WO2022128712A1

WO2022128712A1 - Method for treating air from a confined space in a bubble column

Info

Publication number: WO2022128712A1
Application number: PCT/EP2021/084888
Authority: WO
Inventors: Pascal Alix; Bastien DAUTRICHE; Pedro MAXIMIANO RAIMUNDO
Original assignee: IFP Energies Nouvelles
Priority date: 2020-12-18
Filing date: 2021-12-09
Publication date: 2022-06-23
Also published as: FR3117885B1; EP4263025A1; JP2023554246A; KR20230123487A; FR3117885A1

Abstract

The present invention relates to the use of a bubble column for the treatment of air contained in and/or entering and/or leaving a confined space in order to deplete said air of polluting gaseous compounds, especially NOx, SOx and/or VOC, and solid particles. The bubble column (100) comprises an enclosure, preferably cylindrical, with a ratio H/D ≦ 1.5 (H: height, D: diameter), filled with liquid capable of capturing said particles and polluting gaseous compounds. The air is injected into the liquid at the bottom of the enclosure (1) so as to form bubbles, and at a flow rate such that the operating gas surface velocity Ug is 0.35 to 0.50 m/s. The air in the form of bubbles is thus treated by contact with the liquid such that at least a portion of the particles and/or the at least one polluting gaseous compound is collected by the liquid, and the treated air is discharged at the top of the enclosure.

Description

METHOD FOR AIR TREATMENT IN A CONFINED SPACE IN A COLUMN

WITH BUBBLES

Technical area

The present invention relates to the field of air treatment in confined spaces, whether closed or semi-closed, in particular the elimination of pollutants in the form of particles and / or gaseous compounds in the air contained and / or entering and/or leaving such spaces, by means of bubble columns.

General background and prior art

The air in confined environments, in particular semi-enclosed such as railway tunnels, road tunnels or car parks, is generally much more polluted than the air outside.

These confined spaces can be frequented by a transient population, users, and/or by a more or less permanent population, such as operating personnel or shopkeepers.

These confined spaces can be underground transport networks of the rail type. The acronym EFS defines all the covered spaces located below ground level, connected to an underground rail transport route where workers work. This definition therefore concerns all spaces where people work on a regular basis, including stations, corridors, trains, tunnels, commercial premises, technical rooms and train repair centres. In France, seven cities have EFS networks, in other words “metros”.

It can also be parking lots for covered and underground vehicles, or even road tunnels.

In these different scenarios, ventilation and extraction and/or air blowing systems can be used, the purpose of which is to make the air present in these confined places more breathable, by renewing it with new the "fresh" air blown in taken from outside and/or by extraction and rejection outside of stale air. In some cases, polluted air is depolluted in so-called “bypass” installations, the air being extracted, depolluted, then reinjected into the tunnel.

However, these systems are often insufficient to guarantee correct air quality in these confined places. In some cases, in particular covered/underground car parks, urban outside air is drawn off to renew the air. However, urban air can already present a significant level of pollution, particularly in terms of fine particles, and polluting gaseous compounds such as nitrogen oxides NOx, or other polluting compounds such as volatile organic compounds (or VOC for the English acronym Volatile Organic Compound), or sulfur derivatives, such as sulfur oxides SOx, in particular due to automobile traffic, district heating, or nearby industrial activities. For confined spaces such as road tunnels or car parks, the air is loaded with particles and polluting gases due to underground road traffic. For EFS-type rail networks, the pollution is essentially particulate, it comes from the braking phases but also from friction with the tracks and the pantograph. In all cases, this polluted air is extracted in order to reject it outside, thus polluting the outside atmosphere close to these confined spaces.

Whether the pollutants are emitted in the confined spaces mentioned above, or reintroduced from the outside, we see that they can be classified into two categories:

- solid particles can come from imperfect combustion (soot), wear of tires, vehicle braking components, degradation of road surfaces or rails, etc. Their small size, of the order of a few microns, explains their maintenance in suspension in the air. For underground railway enclosures (EFS), the major constituents identified are different metals including iron, elemental carbon and organic carbon. It is also possible to add terrigenous dust, in particular composed of silica. Particles are commonly classified according to their size, in particular according to the diameter that a sphere of equivalent aerodynamic behavior would have. Thus, reference is traditionally made in the context of air pollution to two types of particles, subject to regulation because of their effects on health: particles of the PM10 type (PM for "Particulate Matter » in English), i.e. whose size is less than 10 pm, and PM2.5 type particles, i.e. whose size is less than 2.5 pm. The so-called “fine” particles are particles of the PM2.5 type, and also include smaller particles classified as PMI (submicron particles) or PM0.1 (ultrafine particles or nanoparticles).

- gaseous compounds, in particular nitrogen oxides, NOx including monoxide and/or nitrogen dioxide (NO, NO2), but also carbon monoxide CO, sulfur compounds such as SOx, and VOCs (to note that NO can spontaneously oxidize to NO2 under the effect of sunlight and the presence of oxygen, so even if it is potentially less harmful than NO2 at equal concentrations, it is also potentially a precursor of NO2) .

