WO2014177155A1

WO2014177155A1 - Flue gas filter and use hereof

Info

Publication number: WO2014177155A1
Application number: PCT/DK2014/050115
Authority: WO
Inventors: Jan Mahler
Original assignee: Aagaard A/S
Priority date: 2013-05-02
Filing date: 2014-05-01
Publication date: 2014-11-06

Abstract

The invention relates to a flue gas filter (1) comprising a filter casing (2) divided into at least a filter section (20), wherein a curved air deflection plate (14) is arranged in the filter section (20) in such a way that said air deflection plate (14) curves downwards, and an air inlet (3) arranged on top of the filter casing (2) opening into the filter section (20) centrally above the air deflection plate (14). The flue gas filter (1) further comprises an air outlet (4) for discharging filtered air, which has passed through the air inlet (3) and the filter casing (2). The invention also relates to use of a flue gas filter (1) in connection with a combined heat and power plant running on biofuel or natural gas, a processing plant generating smoke or other fumes at high temperatures, a plant working with laser cutting, plasma cutting, flame cutting, grinding, lacquering and/or sandblasting, or a plant working with torrification of biomass.

Description

FLUE GAS FILTER AND USE HEREOF

The present invention relates to a flue gas filter configuration, which may be used in flue gas filters dedicated various types of flue gas filtration and use hereof.

Background of the invention

Various types of flue gas filters are known in the art in which air is filtered using a number of substantially cylindrical filter cartridges arranged in a filter casing, where the curved surface of each of these filter cartridges is formed by a filter bag of a suitable filtering material. In these types of filters, the air moves radially into the filter cartridges through the filtering material and leaves the filter cartridges in an axial direction at one of the ends thereof. A known example of a flue gas filter is disclosed in US patent no. 5,223,008.

A well-known problem of flue gas filters known in the art is that the filtering efficiency rapidly declines as the filter cartridges are choked by particles being caught by the filtering material of the filter bags. Another disadvantage is that such flue gas filters are typically rather large in relation to the area of the filtering material and consumes a relatively large amount of space if they have the filtering capacity necessary for many common applications.

Brief description of the invention

It is an object of the present invention to provide flue gas filters, in which the above- mentioned disadvantages of flue gas filters known in the art are significantly reduced.

The present invention relates to a flue gas filter comprising a filter casing divided into at least a filter section, wherein a curved air deflection plate is arranged in the filter section in such a way that said air deflection plate curves downwards, and an air inlet arranged on top of the filter casing opening into the filter section centrally above the air deflection plate, and the flue gas filter further comprises an air outlet for discharging filtered air, which has passed through the air inlet and the filter casing.

A flue gas filter of the invention with the curvature of the air deflection plate permits the incoming air to flow smoothly through the filter whereby less filter space is required and energy consumption is reduced.

In an embodiment of the invention, an flue gas filter comprising a filter casing divided into at least an air outlet and filter cartridge cleaning section and a filter section, in which filter section one or more elongated filter cartridges are arranged parallel to each other with substantially horizontal longitudinal axes, wherein a substantially rectangular and curved air deflection plate is arranged in the filter section above the one or more filter cartridges in such a way that said air deflection plate curves downwards from a substantially horizontal centre line, which is parallel to the longitudinal axes of the one or more filter cartridges, in both directions perpendicular to the centre line, two perforated air pressure relief plates are arranged substantially vertically and parallel to the longitudinal axes of the one or more filter cartridges, each of the air pressure relief plates abutting one of the two lower edges of the air deflection plate, respectively, so that the one or more filter cartridges are enclosed upwards by the air deflection plate and to two opposing sides by the air pressure relief plates, an air inlet is arranged on top of the filter casing opening into the filter casing centrally above the air deflection plate, and the flue gas filter further comprises an air outlet for discharging filtered air, which has passed through the air inlet, the filter casing and the one or more filter cartridges.

This configuration of the flue gas filter with the air inlet at the top, the curved air deflection plate and the two air pressure relief plates makes use of the so-called

Coanda effect, which is the tendency of a fluid jet to be attracted to a nearby surface. The curvature of the air deflection plate is optimised so that the incoming air flow from the air inlet flows smoothly towards the two lowest edges of the air deflection plate and further down along the two air pressure relief plates with significantly less turbulence and, thereby, less pressure loss and energy consumption than in flue gas filters known in the art.

