JPS643525B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides water removal of suspensions of finely divided solids or colloidal solids suspended in a carrier liquid, such as suspensions of clay in water, by the action of a vacuum and with the aid of an electric field. Regarding technology. Such an electric field is created by passing an electrical current through the suspension through a pair of active electrodes, a cathode and an anode, immersed spaced apart within the suspension. According to the present invention, a suspension of finely divided solids can be directly dehydrated with efficiency and economy that could not be achieved using conventional water removal techniques. The product thus obtained may be in the form of a cake material (mass) or in the form of a slurry of a desired or specific solids concentration, depending on the respective industrial needs. can. According to the principle underlying the invention, a solid substance in suspension between two electrodes (which, depending on its material properties, carries a negative or positive intrinsic charge) is subjected to the action of an electric field. relative to the carrier liquid towards each corresponding electrode. This phenomenon is called electrophoresis. When such electrophoretic solids reach the electrode surface, they are deposited one after another in layers. Such deposition occurs even when the liquid or water in the material gap is being pushed out from the material gap due to the phenomenon of densification of the solid layer due to so-called electroosmosis. As a result, a layer of sufficiently compressed and dehydrated material is formed on the surface of the electrode, such that it can, for example, be pulled out of the suspension and peeled from the electrode. Moreover, according to this electric water removal device, the dehydrated solid matter is made into a suspension, that is, in the state of a fluid.
Moreover, it can be directly and economically extracted at a high solids concentration that cannot be obtained by conventional water removal devices such as cyclones, centrifuges, and filters. The product thus obtained with a specific solids concentration can meet specific industrial needs. A slurry product of the desired solids concentration can also be obtained by blending the recovered cake material with the feed slurry or overflow suspension from the treatment tank of the electrowater removal system. The electric current flowing through the suspension produces the electrophoretic effect described above and at the same time decomposes the carrier water into hydrogen and alkali at the cathode and oxidation reaction products such as oxygen and acids at the anode. The amount resolved is proportional to the density of the controllable current. It is an object of the present invention to provide an improved cathode structure and a mode of operation of the cathode in which a cake is deposited on the cathode which serves to protect the cathode from corrosive environments and operating conditions. It is to be. The cake product obtained economically, continuously, and uniformly under controlled conditions by the present invention has a relatively high solids content not obtainable with conventional water removal equipment. It can be repulped to a flowable or pumpable condition, although it is still concentrated. An example of an industrially required suspension is approximately 70% for transport in tank cars, as opposed to a spray-dried product carried in bags or bulk. There are well-dispersed colloidal clay suspensions with a solids concentration of 100.degree. C., and according to the present invention such suspensions can be obtained economically. The electrowater removal apparatus of the present invention can also be operated in such a manner that a slurry having the desired solids concentration is obtained directly in the form of an overflow from the treatment tank. To carry out the method of the invention, a plurality of self-contained hollow electrode structures are immersed in a suspension so that they can be withdrawn as a whole as one unit for inspection or other purposes. . These hollow electrode structures are provided with liquid-permeable or ion-permeable wall surfaces. Preferably, the wall surface is constituted by a chemically and electrically neutral material or a permeable porous membrane backed by a support grid, presenting a flat electrode surface. An electrode member is disposed within an enclosure defined by the wall surface and is protected from direct contact with the suspension. In the case of electrodes with liquid-permeable walls, a vacuum source communicated within the hollow structure creates a constant controllable pressure differential to force carrier liquid into the interior of the electrode through the surface; Meanwhile, the solid matter migrates in the direction opposite to the carrier liquid towards the counter electrode under the action of the electric field. The liquid, ie, the carrier liquid from which solids have been removed, can be extracted from the interior of the hollow electrode structure at a controllable rate, such as by pumping. The self-contained counter electrode structure deposits suspended solids in a layer or cake on the ion permeable surface of the electrode. This ion permeable surface corresponds to the opposing liquid permeable surface of the electrode structure. The counter electrode structure with an ion-permeable surface is also a hollow structure, housing the electrode element within a chamber having ion-permeable walls. The chamber of this counterelectrode structure is filled with an electrolyte, and the electrode elements are immersed in the electrolyte. The electrolyte is specially selected for its conductivity and compatibility with the electrode elements. As used herein, "compatibility" refers to the fact that the electrolyte is not corrosive to the electrode under conditions normally present within the hollow counterelectrode structure. As a component of the electrolyte is discharged or released at the electrode element, steps are taken to flow the electrolyte into the chamber of the counter electrode in order to maintain the electrolyte at a predetermined composition. The ion-permeable wall of the counter electrode is composed of a chemically and electrically neutral material or a porous membrane.
