FIELD OF THE INVENTION

The present invention relates generally to disc filters.

BACKGROUND OF THE INVENTION

Filtration is a widely used process whereby a slurry or solid liquid mixture is forced through a media, with the solids retained on the media and the liquid phase passing through. This process is generally well understood in the industry. Examples of filtration types include depth filtration, pressure and vacuum filtration, and gravity and centrifugal filtration.

Both pressure and vacuum filters are used in the dewatering of mineral concentrates. The principal difference between pressure and vacuum filters is the way the driving force for filtration is generated. In pressure filtration, overpressure within the filtration chamber is generated with the help of e.g. a diaphragm, a piston, or external devices, e.g. a feed pump. Consequently, solids are deposited onto the filter medium and filtrate flows through into the filtrate channels. Pressure filters often operate in batch mode because continuous cake discharge is more difficult to achieve.

The cake formation in vacuum filtration is based on generating suction within the filtrate channels. The most commonly used filter media for vacuum filters are filter cloths and coated media, e.g. the ceramic filter medium. Although several types of vacuum filters, ranging from belt filters to drums, exist, only the specifics of rotary vacuum disc filters are included here.

Rotary vacuum disc filters are used for the filtration of relatively free filtering suspensions on a large scale, such as the dewatering of mineral concentrates. The dewatering of mineral concentrates requires large capacity in addition to producing a cake with low moisture content. Such large processes are commonly energy intensive and means to lower the specific energy consumption are needed. The vacuum disc filter may comprise a plurality of filter discs arranged in line co-axially d around a central pipe or shaft. Each filter disc may be formed of a number of individual filter sectors, called filter plates, that are mounted circumferentially in a radial plane around the central pipe or shaft to form the filter disc, and as the shaft is fitted so as to revolve, each filter plate or sector is, in its turn, displaced into a slurry basin and further, as the shaft of rotation revolves, rises out of the basin. When the filter medium is submerged in the slurry basin where, under the influence of the vacuum, the cake forms onto the medium. Once the filter sector or plate comes out of the basin, the pores are emptied as the cake is deliquored for a predetermined time which is essentially limited by the rotation speed of the disc. The cake can be discharged by a back-pulse of air or by scraping, after which the cycle begins again. Whereas the use of a cloth filter medium requires heavy duty vacuum pumps, due to vacuum losses through the cloth during cake deliquoring, the ceramic filter medium, when wetted, does not allow air to pass through which does not allow air to pass through, which further decreases the necessary vacuum level, enables the use of smaller vacuum pumps and, consequently, yields significant energy savings.

The filter plate is affected by slurry particles and extraneous compounds, especially in the field of dewatering of mineral concentrates, and as the replacement of a plate can be expensive, the regeneration of the filter medium becomes a critical factor when the time-in-operation of an individual filter plate needs to be increased. The filter medium is periodically regenerated with the use of one or more of three different methods, for example: (1 ) backwashing, (2) ultrasonic cleaning, and (3) acid washing. Whereas the regenerative effect of backwashing and ultrasound are more or less mechanical, regeneration with acids is based on chemistry. As another benefit of a ceramic filter medium, the ceramic filter plate is mechanically and chemically more durable than, for example, filter cloths and can, thus, withstand harsh operating conditions and possible regeneration better than other types of filter media. These attributes allow for chemical regeneration of the filter plates with acids, whereas a cloth would have to be discarded, after being blinded by particles, and replaced several times during a year's operation.

Typically, the regeneration is performed periodically, for example 1 ...3 times per day. In an automatic processing, after the disc filter reach a preset filtering time, system may clean itself and go back to the automatic filter- ing process after the cleaning. The regenation or cleaning time is also preset time. The time intervals between regenerations as the duration of the regenerations are typically set once when the disc filter is setup the first time. A problem is that these preset times are typically not optimal ones for achieving the best performance of the disc filter. Moreover, some filter operators may hesitate to the regererate the filter media often enough because the filter is not producing a filter cake during the regeneration period. BRIEF DESCRI PTION OF THE INVENTION

An object of the present invention is to improve the performance of a disc filter. The object of the invention is achieved by an apparatus, a method, a system and a computer program according to the independent claims. Em- bodiments of the invention are disclosed in the dependent claims.

