Background

The present invention relates to filter apparatuses having filter comprising multiple filter elements.

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, as a cake, 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.

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 and 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.

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 are affected by slurry particles and extraneous compounds, especially in the field of dewatering of mineral concentrates. Filter element breakages happen once a while in operation when the filter elements are old, something gets stuck to scrapers or for some other reason. Broken ceramic element has to be removed because there is a significant risk that breakage of one element causes domino effect as the pieces of the broken element may break neighbouring filter plates etc, which may lead to a massive consquential damage of broken plates, and the filter apparatus is out of operation for many days. Broken cloth element may cause excessive energy consumption due to air leakages.

Common for the rotary vacuum disc filter apparatuses and rotary vacuum drum filter apparatuses is a great number of filter elements. This fact leads to a problem that it may be challenging to find the broken filter element in the apparatus quickly. Brief description

Viewed from an aspect, there can be provided a filter apparatus, comprising a filter formed by a plurality of filter elements, the filter arranged around a central shaft, the central shaft and the filter being revolvable around longitudinal axis of the central shaft, the filter element comprising a permeable membrane layer constituting a suction wall of said filter element, an indicator arranged to generate a break indication upon breakage of the filter element, wherein the filter elements are arranged into break indication location cells, and that at least two break indication location cells are arranged successively in direction of the central shaft, the break indication location cell comprising a transmitter apparatus connected to the indicators of the filter elements arranged to said break indication location cell, the transmitter apparatus comprising transmitter means for wireless communication of a break signal based on the break indication in at least one indicator included in said break indication location cell, the break signal thus arranged to indicate the break indication location cell wherein said break indication has been generated.

Thereby a filter apparatus where the broken filter element is found quickly may be achieved.

In one embodiment, the transmitter apparatus is arranged in a part of the apparatus not changed in replacing procedure of the filter elements. An advantage is that the transmitter apparatus has not to be changed in vain, and more expensive and high-quality transmitters can be used.

In one embodiment, the transmitter apparatus is arranged in the central shaft of the filter apparatus. An advantage is that the risk for the transmitter apparatus being exposed to slurry and discharging liquids is minimized.

In one embodiment, the transmitter apparatus is arranged in a support structure attaching the filter element to the central shaft of the filter apparatus. An advantage is that the transmitter apparatus is attached to the apparatus and thus the location information of the transmitter apparatus may be coded in the transmitter apparatus. Furthermore, the transmitter is protected against process liquids and mechanical stresses.

In one embodiment, the transmitter apparatus is arranged in a fluid channel arranged to convey fluids to and from the filter element. An advantage is that the transmitter apparatus is attached to the apparatus and thus the location information of the transmitter apparatus may be coded in the transmitter apparatus. Furthermore, an operator can easily reach the transmitter apparatus and thus connect it to cabling of the apparatus quickly.

In one embodiment, the transmitter apparatus comprises a RFID tag/transmitter. An advantage is that a small and durable transmitter apparatus may be achieved.

In one embodiment, the transmitter apparatus is a passive RFID tag/transmitter. An advantage is that there is no need for an internal energy source in the transmitter.

In one embodiment, the permeable membrane layer is a porous ceramic membrane layer. An advantage is that a mechanically and chemically durable membrane layer may be achieved.

In one embodiment, at least a portion of the indicator is arranged in the porous ceramic membrane layer. An advantage is that an immediate break indication upon breakage of the membrane layer may be achieved.

In one embodiment, said portion of the indicator is arranged between the porous ceramic membrane layer and a substrate supporting said membrane layer. An advantage is that the membrane protects the indicator against the direct mechanical and chemical stress from the from the process environment.

In one embodiment, at least a portion of the indicator is arranged on the peripheral outer edge surface of the filter element. An advantage is that the indicator is not exposed to direct mechanical stress caused e.g. by scrapers.

In one embodiment, the permeable membrane layer comprises fibrous material, such as a fabric comprising monofilaments and/or multifilaments. An advantage is that the membrane layer may be cheap to manufacture and quickly to replace.

In one embodiment, the at least one indicator comprises an electrically conductive wire. An advantage is that the monitoring of the integrity of the wire may be simple.

