WO2017017312A1

WO2017017312A1 - Method for controlling a filtering process

Info

Publication number: WO2017017312A1
Application number: PCT/FI2016/050540
Authority: WO
Inventors: Antti VESALA; Mika ILLI; Kari VÄNTTINEN
Original assignee: Outotec (Finland) Oy
Priority date: 2015-07-24
Filing date: 2016-07-22
Publication date: 2017-02-02
Also published as: FI126541B; FI20155563A; CL2018000152A1; BR112018001095B1; BR112018001095A2

Abstract

A method for controlling a filter apparatus (1), the filter apparatus (1), comprising a filter (2) formed by a plurality of filter elements (3), the filter (2) being rotatable around longitudinal axis (X) of the filter (2). The method comprises: providing the filter apparatus (1) with several filter elements (3) comprising an identification unit (5) arranged to store an identification code specific for the filter element (3), reading the identification codes of said several filter elements (3) during rotation of the filter (2), performing said reading at least following a change of at least one of the filter elements (3) in the filter (2), repeating said reading at prescribed time intervals, and showing information based on the readings in a visual form, wherein the information includes symbols corresponding to the operation time of an individual filter element (3).

Description

METHOD FOR CONTROLLING A FILTERING PROCESS

Background

The present invention relates to a method for controlling a filter apparatus.

The present invention further relates to a computer program product loadable to a memory of a computer.

The present invention still further relates to a memory means.

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 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. These filter media are commonly used in filter apparatuses having filter comprising multiple filter elements, e.g. in rotary vacuum disc filters and rotary vacuum drum filters.

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 elements or 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.

Vacuum filtration is based on producing a suction within the filtrate channels and thereby forming a cake of mineral on the surface of the filter medium. The most commonly used filter elements in vacuum filters are filter cloths and ceramic filters.

Rotary vacuum drum 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. The vacuum drum filter may comprise a cylindrical support structure rotating around a longitudinal shaft forming a centre axis for the drum. There are a plurality of filter elements or plates arranged on the outer surface of the cylinder. Each filter plate forms a portion of the cylindrical outer surface of the cylinder. Each filter plate is during each revolution of the shaft displaced for a certain period into a slurry basin situated below the shaft. The filter plate rises out of the basin when the revolution of the shaft proceeds. When the filter plate is submerged in the slurry basin a cake forms onto the outer surface of the filter plate due to the vacuum within the filter plate. Once the filter 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 drum. The cake can be discharged by a back- pulse of air or by scraping, after which the cycle begins again. The filter elements of rotary vacuum drum filters are advantageously made of porous ceramic. The filter elements contain micro sized pores, i.e. micropores that create strong capillary action in contact with liquid. This microporous filter medium allows only liquid to flow through.

Common for all said filters is typically a great number of filter elements. This arises a problem that the management of the filter elements, i.e. their history, e.g. installation date or operating hours of a specific element, is very difficult and burdensome to handle.

Brief description

Viewed from a first aspect, there can be provided a method for con- trolling a filter apparatus, the filter apparatus comprising a filter formed by a plurality of filter elements, the filter being rotatable around longitudinal axis of the filter, the method comprising: providing the filter apparatus with several filter elements comprising an identification unit arranged to store an identification code specific for the filter element, reading the identification codes of said several filter elements during rotation of the filter, performing said reading at least following a change of at least one of the filter elements in the filter, repeating said reading at prescribed time intervals, and showing information based on the readings in a visual form, wherein the information includes symbols corresponding to the operation time of an individual filter element.

Thereby a method facilitating of the management of the filter elements may be achieved.

Viewed from a second aspect, there can be provided a computer program product for executing the method of claim 1 and loadable to a memory of a filter control unit, the computer program product comprising pro- gram code which, when executed by the processor of filter control unit, makes the filter control unit: read the identification codes of said several filter elements during rotation of the filter, perform said reading at least following a change of at least one of the filter elements in the filter, repeat said reading at prescribed time intervals, and show information based on the readings in a visual form, the information including symbols corresponding to the operation time of an individual filter element.

