GB1560730A

GB1560730A - Electrolytic cell for treatment of water

Info

Publication number: GB1560730A
Application number: GB27000/76A
Authority: GB
Original assignee: Hans Einhell GmbH Industriegelande
Current assignee: Einhell Germany AG
Priority date: 1975-07-16
Filing date: 1976-06-29
Publication date: 1980-02-06
Also published as: BR7604451A; AT353707B; IN143282B; SE7607833L; IL49852A0; CA1090292A; AU1528376A; IL49852A; ES449887A1; FR2318115A1; DK320376A; CH598138A5; AU504005B2; MX143221A; JPS5212752A; ATA450976A; NO762273L; NL7607843A

Description

(54) AN ELECTROLYTIC CELL FOR TREATMENT OF WATER (71) We, HANS EINHELL G.m.b.H., a German limited liability company, of Indus triegelände, D-8380 Landau, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a continuous process for treatment of water and simultaneously for keeping clean electrodes in an electrolytic water treatment cell. The invention also includes an electrolytic cell for carrying out the process. Such treatment may for example be purification and sterilization of water. The invention relates in particular to a multipole electrolytic cell, which can be used in various ways for treatment, and more particularly for purification and sterilization, of water and comprises a closed container with a lower inlet opening and an upper outlet opening for the water and electrodes within the container, which are arranged to be connected to the positive and negative poles of a DC source.

Various electrolytic cells are known for treatment, and more particularly for purification and sterilization, of water. With these known cells it is possible to remove dissolved and suspended contaminating materials in the water to be treated electrolytically by using either consumable or non-consumable electrodes of iron, aluminium, copper, silver, platinum, or carbon. However during operation of such electrolytic cells problems are encountered due to different causes.

Normally during electrolysis of water, especially hard water, the cathode is rapidly covered by a coating of calcium carbonate which inhibits flow of the electric current; anodes of silver, copper, iron, or aluminium during electrolysis are covered with oxide films. In the case of aluminium anodes the formed aluminium oxide prevents flow of current. In the case of silver, iron or copper anodes the formed oxide film is highly conductive, so that dissolution of the metal is prevented and oxygen is produced at the electrodes.

Another problem encountered is that water to be treated usually has only a small number of ions and that, although platinum anodes can provide oxidation, the oxidation-reduction potential of the water remains low. For example, if chlorine is to be produced, the chloride concentration in the water must be high and this concentration is normally not encountered in fresh water, particularly drinking water.

The standard electrolytic technique to chlorinate water in a swimming-pool is to provide a separate cell containing a high concentration of common salt which upon electrolysis gives sodium hypochlorite or chlorine which is fed into the swimmingpool. Theoretically it is possible to add sufficient common salt to the swimming-pool water and to electrolyze it directly. This technique has the disadvantage that the water tastes salty and that the calcium in the water deposits on the cathodes to such an extent that the flow of current stops. Changing polarity to remove the calcium deposit on the cathodes has been found in practice only to lead to corrosion of the cathodes, and aggravates the problem.

It is an object of the invention to prevent as far as possible formation of deposits on the electrodes which hinder the flow of current and the dissolution of metal electrodes required for water purification.

According to this invention there is provided a continuous process for treatment of water and simultaneously for keeping clean electrodes in an electrolytic cell, comprising flowing a stream of water to be treated upwardly past electrodes in the cell which contains freely movable particles whose density is greater than that of the water, controlling the velocity of the flowing stream so as to form a fluidized bed of the particles in the cell and so as mechanically to keep the electrodes clean by virtue of the kinetic energy generated by fluidization of the particlefs.

Also according to this invention there is provided an electrolytic cell when used for carrying out the process, the cell comprising a closed container with a lower inlet opening and an upper outlet opening for the water to be treated, electrodes in the container for connection to the positive and the negative poles of a D.C. source, particles whose density is greater than that of the water to be treated, and means for retaining the particles within the container, wherein the particles are freely movable and are fluidized by the flowing movement of water to be treated at a velocity such as to form a fluidized bed whose particles mechanically keep the electrodes clean.

According to a preferred embodiment of the invention, the electrolytic cell comprises a cylindrical container with a lower inlet opening and an upper outlet opening for the water flow, radially disposed cathodes, and a centrally located anode surrounded by a porous electrodialysis diaphragm completely surrounding it and forming a closed anode compartment having a small upper aperture for the escape of produced gases and of liquids that have permeated through the porous diaphragm.

