FR2564331A1 - IMPROVEMENTS RELATING TO POLLUTION GAS CLEANING PLANTS BY SOLID AND / OR LIQUID PARTICLES - Google Patents

Abstract

THE INSTALLATION INCLUDES A FIRST WASHING DEVICE 4 WITH RUNOFF PATCHES PROVIDED NEAR WORKING SPACE 1, A SECOND WASHING DEVICE 20 IN VENTURI AND SPRAY JET PROVIDED DOWNSTREAM OF THE FIRST WASHING DEVICE 4, AND A CENTRIFUGAL SEPARATOR DEVICE 29 DOWNSTREAM OF THE SECOND WASHER 20.

Description

- 1 -

  Improvements to pollution control facilities

  of a gas polluted by solid and / or liquid particles.

  The invention relates to depollution installations.

  lution of a gas polluted by solid and / or liquid particles and extracted from a working enclosure in which objects are subjected to a surface treatment. The invention applies more particularly, but not exclusively, to installations for cleaning up air polluted by a suspension of fine particles of paint and extracted from a paint booth in which objects, in particular bodywork of

  motor vehicles, are coated with layers of paint

  ture. It has already been proposed to include such

  installations a washing device with streams

  ment in which the polluted gas coming from the working enclosure passes through sheets of washing liquid, said washing device being arranged near the enclosure

of work.

  If one is satisfied with this single washing device with runoff layers, and in order to obtain an effective depollution, one is led to make a bulky washing device (multiplicity and arrangement in series of the runoff layers) and noisy (dimensions of the layers of runoff, small cross sections of the

gas).

  The requirements are becoming more and more stringent,

  both for the effectiveness of pollution control and for the harmful

  acoustic sessions of the environment. A solution using this single washing device with runoff plies is therefore hardly conceivable, all the more so as its costs of production and operation

are high.

  There are other types of washing devices, such as venturi and spray jet washing devices in which the polluted gas passes through at least one venturi into which opens, at the neck, at least one jet of washing liquid. spray intended to produce a mist of washing liquid through which the polluted gas passes.

  However, if we are content with only

  washing agents of this type, it quickly encounters problems of fouling, in particular when it is a gas polluted by a suspension of fine particles

paint.

  Finally, separating devices are known which operate by weight difference, in particular by centrifugation, to collect the solid and / or liquid particles from a

  polluted gas, but, as in the previous case, these dispo-

  sitives clog up quickly if the material from which these particles are made cannot be removed easily, which is of course the case when these particles are

fine particles of paint.

  The object of the invention is precisely to avoid

  above mentioned, about the different

  washing or separating devices used in isolation.

  According to the invention, the installation comprises in combination

  naison, - a first washing device with runoff plies in which the polluted gas coming from the working enclosure passes through sheets of washing liquid, said device being arranged near the working enclosure, said

  device being arranged so that its capture efficiency

  tion is such that it captures almost all of the particles of average dimensions greater than 6 microns, and approximately half of the particles of average dimensions less than 6 microns, - a second washing device with venturi and spray jet -3 - in which the partially depolluted gas coming from the first washing device passes through at least one venturi into which opens, at the level of the neck, at least one jet of sprayed washing liquid, said device being arranged so that its capture efficiency is such that it captures the almost all of the particles of average dimensions less than 6 microns still present in the partially depolluted gas, - and a centrifugal separator device in which the depolluted gas but charged with droplets of washing liquid having captured particles of average dimensions less than 6 microns in the second washing device is freed from these droplets which are deposited by centrifugation on the walls of said device parator

  and flow by gravity along these walls.

  It is therefore conceivable that, thanks to the combination of these two washing devices, and of this separating device, - the first washing device, due to its relatively low efficiency (100% of the particles of dimensions greater than 6 microns and only 50% of the particles smaller than 6 microns), is compact, generates acceptable noise pollution and

  cost of implementation and of a relative operating cost

  low, - the second washing device, because it treats a

  air already cleaned (containing only 50% of the particles

  cules of dimensions less than 6 microns), does not pose a problem of rapid fouling, - and the separating device, because it collects droplets of washing liquid having captured only particles of small dimensions and in quantity relatively small (50% of particles of dimensions

  less than 6 microns), does not pose a problem of

  fouling, said droplets being eliminated by -4

  runoff without risk of adhesion to the walls.

