WO2014181039A1

WO2014181039A1 - Fabric filter

Info

Publication number: WO2014181039A1
Application number: PCT/FI2014/050331
Authority: WO
Inventors: Jukka Hirvenoja
Original assignee: Andritz Oy
Priority date: 2013-05-07
Filing date: 2014-05-06
Publication date: 2014-11-13
Also published as: FI20135474L; FI20135474A7

Abstract

A fabric filter for filtering flue gases of a power plant having a cylindrical shell (2) with a diameter of at least 3 meters and having tubular filtering elements (5) open at their upper ends and closed at the bottom, and the feed flow into the filtering chamber is fed tangentially from a feed conduit (1) through a feed aperture (8) in the cylindrical shell (2) of the filtering chamber located in the upper part of the filtering chamber. Flow deflectors (11) having a substantial radial extent are arranged within the feed aperture (8) of the filter to form a substantially continuous grate (12) covering at least the initial end of the feed aperture (8), which flow deflectors (11) and the gaps between them cause a substantial turn of the tangential feed flow in the horizontal plane and the trailing end of the feed conduit (1) is provided with a flow channel (14) of substantial width for ensuring the tangential flow to continue into the filtering chamber.

Description

Fabric filter

The present invention relates to a fabric filter used for filtering gases, and especially a grate mounted therein for diverting the flow of gas to be cleaned entering the filtering chamber.

In fabric filters the gas to be cleaned is led through a filtering material, whereby solid particles remain on the surface of the filter. Typically the filtering material comprises woven or felt-like fiber. Particles are separated or stick into the fiber by means of direct retention, diffusion, electrostatic attraction and gravitation deposition. During operation, a dust layer (dust cake) is formed on the surface of the filter, which has to be removed at certain intervals. The removal can be effected e.g. by means of compressed air pulses, counter-current cleaning, by shaking or acoustic waves. Filtering elements used in a fabric filter typically comprise tubular filtering elements that are made of a porous material and closed at their lower ends, which elements are at their upper ends attached to openings in an intermediate floor separating the filtering chamber and the space for filtered gas. A framework is usually arranged inside the filtering elements, which keeps the flow channel open when the pressure inside the filtering element is lower than outside of it. Fabric filters are commonly used in numerous applications requiring a large flow volume. Very large fabric filters are commonly used for separating solids from flue gases of power plants.

When the cross section of the filtering chamber is circular, the gas to be cleaned is often fed in tangentially, which generates an intense flow conforming to the feed conduit and the shell of the filtering chamber, from which flow the coarsest particles are separated under centrifugal force in the feed conduit and the space between the filtering chamber and the filtering elements, falling directly to the bottom of the filtering chamber before drifting onto the surfaces of the filtering elements. Thus the filter operates partly according to the centrifugal cleaning principle. The feed flow is not decelerated notably when the gas to be cleaned flows through a completely open feed aperture into the filtering chamber and towards the filtering elements, but it is almost undecelerated confronted towards the filtering elements close to the feed aperture. Especially the coarsest particles travelling entrained in the feed gas have a highly abrasive impact on the filtering elements. Additionally, shaking of the filtering elements inflicted by the flow wears the elements. Turbulence and other variations of the flow amplify significantly the shaking and the wearing caused by it. Pre-fltering of dust and ash particles of flue gases from power plants by means of e.g. a cyclone is avoided, because it is a too space-consuming and expensive solution compared to the advantages of a cyclone. Attempts have been made to decelerate the abrasive flow directing to the filtering elements by various planar, i.e. cylindrical barriers arranged between the feed flow and the filtering elements. An example of such a solution is publication US7776278, in which a cylinder inside the filtering chamber of the filter prevents the incoming flow from being directed straight to the filtering elements. Further, numerous solutions are known, such as presented in publication US6887290, in which a cylindrical flow shield of the cyclone cleaner, which shield is perforated at its lower part directs the flow to enter the filtering elements downwardly. Directing the flow to the filtering elements from down upwards is disadvantageous, since particles being released during cleaning of the filtering elements float in the upward stream and in a significant extent end up back to the surfaces of the filtering elements. In small filters an arcuate or circular structure between the filtering chamber and the filtering elements for diverting the flows is reasonably feasible, but in large fabric filters of power plants the use of arcuate structures is not cost-effective due to their heavy weight, cost of the structure, difficulty of assembly and space consumption. Especially as retrofit this kind of solution would be impossible to carry out.

