WO2007003777A1 - Method and device for processing gaseous wastes in particular containing a hydrofluoric acid - Google Patents

Method and device for processing gaseous wastes in particular containing a hydrofluoric acid Download PDF

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Publication number
WO2007003777A1
WO2007003777A1 PCT/FR2006/001538 FR2006001538W WO2007003777A1 WO 2007003777 A1 WO2007003777 A1 WO 2007003777A1 FR 2006001538 W FR2006001538 W FR 2006001538W WO 2007003777 A1 WO2007003777 A1 WO 2007003777A1
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WO
WIPO (PCT)
Prior art keywords
alumina
hydrofluoric acid
zone
effluents
alumina powder
Prior art date
Application number
PCT/FR2006/001538
Other languages
French (fr)
Inventor
Mathieu Frainais
Thierry Malard
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Solios Environnement
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Publication date
Application filed by Solios Environnement filed Critical Solios Environnement
Priority to CA002608551A priority Critical patent/CA2608551A1/en
Publication of WO2007003777A1 publication Critical patent/WO2007003777A1/en
Priority to NO20080581A priority patent/NO20080581L/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
    • B01D53/06—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds
    • B01D53/10—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds with dispersed adsorbents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/68—Halogens or halogen compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/20—Halogens or halogen compounds
    • B01D2257/204—Inorganic halogen compounds
    • B01D2257/2047—Hydrofluoric acid
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/30—Capture or disposal of greenhouse gases of perfluorocarbons [PFC], hydrofluorocarbons [HFC] or sulfur hexafluoride [SF6]

Definitions

  • the invention relates to a treatment process, with a high extraction capacity, of gaseous effluents containing fluorinated compounds. It relates more particularly to the treatment of gaseous effluents generated by the cells used for the production of aluminum by igneous electrolysis according to the Hall-Héroult process.
  • the invention relates precisely to the extraction as complete as possible of fluorinated pollutants, and more particularly of hydrofluoric acid, by means of pulverulent mineral particles, alumina, which capture and adsorb said fluorinated pollutants.
  • gaseous effluents containing pollutants results in particular from the industrial production of aluminum by the igneous electrolysis of alumina in solution in an electrolysis bath formed from molten cryolite (HaIl-Heroult process): gaseous effluents are the consequence of the electrochemical reactions which occur at high temperature (about 1000 ° C.) during the igneous electrolysis of alumina in the molten salt bath comprising in particular alumina and cryolite, and which is crossed by very intense electric currents, of the order of several hundreds of thousands of amperes.
  • the effluents are formed of a mixture containing mainly CO 2 (which comes mainly from the consumption of carbon anodes) and in a minority of fluorinated compounds, in particular hydrofluoric acid. These fluorinated compounds must be removed before being released into the atmosphere.
  • WO 2004-64984 discloses a method of injecting droplets of a cooling fluid (water) into the HF-containing gas delivery conduit from the igneous electrolysis cells of the alumina, the injection being producing upstream of the reaction zone between the HF of the gaseous effluents and alumina introduced into the reaction zone for adsorbing said HF.
  • This very controlled injection of the coolant is carried out at a distance of at least 15 meters from the reaction zone between the HF and the alumina, to allow a total vaporization, this coolant being heated, before its injection at a temperature of less than 10 ° C. at 20 ° C. to that of the evaporation temperature of said liquid.
  • this process essentially relates to lowering the temperature of the polluted gaseous effluents to limit the flow of gas to be treated, but also to protect the treatment plants and more particularly the filtration technical textiles made with thermoplastic synthetic polymers.
  • US 5,878,677 relates to a process for cooling and purifying a gas stream containing SO 2 and HCl, the polluting gases being treated with solid particles (Ca (OH) 2 , CaCO 3 ).
  • the gas stream to be treated is treated in a fluidized bed in a reactor by the solid particles suspended in the gas stream, the fluidized bed being cooled in the reaction zone by means of heat exchangers.
  • the fluidized bed undergoes a gas / solid separation, the gases being released into the atmosphere and the separated solid particles being cooled in a specific cooling zone before being re-introduced at the base of the reactor for treating the incoming gas stream to be cleaned up.
  • the method also relates to lowering the temperature of polluted waste gas in order to protect the treatment and separation facilities and to limit the losses in the performance of the treatment.
  • Document EP 0 668 343 A1 (Foster Wheeler Energy Corp.) relates to a process for purifying and cooling hot waste gases containing gaseous effluents such as sulfur-containing compounds and corrosive compounds such as HCl, CO, NH 3, etc.).
  • the polluted gas stream is treated in a circulating fluidized bed treatment reactor comprising solid particles suspended in polluted waste gas.
  • a gas / solid separation is practiced.
  • the fraction of the separated solid particles is cooled in a specific heat exchanger and re-introduced into the gas stream to be treated in the reactor.
  • the method thus proposed also relates to the lowering of the temperature of the gaseous effluents to be decontaminated, in particular by cooling the solid particles prior to their introduction into the gaseous effluents to be treated for reasons similar to those already practiced for the protection of the installations. industrial remediation.
  • EP 0 368 861 B1 discloses a process for treating industrial gases containing gaseous pollutants, comprising:
  • the method described in this document also relates to the lowering of the temperature of the polluted gaseous effluents entering the treatment chamber to be treated by the solid particles entering at a temperature below that of polluted gaseous effluents.
  • US 4,310,501 relates to a method for recovering fluorinated compounds from gaseous effluents from the igneous electrolysis tanks of alumina in which the polluted gaseous effluents are treated with alumina in an expanded fluidized bed.
  • the invention consists in cooling the gaseous effluents of the fluidized bed containing fluorine (HF) compounds by direct contact with pulverulent solids initially cooled in a particular cooling circuit.
  • HF fluorine
  • 4,006,066 and 4,065,271 disclose other methods of treating HF-containing effluents using alumina powder, into which water is injected into the fluidized bed so adjust the electrical conductivity of the medium to optimize the efficiency of the electrostatic separator.
  • the person skilled in the art knows that, with the installations according to the state of the art, it is possible to reduce the hydrofluoric acid concentration of the effluents from approximately 300 mg / Nm 3 to approximately 0.5 mg / Nm 3 in annual average.
  • the seasonal variation in the HF concentration of the effluent discharged can be quite significant: it can be of the order of 1 mg / Nm 3 in hot weather, and of the order of 0.25 mg / Nm 3 in cold weather .
  • the present inventors have sought new industrially acceptable and economically viable means for the elimination as complete as possible of the fluorinated pollutants of gaseous effluents from an aluminum production plant by igneous electrolysis.
  • a first object of the invention is a gaseous effluent treatment process (E) containing hydrofluoric acid, wherein successively a) said gaseous effluents (E) are collected, d) said gaseous effluents (E) are treated containing hydrofluoric acid by means of alumina powder (A), said alumina powder (A) fixing at least a portion of the hydrofluoric acid, e) separating the treated gaseous effluents (Et) and the powder of alumina charged with hydrofluoric acid (Af), f) recycling at least a portion of said hydrofluoric acid-loaded alumina powder (Af) in the effluent treatment step (e) (E), said process being characterized in that said alumina powder charged with hydrofluoric acid (Af), resulting from the separation (step (e)) or fresh or a mixture of the two, is wetted before or during its introduction into the flow of said gaseous effluents (E) to
  • At least a portion of said hydrofluoric acid-loaded alumina powder (Af) is recycled to the effluent treatment step (e) (E).
  • Another object is an effluent treatment device (E) containing hydrofluoric acid, said device comprising:
  • Yet another object is the use of the device or method according to the invention for the pollution control of gaseous effluents containing hydrofluoric acid.
  • Figures 1 and 2 schematically show a device that corresponds to an advantageous embodiment of the present invention.
  • Figure 1 gives an overview of a device according to the invention.
  • Figure 2 shows an embodiment of the alumina conditioning zone.
  • the gaseous effluents to be treated (E) can come from any industrial process capable of generating gaseous effluents loaded with fluorine or hydrofluoric acid, such as electrometallurgical processes involving electrolysis in the presence of fluorides. More particularly, the effluents to be treated come from an aluminum production cell by igneous electrolysis. This process, called the Hall-Héroult process, is based on the electrolysis of alumina in a melt containing mainly alumina and cryolite.
  • the device according to the invention comprises at least one depollution zone (4) of said effluents (E) by means of alumina powder (A), and at least one separation zone (5) in which the treated gaseous effluents are separated. (Et) and the alumina powder loaded with hydrofluoric acid (Af).
  • the depollution zone (4) may advantageously comprise an injection system (43), which is put in contact with the effluents to be treated (E) with alumina powder.
  • gaseous effluents (E) containing hydrofluoric acid are treated.
  • Said effluents (E) come into intimate contact with alumina powder (A), which during this contact fixes at least part of the hydrofluoric acid contained in the effluents to be treated (E) and becomes what we call
  • alumina charged with hydrofluoric acid (Af) while the effluents are depleted in hydrofluoric acid and become what we call here treated effluents (Et).
  • the treated effluents (Et) and the alumina charged with hydrofluoric acid (Af) are then conveyed into the separation zone (5).
  • the residence time in the depollution zone (4) may be of the order of one second, for example two seconds.
  • the acid-laden alumina Hydrofluoric acid (Af) is separated from the treated gaseous effluents (Et). All or part of this separated alumina (As) can be recycled (ie reinjected) into the effluent treatment step d), either immediately or after transfer to an intermediate storage means. This makes it possible to increase its load of hydrofluoric acid.
  • the part of the separated alumina (As) which is not recycled to the depollution zone (4) can be introduced, possibly after its transfer into a temporary storage means such as a silo, in an igneous electrolysis cell of alumina.