An aspect of the invention is a rotary disc filter apparatus, particularly a capillary action disc filter, comprising

a rotary drum with a plurality of consecutive co-axial filter discs formed by a plurality of sector-shaped filter plates,

at least one pressure sensor configured to measure the backwash pressure of a washing liquid pumped through a filtrate collector piping to the filter plates in a reverse direction during a backwash zone of each rotation of the filter discs, and

a control system configured to controlling regeneration of the filter plates based on the measured backwash pressure.

In an embodiment, the apparatus comprises

a basin for containing a suspension of particulate material, the sector-shaped filter plates are mounted circumferentially in a radial plane around the central longitudinal axis of the rotary drum to form a re- spective disc,

the filtrate collector piping is in fluid communication with interiors of the filter plates,

means for revolving the rotary drum around the central longitudinal axis such that each filter plate in turn is displaced into the basin and out of the basin,

means for providing a partial vacuum to the filter collector piping and to the filter plates so as to dry the suspension of particulate material in a basin of by suction of a filtrate of the suspension through the filtrate collector piping and the filter plates onto which filtrate cakes are formed and removed from the filter plates during a first portion of each rotation,

means for cleaning the filter plates by pumping the washing liquid through the collector piping and the filter plates in a reverse direction with a backwash pressure during a second portion of each rotation,

at least one pressure sensor configured to measure the backwash pressure in the collector piping,

a controller configured to monitor the measured backwash pressure from the at least one pressure sensor.

In an embodiment, the filtrate collector piping comprises a dedicated collector pipe for each row of the filter plates of a same sector of the consecutive co-axial filter discs, and wherein the at least one pressure sensor compris- es at least one pressure sensor in each of the dedicated collector pipes, preferably one pressure sensor in each of the dedicated collector pipes at one end of the rotary drum.

In an embodiment, the filtrate collector piping comprises a dedicated collector pipe for each row of the filter plates of a same sector of the consecu- tive co-axial filter discs, and wherein the filtrate collector piping comprises a dedicated filtrate tube for each filter plate for connecting the filter plate to the respective collector pipe, and wherein the at least one pressure sensor comprises a pressure sensor in at least one of the dedicated filtrate tube in each row of the filter plates, preferably in the dedicated filtrate tube of the last filter plate in each row of the filter plates.

In an embodiment, the apparatus comprises a controller configured to monitor measured peak values of the backwash pressure from the at least one pressure sensor and to perform a predetermined action if the measured peak value of the backwash pressure reaches a predetermined threshold val- ue.

In an embodiment, the apparatus comprises a position sensor, preferably an inclinometer, providing position data on the row of the filter plates where the peak value of the backwash pressure reaching a predetermined threshold value is measured.

In an embodiment, the controller is arranged in the rotary drum of the disc filter apparatus, and the apparatus comprising an inductive power transfer unit arranged to energize the controller from a stationary part of the disc filter apparatus by means of an inductive power transmission

In an embodiment, the controller is arranged in the rotary drum of the disc filter apparatus, and the apparatus comprising a wireless, preferably inductive, signal transfer unit arranged to transfer signals from the controller to a stationary part of the apparatus.

Another aspect of the invention is a method for controlling a for a rotary disc filter, particularly a capillary action disc filter, comprising a rotary drum with a plurality of consecutive co-axial filter discs formed by a plurality of sector-shaped filter plates, the method comprising measuring a backwash pressure of a washing liquid pumped through a collector piping to the filter plates in a reverse direction during a backwash zone of each rotation of the filter discs, and

controlling regeneration of the filter plates based on the measured backwash pressure.

In an embodiment, the controlling comprises controlling the rotary disc filter into a regeneration mode of operation, if a measured peak value of the backwash pressure reaches a predetermined threshold value.

In an embodiment, the controlling comprises notifying an operator of the rotary disc filter, if a measured peak value of the backwash pressure reaches a predetermined threshold value, in order to prompt the operator to manually control the rotary filter disc apparatus into a regeneration mode of operation.

In an embodiment, the controlling comprises controlling duration of an individual regeneration of the filter plates based on the measured backwash pressure.

In an embodiment, the controlling comprises controlling a time interval between individual regenerations based on the measured backwash pressure.

In an embodiment, the controlling comprises optimizing an average filtering capacity of the filter plates and/or the minimizing the regeneration time.

