Patent Description:
One of the major challenges in the world today is to provide safe drinking water for humans and animals. Some main contributions to pollution of water come from untreated sewage, untreated process water from industries, agricultural waste and runoff water. This water needs to be treated before it is safe to drink.

One way to provide safe drinking water from polluted water is to evaporate the polluted water under vacuum. By changing the phase of the water to steam under vacuum, the water is boiling at a low temperature. The disadvantage with this method is that it requires a lot of energy to change the phase of the water to steam under vacuum.

<CIT> discloses a filtration apparatus for filtrating particles from fluid, the filtration apparatus comprising a filtration vessel; at least one filtering element for removing particles from fluid passing therethrough, the at least one filtering element being arranged to move along a path into the filtration vessel, and out from the filtration vessel; a filtration inlet arranged to convey a mixture of particles and fluid to the at least one filtering element within the filtration vessel; and a filtration outlet arranged to convey fluid, filtrated by the at least one filtering element, out from the filtration vessel; wherein the filtration apparatus is configured to establish a differential pressure over the at least one filtering element inside the filtration vessel.

<CIT> discloses a filter device comprising a first compartment, a second compartment, a plate between the compartments, a filter cloth and transport wheels. In operational mode, longitudinal edges of the filter cloth will be clamped between the transport wheels on the one hand and plate on the other.

<CIT> discloses a filter device comprising a first compartment, a second compartment, a perforated, semicircular plate, a filter cloth and one or more rotatable transport wheels which, with interposing of the filter cloth, engage in substantially form-fitting manner and under bias on the curved plate.

<CIT> discloses a filtering device comprising an inner tank and two walls defining a first chamber.

One object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement has an improved performance.

A further object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement improves cleanliness of a filtrated liquid.

A still further object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement has an energy efficient operation.

A still further object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement has reduced friction losses.

A still further object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement has improved sealing.

A still further object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement enables a more efficient cleaning of a filter cloth.

A still further object of the present disclosure is to provide a filtration arrangement for a filtration apparatus, which filtration arrangement solves several or all of the foregoing objects.

A still further object of the present disclosure is to provide a filtration apparatus comprising a filtration arrangement, which filtration apparatus solves one, several or all of the foregoing objects.

According to a first aspect, there is provided a filtration arrangement for a filtration apparatus for filtrating liquid according to claim <NUM>. The filtration arrangement comprises a filtration vessel; a continuous filtering element for removing particles from liquid passing therethrough, the filtering element being arranged to move along a path into the filtration vessel and out from the filtration vessel; and two wheels sealingly engaging the filtering element on opposite sides thereof inside the filtration vessel, where each of the two wheels is rotatable relative to the filtration vessel along with movement of the filtering element. The filtration vessel further comprises two circular portions. The two wheels are forced into a respective of the circular portions with the filtering element therebetween. The filtration arrangement further comprises at least one stationary wheel sealing member. The stationary wheel sealing member is arranged to seal between the filtering element and a respective of the circular portions.

The filtration arrangement may comprise a filtration volume. The filtration volume may be delimited by the two wheels and the part of the filtering element currently engaged by the wheels.

Since the wheels sealingly engage the filtering element and rotate along with the movement of the filtering element, friction losses between the wheels and the filtering element can be eliminated while at the same time providing an efficient sealing of the filtration volume inside the filtration vessel. A tight sealing is particularly valuable when the filtration apparatus is used with an underpressure downstream of the filtering element. Should the sealing not be tight, there is a risk that unfiltered liquid passes on the side of the filtering element and the filtration performance is reduced. The wheels may press the filtering element against the filtration vessel.

The filtration arrangement enables a tangential speed of the wheels to be the same as a speed of the filtering element. Since there is no friction due to relative movements between the wheels and the filtering element, the filtration arrangement is more energy efficient. Friction induced vibrations with consequential leakage can also be avoided. Since the wheels rotate together with the filtering element, the wheels and the filtering element may be said to provide a rotatable seal.

The filtering element may be of any type as described herein. The filtering element may comprise a filter cloth and a carrier supporting the filter cloth. Each of the filter cloth and the carrier may be continuous. The filter cloth and the carrier may have substantially the same, or the same, width in a lateral direction. As used herein, a lateral direction is perpendicular to the path. The carrier may be a carrier belt.

The two wheels may rotate independently or may be fixed to each other. The two wheels may have the same shape, dimension and/or mass. The two wheels may be separated from each other in the lateral direction.

