Study on Nitrogen-Argon Switching and Full-Bottom Blowing Nitrogen Process in 150t Combined Blowing Converter
The top and bottom composite blowing technology of the converter adopts top blowing O 2 , and the bottom blowing gas may be N 2 , Ar, O 2 , CO 2 , CO and the like. Considering the process and cost, most of the bottom-blowing converters of the existing top-bottom combined blown converter are N 2 /Ar switching, that is, the mode of blowing N 2 in the pre-smelting stage and switching to Ar in the later stage. At present, the pressure on steel mills to reduce production costs is increasing. The cost of N 2 is much lower than that of Ar. If the whole process of bottom blowing N 2 smelting can be achieved, it can not only reduce the smelting cost, but also simplify the operation process. To this end, the author conducted a smelting low-nitrogen steel industrial test on the 150t top-bottom combined blown converter of Tangshan Iron and Steel Co., Ltd., and concluded that the top-low double-blown converter can be smelted by the whole process of bottom-blowing N 2 process, and denitrification according to molten steel. The theory of nitrogen absorption thermodynamics and kinetics is discussed in the whole process of bottom blowing N 2 process, which provides a basis for determining the reasonable low nitrogen steel production process. In order to further verify the above conclusions, the author repeated the test on the 150t top-bottom combined blown converter of Anyang Steel Plant, and improved the test method to better explore the nitrogen increase and desorption of molten steel during converter smelting. Nitrogen law. First, test conditions and test methods (1) Test conditions The actual tapping capacity of the 150t top-bottom combined blown converter is about 160t. The top-blowing lance is a 4-hole or 5-hole Laval nozzle with an oxygen pressure of 0.9MPa. The oxygen supply intensity (standard state, gas flow not specifically mentioned in the text) The unit of strength is the standard state unit) around 2.8 m 3 ·min -1 ·t -1 , and the pure oxygen blowing time is 14-15 min. The bottom blowing air supply device uses 8 permeable bricks. The bottom blowing gas is N 2 and Ar, and the flow rate can be adjusted between 0 and 800 m 3 ·t -1 . According to the actual tapping amount of 160 t, the bottom blowing N 2 and Ar intensity can be converted into 0 to 0.08 m 3 ·min. -1 ·t -1 . The converter smelting adopts a staged quantitative loading method with a scrap ratio of 18% to 22%. The final slag basicity is controlled at 2.8 to 3.2. Iron water (2) Test methods 1. Nitrogen and argon switching test The nitrogen and argon switching test steel type is ship plate A. The test scheme is as follows: after the start of the converter smelting, O 2 is blown at the top, N 2 is blown at the bottom, and the bottom blowing gas is switched to Ar after a certain period of oxygen blowing. Set different switching time points, switch the time point according to the oxygen blowing time setting, and test 3 furnaces in each switching mode. The nitrogen and argon switching test parameters are shown in Table 1. Table 1 Nitrogen and argon switching test parameters N 2 , Ar switching time point Bottom blowing N 2 , Ar flow / (m 3 · h -1 ) Bottom blowing N 2 , Ar intensity (m 3 ·min -1 ·t -1 ) Blowing oxygen for 7min Oxygen blowing for 10min Oxygen blowing 13min 250 250 250 0.028 0.028 0.028 2. Constant flow bottom blowing N 2 test The test steel grade is ship plate A. The test plan is as follows: the flow rate of the bottom blowing N 2 is constant in each steel smelting process, and five bottom blowing N 2 flows are set from small to large, and three furnaces are tested under each flow rate, and a total of 15 furnaces are tested. Each steel smelting process ships bottom blowing gas strength of 0.02 ~ 0.05 m 3 · min -1 · t -1, ensure smooth smelting process, while achieving significant metallurgical effects. If the bottom blow air supply strength increases, it will make the smelting control difficult. Therefore, the N 2 intensity of the bottom flow of the constant flow set in the test is not more than 0.05 m 3 ·min -1 ·t -1 , and the test parameters are shown in Tables 2 and 3. Table 2 Blowing N 2 flow at the bottom to smelt the end point molten steel Stove number Set bottom blow N 2 flow rate / ( m 3 ·h -1 ) Set the bottom blowing N 2 intensity / ( m 3 ·min -1 ·t -1 ) Actual bottom blowing N 2 flow / ( m 3 · h -1 ) Actual bottom blowing N 2 intensity / ( m 3 ·min -1 ·t -1 ) 1481 1482 1483 180 0.020 191 218 196 0.021 0.024 0.022 1484 1485 1486 225 0.025 252 240 248 0.028 0.027 0.028 1487 1488 1489 270 0.030 279 289 288 0.031 0.032 0.032 1490 1491 1506 360 0.040 360 360 412 0.040 0.040 0.045 1507 1508 1509 450 0.050 439 460 454 0.049 0.051 0.050 Table 3 bottom blowing N 2 flow to smelt the end point molten steel