EP3802438A1

EP3802438A1 - Electrocoagulation cell with integrated mechanism of homogeneous anode consumption

Info

Publication number: EP3802438A1
Application number: EP19733861.9A
Authority: EP
Inventors: Eleni POLYCHRONOPOULOU; Dimitrios KOUTSAFTIS
Original assignee: Enviromental Protection Engineering SA
Current assignee: Enviromental Protection Engineering SA
Priority date: 2018-06-08
Filing date: 2019-05-16
Publication date: 2021-04-14
Also published as: KR20210016460A; GR1009590B; CN112272656A; WO2019234459A1

Abstract

The present invention describes a cylindrical electrochemical cell (Figure 1) designed to treat wastewater of various compositions utilizing the electrocoagulation method. The cell incorporates and mechanically rotating spacer (Figure 1) (5) to ensure the uniform consumption of the anode plate (Figure 1) (3) and to prevent anodic and cathodic depositions. The spacer is positioned between the anode (Figure 1) (3), which is located at the bottom plate of the cell, (Figure 1) (6) and the cathode (Figure 1) (9). Its slow rotary motion is provided by a shaft (Figure 1) (9) which passes through the center of the base plate of the cell and it is shaped in a way that allows the vertical drop of both the spacer and the cathode (Figure 1) (4). This device has the advantage of operating under conditions of steady voltage and with constant power consumption. In addition, the electrocoagulation cell has the ability to operate at pressures of 1 to 10 bar.

Description

DESCRIPTION

ELECTROCOAGULATION CELL WITH INTEGRATED MECHANISM OF HOMOGENEOUS ANODE CONSUMPTION

The present invention concerns an Electrolytic Cell (EC) apparatus, designed to treat wastewater (Figure 1 ). The electrolytic cell is enclosed within a cylindrical outer housing (16), a removable upper cover (15) and a bottom baseplate (6). The purpose of this patent is to describe the components of an electrolytic cell, capable of producing coagulants on-site, while with the utilization of an integrated mechanism, the homogeneous consumption of the sacrificial anode is ensured. Thus, the EC is able to operate in conditions of relatively high pressures (1 to 10 bar) and with a low and predictable maintenance frequency.

Methods for the on-site production of coagulants electrochemically, (by the electrodissolution of a suitable anode usually made of aluminum or iron) are well known and widespread. However, most of them encounter problems originating from the deposition of insoluble compounds (mainly calcium and magnesium) on the cathode’s surface and from the precipitation of the coagulant itself on the anode’s surface. As a result, the rate of electrodissolution / consumption of the anode becomes unpredictable and the efficiency of the EC gradually decreases. Moreover, the electrodissolution of the anode, leads to an increased power consumption that requires frequent process stops to carry out the proper remedial actions. Based on the so far international experience, as remedial actions are suggested the frequent maintenance and / or electrode replacement and / or the mechanical or chemical cleaning using acid solutions such as citric acid. Electrodes’ frequency of replacement largely depends not only on the applied current density but also on the physicochemical characteristics of the fluid that is treated. The effect of the two aforementioned parameters leads to increased uncertainty regarding the prediction of electrodes’ useful operational life. Consequently, the operator has to take into account that the costs on anode replacement and chemicals for acid cleaning are variable and cannot be estimated with safety. In the above, it should be also added any sudden shutdowns of the electrocoagulation units due to maintenance and the reduced wastewater treatment efficiency.

In US Patent 8,945,357 B2 an apparatus is described, consisting of a cylindrical electrochemical cell for wastewater treatment, which, similarly to the present invention is based on the on-site production of coagulants, electrochemically. In addition, in the electrolytic cell that is presented in the aforementioned patent, electrochemical oxidation actions are also carried out on the surface of non-consumable anodes. Moreover, this device incorporates a rotating non-consumable cathode plate, positioned between two fixed anodes, of which only the bottom one is utilized for the coagulant production (consumable). The principal difference with respect to the present invention relates to the number of electrodes and the presence of non consumable anodes to conduct electrochemical oxidation reactions. As the US patent claims, the rotation of the cathode prevents the deposition of compounds at the surface of the anode while there is no provision to keep the distance between the electrodes stable. As a result of this omission, the cathode’s height should be constantly observed by the operator in order to perform the necessary adjustments to maintain a stable electrode distance as the consumable anode’s thickness decreases. In addition, the effect of cathodic deposits (whose effect is particularly visible in aqueous wastewater with high content of calcium and magnesium ions) has not been considered by the inventor. These deposits have a serious effect on the power consumption of the electrolytic cell due to the gradual increase of the cathodic potential.

The invention presented in detail below is capable to successfully address the aforementioned problems, providing the user with reliable and uninterrupted operation over a wide range of wastewater compositions and flow rates. In particular, it is simpler in design and easier in maintenance since it includes only two non-rotating electrodes. Most importantly, the distance increase between them, (due to anode consumption) has been taken into account through the incorporation of a mechanically rotating spacer. This spacer is in contact with the top of the anode supporting the weight of the cathode and maintains the distance between them constantly stable. At the same time, its rotation and continuous contact with both electrodes prevents the deposition of solids on the surface of both of the anode and the cathode. The EC has also been tested and proved to operate efficiently under conditions of high pressure and of high concentration of pollutants.