The use of cylinders or large arches for directing the flow is not an appropriate solution in connection with large fabric filters used in power plants. Their filtering chamber has a diameter of several meters, i.e. minimum 3 meters, and typically 5 - 6 m. Also, the filtering chamber is very high, e.g. 10 - 15 m. Locating a large cylinder, baffle or arch weighing up to thousands of kilos would lead to the use of filtering chamber diameter wider than usual. Enlarged chamber size and a large cylinder therein would significantly increase the material, manufacturing and mounting costs of the structure. The structure usually does not have enough space available for an arcuate flow shield, especially when added as a retrofit. Transportabilityof the filter substantially limits the increase of the diameter over 5 meters. The size limitation may lead to the use of several filters, which problem does not exist with rectangular filters. Therefore, it is critical to obtain the highest possible filtering capacity for the space available in a round filter. Pre-separation allowed by tangential flow increases the limited capacity of a round filter and thus competitivness of this kind of filter, and problems relating to the construction are critical to be solved.

Publication SU893232 describes the use of tangential gas feed into a round fabric filter, wherein a dust-separation grate and an intermittent wall are arranged deep inside the feed conduit. Said dust-separation grate is a significant flow resistance and it does not direct the flow going into the filtering chamber in any way, but mostly decelerates it and causes unnecessary turbulence. Separating coarse particles by an intermediate wall efficiently separates them to the edges of the feed conduit and the filtering chamber, and it acts as a pre-separation phase. Pre-separation is not based on the centrifugal force of the feed conduit, but on the diverting efferct of the dust- separation grate on the particles. The grate is almost transverse against the flow of the abrasive particles, so that the abrasive particles wear it out quickly. The solution according to the publication can be usable in small and moderate-sized filters of light construction, but it is not feasible in large flue gas filters with abrasive particles. A large-sized intermediate wall in a large fabric filter of a power plant would be prone to get clogged, when pressure loss in a long narrow gap decelerates the flow. An intermediate wall would be too heavy and too expensive to manufacture, and in practice it cannot be retrofitted.

The purpose and solution of the invention

A novel solution has been developed for the abocve mentioned problems. A purpose of the invention is to provide a solution for the problems limiting the purpose, which solution is as wide and versatile as possible. The purpose is achieved such that a filter defined in the preamble of the independent claims is implemented as defined in the characterizing part of the claims. Preferred embodiments of the invention may correspond to the dependent claims. According to the present invention, tangential feed flow of a large fabric filter with a diameter over 3 m is diverted by means of a substantially continuous grate comprised of flow deflectors and arranged in the feed aperture or in the filtering chamber in immediate vicinity of the feed aperture, at a distance of 50 mm at the most, the trailing end of the grate being provided with a flow channel of substantial width for allowing the tangential flow continue into the filtering chamber. The flow deflectors have a substantial radial extent, and therefore the feed flow turns in the horizontal plane from substantially tangential to more radial inside the grate. Simultaneously the flow velocity decreases substantially, when the gas to be cleaned flows through the grate towards the filtering elements in the filtering chamber. When implemented in accordance with invention, a grate in the feed aperture does not cause notable pressure loss and it does significantly consume the effective space and operational capacity of the chamber. When an alternative for a grate is locating the filtering elements adequately far from the feed aperture, the number and thus capacity of the filtering elements can in practice be greater, which is boosted by the centrifugal cleaning effect of the tangential feed.

When traveling between the flow deflectors, the gas may simultaneously change its direction in the vertical direction. This change, too, can be controlled if needed by means of flow deflectors. Most critical in diverting the inflow to the filtering elements is horizontal deflection of the flow and the continuity of the tangential flow of the trailing end of the feed conduit aside the wall of the filtering chamber.

