Novel Mixing and Separation Method through Vortex Stirrer

Transcription

1 Novel Mixing and Separation Method through Vortex Stirrer Dep. of Mechanical Engineering, Nippon Institute of Technology, S. YOKOYA, K. TADA, S. TAKAGI Department of Metallurgy Graduate School of Engineering, Tohoku University Y. SASAKI Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, M. IGUCHI There is a strong demand for innovation of steel-making processes, because the preservation of global-environment, energy and resource saving as well as productivity cost and quality on steel are important issues for sustainable-development of steel industry. Without imparting artificial energy, vortex stirrer using only a gravitational energy is invented and studied. Obtained results are as follows: The refining reagent can be completely sucked into the hot metal through the vortex effect. The tangential velocity decreases inversely with increasing radially the distance from the free surface. The calculated results coincide well with the experimental results. 1. Introduction With increasing requirement of the preservation of global-environment, energy and resource saving as well as productivity cost and quality on steel, innovation of steel-making processes are urgently required for sustainable development of the steel industry. So far, in order to well mix the refining reagent with hot metal, special energy methods such as gas injection, mechanical stirring and electromagnetic agitation are applied. Accordingly, it is necessary to develop the innovative mixing method without external special energy for both saving the artificial energy and mixing efficiently the refining reagent with hot metal. In this study, we propose a vortex stirrer of novel mixing method shown in Fig.1. A hot metal flowing down on the funnel forms a kind of free vortex through the potential energy and gas column around the axis of funnel. Through an effect of contraction at the downstream end of the funnel, an annular impinging flow is constructed, flow into the free surface of the mixing tube as a impinging flow and construct a kind of fierce stirring flow in the mixing tube 1-3). Because the impinging flow suck completely the refining reagent into the hot metal from the shearing effect interacting between impinging flow and bulk flow in the mixing tube with the gas babbles, it is our target to discuss how to disperse uniformly the refining reagent into the hot metal, to increase the interfacial area for reactions as much as possible during the reaction stage, and also to decrease it as soon as possible, after the reaction completed x x y,w z,v Fig.2 Experimental apparatus. Fig. 1. Vortex stirrer and its mixing Shinichiro YOKOYA (Nippon Institute of Technology, Miyashiro, Saitama, ) 1

2 2. Experimental method Figure 2 shows a experimental apparatus of vortex stirring in a plane through the axis of symmetry. Stirring apparatus consisted from three sections, funnel creating free vortex, mixing tube and tube of a kind of overflow-tank for keeping the level of water constant. After the flow pattern in the funnel becomes steady-state, flow patterns in both the funnel and mixing tube were measured through the LDV every 90 the axis. 3. Results and considerations 3.1 Funnel (1) Radial profiles of tangential velocity of u Figure 3 shows a radial profile of tangential velocity in the plane oriented perpendicular to the axis of funnel at the position of z=40 mm upwards from the outlet of the funnel. It was found that the values measured every 90 then the flow pattern is said to be axi-symmetric. A profile of the tangential velocity has a maximum near the y=0, namely, the free surface between the bulk of water and gas-column. On the other hand, the tangential velocity decreases with the measurement point increasing radially in distance from the free surface between the bulk of water and gas-column to the wall of funnel. Namely, the tangential velocity decreases inversely with increasing radially the distance from the free surface at the same plane perpendicular to the axis. The calculated results coincide well with the experimental results. The same tendency for the tangential velocity at the mid-height z=100 mm of funnel can be observed in Fig.4 The profiles of tangential velocity on the planes perpendicular to the axis corresponding to the various axial positions are shown in Fig.5. It was found that the profiles of the tangential velocity on the planes at the various positions upwards from the outlet of the funnel can be represented in the only one inverse curve and that is reproduced by the calculated result. (2) Radial profiles of axial vertical of v Figure 6 and 7 show radial profiles of axial velocity in the plane oriented perpendicular to the axis of the funnel at the axial positions, z=40, z=100 mm upwards from the outlet of the funnel. Comparatively large downward velocity and a bit upward velocity distributions can be observed near the free surface between the gas column and bulk of liquid, and somewhat upward flow velocity decreases to the magnitude of almost zero with increasing the radial distance from near the free surface to the wall of the funnel on the same plane. It was found that the flow pattern is very complex because there is not only upward flow, but also downward flow. The difference between the calculated and experimental results can be observed near the free surface through the some asymmetry at the outlet of the funnel. However, Fig.3 Comparison of measurement results velocity u at z=40mm. Fig.4 Comparison of measurement results velocity u at z=100mm. Fig.5 Comparison of measurement results velocity u. 2

3 from the above-mentioned results, it appears that the calculated results can reproduce the experimental results. Fig.6 Comparison of measurement results with calculated ones for axial velocity u at z=40mm. Fig.7 Comparison of measurement results with calculated ones for axial velocity u at z=100mm. 3.2 Mixing tube The flow pattern in the mixing tube after flowing into the mixing tube as an annular impinging flow, are shown in Fig. 8 and 9, respectively. It is observed that a gas-column is created at the center part of the funnel, the annular impinging flow with vertical angle of 40 degree flow into the mixing tube and then create the bubble in the mixing phase. The flowing down flow near the wall of the mixing tube is observed and flowing up flow at the core of the tube is shown. Namely, a kind of circulation flow is formed in the mixing tube. 1.5 m/s Fig. 8 Calculated annular impinging flow and its resulted two phase flow in mixing tube: water phase is shown as black and air phase is also shown as gray color. Fig. 9 Calculated annular impinging flow and its resulted flow pattern in mixing tube: arrow length shows velocity magnitude. 3

4 (1) Radial profiles of tangential velocity Figures 8 and 9 show the radial profiles of tangential velocity in the plane oriented perpendicular to the mixing tube at the axial positions z=-80 mm, z=- 160 mm, respectively. The flow pattern shows a forced vortex because the tangential velocity increases with increasing the radial position as shown in Fig. 8. On the other hand, a bit The calculated results coincides with experimental results, fairly. (2) Radial profiles of axial velocity Figures 10 and 11 show the radial profiles of axial velocity in the plane perpendicular to the axis of the mixing tube at the axial positions z=-80 mm, z=- 160 mm downwards from the outlet of the funnel, respectively. Some upward velocity near the axis and downward velocity in the outer area are observed. Fig.8 Radial profile of tangential velocity u at position z = -80 mm. Fig.9 Radial profile of tangential velocity u at position z = -160 mm. Fig.10 Radial profile of axial velocity v at position z = -80 mm. Fig.11 Radial profile of axial velocity v at position z = -160 mm. 4. Conclusion (1) The refining reagent can be completely sucked into the hot metal through the vortex effect. (2) The flow pattern in the funnel and mixing tube can be reproduced by numerical analysis for the condition that liquid is wetted with the funnel wall. 4

5 References 1) YOKOYA et al. Research group on Creation of Innovative Metallurgical Reactor for Mixing/Separation (First meeting) 2) YOKOYA et al. CAMP-ISIJ. Vol(2000),81 3) SASAKI et al. New development concerning innovative metallurgical reactor ; Research group on Creation of Innovative Metallurgical Reactor for Mixing/Separation (2002), 21. 5