Thereby a computer program product facilitating of the management of the filter elements may be achieved.

Viewed from a third aspect, there can be provided a memory means for a memory means, comprising a computer program product as claimed in claim 22.

Thereby a memory means facilitating of the management of the filter elements may be achieved.

The method, the computer program product and the memory means are characterised by what is stated in the independent claims. Some other embodiments are characterised by what is stated in the other claims. Inventive embodiments are also disclosed in the specification and drawings of this patent application. The inventive content of the patent application may also be defined in other ways than defined in the following claims. The inventive con- tent may also be formed of several separate inventions, especially if the invention is examined in the light of expressed or implicit sub-tasks or in view of obtained benefits or benefit groups. Some of the definitions contained in the following claims may then be unnecessary in view of the separate inventive ideas. Features of the different embodiments of the invention may, within the scope of the basic inventive idea, be applied to other embodiments.

Brief description of figures

Some embodiments illustrating the present disclosure are described in more detail in the attached drawings, in which

Figure 1 is a perspective top view of an exemplary disc filter apparatus,

Figure 2 is a cutaway view of the disc filter apparatus shown in Figure 1 and seen in axial direction,

Figure 3 is a perspective top view of an exemplary drum filter apparatus,

Figure 4 illustrates an embodiment of a disc filter element,

Figure 5 illustrates an embodiment of a drum filter element, Figure 6 illustrates an embodiment of a method for controlling a filter apparatus, and

Figure 7 is showing an embodiment of visualisation of the infor- mation based on the readings of the identification units.

In the figures, some embodiments are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.

Detailed description

Principles of the embodiments can be applied for drying or dewater- ing 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 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 is a perspective top view illustrating an exemplary filter apparatus, and Figure 2 is a cutaway view of the filter apparatus shown in Figure 1 .

The filter apparatus 1 shown here is a disc filter apparatus that comprises a filter 2 consisting of several consecutive co-axial filter discs 16 arranged in line co-axially around the central shaft 4 of the filter 2.

The filter 2 is supported by bearings on a frame 23 of the filter apparatus 23 and is rotatable about the longitudinal axis X of the filter 2 such that the lower portion of the filter 2 is submerged in a slurry basin 24 located below the filter 2. The filter is rotated by e.g. an electric motor not shown in Figure 1 .

The number of the filter discs 16 may range from 2 to 20, for example. The diameter of each disc 16 may be ranging from 1 .5 m to 4 m, for example. Examples of commercially available disc filters include Outotec Larox CC filters, models CC-6, CC-15, CC-30, CC-45, CC-60, CC-96 and CC-144 manufactured by Outotec Inc.

All the filter discs 16 can be preferably essentially similar in structure. Each filter disc 16 may be formed of a number of individual sector-shaped filter elements 3, called filter plates, which are mounted circumferentially in a radial planar plane around the central shaft 4 of the filter to form an essentially continuous and planar disc surface. The number of the filter plates may be 12 or 15, for example.

Operation of the disc filter apparatus may be controlled by a filter control unit, such as a Programmable Logic Controller, PLC.

Function of disc filter apparatus has already described in background part of this description.

The filter apparatus 1 comprises several filter elements 3 comprising an identification unit 5. In an embodiment, all the filter elements 3 of the filter 2 are provided with the identification unit 5.

The identification unit 5 stores an identification code specific for the filter element 3. The identification unit 5 comprises a transmitter apparatus 6 for wireless communication of an identification signal comprising said identification code such that the identification code is readable or receivable by the receiver means 8 of a receiver apparatus 7.

Just one identification unit 5 is shown in Figure 2 for sake of clarity, but it is clear that every filter element 3 may comprise an identification unit of its own.

