Appliance for the wet cleaning of filter cartridges in fluidized-bed apparatuses, spray driers and moving bed installations

The wet cleaning of filter cartridges (4) in fluidised-bed apparatuses and similar process units, without their being dismantled, is carried out by means of cleaning fluid sprayed out of nozzle orifices (10) arranged in the form of a ring, the nozzle orifices (10) being installed in the filtered exhaust-gas space (7) and the filter cartridge (4) being moved through this ring of nozzle orifices (10) by a lifting device (17). In a preceding flushing cycle, the filter cartridge (4) is filled with cleaning fluid and is then subjected to an ultrasonic transmitter (26) and with pressure pulses. The nozzle orifices (10) are designed and arranged in such a way that the issuing cleaning jets strike the filter casing (5) tangentially at an angle of inclination .alpha. and thus set the filter cartridge (4) in rotation. The best possible cleaning effect is achieved by the rotation and lift of the filter cartridge (4).

The invention relates to an appliance for the washing of filters, 
particularly star-folded filter cartridges in fluidised-bed apparatuses 
and similar process units, such as spray driers and moving-bed 
installations. 
The above units are nowadays in widespread use for drying, granulation and 
encapsulation in the pharmaceutical and food industries and for the 
production of washing agents and other chemical products. For the sake of 
simplified illustration, reference is made hereafter only to fluidised-bed 
apparatuses. 
A fluidised-bed apparatus typically consists of the fluidising chamber and 
of an adjoining head part, in which a number of filters for separating the 
fluidisable material from the gas stream, usually air, are arranged. It 
has been customary to use fabrics or felts made of natural or synthetic 
fibres as filter material. An increasing layer of product dust is 
precipitated on the filter during the production process, thus leading to 
pressure losses and therefore to a decreasing separating capacity. 
To free this precipitation from the filters, it is known, during continuous 
operation, to subject the filter to pressure pulses, preferably 
compressed-air surges, directed counter to the main gas stream. The 
precipitation is thereby blown off from the inside of the filter. In an 
effort to reduce the precipitation of product dust from the outset and, at 
the same time, increase the filtration fineness, a filter material, 
consisting of a supporting fleece together with the attached actual filter 
layer made of anti-adhesive polytetrafiuoroethylene, was developed. Even 
with the filter materials which are now more efficient, a more thorough 
cleaning, beyond the degree of cleaning obtainable by means of 
compressed-air pulses, has to be carried out repeatedly. Such a basic 
cleaning, including that of the filter, is necessary when the product 
generated in the fluidised-bed apparatus is changed, so as not to cause 
any contamination of the subsequent product. A thorough filter cleaning 
can likewise become necessary cyclically, depending on the duration of the 
production phase and on the type of product, when the filter material 
becomes clogged successively with the product dust over a relatively long 
period of operation, despite being blown free periodically. 
Various washing processes and appliances have already been developed for 
such a kind of basic cleaning of gas-borne liquid-soluble particles from 
filters. Removing the filters from the fluidised-bed apparatus, washing 
the filters outside the installation and subsequently reinstalling them is 
unjustifiable in view of the high outlay in terms of assembly, the long 
standstill time of the apparatus and the possible danger to personnel from 
products involving a health risk. 
German Offenlegungsschrift 3,316,527 discloses a washing appliance, where a 
flushing-fluid line having a plurality of spray nozzles can be moved 
within a cascade of filter hoses, in order to flush the filter surface 
free as completely as possible with the fluid jets. Two versions are 
proposed there. First, the spraying off of the exterior of the filter 
hoses, and second the introduction of the spray nozzles into the filter 
hoses with flushing from inside. 
This appliance is unsuitable for the filter cartridges predominantly used 
in fluidised-bed apparatuses. When polytetrafiuoroethylene is used as a 
filter layer, a flushing operation from the inside of the cartridge 
outwards is unsuccessful because of its impermeability to fluids. A basic 
cleaning of large filter cartridges, especially with star-folded filter 
material, by external spraying by means of the construction described 
remains inadequate. Not all the surface portions of the filter cartridge 
are attacked directly by the flushing jets. 
Depending on the specific use, not only the various fabrics, felts or 
nettings made of natural or synthetic fibres, composed of a layer of 
anti-adhesive polytetrafiuoroethylene attached to a supporting fleece, but 
also multi-layered steel nettings are employed as filter material. The 
structure and strength of the different filter materials necessitate and 
allow a differentiated washing treatment. 