When traveling inside the feed conduit, the tangential feed flow is not notably decelerated, but remains substantially as fast as in the initial end of the feed conduit, from where the gas to be cleaned flows in typically at a rate of 18 m/s. If an excessive flow resistance prevails in the grate of the feed aperture, the flow velocity may even increase towards the end of the feed conduit. With the typical dimensions, the width of the feed conduit of a fabric filter of a power plant is in the range of 1 - 2 m and the height 2 - 4 m. Typically the feed aperture covers at least half and most usually 270 degrees of the circumference of the filtering chamber. This arrangement is also the most advantageous for the solution according to the invention. A shorter feed aperture decreases the centrifugal cleaning effect and in an aperture wider than 300 degrees the flow of the trailing end starts disturbing the flow at the initial end. With a 5 meter diameter of a filtering chamber, the width of a 270 degrees feed aperture is π x 5 m x 3/4, i.e. 12 m. The area of the feed aperture is thus in the range of 5 - 10 -fold compared to the area of the initial end of the feed conduit. The velocities of the flows entering the feed conduit and the filtering chamber have in an ideal case the same mutual ratio as the area of the initial end of the feed conduit and the area of the feed aperture of the filtering chamber. By means of a grate in the feed aperture, a tangential flow can be deflected mainly to radial and simultaneously the flow velocity of the feed flow can be decelerated to a fraction of the original. Even decelerating the flow velocity to half would considerably decrease wearing, because both the force effect caused by the flow and the kinetic energy of the abrasive particles changes to the second power of the flow velocity proportionally. In practice the impact of the flow velocity on the wearing of the filtering elements can be even stronger. It is often enough, if the flow velocity directed to the filtering elements and its changes remain below a critical level. Then the particles accumulating on the filtering elements can protect the filtering surface against hits of abrasive particles and other impacts of the feed flow. The aim is to make the wearing of the filtering elements caused by the feed flow insignificant, i.e. substantially smaller than normal wearing caused by cleaning impulses and the filtration process.

In practice, the flow will not be ideal, but local flow velocities higher than average are met in the filtering chamber. The longer radial extent of the flow deflectors is compared to the gaps between the flow deflectors, the more homogeneous flow is achieved. Advantageously the extent of the flow deflectors in the radial direction is at least half of the width of the gaps between them, in order to adequately deflect the flow to the radial direction. Too short an extent in the radial direction does not cause adequate deflection of the flow, but makes the flow turbulent, whereby the flow directed to the filtering elements may at some locations be too abrasive. Advantageously, the radial extent of the flow deflectors is equal to or larger than the width of the gaps between them. The flow is stabilized along the whole flow path and deflected almost completely to the radial direction or to the direction of the center line of the gaps between the flow deflectors, when the width of the flow deflectors is at least two-fold the width of the gap between them. In view of space consumption, expenses and flow characteristics, the optimum is that the radial extent of the flow deflectors is 1-2 -fold the distance between the gaps. Preferably the radial extent of the flow deflectors is 50-200 mm. The minimum is restricted by the efficiency and vibrations of the flow deflectors and the maximum by material and assembly expenses and distance to the closest filtering elements. Advantageously the distance between the grate and the filtering elements is 100-200 mm, whereby the flow has time to stabilize and a maximum number of filtering elements can be located in the chamber.

A perforated plate can provide the same situation with respect to the stabilizing of the flow as deflectors extending radially. However, then the plate would act more as an obstacle to the flow than a structure guiding the flow, whereby flow resistance and thus pressure loss would be too high. Simultaneously the velocity and volume of the tangential flow in the trailing end of the feed aperture would increase too high for adequately quick stabilization.

Tangential feed flow and its wearing impact is concentrated at strongest to individual filtering elements in front of the feed aperture, the service life of which easily remains a fraction of the service life of the other filtering elements. Further, with a fluidized bed boiler, part of the highly abrasive sand of the bed is passed entrained with flue gases into the filter. Due to these factors, the service interval of the filter is only a fraction of what it would be, if the wearing impact of the feed flow on individual elements would be eliminated. When the flow velocity is decelerated and stabilized adequately, the feed flow is not concentrated too strong and wearing to individual filtering elements. Then the wearing of the filtering elements is as homogeneous as possible in the whole filter and the service intervals are maximal.