Furthermore, the flow path of the air flowing through the flue gas filter causes a significant part of the particles in the air to be separated from the air before the air reaches the filter cartridges. This effect minimises the load on the filter cartridges.

In an embodiment of the invention, the air inlet is rotatably arranged on the top of the filter casing so that the horizontal direction from which air is directed into the air inlet can be optimized in relation to the surroundings in which the flue gas filter is installed.

This flexible solution facilitates the design and planning of filter systems of which one or more flue gas filters according to the present invention are a part.

In an embodiment of the invention, the air outlet is arranged on top of the filter casing.

Arranging the outlet on top of the filter casing reduces the amount of necessary space around the flue gas filter. In an embodiment of the invention, each of the filter cartridges is substantially cylindrical in shape with the curved surface formed by a filter bag made of a filtering material so that, in use, air moves radially into the filter cartridge through the filtering material and leaves the filter cartridge in an axial direction at one of the ends thereof.

This type of filter cartridges is known to be effective and reliable. In an embodiment of the invention, the filter bags are pleated by repeatingly folding the filtering material, from which the filter bags are made.

Pleating the filter bags significantly increases the available surface area of the filtering material and, thereby, the capacity of the filter cartridges.

In an embodiment of the invention, the flue gas filter further comprises an airtight rotary valve for removal of filtered off solids from the filter casing. The use of an airtight rotary valve for removal of solids ensures that solids can be removed from the filter casing while there is a high air pressure within the filter casing i.e. without having to halt the operation of the filter.

In an embodiment of the invention, the flue gas filter further comprises a device for cleaning the one or more filter cartridges by means of pressurised air.

In an embodiment of the invention, operation of the device for cleaning the one or more filter cartridges is controlled to be initiated at regular time intervals and/or when a differential pressure measured between the outside and the inside of one or more of the filter cartridges exceeds a predefined threshold value.

Intermittent use of pressurised air is a well-known and reliable method for cleaning filter cartridges. In an embodiment of the invention, the flue gas filter further comprises a heater unit so that the flue gas filter can be operated at optimal temperatures depending on the type of filtering being performed.

The efficiency of the filtering can vary significantly with the temperature of the air being filtered, the optimal temperature range depending on the type of filtering. In an embodiment of the invention, at least a part of the filter is constructed by combining two or more modules, each containing one or more filter cartridges.

The modularity makes it possible to construct flue gas filters of many different sizes and capacities using only a few different types of modules as "building blocks".

In another embodiment of the invention, said air deflection plate curves in the full width of the plate or in part or parts of the full width. Hereby, an advantageous embodiment of the invention is achieved.

In a further embodiment of the invention, said air deflection plate is substantially dome or semi-dome shaped and/or is a combination of shapes such as rectangular and semi-dome shapes.

Hereby, an advantageous embodiment of the invention is achieved.

In an even further embodiment of the invention, said one or more perforated air pressure relief plates comprise symmetrically located perforation holes in a vertical direction e.g. with a hole diameter between 1 and 5 millimeters such as a diameter of 2 or 3 millimeters and/or a pitch range of 3.5 or 5. Hereby it is possible to ensure an advantageous air flow of 30 to 40% through the perforated plates such as approx. 30% (2 millimeters) or approx. 33% (3 millimeters). Further, it is possible to use standard perforated metal plates in relation to diameter and pitch and hereby achieve lower filter construction costs.

In embodiments of the invention, said air deflection plate is curved with a central radius (Ri) substantially larger than one or more radiuses (R₂, R₃) at the plate edge or edges in establishing at least one air foil shape and curvature of the air deflection plate being configured for the Coanda effect. Hereby, advantageous embodiments of the invention are achieved in establishing smooth air flows in the filter.

In an embodiment of the invention, the air deflection plate is mirror symmetric in relation to a vertical centre line. Hereby it is ensured that the air flow from the air inlet is symmetrically divided into air flows over the air deflection plate.

