AU2005284072B2

AU2005284072B2 - Device for supplying and dispensing a powdery material in an ascending gas stream, and reactor equipped with same

Info

Publication number: AU2005284072B2
Application number: AU2005284072A
Authority: AU
Inventors: Jean-Pierre Depauw; Jean-Pierre Guibet
Original assignee: Solios Environnement SA
Current assignee: Solios Environnement SA
Priority date: 2004-09-10
Filing date: 2005-09-05
Publication date: 2010-12-09
Anticipated expiration: 2025-09-05
Also published as: CA2578654A1; CA2578654C; AU2005284072A1; FR2875147B1; WO2006030096A1; ZA200701869B; EP1796826A1; ATE473045T1; DE602005022207D1; EP1796826B1; NO20071815L; FR2875147A1

Abstract

The invention concerns a device for supplying and dispensing a powdery material in an ascending gas stream (F), in a substantially vertical reactor contacting said powdery material, in particular a chemical and/or physical neutralizing agent of at least one effluent of the gas stream to be purified, with said gas stream, comprising means for distributing said powdery material in said gas stream which are fed by gravity feeding means and means conveying said powdery material in fluidized bed (10). Said conveying means comprise at least one airslide (3) outside the reactor and directly adjacent the reactor side wall (4), and said gravity feeding means are gravity distributors (13) each of which has one end (14), wherein emerges a feeding orifice (12) into the reactor side wall (4), and through which the powdery material from the fluidized bed (10) flows.