In the confined spaces mentioned above, the recommended air quality thresholds are regularly exceeded, particularly with regard to fine particles or NOx.

It is becoming increasingly urgent to reduce these levels of pollutants, whether by attacking the source of the pollution or by treating the air in these environments. The present invention aims to respond to this general problem of reducing the pollutants of the air contained in and/or arriving in and/or extracted from these confined spaces, in order to improve their quality, by means of an air treatment technique.

Generally, the treatment of the air in these confined spaces is carried out by means of filters with physical barriers, electrostatic filters, or even by the use of activated carbons acting as adsorbents.

Physical filters have the disadvantage of generating a high pressure drop, which translates into a high operating cost, and also present risks of clogging which require the intervention of operators and therefore significant maintenance.

The same problem arises for electrostatic filters, with moreover complex handling (interventions in the presence of high voltage) which generates significant costs and operational stoppages.

Furthermore, in the field of the treatment of industrial gaseous discharges, the use of gas/liquid contacting devices such as plate columns, packed columns, spray columns, venturi washing chambers, which make it possible to "wash" a gas to rid it of various pollutants. Some of these devices can be used for the treatment of air in confined spaces. For example, application WO2019/192827 discloses a process for treating confined air aimed at eliminating polluting gaseous compounds such as NOx and solid particles, using a packed column to wash the air in contact with a liquid. containing an absorbent compound such as potassium hydroxide (KOH).

However, the use of columns comprising internals, whether packing as in application WO2019/192827, or trays, although generally requiring less maintenance than the use of filtration systems, is an expensive solution in terms of investment and operation, in particular because to treat the same air flow, it is necessary to implement appropriate gas and liquid circulation means (pumps, compressors), and because a liquid storage tank is required. Moreover, these columns as well as the internals themselves are expensive, and require rigorous dimensioning, which can limit the flexibility of the use of the column with regard to the flow rates treated.

Air purification can also be carried out in devices based on the principle of operation of bubble columns, where the gas is injected at the base of a tank filled with water so as to generate bubbles which rise in the tank. , thus allowing a transfer of matter between liquid and gas. Bubble columns are types of gas/liquid reactors widely used in process engineering, in particular as aerobic fermenters in the biological industry, in petrochemicals or for water treatment. In the context of air purification, patent application CN105289161A describes an air purifier comprising a cuboid-shaped water tank into which air containing dust is injected by means of a compressor at the bottom from the reservoir and rises as bubbles in the reservoir, which further comprises a porous partition plate for dividing the rising large bubbles into finer bubbles, so as to increase the efficiency of removing particles from the air by contact with water. Another example of an atmospheric air purifier of this type is described in patent KR100529857. The purifier comprises a cylindrical chamber arranged vertically, partly filled with an aqueous solution, at the base of which the air to be purified is injected through a plurality of nozzles so as to form bubbles. The enclosure comprises a grid used to divide the bubbles rising in the column, as well as a stirrer forming a vortex in the aqueous solution, and an aqueous solution spraying system arranged between the gas outlet at the top of the column and the gas/liquid interface in the column. This system is complex and expensive, in particular because it requires a compressor to generate the bubbles, a motor to rotate the agitator and a pump for the liquid sprinkling system.

Objects and Summary of the Invention

The object of the present invention is to overcome at least in part the problems of the prior art mentioned above, and generally aims to provide a method and a device for treating the air contained/arriving in and/or extracted from a confined space, typically an EFS network, a covered/underground vehicle parking lot or a road tunnel, so as to deplete this air of polluting gaseous compounds, such as NOx, SOx, VOCs, and of solid particles.

More particularly, the present invention aims to provide such a method and device which makes it possible to achieve at least one of the following objectives: avoid resorting to moving mechanical parts,

- present a relatively low cost of installation and operation and/or reduced maintenance compared to the technologies of mechanical, electrostatic filtration, washing by gas/liquid contacting columns comprising plates or packings, minimize the size of the air treatment device so that it is suitable for a confined environment with very limited available space, - allow the treatment of large air flows, typically ranging from a few thousand to a few tens, or even hundreds, of thousands of m ³ /h.

Thus, to achieve at least one of the aforementioned objectives, among others, the present invention proposes, according to a first aspect, a process for treating air contained in and/or entering into and/or leaving out of a confined space to deplete it in at least one polluting gaseous compound, in particular in NOx, SOx and/or VOC, and in solid particles, implementing a bubble column comprising an enclosure with an H/D ratio < 1.5 filled with a liquid capable of capturing said polluting particles and gaseous compounds, H and D being respectively the height and the diameter of said enclosure, in which:

- air is injected into the liquid at the bottom of the enclosure so as to form bubbles, and at a rate such that the superficial operating gas velocity Ug is between 0.35 m/s and 0.50 m/ s,

- the air injected is treated in the form of bubbles by contact with the liquid so that at least part of the particles and/or of the polluting gaseous compound(s) is captured by the liquid, and

- the treated air is evacuated at the top of the enclosure.

