Abstract:
In order to provide a method for supplying fresh auxiliary material, which is added to a stream ( 120 ) of crude gas laden with wet paint overspray before the stream of crude gas passes through at least one filter element ( 172 ) for separating the overspray from the steam of crude gas, to at least one filter device ( 132 ) which comprises at least one receptacle ( 176 ) for auxiliary material, which is in its operating position, while the stream of crude gas is passing through the filter element, which method enables better action of the auxiliary material on the stream of crude gas and makes a particularly efficient supply of fresh auxiliary material to the at least one filter device possible, it is suggested that the fresh auxiliary material be supplied directly into the receptacle for auxiliary material while the receptacle for auxiliary material is in the operating position.

Description:
[0001]    This application is a continuation of international application number PCT/EP2008/005483 filed on Jul. 4, 2008. 
         [0002]    The present disclosure relates to the subject matter disclosed in international application number PCT/EP2008/005483 of Jul. 4, 2008 and German application number 10 2007 040 899.6 of Aug. 24, 2007, which are incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to a method for supplying fresh auxiliary material, which is added to a stream of crude gas laden with wet paint overspray before the stream of crude gas passes through at least one filter element for separating the overspray from the stream of crude gas, to at least one filter device which comprises at least one receptacle for auxiliary material, which is in an operating position, while the stream of crude gas is passing through the filter element. 
         [0004]    Such a method is known, for example, from DE 10 2005 048 579 A1. 
         [0005]    With this known method, the dry separation of the wet paint overspray from the stream of crude gas of a spray booth takes place in the filter device once fresh, flowable, particulate auxiliary material designated as “precoat” material has been released into the stream of crude gas with a nozzle arrangement. 
         [0006]    This auxiliary material serves the purpose of being deposited on the surfaces of the filter element as a barrier layer in order to prevent these surfaces from becoming clogged due to overspray particles adhering thereto. As a result of periodic cleaning of the filter elements of the filter device, the mixture consisting of auxiliary material and wet paint overspray passes from the filter elements into receptacles for auxiliary material, from which it can be withdrawn by suction in order to be supplied to the nozzle arrangement for renewed use as auxiliary material. Furthermore, the mixture consisting of auxiliary material and wet paint overspray which is present in the receptacle for auxiliary material can be whirled up by means of pulses of compressed air from a compressed air lance in order to rise up out of the receptacle for auxiliary material to the filter elements and be deposited on them. 
         [0007]    In order to prevent auxiliary material passing into the application area of the paint plant while auxiliary material is being supplied to the stream of crude gas from the nozzle arrangement, the flow path of the stream of crude gas from the application area to the filter device is closed periodically in this known method. The auxiliary material which has been whirled up from the receptacles for auxiliary material is not sufficient to generate an adequate protection layer on the filter elements. In addition, fresh auxiliary material can be introduced into the stream of crude gas only through the nozzle arrangement. 
         [0008]    The object underlying the present invention is to provide a method of the type specified at the outset which enables better action of the auxiliary material on the stream of crude gas and makes a particularly efficient supply of fresh auxiliary material to the at least one filter device possible. 
       SUMMARY OF THE INVENTION 
       [0009]    This object is accomplished in accordance with the invention, in a method having the features of the preamble to claim  1 , in that the fresh auxiliary material is supplied directly into the receptacle for auxiliary material while the receptacle for auxiliary material is in the operating position. 
         [0010]    The receptacle for auxiliary material is preferably arranged in the operating position beneath at least one filter element such that the mixture consisting of auxiliary material and wet paint overspray which is cleaned from the filter element passes downwards into the receptacle for auxiliary material during the cleaning. 
         [0011]    Furthermore, it is preferably provided for the fresh auxiliary material from the receptacle for auxiliary material to pass directly into the stream of crude gas. 
         [0012]    For this purpose, it is particularly favorable when the stream of crude gas is conveyed through the receptacle for auxiliary material. 
         [0013]    The incorporation of the auxiliary material from the receptacle for auxiliary material into the stream of crude gas can be improved when the auxiliary material is whirled up in the receptacle for auxiliary material by means of a whirling device. 
         [0014]    The solution according to the invention offers the advantage that a nozzle arrangement for the supply of fresh auxiliary material to the filter device can be dispensed with. As a result, it is also not necessary to close the flow path of the stream of crude gas from the application area to the filter device periodically in order to prevent auxiliary material reaching the application area. 
         [0015]    In one preferred development of the invention, it is provided for the at least one receptacle for auxiliary material to be mounted in the operating position so as to be immovable. 
         [0016]    As a result, the receptacle for auxiliary material, together with boundary walls of the filter device, can form an air-tight unit which ensures a dust-free handling of the particulate materials (auxiliary material and wet paint overspray). 
         [0017]    In addition, the receptacle for auxiliary material need not be disconnected from other boundary walls of the filter device in order to supply fresh auxiliary material to the receptacle for auxiliary material. As a result, contamination of the surroundings, which could be caused by the exiting of dust during the disconnection of the receptacle for auxiliary material from adjoining boundary walls, will be avoided. 
         [0018]    Furthermore, a receptacle for auxiliary material which is mounted in the operating position so as to be immovable is particularly easy to produce. 
         [0019]    In one preferred development of the invention, it is provided for the auxiliary material to be supplied to the receptacle for auxiliary material through a supply line for auxiliary material which is connected to the receptacle for auxiliary material. 
         [0020]    In this respect, it may be provided, in particular, for the supply line for auxiliary material to comprise a flexible hose line. 
         [0021]    The fresh auxiliary material will preferably be conveyed into the at least one receptacle for auxiliary material from at least one storage receptacle. 
         [0022]    This conveyance can be brought about by means of a so-called blow pot or a powder metering pump, for example, a so-called DDF pump or another metering pump conveying with suction/pressure alternation in accordance with the principle of a dense flow. Powdered substances are conveyed in a particularly gentle and exactly meterable manner over relatively large distances by means of such pumps, in particular DDF pumps. 
         [0023]    Blow pots are known per se, for example, from JP 02123025 A or JP 06278868 A and have, up to now, been used in coating plants for the purpose of conveying powdered paint to the application receptacles located in the vicinity of the sprayers. The receptacles are relatively small, closable containers with a base permeable to air, through which air can be conveyed into the receptacle for the fluidization of the powder and for its conveyance. 
         [0024]    In order to make room in the receptacle for auxiliary material for fresh auxiliary material, it may be provided for auxiliary material mixed with overspray to be removed from the at least one receptacle for auxiliary material through a discharge line for auxiliary material which is connected to the receptacle for auxiliary material. 
         [0025]    In this respect, it is favorable for an efficient and as complete an emptying of the receptacle for auxiliary material as possible when at least one discharge line for auxiliary material opens into an interior space of the receptacle for auxiliary material in a corner area of the receptacle for auxiliary material. 
         [0026]    It is particularly favorable for a complete emptying when at least two discharge lines for auxiliary material open into an interior space of the receptacle for auxiliary material, preferably in corner areas of the receptacle for auxiliary material which are different to one another. 
         [0027]    The auxiliary material mixed with overspray from the at least one receptacle for auxiliary material is preferably conveyed into a collecting receptacle, from where it is supplied for reuse, further processing or waste disposal. 
         [0028]    It has proven to be particularly favorable when the auxiliary material mixed with overspray is drawn out of the at least one receptacle for auxiliary material by suction. 
         [0029]    Auxiliary material mixed with overspray is preferably removed from at least one receptacle for auxiliary material in order to empty the receptacle for auxiliary material before fresh auxiliary material is supplied to the receptacle for auxiliary material. In this way, it is possible to prevent overspray still located in the receptacle for auxiliary material from degrading the quality of the fresh auxiliary material supplied. 
         [0030]    The auxiliary material mixed with overspray can be removed from at least one receptacle for auxiliary material when the auxiliary material in the relevant receptacle for auxiliary material reaches a predetermined filling level. 
         [0031]    This filling level of the auxiliary material can be measured, in particular, by means of a filling level sensor arranged in the receptacle for auxiliary material, whereby a particularly reliable control of the emptying of the respective receptacle for auxiliary material is made possible. 
         [0032]    As a result of the accumulation of wet paint overspray, which has a lower density than the auxiliary material, in the mixture consisting of auxiliary material and overspray which is present in the receptacle for auxiliary material, the density of this mixture decreases during operation of the filter device ever further and so the barrier layer which is built up on the at least one filter element of the filter device has an ever greater volume. 
         [0033]    The filling level of the material in the receptacle for auxiliary material therefore decreases ever further immediately prior to a cleaning procedure of the filter element. 
