AU2009279227A1 - Inlet nozzle for a degassing vessel for metallurgical melting operating according to the RH method - Google Patents

Description

5095-102PUS INLET NOZZLE FOR A DEGASSING VESSEL FOR METALLURGICAL MELTING OPERATING ACCORDING TO THE RH METHOD The invention is directed to an inlet snorkel for a degassing vessel for metallurgical melting using the RH process. In the RH (Ruhrstahl-Heraeus) process, the molten steel is conveyed from a ladle in an up leg by means of a delivery gas, particularly argon, which is fed into the up leg above the liquid steel level, into the evacuation vessel due to the expansion in volume of the delivery gas in the up leg and the pressure difference between the outside air pressure and the negative pressure in the evacuation vessel. The argon bubbles present nuclei for CO formation and promote deoxidation and the removal of nonmetal particles. The steel sucked into the evacuation vessel is atomized resulting in an increased surface and, therefore, good degassing. It is known from EP 297 850 A l to arrange a plurality of conduits around the circumference of the inlet snorkel so as to be divided into two groups, with gas under high pressure being admitted to one group and gas under low pressure to another group. In this way, the supplied gas flows penetrate to different depths in the molten metal guided through the snorkel and allow a uniform gassing of the molten metal over the cross section of the snorkel. It is known from the literature to influence flow through a magnetic field: "Modeling of Two-Phase in RIH Vacuum Degassing Vessel with the Effect of the Rotation Magnetic Field", AISTech 2004 Proceedings, Volume 1, pp. 1125-1133, Baokuan Li et al. (PRC). This solution for exerting a magnetohydrodynamic effect on the melt flow provides a water-cooled component below the floor of the RH vessel. This construction is too large for technical application. Further, the water cooling presents a safety hazard. It is the object of the invention to improve the flow conditions within the inlet snorkel. According to the invention, this objet is met by an inlet snorkel for a degassing vessel for metallurgical melting using the RH process which is characterized in that gas injection pipes through which inert gas can be introduced into the inlet snorkel are distributed along the axial length of the inlet snorkel, and in that groove-like guide shapes are provided upstream of these gas injection pipes so as to project into the clear cross section of the inlet snorkel. Accordingly, the core of the invention consists in realizing a passive flow guidance in the inlet snorkel of the RH installation. By means of the invention, the melt rising in the inlet snorkel of a RH installation and the emulsified inert gas bubbles are homogenized through a passive flow guidance. In passive influencing of flow, as distinct from active influencing of flow (e.g., bubbling in of gas), the primary fluid is influenced exclusively by formative steps. This goal is achieved by a special shaping of the refractory lining in axial direction of the inlet snorkel. The lining proceeds from the inlet side, i.e., from bottom to top, through a plurality of groove-like guide shapes which are twisted by a determined angle and project into the melt. These guide shapes extend into the inlet snorkel and induce a swirling in the rising multiphase mixture of melt and gas bubbles. As a result, the gas bubbles are transported away from the refractory wall in direction of the axis of the inlet snorkel. A homogenization of the characteristic flow profile takes place. This process brings about a more intensive mixing in the inlet snorkel. Twisted guide shapes of refractory material are installed between the delivery locations of the inert gas (gas injection pipes). The quantity of guide shapes is determined by the quantity of gas injection pipes. The guide shapes having a thickness D, depth T and radius R are twisted at an angle a from bottom to top, i.e., in direction of the longitudinal axis of the snorkel. This angle is preferably on the order of 20' to 45'. Accordingly, a spiral-shaped motion is imposed on the gas bubbles rising between the guide shapes which, considered over a large area, leads to a homogenization of the radial flow profile. Due to the induced whirling, the gas bubbles no longer rise only in the vicinity of the wall, but also to a greater extent in the center of the inlet snorkel. As a result, the previously experienced elevation of the melt above the inlet snorkel in the RH vessel is reduced. The potential energy saved in this way translates to kinetic energy.

As a result, the treatment time and circulating time of the melt can be reduced. Beyond this, a reduction in the overall height of the RH vessels can be expected. Accordingly, the advantage of the invention consists in that the treatment time and circulating time in the RH installation can be reduced as a result of the improved homogenization of the multiphase mixture of melt and gas bubbles. Larger quantities of gas could be used so that the kinetics of the metallurgy can be improved. Consequently, the productivity of the RH installation is increased. The invention will be described more fully in the following with reference to the drawings. The drawings show: Fig. I a perspective view of a portion of the inlet snorkel provided with guide shapes; and Fig. 2 a corresponding cross section. As can be seen, the guide shapes having a thickness D, a depth T and a radius R are twisted in longitudinal direction of the snorkel, namely, by an angle a.

Claims (3)

1. 2. Inlet snorkel according to claim 1, characterized in that the guide shapes are made of refractory material.
2. 3. Inlet snorkel according to one of the preceding claims, characterized in that the guide shapes having a thickness D, a depth T and a radius R and are twisted at an angle a in direction of the longitudinal axis of the snorkel.
3. 4. Inlet snorkel according to claim 3, characterized in that the angle a is between 200 and 45'.