NZ204646A

NZ204646A - Cleaning granular filter bed by recirculating granules

Info

Publication number: NZ204646A
Application number: NZ204646A
Authority: NZ
Inventors: Wolfgang Berz
Original assignee: Gimag Ag
Priority date: 1982-06-22
Filing date: 1983-06-20
Publication date: 1986-10-08
Also published as: KR880002006B1; ATE22016T1; AU1597783A; BR8303289A; ES523431A0; EP0097310A1; ES8404868A1; EG15956A; NO832247L; EP0097310B1; CS264312B2; KR840004870A; CS450683A2; IN160145B; DK285883D0; DK285883A; DE3366048D1; GR78597B; AU565097B2; DD209974A5

Abstract

1. Process for the regenerative purification of a filter medium in granulate form charged with impurities which forms a filter bed (F) between the gas-permeable walls (W1, W2) of a vertically positioned filter element and which is sucked upwards at least partially during a regeneration phase from the lower area of the filter element into a lower inlet opening (5a) of a conveying tube (5) arranged in the centre of the filter element and is sucked upwards in this conveying tube and fed into a separation process taking place above the filter element in a separating apparatus (1, 53, 54, 29), in which the impurities are separated from the filter medium and the purified filter medium is fed back into the filter bed in the upper region of the filter element, characterized by regulation of the quantity of granular filter medium fed into the lower inlet opening 5 a of the conveying tube in the lower region of the filter element so that the upper limit of the portion of the filter medium arriving in the vicinity of the inlet opening (5a) of the conveying tube is below the lower edge of this inlet opening and a fluidised zone is formed from the said portion of the filter medium in the vicinity of the lower inlet opening (5a) of the conveying tube, using the suction in the conveying tube (5) as well as a supply of cleaning or flushing gas into this protion of the filter medium from an area above the inlet opening of the conveying tube.