Description

Device for supplying and dispensing a powdery material in an ascending gas stream, and reactor equipped with same 5 The invention relates to a device for supplying and dispensing a powdery material in an ascending gas stream, possibly hot and dust-laden, in a substantially vertical reactor for contacting this powdery material with the gas flow, and a further subject of the 10 invention is a reactor, in particular for stripping at least one pollutant effluent from a gas upflow in the reactor, which is equipped with a powdery material feed and distribution device according to the present invention. 15 Devices for feeding and distributing powdery materials as described above are already known, mounted on vertical reactors for contacting powdery materials, particularly agents for the chemical and/or physical neutralization of at least one effluent to be stripped 20 from the gas upflows in the reactors, with these gas flows, these known devices comprising means for distributing at least one powdery material in the corresponding gas flow, which is supplied by means for gravity feeding and means for transporting the powdery 25 material in a fluidized bed. These known feed and distribution devices are used for contacting a powdery material, in particular an adsorbent or chemically reactive material, with gases, possibly hot and dust-laden, containing pollutant 30 effluents that should be removed, in the reactors equipped for this purpose. These treatments, resulting from the contacting of the gas upflows in these reactors with particles of these powdery materials, have the purpose, in particular, of ridding the gases 35 of fines that are fixed on these particles, and/or pollutant gaseous compounds that are adsorbed on or combined with them. For convenience, in the rest of the present description, the chemical and/or physical neutralization agent used, consisting of an adsorbent or chemically reactive powdery material, may be designated as adsorbent material. Many methods other than the methods of physicochemical stripping and recovery of effluents 5 present in gas flows, and implying the contacting of particles of a powdery material with the said gas flows, can be put into practice in many industry sectors, with the help of feed and distribution devices. It is known to use feed and distribution 10 devices for the stripping of at least one pollutant effluent from a gas upflow, and in particular, from a gas flow issuing from aluminium electrolysis cells or furnaces for baking anodes for aluminium electrolysis, and in which reactor a powdery material is introduced 15 and distributed as an agent for chemical and/or physical neutralization of the said pollutant effluents, particularly fresh and/or recycled alumina, or coke powder, so as to neutralize, by adsorption or by chemical reaction in particular, fluorinated 20 elements, particularly HF, fluorinated gaseous compounds, tars, pitch and other organic elements such as polycyclic aromatic hydrocarbons. It is well known that the abovementioned treatments require good contact between the particles 25 of powdery material and the components of the gas upflows treated, hence a good distribution of the powdery material in the gas flows containing pollutant effluents in the form of gases and/or fines. The first installations for treating polluted 30 gases used wet scrubbers, which have a number of drawbacks, associated in particular with the storage, feed, distribution, recovery, filtering and recycling of liquids. 239955_1 (GHMatters) - 3 Over the years, these installations have been replaced by dry treatment units, particularly using adsorbent materials. Depending on the industries which generate them 5 upstream, the pollutant effluents to be recovered, for neutralization and/or purification, are numerous. Besides CO 2 and NOx, the discharged gases may, before treatment, contain SO 2 , HCl, HF, other fluorinated compounds, tars, pitch and other organic elements such 10 as polycyclic aromatic hydrocarbons, referred to as PAHs. These elements can be covered by dry gas treatment requiring the distribution of specific adsorbents in these gases. In the first installations for the dry treatment 15 of gases containing pollutant elements, the specific adsorbent powdery material was introduced through a line terminating laterally in vertical and/or horizontal lines of the aeraulic circuit for discharging the gases to the atmosphere and in which 20 the flow conditions approached steady state. In such installations, the adsorbent material was entrained in co-current flow, but the mixing of adsorbent particles and gases, and hence adsorbent particles and pollutant elements, was too limited to guarantee satisfactory 25 purification. A first improvement consisted in creating turbulence in the gas flow treated in order to improve the mixing between the gas and the solid particles of the powdery material, as well as the contact time 30 between the pollutant effluents and the adsorbent particles. However, this method caused a substantial increase in abrasion of the inside walls of the reactor and also of the exposed walls in the reactor, components of circuits passing through the reactor or 35 arranged therein, entailing more extensive and more costly maintenance. In the particular case of the treatment of gas flows issuing from aluminium electrolysis cells, and for which the neutralizing agent is alumina, the - 4 turbulence created in the gas flow to improve the mixing and the contact time between the alumina powder and the pollutant effluents, also favours a reduction of the size of the alumina particles by attrition, and 5 hence a loss of effectiveness of the alumina powder, which is detrimental for the method of manufacture of aluminium by re-injection, in the electrolysis cells, of the alumina recovered after the purification treatment and containing fluorinated compounds also 10 necessary for the electrolysis of the aluminium. Patent FR 2 534 831 proposed another improvement, consisting in using multiple and distributed injection nozzles to inject adsorbent powdery material into a vertical line, cylindrical or with a venturi 15 (convergent-divergent section), with a central nozzle injecting fresh adsorbent material and offset nozzles for injecting recycled adsorbent material, these nozzles being distributed to as to achieve the most uniform possible injection of the powdery material 20 throughout the cross section of the vertical line or column. For this purpose, furthermore, each nozzle is equipped with a jet breaker, to permit the diffusion of the adsorbent powdery material in the form of a layer that is easily dispersed and mixed with the gas upflow. 25 The drawback of such an installation is that the combination of nozzles and jet breakers creates a non negligible pressure drop, due to the space occupied by these components in the vertical column and, furthermore, maintenance problems are associated in 30 particular with the piping constituting the bodies of the nozzles. Documents WO 92/02 289 and WO 95/13 866 have described other installations in which a substantially vertical cylindrical reactor comprises one or more 35 stages of superimposed peripheral rings, through which the flow to be purified is circulated. The bottom of each ring consists of radial plates each inclined about a respective radial axis and between which the gas flows in a helical upflow movement. The adsorbent - 5 powdery material is introduced into the gas swirl above the upper ring and, with the gas flow, forms a sort of rotating fluidized bed, from which the powdery material exits by overflow, and, if the installation comprises 5 at least two stages, is then directed to the next ring immediately below, and so on up to the last ring or bottom ring, from which the powdery material leaves the reactor by flowing into a central axial flow manifold. This arrangement creates a high pressure drop, as 10 well as non-negligible abrasion of the reactor walls by the adsorbent powdery material, and attrition thereof, which is detrimental for the abovementioned reasons, when this adsorbent powdery material is alumina. US 4 501 599 and EP 0 117 338 describe another 15 installation in which the adsorbent powdery material is injected radially into the annular gas upflow, from an injector arranged axially in the reactor. This multiple radial injector comprises a cylindrical or biconical body comprising a base opening, through which 20 the fresh and recycled adsorbent powdery material is introduced under a given pressure, determined by the gravity feed means consisting of a vertical line supplied axially from the top, so that the powdery material reaches openings that are radially oriented in 25 the upper part of the injector and permitting the injection of the adsorbent powdery material into the gas flow to be purified under a pressure higher than that prevailing in the reactor. The advance of the powdery material, from the gravity feed means to the 30 central axis of the multiple injector, can be ensured by means for transporting this powdery material in a fluidized bed. All the installations described in the abovementioned patent documents yield good results, but 35 generally require injecting the powdery material with a sufficient hydraulic head with respect to the reactor, giving rise to high power consumption, particularly when the injection system creates a high pressure drop in the reactor on account of the volume that it occupies in the reactor. Furthermore, these installations are essentially suitable for reactors of limited size, cylindrical, with 5 circular or rectangular cross section, and, in the latter case, with a low ratio (lower than 4) of the length to the width of the cross section. Moreover, in these various installations, the satisfactory application of the treatment method 10 requires high velocities (up to 30 to 35 m/s at the neck of a venturi) of the gas upflow to prevent the countercurrent settling of the powdery material. In fact, the systems used to inject this material create fairly cohesive aggregates, which react as single 15 particles having the dimensions of these aggregates, and accordingly have much higher velocities of fall, in the upflow, than those of the initial particles of the powdery material used. In a first aspect, there is provided a device for 20 feeding and distributing a powdery material in a gas upflow possibly hot and dust-laden, in a substantially vertical reactor for contacting said powdery material, particularly an agent for the chemical and/or physical neutralization of at least one effluent to be stripped 25 from said gas flow, with said gas flow, comprising means for distributing said powdery material in said gas flow which are supplied by means for gravity feeding and means for transporting said powdery material in a fluidized bed said means for transporting said powdery 30 material in a fluidized bed comprises at least one air slide, substantially horizontal, outside the reactor and directly adjacent to the side wall of the reactor at least at the level of several openings for feeding the reactor with powdery material, which drops from said air 35 slide into the reactor via said feed openings arranged laterally in walls of the air slide and of the reactor, and said gravity feed means are gravity distributors, 2399755_2 (GHMatters) arranged in chutes fixed in the reactor in inclined positions with a slope of less than 900 to the horizontal, and each of which has one end, in the upper and radially external position, in which one of said 5 feed openings in the side wall of the reactor terminates respectively, so that all the powdery material flowing through said feed opening is collected in said upper end of the inclined gravity distributor, and flows in the latter towards its lower end, in a radially internal 10 position with respect to its upper end, and through which the powdery material is injected, with the velocity of fall acquired in the gravity distributor, into the gas upflow, said lower ends of the gravity distributors being distributed in the horizontal cross 15 section of the reactor. Thus the particles of powdery material introduced into the gas flow at the level of the lower end of each gravity distributor are picked up by the gas upflow and distributed substantially uniformly in a zone of influence of the gravity 20 distributor, by the gas upf low, of which the velocity may be significantly lower than the velocity in the installations of the prior art. Furthermore, the powdery material, properly channelled in the upper end parts of the gravity distributors, is not entrained by 25 the gas upf low, so that the inside wall of the reactor is protected against abrasion, and the limited velocity of travel of the powdery material in the gravity distributors, due to the limited height of fall, limits the attrition of the particles of this material, which 30 is particularly advantageous when this powdery material is alumina. At least one air slide, but preferably each of them, is arranged substantially in an elongated chamber comprising, on its substantially horizontal base, and 35 between two side walls, an air distribution manifold above which a porous bottom extends, separating the manifold from a substantially horizontal channel supplied with powdery material, the porous bottom 2399755_2 (GHMatters) permitting a distributed and substantially uniform passage of air from the manifold into the channel effecting the fluidization and the transport of said powdery material in a fluidized bed. 5 Advantageously furthermore, due to the extreme fineness of the powdery material that may be used, and to eliminate losses, the fluidization channel of the air slide is outwardly closed, and its internal side wall, on the reactor side, possibly common with a wall of the 10 reactor when said reactor wall is plane, has slits also arranged in the wall of the reactor, and located above the feed openings to permit the fluidization air to degasify towards the interior of the reactor without passing through the feed openings, the number of said 15 degassing slits preferably being at least equal to the number of feed openings. These degassing slits, widely dimensioned, permit the degassing of the fluidization air towards the interior of the reactor without disturbing the aeraulic equilibrium, insofar as these 20 degassing slits are sufficiently large to avoid creating a high overspeed along the inside wall of the reactor, this degassing nevertheless serving to protect this inside wall from abrasion by the powdery material. Advantageously, furthermore, each feed opening of 25 the reactor is conformed as a self-regulating opening of the flow of the powdery material passing through it to flow into the corresponding gravity distributor, said self-regulating opening comprising a lower part of substantially round or oblong shape, prolonged upwardly 30 by an upper part in the shape of a substantially vertical slit, smaller in width than the width of the lower part, and is preferably arranged in a movable plate added on to a corresponding window in at least one of the walls of the reactor and of the air slide, and to 35 which plate the gravity distributor is preferably fixed. Preferably, these self-regulating openings are at the same horizontal level, particularly at the level of their lower part of substantially round or oblong shape, 2399755_2 (GHMatters) to guarantee uniform flow from one self-regulating opening to the next. For certain reactors of rectangular or cylindrical cross section, it may be advantageous for at least one 5 movable plate, but preferably each of them, covering a window of at least one of the walls of the reactor and of the air slide, to have two neighbouring self regulating openings of the same shape and dimensions, each terminating respectively in one of two gravity 10 distributors, preferably supported by the plate, each symmetrical to the other about a vertical plane, perpendicular to the wall of the reactor and midway between the two self-regulating openings, the two gravity distributors also being inclined to said 15 vertical plane and separating from one another towards the interior of the reactor by an angle preferably in a range of about 400 to about 900 in projection in a horizontal plane. Thus the position of the gravity distributors can 20 be adjusted by positioning the plate with respect to the corresponding window of the reactor wall, and the spacing between the two distributors of the same plate can be adapted to the type of reactor and to the environmental conditions. 25 Concerning the gravity distributors, at least one of them, but preferably both, is arranged in a chute always remaining upwardly open, and of which the depth, between its bottom and the upper edge of its two sides, at the level of its upper end, is at least equal to the 30 height of the corresponding feed opening, the shape of the bottom and of the sides of the chute and the spacing between said sides being such that the horizontal projection of the upper end of the chute on the wall of the reactor at the level of the corresponding feed 35 opening, envelops said feed opening. Other advantageous features of the gravity distributors are as follows: 23997552 (GHMatters) - lIu - the chute of each gravity distributor has, in a cross section, a general "U" or "V" shape with a flat or convex or "V" shaped bottom, joined to convex or linear and substantially vertical or inclined sides; 5 - the bottom and/or the upper edges of the sides of the chute is/are linear, in a broken line, convex in a parabola shape, "S" shaped, with an average slope between the upper and lower ends of which the angle to the horizontal is at least equal to the angle of repose 10 of the powdery material, and a maximum of 800, and preferably of between about 40* and about 60*; - the height of the sides of the chute decreases linearly from the upper end, at the level of the wall of the reactor, to the lower end of the chute; 15 - in its lower end part, the chute is limited to its bottom, preferably of a curved shape with upward concavity, or the bottom extends between the sides of lower limited height than the height of the sides outside the lower end part of the chute; 20 - openings are arranged in the bottom and/or the sides of the chute, so as to permit the removal by the gas upflow of a part of the powdery material flowing in the chute; and - the gravity distributors extend in substantially 25 vertical planes perpendicular to the wall of the reactor or in vertical planes inclined to planes perpendicular to the wall of the reactor. In the particular case of a cylindrical reactor with substantially circular cross section, it is 30 advantageous for at least one air slide, and preferably each of them, to comprise at least two linear sections forming, in succession, a part of a polygon, and each externally tangent to the side wall of the reactor, at the level of a respective feed opening of the reactor. 