JPS58133815A - Fluidized bed type filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluidized bed filter, particularly an absorption filter, for purifying a gaseous or vaporous medium (hereinafter simply referred to as gas) as described in the preamble of claim 1. Regarding. The invention therefore lies in the field of filtration industry, particularly in the case of absorbers in which the absorbent in the form of activated carbon granules flows discontinuously from top to bottom in units of 1 fl and the gas to be filtered flows continuously from top to bottom. Commonly used in the structural formation of filters.

This type of absorption filter is known from Japanese Patent Laid-Open No. 143485/1985. The absorption filter consists of a rectangular container filled with absorbent, which has a closable overhead inlet opening for supplying the absorbent and a downwardly narrowed and closable absorbent outlet opening. A bottom having a bottom is provided.

The inlet for the gas to be filtered is located in the bottom region. In contrast, the exhaust pipe for the filtered gas is arranged in the upper region of the container,
These exhaust pipes then run parallel to one another from the container wall on one side to the container wall on the opposite side. The upper and lower regions of the container are provided with installations for uniform flow of the absorbent over the entire cross-sectional area of the container. As an installation in the upper region of the container, an exhaust pipe is used which is provided with a roof or a V-shaped profile on the upstream and downstream sides.

The installation in the dry region of the container consists of an absorbent arranged regularly distributed over the entire cross-sectional area and a supporting grid with rectangular through-flow openings for the gas to be filtered. This support grid is arranged above the outlet opening of the absorbent and above the inlet opening of the gas to be filtered, such that when the outlet opening of the absorbent is opened, the absorbent settles widely and uniformly. .

The invention consists in improving this known absorption filter in such a way that the flow through the filter layer is more uniform. The flow-friendly shape and arrangement of the upper and lower inserts is then largely influenced, as has already been made clear, by their opening cross-sectional area and the flow regulating device. The present invention refreshingly allows the flow state of the filter layer in the sense of the ideal flow of the one-sided layer (pivotal flow as opposed to piston flow or nuclear flow) when replacing or partially renewing the filter layer. We are trying to improve it further.

In the case of another known absorption filter, which is described in British Patent No. 588,297, the lower region of the container is provided with a supporting grid with roof-like integrations, in which case the roofs of adjacent Between the edges there is arranged a cylinder with slits divided into sectors (rotary slide valve), through which the used absorbent is discharged in portions. However, this does not allow the absorbent to be discharged in a predetermined layered manner. This is based on the reason that the supporting grid can only be carried out in a manner limited by the capacity of the rotating Beshi valve Ω for each rotational movement of the rotating Beshi valve. A number of rotational movements have to be carried out in order to discharge a layer of bulk material. In known filters, the rotating Vessel valves are operated independently of each other, so that bulk deposition or non-uniform settling of each layer within the filter layer takes place.

In the case of a further known absorption filter, which is described in German Patent No. 1 383 598, the continuous and uniform settling of the absorbent in the treatment region is ensured by a regulating device being connected downstream in the lower extension range of the container. It is sought by arranging a gate-like device.

This gate-like device is composed of roof-like guide plates that are interdigitated with each other and dam plates that are located under the adjacent roof edges. This dam plate prevents the absorbent from falling freely and only allows the absorbent to flow in accordance with the natural slope. The downstream adjustment device consists of a fixed bottom and a movable floor, both of which are provided with openings. The overlap of these openings can be adjusted, so that the desired amount of absorbent can be discharged in each case.

Conditioned by the horizontal dam plates placed in the area of the roof gaps between the blind-shaped roofs, a so-called dead space for bulk loading occurs, which is responsible for the non-uniform loading of the filter layer placed above it. will occur. Furthermore, the equalizing effect of the gate-shaped device is impaired by the generation of backflow stagnation by the adjusting device located below and at a large distance from the gate-like device; Obstructing the free fall of bulk or absorbent material as it passes through the equipment. A gate-like device only fully develops its homogenizing effect if a single particle, after passing through it, travels at least a short distance in free fall. Furthermore, this known absorption filter does not have all the features mentioned at the outset, and is therefore particularly arranged in the upper region of the container, extending parallel to each other from the container wall on one side to the container wall on the other side, and in the upstream region thereof. Since there is no exhaust pipe provided with a roof or a V-shaped cover on the side 2 and the downstream side, the flow equalizing effect of the symmetrical flow guides is not utilized. Fluidized bed filters, in particular absorption filters, are also described. This absorption filter has support grids on the lower and upper sides of the filter nozzle, and these support grids are comprised of T-shaped rails arranged parallel to the filter, and a penetrating longitudinal section installed between these T-shaped rails. It has a slit and a roof-like flow guide (inverted V-shaped member) provided above the longitudinal slit,
In this case, on the upper side of the T-shaped rail, in the area of the opening of the flow guide, on its lower side, parallel to the T-shaped rail.