         [0034]    It may, therefore, be provided for auxiliary material mixed with overspray to be removed from at least one receptacle for auxiliary material when the filling level of the auxiliary material in the receptacle for auxiliary material has been reduced to a predetermined minimum filling level, for example, approximately 10% of the capacity of the receptacle for auxiliary material. 
         [0035]    Alternatively hereto, the filling level of the material in the receptacle for auxiliary material can be measured after each cleaning procedure of the at least one filter element of the filter device and auxiliary material mixed with overspray removed from at least one receptacle for auxiliary material when the filling level of the auxiliary material in the receptacle for auxiliary material has risen to a predetermined maximum filling level, for example, 90% of the maximum capacity of the receptacle for auxiliary material. 
         [0036]    It can, in particular, also be provided for at least one filter element associated with a receptacle for auxiliary material to be cleaned and auxiliary material mixed with overspray to be removed from the receptacle for auxiliary material when the filling level of the auxiliary material in the receptacle for auxiliary material, which has risen as a result of cleaning, has reached a predetermined maximum filling level. 
         [0037]    In order to facilitate the removal of the auxiliary material mixed with overspray from the receptacle for auxiliary material, it is favorable when the auxiliary material mixed with overspray is fluidized in at least one receptacle for auxiliary material while auxiliary material mixed with overspray is being removed from the receptacle for auxiliary material. 
         [0038]    Alternatively or in addition hereto, the withdrawal of the used material from the receptacle for auxiliary material by suction can be aided by the fact that the auxiliary material in at least one receptacle for auxiliary material is whirled up at least periodically by means of a whirling device while auxiliary material mixed with overspray is being removed from the receptacle for auxiliary material. The material to be removed will be loosened by the whirling up and moved to the inlet openings of the discharge lines. 
         [0039]    The present invention relates, in addition, to a receptacle for auxiliary material for accommodating an auxiliary material which is added to a stream of crude gas laden with wet paint overspray before the steam of crude gas passes through at least one filter element for separating the overspray from the stream of crude gas while the receptacle for auxiliary material is in an operating position. 
         [0040]    The object underlying the present invention is to provide such a receptacle for auxiliary material, to which fresh auxiliary material can be supplied in a simple and efficient manner without such auxiliary material reaching the application area of a paint plant. 
         [0041]    This object is accomplished in accordance with the invention, in a receptacle for auxiliary material having the features of the preamble to claim  18 , in that the receptacle for auxiliary material is connected to a supply device for auxiliary material for supplying fresh auxiliary material directly into the receptacle for auxiliary material which is in an operating position. 
         [0042]    Special developments of the receptacle for auxiliary material according to the invention are the subject matter of claims  19  to  21 , the features and advantages of which have already been explained in the above in conjunction with special developments of the method according to the invention. 
         [0043]    The receptacle for auxiliary material according to the invention is suitable, in particular, for use in a device for separating wet paint overspray from a stream of crude gas containing overspray particles which comprises at least one filter element for separating the overspray from the stream of crude gas and at least one receptacle for auxiliary material according to the invention. 
         [0044]    Special developments of such a device for separating wet paint overspray are the subject matter of claims  23  to  32 , the features and advantages of which have already been explained in the above in conjunction with special developments of the method according to the invention. 
         [0045]    The device according to the invention for separating wet paint overspray is suitable, in particular, for use in a plant for painting objects, in particular vehicle bodies, which comprises at least one application area for applying wet paint to the objects to be painted and at least one device according to the invention for separating wet paint overspray. 
         [0046]    The invention is suitable, in particular, for use in a dry separation system for wet paint overspray for painting booths in the automobile industry or, in general, in the field of industrial paint plants. 
         [0047]    Additional features and advantages of the invention are the subject matter of the following description and the drawings illustrating embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]      FIG. 1  shows a schematic perspective illustration of a painting booth with a device arranged under it for separating wet paint overspray from a stream of crude gas containing overspray particles, the device comprising a flow chamber arranged beneath the painting booth and three filter modules arranged on each side of the flow chamber; 
           [0049]      FIG. 2  shows a schematic vertical cross section through the plant from  FIG. 1 ; 
           [0050]      FIG. 3  shows a schematic vertical cross section corresponding to  FIG. 2  through the plant from  FIG. 1 , wherein the respective flow directions of the crude gas, the exhaust air exiting from the filter modules and the incoming air fed into the flow chamber for generating transverse curtains of air are indicated, in addition, by arrows; 
           [0051]      FIG. 4  shows a schematic plan view from above of the plant from  FIGS. 1 to 3 ; 
           [0052]      FIG. 5  shows a schematic side view of the plant from  FIGS. 1 to 4 ; 
           [0053]      FIG. 6  shows a schematic perspective illustration of the device for separating wet paint overspray from a stream of crude gas containing overspray particles, the device being arranged beneath the painting booth of the plant from  FIGS. 1 to 5  and having transverse partition walls subdividing the flow chamber into sections following one another along the longitudinal direction of the flow chamber; 
           [0054]      FIG. 7  shows a schematic perspective illustration of a single filter module which is provided for arrangement between two adjacent, additional filter modules (central module); 
           [0055]      FIG. 8  shows a schematic perspective illustration of a single filter module which is provided for arrangement next to an additional filter module and forms one end of a row of filter modules on the oppositely located side (corner module); 
           [0056]      FIG. 9  shows a schematic vertical cross section through a filter module; 
           [0057]      FIG. 10  shows a schematic vertical cross section through a filter module and the adjoining area of the flow chamber, in which the respective local flow direction of the stream of crude gas is indicated by arrows; 
           [0058]      FIG. 11  shows a schematic perspective illustration of an edge area of an inlet opening of a filter module; 
           [0059]      FIG. 12  shows a schematic front view of a filter module; 
           [0060]      FIG. 13  shows a schematic vertical section through a receptacle for auxiliary material with a filling level sensor and whirling device arranged in the interior of the receptacle; 
           [0061]      FIG. 14  shows a schematic side view of an inspection door in the receptacle for auxiliary material from  FIG. 13 , with a filling level sensor and whirling device held on the inspection door; 
           [0062]      FIG. 15  shows a schematic plan view of the outer side of the inspection door from  FIG. 14 ; 
           [0063]      FIG. 16  shows a schematic plan view from above of a collector grating arranged in the receptacle for auxiliary material from  FIG. 13 ; 
           [0064]      FIG. 17  shows a schematic illustration of a device for supplying fresh auxiliary material from a storage receptacle to receptacles for auxiliary material of the type illustrated in  FIG. 13  which are in their operating position; 
           [0065]      FIG. 18  shows a schematic illustration of a discharge device for discharging auxiliary material mixed with overspray from the receptacles for auxiliary material to a collecting receptacle; 
           [0066]      FIG. 19  shows a schematic illustration of a filter module and an exhaust air line with a blower arranged downstream of the filter module as well as various devices for monitoring the operational state of the blower and a device for supplying compressed air to the filter elements, to a whirling unit and to a fluid base of the filter module; 
           [0067]      FIG. 20  shows a schematic vertical cross section through a second embodiment of a device for separating wet paint overspray from a stream of exhaust air containing overspray particles, the device comprising inclined flow guide plates for guiding a transverse stream of air and a walkable catwalk with an inclined upper side between the filter modules; 
           [0068]      FIG. 21  shows a schematic vertical cross section through an alternative embodiment of a receptacle for auxiliary material which is provided with a pneumatically driven mixing apparatus for thoroughly mixing the material located in the receptacle for auxiliary material and for homogenizing the supply; 
           [0069]      FIG. 22  shows a schematic plan view from above of the receptacle for auxiliary material with a pneumatically driven mixing apparatus from  FIG. 21 ; 
           [0070]      FIG. 23  shows a schematic vertical section through an additional, alternative embodiment of a receptacle for auxiliary material which is provided with an electrically driven shaft and paddles for thoroughly mixing the material located in the receptacle for auxiliary material and for homogenizing the supply; and 
           [0071]      FIG. 24  shows a schematic plan view from above of the receptacle for auxiliary material with an electrically driven shaft from  FIG. 23 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0072]    The same or functionally equivalent elements are designated in all the Figures with the same reference numerals. 
         [0073]    A plant for the spray painting of vehicle bodies  102 , which is illustrated in  FIGS. 1 to 19  and designated as a whole as  100 , comprises a conveying device  104  which is illustrated purely schematically and by means of which the vehicle bodies  102  can be moved along a direction  106  of conveyance through an application area  108  of a painting booth designated as a whole as  110 . 
