Water electrolysis device and method for the purification of water used in water cooled systems

Abstract

The present invention relates to a water electrolysis device (1), in particular for the purification of water used in water cooled systems, the water electrolysis device (1) comprising - a housing with therein provided an electrolysis chamber (2), wherein the housing comprises a fluid inlet (4, 6) and a fluid outlet (6, 4) for allowing a fluid to flow through the electrolysis chamber (2), - an anode (26) and a cathode (27) configured for performing a water electrolysis reaction and for during the electrolysis reaction having solids depositing on a surface of the cathode (27), and - a solid removal mechanism (14) having at least one scraper (16) configured for scraping the deposited solids of the surface of the cathode (27), characterized in that the housing is formed by a stationary elongate tubular cathode (27) having a circumferential wall (28) 28 that defines the electrolysis chamber (2) and a central axis (X) that is preferably substantially vertical, in that the anode (26) is provided within (a central part) the electrolysis chamber (2) spaced apart from an inner surface of the circumferential wall (28) of the cathode (27), and in that the at least one scraper (16) is provided within the electrolysis chamber (2) and is configured for at least partially rotating around the central axis (X) such that the at least one scraper (16) is configured for during rotation scraping the deposited solids from the cathode (27) inner surface, and to a method therefore.

Description

[0001] P36854PCOO / MOV

[0002] Title: Water electrolysis device and method for the purification of water used in water cooled systems

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to water electrolysis device, in particular for water particular for the purification of water used in water cooled systems, as well as to a method for removing solids from such a water electrolysis device.

[0005] BACKGROUND TO THE INVENTION

[0006] The presence of solids, in particular deposited minerals such as calcium carbonate (CaCO3), often referred to as scale, in water systems poses significant challenges. The solids tend to precipitate and form hard, adherent scale on surfaces which can lead to blockages and inefficiencies. For example in water cooling systems, precipitated solids can cause reduced heat transfer efficiency and increased energy consumption as the system then must work harder to achieve the desired cooling. Additionally, solid deposits can narrow flow paths within the systems, which may lead to restricted water flow and increased pressure drop. If solids deposition occurs within the water (cooling) system, the solids should be regularly removed by e.g. mechanical cleaning or chemical treatments. These both are costly and timeconsuming. If however not cleaned, the scale could damage components or reduce the reliability or lifespan of the installations.

[0007] To prevent the above disadvantages, it is desirable to remove as much solids as possible from the water before it precipitates within all components of the cooling systems. Optionally the calcium carbonate may be removed by using an electrolysis system that may also be used for e.g. to control the pH of the water in the water system. Such an electrolysis system in which excess solids are removed from a reactor is for example disclosed in WO2014 / 188432 A1. The electrolysis system is used for water purification and disinfection in substantially closed circulating water systems that uses electrolysis to produce e.g. free chlorine. The system comprises a stationary frame in which multiple anodes and disc shaped cathodes are provided. The cathodes are mounted on an axle that is driven in rotation while the system is operational, and the electrolysis process is ongoing. To remove this scale build up, WO2014 / 118432 has provided multiple stationary cathode cleaning elements that are in contact with the surface of the cathodes. Thus, when during the electrolysis process scale builds up on the surface of the rotating cathodes, the scale is immediately removed from the cathode by the stationary cathode cleaning elements that scrape over the cathode surface. The removed scale ends up in the water stream within the tank or falls to the bottom of the stationary frame. The accumulated scale at the bottom of the tank could be removed by draining and flushing the tank via a separate outlet.

[0008] The system described in WO2014 / 188432 A1 has several disadvantages. One such disadvantage is that the electrolysis system is inefficient at removing calcium components from the water flowing through the tank, as the WO2014 / 188432A1 primarily focuses only on removing the scale buildup on the cathodes, rather than on removing as much minerals, such as calcium, as possible from the water itself to prevent deposition of these minerals in other components of the closed circulating water system. That is to say, WO2014 / 188432 does not provide the right conditions to maximize mineral deposition on the cathode. For example, the rotation of the cathodes and the cathode’s closeness to the anodes cause a relatively high flow rate of water along the cathode surface. The high flow rate increases the dispersion of the mineral (calcium) ions and decreases the likelihood of the minerals to settle on the cathode’s surface. In addition, during electrolysis, the cathodes rotate, and the electrical connection of the cathode plates runs through the stationary cathode cleaning elements. To establish a good electrical connection between the cathode and the power source, the deposited calcium must be completely removed from the cathode surface. This however results in reduced crystallization of new solid deposits on the cathode surface, as no seed crystals are present on the cathode surface, which disadvantageously slows down the crystallization rate.

[0009] Another disadvantage is that the cathode cleaning elements clean the cathode surface while the electrolysis reaction is ongoing. As a result, the majority of the scale that detaches during cleaning will be carried along in the water flow to, for instance, the water storage tanks. Only the excess scale that falls to the bottom of the tank will be flushed out via the separate outlet. This results in a large part of the scale ending up in the water system, which can lead to greater buildup of scale on different components of said water system.

[0010] Yet another disadvantage is that the outer sides cathode plates are not provided with a cathode cleaning element. These cathode plates will thus inherently grow scale as well and will require periodic cleaning to prevent the tank from clogging.

[0011] Yet another disadvantage of the system is that the system consists of a multitude of parts moving relative to each other, of which especially the mechanical components of the stationary cathode cleaning element that directly scrape over the cathode surface are prone to breakage. Moreover, having the rotating cathodes connected to the power source via the stationary cathode cleaning element, might introduce fluctuations or noise in the power supply, which can negatively impact the electrochemical reaction. DESCRIPTION OF THE INVENTION

[0012] The present invention aims to overcome those disadvantages at least partly or to provide a usable alternative. In particular the present invention aims to provide a water electrolysis device that is better suited for removing sufficient solid materials, such as calcium carbonate, from water in (closed circulating) water systems.

[0013] According to the present invention this aim is achieved by the water electrolysis device according to claim 1. The water electrolysis device comprises:

[0014] - a housing with therein provide an electrolysis chamber, wherein the housing comprises a water inlet and a water outlet for allowing a water to flow through the electrolysis chamber,

[0015] - an anode and a cathode configured for performing a water electrolysis reaction and for during the electrolysis reaction having solids depositing on a surface of the cathode, and

[0016] - a solid removal mechanism having at least one scraper configured for scraping the deposited solids of the surface of the cathode.