Stove number Actual bottom blown N 2 intensity average / ( m 3 ·min -1 ·t -1 ) 1 sample 1 sample 2 countdown 1481 1482 1483 0.022 12 12 11 11.7 10 12 - 1484 1485 1486 0.028 10 10 8 9.3 - - - 1487 1488 1489 0.032 10 10 12 10.7 10 - - 1490 1491 1506 0.042 12 14 18 13.0 - - - 1507 1508 1509 0.050 18 16 18 17.5 - 20 18 3, variable flow bottom blowing N 2 test In order to investigate the main reason for the increase of nitrogen in the molten steel during the bottom blowing of N 2 in the whole process of the converter, and the effect of the bottom blowing N 2 flow rate on the nitrogen content of the end steel in different periods, the variable flow bottom blowing N 2 test was carried out: for the switching point, the switching point is set before and after 12min different lance smelting N 2 flow, respectively, using a large bottom blowing N 2 flow early, late bottom blowing N 2 flow rate and the small pre small bottom blowing N 2 flow, post bottom blowing N 2 The flow rate is 2 modes, and 3 furnaces are tested in each mode, and 6 furnaces are tested. The test steel grade is Q235B. The set variable flow rate bottom blowing N 2 test parameters are shown in Tables 4 and 5. Table 4 Variable flow bottom blowing N2 mode for smelting end point molten steel Stove number Set bottom blow N 2 flow rate / ( m 3 ·h -1 ) Set the bottom blowing N 2 intensity / ( m 3 ·min -1 ·t -1 ) Actual bottom blowing N 2 flow / ( m 3 · h -1 ) Actual bottom blowing N 2 intensity / ( m 3 ·min -1 ·t -1 ) 1510 1511 1512 Early 180 Late 450 Earlier 0.020 Late 0.050 Early stage 186 Late stage 423 Early stage 210 Late 426 Early stage 220 Late 456 0.021 0.047 0.023 0.047 0.024 0.051 1513 1514 Early stage 450 Late 180 Early stage 0.050 Late 0.020 Early 447 Late 180 Early stage 420 Late 180 0.050 0.020 0.047 0.020 Table 5 Variable flow bottom blowing N2 mode for smelting end point molten steel Stove number Actual bottom blown N 2 intensity average / ( m 3 ·min -1 ·t -1 ) 1 sample 2 countdown 1510 1511 1512 Previous period 0.023 Late 0.048 12 16 12 - - - 1513 1514 Early period 0.048 Late 0.020 16 18 18 - (3) Sampling and testing methods In order to influence the influence of tapping, refining and continuous casting process on the nitrogen content of molten steel, this paper only analyzes the nitrogen content of the converter end point. In order to understand the effect of supplemental blowing on the nitrogen content of the converter tapping during converter smelting, the nitrogen content of the converter was sampled and analyzed every time the converter was smelted. Samples taken from the field are processed by a wire cutter Second, the test results (1) N 2 , Ar switching point to the smelting end point molten steel The nitrogen-argon switching test results are shown in Fig. 1, in which the N 2 and Ar switching points are less than 1 furnace data when the switching point is 7 min. The test results in Fig. 1 show that when the bottom blowing N 2 and Ar strength is 0.028 m 3 ·min -1 ·t -1 , the nitrogen content of the molten steel end point before tapping is about 0.0010%, and the top and bottom combined blowing converter At the end of the whole process, when the small flow rate N 2 is blown, the steel liquid ends the steel sample. (2) Blowing N 2 flow rate to the smelting end point molten steel During the field test, it was found that the bottom blowing N 2 flow rate deviated from the set values ​​in Tables 2 and 3. According to the instrument, the actual value of the bottom blowing N 2 flow rate and the smelting end point molten steel In Tables 2 and 3, there are 15 furnace steel data, and each 3 furnaces is 1 set. The actual bottom blowing N 2 intensity of each group is averaged, and then the corresponding 1 is inverted. The nitrogen content in molten iron is around 0.0060%. It can be seen from Tables 2, 3 and 2 that when the strength of the bottom blowing N 2 does not exceed 0.032 m 3 ·min -1 ·t -1 , the steel sample at the end of the converter smelting (3) Variable flow bottom blowing N 2 mode for smelting end point molten steel According to the instrument, the actual value of the bottom blowing N 2 flow rate and the smelting end point molten steel It can be seen from Tables 4 and 5 that in the early stage, the N 2 flow rate is large, and the bottom blowing N 2 flow rate is small. (4) Supplementary blowing on the smelting end point molten steel In the test of Tables 2, 3 and 4 and 5, a total of 6 furnace steels were blown once, that is, the converter was tapped 2 times and sampled and tapped. 