The strongest turbulence of the flow that has passed the grate takes place in the initial end of the feed aperture when radial flow deflectors are used. This phenomenon can mainly be avoided by using tighter spacing between the flow deflectors. This would lead into excessive pressure loss. Most advantageously the flow deflectors are arranged in an alignment which deviates from the direction of the radius so that their outer edges are in the direction of the feed flow further than their inner edges. Due to strong turbulence, the initial end of the grate cannot have a gap uncovered by the grate that would be in the tangential direction wider than the gap between the flow deflectors in the initial end of the grate. If a radial gap exists between the grate and the initial end of the feed aperture, the grate advantageoulsly extends into the filtering chamber further than the initial end of the feed aperture so that a flow channel remains between the grate and the cylindrical shell of the filtering chamber.

Through the gap between the trailing end of the grate and the feed conduit the tangential flow with entrained coarsest particles can well continue at approximately initial velocity along the side of the filtering chamber. Since the flow volume is only a fraction of the initial volume, the flow when released into the filtering chamber is attenuated and stabilized very quickly and the coarsest particles can drop downwards. Advantageously the flow in the trailing end is diverted transversely downwards for pre-directing the motion of the particles downwards. Simultaneously the flow in the trailing end is widened and thus also decelerated.

Advantageously the flow in the trailing end comes to a point in the filtering chamber where the filtering elements are located inner than average. A corresponding arrangement is advantageous at the initial end of the feed aperture, where the incoming flow will form more turbulent than average.

Most advantageously the flow deflectors are fixed in the feed opening to form a gratelike structure. The flow deflectors are arranged in the feed aperture so that they extend into the feed conduit maximum at the length of their radial extent or in front of the feed aperture, whereby their outer edge is at the most 50 mm to the side of the filtering chamber. Then the flow deflectors do not excessively clog the flow in the feed conduit and do not consume excessively space from the filtering elements. In the initial and/or trailing end of the grate the flow deflectors are advantageously completely on the side of the filtering chamber for controlling the flows at the ends. The flow deflectors extending into the feed conduit must not excessively disturb the flow inside the feed conduit. The flow deflectors are positioned substantially covering the whole width of the initial part of the feed aperture, but an uncovered portion may remain in the trailing end. The free portion of the trailing end of the feed aperture can be up to 25% of the tangential length of the feed aperture. Lenghtening of the uncovered portion correspondingly decreases the costs of the grate. Most advantageously a flow channel of 50 - 200 mm should remain between the feed conduit and the grate in the radial direction for ensuring continuous tangential flow and its separation effect. If the width is smaller, strong turbulence is formed in the trailing end of the grate and the advantages of the centrifugal cleaning impact of the tangential feed are not obtained. If the flow channel is wider than the mentioned, the mass of the flow remains so voluminous that it is not attenuated adequately quickly when released into the chamber. If the grate covers the whole aperture, the trailing end of the grate must be located inside the filtering chamber for keeping the flow channel between the grate and the feed conduit or the cylindrical shell of the filtering chamber open for the tangential flow.

Advantageously the radial extent of at least 1 - 10 last flow deflectors in the ftrailing end of the grate is substantially shorter than the width of the flow deflectors in the first half of the grate. Then the trailing end of the grate can be closer to the trailing end of the feed aperture and it can even fit between the filtering chamber and the filtering elements. In the trailing end of the grate at least the last flow deflector is advantageously directed substantially tangentially for controlling the turbulence in the trailing end. The initial end of the grate can correspondingly extend into the filtering chamber further than the initial end of the feed aperture.