The control board connected to the horizontal bar is extended. Along with the movement of the horizontal bar, the control plate can be reciprocated at right angles to the longitudinal direction of the longitudinal slit by an eccentric wheel drive device.
It acts to cause the normally stationary crosspiece to flow on the damming surface of the T-shaped rail based on the settling angle. A disadvantage in any known filter is that the gas inlet region (where the gas to be purified flows from the bottom upwards) is located in the area of the inclined surface of the bulk crosspiece, which on the one hand prevents the flow movement of the bulk crosspiece. is affected by the gas flow and, on the other hand, is loaded very heavily in just this range, whereas the other filter areas are only slightly loaded.

The object of the invention is to design a fluidized bed filter, in particular an absorption filter, of the type mentioned at the outset, in such a way that the disadvantages and problems of the known filters mentioned above are avoided. In particular, in the interior of the filter container: (1) the flow movement of the bulk cross-piece is not disturbed by the gas flow; and (2) no uneven loading of the bulk material occurs in the inlet a area (C) of the support grid.

■ There are no dead areas of loose cross members within the range of the support grid, ■
Back-flow stagnation of loose cross-pieces or filter media from the filter container enclosure to the support grid with flow TA4 arrangement holes is avoided, thereby making smooth extrusion possible, ■ new fluidized-bed filters, especially absorption filters. This improves the economical consumption of the absorbent employed, so that at a constant height of the effective filter layer, a layered discharge of the absorbent always takes place from top to bottom, and a uniform loading of the filter layer from below. It consists in forming something like this, which is done upwards.

According to the invention, this object is achieved in a fluidized bed filter, in particular an absorption filter, of the type mentioned at the outset, by the measures set out in the characterizing part of claim 1.

Advantageous embodiments of the invention are listed in claims 2 to 13.

In the case of a filter constructed according to the invention, firstly the exhaust pipe, which is designed as a flow guide, ensures that the absorbent present therein flows in a uniformly distributed manner into the active region of the filter. and fluidity. The blind-shaped roof-like incorporation in the lower part of the container prevents the formation of bridges in the flowing absorbent when the sliding valve is opened, and also allows the absorbent to especially flow out from certain cross-sectional areas. This prevents the occurrence of so-called nuclear flow.

The desired mass flow of absorbent, characterized by a uniform and very low settling velocity, can be achieved by integrating the sliding valves with the transom-shaped roof-like incorporation of the support grid, thereby freeing up the free space below the support grid. This is ensured by the free fall of the absorbent into this free space when the slide valve is opened. In this case, a dynamic dome of flowing absorbent material is created between the blind-shaped roof components. The prerequisite here is that the volume in the bottom region of the container is greater than the volume of the portion or layer of absorbent that leaves the filter active region in each case. If the term absorbent is understood here to also cover renewable filter materials or media, the invention correspondingly covers gaseous substances which are continuously or intermittently penetrated through the filter material. A discussion also extends to fluidized bed filters for purifying or reacting vaporous media.

The design according to the invention ensures that the used absorbent is separated from the absorption filter in layers and that it can be consumed particularly well.

Next, structural embodiments listed in the embodiment section of the claims will be described.

First, the width of the roof gap is 15 mm depending on the size of the absorption filter.
~50. (Claim 2) characterized in that the selection is made within the range of u. The upper roof gap between two mutually adjacent blind-shaped roofs is set to 50 to 100w1 (Claim 3). The distances between the roof-like upper covers and between the axes of the roof-like incorporations correspond to the above-mentioned dimensions and are between 100 and 500 degrees. In that case, a short axial distance promotes uniform dispersion and uniform settling of the absorbent. The particle size of the absorbent, especially the activated carbon, is then in units of υ. In particular, the length is 1 to 2 mm and the diameter is 1 to 2 mm.
A small cylindrical body of 2.- is used.