  • the essential means of the present invention which makes it possible to solve the problem posed is the humidification of the alumina before or during, and preferably before, its introduction into the decontamination zone (4).
  • the alumina introduced into the depollution zone (4) may be fresh alumina, that is to say alumina which has not yet been in contact with effluents charged with hydrofluoric acid, fluorine or other gases containing this element.
  • this pulverulent alumina introduced into the separation zone (5) must be moistened. During the humidification, it eventually cools by the effect of the vaporization of the liquid.
  • the humidification of the alumina can be carried out at different places.
  • the alumina may be moistened before it is introduced into the depollution zone (4), for example in a conditioning zone (6), for example a buffer hopper, annexed to the depollution zone (4). It may also be wetted in the injector (43), that is to say during the contact between the gaseous effluent to be treated (E) and the alumina powder in the pollution control zone (4).
  • the humidification of the alumina can be carried out using various means. For example, if a conditioning hopper (65) is used, a fluidizing air can be used which is moistened, or a liquid such as water can be sprayed, or any other suitable means can be used.
  • the moisture content of the moistened alumina can vary within fairly wide limits, typically ranging from 0.5% by weight to 10% by weight.
  • it is between 0.5% and 3%, more preferably between 0.5% and 2%, and the most preferred embodiment uses between 0.5% and 1.5%.
  • the water If the water is sprayed on the alumina after the introduction of the alumina in the depollution zone (4), the water does not settle on the alumina but evaporates simply on contact with the effluents, contributing thus cooling the effluents, but without lowering the temperature of the alumina.
  • the inventors have found that the humidified alumina, once in contact with the gaseous effluents to be treated, has its moisture content decrease, finally ending up in the separation zone with a relative humidity level close to 0%, and regardless of the initial moisture content added to the alumina Af. This same effect is also observed with fresh alumina.
  • This low value of the moisture content of the alumina favors the use of the hydrofluoric acid-loaded alumina powder Af extracted from the separation zone (5) in an igneous electrolysis cell of the alumina, because it is preferable that the operation of said electrolysis cell, which is very difficult to control, is not disturbed by excessive variations in the moisture content of the alumina.
  • the possibility of being able to recycle the separated alumina powder directly into the electrolysis process which generates the gaseous effluents to be treated is essential for the economic viability of such a depollution process.
  • the process according to the invention turns out to be a "robust" process in the sense that a variation of the process parameters, in particular the humidification parameters, does not significantly affect the humidity of the separated alumina.
  • the moisture content of the separated alumina is not higher than that of the alumina usually used in the Hall-Héroult igneous electrolysis process.
  • the use of the process according to the invention does not entail the need to modify the settings of the igneous electrolysis process which generates the effluents to be treated, but on the contrary, the process according to the invention is capable of being easily adapted to variations in the chemical composition and pollutant concentration of the effluents to be treated.
  • the process for treating gaseous effluents (E) containing hydrofluoric acid comprises, according to the invention, at least the following successive stages: a) said gaseous effluents (E) are collected, d) said gaseous effluents (E) are treated containing hydrofluoric acid by means of alumina powder (A), said alumina powder (A) fixing at least a portion of the hydrofluoric acid, e) separating the treated gaseous effluents (Et) and the powder hydrofluoric acid-loaded alumina (Af), f) at least a portion of said hydrofluoric acid-loaded alumina powder (Af) is recycled to the effluent treatment step (e), said method being characterized in that said alumina powder (A) 5 which may already be loaded with hydrofluoric acid (Af), resulting from the separation (stage (e)), or fresh alumina (Av) 5 or a mixture of the two is humidified before being introduced into the flow of said
  • the temperature of the said gaseous effluents (E) at the beginning of the treatment step d) is less than 145 ° C. and preferably less than 115 ° C. If the effluents (E) are hotter, they are cooled before being introduced into the depollution zone (4). In general, any suitable cooling means may be used, but two means are particularly preferred; they can be used separately or in combination. The inventors have obtained good results with a temperature of the effluents at the entry of the depollution zone (4) of less than 90 ° C. or even less than 70 ° C.
  • the separating means (52) is a bag filter that the temperature of the gaseous effluents (E) at the inlet of the depollution zone (4) is critical, because for reasons of economy, we do not wish to resort to the use of special fabrics that withstand high temperatures: it is therefore in this case particularly advantageous that this effluent temperature is less than 145 ° C and preferably less than 115 ° C.
  • the first means is the injection of a liquid (L) into a liquid injection zone (2).
  • a liquid typically, water, and typically in the form of droplets, is injected, for example by at least one spray nozzle (21), into the effluent conveying duct upstream of the treatment zone. It is preferable that the amount of water injected be adjusted so that the vaporization of the water is complete.
  • the vaporization rate of the droplets is controlled by means of a detector located in the liquid injection zone (2) or downstream thereof. It is also possible to provide an adjustment of the temperature of the liquid (L) injected, but in practice it will only be in exceptional cases where the additional investment and exploitation costs that this entails will be considered justified.
  • the liquid (L) can also be heated before injection.
  • the liquid injection zone (2) may or may comprise a cooling tower of known type.
  • a cooling tower of known type.
  • the second means is the dilution of the effluent to be treated (E) by a gaseous fluid which is injected into the effluents in an injection zone of a gas stream (3).
  • the gaseous dilution fluid may be air, or treated gaseous effluents (Et) that leave the separation zone (5) and are reinjected into the circuit, or a mixture of the two.
  • the volume of gas flow injected should not unacceptably increase the volumes of gas to be treated by the separation zone (5), since this requires an oversizing of the capacity of the separation means (52).
  • the gaseous volume injected does not exceed about 10% by volume of the effluent volume (E).
  • the gaseous fluid is injected downstream of the liquid injection zone (2).
  • the need to use one or both of these cooling means, or both depends on the temperature and the flow rate of the gaseous effluent (E) to be treated.
  • This temperature depends on numerous factors, notably related to the operating conditions of the industrial process that generates the said effluents to be treated, to the conditions of collection and conveyance, and to the climatic and meteorological conditions of the site of the plant in which the plant is installed.
  • device according to the invention It is advantageous that the device according to the invention comprises these two cooling means, namely the injection zone liquid (2) and the injection zone of a gas stream (3), as this confers on the process according to the invention a great ease of adaptation of the pipe of the process.
  • the alumina powder introduced into the decontamination zone (4) has been previously cooled with cooling means other than the vaporization of the liquid used for humidification.
  • a separate cooling zone (9) is added to the device.
  • This zone may be in the conditioning zone (6) or elsewhere. Any means for cooling the powdery mineral particles may be suitable.
  • the conditioning zone (6) comprises at least one conditioning hopper (62) equipped with coils in which circulates a coolant.
  • the conditioning hopper (62) is placed below the separating means (52) and comprises coils in which a refrigerant circulates.
  • the fluidized bottom of the hopper (62) it is also possible to divide the fluidized bottom of the hopper (62) into several sectors in which the alumina passes successively. The entire fluidization surface of this hopper is covered by the refrigeration network.
  • the refrigerant circulates in the opposite direction of the recycled alumina. From the last sector (ie the coldest sector), the recycled alumina is reinjected into the effluents to be treated, upstream of the pollution control zone (4) or directly in this zone.
  • the hydrofluoric acid-loaded alumina (Af) can be cooled before being recycled, and this cooling is independent of the cooling means used to adjust the temperature of the effluents to be treated that enter the pollution control zone (4). .
  • the temperature of the alumina powder introduced into the decontamination zone (4) is less than 70 ° C., and preferably between 25 ° C. and 50 ° C.
  • a separate cooling zone (9) may also use a fluidized hopper, single or subdivided bottom, as described above.
  • the fresh alumina (Av) comes from a storage silo, its temperature will normally be less than 50 ° C, or even lower than 40 ° C. It may be injected upstream of the depollution zone (4), or directly in this area. However, it is preferred to inject it into the packaging zone (6), where it mixes with the recycled alumina and is at the same time humidified and cooled time. If it is necessary to further cool the fresh alumina (Av) 3 it can be injected into the cooling zone (9).
  • Any alumina of the type and particle size of those used for the HaIlHeroult process may be suitable.
  • This alumina is known as Smelter Grade Alumina (SGA).
  • the temperature is between 110 and 120 ° C, there is a fluorine uptake efficiency of about 37%, while the use of a wet fluorinated alumina with 3% by weight of water increases the capture efficiency at about 78% This clearly illustrates the effect of humidification which is the first order parameter.
  • the temperature of the alumina and the temperature of the effluents in the depollution zone (4) are second-order parameters, the judicious choice of which allowed the inventors to obtain, in the pilot plant of reduced size, a capture efficiency. of about 93% with a wet fluorinated alumina at a temperature of about 35 ° C injected into effluents to be treated whose temperature was about 73 ° C, while under the same temperature conditions, a dry fluorinated alumina does not led to a capture efficiency of about 80%.
  • the process according to the invention makes it possible to obtain a hydrofluoric acid uptake efficiency of greater than 85%, and preferably significantly greater than 90%, with 100% fluorinated alumina without adding fresh alumina which has a better uptake than fluorinated alumina.