         [0074]    The application area  108  is the interior space of the painting booth  110  which is delimited by a respective booth wall  114  on both sides of the conveying device  104  in a horizontal transverse direction  112  which extends at right angles to the direction  106  of conveyance which corresponds to the longitudinal direction of the painting booth  110 . 
         [0075]    Spray painting devices  116 , for example, in the form of painting robots are arranged on both sides of the conveying device  104  in the painting booth  110 . 
         [0076]    A stream of air is generated by means of a circuit of circulating air (illustrated only in sections) and this passes through the application area  108  essentially vertically from the top to the bottom, as indicated in  FIG. 3  by the arrows  118 . 
         [0077]    This stream of air absorbs paint overspray in the form of overspray particles in the application area  108 . The term “particles” comprises not only solid but also liquid particles, in particular droplets. 
         [0078]    When wet paint is used, the wet paint overspray consists of paint droplets. The majority of the overspray particles have a greatest dimension in the range of approximately 1 μm to approximately 100 μm. 
         [0079]    The stream of exhaust air laden with the overspray particles from the application area  108  is designated in the following as stream of crude gas. The flow direction of the stream of crude gas is illustrated in  FIGS. 3 and 10  by arrows  120 . 
         [0080]    The stream of crude gas leaves the painting booth  110  downwards and passes into a device for separating wet paint overspray from the stream of crude gas, this device being designated as a whole as  126  and arranged beneath the application area  108 . 
         [0081]    The device  126  comprises an essentially parallelepiped flow chamber  128  which extends over the entire length of the painting booth  110  in the direction  106  of conveyance and is limited in the transverse direction  112  by vertical side walls  130  which are essentially in alignment with the lateral booth walls  114  of the painting booth  110  so that the flow chamber  128  has essentially the same horizontal cross sectional surface area as the painting booth  110  and is essentially arranged completely within the vertical projection of the basic surface area of the painting booth  110 . 
         [0082]    As is best apparent from  FIG. 6 , several, for example, three filter modules  132  are arranged on each of the two sides of the flow chamber  128  and form two rows  136  of modules extending in the longitudinal direction  134  (which corresponds to the direction  106  of conveyance) of the device  126  for separating wet paint overspray. 
         [0083]    Each of the rows  136  of modules comprises two corner modules  138  which each form an end of a row  136  of modules and at least one central module  140  arranged between two adjacent filter modules  132 . 
         [0084]    In order to avoid longitudinal flows of the stream of crude gas in the longitudinal direction  134  of the flow chamber  128  and to avoid flows of the crude gas between the individual filter modules  132 , vertical transverse dividing walls  142  can be provided which extend in the transverse direction  112 , are arranged between two respective filter modules  132  following one another in the longitudinal direction  134  and divide the flow chamber  128  into flow chamber sections  144  which follow one another along the longitudinal direction  134 . 
         [0085]    A defined adjustment of the flow of crude gas is possible for each individual filter module  132  as a result of these transverse dividing walls  142  irrespective of the flow of crude gas through the other filter modules  132 . 
         [0086]    As is best apparent from  FIG. 2 , a catwalk  146 , along which an operator can walk, is provided between the two rows  136  of modules. 
         [0087]    In order to be able to walk on the sections of the catwalk  146  which are arranged in the consecutive flow chamber sections  144  uninterruptedly, doors  148  are provided in the transverse dividing walls  142  ( FIG. 6 ). 
         [0088]    The end walls  150  of the flow chamber  128  closing the flow chamber  128  at its front end and its rear end, respectively, are provided with access doors  152 , through which an operator can pass into the flow chamber  128  from outside. 
         [0089]    Each of the filter modules  132  is designed as a preassembled unit  154  which is produced at a location remote from the point of assembly of the paint plant and transported to the point of assembly of the paint plant as a unit. At the point of assembly, the preassembled unit  154  is arranged in the operating position provided and connected to one or several adjacent, preassembled units  154  or to the transverse dividing walls  142  arranged therebetween as well as to a support construction of the application area  108 . 
         [0090]    The construction of a filter module  132  will be described in the following based on the example of a central module  140  and with reference to  FIGS. 7 and 9  to  16 : 
         [0091]    The module comprises a support construction  156  consisting of two vertical rear supports  158  and two vertical front supports  160  which are connected at their upper ends via horizontal crossbars  162  to one of the respective rear supports  158  ( FIG. 7 ). 
         [0092]    Furthermore, the front supports  160  are connected to one another at their upper ends by means of an additional crossbar (not illustrated). 
         [0093]    The rear supports  158  are also connected to one another by means of crossbars (not illustrated) or by means of a connecting frame (not illustrated). 
         [0094]    The crossbars at the upper end of the support construction  156  bear a horizontal ceiling wall  164 . 
         [0095]    A vertical front wall  166  of the filter module  132  is held at the front sides of the front supports  160 . 
         [0096]    The ceiling wall  164  and the front wall  166  form dividing walls  168  of the filter module  132  which separate a filter element chamber  170  arranged within the filter module  132  from the area of the flow chamber  128  located outside the filter module  132 . 
         [0097]    Several, for example, ten filter elements  172  are arranged in the filter element chamber  170  of the filter module  132  in two rows one above the other which project in a horizontal direction from a common base member  174  which is held at the rear sides of the rear supports  158 . 
         [0098]    The filter elements  172  can be designed, for example, from plates consisting of sintered polyethylene which are provided on their outer surfaces with a membrane consisting of polytetrafluoroethylene (PTFE). 
         [0099]    The coating consisting of PTFE serves the purpose of upgrading the filter category of the filter elements  172  (i.e., of reducing their permeability) and, furthermore, of preventing the permanent adhesion of the wet paint overspray separated from the stream of crude gas. 
         [0100]    The porosity of both the basic material of the filter elements  172  and their PTFE coating is such that the crude gas can pass through the pores into the interior space of the respective filter element  172 . 
         [0101]    In order to prevent the filter surfaces becoming clogged, they are provided, in addition, with a barrier layer consisting of auxiliary material discharged into the stream of crude gas. This preferably particulate auxiliary material is also normally designated as a “precoat” material. 
         [0102]    The barrier layer is formed during operation of the device  126  as a result of deposition of the auxiliary material discharged into the stream  120  of crude gas at the filter surfaces and prevents the filter surfaces becoming clogged by wet paint overspray adhering thereto. 
         [0103]    Auxiliary material from the stream  120  of crude gas is also deposited on the inner sides of the ceiling wall  164  and the front wall  166  of the filter module  132  where it likewise prevents wet paint overspray adhering thereto. 
         [0104]    Any medium which is capable of absorbing the liquid content of the wet paint overspray can, in principle, be used as auxiliary material. 
         [0105]    In particular, lime, rock meal, aluminum silicates, aluminum oxides, silicon oxides, coating powder or the like can, for example, be considered as auxiliary materials. 
         [0106]    Alternatively or in addition hereto, particles having a cavity structure and a large inner surface area relative to their outer dimensions, for example, zeolites or other hollow, for example, spherical bodies consisting of polymers, glass or aluminum silicate and/or natural or synthetically generated fibers can also be used as auxiliary material for absorbing and/or binding the overspray. 
         [0107]    Alternatively or in addition hereto, particles which react chemically with the overspray, for example, chemically reactive particles consisting of amine, epoxide, carboxyl, hydroxyl or isocyanates groups, chemically reactive particles consisting of aluminum oxide subsequently treated with octylsilane or solid or liquid monomers, oligomers or polymers, monosilanes, silanols or siloxanes can also be used as auxiliary material for absorbing and/or binding the overspray. 
         [0108]    The auxiliary material preferably consists of a plurality of auxiliary material particles which have an average diameter in the range of, for example, approximately 10 μm to approximately 100 μm. 
         [0109]    In order to be able to add the auxiliary material to the stream of crude gas without there being the risk of the auxiliary material passing into the application area  108  of the paint plant  100 , each filter module  132  is provided with a receptacle  176  for auxiliary material which is held on the support construction  156  and has, for example, a funnel-like shape in the form of an upturned truncated pyramid ( FIG. 13 ). 
         [0110]    The four trapezoidal side walls  178  of the receptacle  176  for auxiliary material are inclined in relation to the vertical at an angle of at least approximately 60°. 
         [0111]    The height of the receptacle  176  for auxiliary material is, for example, approximately 1.1 m. 
         [0112]    The upper edges of the side walls  178  surround an access opening  180  of the receptacle  176  for auxiliary material, through which the stream  120  of crude gas laden with overspray can enter the receptacle  176  for auxiliary material and escape from it again. 