Crushed charcoal with the same particle size may also be used.

The roof gaps between the blind roofs and the roof gaps between the upper covers narrow approximately hyperbolically from the edges of the container toward the center (% claim 4). This allows consideration of the friction losses that occur on the container walls when the absorbent settles.

Between the roof-like upper parts of the blind roof and between this upper part' and the respective container wall, the desired amount of absorbent can be distributed by means of flow guides arranged above the lower roof gap. The mass flow of is increased by -1 (Claim 5). This auxiliary flow guide is designed in the form of a pointed roof, or as a rectangular or polygonal or circular cross section fitted with a peak (Claim 6).

This auxiliary flow guide equalizes the distance traveled by each particle of absorbent during its evacuation stroke.

Furthermore, the mass flow of absorbent and the free substrate of 79T between the comb-shaped roof assembly and the bottom of the container is 79T.

Improved by the shape and opening/closing movement of the slide valve. For this purpose, the valve can be moved to either side of the respective roof gap (claim 9). In this case, in order to ensure that all areas in the area of the slit are uniformly controlled by the sliding valve relative to each other, the sliding valve can be moved alternately to one side and the other side of the slit when opening the roof gap. A slide valve movement is particularly advantageous (claim 10). So for this movement rhythm.

Each slit is first opened by a movement of the slide valve, for example to the left, and then closed by a movement to the right. Each slit is then opened by a rightward movement of the slide valve and subsequently closed by a leftward movement. Such a sliding cell movement is of particular value when small height absorbent layers are to be pulled out of the absorption filter.

Regarding the structural shape of the slide valve, each slide valve has a cross section T
It is advantageous if it is made of a letter-shaped profile (claim 11). This suppresses any possible damming effect of the flow absorber on the side walls of the slide valve, so that a flow cone forms under the slit in the blind-shaped roof installation without any hindrance.

In order to prevent the flow of absorbent between the roof edge of the support grid and the bevel valve in the closed position of the bevel valve, the lower roof edge of the blind roof is provided with a narrow blunt that abuts the slide valve. Claim 12). The brushes then allow simultaneous passage of the gas to be purified in the area of the slide valve.

Below, four embodiments of the present invention shown in the drawings will be described in detail.

FIG. 1 shows a sectional view of an absorption filter designed as a bulk P-material filter, in which the height of the active layer of the absorbent is several times the theoretical minimum layer height for safety reasons. Such filters have a high consumption rate of absorbent, if only the actually consumed layer of absorbent is discharged each time.

This assumes that the absorbent in the active area of the filter settles uniformly over the entire cross-sectional area and that new absorbent flows uniformly to replenish the active area.

In this case, the spent absorbent can be discharged once or several times during operation without stopping the plant.

The illustrated filter is used in particular in nuclear power plants for purifying contaminated air enriched with radioactive iodine, for example, and is suitably loaded with specially prepared activated carbon for this purpose. Such a filter structure then ensures a uniformly allowed throughflow over the cross-sectional area of the air to be purified as well as a supply and discharge parallel to the plane of the absorbent in the area of the active area and without sliding friction. do.

The absorption filter shown is mainly a box-shaped container l with a closable lid 2 and a funnel-shaped bottom 3 tapering conically downwards with an outlet with a closing valve 4.

Upper built-in 10. Lower built-in part 20 and gas supply port 3
It consists of 0. The absorbent 5 is mainly located in the area between the lower built-in part 20 and the lid 2, and is located between the lower built-in part 20 and the upper built-in part l.
It completely fills the space between O. Instead of a lid 2 that can be disassembled and reassembled.

The flow regulating device can be provided in the normally closable inlet opening, for example in the smallest cross section of the conically or pyramidally tapered inlet chamber.

The gas to be purified enters the filter along the arrow 31 through the gas supply port 30;
The short supply pipe has a sharp roof against the falling absorbent.
It is protected by a door lock 33 with a large area. The gas leaves the filter through the upper installation 10 in exhaust pipes arranged parallel to each other and extending from the front wall of the container to the rear wall of the container. This exhaust pipe consists of a roof-like upper cover 11 and a downwardly directed V-shaped p-mesh cover 12, the edges 13 of each upper cover 11 projecting above the downwardly directed cover 12.

The exhaust pipe IO is connected to a collecting pipe 14, which is attached to the rear wall of the container with a flan (not shown).

