Arrangement for cleaning ventilation air polluted with paint particles

(54) NAME Apparatus for the purification of paint particles contaminated with paint from a spray booth for painting (56) QUOTE PUBLICATIONS: EP 280 360, FR 2 344 318, EP 047 432 (57) SUMMARY:

A device for purifying paint particles contaminated ventilation air from a spray box (1) for painting, for example, car bodies (2) comprises means (9) for bringing the ventilation air into contact with a liquid flow for separating part of the paint particles of the ventilation air. Downstream of said means, at least one, wet electrostatic dust separator (6) located in an enclosure (7) is arranged for the separation of residual particles and liquid droplets in the ventilation air. The enclosure is placed under the floor of the spray box, the portion of the enclosure with which the ventilation air first comes into contact is formed as a liquid-poured inclined plane, the lower end of which is connected to said means, which forms part of the enclosure and is liquid-embedded. The enclosure (7) is further designed so that the ventilation air is forced to be diverted at an angle of 10 ° to 170 ° relative to its substantially vertical flow direction through the spray box (1), before being passed through the aforementioned means (9).

PRV 328 ALLF 138 9 132 AA

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The numbers in brackets indicate the international identification code. INID code. Letters in clamps indicate international document code.

463 604

The present invention relates to a device for purifying paint particles contaminated ventilation air from a spray booth for painting, for example, car bodies, comprising means for bringing the ventilation air into contact with a liquid flow for separating part of the paint particles of the ventilation air, downstream of said means. at least one wet electrostatic dust separator placed in a containment for the separation of residual particles and, from the liquid flow, liquid drops in the ventilation air.

For a long time, venturi separators, known as split venturi, have been used for the removal of sticky paint particles from ventilation air from spray booths.

In the venturi separator, the polluted ventilation air is accelerated and contacted at high speed with a circulating water flow, which is then decomposed into fine droplets, whereby some of the paint particles collide with the water droplets and are captured by them. See, for example, SE 196 718.

A disadvantage of venturi separators is that sound, with a very high level, is produced in these in connection with the passage of the ventilation air through the venturi itself.

Another disadvantage of venturi separators is that the ventilation air will contain water droplets, in addition to residual paint particles, as well as evaporated solvents in the spray box after passing through the venturi separator.

In order for the objects, such as car bodies, painted in spray booths to maintain an acceptable surface layer, it is necessary, inter alia, that the ventilation air has a certain temperature and relative humidity. Usually, the ventilation air is conditioned to about 23 ° C and 60-70% relative humidity. This means that in cold climate zones a lot of energy is needed to condition the ventilation air, if the ventilation air is not recirculated to the spray box.

As the ventilation air, as pointed out above, contains both paint particles and water droplets and evaporated solvents in the spray box after passing through the venturi separator, the ventilation air must be further purified if it is to be recirculated to the spray box. Otherwise, these remaining paint particles and water droplets would have a devastating effect on the quality of the surface layer on the objects painted in the spray booth. Furthermore, when painting is to be carried out by people, it is important to remove the above-mentioned solvent songs from the ventilation air.

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For example, SE 8601290-3 describes a method for recirculating the majority of the ventilation air to the spray booth. This is made possible by allowing the ventilation air emitted from the venturi separator to pass through an electrostatic dust separator which operates according to the wet separation method, before returning it to the spray booth. This dust separator effectively separates the particulate pollutants of the ventilation air, ie, color particles and water droplets, but not its solvent vapors. It is not necessary to remove the solvent vapors from the ventilation air if painting robots are used in the spray booth.

Recirculation of ventilation air according to the above-mentioned method reduces the energy consumption of the painting plant, but since a conventional venturi separator is still used, this method suffers from the above-mentioned high noise level disadvantage, and the use of an additional purification device in the form of an electrostatic dust separator and additional costing equipment means.

DE 37 05 634 discloses a method of purifying contaminated ventilation air from a spray booth by directly introducing it into a conventional electrofilter operating according to the wet separation method.

According to this method, the venturi separator has thus been replaced with an electro filter, which means that no troublesome sound generation is obtained, although an effective separation of the particulate pollutants of the ventilation air can theoretically be achieved. However, it would be difficult to fit a conventional electrostatic dust separator in the volume normally occupied by the venturi separator under a spray booth.

Since the electrostatic dust separator according to the latter patent is placed directly under the grid-shaped floor of the spray booth, there is a risk that persons working in the spray booth come into contact with high voltage conductive details in the dust separator. The paint should therefore be applied with the help of painting robots.

The above-mentioned placement of the electrostatic dust separator also carries an increased risk of fire and explosion.