According to one or more embodiments of the invention, the superficial operational gas velocity Ug is between 0.40 m/s and 0.50 m/s.

Advantageously, the only driving force behind the upward air flow in the form of bubbles results from buoyancy.

According to one or more implementations of the invention, the liquid is an aqueous solution, and preferably consists of water.

According to one or more implementations of the invention, the liquid is an aqueous solution comprising at least one absorbent compound with respect to said at least one gaseous polluting compound, and/or comprises a solubility promoter of said at least one compound polluting gas.

According to one or more embodiments of the invention, the liquid is renewed in the enclosure, preferably discontinuously.

According to one or more embodiments of the invention, the bubble column is operated at ambient temperature and pressure. According to one or more implementations of the invention, a peripheral zone for settling and concentration of particles is created in the enclosure between said enclosure and a tube arranged in and centered in said enclosure, the liquid having an overall downward movement in said peripheral zone.

According to one or more implementations of the invention, liquid comprising particles and/or polluting components is withdrawn from said peripheral zone by means of at least one liquid evacuation pipe opening on the side wall of the said enclosure, preferably in the upper half of said enclosure.

According to one or more implementations of the invention, the enclosure of the column is cylindrical.

According to a second aspect, the present invention relates to a column for carrying out the method according to the invention for treating the air contained in and/or entering and/or leaving outside a confined space in order to deplete it of compounds gaseous pollutants, in particular in NOx, SOx and/or VOC, and in solid particles, configured to operate at a superficial operating gas velocity Ug is between 0.35 m/s and 0.50 m/s, the bubble column comprising:

- an enclosure, preferably cylindrical, with a ratio H/D < 1.5, H and D being respectively the height and the diameter of the enclosure, configured to be filled with a liquid capable of capturing said polluting particles and gaseous compounds,

- an air inlet pipe,

- means for dispersing said air within the liquid, connected to the air inlet pipe and arranged in the bottom of the enclosure,

- a treated air outlet pipe arranged at the top of the enclosure,

- a liquid supply line opening at the top of the enclosure, and

- At least one conduit for discharging the liquid from the enclosure.

According to one or more embodiments of the invention, the column comprises a liquid renewal and purge circuit.

According to one or more embodiments of the invention, the column further comprises an inner tube disposed in and centered in the enclosure, dividing the enclosure vertically into a peripheral zone for settling and concentrating particles formed between the enclosure and the tube, and in a central zone formed inside the tube. According to one or more embodiments of the invention, said at least one liquid discharge pipe opens on the side wall of the enclosure, preferably in the upper half of the enclosure.

According to a third aspect, the present invention relates to an installation for treating the air contained in and/or entering into and/or leaving outside a confined space in order to deplete it of polluting gaseous compounds, in particular of NOx, SOx and / or VOC, and in solid particles, comprising several bubble columns according to the invention, configured to operate in parallel.

Other objects and advantages of the invention will appear on reading the following description of examples of particular embodiments of the invention, given by way of non-limiting examples, the description being made with reference to the appended figures described below. -after.

List of Figures

Figure 1 is a block diagram of the bubble column and its operation for the treatment of air according to the invention.

Figure 2 is a diagram of a bubble column according to a first embodiment of the invention.

Figure 3 is a diagram of a bubble column according to a second embodiment of the invention.

Figure 4 is a diagram of a bubble column according to a third embodiment of the invention.

In the figures, the same references designate identical or similar elements.

Description of embodiments

The object of the invention is to propose a particular bubble column and a specific method implementing it for the treatment of the air contained in and/or entering and/or leaving outside a confined space in order to deplete it. into at least one polluting gaseous compound, in particular NOx, SOx and/or VOC, and into solid particles.

By confined space, we mean a closed or semi-closed space, and preferably a semi-closed space such as a railway tunnel, a road tunnel, a car park, or an EFS network (all covered spaces located below ground level , connected to an underground rail transport track where workers work, including stations, corridors, trains, tunnels, commercial premises, technical rooms and breakdown centers for trains meeting this definition). The air to be treated, contained and/or entering and/or leaving outside a confined space, contains solid particles and/or at least one polluting gaseous compound, such as NOx, SOx, VOC, NH3, and in especially NOx.

FIG. 1 schematically illustrates a bubble column and its operation for the treatment of air according to the invention.

Embodiments of the method and the bubble column are described below in detail. Many specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the method and the bubble column can be implemented without all these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

In the present description, the term "include" is synonymous with (means the same thing as) "include" and "contain", and is inclusive or open and does not exclude other elements which would not be mentioned. It is understood that the term “include” includes the exclusive and closed term “consist”.

Furthermore, in the present description, the terms "essentially" or "substantially" correspond to an approximation of ±5%, preferably ±1%. For example, an element covering substantially an entire surface corresponds to an element covering at least 95% of said surface.

In the present description, cylindrical refers to a cylinder of revolution.

In the remainder of the description and in the claims, the positions (“bottom”, “top”, “above”, “below”, “horizontal”, “vertical”, “lower half”, etc.) of the various elements are defined with respect to the column in the operating position.

