Effect of Traveling Magnetic Field on Flow, Mixing, Decarburization and Inclusion Removal during RH Refining Process

Transcription

1 , pp Effect of Traveing Magnetic Fied on Fow, Mixing, Decarburization and Incusion Remova during RH Refining Process Dian-Qiao GEG, Hong LEI and Ji-Cheng HE Key Laboratory of Eectromagnetic Processing of Materias, Ministry of Education, ortheastern University, Shenyang, Liaoning Province, P.R. China. E-mai: (Received on ovember 9, 2011; accepted on January 4, 2012) In order to improve productivity during RH refining, the traveing magnetic fied was imposed around the snorkes. The numerica method was empoyed to investigate the fow, mixing, decarburization and incusion remova in RH degasser. umerica resuts showed that the predicted resuts agree we with the experimenta data. With the increasing current, the circuation fow rate increases and the mixing time decreases. If the current frequency ies in the range of 10 0 Hz, with the increasing current frequency, the circuation fow rate increases whie the mixing time decreases. If the current frequency ies in the range of 0 60 Hz, with the increasing current frequency, the circuation fow rate decreases whie the mixing time increases. In order to increase circuation fow rate and shorten mixing time, the most effective measure is to appy the traveing magnetic fied around the up snorke, and the second choice is to appy the traveing magnetic fied around the down snorke if the gas fow rate is smaer than the saturation vaue. Appying the traveing magnetic fied can acceerate the decarburization rate during the process, but can not decrease the fina carbon mass concentration. For incusion remova, the most effective measure is to appy the traveing magnetic fied around the up snorke and down snorke, and to appy the traveing magnetic fied around the up snorke has the minor effect. Furthermore, the appication of traveing magnetic fied can decrease the maximum incusion characteristic radius and the reated peak vaue time. KEY WORDS: numerica simuation; RH; traveing magnetic fied; circuation fow rate; mixing time; decarburization; incusion remova. 1. Introduction During the past severa decades, as one of the main metaurgica reactors to produce utra-ow carbon stee, Rheinsah Heraeus (RH) degasser pays a more and more important roe in the refining process for degassing, mixing, and decarburization before continuous casting process. 1 ) Furthermore, RH degasser is aso an important metaurgica reactor for incusion remova after deoxidization. 4) During the industria production, the stee temperature often drops inevitaby, so the auminum addition or the post combustion of carbon monoxide with oxygen is often empoyed to raise the temperature of iquid stee. 5,6) However, the excessive oxygen from top-bowing ance has to be removed by deoxidization which woud proong the RH refining time. 4,7) Therefore, the decarburization, degassing, aoying and incusion remova shoud be enhanced by increasing the circuation fow rate and shortening the mixing time. In order to improve the RH refining productivity, ots of studies concerning the circuation fow rate have been conducted. 8 19) Some researches showed that the circuation fow rate is mainy determined by the vacuum degree and the ifting gas fow rate, 8 12) and it is difficut to increase the circuation fow rate after reaching its saturation vaue. 8,9) Meanwhie, severa measures have aso been taken to increase the circuation fow rate and shorten mixing time, such as increasing the diameter of the up snorke and the down snorke, 1) using the ova-shape-snorkes, 10) repacing one up snorke and one down snorke by three up snorkes and one down snorke, 14) two up snorkes and one down snorke or one up snorke and two down snorkes, 12) appying rotating magnetic fied around the up snorke, 15) bowing additiona argon gas, (e.g. bowing argon gas through vacuum chamber bottom 16) and ade bottom 17,18) ) and so on. On the other hand, based on the mechanism that the iquid stee can be acceerated by eectromagnetic force, Zhang et a. 19) proposed that the