Patent Publication Number: US-8974579-B2

Title: Device for separating paint overspray

Description:
RELATED APPLICATIONS 
     This application claims the filing benefit of International Patent Application No. PCT/EP2009/006105, filed Aug. 22, 2009, which claims the filing benefit of German Patent Application No. 10 2008 046 413.9 filed Sep. 4, 2008, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a device for separating paint overspray from the overspray-laden booth exhaust air from paint shops having
     a) at least one separation surface, along which the booth exhaust air may be guided and which is connected electrically conductively and with one pole of a high voltage source;   b) an electrode apparatus arranged in the air stream which is associated with the separation surface and is connected with the other pole of the high voltage source;   c) means with which the separated paint overspray is conveyed away from the separation surface.   

     BACKGROUND OF THE INVENTION 
     On manual or automatic application of paints onto objects, a sub-stream of the paint, which generally contains both solids and solvent and/or binder, is not applied onto the object. In specialist circles, this sub-stream is known as “overspray”. The overspray is entrained by the air stream in the spray booth and sent for separation. 
     In particular in installations with relatively high paint consumption, for example in installations for painting vehicle bodies, wet separation systems are preferably used. In commercially known wet separators, water flows together with the booth exhaust air arriving from above to a nozzle which accelerates air flow. In this nozzle, the through-flowing booth exhaust air is swirled with the water. As this happens, the overspray particles largely pass over into the water, such that the air leaves the wet separator in a substantially purified state and the paint overspray particles are located in the water, from which they may then be recovered or disposed of. 
     In known wet separators, a relatively large amount of energy is required to circulate the very large quantities of water which are necessary. Treating the rinsing water is costly due to the elevated use of paint-binding and detackifying chemicals and disposal of paint sludge. Furthermore, due to intimate contact with the rinsing water, the air absorbs a great deal of moisture which, when the air is recirculated, in turn results in elevated energy consumption for air treatment. 
     In contrast, in commercially known devices of the above-mentioned type separation is performed by dry methods in that the paint overspray particles entrained by the booth exhaust air are ionised as they flow past the electrode apparatus and, due to the electric field established between the separation surface and the electrode apparatus, migrate to the separation surface, on which they separate out. The paint overspray particles adhering to the separation surface may then for example be mechanically scraped off therefrom and conveyed away. 
     Such separators have a very effective cleaning action. However, if operation is to be continuous, constant care must be taken to ensure that a sufficiently strong electric field can form between the separation surface and the electrode apparatus, something which is only possible up to a certain layer thickness of paint overspray on the separation surface, since such a layer has an insulating action. The necessary continuous removal of the paint overspray from the separation surface is, however, associated with very considerable structural complexity and may be susceptible to breakdown. 
     The present invention is directed to resolving these and other matters. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is accordingly to provide a separation device of the above-mentioned type, in which conveying of paint overspray away from the separation surface is improved and simplified. 
     This object may be achieved in a device of the above-mentioned type in that
     d) an electrically conductive separation liquid may be supplied to the separation surface, which separation liquid flows over the separation surface, such that a majority of at least the solids passes from the booth exhaust air which is flowing past into the separation liquid and is conveyed away thereby.   

     The invention thus combines the advantage of good separation of paint overspray from booth exhaust air by means of an electric field with good transport of paint overspray in a liquid. 
     Thanks to the separation liquid constantly flowing along the separation surface, paint overspray absorbed thereby is continuously conveyed away, such that adhesion of paint overspray to the separation surface is reduced, which adhesion would result in insulation thereof. 
     It is favourable for the electrode apparatus to comprise a plate-shaped electrode and at least one wire electrode. A wire electrode acts as a discharge electrode, by means of which the paint overspray particles entrained by the booth exhaust air may be effectively ionised. Thanks to the interplay between a plate-shaped electrode and the separation surface, a homogeneous field can be formed, by means of which the ionised paint overspray particles may be reliably directed to the separation surface. 
