NL1014806C2 - Electrochemical apparatus for separating solids from water, using electrochemical reactor with rotating electrodes, followed by flotation chamber also containing electrodes - Google Patents

Abstract

The apparatus includes at least one electrochemical reactor (32) with two electrodes (64, 66), a voltage source, an inlet and outlet for the liquid, and a solid/liquid separator. An apparatus for removing substances from a liquid medium using an electrochemical technique comprises at least one electrochemical reactor with two electrodes, a voltage source, an inlet and outlet for the liquid, and a solid/liquid separator on the downstream side of the outlet. Independent claims are also included for (a) an electrochemical reactor with an inlet and outlet for a liquid medium, and two electrode plates, one set of electrodes being mounted on a driven shaft (65) and part of this set of electrodes protruding above the level of liquid inside the reactor, as well as a drive mechanism for the shaft and scrapers which are in contact with the rotating electrodes, (b) a flotation chamber (37) with two electrodes mounted in an essentially horizontal surface close to the bottom of the chamber and insulated from the chamber walls, a voltage source for the electrodes, an inlet and outlet for a liquid medium, and a device (40) for removing at least part of the solid layer floating on top of the liquid, and (c) a method for removing substances and/or impurities from a liquid medium by supplying it to this reactor and then to this flotation chamber.

Description

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Device and method for the electrochemical removal of substances from a liquid medium.

The invention relates to a device for electrochemically removing substances from a liquid medium, regardless of the aggregation state of those substances. According to the invention, there is provided for this purpose a device for electrochemically removing substances from a liquid medium containing at least one electrochemical reactor with first and second electrodes, a voltage source, a supply and a discharge for the medium and a solid downstream dust / liquid separator 10.

It is further provided that the electrodes of the electrochemical reactor consist of a first and a second set of plates, which are arranged alternately with respect to each other and wherein at least one set can be moved with respect to the other set of plates.

According to a preferred embodiment, it is further provided that one set of plates is arranged on a shaft and the displacement is a rotation, further providing a drive for that shaft. At least one set of the electrodes is preferably manufactured substantially from a bivalent or trivalent metal or alloy with such a metal, for example iron, aluminum or copper. 25

The use of, for example, an aluminum electrode as an anode in separation techniques is known per se, reference is made to, for example, NL-A-75.13794. This known device is used to clean emulsions and oil-containing water. To this end, the aluminum anode is held at a predetermined distance from the negative pole with a supply member. In practice, such a device appears to be mainly only suitable for separating certain individual elements and, moreover, the dissolving of the aluminum anode and thus the coagulation of the impurities with the aluminum flakes in the liquid medium difficult to control, which also applies to gas formation at the electrodes. An additional drawback is that the electrodes in such an uncontrolled process can become partially or completely insulated quite quickly.

It is also known per se to apply an alternating voltage instead of a direct voltage. However, this greatly reduces the separating action of the redox reactions important for the electrochemical separation technique, since these reactions are at least partly reversible. A further drawback is the energy losses that occur as a result of the constantly changing direction of current, as a result of which the necessary ion currents will also hardly be able to start.

According to the invention, in order to prevent the electrodes from being insulated and to achieve the desired separation, it is provided, inter alia, that the voltage source is a DC voltage source, further providing means for controlling the voltage and means for polarity reversal of the tension. The range of the voltage to be applied across the electrodes preferably ranges from 3-70 V and the time range between the polarity reversal from 30 seconds to 24 hours.

In connection with the rotary electrode, which preferably comprises a number of disc-shaped plates, a reactor 30 is obtained which is particularly suitable for use for a highly contaminated medium. It is important here that the electrode plates are arranged vertically and insert far below the liquid level in the liquid medium for the largest possible contact area and also to ensure that contact with the medium is not lost in the case of large foaming. .

According to a further elaboration, scraping members are provided which abut against the plate surfaces of the rotatable disc-shaped plates. The driven shaft on which the disc-shaped electrode plates are mounted is preferably kept above the liquid level, whereby a large part of the plates protrude above the liquid level. The scraper members engage on the relatively protruding part of the plates some distance above the liquid level, whereby foam and at least a large part of other separating components can be removed from the plates relatively quickly, which can considerably increase the service life of the plates.