Description

<div class="application article clearfix" id="description"> 204G46 Priority Date(s): ?V?... J.'.?.-?: Complete Specification Filed: Ciass: Publication Date: P.O. Journal, No: 18 OCT 1986 i.. No.: Date: NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION A PROCESS AND APPARATUS FOR THE REGENERATIVE PURIFICATION OF A GRANULAR FILTER BED IXWe, GIMAG AKTIENGESELLSCHAFT, a Swiss Company, of Martinsplatz 8, CH-7002, Chur, Switzerland, hereby declare the invention for which }fx/ we pray that a patent may be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by la) - la - ;• #«*.(, «W«4« The present invention relates to a process for the regenerative purification of a filter medium which, in one or more regeneration phases, drops down in granular form between gas-permeable elements and is subsequently conveyed up again through a conveying pipe. Filter installations are known in which the granular filter material is moved upward, at least periodically, in a centrally arranged conveying pipe by means of a stream of conveying gas, subsequently drops into the zone of action of the stream of conveying gas and is thus conveyed in a circulatory manner between the gas-permeable walls. In such a case, the granular filter medium is conveyed by compressed air which is applied from below to the conically tapering filter bed and entrains the filter medium upward through the conveying pipe. It has proved to be a disadvantage of the known arrangement that slippage of the filter medium which drops down within the filter bed is difficult to control, so that unsymmetrical entry conditions result at the lower orifice of the conveying pipe and continuous conveying of the medium through the conveying pipe can only be ensured with difficulty. Moreover, it has been found, that the sieve insert which separates the compressed air channel from the filter medium above it is clogged relatively rapidly by caking dust and impurities in the conveying air, also leading to operational faults. Furthermore, the known installation is made relatively complicated by the wall passages and compressed air line run required. It is further to be regarded as a disadvantage of these known installations that their operating characteristics do not respond to the unavoidable fluctuations in pressure and/.or conveying rate in the crude gas inlet. If, for example, the pressure in the crude gas inlet rises, this pressure rise acts counter to the conveying gas stream and there is the danger that not only does the volume transported drop but that the granular material collapses within the conveying pipe and hence the entire transportation system collapses. British Patent Specification No. 2,038,200 describes - 2 - 204646 a system according to which a granular filter medium drops downward in the filter bed during the regeneration phase, in doing so is freed from dust, and is subsequently conveyed upwards through a central pipe by means of compressed air blown in at the lower end of this pipe. The transport gas which has been used for conveying in the central pipe is in this case fed into the pipe gas space. This system, which has already been tested in industrial practice, however suffers from a major disadvantage. The screen required at the orifice of the line used to feed the central pipe with compressed air must necessarily be so chosen that its mesh width is less than the smallest particule size of the granular material above the screen. Hence, it has in practice proved unavoidable that the screen meshes become clogged with dust after a short period of operation, and this reduces the conveying of the granules. Moreover, the distance which must be maintained between the orifice of the compressed air pipe and the inlet of the central pipe is a further source of pressure loss and of lateral flowing-away of the compressed air. Hence, experience has shown that there is an undesirable variability in the conveying stream in the central pipe, which, after brief pulsating operation, * causes the conveying system to collapse. The same disadvantage applies to the system described in British Patent Specification No. 1,574,777. Accordingly, it is an object of the present invention to propose an apparatus for the regenerative purification of a granular filter bed which avoids the disadvantages of the known installations and in particular ensures fully satisfactory conveying of the filter medium during the regeneration phase, under clearly defined and controllable flow conditions of the filter medium. The apparatus is intended to function fully satisfactorily whilst if possible avoiding the use of 20464-6 screens and similar elements which require periodic cleaning, and is further intended to permit adjustment to optimum operating conditions by virtue of its control capabilities, and to ensure practically constant transport of the filter medium regardless of fluctuations of the crude gas pressure and/or the crude gas conveying rate. The invention therefore comprises an apparatus for the regenerative purification of a granular filter bed, having a filter bed which is located on the periphery of a pure gas space and contains granules serving