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Abstract

The invention relates to a method for processing hydrofluoric acid-containing gaseous wastes (E) consisting (a) in capturing said gaseous wastes (E), (d) in processing said hydrofluoric acid-containing gaseous wastes (E) by means of an alumina powder (A) for fixing at least one part of hydrofluoric acid, (e) in separating the processed gaseous wastes (E) and the alumina powder loaded with the hydrofluoric acid (Af), (f) in recycling at least one part of said alumina powder loaded with the hydrofluoric acid (Af) at stage d) for processing said wastes (E), wherein said process is characterised in that the alumina powder which is loaded with the hydrofluoric acid (Af), obtainable by the separation (stage (e)) of is fresh of by the mixture thereof, is humidified prior to or during the introduction thereof into said processable gaseous wastes (E).

Description

Procédé et dispositif de traitement d'effluents gazeux contenant en particulier de l'acide fluorhydrique. Process and device for treating gaseous effluents containing, in particular, hydrofluoric acid.
Domaine de l'invention :Field of the invention
L'invention concerne un procédé de traitement, à haut pouvoir d'extraction, d'effluents gazeux contenant des composés fluorés. Elle concerne plus particulièrement le traitement d'effluents gazeux générés par les cellules utilisées pour la production d'aluminium par électrolyse ignée selon le procédé Hall-Héroult. L'invention concerne précisément l'extraction aussi complète que possible de polluants fluorés, et plus particulièrement de l'acide fluorhydrique, au moyen de particules minérales pulvérulentes, de l'alumine, qui captent et adsorbent lesdits polluants fluorés.The invention relates to a treatment process, with a high extraction capacity, of gaseous effluents containing fluorinated compounds. It relates more particularly to the treatment of gaseous effluents generated by the cells used for the production of aluminum by igneous electrolysis according to the Hall-Héroult process. The invention relates precisely to the extraction as complete as possible of fluorinated pollutants, and more particularly of hydrofluoric acid, by means of pulverulent mineral particles, alumina, which capture and adsorb said fluorinated pollutants.
Etat de la technique :State of the art:
L'augmentation de la pollution gazeuse de l'atmosphère locale, régionale et planétaire, ainsi que le réchauffement de l'atmosphère constaté, interpelle d'une manière permanente les responsables des industries qui rejettent des effluents gazeux pollués dans l'atmosphère. Elle interpelle également et les acteurs politiques et le public. La dépollution d'effluents gazeux est aussi nécessaire pour préserver la santé du personnel des usines qui les génèrent. Pour toutes ces raisons, les réglementations régionales, nationales et internationales imposent des limites toujours plus basses aux quantités de polluants rejetées dans l'atmosphère.The increase in gaseous pollution of the local, regional and global atmosphere, as well as the warming of the atmosphere, is a permanent challenge for industry managers who discharge polluted gaseous effluents into the atmosphere. It also challenges the political actors and the public. The clearance of gaseous effluents is also necessary to preserve the health of the personnel of the factories that generate them. For all these reasons, regional, national and international regulations impose ever-lower limits on the quantities of pollutants released into the atmosphere.
On connaît de nombreux procédés de dépollution d'effluents gazeux, par voie humide, par lavage par exemple, ou par voie sèche, au moyen par exemple de particules solides pulvérulentes mises en contact avec les effluents gazeux à dépolluer (voir par exemple le procédé décrit dans la demande de brevet FR 2 626 292 de la société Walther & Cie.) , ces particules intervenant comme réactifs chimiques, ou comme adsorbants physiques, ou comme supports de condensation. La dépollution d'effluents par lavage pose toutefois le problème du traitement des effluents liquides qui en résultent. Cela est un problème à la fois technique et économique. De même, un procédé de dépollution d'effluents au moyen de particules solides doit prendre en compte le devenir des particules solides chargées de polluants.Numerous processes are known for the depollution of gaseous effluents, by the wet route, by washing for example, or by the dry route, by means, for example, of solid powdery particles brought into contact with the gaseous effluents to be treated (see, for example, the method described). in patent application FR 2 626 292 from Walther & Co.), these particles acting as chemical reagents, or as physical adsorbents, or as condensation supports. The cleaning of effluents by washing, however, poses the problem of treating the liquid effluents that result. This is a problem both technical and economic. Similarly, a process for the depollution of effluents by means of solid particles must take into account the fate of solid particles loaded with pollutants.
Mais tous les procédés disponibles, même s'ils développent déjà une bonne capacité à dépolluer les effluents gazeux chauds résultants des activités industrielles et/ou humaines, ne parviennent pas à une dépollution poussée c'est-à-dire suffisamment complète desdits effluents pour que les composants les plus essentiels et les plus dangereux de ces polluants pour l'environnement, tels que l'acide fluorhydrique, le SO2, le HCl et autres encore, soient complètement éliminés desdits effluents gazeux avant leur rejet dans l'atmosphère.But all available processes, even if they already develop a good ability to depollute the hot gaseous effluents resulting from industrial and / or human activities, do not achieve a thorough depollution that is to say sufficiently complete of said effluents for that the most essential and dangerous components of these environmental pollutants, such as hydrofluoric acid, SO 2 , HCl and others, are completely removed from the said off-gases before being released into the atmosphere.
C'est pourquoi, il existe encore aujourd'hui un vrai problème de protection de l'environnement qui résulte d'une insuffisante dépollution des effluents gazeux pollués, en particulier par du HF, avant leur rejet dans l'atmosphère.Therefore, there is still a real problem of environmental protection that results from insufficient pollution of gaseous effluents, especially by HF, before their release into the atmosphere.
La production d' effluents gazeux contenant des polluants en particulier du HF découle notamment de la production industrielle de l'aluminium par Pélectrolyse ignée de l'alumine en solution dans un bain d'électrolyse formé de cryolithe fondue (Procédé HaIl- Heroult) : les effluents gazeux sont la conséquence des réactions électrochimiques qui se produisent à haute température (environ 10000C) lors de l'électrolyse ignée de l'alumine dans le bain de sel fondu comportant notamment de l'alumine et de la cryolithe, et qui est traversé de courants électriques très intenses, de l'ordre de plusieurs centaines de milliers d'ampères. Les effluents sont formés d'un mélange contenant majoritairement du CO2 (qui provient surtout de la consommation des anodes en carbone) et minoritairement des composés fluorés, en particulier l'acide fluorhydrique. Ces composés fluorés doivent être éliminés avant leur rejet dans l'atmosphère.The production of gaseous effluents containing pollutants, in particular HF, results in particular from the industrial production of aluminum by the igneous electrolysis of alumina in solution in an electrolysis bath formed from molten cryolite (HaIl-Heroult process): gaseous effluents are the consequence of the electrochemical reactions which occur at high temperature (about 1000 ° C.) during the igneous electrolysis of alumina in the molten salt bath comprising in particular alumina and cryolite, and which is crossed by very intense electric currents, of the order of several hundreds of thousands of amperes. The effluents are formed of a mixture containing mainly CO 2 (which comes mainly from the consumption of carbon anodes) and in a minority of fluorinated compounds, in particular hydrofluoric acid. These fluorinated compounds must be removed before being released into the atmosphere.
D'incessantes et d'importantes améliorations technologiques de traitement ont été apportées aux installations industrielles, pour confiner, capter et traiter les effluents gazeux industriels contenant des polluants tels que SO2, NH3, HF, HCl et autres.Incessant and significant technological improvements have been made to industrial facilities to contain, capture and treat industrial effluents containing pollutants such as SO 2 , NH 3 , HF, HCl and others.
Dans le cas de l'électrolyse ignée de l'alumine par exemple, le capotage des cuves d'électrolyse, l'aspiration des effluents gazeux, leur traitement dans des installations appropriées au moyen d'alumine pulvérulente adsorbant les composés fluorés et leur évacuation une fois traités dans l'atmosphère après une séparation solide/gaz, ont permis d'abaisser de plus en plus le taux de composés fluorés encore présents dans les effluents dépollués et rejetés dans l'atmosphère.In the case of the igneous electrolysis of alumina for example, the overturning of the electrolytic cells, the suction of the gaseous effluents, their treatment in appropriate installations by means of pulverulent alumina adsorb the fluorinated compounds and their evacuation a once treated in the atmosphere after a solid / gas separation, allowed to lower more and more the rate of fluorinated compounds still present in the effluent cleaned up and released into the atmosphere.
De nombreux documents de l'état de la technique témoignent des efforts déployés pour dépolluer de plus en plus finement les effluents gazeux destinés à être rejetés dans l'atmosphère.Many documents of the state of the art testify to the efforts made to depollute more and more finely the gaseous effluents intended to be released into the atmosphere.
Le document WO 2004-64984 décrit un procédé qui consiste à injecter des gouttelettes d'un fluide de refroidissement (eau) dans le conduit d'acheminement gazeux contenant du HF provenant des cuves d'électrolyse ignée de l'alumine, l'injection se produisant en amont de la zone de réaction entre le HF des effluents gazeux et de l'alumine introduite dans la zone de réaction pour adsorber ledit HF. Cette injection très contrôlée du liquide de refroidissement s'effectue à une distance d'au moins 15 mètres de la zone de réaction entre le HF et l'alumine, pour en permettre une vaporisation totale, ce liquide de refroidissement étant réchauffé, avant son injection, à une température inférieure de 1O0C à 20°C à celle de la température d'évaporation dudit liquide.WO 2004-64984 discloses a method of injecting droplets of a cooling fluid (water) into the HF-containing gas delivery conduit from the igneous electrolysis cells of the alumina, the injection being producing upstream of the reaction zone between the HF of the gaseous effluents and alumina introduced into the reaction zone for adsorbing said HF. This very controlled injection of the coolant is carried out at a distance of at least 15 meters from the reaction zone between the HF and the alumina, to allow a total vaporization, this coolant being heated, before its injection at a temperature of less than 10 ° C. at 20 ° C. to that of the evaporation temperature of said liquid.
Ainsi ce procédé porte essentiellement sur l'abaissement de la température des effluents gazeux pollués pour limiter le débit de gaz à traiter, mais aussi pour protéger les installations de traitement et plus particulièrement les textiles techniques de fïltration réalisés avec des polymères de synthèse thermoplastiques.Thus, this process essentially relates to lowering the temperature of the polluted gaseous effluents to limit the flow of gas to be treated, but also to protect the treatment plants and more particularly the filtration technical textiles made with thermoplastic synthetic polymers.