In an embodiment, the identification unit 5 is a RFID (Radio Frequency Identification) tag or transponder and the transmitter apparatus 6 is the antenna of said RFID tag. Thus the identification signal is a radio frequency signal, and the receiver apparatus 7 is a RFID reader device. The RFID tag may be passive, semi-passive or active RFID tag. As an embodiment of RFID technology, NFC (Near Field Communication) equipment may be used.

The receiver means 8 comprises an antenna 10 tuned to receive the identification signal send by the identification unit 5. In the embodiment shown in Figure 1 , the antenna 10 is arranged into an antenna module 1 1 .In embodiments using RFID technology, the antenna 10 is an RFID reader antenna, the type of which may be e.g. dipole antenna, circular polarization antenna, mono- static circular antenna or bistatic circular antenna.

In an embodiment, the identification unit 5 is an optically readable identification unit and the receiver apparatus 7 comprises an optical reader, the identification signal being thus an optical signal. The optically readable identification unit may comprise e.g. a bar code, data matrix code or QR (Quick Response) code.

In an embodiment, the filter apparatus 1 comprises one receiver ap- paratus 7 per one filter disc 16 such that each of the receiver apparatus 7 is arranged for receive the identification codes from the transmitter apparatuses 6 of one specific filter disc 16 only. An advantage is that a reliable and correct reading of the transmitter apparatuses 6 can be ensured although the filter elements 3 are covered by a layer of ore.

In an embodiment, the rotational position of the filter 2 is determined by a position indicator 42. This way the row of the filter element(s) 3 being read by the receiver apparatus 7 can be identified.

An advantage is that not only the filter elements 3 can be monitored and their history data collected, but also data about the filter body 43 can be collected. The filter body 43 is provided with mounting means to which the filter elements 3 are attached. There may be variations in the properties of the filter body 43, e.g. in the mounting means, that have contribution to the service life of the filter elements 3. These variations can be discovered in history data collected in a long-term monitoring of the filter. Thanks to the position indicator 42, this history data is not lost even in case where all the filter elements 3 in the filter 2 are changed at the same time.

The position indicator 42 may comprise e.g. an inductive sensor, inclinometer, an identification tag fixedly arranged in the filter 2, such as a RFID tag, etc.

In an embodiment, the output signal is send to a database 22 that comprises identification information of all the filter elements 3 of the filter apparatus 1 . This embodiment is discussed more detailed later in this description.

In an embodiment, the receiver means 8 comprises an antenna 10 that is arranged in an antenna module 1 1 . The antenna module 1 1 may comprise a frame 12 supporting the antenna 10 and a support structure 13 keeping the antenna 10 at a suitable distance from the filter 2. The antenna module may be constructed from one or more antenna module elements 14.

The suitable distance may be selected so that the reading distance, i.e. the distance between the antenna 10 and the identification unit 5 to be read by said antenna 10 is in range of 1 cm - 3 m. In this range the reading of the identification signal can be realized precisely enough for various signalling technology, e.g. RFID, NFC, optical. The reading distance is preferably in range of 2 cm - 2 m. In this range a passive identification unit, e.g. a passive RFID unit, works well during the filtration process. The reading distance is more preferably 5 cm - 70 cm. In this range the reading of the identification signal can be realized optimally and errors in the readings minimized. Additionally, this range is especially suitable for passive RFID unit.

According to another embodiment, the receiver apparatus 7 is fixed in a support frame 26 separate from the frame 23 of the filter apparatus. One example of this embodiment is shown by dashed line in Figure 2. The support frame 26 may be e.g. a part of building structure covering the filter apparatus 1 or a purposively made support structure separate from the frame 23 of the filter apparatus.

Figure 3 is a perspective top view illustrating an exemplary drum filter apparatus.

The drum filter apparatus 1 comprises a filter drum 19, and the filter element 3 is a part of outer surface of said filter drum 19. The diameter of the filter drum 19 may be e.g. in range of 1 .8 m - 4.8 m and length in axial direction 1 m - 10 m. The surface area of the filter may be e.g. in range of 2 - 200 m².