Exact arrangement of the components of this invention is presented in Figure 1. The most important of the above are the anode displayed in Figure 2, the cathode presented in Figure 3 and the cathode’s support plate presented in Figure 4. Figures 5, 5.1 and 5.2 refer to the spacer and its means of rotation, provided by an axis constructed of plastic (Figure 5) (9). Apparatus of the present invention (Figure 1), capable of effectively treating liquids of a wide range of pollutant loads, consists of a cylindrical monopolar electrolytic cell with a consumable anode (3) and a non-consumable cathode (4). It is enclosed within a top cover, bottom plate and a cylindrical middle shell, having a bottom inlet (1) and an upper outlet (2). The two electrodes have a specified distance between them, equal to the rotating spacer’s thickness (5), creating a zone in which the wastewater is treated. Rotation to the spacer is provided by an electric motor which is not displayed in the present patent’s figures. The liquid’s direction is from the bottom inlet to the treatment zone, flowing between the two electrodes and after passing through the perimeter of the cathode, it exits the electrocoagulation cell from the top cover’s outlet. The anode plate (Figure 2) (3) is permanently fixed to the bottom base plate of the electrochemical cell (Figure 1) (6) through a specified number of two (2) to four (4) bolts which act as current collectors (Figure 2) (12), Electric current is supplied to the anode plate by a respective number of cables which are securely connected to the current collectors. Anode plate’s material of construction may be aluminum or iron and it has a cylindrical shape. Its overall dimensions such as diameter and thickness may vary, as they depend on the application in which the invention will be used and on the operational lifetime and the required consumption rate of the anode. Cathode plate (Figure 3) is positioned in a predetermined distance (3 to 10 mm) above the anode plate, equal to the thickness of the spacer (Figure 1) (5), being able to move only vertically due to the total force applied. This force is the result of its weight and buoyancy force, as it is always completely immersed in the liquid that flows through the electrolytic cell.

The vertical movement of the cathode towards the anode is due to the gradual consumption of the latter. Cathode plate’s material of construction may be stainless steel or titanium and has a cylindrical shape with a cylindrical opening in the center (Figure 3). It has a completely smooth surface without holes, cavities or other blemishes. During the operation of the EC the cathode will only move downwards, to the direction of the anode until the predetermined operation period has elapsed, when the thickness of the latter has been reduced to such an extent that it will need replacement. The upper surface of the cathode will be securely fixed to a disc (Figure 4) of the same dimensions, constructed of plastic (Figure 1) (7). in the upper part of the plastic disc, cylindrical rods (Figure 1) (8) are mounted in order to prevent the cathode from rotating (by contact with the rotating spacer). At the same time these rods will allow only the vertical movement of the cathode. Said rods pass through two circular holes made on a flat bar (Figure 1) (18), which is embedded in the electrolytic cell’s top cover. Power supply to the cathode is provided by means of flexible cables that are suitable for such applications (Figure 1) (17), as they will be constantly in embedded in the electrolyte. The cables will connect to the current collectors (Figure 1) (1 1 ) at the upper surface of the cathode plate. At the center of the cathode’s plastic support plate, a plastic cover (Figure 1) (14) will securely fit preventing the liquid from flowing through the center of the support plate. This plastic cover will have a length equal to the expected drop of the cathode and a diameter of at least 40 mm greater than the spacer’s rotation axis diameter.

The spacer (Figure 5), positioned between the two electrodes (Figure 1) (3) and (4) may have four (4), six (6) or eight (8) arms (Figures 5, 5 - 1 , 5 - 2). Its thickness may be between 3 to 10 mm and it will be made of plastic materials. The length of each arm should be equal or greater than the outer electrode diameter. The spacer will have a free vertical movement due to the total force applied to the cathode. Its slow and steady rotation (of 10 rpm) will guarantee the homogeneous electrodissolution of the anode, and at the same time, it will allow the free flow of liquid between the two electrodes. The spacer’s rotation is provided by a shaft (Figure 1) (9) that will pass through the center of the bottom plate of the EC and will be securely connected to the gear motor (not displayed in the present document). Aforementioned shaft will have a shape that will allow the downward movement of the spacer due to the consumption of the anode. Its materials of construction will be a plastic / metal combination, so that the plastic part (Figure 5) (9a) will be in contact with the liquid and the metallic part (Figure 5) (9b) will be the non-wetted. The axis will have a mechanical seal (Figure 1) (10) at the bottom plate of the EC.

Electrocoagulation Cell’s housing is constructed from non-conductive materials that will be resistant to conditions of high pressures and high temperature and also to a highly corrosive environment as well. Suitable materials of construction may be steel epoxy coated, plastic or a combination thereof. In the top cover of the cell there are sealing provisions (Figure 1) (13) for the cathode’s current supply cables to keep the cell watertight.

