WO2000029118A1

WO2000029118A1 - Electrostatic method for purifying air and fixing solids

Info

Publication number: WO2000029118A1
Application number: PCT/FR1998/002461
Authority: WO
Inventors: René MASSARD
Original assignee: Massard Rene
Priority date: 1997-05-14
Filing date: 1998-11-18
Publication date: 2000-05-25
Also published as: FR2763264A1; FR2763264B1

Abstract

The invention concerns a method for cleaning up air in closed premises and fixing harmful fibres or particles by electrostatic spraying of a resin on a fibrous or contaminated support. The invention concerns a method for purifying air and encapsulating or fixing on a fibrous or contaminated support toxic or harmful products. Said method consists in applying on the support by electrostatic spraying a solvent-free resin such as polyurethane, epoxide, or phenolic resin to produce a film capable of being interfaced and providing the fibrous support with a superficial mechanical strength while making it inert. The sprayed film can also have low viscosity or solvency, enabling upward leaching for improving mechanical strength in the support core, after the resin has set. The film can also be expanded after it has been applied on the support for improved coating of the fibres. Said electrostatic method also includes fixing a copper ring or a ring of another conductor metal behind the spray head generating an electrical counterflow driving the cloud of charged particles towards the support, without requiring an air stream to blow the cloud towards the support.

Description

ELECTROSTATIC AIR CLEANING AND FIXING SOLIDS PROCESS

The present invention describes a method of fixing or impregnating a fibrous support of poor mechanical strength, which is the case for example of flocking asbestos fibers, rock wool, slag or glass, fibers synthetic (aramids, polyester, etc.) or textiles, vegetable fibers (cellulose or other), or panels of insulating materials composed from such fibers The poor mechanical strength of these supports and the environmental conditions (temperature variations, humidity, ventilation, etc.) or various mechanical stresses (shocks, maintenance interventions, etc.) create a dusting of the ambient air by detaching the fibers which remain in suspension in the air, creating in certain conditions major nuisances Depending on the nature of the fibers, this dust can be very damaging to health (case of asbestos fibers, glass, rock wool for example), or creates incomp atible with the activity carried out in the premises exposed to this dustiness (case of the electronic industry, medical or pharmaceutical laboratories, hospitals, food industries, etc.) The very uneven structure of the flocked supports for example also traps the dust ambient, dust impossible to remove, mechanical pressure exerted by cleaning - even very low - degrading flocking, and which, therefore, only accumulates on these supports. It also happens that contaminating fibers or particles - toxic or others (radioactive for example) - have contaminated a support (walls, ceilings or floor of a room) In such a case it is also necessary to neutralize the risk caused by these toxic fibers or particles by fixing them to the support and making them inert

Currently, in the case where a fibrous support has a sanitary or other πsque (which is measured by the dust content of the ambient air), several technical solutions are envisaged and implemented. - removal of the fibrous support (de-flocking by mechanical means, mainly scraping) This preliminary treatment is then followed by the laying or projection of a new flocking, supposed to be less polluting or toxic

- enclosure of the support by making a double envelope confining the fibrous support which detaches in the confined volume - fixing the flock fibers or the fibrous support by spraying a paint or resin film which, after hardening or drying, "sticks" the fibers to prevent them from coming off

- Impregnation of the support with a very low viscosity resin which, after hardening, mechanically consolidates the flocking

These various treatments of a flocking or a fibrous support to make it inert all have the major drawback of being detrimental to the good performance of the flocking or fibrous support, creating significant dust pollution, which requires setting up containment of the premises during the intervention, in order to avoid contamination of the ambient air o by loose fibrous particles

Some patents describe inventions intended to fix contaminating fibers or particles on a support

- Thus CEA patent No. EP 0 055 671 A describes a device for electrostatic spraying of powder or paint onto contaminated equipment to fix the contamination. This invention is applicable only on equipment and not walls or ceilings, and considers the use of solvent-based resins conventionally applied electrostatically by spray nozzle. The deposit of a film of a certain thickness requires several layers, with intermediate drying. The confinement is compulsory and carried out by a fume cupboard, impractical to use on a site. , and 0 not applicable for the treatment of walls or ceilings

- Patent XP002056682 and JP 59 102 199 A describes a technique for fixing radioactive contamination by electrostatic powder or paint spraying process similar to the previous patent inside pipes or tanks, spraying being carried out by nozzle through a hole drilled in the tank or the pipe 5 - Patent DE 41 19 309 A envisages the spraying on a flock of asbestos of resins in aqueous phase to avoid the inconvenience of the solvents, such a spraying also being able to be made in electrostatic by projection by nozzle L ' The use of resins in the aqueous phase requires several coats to obtain a sufficient thickness, with a long drying time between coats. The method of application and spraying by

