NO344253B1 - Seal for passing a rod-shaped electrode through a wall made of a polymeric material - Google Patents

Description

SEAL FOR PASSING A ROD-FORMED ELECTRODE THROUGH A WALL MADE OF A POLYMER MATERIAL

The invention relates to a seal for liquid-tight passage of a body through an opening in a wall. More specifically, the invention relates to a seal for an electrode which, during operation, is supplied with a high voltage and a large current so that the electrode becomes hot. The electrode can be rod-shaped. Even more specifically, the invention relates to a seal which is adapted for insertion into a wall which is made of a polymer material, and where the polymer material will deform or melt at the electrode's operating temperature. The invention relates to a seal which is suitable for use in an apparatus where a crustacean parasite in seawater is killed in an electric field which is formed between at least two electrodes which are immersed in the seawater in a treatment chamber.

Farming fish in closed enclosures means that a large number of fish are kept together in a small area. This provides good conditions for parasites. In salmonid farming, external crustacean parasites have become a problem. In particular, salmon lice (Lepeophtheirus salmonis) are present in large numbers. It is necessary to treat fish infected with salmon lice in order to keep the number of parasites down and to safeguard the welfare of the fish.

There are several known treatment methods for salmon lice. These include, among other things, the use of drugs that can be dissolved in the water, so-called bath treatment, or that can be mixed into the fish's feed. Bath treatment in hydrogen peroxide is also known. It is also known to bathe the fish in warm water and in water with added salts. The use of cleaning fish is an alternative method.

Several of the bathing treatments are carried out by leading the fish into a pipe system or into tanks. This has the advantage that there is better control over the treatment time compared to bathing the fish in a cage. It also has the advantage that the amount of treatment solution is reduced. For some of the forms of treatment, such as the use of hot water, the use of pipes or tanks is a prerequisite for the method to work. Some of the forms of treatment can be combined with rinsing the fish to wash off salmon lice.

It has been shown that salmon lice, especially the pre-adult and adult salmon lice, can detach from the fish skin when the fish is fed into a pipe system, such as a fish pump. Additional salmon lice fall off the fish skin due to the treatment. Salmon lice, if they fall off, may be alive, and these are able to reinfect fish if the parasites get out into the water masses. The salmon females can release the egg strings. The eggs can hatch and produce new infective salmon louse larvae.

It is therefore necessary to remove salmon lice and egg strings from the treatment water before the treatment water is returned to the sea. Collected salmon lice and egg strings are killed. Removal of salmon lice, egg strings and eggs from the treatment water can be done by filtration. Drum filters are suitable for the purpose because there is a large volume of water that needs to be filtered. In addition to salmon lice, the water also contains slime and fish scales from the fish. The eggs are relatively small with a diameter of around 90 µm. A suitable filter cloth must therefore have a fine mesh. The fish scales and slime will clog the filter after a relatively short time. Drum filters have a backwash to clean the filter cloth, but it has been shown that cleaning the filter cloth is a limitation in facilities that treat fish with salmon lice. Treatment must be stopped while the filter is being cleaned.

There is therefore a need for an alternative method to ensure that the salmon lice and eggs in the treatment water are dead before the treatment water is released back into the sea while the treatment plant can be operated without downtime. It is known that an electric field between submerged electrodes can kill salmon lice. The electric field must have a quality that kills salmon lice and eggs. Quality means that there must be a sufficient voltage difference between the electrodes, and the electric field must have sufficient strength. It is known that it is advantageous to use direct current that alternates between being on and off, so-called pulses, and that the electrodes can alternate in polarity. That is, a positive electrode is a negative electrode at the next electrical pulse.

Seawater is an electrolyte. It is well known that electrodes in seawater corrode within a relatively short time. The time it takes depends, among other things, on the voltage and amperage. Titanium electrodes have relatively good resistance to corrosion, but even titanium electrodes will also corrode away.