In an embodiment of the invention, the position of said air deflection plate is vertically adaptable in relation to a change in size of the air inlet. Hereby it is possible to keep an optimized size of the filter in response to an air inlet size by adapting the plate position to maintain sufficient space for a smooth and optimal air flow.

In an embodiment of the invention, said filter casing comprises one or more filter cartridges, filter bags and/or other types of flue gas filtering means.

Hereby, an advantageous embodiment of the invention is achieved.

In an embodiment of the invention, said heater unit includes an electrical heating device e.g. located on an outer surface of said filter casing and an electrical power supply. Hereby it is possible to heat the internal air flows in the filter without the heater unit coming in direct contact with the air flows and thus ensuring a longer lifespan for the heater unit. The invention also relates to a use of a flue gas filter in connection with a combined heat and power plant running on biofuel or natural gas, a processing plant generating smoke or other fumes at high temperatures, a plant working with laser cutting, plasma cutting, flame cutting, grinding, lacquering and/or sandblasting, or a plant working with torrification of biomass. The figures

In the following, a few exemplary embodiments of the invention are described with reference to the figures, of which

Fig. 1 is a perspective view of a flue gas filter according to an embodiment of the invention,

Fig. 2 is a perspective view of the flue gas filter illustrated in Fig. 1, in which approximately half of the flue gas filter has been removed in order to view the inner configuration of the flue gas filter,

Fig. 3 is a side view of the flue gas filter illustrated in Fig. 1, Fig. 4 is a schematic cross-sectional view of the same flue gas filter,

Fig. 5 is an enlargement of the uppermost part of Fig. 4,

Fig. 6A is a principle sketch illustrating the flows of air through the flue gas filter casing, when the flue gas filter illustrated in Fig. 1 is in use,

Fig. 6B is a principle sketch illustrating means of a flue gas filter according to an embodiment of the invention, Fig. 6C is an enlargement of an air deflection plate of a flue gas filter according to an embodiment of the invention,

Figs. 6D-E are views of alternative embodiments of an air deflection plate, Figs. 6F-G are front and side views of a flue gas filter according to an embodiment of the invention, Fig. 7A is a side view of an air deflection plate of a flue gas filter according to an embodiment of the invention,

Fig. 7B is a side view from another side of the air deflection plate illustrated in

Fig. 7A,

Fig. 7C is a perspective view of the air deflection plate illustrated in Figs. 7A and

7B, Fig. 7D is a top view of the air deflection plate illustrated in Figs. 7A-C,

Figs. 7E-F are views of alternative embodiments of an air deflection plate according to the invention, and Fig. 8 is a view of a flue gas filter in an embodiment with a heater unit installed.

Detailed description of the invention Fig. 1 is a perspective view of a flue gas filter 1 according to an embodiment of the invention.

The filter casing 2 of the illustrated embodiment basically consists of a conical bottom part 9 and three rectangular modules 12, 13, the two lower 12 of which are identical and larger than the module 13 at the top.

The illustrated flue gas filter 1 is supported by four filter supports 6, each supporting a corner of the lowermost rectangular module 12. As indicated in the figure, the height of these filter supports 6 can be individually adjustable. At the downward pointing apex of the conical bottom part 9, the illustrated flue gas filter 1 is equipped with a preferably airtight rotary valve 7, driven by a motor 8, for removal of solids from the filter casing 2. In other embodiments of the flue gas filter 1, the rotary valve 7 may, for instance, be equipped with a screw conveyor (not shown) for transporting the solids from the filter casing 2 away, or it may be replaced by a simple opening for manual removal of the solids from the filter casing 2. A major advantage of using an airtight rotary valve 7 is that solids can be removed from the filter casing 2 while there is still a relative high air pressure inside the filter casing 2, i.e. without halting the operation of the flue gas filter 1.

Each of the modules 12, 13 and, thereby, the rectangular part of the filter casing 2 of the illustrated flue gas filter 1 are divided into a filter section 20 and an air outlet and filter cartridge cleaning section 21. On top of the filter section 20 of the uppermost module 13 is mounted an air inlet 3, while the air outlet and filter cartridge cleaning section 21 of the uppermost module 13 is covered on its upper side by an air outlet 4.