In an embodiment, the controlling comprises the optimizing a filtrate cake production time of the rotary filter disc apparatus.

In an embodiment, the controlling comprises

evaluating a permeability of the filter plates based on the measured backwash pressure,

increasing duration of an individual regeneration if the permeability is evaluated to be less than a first threshold,

decreasing duration of an individual regeneration if the permeability is evaluated to be less than a second threshold.

In an embodiment, the controlling comprises

evaluating a permeability of the filter plates based on the measured backwash pressure,

notifying an operator of the rotary disc filter if at least one of the filter plates remains blocked based on the evaluated permeability after several regenerations. In an embodiment, the measuring comprises measuring a backwash pressure separately for each row of the filter plates of a same sector of the consecutive co-axial filter discs.

In an embodiment, the measuring comprises measuring a backwash pressure at or close to location of the last filter plate in each row of the filter plates.

In an embodiment, the method comprises determining the measured sector of the consecutive co-axial filter discs based on an angular position of the filter discs at the time of measurement.

Still another aspect of the invention is a control system for implementing the control method.

Still another aspect of the invention is a computer program comprising program code for performing the control method, when the program is run on one or more computer or processor. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of example embodiments with reference to the accompanying drawings, in which

Figure 1 is a perspective top view illustrating an exemplary disc filter apparatus, wherein embodiments of the invention may be applied;

Figure 2 is a perspective top view illustrating an exemplary drum, wherein embodiments of the invention may be applied;

Figure 3 is a perspective cutaway diagram illustrating details of an exemplary drum;

Figure 4 is a front view illustrating details of an exemplary drum;

Figure 5 is a perspective top view of an exemplary sector-shaped ceramic filter plate;

Figures. 6A, 6B and 6C illustrate exemplary structures of a ceramic filter plate wherein embodiments of the invention may be applied;

Figures 7A, 7B, 7C, 7D and 7E illustrate different phases of a filtering process;

Figure 8A illustrates a backwash pressure sensor provided in a filtrate tube according to exemplary embodiments of the invention;

Figure 8B illustrates a connection of a backwash pressure sensor to in a filtrate tube according to exemplary embodiments of the invention; Figure 9 illustrates a connection of a backwash pressure sensor to in a filtrate collector pipe according to exemplary embodiments of the invention;

Figure 10 is a block diagram illustrating a sensor control unit accord- ing to an exemplary embodiment of the invention;

Figure 10B is a flow diagram illustrating an exemplary operation of a sensor control unit;

Figure 1 1 is a perspective top view illustrating an inductive power and signal transfer unit according to an exemplary embodiment of the inven- tion;

Figure 12 is a flow diagram illustrating a regeneration optimization according to an exemplary embodiment; and

Figure 13 is a flow diagram illustrating a regeneration optimization according to another exemplary embodiment. DESCRIPTION OF EXEMPLARY EMBODIMENTS

Principles of the invention can be applied for drying or dewatering fluid materials in any industrial processes, particularly in mineral and mining industries. In embodiments described herein, a material to be filtered is referred to as a slurry, but embodiments of the invention are not intended to be restricted to this type of fluid material. The slurry may have high solids concentration, e.g. base metal concentrates, iron ore, chromite, ferrochrome, copper, gold, cobalt, nickel, zinc, lead and pyrite.

Figure 1 and 2 are perspective top views illustrating an exemplary disc filter apparatus and an exemplary drum 20, respectively, in which embodiments of the invention may be applied. The exemplary disc filter apparatus 10 comprises a cylindrical-shaped drum 20 that is supported by bearings 13 and 17 on a frame 8 and rotatable about the longitudial axis of the drum 20 such that the lower portion of the drum is submerged in a slurry basin 9 located below the drum 20. A drum drive 12 is provided with a drive unit 12 (such as an electric motor, a gear box,) for rotating the drum 20. The drum 20 comprises a plurality of ceramic filter discs 21 arranged in line co-axially around the central axis of the drum 20. For example, the number of the ceramic filter discs may range from 2 to 20. The diameter of each disc 21 may large, ranging from 1 ,5 m to 4 m, for example. Examples of commercially available disc filters wherein in which embodiments of the invention may be applied, include Ceramec CC filters, models CC-6, CC-15, CC-30, CC-45, CC- 60, CC-96 and CC-144 manufactured by Outotec Inc.