The object of the present invention is therefore to provide a compact zl6X 6^r&gt; A ik / sJ s- # 1 and efficient, non-emitting, fire- and explosion-proof device for the purification of paint particles contaminated with ventilation air, which device can also be installed in existing painting plants, without requiring any additions. This device should also be used for spray booths where painting is done manually.

This object is achieved according to the present invention with a device which is of the type initially specified and characterized in that the enclosure is placed under the floor of the spray box, that the part of the enclosure with which the ventilation air first comes into contact is designed as a liquid embedded inclined plane. , the lower end of which is connected to said means, which form part of the enclosure and are fluid-embedded and that the enclosure is designed so that the ventilation air is forced to be diverted at an angle of 10 ° to 170 ° relative to its substantially vertical flow direction through the syringe box before being passed through the above means.

Said angle is about 90 °.

The inclined plane is preferably arranged to be sprayed by overflowing water from an upstream enclosed basin.

Said means is preferably a perforated sheet.

The electrostatic precipitator preferably contains at least one emission source acting as an ion source and at least one solid, liquid-injected, gas-permeable precipitating electrode disposed across the flow direction of the ventilation air through the electrostatic dust separator.

The emission electrode is preferably formed as a row of wires or sheet metal, substantially parallel to the deposition electrode.

Preferably, a control electrode located at the same potential as the emission electrode is located downstream of the precipitation electrode.

The emission electrode and the control electrode may be located at the same potential, which is preferably in the range of -100 - -10 kv, especially about -20 kv.

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The control electrode is preferably designed as a row of thin-walled tubes lying parallel to the precipitation electrode.

The invention will be described in more detail below with reference to the accompanying drawing, which shows a vertical section through a painting unit, comprising a spray booth and a device according to the invention for purifying ventilation air contaminated with sticky paint particles from the spray booth.

The painting unit shown in the drawing thus comprises a spray box 1, through which car bodies 2 are advanced while being sprayed with paint. The paint is applied either with the aid of robots or humans, whereby in the latter case it is only possible to recycle the ventilation air if solvent vapors contained in the spray box have been removed from the ventilation air.

The car bodies 2 rest on a conveyor 3, which is advanced through the spray box 1 just above its grid-shaped floor 4. Below the grid-shaped floor 4, the spray box passes into a channel 5 in which two electrostatic dust separators 6 operating according to the wet separation method are arranged. Since these dust separators are identical, only one is shown in the drawing.

These dust separators are located in each enclosure 7, which is designed as a plate box with a sloping, liftable top. These enclosures are so positioned in the duct 5 at its outer walls that the duct is delimited in such a way that the ventilation air is forced to flow through a conical duct cross-section which opens into an inner duct 8 with smaller cross-sectional area. As further shown in the figure, the side of the enclosures facing the inner channel is constituted by a perforated plate 9 with circular or slit-shaped openings having a diameter of 5-10 mm and a length of 5-10 mm, respectively. The plates have a perforation rate of about 80%. Furthermore, the plates are so fixed in the enclosures that their inclination relative to the vertical plane can be varied. This facilitates the formation of a well-covered water film along the upstream portions of the plates 9.

A pool 10 is provided at the upper end of each containment peak

463 604 for watering the top and the perforated plate 9. The basin is connected via a conduit 11 to a water tank 12, which in turn communicates with the bottom of the inner channel 8 via a drainage line 13.

The electrostatic dust separators located within the enclosures consist of precipitating electrodes 14 and the emission and control electrodes 15 and 16 respectively. with points directed in the flow direction of the ventilation air. The control electrodes, on the other hand, are formed as rows of thin-walled tubes lying parallel to the precipitation electrodes, which have a substantially larger diameter than the wire diameter of the emission electrodes wire coils or the tips of the emission electrodes. The rows of emission and control electrodes are attached to frames not shown, which are relieved by insulators in the sides of the enclosures.

An emission electrode 15 and a control electrode 16 are located upstream and downstream of each precipitation electrode, respectively. As shown in the figure, each dust separator 6 is provided with four precipitation electrodes and thus four emission and control electrodes. The emission electrodes 15 and the control electrodes are electrically coupled and connected to the negative terminal of a direct current source. The positive voltage source of the DC source is connected to the precipitation electrodes via the enclosures and grounded. For example, the emission electrodes and the control electrodes are located at a potential of -20 kv. Furthermore, since the emission electrodes and the control electrodes are located at the same distance from the precipitation electrodes, the resulting mean field strength is equal on both sides of the precipitation electrodes.