In preferred embodiments of the flue gas filter 1, the orientation of the air outlet 4 can be reversed so that there are two possible horizontal air discharge directions from the flue gas filter 1.

Furthermore, in preferred embodiments of the flue gas filter 1, the air inlet 3 is rotatable, for instance in steps of 15°, around a vertical centre axis of the filter section 20 of the filter casing 2, so that a large number of different horizontal air intake directions are possible for a given orientation of the filter casing 2. The air inlet 3 is arranged to open into the filter casing 2 directly over the centre of the filter section 20 and, as illustrated in Figs. 2-6, the internal parts of the filter section 20 are arranged symmetrically so that the efficiency of the flue gas filter 1 does not depend on the orientation of the rotatable air inlet 3. A number of pressurised air devices 5 are arranged on the outside of the rectangular modules 12, 13 of the filter casing 2 on the side thereof corresponding to the air outlet and filter cartridge cleaning section 21. These devices 5 are connected to the air outlet and filter cartridge cleaning section 21 and are used for cleaning filter cartridges 9 (not shown in Fig. 1) of the flue gas filter 1 as described further below. Fig. 2 is a perspective view of the flue gas filter 1 illustrated in Fig. 1, in which approximately half of the flue gas filter 1 has been removed in order to view the inner configuration of the flue gas filter 1.

As can be seen, each of the two identical larger modules 12 comprises four filter cartridges 9, while the smaller uppermost module 13 comprises only two such filter cartridges 9, meaning that the total number of filter cartridges 9 for the illustrated embodiment is 10.

Each of the filter cartridges 9 is cylindrical and covered all along its curved surface by a filter bag 10 made of a suitable filtering material. The end of the cylinder nearest the back side of the filter casing 2 (as seen in Fig. 2) is closed, while the other end (in the part of the flue gas filter 1 that has been removed in Fig. 2) is connected to the air outlet and filter cartridge cleaning section 21 (not shown in Fig. 2) and the pressurised air device 5 (not shown in Fig. 2) connected thereto.

During operation of the flue gas filter 1, the air being filtered passes from the filter casing 2 through the filtering material of the filter bags 10 into the filter cartridges 9, from where it is discharged from the flue gas filter 1 through the air outlet and filter cartridge cleaning section 21 and the air outlet 4.

The filter cartridges 9 are cleaned by means of pressurised air blown from the device 5 through the air outlet and filter cartridge cleaning section 21 and directly into the filter cartridges 9 and out through the enclosing filter bags 10, i.e. in the reverse direction. Hereby dust and other particles caught by the filtering material of the filter bags 10 are blown off and falls down to the bottom of the filter casing 2, from where it can be removed from the filter casing 2. In the illustrated embodiment, the removal takes place using a rotary valve 7 by rotation of a rotary valve rotor forming six rotary valve chambers within the rotary valve 7.

As indicated in the figure, the filter bags 10 may be pleated by repeated folding of the filtering material forming the filter bags 10. This significantly increases the filtering area of the filter cartridges 9, for instance from approximately 5 m² to approximately 40 m² for a given filter cartridge 9.

In preferred embodiments of the invention, the filter cartridges 9 are easily replaceable through gates in the outer wall of the filter casing 2.

Fig. 2 further illustrates how a rectangular and curved air deflection plate 14 is arranged above the filter cartridges 9 in such a way that the air deflection plate 14 curves downwards from a horizontal centre line, which is parallel to the longitudinal axes of the filter cartridges 9, in both directions perpendicular to this centre line.

Furthermore, two perforated air pressure relief plates 15 are arranged vertically and parallel to the longitudinal axes of the filter cartridges 9. Each of the air pressure relief plates 15 abuts one of the two lower edges of the air deflection plate 15, respectively, so that the filter cartridges 9 are enclosed upwards by the air deflection plate 14 and to two opposing sides by the air pressure relief plates 15.

In modular flue gas filters 1 according to the invention, like the one illustrated in Fig. 2, the air deflection plate 14 is always mounted in the uppermost module 13 above the uppermost filter cartridges 9, whereas each of the air pressure relief plates 15 consists of an assembly of a number of plate parts corresponding to the number of modules 12, 13 used to construct the flue gas filter 1.