Figure 3 is a perspective cutaway diagram and Figure 4 is a front view illustrating details of an exemplary drum 20 wherein embodiments of the invention may be applied. Figure 5 is a perspective top view of an exemplary sector-shaped ceramic filter plate 22. In Figures 3 and 4, only one of the plurality of filter discs 21 is shown, but the other filter discs in the disc row can be preferably essentially similar in structure as can be seen in Figures 1 and 2. Each filter disc 22 may be formed of a number of individual sector-shaped ceramic filter elements, called filter plates 22, that are mounted circumferentially in a radial planar plane around the central axis of the drum to form an essentially continuous and planar disc surface. The number of the filter plates may be 12 or 15, for example. The filter plate 22 may be provided with mounting parts, such as fastening openings 26, 27 and 28 which function as means for attaching the plate 22 to mounting means in the drum. In example embodiments shown in Figures 3 and 4 the filter plates 22 may be assembled on a round rim structure 23 that can be mounted on a central sylinder or shaft 25 by means of radial spokes 24a (similar to a spoke wheel). The rim structure 23 may have holes or other means in which the mounting parts 26, 27 and 28 of the filter plates 22 can be attached. The filter plate 22 may also be provided with mounting part 29, such as a tube connector 29, which functions as means for providing the internal fluid duct of the filter plate 22 with a fluid connection with a collector piping 30 in the drum. In example embodiments shown in Figures 3 and 4 each filter plate 22 is connected to collector piping 30 with hoses 31 . In exemplary embodiments the filter plates 22 are disposed in rows and there may be a number of collector pipes 30 the longitudinal direction of the drum, the task of which is to connect the filter plates that are disposed in the same row; i.e. there may be as many collector pipes 30 as there are rows of filter plates 3 (preferably one collector pipe 30 for each sector of the filter disc 21 ). As illustrated in Figure 2, the collector pipes 30 may be connected to a distributing valve 14 disposed on the axis of the filter, the task of which distributing valve 14 is to transmit the partial vacuum or overpressure to the filter plates 22. The distributing valve 14 may comprise zones such that a part of the filter plates 22 contain a partial vacuum (in this case there is cake formation and cake drying) or overpressure (in which case cleaning of the filter elements with water or filtrate is performed with reverse pressure). If a long drum is used, it can be advantageous to dispose the distributing valve at both ends of the drum. A vacuum system may be provided that may comprise a filtrate tank 2 and a vacuum pump 3 and a filtrate pump 1 . The vacuum pump 3 maintains a partial vacuum in the piping 30 of the filter and the filtrate pump 1 removes the filtrate. It is possible to arrange reverse flushing or backwash either such that some of the filtrate or clean water from an external water source is led back to the collector piping by means of a backwash system, such as a backwash pump. The filter plates 22 may be periodically regenerated with the use of one or more of three different methods, for example: backwashing 4, ultrasonic cleaning 6, and acid washing 7. Operation of the disc filter may be controlled by a filter control unit 5, such as a Programmable Logic Controller, PLC.

Figures. 6A, 6B and 6C illustrate exemplary structures of a ceramic filter plate wherein embodiments of the invention may be applied. A micropro- rous filter plate may be made of alumina sintered in high temperature to achieve mechanically strong and abrasion resistant material. A microporous filter plate 22 may comprises a first suction wall 61 A, 62A and an opposed second suction wall 61 B, 62B. The first suction wall comprises a microporous membrane 61 A and a microporous substrate 62A, whereon the membrane 61 A is positioned. Similarly, the second suction wall comprises a microporous membrane 61 B and a microporous substrate 62B. An interior space 63 is defined between the opposed first and second suction walls 61 A, 62A and 61 B, 62B resulting in a sandwich structure. The interior space 63 is provides a flow canal or canals which will have a flow connection with collector pipe 30 in the drum 20 through the connecting means 29 and the hose 31 . When the collector pipe 30 is connected to a vacuum pump, the interior 63 of the filter plate 22 is maintained at a negative pressure, i.e. a pressure difference is maintained over the suction wall. The membrane 61 contains micropores that create strong capillary action in contact with water. This microporous filter medium allows only liquid to flow through. Filtrate is drawn through the ceramic plate 22 as it is immersed into the slurry basin 9, and a cake 65 forms on the surface of the plate 22. The liquid or filtrate into the central interior space 63 is then transferred along the filtrate tube 31 into the collector pipe and further out of the drum 20. The interior space 64 may be an open space or it may be filled with a granular material which acts as a reinforcement for the structure of the plate. Due to its granular nature, the material does not prevent the flow of liquid that enters into the central interior space 63 since the granular material does not present a major resistance to liquid flow. The interior space 63 may further comprise supporting elements or partition walls to further reinforce the structure of the plate 22. The edges 64 of the plate may be reinforced by means of glazing.