In one embodiment, the at least one indicator comprises an optical fibre. An advantage is that the optical fibres are made of chemically resistant materials. Furthermore, they are easy to install in the apparatus. Still further, the optical fibre may be very sensitive to the breakages or fractures and thus the break signal is able to be created et very early state of the breaking.

In one embodiment the at least one indicator comprises a device for audible signal. An advantage is that the audible signal can be heard even if the indicator is covered by residues or ore.

In one embodiment, the apparatus comprises at least three break indication location cells arranged successively in direction of the central shaft. An advantage is that the break indication location cell may be short enough for the personnel to discover the broken element at a glance.

In one embodiment, the apparatus comprises at least five break indication location cells arranged successively in direction of the central shaft. An advantage is that the break indication location cell may be short enough for the personnel to discover the broken element at a glance even in very large filter apparatus.

In one embodiment, the filter apparatus comprises consecutive coaxial filter discs with sectors formed by a plurality of sector-shaped filter elements, and wherein the break indication location cell extends over at most four filter discs and comprises, at the maximum, four adjacent filter elements in circumferential direction of the filter disc. An advantage is that the break indication location cell may be small enough for the personnel to discover the broken element at a glance.

In one embodiment, the break indication location cell comprises, at the maximum, two filter elements in circumferential direction of the filter disc. An advantage is that the broken element may be discovered very quickly.

In one embodiment, the break indication location cell comprises not more than one filter element in circumferential direction of the filter disc. An advantage is that the broken element may be discovered even more quickly.

In one embodiment, the break indication location cell extends, at the maximum, over two filter discs. An advantage is that the broken element may be discovered very quickly.

In one embodiment, the break indication location cell extends over one filter disc only. An advantage is that the broken element may be discovered even more quickly.

In one embodiment, the break indication location cell comprises one filter element only. An advantage is that the broken element may be identified immediately upon the break indication.

In one embodiment, the filter apparatus comprises a filter drum, wherein the filter element is a part of outer surface of said filter drum, and the break indication location cell comprises, at the maximum, two filter elements in circumferential direction of the filter drum. An advantage is that the broken element may be discovered very quickly.

In one embodiment, the break indication location cell comprises not more than one filter element in circumferential direction of the filter drum. An advantage is that the broken element may be discovered even more quickly.

In one embodiment, the break indication location cell comprises not more than two filter elements in direction of the central shaft. An advantage is that the broken element may be discovered very quickly.

In one embodiment, the break indication location cell comprises not more than one filter element in direction of the central shaft. An advantage is that the broken element may be discovered even more quickly.

In one embodiment, the transmitter apparatus is arranged in the filter element. An advantage is that the transmitter apparatus is automatically changed together with the filter element, and thus the reliability of the apparatus may be improved. Furthermore, the quality of signalling of the transmitter apparatus may be stronger and easier to read by reading equipment.

In one embodiment, the transmitter apparatus comprises an indication device arranged to indicate the transmitter apparatus creating the break signal, such as a light element, preferably a LED, or a device for audible signal. An advantage is that personnel may localize the transmitter apparatus more quickly.

In one embodiment, the wireless signal is a digital signal. An advantage is that the handling and processing of the signal is easy.

In one embodiment, the transmitter apparatuses of two oppositely located filter elements are connected to each other and the wireless break signal is arranged to be communicated based on the break indication originating at least one of said two oppositely located filter elements. An advantage is that breaking of a filter element being sunken in the slurry can be noticed immediately.

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 content 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 illustrating an exemplary vacuum filter apparatus,

Figure 2a is a schematic side view of an embodiment of a vacuum filter,

Figure 2b is a cutaway view of the filter shown in Figure 2a, Figure 3a is a schematic side view of another embodiment of a vacuum filter,

Figure 3b is a cutaway view of the filter shown in Figure 3a,

Figure 4a is a schematic side view of third embodiment of a vacuum filter,

Figure 4b is a cutaway view of the filter shown in Figure 4a,

Figure 5a illustrates a vacuum filter element,

Figure 5b is a side view of an embodiment of the filter element shown in Figure 5a,

Figure 5c is a side view of another embodiment of the filter element shown in Figure 5a,