Water to be treated with an electric field can be led through an electric field in a channel. It is professional that such a channel must be made of a non-conductive material. A metal channel will conduct current, and the current will migrate out into the entire facility if a metal channel is connected to a metal piping system. This will lead to extensive corrosion damage throughout the plant. Polyethylene (PE) is an example of a suitable plastic material for such a channel.

There are relatively large quantities of water that must be treated per time unit and the channel must be dimensioned accordingly. For example, the channel can have an inner diameter of 50 cm. A voltage between 50 and 500 V combined with a current between 500 and 2500 A may be necessary to achieve the desired quality in the electric field. The person skilled in the art will know that the combination of such voltages and currents will produce very hot electrodes. Electrodes immersed in water flowing past the electrodes will be cooled by the water. The professional will also know that even if the electrodes are made of titanium, the electrodes will corrode relatively quickly when they are immersed in seawater and applied voltage and amperage as described. The electrodes must also be connected to electrical wires. To avoid a short circuit, it is easiest that the connection between the wire and the electrode is dry, that is, the connection is not submerged in seawater. To achieve this, a part of the electrode must be passed through a wall in the channel and the part protrudes dry past the treatment channel. The dry part will thus not be cooled by the water, and the dry part will be heated to a temperature that makes the plastic material in the wall malleable or even to such a high temperature that it melts. This is unfortunate as seawater can leak out through the wall and this can cause a short circuit in the connection.

Patent document GB 1592662 shows a liquid-tight passage of an anode in a hot water tank. The hot water tank is made of metal and the anode prevents corrosion in the hot water tank. Patent document US 2011/0041620 shows a tubular flow meter with a liquid-tight passage of an electrode.

The professional thus faces several problems by using electricity to ensure that all salmon lice and eggs are killed in the treatment water from a plant that de-lices fish.

The purpose of the invention is to remedy or to reduce at least one of the disadvantages of known technology, or at least to provide a useful alternative to known technology.

The purpose is achieved by the features indicated in the description below and in the subsequent patent claims.

It is desired to use a direct current between 50 and 500 V and with an amperage between 500 and 2500 A for the treatment of water. Such a current causes the electrodes to corrode within a relatively short time. It is therefore desirable that the electrodes can be replaced in a simple way. It is also a requirement that a channel where the electric field is established is made of a non-conductive material, such as plastic. It is also desirable that the electrical connections for the electrodes are positioned on the outside of the channel. The electrodes must therefore be passed through an opening in the canal's wall. Such an opening must be liquid-tight to avoid a short circuit in the connection between an electrical wire and the electrode. This can be achieved by passing the electrode through a seal shaped like a cork or a plug and the cork or plug sealing against the opening in the wall.

Such a seal cannot be made of a heat-conducting material, as the heat from the electrode will heat up the seal. The opening in the wall will be deformed by the heat, and leakage will occur.

Tests have shown that a seal made of a heat-resistant polymer material, such as polyurethane, silicone or polytetrafluoroethylene (Teflon<®>) will not withstand the heat from the electrode. The seal will deform and leakage will occur in the passage in the wall.

It has surprisingly turned out that the problem can be solved by increasing the heat-conducting diameter of the metal inside the seal. A sleeve or a plug with a continuous axial opening for the electrode is positioned around a portion of a rod-shaped electrode. The sleeve or plug can be made of a different metal than the electrode. A suitable metal is aluminium. Such an increase in diameter has proven to be sufficient so that the surface temperature of the sleeve or plug does not exceed the deformation temperature of an ambient temperature-resistant plastic material. The surrounding plastic material forms a sheath in the seal. The cover will not conduct heat to the opening in the wall. The opening will therefore be stable.

It has proven to be advantageous that the sleeve or plug is provided with a flange in the end portion which faces the electrical connection to the rod-shaped electrode. The flange will increase the surface area of the sleeve or plug so that even more heat is conducted away. In addition, the flange will act as a disc at one end of the seal. This can be used to put pressure on the seal in a direction towards the wall, so that the somewhat elastic cover is pressed against the inner wall of the opening and ensures a liquid-tight passage in the wall. The pressure will be directed via the flange so that the jacket is not deformed by the pressure.