     It is here advantageous for the plate-shaped electrode to take the form of a grid electrode. Swirling occurs at the grid which results in a more uniform distribution of the paint overspray particles in the booth exhaust air flowing past the grid, which in turn has a favourable impact on the separation thereof on the separation surface. 
     The efficiency of ionisation of the paint overspray particles is increased if the electrode apparatus comprises a plurality of wire electrodes which extend parallel to one another. 
     It is advantageous for a separation unit to be provided which comprises two separation surfaces oriented in different directions. If the separation surfaces of at least one separation unit extend parallel to one another in at least one portion, a plurality of separation units may be arranged in a cascading series, whereby good use is made of the available structural space. 
     It is in particular favourable for a plurality of separation units to be arranged such that two separation units in each case having one separation surface are opposite one another and an electrode apparatus is in each case arranged between the opposite separation surfaces of two separation units. As a result, a single electrode apparatus interacts with two separation surfaces, so improving the effectiveness of the device. 
     If the at least one separation surface comprises at least one curved portion which extends along the at least one wire electrode, it is possible to bring about a reduction in the flow velocity of the booth exhaust air in the region of the wire electrode. A volume of the booth exhaust air accordingly spends longer in the region of influence of the wire electrode, such that a larger proportion of paint overspray particles is ionised in this volume. In addition, swirling and turbulence arises in the region of curvature which makes the distribution of paint overspray particles in the booth exhaust air more uniform. 
     It is here favourable for the number of curved portions of the at least one separation surface to match the number of wire electrodes, such that the stated effects occur in the region of each wire electrode. 
     Particularly good separation results may be achieved with a device in which the curvature of one or more curved portions extends in cross-section over a circular arc, the centre point of which is concentric to the wire electrode. 
     Overall, it is advantageous for effective separation for the at least one wire electrode to be arranged such that the overspray-laden booth exhaust air reaches it before the plate-shaped electrode. 
     It is to be understood that the aspects and objects of the present invention described above may be combinable and that other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a painting booth of a surface treatment installation with a first exemplary embodiment of an overspray separation device; 
         FIG. 2  is the painting booth of  FIG. 1  in perspective view; 
         FIG. 3  is a perspective view of two separation units and three electrode apparatuses of the separation device of  FIG. 1 ; 
         FIG. 4  is a vertical section through the two separation units with electrode apparatuses of  FIG. 3 ; 
         FIG. 5  is a perspective view of two separation units and three electrode apparatuses in each case according to a second exemplary embodiment; 
         FIG. 6  is a perspective view of a second exemplary embodiment of an overspray separation device which comprises a plurality of separation units and electrode apparatuses according to  FIG. 5 ; 
         FIG. 7  is a perspective view of two separation units according to a third exemplary embodiment and three electrode apparatuses according to the first exemplary embodiment according to  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. 
     Reference will be made first of all to  FIGS. 1 and 2 . A painting booth of a surface treatment installation is here denoted overall  2 , in which vehicle bodies  4  are painted once they have, for example, been cleaned and degreased in pretreatment stations, not separately shown, upstream of the painting booth  2 . 
     The painting booth  2  comprises a painting tunnel  6  arranged on top, which is bounded by vertical side walls  8   a ,  8   b  and a horizontal booth ceiling  10 , but is open at the end faces and downwards in such a manner that overspray-laden booth exhaust air can flow downwards. The booth ceiling  10  is configured in conventional manner as the lower boundary of the air feed chamber (not shown) with a filter ceiling. 
     A steel construction  14  is arranged at the level of the lower opening  12  of the painting tunnel  6  flanked by the lower edges of the side walls  8   a ,  8   b , which construction carries a per se known conveying system  16 , which is not described in greater detail here. The latter is capable of conveying vehicle bodies  4  to be painted from the input side of the painting tunnel  6  to its output side. In the interior of the painting tunnel  6  are located application devices (not separately shown), by means of which the vehicle bodies  4  may be coated with paint in a manner known per se. 