whether such material or membrane is in the form of a film;
Alternatively, if some support is required, the material or membrane may be backed by a chemically and electrically neutral grid so that a flat electrode filter surface is presented to the slurry being treated. do. Cake material builds up on the counter electrode during electrical overloading and must be removed by contacting with a doctor blade. A friction cage is provided to protect the material from direct contact with the doctor blade. The friction cage is an open screen construction made of a relatively hard material for contact with the doctor blade. In order to recover the cake, the counter-electrode structure can be lifted to a position where it is removed from the suspension together with the layer of solids deposited on its surface or the cake layer attached. Since the electrolyte remains inside the raised counter electrode, a vacuum is applied inside the electrode to reduce the pressure on the material, thereby preventing loss of electrolyte and/or rupture of the material. When the counter electrode is immersed and in operation, the vacuum applied inside the electrode serves to remove gaseous products, such as chlorine, generated at the electrode element. According to the invention, a decaking device is provided to catch caked material flaked or scraped from the surface of the electrode during the downward movement of lifting the electrode out of the suspension or re-immersing it into the suspension. Preferably, the decaking device comprises a conveyor capable of rapidly removing the caked material from the processing tank in cooperation with decaking or scraping means. Means are also provided for manual or automatic control so that the flow rate of liquid through the hollow liquid permeable electrode structure is maintained properly relative to the rate of migration of solids in the opposite direction. One embodiment for this purpose includes an automatic control device that maintains the vacuum applied to the liquid permeable electrode structure at a constant value relative to the intermediate or normal liquid level of the liquid held by the vacuum. is provided. That is, the change in the liquid level is used as a master control or indicator factor to adjust or modify one or more of several individual control factors in the control system through relay action to adjust the liquid level. Restore to standard height. Such factors include current density, liquid pumping flow rate, or vacuum. However, the vacuum factor surprisingly does not have much of an effect. In this way, the current density of the electrode, the flow rate of liquid extraction by the pump, or the magnitude of the vacuum suction force is adjusted so as to restore the height of the liquid level held by the vacuum action, As a result, the velocity of migration of the solids relative to the countercurrent flow of the carrier liquid between the electrodes can be maintained at the desired value. When the modulation of the electric field is used for control purposes,
Increasing the current density accelerates the migration velocity of the solids for cake formation, and decreasing the current density slows the migration velocity of the solid particles relative to the flow of carrier liquid in the opposite direction. In practical terms, this means that if the migration of some of the suspended particles is too slow compared to the rate of material penetration of the carrier fluid, such stagnant particles will be deposited as a film on the material. do. The result is an increase in the permeation resistance of the material and a corresponding reduction in the liquid level maintained by the vacuum action. This liquid level displacement is sensed and the current density is increased through the relay action described above, thereby reducing the coating on the material and returning the liquid level to normal. Similarly, if the liquid level drops too much, the drop in the liquid level is transmitted as a decrease in current density, causing a parallel increase in the film thickness; It is also possible to set a control mode that continues until the liquid level returns to a normal level. In practical use, the coating thickness can vary between 1.8 mm and 6.4 mm. Under extreme conditions, e.g. when the migration speed of solids is high and the permeation flow rate of liquid is correspondingly excessive, solid particles may deposit on the surface of the material in extremely thin layers. The control device can be operated to slow down the migration of the solid particles, thereby slightly increasing the overresistance of the material and correspondingly reducing the permeation flow rate of the liquid. Manual control is often sufficient for some applications, in which case product formation can be visually observed and the feed rate or current density adjusted accordingly. Therefore, the rate of solid matter deposition can be controlled. For example, if the repulped product is too lean and has too much moisture,
Decrease the feed rate (or increase the current density); if the product is too thick, increase the feed rate (or decrease the current density). For example, in one practical embodiment, a treatment tank is continuously supplied with a feed liquid and is flooded to maintain a normal level of suspension in the tank. You can do it like this. In this embodiment, a series of self-contained cathode structures and self-contained anode structures are alternately spaced in suspension and their planar electrode surfaces are parallel to each other. Deploy. Hollow electrode structures with liquid permeable walls deliver liquid as described above, while hollow electrode structures with ion permeable walls deposit cake material. An overhead carriage is installed above the tank. This carriage is equipped with a hoisting mechanism for lifting the electrodes out of the suspension and is configured so that a layer of cake material can be stopped in sequence over the electrodes having been deposited to a predetermined thickness. The carriage scrapes and receives cake material from the electrode, e.g. by a doctor blade, while the electrode is exposed from the suspension, e.g. when lowering the lifted electrode back into the suspension. It is preferable to configure it integrally with a series of mechanisms for. The flaked cake material is allowed to fall onto a conveyor and is carried away directly from the processing tank. After the carriage, which is