oxygen lance is that the main and auxiliary oxygen holes are controlled by independent oxygen channels. The oxygen flow and oxygen pressure of the main oxygen flow and the auxiliary oxygen flow can be controlled separately in different smelting periods. The oxygen stream ejected from the main hole is mainly used for decarburization and stirring the molten pool, while the oxygen stream ejected from the secondary hole is mainly used for secondary combustion of carbon monoxide and heat release. Figure 2 is a schematic diagram of a typical dual-channel secondary combustion oxygen lance nozzle. The gun body is composed of four layers of steel pipes. The innermost layer is the main oxygen flow channel, the second inner layer is the auxiliary oxygen flow channel, and the third layer is the cooling water inlet. Water pipe, the outermost layer is the cooling water return pipe. The auxiliary oxygen hole is about 1 m above the main oxygen hole. The installation and manufacturing of the gun head are relatively complicated and the cost is high.
Fig. 2 Schematic Diagram for Nozzles of TypicalDouble Channel SecondaryCombustion Oxygen Lance
Figure 3 is a schematic diagram of a simple structure double-channel secondary combustion oxygen lance nozzle. Compared with the typical dual-channel secondary combustion oxygen lance nozzle shown in Figure 2, the secondary hole stream of this nozzle can still independently control the flow rate, but the secondary hole and the main hole are on the same lance head section. The gun head has a simple structure and low production cost, but the secondary combustion rate will be reduced.
Fig. 3 Schematic Diagram for Nozzles of Double Channel Secondary Combustion Oxygen Lance with Simple Structure
Taken together, the dual-flow channel secondary combustion oxygen lance has the advantage of high secondary combustion rate, but its structure is relatively complex and difficult to manufacture. It requires the oxygen supply system of the original oxygen lance (gun body, pipeline, counterweight, instrument etc.), the investment cost is high and it is not suitable for large-scale production promotion and application.
Single-channel secondary combustion oxygen lance
The characteristic of the single-channel secondary combustion oxygen lance is that the main and auxiliary oxygen holes share one oxygen channel, and the oxygen flow is injected into the molten pool from the main hole and the auxiliary hole respectively. Like the dual-channel secondary combustion oxygen lance, the main hole oxygen jet decarburizes, heats up and stirs the molten pool; the secondary hole oxygen stream mainly performs secondary combustion and releases heat, but the flow and pressure of the main and secondary hole oxygen cannot be controlled independently. . Figure 4 is a schematic diagram of a single-flow channel secondary combustion oxygen lance nozzle.
Fig. 4 Schematic Diagram for Nozzles of Single Channel Secondary Combustion Oxygen Lance
As can be seen from Figure 4, the gun body is a three-layer steel pipe structure with only one oxygen channel. The central pipe supplies oxygen, the middle ring seam leads to cooling water, and the outermost pipe returns water. The nozzle has the advantages of simple structure, low investment and quick results.
To sum up, compared with the double-channel secondary combustion oxygen lance, the single-channel secondary combustion oxygen lance only needs to replace the ordinary oxygen lance nozzle with the secondary combustion oxygen lance nozzle, and does not need to modify the original gun body. There is no need to add oxygen channels, valves and instruments. It can be seen that the single-channel secondary combustion oxygen lance technology is suitable for large-scale production promotion and application.
New progress in industrial application of secondary combustion oxygen lance technology
Research on the large-scale industrial application of secondary combustion oxygen lance technology
The author researched and designed a single-channel secondary combustion oxygen lance suitable for large-scale production applications for a 120-ton converter in a domestic steel plant, and implemented large-scale production applications in this converter. Comparative analysis of typical industrial production data of 30 furnaces of ordinary oxygen lances and secondary combustion oxygen lances was conducted to provide a basis for the comprehensive promotion and application of this technology in large-scale production.
The impact of secondary combustion oxygen lance technology on scrap ratio
By analyzing the temperature of the molten pool after adding cold material during the on-site steelmaking process, the relationship between the cold material entering the furnace and the temperature drop of the molten pool is shown in Table 1. Comparative analysis of cold material entering the furnace, molten iron and converter endpoint data before and after the use of secondary combustion oxygen lances. It is concluded that after the use of secondary combustion oxygen lances, the molten steel temperature in the molten pool increases by about 30°C on average, which can correspondingly increase the scrap steel ratio entering the furnace by about 1.5 %.
Table 1 Relationship between Cold Burden Charged into Converter and Temperature Drop of Molten Pool
| project | ore | dolomite | raw dolomite | Lime | iron ball | steel slag | scrap steel | Jiao Ding | briquettes | Slag remover |
| cooling coefficient | 3.0 | 1.2 | 3.0 | 1.2 | 2.2 | 2.0 | 1.0 | 4.0 | 3 | 2.5 |
| Temperature drop/℃ per ton | 39 | 16 | 39 | 16 | 29 | 26 | 13 | 52 | 39 | 32.5 |
The impact of secondary combustion oxygen lance technology on changes in lance position during the smelting process
The statistical comparison of the frequency of gun position changes during the smelting process of a single furnace is shown in Figure 5.
