RU2540303C1 - Electrochemical water treatment device - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device for electrochemical treatment of drinking water contains a reactor 1 with located in it above its bottom the package of electrodes 3, comprising the cathodes and, at least, one soluble anode, and the power supply 2, the outputs of which are connected to the package of electrodes, meanwhile the lateral clearances of the package of electrodes are enclosed by inter-electrode gaskets 4, made from dielectric material. At the upper end of the package of electrodes symmetrically with reference to its lateral faces the gasket 5 is placed. The gasket is made with punching from metal or dielectric material.

EFFECT: increase of service life of soluble electrodes, increase of cost efficiency at the expense of minimising of losses of material of soluble electrodes, inevitable at a mechanical square-wave stripping, and lowering of labour expenditures for servicing of the device at keeping of high quality of cleaning of treated water and simplicity of the device design.

4 cl, 8 dwg

Description

The invention relates to a means of providing drinking water supply, in particular to devices for electrochemical treatment of drinking water, and can be used in domestic conditions for the purification of tap water, as well as for the treatment of natural waters, and to bring its sanitary-epidemiological, physicochemical and organoleptic properties before meeting the requirements for drinking water.

Known household water purifiers that implement in their work sorption and membrane processes. Their significant disadvantages are the accumulation of harmful impurities with their subsequent release into the treated water, as well as the deionization of the treated water.

Devices that use electrochemical methods to purify water from anthropogenic impurities in flowing or non-flowing regimes most effectively purify water.

It is known that all electrolysis processes are accompanied by the formation of gases at the electrodes: hydrogen at the cathode, atomic oxygen at the anode. The presence of gases in the near electrode space (for example, oxygen at the anode) accelerates passivation, which consists in blocking the electrodes by surface deposits, which increases the electrical resistance in the electrode cells and inhibits the electrode reactions. Anodes are passivated as a result of the formation of thin and barely noticeable oxide films on their surface during sorption on the anodes of oxygen and other components, which, in turn, sorb particles of aqueous impurities (hardness salts). The process of passivation of soluble anodes is a significant drawback of electroflotocoagulation, as it reduces the production of active coagulant, violates the stability of the physicochemical and organoleptic properties of the treated water during long-term operation of the installation, and reduces the periods between replacement of the electrode block.

It is known that to combat passivation, a number of constructive measures have been developed that are used in practice: ultrasonic cleaning of the electrodes, vibration, shaking, high speed of water in the interelectrode space during pressure mode or due to recirculation, single-flow water flow pattern, machining of electrodes with scrapers, purging of interelectrode gas spaces, a rotating soluble anode, and others (S.V. Yakovlev et al. // Technology of electrochemical water purification. L., Stroyizdat, 1987, p.119).

A device for water purification by electrocoagulation is known, in which, when the perforated anode and cathode are rotated under the action of centrifugal force, the pressure in the central part of the device decreases, and in the peripheral part it increases, as a result of which water enters holes made in the electrodes and exits radially many times circulating in the interelectrode space. Perforation of the cathode and anode, as well as multi-threaded circulation of the treated water, contribute to more efficient dissolution of the electrodes in one revolution and slow down the process of their passivation (copyright certificate SU 857006 A1, C02F 1/463, 1981). However, the device has a rather complicated design, due to the presence of the engine and the need to seal the node, providing the rotation of the electrodes.

A device is known for electric water treatment in an installation for producing drinking water by electrochemical coagulation (patent RU 2390499 C2, C02F 1/463, 2010). The device comprises an electrode unit, made in a separate housing, inlet and outlet conduits, a power source. The electrode block is made of two groups of electrodes - soluble and insoluble, while the insoluble group of electrodes, which are the common cathode, is made in the form of an electrode block housing having pockets with parallel walls, inside of which are located soluble anodes and soluble electrodes parallel to each other, not directly connected with a power source. The stainless steel case is made collapsible and waterproof, soluble electrodes not directly connected to the power source are made of iron plates, soluble anodes are made of aluminum plates, while the ratio of the areas of iron and aluminum plates does not exceed 1: 1. The design of the device allows you to choose the thickness of the electrodes sufficiently small for the effective use of the material of the electrodes, to the necessity of replacing them (use disposable electrodes), which eliminates the periodic mechanical cleaning of the surface of the electrodes from deposits that impede the release of the material of the electrodes into the water, reduces the consumption of soluble electrodes and labor costs for servicing the device . The disadvantage of this technical solution is the low mechanical strength of the structure, due to the use of thin disposable soluble electrodes, while the source water for electrical processing enters the electrode block under pressure.