[0017] According to the inventive thought the housing of the electrolysis device is (at least partially) formed by a stationary elongate tubular cathode having a central axis and a circumferential wall that defines the electrolysis chamber. The anode is provided within the electrolysis chamber and is spaced apart from an inner surface of the circumferential wall of the cathode. Moreover, at least one scraper is provided within the electrolysis chamber and is configured for at least partially rotating around the central axis such that the at least one scraper is configured for during rotation scraping the deposited solids from the cathode inner surface.

[0018] An advantage of the water electrolysis device according to the invention is that the tubular cathode may provide improved conditions for solids, in particular mineral deposits such as calcium carbonate, to settle within the electrolysis chamber of the water electrolysis device. By removing as much of these minerals as possible from the water flowing through the electrolysis chamber, it is prevented that these will deposit within other parts of the system, e.g. in the water storage tanks, heat exchanger parts, etc. In particular when having a laminar flow within the electrolysis chamber, the tubular shape of the cathode causes the water to follow a parabolic fluid velocity profile with the maximum velocity occurring within the center of the tubular cathode and the velocity decreasing towards the circumferential wall of the cathode. The water reaches a theoretical zero velocity at the inner surface of the circumferential wall of the cathode. This minimal water velocity near the inner surface of the cathode provides for locally favorable conditions, such a slightly alkaline concentration due to the formation of hydroxide ions at the cathode and a higher concentration of mineral ions, such as calcium ions, which are to be deposited on the cathode surface. If there is a higher flow rate near the cathode surface, these locally favorable conditions will be disturbed and thus there will be less deposition of the solids on the cathode surface.

[0019] Another important advantage of the water electrolysis device according to the invention is that substantially all minerals that deposit within the device will deposit on the inner surface of the circumferential wall of the cathode. The at least one scraper may therefore efficiently scrape along the entire surface of the cathode in a single rotational motion to remove the solids from the cathode’s inner surface. This allows the at least one scraper to efficiently remove the solids from the cathode.

[0020] Yet another advantage is that the cathode is a stationary part within the system, which thus allows efficient electrical connection of the cathode to a power source. Having the stationary cathode in direct connection with the power source provides a more stable and consistent voltage and current supply to the cathode and eliminates the requirement of cumbersome sleeve contact connections and the like, which generally experience significant wear and tear due to the constant friction of the sleeve contact and are in general mechanically complex to use.

[0021] Yet another advantage is that the anode surface area and cathode surface area can be easily adjusted in proportion by, for example, increasing or decreasing the cross-sectional area of the cathode. Thereby, the fluid flow dynamics can be conveniently optimized by adjusting the distance between the inner surface of the cathode and the surface of the anode. It has in particular been found that a ratio of cathode inner surface area relative to the anode surface area the range of 10-100, preferably a ratio in the range of 20-50, such as a ratio in the range of 30-40 provides several advantages. For example, the anode is often the most expensive part of an electrolysis device. It is therefore advantageous to reduce the amount of anode to as little as possible, as long as the efficiency and current density within the electrolysis device remain uncompromised. Preferably, the distance between the anode and the cathode is at least 7 cm, more preferably at least 10 cm. For example, the distance between the anode and cathode is in the range of 7-50 cm, such as 10-30 cm. This spacing ensures that a sufficiently thick hydrodynamic boundary layer can be created adjacent the cathode surface, with a pH that is favorable for the controlled precipitation of solids.

[0022] The anode and cathode may be made of a variety of electrically conductive materials. Preferably, however, the anode is formed of titanium and provided with a mixed metal oxide (MMO) coating. An MMO coating (for example, iridium oxide, ruthenium oxide, or combinations) provides a stable conductive surface that resists corrosion.

[0023] Preferably, electrolysis chamber is free of a diaphragm. The presence of a diaphragm may interrupt the natural water flow and makes it less likely that a suitable parabolic flow profile can develop. When the space between the anode and the cathode is substantially free of components, except for the scraper mechanism, a stable flow profile can be maintained to facilitate deposition of solids on the cathode inner surface.

[0024] In a preferred embodiment, the water electrolysis device is configured to operate with water having a salt concentration in the range of 0.1-0.3 g / L. Operating at such low salinity is particularly advantageous in closed-loop water systems, where water is in continuous contact with metallic components such as stainless steel (RVS). At higher salinity levels, chloride ions may promote corrosion phenomena such as pitting and crevice corrosion. These phenomena rapidly degrade stainless steel parts of the water system. This range provides sufficient ionic conductivity to allow stable electrolysis, while remaining low enough to minimize chloride- induced pitting corrosion of stainless steel components.

[0025] The anode may have a variety of shapes. Preferably, however, the anode is elongated, for example rod-shaped, and located in a central part of the cathode. Preferably the rod-shaped anode coincides with the central axis of the cathode such that the anode is evenly spaced from the cathode inner surface. It is even more advantageous when the anode extends along a part of the cathode inner surface, such as along substantially the entire length of the cathode circumferential wall. By having an elongated anode in a central part of the cathode that also extends along a substantial part of the cathode surface, an even current density is achieved over the electrolysis chamber.

[0026] In an embodiment, the at least one scraper is rotated at an axial end thereof. The electrolysis device may for example at one end thereof be closed by an end cap that provides a water tight seal at one side of the tubular cathode. Preferably, both the end cap and the cathode have a flange that are connected, such as welded, together to provide a watertight connection. The at least one scraper or other parts of the solid removal mechanism that are used for driving the at least one scraper in rotation may extend through an opening of said end cap for connecting the solid removal mechanism to a rotational drive. Preferably, watertight seals (such as o-rings) and / or bearings are provided at the opening to prevent water leaking out of the electrolysis chamber.

[0027] In a preferred embodiment, the solid removal mechanism comprises a plurality of elongate scrapers, such as 3-5 scrapers, which lie tangentially (preferably at an equidistance) spaced apart within the electrolysis chamber and extend along at least a part of the cathode inner surface. Having multiple scrapers improves the efficiency with which the solids are removed from the cathode surface. Preferably the plurality of scrapers extend parallel to the central axis of the cathode. Optionally, some of the scrapers extend along a part of the cathode inner surface or along the entire cathode inner surface. Preferably, each of the scrapers extend along substantially the entire length of the cathode inner surface. The scrapers may have a variety of shapes, such as angled, curved, convex or spiraling. Preferably however, the scrapers are straight edged, as this improves the simplicity of the design and allows for most convenient removal of the solids along the tubular circumferential wall of the cathode.