The filter apparatus 1 comprises several filter elements 3 comprising an identification unit 5. In an embodiment, all the filter elements 3 are provided with the identification unit 5.

According to an aspect, the antenna module 1 1 is arranged to locate between a washing station 35 of the filter elements and the slurry basin 24 such that, in direction of rotation of the filter, the antenna module 1 1 follows the washing station 35 and the slurry basin 24 follows the antenna module 1 1 .

Function of drum filter apparatus has already described in background part of this description.

Examples of commercially available drum filters include CDF-6/1 .8 manufactured by Outotec Inc.

Figure 4 illustrates an embodiment of a disc filter element. The filter element 3 comprises a permeable membrane layer 17 made of a porous ceramic on both sides of the filter element 3, and a substrate arranged between said membrane layers 17.

An identification unit 5 described above is arranged in the filter ele- ment 3. In embodiment shown in Figure 4, the identification unit 5 is arranged on the peripheral outer edge surface 28 of the filter element. Thus the distance to the receiver apparatus 7 may be minimized. Of course, the identification unit 5 may be placed in some other part of the filter element. An alternative placement of the identification unit 5 is shown in Figure 4 by dash line. In this em- bodiment the identification unit 5 is arranged close to mounting parts 30 which function as means for attaching the filter element 3 to mounting means in the central shaft of the filter apparatus.

The identification unit 5 may be secured to the filter element by adhesive, fastening elements e.g. screws etc. The identification unit 5 is protect- ed against harsh environment by sealing and/or encapsulation.

Figure 5 illustrates an embodiment of a drum filter element. The main difference of the filter elements of drum filters compared to the filter elements of disc filters is that the latter typically has suction walls on both sides of the filter element, whereas the filter elements of drum filter typically has one suction wall only, on its outer surface. Furthermore, the elements of drum filters have typically rectangular shape as shown in Figure 5. An identification unit 5 described above is arranged in the filter element 3. The placement of the identification unit 5 may be chosen differently to that shown in Figure 5.

Figure 6 illustrates an embodiment of a method for controlling a filter apparatus.

According to an aspect, the information about the identification of the filter elements 3 is collected in a database 22. This information is based on identification codes stored in the identification units 5 and read by receiver means 8 of the receiver apparatus 7 of said filter apparatus 1 .

In an embodiment, the database 22 is arranged in the filter control unit 27. A wireless radio transmitter or other kind of wireless transmission medium may be employed to transfer signals from the receiver means 8 to the filter control unit 27. In another embodiment, a wire communication is employed to transfer signals from the receiver means 8 to the filter control unit 27.

In another embodiment, the database 22' is arranged in a network server that is connected to the filter control unit 27 by wire or wirelessly, e.g. over Internet connection.

In still another embodiment, the database 22" is arranged in a separate external memory means 39, such as an USB stick, a SSD card or a CD-ROM connectable to the filter control unit 27.

It is to be noted that there can be several filter apparatuses 1 situated in different production plants connected to the database 22, 22'.

Receiver apparatuses 7 read the identification units 5 in certain periods or following certain process steps.

According to an aspect, the identification units 5 are read at least following a change of at least one of the filter elements 3 in the filter apparatus 1 . Thus the database 22, 22' is updated automatically in case of change of one or more filter element(s) 3. In other words, the database 22, 22' is synchronized and the individual filter elements 3 are monitored online. This way the identity information of the filter elements 3 in the filter apparatus 1 is always known.

In an embodiment, the identification units 5 are read after every stop of the rotation of the filter 1 .

The identification units 5 may also be read by repeating said reading at prescribed time intervals, e.g. performing the reading on every rotation of the filter 1 . In an embodiment of the method, the identification units 5 or identification data are read only once after every stop of the rotation of the filter 1 . Between said readings, only duration of time, i.e. the operation time of the filter is measured.