The exhaust pipe IO at the same time forms a flow wJ guide for uniformly distributing the absorbent 5 present in the storage chamber 15 into the absorption chamber 16 . For this purpose, the distance 17 between the axes of the exhaust pipe 10 is in the range of 100 to 500 m, depending on the size of the structure; In other words, it is approximately six times as large as the roof gap 18 between the flow guide and the container wall. The angle between the roof surface of the roof cover 11, which is made of special steel for a good coefficient of friction, and the vertical is about 45°, and the angle of the tip of the roof cover 11 is therefore about 90°. This tip angle is then greater than the tip angle of the V-shaped cup <-12. The complementary angle of the half-cusp angle of the roof-shaped cover 11 is correspondingly likewise approximately 45°, and the complementary angle of the V-shaped cover 12 is correspondingly larger. If another material is used, the tip angle is matched to the coefficient of friction.

The absorbent charged from above impinges on one side installation in the form of a support grid 20 in the lower region of the container I.

The support grid 20 is designed to uniformly introduce the gas to be purified into the absorption chamber 16 in order to support the absorbent.
and structural elements for the uniform evacuation of spent sorbents or load layers.

The support grid 20 has a trapezoidal lower part 21 and a roof-like upper part 2
It consists of a symmetrical blind-shaped roof with a two-part structure. Each of these roofs is perpendicular to the lower side of the exhaust pipes 10 and parallel to these exhaust pipes IO, and the distance between their axes 19 is between two blind-shaped roofs or blind cedar roofs that are similarly adjacent to each other. It is arranged so that it is approximately six times the lower roof gap 24 of 9 between adjacent container walls. In this case, each container wall is suitably provided with a lower appendage 23 of a trapezoidal extension 1 part 21. As a result, slits 24 are formed not only between the blind roofs, but also between the outer blind roof and the lateral container walls, these slits 24 being connected to the underside of the support grid. All nine valves 25 arranged and interconnected and occupying the axial length of the support grid can be closed.

The trapezoidal lower portion 20 and the roof-like upper portion 22 of the blind-shaped roof 20 weigh approximately 50 to 50 g (Ha) depending on the size of the structure.
The roof gap 26 between adjacent roof-like upper parts on one side has a width of 50 to 100''. The lower roof gap 24 corresponds to the dimensions of the slot 18 in the upper installation 10.

The width of the upper slit 28 of the trapezoidal lower part 21 is 20~
801M and these slits 28 are F II! 1
In conjunction with the interdigital shape of the inserts, provision is made for the passage of gas through the support grid 20 in a known manner. Support grid 20
The interdigital shape further causes agitation and softening of the absorbent during its downward movement, thereby preventing the formation of bridges when withdrawing the absorbent.

The semi-cusp angle of the supporting grid 20 and correspondingly the inclination angle of all roof slopes is approximately 45°. The support grid 20 is made of special steel plate like the roof-like cover 11.

The absorption chamber 16, ie the active area of the filter, is located within the supporting grid 2.
It is formed by the distance 27 between the upper apex of 0 and the lower apex of the upper incorporation 1O. This distance 27 is between 200 and 1000 νa, depending on the size of the structure.

The closing device arranged in a known manner in the area of the lower roof gap 24 is designed as a slide valve 25 as described above;
This is completely opened when the spent or loaded layer of absorbent is withdrawn, so that the absorbent can flow out without hindrance under mass flow conditions. For this purpose, the valves are connected to each other via a lever device 29, which can be manually or electrically operated from the outside.

The absorbent flowing through the roof gap 24 enters the operating chamber 6 in an eye-dropping manner, into which one or several loads are collected and subsequently removed from the closing device 4 without contamination.
It can be discharged into a tank located on the underside of the tank.

A preferred embodiment of the sliding valve 25, as shown schematically in FIG. Occurs when This allows the slide valve 25
Obstruction of the flow cone of outflowing absorbent in the open position is prevented.

In this embodiment, the flow process itself takes place in the roof-like upper part 22.
This is effected by a tubular flow guide 34 arranged between the roof-like upper part 22 and the container wall. Furthermore, according to a further embodiment shown in FIG. 3, the lower edge of the trapezoidal lower part 21 is provided with a plastic or steel plate 37, the brushes 37 of which have closed slide valves. To prevent an accidental escape of the absorbent in case of an accident, and at the same time to allow the gas to pass through the roof gap 24 without any hindrance.