The filter cloth may comprise a wire cloth, such as a metal wire cloth or alloy wire cloth, having a three-dimensional pore geometry. Such filter cloth can provide a substantially constant, or constant, permeability for filtrations after a nominal degree of clogging of the filter cloth. The wire cloth may comprise warp wires and weft wires crossing each other and interwoven by a weave pattern. The warp wires may be formed in at least two different configurations to define warp wires of first and second types. A length of the first type of warp wires may deviate from a length of the second type of warp wires in relation to a particular length unit. Pores may be formed in interstices between sections of two neighbouring warp wires and crossing sections of two neighbouring weft wires.

The filtration arrangement may comprise a motor. The motor may be configured to drive the filtering element along the path. In case the filter cloth is arranged on a continuous carrier, the motor may drive the carrier. The filtering element may be moved continuously or intermittently in operation of the filtration apparatus.

Throughout the present disclosure, the liquid may be water. The filtration vessel may be made of steel. The filtration arrangement according to the first aspect may or may not comprise the fluid ejecting device according to the example useful for understanding the invention. The filtration arrangement according to the first aspect may however be the same as the example useful for understanding the invention.

The two wheels may be vertically movable relative to the filtration vessel. The two wheels are thereby allowed to rest on the filtering element. By allowing the wheels to move downwards, the filtering element is compressed and the sealing is improved. The two wheels may be arranged to move vertically downwards by means of gravity. Thus, the larger the weight of the wheels is, the tighter the sealing of the filtering element and the filtration volume becomes. Optionally, a forcing device, such as a spring, can be provided for each wheel to provide an additional force of the wheels against the filtering element. A vertical movement comprises any movement having a vertical component. The wheels may for example move purely vertically or in a direction inclined with respect to vertical.

Each wheel may comprise at least one seat. In this case, the filtering element may be received in the seats. Each seat may extend along the perimeter of the respective wheel. Optionally, each wheel may comprise a tortous structure and the filtering element may be received in the tortous structure. In this way, the filtration arrangement comprises a rotatable labyrinth seal. Each such labyrinth seal comprises several seats.

Each circular portion may have an angular extension of <NUM> degrees to <NUM> degrees, such as <NUM> degrees to <NUM> degrees.

Each stationary wheel sealing member may be received in a respective of the seat. Thus, each of the stationary wheel sealing members and the filtering element may be received in a seat, either in a common seat or in unique seats.

The at least one stationary wheel sealing member may be made of plastic material. The plastic material reduces friction between the filtering element and the one or more stationary wheel sealing members.

The filtration vessel may comprise two cavities laterally outside the respective wheels. The cavities may collect any overspill from the filtration volume due to splashing. Due to the tight sealing of the filtering element by the wheels, liquid in the cavities is prevented from passing to a region downstream of the filtering element. The filtration arrangement thus prevent any unfiltered liquid from reaching filtered liquid. Liquid in the cavities may be guided back into the filtration volume at least intermittently, for example by pumping out the liquid or by injecting liquid thereto to establish circulation. It can thereby be prevented that liquid remains in the cavities for long periods of time.

The filtration arrangement may further comprise a stationary cavity sealing member in a bottom of each cavity. Each stationary cavity sealing member may be made of a foam material and/or rubber.

According to an example useful for understanding the invention, there is provided a filtration arrangement for a filtration apparatus for filtrating liquid, the filtration arrangement comprising a filtration vessel; a continuous filtering element for removing particles from liquid passing therethrough, the filtering element being arranged to move along a path into the filtration vessel and out from the filtration vessel, and the filtering element comprising a filter cloth and a carrier supporting the filter cloth; and a fluid ejecting device configured to provide a varying stream of fluid towards the filter cloth to induce vibrations in the filter cloth.

Due to the fluid stream, particles are blown away from the filter cloth, such as blown through the filter cloth. The variations or oscillations of the fluid stream however also induces vibrations in the filter cloth. These vibrations also serve to remove particles from the filter cloth. That is, the vibrations cause the particles to be shaken out from the filter cloth. Thereby, the cleaning of the filter cloth is more efficient. The vibrations have a great impact on the cleaning efficiency, in addition to the fluid stream as such. The filtration arrangement according to this example thus has a greatly improved cleaning efficiency in comparison with using a fluid ejecting device that supplies a constant fluid stream. Optionally, the fluid ejecting device may be configured to provide a stream of fluid that varies such that an Eigenfrequency of the filter cloth is excited. In this way, the cleaning efficiency can be further improved.

Since the filtering element is continuous, the filtering element forms a loop. The filter cloth may surround the carrier. That is, the carrier may be arranged inside the filter cloth. The fluid ejecting device may be configured to provide the fluid stream in an outward direction with respect to the loop. Alternatively, or in addition, the fluid ejecting device may be configured to provide the fluid stream vertically downwards. A vertically downward direction in this regard may be angled <NUM> degree to <NUM> degrees to horizontal.

