Patent Description:
Filter elements may be used in filtering devices for example in microfiltration processes or cleaning of liquids. The microfiltration may be used, for example in mining and processing industries and in food and pharmaceutical industries. In addition, for example in pretreatment of ship ballast water and in production of clean water, microfiltration is applicable. Some example applications for microfiltration may be cooling water treatment, treating flue gas waste water, treating waste water before discharge, and providing solids-free water for reverse osmosis. In a wider sense, in all fields where water or any liquid is treated, there may arise a need to filter the finely divided solid material away from the liquid, because the end products of the filtering process are clarified aqueous filtrate and concentrate, i.e. reject.

Typically, the filter elements may be made of porous material, such as ceramic or silicon carbide, or also of sintered metallic powder or wire mesh. The filter element must be washable for securing a good filtering efficiency of the filtering device. Especially, the filter elements having micron size pore size, such as less than <NUM>, are prone to clogging, because particles from the liquid to be clarified get stuck in the pores of the filter element sometimes even leading to cake formation on the filter element.

According to one prior art solution ultrasound is used at feed side of the filtering device, i.e. an ultrasonic element residing outside the filtering device, in order to enhance flux. The ultrasound prevents at least partly the cake formation on the filter element, but it fails to prevent fouling inside the pores of the filter element. Running the ultrasound during the filtering process increases flux, i.e. flow, momentarily, but it allows the particles pass through the filter element resulting that the filtrate may comprise particulates. Furthermore, in the long run, there might be a risk that the ultrasound invites particulates inside the filter element, which in turn decreases the flux in the long run.

According to one prior art solution, disclosed in the patent application <CIT>, the filter element may be clarified by using so called backwash, where a filtrate filtered by the filtering device is led back to the filtering device in the opposite direction of normal filtration flow. Furthermore, an ultrasonic element inside the filtering device may be started for cavitating the surface of the filter element at the same time, when the surface of the filter element is flushed with the filtrate by means of the backwash. Moreover, a chemical, such as acid or alkali, cleaning may be combined to the backwash and ultrasound cleaning. The feed of a liquid to be clarified must be interrupted during the cleaning operation causing that the filtering process is on hold during the cleaning of the filter element. Typically, in order to improve the efficiency a double system is employed, wherein one system is filtering and the other system is cleaning. Furthermore, at least one drawback of the prior art solution is that it is not capable to remove particles from the surface of the filter element having micron size pores. Thus, the life-time of the filter elements is substantially short and the filter element needs to be replaced with a new filter element substantially frequently.

A patent application <CIT> discloses a method, wherein backwashing and ultrasound are used to clean a membrane filter.

A patent application <CIT> discloses a nozzle device and a nozzle for atomisation and/or filtration.

An objective of the invention is to present a method for cleaning a filter element made of a porous material and a filtering device comprising a filter element made of porous material. Another objective of the invention is that the method for cleaning a filter element made of a porous material and the filtering device improve at least partly the cleaning effect on the surface of the filter element.

The objectives of the invention are reached by a method and a filtering device as defined by the respective independent claims.

According to a first aspect, a method for cleaning a filter element made of a porous material is provided, wherein the method comprising: directing ultrasound to the filter element, and directing after a predefined time from starting of the ultrasound an impulse to a filtrate reservoir causing filtrate inside the filtrate reservoir to be forced inside the filter element in order to remove particles from the surface of the filter element.

The pressure of the impulse may be between <NUM> to <NUM> times higher than the forward pressure and also that the reverse flux, measured in volume per area time, caused by the impulse may be at the minimum <NUM> to <NUM> times the feed flux.

The impulse may be one of the following: a pneumatic impulse, liquid impulse.

The control of the feeding of a liquid to be clarified to the filtering element may not be interrupted during the cleaning of the filter element.

The method may further comprise discharging the impulse from the filter element by adjusting concentrate outflow by means an adjustable concentrate valve.

Alternatively or in addition, the method may further comprise discharging the impulse from the filter element by actuating a discharging device by the force of the impact.