[0028] In a further preferred or alternative embodiment, the at least one scraper has a scraping edge that is positioned non-tangentially relative to the circumferential wall of the cathode. The scraping edge may for example be positioned at an angle in the range of IQ- 900, more preferably in the range of 25-75°, such as in the range of 30-50° relative to the tangential direction of the circumferential wall. The tilting of the scraping edge in the rotation direction provides a slicing component to the scraper when rotating, in addition to pushing against the solid deposits on the inner surface of the cathode. This reduces the force that is required to remove the solids, which therefore reduces the required energy for scraping and also extends the lifetime of the scrapers.

[0029] It may be advantageous to also have at least one other scraper that comprises a scraping edge that is positioned non-tangentially relative to the circumferential wall in another direction, preferably opposite, of the scraping edge of the at least one scraper. The scraping edge of the at least one other scraper may for example be positioned at an angle in the range of 10-90°, more preferably in the range of 25-75°, such as in the range of 30-50° relative to the tangential direction of the circumferential wall. This advantageously allows the solid removal mechanism, when at least partially rotating in a back-and-forth motion around the central axis, to have an improved scraping performance in both directions during rotation, as the scraping edges of the at least one and the at least one other scraper are provided at different (preferably opposite) angles.

[0030] In a preferred embodiment, each of the scrapers comprises two scraping edges that are outwardly angled relative to each other, i.e. that each scraper has a first scraping edge that is positioned non-tangentially and a second scraping edge that is positioned non- tangentially and opposite to the first scraping edge, relative to the circumferential wall. As such each scraper has at least one scraping edge that effectively scrapes during rotation in a first rotation direction around the central axis and a second scraping edge that effectively scrapes during rotation in the second rotation direction around the central axis.

[0031] In a preferred further or alternative embodiment, the at least one scraper comprises at least one scraping edge that is provided at a distance from the cathode inner surface. The distance between the scraping edge and the cathode inner surface causes the at least one scraper to scrape only a part of the solids from the cathode inner surface while simultaneously leaving a remaining part of the solids on the cathode inner surface during rotation of the scraper. The layer of the remaining part of the solids forms seed crystals or nucleation sites that provide a surface for new crystals to start forming. Such layer may e.g. be a continuous layer on the cathode inner surface, the layer having a thickness in the range of preferably 0.1-5 mm, such as 0.5-4 mm. This speeds up the crystallization process and thus increases the amount of solids that are deposited on the cathode inner surface. As such a larger amount of minerals, such as calcium carbonate, are removed from the water, which prevents them from later entering into the (closed circulation) water system. The distance at which the scraping edge is provided from the cathode inner surface may vary depending on the cathode size etc. but is preferably one or a few millimeters.

[0032] In a preferred further or alternative embodiment, the at least one scraper is configured to reciprocate back and forth during at least partially rotating around the central axis. Reciprocating back and forth eliminates the need of complex rotary and electrical connections (e.g. sleeve contact connections) to the solid removal mechanism, which thus simplifies the design of the water electrolysis device. Preferably, the solid removal mechanism comprises n scrapers, and the scrapers may reciprocate back and forth within a range of 360 / n degrees during at least partially rotating around the central axis. For example, when the solid removal mechanism comprises four scrapers, the scrapers each rotate back and forth within a range of 90° (=36074). Each scraper therefore scrapes only a part of the inner surface of the cathode circumferential wall. Thus only limited rotation in a small range is required while still cleaning along the entire cathode inner surface.

[0033] In a preferred embodiment, the scraper is configured to rotate in absence of an electrolysis reaction. In this way, the solids that have accumulated on the cathode surface can be removed in a controlled discharge step without being entrained in the electrolyzed water stream. This ensures that the deposits are captured and discharged from the electrolysis device rather than transferred into the water system.

[0034] In a preferred embodiment, the electrolysis device comprises a discharge water outlet that is different from the water outlet, wherein the scraper is configured to rotate when water is discharged through the discharge water outlet. Preferably, the scraper is configured to rotate only when water is discharged through the discharge water outlet. By providing a dedicated discharge outlet, the electrolyzed water from which the scale / solids have been removed is kept separate from the water which is used during scraping and is thus high in scale / solids, so that the solid-laden discharge stream can be expelled without contaminating the recirculating water of the closed-loop system. In a preferred further or alternative embodiment, the electrolysis device comprises at least two states. In a first (operative) state, the anode and the cathode perform the electrolysis reaction. In said operative state the water in the electrolysis chamber flows in an operation direction. In a second (discharge) state, the at least one scraper scrapes the deposited solids from the cathode inner surface. In this discharge state, the water flows in a discharge direction that is different, in particular opposite, to the operation direction. Having the water flow in a different direction during the operation and discharge states advantageously allows to help flush out the scraped solids more effectively. Preferably no electrolysis reaction takes place during the discharge state, e.g. no power is supplied by a power source to the anode and cathode such that the anode and cathode are inoperative during the discharge state. Preferably, the solid removal mechanism is inoperative (i.e. not rotating around the central axis) during the operation state.

[0035] Preferably, the central axis of the cathode is substantially vertical, and the water flow operation direction is substantially upwards within the electrolysis chamber and the water flow discharge direction is substantially downwards within the electrolysis chamber. That is to say, in use, discharge water moves downwards through the electrolysis chamber. The downwards discharge direction allows effective removal of the scraped solids from the electrolysis chamber, as these will fall downwards under the influence of gravity and will thus be flushed together with the discharged water. When having other discharge directions that are not downwards, it may be required to have a higher water flow rate through the electrolysis chamber to truly remove all of the scraped solids. For removing the water in the downwards discharge direction is it preferred to have an outlet out of the electrolysis chamber that is provided at a bottom axial end of the electrolysis chamber. The outlet may for example be of a funnel-shape. Due to the cross-sectional area decrease of a funnel the water that flows through it is accelerated, and any trapped solid particles are more easily flushed away, which may prevent the clogging of the outlet.

[0036] In a preferred further or alternative embodiment, in the operative state, the water flows into the electrolysis chamber via the operation water inlet and flows out of the electrolysis chamber via the operation water outlet, and wherein in the discharge state the water flows into the electrolysis chamber via the discharge water inlet and out of the electrolysis chamber via the discharge water outlet. In particular it is preferred that the operation water inlet is the same as the discharge water outlet, and / or that the operation water outlet is the same as the discharge water inlet. Using inlets / outlets that perform both functions allows a simple yet efficient design of the water electrolysis device. After discharge of the discharge water from the discharge water outlet / operation water inlet, the discharge water outlet / operation water inlet may have a split or similar setup to stop discharged water from mixing with the main water supply. Switching between water supply and discharge water removal can be regulated using e.g. a valve mechanism.