Furthermore, the following factors are important for good control of the separation processes in the reactor: the choice of the electrode material and the control of the voltage source to obtain an optimum balance between anode wear and insulation of the electrodes; temperature control in the reactor by cooling or dosing of conductive material; 20 - fluctuating pH control to prevent electrode isolation by metal oxides; prevention of isolation by lime deposits by adding polyphosphates and / or other substances that can form complex compounds with calcium; 25 - recirculation of flocked material; regulation of the voltage applied across the electrodes.

In addition, corrosion inhibitors can be added to counteract electrode wear when the reactor is overloaded. The inhibitors can be added to the electrolyte (e.g., sodium and potassium phosphates) or to the pH regulators (e.g., film-forming and neutralizing amines).

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Flocculation of coagulated impurities and the filterability of these separations can be enhanced in some applications by recirculation of flocculated material. If necessary, polyelek * M d0 6 -4 - trolytic flake aids can also be added.

In the reactor according to the invention, the coagulation of the colloids in the liquid medium is strongly promoted by the magnetic and electric fields generated thereby, which inter alia ensure: influencing the distribution of the zeta potential on the surface of the colloidal structures, whereby the structures can approach each other locally at a distance at which the van der Waals forces are greater than the electrostatic repulsion forces; occurrence of mutual speed differences between the particles in the electric field; discharge of the particles at the electrode surface 15 so that they can merge and in turn can also receive smaller particles in the solution.

The result of this is that the dosage of the flocculant in the anode dissolution form may be tens of percent lower than would otherwise be required when using chemical / attractants.

Furthermore, depending on the electrodes, electrolyte and voltage applied, different gases will be released in the reactor. These gases are important as a carrier of the various impurities, whether coagulated or not. Capillary gas entrapment further increases the buoyancy of the contaminants referred to so that they float to the surface and are easy to dispose of. In order to prevent a possible explosion hazard in the event of an overproduction of gas, ventilation means connected to the reactor space are provided.

The invention further provides, in combination with the reactor 35, a solid / liquid separator which preferably consists of a flotation chamber. In this flotation chamber, near the bottom, is insulated from the walls and approximately horizontally arranged an assembly of electrodes alternating between them; another pole of a voltage source are connected.

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With the relatively small gas bubbles to be generated therewith, the coagulated secretions in the liquid medium coming from the reactor are fed to the liquid surface in the flotation chamber. In this manner, a dense, firm layer is formed on the liquid surface, from which part of it is removed from time to time with a take-off member and can be supplied to, for instance, a further conveying member, such as for instance a conveyor belt.

The liquid medium from the flotation chamber, from which a large part of the impurities is then removed, can then be filtered in one or more steps before being discharged or discharged for reuse for certain purposes.

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The device according to the invention is further elucidated on the basis of the examples given in the drawing, in which: fig. 1 shows a diagram for a basic embodiment of the device, fig. 2 shows a diagram of a specific for the processing of slurry suitable embodiment, fig. 3 shows an embodiment of a device for processing slurry, fig. 4 shows a cross section of the electrochemical reactor of the device, fig. 5 shows a top view of the electrochemical reactor of the device, fig. .6 show some views of the electrode assembly in the flotation chamber, and FIG. 7 shows a detail of the electrode assembly.

The scheme according to Fig. 1 shows the device with a sedimentation tank 1 with a supply 2 of contaminated liquid medium, which will usually be water, and a sediment discharge 3 with, for example, a driven screw.

From the sedimentation tank 1, the contaminated water goes via outlet 4 to the reactor 5. In the reactor 5, there are electricity; / n

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6, and a DC voltage source 7 is further provided for applying a preferably adjustable voltage to the electrodes and a ventilation means 8 for discharging large amounts of gas generated at the electrodes. The reactor is further provided with a discharge 9 of the foam formed in the process, with substances separated from the water therein, and a discharge 10 for the discharge of the water to a further solid / liquid separator 11.