The power of the ultrasound at the surface of the filter element may be between <NUM> and <NUM> watts/square meter, preferably <NUM> watts/square meter.

The method may further comprise adjusting the pressure and/or the duration of the impulse.

A pore size of the filter element may be between <NUM> to <NUM> micrometers.

The predefined time from starting of the ultrasound may be at least <NUM> second.

According to a second aspect, a filtering device is provided, wherein the filtering device comprising: a filter element made of a porous material, an impulse connection arranged to at least one filtrate outlet connection of the filtering device, a filtrate reservoir arranged between the filter element and the at least one filtrate outlet connection, and an ultrasonic element, wherein the ultrasonic element is configured to direct ultrasound to the filter element and after a predefined time from starting the ultrasound the impulse is directed from an impulse source via the impulse connection to the filtrate reservoir causing that the content of the filtrate reservoir is forced inside the filter element in order to remove particles from the surface of the porous material.

The pressure of the impulse may be between <NUM> to <NUM> times higher than the forward pressure and also that the reverse flux, measured in volume per area time, caused by the impulse, may be at the minimum <NUM> to <NUM> times the feed flux.

The control of the feeding of a liquid to be clarified to the filtering device may not be interrupted during the cleaning of the filter element.

The filtering device may further comprise an adjustable concentrate valve arranged to a concentrate outlet connection of the filtering device, wherein the adjustable concentrate valve may be configured to adjust the concentrate outflow in order to discharge the impulse from the filter element and the filtering device through the concentrate outlet connection.

Alternatively or in addition, the filtering device may further comprise a discharge device arranged to the concentrate outlet connection of the filtering device, the discharge device may be actuated by the force of the impact in order to discharge the impulse from the filter element and the filtering device through the concentrate outlet connection.

The filtering device may further comprise an impulse connection valve configured to adjust the pressure and/or duration of the impulse.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also un-recited features.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objectives and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

<FIG> illustrates schematically an example of a microfiltration system <NUM>, wherein the embodiments according to the invention may be implemented. The microfiltration system <NUM> may comprise a feed source <NUM>, a feed pump <NUM>, and a filtering device <NUM>. Said components of the system may be connected to each other by lines or pipes, and are thus are in fluid communication. Furthermore, the microfiltration system <NUM> may further comprise a control unit <NUM> configured to control the operation of microfiltration system <NUM>.

The feed pump <NUM> may be configured to feed from the feed source <NUM> a liquid feed flow comprising solids to the filtering device <NUM> that is configured to filter the solids away from the liquid feed flow in order to form clarified aqueous filtrate, i.e. product, and concentrate, i.e. reject. The feed source <NUM> may comprise a reservoir and/or a mixing tank for preserving and/or pre-mixing the liquid feed flow. The liquid to be clarified may be mixed with a sorbent to form a suspension, in which impurities are adsorbed or absorbed by the sorbent particles, so as to form a premixed suspension.

The filtering device <NUM> may be a cross-flow filter or a dead-end filter, for example. <FIG> illustrates schematically a simple example of the cross-section of a cylindrical filtering device <NUM> according to the invention. The filtering device <NUM> comprises at least one inlet connection <NUM> for feeding liquid to be clarified <NUM> into the filtering device <NUM>, a filter element <NUM>, at least one filtrate outlet connection <NUM> for discharging the clarified filtrate <NUM> from the filtering device <NUM>, and at least one concentrate outlet connection <NUM> for discharging the concentrate <NUM> from the filtering device <NUM> in order to circulate the liquid to be clarified <NUM>. The filtering device <NUM> further comprises a filtrate reservoir <NUM> arranged between the filter element <NUM> and the at least one filtrate outlet connection <NUM>.