integrally equipped with a hoisting mechanism, a stripping mechanism, and a conveyor, has finished removing cake material from one electrode, it is moved directly above the electrode that is waiting to remove the cake from the next electrode. Here, the term "self-contained electrode structure" refers to a structure containing electrodes. Other features and advantages of the invention will become more apparent from the following description of the examples. In the example of FIGS. 1-4, a schematic diagram of the sequential operation of a power-assisted vacuum water removal operation according to one embodiment of the present invention is shown, including a schematically illustrated liquid flow control system. In this example, negatively charged solid particles migrate towards an ion permeable hollow anode structure and the resulting cake layer is recovered from the anode structure. The carrier liquid, in turn, permeates through a hollow liquid permeable cathode structure operatively connected to a liquid flow control device. Among the suspensions to be treated by electric water removal devices are those having solids with a predominance of either negative or positive charge. The following explanation of the principles of the invention is based on the assumption that negative charges predominate, such as solids in clay suspensions. One embodiment of the electric water removal device of the present invention includes first to
This is shown schematically in Figure 4. In this embodiment, the water removal device comprises the water removal unit itself and its associated structural and mechanical attachments (both collectively designated by the symbol "D");
and a liquid flow control device S-1 (the purpose and function of which will be described in detail later). The basic structure of water removal unit D is a tank 10,
It has a supply pipe 11 for supplying suspension to it. In this example, the suspension to be treated will be described as a clay suspension, ie, a suspension in which negatively charged finely divided solids of colloidal particle size are uniformly dispersed. The required depth of the suspension in the tank 10 is defined and ensured by the overflow edge 12 so that the electrode structure can be completely immersed in the suspension. An overflow receiving tank 13 is provided in association with the overflow edge 12. The feed suspension is fed at such a flow rate that any excess thereof is constantly overflowed from the tank 10 and the suspension in the tank is constantly replaced. Furthermore, the contents in the tank are always maintained in a fluid state by a circulation pump 14 connected to the tank 10 at connections 14a and 14b,
Proper dispersion of solids within the suspension ensures proper and uniform functioning of the negative and positive electrode surfaces exposed to the suspension in the tank. In this example, the negative and positive electrode surfaces are provided in the form of self-contained electrode structures in planar form, parallel to each other, each electrode structure being separated from the suspension in its own plane. It is configured so that it can be raised vertically to the withdrawn position and lowered to its original position within the suspension. Based on the above assumption, that is, if the suspended solids (e.g. clay) are negatively charged, the hollow self-contained positive electrode structure 15 should occupy the center of the tank. Place it in This anode structure 15 is also designated separately by the reference numeral A. raising the electrode structure vertically in its own plane to a position where it is withdrawn from the suspension;
A vertical guide device is provided so that it can be returned to the suspension again. Also, the cake material that has separated from the suspension and deposited on the surface of the positive electrode can be peeled off and deposited on the surface of the positive electrode when the electrode structure is lifted out of the suspension and lowered back into the original suspension. Processing equipment is also provided for transporting it to a location. In one embodiment, these processing devices include a pair of doctor blades 17 arranged symmetrically so as to be able to swing about a horizontal axis between a neutral position and a cake-stripping position.
It is illustrated as consisting of 18 pieces. The cake material stripped in this way can be transported by means of conveying means, designated as belt conveyors 19, 20, respectively. Alternatively, and conversely, the stripping device can be configured such that the cake is stripped and removed when the electrode structure is lifted upwards from the suspension, as illustrated in FIG. 4a. The anode structure 15 includes a rectangular frame member 21, as shown in detail in FIGS.
A pair of ion-permeable walls 2 fixed on both sides of the
It consists of 2 and 22. The frame member 21 has an outwardly open U-shaped cross-section to which an ion-permeable wall 22 can be attached. Each ion permeable wall 22 is a multilayer assembly consisting of a material 22a, a support grid 22b and a protective cage 22c configured to deposit negatively charged solids from a suspension as a layer or cake. . The electrode structure 15 is assembled by fixing a pair of support brackets 15a to the upper end of the frame member 21 and attaching these brackets to the wall of the tank 10.
is positioned and supported within the tank 10. A terminal of positive polarity in the form of a vertical rod 26 projects into the interior of the electrode structure 15 and is connected to the electrode 27 thereof. The exposed upper end of the terminal rod 26 is connected to a connecting cable 26a. The frame member 21 and the wall member 22 of the electrode structure 15 are electrically neutral and therefore constructed of non-conductive material, such as plastic, or alternatively, the electrode 27 and the electrical wires 26, 26a
cut off from contact with Furthermore, measures are taken to fill the inside of this electrode structure 15 with a suitable electrolyte (anolyte). The hollow interior or anode compartment defined by the ion-permeable wall 22 of the electrode structure 15 is filled with electrolyte by an electrode element ( Anode) 27 is placed around the outer surface of the ion permeable wall 22 of the treatment tank 1.
The ion-permeable wall 22 acts on the negatively charged solids in the suspension to be treated, which are present in the ion-permeable wall 22.