Claims

1. Cylindrical electrochemical cell (Figure 1) used for the on-site production of coagulants that incorporates a mechanically rotating spacer (Figure 1) (5), positioned between two electrodes. The consumable electrode (anode plate) (Figure 1) (3) is firmly attached to the cell’s bottom plate (Figure 1) (6), where the power supply cables are connected (Figure 1) (12). Anode’s thickness depends on its operational lifespan and it is specified by its consumption rate. As appropriate materials of construction aluminum or iron may be chosen and it has a cylindrical shape with a cylindrical opening at its center, from which the wastewater passes (Figure 2) (3). At the anode’s upper active surface rests the rotating spacer (Figure 5) (5), consisting of four (4) arms and has a thickness of 3 to 10 mm. The spacer allows the treated liquid to flow only through the gap it creates between the cathode and the anode and at the same time it ensures the homogeneous electrodissolution of the anode, due to its continuous contact with the two electrodes and to its rotational movement, preventing the formation of deposits. The slow rotation of the spacer is supplied through a shaft (Figure 5) (9) which passes through the center of the cell’s bottom plate and permits its vertical downward movement due to the force applied to the cathode and the gradual reduction of the anode’s thickness. At the upper surface of the spacer, rests the completely smooth active surface of the cathode (Figure 3)

(4). The cathode may be constructed from stainless steel or titanium. Cathode’s shape is cylindrical with a cylindrical opening on its center. On its non-active surface a plastic disc, of the same diameter, is mounted (Figure 4) (7), in which a set of rods (Figure 4) (8) are securely fastened. These rods allow only the vertical movement of the cathode as the thickness of the anode decreases and prevent it from rotating due to the rotation of the spacer. The rods pass through a flat bar with the same openings as their number (Figure 4) (8). The bar is embedded in the electrolytic cells top cover (Figure 1) (18).

2. Electrolytic cell according to claim 1, wherein the spacer (Figure 5.1.) has six (6) arms and a thickness of 3 to 10 mm.

3. Electrolytic cell according to claim 1 , wherein the spacer (Figure 5.2.) has eight (8) arms and a thickness of 3 to 10 mm.

4. Electrolytic cell according to claim 1, wherein it incorporates a mechanically rotating spacer (Figure 1) (5) in order to keep a stable distance between the anode (Figure 1) (3) and the cathode (Figure 1) (4). The distance between them corresponds to the spacer’s thickness, which may be from 3 to 10 mm. The gap created by the spacer allows the free flow of the liquid between the two electrodes.

5. Electrolytic cell according to claim 2, wherein the spacer (Figure 1) (5) is constructed from materials that are non-conductive and durable in highly corrosive environments of high temperatures.

6. Electrolytic cell according to claims 2 and 3, wherein the spacer (Figure 1)

(5) is capable of maintaining its thickness unchanged (defined at 3 to 10 mm) during its operation, exhibiting excellent frictional resistance while being always in contact with the two electrodes’ active surfaces.

7. Electrolytic cell according to claim 2, wherein the spacer’s rotation (Figure 1) (5) ensures the homogeneous electrodialysis of the anode (Figure 1) (3), due to its continuous contact with the two electrodes and to its rotational movement, preventing the formation of deposits.

8. Electrolytic cell according to claims from 2 to 7, wherein the spacer (Figure 1) (5) by maintaining a constant distance (3 to 10 mm) between the anode and the cathode, gives to the present invention the ability to operate under conditions of stable electrical potential.

9. Electrolytic cell according to claim 2, wherein the spacer (Figure 1) (5) is allowed to freely move vertically with respect to the axis that gives it its rotary motion. The spacer’s vertical movement is the result of the total force applied to the cathode assembly (Figure 1) (4), that rests at the top surface of it.

10. Electrolytic cell according to claims 1 and 9, wherein the axis of rotation (Figure 1) (9) of the spacer (Figure 1) (5) has a shape that fits to a corresponding opening at the spacer’s center (Figure 5) (19), allowing it to rotate and move vertically as well.

1 1. Electrolytic cell according to claim 10, wherein the rotation axis (Figure 1) (9) of the spacer (Figure 1) (5) consists of two parts, one that is completely immersed in the liquid (Figure 5) (9a) and one that is on the outside (Figure 5) (9b) of the cell and connected to a gear motor.

12. Electrolytic cell according to claim 11, wherein the rotation axis (Figure 1) (9) is constructed from plastic materials.

13. Electrolytic cell according to claim 11, wherein the lower part of the axis (Figure 1) (9b) is sealed by means of a mechanical seal (Figure 1) (10).

14. Electrolytic cell according to claim 6, wherein the rotational motion of the spacer (Figure 1) (5) ensures that the stable distance of 3 to 10 mm between the anode and the cathode. In that way, a constant electrolyte voltage drop is achieved and a constant power consumption during operation, unlike conventional cells where consumption gradually increases.

15. Electrolytic cell according to claim 1, wherein the apparatus (Figure 1) is constructed from materials that exhibit high resistance against pressures of 1 to 10 bar. As such may be materials with non-conductive coating, suitable for operation in highly corrosive environments. Other materials of construction, may be plastics such as glass fiber reinforced plastics.