         [0113]    The base  182  which is aligned essentially horizontal is designed as a porous fluid base  184  which can be flushed with a gaseous medium, in particular with compressed air, in order to fluidize the auxiliary material arranged in the interior space  186  of the receptacle  176  for auxiliary material and to level locally varying filling heights of the auxiliary material within the receptacle  176  for auxiliary material. 
         [0114]    During operation of the plant  100 , the fluid base is put into operation intermittently, for example, three times per minute for approximately two seconds each time. 
         [0115]    In order to prevent damage to the fluid base  184  due to larger objects falling onto it, a collector grating or retention grating  187  is arranged at a distance of, for example, 20 cm above the fluid base  184  and this grating extends in a horizontal direction over the entire cross section of the interior space  186  of the receptacle  176  for auxiliary material and has a plurality of rows of honeycomb-like or rectangular openings  189  for the passage of auxiliary material through the retention grating  187 . The openings are arranged so as to be offset relative to one another from row to row and have a size of, for example, approximately 30 mm×30 mm ( FIG. 16 ). 
         [0116]    In order to enable access to the interior space  186  of the receptacle for auxiliary material  176  for maintenance purposes, one of the side walls  178  is provided with an inspection opening which is closed during operation of the filter modules  132  by an inspection door  188  with a handle  190  (cf.  FIGS. 13 to 15 ). 
         [0117]    As is apparent from  FIG. 15 , the inspection door  188  is detachably held on the associated side wall  178  of the receptacle  176  for auxiliary material by means of clamps  192  with butterfly nuts  194 . 
         [0118]    A pipe  196  for compressed air which leads to a whirling device  198  is held on the inspection door  188  ( FIG. 14 ). 
         [0119]    The whirling device  198  serves the purpose of sending pulses of compressed air into the auxiliary material located therebelow in order to whirl up this auxiliary material and thus introduce it into the stream of crude gas conveyed through the receptacle  176  for auxiliary material. 
         [0120]    In addition, a homogenization of the mixture of auxiliary material and overspray bonded thereto, which is present in the receptacle  176  for auxiliary material, is achieved when the auxiliary material is whirled up by means of the whirling device  198 . 
         [0121]    During operation of the plant  100 , the whirling device  198  is put into operation intermittently, for example, four times per minute for approximately 5 seconds each time. 
         [0122]    The whirling device  198  comprises several, for example, two exit nozzles  200  for compressed air which are designed as conical nozzles and can each generate a cone of compressed air which widens downwards towards the base  182  of the receptacle  176  for auxiliary material. 
         [0123]    The exit nozzles  200  are preferably designed and arranged such that the cones of compressed air generated by the exit nozzles  200  together sweep over the entire floor surface of the receptacle  176  for auxiliary material. 
         [0124]    Furthermore, a holder  202  for a filling level sensor  204  is arranged on the pipe  196  for compressed air and comprises a rod-like sensor element  206  and a sensor housing  208  with sensor electronics accommodated therein ( FIG. 14 ). 
         [0125]    The filling level sensor  204  is designed as an analog, in particular capacitive sensor and serves the purpose of generating a signal which corresponds each time to a value from a plurality of discrete filling level heights or from a continuum of filling level heights in order to be able to determine the filling level of the auxiliary material in the receptacle  176  for auxiliary material as exactly as possible. 
         [0126]    The rod-like sensor element  206  of the filling level sensor  204  is aligned essentially vertically and arranged as far as possible from the side walls  178  of the receptacle  176  for auxiliary material in the vicinity of the center of the interior space  186  of the receptacle  176  for auxiliary material in order for the measurement result of the filling level sensor  204  to be affected as little as possible as a result of marginal effects ( FIG. 13 ). 
         [0127]    The rod-like sensor element  206  of the filling level sensor  204  is aligned essentially at right angles to the horizontal base  182  of the receptacle  176  for auxiliary material. 
         [0128]    The signal which is generated by the filling level sensor  204  is transmitted via a signal line (not illustrated) to an electrical connection box  209  of the filter module  132  which is arranged on the base member  174  of the filter elements  172  (cf.  FIG. 7 ) and from there to a control device of the plant  100  which is illustrated schematically in  FIG. 19  and designated as  210 . 
         [0129]    In order to convey the stream of crude gas entering the filter module  132  into the interior space  186  of the receptacle  176  for auxiliary material in a targeted manner and to prevent any direct access of the stream of crude gas from the flow chamber  128  to the filter elements  172 , each filter module  132  is provided, in addition, with a slit-like inlet opening  212  which is designed as an inlet channel  214  which has, for example, as is apparent, in particular, from  FIG. 9 , a flow-through cross section narrowing in the flow direction of the stream of crude gas as far as a narrow point  240 . 
         [0130]    Alternatively or in addition hereto, it may also be provided for the inlet channel  214  to have a flow-through cross section widening in the flow direction of the stream of crude gas proceeding from a narrow point  240 . 
         [0131]    The inlet channel  214  is limited downwards by an inclined inlet surface  216 , which extends at an angle upwards from the front supports  160  of the support construction  156 , inclined at an angle of, for example, approximately 40° to approximately 65° in relation to the horizontal, and by a lower guide plate  218  which adjoins the lower end of the inclined inlet surface  216  and is inclined at a greater angle in relation to the horizontal than the inclined inlet surface  216 , for example, at an angle of approximately 55° to approximately 70° and which projects beyond an upper section  220  of a side wall  178  of the receptacle  176  for auxiliary material aligned essentially vertically and projects into the interior space  186  of the receptacle  176  for auxiliary material. 
         [0132]    In this way, the lower guide plate  218  acts as a retention element  222  which keeps auxiliary material from the receptacle  176  for auxiliary material away from the inlet opening  212  and prevents auxiliary material which has been whirled up from passing out of the receptacle  176  for auxiliary material along the side wall  178  on the side of the inlet opening  212 . 
         [0133]    In addition, the lower guide plate  218  prevents any breakdown in the flow of crude gas after it has passed the inclined inlet surface  216  and ensures an oriented flow of crude gas into the receptacle  176  for auxiliary material. 
         [0134]    The lower guide plate  218  has a depth (i.e., an extension in the flow direction of the stream of crude gas) of, for example, approximately 100 mm. 
         [0135]    The inclined inlet surface  216  and the lower guide plate  218  extend in the longitudinal direction  134  of the flow chamber  128  over essentially the entire length of the inlet opening  212  of, for example, approximately 1 m to approximately 2 m which corresponds more or less to the extension of the entire filter module  132  in the longitudinal direction  134 . 
         [0136]    The upper side of the inclined inlet surface  216  and the upper side of the lower guide plate  218  together form a lower guide surface  224  of the inlet opening  212  which limits the inlet opening  212  downwards and in its upper section  226 , which is formed by the inclined inlet surface  216 , has an inclination in relation to the horizontal of approximately 40° to approximately 65° and in its lower section  228 , which is formed by the lower guide plate  218 , has a greater inclination in relation to the horizontal of approximately 55° to approximately 70°. 
         [0137]    Upwardly, the inlet opening  212  is limited by the lower edge of the front wall  166  and by an upper guide plate  230  which projects from the lower edge of the front wall  166  at an angle downwards into the interior space of the filter module  132 . 
         [0138]    The upper guide plate  230  is, in the same way as the lower guide plate  218 , inclined in relation to the horizontal by an angle of, for example, approximately 55° to approximately 70° and extends in the longitudinal direction  134  over essentially the entire width of the inlet opening  212  of, for example, 1 m or 2 m. 
         [0139]    The upper guide plate  230  has a depth (i.e., an extension along the flow direction of the stream of crude gas) of, for example, approximately 150 mm. 
         [0140]    The lower side of the upper guide plate  230  forms an upper guide surface  232  which limits the inlet opening  212  upwards and is inclined in relation to the horizontal at an angle of, for example, approximately 55° to approximately 70°. 
         [0141]    As a result of this upper guide surface  232  for the stream of crude gas, the flow of crude gas does not break down at the front wall  166  of the filter module  132  but is rather conveyed directly into the receptacle  176  for auxiliary material. 
         [0142]    The upper guide plate  230  serves, in addition, as a filter shielding element  234  since it is designed and arranged at the inlet opening  212  such that it prevents the crude gas entering the filter module  132  from flowing directly to the filter elements  172 . 
         [0143]    Furthermore, the upper guide plate  230  serves as a deflector element  236  which keeps material, which has been cleaned off the filter elements  170  and contains auxiliary material and overspray particles bonded to the auxiliary material, away from the inlet opening  212 . 
         [0144]    Material dropping from the filter elements  172  onto the upper side of the upper guide plate  230  will, on the contrary, be directed into the receptacle  176  for auxiliary material as a result of the inclined position of the upper guide plate  230 . 