[0037] In a preferred further or alternative embodiment, the water electrolysis device comprises a power source that is configured for creating a potential difference between the anode and the cathode, and the solid removal mechanism is electrically connected to said power source, in particular to the negative pole of the power source, for also creating a potential difference between the anode and the solid removal mechanism. Electrically connecting the solid removal mechanism to the power source advantageously prevents corrosion of the solid removal mechanism. The reduced corrosion increases the lifespan of the solid removal mechanism and reduces the costs for maintenance. The electrical connection may be achieved via suitable lines or cables. The electrical connection may be a direct connection between the scraping mechanism and the power source, e.g. other than a sleeve contact, especially when the scrapers are also configured for reciprocating back and forth during at least partially rotating around the central axis, as has been described previously. It may be advantageous to provide an additional resistor between the scraping mechanism and the power source to reduce the potential difference and therewith the amount of solids deposited on the scraping mechanism, and / or to powder coat the scraping mechanism such that the scraping mechanism is insulated and little to no solids are deposited on the scraping mechanism while it is in contact with the power source.

[0038] Preferably, the at least one scraper is made of electrically conductive material.

[0039] In a preferred further or alternative embodiment, the anode is connected to the solid removal mechanism for simultaneous rotation of the anode with the at least one scraper. The anode may for example be provided extending through a part of the solid removal mechanism, e.g. through a drive tube of the solid removal mechanism to which the at least one scraper is (in)directly connected. The anode preferably projects out of said solid removal mechanism to conveniently connect the anode to the power source.

[0040] Preferably the anode is connected to the solid removal mechanism via at least one electrically insulating connecting member, such as two electrically insulating connecting members that are spaced along the length of the supporting tube for providing a stable connection between the anode and the scraping mechanism. Having an electrically insulating connecting member advantageously prevents unwanted side reactions, such as corrosion of the solid removal mechanism or, in the situation that the scraping mechanism is also connected to the power source, a short circuit. The electrically insulating connecting member(s) are e.g. 3D printed and made of an insulating material, such as some type of polymers or rubbers. The insulating connecting members preferably comprise one or more o- rings to provide a watertight connection between the anode and scraping mechanism.

[0041] Preferably, each insulating connection member comprises at least two o-rings of different diameters to

[0042] In a second aspect, the invention relates to a method for removing solids from a water electrolysis device according to the invention, comprising the steps of

[0043] - flowing water through the electrolysis chamber while an electrolysis reaction takes place such that during the electrolysis reaction solids deposit on the cathode surface, and

[0044] - at least partially rotating the one or more scrapers around the central axis such that rotation of the scraper scrapes the deposited solids from the cathode inner surface.

[0045] In a preferred embodiment of the method according to the invention, the step of scraping comprises scraping only a part of the solids from the cathode inner surface while simultaneously leaving a remaining part of solids on the inner surface of the cathode.

[0046] In a preferred embodiment, the method comprises that the scraper is rotated intermittently. With intermittently, it is meant that the scraper is sometimes rotated and sometimes left stationary. The intermittent operation of the scraper is advantageous because it allows solids, e.g. scale, to accumulate on the cathode surface up to a desired thickness before removal. This residual layer functions as crystallization nuclei and may promote further controlled deposition of scale within the electrolysis device. Continuous scraping, as in the prior art, prevents such a layer from forming and causes scale particles to be carried away with the flowing water into the cooling components. Moreover, the continuous scraping prevents the formation of the boundary layer near the cathode surface.

[0047] Preferably, the scraper is rotated in the absence of an electrolysis reaction. In this way, the solids that have accumulated on the cathode surface can be removed in a controlled discharge step without being entrained in the electrolyzed water stream. This ensures that the deposits are captured and discharged from the electrolysis device rather than transferred into the water system.

[0048] In a further preferred or alternative embodiment of the method according to the invention, the method comprises

[0049] - in an operative state, having the anode and cathode perform the electrolysis reaction while water flows in an operation direction, and - in a discharge state, scraping the deposited solids from the cathode inner surface while water flows in a discharge direction that is different, in particular opposite, of the operation direction.

[0050] Preferably, during the discharge state, scraped solids fall downwardly towards discharge water outlet under the influence of gravity. This allows the solids that have been detached from the cathode surface to be removed from the electrolysis chamber in a simple and energy-efficient manner, without the need for additional pumps, high flow velocities or mechanical conveying devices. By relying on gravity-assisted settling, the solids are guided directly towards the (optionally funnel-shaped) discharge outlet, where they can be discharged from the device.

[0051] In a preferred embodiment, the water electrolysis device is configured to operate with a salt concentration of 0.1 -0.3 g / L. Operating at such low salinity is particularly advantageous in closed-loop water systems, where water is in continuous contact with metallic components such as stainless steel (RVS). At higher salinity levels, chloride ions may promote corrosion phenomena such as pitting and crevice corrosion. These phenomena rapidly degrade stainless steel parts of the water system. The range of 0.1 - 0.3 provides sufficient ionic conductivity to allow stable electrolysis, while remaining low enough to minimize chloride- induced pitting corrosion of stainless steel components.

[0052] In a preferred embodiment, the water flow in the electrolysis chamber is substantially laminar. Laminar flow conditions are advantageous because they promote the formation of a stable hydrodynamic boundary layer along the cathode wall. Within this boundary layer, the flow velocity is reduced, which allows the local pH near the cathode surface to rise during electrolysis. The combination of elevated pH and low flow velocity creates favorable conditions for dissolved salts such as calcium carbonate and magnesium hydroxide to precipitate and adhere as a solid layer on the cathode surface.

[0053] The embodiments according to the first aspect of the invention similarly apply to the second aspect of the invention.

[0054] In a third aspect, the invention relates to a closed-loop water system comprising a water electrolysis device according to the first aspect of the invention. All embodiments of the first aspect of the invention are similarly applicable to the third aspect of the invention.

[0055] The closed-loop water system further comprises a circulation circuit connected to the inlet and outlet of the water electrolysis device for circulating water through the water electrolysis device, and a discharge outlet configured to discharge water from the water electrolysis device and / or circulation circuit. The at least one scraper is configured to rotate during water discharge through the discharge outlet. In this way, the solids that have accumulated on the cathode surface are detached and guided together with the discharge water through the discharge outlet. As a result, the deposits are removed from the closed-loop water system in a controlled manner and are not carried over into the recirculating water flow. This ensures that solid build-up is effectively confined to the electrolysis device, while the other components of the closed-loop system remain substantially free of deposits.