In order to filter the solids away from the incoming liquid <NUM>, the incoming liquid <NUM> is fed into the filtering device <NUM> through one or more inlet connections <NUM> and directed through the filter element <NUM>. The liquid is filtered, when passing through the filter element <NUM>, and is discharged as clarified filtrate <NUM> through the at least one filtrate outlet connection <NUM>. The concentrate <NUM> may be circulated from at least one concentrate outlet connection <NUM> back through to the feed flow <NUM> of the filtering device <NUM> to be returned into the filtering device <NUM>. This forms a so-called circulation loop (concentrate circulation) that maintains the velocity of the liquid across the filter element <NUM>.

The filter element <NUM> is made of porous material, such as ceramic or silicon carbide, or also of sintered metallic powder or wire mesh. The filter element <NUM> may have a pore size of <NUM> to <NUM> micrometers.

The filtering device <NUM> further comprises an ultrasonic element <NUM> inside the filter element <NUM> for cleaning the filter element <NUM>. Preferably, the ultrasonic element <NUM> may be rod-like. The filter element <NUM> is clarified for securing a good filtering efficiency of the filtering device <NUM>.

In the method according to the invention the cleaning of the filter element <NUM> is based on a combination of directing ultrasound and high intensity energy impulse to the filter element <NUM> in order to remove particles from the surface of the filter element <NUM>. In order to provide the impulse, the filtering device <NUM> comprises further an impulse connection <NUM> arranged to at least one filtrate outlet connection <NUM> of the filtering device <NUM>.

Next, an example of the method for cleaning a filter element <NUM> made of a porous material according to the invention is described by referring to <FIG>. The method may be implemented in a filtering device <NUM> according to the invention described above. <FIG> schematically illustrates the invention as a flow chart. First the ultrasonic element <NUM> is started and ultrasound is directed <NUM> to the filter element <NUM>. After a predefined time from starting of the ultrasound the impulse is directed <NUM> to the filtrate reservoir <NUM> causing that filtrate inside the filtrate reservoir <NUM> is forced inside the filter element <NUM> in order to remove particles from the surface of the filter element <NUM>. The impulse may be provided by the impulse source and directed via the impulse connection <NUM> to the filtrate reservoir <NUM>.

Because the ultrasound is directed to the filter element <NUM> before providing the impulse, the ultrasound aids in dislodging the particles on the surface of the filter element <NUM> loose. Furthermore, because the ultrasound is directed to the filter element <NUM> before providing the impulse, there exist no ultrasound absorbing gas bubbles inside the filtering element <NUM> yet at this stage. The impulse directed to the filtering element <NUM> disturbs the flow and ultrasound absorbing gas bubbles are formed inside the filtering element <NUM> causing the efficiency of the ultrasound to decrease. The predefined time from starting of the ultrasound may be for example at least <NUM> second. Preferably, the predefined time from starting of the ultrasound may be for example between <NUM> to <NUM> seconds. The power of the ultrasonic element <NUM> may be defined as a power at the surface of the filtering element <NUM> per area unit. For example, the power of the ultrasonic element <NUM> at the surface of the filtering element <NUM> may be between <NUM> and <NUM> watts/square meter, preferably <NUM> watts/square meter. Alternatively or in addition, the power of the ultrasonic element <NUM> may be defined by power per liter. For example, if the volume of the filter element <NUM> is <NUM> liters, the power per liter is between <NUM> and <NUM> watts/liter, preferably <NUM> watts/liter for above presented power values of the ultrasonic element <NUM> per area unit. The frequency of the ultrasound may be between <NUM> and <NUM> kilohertz.

The impulse may be one of the following: a pneumatic impulse, liquid impulse. The impulse may be provided by an impulse source, for example an air compressor, a gas tank, a water supply network, or any source suitable for providing needed pressure for the impulse. The pressure of the impulse may be between <NUM> to <NUM> times higher than the forward pressure, i.e. feed pressure. The impulse source may be an internal part of the filtering device <NUM> connected to the impulse connection <NUM>. Alternatively, the impulse source may be an external impulse source connectable to the impulse connection <NUM>.