35 On the contrary, in the particular case of a reactor of four-sided horizontal, and preferably elongated rectangular cross section, the device may advantageously comprise at least one air slide extending 2399755_2 (GHMatters) - 11 along the whole of at least one of the sides, preferably a long side, of the cross section, and supplying feed openings and gravity distributors substantially uniformly spaced along said side of the cross section of 5 the reactor, the uniform or non-uniform spacing of the gravity distributors possibly corresponding substantially to the width of their zone of influence in the reactor. However, if justified in particular by the width of 10 the rectangular section reactor, the device may comprise at least two air slides each extending along respectively one of the two long opposite sides of the rectangular cross section of the reactor, the two air slides preferably having a common feed via their end 15 located in a same short side of the cross section. In both cases, whether the reactor is equipped with a single air slide along a long side of its section, or with two air slides on the two opposite long sides, it is possible for the gravity distributors to be identical 20 to one another and have their lower end substantially aligned with a mid-axis of the cross section of the reactor, preferably the longitudinal mid-axis of said cross section. However, it is also possible for the lengths of the 25 gravity distributors to be adapted so that their lower ends are placed alternately in a staggered arrangement with respect to a mid-axis of the cross section, preferably the longitudinal mid-axis of said section. In another aspect, there is provided a 30 substantially vertical reactor for contacting a powdery material with a gas upf low in the reactor, which is in particular a reactor for stripping at least one pollutant effluent from the gas upflow, particularly from a gas flow issuing from aluminium electrolysis 35 cells or furnaces for baking anodes for aluminium electrolysis, and in which reactor a powdery material is introduced and distributed as an agent for chemical and/or physical neutralization of said pollutant 239755_2 (GHMatters) - 12 effluents, particularly fresh and/or recycled alumina, or coke powder, and the reactor of the invention is characterized in that it is equipped with a device for feeding and distributing powdery material as described 5 above, so as to neutralize, by adsorption or by chemical reaction in particular, fluorinated elements, particularly HF, fluorinated gaseous compounds, tars, pitch and other organic elements such as polycyclic aromatic hydrocarbons. 10 One advantage of an embodiment is to remedy the abovementioned drawbacks of the known installations, and to propose a device of the type described above, guaranteeing a better feed and distribution of the particles of powdery material, particularly of reactive 15 or adsorbent material, substantially throughout the cross section of the reactor, by improving the contacts between the particles of powdery material and the gas flow, and by increasing the contact time, in order to improve the stripping efficiency, particularly of 20 gaseous or solid pollutant elements, in the gases and/or elements to be recovered for utilization by recycling. Another advantage of an embodiment is to provide a feed and distribution device of the type described above, suitable for maintaining the stripping efficiency 25 in large reactors, and, in general, for better satisfying the various requirements of the practice than the known similar devices. Another advantage is to provide a feed and distribution device that serves to limit the abrasion of 30 the inside wall of the reactor by the powdery material, and to limit the attrition of the particles of powdery material, to avoid the abovementioned drawbacks observed with the use of alumina by recycling in an industrial treatment such as aluminium electrolysis, and whereby 35 the feed and distribution device ensures an excellent distribution of the powdery material in a gas upflow, of which the velocity is reduced in comparison with that of the installations of the prior art. 239975_2 (GHMatters) Another advantage is to provide a feed and distribution device of the abovementioned type, serving to reduce the pressure drop in the gas flow in the reactor, and hence the power necessary for the treatment 5 of the gases, by limiting the velocity of the particles of powdery material at the outlet into the gas flow, and preferably by limiting the upward velocity of the gases in the reactor, through the exclusive use of gravitational forces acting on the particles of powdery 10 material during the limited height of fall. Another advantage of an embodiment is to provide a device of the abovementioned type serving to prevent the formation of aggregates of particles of powdery material before their feed and distribution in the gas flow. 15 In the particular application of the purification of gases resulting from the production of aluminium by electrolysis, or the baking of anodes for aluminium electrolysis, another advantage of an embodiment is to provide a device of the type described above serving to 20 improve the recovery of the gaseous or solid fluorinated compounds in the gases issuing from the series of electrolysis cells or baking furnaces, by a better feed, distribution and penetration of the particles of alumina powder in the gas flow, the alumina powder acting as 25 adsorbent and chemical reagent. Another advantage of an embodiment is to provide a feed and distribution device serving to guarantee a proper distribution of the powdery material, particularly of adsorbent material, throughout the gas 30 flow, while limiting the concentration of this powdery material in the zones close to the reactor walls. In fact, it is known that in a reactor in which polluted gas flows are treated by adsorption, the higher the gas flow to be treated, the larger the cross section 35 required of these reactors, and it becomes increasingly difficult to distribute the adsorbent powdery material uniformly, and particularly towards the centre of the cross section of the reactor with feed means distributed 2399755_2 (GHMatters) - .Lq along the whole perimeter of the reactor. It so happens that the solution whereby injectors are used under a pressure higher than that of the internal chamber of the reactor, and extending up to the centre of the reactor, 5 has the major drawback of requiring higher power and a pressurized feed circuit. Other features and advantages will appear from the description given below, which is non-limiting, of embodiments described with reference to the drawings 10 appended hereto in which: - Figure 1 shows, in a horizontal cross section, a purification reactor of elongated rectangular cross section, equipped with a first example of a feed and distribution device, 15 - Figure 2 shows a partial view in a vertical cross section of the reactor and of the device in Figure 1, at the level of a feed opening and of a gravity distributor of the device, - Figure 3 is a partial schematic view showing, in 20 a horizontal projection on the inside wall of the reactor, the upper end of a gravity distributor enveloping a feed opening arranged as a self-regulating opening, - Figure 4 is a similar view to Figure 3 for an 25 arrangement with two neighbouring self-regulating openings, - Figure 5 schematically shows, in a plan view, the arrangement of the two gravity distributors associated with the two self-regulating openings in Figure 4, in a 30 variant of the reactor according to Figure 1, - Figure 6 schematically shows, in a side elevation, three different forms of distributor identified at (a), (b) and (c), between their upper A and lower B ends, 35 23997552 (GHMatters) - 15 - Figure 7 shows four different forms, shown at (a), (b), (c) and (d) of the cross section of the bottom of the gravity distributors, - Figure 8 shows a similar view to Figure 1 of a 5 variant of a reactor with an elongated rectangular cross section, with gravity distributors which have their lower ends positioned in a staggered arrangement in the reactor, - Figure 9 is a similar view to Figures 1 and 8 of 10 another variant of a reactor with a rectangular cross section, of a larger width than those of Figures 1 and 8, and in which the feed and distribution device comprises two air slides, and - Figure 10 is a similar view to Figures 1, 8 and 15 9 of another variant of the reactor, cylindrical with a circular horizontal cross section, equipped with a feed and distribution device in which the air slide is conformed as part of a polygon. In the following discussion, the reactor and the 20 associated feed and distribution device are respectively a reactor for purifying a gas upflow issuing from aluminium electrolysis cells, and a device for distributing alumina powder in the reactor, as adsorbent and reactive powdery material, for the 25 recovery of pollutant and/or to be recycled effluents which are present in the gas flow, particularly fluorinated compounds. In Figure 1, the vertical reactor 1, of elongated rectangular horizontal cross section, has its side wall 30 2 bordered, along the whole of one of the two long sides of its cross section, by a horizontal air slide 3 of the device for feeding and distributing alumina powder to the reactor 1. As shown in Figure 2, the air slide 3, outside the 35 reactor 1, but possibly inside a filter (not shown) associated with the reactor 1, has an internal side wall (on the side of the reactor 1) which is a common wall 4 with the reactor 1, this being made possible by the fact that the air slide 3 extends horizontally - 16 against a large vertical and plane side face of the reactor 1. Towards the exterior, the air slide 3 is bounded by an external side wall 5 joined to the common wall or internal wall 4, on the one hand, by a 5 horizontal bottom 6 and, on the other, by a roof 7 which, with the external wall 5, closes the air slide 3 outwardly, in order to prevent losses of the extremely fine alumina powder used. An air distribution manifold 8 is bounded in the air slide 3, above its bottom or 10 base 6 and below a porous bottom 9 extending between the side walls 4 and 5 of the air slide 3, and permitting a distributed and substantially uniform passage of air to the top of the porous bottom 9, in order to ensure the fluidization and transport in a 15 fluidized bed 10 of the alumina powder fed into the horizontal channel thus formed above the air distribution manifold 8, from a feed manifold 11 at an end of the air slide 3 that is preferably located on a short side of the rectangular section of the reactor 1, 20 as shown in Figure 1. This alumina feed manifold 11 receives fresh alumina, issuing for example from a feed hopper (not shown) and/or recycled alumina, previously already injected and distributed in the gas upflow F (see 25 Figure 2) in the reactor 1, and collected at the upper outlet of this reactor by a filtration device (also not shown) collecting the alumina containing fluorinated compounds to recycle it, partly to the fluidized bed 10 of the air slide 3, and/or partly to the aluminium 30 electrolysis cells. The transport channel of the alumina fluidized bed 10, thus bounded in the air slide 3 in the form of an elongated chamber above the porous bottom 9, communicates with the internal chamber of the reactor 1 35 via openings 12 arranged through the common wall 4 for feeding this chamber with alumina. If the internal side wall of the air slide 3 is different from the side wall 2 of the reactor 1, but applied against this side wall 2, at least at the level - 17 of the feed openings 12, it is clear that these openings are arranged laterally in the walls that are directly adjacent and in contact both of the air slide 3 and the reactor 1. 5 Each feed opening 12 terminates, at the level of the inside of the wall 2 of the reactor 1, in the upper end of a gravity distributor 13, tilted downward and towards the interior of the reactor 1, as shown in Figure 2, with an inclination to the horizontal that is 10 less than 900. This distributor 13 is arranged as a chute occupying a fixed position in the reactor 1, and channelling the flow of alumina powder which flows from the fluidized bed 10 in the air slide 3 to the reactor 1, by overflow via the feed opening 12 terminating in 15 the upper end 14 of the gravity distributor 13. Thus all the alumina powder flowing through a feed opening 12 is collected in the upper end 14 of a corresponding tilted gravity distributor 13, and flows into the distributor to its lower end 15 in an internal 20 position (towards the centre of the reactor 1) with respect to its upper end 14, in an external position and against the inside of the side wall 2 of the reactor 1. The alumina powder is thus injected, with the velocity of fall acquired by the effect of gravity 25 in the tilted distributor 13, into the gas upflow F in the reactor 1, this gas flow F picking up the alumina particles thus released from the distributor 13 to distribute them substantially uniformly in the gas flow, within a zone of influence of this distributor 30 13. For the alumina powder to be distributed substantially over the whole area of the rectangular cross section of the reactor 1, without any accumulation near its side wall 2, the lower ends 15 of the distributors 13 are appropriately distributed in 35 this horizontal cross section of the reactor 1. In Figure 1, the distributors 13 are tilted in vertical planes, perpendicular to the common wall 4 of the reactor 1 and the air slide 3, and are uniformly spaced from one another by a distance that - 18 substantially corresponds to the width of the zone of influence of each of them in the reactor 1, the lower ends 15 of the distributors 13, which are all identical in this example, being substantially aligned with the 5 longitudinal mid-axis of the rectangular cross section of the reactor 1. In addition to the feed openings 12, the common wall 4 of the air slide 3 and the reactor 1 has degassing slits 16, which are located above the feed 10 openings 12 in order to permit the air for fluidizing the alumina in a fluidized bed 10 in the channel of the air slide 3 to degasify towards the interior of the reactor 1, without disturbing the aeraulic equilibrium, and without the passage of this degassed air at the 15 level of the feed openings 12. These degassing slits 16, of which the number is preferably at least equal to that of the feed openings 12 of the reactor 1, are widely dimensioned, and sufficiently large to avoid creating a high overspeed of the gas upf low along the 20 inside of the wall 2 of the reactor 1, this degassing nevertheless serving to protect the inside of the wall 2 of the reactor 1 from abrasion by the alumina powder, which is distributed in the gas flow by the distributors 13, because, at the level of the upper 25 ends 14 of these distributors, all the alumina powder flowing in the reactor 1 is channelled in the gravity distributors 13. For this purpose, each distributor 13 is made like a chute which, in the reactor 1, is upwardly open along 30 its whole length, between its upper 14 and lower 15 ends, and its depth is at least equal to, and preferably slightly higher than the height of the corresponding feed opening 12, at least at the level of its upper end 14. The depth of the chute is defined 35 between the lower end of its bottom 17 and the upper edge 19 of its two sides 18, which, in the example of the distributor 13 in Figure 3, are two plane vertical and parallel sides 18, upwardly prolonging respectively each of the ends of a bottom 17 in the form of a half- - 19 cylinder of circular cross section, the two sides 18 having the same height along their whole length, between the upper 14 and lower 15 ends, but also possibly having a progressively and linearly decreasing 5 height from the upper end 14 to the lower end 15, as shown schematically in Figure 6 (a). In all cases, the shape of the bottom 17 and the sides 18 of the chute, as well as the spacing between the sides 18, are such that the horizontal projection 10 of the upper end 14 of the chute of each distributor 13 on the wall 4 of the reactor 1 at the level of the corresponding feed opening 12, defines a shape that envelops the feed opening 12. The general U-shaped cross section of the 15 distributor 13 in Figure 3 with a convex bottom 17 with an upward concavity and joined to linear and vertical sides 18, lends itself favourably, at the level of the upper end 14 of the distributor 13, to the enveloping of the corresponding feed opening 12, when this opening 20 is conformed as a self-regulating opening of the flow of alumina powder flowing through it from the fluidized bed 10 of the air slide 3 into the corresponding distributor 13. In fact, in this conformation as a self-regulating 25 opening, the opening 12 comprises a lower part 20 which is a circular opening, and which is upwardly and vertically prolonged by an upper part in the form of a slit 21, smaller in width than the width or diameter of the lower part 20. Such a self-regulating opening 30 operates as a nozzle, the level of the alumina passing through the opening 12 normally being in the lower part of the slit 21, as shown for example at 22 in Figure 3. Thus for a complete collection of the alumina flowing through the self-regulating opening 12 into the 35 corresponding distributor 13, the spacing between the two sides 18 and the diameter of the semicylindrical bottom 17 are slightly higher than the diameter of the lower part 20 of this opening 12, substantially having the shape of an alcohol or mercury thermometer.