         [0145]    During operation of the filter module  132 , both the upper guide surface  232  and also the upper side of the upper guide plate  230  are provided with a coating consisting of the auxiliary material so that these surfaces of the upper guide plate  230  are easy to clean and no overspray adheres directly to the upper guide plate  230 . 
         [0146]    As is best apparent from  FIG. 12 , the filter module  132  comprises, in addition, two cover elements  238  in the form of approximately triangular cover plates which cover the left and the right lower corner areas of the inlet opening  212  such that auxiliary material and overspray from the stream of crude gas will be kept away from these corner areas of the inlet opening  212  and deposits of auxiliary material and of overspray particles in these corner areas and outside the filter module  132  on the inclined inlet surface  216  are prevented. 
         [0147]    The upper sides of the cover elements  238  are aligned at an angle to the vertical and at an angle to the horizontal and each have a surface normal which is directed upwards into the external space of the filter module  132 . 
         [0148]    As a result of the configuration of the geometry of the inlet opening  212  described above, the inlet opening  212  has a narrow point  240 , at which the flow-through cross section of the inlet opening  212  is at its smallest and, therefore, the velocity of the crude gas at its greatest. 
         [0149]    The velocity of the crude gas in the narrow point is preferably from approximately 2 m/s to approximately 8 m/s, in particular from approximately 3 m/s to approximately 5 m/s. 
         [0150]    In this way, auxiliary material from the interior of the filter module  132 , which forms a closed box, is effectively prevented from reaching the flow chamber  128  and, from there, the application area  108 . The whirling up of the auxiliary material in the receptacle  176  for auxiliary material and the cleaning of the filter elements  172  can, therefore, take place at any optional point of time without the supply of crude gas to the filter module  132  or even the operation of the spray painting devices  116  in the application area  108  needing to be interrupted. 
         [0151]    Furthermore, it is ensured, as a result of the fact that the stream of crude gas exits from the inlet opening  212  in a manner directed into the receptacle  176  for auxiliary material, that the stream of crude gas in the interior space  186  of the receptacle  176  for auxiliary material is redirected. As a result, a sufficient amount of auxiliary material, which is generated by it being whirled up from the supply located in the receptacle  176  for auxiliary material, is taken along by the stream of crude gas. 
         [0152]    The flow of crude gas out of the flow chamber  128  through the inlet opening  212  into the interior space of the filter module  132  is illustrated in  FIG. 10  as the result of a flow simulation. It is clearly apparent from this that a cylindrical flow is formed in the interior space of the filter module  132 , the horizontally extending axis of which lies somewhat deeper than the upper edge of the receptacle  176  for auxiliary material. 
         [0153]    On the side of the receptacle  176  for auxiliary material which is located opposite the inlet opening  212 , the flow of crude gas laden with auxiliary material flows out of the receptacle  176  for auxiliary material again and is then distributed over the entire depth of the filter element chamber  170  so that a vortex is formed around the filter elements  172  and a homogeneous distribution of the auxiliary material to the individual filter elements  172  is ensured on account of the considerable dynamics which the stream of crude gas has attained in the narrow point  240 . 
         [0154]    Since hardly any components of the filter module  132  are located in the flow path of the incoming stream of crude gas, any soiling of components by sticky paint is avoided to a great extent and, nevertheless, the flow to the filter elements  172  is favorable for the filtering. 
         [0155]    As a result of the fact that the average flow direction of the stream of crude gas entering the filter module  132  through the narrow point  240  is inclined at an angle of more than 40° in relation to the horizontal, an air lock, which would convey material cleaned off from the filter elements  172  immediately back to the filter elements  172  again and could lead to the formation of swirls of air within the filter module  132  which are opposite to one another, is prevented from being formed in the lower area of the filter element chamber  170 . 
         [0156]    In order to be able to connect to one another two filter modules  132 , which are arranged next to one another in a row  136  of modules, in a simple and stable manner or in order to be able to connect one filter module  132  to an adjoining transverse dividing wall  142 , the support construction  156  of each filter module  132  comprises at least one rear support  158  which has an essentially flat contact surface  242  which is aligned vertically and in the transverse direction  112  and can abut on a corresponding contact surface  242  of an adjacent filter module  132  or on an adjacent transverse dividing wall  142  ( FIG. 7 ). 
         [0157]    Openings  244  for the passage of attachment elements, by means of which the rear support  158  serving as connecting element  246  can be connected to a connecting element  246  of an adjacent filter module  132  or to an adjacent transverse dividing wall  142 , are provided, in addition, in the contact surface  242 . 
         [0158]    The rear support  158  serving as connecting element  246  preferably has an approximately U-shaped profile. 
         [0159]    As is apparent from  FIG. 7 , each central module  140  has two rear supports  158  which serve as connecting elements  246  and have U-shaped profiles, the open sides of which face one another so that the central module  140  can be connected on both sides to an adjoining, additional filter module  132  or to a transverse dividing wall  142 . 
         [0160]    As is apparent from  FIG. 8 , each corner module  138  has only one rear support  158  which is designed as a connecting element  246  and has a U-shaped profile; the oppositely located rear support  158   a , which need not be connected either to an adjacent filter module  132  or to an adjacent transverse dividing wall  142 , can have, for example, a T-shaped profile instead of a U-shaped profile for increasing its mechanical strength. 
         [0161]    As for the rest, the corner modules  138  correspond to the central modules  140  described in detail above with respect to construction and function. 
         [0162]    During operation of each filter module  132 , the stream  120  of crude gas sweeps over the filter surfaces of the filter elements  172 , wherein both the auxiliary material carried along and the wet paint overspray carried along will be deposited on the filter surfaces and the filtered crude gas passes as a stream of exhaust air through the porous filter surfaces into the interior spaces of the filter elements  172  which are connected to a cavity within the base member  174 , from which the filter elements  172  project. The cleaned stream of exhaust air passes from this cavity into a respective pipe  248  for exhaust air which leads from the base member  174  of the filter elements  172  of each filter module  132  to a channel  250  for exhaust air which is arranged approximately centrally under the flow chamber  128  and extends parallel to the longitudinal direction  134  of the flow chamber  128  (cf., in particular,  FIGS. 2 and 3 ). 
         [0163]    As is apparent from the schematic illustration of  FIG. 19 , the exhaust air cleaned of the wet paint overspray passes out of the channel  250  for exhaust air to a blower  252  for exhaust air, from where the cleaned exhaust air is supplied via a cooling apparatus (not illustrated) and a supply line (not illustrated) to an air chamber (not illustrated), the so-called plenum, which is arranged above the application area  108 . 
         [0164]    The cleaned exhaust air passes from this air chamber via a filter cover back into the application area  108 . 
         [0165]    A line for exhaust air (not illustrated) branches off the supply line and part of the cleaned stream of exhaust air will be discharged to the surroundings through this line for exhaust air (for example, via a chimney). 
         [0166]    This part of the stream of exhaust air which is discharged to the surroundings will be replaced by fresh air which is fed into the flow chamber  128  via two devices  254  for generating curtains of air which are each connected to an incoming air system (not illustrated) via a line for incoming air  256  ( FIGS. 1 to 3 ). 
         [0167]    Each of the devices  254  for generating curtains of air comprises a respective chamber for incoming air which extends in the longitudinal direction  134  of the flow chamber  128  and is fed with incoming air via the line  256  for incoming air and via a gap  258  which extends along the longitudinal direction  134 , has in a vertical direction an extension in the range of, for example, approximately 15 cm to approximately 50 cm and opens into an upper section  260  of the flow chamber  128  which is limited upwards by the application area  108  and downwards by the ceiling walls  164  of the filter modules  132 . 
         [0168]    The gap  258  of each chamber for incoming air is arranged just above the ceiling walls  164  of the filter modules  132  so that a curtain of air is formed at the upper side of the respective filter modules  132  as a result of the incoming air from the chambers for incoming air flowing into the flow chamber  128  in an essentially horizontal direction along the upper sides of the ceiling walls  164  of the filter modules  132 , the curtain of air being directed from the respectively associated device  254  for generating curtains of air to a narrow point  262  between the upper edges of the rows  136  of modules which are located opposite one another and thereby preventing the stream  120  of crude gas laden with wet paint overspray from passing out of the application area  108  to the upper side of the filter modules  132  and the wet paint overspray from the stream  120  of crude gas from being deposited on the upper side of the filter modules  132 . 
