Effect of KTB Oxygen Gun Position on Gas Flow in RH Vacuum Chamber

Effect of KTB Oxygen Gun Position on Gas Flow in RH Vacuum Chamber CHEN Yi-Sheng 1 HE You-Duo 1 CANG Da-Qiang 2 HUANG Zong-Ze 3 (Institute of Metallurgical Engineering, Baotou Iron and Steel Institute, Baotou 014010, China; School of Metallurgy, University of Science and Technology Beijing, Beijing 100083, China) Shanghai Baoshan Iron and Steel Group Corporation Technical Center, Shanghai 2) 1900) The influence of the dynamic field laid a theoretical foundation for understanding the role of the top gun in vacuum refining and the operational control of the top gun.

In the RH vacuum refining process, the mixed gas of CO, H2, and N2, which is discharged from the molten steel in the vacuum chamber and flows out of the molten steel, escapes from the molten steel surface of the vacuum chamber. The escaping gas flow rate is very fast, and turbulent flow forms in the vacuum chamber. In the RH-KTB operation, the high-speed jetted oxygen stream and the rising mixed gas form a counter-current turbulent diffusion combustion flame in the vacuum chamber. The reasonable control of the flame can partially compensate the heat loss of the molten steel during the treatment process or the condensing cold steel on the wall of the melting vacuum chamber. Therefore, it is necessary to establish a reasonable mathematical model for the physicochemical behavior of the vacuum chamber to carry out a simulation study and propose an RH optimization. The operating mode provides suggestions for RH equipment retrofit.

1 Analysis of the gas flow state of the vacuum chamber In the vacuum refining process of RH, the normal working pressure in the vacuum chamber is 105Pa)). According to the concept in physics, gas systems below normal pressure are called lean gases. The RH vacuum refining system has rough vacuum and low vacuum. The consideration here is whether the gas flow is turbulent flow or laminar flow under such conditions, so as to determine the mathematical model to be used for gas flow in the vacuum chamber. If it is a molecular flow, the gas flow in the vacuum chamber cannot be solved by the ke model; if it is a laminar or turbulent flow, the gas flow in the vacuum chamber is calculated by the turbulence model.

The gas in the RH vacuum refining system is in a rough vacuum and a low vacuum state. The gas flow is close to the gas flow properties at atmospheric pressure. In other words, there are enough gas molecules in the studied unit, and the distance between the gas molecules is much smaller than the free path of the gas molecules. There will be no molecular flow characteristics. In 1833, Reynods first proposed the most direct factor and quantitative relationship (Reynolds number Re) that affects the change of gas flow characteristics: e = and å…€ 1) 2 When the constant coefficient is not considered, the above formula is simplified as: = Df2, where D is the vacuum chamber. Diameter (D = 23m) u is the gas flow velocity (m/s); is a vacuum f:: Yisheng (960-) Male Male in Inner Mongolia Liangcheng Ren Baotou Institute of Iron and Steel, mainly engaged in metallurgical process computer simulation research. u++ 1 chamber gas density (kg/m3); is the kinetic viscosity (Pas) of the gas; is the height of the vacuum chamber (m). According to a large number of experiments, 1200 was obtained as a laminar flow. In the RH vacuum refining chamber we studied, the average flow rate of the gas varied with the process and varied from 3 to 30 m/s; the gas temperature was above 1400, and the gas working pressure was changed at 1.104 Pa. When the aerodynamic viscosity of the vacuum chamber is 1. 1.0X1 (on the magnitude of T7Pas, the vacuum chamber gas movement is on the order of 1.0X104m2/s, according to the criterion obtained by the Reynods experiment, the gas flow in the vacuum chamber during the RH vacuum refining process can be known (Re > 1200) in the transition zone or turbulent zone, the simulation of the vacuum chamber gas flow process uses a two-equation model describing the turbulent flow of the fluid.

The vacuum chamber mathematical model bookmark2 21 gas field model bookmark31 simulates the turbulent flow of the vacuum chamber gas with a model 1'2 (in the RH vacuum refining condition, the degree of vacuum is maintained at 133.32 Pa (1 Torr) or more, under such conditions, the gas molecules Still continuous, with continuous media properties) Continuous Equation: Momentum Equation: Turbulent Dissipation (e:RH operation is based on the calculation of the RH 1/2 of the riser and downcomer centerlines. RH Vacuum Chamber bottom It is the molten steel surface. Two factors are considered here: According to the relevant data, the curved surface of the molten steel surface is subjected to a one-time approximate correction; the amount of gas escaping from the molten steel surface is different in each part, in the RH. In the cross-section, it is an asymmetrical distribution with the largest riser center. To make the simulation practical, the vacuum chamber gas inlet condition does not give the average flow velocity over the entire cross-section, but the riser is given on the RH cross-section. The truncated normal distribution centered: standard; 1, b2 is the x direction and direction intensity factor; Q is the total gas evolution; it is the RH vacuum chamber cross-sectional area.