Figs. 3 and 4 are a side view and a schematic cross-sectional view, respectively; of the same flue gas filter 1 as illustrated in Figs. 1 and 2, whereas Fig. 5 is an enlargement of the uppermost part of Fig. 4. As indicated in Figs. 4 and 5 (and shown in further detail in Fig. 7), the air deflection plate 14 can be mounted to the filter casing 2 and the partition between the filter section 20 and the air outlet and filter cartridge cleaning section 21, respectively, by means of a pair of flanges 19.

Fig. 6 A is a principle sketch illustrating the flows 16, 17 of air through the flue gas filter 1, when the flue gas filter 1 illustrated in the previous figures is in use.

The incoming flow of air 16 through the air inlet 4 enters the filter casing 2 from the top at the vertical centre axis of the filter section 20, i.e. at the centre of the air deflection plate 14, the shape of which causes the incoming flow of air 16 to divide into two basically oppositely directed flows of air 17.

Due to the Coanda effect, these two flows of air 17 follow the curvature of the air deflection plate 14 and continue downwards between the perforated air pressure relief plates 15 and the outer wall of the filter casing 2 towards the bottom of the filter casing 2 with only a minimal amount of pressure loss due to turbulence.

Furthermore, the filter casing 2 is designed so that the volume increases where the incoming flow of air 16 enters the filter casing 2, which further reduces the pressure loss by reducing the pneumatic resistance along the flow path.

As the flows of air 17 approaches the bottom of the filter casing 2, the air pressure increases, and some (typically about 30-40 % depending on the design of the flue gas filter 1) of the air passes through the perforations of the air pressure relief plates 15 and reaches the filter cartridges this way. The remaining 60-70 % of the air continues downwards to the conical bottom part 9 of the filter casing 2 and reaches the filter cartridges 9 from below.

The air pressure relief plates may have a hole diameter between 1 and 5 millimeters such as a diameter of 2 or 3 millimeters and/or a pitch range of 3.5 or 5 in one embodiment. Hereby it is possible to ensure the advantageous air flow of 30 to 40% through the perforated plates such as approx. 30% (2 millimeters) or approx. 33% (3 millimeters). Due to the raising air pressure, the flows of air 17 are somewhat decelerated when passing downward along the air pressure relief plates 15. Dust and other solid particles in the air, however, continue falling toward the bottom of the filter casing 2 due to gravity as indicated by the arrows 18 in Fig. 6. Hence, in flue gas filters 1 according to the invention, a significant part of the particles in the air are separated from the air before the air reaches the filter cartridges 9, which minimises the load on the filter cartridges 9.

Thus, flue gas filters 1 according to the present invention are constructed to have at least two characteristic features contributing to an increased efficiency as compared to flue gas filters known in the art, namely less pressure loss and larger separation of particles from the air before the air reaches the filter cartridges 9. In embodiments with pleated filter bags 10, the increased surface area of the filter bags 10 further contributes to this increase of the efficiency of the flue gas filter 1. The air inlet 3 and the upper part of the filter casing 2 of the present filter embodiment are schematically illustrated in the Figure with rounded corners to pinpoint the necessary of a smooth passage for the air flow.

Fig. 6B shows means of a flue gas filter 1 according to an embodiment of the invention including the air deflection plate 14 arranged in the filter section 20 of the filter casing 2. The air inlet 3 arranged on top of the filter casing 2 opening into the filter section 20 centrally above the air deflection plate 14. The flue gas filter 1 further comprises an air outlet 4 for discharging filtered air, which has passed through the air inlet 3 and the filter casing 2. The air inlet and outlet 3, 4 of this embodiment are illustrated as located in the same plane. The filter section 20 of the filter 1 comprises filter cartridges, filter bags and/or other types of flue gas filtering means 24 located below the air deflection plate 14.

The figure further illustrates that the location of the air deflection plate 14 is vertically adaptable in relation to a change in size of the air inlet 3.

In an example of the flue gas filter is the size (X - diameter) of the air inlet 3 picked in relation to the amount of air inflow and the vertical location (Y - distance from an upper ceiling of the filter casing 2) of the air deflection plate is subsequently adapted to ensure a smooth air flow.