A device for implementing the method of electrochemical water purification by passing it inside the interelectrode spaces of a packet of parallel soluble electrodes with periodic polarity changes simultaneously in flowing and non-flowing modes. To do this, the interelectrode spaces are blocked through one to create a non-flow regime for cleaning the liquid. When changing the polarity of the electrodes, previously opened interelectrode spaces are blocked (copyright certificate SU 1165639 A, C02F 1/46, 1985). Such a method for a limited time can be effective, however, since the polarity reversal is carried out in a package of soluble electrodes, both groups of the package (i.e., cathodes and anodes) must be made of the same metal, for example, an aluminum alloy. In this case, passivation of both groups of the packet is observed, accompanied by a significant decrease in the yield of active aluminum ion and, as a result, the need for a complete replacement of the packet of soluble electrodes. When performing the cathodes of a packet of soluble electrodes of iron alloys, and the anodes of aluminum alloys, any polarity reversal becomes undesirable. In addition, in the flow mode of water purification, there is a constant supply to the anode and deposition of hardness salts on it, which prevent the dissolution of the anode and thereby reduce the degree of water purification. The device has a rather complicated design and the cleaning process is difficult to implement when creating simultaneously flowing and non-flowing modes in each pair of adjacent interelectrode spaces, as well as providing a change of modes when switching the polarity of the electrodes. Using the known method of electric water purification in domestic conditions is of great difficulty.

A device is known for electrochemical purification of drinking water (patent RU 2203227 C2, C02F 1/463, C02F 1/465, 2003), in the lower part of which there is an electrode block containing three groups of electrodes, two of which form a package of electrocoagulation electrodes. The third group is represented by an electroflotation anode. The electrodes are connected through a switching device to a power source. Accordingly, during electrocoagulation, the cathodes of the electrode stack are connected to the negative pole of the power source, and the anodes to the positive. During electroflotation by means of a switching device, the electroflotation anode is connected to the positive pole of the power source, the cathodes of the electrode package are disconnected from the power source, and the polarity of the package anodes is reversed, as a result, they become the cathodes of the electroflotation electrode group. In accordance with the laws of electrochemistry, hydrogenation (hydrogenation) of the indicated electrodes and their activation (depassivation) occur in this case. The known technical solution allows you to keep the electrodes that perform electrolytic coagulation in an activated state, delaying the development of passivation, which helps to stabilize the physicochemical and organoleptic properties of the treated water at a high level for a period comparable to the dissolution time of the anodes of the coagulation electrode package. The disadvantage of this device is the sufficient complexity of the design, due to the need to change modes when switching the polarity of the electrodes. Polarity reversal, that is, cleaning the electrode with hydrogen, also leads to excessive hydrogen generation during the process of electroflotation and a change in the pH of the aqueous medium.

It is known "Device for electrochemical purification of drinking water" (patent RU 2398742 C2, C02F 1/463, C02F 1/465, 2010). One of the objectives of this invention is to increase the life of soluble electrodes due to the "inhibition" of the process of their passivation. The device contains a power source that converts AC voltage to DC voltage, and a reactor capacity with a packet of electrodes with a soluble anode based on aluminum located in it, and a packet of electrodes with an insoluble anode is located parallel to the packet of electrodes with a soluble anode in the lower part of the reactor capacitance. This technical solution uses two modes of operation of the device to carry out the process of active coagulation when you turn on the package of electrodes with a soluble anode and the process of active flotation when you turn off the package of electrodes with a soluble anode and turn on the package of electrodes with an insoluble anode.