Le document US 5,878,677 traite d'un procédé pour le refroidissement et la purification d'un flux gazeux contenant du SO2 et du HCl, les gaz polluants étant traités par des particules solides (Ca(OH)2, CaCO3). Le flux gazeux à dépolluer est traité en lit fluidisé dans un réacteur par les particules solides mises en suspension dans le flux gazeux, le lit fluidisé étant refroidi dans la zone de réaction au moyen d'échangeurs thermiques. A la sortie du réacteur de traitement, le lit fluidisé subit une séparation gaz/solide, les gaz étant rejetés dans l'atmosphère et les particules solides séparées étant refroidies dans une zone de refroidissement spécifique avant d'être ré-introduites à la base du réacteur pour traiter le flux gazeux entrant à dépolluer. Ainsi le procédé porte également sur l'abaissement de la température des effluents gazeux pollués dans le but de protéger les installations de traitement et de séparation et limiter les pertes des performances du traitement.US 5,878,677 relates to a process for cooling and purifying a gas stream containing SO 2 and HCl, the polluting gases being treated with solid particles (Ca (OH) 2 , CaCO 3 ). The gas stream to be treated is treated in a fluidized bed in a reactor by the solid particles suspended in the gas stream, the fluidized bed being cooled in the reaction zone by means of heat exchangers. At the outlet of the treatment reactor, the fluidized bed undergoes a gas / solid separation, the gases being released into the atmosphere and the separated solid particles being cooled in a specific cooling zone before being re-introduced at the base of the reactor for treating the incoming gas stream to be cleaned up. Thus, the method also relates to lowering the temperature of polluted waste gas in order to protect the treatment and separation facilities and to limit the losses in the performance of the treatment.
Le document EP 0 668 343 Al (Foster Wheeler Energy Corp.) concerne un procédé de purification et refroidissement des effluents gazeux chauds contenant des effluents gazeux tels que des composés soufrés et des composés corrosifs comme HCl, CO, NH3...). Le flux gazeux pollué est traité dans un réacteur de traitement à lit fluidisé circulant comportant des particules solides en suspension dans les effluents gazeux pollués. A la sortie du réacteur de traitement, une séparation gaz/solide est pratiquée. La fraction des particules solides séparée est refroidie dans un échangeur thermique spécifique et ré-introduite dans le flux gazeux à traiter au sein du réacteur.Document EP 0 668 343 A1 (Foster Wheeler Energy Corp.) relates to a process for purifying and cooling hot waste gases containing gaseous effluents such as sulfur-containing compounds and corrosive compounds such as HCl, CO, NH 3, etc.). The polluted gas stream is treated in a circulating fluidized bed treatment reactor comprising solid particles suspended in polluted waste gas. At the outlet of the treatment reactor, a gas / solid separation is practiced. The fraction of the separated solid particles is cooled in a specific heat exchanger and re-introduced into the gas stream to be treated in the reactor.
Le procédé ainsi proposé porte également sur l'abaissement de la température des effluents gazeux à dépolluer par le truchement en particulier du refroidissement des particules solides préalablement à leur introduction dans les effluents gazeux à traiter pour des raisons similaires à celles déjà pratiquées de protection des installations industrielles de dépollution.The method thus proposed also relates to the lowering of the temperature of the gaseous effluents to be decontaminated, in particular by cooling the solid particles prior to their introduction into the gaseous effluents to be treated for reasons similar to those already practiced for the protection of the installations. industrial remediation.
Le document EP 0 368 861 Bl (A. Ahlstôm Corp.) décrit un procédé de traitement de gaz industriels chargés de polluants gazeux consistant :EP 0 368 861 B1 (A. Ahlstom Corp.) discloses a process for treating industrial gases containing gaseous pollutants, comprising:
(i) à mettre dans une chambre de traitement à lit fluidisé, les gaz industriels pollués au contact de particules solides, (ii) à refroidir le milieu fluidisé (gaz industriels pollués et particules solides) au moyen d'échangeurs thermiques présents dans la chambre de traitement,(i) to put in a fluidized bed treatment chamber, the polluted industrial gases in contact with solid particles, (ii) to cool the fluidized medium (polluted industrial gases and solid particles) by means of heat exchangers present in the chamber treatment,
(iii) puis à réaliser une séparation gaz/solide en ré-introduisant dans la chambre de traitement les particules séparées et refroidies et une partie des gaz dépollués refroidis, de telle sorte que la température des particules solides recyclées et des gaz dépollués recyclés soit inférieure à la température des gaz industriels pollués à traiter.(iii) then performing a gas / solid separation by re-introducing into the treatment chamber the separated and cooled particles and a portion of the cooled off-gases, so that the temperature of the recycled solid particles and the recycled clean-up gases is lower; at the temperature of the polluted industrial gases to be treated.
Le procédé décrit dans ce document concerne également l'abaissement de la température des effluents gazeux pollués entrant dans la chambre de traitement pour y être traités par les particules solides y entrant à une température inférieure à celle des effluents gazeux pollués. Le document US 4,310,501 concerne une méthode de récupération de composés fluorés à partir d'effluents gazeux provenant des cuves d'électrolyse ignées de l'alumine dans laquelle les effluents gazeux pollués sont traités par de l'alumine dans un lit fluidisé expansé. L'invention consiste à refroidir les effluents gazeux du lit fluidisé contenant des composés du fluor (HF) par un contact direct avec des matières solides pulvérulentes initialement refroidies dans un circuit de refroidissement particulier. Les brevets US 4,006,066 et US 4,065,271 (Vereinigte Aluminium-Werke) décrivent d'autres procédés de traitement d'effluents contenant du HF à l'aide de poudre d'alumine, dans lesquels on injecte de l'eau dans le lit fluidisé, afin d'ajuster la conductivité électrique du milieu pour optimiser l'efficacité du séparateur électrostatique.The method described in this document also relates to the lowering of the temperature of the polluted gaseous effluents entering the treatment chamber to be treated by the solid particles entering at a temperature below that of polluted gaseous effluents. US 4,310,501 relates to a method for recovering fluorinated compounds from gaseous effluents from the igneous electrolysis tanks of alumina in which the polluted gaseous effluents are treated with alumina in an expanded fluidized bed. The invention consists in cooling the gaseous effluents of the fluidized bed containing fluorine (HF) compounds by direct contact with pulverulent solids initially cooled in a particular cooling circuit. US Pat. Nos. 4,006,066 and 4,065,271 (Vereinigte Aluminum-Werke) disclose other methods of treating HF-containing effluents using alumina powder, into which water is injected into the fluidized bed so adjust the electrical conductivity of the medium to optimize the efficiency of the electrostatic separator.
L'homme du métier sait qu'avec les installations selon l'état de la technique, on arrive à baisser la concentration en acide fluorhydrique des effluents d'environ 300 mg/Nm3 jusqu'à environ 0,5 mg/Nm3 en moyenne annuelle. La variation saisonnière de la concentration en HF des effluents dépollués peut cependant être assez importante : elle peut être de l'ordre de 1 mg/Nm3 par temps chaud, et de l'ordre de 0,25 mg/Nm3 par temps froid.The person skilled in the art knows that, with the installations according to the state of the art, it is possible to reduce the hydrofluoric acid concentration of the effluents from approximately 300 mg / Nm 3 to approximately 0.5 mg / Nm 3 in annual average. However, the seasonal variation in the HF concentration of the effluent discharged can be quite significant: it can be of the order of 1 mg / Nm 3 in hot weather, and of the order of 0.25 mg / Nm 3 in cold weather .
Les présents inventeurs ont recherché de nouveaux moyens industriellement acceptables et économiquement viables permettant l'élimination aussi complète que possible des polluants fluorés d'effluents gazeux issus d'une usine de production d'aluminium par électrolyse ignée.The present inventors have sought new industrially acceptable and economically viable means for the elimination as complete as possible of the fluorinated pollutants of gaseous effluents from an aluminum production plant by igneous electrolysis.
Objets de l'inventionObjects of the invention
Un premier objet de l'invention est un procédé de traitement d'effluents gazeux (E) contenant de l'acide fluorhydrique, dans lequel successivement a) on capte lesdits effluents gazeux (E), d) on traite lesdits effluents gazeux (E) contenant de l'acide fluorhydrique au moyen de poudre d'alumine (A), ladite poudre d'alumine (A) fixant au moins une partie de l'acide fluorhydrique, e) on sépare les effluents gazeux traités (Et) et la poudre d'alumine chargée d'acide fluorhydrique (Af), f) on recycle au moins une partie de ladite poudre d'alumine chargée d'acide fluorhydrique (Af) dans l'étape d) de traitement des effluents (E), ledit procédé étant caractérisé en ce que ladite poudre d'alumine chargée d'acide fluorhydrique (Af), issue de la séparation (étape (e)) ou fraîche ou un mélange des deux, est humidifiée avant ou pendant son introduction dans le flux desdits effluents gazeux (E) à traiter (c'est-à-dire avant ou pendant son introduction dans la zone de dépollution (4)).A first object of the invention is a gaseous effluent treatment process (E) containing hydrofluoric acid, wherein successively a) said gaseous effluents (E) are collected, d) said gaseous effluents (E) are treated containing hydrofluoric acid by means of alumina powder (A), said alumina powder (A) fixing at least a portion of the hydrofluoric acid, e) separating the treated gaseous effluents (Et) and the powder of alumina charged with hydrofluoric acid (Af), f) recycling at least a portion of said hydrofluoric acid-loaded alumina powder (Af) in the effluent treatment step (e) (E), said process being characterized in that said alumina powder charged with hydrofluoric acid (Af), resulting from the separation (step (e)) or fresh or a mixture of the two, is wetted before or during its introduction into the flow of said gaseous effluents (E) to be treated (i.e. say before or during its introduction in the depollution zone (4)).
Avantageusement, on recycle au moins une partie de ladite poudre d'alumine chargée d'acide fluorhydrique (Af) dans l'étape d) de traitement des effluents (E).Advantageously, at least a portion of said hydrofluoric acid-loaded alumina powder (Af) is recycled to the effluent treatment step (e) (E).
Un autre objet est un dispositif de traitement d'effluents gazeux (E) contenant de l'acide fluorhydrique, ledit dispositif comportant :Another object is an effluent treatment device (E) containing hydrofluoric acid, said device comprising:
(i) une zone de dépollution (4) desdits effluents (E) au moyen de poudre d'alumine (A),(i) a depollution zone (4) of said effluents (E) using alumina powder (A),
(ii) une zone de séparation (5) où on sépare les effluents gazeux traités (Et) et la poudre d'alumine chargée d'acide fluorhydrique (Af),(ii) a separation zone (5) separating the treated gaseous effluents (Et) and the hydrofluoric acid-loaded alumina powder (Af),
(iii) une zone de conditionnement (6) de l'alumine où ladite poudre d'alumine chargée d'acide fluorhydrique (Af), issue de la zone de séparation (5) est humidifiée avant d'être introduite dans la zone de dépollution (4).(iii) a conditioning zone (6) of the alumina wherein said hydrofluoric acid-loaded alumina powder (Af) from the separation zone (5) is humidified before being introduced into the depollution zone (4).
Encore un autre objet est l'utilisation du dispositif ou du procédé selon l'invention pour la dépollution d'effluents gazeux contenant de l'acide fluorhydrique.Yet another object is the use of the device or method according to the invention for the pollution control of gaseous effluents containing hydrofluoric acid.
Description des figuresDescription of figures
Les figures 1 et 2 montrent de manière schématique un dispositif qui correspond à un mode de réalisation avantageux de la présente invention.Figures 1 and 2 schematically show a device that corresponds to an advantageous embodiment of the present invention.