1 down and 2 down Third, analysis and discussion (1) Denitrification and nitrogen absorption of molten steel during smelting of top and bottom complex During the smelting process of the top and bottom double-blown converter, there are both nitrogen absorption and denitrification processes, and the molten steel at a certain moment in the smelting process. In the oxygen blowing and decarburization process of the converter, there is a strong CO reaction, which generates a large amount of CO bubbles. The molten steel can be denitrified by the CO bubble carrying method. The mechanism of nitrogen removal is the same as that of vacuum denitrification. Chinese specific law interpretation. The empirical relationship between the denitrification rate and the decarburization rate in the oxygen and decarburization process of the converter indicates that the denitrification rate of the molten steel is proportional to the decarburization rate. In the early stage of converter smelting, the carbon-oxygen reaction is gradually intense, the decarburization rate is gradually increased, and the denitrification rate is gradually increased. A large amount of carbon is oxidized to form CO, and the nitrogen in the molten pool is taken out, and the amount of nitrogen removal is much larger than the amount of nitrogen absorption, so the carbon-oxygen reaction can effectively denitrify. In the late stage of converter smelting, the carbon-oxygen reaction gradually weakened, the decarburization rate gradually decreased, the denitrification rate also gradually decreased, and the denitrification amount gradually decreased. By using the top-bottom composite blowing method, after the top blowing oxygen is stopped, the decarburization reaction can be continued due to the stirring of the bottom blowing gas and the reduction of the P CO value. The combined blowing converter can decarburize to 0.02%, and there is still a CO reaction after stopping the oxygen blowing. It can be seen that even after the top blowing oxygen is stopped, since the decarburization reaction still exists, the converter still has a denitrification function. At present, there has been consensus on the research on surface active elements such as oxygen and sulfur which can significantly hinder the absorption of nitrogen by molten steel. When in steel Since most steel grades do not require high levels of nitrogen in the steel, it is possible to use the process of blowing N 2 at the bottom of the double-blown converter for smelting, which can meet the quality requirements of molten steel. (2) Bottom blowing N 2 strength to the molten steel end point In addition to the influence of oxygen and sulfur content in the steel, the nitrogen absorption rate of the molten steel is also affected by the strength of the bottom blowing N 2 . Increasing the bottom blowing N 2 intensity, that is, increasing the gas/liquid reaction interface, speeds up the nitrogen absorption reaction rate. The rate of nitrogen uptake is proportional to the strength of the bottom blowing N 2 . Therefore, for a particular converter, the change in the rate of nitrogen removal is consistent with the change in the rate of decarburization, with a certain limit, while the rate of nitrogen uptake increases with the increase in the strength of the bottom blowing N 2 . When different bottom blowing N 2 intensities are used, the oxygen blowing system is the same for the same converter, and the decarburization reaction rate is the same, and the denitrification rate of the molten steel is proportional to the decarburization speed, so the denitrification amount is also the same, but the nitrogen absorption amount is different. In the early stage of converter smelting, the molten steel has a high carbon content and a low oxygen content. When the mass fraction of oxygen in the molten steel is less than 0.02%, the molten steel can absorb nitrogen. If a large flow rate N 2 is blown at the bottom of the converter smelting, the nitrogen absorption of the molten steel increases, so as the strength of the bottom blowing N 2 increases, the smelting end point molten steel On the other hand, if a small flow rate N 2 is blown at the bottom of the converter smelting, the nitrogen absorption of the molten steel is smaller than that when the large flow rate N 2 is blown at the bottom of the converter smelting period, even if the large flow rate N 2 is blown at the bottom of the converter smelting, the molten steel after the oxidation was not absorbing nitrogen, so that the end of tapping the molten steel [N] than the large pre-bottom blowing N 2 flow, the bottom blowing N 2 late small low traffic patterns, which may explain the test results of tables 4 and 5 . (3) Filling the end of the molten steel Because the molten steel is oxidized in the later stage of converter smelting, and there is still a certain carbon-oxygen reaction in the process of re-blowing, and the re-blowing time is also very short, the molten steel does not increase nitrogen during the re-blowing process. Fourth, the conclusion (1) Under the test conditions of this paper, the N 2 process is applied at the bottom of the constant flow, and when the strength of the