The most advantageous form for the flow deflectors in view of cost, mountability and availability is planar form. The structure can comprise one or several parts of a grate, which form a substantially continuous grate. Adequately wide flow deflector plates, their appropriate direction and positioning provide an adequately stabilized flow. The flow deflectors are attached at the zone of their ends either directly and/or by means of support arches of the intermediate floor to the feed, the support bars of the feed aperture or to the shell of the filtering chamber of the filter. Due to vibrations, in addition to their ends, they are preferably attached to each other depending on the height at adequately dense spacing at least at one point by means of support arches. Notches that facilitate the assembly can be arranged at the ends of the flow deflectors. At least a part of the flow deflectors can be round or oval-shaped and they can also be bended to curved or to wing profiles. The use of round, oval-shaped and rectangular tubes in the grate structure at appropriate spacing facilitates the use of the grate simultaneously for supporting the ceiling of the filtering chamber, in the openings of which the filtering elements are suspended. Planar flow deflectors have a low buckling strength. Therefore using them in supporting the top requires very rigid supporting of them to each other. Flow deflectors acting as supporting members can also be separate from the primary grate structure. The flow deflectors in form of a level rod, a plate, a rectangular tube, oval shape or otherwise flat form attached in connection with the feed opening are directed i.e. in view of flows and production, when possible, substantially parallel to the radius of the filtering chamber. For the purpose of widening the distribution of the feed flow and decreasing the turbulence it is often advantageous that at least the flow deflectors located at the initial portion of the feed opening are directed or formed so that they deflect the flow somewhat more than required for deflecting it to be parallel to the radius. Then the flow is deflected more stabilized and partly tangentially towards the filtering elements, which are located in the filtering chamber in the opposite direction with respect to the feed flow. Preferably the deviation from the direction of the radius is at the most 45 degrees. A deviation wider than that excessively increases the flow resistance. In different zones of the feed aperture, the flow can be stabilized by altering the width of the gaps between the flow deflectors, the thickness and width of the flow deflectors, or by setting the angle of attack of the flow deflectors so that the flue gases flow as uniformly as possible into the filter.

Especially when cleaning flue gases containing fluidized bed material from the fluidized bed boiler the wearing of the flow deflectors can be decreased with a wear- resistant coating. A significant advantage of the grate construction in the feed aperture is that the abrasive particle-containing flow hits only to the edge of the flow deflectors on the side of the feed conduit. A preceding flow deflector protects the subsequent against wearing. Further, the most abrasive particles are resettled alongside the outer wall of the feed conduit. Therefore, coating is usually unnecessary. The invention can be applied in many various detailed ways within the scope of the claims. Case-specifically the shape, radial extent and position of the flow deflectors can be varied to a wide extent. The positioning and shape of the flow deflectors in various zones of the feed aperture and in the filtering chamber and the impacts of the supporting members are best controlled by simulating the flows. Simulation allows optimizing the flows and the positions of the filtering elements and the feed aperture so that at locations where the filtering elements are furthest from the flow deflectors a more intense or more turbulent flow can be generated than elsewhere in the filtering chamber.

Lisf of drawings

In the following, the invention is disclosed in more detail with reference to the appended drawings, of which

Fig. 1 illustrates the structure of a typical cylindrical bag filter,

Fig. 2 illustrates a solution according to an embodiment of the invention, where the flow deflectors are located within the feed aperture,

Fig. 3 is an enlarged view of the structure of the trailing end of the grate in Fig. 2 and

Fig. 4 illustrates an enlarged view of the structure of the trailing end of the grate according to an embodiment of the invention.

Detailed description of the invention

Fig. 1 illustrates as a vertical cross section a typical structure of a tangentially fed cylindrical fabric filter for filtration of flue gases of a power plant. The gas to be cleaned flows into the filter via feed conduit 1. From the feed conduit 1 the gas flows tangentially into a filtering chamber having a cylindrical outer shell 2 with a large, normally over 3 meter diameter. The filtering chamber has a conical bottom 3 and its top is an intermediate floor 4 with openings. Tubular filtering elements 5 made of nonwoven fabric or felted cloth and closed at their bottom are attached at the upper ends to the openings of the intermediate floor 4. The number of filtering elements 5 in a typical flue gas filter is at least several tens. The interior of the filtering elements 5 can be provided with frames that keep the flow channel inside the filtering elements open. From the interior of the filtering elements 5 the cleaned gas flows via the openings in the intermediate floor into a chamber 6 for cleaned gas. The cleaned gas exits the filter via a discharge duct 7.

A feed aperture 8 (Fig. 2), which is the aperture in the outer shell 2 at the trailing end of the feed conduit, is a boundary between the feed conduit 1 attached to the upper part of the filtering chamber and the filtering chamber itself. Particles of the gas to be cleaned, which enters the filtering chamber via feed opening 8, are separated directly to the bottom 3 of the filtering chamber or onto the surfaces of the filtering elements 5. Particles accumulated on the surfaces of the filtering elements 5 are periodically dropped typically by means of counter-currently fed cleaned gas onto the bottom 3 of the filtering chamber. When the gas to be cleaned is fed into the filtering chamber from above and it flows downwards, the flow assists the dropping of the particles downwards. The particles are removed from the bottom 3 of the filtering chamber the particles e.g. by means of a rotary feeder 9. The tangential feed flow does not attenuate straight upon entry into the filtering chamber, but it hits with full strength especially the filtering elements 5 closest to the feed aperture 8. The feed flow wears the filtering elements 5 both due to the hits of the particles and by swinging the filtering elements against each other and against the support frames. Since the motion of the filtering elements 5 continuously shakes off the particle cake protecting them, the particles can hit the filtering material and wear it efficiently.