The bubble column 100 according to the invention comprises an enclosure 1, of height H and of diameter D, configured to be filled with a liquid capable of capturing the polluting particles and/or gaseous compounds of a polluted air Ap to be treated.

The bubble column 100 comprises:

- an inlet pipe 2 for the air to be treated Ap,

- means for dispersing the air within the liquid contained in the said enclosure, connected to the air inlet pipe 2 and arranged in the bottom of the enclosure 1,

- an outlet pipe 6 for the treated air At arranged at the top of the enclosure 1, - a liquid supply line 4 opening out at the top of enclosure 1, and

- at least one liquid discharge pipe 5 from the enclosure 1.

The air to be treated Ap is advantageously introduced using a blower 17, or any other aeraulic means such as a compressor or a fan, into the enclosure 1 of the column 100 via the arrival duct of air 2. The air flow injected is such that the superficial operational gas velocity Ug (superficial gas velocity when the column is in operation) is between 0.35 m/s and 0.50 m/s, and l The air is injected so as to form bubbles within the liquid at the bottom of the enclosure 1 by means of gas dispersion means (not shown in FIG. 1) connected to the air inlet pipe 2. The The air injected in the form of bubbles is then treated by contact with the liquid so that at least some of the particles and/or of the polluting gaseous compound(s) is captured by the liquid. The air thus treated At is evacuated at the top of enclosure 1.

According to a preferred embodiment, the enclosure 1 is cylindrical. In the case of a cylindrical enclosure, the diameter D is the diameter of the cylinder. Such a geometry makes it possible in particular to limit the presence of “dead” volumes in the column.

The enclosure 1 of the column can also be parallelepiped, typically a rectangular parallelepiped or a cube, which can be advantageous in certain cases to optimize the grip on the ground and facilitate the installation of the column in built spaces. In the case of a parallelepipedic enclosure, in particular a rectangular parallelepiped or a cube, the diameter D must be understood as an equivalent diameter, defined as being the diameter of the circle inscribed in the section (horizontal cross section) of the pregnant.

The enclosure 1 of the column 100 is preferably filled with the liquid over substantially its entire height, with the exception of an area at the top of the enclosure known as the gas disengagement area, where the air dissociates from the continuous phase, i.e. the liquid. The air/liquid interface, marking the start of the disengagement zone, is generally located in the upper half of the enclosure, preferably in the upper third or even the upper quarter of the enclosure.

The liquid is preferably an aqueous solution. The liquid may consist of water. Contact between water and polluted air allows certain gaseous polluting compounds and particles to be picked up by the water.

According to other embodiments, the liquid can be an aqueous solution comprising at least one chemically active absorbent compound with respect to one or more polluting gaseous compounds, that is to say a compound allowing absorption of the polluting compound by chemical reaction with said polluting compound present in the air to be treated, and/or comprises a solubility promoter for one or more polluting gaseous compounds, that is to say a compound which increases the solubility of the polluting compound without a direct chemical reaction with said compound polluting.

As is known from the general operation of a bubble column, and as it applies to the present invention, the two-phase flows in the bubble column are driven by gravity, without an overriding external force (such as a stirrer, an external pressure gradient, bubbling flow heat transfers, etc.) so that the sole driver of the upward gas flow as bubbles results from buoyancy. The air, dispersed in bubbles, has a mainly upward movement. The column is preferably operated in a discontinuous manner (“batch” operation according to Anglo-Saxon terminology): even if liquid is added or withdrawn from the enclosure of the column, as described later, the flow rate of liquid remains very low compared to the air flow injected at the bottom of the column. There is an accumulation of pollutants in the liquid, which can be purged punctually. On the one hand, the bubbles communicate momentum to the liquid and impose their dynamics on it. On the other hand, the movement of the air inclusions remains constrained by the inertia of the liquid phase which also serves as an intermediary for the interactions between inclusions. Such a dynamic equilibrium between phases involves non-trivial processes of momentum exchange between gas and liquid but also of production/dissipation of turbulence: this dynamic equilibrium gives rise to complex flow structures. Thus, in the bubble column, an average recirculation is set up on the scale of the column, with an ascending liquid flow in the center and descending on the periphery, on which are superimposed secondary circulations qualified as “chaotic”. It is in particular the presence of these circulations, at different scales, which ensure a very good level of mass transfer between the gas and the liquid and a good homogeneity of the concentrations in the liquid phase, ensuring the conditions necessary to be able to capture the particles. suspended in the air injected in the form of bubbles, and the transfer of gaseous polluting compounds from the air to the liquid. This transfer is therefore obtained without recourse to moving parts (so-called mechanical agitation defined as caused by the physical movement of one or more rigid or flexible elements in the column as opposed to the agitation linked to buoyancy alone), which is results in low installation and operating cost, as well as low column maintenance.

