EP1124621A1

EP1124621A1 - Gas filtering device

Info

Publication number: EP1124621A1
Application number: EP99947593A
Authority: EP
Inventors: François Simon
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-10-16
Filing date: 1999-10-15
Publication date: 2001-08-22
Also published as: WO2000023173A1; AU6098399A; FR2784607B1; US6627166B1; FR2784607A1

Abstract

The invention concerns in the widest sense of the word a device for filtering gas comprising a microporous or microfibrous adsorbent filter (6) and means for forcing an air flow between an exhaust hood (2) and outlet duct (3) for the filtered air. The invention is characterised in that it comprises liquid spraying means (18) and centrifuging means arranged between the spray means and the filtered gas outlet. The particles wetted by the sprayer are blocked by the internal rotary filter and discharged with the carrier liquid towards an external container (10).

Description

DEVICE FOR GAS FILTRATION

The present invention relates to the field of filtration of gases including air. There are many applications for such devices: vacuum cleaners for household or industrial work, air filtration for industrial or surgical clean rooms, air purification for forced ventilation or air conditioning ...

In the state of the art, the filtration devices essentially consist of mechanical systems comprising at least one microporous filter separating the solid particles from the gaseous medium.

We know the patents DE8905182, GB2279271 GB1356866 which describe conventional filter assemblies using filter washing means for lubrication purposes.

The patent GB1303250 relates to a filtering assembly whose particle capture process is different from the invention. The particles are captured by impact of the particles on rotating fibers. The basis of the process consists in obtaining the greatest possible number of shocks between particles and fibers in rotation. Its effectiveness of the process is a function of the number of shocks, a number which must be optimized. This patent discusses the problems posed by the attachment of particles to filaments and proposes as a solution to give the fibers, charged collect by impact particles, complex curved cylindrical-conical shapes. The method used in this patent has drawbacks, in particular the explosion of the water drops sprayed to wash the fibers. The sprayed liquid is only used to wash the fibers and not to fix particles or dissolve gases. The method according to the invention poses none of the problems of implementation of this patent. Application WO 9741943 relates to a filter made of brushes or a conventional filter washed with a cleaning solution. Liquid is sprayed or not in the gas depending on the degree of dryness of the gas to be treated. It is the degree of dryness of the gas to be treated which determines whether water is sprayed into the gas to be filtered. This spraying is incidental and dependent on conditions.

Application WO97 / 44117 describes a gas purification system which uses a rotating body of complex structure which makes it possible to create a large contact surface between a liquid film and the polluted gas. Spraying serves only to create the contact film between polluted gas and a liquid which is then centrifuged. This process has the limitations of conventional filters with regard to the size of the particles to be captured. Large particles clog it which can be avoided by increasing the section of the tubes but the capture efficiency of small particles is then reduced.

The devices of the prior art use water to wash conventional filters or increase air / gas contact by spreading a liquid film on more or less complex surfaces.

None uses the fixing capacities of the mists, nor the very large contact surface of the spherical droplets of the mists.

Such devices are not entirely satisfactory, for several reasons.

Firstly, this filtration method requires the use of successive increasingly fine filters in order to be able to stop particles of different sizes and these filters must often be supplemented by, for example, electrostatic filters to stop the finest particles.

In addition, the succession of filters obstructs the flow of the treated gas. During use, the more particles have stopped the filters, the more they obstruct the flow of gas to be treated which causes clogging of the filters and requires frequent replacement or cleaning to keep the filtration performance acceptable.

Furthermore, the materials separated from the filtered gas remain pulverulent and inconvenient to handle, which often requires treatment of the dust and waste collected. These separate materials are bulky and quickly fill the device intended to receive them, while clogging it if it is a filter, as may be the case for a household vacuum cleaner.

In addition, these current filters are ill-suited for the filtration of very small particles, or in very low concentration, or for the filtration of gases highly charged with smoke, particles or dust. Finally, these filters do not have the capacity to eliminate undesirable or toxic gases mixed with, for example, air to be purified.

The aim of the present invention is to propose a new solution for filtering gases, including air, overcoming these drawbacks.