This is so that it can be adsorbed to the outer surface of the. Fresh electrolyte is constantly flushed through this electrode structure to maintain a relatively constant electrolyte composition during operation of the electrically assisted vacuum filtration device and to wash away any solids that may have entered the anode compartment. Make it. The device for maintaining such an electrolyte flow may in its simplest form be a gravity feed system, connecting an elevated electrolyte supply tank by a supply conduit to the positive electrode structure 15, which Connect the waste conduit from the waste tank to the waste tank. The gas generated at the anode is carried away along with the spent electrolyte. Such circulation of electrolytes can also be achieved by more sophisticated systems. In that case (see FIG. 11), electrolyte is circulated through the electrode structure by inlet tube 28 and outlet tube 29 to maintain a relatively constant electrolyte composition during operation of the electrically assisted vacuum filtration device. The discharge pipe 29 connects to the receiver 61 . The gas generated within the electrode structure 15 is extracted from the system through a vacuum conduit 62 equipped with a valve 63 and the electrolyte is delivered through a conduit 64 to a supply tank 66. Additional electrolyte can be introduced into supply tank 66 from replenishment tank 73 to replenish the electrolyte consumed in the process. Replenishment tank 73 connects to conduit 64 via conduit 74 with control valve 79 . Electrolyte is extracted from the supply tank 66 by a pump 71 connected to the inlet pipe 28 and delivered to the electrode structure 15 . Excess used electrolyte can be drained from the system through an overflow outlet 29. In this circulation system, in addition to the pump 71 for circulating the electrolyte, a vacuum pump (not shown) acting on the conduit 62 for extracting the gas is required. The conduit 64 is the atmospheric leg and the electrode 1
Balance the vacuum required to extract the gas generated within 5. The preferred electrolyte for use in positive electrode structure 15 is 1 normal sodium chloride solution. When sodium chloride is used as the electrolyte, chlorine gas is generated at the anode 27 and is ultimately exhausted through the vacuum conduit 62.
This environment, which generates chlorine gas, was found to be well suited to electrodes made of titanium and coated with commercially available materials such as ruthenium. Such electrodes are subject to severe erosion in environments where oxygen is generated. Carbon electrodes may also be used. The gases generated at the anode must be extracted from the system through vacuum conduits and either disposed of or utilized in some way. This chlorine can be reintroduced to the cathode. At the cathode, this chlorine then acts to suppress the evolution of hydrogen by forming NaCl, thereby reducing or avoiding the need to dispose of the hydrogen or caustic by-product, yet disposing of the chlorine gas. problems can be alleviated. Alternatively, chlorine gas may be mixed with the catholyte to produce neutral hypochlorite which can be used for bleaching or other purposes. Yet another method is to use special vacuum pumps to concentrate pure chlorine gas for use or sale elsewhere. As the electrolyte (anolyte), sodium chloride solution is preferred, but sodium sulfate, potassium sulfate,
Mineral acids or neutral salts such as H ₂ SO ₄ may be used as electrolytes, with considerable results. In some cases, an acidic cake is desired, in which case HCl should be used as the electrolyte.
Alternatively, if a neutral cake is desired, a neutral or alkaline electrolyte should be used, such as a mixture of sodium bicarbonate and sodium chloride (both at 1 normal concentration). As previously mentioned, the positive electrode structure is lifted from the tank to remove any cake that has accumulated thereon. In such an elevated position, the electrolyte within the electrode structure exerts considerable outward pressure against the walls of the structure. Under this pressure, the electrolyte is forced outward through the material or
Otherwise, the material may break. However, if a vacuum is maintained within the receiver 61, the negative pressure will relieve the pressure on the inner walls of the electrode structure, preventing electrolyte leakage or material rupture. As mentioned above, the surrounding wall of the electrode structure is formed of the ion-permeable wall 22 instead of the solid metal wall that constitutes the electrode as in the conventional case, and the electrode element 27 is surrounded by the ion-permeable wall. The ion permeable wall 22 and the electrode element 2 are disposed within the hollow body separated from the ion permeable wall.
The electrode structure 15 or A of the present invention, characterized in that the space between the electrode structure 15 and the electrode structure 7 is filled with a conductive electrolyte.
According to the method, the electrode element 27 in the hollow body is isolated from the suspension to be treated in the tank 10 and is not subject to the erosive action of the suspension. Furthermore, the electrode element 27 is
The electrodes of conventional electrode structures of this type are isolated from the cake deposited on the ion-permeable wall and from the mechanical action of the doctor blades 17, 18 for later removal of the cake. The inevitable wear and tear caused by cake removal work,
No accidental damage. In this manner, the electrode structure 15 of the present invention maintains its electrode element 27 separated from corrosive and erosive treatment suspensions or slurries and decakes the outer surface of the ion permeable wall 22. This makes it possible to operate in a protected environment, isolated from the mechanical action of the doctor blades 17, 18, extending the life of the expensive electrode elements 27. Furthermore, in this embodiment, self-contained cathode structures 31, 32 of negative polarity are arranged on either side of the central anode structure 15 and spaced a distance d therefrom. These cathode structures, also designated by C, are special hollow structures. This hollow structure allows the carrier liquid from the surrounding suspension to be drawn through the liquid-permeable electrode wall into the interior of the hollow electrode structure, from where it can be extracted or pumped to the outside for disposal. It is structured as follows.
These cathode structures communicate with the liquid flow control device S-1 mentioned above. The purpose, function, and operation of the control device S-1 will be described later. The cathode structure consists of a rectangular frame 33 of similar dimensions to the frame 21 of the central anode structure 15, but with a liquid permeable wall connected to the frame member 33, as shown in detail in FIGS. 7 and 8. 34,
It differs from the anode structure in that it has 35. The liquid permeable walls 34, 35 constitute a passage for the passage of carrier liquid from the slurry or suspension. The frame member 33 has a liquid permeable wall 3 thereto.