In order to open and close the roof gap 24, the drive device 29 of the slide valve 35 is expedient so that the slide valve 35 is alternately placed on one side and the other side of each roof gap 24, as shown in FIGS. 4 and 5. It is arranged to be moved. This ensures that each area of the roof gap all has the same opening time. In response to actuation of this sliding valve, a sliding valve located on the outside in each case is arranged in such a way that the respective roof gap can also be completely opened when it is moved in the direction of the container l. It is recommended to provide a concave F9T (t'' in the figure).

It is known from US Pat. No. 1,095,676, which is mentioned in the fourth place at the beginning, that a flow regulating device in the form of a chisel plate is reciprocated by an eccentric drive. In this case, flat edge plates placed immediately above the damming surface and immediately below the roof gap are used to cause the cone of the piled-up material that is formed on the damming surface to flow out. In contrast, no consideration is given to completely opening and closing the roof gap with respect to the filter mass by means of a sliding valve.

FIG. 6 shows a third modified example of the filter based on FIG. 1, and specifically shows a cross section of the support grid 20 of the container 1 at the height of the roof gap 24. From this drawing, roof gap 2
4 is narrowed from the edges (longitudinal sides a, b) toward the vertical central plane m in a substantially hyperbolic shape. For the absorption filter and its underlying dimensions shown in Figure 1, a representative gap 'i' MS (X, y) running parallel to the longitudinal sides a, b of the filter in Figure 6 is shown. It is shown in units of l on the cut plane y1. Eight cutting planes y1 are shown in the drawing. The gap width S is calculated using the formula S(x).

As is evident in y), it is related not only to the X coordinate oriented in the direction of the filter width C to d, but also to the X coordinate running parallel to the filter longitudinal sides a to b ( (see small coordinate intersection X/y). For the roof gaps 24 distributed over the filter plane, in FIG.
Among these roof gaps, the minimum gap width, maximum gap width and intermediate gap width of the roof gap 24.2 in the central area, or the roof gap 24.l, 24.2 in the edge area.
3 corresponding minimum gap width, maximum gap width and intermediate gap width thereof. For the roof gaps 24・I, 24・3 in the edge range, continuous gap width (+l1jA
) increasing stages 22-23-24-25 are occurring.

A continuous increase from the center towards the edge area likewise occurs for the somewhat narrower central roof gap 24.2 which lies on both sides of the central plane of symmetry n. FIG. 6 f for the roof gap 24 of the support grid 20! : The above descriptions referred to apply in the same sense to the roof gap 18 of the upper assembly and can therefore be read from this drawing. As already mentioned above, due to the almost hyperbolic pinching from the edges of the roof gap towards the center or the spreading from the central area towards the edges, the flow loss of the absorbent in the edge area is taken into account; This means that flow friction can be compensated in connection with obtaining a layer as parallel to the plane as possible during the advancement of the filter layer. The course of the gap width depends on the size of the container and the filter layer; in order to obtain the exact value of the gap width empirically, a filter model closed with a transparent glass wall is used until the desired quality fim is achieved. You can experiment well with this.

Upper built-in lO explained with reference to FIGS. 1 to 6
Although the dimensions of the supporting grid 20 and the roof slope are advantageous embodiments, they can be modified within the scope of the claims. The symmetrical roofs 21 and 22 are of a two-part construction as shown in the preferred embodiment, but the symmetrical roofs 21 and 22 are
, 22 is divided into two or more, for example, in a three-part structure,
A gas introduction effect parallel to or independent of the roof gap 24 is obtained, which is advantageous for a uniform gas distribution in the case of filters with a large base plane.

[Brief explanation of the drawing]

J1 diagram is a cross-sectional i+o diagram of the absorption filter based on the present invention,
Fig. 2 is an enlarged detailed view of the supporting grid portion of an absorption filter with different shapes of sliding valves, and Figs. FIG. 6 is a plan view of the support grid showing the hyperbolic roof gap of the support grid. ■...Box-shaped container, 2...M, 3...Bottom, 5...
Absorbent, lO... Upper built-in part (exhaust pipe), 11...
Roof-shaped upper cover, 12... V-shaped cover, 17...
・Distance between the axes of the upper 11 Il1 built-in parts, 18... Roof gap, 19... Distance between the axes of the upper built-in parts, 20...) Thin built-in parts (support grid), 21... Stands Shape lower part, 22.
... Roof-like upper part, 24... Roof gap, 25...
Slip valve, 26... Roof gap, 30... Gas supply port,
34... Auxiliary flow guide body. 35...T-shaped cross section, 37...Plan.