30 nozzle requires prior containment of premises

The invention described in the present invention makes it possible to stabilize a fibrous support or polluted by toxic or harmful fibers or particles, without the need for confining the premises since its implementation does not create dust by detaching fibers and without disturbing the activities carried out in the buildings, while

35 eliminating all the nuisances caused by the dusting of toxic fibers or particles The process consists in projecting onto the fibrous support a film of a cold-hardenable two-component resin by an electrostatic spraying process by bowl, and not by nozzle. particles on the support is not entrained by an air flow as is the case with conventional paint spraying techniques (case of air mix spraying, requiring a spray nozzle) and does not exert significant pressure on the support as is the case when spraying is done in airless Indeed, these two modes of applying a film exert on a fragile and brittle support significant disturbances capable of greatly degrading the support, by releasing a quantity of fibers in the ambient air and thus unbearably accentuating the pollution. Prior confinement of the premises is essential The electrostatic deposition process of a resin film proposed in the present invention is carried out at low pressure by spraying by a rotating bowl at high speed (30 to 50,000 rpm) connected to a generator high voltage electrostatic (100,000 volts for example) This projection creates a cloud of electrically charged particles which is deposited on the fibrous support by electric attraction effect following the field lines defined by the cloud of particles and the support connected to the ground The particles thus sprayed are deposited on the support without exerting any pressure capable of altering its behavior There is therefore no no risk of creating dust during the implementation process, which no longer requires prior containment of the premises

Dust control on site carried out by the INRS made it possible to verify that during projection the level of dust is significantly lower than the initial level of dust before the implementation of the treatment These measurements were carried out first time during a spray treatment of a two-component polyurethane resin without solvent, the "SOUPLETHANE" from Ste KEMICA, and subsequently confirmed during a simulation carried out with water spraying according to the same technique of electrostatic projection During this experiment, the initial level of dust was 0.25 fibers / cm3 During projection, this threshold fell to 0.04 fιbres / cm3i This result was unexpected and surprising indeed, it shows that this projection process not only does not create dust, but on the contrary reduces the initial level of dust, by purifying the contaminated air in a way ine by asbestos fibersi This is explained by an equivalence with the well-known phenomenon of the effect of fog which purifies the air when it falls, all the particles of the atmosphere being carried to the ground by the droplets of water in suspension In the case of our invention, the very fine droplets of resin sprayed by the rotating bowl at high speed, also fix the fibers of the ambient air, and entrain them on the support, on which they remain fixed and glued in the resin after hardening The technique presented in this invention therefore makes it possible to purify and sanitize the ambient air while eliminating the subsequent risks of detachment of fibers from the support.

This inerting process by encapsulating a fibrous support simultaneously strengthens the surface mechanical strength of the support, avoids any subsequent risk of dusting and allows then the cleaning of the support in order to eliminate any accumulation of dust for example The process also allows the treatment of floors, walls and ceilings II also allows the treatment of more or less complex structures such as U irons, I, sheaths and pipes, etc., electrostatic projection allowing the deposition of a continuous and closed film on such surfaces sometimes difficult to access by other methods

In the conventional configurations of the electrostatic spraying process of paints, the paints are sprayed by bursting in a gun nozzle or by bursting by centrifugation of a rotating bowl at high speed (more than 1000 revolutions / min) The movement of particles is controlled by the lines of the electric field created, but often an air flow with adjustable flow is created voluntarily to direct the cloud of particles towards the support This air flow comes from a ring pierced with holes located at the rear of the rotating bowl For the envisaged application of the treatment of fibrous supports with low mechanical strength, it is essential not to disturb the very friable support by turbulence caused by air flows, however weak they are. This is the reason for which we will preferably choose the following configuration of the electrostatic projection equipment