An advantage of the present invention lies in the implementation of a bubble column for the treatment of polluted air contained in and/or entering and/or leaving a confined space, which has particular dimensions, ie a very low H/D ratio, more specifically less than or equal to 1.5, and based on the operation of a high superficial gas velocity Ug in the bubble column, ie between 0.35 m/s and 0.50 m/s. According to the invention, the enclosure 1 of the bubble column 100 has an H/D ratio less than or equal to 1.5, or even less than or equal to 1. A minimum height is necessary to allow sufficient contact time between the gas to be treated and the liquid so that the latter becomes charged with particles and/or gaseous polluting compounds. Thus, the bubble column according to the invention has an H/D ratio preferably greater than or equal to 0.5.

Such a geometry of the column makes it possible in particular to minimize the pressure drop while maintaining a useful volume sufficient to carry out a good transfer of material, thus contributing to minimizing the operating costs while ensuring good air treatment efficiency. Such an H/D ratio also makes it possible to limit the size of the column, in particular by minimizing the height of the column, which allows installation of the column in spaces constrained in height such as the confined spaces mentioned above.

According to the invention, the operational superficial gas velocity Ug is between 0.35 m/s and 0.50 m/s, and preferably between 0.40 m/s and 0.50 m/s, for example equal to 0.40 m/s. Such a speed Ug makes it possible in particular to reduce the size of the column by allowing a reduced passage section adapted to reach the values of Ug mentioned which minimizes the occupation of the floor of the column. Such a speed Ug also makes it possible to generate strong transfers of material on the liquid side favorable to the capture of particulate and gaseous pollutants.

Thus, such a superficial operational gas velocity in association with the specific H/D ratio of the enclosure of the column makes it possible to provide a compact polluted air treatment installation, in accordance with the space constraints of confined environments such as than described, being able to treat large flows of air to be depolluted, eg a few thousand to a few tens of thousands, or even hundreds of thousands of m ³ /h, which are essential aspects to have good air treatment efficiency at the global scale.

When the liquid is too loaded with particles or it no longer absorbs the gaseous compounds targeted, it can be completely drained and replaced by a simple pumping operation.

It is also possible to carry out a renewal, preferably discontinuous, or alternatively continuous, of the liquid by means of a circuit for renewing and purging the liquid.

The column can thus advantageously comprise a liquid renewal and purge circuit comprising the liquid supply pipe 4 and the liquid evacuation pipe or pipes 5, a hydraulic pump 16 connecting the liquid evacuation pipe or pipes 5 to the liquid supply pipe 4, a fresh liquid inlet pipe 11 connected to the liquid evacuation pipes 5, a purge pipe 12 connected to the pump 16 to evacuate the liquid from the liquid renewal circuit, liquid flow control means making it possible in operation to supply the enclosure with liquid via fresh liquid inlet line 11, pump 16 and liquid supply line 4, or to bleed liquid via liquid discharge line(s) 5, pump 16 and bleed line 12. The liquid renewal and purge circuit may also include means for purifying the liquid to rid it, at least in part, of the polluting particles and/or compounds that it contains (not shown in FIG. 1).

The hydraulic pump 16 can advantageously be a low-power pump, typically with a power of between 1 kW and 3 kW, adapted to the low flow rate of renewed liquid which may be required by the bubble column in operation.

Preferably, the liquid flow control means comprise at least one valve 13 arranged on the fresh liquid inlet pipe 11, a valve 14 on the liquid supply pipe 4 and a valve 15 on the purge pipe. 12.

The liquid is preferably renewed in the enclosure 1 discontinuously. The renewal of liquid can also be done continuously, e.g. there is always liquid leaving the enclosure of the column and liquid entering the enclosure, the flow rate of liquid withdrawn from the column equivalent to the flow rate liquid entering the column. In this case, this renewed liquid flow rate can be between 0.1% vol. and 0.4% vol. the injected air flow.

The renewed liquid can comprise liquid withdrawn from the column and purified by any means known to those skilled in the art. The renewed liquid can also include “fresh” liquid, i.e. not loaded with initially gaseous polluting particles and compounds, coming from outside and never having stayed in the column. Topping up with fresh liquid makes it possible in particular to compensate for liquid losses.

During the renewal and draining of liquid, part of the liquid can be drawn off via the liquid evacuation pipe(s) 5, by means of the pump 16, the valves 13 and 14 being closed and the valve 15 being open to the evacuation of said part of the liquid through the purge line 12. Fresh liquid can then be supplied by the fresh liquid inlet pipe 11, and routed, via the pump 16, to the top of the enclosure 1 by the liquid supply line 4, valves 13 and 14 then being open and valve 15 closed. Advantageously, the liquid is renewed in the enclosure 1 so that the concentration of particles and/or of polluting compounds in the liquid and/or in the treated gas, and/or the pH of the liquid respects a given threshold or a range of given values. For example, the liquid is renewed in the enclosure so that the concentration either of particles or of gaseous polluting compounds or both, in the treated air or in the liquid inside the enclosure 1 is less than one given threshold, in order to guarantee a good level of air treatment performance. Liquid pH monitoring can also be used to trigger liquid renewal in enclosure 1.

The column can indeed be advantageously equipped with on-line analyzers allowing the monitoring of the treatment of the air in the column and the preventive maintenance of the column, for example by emptying and replacing the entire volume of liquid in the column. or by partial renewal and purging of liquid, for example by pH control.