The filtration arrangement may comprise a plurality of rollers for supporting the filtering element and guiding the filtering element along the path. The fluid ejecting device may be arranged at a position where the filter cloth hangs freely. The filter cloth may be suspended with a slack between two rollers. In this way, larger vibrations of the filter cloth are allowed.

The fluid may be air. The fluid stream may oscillate to vary, such as by a directional oscillation and/or by a flow oscillation. With a directional oscillation, the fluid stream may have a substantially constant, or constant, flow, but the flow direction of the fluid stream varies. With a flow oscillation, the fluid stream may have a substantially constant, or constant, flow direction, but the flow of the fluid stream varies.

The filtration arrangement according to the example useful for understanding the invention may or may not comprise the wheels according to the first aspect. The filtration arrangement according to the example useful for understanding the invention may however be the same as the first aspect.

The filtration arrangement may be configured to separate the filter cloth from the carrier outside of the filtration vessel. In this case, the fluid ejecting device may be positioned between the carrier and the filter cloth. In this way, the fluid ejecting device can simultaneously provide the stream of fluid and support the carrier. Moreover, this enables the fluid ejecting device to be positioned close to the filter cloth to improve cleaning. In many implementations, the carrier will never "see" the particles and does therefore not need cleaning.

The fluid ejecting device may comprise at least one fluid ejecting tube arranged to oscillate in a lateral direction with respect to the path. In this way, the fluid ejecting device can provide a varying stream of fluid towards the filter cloth to induce vibrations in the filter cloth. Each fluid ejecting tube may be flexible and/or may be flexibly suspended. By increasing a fluid pressure supplied to the fluid ejecting device, the oscillation frequency of the one or more fluid ejecting tubes can be increased and vice versa. The fluid ejecting device may comprise a plurality of fluid ejecting tubes, such as at least three fluid ejecting tubes.

The fluid ejecting device may comprise a tube guide associated with each fluid ejecting tube. Each tube guide may be configured to guide the fluid ejecting tube in the lateral direction.

The fluid ejecting device may be configured to provide a varying flow of fluid towards the filter cloth. Also in this way, the fluid ejecting device can provide a varying stream of fluid towards the filter cloth to induce vibrations in the filter cloth.

The fluid ejecting device may comprise at least one carrier support for supporting the carrier. The fluid ejecting device may further comprise a fluid pipe for supplying fluid to the one or more fluid ejecting tubes. In this case, each carrier support may at least partly enclose the fluid pipe. The fluid pipe may extend in the lateral direction.

According to a second aspect, there is provided a filtration apparatus for filtrating liquid , the filtration apparatus comprising a filtration arrangement according to the first aspect and/or according to the example useful for understanding the invention. The filtration apparatus may be of the type described in international patent application <CIT>, the full content of which is hereby incorporated by reference. The filtration apparatus may be configured to filtrate liquid by controlling a differential pressure of the liquid over the filtering element, and controlling a passing time of a filter flow of the liquid through the filtering element in conjunction with the differential pressure, as described in international patent application <CIT>. By providing a rapid pressure drop over the filtering element, any bacteria and parasites in the liquid will be killed.

The filtration apparatus may be used to filtrate any liquid where it is desired to reduce an amount of living organisms. The inlet water to the filtering element may or may not be pretreated. Examples of pretreatment include precleaning and preheating.

The filtration apparatus may further comprise an outlet line downstream of the filtering element, a collection volume downstream of the outlet line, a liquid outlet device configured to control a collection volume liquid flow of the liquid out from the collection volume, a gas outlet device configured to control a gas flow out from the collection volume, and a control system configured to control a differential pressure of the liquid over the filtering element and to control a passing time of a filter flow of the liquid through the filtering element in conjunction with the differential pressure. The control of the differential pressure and the passing time may comprise controlling the liquid outlet device to control the collection volume liquid flow, and controlling the gas outlet device to control the gas flow.

The outlet line may be arranged downstream of the filtration vessel, such as between the filtration vessel and the collection volume. The collection volume may be closed to atmosphere.

The filtration apparatus may further comprise a liquid inlet device positioned upstream of the filtering element, e.g. on an inlet line. By means of the liquid inlet device, the inlet flow of the liquid to the filtering element can be controlled.

The filtration apparatus may further comprise an upstream filter. The upstream filter may be positioned between the inlet line and the filtering element or in the inlet line.