- spraying by rotating bowl or disc (does not require pressure for bursting as for the spray nozzles) - suppression of the air flow accompanying the displacement of the cloud arranged in a ring behind the bowl or the disc To avoid too great dispersion of the cloud of particles, we will opt for the solution consisting in creating behind the bowl an electric counter-electrically charged counter-field of the same sign as the cloud of particles, thus electrically pushing the cloud towards the support This counter-field is carried out in a simple way by fixing behind the spray head a crown made of copper or conductive metal wire of 20 to 40 cm in diameter for example, connected to the head by a wire (fig 1) This crown is at the same potential as the rotating bowl, c - 100,000 volts for example, and is charged with the same sign as the particles. This ring therefore exerts on the cloud an electric field contributing to repel it and direct it towards the support connected to the ground In the case of a support which is insufficiently conductive, it can be treated beforehand to make it conductive by electrostatic spraying of a solution aqueous leaving after drying a thin monomolecular layer of a conductive chemical agent, which is sufficient to ensure the conduction of electrical charges In the case of supports with complex shapes (holes, caves, etc.), the electrostatic deposit effect alone does not will not allow it to penetrate into the hollows or the holes when these are deep, the particles depositing preferentially on the edges In this case, the application of resin is done in several passes The first layer deposited during the first pass having already become insulating after the resin has cured, the resin will be deposited during the second or third passages preferably in the uncoated areas, because they are more conductive, and also the effect of the repellant field created by the copper crown behind the bowl will create a displacement of the particles towards areas difficult to access thanks to to the movement caused by the pushing force of the particles, the effect of attraction of the support being, as for it, more reduced and thus modifying only little the trajectory of the particles pushed by the electric counter-field II is thus possible to deposit the film on areas that are difficult to access The same electric backlighting effect also allows it to be deposited on moderately conductive supports which do not require prior treatment to make the support conductive. However, there are cases where the support is too strongly degraded (shocks having deep holes in the fibrous support) In this case it is possible, after pu spraying the resin in a first thin layer, fix on the resin by gluing a very fine non-woven felt (for example from 10 to 50 g / m ² ) Such a film requires very low pressure to fix it to the support This felt will bridge the damaged area, and will be glued to the edges (fig 2) Once this treatment is done on all degraded areas, we will then apply a thicker resin film over the entire surface. continuous film on the entire support In the case of a generally very degraded support, it is thus possible by this technique to glue a non-woven felt on the entire surface to be protected It is also possible by this principle to confine areas inaccessible, such as the back of the ducts and the ceiling behind these ducts when they are located near the ceiling and are very close to each other (fig 3) In this case, the felt non-woven fabric is bonded to the resin film, ensuring that the non-accessible areas are bridged, thereby confining the non-accessible areas. The process described allows the use of any type of resin or paint that can be sprayed electrostatically. polyurethanes, epoxides, phenolics without solvent in the case where a surface mechanical consolidation of the support is sought Depending on the choice of resin, solvent or not, the function of the projected film may be different Indeed, we preferentially use a resin without solvent when the '' we wish to deposit a waterproof, closed film, vapor barrier, possibly flexible, of great thickness (from 100 microns to 2 mm if necessary) to encapsulate the fibers and inert them In this case of application, it is also possible to spray aggregates (sand, quartz, etc.) on the resin film, which can also be sprayed electrosta which will seal in the resin film by hardening it even more, or by serving as an interface for the subsequent projection of a thick coating intended to mechanically protect the fibrous support or to reinforce its qualities of protection against fire for example

On the contrary, it is also possible to electrostatically spray fluid resins with very low viscosities or solvents onto a fibrous support. These resins in contact with the support. fibrous will rise by capillarity to the heart of the support, which will mechanically consolidate the support in its mass after hardening of the resin It is possible then to project in finish an encapsulation film which will finish stabilizing and neutralizing the support The resins will also be chosen for their fire behavior, and could be for example of the phenolic type, of vmyle acetate. of butyl acrylate, epoxide, etc. It is also possible by the same principle to project other products than polymers such as silicates

In the case where it is necessary both to consolidate the fibrous support by injection into the heart of the support of a resin, and to fix it by encapsulation of the fibers with a resin film it is however preferable to proceed first to the application of a thick solvent-free resin film encapsulating the fibers, and covering the entire surface with a non-woven fabric to give a better surface mechanical strength of the support The fabric will then be pierced at different regularly spaced points (for example all 30 or 50 cm) by which a very fluid resin will be injected which will permeate the core of the flocking or fibrous support This very fluid resin will not run the risk of flowing from the support, even for ceiling applications, since the encapsulation film will ensure waterproofness of the support

It is also possible to spray by the same principle a polyurethane or other resin which during its hardening expands, to form a film with a thickness of 2 to 5 times greater than the thickness of the film deposited. This process is described in patent N ° 98 10415 which presents the principle of the controlled expansion of a resin film and various applications of this principle This expanded resin is also sprayable by electrostatic process, and thus makes it possible to deposit a film of 1 mm before expansion, which after expansion will have a thickness of 2 to 5 mm approx This principle ensures perfect coating of the fibers which disappear embedded in the expanded resin, which allows to remove any uncertainty as to the perfect coating of the fibers which otherwise sometimes remain apparent