To this end, the invention relates in its most general sense to a process and a device for filtering gases using the separation of the liquid and gaseous phases. The gas to be treated is sucked in by suction means such as a propeller which rotates in the opposite direction to the adsorbent mass. An adsorbent mist is added to the incoming flow to be treated by a mist generator. The gas is mixed with the adsorbent mist and travels along a "gas path". The adsorbent / gas mist mixture passes through a rotating adsorbent structure and then the treated gas is discharged through the outlet. The reformed liquid, and what it has fixed, is evacuated, possibly treated and recycled ... The invention uses the adsorption phenomenon which consists of the accumulation of a substance at the interface between two phases (gas / liquid or liquid / liquid for example). It comes from intermolecular attraction forces, of various nature and intensity, which are responsible for the cohesion of the condensed phases, liquid or solid. A molecule attracted unequally by the other molecules of two phases will find an energetically favorable position on the surface of the phase which most attracts it; this will be called the adsorbent. The molecules thus adsorbed constitute the adsorbate. If the energetic or kinetic conditions allow the molecule to penetrate within the adsorbent phase, there is absorption. Absorption is a phenomenon of penetration with fixation of molecules in an absorbent medium.

Each step of the treatment can be done in different ways.

The adsorbent mist is most simply obtained from water. It can also be obtained from liquid fatty substances, solvents, various chemical solutions. The droplet diameters may vary depending on the application.

The type of liquid sprayed can vary as required. A spray of larger drops can be added to the mist, which coalesce the droplets of the water for the first time. The mist generator can be a sprinkler, an ultrasonic system, etc. It is possible to add various chemicals, in particular detergents, amphiphylic substances (hydophyls and lipophyls) to the liquid used to make the mist. Electrical, electrostatic, thermal, light and pressure means can be added at this stage of the process.

A linear gas path is the simplest and may be sufficient.

It is possible to add different elements to the system that optimize its operation. For example, it is possible to add one or more helical windscreen wipers which, when rotated, scrape the wall of the gas path and bring the materials or liquids which may have deposited on the wall of the gas path to the rotary adsorbent structure.

It is possible to increase the distance traveled by the fog-gas mixture, to add different means to promote gas-fog contacts

(fins, baffles ...) and cause turbulence which also favors the fog / gas contact to be treated.

It is possible to increase the pressure in the gas path and at the level of the rotary adsorbent structure by a system of rotary vanes with increasing pitch (then decreasing after passing through the rotary adsorbent structure).

It is possible, during the crossing of the gas path, to reinject fog, a fog different from the first fog; droplets.

The rotary adsorbent structure can be produced according to numerous methods depending on the applications of the process. The simplest structure consists of a more or less thick disc of natural or synthetic microfibers organized in a sufficiently loose network not to slow down too much the gases to be treated and sufficiently dense or thick to completely adsorb the fog and what it has captured or what he set out to do.

Other adsorbent structures can be used such as, for example, blades or rotary fins adsorbent in themselves or covered with adsorbent substances.

Certain materials such as polypropylene can advantageously be used given their capacity for simultaneous adsorption and absorption.

All materials with a high adsorption capacity can be used, such as fibers, or open cell foams, natural or synthetic, certain ceramics having a favorable mass / surface ratio, catalytic ceramics, zeolites, graphite, lamellar halides, aerogels ...

The list is not exhaustive, some applications may require very specifically adapted materials.

In order to facilitate the phenomenon of desorption, it is possible to spray directly onto the rotary adsorbent or to rinse it by injection of liquid in its center and / or to apply to it electrical, electrostatic, thermal, chemical, pressure or depression...

The desorbent liquids can be different from the liquid (s) used to create the adsorbent mist. It is possible to add to the disc-shaped rotary structure one or more peripheral rings of adsorbent materials which may be different from those of the central adsorbent material.

It is also possible to add to it a conventional peripheral filter on which the filtered materials are compacted and through which the reformed liquid passes.

It is possible to add electrical, electrostatic, chemical, thermal ... means to the rotating adsorbent material, as well as to the rings or peripheral filters. It may be advantageous to give the rotary adsorbent material a shape other than simply cylindrical (conical, double conical, concave, convex, etc.).

It is possible to place several rotary structures, identical or different in shape or material, successive in the flow of the gas or gases to be treated and to apply there all the different means described for a single adsorbing rotary structure, gaseous and possible to interpose between these structures all the means (mists, droplets, chemical, electrical, electrostatic means, peripheral rings, periherical filters, evacuation of liquids ...) described for a single adsorbent rotary structure.

