GB2038200A - Method and apparatus for the intermittent, regenerating cleaning of a filter bed - Google Patents

Abstract

To free the granular material forming annular filter bed (11) from dust, it is periodically circulated in a closed cycle through a conveyor tube (14) and back to the bed via drop pipes (24), while a scavenging gas from inlet 2 flows through the bed in the reverse direction. In a separating housing (18) the granules swept along by the conveying gas stream from inlet (12) strike a deflecting member (15) and are deflected against the inner wall of the housing (18) and thence to pipes (24), while the dust-laden conveying gas is recirculated through a connecting pipe (19) into the crude gas chamber (20). The conveying gas enters chamber (20) tangentially and creates a cyclone-like rotational movement which separates the dust from the conveying gas and from the scavenging gas emerging from the bed. The entrance point E of the pipe (19) is chosen so that the end point of the helical line (S) comes to lie approximately opposite the gas exit (35) so that a large part (D) of the dust settles in zone (26) and is not carried into the crude gas channel (21) and thence to neighbouring filters. <IMAGE>

Description

SPECIFICATION Method and apparatus for the intermittent, regenerating cleaning of a filter bed The present invention relates to a method for the intermittent, regenerating cleaning of a filter bed which is kept in the form of granular material between two gas-permeable walls, through which polluted crude gas flows, whereby the granular material is moved upwards by a conveying gas stream, then falls back again in the space between the gaspermeable walls into the effective range of the conveying gas steam and is thereby circulated in the cycle, and during the cleaning process, a scavenging gas is blown through the granular material falling downwards between the gas-permeable walls and is collected and drawn off into a crude gas space surrounding the filter bed.

Further the invention relates to an apparatus to carry out said method.

Dust-laden gases or those which are loaded with other impurities can be cleaned as known in that the crude gas stream is allowed to flow through a layer of granular filter material, consisting for example of silica sand. During the course of operation, the granular filter bed becomes more and more concentrated with dust particles until its increase in flow resistance necessitates a regeneration, i.e. freeing the granular filter bed from dust.

Several methods for regenerative cleaning of granular filter material are known. It has for instance been suggested to draw off the filter material from time to time, to lead it outside of the filter system through a cleaning apparatus (cyclone) and then to return it to the filter after the dust has been successfully extracted. These systems require a large amount of conveying means since the filter material must firstly be drawn off at the lower part of the filter system, then conveyed vertically upwards and finally lead into the filter again from above.

In order to overcome this disadvantage, the suggestion has been made to arrange the granular filter bed between two gas-permeable, coaxial tubes and to circulate the filter material during the regenerative cleaning in a closed cycle. Forthis purpose, the material is carried upwards by a conveyor gas stream in a central conveyor tube and then falls again through the annular filter bed into the range of the conveying gas stream.

Arranged in such systems between the outer limiting tube of the filter bed and an outer shell is a crude gas chamber, through which crude gas flows during filtration and dustladen scavenging gas flows during the regeneration phase. It is unavoidable thereby that the dust swirling around in the crude gas space also settles on the outer side and thereby impairs the effectiveness of the filter system in the long run.

Besides this, the dust-laden conveying gas must be lead out of the filter system and be cleaned by a separator before flowing outside.

It is the aim of the present invention to provide a method and an apparatus for the regenerative cleaning of such filter beds, wherein on the one hand the conveying gas does not have to be drawn off to the outside and on the other hand a purposive separation of the dust is achieved in the crude gas space.

This problem is solved according to the invention by a combination of features as defined in independent claims 1 and 4.

An embodiment of the inventive subject matter is illustrated on the enclosed drawing.

Figure 1 is a simplified vertical section of a filter unit and shows the same in its operational phase (cleaning crude gas), Figure 2 is a cross-section across line Il-Il in Fig. 1 and simultaneously illustrates the parallel connection of several filter units, Figure 3 is a cross-section along line Ill-Ill in Figure 1, Fig. 4 is a cross-section along line IV-IV in Figure 5, Figure 5 shows the filter unit shown in Figures 1/2 during the regenerative cleaning phase (cleaning fil ter bed) and Figure 6 is a vertical cross-section of a variant.

The schematic filter unit, illustrated without unimportant details has a casing 1 which has on its upper part an inlet opening 2 for scavenging gas which enters over a scavenging gas pipe 3. On the opposite side of the casing 1 there is an outlet opening 4 for the purified gas which flows off through a pipes. By means of two gates 7 and 8 the openings 2 and 4 can be closed alternately, whereby the command impulse can for example originate from a schematically indicated servomotor M.

Inside the practically circular cylindrical casing 1 are two gas-permeable, coaxial, also circular cyclindrical pipes 9/10; the interstice defined by these two pipes is filled with a filter bed 11. The latter consists of a granular material, for example silica sand.