as the filter medium, which granules are, at least during a regeneration phase, conveyed upward in a conveying pipe and fall down in the zone of the filter bed, the filter bed, in its lower zone adjacent to the conveying pipe inlet orifice, not being bounded in the direction of this orifice, characterised in that means are provided which produce an upwardly-directed suction within the conveying pipe, and that means are also provided which, in the zone of the conveying pipe inlet orifice, cause a change in direction of the gas, contained in the pure gas space, when it passes into the conveying pipe, so that the granular filter medium which flows from the filter bed against the conveying pipe inlet orifice is entrained by the gas stream whose direction has been changed and is conveyed upward through the conveying pipe. The invention further comprises a process for the regenerative purification of a filter medium which, in one or more regeneration phases, drops down in granular form between gas-permeable elements and is subsequently conveyed up again through a conveying pipe, characterised in that either a proportion of the pure gas or a proportion of the flushing gas used to remove dust from the filter medium is employed to convey the granules through the conveying pipe, the granules being sucked upward through the conveying pipe to the upper orifice thereof and being entrained into the conveying pipe, at the lower orifice thereof by the said portion of the pure gas or flushing gas. An illustrative embodiment of the subject of the invention is described below with reference to the attached drawings. Figure 1 shows a diagrammatically simplified vertical section of an apparatus of this type, used for the intermittent regeneration of a filter medium. Figure 2 shows the apparatus depicted in Figure 1, in a different operating phase. Figure 3 is a vertical section through the lower zone of the conveying pipe and Figure 4 shews an embodiment of a spacer el -4- 204646 The apparatus shown in Figure 1, without nonessential details, has a housing 1 of virtually square or circular cross-section. The gas-imperraeable housing 1 which extends up to position G surrounds, in its lower section, a series of filling pipes Z which are fixed at a distance from one another and are held by an inner housing 3 which is also gas-impermeable. Ml the filling pipes 2 are provided with orifices o which are open at the top, whilst their lower orifices u open into a filter bed F which is bounded by two concentric gas-permeable walls and arranged at a distance from one another. These two walls which may for example be in the form of metal mesh, are suspended fran the lower edge of the filling pipes 2, so that granules dropping fran above through i the filling pipes 2 enter the filter bed F. The upper portion of the tubes z is, as mentioned, inwardly bounded by a gas-impermeable cover 3 which is continued upward in the form of a cap 4 in the shape of a truncated pyramid. The cover 3 and cap 4 are preferably a single member which is fixed to the inner wall of the housing 1 via fixing ribs which are not shown. At the upper edge of the cap 4 there is suspended a conveying pipe 5 which runs downward coaxially with the filter bed F formed by the gas-permeable walls and is also open at both ends. The lower portion of the conveying pipe 5 protudes into a spacer element 6 which, in the embodiment shown, is constructed as a cylindrical pipe portion and is so arranged that an interspace Z remains between the lower conveying pipe portion and the spacer element 6. Accordingly, the inlet zone of the conveying pipe 5 is surrounded by the tubular spacer element 6, which rests on the bottom below it. In the lower end portion, this spacer element has several downwardly-open slits 6b (Figure 4), which extend upward beyond the lower end 5a of the conveying pipe 5. A cylindrical collar 6a is slidably mounted on the periphery of the spacer element 6. This collar can be locked at any desired height by a fixing member known per se, for example a screw 6c, so that the collar partially masks the slits 6b of the spacer element 6. Below the inlet orifice 5a of the conveying pipe 5 there is located, in the bottom belcw the pipe, a filter insert 56 below which is a blow jet 57 fed with compressed air. The blow jet 57 is connected via a line 58 to a source of compressed air, and the supply of compressed air can be opened or shut as desired by means of a shut-off valve. The slits 6b provided in the lower portion of the spacer sleeve 6 have the effect that the downward-flowing granules enter in a tongue-like manner into the space surrounded by the spacer sleeve and above these granules which penetrate there always still remains sufficient space for the conveying air which flows downward through the annular space between the spacer sleeve 6 and the conveying pipe 5 and is re-routed into the conveying pipe in the zone of the lower end of said pipe. At the same time, this conveying air entrains granules, present in - 5 - 304646 the rerouting zone, upward through the conveying pipe. In the event of an operating fault, for example an electricity failure, it