The process and appliance according to German Patent Specification 
4,029,804 were developed for the thorough cleaning of filter cartridges in 
the installed state. In this version, the individual filter cartridge is 
surrounded at the head end, below the partition relative to the clean 
space of the fluidised-bed apparatus, with a ring line which has a ring of 
nozzle bores or a nozzle gap directed perpendicularly to the filter 
surface. The filter is sprayed with washing fluid via these orifices. The 
cleaning fluid running down the filter dissolves the layer of product dust 
adhering to it and flushes this off. During the flushing operation, the 
filter is subjected to compression-gas pulses which act outwards from 
inside the filter and which thus assist the breakaway of the particles 
located on the outer skin of the filter. 
The satisfactory wet cleaning of star-folded filter is acknowledged, in the 
literature, as presenting problems. When there are extreme cleanliness 
requirements, as in pharmacy or food technology, the degree of cleaning 
achieved by the state of the art known hitherto is insufficient. There are 
two causes of this, both having an adverse effect. On the one hand, the 
more intensively cleaning jet of cleaning fluid strikes directly only a 
narrow band surface on the filter circumference with a corresponding jet 
pressure, whereas the much larger surface located downwards on the filter 
is in fact only flushed extensively free of the adhering product dust 
merely by the cleaning fluid flowing downwards. On the other hand, the 
washing nozzles themselves are located in the reaction space of the 
fluidised-bed apparatus. They are therefore contaminated by the product 
swirling round, are clogged partially or even completely and thus lose 
their operating capacity. This causes a standstill of the installation and 
an outlay in cleaning the nozzle orifices again. 
The object of the invention is to provide a wet cleaning for the 
above-described purpose and, at the same time, eliminate the deficiencies 
occurring hitherto. That is to say, at as low an outlay as possible in 
terms of construction, to achieve a high degree of cleaning, even in 
respect of fluid-insoluble products, by a direct spraying of the entire 
filter surface clogged by particles with cleaning fluid and, at the same 
time, to protect the washing nozzles against contamination during 
continuous operation. In conjunction with this, the cleaning fluid used is 
to be utilised efficiently and a washing treatment satisfying the 
different requirements and prevailing conditions, also in terms of the 
various fluid-impermeable or fluid-permeable filter materials used, is to 
be provided. 
The entire washing treatment is to be automated, in order to achieve a 
constantly high cleaning quality and largely eliminate changing human 
influences. The strict regulations regarding apparatus construction from 
pharmacy and the food industry are applicable as premises. 
The necessary high degree of cleaning and the complete avoidance of the 
clogging of the washing nozzles were unattainable with the previous 
principle of construction of filter-washing appliances. 
There had to be a completely new departure. An improved process for wet 
cleaning of filter cartridges and the appliance according to the present 
invention for carrying out that process and attaining the above stated 
object will now be described. 
The wet-cleaning process provided by the invention and the associated 
appliance guarantee a high degree of cleaning, even where fluid-insoluble 
products are concerned, since all the regions of the active filter 
surface, even with star folding, are directly sprayed with cleaning fluid, 
and, with the fluidised-bed apparatus continuing to operate, the washing 
nozzles are no longer exposed to the product swirling round in the 
reaction space, with the result that they remain free of impurities. A 
washing treatment which conforms to the particular cleanliness 
requirements and is dependent on the "degree of contamination" and which 
is matched to the filter material used becomes possible. Even stubborn 
encrustations extending into the filter fabric are eliminated reliably, 
with cleaning fluid being used sparingly. The program-controlled execution 
of the washing treatment guarantees a uniformly high thoroughness, without 
the influence of subjective factors. The novel principle of construction 
meets internationally valid standards of apparatus construction, even in 
the most sensitive sectors. 
It is proposed to install outside the reaction space, in the filtered 
exhaust-gas space, washing nozzles which are arranged in the form of a 
ring and surround the respective filter cartridge in cross-section and 
through which the cleaning fluid is conventionally sprayed onto the filter 
casing, and, by means of a sliding lifting movement, move the entire 
active filter surface through the jet range of the nozzle ring. In an 
extended washing programme, the filter cartridge is previously thoroughly 
flushed through with cleaning fluid and, in the filled state, subjected to 
ultrasound, if appropriate additionally with compressed air. The cleaning 
fluid can be drained off via a bottom valve in the filter cartridge. Such 
an extended washing programme consists of the flushing cycle, the prewash, 
the fine wash and the concluding aftertreatment. 