     Below the lower opening  12  of the painting tunnel  6 , there is a separation chamber  18  open at the top towards the painting tunnel  6 , in which chamber paint overspray arising during the painting process is separated. 
     The separation chamber  18  is bounded by a base plate  20  visible in  FIG. 2 , two vertical side walls  22   a ,  22   b  and two vertical end walls, the latter two being omitted from  FIGS. 1 and 2 . 
     In the separation chamber  18  there is arranged a separation device  24  having a plurality of separation units  26  arranged in series in the longitudinal direction of the separation chamber  18 , which will be described in greater detail below. 
     In the region of the separation chamber  18  between the separation device  24  and the painting tunnel  6  are located two air baffle plates  28   a ,  28   b , which, starting from the side walls  22   a ,  22   b  of the separation chamber  18 , initially converge downwards and, in the end region thereof facing the separation device  24 , diverge towards the lateral boundaries of the separation device  24 . The air baffle plates  28   a ,  28   b  and corresponding air baffle plates (not shown) at the end faces extend from above down to the separation device  24 . 
     The separation units  26  rest on a mounting frame  30 , which allows air to flow downwards out of the separation device  24 . Below the separation device  24  is located a further air baffle plate  32 , which extends along the separation device  24  in the separation chamber  18 . The air baffle plate  32  comprises a vertical portion  32   a , which faces the left-hand side wall  22   a  in  FIGS. 1 and 2  of the separation chamber  18 , and a portion  32   b  which extends obliquely downwards towards the opposite side wall  22   b  of the separation chamber  18 . 
     Between the vertical portion  32   a  of the air baffle plate  32  and the left-hand side wall  22   a  in  FIGS. 1 and 2  of the separation chamber  18 , there is arranged a collecting channel  34 , shown only schematically in  FIG. 1 , which extends parallel to the vertical portion  32   a  of the air baffle plate  32  and which is inclined in the longitudinal direction relative to a horizontal plane. 
       FIGS. 3 and 4  show are two adjacent separation units  26  of the separation device  24 . As may be seen therein, a separation unit  26  comprises two mutually spaced parallel rectangular side plates  36   a ,  36   b  which are joined together at their upper opposite end edges via a curved portion  38 , the overall outer contour of which is semicircular in cross-section and forms the top of the separation unit  26 . 
     An overflow channel  40 , which will be described in greater detail below, is provided at the vertex of the curved portion  38  of the separation units  26 . 
     The respective outer faces of the side plates  36   a ,  36   b  form separation surfaces  42   a  or  42   b , which will likewise be described again further below. 
     At their lower edges, the side plates  36   a ,  36   b  in each case bear an outlet channel  44   a ,  44   b , which extends parallel to the side plates  36   a ,  36   b  of the separation units  26  and is inclined downwards towards a first end face  46 , at the front in  FIG. 3 , of the separation unit  26 . The outlet channels  44   a ,  44   b  terminate at their end faces with the side plates  36   a ,  36   b  of the separation unit  26  (cf.  FIG. 3 ). The outlet channels  44   a ,  44   b  are open at their respective ends  48   a  and  48   b  at the first end face  46  (cf.  FIG. 3 ) of the separation unit  26 . 
     As may be seen in  FIGS. 1 and 2 , each separation unit  26  comprises a first end wall  50   a  which is arranged at the first end face  46  thereof. The opposite end face of the separation units  26 , which is not provided with a separate reference numeral, is covered by a second end wall  50   b . The end walls  50   a ,  50   b  of the separation units  26  close the end faces of the associated overflow channel  40 . The two end walls  50   a ,  50   b  are made of plastics. The first end wall  50   a  of the separation unit  26  comprises two openings  52   a ,  52   b , into which in each case opens an outlet channel  44   a ,  44   b  with the ends  48   a ,  48   b  thereof. Drip plates  54   a ,  54   b  are positioned at the openings  52   a ,  52   b  on the opposite side of each end wall  50   a  to the outlet channels  44   a ,  44   b . Said drip plates take the form of a profile, the cross-section of which corresponds to that of the outlet channels  44   a ,  44   b.    