Figure 6a illustrates a second vacuum filter element,

Figure 6b is a cross-section view of the filter element shown in

Figure 6a,

Figure 7a illustrates a third vacuum filter element,

Figure 7b is a side view of the filter element shown in Figure 7a, Figure 8a illustrates a fourth vacuum filter element,

Figure 8b is a side view of the filter element shown in Figure 8a, Figure 9a is a perspective top view illustrating another exemplary vacuum filter apparatus,

Figure 9b is side view of an embodiment of the filter shown in Figure

9a,

Figure 9c is a cutaway view of the filter shown in Figure 9a, and Figure 9d illustrates a filter element of the filter shown in Figure 9a.

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 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 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.

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 12 of the filter apparatus 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 21 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 filter apparatus shown in Figure 1 comprises twelve (12) filter discs. 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 Ceramec 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.

The filter discs 16 are formed by a plurality of sector-shaped filter elements 3. The filter element 3 comprises a permeable membrane layer 17 that constitutes a suction wall of said filter element 3. Furthermore, the filter element 3 comprises an indicator 20 arranged to generate a break indication upon breakage of the filter element 3.

Operation of the disc filter apparatus 1 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.

Figure 2a is a schematic side view of an embodiment of a filter, and Figure 2b is a cutaway view of the filter shown in Figure 2a.

The filter elements 3 are arranged into break indication location cells

5, shown by dash lines in Figures. According to an aspect, there are at least two break indication location cells 5 arranged successively in direction of the central shaft X. The embodiment shown in Figures 2a, 2b comprises successive break indication location sells 5, but the number of the successive cells can be varied, e.g. the following Figures are showing some examples of potential alternatives.

According to an aspect, the break indication location cells 5 comprises, at the maximum, four adjacent filter elements 3, i.e. parallel in circumferential direction of the filter disc 16. In the embodiment shown in Figures 2a, 2b, each of the break indication location cells 5 comprises three adjacent filter elements 3 in circumferential direction of the filter disc 16. In order to distinguish the break indication location cells 5, the filter elements 3 are filled with lineation in Figure 2b. The number of the adjacent filter elements 3 included in one cell 5 can be varied, e.g. the following Figures are showing some examples of potential alternatives.

The break indication location cell 5 comprises a transmitter apparatus 6 connected to the indicator(s) 20 of the filter element(s) 3 arranged to said break indication location cell 5. Said connection may be wired or wireless connection. The transmitter apparatus 6 comprises transmitter means 7 that is able to communicate wirelessly a break signal based on the break indication in at least one indicator 20 included in said break indication location cell 5. The break signal indicates the break indication location cell 5 wherein said break indication has been generated, and thus the broken filter element 3 can be located in the apparatus 1 at the level of the break indication location cells 5.

In an embodiment, the wireless break signal is a signal in digital form. For this purpose, the transmitter apparatus 6 may comprise means for converting analogical break indication to digital form, i.e. A D converter, but this is not always necessary.

In another embodiment, the wireless break signal is analog signal. The break signal sent by transmitter means 7 is received by a receiver means and sent e.g. to the filter control unit for further processing. The receiver means may be e.g. RFID receiver arranged to the filter apparatus 1 or outside the filter apparatus 1 . It is to be noted that the receiver means and the filter control unit are not shown in the Figures.

In an embodiment, the transmitter apparatus 6 is arranged in a part of the apparatus 1 that is not changed in replacing procedure of the filter elements 3. Thus the transmitter apparatus 6 remains in the apparatus 1 while the filter element 3 is detached from the apparatus 1 .

In an embodiment, the transmitter apparatus 6 is arranged in the central shaft 4 of the filter apparatus.

However, in another embodiment the transmitter apparatus 6 is arranged in the filter element 3.

According to an aspect, the transmitter apparatus 6 comprises a RFID tag/transmitter. A passive RFID tag has an advantage that it does not need an energy source of its own but it is harvesting its energy from signals send by an RFID reader arranged to read the break signal. It is to be noted that the RFID reader is not shown in Figures of this description.

However, the transmitter apparatus 6 may alternatively be a semi- active or active RFID tag.