The two gas-permeable pipes 9/10 taper towards the bottom; joining onto the lowest part of the outer pipe 9 is a conveying gas pipe 12, into which a throttle valve 13 and a porous. i.e. gas-permeable plate 29 are mounted. A central conveyor tube 14 comes out of the lowest, central point of the inner pipe 10.

Above the upper mouth of the conveyor tube 14 is a deflecting member 15 which is shaped like a cone tapering downwards and therefore has a downward-tapering deflection surface. The deflecting member 15 is attached to the housing 18 of a separating device by means of struts 16. The housing 18 is construced as a double cone, the widest section of which lies approximately in its middle area. This housing 18 is connected over a pipe 19 to the interstice between the outer pipe 9 and the casing 1, which should from now on be called the crude gas chamber 20.

The two gates 7 and 8 are joined together over two rods 6 and not visible traverses arranged in the region of the gates. The rods 6 lie therefore on both sides of the separating housing 18 and rigidly couple the gates 7/8.

A crude gas channel 21 further opens into the casing 1 and arranged in the lower section of the also conically tapering casing is in a conduit 22 a discharge conveyor, preferably a discharge screw 23.

The crude gas chahnel 21 is limited laterally bytwo parallel, vertical walls 39 and 40.

As shown in Fig. 1 in connection with Fig. 2, sev eral filter units are arranged consecutively in a filter system and are fed by the mutual crude gas channel 21. The neighbouring filter units are separated from one another in their lower sections below a floor 34 by vertical walls 33 and are connected to the crude gas channel 21 by openings 35.

Four radially-directed drop pipes 24 open into the floor of the housing 18, connecting the space enclosed within the housing 18 to the filter bed 11.

The drop pipes 24 are inclined downwards towards their junction into the filter bed, whereby the angle of slant should be larger than the angle of repose of the granular material used.

The connecting pipe 19 from the separating housing 18 to the crude gas chamber 20 opens out, as shown in Fig. 3, preferablytangentially into the upper section of the crude gas chamber 20.

As mentioned before, the filter element shown in Fig. 1 is to be thought of as part of a system which comprises several such elements, so that one of the elements can be regenerated as desired while the other elements maintain the cleaning operation of the crude gas.

In the crude gas cleaning operation, the dust-laden crude gas flows according to Figure 1 through the channel 21 into the crude gas chamber 20, flows subsequently through the filter bed 11 and leaves the inner, clean gas chamber surrounded by the filter bed through the spaces 25 of the pipes 24 (Fig. 3).

The clean gas then reaches the outlet 5 over the opening 4. The conveying gas valve 13 is closed.

If the filter bed material is to be regenerated, the conveying gas throttle valve 13 is opened (Fig. 5).

The gate 7 releases the flow-in opening for scavenging gas which then flows through the spaces 25 (Fig.

3) into the clean gas chamber of the filter and from there through the filter bed 11 radially outwards (arrows 27) into the crude gas chamber 20.

The conveying gas stream flows, as mentioned, through the pipe 19 tangentially into the crude gas chamber 20. Since the crude gas chamber 20 is one of two annular spaces limited by two circular cylindrical walls 1/9, the conveying gas stream flows downwards in the shape of a helical line S (Fig. 5). In this way, it mixes with the dust laden scavenging gas stream (arrows 27) so that even those dust granules which were rinsed out of the filter bed 11 by the scavenging gas follow the downward helical line.

If this dust-laden gas stream were to enter the lower collecting room 26 at any point, a large portion of the dust would then enter the crude gas channel 21 and therefore the subsequent filter elements. In orderto avoid this, the entrance point E of the conveying gas pipe 19 is arranged under consideration of the dimensions of the casing 1 and the gas streaming speed in such a position on the circumference of the casing 1 that the end point Z of the helical line S lies at least substantially diametrical in respect of the flow-off opening 35 (which serves as a flow-in opening during the crude gas cleaning operation).

Thanks to this arrangement, the main amount D of the dust is separated from the gas, not in the flow out region of the gas, but opposite the outlet opening 35, glides along the inclined wall 36 downwards and is then transported away from there by the screw conveyor.

It is clear to the person skilled in the art that the pointZ does not only lie at a certain point diametrically opposite the opening 35, but covers a relatively wide zone, as shown in Figure 2.

The entrance point E (Fig. 5) is determined experimentally by firstly determining the pitch h of the helical line S and then, beginning from point Z, plotting the helical line along the inner wall of the casing 1.

The vertical distance of the points E and Z is a whole multiple of the pitch h.

Thanks to the co-operation of the radially directed scavenging gas stream 27 and the tangentially inflowing conveying gas stream 28, a cyclone effect results which leads to an intensive dust separation and prevents the fast contamination of the outer su rface of the pipe 9.

Due to the abrupt interruption of the helical line S at pointZ caused by the sudden widening of the lower room 26, the dust circulating near the walls quickly falls down.

Since the crude gas is sucked through the crude gas channel 21 by means of a suction fan arranged at the end of the channel, there is a sub-pressure in the same so that the mixed scavenging and conveying gas stream is taken up without difficulty by the crude gas through the opening 35 (Figures 2 and 5).