         [0169]    At the narrow point  262  of the flow chamber  128 , the horizontal cross section of the flow chamber  128  which has the stream of crude gas flowing through it decreases suddenly so that the flow velocity of the stream of crude gas in the lower section  263  of the flow chamber  128  located beneath the narrow point  262  is considerably greater than in the upper section  260  of the flow chamber  128  located above the narrow point  262 . 
         [0170]    The average flow direction of the air in the transverse curtains of air generated by the devices  254  for generating curtains of air at the upper side of the filter modules  132  is illustrated in  FIG. 3  by the arrows  264 . 
         [0171]    The majority of the air conveyed through the application area  108  is, therefore, guided in a circuit of circulating air which comprises the application area  108 , the flow chamber  128 , the filter modules  132 , the pipes  248  for exhaust air, the channel  250  for exhaust air, the blower  252  for exhaust air as well as the supply line and the air chamber over the application area  108 , wherein a constant heating up of the air guided in the circuit of circulating air is avoided as a result of the supply of fresh air via the devices  254  for generating curtains of air. 
         [0172]    Since the separation of the wet paint overspray from the stream  120  of crude gas by means of the filter elements  172  is done in a dry manner, i.e., without any washing out with a cleaning liquid, the air guided in the circuit of circulating air will not be moistened during the separation of the wet paint overspray and so no devices whatsoever for dehumidifying the air guided in the circuit of circulating air are necessary. 
         [0173]    Furthermore, no devices are again required for separating wet paint overspray from any wash-out cleaning liquid. 
         [0174]    As a result of the fact that the horizontal cross section of the flow chamber  128 , which has the stream of crude gas flowing through it, is considerably smaller in the lower section  263  of the flow chamber  128  located beneath the narrow point  262  than in the upper section  260  of the flow chamber  128  due to the presence of the filter modules  132  (in the lower section  263 , for example, it is only approximately 35% to approximately 50% of the horizontal cross sectional surface area of the flow chamber  128  in the upper section  260  thereof), the flow velocity of the stream of crude gas will be continuously increased on its way from the application area  108  through the flow chamber  128  to the inlet openings  212  of the filter modules  132  and so an ascending velocity profile will result in the stream of crude gas. 
         [0175]    This ascending velocity profile has the effect that particles exiting from the filter modules  132  cannot reach the application area  108 . 
         [0176]    In this respect, the velocity of the flow of crude gas in the application area  108  and in the upper section  260  of the flow chamber  128  is, for example, up to approximately 0.6 m/s whereas in the lower section  263  of the flow chamber it is, for example, in the range of approximately 0.6 m/s to approximately 3 m/s and increases in the inlet openings  212  of the filter modules  132  up to a maximum value in the range of approximately 3 m/s to approximately 5 m/s. 
         [0177]    As a result of the fact that the filter elements  172  in the filter modules  132  are completely enclosed, activation of the filter elements  172  by applying auxiliary material and cleaning of the filter elements  172  are possible at any time while the painting process is running in the application area  108 . 
         [0178]    If the width of the painting booth  110 , i.e., its extension in the transverse direction  112 , is altered, filter modules  132  of the same size are, nevertheless, used; the adaptation of the device  126  for separating wet paint overspray takes place, in this case, merely by way of an increase in the distance of the two rows  136  of modules from one another and by way of an increase in the width of the walkable catwalk  146 . 
         [0179]    The velocity profile of the flow of crude gas therefore alters with such a widening of the painting booth  110  only in the area up to the walkable catwalk  146 ; from here, i.e., in particular when passing through the inlet openings  212  of the filter modules  132 , the velocity profile of the flow of crude gas is dependent only on the amount of crude gas flowing through per unit of time but not on the geometry of the flow chamber  128 . 
         [0180]    The distance of the (walkable) ceiling walls  164  of the filter modules  132  from the lower edge of the vehicle bodies  102  conveyed through the painting booth  110  is at least approximately 1.5 m for reasons of maintenance. 
         [0181]    The filter elements  172  will be cleaned by pulses of compressed air at specific time intervals when their load of wet paint overspray and auxiliary material has reached a predetermined quantity. 
         [0182]    This cleaning can take place (as a function of the increase in pressure loss at the filter elements  172 ), for example, one to six times per 8 hour work shift, i.e., approximately every 1 to 8 hours. 
         [0183]    The necessary pulses of compressed air are generated by means of a pulsing unit  266  which is arranged on the base member  174  of the filter elements  172  of each filter module  132 , wherein the pulsing unit  266  is in a position to discharge pulses of compressed air to pipes for compressed air which extend within the respective base member  174  and lead from the pulsing unit  266  into the interior spaces of the filter elements  172  ( FIG. 19 ). 
         [0184]    The pulses of compressed air pass from the interior spaces of the filter elements  172  through the porous filter surfaces into the filter element chamber  170 , wherein the barrier layers consisting of auxiliary material formed on the filter surfaces and the wet paint overspray deposited thereon will be released from the filter surfaces so that the filter surfaces are returned to their cleaned original state. 
         [0185]    The pulsing unit  266  comprises a pulsing valve  268 , via which the pulsing unit  266  can be supplied with compressed air from a supply line  270  for compressed air which is fed from a compressor  272  (cf.  FIG. 19 ). 
         [0186]    The pipe  196  for compressed air, which leads to the exit nozzles  200  of the whirling device  198 , is also connected to this supply line  270  for compressed air via a valve  274  for compressed air. 
         [0187]    Furthermore, the fluid base  184  of each receptacle  176  for auxiliary material is also connected to the supply line  270  for compressed air via a line  278  for compressed air which is provided with a valve  276  for compressed air. 
         [0188]    As a result of the pulsing valve  268  of the valve  274  for compressed air or of the valve  276  for compressed air being opened, cleaning of the filter elements  172 , whirling up of the auxiliary material in the receptacle  176  for auxiliary material or a fluidization of the auxiliary material in the receptacle  176  for auxiliary material can, therefore, be triggered, alternatingly or at the same time, by means of the fluid base  184 . 
         [0189]    A check valve  280 , which can be activated by the control device  210  in the local control station, is arranged in the supply line  270  for compressed air between the specified valves for compressed air and the compressor  272 . 
         [0190]    The control device  210  blocks the supply of compressed air from the compressor  272  to the specified compressed air users of a filter module  132  or of all the filter modules  132  by closing the check valve  280  when it ascertains that no adequate flow of crude gas through the filter elements  172  is present. 
         [0191]    In order to ascertain whether an adequate flow of crude gas through the filter elements  172  is present, it may, for example, be provided for the control device  210  to monitor the operating state of the blower  252  for exhaust air. 
         [0192]    This monitoring of the operating state of the blower  252  for exhaust air can be brought about, for example, by means of a differential pressure meter (PDIA)  282  which measures the drop in pressure between the pressure side and the suction side of the blower  252  for exhaust air. 
         [0193]    Alternatively or in addition hereto, the operating state of the blower  252  for exhaust air can also be monitored by the control device  210  by means of a voltage monitoring device (ESA)  284  and/or by means of a frequency converter (SC)  286 . 
         [0194]    Furthermore, it may be provided for the absence of an adequate flow of crude gas through the filter elements  172  to be determined by means of a flow meter (FIA)  288  which measures the flow of gas through the channel  250  for exhaust air or through one or more of the pipes  248  for exhaust air. 
         [0195]    Furthermore, it is possible to ascertain the absence of an adequate flow of crude gas through the filter elements  172  by measuring the drop in pressure at the filter elements  172  of a filter module  132  or of all the filter modules  132 . 
         [0196]    When the control device  210  ascertains, on account of the signals transmitted to it from the differential pressure meter  282 , the voltage monitoring device  284 , the frequency converter  286  and/or the flow meter  288 , that the flow of crude gas through the filter elements  172  is below a predetermined threshold value, the supply of compressed air will be blocked to at least one of the filter modules  132  by closure of the check valve  280 . 
         [0197]    In this way, auxiliary material is prevented from passing into the flow path of the crude gas and, in particular, through the inlet opening  212  of a filter module  132  into the flow chamber  128  and from there into the application area  108  as a result of whirling up by means of the whirling unit  198 , as a result of cleaning of the filter elements  172  or as a result of fluidization of the supply of auxiliary material in the receptacle  176  for auxiliary material. 
         [0198]    This blocking of the supply of compressed air can take place for all the filter modules  132  together or for the individual filter modules  132  separately from one another. In the latter case, the determination of the absence of an adequate flow of crude gas through the filter elements  172  takes place for each of the filter modules  132  separately and either each filter module  132  is provided with its own compressor  272  or the supply lines  270  for compressed air to the individual filter modules  132  can be blocked or released individually via check valves  280  which can be switched separately from one another. 