It is a U-shaped groove that is open to the outside and allows attachment of 4, 35. Each liquid-permeable wall is itself an assembly of material 41 or fabric, the periphery of which is fastened to the frame member 33, for example by a retaining strip 42. Each member 41 is supported against external pressure by a support grid 42a which is secured or welded to the peripheral frame member 33 at its peripheral edge. These backing grids 42a form part of the electrode structure and each form an electrode surface. By fixing the grid and material to the frame member in this manner, the electrode structure presents an unobstructed planar surface P-1, P-2. Furthermore, each cathode structure 31, 32 has a terminal rod 4 similar to the terminal rod 26 of the cathode structure described above.
5, to which a connecting electrical cable 46 is attached to provide the required polarity. As shown in FIGS. 1 to 4, all of these cathode structures are connected to the liquid flow control device S-
1, and a connecting pipe 46 is connected by a pump 45a.
applying a vacuum to the cathode structure via a, drawing carrier liquid from the surrounding suspension or slurry through the material 41, so that the interior of the cathode structure is constantly filled with carrier liquid; .
The filtered carrier fluid is extracted from the interior of the electrode structure through conduit 46c by pump 46b. The carrier liquid is extracted at a proportion proportional to the amount of carrier liquid sucked into the electrode structure, so even when the carrier liquid is being extracted, there is no carrier liquid inside the electrode structure. be satisfied. Now assuming that the liquid (filtered carrier liquid) flow control device S-1 serves to maintain a uniform flow of carrier liquid through the cathode structure and that the water removal operation is in equilibrium, The operating cycle of the water removal unit shown in Figures 1 to 4 is as follows. A slurry or suspension, such as a clay suspension, is continuously fed into the processing tank 10 through the inlet connection 11 at a flow rate sufficient to overflow into the overflow receiving tank 13 at all times. This ensures that the effective electrode surface of each electrode structure is completely immersed in this suspension during operation of the device. When the suspension to be treated is a clay suspension, the electric field created between each electrode causes the negatively charged clay colloidal particles to move into the anode structure A relative to the carrier liquid. Move toward the direction. Concurrently, the carrier liquid moves in a direction opposite to the colloidal particles, passes through the hollow cathode structure, and is discharged from the treatment device. In the starting state of the water removal process shown in Figure 1, water reaches the ion-permeable anode surface under the influence of an electric field.
It shows the initial formation of a cake layer consisting of clay particles adhering to it. At this point, the scraper or doctor blades 17, 18 have been pivoted to a neutral or spaced apart position, and the anode structure can later be lifted through the blades 17 and 18 to eject the cake. It is made possible to do so. FIG. 2 shows the state in which the formation of the cake layer O has been completed, and the doctor blades 17, 18 can lift the anode structure carrying the cake to the fully extended position as shown in FIG. like,
It is still in a neutral position. When the anode structure is lifted to the uppermost extended position, the doctor blades 17, 18 are rotated toward each other toward the cake stripping position, and the anode structure is lowered as shown in FIG. Be prepared to do so. Thus, by lowering the anode structure into the tank 10, the cake layer is stripped off and dropped directly onto the belt conveyors 19,20. Upon completion of this downward movement of the anode structure, the water removal device is returned to its initial operating state, the doctor blade is returned to its neutral position, and the next operating cycle begins. FIG. 9 schematically shows a lifting device H for raising and lowering the anode structure in connection with the cake stripping operation described above. As mentioned above, the slurry or suspension to be dewatered in this manner may be of a type containing suspended solids with a predominant positive charge. In that case, the solid matter migrates towards the negative polarity of the cathode structure under the influence of the electric field. Concurrently, a carrier liquid is passed through a hollow anode structure having a liquid permeable wall as described above;
Extracted. In this case, the anode structure is the above-mentioned liquid flow rate control device S-1 that adjusts the permeation flow rate of the liquid.
It is connected to. In order to implement such a modified operating mode,
As shown in Figure 10, it is sufficient to simply change the polarity of each electrode, so that the central electrode structure becomes the cathode C-1 and the electrode structures on both sides become the anode A-1. Bye. Otherwise, the operating cycle is similar to that described in connection with FIGS. 1-4, with the central cathode structure C-1 being able to be raised and lowered for decaking operations, and the central cathode structure C-1 being The evacuated carrier liquid can be extracted from the inside of the anode structure at a rate controlled by the control device S-1. However, in this case, the anolyte must consist of a component that will generate oxygen at the anode. FIG. 4a shows that the cake is removed during the upward motion of withdrawing the electrode structure from the tank, rather than during the downward motion of re-immersing the lifted electrode structure into the tank as in the arrangement shown in FIGS. 1-4. This shows a modified configuration in which stripping is performed. This configuration is obvious from FIG. 4a, but when raising the electrode structure, the scraper blade is
The cake material is peeled off by making elastic sliding contact with the electrode structure, with the tip pointing downward rather than upward. To simplify the construction, the scraper blade may remain in sliding contact with the electrode structure when the caked electrode structure is lowered. Or the first
A blade actuation mechanism similar to that described in connection with FIGS. -4 may be used. Next, the automatic liquid flow rate control device S-1 shown in FIG.