bottom blowing N 2 does not exceed 0.032 m 3 ·min -1 ·t -1 , the nitrogen content of the molten steel at the end of the tapping is 0.0010% or so, which is equivalent to the nitrogen-nitrogen switching process, and the nitrogen-hydrogen switching point is used to extract the steel sample at the end of the converter smelting. (2) The nitrogen absorption of molten steel during converter smelting mainly occurs in the early stage of smelting; in the later stage of converter smelting, the molten steel is oxidized, in the molten steel (3) Blowing the steel sample at the end of the smelting (4) The top low-blown converter can adopt the full-end bottom blowing N 2 process. Crankshaft Pulley,Engine Crankshaft Pulley,Crankshaft Belt Pulley,Car Crankshaft Pulley Taizhou Chenhui Machinery Manufacturing Co., Ltd , https://www.chenhuipulley.com
[N] is approximately 0.0060%. [N] impact (1) The influence of [N] (2) [N] /10 -6 [N] average/10 -6 [N] /10 -6 [N] impact (1) The influence of [N] (2) [N] /10 -6 [N] /10 -6 The 4mm round bar sample was sent to the National Nonferrous Metals and Electronic Materials Analysis and Testing Center of the Research Institute of Nonferrous Metals for analysis of N mass fraction. The analytical method is inert gas pulse-infrared-thermal conductivity method. [N] effect [N] is equivalent, indicating the nitrogen and argon switching time point to the steel sample at the end of the converter smelting [N] The impact is small. [N] effect [N] recorded in Tables 2 and 3, the carbon mass fraction of the molten steel end point is about 0.1%. In Tables 2 and 3, there are 2 inverted furnaces that are blown once. [N] also takes the average value, and then according to the actual bottom blowing N 2 intensity average and the corresponding 1 sample [N] The average value is shown in Figure 2, which can show the bottom blowing N2 intensity to the molten steel end point. [N] The law of influence. [N] is about 0.0010%, and most of the nitrogen in the molten iron is removed; even when the strength of the bottom blowing N 2 is increased to 0.050 m 3 ·min -1 ·t -1 , the steel solution at the end of the converter molten steel is discharged. [N] is not more than 0.0020%, most of the nitrogen in the molten iron is still removed, but the nitrogen content of the molten steel end point is significantly increased compared with the nitrogen supply strength not exceeding 0.032 m 3 ·min -1 ·t -1 . . It can be seen that in the test of this paper, when the 150t top-bottom combined blown converter bottom blows a small flow rate N 2 (<0.032 m 3 ·min -1 ·t -1 ), it is not necessary to switch N 2 to Ar in the later stage of smelting. [N] effect The [N] values ​​are recorded in Tables 4 and 5, in which the first bottom blowing N 2 flow rate is large, and the late bottom blowing N 2 flow rate is small, and the furnace data is less than one furnace data. In Tables 4 and 5, there are 2 inverted furnaces that are blown once. The nitrogen flow rate was changed when oxygen was blown for 12 minutes. [N] is significantly larger than the small interval of bottom blowing N 2 flow, a large bottom late blowing N 2 flow patterns described molten steel nitrogen absorption mainly occurs in the early smelting. [N] effect [N] Data comparison can be seen that the 150t converter smelting is blown once, and the lead steel solution for the smelting end point [N] has less impact. [N] depends mainly on the difference between the nitrogen absorption rate and the denitrification rate at this time. [o] ≥0.02%, the amount of nitrogen absorbed by the molten steel is small. With the progress of the converter smelting process, in the molten steel [C] is getting lower and lower, balanced [o] getting higher and higher, when blowing oxygen decarburization into molten steel [C] ≤0.2%, [O] ≥ 0.02%. In the later stage of converter smelting, the molten steel is oxidizing, and the mass fraction of dissolved oxygen in the steel is high, usually greater than the critical value of 0.02%, which can hinder the nitrogen absorption of the molten steel, so the nitrogen absorption rate in the late stage of converter smelting is also gradually reduced. As long as the strength of the bottom blowing N 2 does not exceed a certain limit, the nitrogen absorption of the molten steel is less than the amount of nitrogen removal. The macroscopic performance is that most of the nitrogen in the molten iron is removed, and the molten steel at the end of the smelting is [N] 0.0010% or so. [N] effect [N] increased. This can explain the test results of Figure 2. [N] effect [N] has little effect; when the bottom blowing N 2 intensity exceeds 0.032 m 3 ·min -1 ·t -1 with the bottom blowing N 2 strength increases the steel front smelting end point molten steel [N] will gradually increase. [O] can hinder the absorption of nitrogen by molten steel. [N] has little effect.