[0056] The term closed-loop water system as used herein refers to a system in which the same body of water is essentially reused continuously. Although small amounts of fresh water may be added to refresh or replenish the system, for example to compensate for evaporation, leakage, or deliberate blowdown, the water is not discharged and replaced in bulk. Instead, it is circulated between the cooling components and the electrolysis device, where it is purified and conditioned before being returned into the loop.

[0057] Closed-loop water systems are in particular used as closed-loop heat exchanging systems, such as closed-loop water cooling systems, for industrial and power-generation environments. Such systems are preferred because they minimize water consumption in comparison with once-through cooling, they reduce environmental impact since large volumes of heated or chemically treated water are not released to the environment, and they enable precise control of water chemistry. In addition, they protect sensitive cooling components from scaling and fouling, since deposition is captured and removed inside the electrolysis device rather than occurring on the heat exchangers or other cooling elements.

[0058] The closed-loop water cooling system may comprise the water electrolysis device according to the first aspect of the invention and heat exchanging components, such as heat exchangers, condensers, evaporators or chillers, wherein the system is configured for continuously circulating the water between the heat exchanging components and the water electrolysis device. The continuous circulation ensures that solid deposits present in the water are captured and removed within the electrolysis device before they can reach and deposit on the heat-transfer surfaces of the heat-exchanging components. The system may be provided with a make-up water inlet for replenishing minor losses.

[0059] DETAILED DESCRIPTION OF THE DRAWINGS

[0060] The invention shall now be explained in more detail below by means of describing some exemplary embodiments in a non-limiting way with reference to the accompanying drawings, in which: Fig. 1 shows a perspective view of a preferred embodiment of the water electrolysis device without a cathode according to the present invention; Fig. 2 shows a cross-sectional top view of a preferred embodiment of the water electrolysis device according to the invention;

[0061] Fig. 3 shows a cross-sectional front view of a head assembly of the water electrolysis device of fig. 1 ;

[0062] Fig. 4 furthermore shows a cross-sectional front view of a head assembly of the water electrolysis device of fig. 1 ;

[0063] Fig. 5a shows a solid removal mechanism according to the embodiment of fig. 1 in detail;

[0064] Fig. 5b shows an end cap according to the embodiment of fig. 1 in detail;

[0065] Fig. 5c shows an upper part of the tubular cathode according to the embodiment of fig. 1 in detail.

[0066] Fig. 6a and 6b show a cross-sectional side and top view, respectively, of an embodiment of an insulating connecting member;

[0067] Fig. 7a and 7b show a cross-sectional side and top view, respectively, of an embodiment of a bearing.

[0068] Fig. 8 shows a parabolic flow profile within the electrolysis chamber according to the invention;

[0069] Fig. 9A and 9B show a process diagram of the water flows during operation and during discharge.

[0070] In fig. 1 a water electrolysis device 1 according to an embodiment of the invention is shown. The water electrolysis device 1 comprises an elongate tubular cathode which has a central axis X and a circumferential wall 28 that delimits an electrolysis chamber 2. In fig. 1 the circumferential wall 28 of the cathode is purposefully not shown to provide a better view of the inside of the water electrolysis device 1. The water electrolysis device 1 has an elongate electrolysis chamber 2 wherein during an electrolysis reaction water enters through an inlet 4 and flows upward towards an outlet 6. The inlet 4 is provided at an axial bottom end of the electrolysis chamber 2, and the outlet 6 is provided at or near the top of the electrolysis chamber 2, such that the water flows radially out of the electrolysis chamber 2. At the axial upper end of the electrolysis chamber 2, the electrolysis chamber 2 is sealed by means of an end cap 8. This end cap 8 has a flange 10 with which the end cap 8 is connected, such as bolted, to a flange 12 combined with a gasket of the tubular cathode for watertight sealing of the electrolysis chamber 2.

[0071] Within the electrolysis chamber 2, a solid removal mechanism 14 is provided that is used for scraping solids of an inner surface of the circumferential wall 28 of the cathode (not shown). The solid removal mechanism 14 in fig. 1 has four scrapers 16 that are spaced apart tangentially 2 and extend along substantially the entire circumferential wall 28 of the cathode within the electrolysis chamber 2. Advantageously, the use of four scrapers 16 allows the scrapers 16 to only partially rotate around the central axis X while still scraping along the entire inner surface of the cathode. The four scrapers 16 may in particular each rotate within a range of 90° to fully scrape around the full periphery of the circumferential wall of the cathode. This advantageously allows the use of less complex cabling and rotational drives. Furthermore, as is shown in more detail in fig. 2, the scrapers 16 each have two scraping edges 17 that are provided non-tangentially relative to the circumferential wall of the cathode at an angle of 45°. Having a scraping edge 17 at a non-tangential angle provides a slicing component to the scraper 16 when rotating, in addition to pushing against the solid deposits on the inner surface of the cathode. In particular in fig. 1 each scraper 16 has two scraping edges 17 that are positioned opposite to each other, which allow the scrapers 16 to scrape in both directions when the scraper 16 reciprocates back and forth during partial rotation around the central axis X.

[0072] The four scrapers 16 are connected to each other, such as welded together at the ends thereof, to facilitate their simultaneous rotation. In fig. 1 the scrapers 16 are connected to each other via two scraper support plates 18 (see for more details fig. 3 and fig. 4). These scraper support plates 18 are connected to a drive tube 19 that in turn extends through a support tube 20 of the end cap 8. To drive the scrapers 16 into rotation, the drive tube 19 is rotated by e.g. a rotational drive (not shown) that drives a drive arm 22. By driving the drive arm 22, the drive tube 19, scraper support plates 18 and thus the scrapers 16 all rotate simultaneously around the central axis X (preferably rotating partially in a reciprocating back and forth motion around the central axis X). Further details of the end cap 8 with the solid removal mechanism 14 are shown in fig. 3, 4, 5a and 5b. The scrapers 16 are additionally connected by reinforcing ribs 24 to prevent excessive separation of the scrapers 16 relative to each other. Additionally, the reinforcing ribs 24 ensure that the scrapers 16 can exert sufficient force during the scraping of the solids. Multiple reinforcing ribs 24 may be positioned along the length of the scrapers 16.