Near the inlet and outlet, grids may be located whose function is to prevent particles in the cell from escaping through the inlet or outlet. The particles, due to the velocity of the water flow, are agitated thus forming an unrestricted fluidized bed of particles surrounding the cathodes, and by their movement continuously clean the electrode in a mechanical way. Due to the electrical potential difference between the electrodes, a concentration gradient is established which serves through the electrodialysis to concentrate the anions within the anode compartment. For example, if water containing 3 ppm chloride ions is electrolyzed without using an electrodialysis diaphragm no chlorine is produced, but only oxygen is produced at the anode. Once the diaphragm is used, the chloride concentration increases within the anode compartment up to a level which causes formation of free chlorine. If chloride ions are absent, other ions for example carbonate ions or sulphate ions in the water, concentrate in the anode compartment forming through electrolysis percarbonate or persulphate which are also excellent oxidizing agents. In the same way any organic acid will be oxidized.

In another preferred embodiment of the invention an electrolytic cell comprises a transparent cylinder as the container having a lower inlet opening and an upper outlet opening, each provided with a grid. In the interior of the cylinder are radially disposed electrodes whose length in the axial direction of the cylinder is about 1/2 to 2/3 the length of the cylinder, and in the centre of the cylinder there is a concentric cylindrical anode ring compartment defined by an outer cylindrical diaphragm and an inner concentric cylindrical pipe with the anode between them. The anode ring compartment is closed at both ends and has at least one upper small opening to permit escape of products formed within the anode compartment. The axial length of anode, anode compartment and inner pipe is substantially the same as that of the cathodes outside the anode compartment. Within the cylinder (i.e. the outer wall of the cell) and outside the anode compartment, there are sufficient particles whose size is greater than that of the openings of the grids. These particles are agitated by the flowing water in the cell and rise up to surround the cathodes (in the cathode compartment), thereby cleaning them mechanically through impact and scratching. The upper free space in the interior of the cell serves as a disengaging space for the particles so that, in case the water flow rate is too high, the particles do not become entrained and held at the upper grid. The purpose of the central pipe (inner boundary of the anode ring compartment) is to permit recirculation of the particles flowing upwardly in the cathode compartment and downwardly through the inner pipe, especially when the lower grid below the lower end of the central pipe is blocked at its centre, i.e. has no apertures.

The invention will now be described by way of example, with reference to the drawings, in which: Fig.1 is a section through a first embodiment; Fig. 2 is a section through a second embodiment; Fig. 3 is a section through a third embodiment; and Fig. 4 is a section through a fourth embodiment.

Referring to Figure 1 an electrolytic cell has a cylindrical container 1 with a lower inlet 2 and an upper outlet 3 for water flow radially disposed cathodes 4, and a central axial anode 5 with a porous electrodialysis diaphragm 6 completely surrounding it and forming a closed anode compartment 7 having a small upper aperture 8 for the escape of produced gases and of liquids that have permeated through the porous diaphragm 6.

Located below, near the inlet 2 and above, near the outlet 3 there are grids 9 and 10, respectively, whose function is to prevent particles 11 within the cell escaping through the inlet 2 or outlet 3 of the cell.

Fig. 2 shows an electrolytic cell comprising a cylinder 1 having a lower inlet 2 and an upper outlet 3 with grids 9 and 10, respectively. In the cylinder 1 are radially disposed cathodes 4 whose length in the axial direction of the cylinder 1 is shorter than the total length of the cylinder 1. The axial length of the anode 5, anode compartment 7 and an inner pipe 12 is the same as that of the cathodes 4. The compartment 7 has the small upper aperture 8. Within the cylinder 1 are sufficient particles 11 whose size is greater than that of the openings of grids 9, 10. The upper free space in the interior of cell 1 serves as a disengaging space 13 for the particles. The central part 9' of lower grid 9 has no apertures. The upper grid 10 has apertures both in the horizontal portions and in the vertical cylindrical portions 10' to provide a greater area. The distances between the pipe 12 and each grid is greater than the largest particle size. The distance between the upper end of the pipe 12 and the upper grid is not less than 10% of the length of the pipe.

Fig. 3 shows an electrolytic cell comprising a cylinder 1 having a lower inlet 2 and an upper outlet 3 provided with grids 9 and 10, respectively. In the interior of the cylinder 1 are radially disposed alternate cathodes 4 and anodes 5'. The centre of the cell 1 has a pipe 12 open at both ends which serves to direct the particles 11 downwardly. Below pipe 12 there is positioned a grid 9 whose central part 9' is closed to the flow of water, and above the electrodes 4 and 5' and the pipe 12 is a disengaging space 13 for the particles.

Fig. 4 shows a cell 1 in which the inlet 2 and the outlet 3 are connected to a by-pass conduit 15 outside the cell 1. In the by-pass conduit 15 is interposed a pump 14 which recirculates water through the cell 1 to provide a sufficient flow rate to agitate and entrain the particles within the cell 1. It is also provided with an inlet 16 for the untreated water and an outlet 17 for treated water.