1 Entrée des effluents à traiter1 Entry of the effluents to be treated
2 Zone d'injection liquide2 Liquid injection area
21 Injecteur (pulvérisateur) d'eau21 Injector (spray) of water
22 Entrée d'eau22 Water inlet
3 Zone d'injection de gaz3 Gas injection area
31 Entrée d'air31 Air inlet
32 Régulateur de débit des gaz de dilution 33 Sortie vers la zone de dépollution32 Dilution gas flow regulator 33 Exit to the depollution zone
34 Sortie vers la zone de dépollution mise en parallèle34 Exit to the depollution zone in parallel
4 Zone de dépollution4 Pollution control area
42 Entrée d'alumine fraîche42 Fresh alumina inlet
43 Entrée d'alumine recyclée et / ou fraîche43 Entry of recycled and / or fresh alumina
5 Zone de séparation5 Separation area
51 Zone de récupération de l'alumine fluorée51 Recovery zone of fluorinated alumina
52 Moyen de séparation (p.ex. filtre à manches)52 Means of separation (eg bag filter)
53 Evacuation de l'alumine séparée pour recyclage53 Evacuation of separated alumina for recycling
54 Evacuation de l'alumine fluorée54 Evacuation of fluorinated alumina
6 Zone de conditionnement 62 Entrée d'alumine fraîche 65 Trémie de conditionnement6 Packing area 62 Fresh alumina inlet 65 Packing hopper
652 Entrée d'air de fluidisation652 Fluidizing air inlet
653 Evacuation de l'alumine humidifiée653 Evacuation of humidified alumina
655 Pulvérisateur d'eau655 Water sprayer
656 Alimentation en eau 659 Toile de fluidisation656 Water supply 659 Fluidizing fabric
7 Ventilateur7 Fan
8 Sortie des effluents dépollués (p.ex. cheminée)8 Exit of cleaned effluent (eg chimney)
9 Zone de refroidissement de l'alumine9 Alumina cooling zone
La figure 1 donne une vue d'ensemble d'un dispositif selon l'invention.Figure 1 gives an overview of a device according to the invention.
La figure 2 montre un mode de réalisation de la zone de conditionnement de l'alumine.Figure 2 shows an embodiment of the alumina conditioning zone.
Description détaillée de l'inventionDetailed description of the invention
Les effluents gazeux à traiter (E) peuvent provenir de n'importe quel procédé industriel susceptible de générer des effluents gazeux chargés de fluor ou d'acide fluorhydrique, tels que les procédés électrométallurgiques impliquant Pélectrolyse en présence de fluorures. Plus particulièrement, les effluents à traiter proviennent d'une cellule de production d'aluminium par électrolyse ignée. Ce procédé, appelé procédé Hall-Héroult, est basé sur F électrolyse de l'alumine dans un bain fondu contenant principalement de l'alumine et de la cryolithe.The gaseous effluents to be treated (E) can come from any industrial process capable of generating gaseous effluents loaded with fluorine or hydrofluoric acid, such as electrometallurgical processes involving electrolysis in the presence of fluorides. More particularly, the effluents to be treated come from an aluminum production cell by igneous electrolysis. This process, called the Hall-Héroult process, is based on the electrolysis of alumina in a melt containing mainly alumina and cryolite.
Ces effluents sont captés et acheminés à travers au moins un conduit d'acheminement vers le dispositif de traitement d'effluents gazeux selon l'invention. Dans le cas d'une usine d' électrolyse ignée d'aluminium, leur température à l'entrée dans un dispositif de dépollution est typiquement supérieure à 120°C, compte tenu notamment de la température des bains d'électrolyse, de la nature et dimension des moyens de captation, et de la longueur des moyens d'acheminement des effluents vers les installations de dépollution. Dans certaines usines, cette température peut dépasser 13O0C ou même 1400C, au moins temporairement. En effet, cette température dépend aussi de la température ambiante et montre des variations saisonnières. De même, en phase de démarrage d'une cellule d'électrolyse, elle peut atteindre temporairement des valeurs plus élevées qu'en régime stationnaire.These effluents are collected and conveyed through at least one conveying conduit to the waste gas treatment device according to the invention. In the case of an igneous aluminum electrolysis plant, their temperature at the entrance to a depollution is typically greater than 120 ° C, especially taking into account the temperature of the electrolysis baths, the nature and size of the collection means, and the length of the means for conveying the effluents to the pollution control facilities. In some plants, this temperature may exceed 130 ° C. or even 140 ° C., at least temporarily. Indeed, this temperature also depends on the ambient temperature and shows seasonal variations. Similarly, in the start-up phase of an electrolysis cell, it can temporarily reach higher values than in stationary mode.
Le dispositif selon l'invention comporte au moins une zone de dépollution (4) desdits effluents (E) au moyen de poudre d'alumine (A), et au moins une zone de séparation (5) dans laquelle on sépare les effluents gazeux traités (Et) et la poudre d'alumine chargée d'acide fluorhydrique (Af).The device according to the invention comprises at least one depollution zone (4) of said effluents (E) by means of alumina powder (A), and at least one separation zone (5) in which the treated gaseous effluents are separated. (Et) and the alumina powder loaded with hydrofluoric acid (Af).
La zone de dépollution (4) peut comporter avantageusement un système d'injection (43) , lequel on met en contact les effluents à traiter (E) avec de la poudre d'alumine. Dans cette zone de dépollution, on traite les effluents gazeux (E) contenant de l'acide fluorhydrique. Lesdits effluents (E) entrent en contact intime avec de la poudre d'alumine (A), qui fixe lors de ce contact au moins une partie de l'acide fluorhydrique contenue dans les effluents à traiter (E) et devient ce que nous appelons ici de l'alumine chargée d'acide fluorhydrique (Af), alors que les effluents s'appauvrissent en acide fluorhydrique et deviennent que ce nous appelons ici des effluents traités (Et). Les effluents traités (Et) et l'alumine chargée d'acide fluorhydrique (Af) sont ensuite acheminés dans la zone de séparation (5). Le temps de résidence dans la zone de dépollution (4) peut être de l'ordre de la seconde, par exemple deux secondes.The depollution zone (4) may advantageously comprise an injection system (43), which is put in contact with the effluents to be treated (E) with alumina powder. In this depollution zone, gaseous effluents (E) containing hydrofluoric acid are treated. Said effluents (E) come into intimate contact with alumina powder (A), which during this contact fixes at least part of the hydrofluoric acid contained in the effluents to be treated (E) and becomes what we call Here, alumina charged with hydrofluoric acid (Af), while the effluents are depleted in hydrofluoric acid and become what we call here treated effluents (Et). The treated effluents (Et) and the alumina charged with hydrofluoric acid (Af) are then conveyed into the separation zone (5). The residence time in the depollution zone (4) may be of the order of one second, for example two seconds.
Dans la zone de séparation (5), qui comporte au moins un moyen de séparation (52), par exemple un cyclone ou, dans une réalisation préférée, un filtre à manches, ou tout autre moyen approprié, l'alumine chargée d'acide fluorhydrique (Af) est séparée des effluents gazeux traités (Et). Tout ou partie de cette alumine séparée (As) peut être recyclée (i.e. réinjectée) dans l'étape d) de traitement des effluents, soit immédiatement, soit après le transfert dans un moyen de stockage intermédiaire. Cela permet d'augmenter sa charge d'acide fluorhydrique. La partie de l'alumine séparée (As) qui n'est pas recyclée dans la zone de dépollution (4) peut être introduite, éventuellement après son transfert dans un moyen de stockage temporaire tel qu'un silo, dans une cellule d'électrolyse ignée de l'alumine.In the separation zone (5), which comprises at least one separation means (52), for example a cyclone or, in a preferred embodiment, a bag filter, or any other appropriate means, the acid-laden alumina Hydrofluoric acid (Af) is separated from the treated gaseous effluents (Et). All or part of this separated alumina (As) can be recycled (ie reinjected) into the effluent treatment step d), either immediately or after transfer to an intermediate storage means. This makes it possible to increase its load of hydrofluoric acid. The part of the separated alumina (As) which is not recycled to the depollution zone (4) can be introduced, possibly after its transfer into a temporary storage means such as a silo, in an igneous electrolysis cell of alumina.
Le moyen essentiel de la présente invention qui permet de résoudre le problème posé est l'humidification de l'alumine avant ou pendant, et de préférence avant, son introduction dans la zone de dépollution (4). L'alumine introduite dans la zone de dépollution (4) peut être de l'alumine fraîche, c'est-à-dire de l'alumine qui n'a pas encore été en contact avec des effluents chargés d'acide fluorhydrique, de fluor ou d'autres gaz contenant cet élément. Nous désignons cette alumine par Av. On peut aussi introduire de l'alumine chargée d'acide fluorhydrique (Af) qui a été récupérée dans la zone de séparation, ou un mélange d'alumine fraîche (Av) et de l'alumine chargée d'acide fluorhydrique (Af). Quelle que soit son origine, cette alumine pulvérulente introduite dans la zone de séparation (5) doit être humidifiée. Au cours de l' humidification, elle se refroidit éventuellement par l'effet de la vaporisation du liquide.The essential means of the present invention which makes it possible to solve the problem posed is the humidification of the alumina before or during, and preferably before, its introduction into the decontamination zone (4). The alumina introduced into the depollution zone (4) may be fresh alumina, that is to say alumina which has not yet been in contact with effluents charged with hydrofluoric acid, fluorine or other gases containing this element. We designate this alumina by Av. We can also introduce the alumina loaded with hydrofluoric acid (Af) which has been recovered in the separation zone, or a mixture of fresh alumina (Av) and alumina charged with hydrofluoric acid (Af). Whatever its origin, this pulverulent alumina introduced into the separation zone (5) must be moistened. During the humidification, it eventually cools by the effect of the vaporization of the liquid.
L'humidification de l'alumine peut être effectuée à différents endroits. L'alumine peut être humidifiée avant son introduction dans la zone de dépollution (4), par exemple dans une zone de conditionnement (6), par exemple une trémie tampon, annexe à la zone de dépollution (4). Elle peut aussi être humidifiée dans Pinjecteur (43), c'est-à-dire pendant la mise en contact entre Peffluent gazeux à traiter (E) et la poudre d'alumine dans la zone de dépollution (4).The humidification of the alumina can be carried out at different places. The alumina may be moistened before it is introduced into the depollution zone (4), for example in a conditioning zone (6), for example a buffer hopper, annexed to the depollution zone (4). It may also be wetted in the injector (43), that is to say during the contact between the gaseous effluent to be treated (E) and the alumina powder in the pollution control zone (4).