The boundary condition of the symmetry plane is: the partial velocity perpendicular to the symmetry plane v = the partial velocity parallel to the symmetry plane! The RH vacuum chamber top and other sides are solid walls. The boundary conditions are: Take 1/2 of the RH vacuum chamber with its symmetry plane as the boundary as the simulation calculation object, and spatially segment the selected simulation object (/= 1~27 It is a node divided by the x direction, = 1 to 15 are the nodes divided by the y direction, and K=1 to 41 are the nodes divided by the z direction). Each space partition is called a control unit. The mathematical model is integrated and discretized on the control unit to form a discrete system of equations on the control node. The iterative solution to the discretized equations gives an exact solution.

The RH vacuum treatment process is classified according to the purpose of treatment and is divided into: pipeline steel treatment process, RHHOB process, RH-KTB process. The gas flow patterns in the vacuum chambers of the three types of processes are shown. It can be seen that the general trend of the gas flow in the vacuum chamber during the RH process is that the gas in the lower part of the vacuum chamber flows mainly from the riser side. Here, the gas flow escapes from the molten steel at a high speed and increases along with the rise height across the entire vacuum chamber section. It tends to be uniform until the upper outlet of the vacuum chamber turns - the cross section is a plane of symmetry. However, due to the difference in the way and the manner of gas supply bookmark11, the gas flow pattern in the vacuum chamber is greatly different. In the process of (a) pipeline steel, no gas escapes from the side of the downcomer, and a swirling flow is formed on the side of the riser driven by the main gas stream. The height of the raceway can reach 3m. This is the process of the pipeline steel. Common characteristics of the gas flow in the middle vacuum chamber; in the process of (b) oxygen-free treatment of IF steel in the 0B mode, due to the effect of 0B oxygen supply, the gas flow morphology in the vicinity of the molten steel surface has undergone certain changes, in particular oxygen supply to the OB. The large amount of smelting process changes are particularly noticeable. The gas flow pattern at the upper part of the vacuum chamber does not change significantly, but only changes in the flow rate. In (c) RH-IKTB treatment of IF steel, due to the reverse flow of oxygen gun upper surface The impact of the oxygen supply stream caused a great change in the flow pattern of the lower gas in the vacuum chamber. This strong disturbance accelerated the homogenization of the gas flow distribution in the vacuum chamber. The upper gas flow pattern did not change significantly, only the flow velocity. Variety.

3.2 Effect of Oxygen Gun Position on Gas Flow Field in a Vacuum Chamber When the IF steel is treated by the RH-IKTB method with top-blown oxygen, the simulation of the flow field under different degrees of vacuum shows that the vacuum degree also only affects the gas flow rate in the vacuum chamber. The absolute size does not change the flow pattern, but as the vacuum level decreases, the impact kinetic energy of the oxygen stream will be significantly reduced. Therefore, when the molten steel is treated at a low vacuum, the oxygen in the molten pool is effectively supplied and the oxygen is blown twice. The thermal compensation for the combustion of the molten steel should be reduced accordingly to compensate for the lack of kinetic energy of the oxygen stream at low vacuum, or to change the top gun diameter plus the kinetic energy of the oxygen outlet; the effect of blowing volume also only changes the vacuum chamber. The absolute size of the gas flow rate does not change the flow pattern. Oxygen gun position impact on the gas flow field of the vacuum chamber (this is simulated at a vacuum degree of 10532Pa, blowing volume of 1.608m3/min, equivalent oxygen supply conditions) can be seen from the simulation of the vacuum chamber gas flow field, oxygen The impact force of the stream is large. In the reverse flow environment, an impact area of ​​3 to 4m can be formed. When the gun position is low (see (a), the gun position is 1m), the high-speed oxygen stream is almost impossible to spread and directly impact. The liquid level of the steel will inevitably cause a large amount of molten steel splashing and over oxidation of the molten steel, so that CO (a) gun head is 1m (b) from the vacuum chamber molten pool steel surface from the vacuum chamber molten pool steel surface 2m; (c) The distance between the tip of the gunhead and the molten pool steel surface in the vacuum chamber is 3m. The combustion cannot be completed completely near the molten steel surface. As a result, the combustion zone is enlarged and the combustion flame is away from the molten steel surface, which is not conducive to the heat of the secondary combustion heat on the molten steel. make up. When the gun position is too high (see the gun position 3m), the oxygen impact stream exhausts the kinetic energy in front of the molten steel and is reversed by the reverse stream. It does not over-oxidize the molten steel, but the oxidation zone is far from the steel. Near the liquid surface, the secondary combustion of CO caused the difficulty of heating the molten steel. Oxygen streams are difficult to heat the molten steel, which will inevitably bring difficulties to the transfer of oxygen to molten steel. (h) (Oxygen gun position 2m) The height of the gun position is between the above two conditions. It can be seen that the oxygen stream can not only achieve the heating of the liquid surface of the molten steel by the combustion of CO, but also avoid the oxidation of the molten steel surface. At the same time, it can moderately transfer oxygen that accelerates decarburization to molten steel. From the analysis of the flow field simulation results, under the current operating conditions of Baosteel's straight oxygen lance, the oxygen gun position for RH-KTB top gun is about 2m. Through the simulation of the oxygen gun impact strength under different vacuum degrees, the optimal oxygen gun position changes with the operating vacuum degree.

4 Conclusion Oxygen gun position during RH-KTB treatment has a direct effect on KTB treatment. There is a non-linear relationship between the best gun position and the vacuum degree of the operation process of the straight type gun.

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