appication of the traveing magnetic fied around the up snorke or the down snorke can increase the circuation fow rate in RH degasser. As shown in Fig. 1, the traveing magnetic fied is imposed around the up snorke or the down snorke. The origin of the rectanguar coordinate system is ocated at the center of the up snorke. The windings were connected to the three-phase aternating current to generate the traveing magnetic fied. By changing the phase sequence of the exciting current, 20) the axia eectromagnetic force can direct upward or downward. Thus, the iquid stee can be acceerated both in up snorke and down snorke ISIJ 106

2 0 = ( ) = r = 6 A f r dr, C 4 A = and B πr f ( r) dr = 8π 0 4 B B respectivey. Furthermore, C can aso be expre- ssed as the function of and r: C = 4 r. π Fig. 1. Schematic of RH degasser with traveing magnetic fied. Assumptions concerning decarburization process 1,27 1) (12) The contents of carbon and oxygen at the gas-iquid interface are in equiibrium with CO partia pressure in gas phase. (1) The decarburization rate is controed by the mass transfer of carbon and oxygen in iquid stee. (14) The decarburization in RH degasser takes pace at the free surface of vacuum chamber, the inner site of iquid stee and the bubbe surface of gas-iquid pume. The purpose of the present study is to promote the RH refining productivity by appying the traveing magnetic fied around the up snorke or the down snorke. And the numerica simuation method has been empoyed to understand the two-phase fow under the traveing magnetic fied in RH degasser. Moreover, the decarburization and incusion remova have aso been investigated. 2. Mathematica Mode The deveoped mathematica mode consists of the foowing four parts: traveing magnetic fied, gas-iquid fow fied, decarburization and incusion remova in RH degasser on the base of the foowing assumptions. Assumptions concerning traveing magnetic fied 20,21) (1) Since the exciting current is the ow frequency sinusoida current, the quasi-static condition is satisfied and the dispacement current can be negected. (2) The iquid stee, windings, iron core and air are the isotropic materias. () The effect of eectromagnetic fied on gas bubbes can be negected. Assumptions concerning gas-iquid fow 8,9,1,14,22,2) (4) The fuids in both the gas and iquid phases are ewtonian, viscous and incompressibe, and the fuid fow is at the steady state. (5) The effect of top sag on fuid fow is negected and the free surface is fat. (6) The gas bubbes are spherica and the interactions among bubbes are not considered. (7) The fuid fow in RH degasser is an isotherma process. Assumptions concerning incusion remova process 24 26) (8) The effect of incusion movement on fuid fow in RH degasser is negected. (9) The incusions are spherica and each incusion moves independenty before the coision occurs. (10) The effect of bubbes on incusion remova can be negected because there is no top sag in vacuum chamber. (11) The fractiona incusion number density has an exponentia reationship with the incusion radius and can be expressed as: f ( r)= Ae Br. So the incusion number density, the incusion voume concentration and the characteristic incusion radius can be expressed as: 2.1. Governing Equations Traveing Magnetic Fied Since the magnetic Reynods number is much smaer than 1, the effect of fuid fow on eectromagnetic fied can be negected. Consequenty, the current J and the magnetic fux density B are governed by the Maxwe equations as foows, H = J... (1) = B E... (2) t B = 0... () B = μ B H... (4) J = σ E E... (5) where H is the magnetic density, Am; E is the eectric fied intensity, Vm; μ B is the magnetic permeabiity, Hm; σ E is the eectric conductivity, Sm. Moreover, the actua eectromagnetic force which acceerates the fuid fow can be expressed as a time-averaging form, 1 F... (6) em = Re( J B ) 2 where B is the conjugate compex number of B. Moreover, the cacuated time-averaging eectromagnetic force vector is incorporated into the gas-iquid two phase fow mode as the source term of the momentum conservation equation Fow Fied and Mixing