L'humidification de l'alumine peut être réalisée à l'aide de différents moyens. A titre d'exemple, si une trémie de conditionnement (65) est utilisée, on peut utiliser un air de fluidisation qui est humidifié, ou on peut pulvériser un liquide, par exemple de l'eau, ou employer tout autre moyen approprié. Le taux d'humidité de l'alumine humidifiée peut varier dans des limites assez larges, comprises typiquement entre 0,5% en masse et 10% en masse. Avantageusement, il est compris entre 0,5% et 3%, plus avantageusement entre 0,5% et 2%, et le mode de réalisation le plus préféré utilise entre 0,5% et 1,5%. Si l'eau est pulvérisée sur l'alumine après l'introduction de l'alumine dans la zone de dépollution (4), l'eau ne se fixe pas sur l'alumine mais s'évapore simplement au contact avec les effluents, contribuant ainsi au refroidissement des effluents, mais sans abaisser la température de l'alumine. Les inventeurs ont constaté que l'alumine humidifiée, une fois en contact avec les effluents gazeux à traiter, voit son taux d'humidité décroître pour finalement se retrouver dans la zone de séparation avec un taux d'humidité relativement proche de 0%, et ce, quel que soit le taux d'humidité initial rajoutée à l'alumine Af. Ce même effet est également observé avec l'alumine fraîche.The humidification of the alumina can be carried out using various means. For example, if a conditioning hopper (65) is used, a fluidizing air can be used which is moistened, or a liquid such as water can be sprayed, or any other suitable means can be used. The moisture content of the moistened alumina can vary within fairly wide limits, typically ranging from 0.5% by weight to 10% by weight. Advantageously, it is between 0.5% and 3%, more preferably between 0.5% and 2%, and the most preferred embodiment uses between 0.5% and 1.5%. If the water is sprayed on the alumina after the introduction of the alumina in the depollution zone (4), the water does not settle on the alumina but evaporates simply on contact with the effluents, contributing thus cooling the effluents, but without lowering the temperature of the alumina. The inventors have found that the humidified alumina, once in contact with the gaseous effluents to be treated, has its moisture content decrease, finally ending up in the separation zone with a relative humidity level close to 0%, and regardless of the initial moisture content added to the alumina Af. This same effect is also observed with fresh alumina.
Cette faible valeur du taux d'humidité de l'alumine favorise l'utilisation de la poudre d'alumine chargée d'acide fluorhydrique Af extraite de la zone de séparation (5) dans une cellule d'électrolyse ignée de l'alumine, car il est préférable que le fonctionnement de ladite cellule d'électrolyse, qui est très délicat à réguler, ne soit pas perturbé par des variations excessives du taux d'humidité de l'alumine. La possibilité de pouvoir recycler la poudre d'alumine séparée directement dans le procédé d'électrolyse qui génère les effluents gazeux à traiter est primordiale pour la viabilité économique d'un tel procédé de dépollution. Le procédé selon l'invention s'avère être un procédé « robuste » au sens qu'une variation des paramètres du procédé, notamment les paramètres d'humidification, n'influe pas de manière significative sur l'humidité de l'alumine séparée. Ainsi, le taux d'humidité de l'alumine séparée n'est pas plus élevé que celui de l'alumine habituellement utilisé dans le procédé d'électrolyse ignée Hall-Héroult.This low value of the moisture content of the alumina favors the use of the hydrofluoric acid-loaded alumina powder Af extracted from the separation zone (5) in an igneous electrolysis cell of the alumina, because it is preferable that the operation of said electrolysis cell, which is very difficult to control, is not disturbed by excessive variations in the moisture content of the alumina. The possibility of being able to recycle the separated alumina powder directly into the electrolysis process which generates the gaseous effluents to be treated is essential for the economic viability of such a depollution process. The process according to the invention turns out to be a "robust" process in the sense that a variation of the process parameters, in particular the humidification parameters, does not significantly affect the humidity of the separated alumina. Thus, the moisture content of the separated alumina is not higher than that of the alumina usually used in the Hall-Héroult igneous electrolysis process.
Par ailleurs, l'utilisation du procédé selon l'invention n'entraîne pas le besoin de modifier les réglages du procédé d'électrolyse ignée qui génère les effluents à traiter, mais au contraire, le procédé selon l'invention est capable d'être adapté aisément aux variations de la composition chimique et concentration en polluants des effluents à traiter.Moreover, the use of the process according to the invention does not entail the need to modify the settings of the igneous electrolysis process which generates the effluents to be treated, but on the contrary, the process according to the invention is capable of being easily adapted to variations in the chemical composition and pollutant concentration of the effluents to be treated.
Le procédé de traitement d'effluents gazeux (E) contenant de l'acide fluorhydrique comporte selon l'invention au moins les étapes successives suivantes : a) on capte lesdits effluents gazeux (E), d) on traite lesdits effluents gazeux (E) contenant de l'acide fluorhydrique au moyen de poudre d'alumine (A), ladite poudre d'alumine (A) fixant au moins une partie de l'acide fluorhydrique, e) on sépare les effluents gazeux traités (Et) et la poudre d'alumine chargée d'acide fluorhydrique (Af), f) on recycle au moins une partie de ladite poudre d'alumine chargée d'acide fluorhydrique (Af) dans l'étape d) de traitement des effluents (E), ledit procédé étant caractérisé en ce que ladite poudre d'alumine (A)5 qui peut être déjà chargée d'acide fluorhydrique (Af), issue de la séparation (étape (e)), ou de l'alumine fraîche (Av)5 ou un mélange des deux, est humidifiée avant d'être introduite dans le flux desdits effluents gazeux (E) à traiter.The process for treating gaseous effluents (E) containing hydrofluoric acid comprises, according to the invention, at least the following successive stages: a) said gaseous effluents (E) are collected, d) said gaseous effluents (E) are treated containing hydrofluoric acid by means of alumina powder (A), said alumina powder (A) fixing at least a portion of the hydrofluoric acid, e) separating the treated gaseous effluents (Et) and the powder hydrofluoric acid-loaded alumina (Af), f) at least a portion of said hydrofluoric acid-loaded alumina powder (Af) is recycled to the effluent treatment step (e), said method being characterized in that said alumina powder (A) 5 which may already be loaded with hydrofluoric acid (Af), resulting from the separation (stage (e)), or fresh alumina (Av) 5 or a mixture of the two is humidified before being introduced into the flow of said gaseous effluents (E) to be treated.
Dans une réalisation très avantageuse du procédé selon l'invention, la température desdits effluents gazeux (E) au début de l'étape de traitement d) (c'est-à-dire à l'entrée de la zone de dépollution (4)) est inférieure à 1450C et préférentiellement inférieure à 1150C. Si les effluents (E) sont plus chauds, on les refroidit avant de les introduire dans la zone de dépollution (4). D'une manière générale, tout moyen de refroidissement approprié peut être utilisé, mais deux moyens sont particulièrement préférés ; ils peuvent être utilisés séparément ou en combinaison. Les inventeurs ont obtenu de bons résultats avec une température des effluents à l'entrée de la zone de dépollution (4) inférieure à 90°C ou même inférieure à 700C avec une alumine humidifiée et refroidie à 25°C. Une température des effluents trop basse peut cependant conduire à la condensation de liquides corrosifs dans les conduits d'acheminement des effluents ou dans la zone de séparation (5) ; cette condensation doit être évitée. C'est surtout dans le mode de réalisation préféré dans lequel le moyen de séparation (52) est un filtre à manches que la température des effluents gazeux (E) à l'entrée de la zone de dépollution (4) est critique, car pour des raisons d'économie, on ne souhaite pas devoir recourir à l'utilisation de tissus spéciaux qui résistent à des températures élevées : il est donc dans ce cas particulièrement avantageux que cette température des effluents soit inférieure à 145°C et préférentiellement inférieure à 115°C.In a very advantageous embodiment of the process according to the invention, the temperature of the said gaseous effluents (E) at the beginning of the treatment step d) (that is to say at the entry of the depollution zone (4) ) is less than 145 ° C. and preferably less than 115 ° C. If the effluents (E) are hotter, they are cooled before being introduced into the depollution zone (4). In general, any suitable cooling means may be used, but two means are particularly preferred; they can be used separately or in combination. The inventors have obtained good results with a temperature of the effluents at the entry of the depollution zone (4) of less than 90 ° C. or even less than 70 ° C. with a humidified alumina and cooled to 25 ° C. However, an effluent temperature that is too low can lead to the condensation of corrosive liquids in the effluent conveyance pipes or in the separation zone (5); this condensation should be avoided. It is especially in the preferred embodiment in which the separating means (52) is a bag filter that the temperature of the gaseous effluents (E) at the inlet of the depollution zone (4) is critical, because for reasons of economy, we do not wish to resort to the use of special fabrics that withstand high temperatures: it is therefore in this case particularly advantageous that this effluent temperature is less than 145 ° C and preferably less than 115 ° C.
Le premier moyen est l'injection d'un liquide (L) dans une zone d'injection liquide (2). Typiquement, on injecte de l'eau, et typiquement sous forme de gouttelettes, par exemple par au moins une buse de pulvérisation (21), dans le conduit d'acheminement des effluents en amont de la zone de traitement. Il est préférable que la quantité d'eau injectée soit réglée de manière à ce que la vaporisation de l'eau soit complète. En effet, on préfère éviter la condensation d'eau à un quelconque endroit du système de dépollution en aval du point d'injection d'eau (21), car cela peut favoriser la corrosion des composantes du dispositif, par exemple des tuyauteries, et cela d'autant plus que l'eau est susceptible de dissoudre l'acide fluorhydrique contenu dans les effluents gazeux à traiter (E), lesdits effluents pouvant de surcroît contenir encore des gaz tels que le SO2; le HCl, le CO2 ou éventuellement le NH3, qui forment également des solutions aqueuses corrosives. Avantageusement, on contrôle le taux de vaporisation des gouttelettes à l'aide d'un détecteur situé dans la zone d'injection liquide (2) ou en aval de celle-ci. On peut également prévoir un réglage de la température du liquide (L) injecté, mais en pratique, ce ne sera que dans des cas exceptionnels où les surcoûts d'investissement et d'exploitation que cela engendre seront considérés comme justifiés. Le liquide (L) peut aussi être chauffé avant son injection.The first means is the injection of a liquid (L) into a liquid injection zone (2). Typically, water, and typically in the form of droplets, is injected, for example by at least one spray nozzle (21), into the effluent conveying duct upstream of the treatment zone. It is preferable that the amount of water injected be adjusted so that the vaporization of the water is complete. Indeed, it is preferred to avoid the condensation of water at any point in the pollution control system downstream of the water injection point (21), since this may promote the corrosion of the components of the device, for example pipes, and this especially as the water is likely to dissolve the hydrofluoric acid contained in the gaseous effluents to be treated (E), said effluents may additionally contain gases such as SO 2; HCl, CO 2 or optionally NH 3 , which also form corrosive aqueous solutions. Advantageously, the vaporization rate of the droplets is controlled by means of a detector located in the liquid injection zone (2) or downstream thereof. It is also possible to provide an adjustment of the temperature of the liquid (L) injected, but in practice it will only be in exceptional cases where the additional investment and exploitation costs that this entails will be considered justified. The liquid (L) can also be heated before injection.
La zone d'injection liquide (2) peut être ou peut comporter une tour de refroidissement de type connu. A titre d'exemple, on peut faire circuler les effluents à traiter dans un venturi et on injecte tout ou partie des gouttelettes de fluide dans le venturi ou en amont du venturi. Cela permet d'accélérer la vaporisation des gouttelettes en contact avec les effluents chauds. On peut éventuellement injecter une partie des gouttelettes en aval du venturi.The liquid injection zone (2) may or may comprise a cooling tower of known type. For example, it is possible to circulate the effluents to be treated in a venturi and all or part of the fluid droplets are injected into the venturi or upstream of the venturi. This makes it possible to accelerate the vaporization of the droplets in contact with the hot effluents. It is possible to inject some of the droplets downstream of the venturi.