[0073] A rod-like anode 26 is positioned at a central part of the electrolysis chamber 2, preferably coinciding with the central axis X of the cathode. The anode 26 extends along a substantial part, preferably along substantially the entire length, of the cathode circumferential wall. As the anode 26 and cathode extend alongside each other for almost the entire length of the electrolysis chamber 2, the current density is substantially uniform across the electrolysis chamber 2. The anode 26 in fig. 1 is via electrically insulating connecting members 30 (see fig. 3) connected to the drive tube 19 of the solid removal mechanism 14. As such, the anode 26 rotates simultaneously with the scrapers 16 when the scrapers 16 are driven in rotation. Further details of the connection between the anode 26 and the solid removal mechanism 14 are shown in Fig. 3 and 4.

[0074] The water electrolysis device 1 in fig. 1 can advantageously be used in two different states: in the first (operative) state the anode 26 and the cathode perform an electrolysis reaction during which solids are deposited on the cathode inner surface. In this operative state the water flows through the electrolysis chamber 2 in an operation direction O. In the operation direction O, water flows in the electrolysis chamber 2 via the operation water inlet 4 and flows out of the electrolysis chamber 2 via the operation water outlet 6. In fig. 1 this operation direction O is upwards. In the second (discharge) state, the scrapers 16 scrape the deposited solids from the cathode inner surface. In the discharge state water flows through the electrolysis chamber 2 in a discharge direction D that is opposite to the operation direction O. The water electrolysis device 1 in fig. 1 is vertically positioned and the discharge direction D is downwards such that advantageously the scraped solids fall down towards the discharge outlet of the device 1. Scraped solids are thus prevented from ending up in the water stream that flows to the other components (water storage tank, heat exchanger, etc.) of the water system. The discharged water that exits the device 1 may be discharged towards a sewer or other wastewater discharge.

[0075] In the embodiment shown in fig. 1 the water in the discharge state D flows into the electrolysis chamber 2 via the discharge water inlet 6 that is the same as the operation water outlet 6. Similarly thereto, the water flows out of the electrolysis chamber 2 via the discharge water outlet 4 that is the same as the operation water inlet 4. The discharge water outlet 4 in fig. 1 is of a funnel-shape. Due to the cross-sectional area decrease of the funnel-shaped outlet 4, the water that flows through it is accelerated, and any trapped solid particles are more easily flushed away. This advantageously prevent clogging of the discharge water outlet 4.

[0076] By having multiple purposes for the inlets and outlets 4, 6 the water electrolysis device has a simple yet efficient design. After discharge from the water electrolysis device 1 , the discharge outlet 4 of the discharge tube may have a split or similar setup to stop discharged water from mixing with the main water supply. Switching between water supply and discharge water removal can be regulated using e.g. a valve mechanism.

[0077] The water electrolysis device 1 comprises a power source (not shown) with which a potential difference over the anode 26 and the cathode 27 is obtained. In a preferred embodiment, the solid removal mechanism 14 is also electronically connected to the power source (not shown) via e.g. suitable cabling to also obtain a potential difference over the solid removal mechanism 14 relative to the anode 26. Having the solid removal mechanism 14 connected to (the negative pole of) the power source advantageously prevents corrosion of the solid removal mechanism 14. If an excess of solids deposit on the scraping mechanism 14 due to the connection to the power source (not shown), it may be advantageous to provide an additional resistor between the scraping mechanism 14 and the power source to reduce the potential difference and therewith the amount of solids deposited on the scraping mechanism 14 or the scraping mechanism is insulated with a powder coating layer.

[0078] In fig. 2 a cross-sectional top view of the water electrolysis device 1 is shown. Fig. 2 shows the elongate tubular cathode 27, having a circumferential wall 28 that forms the outer wall of the water electrolysis device 1. Delimited by the cathode circumferential wall 28 is the electrolysis chamber 2 in which the scrapers 16 and the anode 26 are positioned. The discharge water outlet / operation water inlet 4 is shown at the bottom axial end of the tubular cathode 27. The four scrapers 16 of the solid removal mechanism 14 are spaced tangentially apart from each other and each have two scraping edges 17 that are each tilted, in opposite directions, relative to the tangential line of the circumferential wall. The scrapers 16 are interconnected via reinforcing ribs 24. The reinforcing ribs have a narrow cross-section as seen in fig. 2 to prevent scraped solids that fall downwards from accumulating on the top surface of the reinforcing ribs 24. As such, when the scrapers 16 rotate back and forth around the central axis X, for example, intermittently rotating in a range of 90°, the scrapers 16 will scrape both during the forwards and backwards motion.

[0079] Also shown in fig. 2 is that the scraping edges 17 of the scrapers 16 are provided at a distance from the cathode 27 inner surface. As such, during rotation of the scrapers 16, the scraping edges 17 of the scrapers 16 remove only the top layer of the solids that are deposited on the cathode 27 inner surface. Simultaneously a layer of the solids remains on the cathode 27 inner surface during scraping. This layer of solids forms seed crystals or nucleation sites that provide a surface for new crystals to start forming, which speeds op the crystallization process and thus speeds up the deposition of solids on the cathode 27 inner surface. This allows a greater amount of minerals, such as calcium carbonate, to be removed from the water to prevent it from later entering into the water system.

[0080] In fig. 3 a cross-sectional view of the head assembly of the water electrolysis device 1 of fig. 1 is shown. The tubular cathode 27 is at the axial upper end thereof closed by an end cap 8, by connecting a flange 10 of the end cap 8 to the flange 12 of the cathode 27, e.g. by welding the flanges together.

[0081] The solid removal mechanism 14 comprises scrapers 16 that are at an end thereof connected, such as welded, to a scraper support plate 18. In fig. 3 two scraper support plates 18 are used to connect the four scrapers 16. The scraper support plates 18 are connected, such as welded, to a drive tube 19 that extends through and projects out of the support tube 20 of the end cap 8. The drive tube 19 is, in fig. 3 via a drive arm 22 driven in rotation such that the scraper support plates 18 and therewith the scrapers 16 simultaneously rotate around the central axis X, preferably reciprocating back and forth while partially rotating around the central axis X.