In another embodiment the database 22, 22' is synchronized offline, e.g. via USB stick 39 or some other external memory means.

According to an aspect, the database 22, 22' may further include information about installation date and working hours of the filter elements 3. Thus old, soon to be changed filter elements 3 can be found and it is possible to forecast when new filter elements 3 should be purchased. Thus the number of the filter elements 3 kept in stock can be optimized and the maintenance planning of the filter apparatus 1 is easier.

As disclosed earlier in this description, the operation of the filter apparatus may be controlled by a filter control unit 27, such as a Programmable Logic Controller, PLC. The filter control unit 27 may comprise a processor known as such. A computer program product is executed in the processor, and the method being controlled by means of the computer program product. The computer program product comprises program code which, when executed by the processor of filter control unit 27, makes the filter control unit 27:

read the identification codes of said several filter elements 3 during rotation of the filter 2, perform said reading at least following a change of at least one of the filter elements 3 in the filter 2, repeating said reading at prescribed time intervals, and show information based on the readings in a visual form, the information including symbols corresponding to the operation time of an individual filter element 3.

The computer program product may be loaded from an internal memory of the control unit 27. The computer program product may be transferred to the control unit 27 from a separate external memory means 40, such as an USB stick, a SSD card or a CD-ROM. It may also be transferred via a telecommunication network, for example by connecting the control unit 27via a wireless access network to the Internet.

The control unit 27 also comprises a user interface, comprising e.g. a display 41 , via which the operator using the filter apparatus 1 can control the functions of the apparatus and the method. Figure 6 is also showing some process steps relating to the manufacturing of the filter elements 3 and taking place e.g. in filter element factory 32. In this embodiment, the identification units 5 are RFID tags which are encoded, i.e. provided with an identification code, with a RFID printer 31 and attached to the filter elements 3.

In an embodiment, at least part of the information based on the reading of the identification units 5 is reported to a filter element provider, such as the filter element factory 32.

An advantage is that purchasing needs of the filter elements 3 can be forecast and the stock level of the filter elements 3 can be minimized. This decreases operating costs and improves equipment efficiency.

It is to be noted that the process steps disclosed here in connection with Figure 6 are adaptable to both disc filter appartuses and drum filter apparatuses.

Figure 7 is showing an embodiment of visualisation of the information based on the readings of the identification units 5.

The information includes visual symbols 36 corresponding to the operation time of an individual filter element 3. In the embodiment shown in Figure 7, the visual symbol 36 is a pattern style. In another embodiment, the visual symbol 36 may be a colour code.

In an embodiment, the visualization is based on dividing the average life expectation of the filter element 3 into periods of time. For each of the periods of time it is given a visual symbol that is preferably clearly distinct from other said visual symbols. The visual symbol 36 corresponding the operation time of the filter element 3 at the moment of the reading is shown for operators controlling the use of the filter apparatus 1 .

In an embodiment, the life expectation of the filter element 3 is divided into three periods of time:

first period: the operation time of the filter element 3 has not reached more than half of the life expectation;

second period: the operation time of the filter element 3 is more than half of the life expectation but not reached the life expectation; and

third period: the operation time of the filter element 3 exceeds the life expectation.

For instance, the life expectation of the filter element may be 2 years. It is to be noted, however, this just one option to carry out the visualisation and that there are alternative ways to do this.

In an embodiment shown in Figure 7, the visual information relates to a disc filter apparatus. The information is shown in a two-dimensional map 37 where the number of columns corresponds to the number of filter discs 16 and the number of rows corresponds to the number of filter elements 3 arranged in one filter disc 16. In this case, the disc filter apparatus comprises twenty (20) filter discs symbolized by letters A to R, and each filter disc comprises twelve (12) filter elements symbolized by numbers 1 to 12.