Fig. 2 illustrates a solution according to an embodiment of the invention at the point of the feed conduit 1 in horizontal cross section. Flow deflectors 11 are mounted to form a grate 12 in the feed aperture 8, and via gaps between the flow deflectors the gas to be cleaned flows into the filtering chamber and towards the filtering elements 5. The flow deflector plates may have a thickness of e.g. 5 mm and a width of 200 mm, with a gap of 100 mm between them. The flow deflectors 11 are in figure 2 arranged to extend partially inside the feed conduit 1 and partially to the side of the filtering chamber. By the extent of the deflectors 11 inside the feed conduit 1 it is possible to control the flow velocity in the gap between the flow deflectors at different points of the feed aperture 8 and thus to obtain the most stabilized or desired possible flow distribution into the filtering chamber. Therefore, the radial location of the flow deflectors 11 with compared to the feed aperture 8 can advantageously be different in the initial end, middle portion and the trailing end of the feed aperture. In the example of Fig. 2 the flow deflectors 11 at the initial portion of the feed opening 8 are not directed radially but turned somewhat to co-current direction. Then the center lines of the flow deflectors 11 deviate from the radial direction so that the outer edges of the flow deflectors 11 extend in the direction of the tangential feed flow further than the inner edges.

In the example of Fig. 2 at the initial end of the feed aperture the distance of the filtering elements from the cylindrical shell 2 of the filtering chamber is longer than average, which is advantageous in view of stabilizing the flow. This does not apply to the trailing end of the feed aperture. For new filters this situation can be corrected so that these critical zones are taken into account when locating the filtering elements and the feed conduit. With already operating filters the situation can be improved by removing filtering elements from the critical zones so that their increased maintenance or replacement requirement does not affect the operational cycles of the whole filter.

In Fig. 3 the flow deflectors 11 in the trailing end of the feed aperture 8 do not extend quite to the end of the feed aperture 8, and there will remain a flow channel 14 having a substantial width, which allows tangential flow. Since the flow deflectors 11 extend into the interior of the feed conduit 1 , a grate 12 covering the whole feed aperture 8 would stop the tangential flow. A flow barrier is located between a tube 10 acting as a support member and the adjacent flow deflector 11. The flow barrier prevents the formation of excessive turbulence in the filtering chamber at the site of the tube 10. The grate 12 covers preferably at least 75 % of the tangential length of the feed aperture 8 so that it begins from the initial end of the feed aperture and is substantially continuous. Most advantageously this portion is over 90 %, whereby a more stabilized flow is obtained in the trailing end. The distance between the feed conduit 1 or the cylindrical shell 2 of the filtering chamber to the trailing end of the grate 12, i.e. at the width of the flow channel 14 is at the narrowest point at least 50 mm and at the most 200 mm.

Fig. 4 illustrates some preferred embodiments of the trailing end of the grate 12. Advantageously the radial extent of the last 1-10 flow deflectors 11 in the trailing end of the grate 12 is shorter than elsewhere in the grate 12. The shortest distance of the grate 12 from the feed conduit 1 or the cylindrical shell 2 of the filtering chamber is not necessarily in the trailing end of the grate, but it may be more advantageous to locate it at an earlier point. In Fig. 4 this point is located in the vicinity of the last support member 10. The last flow deflector 11 is aligned substantially tangential in order to direct the feed flow as tangentially as possible along the side of the cylindrical shell 2. Also other angular alignments of the flow deflectors 11 are possible, but radial or tangential flow deflectors are implemented most inexpensively. A tapering initial end of the grate 12 corresponding to Fig. 4 can be arranged in the initial end of the feed aperture 8, which initial end extends to the front side of the feed aperture.

