Abstract:
An inductor is used to generate an electromagnetic AC field at a pipe-in-pipe discharge element of a metallurgical vessel. The inductor has at least two cooling fluid regions for the flow of cooling fluid therethrough. First supply and drain lines are connected to a first of the cooling fluid regions for supplying the first cooling fluid thereto. Second supply and drain lines are connected to a second region. The second cooling fluid is different than the first cooling fluid so that separate regions can be separately cooled with different cooling fluids having different properties.

Description:
This application is a 371 of PTC/DE97/02784 filed on Nov. 28, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an inductor for generating an electromagnetic AC field at a discharge element of a melt vessel through which, for the purpose of cooling, flows a cooling fluid. 
     2. State of the Prior Art 
     In DE 195 00 012 A1 is described an inductor in a regulation and closure device of a metallurgical vessel which comprises a stator disposed in the vessel wall and a rotor rotatable in the stator for choking or shutting off the melt flow (a pipe-in-pipe closure system). Cooling takes place uniformly by means of a single cooling fluid. For reasons of safety, compressed air is used as the cooling fluid so that in the event of leakage, for example through wear of the vessel wall, water vapor or oxyhydrogen gas cannot develop. 
     In an older patent application, 196 03 317.9-34, it is specified that the inductor, during an operating phase, is cooled with liquid gas, and with air during a stand-by phase. Cooling with water is also avoided here. 
     GB 22 79 543 A describes a two-part inductor with separate electrical connections at the discharge element of a melt vessel. Nothing is mentioned about cooling. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an inductor of the above described type so that it can be operated with differing cooling means for the purpose of being able to adapt to various cooling requirements. 
     According to the present invention, the above object is achieved through the following characteristics of the invention. An inductor is provided with different regions with separate conveyances for conveying the cooling fluid to and from the region. It is thereby possible to act upon the differing regions of the inductor simultaneously or successively with different cooling fluids. This permits the cooling in the individual regions to be adapted to the particular requirements obtaining at the regions. It is, in particular, possible to carry out cooling in a region in the proximity of a danger zone in which the use of water as a cooling means is dangerous, by means of a gas, and in particular by air. The danger zone is located where the inductor is closest to the melt disposed in the melt vessel because at this location, due to wear and/or the formation of cracks in the wall of the melt vessel, it is possible for the melt to come into contact with the inductor. In other regions, water or water vapor can be used for cooling. 
     For a particular region of the inductor, the cooling fluid is always used which, in each instance, is most suitable for cooling the region and its environment. The various cooling fluids are preferably liquid gas or dry ice or water or water vapor or gas or compressed air. When using gases as the cooling fluid, which is especially preferred in danger zones, it is also possible, in order to adapt to the cooling performance required in each instance, to use a variably adjustable ratio of several gases, for example compressed air and supercooled air or nitrogen or carbon dioxide or oxygen or the like. By using differing cooling fluids, and thus different cooling performances, in the individual regions of the inductor, the electromagnetic AC field generated by the inductor can be utilized for differing functions. These include, in particular, inductive heating and/or the generation of a reference field for temperature measurements and/or slag detection and/or generation of a directed electromagnetic field for the purpose of exerting a force component onto the melt, which, for example, can be used for gap sealing in the discharge element. 
     The regions of the inductor can preferably be acted upon with differing electric frequencies and/or differing electric powers depending on the purpose of the particular region. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Further advantages and features of the present invention will become evident from the following description of a preferred embodiment with reference to the accompanying FIGURE. 
     The FIGURE depicts an inductor for a discharge element, implemented as a pipe-in-pipe rotary closure, at the bottom of a melt vessel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In a bottom (1) of a melt vessel, for example for a steel melt, a pipe-in-pipe closure system (R) is installed. It comprises a nozzle brick (2) in which, by means of a mounting device (3), a stator (4) comprising a refractory ceramic material is fastened. In the stator (4), which has a melt inlet opening (5), a rotor (6) comprising a refractory ceramic material is rotatably supported. Between stator (4) and rotor (6) exists a gap (7). Within the rotor (6) a melt outflow channel (8) is formed. By rotating the rotor (6) its melt outflow channel (8) can be moved to coincide more, less or not at all with the inlet opening (5), whereby the melt outflow can be controlled or interrupted. 