The outlet line may have a geodetic difference in height of at least one meter. The filtration apparatus may be configured to establish the differential pressure by means of downstream movement of the liquid in the outlet line.

Further details, advantages and aspects of the present disclosure will become apparent from the following description taken in conjunction with the drawings, wherein:.

In the following, a filtration arrangement comprising two wheels, a filtration arrangement comprising a fluid ejecting device, and a filtration apparatus comprising such filtration arrangement, will be described. The same or similar reference numerals will be used to denote the same or similar structural features.

<FIG> schematically represents a cross-sectional side view of a filtration apparatus <NUM>. The filtration apparatus <NUM> comprises a filtration arrangement <NUM>. The filtration apparatus <NUM> comprises a filtration vessel <NUM>, a continuous filtering element <NUM> and two wheels 18a, 18b (only one wheel 18b is visible in <FIG>). The filtering element <NUM> is configured to remove particles from a liquid passing therethrough. The liquid is here exemplified as water <NUM>.

A filtration volume <NUM> is delimited by the two wheels 18a, 18b and by the filtering element <NUM> inside the filtration vessel <NUM>. Water <NUM> to be filtrated is received in the filtration volume <NUM>. The wheel 18b comprises a seat 24b. The wheel 18a comprises a corresponding seat 24a (<FIG>).

As shown in <FIG>, the filtering element <NUM> is movable in a loop along a path <NUM>. The filtering element <NUM> can move continuously or intermittently into a filtration region inside the filtration vessel <NUM> and out from the filtration vessel <NUM>. The filtration vessel <NUM> may be made of steel.

The filtering element <NUM> here comprises a continuous filter cloth <NUM> and a continuous carrier, here exemplified as a carrier belt <NUM>. The carrier belt <NUM> supports the filter cloth <NUM>. The filter cloth <NUM> is arranged outside the carrier belt <NUM>. The filter cloth <NUM> may for example be a Minimesh ® RPD HIFLO-S sold by Haver & Boecker, such as RPD HIFLO <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

The filter cloth <NUM> may for example have a pore size of at least <NUM> and/or less than <NUM>. The filter cloth <NUM> may for example have a thickness of <NUM> to <NUM>. The carrier belt <NUM> may for example have a thickness of at least <NUM> and/or less than <NUM>.

The filtration arrangement <NUM> further comprises an electric motor <NUM>. The motor <NUM> is configured drive the filtering element <NUM> along the path <NUM> and is configured to control the speed of the filtering element <NUM>.

The filtration arrangement <NUM> of this example further comprises a plurality of rollers. In <FIG>, three rollers 34a, 34b and 34c can be seen. The rollers 34a-34c support and guide the filtering element <NUM> along the path <NUM>. The motor <NUM> is here arranged to drive one of the rollers 34a engaging the carrier belt <NUM> to cause the filtering element <NUM> to move along the path <NUM>. Also the wheels 18a, 18b support and guide the filtering element <NUM> and thereby function as rollers.

The filtration apparatus <NUM> further comprises a fluid ejecting device <NUM>. The fluid ejecting device <NUM> is configured to clean a passive part the filtering element <NUM>, i.e. outside the filtration volume <NUM>, here below the filtration vessel <NUM>. The fluid ejecting device <NUM> is configured to force filtride or filter cake away from the filtering element <NUM> by pressurized air. The fluid ejecting device <NUM> is described in greater detail below.

The filtration apparatus <NUM> of this example further comprises an inlet line <NUM>. The inlet line <NUM> is here exemplified as a vertical pipe for conducting water <NUM> to be filtrated to the filtration vessel <NUM>.

The filtration apparatus <NUM> of this example further comprises an upstream filter <NUM>. The upstream filter <NUM> has a substantially higher permeability than the filtering element <NUM> and may therefore be referred to as a coarse filter.

The filtration apparatus <NUM> of this example further comprises a collection arrangement <NUM>. As shown in <FIG>, the collection arrangement <NUM> is positioned vertically below the filtration arrangement <NUM>. The collection arrangement <NUM> comprises a collection tank <NUM>. The collection tank <NUM> is one example of a collection volume according to the present disclosure.

The filtration apparatus <NUM> further comprises a control system <NUM>. The control system <NUM> comprises a data processing device <NUM> and a memory <NUM> having a computer program stored thereon. The computer program comprises program code which, when executed by the data processing device <NUM> causes the data processing device <NUM> to perform, or command performance of, various steps as described herein. The control system <NUM> is for example in signal communication with the motor <NUM> to control the motor <NUM>.