     If the separation device  24  is arranged in the separation chamber  18  of the painting booth  2 , the drip plates  54   a ,  54   b  of each separation unit  26  project over the collecting channel  34 . 
     Two adjacent separation units  26  are arranged, while maintaining mutual spacing, in the separation device  24 , Between two adjacent separation units  26  and at the free side plates  36   a  or  36   b  of the two outermost separation units  26  within the separation device  24 , there extends in each case an electrode apparatus  56 , each of which is connected with a high voltage source which is not shown separately in  FIG. 4 . In a variant, the electrode apparatuses  56  may also be supplied by a single high voltage source. The separation units  26  are at earth potential. 
     Each electrode apparatus  56  comprises two straight electrode rails  58   a ,  58   b  which extend parallel to one another. In a field portion  60  of the electrode apparatus  56 , these hold a grid electrode  62 , whose edges  64   a ,  64   b , which extend between the electrode rails  58   a ,  58   b , are perpendicular to the latter. In a corona portion  66  of the electrode apparatus  56 , the electrode rails  58   a ,  58   b  hold a plurality of corona wires  68  acting as a discharge electrode. The corona wires  68  extend in a plane defined by the electrode rails  58   a ,  58   b  parallel to the edges  64   a ,  64   b  of the grid electrode  62  and are identically spaced apart from one another. 
     As may be seen in  FIGS. 3 and 4 , the electrode apparatuses  56  have an overall extent which substantially corresponds to the extent of the side plates  36   a ,  36   b  of the separation units  26 . The electrode apparatuses  56  are arranged such that the lower edge  64   b  of the grid electrode  62  is arranged roughly at the height of the lower end of the side plates  36   a  or  36   b.    
     When the separation device  24  is in operation, a separation liquid flows on the respective separation surface  42   a ,  42   b  of the side plates  36   a ,  36   b  of the separation units  26  from the top downwards into the outlet channels  44   a ,  44   b , which separation liquid is suitable for absorbing solid particles from the paint overspray arising during the painting process. 
     To this end, said separation liquid is supplied to the overflow channel  40  in the curved portion  38  of the separation units  26 . The separation liquid passes from there over the curved flanks  70   a ,  70   b , which are adjacent to the overflow channel  40 , of the curved portion  38  of the separation unit  26  in each case as a continuous film to the side plates  36   a ,  36   b  and flows down over the separation surfaces  42   a ,  42   b  thereof, still as a continuous film of separation liquid. 
     The number of corona wires  68  of the electrode apparatus  56  and their spacing from one another may vary as a function of the separation behaviour of the overspray particles. In the present exemplary embodiment, four corona wires  68  are provided, the uppermost of which is arranged next to the curved portion  38  of the separation unit  26 , while the corona wire  68  located therebelow is still located in the region next to the respective side plate  36   a  or  36   b  of the separation unit  26 . 
       FIG. 5  shows, in each case as a second exemplary embodiment, a modified separation unit  126  together with a modified electrode apparatus  156  while  FIG. 6  shows a modified separation device  124  comprising these. Components of the separation unit  126 , the electrode apparatus  156  and the separation device  124  which correspond to those of the separation unit  26 , the electrode apparatus  56  and the separation device  24  according to  FIGS. 1 to 4 , are designated with the same reference numerals plus 100. 
     The separation unit  126  differs from the separation unit  26  inter alia in that the outlet channels  144   a ,  144   b  project beyond the end face  146  of the separation unit  126 . The projecting portions  172   a ,  172   b  correspond to the drip plates  54   a ,  54   b  described above, which may therefore be omitted from the separation device  124 . 
     As may be seen in  FIG. 6 , the projecting portions  172   a ,  172   b  of the outlet channels  144   a ,  144   b  of the separation unit  126  extend through the respective openings  152   a ,  152   b  in each end wall  150   a  of the separation device  124 . 