In an embodiment, the transmitter apparatus 6 comprises an indication device 13 arranged to indicate the transmitter apparatus 6 creating the break signal, especially for purpose to indicate the location of the transmitter apparatus 6 to an operator going to remove the broken filter element. An advantage is that the changing procedure may be shortened. In an embodiment, the indication device 13 comprises a light element 14, preferably a LED. In another embodiment, the indication device 13 comprises a device 15 for audible signal, such as a loudspeaker. In an embodiment, there is an indication device 13, such as a light element 14, for each filter element 3. Thus the broken filter element is very easy to notice.

Figure 3a is a schematic side view of another embodiment of a disc filter apparatus, and Figure 3b is a cutaway view of the disc filter apparatus shown in Figure 3a. This embodiment comprises three break indication location cells 5 arranged successively in direction of the central shaft X. The break indication location cell 5 extends over four filter discs 16 and comprises just one filter element 3 in circumferential direction of the filter disc 16. Thus there are four filter elements in each of the break indication location cell 5.

In an embodiment, the transmitter apparatus 6 is arranged in a support structure 8 attaching the filter element 3 to the central shaft 4 of the filter apparatus.

Figure 4a is a schematic side view of third embodiment of a filter, and Figure 4b is a cutaway view of the filter shown in Figure 4a.

According to an aspect, the filter apparatus 1 may comprise at least five break indication location cells 5 arranged successively in direction of the central shaft X. In the embodiment shown in Figures 4a, 4b the break indication location cell 5 extends over one filter disc 16 only, i.e. the number of the successive break indication location cells 5 is equal to the number of the filter discs 16. The filter apparatus 1 here comprises twelve (12) filter discs 16 and thus twelve successive break indication location cells 5.

Furthermore, each of the break indication location cells 5 comprises just one filter element 3 in circumferential direction of the filter disc 16. Thus each of the break indication location cells 5 shown in Figures 4a, 4b comprise one filter element 3 only.

According to an aspect, the break indication location cell 5 comprises, at the maximum, two filter elements 3 in circumferential direction of the filter disc 16.

According to another aspect, the break indication location cell 5 extends, at the maximum, over two filter discs 16.

In an embodiment, the transmitter apparatus 6 is arranged in a fluid channel 9, e.g. fluid hose or pipe, arranged to convey fluids to and/or from the filter element 3.

Figure 5a illustrates a filter element, Figure 5b is a side view of an embodiment of the filter element shown in Figure 5a, and Figure 5c is a side view of another embodiment of the filter element shown in Figure 5a.

According to an aspect, the permeable membrane layer 17 may be a porous ceramic membrane layer, whereby at least a portion of the indicator 20 may be arranged in said porous ceramic membrane layer.

The filter element 3 comprises two membrane layers 17 arranged on opposed sides of the filter element. The membrane layers are supported by substrate layers 18.

An interior space may be defined between the opposed membrane layers 17 resulting in a sandwich structure. The interior space provides a flow canal or canals where a negative pressure is maintained, i.e. a pressure difference is maintained over the suction wall.

The membrane layer 17 contains micropores that create strong capillary action in contact with liquid. This microporous filter medium allows only liquid to flow through. Filtrate is drawn through the membrane layer 17 and the substrate layer 18 as the filter element 3 is immersed into the slurry to be filtered, and a cake of solid particulate material forms on the membrane layers 17.

According to an aspect, the filter element 3 is provided with at least one indicator 20 extending along the filter element 3 to form a continuous circuit and arranged to break upon breakage of the filter element 3.

In an embodiment, the indicator 20 comprises an electrically conductive layer 10, e.g. a printed electric wire, a casted electric wire, a microstrip line, separate electric wire, a metal tape or a painted electric circuit, for example.

In the embodiment shown in Figure 5a, the indicator 20 is arranged along the peripheral outer edge surface 22 of the filter element 3. The indicator 20 can be coated with an acid-proof coating, such as epoxy based painting or enamel. Therefore, in embodiments based on electrically conductive layers, cheaper materials (such as copper tape) which are not acid-proof can be used.

Alternatively, the electrically conductive indicator is made of acid- proof material, e.g. platinum or palladium or compositions thereof are especially advantageous materials for implementing acid-proof wiring.