may happen that the vacuum applied to the conveying pipe fails and the granules present in this pipe fall down, and in the case of such unforeseen faults, it must be assumed that the installation is not shut off suddenly but continues to operate for several seconds longer, with a slowly decreasing vacuum. Under these conditions it may happen that the annular space present between the conveying pipe 5 and the spacer sleeve 6 will become partially filled with granules, to a point extending into the conveying pipe, and this would add to the difficulty of renewed start-up of the apparatus. The blow jet 57 already referred to is provided to meet such a situation. If the apparatus is to be restarted after one of the breakdowns mentioned, it suffices briefly to open the shut-off valve, whereupon the granules present below the conveying pipe inlet are entrained upward through the conveying pipe so that normal operation by the vacuum which now comes into effect can be resumed without problems. Care must be taken that the vacuum should come into effect simultaneously with, or preferably even before, the compressed air is switched on. The upper exit orifice, marked 5b, of the conveying pipe is surrounded by a cyclindrical separating pipe 53 which can be suspended from the housing wall by ribs 60 and whose internal diameter is in any case greater than that of the conveying pipe 5. The lower portion of the separation pipe 53 is pushed over the lower orifice of the conveying pipe in such a way as to produce a free annular space 54 which is open downwardly, i.e. in the direction of the granule buffer marked P. The separation pipe 5 3 extends upward over a considerable distance, which in every case is several times greater than its diameter, and then terminates in a suction line 28, in front of whose inlet orifice is located a deflecting member 55. In regenerative purification of the granules, the latter are sucked upward through the conveying pipe 5 and - 6 - 204646 leave the upper orifice 5b of the conveying pipe at relatively high velocity. However, on entering the separation pipe 53, the granules entrained by the stream of conveying gas slow down and drop downward, thereby passing through the interspace 54 between the conveying pipe 5 and the separation pipe 53 into the buffer zone P and from there via the downpipes 2 into the filter bed F. On the other hand, the dust entrained by the conveying gas stream is conveyed by the said gas via the suction line 2 8 to the separator 3 0 and is discharged from the latter via an air shut-off and dust discharge device 35. The function of the deflecting element 5 5 is so to deflect any granular particules which may have penetrated as far as this point that they nevertheless drop downward and do not enter the suction line 28. Experiments run with the apparatus described have shown that, by virtue of the construction, described above, of the slits 6b on the spacer sleeve 6, fully satisfactory transition of the granules from the filter bed into the conveying pipe is achieved, whilst on the other hand the separation, described above, of granules from dust, taking place in the separation pipe 53, ensures minimum damage to the granules. The abrasion of granules, which in apparatus of this type is extremely troublesome, can thus be reduced to a minimum. Further avoidance of damage to the granules is also achieved in the inlet zone 5a of the conveying pipe 5. As is shown in particular in Fig. 3, the granules are kept away from the inlet edge 5a of the conveying pipe during conveying, since the air deflected in this zone tends to seize the granules from above and convey them towards the centre of the conveying pipe. Only subsequently do the granules become distributed over the entire conveying pipe cross-section. The suspension of the conveying pipe in the upper portion of the cap 4 (Fig. 1) is preferably so effected, by known means, that the conveying pipe can be adjusted in height by several centimetres. As Figure 1 shows, the space which is surrounded - 7 - 804646 by the filter bed F and which hereafter will be referred to as the pure gas space Rei, terminates in an annular channel 9 which at a plurality of positions extends between two adjacent pipes 2. The annular channel 9 leads, via a control valve 11, into a pure gas channel 12. The control valve 11 has a lower annular seat 13 and an upper seat 14 between which a closing member 15 can be moved by means of a piston 16 which is known per se and is, for example, pneumatically operated. In the operating phase shown in Fig. 1 the closing member 15 rests against the upper seat 14 and thereby opens the path from the annular channel 9 into the pure gas channel 12. According to Figure 1, a further housing 17, of circular cross-section, is moreover arranged at a distance from the filter bed F, so that a crude gas space Ro is formed between the filter bed F and the housing 17. Below the housing 17 a collecting funnel 18 may be arranged, as shown in Fig. 2, which funnel leads dust, dropping down under gravity in the regeneration phase, downward into a conveyor 19 from which it can be discharged in the direction of the