One relation may be:

Air inflow X Y

6000 400 60

8500 450 62

11800 500 65

15500 550 68

19800 600 75

The filter 1 in the figure is also illustrated with horizontal and vertical centre lines - hcl and vcl - which go through a top point of the curved air deflection plate 14. The centre lines of the illustrated filter embodiment are drawn in relation to the centre of a circle arc defining a central part of the curved air deflection plate 14 as further illustrated in Fig. 6C with the radius Ri for the circle arc.

Fig. 6C shows the curvature of an air deflection plate 14 wherein a central radius (Ri) is followed by still smaller bending radii (R₂ and R₃) as the distance from the centre of the plate 14 increases in establishing at least one air foil type of shape. The central radius (Ri) is substantially larger than the one or more radiuses (R₂ and R₃) at the plate edge or edges in establishing the air foil shape.

Figs. 6D-E show views of alternative embodiments of an air deflection plate with a partly curved width. Fig. 6D illustrates a small ridge on the curved width at vertical centre line and Fig. 6E illustrates the plate with a combination of curved and a linear parts wherein the linear parts are on opposite side of the vertical centre line e.g. as very insignificant parts in relation to the size of the curved parts. Figs. 6F-G show front and side views of a flue gas filter according to an embodiment of the invention.

The arrows illustrates the air flow through the filter from the air inlet 3 to the air outlet 4, via the air deflection plate 14, the filter cartridges, filter bags and/or other types of flue gas filtering means 24, and the air outlet and filter cartridge cleaning section 21.

Figs. 7 A, 7B and 7C are two side views and a perspective view, respectively, of an air deflection plate 14 of a flue gas filter 1 according to an embodiment of the invention.

Fig. 7 A shows how the curvature of the air deflection plate 14 follows still smaller bending radii as the distance from the centre of the plate 14 increases. This ensures an equal distribution of the incoming mixture 16 of dust, gas and air and an optimal utilisation of the Coanda effect on the air flow 17 along the air deflection plate 14 and the air pressure relief plates 15 as discussed above.

Typically, the curvature of the air deflection plate 14 follows two different bending radii, the ratio between which are in the range from 1.5 to 20. In a preferred embodiment, the ratio between the two bending radii is 4.2. The optimal bending radii and the ratio between these radii are determined empirically, whereas the formula for calculating the maximum Coanda drag can be found in the literature, for instance at the URL: http://naca.central.cranfield.ac.uk/reports/1958/naca-tn- 4377.pdf (Formula 2 on page 7). Furthermore, preferred embodiments of the flue gas filter 1 is equipped with a heater unit, such as for instance a 3 kW electrical heater, so that the flue gas filter 1 can be operated at optimal temperatures depending on the type of filtering being performed.

As mentioned above, the efficiency of the filtering can vary significantly with the temperature of the air being filtered, the optimal temperature range depending on the type of filtering. For filtration of flue gas, for instance, the optimal temperature range is between 110 °C and 170 °C.

Typically, flue gas filters 1 according to the invention are dimensioned to be able to handle pressure differences of more than 10 kPa and temperatures of 200 °C or more.

The dimensions of the flue gas filter 1 depend on the desired filtration capacity, but typical horizontal dimensions are between 1 m and 1.5 m with a total height of the flue gas filter 1 (including filter supports 6, air inlet 3 and air outlet 4) between 2 m and 6 m.

Air inlets 3 and air outlets 4 can be available in different dimensions depending on the load on the flue gas filter 1 and the type of filter cartridges 9 used therein. Flue gas filters 1 according to the invention are particular well-suited for filtration of relatively large amounts of air containing a low amount of dust. However, it can be configured for a large variety of different types of filtration, depending on the number (typically between 2 and 10) of filter cartridges 9 in the flue gas filter 1, the dimensions of the filter cartridges 9 and the filtering materials (for instance PPS HT, polyester or paper) from which the filter bags 10 are made. Fig. 7D shows the embodiment of the air deflection plate 14 illustrated in Fig. 7 A as seen from above being substantially rectangular with mounting flanges for the air deflection plate 19 and dotted drawing lines illustrating different radii. Figs. 7E-F show views of alternative embodiments of an air deflection plate according to the invention.