         [0199]    The auxiliary material will be supplied to the stream of crude gas, in the case of the device  126  for separating wet paint overspray described above, exclusively within the filter modules  132  by the auxiliary material in the respective receptacle  176  for auxiliary material being whirled up. 
         [0200]    In order to be able to supply fresh auxiliary material to the receptacles  176  for auxiliary material which are rigidly mounted within the filter modules  132  in their operating position, the device  126  for separating wet paint overspray comprises a supply device  290  for auxiliary material which is illustrated schematically in  FIG. 17  and comprises a storage receptacle  292  which can be designed as a blow pot or as a simple fluidization receptacle. 
         [0201]    Blow pots are known per se, for example, from JP 02123025 A or JP 06278868 A and have previously been used in coating plants for the purpose of conveying powdered paint to the application receptacles located in the vicinity of the sprayers. The receptacles are relatively small, closable containers with a base permeable to air, through which air is conveyed into the container for fluidizing the powder and for its conveyance. 
         [0202]    While a blow pot can be emptied as a result of the pressure of the fluidizing air, the fluidizing receptacle will have a powder metering pump  293  connected to its outlet for the conveyance of material (cf.  FIG. 1 ), such as, for example, the so-called DDF pump described in WO 03/024612 A1 or another metering pump conveying with suction/pressure alternation in accordance with the principle of a dense flow, such as, for example, those known from EP 1 427 536 B1, WO 2004/087331 A1 or from  FIG. 3  of DE 101 30 173 A1. 
         [0203]    For the purpose of filling the storage receptacle  292 , a larger supply receptacle (container or “big bag”)  294  for the fresh auxiliary material is arranged above it and the material can, in the simplest case, trickle from it through an opening in the storage receptacle (silo)  292  which can be closed by a flap. In order to be able to continuously refill the storage receptacle  292  even during conveyance of the material and to avoid any losses in time during operation, a mechanical conveying device  246 , for example, a rotary vane feeder or a conveying worm, is preferably arranged between the supply receptacle  294  and the storage receptacle  292 . When such a conveying device is used, a desired filling quantity can also be advantageously set, in the case of a rotary vane feeder via the filling quantity per cell which is determined beforehand. 
         [0204]    The storage receptacle  292  is connected to each of the receptacles  176  for auxiliary material via a main line  300  which is divided into two branches  298   a ,  298   b  and from which stub lines  302  lead each time to one of the receptacles  176  for auxiliary material. In this respect, each of the branches  298   a ,  298   b  of the main line  300  leads each time to the receptacles  176  for auxiliary material of one row  136  of modules. 
         [0205]    The main line  300  preferably consists of flexible hoses. 
         [0206]    For this purpose, hoses with an internal diameter of up to approximately 14 mm, in particular from approximately 6 mm to approximately 12 mm, can be used. 
         [0207]    The stub lines  302  can be of a tubular design and are each provided with a mechanical pinch valve  304 , wherein a second pinch valve  306  is arranged each time behind the branch-off of the respective stub line  302  in the direction of flow of the auxiliary material. 
         [0208]    Additional pinch valves  309  are arranged at the branch-off of the two branches  298   a ,  298   b  of the main line  300  in order to be able to open or close these two branches  298   a ,  298   b  as required. 
         [0209]    During operation of the supply device  290  for auxiliary material, the main line  300  and all the stub lines  302  are, first of all, empty. When a specific receptacle  176  for auxiliary material is intended to be supplied with fresh auxiliary material, the main line will be blocked behind the branch-off point of the associated stub line  302  by closing the respectively associated pinch valve  306 , the relevant stub line  302  opened by opening the associated pinch valve  304  and, subsequently, the auxiliary material from the storage receptacle  292  conveyed to the relevant receptacle  176  for auxiliary material. 
         [0210]    Subsequently, the line path described above to the relevant receptacle  176  for auxiliary material will be emptied and flushed cleaned. This offers the advantage that the batch quantity is always determined and can be metered exactly and that the line path cannot be blocked since flush cleaning always takes place into the supplied receptacle  176  for auxiliary material. 
         [0211]    Each of the stub lines  302  opens into one of the side walls  178  of the respectively associated receptacle  176  for auxiliary material, preferably in an area close to the upper edge of the receptacle  176  for auxiliary material, so that as large an amount of auxiliary material as possible can be supplied through the stub line  302 . 
         [0212]    The stub line  302 , which leads to the respectively last receptacle  176  for auxiliary material of a row  136  of modules, does not require any pinch valve arrangement since it is merely necessary for all the pinch valves  306  and  309  arranged in the main line  300  downstream of the last receptacle  176  for auxiliary material to be opened for supplying this receptacle  176  for auxiliary material. 
         [0213]    Instead of the pinch valve arrangements described above, mechanical pinch shunts or other types of powder shunts which are known per se from the state of the art can also be provided at the branches of the line system for auxiliary material. 
         [0214]    In order to be able to remove the auxiliary material mixed with overspray, which has collected in a receptacle  176  for auxiliary material, and supply it for waste disposal or further use prior to fresh auxiliary material being supplied to the receptacle  176  for auxiliary material, the device  126  for separating wet paint overspray comprises, in addition, a discharge device  308  for auxiliary material which is illustrated schematically in  FIG. 18 . 
         [0215]    The discharge device  308  for auxiliary material comprises, for its part, a suction blower  310 , for example, a dust exhaust blower which conveys used auxiliary material from a main line  312 , which branches into two branches  314   a ,  314   b , into a collecting receptacle  316  arranged beneath the suction blower  310 . 
         [0216]    Each respective one of the branches  314   a ,  314   b  of the main line  312  leads to the receptacles  176  for auxiliary material of one row  136  of modules and is connected to each of the receptacles  176  for auxiliary material of the relevant row  136  of modules via a respective stub line  318  which can be closed by means of a pinch valve  320 . 
         [0217]    A respective ball valve  322  is arranged at the end of each branch  314   a ,  314   b  of the main line  312  and conveying air can be supplied to the main line  312  through the ball valve as required in order to make the removal of the auxiliary material by suction from the main line  312  to the suction blower  310  easier. 
         [0218]    The stub lines  318  each open into the interior space  186  of the respective receptacle  176  for auxiliary material just above the fluid base  184 , preferably in a corner area of the receptacle  176  for auxiliary material, in which two side walls  178  adjoin one another. 
         [0219]    It is particularly favorable for an efficient and as complete a removal by suction as possible of the used auxiliary material from a receptacle  176  for auxiliary material, when the stub line  318  branches into two suction lines, each of which opens into the interior space  186  of the receptacle  176  for auxiliary material at a different corner area. 
         [0220]    When a specific receptacle  176  for auxiliary material is intended to be emptied of used auxiliary material mixed with overspray, the pinch valve  320  of the respectively associated stub line  318  will be opened for this purpose and the material present in the receptacle  176  for auxiliary material will be sucked through the stub line  318  and the main line  312  by means of the suction blower  310  and conveyed to the collecting receptacle  316 . 
         [0221]    The suction process is terminated by closing the respectively associated pinch valve  320 . 
         [0222]    During the suction process, the fluid base  184  of the relevant receptacle  176  for auxiliary material is permanently in operation, i.e., has compressed air flowing through it during the entire suction process in order to fluidize the material to be withdrawn by suction and cause it to flow easily. 
         [0223]    Furthermore, the withdrawal of the used material by suction from the receptacle  176  for auxiliary material can be aided in that during the suction process the whirling device  198  of the relevant receptacle  176  for auxiliary material is in operation continuously or at regular intervals (for example, 6×5 seconds per minute) because the material will be loosened and moved towards the inlet openings of the stub line  318  when the material to be withdrawn by suction is acted upon with compressed air from above through the exit nozzles  200  of the whirling device  198 . 
         [0224]    If the withdrawal of the used auxiliary material by suction from one of the receptacles  176  for auxiliary material does not function perfectly, which becomes apparent from the fact that the associated filling level sensor  204  reports a filling level which is no longer sinking, the operation of the device  126  for separating wet paint overspray need not be interrupted. On the contrary, auxiliary material can, instead, be withdrawn by suction from another receptacle  176  for auxiliary material which is connected to the same branch  314   a  or  314   b  of the main line  312 . As a result, the blocking of the transport of material out of the blocked receptacle  176  for auxiliary material can, in many cases, be rectified and so, subsequently, the material can be withdrawn by suction from the receptacle  176  for auxiliary material which was previously blocked. 
         [0225]    The material removed from the receptacle  176  for auxiliary material by suction, which contains auxiliary material together with overspray particles, can either be disposed of or—where applicable following processing—used again at least partially in the coating plant. 