Claims (1)

[Scope of Claims] 1) Bulk loading or absorbent is flowed from top to bottom, and gaseous or vaporous medium to be filtered (hereinafter simply referred to as gas) is continuously flowed from bottom to top. A fluidized bed filter for purifying said gas, comprising a container filled with an absorbent, said container having at least one closable overhead inlet opening for supplying the absorbent. and a downwardly tapered bottom with a closable absorbent outlet opening, the gas supply opening being in the area of the bottom;
A plurality of exhaust gases U are disposed in the upper region of the container and extend in parallel to each other from the container wall on one side to the image of the container on the opposite side, and an upper roof or a lower V-shaped cover is provided on the upstream and upstream sides thereof. and these covers are used as symmetrical flow guides to equalize the flow for the absorbent; further integration in the form of a support grid in the lower region of the container covers the entire cross-sectional area of the container. In such fluidized bed filters, which are provided in order to uniformize the flow state of the absorbent over the exhaust pipes, an upper cover (11) forming a roof-like symmetrical flow guide in each exhaust pipe (10); A downwardly directed V-shaped cover (12) is then formed in the form of an F net, in which case the distance between the axes (17) of the valley upper cover (II) is the distance between two adjacent flow guides or the flow The width of the roof gap (18) in the darkness between the guide body and the container wall is 4 to IO times larger, and the roof edge of each upper cover (11) is turned downward in each case. Projecting upwards, the support grid (20) consists of at least two-part blind-shaped symmetrical roofs (21, 22), each of which extends vertically below said exhaust pipe (10). In parallel to this exhaust pipe (10), these two axes (19) are adjacent to each other.
The lower roof space between the two blind roofs is arranged so that the width is 4 to 10 times the width of the lower roof gap (24) between the two blind roofs or between the blind roof and the container wall. Fluidized bed filter, characterized in that the gap (24) can be closed by means of nine interconnected valves (25) arranged below the support grid (20). 2) Claim FI characterized in that the width of the roof gap (18, 24) is 15 to 50U! i. The filter according to item 1. 3) The filter according to claim 2, characterized in that the upper roof gap (26) between the mutually adjacent blind-shaped roofs (21, 22) is 50 to 100 cm. 4) Roof gap between blind-shaped roofs (21, 22') (
24) or the roof gap (1) between the upper cover (11)
8) is narrowed in a substantially hyperbolic shape from the edge of the container toward the center of the container. 5) Upper part of the roof (21, 22)
2) and between this upper part (22) and the respective container wall, an auxiliary flow guide (34) is arranged above the lower roof gap (24). A filter according to any one of claims 1 to 4. 6) The auxiliary flow guiding body (34) is formed in the shape of a pointed roof, or as a cross section fitted with a pointed end, or in a polygonal or circular shape f: Characteristic patent The filter according to claim 5. 7) Upper roof-like cover (11) and support grid (20)
7. A d-piston filter according to any one of claims 1 to 6, characterized in that the filter is made of special steel plate and has an inclination angle of approximately 45°. 8) The top corner of the plane of the V-shaped cover (12) or the roof (11)
8. The filter according to any one of claims 1 to 7, characterized in that the tip angle is smaller than the tip angle of the filter. 9) A filter according to any one of claims 1 to 8, characterized in that the slide valves (25, 35) are movable on both sides of the roof gap (24). 10) Slip valves (25, 35) are in the roof gap (24)
11. The filter according to claim 11'j+IL, wherein the filter can be moved alternately to one side and the other side during opening of the filter. +1) Claims 1 to 1, characterized in that each slide valve is formed of a cross beam having a T-shaped cross section.
The filter described in any of the θ terms. 12) Filter according to claim 11, characterized in that the lower roof edge of the blind roof (21) is provided with a narrow plan (37) adjoining the sliding valve (35). ta) For a roof gap (24, 18) distributed t'' over the filter plane, the values of the minimum, maximum and intermediate width of the roof gap in its central region are the minimum width of the roof gap in its edge region. 5. A filter according to claim 4, characterized in that the filter is dimensioned smaller than the maximum width and intermediate width values.