Patent Publication Number: US-11660612-B2

Title: Method for processing a flowable product by electrically charging particles in the flowable product and a disc stack of a centrifuge

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a method for processing a flowable product and a centrifuge, in particular a separator. 
     DE 10 2006 022 156 A1 discloses a method and a device for the treatment of liquids in which an inflowing flowable product is separated in a centrifuge into two liquid phases and a solid phase. The product, e.g., a contaminated lubricating oil, is separated into two partial streams which are led past a positive or negative electrode. The particles contained in the first partial flow are positively charged and the particles of the second partial flow are negatively charged. Before the liquid is introduced into the centrifuge, both partial streams are combined in a collection tank, wherein the positively charged particles and the negatively charged particles conglomerate into larger particle clusters due to the mutual electrostatic attraction. These conglomerates are then easier to separate from the liquid in the centrifugal field. 
     SU 5 51 036 discloses a centrifuge that allows electrostatic charging of particles within a non-continuously operating centrifuge. For this purpose, an electrode is arranged in an inlet chamber on the rotational axis of the centrifuge. After the electrostatic charging of the particles, they are transferred to a drum chamber where the particles are separated in solids collection pockets. The clarified liquid is then discharged from the centrifuge. The solids collection pockets are embedded in the wall of the centrifuge. Unlike a conventional centrifuge with one disc stack, however, this centrifuge does not allow continuous operation, as the collection pockets have to be emptied at regular intervals. 
     It is the object of the present invention, based on the prior art, to provide a method for processing a flowable product and to provide a centrifuge which allows an alternative solution for a better separation of particles. 
     In accordance with the invention, a method for processing a flowable product using a centrifuge, in particular a separator having a vertical axis of rotation, having a rotatable centrifuge drum in which a disc stack, at least one product outlet and at least one solids discharge opening is arranged, has the following steps: 
     a) pretreating the flowable product so that particles in this product are more strongly attracted by electrically charged components; 
     b) feeding the flowable product into the disc stack; 
     c) generating an electric charge on the discs of the disc stack, and 
     d) separating the charged particles from the flowable product within the disc stack (and thus under the influence of electrostatic attractive forces and a centrifugal field) 
     The targeted use of electrostatic forces in the disc gaps in the centrifugal field of a centrifuge provides a simple means of achieving better separation behavior of particles at the discs of the disc stack. In addition, the already separated particles adhere to the underside of the disc, so that crossing of the particle and product feed streams at the outside diameter of the disc is prevented and thus also that already separated particles can enter the disc stack a second (or third, . . . ) time. 
     In order to enable the effect of the electrically charged plates on the charged particles over a wide range, it is advantageous if this is generated on the discs of the disc stack by a surface charge. 
     The electrical field between the discs of the disc stack and the remaining part of the centrifuge isolated from it is generated by impressing a charge from a DC voltage source. 
     In this process, the positive or negative charge can be transferred from outside to a centrifuge component, wherein one pole of the DC voltage source is in contact with an outer wall of this component and this component is made of electrically conductive material. After charge transfer, this charge is passed on or transferred to the disc stack of the centrifuge. 
     The pretreatment of step a) is preferably carried out outside the drum. Pretreatment is also preferably carried out in such a way that the particles are attracted by the charge of the disc stack. 
     The pretreatment in step a) can be carried out after a first advantageous variant of the invention by electrostatically charging the particles, for example outside the centrifuge. In this process, the product to be processed passes a positively or negatively charged electrode, wherein particles, for example solid particles, are charged at the electrode before entering the centrifuge. This electrode is preferably located outside the drum. However, it is also conceivable to integrate them into the feed of the drum. 
     During the separation process, these charged particles are increasingly drawn by the electrostatically charged discs towards the disc surface, where they are separated and then adhere. 
     The pretreatment in step a) may be carried out according to an alternative variant of the invention also by adding a ferrofluid in order to achieve the effect mentioned above. 
     After the separation of the particles in step d), it is advantageous to switch off and/or discharge the electric field at the disc stack so that the separated particles slide more easily from the surface of the disc into the solids chamber. 