- 20 For each self-regulating opening 12, the diameter of its circular lower part 20 is, in general, a function of the flow rate of powdery material that must pass through this opening 12. 5 To guarantee a uniform flow from one opening 12 to the next, these openings 12 are positioned so that their lower ends are at the same horizontal level. Substantially the same result can be obtained with the gravity distributors 13 of which the chutes have a 10 cross section of different shape. For example, as shown in Figure 7, the bottom of each chute can be V shaped or U-shaped, being prolonged according to these shapes by the sides 18, or in the shape of a flat bottomed trough prolonged by outwardly tilted sides, 15 themselves prolonged by vertical or inclined plane sides, as shown in diagrams (a) , (b) and (c) of Figure 7, in which diagram (d) corresponds to the semicylindrical bottom 17 in Figure 3. This bottom may be plane or linear and with a constant slope along an 20 angle of inclination a to the horizontal, as shown in Figure 6 (a), between its upper end 14 at A and lower end 15 at B. As a variant, as shown in Figure 6 (b) , the upper edges 19 of the sides of the chute of each distributor 25 13 are linear, but the bottom is longitudinally convex and has an upward concavity, the average slope of inclination, indicated by the angle a, being determined in this case by the inclination to the horizontal of the line connecting the points A and B at the bottom of 30 the chute to the level of the upper end 14 and lower end 15 respectively. In Figure 6 (c), the bottom 17 of the chute has an S-shaped curve, with, on the side of its upper end 14, an upwardly convex part, and, in its lower half, an upwardly concave lower part, the average 35 slope a being determined as in the example in Figure 6 (b), and the upper edges 19 of the sides 18 being curved and upwardly convex. Other shapes of the bottom and of the upper edge of the sides of the chute of the distributors 13 are - 21 possible, for example in a broken line like a Z or in a curved line like a parabola, in which case, the angle a is given by the imaginary line extending from the starting point A at the upper end of the distributor 13 5 and ending at point B where the bottom of the distributor 13 terminates. The distributors 13 using the force of gravity alone, which is applied to the alumina particles that they channel, to convey them to the centre of the 10 corresponding zones of influence, where these particles are picked up by the gas upflow F and distributed in it, each distributor 13 must have a certain slope, to enable the alumina particles to flow and to gain a certain velocity during their travel to the zone of 15 injection of these particles, individually or in a brittle aggregate, in the gas upflow F in the reactor 1. For this purpose, the slope of angle a is at least equal to the angle of repose of the powdery material used, in this case alumina, and no more than 800, and a 20 is preferably between about 400 and about 600. To guarantee the proper relative positioning of each feed opening 12 and of the corresponding gravity distributor 13, the distributor 13 is fixed, by its upper end 14, against a plate 23, for example 25 rectangular, in which the feed opening 12 is arranged, and, to guarantee proper positioning of the combination of the opening 12 and the distributor 13 with respect to the air slide 3 and the fluidized bed 10 in this air slide, the plate 23 is added on, as shown schematically 30 in Figure 3, to a window 24, also rectangular, arranged, at the level where a feed opening 12 must be located, in the wall 4 which is common to the reactor 1 and to the air slide 3, or in the wall 2 of the reactor in the absence of a common wall. The dimensions of the 35 plate 23 are higher than those of the window 24, so that the plate 23 overlaps the window 24, permitting a removable and adjustable fastening of the plate 23 to the wall 4 or 2.