(The part surrounded by the broken line) will be explained. For convenience of explanation, it is assumed here that the suspension to be water removed is a type of suspension containing negatively charged particles, such as a clay suspension. In this liquid flow rate control device, the present invention includes:
a controllable applied current density that creates an electric field; and the relative migration velocity of suspended solids moving in the opposite direction toward the anode relative to the velocity of the carrier fluid flowing toward and through the cathode. Take advantage of the interrelationships that exist between That is, increasing the current density will increase the relative velocity of suspended solids moving toward the anode, and decreasing the current density will decrease the relative velocity. Thus, by varying the current density, the opacity (transmission) of the material of the cathode structure can be decreased or increased. Therefore, when the electric field density is reduced, some suspended particles will be deposited on the material. If the current density is increased to avoid deposition (coating) of solid particles on the material due to increased migration velocity of particles leaving the material, then the vacuum suction is increased to compensate for this condition. On the other hand, in order to obtain the desired liquid flow rate control effect,
The liquid pump extraction flow rate and the suspension supply flow rate can be relatively changed. In the basic form shown schematically in this example, the principle of this control device S-1 is as follows. According to one mode of operation, a steady vacuum action is applied inside the hollow cathode structure by a vacuum pump 45a. In order to maintain the degree of vacuum at a desired constant value, the vacuum gauge 75 can control the operation of the vacuum pump 45a via a relay device 76. In parallel with the vacuum action forcing carrier liquid from the suspension through the liquid permeable walls of the cathode structure, pump 46b draws liquid from the cathode structure against a force in the opposite direction of the vacuum action. aspirate.
As a control element, a constant liquid level L is maintained by vacuum action in the separation chamber 78, which communicates with the electrode structure via the tube 46a. This tube 46a extends downwardly from the separation chamber 78 and terminates at the upper end of the electrode structure so that the mixture of hydrogen gas and liquid produced by electrolysis is deposited at the cathode at the visible liquid level L. Vacuum separation chamber 78 to maintain
Suction inward. From here hydrogen gas is extracted upwardly through a second separation chamber 81, while the degassed liquid is returned to the cathode structure by gravity, for example through a tube 82. Two separation chambers 78 and 8
By providing a bypass connecting pipe 83 between the two separation chambers, parallel communication is established between the two separation chambers. In this bypass connecting pipe, the liquid level L is not disturbed by bubbling or boiling that may occur in the separation chamber 78. Relay device 84, activated in response to excessive changes in liquid level L, adjusts the liquid pump extraction flow rate, ie, the output of pump 46b, to bring the liquid level back within a relatively small range of acceptable normal fluctuations. Do it like this. In the rare case that no coating is formed on the material of the cathode structure, the control device increases the vacuum if the permeation resistance of the material increases. To obtain balanced operation, the liquid flow rate through the cathode structure must be sufficient;
It should not be so large as to interfere with the movement of negatively charged suspended solids migrating in the opposite direction of the liquid towards the anode. Moreover, for the aforementioned control purposes, the liquid level responsive main controller 84 maintains a predetermined, appropriate, and constant pump extraction flow rate with a constant vacuum force, while applying a current density, i.e., to each electrode. Control impulses can be relayed to change the potential applied. As previously mentioned, manual control by visually observing the condition of the slurry product (after make-down) and adjusting the current density accordingly is sufficient for many applications. (“Makedown” refers to the addition of dry clay to a clay slurry in order to obtain a clay product with the desired moisture content in the manufacture of ceramics.) Again, it is important to note that the suspension to be treated has no negative charge. In the case of a clay suspension containing loaded clay particles, the preliminary start-up procedure is to secure the hollow cathode structure in place, fill the processing tank with the clay suspension, and remove the cathode structure. A source of liquid or water sufficient to fill the anode structure and a source of anolyte sufficient to fill the anode structure are available. To fill the system with each liquid, a vacuum is applied to each electrode structure, causing each electrode structure to draw liquid from its respective supply tank. Once each electrode structure is filled with its respective liquid, the water removal operation can begin. The electrode structure is then energized and the liquid is forced through the cathode structure by vacuum action to initiate the water removal operation. The liquid extraction pump is started and its displacement is adjusted to maintain a relatively constant predetermined amount of liquid extraction. During this start-up, electrolyte pump 71 is also activated to circulate electrolyte through the anode structure. Operation of the water removal device is stopped by cutting off the power supply to the electrodes and pumping out the liquid within each electrode structure. Once it is confirmed that each electrode structure is empty due to no more liquid being discharged from the pump, the vacuum pump is de-energized and then each liquid pump is stopped. In the following, an operational example of the device of the invention will be described. EXAMPLE An electrically assisted vacuum filtration apparatus of the type shown schematically in Figures 1 to 8 was prepared using a vacuum filter containing 59% solids by weight.