The column can thus comprise at least one sensor for the concentration of particles and/or polluting compounds present in the liquid or in the treated gas and/or a system for measuring the pH of the liquid, and automatic means for controlling the renewal of liquid configured so that said concentration and/or said pH respects a given threshold (either below or above a given threshold) or a given range of values. The automatic liquid renewal control means can act on the piloting of the liquid flow control means, in particular the valves described above of the liquid renewal and purge circuit.

The liquid renewal and purge circuit can be used to occasionally empty and fill the total volume of liquid in the enclosure.

The bubble column can be equipped with other measuring and monitoring devices. For example, the correct operation of the pump 16 can be monitored by means of cameras, and the valves fitted to the liquid renewal and purge circuit can be controlled.

The control means can control and monitor the bubble column and display the relevant information (alarms, monitoring of measurements by the instruments, video image, etc.) on a remote HMI man-machine interface. The connections between the instrumentation, the controllable elements, the control unit and the HMI are made in known manner, for example by a local Internet network, using optical fibers, modular connectors for RJ45 type Ethernet connection ( with the possible addition of a switch/LAN as close as possible to the bubble column).

It is possible to provide close to the bubble column a reservoir of fresh liquid intended to completely replace the liquid in the enclosure or to gradually renew it. We can also predict a reservoir for the purged or drained liquid, possibly configured to allow sufficient settling time to more easily collect the particles at the bottom of the reservoir. Any gaseous polluting species still present in the purged or drained liquid can be treated on site or subsequently, after emptying the tank once full, and recovery of the liquid phase. All the appropriate fluidic connections are provided (pipes equipped with valves) to easily ensure the purging and the filling of liquid from or towards the enclosure of the bubble column.

Advantageously, the bubble column is operated at ambient temperature and pressure. The ambient temperature varies according to the given environment, and temperatures ranging from 0°C to 40°C can be encountered as an indication. The ambient pressure is substantially atmospheric pressure, e.g. the operating pressure is preferably between 0.1 MPa and 0.12 MPa absolute. The operation of the column at ambient temperature and pressure is a considerable advantage in view of the layout and the air flow rates to be treated, as this greatly simplifies the implementation of the process and the installation, since this limits the equipment (no heating or pressurizing means required) and the energy consumption of the treatment.

To give dimensional orders of magnitude, enclosure 1 may have a diameter D of between 1 and 5 m, preferably between 1 and 3 m, for example a diameter of 1.5 m.

To give orders of magnitude of process parameters, one can take the example of an air flow to be treated having a flow rate of between 1000 m ³ /h and 300,000 m ³ /h, for example 10,000 m ³ /h. The air is at 20°C and the pressure is ambient pressure which is atmospheric pressure (0.1013 MPa). To absorb almost all of the NO ₂ and particles, an operational superficial gas velocity of 0.40 m/s is provided.

FIG. 2 illustrates a bubble column 200 according to a first embodiment of the invention, configured and operating as described in relation to FIG. 1. The numerical references in FIG. 2 designate the elements with the same reference described above in compared with Figure 1. Although the entire renewal and liquid circuit is not shown, the latter operates and is configured as previously described. The means for dispersing the air within the liquid at the bottom of the enclosure 1 are represented schematically under the reference 3. The means for dispersing the gas make it possible to form bubbles 7 in the liquid, and can be chosen from a pipe , a network of pipes, a multitubular distributor, a perforated plate, a combination of these elements, or any other means known to those skilled in the art. For example, the gas dispersion means comprise, and preferably consist of, a network of tubes, for example provided with orifices and/or sparger slots.

Preferably, the gas dispersion means 3 cover substantially the entire section of the enclosure.

FIG. 3 illustrates a bubble column 300 according to a second embodiment of the invention, in all respects identical to the bubble column of FIG. 2, with the exception of the fact that it additionally comprises an internal tube 8 placed in and centered in the enclosure 1. The tube 8 thus divides the enclosure 1 into a peripheral zone 18 for settling and concentration of particles formed between the enclosure and the tube 8, more precisely between the side wall of the enclosure and the wall of the tube which is arranged vertically in the enclosure, and in a central zone 19 formed inside the tube 8.

The tube 8 is for example a metal tube. It is advantageously arranged vertically in the enclosure 1, just above the air dispersion means 3 that it circumscribes. It preferably extends over a height less than the height of the liquid/gas interface in the enclosure, so as to allow the passage of the liquid towards the peripheral zone 18 and the flow of the liquid descending into said zone 18.

Preferably the tube 8 has a height h of between 50% and 80% of the height of the enclosure H.

The tube can be fixed to the walls of the enclosure, for example the side, top or bottom wall of the enclosure 1, by any means known to those skilled in the art.

While in the peripheral zone 18 the liquid has an overall downward movement, the liquid has an overall upward movement in the central part of the enclosure 1, inside the tube 8.