- 22 For certain reactors with a horizontal circular or rectangular cross section, at least one removable plate 23' (see Figures 4 and 5), and possibly each of them, blocking a window 24 in the wall 2 of the reactor 1 or 5 in the common wall 4, has two neighbouring and identical (same shapes and dimensions) self-regulating openings 12, as well as two distributors 13, each associated respectively with one of the two openings 12, and fixed against the plate 23' by their upper end 10 14, and both symmetrical about the vertical plane that is perpendicular to the wall 2 or 4 and midway between the two openings 12, with the same inclination, in a horizontal plane, to this vertical mid-plane, or to the local radial direction, in the case of a cylindrical 15 reactor, by an angle of preferably between about 400 and about 90* depending on the type of reactor and the environmental conditions, so that the two distributors 13 separate from one another towards the interior of the reactor 1, while naturally being inclined toward 20 the bottom of this reactor 1. As a variant of Figures 1 to 3, the distributors 13 may deviate from the vertical planes perpendicular to the wall 2 of the reactor 1 or to the common wall 4, all on the same side and, possibly, by the same angle, 25 for example substantially 100, depending on the method or design requirements. To avoid creating high pressure drops in the aeraulic circuit, the sides 18 of the distributors 13 are vertical or substantially vertical, and the depth 30 of the distributors 13, which is always greater than the height of the openings 12 at the level of their upper end 14, has the effect, in addition to receiving all the powdery material flowing through the opening 12, of ensuring that the gas upf low F in the reactor 1 35 cannot entrain a part of the adsorbent alumina along the wall 2 of the reactor 1 or the common wall 4, which can cause significant abrasion of this wall by the alumina, and, simultaneously, a deterioration of the grain size distribution of this alumina by attrition, - 23 mechanisms that may occur in the reactors of the prior art. Whether the sides 18 of the distributors 13 have a height that is constant or that decreases, possibly 5 linearly or in steps or echelons, up to the lower end 15, until being no more than about 20 to 30 mm at this end 15, the introduction of the adsorbent alumina into the gas flow F can be considered as made at a point in space, and the maximum of alumina particles has a 10 countercurrent trajectory in the gas upflow F to be treated, thereby increasing the efficiency of fixing pollutant elements, before these particles are entrained by the gas flow F. The diffusion of the alumina particles in the gas upflow F then takes place 15 naturally. However, depending on the physicochemical properties of the powdery material used and of the gases, of the quantity of powdery material to be fed and the dimensional characteristics of the reactor 1, a 20 slightly more complex arrangement of the gravity distributors 13, particularly at the level of their lower end 15, may be necessary in order to enlarge the zone of influence of each distributor 13. This is why use can be made of the various 25 abovementioned forms of the bottom 17, the sides 18 and the upper edges 19 of the sides of the distributors 13, as described above with reference to Figures 6 and 7. However, according to another particular design, the lower end 15 of the distributor 13 may be limited 30 to the bottom 17 of the distributor 13, preferably of a semicylindrical section or, more generally, a curved shape with an upward concavity. In this case, the absence of a side of the chute of each distributor 13 at the level of its lower end 15 has the effect of 35 increasing the diffusion of the alumina particles projected into the gas upflow F, and of enlarging the zone of influence of the concerned distributor 13. The presence of a bottom, with a curved shape and upward concavity or a semicylindrical section, along - 24 the whole length of the distributor 13, has the advantage of preventing the trapping of alumina in the corners, which can occur with a bottom 17 or a complete chute of a distributor 13 according to Figure 7 (b). 5 In general, the fact that the chute of each distributor 13 is never closed upon itself serves to avoid clogging by the formation of aggregates of powdery material, and also facilitates upkeep and limits maintenance. 10 To modify the conditions of introduction of alumina powder into the gas upflow F, openings can also be arranged in the bottom 17 and/or in the sides 18 of the distributors 13, to permit the removal of a part of the alumina powder flowing in the distributor 13 by the 15 gas upflows, thereby altering the shape and extent of the zone of influence of the concerned distributor 13. By way of example only, an opening 25 of oval or oblong shape, or two openings 25 of the same shape, have been shown at (b) and (c) in Figure 6, each material removal 20 opening 25 being shown arranged in the part of a side 18 near the bottom 17 and near the lower end 15 of the shown distributor 13. According to a variant of the rectangular section reactor in Figure 1, the series of distributors 13 fed 25 by the sole air slide 3 for one treatment stage (whereas the reactor 1 may be equipped with several stages distributed at various height levels, and each comprising an air slide such as 3 and a series of distributors such as 13) is such that all the 30 distributors 13 are not identical with their main introduction points, at their lower end 15, aligned with the longitudinal mid-axis of the rectangular section, but, as shown in Figure 8, the distributors are grouped into two groups of distributors that are 35 identical to one another in each group, and which differ at least in the length of the distributors from the other group. In this way, the longer distributors 13' are alternately placed with the shorter distributors 13'' so that their lower ends 15' and 15'' - 25 are alternately staggered with respect to the longitudinal mid-axis of the rectangular cross section of the reactor 1. However, as in the example of Figure 1, all the gravity distributors 13' and 13'' are fed 5 from a same air slide 3 via feed openings 12 made as previously described. If necessary, the gravity distributors 13' and 13'' may also differ from one another in their lower ends 15' and 15'', in order to make their respective zones of influence substantially 10 uniform despite their different inclinations to the horizontal, if their lower ends 15' and 15'' are located substantially in the same horizontal plane. If the environmental requirements of the installation, and particularly the flow rate of the gas 15 upflow F to be treated, oblige the designer to make a reactor 1 with a much larger rectangular horizontal cross section, the series of distributors 13 or 13' and 13'' of the examples of Figures 1 and 8, fed by a single air slide 3 along the whole of one of the long 20 sides of the rectangular section of the reactor, may be duplicated by another series, parallel to the first, but fed and projecting from the long opposite wall of the reactor. In such an arrangement, as shown in Figure 9, the reactor, at each stage, comprises two 25 horizontal feed air slides 3' and 3'', each made like the air slide 3 previously described, and preferably connected to one another at the middle of a short side of the rectangular cross section by a common feed 11'. In this way, each of the air slides 3' and 3'' extends 30 along respectively one of the two long opposite sides of the rectangular cross section of the reactor, and in the example shown in Figure 9, it is assumed that all the gravity distributors, supplied by one or the other of the air slides 3' and 3'', are identical to the 35 gravity distributor 13 previously described. In this arrangement, the lower ends 15 of the distributors 13 are located between about 15% and about 40% of the width of the reactor, from their upper end 14 and hence from the corresponding long wall of the - 26 reactor, and preferably between about 20% and about 30% of this width. The arrangements in Figures 1, 8 and 9 are well adapted to reactors having very elongated rectangular 5 horizontal cross sections, qualified as "linear", for which the length of the cross section at the level of which the alumina powder is introduced is many times higher than the width of this section, the ratio of the length to the width being up to 12, and, whenever 10 possible, being a multiple of the width "d" of the zone of influence of a distributor 13, and this width may vary in practice between 200 and 800 mm, but is preferably between 400 and 500 mm. The length of the reactor cross section may reach 4000 mm for a width of 15 200 to 1200 mm. However, the reactors according to the invention are not limited, in their horizontal section, to a rectangular shape, and a cylindrical reactor with a circular cross section, as shown in Figure 10, may also 20 be equipped with an alumina powder feed and distribution device according to the invention. In this case, at least one air slide 3'' ' comprises for example three linear sections 26, 27 and 28 each made like the air slide 3 in Figure 2 except that the inside 25 wall 4''' of the air slide 3''' is not common with the cylindrical wall 2' of the reactor 1', the linear sections 26, 27, and 28, in succession, forming a part of a polygon, for example half of a hexagon, and each being externally tangent to the side wall 2' of the 30 reactor 1', at the level of a respective feed opening 12' of the reactor 1'. Due to the fact that the side wall 2' of the reactor 1' is different from the inside wall 4''' of the air slide 3''', each feed opening 12' consists in fact of a feed opening arranged in the 35 inside wall 4''' of the air slide 3''', at the level of the tangential point of the section 26, 27, or 28 concerned, and of an opposite feed opening, arranged in the wall 2' of the reactor 1'.