With reference to Fig. 2 another embodiment is obtained by omitting the electrodialysis diaphragm 6 and by using corrodable metals for anode 5.

It is also possible to dispose an energized turbine or propeller (not shown) within pipe 12 of Figs. 2 and 4 to provide additional reflux and to ensure enough contact time between particles 11 and electrodes 4, 5'.

With reference to Figs 1 to 4 it is also possible to provide an additional outer pipe (not shown) between the radially disposed electrodes 4 or 4, 5' and the outer cylinder 1.

The distance between this pipe and the cylin der 1 must be large enough to allow free downward flow of particles 11. The holes in the lower grid 9 can be closed along the periphery of grid 9 at least to an extent cor responding to the distance between the outer pipe and cylinder 1.

The materials for constructing the electrolytic cell of the invention, e.g. as illustrated in Figs. 1 and 2, are as follows: The anodes are preferably of platinized titanium or niobium in mesh form, although they also can be of any other metal of the platinum family that resists corrosion, or they can be of graphite or carbon or metal oxides. The anodes can be solid or in the form of a grid.

The corrodable anodes of Figs. 3 and 4 are preferably chosen from the metals commonly used in water treatment, for example aluminium, iron and copper for the provision of flocking materials in water treatment processes, or metals for example silver and copper to provide oligodynamic disinfecting ions to the water being treated.

As material for the cathodes, any conductive material can be used, preferably stainless steel or copper.

Materials for the construction of the cylinder, inlet, outlet, grids, pipes and supports are e.g. plastics, porcelain, glass, hard rubber and concrete, or a metal which can act as cathode.

Materials for the electrodialysis diaphragms are e.g. porous porcelain, microporous plastics for example polyolefines and polyvinylchloride, cellulose nitrate, and ion exchange resins. In case the porous diaphragms are mechanically sensitive to impact by the particles they can be shielded with a protective grid of a non-conductive material, for example a plastics material.

The particles in the cell can be spheres of porcelain, hard plastics, stone, glass, alumina and any other hard materials whose density is greater than that of the water to be treated.

Of course, the size of these particles must be larger than that of the openings of the grids which are to retain them within the cell.

The cell need not be cylindrical, but can be elliptical or hexagonal in section. Also the closed grid area can have other shapes depending on the flow pattern required within the cell. It is also possible, for example, to combine the central anode with additional radially disposed anodes of the same or other metals, with or without centrally or outwardly located downflow pipes, or any other combination thereof.

WHAT WE CLAIM IS: 1. A continuous process for treatment of water and simultaneously for keeping clean electrodes in an electrolytic cell, comprising flowing a stream of water to be treated upwardly past electrodes in the cell which contains freely movable particles whose density is greater than that of the water, controlling the velocity of the flowing stream so as to form a fluidized bed of the particles in the cell and so as mechanically to keep the electrodes clean by virtue of the kinetic energy generated by fluidization of the particles.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

upper outlet 3 with grids 9 and 10, respectively. In the cylinder 1 are radially disposed cathodes 4 whose length in the axial direction of the cylinder 1 is shorter than the total length of the cylinder 1. The axial length of the anode 5, anode compartment 7 and an inner pipe 12 is the same as that of the cathodes 4. The compartment 7 has the small upper aperture 8. Within the cylinder 1 are sufficient particles 11 whose size is greater than that of the openings of grids 9, 10. The upper free space in the interior of cell 1 serves as a disengaging space 13 for the particles. The central part 9' of lower grid 9 has no apertures. The upper grid 10 has apertures both in the horizontal portions and in the vertical cylindrical portions 10' to provide a greater area. The distances between the pipe 12 and each grid is greater than the largest particle size. The distance between the upper end of the pipe 12 and the upper grid is not less than 10% of the length of the pipe.

Fig. 3 shows an electrolytic cell comprising a cylinder 1 having a lower inlet 2 and an upper outlet 3 provided with grids 9 and 10, respectively. In the interior of the cylinder 1 are radially disposed alternate cathodes 4 and anodes 5'. The centre of the cell 1 has a pipe 12 open at both ends which serves to direct the particles 11 downwardly. Below pipe 12 there is positioned a grid 9 whose central part 9' is closed to the flow of water, and above the electrodes 4 and 5' and the pipe 12 is a disengaging space 13 for the particles.

Fig. 4 shows a cell 1 in which the inlet 2 and the outlet 3 are connected to a by-pass conduit 15 outside the cell 1. In the by-pass conduit 15 is interposed a pump 14 which recirculates water through the cell 1 to provide a sufficient flow rate to agitate and entrain the particles within the cell 1. It is also provided with an inlet 16 for the untreated water and an outlet 17 for treated water.