The filtration apparatus <NUM> of this example further comprises an inlet valve <NUM>. The inlet valve <NUM> is one example of a liquid inlet device according to the present disclosure. By controlling the inlet valve <NUM>, an inlet flow <NUM> through the inlet line <NUM> of water <NUM> to be filtrated can be controlled. The inlet valve <NUM> is in signal communication with the control system <NUM>. The control system <NUM> can control an opening degree of the inlet valve <NUM>.

The filtration apparatus <NUM> of this example further comprises an outlet line <NUM>. The outlet line <NUM> is here exemplified as a vertical pipe. The outlet line <NUM> does however not necessarily need to be vertically oriented. An upstream and geodetically highest end of the outlet line <NUM> is open to the filtering element <NUM> inside the filtration vessel <NUM>. A downstream and geodetically lowest end of the outlet line <NUM> is open to the collection tank <NUM>. Besides the upstream end and the downstream end, the outlet line <NUM> is closed. The outlet line <NUM> thus conducts water <NUM> from the filtration vessel <NUM> below the filtering element <NUM> to the collection tank <NUM>. Reference numeral <NUM> in <FIG> denotes an outlet line flow through the outlet line <NUM>. The filtration apparatus <NUM> further comprises a one-way outlet line valve <NUM> in the outlet line <NUM>, here exemplified as a check valve.

The outlet line <NUM> may have a vertical extension of one meter to ten meters. A vertical drop of water <NUM> below the filtering element <NUM> is thereby provided by the outlet line <NUM>. For this reason, the outlet line <NUM> may be referred to as a drop pipe. A water drop of five meters in the outlet line <NUM> may correspond to a differential pressure of <NUM> mbar over the filtering element <NUM>, and a water drop of eight meters in the outlet line <NUM> may correspond to a differential pressure of <NUM> mbar over the filtering element <NUM>.

The filtration apparatus <NUM> of this example further comprises an outlet valve <NUM>. The outlet valve <NUM> is one example of a liquid outlet device according to the present disclosure. One alternative example of a liquid outlet device according to the present disclosure is a liquid pump. By controlling the outlet valve <NUM>, a collection volume liquid flow <NUM> out from the collection tank <NUM> through a collection outlet <NUM> can be controlled. The outlet valve <NUM> is positioned in a geodetically low region of the collection tank <NUM>. The outlet valve <NUM> is in signal communication with the control system <NUM>. The control system <NUM> can control an opening degree of the outlet valve <NUM>.

The filtration apparatus <NUM> of this example further comprises a vacuum pump <NUM>. The vacuum pump <NUM> is one example of a gas outlet device according to the present disclosure. The vacuum pump <NUM> is arranged in parallel with the outlet valve <NUM>.

The vacuum pump <NUM> is configured to suck gases <NUM> out from the top of the collection tank <NUM> to thereby evacuate the gases <NUM>. By controlling the vacuum pump <NUM>, a gas flow <NUM> out from the collection tank <NUM> can be controlled. The vacuum pump <NUM> is positioned in, and connected to, a geodetically highest region of the collection tank <NUM>. The vacuum pump <NUM> is in signal communication with the control system <NUM>. The control system <NUM> can control a speed of the vacuum pump <NUM>, for example by means of a variable frequency drive.

The collection tank <NUM> is positioned downstream of the outlet line <NUM>. As shown in <FIG>, the collection tank <NUM> is closed to atmosphere. In this example, the only interfaces out from the interior volume of the collection tank <NUM> are through the outlet line <NUM>, through the outlet valve <NUM> and through the vacuum pump <NUM>.

The filtration apparatus <NUM> of this example further comprises an inlet level sensor <NUM>. By means of the inlet level sensor <NUM>, an inlet level of water <NUM> in the filtration vessel <NUM> can be monitored. The inlet level sensor <NUM> is in signal communication with the control system <NUM>.

The filtration apparatus <NUM> of this example further comprises an outlet level sensor <NUM>. By means of the outlet level sensor <NUM>, an outlet level <NUM> of water <NUM> in the collection tank <NUM> can be monitored. The outlet level sensor <NUM> is in signal communication with the control system <NUM>.

The filtration apparatus <NUM> of this example further comprises a temperature sensor <NUM>. The temperature sensor <NUM> of this example is arranged in the collection tank <NUM>. By means of the temperature sensor <NUM>, a temperature of the water <NUM> in the collection tank <NUM> can be monitored. The temperature sensor <NUM> is in signal communication with the control system <NUM>.

The filtration apparatus <NUM> of this example further comprises a pressure sensor <NUM>. The pressure sensor <NUM> is configured to monitor an underpressure of the water <NUM>. The pressure sensor <NUM> of this example is positioned in the outlet line <NUM>. The pressure sensor <NUM> is in signal communication with the control system <NUM>.