[0082] The anode 26 extends through the drive tube 19 of the solid removal mechanism 14 such that it is aligned with the central axis X of the cathode 27 and it is evenly spaced from the circumferential wall 28 of the cathode 27. The anode 26 is connected to the solid removal mechanism 14 via insulating connecting members 30, which are in fig. 3 provided at two spaced apart positions on the anode 26 to rotate the anode simultaneously with the solid removal mechanism 14. It may be envisaged that more or less insulating connecting members 30 may also be provided, e.g. one insulating connecting member at the electrolysis chamber, and one insulating connecting member near an upper part of the drive tube 19. This keeps the anode stably positioned within the scraping mechanism. The insulating connecting members 30 may for example be of an insulating polymer material, preferably having one or more o-rings to provide a water tight connection between the anode 26 and the scraping mechanism 14 such that no water leaks out of the electrolysis chamber 2 via the anode 26. An exemplary embodiment of the insulating connecting member 30 is shown in fig. 6a and 6b. The anode 26 projects out of the drive tube 19 of the solid removal mechanism 14 and the water electrolysis device 1. This provides easy connection of the anode 26 to the external power source.

[0083] Fig. 4 again shows a cross-sectional view of the head assembly of the water electrolysis device of fig. 1 . The head assembly in this embodiment essentially has four elements: the solid removal mechanism 14 (in detail shown in fig. 5a), the end cap 8 (in detail shown in fig. 5b), the cathode 27 (in detail shown in fig. 5c) and the anode 26. In fig. 5a a detailed close-up of an upper part of the solid removal mechanism 14 is shown. The scrapers are connected, via scraper support plates 18, to a drive tube 19 that may be rotated via a drive arm 22. The drive arm is in turn connected to a rotational drive (not shown). The end cap 8, shown in fig. 5b has a flange 10 and a support tube 20. Within the support tube 20, bearings 34 are provided for reducing friction and supporting the rotation of the drive tube 19 within the support tube 20. Fig. 5c shows an upper part of the tubular cathode 27, with the cathode circumferential wall 28, the flange 12 of the cathode that is connected with the flange 10 of the end cap 8 and the operation water outlet / discharge water inlet 6.

[0084] Fig. 6a shows a cross-section of an insulating connecting member 30 that may be provided between the anode 26 and scraping mechanism 14 to connect the two. The anode 26 extends through a central opening 36 of the connecting member 30. The connecting member 30 is shown to have two o-rings 38, 40, that each have a different diameter. A first (smaller) o-ring 38 provides a watertight connection between the anode 26 and the connecting member 30. The second (larger) o-ring 40 closes of the insulating connecting member 30 and the scraping mechanism 14. Fig 6b furthermore provides a cross-sectional top view of the insulating connecting member 30.

[0085] Fig. 7a shows a cross-section of a (bronze) bearing 34 with a collar 42 that supports rotation of the scraping mechanism 14 within the support tube 20. The bearing 34 comprises an o-ring 44 to provide a water-tight connection between the scraping mechanism 14 and the support tube 20 such that leakage of water along the scraping mechanism 14 is prevented. The bearing 34 itself is with an outer side 46 thereof adhered, e.g. with the use of Loctite, to an inner side of the support tube 20 to prevent rotation of the bearing 34 relative to the support tube 20. Fig 7b furthermore provides a cross-sectional top view of the bearing 34.

[0086] Fig. 8 shows a cross-sectional view of the electrolysis chamber, in which schematically the parabolic flow profile 48 is shown, with a near zero flow velocity near the cathode wall to promote deposition of solids.

[0087] Fig. 9A and 9B show a process diagram of the electrolysis device during operation and during discharge, respectively. In Fig. 9A, water from the cooling tower 50 flows through the electrolysis device 1 , preferably in a first water flow operation direction (e.g. upwardly). After electrolysis, the water flows through a filter 52 into a circulation circuit 54 where water is used for cooling. The filter 52 may, alternatively, also be arranged somewhere else in the system, or if no debris is present in the water, be omitted.

[0088] Fig. 9B shows the discharge of the water when the scraper is operated and the water may thus not flow into the circulation circuit 54. In this embodiment, water flows from the cooling tower first through the filter 52 in the electrolysis device 1. The water flows in an opposite direction relative to the water flow during normal operation. All of this water, in which scraped solids are present that have been removed from the cathode of the electrolysis device 1 , is drained via the discharge outlet 56 to prevent it from flowing into the circulation circuit 54..

[0089] Besides the shown and described embodiments, numerous variants are possible. For example, instead of a solid removal mechanism with four scrapers, another number of scrapers may be used, such as two, three, five or six scrapers. The scrapers need not necessarily be equidistant from each other. The attachment of the scrapers to each other need not necessarily be through the attachment plates of the scrapers: another connection may also be used, such as a direct connection between the scrapers and the drive tube. The anode need not necessarily rotate together with the scrapers but may be stationary.

[0090] It should be understood that various changes and modifications to the presently preferred embodiments can be made without departing from the scope of the invention, and therefore will be apparent to those skilled in the art. It is therefore intended that such changes and modifications be covered by the appended claims.

Claims

CLAIMS1. Closed-loop water system, comprising, a water electrolysis device (1) comprising o a housing with therein provided an electrolysis chamber (2), wherein the housing comprises a water inlet (4, 6) and a water outlet (6,4) for allowing a water to flow through the electrolysis chamber (2), o an anode (26) and a cathode (27) configured for performing a water electrolysis reaction and for during the electrolysis reaction having solids depositing on a surface of the cathode (27), and o a solid removal mechanism (14) having at least one scraper (16) configured for scraping the deposited solids of the surface of the cathode (27), wherein the housing is formed by a stationary elongate tubular cathode (27) having a circumferential wall (28) that defines the electrolysis chamber (2) and a central axis (X) that is preferably substantially vertical, wherein the anode (26) is provided within a central part the electrolysis chamber (2) spaced apart from an inner surface of the circumferential wall (28) of the cathode (27), and wherein the at least one scraper (16) is provided within the electrolysis chamber (2) and is rotatable around the central axis (X) such that the at least one scraper (16) is configured for during rotation scraping the deposited solids from the cathode (27) inner surface, and further comprising a circulation circuit connected to the inlet and outlet of the water electrolysis device (1) for circulating water through the water electrolysis device (1), and a discharge outlet configured to discharge water from the water electrolysis device (1) and / or circulation circuit, wherein the at least one scraper (16) is configured to rotate during water discharge through the discharge outlet.

2. Closed-loop water system according to claim 1 , wherein the water system is a closed- loop heat-exchanging water system further comprising heat exchanging components, and wherein the circulation circuit is configured to circulate water between the heat exchanging components and the water electrolysis device.