Behavior in RH Degasser In order to simuate the gas-iquid fow in RH degasser, the mode deveoped and vaidated in the previous paper was empoyed in the present work. 9) Based on the above assumptions (4) (7), the foowing governing equations are soved in the mode: 9,2) the continuity and momentum equations for the mixture of gas and iquid phases the voume fraction equation for the dispersed phase the k ε two equations The tracer transport equation are soved to obtain the variation of dimensioness tracer concentration with time. Furthermore, the mixing time is defined as the time to reach a 95% eve of homogeneity, i.e., a the monitoring points in ISIJ

3 RH degasser are within ± 5% of the homogeneous concentration vaue. 9) Incusion Remova in RH Degasser The transport equations which describe coision and aggregation among incusions can be expressed as foows: 24,25) 4 t 9 6 = ( Deff )+ S ( ρ ) + ρ ρ ρν t 2 ( ρp) r + u... (7)... (8) Here, ρ 1 and ρ p are the density of iquid stee and incusion, kg/m ; ν 1 is the kinematic viscosity of iquid stee, m 2 /s; g is the gravitationa acceeration, m/s 2 ; D eff is the effective diffusion coefficient, m 2 /s. Moreover, the source term S accounts for the effect of the coaescence among incusions on the incusion number density. Because the effect of turbuent coisions and Stokes coisions on the incusion growth is remarkabe whie the effect of Brownian coisions is negigibe, both the turbuent coisions and Stokes coisions have been taken into account in the present work and the coision rate among incusions with radii r i and r j is given by: 25)... (9) -20 Here, the vaue of Hamaker constant A is J for aumina incusion; 26) r is the initia size of the monomer partice, m. At the top sag, it is assumed that 80% of the incusions reaching top sag are removed whie the remaining 20% of the incusions are entrained into the iquid stee. 24) The incusion adhesion to the refractory wa can be treated as the mass diffusion of boundary ayer ) Moreover, at the ade bottom, the reverse effect of incusion foatation veocity on the incusion adhesion has aso been taken into account. Thus, the boundary fuxes for incusion number density and concentration are isted in Tabe 1. 25) Decarburization in RH Degasser The governing equation for cacuating the concentration distribution of carbon and oxygen can be represented as, 1) g 40 ( ρ ) C + ρ ρ 9 6 ρν = ( Deff C ) g 2 ( ρ ) r + u C p 2 5 S = r 19. 6πρν r 4ε 15πν A 1 2 πε + 1 0gΔρπr ν 9 6ρν ( ) Tabe 1. Boundary Fuxes for incusion number density and concentration. Boundary C Top sag z 08. u D eff z C 08. u C D eff n n Sidewa z τ 0r 4 4 z πτ 0r max u sinθ , 0 max sin + ρν u C θ C 75 6, 0 ρν z τ 0r 4 4 z πτ 0r Bottom max u , 0 max ρν u C , 0 C ρν Here, θ is the incude ange between wa face and vertica direction, and τ 0 is the wa shear stress. μeff ( ρφ )+ ( ρu )=... (10) + φ φ Sφ t Sc where φ represents the mass concentration of carbon and oxygen; μ eff is the effective viscosity, Pa s; Sc is the turbuent Schmit number; S φ is the source or sink of carbon and oxygen and can be obtained as foows, S φ = φ φ φ...(11) 1 2 φ φ φ where, and are the decarburization rates at three different sites. The decarburization rate at the free surface of the vacuum chamber can be expressed as, 0) 1 φ Mφ 21. A V = min kc,l C V M w w C ko,l ( O M w ) w O O ( C),... (12) where M φ is the moar mass of carbon and oxygen, g/mo; w C and w O are the mass concentration of carbon and oxygen at the reaction surface; A v is the cross section area of vacuum chamber, m 2 ; k C,L and k O,L are the mass transfer coefficient of dissoved carbon and oxygen in iquid stee, m/s. The decarburization rate at the surface of argon bubbes can be expressed as, M 6 gab = min kc,b C π d M w w g C ko,b ( wo wo) M 2 φ φ α O ( C)... (1) where A B is the surface area of argon bubbes, m 2 ; d g is the bubbe diameter, m; kφ,b = 2 Dφvb π dg is the mass transfer coefficient of dissoved carbon or oxygen from iquid stee to the bubbe surface, m/s; D φ is the diffusion coefficient of dissoved carbon or oxygen, m 2 /s; v b is the bubbe fotation veocity, m/s. The decarburization in the inner site of the vacuum chamber occurs when the equiibrium CO pressure exceeds the hydrostatic pressure. Thus, CO bubbes can nuceate when the equiibrium CO pressure is great enough. Such a mech-, 2012 ISIJ 108