As the row of the filter discs 21 rotate, the plates 22 of the each disc 22 move into and through the basin 9. Thus, each filter plate 22 goes through four different process phases or sectors during one rotation of the disc 21 . In a cake forming phase, the liquid is passing through the plate 22 when it travels through the slurry, and a cake is formed on the plate surface, as illustrated in Figure 7A. The plate 22 enters the cake drying phase (illustrated in Figure 7B) after it leaves the basin 9. If cake washing is required, it is done in the beginning of the drying phase. In the cake discharge phase illustrated in Figure 7C the cake is scraped off by ceramic scrapers so that a thin cake is left on the plate 22 (gap between the scraper and the plate 22). In the backflush (backwash) phase of sector of each rotation, a backwas liquid is pumped in a reverse directioin through the plate with a sufficiently high pressure, as illustrated in Figure 7D. The backflush liquid removes the particles by an 'in-to- out' flow of liquid across the membrane walls thereby washing off the residual cake and cleans the pores of the filter plate. Proper backflush is important for the filter operation and to maintain high dynamic capacity in the filter media. Backflush pressure may range from about 0,9 bar up to 2,5 bar, for example, depending on the application and the size of the filter discs. It is possible to arrange reverse flushing either such that some of the filtrate is led back to the filter plates or such that an external water source is used.

However, backflushing does not remove all residue. Residue remain on the capillary filter despite the backflushing, which continue to compromise the performance of the capillary filter. Filter media blinding is determined as the phenomena causing the blocking of channels through which the liquid would normally flow. Consequently, a loss in filtration capacity and increased cake moisture can be observed. Blinding of the filter medium has an immediate effect on filtration: the filter medium resistance is increased, leading to a decreased filtrate rate, and sufficient cake discharge becomes more difficult. Consequently, a loss in filtration capacity can be observed.

Therefore, as illustrated in Figure 7E, the filter plate 22 may be periodically regenerated with the use of one or more of three different methods, for example: (1 ) backwashing, (2) ultrasonic cleaning, and (3) acid washing. A combined wash ( acid and ultrasonic ) is most effective. Typical acids used in the acid washing incude nitric acid and oxalic acid. During the cleaning operation, the materials and foreign matters stopped in pores of a filter plate or absorbed on the surface of a filter plate are cleaned out, and the function of the filter plate is restored.

The regeneration or cleaning phase may be started when the capacity of filter has dropped below a predetermined value. Typically, the regeneration may be performed periodically, for example 1 ...3 times per day. In an automatic processing, after the disc filter reach a preset filtering time, system may clean itself and go back to the automatic filtering process after the cleaning. The regenation or cleaning time may typically be 40...60 minutes, for example. Typically, the regeneration is performed periodically, for example 1 ...3 times per day. In an automatic processing, after the disc filter reach a preset filtering time, system may clean itself and go back to the automatic filtering process after the cleaning. The regenation or cleaning time is also preset time. The time intervals between regenerations as the duration of the regenerations are typically set once when the disc filter is setup the first time. A well-operating backwash and sufficiently frequent regeneration will secure a high average filtration capacity. The regeneration interval (the time elapsed between two regenerations) has an essential influence on the overall average titration capacity. A problem is that these preset times are typically not optimal ones for achieving the best performance of the disc filter. Moreover, some filter operators may hesitate to the regererate the filter media often enough because the filter is not producing a filter cake during the regeneration period.

An aspect of the invention is a disc filter that comprises at least one pressure sensor arranged in the filtrate collector piping and configured to measure the backwash pressure of a washing liquid pumped through a filtrate collector piping to the filter plates in a reverse direction during a backwash zone of each rotation of the filter discs. The regeneration of the filter plates may be automatically or manually controlled based on the measured backwash pressure.