In the case where the fibrous support is deposited, it is also necessary to fix the contaminating fibers or particles deposited on the support In such a case, it is sufficient to spray according to the process described a resin film which, by depositing on the support will fix the fibers or the contaminating products, thus making the supports healthy The same treatment is applicable in the event of contamination of the support by harmful or toxic supports (case of contamination of nuclear, chemical, bacteriological, virus, etc. origin)

Claims

1 - Process for cleaning the air in a closed room contaminated by toxic fibers or particles in suspension and fixing toxic fibers or particles on a fibrous support or contaminated with toxic constituents by electrostatic spraying of a liquid resin on said fibrous support friable or contaminated with toxic constituents

5 2 - A method according to claim 1 characterized in that the electrostatic projection is carried out by a projection head by which the resin particles are subjected to a force of attraction towards the support to be impregnated, and to a thrust force created by an electric counter-field produced by a ring of copper or conductive metal located at the back of the projection head and brought to the same electric potential as the head of

T O projection. (Fιg: 1)

3 - Process according to claim 1 characterized in that the sprayed resin is a polyurethane, epoxy, phenolic resin with two components without solvent

4 - Process according to claim 1 and 3 characterized in that the sprayed resin, of polyurethane type or other, is expandable to form after projection a film of 2 to 5 times

15 greater than the initial thickness of the film deposited.

5 - A method according to claim 1 characterized in that when the support is greatly degraded in certain areas or comprises inaccessible areas, it is stripped with a light nonwoven felt all or part of the resin applied, to ensure the confinement of these areas, (fig; 2 and 3) 0

6.- Method according to claims 1 and 3 characterized in that the resin or the impregnated product is of very low viscosity or solvent in order to impregnate the support by capillary rises to harden the support after drying and polymerization. The resin may be of the epoxide, vinyl acetate, butyl acrylate, etc. type, or else the impregnated product may be of the silicate type. 5

7.- A method according to claim 5 characterized in that the resin is of phenolic type for better fire resistance.

8.- Method according to claims 1 and 3 characterized in that it comprises a post-treatment step before polymerization of the resin consisting in projecting onto it an aggregate (sand, quartz,.) Intended to constitute a clean support to ensure a bonding interface 0 between the resin film, and a coating or subsequent flocking

9 - Method according to claims 1, 3 and 4, characterized in that it is injected into the support through the resin film coated with a resin of very low viscosity to impregnate the support

10 - Process according to claim 1 characterized in that the fibers are asbestos fibers, rock wool, glass, aramid, synthetic, cellulose or vegetable origin

11.- Method according to claim 1 characterized in that the support is contaminated with toxic constituents of the radioactive products type, chemical contaminants, toxic bacteria, viruses

AMENDED CLAIMS

[received by the International Bureau on August 17, 1999 (17.08.99); claim 1 as amended; other claims unchanged (1 page)]

1.- Process for cleaning the air in a closed room contaminated with toxic fibers or particles in suspension and fixing toxic fibers or particles on a fibrous support or contaminated with toxic constituents by electrostatic spraying of a liquid resin bicomponent on said friable fibrous support or contaminated with toxic constituents.

2.- Method according to claim 1 characterized in that the electrostatic projection is carried out by a projection head by which the resin particles are subjected to a force of attraction towards the support to be impregnated, and to a thrust force created by an electric counter-field produced by a copper or conductive metal ring located at the rear of the projection head and brought to the same electrical potential as the projection head (fig: 1)

3.- Method according to claim 1 characterized in that the sprayed resin is a polyurethane, epoxy, phenolic resin with two components without solvent.

4.- Method according to claim 1 and 3 characterized in that the sprayed resin, of polyurethane type or other, is expandable to form after projection a film of 2 to 5 times greater than the initial thickness of the film deposited.

5.- Method according to claim 1 characterized in that when the support is severely degraded in certain areas or has inaccessible areas, we start with a light nonwoven felt all or part of the resin applied, to ensure the containment of these areas , (fig; 2 and 3).

6.- Method according to claims 1 and 3 characterized in that the resin or the impregnated product is of very low viscosity or solvent in order to impregnate the support by capillary rises to harden the support after drying and polymerization. The resin may be of the epoxy, vinyl acetate, butyl acrylate, etc. type, or else the impregnated product may be of the silicate type.

8.- Method according to claims 1 and 3 characterized in that it comprises a post-treatment step before polymerization of the resin consisting in projecting onto it an aggregate

(sand, quartz, etc.) intended to constitute a support capable of providing a bonding interface between the resin film, and a coating or subsequent flocking.