     The stator (4) is encompassed by a coil-form inductor (9) which is built into the nozzle brick (2) and is in contact with the stator (4) via insulation (10). The inductor (9) comprises a hollow chamber-form metal section and is connected to an electric frequency converter (11) whose frequency and/or power are adjustable. 
     With respect to its conductance of cooling fluid, the inductor (9) is divided into an upper region (12) and a lower region (13). The upper region (12) is in closer proximity to melt (S) in the vessel. It is close to a danger zone (G) in which, during operation, wear or the formation of cracks must be anticipated. The lower region (13) is further removed from this zone. The upper region (12) comprises a supply line (14) and a drain line (15). The lower region (13) comprises a supply line (16) and a drain line (17) for a different cooling fluid. The supply line (14) supplies cooling fluid from a first cooling fluid source (18). The supply line (16) supplies cooling fluid from a second cooling fluid source (19). The cooling fluid for the upper region (12) is a gas, in particular a compressed gas. The cooling fluid for the lower region (13) is liquid petroleum gas or dry ice or water or water vapor, however, the cooling fluids are changeable depending on the application. From the first cooling fluid source (18) and the second cooling fluid source (19), the regions (12, 13) can be cooled independently of one another with respect to the type of cooling fluid and the cooling performance. 
     As in the case with respect to cooling, in which the inductor (9) is divided into regions (12, 13), it can also be divided electrically into differing regions. To these regions can be connected differing frequencies and/or powers. In the FIGURE, accordingly, to the lower region (13) is connected a frequency converter or transformer (11) by means of electrical connection (21, 22). To the upper region (12) is connected a further frequency converter or transformer (20) by means of electrical connections (23, 24). The frequencies and/or powers of the converters or transformers (11, 20) are adjustable. 
     In particular, the upper region (12) is used for the inductive heating of the melt flowing through the outflow channel (8). Herein either the steel melt itself can be coupled to the electromagnetic AC field of the inductor (9), or the rotor (6) and/or the stator (4) can be coupled to the electromagnetic AC field and subsequently the melt is heated, if applicable, through thermal conduction or heat radiation. The cooling takes place in order to protect the inductor against overheating and, if appropriate, to dissipate heat from its environment. 
     The lower region (13) can also be used for the inductive heating of the melt flowing through the outflow channel (8). Its cooling can be stronger than in the upper region (12) through the corresponding selection of the cooling fluid and/or its throughflow rate. Through intensive cooling, heat dissipation from the environment (the nozzle brick) is also possible here. 
     The lower region (13) can also serve as a reference coil or reference field for temperature measurement of the melt flowing through the outflow channel (8). For this purpose a further (receiver) coil is required (not shown). In this case the lower region (13) is connected to a measuring device (not shown). Since the electrical properties, in particular the conductivity, of the melt is a function of the temperature, it has a different effect on the reference field of the lower region (13) depending on the temperature detected and evaluated by the measuring device. The same applies also to slag detection since slag has a different electrical conductivity than the melt. Herein also the cooling of region (13) can be selected independently of the cooling in region (12). 
     The lower region (13) can also be utilized for generating a directed electromagnetic field which generates in melt which potentially has penetrated into gap (7) a force component which counteracts the melt flow. Sealing of the gap (7) is thereby attained. In this case intensive cooling is favorable since high electric power is required for generating the force component. 
     The described inductor can be used in other discharge systems in a wall or bottom of a metallurgical vessel for teeming liquid metals, in particular steel. But it can also be applied in arrangements for slag run-off in, for example, disposal incinerators.