In an embodiment, a filtrate collector piping comprises a dedicated collector pipe 30 for each row of the filter plates 22 of a same sector of the consecutive co-axial filter discs 20, as discussed above and illustrated in Figures 2, 3 and 4. At least one backwash pressure sensor is provided for each row of the filter plates 22. In practice, although it would be possible to install a dedicated backwash pressure sensor for each filter plate 22 in order to obtain plate-specific pressure data, this is not practical from the point of the number of the pressure sensors required, the amount of installation work and cabling, and the overall cost. Typically it is sufficient to have information of the backwash pressure for each row of the filter plates, for example. The possible blinding of an individual filter plate may not have a significant effect on the overall capacity of the disc filter. Typically one pressure sensor for each row the filter plates may be sufficient. Best result may be achieved if the pressure sensor is locat- ed at an end of the drum.

In an embodiment, a pressure sensor 32 may be arranged in at least one of the filtrate tubes 31 in each row of the filter plates, preferably in the filtrate tube 31 of the last filter plate 22 in each row, as illustrated in Figures 4, 8A and 8B. The pressure sensor 32 may be connected to a T connector 33 installed in the filtrate tube 31 that connects the hose connector 29 of the filter plate to the respective collector pipe 30. The pressure sensor 32 may act as a transducer that generates an electrical pressure signal as a function of the backwash pressure imposed in the filtrate tube 31 . Pressure sensors (called also pressure transducers or pressure transmitters) are generally available with three types of electrical output; millivolt, amplified voltage and 4-20mA current. The electrical pressure signal may be supplied over a measurement wiring 34 to a sensor controller 100 which will be discussed below. Installing the backwash pressure sensor 32 is especially advantageous when the backwash pressure sensing according to the invention is applied to an existing disc filter in a plant.

In an embodiment, a T connector 33 or another type of connector may be integrated in the filter plate 22, such as in a hose connector 29 of the filter plate 22, which allows installing a backwash pressure sensor 32, if required. When a backwash pressure sensor 32 is not installed, the respective port of the T connector or like may be capped.

In an embodiment, the filter plate 22 may be provided with a backwash pressure sensor 32. In an embodiment, the hose connector 29 in the filter plate 22 may be provided with connector means ns, such for connecting a backwash pressure sensor 32.

In an embodiment, at least one pressure sensor 32 may be arranged in the filtrate collector pipe 30 in each row of the filter plates 22. The pressure sensor 32 may be connected to a T connector 33 in the filtrate collector pipe 30 at one end of the rotary drum 20, as illustrated in Figure 9.

In an embodiment the drum 20 of the disc filter is provided with a sensor control unit configured to monitor the backwash pressure sensors 32, when the disc filter 10 is in operation. Figure 10A is a block diagram illustrating an exemplary sensor control unit 100 and its connections to sensors on the drum and to the filter control unit 5 in the stationary part of the disc filter. Figure 10B is a flow diagram illustrating an exemplary operation of the sensor control unit 100. The sensor controller 100 may comprise a processor (CPU) 101 with a memory configured to store program code and dynamic data. For example, the processor 101 may be a C-programmable micro controller. The electrical pressure signals (e.g. 4-20mA currents) received from the backwash pressure sensors 32 over the measurement wiring 34 may be connected to an input unit 102 and read by the processor 101 . The input unit 1 02 may be a digitizer unit. In the exemplary controller, one backwash pressure sensor 32 is provided for each row of the filter plates 22, thereby the input unit 102 is connected to monitor 15 backwash pressure sensor 32 (number of sectors being 15). Digitized inputs corresponding to the 15 received electrical pressure signals may be applied to the processor CPU 101 . The input unit 102 may be a multiplexer type unit so that the processor 101 may read an electrical pressure signal of one backwash pressure sensor 32 at time. The processor 101 may forward the raw backwash pressure sensor data or pre-processed backwash pressure sensor data through the output unit 104 or 105 to the disc filter unit 5, to an operator screen, or to any corresponding control or maintenance system.

In an embodiment, the processor 101 may forward the maximum backwash pressure, or the pressure peak, measured during a backwash phase, through the output unit 104 or 105 to the disc filter unit 5, to an operator screen, or to any corresponding control or maintenance system. The maximum backwash pressure may comprise the maximum backwash pressure among all the backwash pressure sensors 32 or the maximum backwash pressure of each backwash pressure sensor 32.