The impulse may be defined so that it exhausts the filtrate reservoir <NUM>, but does not feed air of the impulse inside the filter element <NUM>. Furthermore, the impulse may be defined so that the reverse flux, i.e. backwash flux, measured in volume per area time, caused by the impulse, is at the minimum <NUM> to <NUM> times the feed flux, i.e. forward flux, of the filtering device <NUM>. The reverse flux direction is opposite with respect to the feed flux direction, i.e. if the sign of the feed flux is considered to be positive, the sign of the reverse flux is negative. The reverse flux caused by the impulse may be defined by the following formula: <MAT> wherein V is the volume of the filtrate directed inside the filter element <NUM> by the impulse per area and t is the duration of the impulse. The volume of the filtrate directed inside the filter element <NUM> by the impulse per one square meter surface area of the filter element <NUM> may be at the minimum <NUM> liters/m<NUM>. For example, if the feed flux of the filtering device <NUM> is <NUM> liters/m<NUM>hour, the reverse flux caused by the impulse is at the minimum <NUM> to <NUM> times the feed flux of the filtering device <NUM> as defined above, and <NUM> liters of filtrate is directed through one square meter of the filter element <NUM>, the duration of the impulse is between <NUM> and <NUM> seconds.

According to an embodiment of the invention the pressure and/or duration of the impulse may be adjusted. The filtering device <NUM> may for example comprise an impulse connection valve arranged to the impulse connection <NUM> configured to adjust the pressure and/or duration of the impulse. Alternatively or in addition, the impulse source may comprise adjusting means in order to adjust the pressure and/or duration of the impulse.

The use of fast and high intensity impulse that has pressure higher than the feed pressure of the filtering device <NUM> enable that the liquid to be clarified may be fed to the filtering device <NUM> during the cleaning of the filter element <NUM>. In other words, the cleaning of the filter element <NUM> according to the invention may be performed while the filtering system <NUM> is in operation and the control of the feeding of the liquid to be clarified is not interrupted, i.e. the feed pump <NUM> does not have to be turned off, during the cleaning operation. Keeping the feed pump <NUM> running during the cleaning of the filter element <NUM> improves at least partly the efficiency of the filtering device <NUM> and the efficiency of the whole filtering system <NUM>. Furthermore, feeding the liquid to be clarified to the filtering device <NUM> during the cleaning of the filter element <NUM> causes that the flow at the surface of the filter element <NUM> accelerates and the high-speed concentrate flow removes the particles away from the surface filter element <NUM>, which improves the cleaning effect on the surface of the filter element <NUM> and is useful specially when the cleaning is provided with the fast impulse. If the feed flow would be interrupted, i.e. stopped, during the cleaning of the filter element <NUM>, the particles would get back to the surface of the filter element <NUM>, when the feed flow would be started again.

According to one embodiment of the invention, the filtering device <NUM> may further comprise an adjustable concentrate valve <NUM> arranged to at least one concentrate outlet connection <NUM> of the filtering device <NUM>. The adjustable concentrate valve <NUM> may be configured to adjust the concentrate outflow <NUM> in order to discharge <NUM> the impulse from the filter element <NUM> and the filtering device <NUM> through the at least one concentrate outlet connection <NUM>. <FIG> illustrates schematically an example of the adjustable concentrate valve <NUM> arranged to the concentrate outlet connection <NUM> of the filtering device <NUM>.

This enables that the impulse may be substantially freely discharged from the filtering device <NUM> through the concentrate outlet connection <NUM> in order to enhance the cleaning of the filter element <NUM>. The adjustable concentrate valve <NUM> may be adjusted to be fully open during the cleaning of the filter element <NUM> and to be fully closed or nearly fully closed during the filtering process. The adjustable concentrate valve <NUM> may be adjusted to be fully open a short time, such as <NUM> to <NUM> second, before the impulse. Preferably, the adjustable concentrate valve <NUM> may be adjusted to be fully open <NUM> seconds before the impulse. In comparison to a fixed adjusted concentrate valve <NUM> the efficiency of the cleaning of the filter element <NUM> may be improved, because the fixed adjusted concentrate valves are typically adjusted during the commissioning phase of the microfiltration process to be nearly closed in order to optimize the filtering process. If the concentrate valve is during the cleaning of the filter element <NUM> in the same position as during the filtering process, i.e. fully closed or nearly fully closed and any other methods to discharge the impulse from the filtering device is not used, the impulse cannot be discharged anywhere from the filtering device <NUM> causing the efficiency of the filtering element <NUM> to decrease.