4 anism can be expressed as, 29) φ = Kh K ww P 0 ( ) CO C O V... (14) where K 0 is a constant with vaue of 2 10 Pa s m ; K CO is the decarburization reaction equiibrium constant; P V is the pressure in vacuum chamber, Pa; h is the distance from the free surface in vacuum chamber, m Boundary Conditions and Parameters For a nodes at the refractory was in RH degasser, wa function method was appied, and the norma gradients of pressure and gas voume fraction were aso set to zero. For the free surfaces in ade and vacuum chamber, the symmetry boundary condition was imposed. Furthermore, the gas bubbes reaching the free surface were assumed to escape at fotation veocity. The tracer was added at the center of the free surface in vacuum chamber. For the computation of magnetic fied, the magnetic fux is set to be parae to the surrounding surface of air. For decarburization process, the initia concentration of carbon and oxygen are 400 ppm and 600 ppm respectivey. For incusion remova process, the initia incusion number density and voume concentration 1 are / m and ppm respectivey. The reative magnetic permeabiity of air, iquid stee and windings are set to be 1, whie the reative magnetic permeabiity of iron core is set to be The conductivity of windings and iquid stee are S/m and S/m respectivey. 20) The density of argon gas (STP) and iquid stee are 1.78 kg/m and kg/m respectivey. And the viscosity of iquid stee is Pa s. 9) Moreover, the dimensions of RH degasser are shown in Tabe 2. oxygen concentration, incusion number density and voume concentration were aso soved by CFX. The finite voume method was used to sove these partia differentia equations. The grids of RH degasser consisted of about contro voumes and the grid sensitivity experiments were conducted. In order to get more detaied information in twophase domain, a densey packed grid system was appied in the snorkes and vacuum chamber. The convergence criteria is that the vaue of the root mean square normaized residua for variabes was ess than and the goba imbaances, which means the ratios of the difference between the tota input mass fux and the tota output mass fux to the tota input gas mass fux was ess than 0.1%.. Resuts and Discussion.1. Mode Vaidation The CT- Tesameter has been empoyed to measure the magnetic induction intensity 2 cm away from the traveing magnetic fied generator. Figure 2 shows that the predicted magnetic induction intensity at different ocations is in good agreement with the experimenta data. ) As shown in Fig., the cacuated circuation fow rate is aso in good agreement with the experimenta data. 4) And with the increasing 2.. Soution Method The whoe computation process can be divided into three parts. (1) The traveing magnetic fied was obtained by finite eement method. The commercia finite eement software package, ASYS, was empoyed to cacuate the externa eectromagnetic fied produced by the eectromagnetic equipments. (2) The steady gas-iquid fow under traveing magnetic fied was cacuated by adding the eectromagnetic force to momentum conservation equation for iquid stee as the source term. The computationa fuid dynamics package, CFX, was empoyed to obtain the fow fied. () The unsteady conservation equations for carbon concentration, Fig. 2. Comparison of cacuated magnetic induction intensities with experimenta resuts. Tabe 2. Dimensions of RH system and cacuation conditions. Parameters vaue Up diameter of ade, mm 190 Down diameter of ade, mm Diameter of snorkes, mm 480 Diameter of vacuum chamber, mm Immersion depth of snorkes, mm 480 Exciting current frequency, Hz Exciting current, A Coi turns 72 Height of magnetic fied generator, mm 800 Fig.. Comparison of cacuated circuation fow rates with experimenta resuts ISIJ