The through opening in the sleeve or plug can be shaped with a somewhat larger internal diameter or cross-section than the electrode. At room temperature, there may be a clearance of approximately 0.2 mm between the inner diameter and the electrode. The clearance means that the seal can easily be moved axially onto the electrode's end part. The massive electrode will expand radially upon heating. The sleeve or plug will expand radially due to the heat. Expanding the electrode will remove the clearance between the electrode and the sleeve or plug so that the sleeve or plug closes liquid-tight around the electrode. Radial expansion of the sleeve or plug means that the jacket closes liquid-tight around the sleeve or plug. The seal thus becomes liquid-tight in the central part.

It has proven advantageous that the jacket is made of a temperature-resistant material that can be shaped by turning. This provides greater accuracy than forming the jacket by casting. The invention can nevertheless be carried out by using a temperature-resistant material that can be cast. The temperature-resistant material can be a plastic material or a rubber material.

The invention is defined by the independent patent claim. The independent claims define advantageous embodiments of the invention.

In a first aspect, the invention relates more specifically to a seal for liquid-tight passage of a rod-shaped electrode which is made of a metal, through an opening in a wall which is made of a polymer material. The seal comprises a jacket adapted to seal against the opening and the jacket is made of a heat-resistant polymer material, and an inner axial plug which is made of a metal, and the plug is provided with a central through bore for the rod-shaped electrode.

More specifically, the sheath can be made of polytetrafluoroethylene.

The plug can be made of aluminium. The plug can be provided with a flange in an end part. The flange can be made of the same material as the plug.

The cap can be provided with a recess in an end part. The recess can be complementary to the flange.

The sheath may be shaped with a plurality of external tapers of decreasing diameters. The cap can be shaped with at least one inclined sealing surface between two successive tapers. As an alternative, the outer casing can be shaped like a truncated cone.

In what follows, an example of a preferred embodiment is described which is illustrated in the accompanying drawings, where:

Fig. 1 shows a side view of a treatment unit for a waste water;

Fig. 2 shows, on the same scale as Fig. 1, a top view of the treatment unit;

Fig. 3 shows, on the same scale as Fig. 1, an end view of the treatment unit; Fig. 4 shows on a larger scale a side view of an electrode shaped like a rod-shaped body and a seal for passing the electrode into a wall;

Fig. 5 shows, on the same scale as Fig. 4, an end view of the electrode and the seal;

Fig. 6 shows the same as Fig. 5, but seen from the opposite end;

Fig. 7 shows, on the same scale as Fig. 4, a section through the rod-shaped body and the seal; and

Fig. 8 shows a perspective view of the treatment unit on a different scale.

In the figures, reference number 1 refers to a treatment unit for a waste water (not shown). The treatment unit 1 is provided at a first end with an inlet part 10 and at an opposite end provided with an outlet part 19. The treatment unit 1 comprises a treatment chamber 11 between the inlet part 10 and the outlet part 19. The treatment chamber 11 has a larger cross-section than the inlet part 10 and the outlet part 19.

The treatment chamber 11 is delimited by a side wall 12, a first end wall 13 and a second end wall 14. The end walls 13, 14 form a fluid-tight wall between the inlet parts 10, 19 and the side wall 12. The treatment chamber 11 is provided at the top with a frame 15 which forms a hatch opening. A hatch 16 seals between the treatment chamber 11 and the surroundings when the hatch 16 is positioned in the frame 15. The treatment unit 1 is advantageously made of a plastic material, such as polyethylene, but other non-conductive plastic materials can also be used.

The inlet portion 10 is provided with a first flange 101 for connection to a pipe system (not shown) for transporting liquid. The outlet portion 19 is provided with a second flange 191 for connection to the pipe system. The processing unit 1 rests on a plurality of supports 17.