Polluted water <NUM> is conducted through the inlet line <NUM> to the filtration vessel <NUM>. The inlet flow <NUM> is controlled by means of the inlet valve <NUM> based on signals from the inlet level sensor <NUM>. In this way, the inlet level of water <NUM> in the filtration vessel <NUM> can be controlled, for example to a constant level. Coarse particles in the water <NUM> are filtered by the upstream filter <NUM>. Finer particles are filtered by the filter cloth <NUM>. The filtering element <NUM> may move continuously during filtration, but the filter speed may be controlled.

As the water <NUM> moves downstream in the outlet line <NUM>, more room is made available upstream of the water <NUM> in the outlet line <NUM> below the filtering element <NUM>. An underpressure is thereby created in the outlet line <NUM> below the filtering element <NUM>. This underpressure can be measured by the pressure sensor <NUM>. The temperature of the water <NUM> may for example be <NUM>. In this case, the water <NUM> boils at an underpressure of <NUM> bar. When the underpressure is reduced (to a lower absolute pressure value), the filter flow through the filtering element <NUM> is increased.

The difference between the atmospheric, or substantially atmospheric, pressure upstream of the filtering element <NUM> and the underpressure downstream of the filtering element <NUM> constitutes a differential pressure over the filtering element <NUM>. By means of the geodetic difference in height of the outlet line <NUM>, the gravity force of the water column in the outlet line <NUM> pulls the water <NUM> through the filtering element <NUM> to establish a differential pressure over the filtering element <NUM>. In this way, a liquid pump for driving the water <NUM> out from the collection tank <NUM> can be avoided and the energy efficiency of the filtration apparatus <NUM> can thereby be improved.

Although bacteria can survive quite rapid and high pressure increases, bacteria cannot survive rapid pressure decreases. By subjecting the water <NUM> to a rapid pressure decrease over the filtering element <NUM>, any living organisms in the water <NUM> will be killed.

The vacuum pump <NUM> sucks gases <NUM> out from the top of the collection tank <NUM> and discharges the gases <NUM> to the atmosphere. In this way, the water level in the collection tank <NUM> can be held constant. The vacuum pump <NUM> is therefore synchronized with the underpressure in the outlet line <NUM>.

<FIG> schematically represents a perspective side view of the filtration arrangement <NUM>. In <FIG>, the two wheels 18a, 18b can be seen. The two wheels 18a, 18b here have the same shape, dimension and mass. Each wheel 18a, 18b is rotatable relative to the filtration vessel <NUM>. The wheels 18a, 18b are also allowed to move vertically up and down relative to the filtration vessel <NUM>. In this example, the wheels 18a, 18b rotate about a common rotation axis provided by a connection shaft <NUM>. The wheels 18a, 18b are here allowed to rotate independently about the rotation axis.

The wheels 18a, 18b sealingly engage the filtering element <NUM> inside the filtration vessel <NUM> on opposite sides of the filtering element <NUM>. Since the wheels 18a, 18b are allowed to rotate and move vertically relative to the filtration vessel <NUM>, the wheels 18a, 18b compress the filtering element <NUM> inside the filtration vessel <NUM> by gravity and rotate together with the filtering element <NUM>. The wheels 18a, 18b and the filtering element <NUM> thereby provide a rotatable seal of the filtration volume <NUM>. The wheels 18a, 18b rotate along with the movement of the filtering element <NUM> along the path <NUM> inside the filtration vessel <NUM>. Since the tangential speed of each of the wheels 18a, 18b corresponds to the speed on the respective side of the filtering element <NUM>, friction losses between the wheels 18a, 18b and the filtering element <NUM> are eliminated.

In <FIG>, the respective seat 24a, 24b on each wheel 18a, 18b can be seen. The seats 24a, 24b extend around the perimeter of the respective wheel 18a, 18b. The filtering element <NUM> is received in each seat 24a, 24b.

<FIG> further shows a lateral direction <NUM>. The lateral direction <NUM> is perpendicular to the path <NUM>. The filter cloth <NUM> and the carrier belt <NUM> have the same width in the lateral direction <NUM>. The width of each of the filter cloth <NUM> and the carrier belt <NUM> may for example be <NUM> or larger, such as <NUM>.

