Field of the invention

The invention relates to a filter apparatus according to the preamble of the appended claim 1.

Background of the invention

With different fabric filter structures the aim is to remove particles from airflows. The collecting efficiency of filters has been aimed to be improved in various manners. Typically the fibre size of the filter material has been decreased and the density has been increased in order to improve collecting efficiency. However, a result of this has been an increase in the flow resistance.

Therefore, the aim has been to find solutions for creating a better collecting efficiency and load capacity with a reasonable flow resistance. A possible solution is to bring the filter structure into a rotating motion, in which case the collecting efficiency and capacity of the filter has been detected to improve. Such a solution has been disclosed in the publication US 3,126,263, wherein a rotating fabric filter is disclosed to be used for particle filtering of a gas flow. Since the particles that adhere to the filter tend to travel to the edge areas of the filter because of centrifugal force and further away form it, the particles and other impurities that detach from the filter must be caught before they go back to the purified flow. The structure according to the publication discloses a stationary filter structure circulating a rotating filter for collecting particles. The collecting efficiency of said structure depends significantly on the tightness between the rotating and stationary structures. Because of this the structure is demanding to implement in several practical applications.

Summary of the invention

Now a rotating filter solution has been invented, which enables an efficient separation in a simple and reliable manner.

To attain this purpose, the filter apparatus according to the invention is primarily characterized in what will be presented in the characterizing part of the independent claim 1. The other, dependent claims will present some preferred embodiments of the invention.

A basic idea of the invention is that the filter structure comprises a rotating filter, which has a diameter that is substantially larger than the diameter of the flow route following it. The filter is advantageously a fabric filter or a membrane filter. In an embodiment the rotating filter is followed by a wall, which comprises a flow opening. In another embodiment the diameter of the channel continuing after the rotating filter is smaller than the diameter of the filter.

According to an advantageous embodiment of the invention the rotating filter is arranged in the immediate vicinity of the wall following it. Thus, the filter and the wall come together in a tight manner, for example, by the effect of a flow created by a centrifugal force, in which case the travel of particles to the side of the cleaned flow is substantially prevented.

When travelling through the rotating filter the medium to be cleaned and the particles contained in it come to a rapidly moving fibre matrix and have to change their flow direction, in which case their collision to fibres is more likely than in a stationary material. The rotation of the filter enables an effective separation of particles with a small amount of rough fibres.

The pressure-difference created by the filter increases as a result of the rotating movement. An advantage of the invention is that by changing the rotating speed, it is possible to move on a desired pressure difference area without changing the structure of the filter.

In addition, in principle it is possible to control the collecting efficiency of the filter continuously as necessary by changing the rotating speed of the filter.

The structure according to the invention has several advantages. A significant advantage is the good particle filtering capability reached by means of a simple structure.

Another significant advantage is the reliable tightening of the rotating filter due to the centrifugal effect. In addition, the filter has a kind of a self-cleaning feature due to the centrifugal force.

In an embodiment the efficiency of the filter is intensified with an electric charging. Thus, the rotation of the filter creates a charging of the filter.

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended principle drawings, in which

Fig. 1 shows an embodiment according to the invention,

Fig. 2 shows a cross-section of an embodiment according to Fig.

1 at point A-A,

Fig. 3 shows a cross-section of an embodiment according to Fig.

1 at point B-B,

Fig. 4 shows the relationship between the areas of the filter and the flow opening following it,

Figs 5 to 9 show some other embodiments of the invention, and

Fig. 10 shows some measurement results.

For the sake of clarity, the figures only show the details necessary for understanding the invention. The structures and details that are not necessary for understanding the invention, but are obvious for anyone skilled in the art, have been omitted from the figures in order to emphasize the characteristics of the invention.

Detailed description of the invention

Fig. 1 shows a rotating filter 4 arranged in a channel 1 ,2 according to the invention. The rotation axis of the filter 4 is parallel to the flow direction F of the medium to be cleaned coming to the filter 4, such as, for example, gas or liquid. The rotating motion of the filter 4 is created by means of a suitable actuator 5, such as, for example, an electric motor. The filter 4 is attached to the rotating apparatus in a suitable manner, such as, for example, by screws, bolts, pins, lock pins, adhesive, and/or adhesive label. In some applications an adhesive attachment enables the fast and easy changeability of the filter 4.