For filter cartridges with filter materials of higher strength which 
withstand even harder jet pressure, the nozzle orifices are designed and 
arranged in such a way that the cleaning jets strike the filter casing 
tangentially at an angle .alpha. and thereby set the filter cartridge in 
rotation. The filter cartridge is moved through the ring of nozzle 
orifices by means of a lifting device. The rotation and simultaneous 
up-and-down stroke of the filter cartridge ensure the best jets striking 
the filter casing. Sealing between the head of the reaction space and the 
exhaust-gas space of the apparatus during the production phase takes 
place, through the filter cartridge suspended at its upper edge in this 
transition, by means of the intermediate lip gasket.

The following description (FIG. 1) first refers only to one filter 
cartridge in the fluidised-bed apparatus; however, in actual fact, in the 
main a plurality of filter cartridges of this type are arranged in it. The 
part of the fluidised-bed apparatus, with the integrated washing 
appliance, which is relevant here consists of an apparatus housing 1, of 
the reaction space 2 with the reaction-space head 3 and of the filter 
cartridge 4 which is arranged therein and which the filter casing 5 
surrounds axially. The filter cartridges 4 and filter casing 5 can have a 
different geometrical shape. Star folding is often employed on account of 
the enlarged active filter surface achieved thereby. For high stress, a 
steel filter fabric is preferred because of its greater strength. 
The reaction-space head 3 and the exhaust-gas space 7 located above it are 
separated hermetically from one another by means of a sealing point 6 
located in this transition. The exhaust-gas space is surrounded by the 
wall 8 which has the gas outlet 9. A shut-off flap 27 is arranged in the 
gas outlet 9. The sealing point 6 is formed (see FIG. 2) in that the 
filter cartridge 4 suspended at its upper edge in the abovementioned 
transition is surrounded by a lip gasket 15 which rests on a semicircle 16 
as an extension of the wall 8. Located directly above the sealing point 6, 
and already directed into the exhaust-gas space 7 and arranged in the wall 
8, is a ring of nozzle orifices 10 which is matched to the cross-sectional 
geometry of the filter cartridge 4 and which allows the filter cartridge 4 
to move through this ring. The nozzle orifices 10 are the flow outlets of 
flat-jet nozzles 24 arranged in a symmetrical distribution. The nozzle 
orifices 10 are fashioned and arranged in such a way that the issuing jets 
of cleaning fluid are directed with a rotational effect onto the filter 
casing 5 tangentially at an angle of inclination .alpha. (see FIG. 3). The 
flat-jet nozzles 24 are supplied via an annular channel 11 and a feed line 
12 as a distribution system for the cleaning fluid. 
The nozzle orifices 10 can also be designed as a radial gap or consist of a 
plurality of centrically oriented bores. The jet of cleaning fluid issuing 
from them does not normally set the filter cartridge 4 in rotation. An 
arrangement of this type would be sufficient for the washing treatment of 
sensitive filter material, where work has to be carried out with a softer 
jet of cleaning fluid which, even as a jet striking tangentially, would 
not be sufficient to set the filter cartridge 4 in rotation. 
On its bottom, the filter cartridge 4 has a filter-cartridge bottom valve 
18 which is connected to a lifting device 17 via a linkage 19. The 
lead-through of the linkage 19 from the lifting device 17 into the filter 
cartridge 4 to the filter-cartridge bottom valve 18 takes place by means 
of a bush 21 seated on the top face of the filter cartridge 4. Underneath 
the bush 21, within the filter cartridge 4, the linkage 19 has a driving 
shoulder 22 which is designed at the same time as a mounting 23 for the 
rotational movement of the filter cartridge 4. The distance between the 
driving shoulder 22 and the bush 21 acting as a stop is governed by the 
maximum stroke of the filter-cartridge bottom valve 18. An ultrasonic 
transmitter 26, seated here on the linkage 19, is placed in operative 
proximity to the filter cartridge 4. 