       FIG. 5  shows a high voltage source  174  which is arranged between the side plates  136   a ,  136   b  of each separation unit  126  and is connected with the electrode apparatus  156 . The high voltage source  174  may correspondingly also be present in each separation unit  26  in accordance with the first exemplary embodiment. In each case, an individual separation unit  126  and an individual electrode apparatus  156  thus form a separation module  176 . Correspondingly, an individual separation unit  26  and an individual electrode apparatus  56  according to  FIGS. 1 to 4  in each case also form a separation module  76 . 
       FIG. 5  moreover shows bracing elements  178   a ,  178   b ,  178   c , which connect the inner faces of the two side plates  136   a ,  136   b  of the separation unit  126  with one another at the bottom, in the middle and at the top. 
     In the electrode apparatus  156  according to the second exemplary embodiment, a protective bar  180  extends perpendicularly between the electrode rails  158   a ,  158   b  above the uppermost corona wire  168 , which protective bar reduces the risk of any objects or particles which may fall down from the painting tunnel  6  onto the electrode apparatus  156  from coming into contact with the corona wires  168 . 
     Otherwise, the above statements regarding the separation unit  26 , the electrode apparatus  56  and the separation device  24  apply mutatis mutandis to the separation unit  126 , the electrode apparatus  156  and the separation device  124 . 
     The basic principle of the devices explained above will now be explained using the separation device  24  according to  FIGS. 1 to 4  by way of example. The separation device  124  according to  FIGS. 5 and 6  is used in a similar manner in the painting booth  2 . 
     When vehicle bodies are painted in the painting tunnel  6 , the booth air located therein becomes laden with paint overspray particles. These may be still liquid and/or tacky but also already more or less solid. The booth exhaust air laden with paint overspray flows through the lower opening  12  of the painting tunnel  6  into the separation chamber  18 . Here, said air is guided by the air baffle plates  28   a ,  28   b  towards the separation device  24  and flows between adjacent separation units  26  towards the lower air baffle plate  32 . 
     Corona discharges occur in a manner known per se at the corona wires  68 , and such discharges effectively ionise the overspray particles in the booth exhaust air as it flows past. 
     The ionised overspray particle pass by the side plates  36   a ,  36   b , which are at earth potential, of two adjacent separation units  26  and the grid electrode  62  extending therebetween in the first portion  60  of the electrode apparatus  56 . Due to the electrical field formed between the grid electrode  62  and side plates  32   a ,  32   b , the ionised overspray particles separate out onto separation surfaces  42   a ,  42   b  of the side plates  36   a ,  36   b  of the separation units  26 , where they are absorbed by the separation liquid flowing thereover. 
     Some of the ionised overspray particles separate out onto the separation units  26  as early as in the second portion  66  of the electrode apparatus  56  in the region of the corona wires  68 . However, the electrical field present between the corona wires  68  and the respective side plate  36   a ,  36   b  of the separation unit  26  is more non-homogeneous than the electrical field in the region of the grid electrode  62 , for which reason more directed and more effective separation of the ionised overspray particles occurs here on the corresponding separation unit  26 . 
     The air purified on passing between the separation units  26  is guided by the lower air baffle plate  32  towards the side wall  22   b , shown on the right-hand side in  FIGS. 1 and 2 , of the separation chamber  18 , from where, optionally after a certain degree of conditioning, it may be resupplied to the painting tunnel  6  as fresh air. Conditioning may in particular involve a readjustment of temperature or atmospheric humidity and optionally removal of solvents still present in the air. 
     The separation liquid flowing down over the separation units  26  which is now laden with the overspray particles passes at the bottom into the outlet channels  44   a ,  44   b  of the separation units  26 . Due to the inclination of the outlet channels  44   a ,  44   b , the laden separation liquid flows towards the openings  52   a ,  52   b  in the respective end walls  50   a , through the latter and thence via the drip plates  54   a ,  54   b  into the collecting channel  34 . The separation liquid laden with overspray particles flows via the collecting channel  34  out of the painting booth  2  and may be sent for purification and reprocessing, in which the overspray particles are removed from the separation liquid, or for disposal. 