The part 1 of the channel preceding the filter 4 seen in the flow direction F in the example of Fig. 1 has a diameter that is substantially equal to the part 2 of the channel after the filter. In the example the diameter of the rotating filter 4 is equal or smaller than the diameter of the channel 1 ,2. A separating wall 3 has been arranged in connection with the channel 1 , 2, which wall is placed immediately after the filter 4 in the flow direction F. There is an opening O in the separating wall 3, which is smaller than the size of the filter 4. The opening O in the separating wall 3 is later called the flow opening.

Fig. 2 shows a cross section of the embodiment of Fig. 1 seen at point A-A towards the filter. As can be seen in Fig. 2, the filter 4 covers the entire flow opening O in the separating wall 3 (the borders of the opening are marked with a dashed line in the figure). Fig. 3 shows a cross section of the embodiment of Fig. 1 seen at point B-B towards the filter. The rotation direction of the filter 4 is not significant from the

point of view of the basic idea of the invention. One possible direction is marked as the rotation direction in Figs. 2 and 3.

Fig. 4 shows, in principle, the mutual location of the filter 4 and the opening formed by the flow opening O following it, i.e. the wall 3 in an embodiment. In accordance with the basic idea of the invention the area A1 towards the wall 3 of the filter 1 is larger than the area A2 of the flow opening O following it. In addition, in Fig. 4 it can be seen that the filter 4 covers the entire flow opening O, i.e. the periphery of the filter 4 defines within its limits the entire opening in the wall 3.

The basic idea of the operation of the filter apparatus according to the invention is that the medium flow F containing impurities is directed to a rotating fabric filter 4, where the impurities travel partly to the periphery and further out of the filter. The travel of impurities towards the periphery of the filter 4 is caused by, inter alia, a centrifugal force. By arranging the periphery of the filter 4 in accordance with the invention further away from the rotation axis than the edge of the flow opening O, the impurities detaching from the periphery of the filter do not go back to the purified flow. In an advantageous embodiment of the invention, such as, for example, in Fig. 1 , the progress of the impurities detaching from the periphery of the filter is limited by a wall 3.

Fig. 5 shows the structure of a filter apparatus, wherein the rotating filter according to an embodiment of the invention is placed in the junction of a wide channel 1 and a narrow channel 2. Thus, the diameter of the rotating filter 4 is as large or smaller than the diameter of the first channel 1 in the flow direction F and larger than the diameter of the second, narrower channel 2 in the flow direction. The filter 4 is placed in such a manner that it is in the immediate vicinity of the wall 3 forming to the junction of the channels 1 , 2. Thus, the cross-sectional area of the flow opening O corresponds substantially to the cross- sectional area of the channel 2.

Fig. 6, in turn, shows a structure, wherein the rotating filter according to an embodiment of the invention is placed before the channel 2. The

cross-sectional area of the rotating filter 4 is larger than the diameter of the channel 2, the opening of which channel forms the flow opening O. The filter 4 is placed in the flow direction F in such a manner that it is in the immediate vicinity of the wall 3 forming around the channel 2. In an embodiment the channel 2 is formed by a pipe, which does not comprise the actual wall 3 shown in figure 6. Thus, the filter 4 is dimensioned in such a manner, that the periphery is outside the edges of the channel 2 (pipe).

Fig. 7 shows an embodiment of the invention, wherein a rotating filter 4 is arranged to the channel 1 , 2 in accordance with the invention. In the example the part 1 of the channel preceding the filter 4 has a diameter that is substantially equal to the part 2 of the channel after the filter. The diameter of the rotating filter 4 is larger than the diameter of channel 1 , 2. Because of this, an expansion structure is arranged in connection with the channel 1 , 2, which structure forms a separating wall 3 on the side of the channel 2. The filter 4 is placed immediately on the front side of the separating wall 3 in the flow direction F.