Le deuxième moyen est la dilution des effluents à traiter (E) par un fluide gazeux qui est injecté dans les effluents dans une zone d'injection d'un flux gazeux (3). Le fluide gazeux de dilution peut être de l'air, ou des effluents gazeux traités (Et) qui sortent de la zone de séparation (5) et qui sont réinjectés dans le circuit, ou un mélange des deux. En pratique, le volume de flux gazeux injecté ne devrait pas augmenter de façon rédhibitoire les volumes de gaz à traiter par la zone de séparation (5), car cela nécessite un surdimensionnement de la capacité des moyens de séparation (52). Dans une réalisation typique du procédé selon l'invention, le volume gazeux injecté ne dépasse pas environ 10% volumiques du volume d'effluents (E).The second means is the dilution of the effluent to be treated (E) by a gaseous fluid which is injected into the effluents in an injection zone of a gas stream (3). The gaseous dilution fluid may be air, or treated gaseous effluents (Et) that leave the separation zone (5) and are reinjected into the circuit, or a mixture of the two. In practice, the volume of gas flow injected should not unacceptably increase the volumes of gas to be treated by the separation zone (5), since this requires an oversizing of the capacity of the separation means (52). In a typical embodiment of the process according to the invention, the gaseous volume injected does not exceed about 10% by volume of the effluent volume (E).
Dans une réalisation avantageuse du procédé selon l'invention, le fluide gazeux est injecté en aval de la zone d'injection liquide (2).In an advantageous embodiment of the process according to the invention, the gaseous fluid is injected downstream of the liquid injection zone (2).
La nécessité d'utiliser l'un ou l'autre de ces deux moyens de refroidissement, ou les deux à la fois, dépend de la température et du débit des effluents gazeux (E) à traiter. Cette température dépend de nombreux facteurs, liés notamment aux conditions d'opération du procédé industriel qui génère lesdits effluents à traiter, aux conditions de captage et d'acheminement, et aux conditions climatiques et météorologiques du site de l'usine dans laquelle est installé le dispositif selon l'invention. Il est avantageux que le dispositif selon l'invention comporte ces deux moyens de refroidissement, à savoir la zone d'injection liquide (2) et la zone d'injection d'un flux gazeux (3), car cela confère au procédé selon l'invention une grande facilité d'adaptation de la conduite du procédé.The need to use one or both of these cooling means, or both, depends on the temperature and the flow rate of the gaseous effluent (E) to be treated. This temperature depends on numerous factors, notably related to the operating conditions of the industrial process that generates the said effluents to be treated, to the conditions of collection and conveyance, and to the climatic and meteorological conditions of the site of the plant in which the plant is installed. device according to the invention. It is advantageous that the device according to the invention comprises these two cooling means, namely the injection zone liquid (2) and the injection zone of a gas stream (3), as this confers on the process according to the invention a great ease of adaptation of the pipe of the process.
Dans une autre réalisation avantageuse de la présente invention, la poudre d'alumine introduite dans la zone de dépollution (4) a été préalablement refroidie avec des moyens de refroidissement autres que la vaporisation du liquide utilisé pour l'humidification. Dans ce cas, on ajoute au dispositif une zone de refroidissement (9) séparée. Cette zone peut se situer dans la zone de conditionnement (6) ou ailleurs. Tout moyen pour refroidir les particules minérales pulvérulentes peut convenir. Dans un mode de réalisation, dans lequel la zone de refroidissement de l'alumine (9) se trouve dans la zone de conditionnement (6), la zone de conditionnement (6) comprend au moins une trémie de conditionnement (62) dotée de serpentins dans lesquels circule un liquide réfrigérant. Dans une réalisation avantageuse de ce mode de réalisation de l'invention, la trémie de conditionnement (62) est placée au-dessous du moyen de séparation (52) et comporte des serpentins dans lesquels circule un fluide frigorifique. On peut aussi diviser le fond fluidisé de la trémie (62) en plusieurs secteurs dans lesquels l'alumine passe successivement. L'ensemble de la surface de fluidisation de cette trémie est couverte par le réseau de réfrigération. Le fluide réfrigérant circule en sens inverse de l'alumine recyclée. A partir du dernier secteur (i.e. le secteur le plus froid), l'alumine recyclée est réinjectée dans les effluents à traiter, en amont de la zone de dépollution (4) ou directement dans cette zone. Ainsi, l'alumine chargée d'acide fluorhydrique (Af) peut être refroidie avant d'être recyclée, et ce refroidissement est indépendant des moyens de refroidissement utilisés pour ajuster la température des effluents à traiter qui entrent dans la zone de dépollution (4). Si on utilise de l'alumine fraîche (Av), elle peut être également refroidie de la même manière. Avantageusement, la température de la poudre d'alumine introduite dans la zone de dépollution (4) est inférieure à 700C, et préférentiellement comprise entre 25°C et 50°C. Une zone de refroidissement (9) séparée peut également utiliser une trémie fluidisée, simple ou à fond subdivisé, comme décrit ci-dessus.In another advantageous embodiment of the present invention, the alumina powder introduced into the decontamination zone (4) has been previously cooled with cooling means other than the vaporization of the liquid used for humidification. In this case, a separate cooling zone (9) is added to the device. This zone may be in the conditioning zone (6) or elsewhere. Any means for cooling the powdery mineral particles may be suitable. In one embodiment, wherein the cooling zone of the alumina (9) is in the conditioning zone (6), the conditioning zone (6) comprises at least one conditioning hopper (62) equipped with coils in which circulates a coolant. In an advantageous embodiment of this embodiment of the invention, the conditioning hopper (62) is placed below the separating means (52) and comprises coils in which a refrigerant circulates. It is also possible to divide the fluidized bottom of the hopper (62) into several sectors in which the alumina passes successively. The entire fluidization surface of this hopper is covered by the refrigeration network. The refrigerant circulates in the opposite direction of the recycled alumina. From the last sector (ie the coldest sector), the recycled alumina is reinjected into the effluents to be treated, upstream of the pollution control zone (4) or directly in this zone. Thus, the hydrofluoric acid-loaded alumina (Af) can be cooled before being recycled, and this cooling is independent of the cooling means used to adjust the temperature of the effluents to be treated that enter the pollution control zone (4). . If fresh alumina (Av) is used, it can also be cooled in the same way. Advantageously, the temperature of the alumina powder introduced into the decontamination zone (4) is less than 70 ° C., and preferably between 25 ° C. and 50 ° C. A separate cooling zone (9) may also use a fluidized hopper, single or subdivided bottom, as described above.
Si l'alumine fraîche (Av) provient d'un silo de stockage, sa température sera normalement inférieure à 50°C, voire inférieure à 4O0C. Elle peut être injectée en amont de la zone de dépollution (4), ou directement dans cette zone. On préfère cependant l'injecter dans la zone de conditionnement (6), où elle se mélange avec l'alumine recyclée et est en même temps humidifiée et refroidie. Si on a besoin de refroidir davantage l'alumine fraîche (Av)3 on peut l'injecter dans la zone de refroidissement (9).If the fresh alumina (Av) comes from a storage silo, its temperature will normally be less than 50 ° C, or even lower than 40 ° C. It may be injected upstream of the depollution zone (4), or directly in this area. However, it is preferred to inject it into the packaging zone (6), where it mixes with the recycled alumina and is at the same time humidified and cooled time. If it is necessary to further cool the fresh alumina (Av) 3 it can be injected into the cooling zone (9).
Toute alumine du type et de la granulométrie de celles utilisées pour le procédé HaIl- Héroult peuvent convenir. Cette alumine est connue sous le nom Smelter Grade Alumina (SGA).Any alumina of the type and particle size of those used for the HaIlHeroult process may be suitable. This alumina is known as Smelter Grade Alumina (SGA).
Les différents essais sur une installation pilote de taille réduite avec injection d'alumine fluorée, ont montré que le rendement de captation dépend des paramètres opératoires du procédé, notamment de la température des effluents dans la zone de dépollution (4) et de la température de l'alumine injectée. Le paramètre qui a l'influence la plus grande est cependant l'humidification de l'alumine. A titre d'exemple, avec de l'alumine fluorée sèche introduite dans la zone de dépollution (4) à une température d'environ 1000C et mise en contact avec les effluents à traiter (contenant de l'acide fluorhydrique) dont la température est comprise entre 110 et 120°C, on trouve un rendement de captation de fluor de l'ordre de 37%, alors que l'utilisation d'une alumine fluorée humide avec 3% en masse d'eau augmente le rendement de captation à environ 78% Cela illustre clairement l'effet de l'humidification qui est le paramètre de premier ordre.The various tests on a pilot plant of reduced size with injection of fluorinated alumina, have shown that the capture efficiency depends on the operating parameters of the process, in particular the temperature of the effluents in the depollution zone (4) and the temperature of the effluent. injected alumina. The parameter that has the greatest influence, however, is the humidification of the alumina. By way of example, with dry fluorinated alumina introduced into the depollution zone (4) at a temperature of approximately 100 ° C. and placed in contact with the effluents to be treated (containing hydrofluoric acid), the temperature is between 110 and 120 ° C, there is a fluorine uptake efficiency of about 37%, while the use of a wet fluorinated alumina with 3% by weight of water increases the capture efficiency at about 78% This clearly illustrates the effect of humidification which is the first order parameter.
La température de l'alumine et la température des effluents dans la zone de dépollution (4) sont des paramètres de second ordre dont le choix judicieux a permis aux inventeurs d'obtenir, dans l'installation pilote de taille réduite, un rendement de captation d'environ 93% avec une alumine fluorée humide à une température d'environ 35°C injectée dans des effluents à traiter dont la température était d'environ 73 °C, alors que dans les mêmes conditions de température, une alumine fluorée sèche ne conduit qu'à un rendement de captation d'environ 80%. Le procédé selon l'invention permet d'obtenir un rendement de captation d'acide fluorhydrique supérieur à 85%, et préférentiellement significativement supérieur à 90%, avec 100% d'alumine fluorée sans apport d'alumine fraîche qui a une captation meilleure que l'alumine fluorée. The temperature of the alumina and the temperature of the effluents in the depollution zone (4) are second-order parameters, the judicious choice of which allowed the inventors to obtain, in the pilot plant of reduced size, a capture efficiency. of about 93% with a wet fluorinated alumina at a temperature of about 35 ° C injected into effluents to be treated whose temperature was about 73 ° C, while under the same temperature conditions, a dry fluorinated alumina does not led to a capture efficiency of about 80%. The process according to the invention makes it possible to obtain a hydrofluoric acid uptake efficiency of greater than 85%, and preferably significantly greater than 90%, with 100% fluorinated alumina without adding fresh alumina which has a better uptake than fluorinated alumina.