The disadvantage of this device is the unevenness of the water treatment process at different levels of the reactor volume, which affects the properties of the treated water. The process of active electrocoagulation, which occurs when the electrode package with the soluble anode is turned on, is slowed down by reducing the flow of water rising into the interelectrode space through the lower gaps of the electrode package, which is caused by the entry of water into the interelectrode space through the side gaps of the electrode package, and at different speeds at different height levels, which leads to uneven deposition of hardness salts on soluble electrodes and reduce the period of their active work.

The cyclic movement of water layers in the upper part of a block of soluble electrodes occurs at a faster rate than the cyclic movement of water flows descending to a greater depth, which can lead to a change in the mineral composition of the upper layers of water and a change in the composition of water as a whole.

To implement the process of active flotation in the known invention additionally use a package of electrodes with an insoluble anode. As a result of electrolysis with a sharply increasing concentration of gas, finely dispersed gas bubbles arise, mainly electrolytic hydrogen, an excess of which leads to a change in the pH of the aqueous medium. Each region has its own characteristic pH of water, therefore, with additional saturation of the treated water with hydrogen, its acidity increases and may not meet the requirements for drinking water.

A package of electrodes with an insoluble anode located in the reactor vessel, as well as a complex power supply, which is additionally equipped with a frequency divider, a unit for switching the supply voltage from a package of electrodes with a soluble anode operating only in electrocoagulation mode, to a package of electrodes with an insoluble anode, connected at the end electrocoagulation, complicate the design of the device according to patent RU 2398742 C2.

Of the known devices by design closest to the claimed invention is a "Device for electrochemical purification of drinking water" (patent RU 2452690 C1, C02F 1/463, C02F 1/465, 2012). The device comprises a reactor with an electrode stack located in it above its bottom, consisting of cathodes and at least one soluble anode, and a power source, the outputs of which are connected to the electrode stack. The side gaps of the electrode package are closed by interelectrode spacers made of dielectric material in the form of a continuous rail with grooves for attaching the electrodes. The treated water at a higher speed rises into the interelectrode space only through the lower gaps of the electrode stack and the coagulation process is accelerated by increasing the number of cycles of the purified water passing through the entire electrode block. Water purification as a whole occurs uniformly throughout the entire volume of the reactor and at a higher speed, which leads to an increase in the efficiency of purification of the treated water and improvement of its physicochemical and organoleptic properties while simplifying the design of the device. The movement of water flows in identical cycles, which eliminates the possibility of changing the mineral composition of the upper layers of the water and changing the composition of trace elements contained in it, eliminates the possibility of a strong change in the acidity of the treated water.

The specified device according to patent RU 2452690 C1 is taken as a prototype.

The operation of the device selected for the prototype is accompanied by oxidation of the electrode (aluminum anode), its passivation and deposition of hardness salts on it, creating the need for periodic mechanical cleaning of the surface of the central electrode with sand paper (scraper, cord brush, etc.) from deposits that impede the exit of the electrode material into water. In the technical solution according to the patent RU 2452690 C1, the overlapping of the side gaps of the electrode stack provides the movement of water flows in the interelectrode space from bottom to top according to the principles of motion of a liquid medium in a flat pipe, which leads to an uneven distribution of deposits of hardness salts on the electrodes, shortening the life of the soluble electrode and complicates maintenance devices.

The aim of the invention is to increase the life of soluble electrodes, increase efficiency by reducing material losses of soluble electrodes that are unavoidable during mechanical cleaning, and reduce labor costs for maintaining the device while maintaining high quality treatment of the treated water and the simplicity of the design of the device.

This goal is achieved by the fact that in the device for electrochemical purification of drinking water containing a reactor with an electrode stack located in it above its bottom, consisting of cathodes and at least one soluble anode, and a power source, the outputs of which are connected to the electrode stack, and the lateral gaps of the electrode stack are closed by interelectrode spacers made of dielectric material, an overlay is installed at the upper end of the electrode stack symmetrically relative to its side faces. The overlay is made with perforation of a metal or dielectric material.