For the evacuation of the treated gases, a final treatment can be added by the methods above or any other method.

The liquid effluents can then undergo a simple evacuation of the used liquids, recycling with or without treatment until partial or complete wear. A treatment before reinjection can consist of all the possible modes of treatment of liquids.

In a particular embodiment,

1 invention relates to a device for the filtration of gas comprising a microporous adsorbent filter or adsorbent microfibrous filter and means for forcing a flow of air between a suction mouth and a filtered air outlet mouth characterized in that it comprises means for spraying a liquid and centrifugal means placed between the spraying means and the filtered gas outlet mouth. The particles wetted by the sprayer are blocked by the internal rotary adsorbent filter and ejected with the carrier liquid to an external receptacle. Advantageously, this receptacle can contain a peripheral filter, concentric with the first which blocks said particles. At this point, the particles compact, out of the way of the gas. Filtration is thus carried out outside the air flow and perpendicular to the direction of flow progression. It does not obstruct its circulation and the eliminated detritus remains outside the flow.

This device can advantageously include electrical biasing means applicable upstream of the suction mouth, at the level of the spraying of the liquid and at the level of the centrifugal means.

Such a device makes it possible to remedy the drawbacks of filters of the prior art, by reducing the pressure losses of the gas flow during use and by ensuring an almost constant maintenance of the filtration qualities, whatever the quantity of gas previously filtered.

In addition, this new device allows the simultaneous elimination, in a single pass of the gas to be purified, of very diverse substances such as, for example, a mixture of air carrying toxic gases, fumes, dust, detritus and micro particles carried by air. The sprayed liquid increases the mass of the transported substances or fixes or modifies them and thus makes it possible to centrifuge bodies for which centrifugation alone would have been ineffective or very difficult. Preferably, the centrifugal means comprise a microporous or microfibrous adsorbent filter, hydrophilic or not, electrically conductive or not, of cylindrical shape.

According to a first variant, the device according to the invention comprises means coaxial with the microporous or microfibrous adsorbent filter for the peripheral collection of liquid effluents transporting the substances to be eliminated.

According to a second variant, the device according to the invention comprises front suction means for the suction of the mixture of gas and liquid sprayed by the upstream front face of the filter.

According to a third variant, the device according to the invention comprises peripheral suction means for sucking the mixture of gas and liquid sprayed by the radial face of the filter.

According to a fourth variant, the device according to the invention comprises central suction means for the suction of the mixture of gas and liquid sprayed by an axial surface of the filter.

Depending on the choice of the desired embodiment, the liquid is either put into the form of a mist, the drops of which have a section of between 0.1 and 60 μm and preferably between 0.5 and 6 μm. For certain embodiments, the liquid is sprayed in droplets or in jets of droplets of the order of a millimeter or fractions of a millimeter. For other embodiments, the liquid is sprayed in a thin sheet to best wet the content of the gas to be purified. According to an alternative embodiment, the device further comprises means for recycling the sprayed liquid.

Advantageously, the recycling means comprise pulverulent activated carbon impregnated or not with germicidal substances. According to an implementation variant, the misting liquid contains a fixing or chemical precipitation reagent.

According to another implementation variant, the sprayed liquid contains surfactants or a highly hydrophilic soluble substance (CaCl2 for example).

The filter according to the invention is not a filter in the conventional sense of the term. The classic filter stops and retains particles thanks to its mechanical characteristics (pore diameter, meshes ...), even if it is sometimes washed). The device according to the invention is essentially a mist associated with a fog ejector fixator. The ejector sensor operates by adsorption / local saturation / desorption of fog and does not have the constraints of conventional filters. It is the fog and the "ejector fixer" that filter.

The method and the device according to the invention make it possible to carry out filtering operations by adding to a gas to be treated a liquid phase in the form of a sprayed liquid followed by recovery by adsorption of the liquid phase added in a single passage of a gas to be purified or treated.

The method and the device according to the invention exploit in a simple way the complex physicochemical properties of the mists as well as the physicochemical properties of the water droplets or of other misted liquids. The advantages of liquid microspheres are manifold. Microspheres of liquids do not need a support like the mobile liquid films in the gas flow to be treated and are not linked to a more or less rigid support and can have fluid and very complex paths favoring interactions with the gas to be treated. They offer a very large gas / liquid contact surface and allow the best use to be made of interface, surface and adsorption phenomena.