In an embodiment, during filtering operation of the disc filter 10 (step 202 in Figure 10B), the processor 101 may monitor or measure the maximum backwash pressure, or the pressure peak, during a backwash phase by means of the pressure sensors 32, preferably for each row of the filter plates 22 (step 204). The processor 101 may send the maximum backwash pressure, or the pressure peak, measured during the backwash phase, through the output unit 104 or 105 to the disc filter control unit 5, to an operator screen, or to any corresponding control or maintenance system (step 210), when a certain criterion is met (step 208), e.g. the maximum backwash pressure or the pressure peak, is reaching a certain level. After sending the backwash pressure in step 210, the process may return to step 204. Also if the criterion is not met in step 208, the procedure may return to step 204.

In an embodiment, a position sensor 107, preferably an inclinometer, may be provided on the shaft or cylinder 25 of the drum 20 to detect the sector of the consecutive co-axial filter discs where the backwash is being performed or where the backwash pressure is measured, based on an angular position of the discs 21 (step 106 in Figure 10B). The output current 4-20mA from the inclinometer 107 corresponds to the position (0-360 degrees) of the drum 20. The inclinometer output current may be received as one input to the input unit 102 that may provide a digitized inclinometer current value for the processor 101 . When the backwash pressure is outputted through the output unit 104 or 105 (step 1 10 in Figure 10B), the processor 101 may also output the inclinometer signal or like data indicating the disc sector which the backwash pressure corresponds to.

In embodiments, the drum 20 may comprise further sensors, such circuit loops 70 arranged in the filter plates 22 for detecting a break in the filter plates 22, which sensors may also be connected to the input unit 102 or 103 and read by the processor 101 . The processor 101 may forward the further sensor information through the output unit 104 or 1 05 to the disc filter controller 9, to an operator screen, or to any corresponding control or maintenance system.

In an embodiment, the disc filter comprises an inductive power transfer unit 106 arranged to energize the sensor controller 100 of the drum 20 from a stationary part of the disc filter by means of an inductive power trans- mission. As result, no additional power source, such as a battery, is required in the drum 20.

In an embodiment, the inductive power transfer unit 106 comprises an inductive transmitter on the drum side and an inductive receiver on the stationary part of the disc filter to inductively transfer signals from the sensor con- trailer 100 to the stationary part of the disc filter.

In an embodiment, wireless radio transmitter or other kind of wire- less transmission medium is employed to transfer signals from the sensor controller 100 to a stationary part of the disc filter.

In an embodiment, a galvanic connection is employed to transfer signals from the sensor controller 100 to a stationary part of the disc filter.

In an embodiment, the inductive power and signal transfer unit 106 comprises an inductive slip ring 120 is attached to the frame 8 of the disc filter, and a pair of inductive half-rings 124 and 125 attached to around the shaft 25 of the drum 25, as illustrated in in Figure 1 1 . The slip ring 120 may contain a permanent magnet. The semi-rings 124 and 125 may each comprise a coil connected to a power supply of the sensor controller 100 within a ring-shaped housing attached around the shaft 25. When the semi-rings 124 and 125 rotate within the slip ring 120, a current is induced in the coils for the power supply which generates a supply voltage for the controller unit 100 and possible other electric circuitry in the drum. The coil of the semi-ring 124 and the coil of the semi-ring 125 may operate as inductive transmitters for signals from the output unit 104 and the output unit 105, respectively. When a signal is outputted from the output unit to the coil of the semi-ring 124, the current in the transmitter coil is modulated accordingly, which can be detected by a receiver coil in an inductive receiver 106A provided on the slip ring 120. The inductive receiver 120 may forward the signal further to the disc filter controller 5 over a cable or like. Similarly, a signal is outputted from the output unit to the transmitter coil of the semi-ring 124 modulates the current in the coil accordingly, which can be detected by the inductive receiver 106A. Thus, using the semi-rings 1 24 and 125, a two-channel inductive signal transfer can be implemented.