     During polarity reversal or when the electric field is switched off, the degree of separation is reduced by a few percent. In order to avoid unnecessary reversal of polarity or switching off, the separation can be monitored, for example by a probe at a product outlet of the fluid phase or liquid phase. If the proportion of solids exceeds a specified value, the separation onto the disc is insufficient. By monitoring the separation, the method can be adapted to the respective product. 
     Alternatively, the inlet can be closed while the electrical field is being reversed or switched off. 
     In accordance with the invention, a centrifuge, in particular a separator, has a centrifugal drum, in particular a continuously operable separator drum with a vertical axis of rotation, in which a disc stack is arranged, wherein the centrifugal drum has at least one product feed for feeding a product to be processed, a disc stack for phase separation and at least one outlet for discharging a liquid phase and an outlet for discharging at least one further phase, in particular a liquid phase or a solid phase. The centrifuge also has at least one means of generating an electric charge on the discs of the disc stack or in disc gaps of the disc stack. 
     In a separator with electrostatically charged discs, particles are separated in the area of a centrifuge where separation usually takes place without the additional influence of electrostatics. If a product with charged particles is processed with the centrifuge, the separation rate of these charged particles is improved, and crossing of the already separated particles with the product feed stream is prevented. 
     A suitable DC voltage source can be used to generate an electrical charge on the discs of a disc stack, wherein the level of the generated voltage is preferably adjustable. A positive pole is connected at one point of the separator and a negative pole at another point of the separator. One of the poles is conductively connected to the disc stack. The disc stack is electrically insulated from the outer wall of the centrifuge drum by a coating or other non-conductive material so that a short circuit cannot occur through contact between the two components. 
     A suitable voltage level for such a DC voltage source is in the range between 5000 and 20000 volts. 
     For ease of operation, the means for generating an electrical charge on the discs of the disc stack is preferably located outside the centrifuge drum. 
     In an advantageous embodiment, a first pole of the DC voltage source with positive or negative charge can be arranged on the outer wall of a pump element of the centrifuge, which is connected to the disc stack. For this purpose, the pole only has to be attached to the pump element, no further design adjustments to the centrifuge drum are necessary. This is advantageous, as it allows an existing centrifuge to be retrofitted. 
     In the following, the invention is described in more detail by means of an embodiment example shown in a drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The FIGURE shows a sectional partial view of a separator drum of hermetically sealed design. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWING 
     A rotatable separator drum  1  with vertical axis of rotation D is placed on a turning spindle  2 , which is driven by a direct drive or by a belt drive, not shown here. 
     The turning spindle  2  is conically shaped along an upper circumferential area and is fastened to the lower part of the drum  20  with a fastening means  6 . 
     A product feed pipe  4  is followed by a product feed pipe  5  which rotates during operation and is aligned concentrically to the axis of rotation D. From the product feed pipe  5 , product P runs into a distributor  7  with distributor holes or ribs from which the flowable product can exit, e.g., in a radial direction into the interior of the separator drum  1 . It is also conceivable (not shown here) to lead the product from the distributor into at least one rising channel in the disc stack. 
     Inside the separator drum  1 , the incoming product flows in disc gaps between conical discs of a disc stack  11  axially spaced by means of spacers. 
     The product is clarified in the disc gaps (and possibly also separated into two or more liquid phases) in that solid particles of the flowable product are deposited on the undersides of the discs, which can then escape into a solids collection chamber  8 . From there, the solid phase SP here is discontinuously discharged in a radial direction from the separator drum  1  via solids discharge openings  10 , which can be opened and closed via a piston slide  9 . The liquid phase LP is led to a pump element  12  and from there it is discharged through a product outlet  13 . 
     In the present case, better separation of solid particles in the disc gaps of a disc stack is made possible by applying an electric charge to disc stack  11 . This also causes particles that have already been separated to adhere to the underside of the disc. 
     For this purpose, an outer wall  18  of the separator drum  1  or an outer wall  19  of the pump element  12  is connected to a positive and a negative pole of a DC voltage source  14  via an electric line  15   a  or  15   b  respectively. 