The filter cloth <NUM> of this example is a metal wire cloth having a three-dimensional pore geometry. The wire cloth comprises warp wires and weft wires crossing each other and interwoven by a weave pattern. The warp wires are formed in at least two different configurations to define warp wires of first and second types. Pores are formed in interstices between sections of two neighboring warp wires and crossing sections of two neighboring weft wires. Due to this three-dimensional pore geometry, the filter cloth <NUM> has a constant permeability after a certain degree of clogging, for example when subjected to backwashing after each filtration cycle. The filter cloth <NUM> may for example be of the type Minimesh ® RPD HIFLO-S sold by Haver & Boecker, such as RPD HIFLO <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

<FIG> schematically represents a partial perspective side view of the filtration arrangement <NUM>. In <FIG>, one example of a structure to realize the vertical movements of the wheels 18a, 18b relative to the filtration vessel <NUM> can be seen. On each side, the filtration arrangement <NUM> of this example comprises two vertical brackets <NUM> and a plate <NUM>. The brackets <NUM> are fixed to the filtration vessel <NUM>. The plates <NUM> are received between the associated brackets <NUM> and are guided vertically between the brackets <NUM>. The wheels 18a, 18b are rotatably supported to the plates <NUM>.

In <FIG>, it can be seen that the filtration vessel <NUM> comprises a circular portion 92a. The circular portion 92a corresponds to the perimeter of the wheel 18a. The filtration vessel <NUM> comprises a corresponding circular portion 92b on the opposite side. The wheels 18a, 18b are forced by gravity into a respective of the circular portions 92a, 92b with the filtering element <NUM> squeezed therebetween. In this example, each circular portion 92a, 92b has an angular extension of approximately <NUM> degrees.

<FIG> further shows that a cavity 94a is provided laterally outside the wheel 18a between the wheel 18a and the filtration vessel <NUM>. The filtration arrangement <NUM> comprises a corresponding cavity 94b (<FIG>) laterally outside the wheel 18b between the wheel 18b and the filtration vessel <NUM>.

<FIG> further shows that the filtration arrangement <NUM> comprises a stationary cavity sealing member 96a in the bottom of the cavity 94a, and a corresponding stationary cavity sealing member 96b (<FIG>) in the bottom of the cavity 94b. Each stationary cavity sealing member 96a, 96b is circular and conforms to the profile of the respective circular portions 92a, 92b. Each stationary cavity sealing member 96a, 96b has an angular extension of approximately <NUM> degrees in this example. The stationary cavity sealing members 96a, 96b may be made of foam.

The cavities 94a, 94b are arranged to collect any overspill of water <NUM> due to splashing. The stationary cavity sealing members 96a, 96b prevent water <NUM> in the cavities 94a, 94b from joining filtrated water <NUM> downstream of the filtering element <NUM>. A small flow of water <NUM> may intentionally be directed to each cavity 94a, 94b to provide some circulation of water <NUM> in the cavities 94a, 94b in order to prevent water <NUM> from resting in the cavities 94a, 94b for long time periods.

<FIG> schematically represents a partial top view of the filtration arrangement <NUM>. In <FIG>, the cavity 94b and the stationary cavity sealing member 96b can be seen. <FIG> further shows that the filtering element <NUM> is received in the seats 24a, 24b of the wheels 18a, 18b.

<FIG> schematically represents a partial cross-sectional top view of the filtration arrangement <NUM>, and <FIG> schematically represents a partial cross-sectional top view of the filtration arrangement <NUM>. In <FIG>, the filtering element <NUM> is removed. With collective reference to <FIG> and <FIG>, the filtration arrangement <NUM> further comprises stationary wheel sealing member <NUM>, 98a, 98b. The stationary wheel sealing members <NUM>, 98a, 98b may be integrally formed or rigidly connected to each other (directly or indirectly). The stationary wheel sealing members <NUM>, 98a, 98b are fixed to the filtration vessel <NUM>. As shown in <FIG> and <FIG>, the stationary wheel sealing members <NUM>, 98a, 98b are also received in the seats 24a, 24b, such that the filtering element <NUM> is positioned between the wheels 18a, 18b and the stationary wheel sealing members <NUM>, 98a, 98b, and such that the stationary wheel sealing members <NUM>, 98a, 98b are positioned between the filtering element <NUM> and the filtration vessel <NUM>. The stationary wheel sealing member 98a is provided between the wheel 18a and the filtration vessel <NUM>. The stationary wheel sealing member 98b is provided between the wheel 18b and the filtration vessel <NUM>. The stationary wheel sealing member <NUM> is provided between both wheels 18a, 18b and the filtration vessel <NUM>. The stationary wheel sealing members <NUM>, 98a, 98b seal between the filtering element <NUM> and the circular portions 92a, 92b of the filtration vessel <NUM>.