arrow 20. However, in a preferred embodiment, the apparatus has, in place of a simple collecting funnel 18, a pre-separator (Fig. 1) which possesses a cylindrical upper portion 22 having an internal insert 23a as well as a collecting funnel 23 in the shape of a truncated cone. The crude gas line, marked 24, opens tangentially into the upper part 22, and, as a result of the cyclone action, a pre-separation of the dust entrained in the crude gas occurs and the dust drops downward in the direction of the arrows into the conveyor 19. The suction line 2 8 connected to the housing 1 leads via a valve 2 9 to the cyclone separator 30 which is connected to a fan 32 via a further connecting line 31. The valve 29 has, in a known manner, a closing member 33 which can be moved by means of a pneumatically or hydraulic-ally operable piston 34. The cyclone separator 30 is known to those skilled in the art and a description of its design is therefore unnecessary. The cyclone separator opens into - 8 - 2044*6 * an air shut-off and dust discharge device 35. The fan 32 is driven by a motor 36 and its direction of rotation is such that suction is created in the upstream apparatuses and lines, i.e. in particular in the separation pipe 53. The apparatus depicted in the drawing having now been described in its essential constructional components, the process aspect will now be discussed. In doing so, it is necessary to differentiate a crude gas purification phase, in which dust-laden crude gas is to flow through the installation and be freed from the entrained dust. This phase is shown in Fig. 1. It can periodically be interrupted by regeneration phases, in which the dust collecting in the granular bed F is again removed from the latter. The illustration in Fig. 2 is based on this regeneration phase. The crude gas enters, in the direction of the arrow 38 (Fig. 1), through the crude gas channel 24 into the pre-separator 21 and is there first of all freed from a proportion of the entrained dust. Thereafter the crude gas, which is still dust-laden, passes upward in the direction of the curved arrows and there flows from the crude gas space Ro through the filter bed F into the pure gas space Rei. The entrained dust remains adhering to the granular filter medium whilst the pure gas can flow out through the annular line 9 and through the opened valve 11 into the pure gas line 12. In intermittent operation, the valve 11 is so adjusted, in the regeneration phase according to Fig. 2, that it seals the pure gas channel 12 but admits the inflow of flushing air. The flushing air which enters in the direction of the arrow 39 passes via a fan 42 and the open valve 11, in the direction of the arrow, through the annular channel 9 into the pure gas space Rei, from where it. flows outward in the direction of the curved arrows (Fig. 2) through the filter medium F, entrains the dust present in the filter medium and leaves the crude gas space through the crude gas inlet channel 2 4 (arrow 43). In the course thereof, a proportion of the dust drops downward, in the direction of the arrows, into the zone 204646 - 9 - of the air shut-off and dust discharge device 19. Since, however, the fan 32 was started up simultaneously with the start of the regeneration phase, a greatly reduced pressure was set up in the zone above the conveying pipe 5 and this acts as intense suction on the filter medium present below the conveying pipe 5. As is indicated by the arrows 40 in Fig. 2, a fraction of the flushing air passes downward as a result of the suction generated in the interspace Z and is entrained, by this suction, through the lower orifice 5a of the conveying pipe and into the latter. The granular filter medium which leaves the filter bed F in a downward direction forms a conical embankment 4 4 in the peripheral zone of the spacer element 6 (Fig. 3), from which embankment the filter medium passes through the lower orifice slits 6b of height a (Fig. 4) into the zone of the flushing air which is entering from above (arrows in Fig. 3) and is entrained by this air into the conveying pipe 5. The passage of the granular medium from the embankment bed 44 into the suction intake zone of the conveying pipe 5 occurs on the one hand by gravity and on the other hand by the suction generated in the conveying pipe and the conveying air motion resulting therefrom below the conveying pipe. By appropriate balancing of the two distances a and b frictionless and continuous transfer of the granular medium from the embankment bed 4 4 into the conveying pipe 5 can be achieved. The filter medium is accordingly entrained upward, in the direction of the arrow, within the conveying pipe 5 and is slowed down on transition into the separation pipe 53, with the granules, by virtue of their higher specific gravity, falling downward through the lower, annular separation pipe orifice. On the other hand, the duist carried along in the conveying pipe 5 is entrained upward by the flushing air, because of the lower weight of the dust, and flows through the connecting line 28, via the valve 2 9 which is now open, into the cyclone separator 30, in which the entrained dust is