They also have a very high surface tension which induces surface effects and reactions which the films cannot cause as well as a very high internal pressure, induced by the very high surface tension. The liquid in the droplets is under pressure, which makes it possible to "work" chemically and physically under high pressure conditions without having to put an entire device under pressure. Liquid particles have electrical, electro-chemical and electrostatic properties which very advantageously differentiate them from liquid films or sprays when it comes to fixing micro-particles or even gases.

The transient fixing capacities of the adsorbent materials joined together in structures which are put in rotation are stronger. These structures are made of microfibers or foams or various substances or supports covered with highly adsorbent materials. What is usually called "filter", but which is not the system according to the invention, can for example consist of a very loose network of adsorbent microfibers which does not block anything as do filters. We can thus use zeolites; aerogels or catalysts ...

Centrifugal force can be replaced by other systems, but has the advantage of being easy to use to separate from the temporary fixing mass (microfibers, adsorption ...) the fog and what it has fixed or what to which it is fixed during its mixing with the gas to be treated.

To which, depending on the applications, it is possible to add the spraying of drops or droplets of liquid in the mist gas mixture and / or on the fixing mass in order to obtain a coalescence of the droplets of the mist.

The process does not use liquid films to create a large gas / liquid contact surface (as do the devices of the prior art) but microspheres (mists) which do not need a support for large surface area and complex shape to spread out as best as it is the case as in the patents which use liquid films.

The invention will be better understood on reading the description which follows, referring to the nonlimiting examples described with reference to the appended drawings in which: - Figure 1 shows a sectional view of a first embodiment;

- Figure 2 shows a sectional view of a second embodiment; - Figure 3 shows the block diagram of filtration with a peripheral filter.

FIG. 1 represents a filtration device comprising a housing (1) having a suction mouth (2) on the upstream front face (4) and a filtered air outlet (3) on the opposite front face (5). The device comprises a cylindrical filter (6) driven in rotation by an electric motor. The filter consists of a microporous material, for example a block of agglomerated fibers or a porous solid material. In the suction cone (7) disposed upstream of the filter (6), injection nozzles (18) spray a liquid in the form of micro-droplets having an average diameter of the order of a micron. The misting liquid can consist of pure water or water containing one or more additives such as:

- chemical or biochemical reagents for the fixation of certain molecules;

- solvents;

- antibacterials; - silver iodide for deodorization or sterilization.

The misting liquid can also consist of other liquids such as oils or alcoholic derivatives. Water or misting liquid is sprayed into the incoming air stream. The solid particles are fixed by micro-droplets which are sucked into the rotary filter (6). The rotary filter (6) drives the charged or uncharged droplets towards a peripheral receptacle (8) containing a rotary peripheral filter under the effect of centrifugal force. A discharge pipe (9) drives the liquid effluents to a recovery tank (10). Liquid effluents can optionally be reprocessed and then recycled to be reinjected into the intake chamber (7).

The filtered air is sucked through the filter (6) to the exhaust duct (3). Optionally, an axial duct (11) allows the radial injection, through a perforated axis, of an additional liquid increasing the flow of liquid inside the filter (6).

Figure 2 shows an alternative embodiment.

The device consists of a lenticular housing (1). It includes an axial suction mouth (2) and an axial discharge mouth (3).

The misting liquid is injected into the intake chamber (7) by one or more axial nozzles (13) oriented in the direction of the suction mouth (2). The flow of misted liquid is thus oriented in the opposite direction to the flow of air to be treated, which increases the useful path where collisions take place between the liquid droplets and the particles to be filtered.

The mist thus formed is then sucked through the filter (6) in a radial direction, until an axial discharge by the discharge mouth (3).

The centrifugal force exerted on the liquid droplets, loaded or not with solid particles, drives them against the flow of filtered air inside the filter. This further increases the possibilities of meetings between the particles to be filtered, and the liquid droplets. The liquid effluents are filtered at the periphery, the filtrate is compacted and the effluents then recovered by a peripheral chute (8) to be recycled or disposed of. FIG. 3 represents the basic diagram of filtration with a peripheral filter which can be installed in all the variant embodiments. The apparatus is a conduit with a gas displacement system and a liquid spraying system (21). A mass of finely porous air permeable material fixes the droplets produced by the spray system (21) as well as what they transport, what they have wetted or what they have attached to. This mass of permeable material (24) is rapidly rotating and projects everything that it has temporarily fixed radially.