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In addition, a number of tanks 12,13,14,15 are connected to the reactor, from which the necessary chemicals can be added to the process in the reactor, such as, for example, acid and caustic for controlling the pH, salts for adding to the reactor. the electrolyte, and auxiliary flocculants.

From the solid / liquid separator 11, which can be, for example, an electrochemical flotation chamber, the water thus far cleaned can be discharged via a drain 16 to the sewerage, storage for reuse or to organs for further cleaning steps.

Figure 2 shows a diagram of a device suitable for slurry processing. The slurry with pump 18 is transferred from a manure cellar 17 to a storage tank 19 with a stirrer 20. A filter is fitted in front of the pump 18 so that the largest parts present in the manure cellar, such as straw strips, stones, afterbirths and the like, cannot come along . In the storage tank 19, the slurry is brought to the desired density by dilution, if necessary, for which purified or non-purified water from the shaving system can be used.

Slurry is pumped from the storage tank 19 with pump 21 to a tank 22. In this tank, the kernel of the medium in the tank is determined with sensors 23, which can be corrected if necessary by adding regulating chemicals with pump 24. In this tank is again 25 hours in a stirrer. brought in.

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The medium is brought to a next tank 26 with an overflow or pump. A stirrer 27 and pH sensors 28 are arranged therein and an oxidant such as, for example, a hydrogen peroxide solution, can be added to the medium 5 with pump 29. With a hydrogen peroxide solution, a violent reaction is caused, accompanied by a large gas development, whereby a first separation is already realized, whereby an amount of substances can be removed in a foam layer that is formed thereby.

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The medium thus cleaned in a first step is transferred to tank 30 from which it can be supplied to reactor 32 with pump 31. The reactor 32 is provided with electrodes not shown in more detail in the figure, a DC voltage source and a ventilation element 33. From the reactor 32 the medium is returned via tank 34 to tank 30. Part of the flocculated particles enter a layer float on the media and can be removed from there. If necessary, auxiliary flocculating means can be supplied to the medium in tank 30 by means of pump 35.

Via a further guide 36, the flocculated medium ends up in flotation chamber 37. In this flotation chamber 37, an assembly of electrodes 38 is arranged, whereby electrolysis produces gassing, the gas bubbles of which bring the flocculated particles up to the surface of the liquid medium. A layer 39 of flocculated particles is formed on the surface, parts of which can always be removed with a take-off member 40 and fed to a discharge member 41. If necessary, the sludge on the discharge member 41 can be dried even further by means of, for example, heat lamps. By means of an overflow system it can also be ensured that the layers formed in the tanks 26, 30 also come within reach of the take-off member 40 or it can be ensured that at least one of these layers is at the same level as the layer 39 Compared to flotation using compressed air, this system has the advantage of 1 0 14 80 6 -8- that the gas bubbles released are relatively small and do not expand as is the case with compressed air, so that the flocculated substances are pulled apart again could be. In this way, a much better and in particular more effective flotation is then realized than with compressed air.

In a number of practical tests it has been found that with the processing of manure with the device according to the invention through the reduction of nitrogen in the electrodes in compounds such as ammonia, with the formation of nitrogen gas, these compounds can be largely removed from the manure. . This is particularly important in connection with the current system of measures and levies with regard to manure surpluses.

The levels in the tanks 22, 26, 30, 37 can be controlled via an unspecified pipe and valve system, whereby the excess medium can be returned with pump 42 to the storage tank 19 for slurry.

From the flotation chamber 37 via line 43, the medium so far cleaned is supplied to one or more successive filtration means. In the example this is a unit with a buffer tank 44 with a stirrer 45 and a pump 46 in order to be able to add a flocculant to the medium if necessary. The medium is supplied from the buffer tank to the bag filter 47.

3C After the bag filter 47, a further filtration can be carried out with the aid of, for example, candle filter 48. The medium enters from the bag filter into buffer tank 49, from which it is passed through the lease filter 48 with a high-pressure pump 50. The filtered part of the medium can be fed to an evaporator or with pump 51 to an undefined clean water storage tank. The other part goes back to the buffer tank 49 via the collecting tank 52 and the recirculation pump 53. If necessary or desired, it is of course possible to carry out further filtrations in a manner known per se.