The treatment unit 1 is provided with an electrical treatment system 2. The electrical treatment system 2 comprises a plurality of elongated electrodes 21 inside the treatment chamber 11. The elongated electrode 21 can be constituted by a rod-shaped body in a metal. One electrode 21 extends from a junction box 23 at the end wall 13, 14, through an opening 18 (see figure 4) in the end wall 13, 14 and axially inwards into the treatment chamber 11. The figures show a first electrode 210 which extends axially inwards in the treatment chamber 11 from the first end wall 13, and a second electrode 219 which extends axially inwards into the treatment chamber 11 from the second end wall 14. The electrodes 21 are fixed inside the treatment chamber 11 with a plurality of fasteners (not shown).

A seal 3 encircles a portion of the electrodes 21, 210, 219 in the opening 18. The seal 3 forms a liquid-tight seal for the passage of the electrodes 21; 210; 219 through the opening 18 in the end walls 13, 14. The seal 3 comprises an outer cover 30 and an inner, axial plug 4. The plug 4 comprises a stem 47 with a central axial through bore 41, as shown in figure 7. The cross section of the axial bore 41 is adapted to the electrode's 21 outer cross-section.

In the figures, the cover 30 is shown with a plurality of external steps 31 with decreasing diameters. Between the steps 31, the cover 30 is formed with inclined sealing surfaces 33. The opening 18 in the end wall 13, 14 is shaped complementary to the cover 30. The opening 18 comprises inclined sealing seats 183. The cover 30 can comprise a heat-resistant polymeric material, such as polytetrafluoroethylene (Teflon<®> ). In an alternative embodiment, the cover 30 can be shaped like a truncated cone. In such an embodiment, the opening 18 is conformal.

The plug 4 is provided with a flange 45 in its one end portion. The flange 45 is complementary to a recess 35 in the jacket 30. The jacket 35 comprises a continuous channel 37. The inner cross-section of the channel 37 is adapted to the outer cross-section of the stem 47.

The electrical treatment system 2 further comprises a transformer, electronics, a control panel and necessary electrical lines and connections (not shown) to supply the electrodes 21 with electrical current.

The connection box 23 is provided with a pressing device (not shown) to be able to press the seal 3 axially against the end wall 13, 14. The pressure is exerted with a nut-and-screw device which presses axially against the flange 45. The sealing surfaces 33 of the casing 30 are thereby pressed axially against the seal seats. 183. Due to the relatively large contact surface between the flange 45 and the recess 35, the seal 3 can absorb relatively large forces from the pressing device without the jacket 30 being deformed.

The electrode 21 can advantageously be made of titanium. The electrical treatment system comprises one electrode 21 on one side of the treatment chamber 11 and a parallel electrode 21 on the other side of the treatment chamber 11 as shown in figure 2. The treatment chamber 11 is partially filled with seawater (not shown) so that the electrodes 210, 219 are covered of the seawater. Seawater constitutes an electrolyte. The plug 4 can be made of another metal, such as aluminium. When the electrical circuit is activated, the electrode 21, 210, 219 will become hot. A part of the electrode 21, 210, 219 that is immersed in the seawater will be cooled continuously by the seawater that flows past the electrode 21 in the treatment chamber 11. A part of the electrode 21, which is passed through the end wall 13, 14, and which protrudes into the junction box 23, will be heated and not cooled. The heat from the electrode 21 will be partially transferred to the plug 4. The plug 4 will expand radially and seal against the electrode 21 which is positioned in the through bore 41. The seal 3 will be liquid-tight against the end wall 13, 14 and against the electrode 21.