With reference to Fig. 2 another embodiment is obtained by omitting the electrodialysis diaphragm 6 and by using corrodable metals for anode 5.

It is also possible to dispose an energized turbine or propeller (not shown) within pipe

12 of Figs. 2 and 4 to provide additional reflux and to ensure enough contact time between particles 11 and electrodes 4, 5'.

With reference to Figs 1 to 4 it is also possible to provide an additional outer pipe (not shown) between the radially disposed electrodes 4 or 4, 5' and the outer cylinder 1.

The distance between this pipe and the cylin der 1 must be large enough to allow free downward flow of particles 11. The holes in the lower grid 9 can be closed along the periphery of grid 9 at least to an extent cor responding to the distance between the outer pipe and cylinder 1.

The materials for constructing the electrolytic cell of the invention, e.g. as illustrated in Figs. 1 and 2, are as follows: The anodes are preferably of platinized titanium or niobium in mesh form, although they also can be of any other metal of the platinum family that resists corrosion, or they can be of graphite or carbon or metal oxides. The anodes can be solid or in the form of a grid.

The corrodable anodes of Figs. 3 and 4 are preferably chosen from the metals commonly used in water treatment, for example aluminium, iron and copper for the provision of flocking materials in water treatment processes, or metals for example silver and copper to provide oligodynamic disinfecting ions to the water being treated.

As material for the cathodes, any conductive material can be used, preferably stainless steel or copper.

Materials for the construction of the cylinder, inlet, outlet, grids, pipes and supports are e.g. plastics, porcelain, glass, hard rubber and concrete, or a metal which can act as cathode.

Materials for the electrodialysis diaphragms are e.g. porous porcelain, microporous plastics for example polyolefines and polyvinylchloride, cellulose nitrate, and ion exchange resins. In case the porous diaphragms are mechanically sensitive to impact by the particles they can be shielded with a protective grid of a non-conductive material, for example a plastics material.

The particles in the cell can be spheres of porcelain, hard plastics, stone, glass, alumina and any other hard materials whose density is greater than that of the water to be treated.

Of course, the size of these particles must be larger than that of the openings of the grids which are to retain them within the cell.

The cell need not be cylindrical, but can be elliptical or hexagonal in section. Also the closed grid area can have other shapes depending on the flow pattern required within the cell. It is also possible, for example, to combine the central anode with additional radially disposed anodes of the same or other metals, with or without centrally or outwardly located downflow pipes, or any other combination thereof.

WHAT WE CLAIM IS: 1. A continuous process for treatment of water and simultaneously for keeping clean electrodes in an electrolytic cell, comprising flowing a stream of water to be treated upwardly past electrodes in the cell which contains freely movable particles whose density is greater than that of the water, controlling the velocity of the flowing stream so as to form a fluidized bed of the particles in the cell and so as mechanically to keep the electrodes clean by virtue of the kinetic energy generated by fluidization of the particles.
2. An electrolytic cell when used for car

rying out the process of claim 1, the cell comprising a closed container with a lower inlet opening and an upper outlet opening for the water to be treated, electrodes in the container for connection to the positive and the negative poles of a D.C. source, particles whose density is greater than that of the water to be treated, and means for retaining the particles within the container, wherein the particles are freely movable and are fluidized by the flowing movement of water to be treated at a velocity such as to form a fluidized bed whose particles mechanically keep the electrodes clean.
3. A cell according to claim 2, wherein a closed anode compartment in the container is defined by an electodialysis diaphragm with an anode therein and provided with a small upper aperture and wherein at least one cathode in the container is outside the anode compartment.
4. A cell according to claim 2 or claim 3, having radially disposed electrodes in the container.
5. A cell according to any of claims 2 to 4, wherein a pipe open at both ends is disposed in the container, the lower end of the pipe being spaced from a lower grid covering the lower inlet opening, and the upper end of the pipe being spaced from an upper grid upstream of the upper outlet opening, the distances between the pipe and each grid being greater than the largest particle size.
6. A cell according to claim 5, wherein the distance between the upper end of the pipe and the upper grid is at least 10 percent of the length of the pipe.
7. A cell according to claim 5 or claim 6, wherein a propeller is disposed in the interior of the pipe.
8. A cell according to any of claims 2 to 6, wherein a bypass conduit is disposed outside the container, the conduit being connected at its respective ends to the outlet and inlet openings, and having a pump in the bypass conduit.
9. A cell according to any of claims 2 to 8, wherein the container is cylindrical and within the container a closed anode ring compartment is disposed centrally and axially, the ring compartment being defined by an inner tube open at both ends and an outer concentric electrodialysis diaphragm which contains an anode and which is provided with an upper small aperture.
10. An electrolytic cell constructed and arranged substantially as herein described and shown in the drawings.