This second embodiment, in which the zone where the liquid rises, i.e. the central zone 19, is separated from the peripheral zone 18 where the liquid descends, allows decantation and a concentration of the particles located in the peripheral zone, in direct link with the bottom of the enclosure where the liquid discharge pipe 5 is located and thus increases the efficiency of extraction of these particles.

Preferably, the tube 8 is a cylindrical tube, arranged in and concentrically to the enclosure 1, itself preferably cylindrical. The peripheral zone 18 thus created between the enclosure 1 and the cylindrical tube 8, more precisely between the side wall of the cylindrical enclosure 1 and the wall of the cylindrical tube 8 which is arranged vertically in the enclosure, is an annular zone, where the particles settle and concentrate.

According to another embodiment, the tube 8 can be of rectangular or square section. FIG. 4 illustrates a bubble column 400 according to a third embodiment of the invention, in all respects identical to the bubble column of FIG. 3, with the exception of the fact that the liquid outlet is carried out at the level of the side wall of the enclosure 1, in the peripheral zone 18.

Liquid containing particles and/or polluting components is thus withdrawn from the peripheral zone 18 by means of at least one liquid discharge pipe 9 opening on the side wall of the enclosure 1, preferably in the upper half of the enclosure 1 in order in particular to avoid the extraction of the liquid laden with particles near the bottom of the enclosure or turbulence generated by the arrival of gas can for example re-entrain the particles in the central zone 19 of the enclosure.

For example, the column represented in FIG. 4 comprises two diametrically opposed liquid discharge pipes 9 and opening onto the wall of the enclosure 1 in its upper half.

Advantageously, the bubble column according to the invention does not include internals, that is to say fixed or moving parts, participating in the agitation (work dissipated in the medium) responsible for the flows of liquid and air in the enclosure. Thus, the column according to the invention and its operation are simple and economical in terms of investment and operation.

According to the invention, several bubble columns as described above, according to the different embodiments, can be combined and configured to operate in parallel and form an installation for treating the air contained in and/or entering and /or leaving a confined space to deplete it of polluting gaseous compounds, in particular of NOx, SOx and/or VOC, and of solid particles.

Without departing from the scope of the present invention, the bubble column or the installation for treating polluted air contained in and/or entering/coming from a confined environment can be associated with an electrostatic filter device preferably associated with a ozone treatment, arranged downstream of the bubble column. It is thus possible to envisage carrying out the treatment in the bubble column or columns in a confined space already equipped with an air treatment device of the electrostatic filter type: on the one hand, it is thus possible to improve the overall efficiency the treatment of the air vis-à-vis the particles by exploiting existing devices rather than deactivating/dismantling them, on the other hand one can take advantage of the ozone treatment of the filter used to ionize the particles before their precipitation electrostatic, because ozone tends to oxidize NO to NO2, and NO2 is more soluble in the liquid phase than NO: this generally facilitates the extraction of NOx by treating the air using one or more columns bubbles according to the invention. Advantageously, since the confined spaces which are of interest to the invention are provided with means for supplying and/or extracting air to and from the confined spaces, it is possible to place the bubble column or the installation comprising several of said columns at bubbles in these means. Concretely, these means are in the form of networks of pipes, chimneys and various enclosures in fluidic connection with each other and equipped with ad hoc fans/extractors to ensure the circulation of the air within the confined environment, from the interior to the exterior of the confined space and/or the reverse. By arranging the bubble column(s) close to these ventilation/extraction means (either "upstream" or "downstream" of these, taking as a reference the direction of the general flow of the air in these means), the air to be treated is caused to circulate in the bubble column or columns, possibly without even having recourse to additional forced circulation devices.

Advantageously, the air treatment can be controlled by an electronic/computer control system allowing manual, automatic or semi-automatic control, for example remotely. Thus, the control system may comprise electronic/computer means connected on the one hand to one or more measurement means associated with the bubble column, in particular a liquid pH sensor or a particle concentration sensor and/or of polluting compounds present in the liquid or in the treated gas, and to one or more means for controlling the process, in particular means for controlling the opening/closing of valves, and connected on the other hand to a man/machine interface. Monitoring of the process can therefore be done remotely, minimizing maintenance operations requiring human intervention.

Preferably, the process for treating air contained in and/or entering and/or leaving outside a confined space according to the invention can implement a bubble column according to any one of the variants or combinations of variants described.

By way of illustration, we can compare three cases (a), (b) and (c) of installations for treating polluted air from a confined space, aiming to deplete it in solid particles and in at least a polluting gaseous compound, in particular NOx, SOx and/or VOC, comprising bubble columns operating in parallel. In all three cases, the airflow to be treated is 10,000 m ³ /h.

In case (a) the installation comprises eight bubble columns, arranged to operate in parallel, with a diameter of 1.5 m and a height of 1.5 m in order to significantly reduce the gaseous polluting compounds (i.e. a ratio H/D = 1), completely filled with water to simplify the calculations, and operating in parallel, at ambient temperature and pressure, with an operational superficial gas velocity Ug of 0.2 m/s. The pressure drop of each column is approximately 0.015 MPa. We calculates an investment price PI and an annual operating cost P2 linked to the electrical consumption of the blower.