  According to a preferred arrangement of the invention, the installation further comprises, downstream of the separating device, a gas purifying device, in particular with a physicochemical effect, for eliminating at least partially the solvent vapors which the gas decontaminated and freed from the droplets of washing liquid. Thanks to this arrangement, the gas thus purified can either be discharged directly into the atmosphere, or be, at least partially recycled in the working enclosure; in the latter case, savings are made

  energy because the gas, thus recycled, presents conditions

  temperature and hygrometry which may be favorable to the treatment carried out in said enclosure, which then avoids having to bring beforehand all of the gas admitted into this enclosure to the above conditions of temperature and hygrometry, this being particularly advantageous in the case of an installation in which the treatment enclosure is made up

by a paint booth.

  According to another arrangement of the invention, part of the washing liquid introduced into the second device

  washer can come from the separating device.

  The invention consists, apart from the provisions

  which has just been mentioned, in certain other provisions

  which are preferably used at the same time and

  which will be more explicitly discussed below.

  The invention could, in any case, be well

  understood using the additional description which follows,

  as well as the attached drawings, which supplement and drawings, relate to a preferred embodiment of the invention and do not, of course, show any

limiting character.

  - 5 - Fig. 1, of these drawings, shows a block diagram

  of an installation established in accordance with the invention.

  Fig. 2 shows a block diagram of an installation

  tion established according to a particularly advantageous arrangement of the invention. In these figures i and 2, a paint booth I has been shown in which motor vehicle bodies 2 are coated with layers of paint, for example by a set of spray guns (not

represented).

  This paint booth 1 is supplied with air

  clean, previously brought to temperature conditions

  deletion and humidity determined by a sheath 39; for example this air is at 20 C and has a humidity

70% relative.

  Below this paint booth is disposed a first washing device 4 with runoff plies in which the air loaded with paint particles

  passes through sheets of washing liquid.

  To this end, the first washing device 4 comprises an inclined floor 5 supplied with washing water by

  lateral overflow chutes 6, themselves supplied

  piped into water by piping 7.

  Passage orifices 8 are provided in the plane

  expensive inclined 5 and allow the formation of runoff layers crossed by the air polluted with paint particles. Other runoff plies are formed between a transverse wall 11 and vertical walls 10 at the level of the passages 9 existing between

  this transverse wall II and these vertical walls 10.

  The air polluted by fine particles of paint crosses the layers of washing water, and by contact

  intimate with the wash water, is partially depolluted.

  The first washing device 4 is arranged to - 6 - capture almost all of the paint particles of average size greater than 6 microns, - and capture approximately half of the paint particles

  with average dimensions less than 6 microns.

  The first washing device 4 can be manufactured in a relatively simple manner (therefore having a low operating cost and a low operating cost), and generating acceptable noise pollution

(less than 80 dBa).

  A system for eliminating droplets of washing water is provided at the outlet of this first washing device 4, this system comprising a passage 13 in which the air is suddenly accelerated and the water droplets fall downstream of the passage 13 by gravity to be collected in a bin 15. The water in this bin 15 is

  then evacuated by a pipe 16 which joins the pipe-

  general outlet 17 for water disposal of the first device

scrubber 4.

  A water treatment system (not shown) can then be provided, which can allow total or partial recycling of the treated water to the piping 7

feeding the chutes 6.

  The air, partially depolluted, from this first washing device 4 is brought, by a sheath 19, to a

  second washer 20 with venturi and spray jet.

  This partially depolluted air passes through a venturi 21 into which opens, at the level of the neck 22, a jet of water

washing spray.

  The jet of washing water thus sprayed is projected orthogonally into the air flow and forms a dense sheet, ensuring intimate contact between the water and the air which still contains about half of the particles of

  painting of average dimensions less than 6 microns.

  -7- This second washing device 20 is arranged so that

  almost all of these particles are then captured.

  The washing water coming from a reservoir 27 is brought to the neck 22 of the venturi 21 by a pipe 25 and a pump

26.

  The air thus cleared, by the first and second dis-

  positive washers 4 and 20, but charged with droplets of washing water having captured, in the second washer 20

  paint particles of smaller average dimensions

  laughing at 6 microns, is then directed, via

  from a sheath 28, to a centrifugal separator device 29.

  This centrifugal separator device 29 has a tangential inlet 30 to which the sheath 28 leads. This tangential inlet 30 ensures a rotational movement of the air containing the water droplets, and this rotational movement is accelerated in an area 31 having a annular passage 32 formed between a central core 33 and a concentric vertical wall 34. A vertical wall

  upper 35 collects dripping water droplets

  then saddle along this upper vertical wall to be collected at the level of the concentric vertical wall 34. This collected water is advantageously recycled to the supply tank 27 of the second washing device 20, said tank being moreover

supplied with new water.