Figure 3 shows an embodiment of the scheme shown in Figure 2 for an apparatus for processing slurry. The device comprises a compartment 55 divided into compartments arranged on a frame 54. The first compartment is the tank 22 in which the medium can be brought to the desired acidity, the second compartment is the tank 26 in which a hydrogen peroxide solution is supplied to the medium. the third compartment is the tank 30 from which the medium is fed to the reactor 32 and the last compartment is the flotation chamber 37.

In the figure, the assembly of electrodes 38 arranged in flotation chamber 37 is not shown.

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Provided on the holder 55 is a guide path 56 for the take-off member 40 with a drive 57 for the take-off member 40 at the free end. A compartment 58 is arranged on compartment 30 for collecting the foam with flocculated particles from the reactor 32. The foam formed in compartment 26 as a result of the introduction of the hydrogen peroxide solution also lands on this plate 58 by pouring parts of said foam layer over the low edge 59 of compartment 26. The path of the take-off member 40 extends over the plate 58 so that the foam containing particles can also be entrained there. With the take-off member 40, foam and an upper part of the layer formed in the flotation chamber are brought to the further discharge member 41.

30

The reactor 32 is placed on top of the guideway 56 and consists of a plastic tray 60 with an inclined bottom part 61 on which a first set of electrodes 64 is arranged. The sloping bottom part 61 rises via the deepest part of the tray to a low overflow edge 62 with adjoining overflow part 63. Along the overflow edge and overflow part, the foam with flocculated substances generated in the reactor can flow off to the plate 58. In the tray is mounted on shaft 65 the second set of electrodes 66, shaft 65 being driven by an electric motor 67 and, for example, a chain transmission 68.

A removable hood 69 is provided on the reactor 32, with an opening 70 intended for connecting ventilation means (not shown in more detail) thereto.

On the left is shown schematically a further storage container 71 with a number of compartments 10 for acid, lye, hydrogen peroxide solution and chemical flocculants to be used in the device. On the right-hand side, 72 indicates a first filtration unit with, for example, buffer tank 44 and bag filter 47 as shown in Fig. 2.

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Figure 4 shows the reactor 32 in more detail. For each of the round electrodes of the set of electrodes 66, a scraper member 73 is provided which engages on both sides of an electrode. The scraper members 73 are mounted on a mounting beam 74 extending transversely across the tray 60.

An inlet chamber 75 is provided on the high side of the tray for uniformly distributing the medium to be treated supplied from tank 30 over the width of the tray and thus over the width of the electrode sets 25. At the level of the deepest part, a drain not further shown in the figure is provided on the side of the tray 60 before it is possible to return the medium guided past the electrodes back to the tank 30.

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And the top view according to fig. 5 shows the distribution of the electrodes over the width of the tray and the distance from each other. The electrodes 64 are coupled by means of a guide 76, whereby the guide 51 'can for instance consist of a guide rod with spacers arranged along the electrodes. Provided on one end 77 of the guide 76 is a provision for connecting the guide to one of the poles of the voltage source not shown.

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A sprocket wheel 78 is arranged on the end of the shaft 65 on the drive side and a contact member 79 at the opposite end. The contact member 79 comprises a number of sliding contacts in order to always ensure a good contact 5 and furthermore has a provision 80 for the contact member 79 to one of the poles of the voltage source (not shown).

Figure 6 shows a top view of the assembly 10 of electrodes 38 which is arranged in the flotation chamber 37 of the device. The electrodes 38 are arranged in a plastic frame 81 with longitudinal and transverse parts 82, 83, the transverse parts of which are provided with chamfers 84 with which they can come to lie on sloping walls in the bottom part of the flotation chamber.