5 gas fow rate, the circuation fow rate increases and reaches a critica maximum vaue, then decreases. Moreover, in our previous work, 9) the mode empoyed has aso been vaidated by comparing the cacuated mixing time, gas penetration depth, veocity and dimensioness tracer concentration with the experimenta data. With respect to the metaurgica phenomena, the measured resuts about the decarburization and the incusion remova were empoyed to verify the numerica mode. 4,5) Figure 4 shows that the cacuated carbon remova rate is consistent with the experimenta data. 5) Besides, Tabe aso shows that the predicted incusion mass fraction is aso in good agreement with the experimenta vaue. 4) And the difference between the numerica resuts and the experimenta data comes from the affection of the samping position in the experiment..2. Effect of Imposing Position of Magnetic Fied Figures 5 and 6 show that by using 200 A of exciting current and 10 Hz of current frequency, the circuation fow rate is up percent, and the mixing time fas 1 17 percent by imposing the traveing magnetic fied around the up snorke. On the other hand, the circuation fow rate is up 16 5 percent, and the mixing time can be decreased by 9 1 percent by imposing the traveing magnetic fied around the down snorke. Furthermore, the circuation fow rate in RH degasser with traveing magnetic fied imposed around the up snorke is greater than that with traveing magnetic fied imposed around the down snorke if the ifting gas fow rate is ess than L/min, but they are amost the same if the ifting gas fow rate is greater than L/min. The effect of centripeta eectromagnetic force is the key factor eading to this interesting phenomenon. When the traveing magnetic fied is imposed around the up snorke, the iquid stee can be moved to the center by centripeta eectromagnetic force, so more gas bubbes can be transported to the center and more iquid stee can be acceerated by gas bubbes. However, the gas voume at up snorke center woud become saturated with the increasing ifting gas fow rate. Thus, such a difference disappears if the gas fow rate is greater than L/min. Moreover, Figs. 5 and 6 aso show that the circuation fow rate is up 0 66 percent, and the mixing time fas percent by imposing the traveing magnetic fied around the up snorke and down snorkes simutaneousy. For exampe, on the condition of L/min of ifting gas fow rate, when the traveing magnetic fied was imposed on the up snorke and down snorke simutaneousy, the circuation fow rate can rise from 77.1 t/min to t/min and the mixing time can fa from 12.9 s to 96.5 s... Effect of Exciting Current Parameters Figure 7 shows that horizonta and vertica components of eectromagnetic force increase with the increasing exciting current. The reason is that both the magnetic induction intensity and the induced eddy current increase with the increasing exciting current. Thus, the eectromagnetic force increases with the increasing exciting current. Moreover, Fig. 5. Effect of different positions of magnetic fied on circuation fow rate. Fig. 4. Comparison of cacuated carbon remova rate with experimenta resuts. Tabe. Comparison of incusion mass fraction with experimenta vaue. Time (s) Measured vaue 4) (ppm) Cacuated vaue (ppm) Error (%) Fig. 6. Effect of different positions of magnetic fied on mixing time ISIJ 1040

6 Fig. 8. Effect of current on circuation fow rate and mixing time (Lifting gas fow rate=1 000 L/min). Fig. 7. Radia distribution of eectromagnetic force at different current intensities (y=0 m, z=0 m). (a) Horizonta component (b) Vertica component. Fig. 7 aso shows that the vertica component of eectromagnetic force is much greater than the horizonta component, so the iquid stee in up snorke or down snorke can be acceerated by the eectromagnetic force effectivey. Figure 8 shows that on the condition of 10 Hz of exciting current frequency, when the current rises from 100 A to 600 A, the circuation fow rate rises from 81.5 t/min to t/min, and the mixing time fas from s to 60.2 s. The reason is that the exciting current has the more profound effect on the axia component of eectromagnetic force than that on the horizonta