Fig. 8 shows a structure, wherein the rotating filter according to an embodiment of the invention is placed before the channel 2. The cross- sectional area of the rotating filter 4 is larger than the diameter of the channel 2, the opening of which channel forms the flow opening O. The filter 4 is placed in the flow direction F in such a manner that it is in the immediate vicinity of the wall 3 forming around the channel 2. There is also a channel 1 on the front side of the filter 4, which in the example has a diameter that is substantially equal to the part 2 of the channel after the filter. The diameter of the channel 1 can also be different than the diameter of the channel 2. For example, before the filter 4 the channel 1 could have a diameter that is larger than the part of the channel 2 after the filter. In the example of Fig. 8 there are no uniform walls circulating the filter at the filter 4. Thus, the impurities travelling on the edge areas of the filter and further from there travel away form the flow F through the opening surrounding the filter.

The above examples have described the rotation of the filter taking place by their own actuator 5, such as, for example, a motor. However, in many targets of use it is advantageous to combine actuators of different operations. Fig. 9 shows yet another embodiment of the invention, wherein the filter structure is connected to a blower 6. Typically, the filter 4 is rotated over 1000 revolutions per minute, such as, for example, 1400 to 3000 rpm when the medium is a gaseous body. In some embodiments, such as, for example, when the medium is a liquid, the resistance caused by the medium can be relatively strong, in which case the rotating speed can be slower.

Fig. 10 shows some measurement results. It is an application, wherein liquid particles have been in the medium, which particles have been aimed to be removed from the flow. The filtering has been performed with a conventional filter apparatus and with a filter apparatus according to the invention. As can be seen from the diagram, the conventional filter does not remove other than the largest particles form the medium flow. The filter apparatus according to the invention, in turn, removes efficiently even particles of the size 1 μm, and the filtering efficiency increases when the particle size increases.

In an embodiment the separating capability of a rotating filter 4 is intensified with an electrical charging. By using a suitable material and/or structure of the filter 4 and separating wall 3, a charging of the filter is achieved when the filter rotates and sweeps the separating wall. In addition, in an embodiment the particles are charged with a suitable charger before the filter 4, in which case the separating capability of the filter is intensified significantly.

In another embodiment the filter apparatus comprises a cleaning system of the filter 4 as well. The cleaner system can be implemented by, for example, arranging the input of a cleaner, such as, for example a liquid, in the filter apparatus before the filter 4 in the flow direction. Thus, the cleaner travels with the flow to the filter 4. In the rotating filter 4 the cleaner travels by the effect of a centrifugal force to the periphery

of the filter and further away from the filter. When travelling in the filter 4 the cleaner advantageously moves the impurities with it.

The filter apparatus according to the invention can be used in various targets of use. It can be, for example, used to remove dry particles and/or liquid drops from a gas flow, such as air. The material and structure of the filter 4 is advantageous to be selected as suitable for the target of use. The filter 4 can be manufactured, for example, of fibre material or some other material with corresponding properties, such as, for example, a membrane.

In an embodiment an impurity collecting unit 7 has been formed in connection with the wall 3. The impurities that are removed from the filter due to the effect of a centrifugal force collect in the collecting unit 7 in question. In an embodiment the collecting unit 7 is a trough-like structure circling the channel 1 , from where the impurities in an embodiment can be further directed away. In another embodiment, such as, for example, in Fig. 9, the collecting unit 7 is a cavity, whose opening is in the interface of the wall and the channel. Naturally the size and shape of the collecting unit 7 may vary significantly. A matter affecting the implementation of the collecting unit 7 is the amount and quality of impurities. The collecting unit 7 may comprise, for example, structures relating to water atomization cleaning.

In the examples presented above, one flow opening O formed in the wall 3 has been used. However, the invention does not depend on the number or form of the openings O formed in the wall 3. In some cases the wall 3 comprises structures, by means of which the rotating apparatus 5 of the filter 4 is supported. Thus, for example two or four flow openings O may be formed in the wall 3.

By combining, in various ways, the modes and structures disclosed in connection with the different embodiments of the invention presented above, it is possible to produce various embodiments of the invention in accordance with the spirit of the invention. Therefore, the above- presented examples must not be interpreted as restrictive to the

invention, but the embodiments of the invention may be freely varied within the scope of the inventive features presented in the claims hereinbelow.