It is known that when the electrode package is turned on, the anodes bear the main load. On them, during electrolysis, active metal ions of the anode (mainly aluminum) are formed, which in the interelectrode space form aluminum hydroxide molecules - the main coagulant during the electrochemical treatment of water. At the same time there is an electrolysis of the treated water. As a result of water electrolysis, atomic oxygen is released at the anodes, which contributes to the oxidation of soluble electrodes and the formation of thin oxide films of Al ₂ O ₃ that adsorb particles of aqueous impurities. With increasing electrolysis time, soluble hardness salts, usually present in water (primarily Ca ²⁺ and Mg ^{2+ ions} ), turn into poorly soluble carbonates and precipitate, aggravating the passivation of soluble electrodes.

In the proposed device, as in the prototype, the treated water enters the interelectrode space only through the lower gaps of the electrode package and rises up according to the principles of laminar flow in a flat pipe. Since in the case of laminar flow, the wall layers move with a minimum speed, conditions arise for the appearance of a gradient perpendicular to the flow, while the flow velocity in the center of the pipe is maximum. As a result, the deposition of hardness salts and the formation of layers on the anode will occur unevenly along the front surface of the anode, and to a greater extent along the side faces of the electrode near the interelectrode spacers. The uneven distribution of layers on the surface of the anode will lead to a speedy decrease in the activity of the soluble electrode and the overall performance of the device, which will lead to the need to more often clean the anode.

The pad mounted on the upper end of the electrode package symmetrically relative to its side faces creates hydraulic resistance to flow, that is, it acts as a hydraulic “brake”. The flow velocity in the interelectrode space is leveled - it decreases in the center of the flow and increases near the side gaps of the electrode stack. The pad with the original perforation allows you to more evenly change the speed of the rising flow of water in its horizontal section. The deposition of hardness salts near the lateral faces of the anode is reduced, the deposition occurs evenly and with a thinner layer over the entire area of the electrode, which increases the effective surface, slows down the process of reducing its activity and allows less frequent periodic mechanical stripping. As a result, the life of the anodes is increased, cost-effectiveness is increased by reducing material losses of soluble electrodes that are unavoidable during mechanical cleaning, and labor costs for servicing the device are reduced.

The implementation of the lining of a metal or dielectric material is due to the availability of raw materials, production needs or economic benefits at the time of manufacture.

The technical result is achieved while maintaining high quality treatment of the treated water and the simplicity of the design of the device. The technical solution eliminates the possibility of changing acidity due to an excess of electrolytic hydrogen, physico-chemical and organoleptic properties of the treated water, its mineral composition and contained trace elements (compared to the prototype). Reducing deposits on soluble electrodes, to some extent, even reduces salt depletion of treated water.

The essence of the proposed technical solution is illustrated by graphic materials and photographs:

Figure 1 - diagram of the movement of the treated water in the reactor device for the electrochemical treatment of drinking water;

Figure 2 - a package of electrodes with an overlay on the upper end;

Figure 3 and Figure 4 - embodiments of the perforation of the lining (hydraulic "brake");

5 is a graph of the distribution of flow velocity in the coordinates z, x;

6 is a graph of the distribution of flow velocity and hydraulic resistance to flow in the interelectrode space;

7 is a photograph of the soluble anode of the prototype device with traces of lateral deposits of hardness salts;

Fig - photograph of a soluble anode of the device.