The integrity of the indicator 20 is monitored by the transmitter apparatus 6, and the operation, particularly the rotation, of the disc filter apparatus is immediately stopped in response to the wireless break signal based on the break indication in the indicator 20. Additionally, the break signal indicates the break indication location cell 5 wherein said break indication has been generated. This action will advantageously save all the other plates of the disc filter from getting broken. Operation downtime decreases as the consquential damage of several broken plates is avoided and the operator of the disc filter can concentrate on displacing the broken plate. The number of broken consumed filter plates decreases which results in lower operational costs.

Figure 5c is a side view of another embodiment of the filter element shown in Figure 5a. This embodiment differs from the embodiment shown in Figure 5b in that, instead of one indicator 20, there are two indicators 20 on the peripheral outer edge surface 22 of the filter element 3. The two indicators 20 are arranged close to the edges of the filter element 3. Thus, the sensitivity of the indicators 20 to breakages taking place in the membrane 17 and/or substrate layer 18 may be enhanced.

Figure 6a illustrates a second filter element, and Figure 6b is a cross-section view of the filter element shown in Figure 6a.

In this embodiment, the indicator 20 is provided between the substrate layer 18 and the membrane layer 17 on the both sides of the filter element 3. In this case the membrane layer 17 protects the indicator 5 against the direct mechanical and chemical stress from the from the process environment.

However, the indicator 20 is preferably made of acid-proof material, advantageously of platinum or palladium. The indicator 20 may be manufactured by, for example, applying (preferably printing) a pattern of conductive paste on the outer surface of the substrate layer 18 prior to making the membrane layer 17. This approach can also detect a stripping of the membrane prior to an actual breakage of the substrate.

Figure 7a illustrates a third filter element, and Figure 7b is a side view of the filter element shown in Figure 7a.

In this embodiment, the indicator 20 is provided mainly on the peripheral outer edge surface 22, but a portion thereof is 3 arranged in/on the membrane layer 17 near the outer end of the of the filter element 4. Said portion may be arranged on sections of the membrane layer 17 which are not scraped by the scrapers of the disc filter apparatus 1 . Alternatively, said portion may be arranged between the substrate layer and the membrane layer of the suction wall.

In another embodiment, there is also another indicator 20 a portion of which is arranged in/on the opposite membrane layer 17.

The indicator 20 shown in Figures 7a, 7b comprises an optical fibre 1 1 .

In another embodiment, the indicator 20 comprises a device for audible signal, e.g. microphone. Of course, the device for audible signal may be attached e.g. in fluid channel 9.

Figure 8a illustrates a fourth filter element, and Figure 8b is a side view of the filter element shown in Figure 8a.

Also in this embodiment, the indicator 20 is provided mainly on the peripheral outer edge surface 22, but a portion thereof is arranged in/on the membrane layer 17 near the attachment means 14 of the of the filter element 3. Said portion may be arranged on sections of the membrane layer 17 which are not scraped by the scrapers of the disc filter apparatus 1 . Alternatively, said portion may be arranged between the substrate layer and the membrane layer.

In another embodiment, there is also another indicator 20 a portion of which is arranged in/on the opposite membrane layer 17.

According to an aspect, the permeable membrane layer 17 comprises fibrous material, such as fabric comprising monofilaments and/or multifilaments.

Figure 9a is a perspective top view illustrating another exemplary filter apparatus, Figure 9b is side view of an embodiment of the filter shown in Figure 9a, Figure 9c is a cutaway view of the filter shown in Figure 9a, and Figure 9d illustrates a filter element of the filter shown in Figure 9a.

The filter apparatus 1 may comprise a filter drum 19, i.e. the filter apparatus is a drum filter apparatus. It is to be noted that the filter apparatus 1 is shown by dash lines in Figure 9a in order to clarify the structure of the filter drum 19.

In the drum filter apparatus 1 the filter element 3 is a part of outer surface of the 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 m ² .

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

The filter elements 3 are divided into break indication location cells 5 basically similar way as described earlier in this description in connection to the disc filters. Thus, according to an aspect, there are at least two break indication location cells 5 arranged successively in direction of the central shaft X of the filter drum 19. The embodiment shown in Figures 9a - 9c comprises two successive break indication location sells 5, but the number of the successive cells can be varied as described earlier in this description.