         [0226]    Furthermore, it may be provided for the substances of the auxiliary material to be selected such that they can be utilized for other purposes than for the coating of workpieces after their use in the coating plant. For example, the used auxiliary material can be used as insulating material or, for example, be thermally exploited in the brick or cement industry or the like, wherein the wet paint overspray bonded to the auxiliary material can likewise be used as an energy carrier during a combustion process required for production. 
         [0227]    Once the used auxiliary material has been withdrawn by suction from a receptacle  176  for auxiliary material, the same can be filled with fresh auxiliary material by means of the supply device  290  for auxiliary material already described above, namely, for example, up to a first filling level of approximately 50% of the entire capacity of the receptacle  176  for auxiliary material. 
         [0228]    As a result of the accumulation of wet paint overspray, which has a lower density than the auxiliary material, in the mixture consisting of auxiliary material and overspray, which is present in the receptacle  176  for auxiliary material, the density of this mixture decreases ever further during operation of a filter module  132  and so the barrier layer which is built up on the filter elements  172  of the filter module  132  has an ever greater volume. 
         [0229]    The filling level of the material in the receptacle  176  for auxiliary material immediately prior to a cleaning procedure for the filter elements  172  therefore decreases ever further. 
         [0230]    In the case of a predetermined residual filling level which corresponds, for example, to approximately 10% of the capacity of the receptacle  176  for auxiliary material, the auxiliary material mixed with overspray will be withdrawn from the receptacle  176  for auxiliary material by suction, as described above. As a result of this withdrawal by suction prior to a cleaning procedure for the filter elements  172 , it is possible for mainly the material which has become unusable, has collected in the receptacle  176  for auxiliary material and does not form the barrier layer on the filter elements  172  to be removed from the receptacle  176  for auxiliary material. 
         [0231]    Alternatively to this procedure, it may also be provided for the filling level of the material in the receptacle  176  for auxiliary material to be measured after each cleaning procedure of the filter elements  172  of the filter module  132  and for a suction process to be initiated when a predetermined maximum filling level, for example, 90% of the maximum capacity of the receptacle  176  for auxiliary material is reached. 
         [0232]    In any case, the filling level of the material in the receptacle  176  for auxiliary material which triggers a suction process will be determined by means of the filling level sensor  204  which is arranged in the respective receptacle  176  for auxiliary material. 
         [0233]    A second embodiment of a plant  100  for painting vehicle bodies  102 , which is illustrated in  FIG. 20  in a schematic cross section, differs from the first embodiment described above in that separate guide plates  324  for transverse curtains of air are arranged above the filter modules  132  and serve the purpose of conducting the air supplied by the devices  254  for generating the curtains of air to the narrow point  262  between the upper section  260  and the lower section  263  of the flow chamber  128 . 
         [0234]    These guide plates  324  for transverse curtains of air are inclined in relation to the respectively adjacent side wall  130  of the flow chamber  128  at an angle of, for example, approximately 1° to approximately 3° in relation to the horizontal so that liquid reaching the guide plates  324  for the transverse curtains of air from above will flow away to the side walls  130 , not to the narrow point  262 . 
         [0235]    In this way, it is ensured that, for example, paint flowing out of the application area  108  on account of a burst hose or water for extinguishing fires cannot pass into the lower section  263  of the flow chamber  128  and from there into the filter modules  132  but rather can flow away to the sides of the flow chamber  128 . 
         [0236]    Furthermore, the walkable catwalk  146  between the rows  136  of modules is divided in this embodiment into two halves  328   a ,  328   b  which are essentially mirror symmetric to a vertical longitudinal central plane  326  of the flow chamber  128  and are inclined in relation to the longitudinal central plane  326  at a respective angle of, for example, approximately 1° to, for example, approximately 3° in relation to the horizontal so that liquid passing onto the walkable catwalk  146  from above, such as, for example, paint or water for extinguishing fires, cannot pass over the side edges  330  of the walkable catwalk  146  to the inlet openings  212  of the filter modules  132  but is rather retained in the center of the walkable catwalk  146 . 
         [0237]    Both the walkable catwalk  146  and the guide plates  324  for the transverse curtains of air can, in addition, be inclined in the longitudinal direction  134  of the flow chamber  128  in relation to the horizontal so that the liquid located on these elements can flow away to an outflow opening on account of the effect of gravity. 
         [0238]    As for the rest, the second embodiment of a plant  100  for painting vehicle bodies  102 , as illustrated in  FIG. 20 , corresponds with respect to construction and functioning to the first embodiment illustrated in  FIGS. 1 to 19 , to the above description of which reference is made in this respect. 
         [0239]    The receptacles  176  for auxiliary material of the filter modules  132  of the plants  100  for painting vehicle bodies  102  described above can, alternatively or in addition to the fluid base  184  illustrated in  FIG. 13 , also have other devices  332  for thoroughly mixing the material located in the receptacle  176  for auxiliary material, for example, a pneumatically operated stirring apparatus  334  which is illustrated schematically in  FIGS. 21 and 22 . 
         [0240]    The pneumatically operated stirring apparatus  334  comprises a stirrer  336  with at least two stirring paddles  340  which are arranged non-rotatably on a stirrer shaft  338  which is aligned essentially vertically and a stirrer turbine  342  which is illustrated merely schematically in  FIGS. 21 and 22  and by means of which the stirrer shaft  338  can be driven to perform a rotary movement about its vertical axis. 
         [0241]    The stirring paddles  340  are arranged on the stirrer shaft  338  so as to be offset relative to one another in the axial direction of the stirrer shaft  338  and at an angular distance of, for example, approximately 180°. 
         [0242]    The stirrer turbine  342  can be supplied with compressed air via a supply line  344  for compressed air. 
         [0243]    If the stirrer turbine  342  is supplied with compressed air via the supply line  344  for compressed air, the compressed air supplied causes the stirrer turbine  342  to perform a rotary movement about its vertical axis, whereupon the stirrer shaft  338 , which is connected non-rotatably to the stirrer turbine  342 , is likewise caused to move. 
         [0244]    In this respect, the material located in the receptacle  176  for auxiliary material will be thoroughly mixed as a result of the rotating stirring paddles  340  and the surface of the material located in the receptacle  176  for auxiliary material will be smoothed. Bridges of material formed in the receptacle  176  for auxiliary material as a result of undermining will be broken up. 
         [0245]    In this way, a good mixing through of the material in the receptacle  176  for auxiliary material and a homogenization of the filling level of the material within the receptacle  176  for auxiliary material will be achieved. 
         [0246]    Any formation of sparks within the receptacle  176  for auxiliary material will be avoided and an adequate protection against explosion ensured by the pneumatic drive for the stirring apparatus  334 . 
         [0247]    An alternative embodiment of a device  332  for thoroughly mixing the material located in the receptacle  176  for auxiliary material, illustrated in  FIGS. 23  and  24 , comprises an electric motor  346  which is arranged to the side next to the receptacle  176  for auxiliary material and the driven shaft  348  of which is guided through a side wall  178  of the receptacle  176  for auxiliary material and provided with several, for example, four paddles  350  which are arranged non-rotatably on the driven shaft  348  and so as to be offset relative to one another at a respective angular distance of, for example, approximately 90° as well as in the axial direction of the driven shaft  348 . 
         [0248]    As a result of rotation of the driven shaft  348  by means of the electric motor  346  about its axis which is aligned essentially horizontally, the paddles  350  are caused to perform a rotary movement, whereby the paddles  350  thoroughly mix the material located in the receptacle  176  for auxiliary material and smooth its surface as well as break up bridges of material resulting in the receptacle  176  for auxiliary material. 
         [0249]    The refitting of an already existing device  126  for separating wet paint overspray from a stream of crude gas containing overspray particles can take place in the following manner with use of the filter modules  132  of the plants  100  described above: 
         [0250]    First of all, part of the existing device will be dismantled so that the space required by a filter module  132  in its operating position will be opened up. 
         [0251]    Subsequently, a filter module  132  will be arranged in the operating position freed up in this manner and connected to the support construction for the application area  108 , in particular to the booth walls  114  of the painting booth  110 . 
         [0252]    Subsequently, these steps will be repeated until all the filter modules  132  are arranged in their operating positions and are connected to the support construction for the application area  108 . 
         [0253]    In this way, an existing device for the wet separation of wet paint overspray can, for example, be replaced by the device  126  for the dry separation of wet paint overspray which is described above and is of a modular construction without it being necessary for this purpose to dismantle the application area  108  of the plant  100  for painting vehicle bodies  102 .