A device for electrochemical purification of drinking water contains a reactor 1 (Fig. 1) and a power supply 2, the outputs of which are connected to a package of electrodes 3 located above the bottom of the reactor. The package of electrodes 3 consists of cathodes 6 (Fig. 2) and at least one soluble anode 7. The side gaps of the package of electrodes 3 are closed from top to bottom by inter-electrode spacers 4 made of dielectric material, for example, special plastic, which during the entire service life inert and does not affect water quality. The interelectrode dielectric spacers can be made in the form of a continuous rail with grooves that allow fastening the electrodes in the package of the electrode block 3 and fix the cathode and anode plates at a distance calculated from each other, while the lateral grooves of the rail rigidly fix the cathode plates (hard fit), and Landing of the anode plate in the central groove is free. The cathodes can be made in the form of a rectangular structure with continuous lines of the side faces and a solid front surface. Cathodes 6 are made of stainless steel, anode 7 is made of an aluminum-based alloy. At the upper end of the package of electrodes 3 symmetrically relative to its lateral faces mounted plate 5 (figure 1, figure 2). The overlay 5 is made with perforation 8, while the area of the holes of the perforation 8 increases from the center of the overlay 5 towards the side faces of the electrode package 3. Various perforations 8 are possible (Fig. 3, Fig. 4), creating the necessary hydraulic resistance to water flow for creating a uniform distribution of flow velocity over the horizontal section of the interelectrode space. The pad 8 is made of an elastic metal or dielectric material, which allows it to be rigidly mounted on the cathodes 6 due to the friction force.

The device operates as follows.

In the capacity of the reactor 1 (Fig. 1), devices for electrochemical purification of drinking water are poured into the source water to the calculated level. The power supply 2 is turned on, and a voltage of typically 12 ÷ 36 volts and a current of several amperes are applied to the electrode package 3. The cathodes 6 (FIG. 1, FIG. 2) of the package of electrodes 3 release electrolytic hydrogen into the water, and the aluminum anode 7 dissolves, releasing aluminum ions in the aqueous solution. Aluminum hydroxide is formed, which coagulates, collecting harmful impurities from water, and rises (floats) in the form of flakes under the action of electrolytic hydrogen to the surface. At the same time, atomic oxygen and ozone are formed on anode 7, which actively oxidize organic impurities and disinfect water and, together with electrolytic hydrogen, contribute to the electroflotation process. Bubbles of hydrogen and oxygen, capturing particles of the smallest suspensions and flakes of coagulant, rise up, carrying out flotation processes. With the help of gas bubbles formed during electrolysis, practically all finely dispersed suspensions of substances, hydroxides of heavy metals, polymers, fats, oils, and oil products are floated due to the high adhesive ability of Al (OH) ₃ molecules.

Water passing between the electrodes 6, 7 is saturated with metal hydroxides of the anode 7 and gas bubbles - hydrogen and oxygen. The resulting near-electrode gases create a fluid flow in the interelectrode space, since as you go up, the density of the resulting stream with gas fractions and the pressure in the interelectrode space decrease. The laminar flow of the treated water in the space between the electrodes creates the conditions for mixing water with gas bubbles, micelles and flakes of metal hydroxide anode 7, as a coagulation electrode. Water passing between the electrodes 6, 7 and subjected to purification due to the processes of electrocoagulation and electroflotation rises up and together with the sludge leaves through the upper gaps of the electrode package 3. The sludge floats to the surface, and the water flow naturally flows into the free, not occupied by electrodes 6 , 7 the volume of the reactor vessel 1. In the free volume, the liquid flow propagates parallel to the surface of the water, and then falls to the bottom of the free zone of the reactor 1. At the bottom of the reactor vessel 1 through the lower gaps of the electrode package 3 approx pulled into the inter-electrode space. A high degree of purification of the treated water is provided due to the fact that water repeatedly passes between the electrodes 6, 7 due to the formation of convection flows. The water cycle in the reactor 1 is maintained continuously during the supply of voltage to the electrodes and some time after the voltage is removed.

After the calculated time of electrocoagulation (active mode), the power source 2 automatically turns off the package of electrodes 3 and the process of sedimentation of the treated water proceeds in the vessel of the reactor 1. Since the density of coagulant flakes is lower than the density of water, and also the treated water contains tiny bubbles of electrolytic hydrogen and oxygen, the settling process continues to be accompanied by flotation (passive mode). As a result, almost all flakes of coagulant (sludge) and fine suspensions are collected on the surface of the treated water.

In the process of electrolysis, the anode 7 is also oxidized by atomic oxygen with the formation of an inconspicuous oxide film, which, in turn, absorbs hardness salts in the water, significantly reducing the activity of the soluble anode. The number of layers formed back to the flow rate - the lower the flow rate, the more hardness salts are absorbed on the anode.