  Via a sheath 37 and a ventila-

  38, the air from the separating device 29 can be evacuated to a chimney 40 (fig. 1) or to a purifying device 41 (fig. 2), in particular with a physico-chemical effect, in order to eliminate solvent vapors which contain the air decontaminated and freed from the droplets of washing water. This purifier device 41 can be of the activated carbon type, or with organic oil spray, or in the field

  plasma, or Beta radiation field.

  -8- Once the air has thus been purified, it is advantageous to recycle it, totally or partially, to the supply sheath 39 of the paint booth 1: in fact, the temperature and hygrometry conditions of the air at the outlet of the purifier device 41 are very close to those required (20 C and 70% relative humidity) for

  painting booth supply 1.

  The installation thus produced has a certain number of advantages, including those summarized in the points below: - it is possible to continuously extract the polluted gas from the working enclosure, with high efficiency; the yield on particles with an average size of less than 6 microns can be close to 95% and then it is possible to pass, in the case of a

  paint booth with a concentration of 20 mg of paint

  ture per m3 of air leaving the cabin, at a concentration

  tration of 1 mg of paint per m3 of air at the outlet of the separating device, - the noise generated in the working enclosure by the circulation of the extracted gas is reduced until it does not exceed a threshold of 80 dBA; this reduction is made possible by the fact that the pressure drop in the first washing device is voluntarily limited (of the order of 1600 Pa for a conventional washing device, this pressure drop is reduced to 800 Pa in the case of the invention), the reduction in efficiency of this first washing device which results therefrom being compensated for by the presence of the second washing device located downstream;

  - the constitution of the second washing device allows its.

  realization at low cost, and its operation (in particular its water consumption) involves an equally low cost; moreover, it does not generate acoustic pollution, and its arrangement, downstream of the first washing device, makes its fouling weak; - effective removal of solid particles and / or

  liquids in the two washing devices and the

  nation of the washing water droplets in the separating device, make it possible to provide a purifying device, in particular for eliminating the solvents, without risk of clogging for this purifying device; - the recycling, at least partially, of the purified gas from the purifying device, in the working enclosure, leads to substantial energy savings; in the particular case of a paint booth, the air admitted into this booth must be around 20 C and have a relative humidity of around 70%, these conditions being practically those of purified air, the recycling of which can therefore be done directly in the paint booth;

  - consumption of washing liquid from the second device

  positive washer can be considerably reduced by recycling in this second washing device at least part of the washing liquid coming from the centrifugal separator device;

  - the location of the various elements of the installation

  tion can be determined based on various impe-

  ratives, only the first washing device being located near the working enclosure, generally below.

- 10 -

Claims (6)

  1.- Installation for depolluting a gas polluted by solid and / or liquid particles, said polluted gas being extracted from a working enclosure in which the objects are subjected to a surface treatment, characterized in that it comprises in combination:   - a first washing device (4) with streams of water -   ment in which the polluted gas coming from the working enclosure (1) passes through sheets of washing liquid, said device (4) being disposed near the working enclosure (1), said device (4) being arranged so that its capture efficiency is such that it captures almost all of the particles of average dimensions greater than 6 microns, and approximately half of the particles of average dimensions less than 6 microns,   - a second washer device (20) with venturi and jet spray   in which the partially depolluted gas from the first washing device (4) passes through at least one venturi (21) into which opens, at the neck (22), at least one jet of sprayed washing liquid, said device (20) being arranged so that its capture efficiency is such that it captures almost all of the particles of average size less than 6 microns still present in the partially depolluted gas, - and a centrifugal separator device (29) in which the depolluted gas but laden with droplets of washing liquid having captured particles of average size less than 6 microns in the second washing device (20) is freed from these droplets which are deposited by centrifugation on the walls of said separating device and rustle by gravity along these walls. - He -   2.- Installation according to claim 1, charac-   terrified by the fact that it further comprises, downstream of the separating device (29), a gas purifying device (41), in particular with a physicochemical effect, for at least partially eliminating solvent vapors which the gas could contain cleared and cleared   washing liquid droplets.   3.- Installation according to claim 1, charac-   terrified by the fact that the gas purified and freed from the droplets of washing liquid is, at least   partially recycled in the work area.   4.- Installation according to claim 2, charac-   terrified by the fact that the depolluted gas, freed from the droplets of washing liquid, and purified is, at least partially, recycled in the working enclosure.   5.- Installation according to any one of the res-   dications 1 to 4, characterized in that at least   part of the washing liquid collected in the dis-   positive separator is recycled in the second washing device.   6.- Installation according to any one of the res-   dications 1 to 5, characterized in that the enclosure   work consists of a paint booth.