The adjustable concentrate valve <NUM> may be any valve, which adjustment may be automatically controlled. The adjustable concentrate valve may comprise an actuator for moving a modulating element, such as ball or butterfly, of the valve in order to provide the opening and/or closing of the valve. The actuator may be one of the following: pneumatic actuator, electrical actuator, hydraulic actuator. The actuator enables that the valve may be adjusted to any position between fully open and fully closed. Preferably, the adjustment of the valve may be defined as percentage, for example <NUM>% means fully open and <NUM>% means fully closed. Furthermore, the adjustable concentrate valve <NUM> may comprise a valve positioner for defining the real position of the valve in order to ensure that the valve has reached the desired degree of the opening. The type of the valve may be at least one of the following: ball valve, butterfly valve.

Alternatively or in addition, according to another embodiment of the invention the filtering device <NUM> may comprise a discharge device arranged to the concentrate outlet connection <NUM> of the filtering device <NUM>. The discharge device may be actuated by the force of the impact in order to discharge <NUM> the impulse from the filter element <NUM> and the filtering device <NUM> through the concentrate outlet connection <NUM>. The discharge device may be a malleable element <NUM> made of flexible material. The flexible material of the malleable element <NUM> may be any material that may sustain constant compression and decompression, for example an elastomer. The malleable element <NUM> may be configured to be squeezed by the force of the impact in order to discharge <NUM> the impulse from the filter element <NUM> and the filtering device <NUM> through the concentrate outlet connection <NUM>. When the pressure settles down after the discharge of the impulse, the malleable element <NUM> returns back to its original shape and is ready for a next impulse. According to a non-limiting example the shape of the malleable element <NUM> may be ball, cube, pyramid or any other shape suitable to be arranged the concentrate outlet connection <NUM> of the filtering device <NUM>. <FIG> illustrates schematically an example of the malleable element <NUM> according to the invention, wherein the malleable element <NUM> is a ball.

Alternatively, the discharge device may be a mechanical device, for example a piston <NUM>. The piston <NUM> is configured to be movable along the concentrate outlet connection <NUM> away from the filter element <NUM> by the force of the impact in order to discharge <NUM> the impulse from the filter element <NUM> and the filtering device <NUM> through the concentrate outlet connection <NUM>. When the pressure settles down after the discharge of the impulse, the piston <NUM> returns back to its original position inside the concentrate outlet connection <NUM> and is ready for a next impulse. <FIG> illustrates schematically an example of the piston <NUM> according to the invention.

If the impulse cannot be discharged from the filter element <NUM> and the filtering device <NUM>, the efficiency of the cleaning may be decreased. Thus, the above described methods to discharge <NUM> the impulse from the filtering device <NUM> improves the efficiency of the cleaning of the filter element <NUM>. The discharging step of the method according to the invention is illustrated in <FIG> with a dashed line that illustrates that the discharging step is an optional step of the method according to the invention in order to improve the efficiency of the cleaning of the filter element <NUM>.

<FIG> discloses a schematic example of a control unit <NUM> according to the invention. Some non-limiting examples of the control unit <NUM> may e.g. be a server, personal computer, laptop computer, computing circuit, a network of computing devices, mobile communication device. The control unit <NUM> may comprise at least one processor <NUM>, at least one memory <NUM> for storing portions of computer program code 505a-505n and any data values, a communication interface <NUM>, and possibly one or more user interface units <NUM>. Said elements of the control unit <NUM> may be communicatively coupled to each other with e.g. an internal bus.