       FIG. 7  shows two further modified separation units  226  according to a third exemplary embodiment. Components of the separation unit  226  which correspond to those of the separation unit  26  according to  FIGS. 1 to 4  are designated with the same reference numerals plus 200. In addition, three electrode apparatuses  256  may be seen in  FIG. 7 , which correspond to the electrode apparatuses  156  according to  FIGS. 3 and 4 . A separation unit  226  and an electrode unit  256  in each case form a module  276 . 
     In the separation unit  226 , the side plates  236   a ,  236   b  have corrugated portions  282   a ,  282   b , which adjoin the respective flanks  270   a ,  270   b  of the curved portion  238  of the separation unit  226 . Between the outlet channels  244   a ,  244   b  and the corrugated portions  282   a ,  282   b , the respective side plate  236   a ,  236   b  comprises a planar portion  284   a ,  284   b.    
     Each corrugated portion  282   a ,  282   b  has, in each case relative to the central plane, which extends between and parallel to the planar portions  284   a ,  284   b , of the separation unit  226 , inwardly curved portions  286   a ,  286   b ,  286   c ,  286   d  as well as outwardly curved portions  288 , which in each case extend along a corona wire  268 . The number of inwardly curved portions  286  of each corrugated portion  282   a ,  282   b  of the side plates  236   a ,  236   b  thus corresponds to the number of corona wires  268  of the electrode apparatus  256 . 
     For clarity&#39;s sake, in each case only one of the inwardly curved portions  286   a ,  286   b ,  286   c  and  286   d  and only one of the outwardly curved portions  288  is provided with a reference numeral. 
     The curvature of the two lower and of the uppermost inwardly curved portions  286   a ,  286   b  and  286   d  follows a circular arc when viewed in cross-section. The inwardly curved portions  286   a ,  286   b  and  286   d  are in each case arranged relative to an adjacent corona wire  268  such that the latter is concentric in cross-section to the circular arc defining by the profile of the respective curved portion  286   a ,  286   b  or  286   d . The uppermost inwardly curved region  86   d  is somewhat shorter in the vertical direction than the lower two inwardly curved regions  286   a  and  286   b.    
     In the inwardly curved portion  286   c  arranged below the uppermost curved portion  286   d , the radius of curvature declines from the bottom upwards, such that, when viewed in cross-section, the inwardly curved portion  286   c  has a parabola-like profile. As a result, the spacing between the outside ends of opposite flanks  270   a ,  270   b  of two adjacent separation units  226  is smaller in a horizontal plane than the spacing between their opposite planar portions  284   a ,  284   b  of the respective side plates  236   a ,  236   b.    
     The spacing of two adjacent separation units  226  with electrode apparatus  256  arranged therebetween is adjusted such that the corona wires  268 , when viewed in cross-section, are in each case concentric to the centre point of the approximately cross-sectionally circular arc-shaped segments defined by two opposite, inwardly curved portions  286   a ,  286   b  or  286   d.    
     Due to the inwardly curved portions  286  of the corrugated portions  282   a ,  282   b  of the separation units  226 , the channel formed there between the separation units  226 , through which channel the overspray-laden booth exhaust air flows, is in each case locally widened at that point. As a result, at the level of the inwardly curved regions  286  of the side plates  236   a ,  236   b , there is in each case a reduction in flow velocity, whereby the booth exhaust air flowing past the respective corona wire  268  remains for longer in its region of influence. As result, a greater proportion of overspray in a given volume of booth exhaust air is in turn ionised by the corona wire  268  in question. Thanks to the inwardly curved portions  286 , which are arranged in series in the direction of flow of the booth exhaust air, of the side plates  236   a ,  236   b  of the separation units  226 , a significantly larger proportion of overspray is ionised in the second electrode portion  266  with the corona wires  268  than would be the case with continuously planar side plates  236   a ,  236   b  at an identical flow velocity of the booth exhaust air. For this reason it is possible to achieve an overall increase in the throughput of booth exhaust air, since the flow velocity of the overspray-laden booth exhaust air may be raised in such a manner that its residence time in the region of the corona wires  268  corresponds to the residence time at a lower flow velocity and with completely planar side plates  236   a ,  236   b.    