At the trailing end of the grate 12 a vertical change in the flow can be intended for diverting the coarsest particles towards the bottom of the filtering chamber. This kind of flow deflector 11 can be e.g. vertically inclined or have a twisted profile, or have a profile which is twisted, or otherwise varying in the vertical direction. Vertical deflection of the flow can be achieved also by means of different widths of the flow channel 4 between the flow deflectors 11 and wall of the feed conduit 1 at the upper and lower ends of the flow deflectors, whereby the flow channel 14 is narrower in its upper end.

Claims

1. A fabric filter for filtering flue gases of a power plant, which filter comprises a substantially round vertical axis filtering chamber having a cylindrical shell (2) with a diameter of at least 3 meters and having as a ceiling an intermediate floor (4) with openings, which openings are provided with vertical tube-like filtering elements (5) which are open at their upper ends and closed at the bottom, via which filtering elements (5) and the intermediate floor (4) the cleaned gas flow passes into a chamber (6) for clean air located above the filtering chamber, and from there via a discharge opening (7) out of the fabric filter, and the feed flow into the filtering chamber is fed in tangentially from a feed conduit (1) via a feed aperture (8) of the cylindrical shell (2) of the filtering chamber located in the upper part of the filtering chamber, characterized in that flow deflectors (8) having a substantial radial extent are arranged within the feed aperture (8) or between the feed aperture (8) and the filtering elements (5), which flow deflectors form a substantially continuous grate (12), said flow deflectors (11) and the gaps between them causing a substantial turn of the tangential feed flow in the horizontal plane and the trailing end of the feed conduit (1) is provided with a flow channel (14) of substantial width for continuity of the tangential flow into the filtering chamber.

2. A fabric filter according to claim 1 , characterized in that the distance of the side wall of the feed conduit (1) from the flow deflectors (11) of the grate (12) in the flow channel (14) of the tangential flow in the trailing end of the feed aperture (8) at the shortest 50 mm and at the most 200 mm.

3. A fabric filter according to claim 1 or 2, characterized in that the radial extent of the flow deflectors (11) in the direction of the radius of the filtering chamber is at least half of the width of the gap adjacent to the flow deflector (11), preferably the radial extent of the flow deflectors (11) in the direction of the radius of the filtering chamber is at least equal to the width of the gap between the flow deflectors (11 ).

4. A fabric filter according to any of the preceding claims, characterized in that the radial extent of the flow deflectors is at least 50 mm and at the most 200 mm.

5. A fabric filter according to any of the preceding claims, characterized in that the flow deflectors (11) are connected by means of a support arch (13) to at least one adjacent flow deflector (11 ) between the ends of the flow deflectors (11).

6. A fabric filter according to any of the preceding claims, characterized in that the gaps between the flow deflectors (11) of the grate (12) are of different size in various areas of the grate (12).

7. A fabric filter according to any of the preceding claims, characterized in that at least in the initial end of the feed aperture the center lines of the flow deflectors (11) deviate from the direction of the radius of the filtering chamber so that the outer edge of the flow deflectors (11) extends in the direction of the tangential feed flow further than the inner edge.

8. A fabric filter according to any of the preceding claims, characterized in that in the trailing end of the grate (12) the feed flow is diverted by means of one or more flow deflectors (11) to turn the vertical direction downwards.

9. A fabric filter according to any of the preceding claims, characterized in that in the trailing end of the grate (12) the upper end of at least the last flow deflector

(11) is located in the radial direction closer to the side wall of the feed conduit (1) or the cylindrical shell (2) of the filtering chamber than the lower end of the flow deflector (11).

10. A fabric filter according to any of the preceding claims, characterized in that in the trailing end of the grate (12) the feed flow is directed to continue tangentially in the vicinity of the cylindrical shell (2) of the filtering chamber by means of a flow deflector (11) aligned substantially tangentially.

11. A fabric filter according to any one of claims 1-8, characterized in that the grate

(12) at its initial and/or trailing ends extends between the cylindrical shell (2) of the filtering chamber and the filtering elements (5).

12. A fabric filter according to any one of the preceding claims, characterized in that the grate (12) covers at least 75 % of the length of the feed aperture (8).

13. A fabric filter according to any one of the preceding claims, characterized in that the distance between the filtering elements (11) and the cylindrical shell (2) of the filtering chamber is longer than average in the vicinity of the initial and/or trailing end of the feed aperture (8).