The at least one processor <NUM> of the control unit <NUM> is at least configured to control the operation of microfiltration system <NUM>. The implementation of the controlling may be achieved by arranging the at least one processor <NUM> to execute at least some portion of computer program code 505a-505n stored in the at least one memory <NUM> causing the at least one processor <NUM>, and thus the control unit <NUM>, to control the operation of the microfiltration system <NUM>. The at least one processor <NUM> is thus arranged to access the at least one memory <NUM> and retrieve and store any information therefrom and thereto.

The control unit <NUM> may be configured to control the operation of the one or more of the components of the microfiltration system <NUM> based on at least one operational parameter the microfiltration process received from one or more sensors arranged to the microfiltration system <NUM> and configured to obtain at least one operational parameter of the microfiltration process. The at least one operational parameter may be one of the following: filtrate flow, feed pressure, concentrate pressure, temperature of the feed, amount of the solids in the feed, turbidity of the feed, conductivity of the feed, pH value of the feed. The at least one sensor for obtaining the at least one operational parameter may be one of the following: flowmeter, pressure meter, temperature meter, water quality monitoring system. Alternatively or in addition, the control unit <NUM> may be configured to control the operation of the one or more of the components of the microfiltration system <NUM> based on user input via the user interface units <NUM>.

Moreover, the at least one processor <NUM> is configured to control the communication through the communication interface <NUM> with the filtering device <NUM>, the impulse source, the feed pump <NUM>, the adjustable concentrate valve <NUM>, and/or any other external unit. The control unit <NUM> may be configured to generate at least one control signal to the filtering device <NUM>, the impulse source, and/or the feed pump <NUM> in order to control the operation of each component of the filtering system <NUM>. Alternatively or in addition, the control unit <NUM> may be configured to generate at least one control signal to the adjustable concentrate valve <NUM> of the filtering device <NUM> in order to control the adjustment of the adjustable concentrate valve <NUM>.

For sake of clarity, the processor herein refers to any unit suitable for processing information and control the operation of the control unit <NUM>, among other tasks. The operations may also be implemented with a microcontroller solution with embedded software. Similarly, the at least one memory <NUM> of the control unit <NUM> is not limited to a certain type of memory only, but any memory type suitable for storing the described pieces of information may be applied in the context of the present invention. Moreover, the at least one memory <NUM> may be volatile or non-volatile.

The communication interface <NUM> may be configured to provide an interface for communication with the filtering device <NUM>, the impulse source, the feed pump <NUM>, the adjustable concentrate valve <NUM>, any external unit, database and/or external systems. The communication interface <NUM> may be based on one or more known communication technologies, either wired or wireless, in order to exchange pieces of information. The one or more user interface units <NUM> may be configured to input control commands, receive information and/or instructions, and/or display information. The user interface units <NUM> may comprise for example at least one of the following: a touchscreen, at least one function key, a wired or wireless remote controller, a display.

Claim 1:
A method for cleaning a filter element (<NUM>) made of a porous material, the method comprising:
- directing (<NUM>) ultrasound by an ultrasonic element (<NUM>) to the filter element, wherein the ultrasonic element (<NUM>) is inside the filter element (<NUM>) for cleaning the filter element (<NUM>), and
- directing (<NUM>) after at least <NUM> second from starting of the ultrasound an impulse to a filtrate reservoir (<NUM>) causing filtrate inside the filtrate reservoir (<NUM>) to be forced inside the filter element (<NUM>) in order to remove particles from the surface of the filter element (<NUM>),
wherein pressure of the impulse is between <NUM> to <NUM> times higher than the forward pressure and the reverse flux, measured in volume of the filtrate directed inside the filter element (<NUM>) by the impulse per area time, caused by the impulse is at the minimum <NUM> to <NUM> times the feed flux, and
wherein feeding of a liquid to be clarified to the filtering element (<NUM>) is not interrupted during the cleaning of the filter element (<NUM>).