According to Figure 5, the granular filter material is caught by the conveying gas stream at the lowest point of the filter bed 11 and is conveyed upwards in the conveyor tube 14. After leaving the conveyor tube 14, the granular material strikes the deflecting member 15. The filter material granules rebound on the deflecting member 15 and are guided downwards by the inner surface of the casing where they reach the filter bed 11 again through the drop pipe 24. The conveying gas leaves the separating device 17 through the pipe 19 and enters, as already mentioned, the crude gas chamber 20 tangentially at point e (Figure 5).

Figure 6 shows a variant where the parts remaining unchanged are marked with the reference numerals already mentioned. Contrary to the embodiment as per Figures 1-5, the conveying gas pipe 37 is lead concentrically downwards into the conveyor tube 14 and opens out into a guide clamp 38 arranged below the conveyor tube 14. The scavenging gas streaming out in the deflection chamber 38 is deflected upwards within the same and sweeps the granules of the filter bed 11 in the annular space 12 along with it upwards. Apart from this difference, the filter unit works as described on the basis of Figures 1 and 4.

Claims (12)

1. Amethodforthe intermittent, regenerating cleaning of a filter bed which is kept in the form of granular material between two gas-permeable walls, through which polluted crude gas flows, whereby the granular material is moved upwards by a conveying gas stream, then falls back again in the space between the gas-permeable walls into the effective range of the conveying gas stream and is thereby circulated in the cycle, and during the cleaning process a scavenging gas is blown through the granular material falling downwards between the gaspermeable walls and is collected and drawn off into a crude gas space surrounding the filter bed, characterized in that the conveying gas stream, subsequent to the upward conveyance of the granular material is separated from the latter and introduced into the crude gas room surrounding the filter bed.

2. The method according to claim 1, whereby the scavenging gas coming out of the filter bed is collected in a practically circular cylindrical crude gas space, characterized in that the conveying gas stream is introduced in a tangential direction into the crude gas space in such a way that the conveying gas combines in the crude gas space with the dustladen scavenging gas and the dust particles swept along in the area of the cylindrical crude gas space are at least partly conveyed downwards in a helical line.

3. The method according to claim 2, characterized in that the entrance point of the conveying gas stream into the crude gas space is selected under consideration of the dimensions of the crude gas space and the flow-in speed that the end point of said helical line lies at least practically opposite the exit opening for the mixed conveying and scavenging gas stream.

4. An apparatus to carry out the method according to claim 1 with two gas-permeable walls distanced from one another and containing a granular filter bed, said walls being formed as practically coaxial pipes and surrounded by a gas-impermeable casing, whereby a conveying tube is arranged within the inner pipe, the lower and upper ends of which are connected to the interstice formed between the two gas-permeable walls, characterized in that the upper end of the conveying tube (14), for the purpose of separating the granules from the conveying gas, opens into a separating device (17) which is in turn connected over a connecting pipe (19) to the crude gas chamber (20) which lies between the outer (9) of the two gas-permeable walls and the gasimpermeable casing (1).

5. The apparatus according to claim 4, characterized in that the connecting pipe (19) opens tangentially into the crude gas chamber (20).

6. The apparatus according to claim 4 or 5, characterized in that arranged within the separating device (17), coaxial to the conveying gas stream is a downward tapering deflecting member(15), whereby the housing (18) surrounding the separating device (17) is lead downwards in the surrounding area of the deflecting device (15) in the form of a run-off incline in order to lead the downwardflowing granular material back to the filter bed.

7. The apparatus according to claim 6, characterized in that the deflecting device (15) has the form of a downward pointing cone.

8. The apparatus according to claim 6 or 7, characterized in that the lower part of the separating device (17) is connected to the upper part of the filter bed (11) over a number of drop pipes (24) which are inclined down towards the filter bed (11).

9. The apparatus according to claim 4, to carry out the method according to claim 2, characterized in that the vertical distance (H) of the entrance point (E) of the conveying gas stream (28) in the crude gas chamber (20) from the end point (2) of the helical line (S) is a whole multiple of the pitch (h) of said helical line.

10. The apparatus according to any one of claims 4 to 9,characterized in that the conveying gas feed pipe is arranged coaxially in the conveying tube (14) and opens out below the conveying tube (14) into a deflection clamp (38), such that the conveying gas deflected upwards in the deflecting clamp (38) flows upwards in the annular ring (R) between the conveying tube (14) and conveying gas pipe (37) and thereby takes granular material with it, Figure 6.

11. A method for the intermittent, regenerating cleaning of a filter bed substantially as hereinbefore described with reference to any one of the accompanying drawings.

12. An apparatus for carrying out a method for the intermittent, regenerating cleaning of filter bed substantially as hereinbefore described with reference to Figs. 1 to 5 or Fig. 6 of the accompanying drawings.