Experiments have shown that round titanium rods with a diameter of 8 mm have proven suitable as electrodes 21. The titanium rods are cut to suitable lengths. Titanium is a metal with good resistance to corrosion. Assembly of the electrode 21 takes place by inserting the electrode 21 through the opening 18. The electrode 21 is attached to the inside of the side wall 12. An installer has access to the treatment chamber 11 through the hatch opening at the top of the treatment chamber 11. It has proven practical to insert an electrode 210 through the end wall 13 and an electrode 219 through the end wall 14. The electrodes 210, 219 extend to approximately the middle of the treatment chamber 11, as shown in Figures 1 and 2. The seal 3 is threaded onto the free end portion of the electrode 21 and is inserted into the opening 18. The seal 3 is pressed axially against the gable wall 13, 14 with the pressing device. Finally, an electric cable is mounted to the electrode 21 in a known manner with a cable lug (not shown).

The electrical treatment system 2 is arranged to supply a direct current to the electrodes 21, 210, 219. The current can have a voltage between 50 and 500 V and a current strength of between 1500 and 1600 A. The current strength is dependent on the conductivity of the seawater. When the seawater is polluted with a lot of sediments, the current strength can be increased to 2500 A. The electrical treatment system 2 is further arranged to deliver a pulsed direct current, and the polarity can change between each pulse. This prevents the precipitation of salts on the electrodes, and it prevents the formation of creep currents in the seawater that flows out of the treatment unit 1. It has proved advantageous that the inlet part 10 and the outlet part 19 form a distance between the electrodes 21 and the flanges 101, 109. In this way, it is avoided creepage currents at the flanges 101, 109 and these can be connected to a pipe system where the pipes are made of a metal.

The treatment unit 1 is designed to kill crustacean parasites, such as salmon lice, which are found in the seawater. Pulsed direct current with alternating polarity has proven to be well suited for the purpose. Direct current with 200 V voltage, 1500-2000 A amperage and with pulses lasting 2 ms with a pause of 15-20 ms between the pulses is an example of a suitable treatment regime.

A treatment unit 1, as described, can have a capacity to treat 2000 m<3> of seawater per hour.

Electrolysis of water leads to the formation of gas (not shown). The gas that is formed in the treatment chamber 11 can be vented through hatch 16 or another suitable opening in an upper part of the treatment chamber 11.

It should be noted that all of the above embodiments illustrate the invention, but do not limit it, and those skilled in the art will be able to devise many alternative embodiments without departing from the scope of the appended claims.

The use of the verb "to comprise" and its various forms does not exclude the presence of elements 1 or steps not mentioned in the claims. The indefinite articles "an", "ei" or "et" before an element do not exclude the presence of several such elements.

The fact that certain features are listed in different mutually dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims (9)

Patent claims 1. Seal (3) for liquid-tight passage of a rod-shaped electrode (21; 210, 219) which is made of a metal, through an opening (18) in a wall (13, 14) which is made of a polymer material, characterized in that the seal (3) comprises a jacket (30) designed to seal against the opening (18 ) and the jacket (30) is made of a heat-resistant polymer material, and an inner axial plug (4) which is made of a metal, and the plug (4) is provided with a central through bore (41) for the rod-shaped electrode (21; 210, 219). 2. Seal (3) according to claim 1, where the sheath (30) consists of polytetrafluoroethylene. 3. Seal (3) according to any of the preceding claims, wherein the plug (4) is made of aluminium. 4. Seal (3) according to any one of the preceding claims, wherein the plug (4) is provided in an end portion with a flange (45). 5. Seal (3) according to claim 4, where the jacket (30) is provided with a recess (35) in an end part. 6. Seal (3) according to claim 5, where the recess (35) is complementary to the flange (45). 7. Seal (3) according to any one of the preceding claims, wherein the jacket (30) is formed with a plurality of external tapers (31) of decreasing diameters. 8. Seal (3) according to claim 7, where the cover (30) is shaped with at least one inclined sealing surface (33) between two successive tapers (31). 9. Seal (3) according to any one of claims 1-6, wherein the jacket (30) is externally shaped like a truncated cone.