According to an aspect, the break indication location cell 5 comprises not more than two filter elements 3 in direction of the central shaft X. In the embodiment shown in Figures 9a - 9c, the break indication location cells 5 include two filter elements 3 in direction of the central shaft X.

According to an aspect, the break indication location cell 5 comprises, at the maximum, two filter elements 3 in circumferential direction of the filter drum 19. As shown in Figure 9c, the embodiment herein comprises three (3) filter elements 3 per break indication location cell 5 in circumferential direction of the filter drum 19.

In an embodiment, the break indication location cell 5 comprises just one filter element 3.

Figure 9d illustrates a filter element of the filter shown in Figure 9a. As described earlier in this description, the filter element 3 comprises a permeable membrane layer 17 that constitutes a suction wall of said filter element 3. Furthermore, the filter element 3 comprises an indicator 20 arranged to generate a break indication upon breakage of the filter element 3.

The main difference of the filter elements of drum filters compares 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 9d.

The indicator 20 may be arranged in the drum filter element 3 similar ways described in connection with Figures 5a - 8b.

Operation of the drum filter apparatus 1 may be controlled by a filter control unit, such as a Programmable Logic Controller, PLC.

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

Similarly as in disc filter apparatuses described earlier in this description, the break indication location cell 5 comprises a transmitter apparatus 6 connected to the indicator(s) 20 of the filter element(s) 3 arranged to said break indication location cell 5. The transmitter apparatus 6 comprises transmitter means 7 that is able to communicate wirelessly a break signal based on the break indication in at least one indicator 20 included in said break indication location cell 5. The break signal indicates the break indication location cell 5 wherein said break indication has been generated, and thus the broken filter element 3 can be located in the apparatus 1 at the level of the break indication location cells 5.

In an embodiment, the wireless break signal is a signal in digital form. For this purpose, the transmitter apparatus 6 may comprise means for converting analogical break indication to digital form, i.e. A D converter, but this is not always necessary.

In another embodiment, the wireless break signal is analog signal.

In an embodiment, the transmitter apparatus 6 is arranged in a part of the apparatus 1 that is not changed in replacing procedure of the filter elements 3. Thus the transmitter apparatus 6 remains in the apparatus 1 while the filter element 3 is detached from the apparatus 1 .

In an embodiment, the transmitter apparatus 6 is arranged in the central shaft 4 of the filter apparatus 1 .

In another embodiment, the transmitter apparatus 6 is arranged in a support structure 8 attaching the filter element 3 to the central shaft 4 of the filter apparatus.

In still another embodiment, the transmitter apparatus 6 is arranged in a fluid channel 9, e.g. fluid hose or pipe, arranged to convey fluids to and/or from the filter element 3.

However, in another embodiment the transmitter apparatus 6 is arranged in the filter element 3 as shown in Figure 9d.

According to an aspect, the transmitter apparatus 6 comprises a RFID tag/transmitter. A passive RFID tag has an advantage that it does not need an energy source of its own but it is harvesting its energy from signals send by an RFID reader arranged to read the break signal. It is to be noted that the RFID reader is not shown in Figures of this description.

However, the transmitter apparatus 6 may alternatively be a semi- active or active RFID tag.

In an embodiment, the transmitter apparatus 6 comprises an indication device 13 arranged to indicate the transmitter apparatus 6 creating the break signal, especially for purpose to indicate the location of the transmitter apparatus 6 to an operator going to remove the broken filter element. An advantage is that the changing procedure may be shortened. In an embodiment, the indication device 13 comprises a light element, preferably a LED. In another embodiment, the indication device 13 comprises a device for audible signal, such as a loudspeaker.

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 break indication location cell

6 transmitter apparatus

7 transmitter means

8 support structure

9 fluid channel

10 electrically conductive layer

1 1 optical fibre

12 frame of the filter apparatus

13 indicator device

14 attachment means

16 filter disc

17 permeable membrane layer

18 substrate layer

19 filter drum

20 indicator

21 slurry basin

22 peripheral outer edge surface

X longitudinal axis