component of eectromagnetic force. So the iquid stee fow can be acceerated and the circuation fow rate increases. Moreover, the axia eectromagnetic force increases with the increasing exciting current. In this way, with the increasing exciting current, the circuation fow rate increases and the mixing time decreases. Therefore, the RH refining efficiency can be improved by increasing the exciting current. However, great joue heat produced by arge exciting current wi destroy the traveing magnetic fied equipment. Meanwhie, Fig. 9 shows the effect of exciting current frequency on the horizonta and vertica components of eectromagnetic force. The induced eddy current in iquid stee is mainy at the horizonta pane and increases with the Fig. 9. Radia distribution of eectromagnetic force at different current frequencies (y=0 m, z=0 m). (a) Horizonta component (b) Vertica component. increasing exciting current frequency. The magnetic induction intensity amost keeps unchanged with the variation of exciting current frequency. Moreover, the vertica component of magnetic induction intensity is much arger than the horizonta component. Therefore, with the increasing exciting current frequency, the horizonta component of eectromagnetic force increases whie the vertica component ISIJ

7 amost keeps unchanged if the current frequency is greater than 0 Hz. As shown in Fig. 10, on the condition of 200 A of exciting current, when the current frequency rises from 10 Hz to 0 Hz, the circuation fow rate rises from 9.9 t/min to 118. t/min, and the mixing time fas from s to 87.7 s. Then the circuation fow rate fas to t/min and the mixing time is up to 91.8 s when the current frequency is equa to 60 Hz. Such phenomena are reated to the bubbes behavior. It is difficut for the gas bubbes to reach the up snorke center in traditiona RH degasser. But with the hep of horizonta eectromagnetic force, the bubbes have more chances to reach the up snorke center. Moreover, the gas bubbes at the up snorke center can acceerate iquid stee more effectivey than that near the sidewa of up snorke. 8) On the other hand, with the increasing exciting current frequency, the horizonta eectromagnetic force increases whie the vertica eectromagnetic force can hardy be affected. So the circuation fow rate increases with the increasing current frequency if the current frequency is smaer than 0 Hz. However, the gas voume becomes saturated when the current frequency is up to 0 Hz. Thus, the circuation fow rate decreases and the mixing time increases if the exciting current frequency is greater than 0 Hz..4. Effect of Traveing Magnetic Fied on Decarburization and Incusion Remova In order to investigate the effect of the traveing magnetic fied on the decarburization and the incusion remova during RH vacuum refining process, the reated numerica simuation were performed on the condition of ifting gas fow rate of L/min, exciting current of 00 A, and current frequency of 10 Hz. And the traveing magnetic fied was Fig. 10. Effect of current frequency on circuation fow rate and mixing time (Lifting gas fow rate=1 000 L/min). Fig. 11. Effect of different positions of magnetic fied on decarburization in RH degasser (Lifting gas fow rate= L/min). Fig. 12. Predicted isometric contour of carbon concentration after 500 seconds. (a) o magnetic fied (b) Magnetic fied imposed around up snorke (c) Magnetic fied imposed around up snorke and down snorke ISIJ 1042

8 imposed around up snorke, up snorke and down snorke, respectivey. Figure 11 shows that the decarburization rate in RH degasser with traveing magnetic fied imposed around up snorke is greater than that without magnetic fied and the decarburization rate with traveing magnetic fied imposed around up snorke and down snorke is greater than that with traveing magnetic fied imposed around up snorke. Severa reasons ead to this phenomenon. Firsty, the turbuent fow of iquid stee in up snorke and vacuum chamber becomes more drastic in RH degasser with traveing magnetic fied imposed around up snorke, so the mass transfer coefficient in up snorke and