In another embodiment, the filter apparatus 1 may be a drum filter apparatus. Then in the two-dimensional map 37 the number of the columns corresponds to the number of filter circles 38 in the drum and the number of rows corresponding to the number of filter elements in one filter circle. The filter apparatus 1 comprises preferably one antenna 10 for one filter circle 38.lt is to be noted, that the visualization can be carried out other way, e.g. by showing the discs or filter circles on the vertical axle of the map and filter elements on the horizontal axle of the map.

The map 37 can be shown in any suitable display connected to the database 22, 22' or filter control unit or any user interface comprising a display.

The map 37 shown in Figure 7 indicates to its reader e.g. that a) there are 214 of totally 240 filter elements are not reached more than half of the life expectation,

b) there are eleven (1 1 ) filter elements the operation time of which is more than half of the life expectation but has not yet reached the life expecta- tion, and

c) there are eight (8) filter elements the operation time of which has exceeded the life expectation.

The operator can read very fast the state of the filter elements in the map 37. The information provided may induce further measures, e.g. the oper- ators can go and check the condition of the filtering process of those filter elements the operation time of which has exceeded the life expectation. If the filtering process looks to be running satisfactory, the filtering process can be kept on without stopping the apparatus.

In case of stopping the apparatus, or at least following a change of at least one of the filter elements 3, the reading of the identification codes of the filter elements 3 is performed. If there is new filter element(s) 3 in the filter 2, the identification code of them is read same way as of the rest of the filter elements 3. The new filter element 3 is automatically identified through its identification code, as well as the placement of the new filter element in the filter is automatically recognized, and calculation of the operation time of the new filter is started.

It is possible that the new filter element is actually not unused. Instead, the new filter element may have been used for some time and have been removed from a filter apparatus for e.g. cleaning or repairing purposes. This kind of newly mounted filter element is identified by its identification code, and the calculation of the operation time is carried on.

In an embodiment, the reason for change or removing of a filter element removed from the filter is shown or indicated in a user interface. In a further embodiment, there is a compulsory stage in the user interface for recording the reason for change, e.g. the starting of the filter apparatus may be prohibited until the reason for change is recorded in the database or the filter control unit.

An embodiment of the visualisation, e.g. the map 37 mentioned above, can include not only the information about the operation time but also further information about the filter elements 3.

In an embodiment, there is provided a visual symbol for a filter element 3 the identification code of which cannot be read. As an example, the map 37 shown in Figure 7 discloses six (6) filter elements 5 in the filter disc Ά', which in some reason are not readable. The reason can be e.g. malfunction of the identification unit.

In an embodiment, there is provided a visual symbol for a filter element 3 the identification code of which has an unidentified nature. As an example, the map 37 shown in Figure 7 discloses one (1 ) filter element 5 in the filter disc 'L', on row '9', which has a readable identification code of that nature.

The method disclosed herein makes it possible to collect lot of in- formation about the filter elements 3, the filter apparatus 1 and the filtering process. Based on said information it is possible to produce statistical information and statistical investigations regarding the filter elements, the filter apparatus and the filtering process. For instance, the average life expectation of the filter element can be revaluated based on realized operation times of the filter ele- ments. It is also possible to find differences, if any, in the average life expectation between different filter apparatuses, or between filter discs or filter circles arranged in the same filter apparatus.

The invention is not limited solely to the embodiments described above, but instead many variations are possible within the scope of the inventive concept defined by the claims below. Within the scope of the inventive concept the attributes of different embodiments and applications can be used in conjunction with or replace the attributes of another embodiment or application.

The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the inventive idea defined in the following claims.

