Improving of Refining Efficiency Using Electromagnetic Force Driven Swirling Flow in Metallurgical Reactor Baokuan Li (Speaker) Fengsheng Qi Northeastern University, China Fumitaka Tsukihashi The University of Tokyo, Japan z y x o

Inclusions are mainly removed by attachment of argon gas bubbles in molten steel. Removal rate of inclusions depend on the number, size, shape, self- motion and distribution of gas bubbles in melt. A optimum behavior of argon gas bubbles for refining efficiency is very important. life of RH equipment is also affected by attachment and action of gas bubbles near wall. Vacuum Molten steel +inclusions Pump Air r θ x z y o Research background Argon gas bubbles

Swirling flow is produced by the application of rotating magnetic field, and effect of swirling flow included: Efficient mixing and Efficient separation of inclusions by improving probability of attachment, collisions and coalescence with dispersed gas bubbles in Refining processes. Vacuum Molten steel + inclusions Pump Air r θ x z y o Innovative Steelmaking - Application of Swirling Flow

Gas distributor Nozzle distribution Rotameter Manometer Ultrasonic flowmeter RH degassing vessel Impeller Water model experiments examine the research ideas

Effect of impeller input power on gas bubbles distribution, shutter speed is 1/125 second. Q=0.25 m3/h. (a) 0, (b) 20 W, (c) 25 W and (d) 35 W (a)(c)(d)(b)

× m 3 /s × m 3 /s × m 3 /s Circulation flow rate, m 3 /s Input power, W Effect of plane blade impeller on circulation flow rate of RH vessel

(Yokoya et al )

Nozzle diameter is 2 mm, gas flow rate is 0.25 m 3 /h, strobe light speed is 1/2000s. swirl number is 0, 0.23, 0.53, 0.68, respectively.

Nozzle diameter is 2 mm Gas flow rate 0.25 l/h Swirl number Averaged gas bubble diameter at outlet of nozzle, mm Effect of swirl number on the gas bubble diameter at outlet of nozzle

Argon gas bubbles Mathematical model A homogeneous model for the two- phase turbulent flow in the RH vessel with the rotating magnetic field in the up-leg. The momentum equation for gas phase is ignored. The previous model is only valid for bottom blown reactors. Vacuum Molten steel + inclusions Pump Air r θ x z y o

Formulation Spitzer et al. [1]

Centripetal force and horizontal slip velocity caused by rotating magnetic field Penetrating velocity and slip velocity Vertical slip velocity Horizontal penetrating velocity: Q g : total argon gas flow rate, n :nozzle number A : cross nozzle inlet area α : gas volume fraction (at inlet α 0 )

Boundary conditions and solution method Flow field Gas volume fraction Self-developed computer code in Fortran language

Vacuum water Pump Air r θ x z y o B 0 = 0.1 mT Frequency = 50 Hz

Calculated flow velocities at horizontal sections of RH degassing vessels, (a) up-leg, (b) bottom of vacuum chamber, (c) middle of vacuum chamber, and (d) surface of vacuum chamber. (a) (d)(c) (b) (a) (b) (c) (d) B 0 = 0.1 mT Frequency = 50 Hz

Computed gas volume fraction at main sections of RH degassing vessels, (a) no swirling flow (b) with swirling flow. (a) (b) B 0 = 0.1 mT Frequency = 50 Hz

Gas volume fraction Diameter of up-leg, m No swirling flow With swirling flow Gas volume distribution of RH degassing vessel Velocity distribution of RH degassing vessel

CONCLUSIONS Water model experiments showed that the gas bubbles may be moved toward the central zone in up-leg in RH vessel under the swirling flow. the size of gas bubbles produced from nozzle become small and number of gas bubbles increases. the gas bubbles are dispersed in the whole up-leg. Residence time and journey of gas bubbles in up-leg is prolonged. The numerical results showed that a swirling flow may be produced and extended into the vacuum chamber in case that rotating magnetic field is applied in up-leg. The maximum of gas volume fraction moves toward the center zone of the up- leg. The upward velocity distribution in up-leg changes from M type to parabolic type.

Control of size, shape and distribution of argon gas bubbles Change of collisions, coalescence and attachment of the inclusions Argon gas bubbles Vacuum Molten steel + inclusions Pump Air r θ x z y o The future works --- application of swirling flow