vacuum chamber increases. Secondy, the circuation fow rate in RH degasser with traveing magnetic fied imposed around up snorke and down snorke is arger than that in RH degasser with traveing magnetic fied imposed around up snorke. At ast, the mixing time decreases with the increasing circuation fow rate, so better mixing effect is in favor of decarburization. Figure 12 shows that the carbon mass concentration in RH degasser with traveing magnetic fied imposed around up snorke is much smaer than that without magnetic fied. And the carbon mass concentration with traveing magnetic fied imposed around up snorke and down snorke is much smaer than that with traveing magnetic fied imposed around up snorke. However, the fina carbon mass concentration is determined by the pressure in vacuum chamber. Thus, the traveing magnetic fied can acceerate the decarburization rate during the process, but can not decrease the target carbon mass concentration. Figure 1 shows that the incusion number density and concentration decrease most quicky in the RH degasser with traveing magnetic fied imposed around up snorke and down snorke, whie the incusion number density and concentration decrease sowy in the traditiona RH degasser. The reasons are as foows. Firsty, the turbuent energy dissipation rate is very great when the traveing magnetic fied was imposed around up snorke or down snorke and greater turbuent energy dissipation rate can promote the coision and coaescence among incusions more effectivey. Secondy, arger incusions can be removed by the adhesion to the top sag because of the greater fotation veocity. In this way, the incusion remova rate in RH degasser with traveing magnetic fied imposed around up snorke is greater than that without magnetic fied. And the incusion remova rate in RH degasser with traveing magnetic fied Fig. 1. Evoution of incusion characteristic parameters during incusion remova process (Lifting gas fow rate= L/min). Fig. 14. Predicted isometric contour of incusion number density after 200 seconds. (a) o magnetic fied (b) Magnetic fied imposed around up snorke (c) Magnetic fied imposed around up snorke and down snorke ISIJ

9 imposed around up snorke and down snorke is greater than that in RH degasser with traveing magnetic fied imposed around up snorke. Figure 1 aso shows that in the traditiona RH degasser, the incusion characteristic size increases at initia stage, and then decreases. Coision and aggregation among incusions ead to such interesting phenomena. At the initia stage, the number of new bigger incusions after aggregation is much more than that of the removed bigger incusions, so the incusion characteristic size increases continuousy. Once the number of big incusions after aggregation is ess than that of big incusions removed, the incusion characteristic size decreases. Furthermore, the maximum incusion characteristic radius r max and the reated peak vaue time t pv (the time corresponding to the maximum of incusion characteristic radius) can be observed in Fig. 1. In the case of no magnetic fied, r max =.85 μm, t pv=460 s. If the traveing magnetic fied is imposed around the up snorke, r max =.97 μm, t pv=705 s. If the traveing magnetic fied is imposed around the up snorke and down snorke, r max =4.29 μm, t pv=884 s. So the appication of traveing magnetic fied can decrease the incusion size and the peak vaue time effectivey. Figure 14 shows that the incusion number density in RH degasser with traveing magnetic fied imposed around up snorke is much smaer than that without magnetic fied. And the incusion number density in RH degasser with traveing magnetic fied imposed around up snorke and down snorke is much smaer than that with traveing magnetic fied imposed around up snorke. 