Claims

Revendications claims
1) Procédé de traitement d'effluents gazeux (E) contenant de l'acide fluorhydrique, dans lequel successivement a) on capte lesdits effluents gazeux (E), d) on traite lesdits effluents gazeux (E) contenant de l'acide fluorhydrique au moyen de poudre d'alumine (A), ladite poudre d'alumine (A) fixant au moins une partie de l'acide fluorhydrique, e) on sépare les effluents gazeux traités (Et) et la poudre d'alumine chargée d'acide fluorhydrique (Af), f) on recycle au moins une partie de ladite poudre d'alumine chargée d'acide fluorhydrique (Af) dans l'étape d) de traitement des effluents (E), ledit procédé étant caractérisé en ce que ladite poudre d'alumine, chargée d'acide fluorhydrique (Af) issue de la séparation (étape (e)) ou fraîche ou un mélange des deux, est humidifiée avant ou pendant son introduction dans le flux desdits effluents gazeux1) Process for treating gaseous effluents (E) containing hydrofluoric acid, wherein successively a) said gaseous effluents (E) are collected, d) said gaseous effluents (E) containing hydrofluoric acid are treated with medium of alumina powder (A), said alumina powder (A) fixing at least a portion of the hydrofluoric acid, e) the treated gaseous effluents (Et) and the acid-laden alumina powder are separated off hydrofluoric (Af), f) recycling at least a portion of said hydrofluoric acid-loaded alumina powder (Af) in the effluent treatment step (e) (E), said method being characterized in that said powder of alumina, charged with hydrofluoric acid (Af) resulting from the separation (step (e)) or fresh or a mixture of both, is wetted before or during its introduction into the flow of said gaseous effluents
(E) à traiter.(E) to be treated.
2) Procédé selon la revendication 1, caractérisé en ce que l'alumine Af est humidifiée avec une quantité d'eau comprise entre 0,5% en masse et 10% en masse, préférentiellement comprise entre 0,5% et 3%, et encore plus préférentiellement comprise entre 0,5% and 2%.2) Process according to claim 1, characterized in that the alumina Af is moistened with a quantity of water of between 0.5% by weight and 10% by weight, preferably between 0.5% and 3%, and more preferably between 0.5% and 2%.
3) Procédé selon une quelconque des revendications 1 ou 2, caractérisé en ce que entre la captation des effluents gazeux (E) (étape (a)) et le traitement desdits effluents (E) (étape (d)), on introduit un flux gazeux (G) (étape c), préférentiellement de l'air, à raison d'au plus 10% en volume dans lesdits effluents (E).3) Process according to any one of claims 1 or 2, characterized in that between the capture of gaseous effluents (E) (step (a)) and the treatment of said effluents (E) (step (d)), a flow is introduced. gaseous (G) (step c), preferably air, at a rate of at most 10% by volume in said effluents (E).
4) Procédé selon une quelconque des revendications 1 à 3, caractérisé en ce que entre la captation (étape (a)) et le traitement (étape (d)), et le cas échéant avant l'introduction du flux gazeux (G) (étape (c), on refroidit lesdits effluents (E) par l'injection d'un liquide (L) (étape b). 5) Procédé selon une quelconque des revendications 1 à 4, caractérisé en ce que ladite poudre d'alumine chargée d'acide fluorhydrique (Af) ou fraîche est refroidie avant d'être recyclée (étape f) dans l'étape de traitement (d).4) Process according to any one of claims 1 to 3, characterized in that between the capture (step (a)) and the treatment (step (d)), and where appropriate before the introduction of the gas stream (G) ( step (c), said effluent (E) is cooled by the injection of a liquid (L) (step b). 5) Process according to any one of claims 1 to 4, characterized in that said alumina powder loaded with hydrofluoric acid (Af) or fresh is cooled before being recycled (step f) in the treatment step (d). ).
6) Procédé selon une quelconque des revendications 1 à 5, caractérisée en ce que la température de la poudre d'alumine introduite dans la zone de dépollution (4) est inférieure à 700C, et préférentiellement comprise entre 25°C et 500C.6) Process according to any one of claims 1 to 5, characterized in that the temperature of the alumina powder introduced into the decontamination zone (4) is less than 70 0 C, and preferably between 25 ° C and 50 0 vs.
7) Dispositif de traitement d'effluents gazeux (E) contenant de l'acide fluorhydrique, ledit dispositif comportant :7) Apparatus for treating gaseous effluents (E) containing hydrofluoric acid, said device comprising:
(i) une zone de dépollution (4) desdits effluents (E) au moyen de poudre d'alumine(i) a depollution zone (4) of said effluents (E) using alumina powder
(A)5 (ii) une zone de séparation (5) où on sépare les effluents gazeux traités (Et) et la poudre d'alumine chargée d'acide fluorhydrique (Af), (iii) une zone de conditionnement (6) de l'alumine où ladite poudre d'alumine chargée d'acide fluorhydrique (Af), issue de la zone de séparation (5) est humidifiée par pulvérisation d'eau avant d'être introduite dans la zone de dépollution (5).(A) 5 (ii) a separation zone (5) where it separates the gaseous effluents treated (Et) and the alumina powder loaded with hydrofluoric acid (Af), (iii) a conditioning zone (6) the alumina wherein said hydrofluoric acid-loaded alumina powder (Af) from the separation zone (5) is moistened by spraying water before being introduced into the decontamination zone (5).
8) Dispositif selon la revendication 7, comportant en plus une zone de refroidissement (9) de l'alumine où ladite poudre d'alumine (A) est refroidie avant d'être introduite dans la zone de dépollution (4).8) Device according to claim 7, further comprising a cooling zone (9) of the alumina wherein said alumina powder (A) is cooled before being introduced into the decontamination zone (4).
9) Dispositif selon une des revendications 7 ou 8, comportant en plus une zone d'injection de gaz (3) en amont de la zone de dépollution (4).9) Device according to one of claims 7 or 8, further comprising a gas injection zone (3) upstream of the pollution control zone (4).
10) Utilisation du procédé selon une quelconque des revendications 1 à 6 ou du dispositif selon une quelconque des revendications 7 à 9 pour la dépollution d'effluents provenant d'une cellule de production d'aluminium par électrolyse ignée. 10) Use of the method according to any one of claims 1 to 6 or the device according to any one of claims 7 to 9 for the depollution of effluent from an aluminum production cell by igneous electrolysis.
PCT/FR2006/001538 2005-07-01 2006-06-30 Method and device for processing gaseous wastes in particular containing a hydrofluoric acid WO2007003777A1 (en)

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CA002608551A CA2608551A1 (en) 2005-07-01 2006-06-30 Method and device for processing gaseous wastes in particular containing a hydrofluoric acid
NO20080581A NO20080581L (en) 2005-07-01 2008-01-31 A method and apparatus for treating gaseous waste especially containing a hydrofluoric acid

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FR0507056A FR2887784B1 (en) 2005-07-01 2005-07-01 PROCESS AND DEVICE FOR TREATING GASEOUS EFFLUENTS CONTAINING PARTICULARLY FLUORHYDRIC ACID
FR0507056 2005-07-01

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CN102953090B (en) * 2011-08-29 2015-06-03 沈阳铝镁设计研究院有限公司 Bottom air inlet type purification system

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4006066A (en) * 1974-01-24 1977-02-01 Vereinigte Aluminum-Werke Aktiengesellschaft Method of and apparatus for the treatment of exhaust-gases in the electrolytic production of aluminum
US4065271A (en) * 1973-09-15 1977-12-27 Metallgesellschaft Aktiengesellschaft Process of separating hydrogen fluoride from gases
FR2626192A1 (en) * 1988-01-23 1989-07-28 Walther & Cie Ag METHOD AND DEVICE FOR EXTRACTING GAS FROM UNDESIRABLE GASEOUS CONSTITUENTS BY ADSORPTION OR CHEMISORPTION ON A PULVERULENT ADSORBENT
FR2836059A1 (en) * 2002-02-19 2003-08-22 Ensmse Continuous recovery process, e.g. for volatile organics, involves condensing or solidifying fraction from gaseous flow
FR2848875A1 (en) * 2002-12-18 2004-06-25 Pechiney Aluminium Method, for treating effluents from Hall Heroult electrolytic cell producing aluminum, involves injecting coolant droplets into effluent line upstream of reactor

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4065271A (en) * 1973-09-15 1977-12-27 Metallgesellschaft Aktiengesellschaft Process of separating hydrogen fluoride from gases
US4006066A (en) * 1974-01-24 1977-02-01 Vereinigte Aluminum-Werke Aktiengesellschaft Method of and apparatus for the treatment of exhaust-gases in the electrolytic production of aluminum
FR2626192A1 (en) * 1988-01-23 1989-07-28 Walther & Cie Ag METHOD AND DEVICE FOR EXTRACTING GAS FROM UNDESIRABLE GASEOUS CONSTITUENTS BY ADSORPTION OR CHEMISORPTION ON A PULVERULENT ADSORBENT
FR2836059A1 (en) * 2002-02-19 2003-08-22 Ensmse Continuous recovery process, e.g. for volatile organics, involves condensing or solidifying fraction from gaseous flow
FR2848875A1 (en) * 2002-12-18 2004-06-25 Pechiney Aluminium Method, for treating effluents from Hall Heroult electrolytic cell producing aluminum, involves injecting coolant droplets into effluent line upstream of reactor

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FR2887784A1 (en) 2007-01-05
CA2608551A1 (en) 2007-01-11
NO20080581L (en) 2008-01-31

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