Fig. 7E shows an embodiment with a full dome shaped air deflection plate 14 e.g. as part of a filter 1 with a circular outer shape. The air deflection plate 14 may also be semi-dome shaped to create more than one separate air flows each air flow flowing over a dome part.

Fig. 7F shows another embodiment of an air deflection plate 14 combing the plate shapes illustrated in Fig. 7A and 7E.

Fig. 8 shows a view of a flue gas filter in an embodiment with a heater unit installed. The heater unit comprises an electric heating device 22 located and mounted on an outer surface of the filter casing 2 such as the outer surface of the conical bottom part 11 of the filter casing 2. The device 22 is connected to an electrical power supply 23 for supplying the necessary electric power to heat the air flow within this section or adjacent sections of the flue gas filter 1. The air flow in the filter is schematically illustrated with arrows in Figs. 6F and Fig. 6G and a heated air flow enters the flue gas filtering means 24 after being in proximity of the heater unit. The device 22 may for example be a type of electric blanket, heating pad or similar means using an insulated electric wire or heating element.

Among the different types of applications for which flue gas filters 1 according to the invention can be configured can be mentioned: decentralised CFIP (combined heat and power) plants running on biofuel or natural gas, processing plants generating smoke or other fumes at high temperatures, plants working with laser cutting, plasma cutting, flame cutting, grinding, lacquering and/or sandblasting, or torrification of biomass.

List of reference numbers

1. Flue gas filter

2. Filter casing

3. Air inlet

4. Air outlet

5. Pressurised air device for filter cartridge cleaning

6. Filter support

7. Rotary valve for removal of solids

8. Motor for rotary valve

9. Filter cartridge

10. Filter bag

11. Conical bottom part of filter casing

12. Four-cartridge module

13. Two-cartridge module

14. Air deflection plate

15. Perforated air pressure relief plate

16. Incoming flow of air

17. Air flow within filter casing

18. Flow of particles within filter casing

19. Mounting flange for air deflection plate

20. Filter section

21. Air outlet and filter cartridge cleaning section

22. Electric heating device

23. Electric power supply

24. Filter cartridges, filter bags and/or other types of flue gas filtering means

Claims

1. A flue gas filter (1) comprising a filter casing (2) divided into at least a filter section (20), wherein a curved air deflection plate (14) is arranged in the filter section (20) in such a way that said air deflection plate (14) curves downwards, and an air inlet (3) arranged on top of the filter casing (2) opening into the filter section (20) centrally above the air deflection plate (14), and the flue gas filter (1) further comprises an air outlet (4) for discharging filtered air, which has passed through the air inlet (3) and the filter casing (2).

2. The flue gas filter (1) according to claim 1, wherein said filter casing (2)

comprises an air outlet and filter cartridge cleaning section (21).

3. The flue gas filter (1) according to claim 1 or 2, in which said filter section (20) one or more elongated filter cartridges (9) are arranged parallel to each other.

4. The flue gas filter (1) according to claim 3 wherein said one or more elongated filter cartridges (9) are arranged parallel to each other with substantially horizontal longitudinal axes.

5. The flue gas filter (1) according to any of the preceding claims, wherein said air deflection plate (14) is substantially rectangular.

6. The flue gas filter (1) according to any of the preceding claims, wherein said air deflection plate (14) is arranged above the one or more filter cartridges.

7. The flue gas filter (1) according to any of the preceding claims, wherein said air deflection plate (14) curves downwards from a substantially horizontal centre line.

8. The flue gas filter (1) according to claim 7, wherein said substantially

horizontal centre line is parallel to the longitudinal axes of the one or more filter cartridges, in both directions perpendicular to the centre line.

9. The flue gas filter (1) according to any of the preceding claims, wherein two perforated air pressure relief plates (15) are arranged substantially vertically.

10. The flue gas filter (1) according to claim 9, wherein the two perforated air pressure relief plates (15) are arranged parallel to the longitudinal axes of the one or more filter cartridges (9).

11. The flue gas filter (1) according to claim 9 or 10, wherein each of the air

pressure relief plates (15) abutting one of the two lower edges of the air deflection plate, respectively.