- 27 As previously, each feed opening 12' corresponds to a gravity distributor such as 13, extending inclined towards the bottom of the reactor 1' in a radial vertical plane, and preferably fixed by its upper end 5 such as 14 to a plate such as 23 (see Figure 3), which may be bent, and in which the feed opening in the wall 2' of the reactor 1' is arranged. As a variant, a second air slide such as 3''', also in the shape of a semi-hexagon, may be tangent at three points, 10 corresponding to as many feed openings 12', of the half of the circular section of the reactor 1' that is not enveloped by the air slide 3''' in Figure 10, that is, the upper half in this Figure. In all these installations, the lower ends 15, 15' 15 and 15'' of the distributors 13, 13', 13'' are open so that the powdery material penetrates into the gas upflow F with the sole velocity of fall acquired. For the coarser particles of powdery material, this permits a countercurrent travel, before the drag force exerted 20 on these particles reverses the direction of their movement, thereby increasing the gas-powdery material contact time, and hence the efficiency of fixing pollutant elements of the gas flow on the particles of powdery material. 25 Also in all the installations, the gravity distributors, which can be dismantled to facilitate maintenance, and can be dismantled in particular with the movable plates such as 23 and 23', are, for example, made from metal, particularly from bent and 30 possibly perforated plate, or from a moulded or thermoformed composite material. The gravity distributors such as 13, 13' and 13'' are designed so that their main point of injection of powdery material, generally their lower end such as 15, 35 15' and 15'', is located between about 15% and about 85% of the reactor diameter, or of its width, from the wall from which the distributors begin, that is, from their upper end such as 14, 14' or 14'', and preferably between about 30% and about 70%.

