Patent Publication Number: US-2013233704-A1

Title: Replaceable Cathode Choking Devices of Aluminum Reduction Cell

Description:
FIELD OF THE INVENTION 
     The present invention relates to replaceable cathode choking devices of an aluminum reduction cell, pertaining to the technical field of aluminum reduction cell. 
     BACKGROUND OF THE INVENTION 
     With improvement of design and operating technical level of the aluminum reduction cell, the international or domestic newly designed and constructed aluminum reduction cells are increasingly developed to be large-scale ones. Potline current will inevitability increase to 550 kA-700 kA, or even more. In recent years, the domestic technology of aluminum reduction has achieved great development, whereby the capacity of the reduction cell has already caught up with or even exceeded the international advanced level. However, there is relative large disparity in terms of energy saving and consumption reducing compared to the world&#39;s advanced level. Currently, each of domestic aluminum factories has a DC consumption of around 13200-3500 kWh/T.Al, some of which even approach 14000 kWh/T.Al. There is considerable potential to reduce the consumption. Especially in the case of current extremely severe economic conditions at home and aboard, the requirement of energy saving is much more imperative. 
     Recently, many designs take the approaches of adding bosses or placing choking devices on cathode surfaces in order to achieve an object of improving flow velocity, lowering molten aluminum-electrolyte interface, decreasing polar distance, and saving energy and reducing consumption. Due to the method of placing choking devices, these approaches are not only suitable for constructing new cells and complete overhauling the cells, but also capable of being used in on-line production cells, thereby obtaining a relatively large-scaled popularization. However, these approaches have a problem in that: when some of the choking devices are put into service or replaced, the positions of remaining choking devices may be offset under a scouring action of molten aluminum, influencing the actual choking effect. One of the designs (e.g., patent application of CN20081018106.2) fixes the choking devices by means of machining bores or channels in cathode surfaces, but this would increase the cost of choking grooves. 
     The present invention alters a cross-sectional shape of the choking devices, enabling them to generate a downward pressure when subjected to the scouring of molten aluminum and to stabilize on cathode surfaces. At the same time, the choking devices with such a cross-sectional shape have a better choking effect than ordinary choking devices. 
     SUMMARY OF THE INVENTION 
     The technical problem to be solved by the present invention is to provide replaceable cathode choking devices of an aluminum reduction cell. These devices can be adapted to various production conditions and firmly placed on cathode surfaces of the aluminum reduction cell, enabling the aluminum reduction cell to achieve good stability, realizing the effect of energy saving and consumption reduction, so as to overcome the shortages of the position offsetting and hence the influence on actual choking effect present in the prior art. 
     The technical solution of the present invention is as follows: it comprises cathode carbon blocks and cathode choking devices placed at the bottom of the aluminum reduction cell, wherein the cathode choking devices are placed on surfaces of the cathode carbon blocks, and the cathode choking devices are made of mullite, spinel or zirconite which is high temperature resistant, corrosion resistant and of high specific gravity. 
     The cathode choking devices have a cross-section of semicircular, arc or streamline shaped. 
     The cathode choking devices have a height of 50-150 mm and a width of 100-300 mm. 
     The cathode choking devices are elongated block-shaped. 
     The cathode choking devices are placed in a direction along a long side of a cathode of the reduction cell, wherein each group of the cathode choking devices can be one or more cathode choking devices. 
     Existing choking devices are generally elongated devices with a rectangular or trapezoidal cross-section. The choking devices are placed on the cathode surfaces of the aluminum reduction cell, in order to eliminate vortices generated by existing cathode carbon blocks. Through tests and calculation analyses, it can be known that this will destroy the distribution of flow velocity field generated by an electromagnetic force of the existing aluminum reduction cell, breaking the field into pieces and preventing the molten aluminum from generating relative large rises and fluctuations, thereby achieving a better stability. Hence a further effect of energy saving and consumption reduction is achieved. However, the existing choking devices have a problem in that: 1) the choking devices may be offset due to the scouring of fluid; 2) due to the shape characteristics of the existing choking devices, they will allow the molten aluminum to flow through areas near two corners of the top surfaces thereof, generating certain vortex, thus weakening the choking effect. The cross-section of the choking devices of the present invention is obtained after a large number of experiments and computer simulations. When these devices are put into an in-production aluminum reduction cell, they can be firmly fixed on the cathode surfaces due to downward forces generated locally. At the same time, a smooth surface structure thereof can also reduce turbulence of the molten aluminum as much as possible, so as to obtain a better choking effect. Material of mullite, spinel or zirconite, which is high temperature resistant (≧1000° C.), molten aluminum and electrolyte corrosion resistant and of higher specific gravity than molten aluminum, can be used for making the present choking devices. Therefore, the present invention has advantages of less modification to the reduction cell, good energy saving effect and broad applications, etc., and has excellent economic benefits, popularization values and use values. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of the prior art; 
         FIG. 2  is a schematic perspective view of the configuration of the present invention; 
         FIG. 3  is a Y-direction view of  FIG. 2 ; 
         FIG. 4  is an X-direction view of  FIG. 2 ; 
         FIG. 5  is a schematic view of placing multiple groups of cathode choking devices of the present invention; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment of the present invention: the present invention comprises cathode carbon blocks  1  and cathode choking devices  2  placed at the bottom of an aluminum reduction cell, wherein the cathode choking devices  2  are placed on surfaces of the cathode carbon blocks, and the cathode choking devices  2  are made of mullite, spinel or zirconite which is high temperature resistant, corrosion resistant and of high specific gravity. 
     The cathode choking devices  2  have a cross-section of semicircular, arc or streamline shaped. 
     The cathode choking devices have a height of 50-150 mm and a width of 100-300 mm. Generally, the height is 100 mm and the width is 200 mm. 
     The cathode choking devices  2  are elongated block-shaped. 
     The cathode choking devices  2  are placed in a direction along a long side of a cathode of the reduction cell, wherein each group of the cathode choking devices can be one or more cathode choking devices  2 . 
     As shown in  FIG. 2 , the cathode carbon blocks  1  are placed at the bottom of an aluminum reduction cell. The cathode choking devices  2  are placed on the surfaces of the cathode carbon blocks  1 . The cross-section of the choking devices is semicircular (as shown in  FIG. 3 ), or arc-shaped or streamline shaped (parabolic or hyperbolic shapes, etc) and the like. The choking devices are placed in a direction along a long side of the surfaces of the cathode carbon blocks (as shown in  FIGS. 2 ,  4  and  5 ), each of which surfaces can be used for placing one group, two groups (as shown in  FIG. 4 ) or multiple groups (as shown in  FIG. 5 ) of cathode choking devices. The cathode choking devices are made of a material which is high temperature resistant, molten aluminum and electrolyte corrosion resistant and of higher specific gravity than molten aluminum. The aforementioned material is current commonly used material and would not increase too much cost. The height and width of the choking devices are required to be 50-200 mm and 100-300 mm, respectively. During normal production, the molten aluminum should overflow these choking devices by 30-150 mm. Then protruding portions of the molten aluminum can well destroy the flow field of the molten aluminum, increasing the stability of the aluminum reduction cell, and can further reduce the polar distance during the normal production, realizing the effect of energy saving and consumption reduction. 
     Said material which is high temperature resistant (≧1000° C.), (molten aluminum and electrolyte) corrosion resistant and of high specific gravity (≧3) is mullite, spinel, zirconite, etc.