separated out in a downward direction via the discharge conveyor 35. - 10 - 204646 The flushing air freed from dust can be introduced, by the fan 32, into the crude gas main line 51 (manifold) via a return line 52. The gas-permeable walls which contain the filter material, are at a mutual distance of from 30 to 150 mm, the preferred embodiment being from 45 to 60 mm. By mutual balance of the distances a and b (Fig. 3 and 4) and of the intensity of the vacuum applied above the conveying pipe it is possible to achieve a situation where the granular filter medium on the one hand passes continuously via the embankment bed 44 into the suction zone of the conveying pipe, whilst on the other hand a sufficient amount of granules is present above the filling pipe orifices o (Fig. 1) to ensure that filter medium follows up continously through the filling pipes 2. This amount of granules, P, which is present above the filling pipe orifices o and which should not have less than a predetermined height h thus exerts a certain buffer action and ensures that the filling pipes Z are always uniformly charged with filter medium and the gas passage resistance is virtually constant over the entire filter pipe length. The present description relates to an apparatus which - as is known to those skilled in the art - is, in industrial practice, rarely used alone but is in most cases assembled with a plurality of such apparatuses, connected in parallel, to form a system. By appropriate arrangements, known to a man skilled in the art, of control valves it is possible always to run in a regeneration phase one of the described apparatuses from this system, whilst the other apparatuses are available for crude gas purification operation. In the crude gas purification phase according to Fig. 1 the valve 2 9 is normally closed and the extractor fan 32 is not in operation. This however, only applies to intermittent operation, in which the crude gas purification is interrupted during regeneration of the granules and no granule regeneration takes place during the crude gas purification. In continuous operation, which is also 204646 - 11 - possible, regeneration can take place simultaneously with crude gas purification. The spacer element 6 used in the embodiment according to Figs. 3 and 4 is merely one example and can be modified in very diverse ways by a man skilled in the art. Thus, Fig. 1 shows a simplified embodiment in which the cylindrical spacer element 6 is supported on the bottom 7a by legs 49 which are arranged at intervals. Where reference has been made to pure gas in relation to the present embodiment it is possible, as already mentioned in connection with the embodiment, to use either pure gas or flushing gas for conveying the filter material through the conveying pipe 5. Figure 2 shows how the apparatus is connected up for flushing gas conveying. In the variant where the pure gas is used to convey the filter medium, the valve 11 is absent. As already described, the crude gas enters through the crude gas channel 2 4 into the crude gas space Ro of the apparatus, passes through the filter bed F and leaves the pure gas space Rei through the channel 9. As a result of the intense suction generated in the conveying pipe 5, a proportion of the pure gas present in the pure gas space is now sucked in through the annular space between the spacer element 6 and conveying pipe 5, in the direction of the arrow (Fig. 2), and causes entrainment of the filter medium, as has already been described in relation to Fig. 2. The regeneration of the filter medium can in this case be carried out either continuously or discontinuously, depending on whether the cyclone 3 0 and the fan 32 run constantly or only intermittently. For the sake of good order it should also be mentioned that the term pure gas is applied to all gas which has flowed through the filter bed F once and is accordingly present in the pure gas space. The apparatus according to the invention can thus be regenerated either discontinuously or continuously. In both types of operation, either pure gas or a special - 12 - 204646 flushing gas can be used as the conveying gas for conveying the filter medium through the conveying pipe 5. When regenerating the granular filter material, the conveyed amounts of crude gas, flushing gas and conveying gas are, in a preferred embodiment, approximately in the ratio of 100:15:2. Accordingly, the proportion of conveying gas in the flushing gas is about 10-15%. The transition of the granules from the separation pipe 53 into the filter bed F can, within the scope of the inventive concept, be varied in many ways by a man skilled in the art. For example, the filling pipes 2 can be replaced by two gas-impermeable walls and/or a plurality of inclined filling pipes can be attached to the cap 4. If, instead of a special flushing gas, the pure gas is to be used for regeneration, the fan 42 (Fig. 2) can be connected to the pure gas channel 12 via a connecting line 25, which can be provided with a shut-off valve 26. As conveying gas it is possible to use not only air but also other gases or gas mixtures, for example inert gases. V *1 SAAUGIM </div>