- 28 The installation of powdery material feed and distribution devices in reactors, with gravity distributors according to the invention, serves to introduce, into the gases to be purified, unaggregated 5 particles of powdery material, but on the contrary, particles which are dispersed from the air slide such as 3, 3'' or 3''' . Accordingly, only the inherent dimensional and physical characteristics of the particles of powdery material are factors in the 10 velocity of fall reached at the lower end of the gravity distributors. The risk of forced settling of powdery material is eliminated, making it possible, at the level of the method of adsorption or chemical reaction, to adopt lower gas upflow F velocities than 15 in the reactors of the prior art, while increasing the duration of the countercurrent travel of the particles of powdery material. These two parameters serve to improve the contact time between the powdery material and the pollutant elements in the gas flow. 20 The feed and distribution devices according to the invention can be used in various types of reactor, in which a powdery material must be contacted with a gas flow, possibly hot and dust-laden, in which the particles must be uniformly distributed. 25 In a particularly advantageous embodiment, the feed and distribution device of the invention is particularly adapted to the purification treatment in a reactor of polluted gases issuing from series of electrolysis cells in the production of aluminium. In 30 this application, fine alumina powder, as an adsorbent powdery material, is introduced into the reactor to collect the fluorinated compounds present in the hot gases issuing from these series of cells, before the loaded alumina is separated from these purified gases 35 in a filtration installation (not shown), which is placed downstream of the feed and distribution device of the invention. The alumina issuing from the filter or filters is then stored, in a fluidized bed, before the reintroduction of a part of this alumina into the reactor, while the remainder is sent to the electrolysis cells and recycled for the production of aluminium. It is clear that fresh alumina and recycled alumina can be introduced, separately or mixed as 5 required, in the reactor by gravity distributors as described above. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary 10 implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the 15 invention. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in 20 Australia or any other country. 2399755_1 (GHMatters)