     A component that is easily accessible from the outside, here the outer wall  19  of pump element  12 , consists of an electrically conductive material and is conductively connected to the disc stack so that it is charged positively or negatively depending on the connection to the DC voltage source. Another component, such as the actual separator drum  1 , is polarized in the opposite direction. 
     In order to avoid a short circuit, the disc stack  11  is insulated to the inner wall of the separator drum  1 , here by one or more non-conductive material layers  16 ,  17  above and below the disc stack  11 . The distributor  7  is also insulated by an upper material layer  17  and a lower material layer  21 . 
     In addition, the lower part of the drum  20  can also be insulated from the rotating spindle  2  by an electrically non-conductive material layer  22 . 
     The product feed pipe  5  and the distributor  7  are preferably made of an electrically non-conductive material or have a non-conductive coating, so that the parts, which are preferably already charged before entering the drum, do not settle or discharge on the components already here. 
     In the following, the function of the separator of the FIGURE is explained in more detail by means of a method for processing, in particular for clarifying, a flowable product. 
     In addition, a pre-treatment according to the type of step a) of claim  1  is carried out. According to a variant of this pre-treatment, before entering the rotating separator drum, the product is first guided past a negatively or positively charged electrode of a DC voltage source, so that the solid particles in the product become electrically charged. This electrode can also be arranged alternatively in the product teed pipe  4  or in the feed pipe  5 . However, the solid particles can also be loaded at another point before the product flow enters the disc gap of disc stack  11 . A suitable voltage level for such a DC voltage source is in the range between 5000 and 20000 volts. 
     If charging of the solid particles takes place before the flowable product stream enters the separator, it is advantageous if the product feed pipe  5  and the distributor  7  are made of non-conductive material or are coated with non-conductive material so that separation preferably takes place only in the disc stack. 
     After the product enters drum  1 , it enters the disc gap of disc stack  11 . The charge of the particles of the product is opposite to the charge of the discs, so that the discs exert an electrostatic attraction on the charged particles, which increasingly collect on the discs. The disc gaps therefore become increasingly narrow over time. 
     By reversing the polarity or switching off the DC voltage source  14 , the collected particles, in particular the solid particles, are then repelled from the disc surface and transported into the solids collection chamber  8  (preferably with interrupted feed). 
     As already explained, the disc stack will become clogged with time. It is therefore advantageous if this is suitably monitored during operation (e.g., on the basis of the feed quantity or the discharge quantity) and if, depending on the monitoring—or periodically at specified intervals—the polarity of the disc stack is reversed and, optionally, the drum is emptied in order to flush out the deposited particles. For this purpose, the DC voltage source is preferably connected to the control and regulation system of the centrifuge (not shown here). 
     The FIGURE shows a separator which enables a solid-liquid separation. However, the process can also be applied analogously to three-phase separators. As an alternative to the design of a separator in which separator drum  1  is mounted on a rotating spindle  2 , the separation of solids on a charged disc stack can be used in other designs, e.g., with suspended drums. 
     The method and centrifuge according to the invention are suitable for a wide variety of products, but especially for cleaning a contaminated oil. 
     It should also be noted that the design as a hermetically sealed machine with a rotating feed pipe and a guiding pump element, in which the product is pumped through the machine, is preferred but not mandatory. 
     LIST OF REFERENCE CHARACTERS 
     
         
         
           
               1  Separator drum 
               2  Turning spindle 
               4  Product feed 
               5  Product feed pipe 
               6  Fastening means 
               7  Distributor 
               8  Solids collection chamber 
               9  Piston slide 
               10  Solids discharge opening 
               11  Disc stack 
               12  Pump element 
               13  Product outlet 
               14  DC voltage source 
               15   a, b  Power lines 
               16  Non-conductive material layers 
               17  Non-conductive material layers 
               18  Outer wall of separator drum 
               19  Outer wall of pump element 
               20  Lower part of the drum 
               21  Non-conductive material layers 
               22  Non-conductive material layers 
             D Axis of rotation 
             SP Solid phase 
             LP Liquid phase 
             P Product