A rotary filter (22) peripheral to the permeable material (24) retains and compacts the effect of the centrifugal force, the solid materials (23) while letting through the liquid injected by the spraying system (21) and collected temporarily by the permeable material (24). The liquid is then, with or without treatment, returned to the spraying system

(21). Here, therefore, is a machine, one of the major properties of which is that it can accumulate, by compacting it, materials transported by a gas flow, outside the path of the treated gas, therefore without interfering with the passage thereof. The path of the treated gas remains in its initial state without any clogging until the filter is completely filled (22)

The material, shape, surface and surface shape of the peripheral filter (22) take account of the following unusual facts:

- the materials to be filtered are wetted and subjected to high pressure due to the centrifugal force; due to the packing due to the wetting effect and to that of the centrifugal force, the peripheral filter (22) must collect and keep a quantity of material much less bulky (important advantage) but much more important than do the filters classics.

The texture, shape, pore size and thickness of the rotary peripheral filter (22) are variable, adapted and optimized for each use. It is possible to apply the electrical, electrostatic or electrochemical phenomena mentioned elsewhere in this text. For example, a simple sheet of conventional laboratory filter paper makes it possible to collect household dust very well, which is transformed into a kind of felt whose handling poses no problem.

The invention is described by way of nonlimiting example. Many alternative embodiments can be envisaged, in particular as regards the structure of the rotary filter, the drive mechanisms, the structure of the intake chamber, and the misting means, as well as the electrical polarization and the use. an electric or electrostatic polarization of the mists, the relative filters and the incoming flows. The addition of a new phase in a gas / particle mixture makes it very simply separable from the phases which are usually difficult to dissociate.

It becomes possible, in a single pass to extract from a polluted gas detritus (paper), dust, microparticles, vapors and gases, toxic or not, odors .... There are no more filter clogging problem. In addition, the separate parts of the carrier gas to be treated can be compacted, dissolved, precipitated, which facilitates their handling.

Claims

1 - Device for gas filtration comprising means for forcing an air flow between a suction mouth and a filtered gas outlet mouth characterized in that it comprises means for spraying a liquid and means centrifuges placed between the spraying means and the filtered gas outlet mouth. 2 - Device for the filtration of gas according to claim 1 characterized in that it comprises means of adsorption placed between the centrifugal means and the spraying means.

3 - Device for gas filtration according to claim 1 or 2 characterized in that the centrifugal means comprise a cylindrical filter.

4 - Device for gas filtration according to claim 3 characterized in that the centrifugal means comprise a microporous filter of cylindrical shape.

5 - Device for gas filtration according to claim 3 characterized in that the centrifugal means comprise a microfibrous filter of cylindrical shape. 6 - Device for gas filtration according to claim 4 or 5 characterized in that it comprises means coaxial with the filter for the peripheral collection of liquid effluents.

7 - Device for gas filtration according to claim 4 or 5 characterized in that it comprises front suction means for the suction of gas vaporized by the upstream front face of the filter.

8 - Device for gas filtration according to claim 4 or 5 characterized in that it comprises peripheral suction means for the suction of the gas sprayed by the radial face of the filter.

9 - Device for gas filtration according to claim 4 or 5 characterized in that it comprises central suction means for the suction of the sprayed gas by an axial surface of the filter.

10 - Device for the filtration of gas according to any one of the preceding claims, characterized in that the sprayer forms drops having a section between 0.5 and 6 μm.

11 - Device for the filtration of gas according to any one of the preceding claims, characterized in that it comprises electrical polarization means applicable upstream of the suction mouth, at the level of the spraying of the liquid and at the level of the means centrifugal.

12 - Device for the filtration of gas according to any one of the preceding claims, characterized in that it comprises means for recycling the spraying liquid.

13 - Device for gas filtration according to claim 12 characterized in that the recycling means comprise pulverulent activated carbon.

14 - Device for filtration according to any one of the preceding claims, characterized in that the spraying liquid contains a fixing reagent.

15 - Device for gas filtration according to any one of the preceding claims, characterized in that it comprises an additional peripheral filter.