     Flow velocity may, for example, be increased by a factor of 4 to 6. If, for example, in a separation apparatus  24  with separation units  26  according to the first exemplary embodiment, a flow velocity of the booth exhaust air laden with overspray particles of 0.25 m/s is possible while satisfactory separation performance is still achievable, then if the separation units  226  are used, the flow velocity of the booth exhaust air may be raised to 1 m/s to 1.5 m/s while nevertheless achieving adequate separation results. If the flow velocity is to be increased, the height of the separation apparatuses may be correspondingly increased to achieve the same separation action. 
     In addition, swirling and turbulence occurs in the region of the corrugated portions  232   a ,  232   b  of opposite side plates  236   a ,  236   b  of two adjacent separation units  226 , whereby the paint overspray particles entrained by the booth exhaust air are uniformly distributed in the region of the corona wires  268  and may thus be more effectively ionised. 
     In a modification of the electrode apparatuses  56  or  156 , which is not shown here in either case, a plate electrode is provided instead of the grid electrode  62  or  162 . However, separation of ionised paint overspray particles from the booth exhaust air proceeds more effectively in the presence of the grid electrode  62  or  162 , since slight swirling of the booth exhaust air is produced on the grid or grid rods thereof and the ionised paint overspray particles are consequently more homogeneously distributed in the region of the grid electrode  62  or  162  than is the case with a plate electrode with a continuous electrode surface. 
     In order to reduce any adhesion to the separation surfaces  242   a ,  242   b  which may still occur of separated paint overspray particles which have been absorbed by the separation liquid on the separation surfaces  242   a ,  242   b  of the separation units  226 , the separation surfaces  242   a ,  242   b  of each separation unit  226  may be coated with a non-stick coating, such as for example Teflon. 
     Instead of the overflow channel, from which separation liquid passes over the outer edges thereof and over the curved flanks  70   a ,  70   b ,  170   a ,  170   b  or  270   a ,  270   b  of the curved portion  38 ,  138  or  238  of the separation units  26 ,  126  or  226  to the side plates  36   a ,  36   b ,  136   a ,  136   b  or  236   a ,  236   b , it is also possible to provide separation units  26 ,  126 ,  226  with an alternative apparatus with which separation liquid may be applied onto the separation units  26 ,  126 ,  226 . For example, a sprinkler apparatus, a slot nozzle or simply a tube with orifices may be arranged for this purpose above the curved portion  38 ,  138  or  238 . 
     It is important for the purposes of interplay with the electrode apparatus  56 ,  156 ,  256  and the side plates  36   a ,  36   b ,  136   a ,  136   b ,  236   a ,  236   b  at earth potential of the separation units  26 ,  126 ,  226  that the separation liquid be electrically conductive. The separation liquid may be based, for example, on water or on an oil and be provided with additives which assist clumping and/or curing and/or detackifying of paint overspray particles in the separation liquid. 
     The conductivity of the separation liquid is preferably in the range from 50 to 5000 μS/cm, in particular from 1000 to 3000 μS/cm, and may be adjusted by means of additives, such as for example salts. 
     Thanks to the above described combination of electrical separation of paint overspray from booth exhaust air laden therewith with the use of the separation liquid for absorbing and conveying away the paint overspray particles, it is possible to achieve efficient and effective purification of overspray-laden booth exhaust air. The purified booth exhaust air may then be resupplied in a circuit to the spray booth as has already been explained above. 
     It is to be understood that additional embodiments of the present invention described herein may be contemplated by one of ordinary skill in the art and that the scope of the present invention is not limited to the embodiments disclosed. While specific embodiments of the present invention have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.