Reference symbols

1 filter apparatus

2 filter

3 filter element

4 central shaft

5 identification unit

6 transmitter apparatus

7 receiver apparatus

8 receiver means

10 antenna

1 1 antenna module

12 frame of the antenna module

13 support structure

14 module element

16 filter disc

17 porous membrane layer

19 filter drum

22, 22', 22" database

23 frame of the filter apparatus

24 slurry basin

26 support frame

27 filter control unit

28 peripheral outer edge surface

30 mounting parts

31 RFID printer

32 filter element factory

35 washing station

36 visual symbol

37 map

38 filter circle

39 external memory means

40 external memory means for computer program product

41 display

42 position indicator

43 filter body

D reading distance

H horizontal level

L, L' line

X longitudinal axis

Claims

1 . A method for controlling a filter apparatus, the filter apparatus comprising a filter formed by a plurality of filter elements,

the filter being rotatable around longitudinal axis of the filter, the method further comprising:

providing the filter apparatus with several filter elements comprising an identification unit arranged to store an identification code specific for the filter element,

reading the identification codes of said several filter elements, repeating said reading at prescribed time intervals,

the method further comprising:

reading the identification codes of said several filter elements during rotation of the filter,

performing said reading at least following a change of at least one of the filter elements in the filter, and

showing information based on the readings in a visual form, wherein the information includes symbols corresponding to the operation time of an individual filter element.

2. The method according to claim 1 , performing the reading following every stop of the rotation of the filter.

3. The method according to claim 1 or 2, performing the reading on every rotation of the filter.

4. The method according to any one of the preceding claims, wherein the visual symbol is a colour code.

5. The method according to any one of the preceding claims, dividing the average life expectation of the filter element into periods of time,

giving a visual symbol for each of the periods of time, and showing the filter element by the visual symbol corresponding the operation time of said filter element at the moment of the reading.

6. The method according to claim 5, dividing the life expectation of the filter element into three periods of time:

first period: the operation time of the filter element has not reached more than half of the life expectation;

second period: the operation time of the filter element is more than half of the life expectation but not reached the life expectation; and

third period: the operation time of the filter element exceeds the life expectation.

7. The method according to any one of the preceding claims, further providing a visual symbol for a filter element the identification code of which cannot be read.

8. The method according to any one of the preceding claims, further providing a visual symbol for a filter element the identification code of which has an unidentified nature.

9. The method according to any one of the preceding claims, comprising reporting the information to a filter element provider.

10. The method according to any one of the preceding claims, comprising showing reason for change of a changed filter element.

1 1 . The method according to claim 10, comprising a compulsory stage in a user interface for recording the reason for change.

12. The method according to any one of the preceding claims, comprising step for revaluating of the average life expectation based on realized operation times of the filter elements.

13. The method according to any one of the preceding claims, providing a RFID tag as the identification unit.

14. The method according to any one of the preceding claims, providing all the filter elements of the filter with the identification unit.

15. The method according to any one of the preceding claims, wherein the filter apparatus is a disc filter apparatus, the method comprising providing the visual information in a two-dimensional map where the number of columns corresponds to the number of filter discs and the number of rows corresponds to the number of filter elements in one filter disc.

16. The method according to claim 15, comprising reading one filter disc by one receiver means, thus the column being defined by the receiver means.

17. The method according to claim 16, comprising reading one filter disc by one antenna.

18. The method according to any one of claims 1 - 14, wherein the filter apparatus is a drum filter apparatus, the method comprising

providing the information in a two-dimensional map where the number of the columns corresponds to the number of filter circles in the drum and the number of rows corresponding to the number of filter elements in one filter circle.

19. The method according to claim 18, comprising reading one filter circle by one receiver means, thus the column being defined by the receiver means.

20. The method according to claim 19, comprising reading one filter circle by one antenna.

21 . The method according to any one of the preceding claims, comprising

determining the rotational position of the filter by a position indicator.

22. A computer program product for executing the method of claim 1 and loadable to a memory of a filter control unit, the computer program product comprising program code which, when executed by the processor of filter con- trol unit, makes the filter control unit: read the identification codes of said several filter elements during rotation of the filter,

perform said reading at least following a change of at least one of the filter elements in the filter,

repeat said reading at prescribed time intervals, and

show information based on the readings in a visual form, the information including symbols corresponding to the operation time of an individual filter element.

23. A memory means, comprising a computer program product as claimed in claim 22.