Of course, this configuration is not the only conceivable one, but the number and position of the precipitation, emission and control electrodes can be varied in many ways. For example, in some applications, all but the first emission electrode in each electrostatic dust separator can be exchanged for control electrodes to reduce the consumption of electrical energy.

As further shown in the drawing, each of the electrostatic

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The separators 6 are provided with nozzles 18 and 19 of the flat or articulated type, which are located above or opposite the precipitating electrodes 14. The nozzles are connected via a not shown pipe lances and a number of conduits 20, 21 and 22 to a water tank 23, which in its in turn communicates with the bottom of the enclosure 7 via a number of drainage lines 24.

A drip separator 25 of the type formed as a mesh or a corrugated plate is located downstream of each dust separator 6 to prevent water from accumulating in a subsequent duct system for recirculating the main portion of the ventilation air to the upper portion of the spray booth 1. The remaining portion of the the ventilation air is delivered to the atmosphere via, for example, an incinerator for combustion of the solvent vapors of the ventilation air. If the paint is to be applied manually, it is necessary to conduct the ventilation air through a solvent concentrator before returning it to the spray booth, in order to reduce the solvent content of the spray booth to a level acceptable to humans.

One or more textile barrier filters may be provided downstream of each of the drip separators 25 to ensure good separation of color particles even in the absence of power supply to the DC voltage source 17 or other electrical failure of the dust separator.

The function of the painting system will be described in more detail below with reference to the drawing. The ventilation air flows into the top of the spray booth and is contaminated during its passage through the spray booth with the paint particles that are not stuck to the car bodies 2 during the painting operation. The air is then sucked by the vacuum created by fans 26 arranged in the duct system down through the floor 4 of the spray box to the sloping peaks of the enclosures 7. The air then flows down through the inner channel 8 and into the enclosures 7 through the openings in the water-perforated, perforated plates 9. The air is hereby directed about 90 ° from a vertical to a horizontal flow direction.

Some of the paint particles of the ventilation air will collide with and be captured by the water droplets of the overflowing water. These paint particles will be transported by the water to the water tank 12 where they are removed from the water in the usual manner by the application of various chemicals, after which

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463 604 the formed sludge is allowed to settle in a sedimentation tank not shown. This water is supplied, inter alia, adhesive to prevent separating paint particles from sticking to the outer surfaces of the enclosure or to the drainage line 13 and the water tank 12 and to facilitate handling of the residual product.

In each of the dust separators 6, the remaining color particles of the ventilation air are emitted from the wire coils of the first emission electrode 15, emitted electrons or formed ions, and then passed through the ventilation air and the electric field formed between the emission electrode 14 and the precipitating electrode 14 between the emission electrode. The color particles which are not trapped by the precipitating electrode, but flow through its perforations to the space between the precipitating electrode and the first control electrode 16, will be partially fed back to the rear side of the precipitating electrode by the electric current of the precipitating electrode formed in the directional current of the precipitating electrode Ing. The color particles that are not trapped by the first precipitating electrode will be trapped by the second, third or fourth precipitating electrode, which acts in the same manner as the first precipitating electrode.

Since the ventilation air has passed through the electrostatic dust separators and drip separators, there are virtually no paint particles and water droplets left in the ventilation air, which can be recirculated to the spray box via the exhaust air duct system without previously having to pass through any additional particle or drip separator.

The precipitating electrodes 14 are continuously sprayed with water from the nozzles and 19 to form a vertical, movable water film along the front and back sides of the precipitating electrodes to remove separated color particles. The paint particles that stick to the emission and control electrodes are removed by means of recoiling water droplets and water spray from the lower nozzles 19. The paint particles are then conveyed by the water to the water tank 23, after which the formed color sludge is allowed to settle in a sedimentation tank not shown. This water is not applied to an anti-sticking agent, since some stripping of the separated paint particles takes place automatically in the electrostatic dust separators. Thus, by separating the water flow within the channel 5 from the water flows through the enclosures 7, the consumption of scraping agents is reduced.

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The invention is, of course, not limited to the embodiment described above, but can be modified in various ways within the scope of the following claims.

Instead of placing the gas-through precipitating precipitating electrodes 14 across the flow direction of the ventilation air through the enclosures 7, impermeable precipitating electrodes could be placed parallel to this direction of flow.

Instead of making the tops of the inclusions removable, inspection and service doors can be placed in the sides of the inclusions.

Instead of placing two enclosures with each electrostatic dust separator under the spray box 1, one could place under it a single enclosure which extends throughout the spray box with an electrostatic dust separator.

Finally, the precipitating electrodes 14 may be mesh or grating instead of perforated sheets.

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