Claims

<div class="application article clearfix printTableText" id="claims"> i3 204646 WHAT WE CLAIM IS;

1. Process for the regenerative purification of a filter medium which, in one or more regeneration phases, drops down in granular form between gas-permeable elements and is subsequently conveyed up again through a conveying pipe, characterised in that either a proportion of the pure gas or a proportion of the flushing gas used to remove dust from the filter medium is employed to convey the granules through the conveying pipe, the granules being sucked upward through the conveying pipe to the upper orifice thereof and being entrained into the conveying pipe, at the lower orifice thereof by the said portion of the pure gas or flushing gas.

2. Process according to Claim 1, characterised in that the granules, after leaving the upper orifice of the conveying pipe, are separated from entrained dust by a reduction in velocity, flushing gas in the upper filter bed portion being passed through the filter bed into the pure gas space surrounded by the latter and a large proportion of the flushing gas flowing from there outwardly through the filter bed, whilst a proportion of the flushing gas is used to convey the filter medium through the conveying pipe.

3. Process according to one of Claims 1 and 2, characterised in that the conveying gas, after having been separated from entrained dust, is fed to the crude gas main line so that a closed system with feedback results inasmuch as the fluctuations in conveying volume and/or pressure which unavoidably occur in the crude gas main feed line produce an automatic adaptation within the closed system.

4. Apparatus for the regenerative purification of a granular filter bed, having a filter bed which is located on the periphery of a pure gas space and contains granules serving as the filter medium, which granules are, at least during a regeneration phase, conveyed upward in a conveying pipe and fall down in the zone of the filter bed, the filter bed, in its lower zone adjacent to the conveying pipe inlet orifice, not being bounded in the direction - 14 - 204646 of this orifice, characterised in that means are provided which produce an upwardly-directed suction within the conveying pipe, and that means are also provided which, in the zone of the conveying pipe inlet orifice, cause a change in direction of the gas, contained in the pure gas space, when it passes into the conveying pipe, so that the granular filter medium which flows from the filter bed against the conveying pipe inlet orifice is entrained by the gas stream whose direction has been changed and is conveyed upward through the conveying pipe.

5. Apparatus according to Claim 4, characterised in that the upper outlet orifice of the conveying pipe is connected interactively to a source of vacuum and the lower inlet orifice of the conveying pipe is surrounded by a tubular spacer element which is open at both end faces and whose lower edge projects to below the lower inlet orifice of the conveying pipe, but leaves one or more inflow orifices free between the inlet orifice of the conveying pipe and a bottom located at a distance below it, so that the granules which form an embankment in the said lower zone of the filter bed run inward against the spacer element and are conveyed, but the conveying gas which flows in through the upper annular orifice of the spacer element, into the conveying pipe and upward in the latter, the said spacer element being a cylindrical pipe portion which is guided on the periphery of the conveying pipe and rests on legs on the bottom below it.

6. Apparatus according to one of Claims 4 and 5, characterised in that the distance of the lower edge of the spacer element from the bottom below it, and hence the inflow cross-section of the granules, can be regulated and that furthermore the distance of the lower edge of the conveying pipe from the bottom below it is adjustable.

7. Apparatus according to one of Claims 4 to 6, characterised in that the inner edges of the upper filling pipe orifices are followed by a cap in the shape - 15 - 204646 of a truncated pyramid or truncated cone, which cap, at its upper end, holds the conveying pipe in a height-adjustable manner, and whose height is such that in the regeneration zone between its peripheral surface and a housing a granule stock, serving as a buffer and having a predetermined minimum height, collects.

8. Apparatus according to one of Claims 4 to 7, characterised in that the conveying pipe terminates, at its upper end, in a separation pipe, whose internal diameter is greater than that of the conveying pipe and whose end, opposite the conveying pipe, is connected to a source of vacuum, the interspace existing between the separation pipe and the conveying pipe furthermore being open at the bottom, so that the granules conveyed upward in the conveying pipe are slowed down in the separation pipe and fall downward into the filter bed whilst the dust entrained in the conveying gas stream is fed through the separation pipe to a device where the dust is separated out.

9. Apparatus according to Claim 5, the conveying pipe having a tubular spacer element in the zone of its inlet orifice, characterised in that the spacer element rests on the bottom below it and is provided with a plurality of slits in order to allow the granules flowing laterally towards them, access to the conveying pipe, a slidably mounted covering sleeve being located on the periphery of the spacer element, which sleeve can be fixed at any desired height in order partially to mask the said slits of the spacer element.

10. Apparatus according to one of Claims 4 to 9, characterised in that the bottom located below the conveying pipe inlet orifice has a screen insert and that a blow nozzle is located below the said bottom. CATEf. THIS U ft- DAY OF 19 5^ A„ J. PARK & SON PEH AGENTS FOR THE APPLICANTS </div>