Fig. 5 Comparison of Change Frequency of Lance Positions during Steel-making by Single Converter
It can be seen from Figure 5 that compared with ordinary oxygen lances, after using a secondary combustion oxygen lance, the number of gun position changes is reduced by about 33%, and the gun position is more stable during the smelting process. This is because after using the secondary combustion oxygen gun, the slag removal speed is fast, the slag removal is smooth, the slag removal time is reduced, the temperature of the molten pool rises evenly, and there is no need to make too many changes to the gun position. It can be seen that the gun position control of the secondary combustion oxygen lance is more stable than that of the ordinary oxygen lance, and there is no need to frequently change the gun position.
Effect of secondary combustion oxygen lance technology on final slag alkalinity
The secondary combustion oxygen lance and the ordinary oxygen lance use the same slag addition system. The comparison of the final slag basicity of each typical furnace is shown in Figure 6. It can be seen from Figure 6 that the alkalinity of converter slag using secondary combustion oxygen lance is higher than that of ordinary oxygen lance. This is because the secondary combustion oxygen lance has a good slag removal effect, so the final slag alkalinity is higher.
Fig. 6 Comparison of Basicity for Final Slag
Industrial Experimental Research on Large Scrap Ratio Technology of Secondary Combustion Oxygen Lance Converter
Using a secondary combustion oxygen lance and adding a special coal with low impurity content to supplement heat, a large-scale production test study of a single converter with a scrap steel ratio exceeding 40% was carried out. The test results were good, and it was a single converter based on a secondary combustion oxygen lance. It has laid the foundation for the large-scale production application of large scrap ratio technology.
The total weight of scrap steel in the test was 59.04 t, and the amount of molten iron added was 83t. Table 2 shows the composition and temperature of the molten iron entering the furnace and the molten steel at the end of the converter. Table 3 shows the main parameters and indicators of the secondary combustion oxygen lance single converter large scrap ratio technology.
Table 2 Compositions in Both Hot Metal Charged into Converter and Molten Steel at End Point and Their Temperatures
| project | w[C]/% | w[Si]/% | w[Mn]/% | w[P]/% | w[S]/ % | temp/℃ |
| molten iron into the furnace | 4.2 | 0.44 | 0.33 | 0.141 | 0.033 | 1347 |
| Converter end point molten steel | 0.088 | 0.107 | 0.006 | 0.010 | 0.024 | 1598 |
As can be seen from Table 2, under the condition of a large scrap ratio in a single converter based on secondary combustion oxygen lance, the end-point temperature of the converter is 1598 °C, and the dephosphorization rate is about 92.9%, which fully meets the requirements of the smelting end-point.
Table 3 Main Parameters and Indexes for Secondary Combustion Oxygen Lance Technology with High Scrap Ratio for Single Converter
| Adding amount of molten iron/t | Scrap added amount/t | Converter tapping capacity/t | Scrap ratio/% | Iron consumption/(kg.t) |
| 83 | 59.04 | 123.7 | 41.6 | 671 |
As shown in Table 3, without scrap preheating, the scrap ratio in a single converter reaches 41.6%, and the molten iron consumption drops to 671 kg/t. It can be seen that this technology has good smelting effect and has the feasibility of large-scale production application. It should be noted that this technology breaks through the 40% scrap ratio of a single converter from a technical perspective. However, in actual production, the cost of scrap steel, the cost of adding special coal, the converter smelting cycle, etc. must be comprehensively considered to determine the best single converter. The scrap ratio should not be blindly pursued for a single converter.
Conclusion
Converter secondary combustion oxygen lance technology is a clean heat compensation technology that can effectively increase the converter scrap ratio. Compared with double-channel secondary combustion oxygen lance, single-channel secondary combustion oxygen lance only needs to replace the ordinary oxygen lance nozzle with The secondary combustion oxygen gun nozzle does not require modification of the original gun body. It has the advantages of simple structure, low investment and quick results, and is suitable for large-scale production promotion and application. Research shows that under the condition of a large scrap ratio (41.6%) in a single converter using a secondary combustion oxygen lance and a heat supplement, the end-point temperature of the converter reaches 1598°C, and the dephosphorization rate is about 92.9%, which fully meets the smelting end-point requirements. However, in actual production, the cost of scrap steel, the cost of adding special coal, the smelting cycle of the converter, etc. must be comprehensively considered to arrive at the optimal scrap ratio for a single converter, instead of blindly pursuing an excessively high scrap ratio for a single converter.