The laminar flow of treated water in the interelectrode space of the electrode block 3, the lateral gaps of which are closed by interelectrode spacers 4, moves like a fluid flow in a flat pipe. The flow rate is affected by friction between the fluid layers due to its viscosity and the friction of the near-wall fluid. Due to friction, the near-wall velocity of water approaches zero, and in the center of the flow, the velocity is maximum. Figure 5 shows a graph of the distribution of flow velocity in the coordinates z, x. Diagram 9 shows the change in water flow rate depending on the coordinate of a point in a section of a flat pipe.

The flow rate in a flat pipe is determined by the formula (Frenkel N.Z. Hydraulics // Gosenergoizdat, M.-L., 1956, p.191):

, $$u=\frac{{\gamma }^J}{2\mu }z(h-z)$$

,

where u is the flow velocity,

J is the hydraulic gradient

γ is the volumetric weight of the liquid,

µ is the kinematic coefficient of viscosity,

h is the width of the slit in a flat pipe.

Therefore, at point A (Fig. 5), at z = 0, the wall velocity of the water flow is u = 0, at point B, at z = h, the wall velocity of the water flow is u = 0, and in the center of the slit of the flat pipe, the flow moves at maximum speed.

The perforated plate 5 mounted on the upper end of the electrode stack 3 symmetrically with respect to its lateral faces creates hydraulic resistance to the flow, mainly in its center, aligning the flow rates of water along the cross-section of the interelectrode space. Figure 6 presents graphs of the distribution of flow rate 9 without a hydraulic "brake", flow rate 10 in the presence of a hydraulic "brake" and hydraulic resistance to flow 11 in the interelectrode space created by the pad 5 installed on the electrode package 3. If there is a hydraulic "brake" plot 9 is leveled, being transformed into a plot 10 while maintaining the mass transfer of the treated water. The hydraulic resistance function 11 is the inverse of the distribution function of the flow rate 10 in the presence of a hydraulic "brake". In the area of perforation (holes) made in the overlay, the hydraulic resistance to the flow is minimal, and in the region of the continuous surface of the overlay, the resistance is maximum, therefore the overlay in which the perforation area increases from the center of the overlay towards the side faces of the electrode package distributes the flow rate most evenly water along the cross-section of the interelectrode space.

A photograph of the soluble anode of the prototype device clearly demonstrates the traces of deposits of hardness salts along the side faces of the electrode formed during the processing of 200 liters of drinking water for 40 cycles of operation of the device (Fig. 7). In the photograph of the soluble anode of the proposed device (Fig. 8), taken after processing 200 liters of drinking water for 40 cycles of operation of the device, there are no traces of lateral deposits formed as a result of deposition of hardness salts on the anode, which confirms a slight and uniform formation of layers on the soluble electrode with an equal amount of treated water. The periods between the necessary mechanical cleanings of the central aluminum electrode plate increase by 1.5–2 times.

The proposed technical solution allows you to keep the electrodes that carry out electrolytic coagulation in an activated state, delaying the development of the passivation process, thereby achieving the goal - to increase the life of soluble electrodes, increase efficiency by reducing material losses of soluble electrodes that are unavoidable during mechanical cleaning, and reduce labor costs by device maintenance while maintaining the high quality of the treated water and the simplicity of the device design. The device allows you to save the mineral composition characteristic of the region, as well as all vital trace elements.

The proposed solution is effective and consistent with the purpose of the invention.

Claims (4)

1. A device for the electrochemical purification of drinking water, comprising a reactor with an electrode stack located in it above its bottom, consisting of cathodes and at least one soluble anode, and a power source, the outputs of which are connected to the electrode stack, with side gaps of the stack the electrodes are closed by interelectrode spacers made of a dielectric material, characterized in that a patch is installed at the upper end of the electrode stack symmetrically relative to its side faces. 2. The device according to claim 1, characterized in that the pad is made with perforation. 3. The device according to claim 1 or 2, characterized in that the patch is made of metal material. 4. The device according to claim 1 or 2, characterized in that the patch is made of dielectric material.

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