4. Concusions The numerica method was empoyed to investigate the two-phase fow fied, mixing time, decarburization and incusion remova on the condition of traveing magnetic fied imposed on the snorkes in RH degasser. And the effect of different exciting current parameters on the RH refining process was aso discussed. For RH imposed by traveing magnetic fied, the foowing concusions can be obtained. (1) With the increasing current, the circuation fow rate increases and the mixing time decreases. (2) If the current frequency ies in the range of 10 0 Hz, with the increasing current frequency, the circuation fow rate increases whie the mixing time decreases. But if the current frequency ies in the range of 0 60 Hz, with the increasing current frequency, the circuation fow rate decreases whie the mixing time increases. () In order to increase circuation fow rate and shorten mixing time, the first measure is to appy the traveing magnetic fied around the up snorke, and the second is to appy the traveing magnetic fied around the down snorke if the gas fow rate is smaer than the saturation vaue. However, such a difference disappears if the gas fow rate is greater than the saturation vaue. (4) For decarburization, by imposing the traveing magnetic fied around up snorke or down snorke can acceerate the decarburization rate during the process, but can not decrease the target carbon mass concentration. (5) For incusion remova, the most effective measure is to appy the traveing magnetic fied around the up snorke and down snorke, and to appy the traveing magnetic fied ony around the up snorke has the minor effect. Acknowedgements This work was supported by the ationa High-tech R&D Program of China (2009AA0Z50), ationa atura Science Foundation of China and Shanghai Baostee ( ), 111 Project (B07015), the Fundamenta Research Funds for the Centra Universities ( ), and the Doctor Startup Foundation of Liaoning Province ( ). REFERECES 1) Y. G. Park and K. W. Yi: ISIJ Int., 4 (200), ) B. Liu, G. Zhu, H. Li, B. Li, Y. Cui and A. Cui: Int. J. Miner. Meta. Mater., 17 (2010), 22. ) S. K. Ajmani, S. K. Dash, S. Chandra and C. Bhanu: ISIJ Int., 44 (2004), 82. 4) Y. Miki and B. G. Thomas: Iron Steemaker, 24 (1997), 1. 5) Y. G. Park, K. W. Yi and S. B. Ahn: ISIJ Int., 41 (2001), 40. 6) I. Sumi, G. Okuyama, S. abeshima, H. Matsuno and Y. Kishimoto: ISIJ Int., 47 (2007), 7. 7) K. Shirabe and J. Szekey: Trans. Iron Stee Inst. Jpn., 2 (198), ) J. H. Wei and H. T. Hu: Stee Res. Int., 77 (2006), 91. 9) D. Q. Geng, H. Lei and J. C. He: Meta. Mater. Trans. B, 41 (2010), ) T. Kuwabara, K. Umezawa, K. Mori and H. Watanabe: Trans. Iron Stee Inst. Jpn., 28 (1988), ) Y. G. Park, W. C. Doo, K. W. Yi and S. B. An: ISIJ Int., 40 (2000), ) P. A. Kishan and S. K. Dash: ISIJ Int., 49 (2009), ) M. Y. Zhu, J. Sha and Z. Z. Huang: Acta Meta. Sin., 6 (2000), ) B. K. Li and F. Tsukihashi: ISIJ Int., 40 (2000), ) B. K. Li and F. Tsukihashi: ISIJ Int., 45 (2005), ) L. eves, H. P. O. Oiveira and R. P. Tavares: ISIJ Int., 49 (2009), ) V. Seshadri, S. C. A. Da, S. I. A. Siva, G. A. Vargas and P. S. B. Lascosqui: Ironmaking Steemaking, (2006), 4. 18) V. Seshadri, C. A. Siva and I. A. D. Siva: Scand. J. Meta., 4 (2005), ) Y. J. Zhang, C. B. Feng and J. C. He: C Patent, , (2005). 20) S. I. Chung, Y. H. Shin and J. K. Yoon: ISIJ Int., 2 (1992), ) A. Giere and P. Masse: IEEE Trans. Magn., 24 (1988), ). Kubo, T. Ishii, J. Kubota and. Aramaki: ISIJ Int., 42 (2002), ) M. Iguchi and H. Tokunaga: Meta. Mater. Trans. B, (2002), ) H. Lei, D. Q. Geng and J. C. He: ISIJ Int., 49 (2009), ) D. Q. Geng, H. Lei and J. C. He: ISIJ Int., 50 (2010), ) S. Linder: Scand. J. Meta., (1974), ) K. Yamaguchi, Y. Kishimoto, T. Sakuraya, F. Tetsuya, M. Aratani and H. ishikawa: ISIJ Int., 2 (1992), ) B. Keimt, S. Koehe, H. J. Ponten, W. Matissik and D. Schewe: Ironmaking Steemaking, 20 (199), ) M. Takahashi, H. Matsumoto and T. Satito: ISIJ Int., 5 (1995), ) T. Kitamura, K. Miyamoto, R. Tsujino, S. Mizoguchi and K. Kato: ISIJ Int., 6 (1996), 95. 1) J. H. Wei and. W. Yu: Stee Res. Int., 7 (2002), 15. 2) M. Manninen and V. Taivassao: On the Mixture Mode for Mutiphase Fow, VTT Pubications 288, Technica Research Center of Finand, Finand, (1996). ) H. L. Zhang: PhD Dissertation, ortheastern University, Shenyang, China, (2002). 4). W. Yu: PhD Dissertation, Shanghai University, Shanghai, China, (2001). 5) M. D. Wang: Steemaking, 19 (200), ISIJ 1044