An aspect of the invention is a regeneration optimization based on backwash pressure data obtained from the backwash pressure sensors 32. Figure 12 is a flow diagram illustrating a regeneration optimization according to an exemplary embodiment. When the disc filter 10 is in operation (step 302 in Figure 12), the pressure sensors 32 are following the maximum backwash pressure or backwash pressure pulses in the piping 30 and 32, and the regeneration optimization process in the disc filter control unit 5 or an may receive (step 304) raw backwash pressure data or maximum backwash pressure data from the sensor control unit 100.

When the backwash pressure peaks reach a certain pressure level or another criterion is met (step 306), e.g. the a filtration capacity or the permeability of the filter plates decreases to a too low level, the disc filter control unit 5 may automatically go to a regeneration mode, particularly to an acid washing mode (step 308). In an alternative embodiment, an operator of the disc filter 10 may turn on the regeneration mode (step 312), particularly to the acid washing mode, based on a notification or data displayed on an operator screen (step 310). Thus, according to an aspect of the invention the starting time of the new regeneration can be dynamically set according to the actual average filtering capacity or the actual average permeability of the filter plates. The filtration capacity and the filtrate production can be maintained at a higher level, since the invention enables to start the regeneration exactly and only when needed.

In the regeneration mode, the disc filter control unit 5 controls the acid washing system 7 and/or the ultrasonic cleaning system 6 to clean out the materials and foreign matters stopped in pores of a filter plate or absorbed on the surface of a filter plate are cleaned out, such that the function of the filter plate is restored. When the regeneration cycle is over, the disc filter control unit 5 may automatically go back to the filtering process. The regenation or cleaning time may be a preset period of time or set dynamically for each regeneration cycle.

In an embodiment, the regenation or cleaning time may be adjusted dynamically (automatically or manually) based on backwash pressure data obtained from the backwash pressure sensors. Figure 13 is a flow diagram illustrating a regeneration optimization according to another exemplary embodiment. When the regeneration cycle is over and the disc filter operation is restarted (step 402), the disc filter wash optimization starts again to receive backwash pressure data, e.g. the values of the pressure pulses, measured for each row of the filter plates during backwash (step 404). The measured backwash pressure pulses may be compared with one or more limits or a desired range (step 406). The one or more limit is preferably lower the regeneration criterion. If the back pressure peak is too high (e.g. in comparison with a limit value) after a regeneration cycle, that may indicate that the regeneration cycle was too short in time to clean the filter plates sufficiently and to restore the best filtration capacity available. Thus, the regeneration time for the next regeneration may be increased to achieve better cleaning result (step 408). Similarly, if the back pressure peak is too low (e.g. in comparison with a limit value) after a regeneration cycle, that may indicate that the regeneration cycle was unnecessary long in time and a shorter regeneration time may be sufficient to clean the filter plates sufficiently and to restore the desired filtration capacity. Thus, the regeneration time for the next regeneration may be shortened (step 408). In an alternative embodiment, an operator of the disc filter 10 may adjust the regeneration time (step 412) based on a notification or data displayed on an op- erator screen (step 410). After the adjusting step 408 or 412, the monitoring process illustrated in Figure 12 may continue.

In other words, this action may decrease a regeneration time (particularly the acid washing time), if the permeability of the ceramic plates is too high (the time has been too long), or increase the regeneration time, if the permeability of the ceramic plates is too low. Thereby, a controlled plate permeability, optimized regeneration time and increased production can be achieved. Also the consumption of acid will be minimized, as the regeneration time is optimized.

The maximum production time can be taken out of the disc filter, when both the intervals between the regenerations and the regeneration times are optimized.

An example of a backwash pressure range during the regular filter operation may be 0.1 .... 1 .1 bar. The threshold backwash pressure which may trigger the regeneration mode may be 1 .2 bar, for example. The desired back- wash pressure range which may be a target of the regeneration time optimization may be 1 .0 ....1 .5 bar, for example.

The control techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a firmware or software, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in any suitable, processor/computer-readable data storage medium(s) or memory unit(s) and executed by one or more processors. The data storage medium or the memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art. Additionally, components of systems described herein may be rearranged and/or complimented by additional components in order to facilitate achieving the various aspects, goals, advantages, etc., de-scribed with regard thereto, and are not limited to the precise configurations set forth in a given figure, as will be appreciated by one skilled in the art.

Upon reading the present application, it will be obvious to a person skilled in the art that the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples de- scribed above but may vary within the scope of the claims.