To subject the filter cartridge 4 to compressed gas by means of 
compressed-gas pulses, a delivery line 14 extends parallel to the linkage 
19 and opens out in a compressed-gas outlet 25 located above the filter 
cartridge 4. In the head of the exhaust-gas space 7 is provided a flushing 
nozzle 20 for the purpose of the flushing of the exhaust-gas space 7, the 
rapid filling of the filter cartridge 4 with cleaning fluid and the 
complete flushing of the fluidised-bed apparatus. 
The description of the operating cycle follows. In this, the washing 
programme explained constitutes a maximum version for especially high 
cleanliness requirements and heavily loaded filter cartridges 4. Under 
simpler conditions, a reduced washing programme is also sufficient 
according to the circumstances. In the production phase (see FIG. 1 ), in 
which fluidisable material is treated, the filter cartridge 4 is in its 
lowest position and, at the same time, is pressed against the sealing 
point 6 (the state according to FIG. 2). Cleaning fluid is not introduced 
either via the flushing nozzle 20 or via the nozzle orifices 10; the 
filter cartridge 4 is not subjected to compressed-gas pulses, the 
ultrasonic transmitter 26 is inactive and the filter-cartridge bottom 
valve 18 is closed. The shut-off flap 27 in the gas outlet 9 is open. 
The gas stream flowing into the head of the reaction space 3 passes through 
the filter casing 5 and leaves the filter cartridge 4 in the direction of 
the exhaust-gas space 7 to the gas outlet 9. When it passes through the 
filter casing 5, the product is separated, but successively clogs the 
latter. The filter casing 5 is roughly blown free from inside the filter 
cartridge 4 periodically or in dependent on a measured 
differential-pressure signal by means of compressed-gas pulses via the 
delivery line 14 and the compressed-gas outlet 25. 
Because the nozzle orifices 10 are arranged completely outside the reaction 
space 2 so as to be partitioned off by the sealing point 6, the nozzle 
orifices 10 remain free of any traces of the product. In particular, the 
risk that nozzle orifices 10 will possibly be blocked is eliminated. 
If a basic cleaning of the filter cartridge 4 becomes necessary because of 
a product change or as a result of a progressive encrustation of the 
filter casing 5, this no longer being dissolvable by compressed-gas 
pulses, there is a change-over to the washing cycle. 
The gas/product stream flowing in the direction of the reaction-space head 
3 is interrupted and the product is emptied from the fluidised-bed 
apparatus. A flushing cycle is carried out before the first actual washing 
phase. For this purpose, cleaning fluid, for example normal mains water, 
is introduced via the flushing nozzle 20 and/or via the nozzle orifices 
10, the filter-cartridge bottom valve 18 remaining in the zero position, 
that is to say closed, and the filter cartridge 4 continuing to be in its 
lowest position seated in the sealing point 6 (see FIG. 2). The cleaning 
fluid runs into the filter cartridge 4 from above and thoroughly flushes 
the filter casing 5 from the inside. If the inflow of cleaning fluid is 
set high, the filter cartridge 4 fills, since the flow-off through the 
fine-mesh filter casing 5 does not take place to the same degree. When the 
desired filling level is reached, the ultrasonic transmitter 26 is 
activated. The stubborn encrustations on the filter casing 5 which may be 
drawn into the filter fabric are dissolved by means of ultrasound. As 
early as while subjection to ultrasound is taking place and/or immediately 
thereafter, the shut-off flap 27 in the gas outlet 9 is closed and an 
adjustable gas pressure is applied via the delivery line 14 and the 
compressed-gas outlet 25 to the filter cartridge 4, that is to say to the 
cleaning fluid now located in it. An intensified flushing effect through 
the filter casing 5 from inside the filter cartridge 4 outwards can thus 
be achieved. The product-laden cleaning fluid can leave the fluidised-bed 
apparatus via an outlet (not shown). The filter fabric must have a 
specific minimum strength according to the stresses caused by the 
ultrasonic treatment; steel filter fabrics are preferably employed. 