In case (b), which is a case according to the invention, the same air flow can be treated with an installation comprising only four bubble columns of the same diameter and the same diameter height (H = D = 1.5 m ), i.e. an H/D ratio = 1, with an operational superficial gas velocity Ug of 0.4 m/s.

Due to the high gas velocity, the transfer coefficient is higher, the capture performance is at least equal to that of the base case (a). This makes it possible to reduce the investment price PI' by 46% compared to PI at an operating cost P2' comparable to P2.

In case (c), which is a case according to the invention, the same airflow can be treated with an installation comprising only four bubble columns of the same diameter (D=1.5 m) but of different height, H= 0.75 m, i.e. an H/D ratio of 0.5. In this case, the capture performance is slightly reduced compared to case (a), however the investment cost PI" is reduced by 20% compared to PI' in case (b), the pressure drop is practically divided by 2, which makes it possible to have an operating cost P2" down 47% compared to P2'. Finally, the installation of case (c) uses more compact columns that are much easier to install in confined environments where the ceiling height is sometimes limited.

Claims

1. Process for treating air contained in and/or entering and/or leaving outside a confined space in order to deplete it of at least one polluting gaseous compound, in particular of NOx, SOx and/or VOCs, and of particles solids, implementing a bubble column (100, 200, 300, 400) comprising an enclosure (1) with an H/D ratio <1.5 filled with a liquid capable of capturing said particles and polluting gaseous compounds, H and D being respectively the height and the diameter of said enclosure, in which:

- air is injected into the liquid at the bottom of said enclosure (1) so as to form bubbles, and at a rate such that the superficial operational gas velocity Ug is between 0.35 m/s and 0.50 m/s,

- said injected air is treated in the form of bubbles by contact with the liquid so that at least a part of the particles and/or of the polluting gaseous compound(s) is captured by the liquid, and

- The treated air is evacuated at the top of said enclosure (1).

2. Process according to claim 1, in which the operating superficial gas velocity Ug is between 0.40 m/s and 0.50 m/s.

3. A method according to claim 1 or claim 2, wherein the only driver of the upward air flow in the form of bubbles results from buoyancy.

4. Method according to any one of the preceding claims, in which the liquid is an aqueous solution, and preferably consists of water.

5. Method according to any one of the preceding claims, in which the liquid is an aqueous solution comprising at least one absorbent compound with respect to said at least one polluting gaseous compound, and/or comprises a solubility promoter of said at least a polluting gaseous compound.

6. Method according to any one of the preceding claims, in which the liquid is renewed in the said chamber, preferably discontinuously.

7. Method according to any one of the preceding claims, in which the bubble column is operated at ambient temperature and pressure.

8. Method according to any one of the preceding claims, in which a peripheral zone for settling and concentration of particles (18) is created in the enclosure between said enclosure (1) and a tube (8) disposed in and centered in said enclosure (1), the liquid having an overall downward movement in said peripheral zone (18).

9. Method according to claim 8, in which liquid containing particles and/or polluting components is withdrawn from said peripheral zone (18) by means of at least one liquid evacuation pipe (9) opening onto the side wall of said enclosure (1), preferably in the upper half of said enclosure (1).

10. Method according to any one of the preceding claims, in which the enclosure (1) of the column is cylindrical.

11. Bubble column (100, 200, 300, 400) for carrying out the process for treating the air contained in and/or entering and/or leaving outside a confined space in order to deplete it of polluting gaseous compounds , in particular in NOx, SOx and/or VOC, and in solid particles according to any one of the preceding claims, configured to operate at an operational superficial gas velocity Ug of between 0.35 m/s and 0.50 m/ s, said bubble column comprising:

- an enclosure (1), preferably cylindrical, with a ratio H/D < 1.5, H and D being respectively the height and the diameter of said enclosure, configured to be filled with a liquid capable of capturing said particles and gaseous compounds pollutants,

- an air inlet pipe (2),

- means for dispersing said air within said liquid (3), connected to said air inlet pipe (2) and arranged in the bottom of the enclosure (1),

- a treated air outlet pipe (6) arranged at the top of said enclosure,

- a liquid supply pipe (4) opening at the top of said enclosure, and

- At least one liquid discharge line (5, 9) from said enclosure.

12. Bubble column according to claim 11, comprising a liquid renewal and purge circuit.

13. Bubble column according to any one of claims 11 or 12, further comprising an inner tube (8) disposed in and centered in said enclosure (1), vertically dividing said enclosure (1) into a peripheral settling zone and particle concentration (18) formed between said enclosure (1) and said tube (8), and in a central zone (19) formed inside said tube (8). Bubble column according to claim 13, wherein said at least one liquid discharge conduit (9) opens on the side wall of said enclosure (1), preferably in the upper half of said enclosure (1). Installation for treating the air contained in and/or entering and/or leaving outside a confined space in order to deplete it of polluting gaseous compounds, in particular of NOx, SOx and/or VOCs, and of solid particles, comprising several bubble columns (100, 200, 300, 400) according to any one of claims 11 to 14, configured to operate in parallel.