12. The flue gas filter (1) according to any of claims 9 to 11, wherein the one or more filter cartridges (9) are enclosed upwards by the air deflection plate (14) and to two opposing sides by the air pressure relief plates (15).

13. The flue gas filter (1) according to any of the preceding claims, wherein the air passed through the one or more filter cartridges (9).

14. The flue gas filter (1) according to claim 1, wherein the air inlet (3) is rotatably arranged on the top of the filter casing (2) so that the horizontal direction from which air is directed into the air inlet (3) can be optimized in relation to the surroundings in which the flue gas filter is installed.

15. The flue gas filter (1) according to any of the preceding claims, in which the air outlet (4) is arranged on top of the filter casing (2).

The flue gas filter (1) according to any of the preceding claims, wherein each of the filter cartridges (9) is substantially cylindrical in shape with the curved surface formed by a filter bag (10) made of a filtering material so that, in use, air moves radially into the filter cartridge through the filtering material and leaves the filter cartridge in an axial direction at one of the ends thereof.

The flue gas filter (1) according to claim 16, wherein the filter bags (10) are pleated by repeatingly folding the filtering material, from which the filter bags (10) are made.

The flue gas filter (1) according to any of the preceding claims, further comprising an airtight rotary valve (7) for removal of filtered off solids from the filter casing (2).

The flue gas filter (1) according to any of the preceding claims, further comprising a device (5) for cleaning the one or more filter cartridges (9) means of pressurised air.

The flue gas filter (1) according to claim 19, wherein operation of the device (5) for cleaning the one or more filter cartridges (9) is controlled to be initiated at regular time intervals and/or when a differential pressure measured between the outside and the inside of one or more of the filter cartridges (9) exceeds a predefined threshold value.

21. The flue gas filter (1) according to any of the preceding claims, further

comprising a heater unit so that the flue gas filter can be operated at optimal temperatures depending on the type of filtering being performed.

22. The flue gas filter (1) according to any of the preceding claims, wherein at least a part of the filter is constructed by combining two or more modules (12, 13), each containing one or more filter cartridges.

23. The flue gas filter (1) according to any of the preceding claims, wherein said air deflection plate (14) curves in the full width of the plate or in part or parts of the full width.

24. The flue gas filter (1) according to any of claims 1 to 4, wherein said air

deflection plate (14) is substantially dome or semi-dome shaped and/or is a combination of shapes such as rectangular and semi-dome shapes.

25. The flue gas filter (1) according to claim 24, wherein one or more perforated air pressure relief plates (15) are arranged substantially vertically below the lower edge or edges of the substantially dome or semi-dome shaped air deflection plate (14).

26. The flue gas filter (1) according to any of claims 9 to 25, wherein said one or more perforated air pressure relief plates (15) comprise symmetrically located perforation holes in a vertical direction e.g. with a hole diameter between 1 and

5 millimeters such as a diameter of 2 or 3 millimeters and/or a pitch range of 3.5 or 5.

27. The flue gas filter (1) according to any of the preceding claims, wherein said air deflection plate (14) is curved with a central radius (Ri) substantially larger than one or more radiuses (R₂, R₃) at the plate edge or edges in establishing at least one air foil shape.

28. The flue gas filter (1) according to any of the preceding claims, wherein

curvature of the air deflection plate (14) being configured for the Coanda effect. The flue gas filter (1) according to any of the preceding claims, wherein the deflection plate (14) is mirror symmetric in relation to a vertical centre line.

The flue gas filter (1) according to any of the preceding claims, wherein the position of said air deflection plate (14) is vertically adaptable in relation to change in size of the air inlet (3).

The flue gas filter (1) according to claim 1, wherein said filter casing (2) comprises one or more filter cartridges, filter bags and/or other types of flue gas filtering means.

32. The flue gas filter (1) according to claim 21, wherein said heater unit includes an electrical heating device (22) e.g. located on an outer surface of said filter casing (2) and an electrical power supply (23).

33. Use of a flue gas filter according to any of claims 1 to 32 in connection with a combined heat and power plant running on biofuel or natural gas, a processing plant generating smoke or other fumes at high temperatures, a plant working with laser cutting, plasma cutting, flame cutting, grinding, lacquering and/or sandblasting, or a plant working with torrification of biomass.