It was run using a feed slurry of No. 1 coating clay. The total effective area for cake deposition is 2.23m ²
(two anodes each with two working surfaces). The anolyte used was a 1 normal solution of NaCl, which was circulated through the anode at a rate of 10.19 ^per minute per square meter of anode area. A vacuum of approximately 508 mm of mercury was maintained for the liquid (cathode) system, and a vacuum of approximately 406 to 432 mm of mercury was maintained for the anode system.
In conducting these experiments, the current was set at the desired level, and the slurry bath temperature and salt addition were set at predetermined values. The feed slurry charge was then adjusted to achieve equilibrium. Salt addition was done to simulate expected variations in the salt content of the feed. In the conventional treatment process,
Salts are added as flocculants or dispersants or for other purposes. The results of the above experiments under equilibrium conditions are shown in the table below.

[Table] In the above table, "load energy" refers to the energy (KWH/ton) required to remove 1 ton of solids from the supplied slurry. In the table above, “energy for liquid” means:
It is the energy consumed to extract 1Kgal (3785) of liquid from the feed slurry. All of the above experiments resulted in a satisfactory product slurry with a solids content of 70% after makedown. As can be seen from the table, an 80% solids cake (which is itself a highly desirable material) is also well within the capabilities of this process. The method of the present invention has proven to be flexible in that it is effective over a wide range of process conditions, including fairly wide variations in feed rates. In addition, the method of the present invention is effective when the conductivity of the slurry is low (the amount of salt added is small,
0 and the bath temperature is low) is found to be somewhat more efficient than the case of a highly conductive slurry. The energy consumption of the present invention is
The amount is considerably lower than that of conventionally commonly used thermal water removal methods. As can be seen from the above description, in the operation of the electrically assisted filtration device (which can also be referred to as an electrical filtration device for separating solids and liquids) of the present invention, the electrodeposited solids are supplied. It can be recovered directly from the colloidal suspension in the form of a relatively hard cake material with very low water content, which may be a desired product in its own right. Alternatively, the recovered cake material can be mixed with a feed slurry or overflow suspension from a processing tank in a predetermined proportion to obtain a predetermined relatively high solid particle concentration slurry as the desired product. In yet another embodiment, the electric water removal system can be operated to obtain the desired product from the overflow suspension from the treatment tank itself in the form of a slurry of the desired solids concentration. In that case, the solid build-up or cake layer adhering to the electrodes is incidental and minimized. In order to obtain good operating results, it is preferable to precondition the feed suspension to be applied to this electroseparator with dispersing aids to obtain the correct suspension. In this manner, the electrical filtration device is able to filtrate even otherwise difficult to filtrate colloidal suspensions at high speeds. This is in contrast to conventional filtration systems in which the feed suspension to be separated or concentrated must be previously subjected to a particle coagulation treatment.

[Brief explanation of drawings]

FIG. 1 shows the start-up condition of the water removal operation and shows the appearance of initial cake formation on the electrode surface of each self-contained electrode structure. FIG. 2 shows the cake formation completed. FIG. 3 shows the electrode structure being lifted into a salvage position to remove the cake layer. At this point the doctor blade is held in the inoperative position. FIG. 4 shows the anode structure being lowered back into the suspension. At this time, the doctor blade peels off the cake layer and causes it to fall onto the respective conveyor. Figure 4a shows another embodiment for performing a cake-stripping operation.
FIG. 5 is an enlarged detail taken along line 5--5 of FIG. 1, showing the hollow anode structure with cooling water connections. 6 is a vertical cross-sectional view of the anode structure taken along line 6--6 of FIG. 5; FIG.
Figure 7 is an enlarged detail taken along line 7--7 of the figure, showing the cathode structure including material supported by a support grid; FIG. 8 is a vertical cross-sectional view of the cathode structure taken along line 8--8 of FIG. 7, and FIG. 9 is a view of the hollow anode structure similar to FIG. Figure 2 shows the hoisting mechanism that raises and lowers the anode structure. FIG. 10 is a diagram similar to that of the embodiment of FIGS. 1-4, including a control device, but configured to be adapted to treat positively charged suspension solids; FIG. An example is shown below. FIG. 11 is a schematic diagram of the electrolyte circulation system. In the figure, 10 is a tank, 11 is a supply pipe, 13 is an overflow receiving tank, 14 is a circulation pump, 15 is an anode structure, 17 and 18 are doctor blades, 19 and 20 are belt conveyors, 21 is a frame member, and 22 is an ion-permeable wall, 22a is a material, 22b is a support grid, 27 is an anode, 28 is an electrolyte inlet tube, 29 is an outlet tube, 31 and 32 are cathode structures, 33 is a frame, and 34 and 35 are liquid-permeable walls. , 41 is wood, 4
5a is a vacuum pump, 46a is a vacuum pump, 46b
is the carrier liquid extraction pump, and 71 is the electrolyte pump.