3. Water electrolysis device (1) for use in a closed-loop water system according to any one of the preceding claims, comprising- a housing with therein provided an electrolysis chamber (2), wherein the housing comprises a water inlet (4, 6) and a water outlet (6,4) for allowing a water to flow through the electrolysis chamber (2),- an anode (26) and a cathode (27) configured for performing a water electrolysis reaction and for during the electrolysis reaction having solids depositing on a surface of the cathode (27), and- a solid removal mechanism (14) having at least one scraper (16) configured for scraping the deposited solids of the surface of the cathode (27), characterized in that the housing is formed by a stationary elongate tubular cathode (27) having a circumferential wall (28) that defines the electrolysis chamber (2) and a central axis (X) that is preferably substantially vertical, in that the anode (26) is provided within a central part the electrolysis chamber (2) spaced apart from an inner surface of the circumferential wall (28) of the cathode (27), and in that the at least one scraper (16) is provided within the electrolysis chamber (2) and is rotatable around the central axis (X) such that the at least one scraper (16) is configured for during rotation scraping the deposited solids from the cathode (27) inner surface.

4. Water electrolysis device (1) according to claim 3, wherein the solid removal mechanism (14) comprises a plurality of elongate scrapers (16), such as 3-5 scrapers (16), that lie tangentially spaced apart within the electrolysis chamber (2) and extend along at least a part of the cathode (27) inner surface.

5. Water electrolysis device (1) according to claim 3 or 4, wherein the at least one scraper (16) comprises one or more scraping edges (17) that are provided at a distance from the cathode (27) inner surface such that the at least one scraper (16) is configured for, during scraping, scraping only a part of the solids from the cathode (27) inner surface while simultaneously leaving a remaining part of solids on the cathode (27) inner surface.

6. Water electrolysis device (1) according to claim any one of the claims 3-5, wherein the remaining part of the solids is a layer of solids on the cathode inner surface, and wherein the scraper edge is preferably arranged at least 1 mm from the cathode inner surface.

7. Water electrolysis device (1) according to any one of the claims 3-6, further comprising a discharge water outlet for discharging water from the electrolysis chamber, wherein the discharge water outlet is funnel shaped.

8. Water electrolysis device (1) according to any one of the claims 3-7, wherein the at least one scraper (16) has a scraping edge (17) that is positioned non-tangentially relative to the circumferential wall (28) of the cathode (27), preferably at an angle in the range of 10-90°, more preferably in the range of 25-75°, such as in the range of 30-50°, and wherein preferably at least one other scraper (16) comprises a scraping edge (17) that is positioned non-tangentially relative to the circumferential wall (28) in another direction, preferably opposite, of the scraping edge (17) of the at least one scraper (16), preferably at an angle in the range of 10-90°, more preferably in the range of 25-75°, such as in the range of 30-50°.

9. Water electrolysis device (1) according to any one of the claims 3-8, wherein the at least one scraper (16) is configured to reciprocate back and forth during at least partially rotating around the central axis (X), preferably wherein the solid removal mechanism (14) comprises n scrapers (16) and wherein the scrapers (16) are configured for reciprocating during at least partially rotating around the central axis (X) within a range of 360 / n degrees.

10. Water electrolysis device (1) according to any one of the claims 3-9, wherein a ratio of the cathode (27) inner surface area relative to the anode (26) surface area is in the range of 10-100, preferably a ratio in the range of 20-50, such as a ratio in the range of 30-40.

11. Water electrolysis device (1) according to according to any one of the claims 3-10, wherein the distance between the anode and cathode is at least 7 cm, preferably of at least 10 cm.

12. Water electrolysis device (1) according to any one of the claims 3-11, further a discharge water outlet that is different from the water outlet, wherein the scraper is configured to rotate when water is discharged through the discharge water outlet.

13. Water electrolysis device (1) according to any one of the claims 3-12, wherein the scraper (16) is made of electrically conductive material.

14. Water electrolysis device (1) according to any one of the claims 3-13, further comprising a power source that is configured for creating a potential difference between the anode (26) and the cathode (27), and wherein the solid removal mechanism (14) is electrically connected to said power source for also creating a potential difference between the anode (26) and the solid removal mechanism (14).

15. Water electrolysis device (1) according to any one of the claims 3-14, wherein the anode (26) is connected to the solid removal mechanism (14) for rotating the anode (26) simultaneously with the at least one scraper, preferably via one or more electrically insulating connecting members (30).

16. Water electrolysis device (1) according to any one of the claims 3-15, wherein the anode (26) is a rod-shaped anode (26) that is provided at the central axis (X) of the cathode (27).

17. Water electrolysis device (1) according to any one of the claims 3-16, wherein the anode is a titanium electrode provided with a mixed metal oxide (MMO) coating18. Method for removing solids from a water electrolysis device (1) according to any one of the preceding claims, comprising the steps of- flowing water through the electrolysis chamber (2) while an electrolysis reaction takes place such that during the electrolysis reaction solids deposit on the cathode (27) surface, and- at least partially rotating the at least one scrapers (16) around the central axis (X) such that during rotation of the scraper (16) the scraper (16) scrapes the deposited solids from the cathode (27) inner surface.

19. Method according to claim 18, wherein the water is low salinity water comprising a salt concentration in the range 0.1 -0.3 g / L.

20. Method according to claim 18 or 19, wherein the electrolysis is performed at a potential difference in the range of 5-12 V.

21. Method according to any one of the claims 18-20, wherein the step of scraping comprises scraping only a part of the solids from the cathode (27) inner surface while simultaneously leaving a remaining part of the solids on the cathode (27) inner surface.

22. Method according to claim 21 , wherein the remaining part of the solids is formed by a layer of solids, the layer of solids preferably having a thickness of at least 1 mm.

23. Method according to any one of the claims 18-22, wherein the step of at least partially rotating the scrapers is performed in the absence of an electrolysis reaction.

24. Method according to any one of the claims 18-23, wherein at least partially rotating comprises rotating around the central axis (X) within a range of 360 / n degrees25. Method according to claim any one of the claims 18-24, wherein the method comprises,- in an operative state, having the anode (26) and cathode (27) perform the electrolysis reaction while water flows in an operation direction (O), and- in a discharge state, scraping the deposited solids from the cathode (27) inner surface while water flows in a discharge direction (D) that is different, in particular opposite, of the operation direction (O), preferably in the absence of performing an electrolysis reaction by the anode (26) and cathode (27).

26. Method according to claim 25, wherein during the discharge state, scraped solids fall downwardly towards discharge water outlet under the influence of gravity.

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