The flushing cycle now changes to the prewashing phase. The ultrasonic 
transmitter 26, which, if appropriate, has been activated up to now, is 
switched off. Subjection to compressed-gas pulses can be continued as 
required. The lifting device 17 which was under prestress in the downward 
direction is now actuated in the upward direction. This prestress via the 
linkage 19 caused the filter-cartridge bottom valve 18 to be pressed 
against the seat of the filter cartridge 4 and, at the same time, by means 
of the downward pull acting on the latter, caused the lip gasket 15 to be 
pressed onto the semi-circle 16, with the result that the sealing point 6 
remained reliably closed. The linkage 19 moves successively upwards, and 
the filter-cartridge bottom valve 18 is raised and frees the seat. The 
residual cleaning fluid still remaining in the filter cartridge 4 from the 
flushing cycle can thus run out. The linkage 19 moves further upwards; the 
driving shoulder 22 butts against the bush 21, with the result that the 
filter cartridge 4 is now moved continuously upwards through the ring of 
nozzle orifices 10 into an end position. This upper end position is 
selected so that even the lowest edge zone of the filter casing 5 is 
covered by the cleaning jets from the nozzle orifices 10. While the filter 
cartridge 4 is being raised, the fiat-jet nozzles 24 are subjected to 
cleaning fluid via the feed line 12 and the annular channel 11. As a 
result of the angle of inclination .alpha. at which the nozzle orifices 10 
are directed towards the filter casing 5, the issuing cleaning jets strike 
the filter casing 5 tangentially and set the filter cartridge 4, suspended 
rotatably on a mounting 23, in rotation, the mounting 23 being located on 
the linkage 19 in the region of the driving shoulder 22. The filter 
cartridge 4 now simultaneously executes an upward lifting movement and a 
rotational movement. All the zones of the filter casing 5 are thereby 
sprayed intensively and efficiently with cleaning fluid. When the upper 
end position is reached, the lifting movement of the filter cartridge 4 is 
reversed, so that the washing operation is continued in the downward 
stroke. However, other parts of the fluidised-bed apparatus could also 
expediently be washed before the downward stroke on account of the opened 
position, the sealing point 6 and the seat of the filter-cartridge bottom 
valve 18 being open. After the downward stroke, the prewash is terminated 
and the predominant part of the product particles is washed out. 
The flushing cycle and prewashing phase are followed by the fine-washing 
phase. Since now only an extremely small fraction of product particles 
still remaining has to be washed out, during the fine-washing phase the 
cleaning fluid can be used repeatedly in closed circuit. The fine-washing 
phase can be initiated by a renewed flooding of the filter cartridge 4 
which is in its lowest position, that is to say the sealing point 6 and 
the filter cartridge bottom valve 18 are closed. The process corresponds 
to the above-described flushing cycle, including the possible additional 
subjection to ultrasound and compressed-gas pulses. The filter cartridge 4 
and the interior of the apparatus are thereby thoroughly flushed out once 
again. After the possible flooding, the lifting device 17 is switched on 
again, in order to move the entire filter casing 5 in the course of a 
plurality of up-and-down strokes through the ring of cleaning jets 
spraying out of the nozzle orifices 10. The duration of this treatment 
phase depends on the degree of cleanliness required. 
For particularly stringent cleanliness requirements, the fine-washing phase 
can be followed by an aftertreatment. For this purpose, a renewed flushing 
cycle and a subsequent fine-washing phase with demineralised water are 
carried out. Finally, a blowing out of the nozzle orifices 10 and of the 
flushing nozzle 20 by means of compressed air takes place. Lastly, before 
a new production phase commences, the interior of the apparatus is 
thoroughly dried, for example with hot air. 
Before the start of the next production phase, the filter cartridge 4 must 
be in its initial position, namely the lowest position. The 
filter-cartridge bottom valve 18, again in the zero position, is closed 
and is subjected to a pressure force by the lifting device 17 via the 
linkage 19 for reliable sealing, with the result that the sealing point 6 
is also sealed off hermetically. The flushing nozzle 20, the nozzle 
orifices 10 and the ultrasonic transmitter 26 are inactive. The shut-off 
flap 27 is open, whereas the outlet (not shown) for the cleaning fluid in 
the fluidised-bed apparatus is closed. 
As a rule, a plurality of filter cartridges 4 are accommodated in a 
fluidised-bed apparatus; the operating systems of the washing appliance 
are then present in a corresponding number and the cleaning cycles are 
coordinated on all the filter cartridges 4, for example in such a way that 
the cleaning cycle on any two filter cartridges 4 proceeds simultaneously 
and, after the end of the cycle, is changed over to the next pair of 
filter cartridges 4.