Claims (1)

[Scope of Claims] 1. A device for removing water from a suspension of solids suspended in a carrier liquid under the action of an electric field, comprising: a treatment tank; and a flow of the suspension is supplied to the tank. a pair of self-contained electrode structures each comprising a hollow body within the treatment tank; The electrode structures are arranged as a cathode and an anode opposite each other to establish a controllable electric field between them during immersion in the suspension, the first of the electrode structures a liquid permeable wall providing a flow zone, the flow zone directing the flow of the carrier liquid to a liquid separated from the solids migrating away from the first electrode structure under the action of the electric field. A first vacuum source is connected to the hollow body of the first electrode structure, the first vacuum source being configured to allow the carrier liquid to pass through the first electrode structure and establishing a pressure differential to allow the carrier liquid to pass through the first electrode structure. providing liquid extraction means for extracting liquid at a controlled flow rate from the hollow body of the structure;
A second electrode structure of the pair of electrode structures comprises an ion permeable wall and an electrode element spaced apart from the ion permeable wall within the hollow body of the electrode structure. and filling the hollow body with an electrolyte filling the space between the ion permeable wall and the electrode element, the second electrode structure being suspended on the ion permeable wall under the action of the electric field. a cake recovery device configured to form a cake layer of turbid solids and comprising a device for lifting the second electrode structure from the tank and removing and carrying away the cake adhering to the second electrode structure; a second electrode assembly with means for extracting gaseous products generated at said electrode element of the second electrode structure and minimizing electrolyte flow outwardly through said ion permeable wall; A vacuum source is connected to the hollow body of the second electrode structure to maintain a relatively constant electrolyte composition within the second electrode structure despite decomposition of the electrolyte at the electrode element. A suspension water removal device comprising electrolyte extraction means for extracting electrolyte from a second electrode structure so that fresh electrolyte can be circulated through the electrode structure. 2. The suspension according to claim 1, wherein the electrolyte extraction means is an atmospheric leg, and is configured to circulate fresh electrolyte through the second electrode structure by a pump. Turbid water removal equipment. 3. The ion-permeable wall of the second electrode structure is
2. A suspension water removal system as claimed in claim 1, comprising a plurality of electrically non-conductive elements including a material and an inner support grid supporting the same. 4. The cake collecting means contacts the cake layer;
a stripping device for stripping the cake layer from the second electrode structure, and the ion permeable wall has an outer barrier to prevent direct contact between the stripping device and the material. 4. The suspension water removal device according to claim 3, further comprising a cage. 5. The second electrode structure is configured to form a cake layer on both sides thereof, and the stripping device is disposed on both sides of the second electrode structure to form a cake layer between a cake stripping position and a non-peeling position. a doctor blade which is movable at the holder and is held in a non-stripping position during the upward movement of the second electrode structure, and in contact with the protective cage during the return movement of the second electrode structure to remove the cake layer. 5. A suspension water removing device according to claim 4, further comprising actuating means for holding said doctor blade in a stripping position so as to perform a stripping action. 6. The second electrode structure is configured to form a cake layer on both sides thereof, and the stripping device is disposed on both sides of the second electrode structure to form a cake layer between a cake stripping position and a non-peeling position. During the upward movement of the second electrode structure, the doctor blade is kept in contact with the protective cage in a stripping position for peeling off the cake layer, and during the upward movement of the second electrode structure, the second electrode structure is moved back and down. 5. The suspension water removal device according to claim 4, further comprising actuating means for holding the doctor blade in the non-stripping position. 7. The suspension water removal device according to claim 1, wherein the electrolyte is a sodium chloride solution. 8. The suspension according to claim 1, wherein the first electrode structure is a cathode structure having a cathode, and the second electrode structure is an anode structure having an anode. Liquid water removal device. 9. Suspension water removal according to claim 8, wherein the means for maintaining the suspension at a predetermined depth comprises an overflow means provided in the tank. Device. 10. The suspension water removal device according to claim 9, wherein the electrolyte is a sodium chloride solution. 11. Claim 10, characterized in that, in order to suppress the generation of hydrogen gas at the cathode, a conduit is provided for guiding chlorine gas generated at the anode to the hollow body of the cathode structure. The suspension water removal device described. 12 A method for dewatering a suspension of solids suspended in a carrier liquid, comprising: supplying a suspension to maintain a predetermined at least minimum depth of suspension; The suspension is always partially replaced by fresh feed suspension, and a pair of opposing electrodes are placed in the suspension and an electric field of controllable strength is established between the electrodes. The energy of the electric field causes the solids in the suspension to migrate toward and deposit on the ion-permeable anode structure and transfer the carrier liquid toward the liquid-permeable cathode structure. pumping the permeated carrier liquid from inside the cathode structure at a flow rate balanced with the relative migration velocity of the solids relative to the carrier liquid; exposing the carrier liquid to a vacuum action, immersing the anode element within the anode structure in fresh electrolyte to facilitate migration into the anode structure; continuously pumping fresh electrolyte into the anode structure to expose the electrolyte to a vacuum field to extract the gas generated at the lifting the anode structure from the suspension while maintaining a vacuum effect on the electrolyte, stripping off the cake material deposited on the anode structure, and recovering the stripped cake material. A suspension water removal method consisting of: 13 The gas generated at the anode element is
13. The chlorine gas is chlorine, and the chlorine gas is guided to the cathode element in order to suppress generation of hydrogen at the cathode element within the cathode structure. Suspension water removal method.