During movement of the filtering element <NUM>, the wheels 18a, 18b rotate and there is no relative movement between the wheels 18a, 18b and the filtering element <NUM>. The filtering element <NUM> slides on the stationary wheel sealing members <NUM>, 98a, 98b. The stationary wheel sealing members <NUM>, 98a, 98b are made of plastic to further reduce friction losses.

<FIG> schematically represents a cross-sectional top view of a further example of a sealing of the filtration arrangement <NUM>. In <FIG>, the wheel 18a comprises two seats 24a1, 24a2. The seats 24a1, 24a2 form a tortous structure. The filter cloth <NUM> is received in the seat 24a1. Both the carrier belt <NUM> and the stationary wheel sealing member <NUM> are received in the seat 24a2. The wheel 18b may be configured in a corresponding way. In this case, the filtration arrangement <NUM> comprises a rotatable labyrinth seal.

<FIG> schematically represents a partial perspective side view of the filtration arrangement <NUM>. As shown in <FIG>, the filtration arrangement <NUM> is configured to separate the filter cloth <NUM> from the carrier belt <NUM> in a region outside the filtration vessel <NUM>, here vertically below the filtration vessel <NUM>. The fluid ejecting device <NUM> is positioned between the carrier belt <NUM> and the filter cloth <NUM> and thereby guides the carrier belt <NUM> above the fluid ejecting device <NUM> and the filter cloth <NUM> below the fluid ejecting device <NUM>. This enables the fluid ejecting device <NUM> to be positioned closer to the filter cloth <NUM>. The fluid ejecting device <NUM> is positioned in a region where the filter cloth <NUM> hangs freely, here between the rollers 34a and 34b.

The fluid ejecting device <NUM> is configured to provide a stream of air to the filter cloth <NUM>. The air stream is provided substantially vertically downwards, and outwards with respect to the loop formed by the filter cloth <NUM>. At the same time, the fluid ejecting device <NUM> supports the carrier belt <NUM>.

<FIG> schematically represents a partial perspective rear view of the filtration arrangement <NUM>. As shown in <FIG>, the fluid ejecting device <NUM> comprises a fluid pipe <NUM> and a plurality of fluid ejecting tubes <NUM>, here ten fluid ejecting tubes <NUM>. The fluid ejecting tubes <NUM> are here aligned in the lateral direction <NUM>. Pressurized air is led into the fluid pipe <NUM> and further to each fluid ejecting tube <NUM>.

The fluid ejecting device <NUM> further comprises a tube guide <NUM> for each fluid ejecting tube <NUM>. Each tube guide <NUM> limits movement of the associated fluid ejecting tube <NUM> to the lateral direction <NUM>. The fluid ejecting tubes <NUM> are flexible. The air stream from the fluid ejecting tubes <NUM> to the filter cloth <NUM> blow particles out from the filter cloth <NUM>. Besides, when air is supplied to the fluid ejecting tubes <NUM>, the fluid ejecting tubes <NUM> oscillate in the lateral direction <NUM>. This causes the air stream onto the filter cloth <NUM> to vary. As a consequence, vibrations are induced in the filter cloth <NUM>. These vibrations provide an additional removal of particles from the filter cloth <NUM>. That is, the filter cloth <NUM> is both subjected to an air stream to remove particles, and is shaken to remove particles.

The oscillations of the fluid ejecting tubes <NUM> also result in that the entire width of the filter cloth <NUM> will be covered by the air stream. The fluid pipe <NUM> may be supplied with a constant flow of air. Alternatively, the flow of air may be varied to provide a varying air stream to induce vibrations of the filter cloth <NUM>.

Claim 1:
A filtration arrangement (<NUM>) for a filtration apparatus (<NUM>) for filtrating liquid (<NUM>), the filtration arrangement (<NUM>) comprising:
- a filtration vessel (<NUM>) comprising two circular portions (92a, 92b);
- a continuous filtering element (<NUM>) for removing particles from liquid (<NUM>) passing therethrough, the filtering element (<NUM>) being arranged to move along a path (<NUM>) into the filtration vessel (<NUM>) and out from the filtration vessel (<NUM>);
- two wheels (18a, 18b) sealingly engaging the filtering element (<NUM>) on opposite sides thereof inside the filtration vessel (<NUM>), where each of the two wheels (18a, 18b) is rotatable relative to the filtration vessel (<NUM>) along with movement of the filtering element (<NUM>), and where the two wheels (18a, 18b) are forced into a respective of the circular portions (92a, 92b) with the filtering element (<NUM>) therebetween; and
at least one stationary wheel sealing member (<NUM>, 98a, 98b) arranged to seal between the filtering element (<NUM>) and a respective of the circular portions (92a, 92b).