Fig. 7 shows in more detail the attachment of the electrodes 38 to the transverse parts 83 of the frame 81. The electrodes protrude into blind holes 85 20 arranged in the transverse parts 83 and are bolted 86,87 which engage in the electrode ends. threaded holes, attached to cross members 83. Conductions 88, 89 are arranged on the sides of the transverse parts 83 remote from the electrodes and can be connected to the poles of an (equal) voltage source in an unspecified manner. By using metal bolts for the bolts 86 and plastic bolts for the bolts 87 or vice versa, the electrodes can be alternately connected to the guides 88 and 89.

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Claims (23)

An apparatus for electrochemically removing substances from a liquid medium, comprising at least one electrochemical reactor with first and second electrodes, a voltage source, a supply and a discharge for the medium and a solid / liquid separator connecting thereafter. 2. Device as claimed in claim 1, characterized in that the electrodes of the electrochemical reactor consist of a first and a second set of plates, which are arranged alternately with respect to each other and wherein at least one set can be moved relative to from the other set of plates. LO 3. Device as claimed in claim 2, characterized in that one set of plates is arranged on a shaft and the displacement is a rotation, furthermore providing a drive for that shaft. Device as claimed in claim 3, characterized in that scraper members are provided which abut against the plate surfaces of the plates to be moved. 5. Device according to claims 1-4, characterized in that 2 "." the voltage source is a DC voltage source, further providing means for controlling the voltage and means for polarizing the voltage. '0 6. Device according to claims 1-5, characterized in that at least one set of the electrodes is substantially made of a bivalent or trivalent metal or alloy with such a metal, for instance iron, aluminum or copper. > 1> 7. Device according to claims 2-6, characterized in that, Your reactor is arranged such that at least part of; a 4 -13- one set of electrodes protrudes above the liquid level in the • reactor. 8. Device according to claim 7, characterized in that the set of electrodes arranged on the rotatable shaft protrudes at least partly above the liquid level. 9. Device according to claims 1-8, characterized in that the solid / liquid separator mainly consists of a flotation chamber. Device as claimed in claim 9, characterized in that the flotation chamber is provided near the bottom with a first and a second set of electrodes which are arranged alternately. 15 Device according to claim 10, characterized in that the electrodes are arranged in an approximately horizontal plane. Device according to claims 10-11, characterized in that the electrodes are arranged insulated from the walls of the flotation chamber. 13. Device according to claims 10-12, characterized in that the electrodes are made of precious metals or precious metal alloys. 14. Device as claimed in claims 9-13, characterized in that a removal member is arranged in the flotation chamber for removing at least a part of a layer of solid material to be floated which can be floated on the liquid. 15. An electrochemical reactor comprising an inlet for a liquid medium to be treated and an outlet, first 35 and second plate-shaped electrodes, one set of which is arranged on a drive shaft with a part of this set of electrodes protruding above the liquid level in the reactor, a drive for the shaft and scraper members which bear against the electrodes to be rotated. * - i 4 80 6 -14- Electrochemical reactor according to claim 15, characterized in that a controllable direct voltage source and means for polarity reversal of voltage are provided. Flotation chamber provided with first and second electrodes arranged alternately near the bottom in an approximately horizontal plane isolated from the walls of the chamber, a voltage source for the electrodes, an inlet and outlet for liquid medium and a take-off member for removing at least a part of a layer of solid material to be floated on the liquid. 18. Method for removing substances and / or impurities from a liquid medium, characterized in that the medium is fed to an electrochemical reactor according to one or more of the preceding claims 2-8,15,16 and subsequently to a flotation chamber according to one or more of the preceding claims 9-14.17. Process according to claim 18, characterized in that one or more of the following steps is preceded by pre-filtration, regulation of the acidity of the medium to be treated, addition of an oxidizing agent such as, for example, a solution of hydrogen peroxide. A method according to claims 18-19, characterized in that chemical flaking aids are added. 30 Method according to claims 18-20, characterized in that the space above the reactor is ventilated. 22. Method according to claims 18-21, characterized in that the liquid medium after the flotation chamber undergoes one or more further filtrations. A method according to claim 22, characterized in that the purified water obtained is evaporated. 1 0 1 4 50 6