Claims

1. Device for feeding and distributing a powdery 5 material in a gas upflow possibly hot and dust-laden, in a substantially vertical reactor for contacting said powdery material, particularly an agent for the chemical and/or physical neutralization of at least one effluent to be stripped from said gas flow, with said 10 gas flow, comprising means for distributing said powdery material in said gas flow which are supplied by means for gravity feeding and means for transporting said powdery material in a fluidized bed, wherein said means for transporting said powdery material in a 15 fluidized bed comprises at least one air slide, substantially horizontal, outside the reactor and directly adjacent to the side wall of the reactor at least at the level of several openings for feeding the reactor with powdery material, which drops from said 20 air slide into the reactor via said feed openings arranged laterally in walls of the air slide and of the reactor, and said gravity feed means are gravity distributors, arranged in chutes fixed in the reactor in inclined positions with a slope of less than 900 to 25 the horizontal, and each of which has one end, in the upper and radially external position, in which one of said feed openings in the side wall of the reactor terminates respectively, so that all the powdery material flowing through said feed opening is collected 30 in said upper end of the inclined gravity distributor, and flows in the latter towards its lower end, in a radially internal position with respect to its upper end, and through which the powdery material is injected, with the velocity of fall acquired in the 35 gravity distributor, into the gas upflow, said lower ends of the gravity distributors being distributed in the horizontal cross section of the reactor. 2399755_1 (GHMatters)

2. Device according to Claim 1, wherein at least one air slide is arranged substantially in an elongated chamber comprising, on its substantially horizontal base, and between two side walls, an air distribution 5 manifold above which a porous bottom extends, separating the manifold from a substantially horizontal channel supplied with powdery material, the porous bottom permitting a distributed and substantially uniform passage of air from the manifold into the 10 channel effecting the fluidization and the transport of said powdery material in a fluidized bed.

3. Device according to Claim 2, wherein the fluidization channel of the air slide is outwardly closed, and its internal side wall, on the reactor 15 side, possibly common with a wall of the reactor when said reactor wall is plane, has slits also arranged in the wall of the reactor, and located above the feed openings to permit the fluidization air to degasify towards the interior of the reactor without passing 20 through the feed openings, the number of said degassing slits preferably being at least equal to the number of feed openings.

4. Device according to any one of Claims 1 to 3, wherein each feed opening of the reactor is conformed 25 as a self-regulating opening of the flow of the powdery material passing through it to flow into the corresponding gravity distributor, said self-regulating opening comprising a lower part of substantially round or oblong shape, prolonged upwardly by an upper part in 30 the shape of a substantially vertical slit, smaller in width than the width of the lower part, and is preferably arranged in a movable plate added on to a corresponding window in at least one of the walls of the reactor and of the air slide, and to which plate 35 the gravity distributor is preferably fixed.

5. Device according to Claim 4, wherein at least one movable plate covering a window of at least one of 2399755_1 (GHMatters) the walls of the reactor and of the air slide, has two neighbouring self-regulating openings of the same shape and dimensions, each terminating respectively in one of two gravity distributors, preferably supported by the 5 plate, each symmetrical to the other about a vertical plane, perpendicular to the wall of the reactor and midway between the two self-regulating openings, the two gravity distributors also being inclined to said vertical plane and separating from one another towards 10 the interior of the reactor by an angle preferably in a range of about 400 to about 900 in projection in a horizontal plane.

6. Device according to any one of Claims 1 to 5, wherein each gravity distributor is arranged in a chute 15 always remaining upwardly open, and of which the depth, between its bottom and the upper edge of its two sides, at the level of its upper end, is at least equal to the height of the corresponding feed opening, the shape of the bottom and of the sides of the channel and the 20 spacing between said sides being such that the horizontal projection of the upper end of the chute on the wall of the reactor at the level of the corresponding feed opening, envelops said feed opening

7. Device as claimed in any one of Claims 1 to 6, 25 wherein the chute of each gravity distributor has, in a cross section, a general "U" or "V" shape with a flat or convex or "V" shaped bottom, joined to convex or linear and substantially vertical or inclined sides.

8. Device according to Claim 7, wherein the 30 bottom and/or the upper edges of the sides of the chute is/are linear, in a broken line, convex in a parabola shape, "S" shaped, with an average slope between the upper and lower ends of which the angle to the horizontal is at least equal to the angle of repose of 35 the powdery material, and a maximum of 800, and preferably of between about 400 and about 600. 2399755_1 (GHMstters) - 33

9. Device according to either of Claims 7 and 8, wherein the height of the sides of the chute decreases linearly from the upper end, at the level of the wall of the reactor, to the lower end of the chute. 5

10. Device according to any one of Claims 7 to 9, wherein in its lower end part the chute is limited to its bottom, preferably of a curved shape with upward concavity, or the bottom extends between the sides of lower limited height than the height of the sides 10 outside the lower end part of the chute.

11. Device according to any one of Claims 7 to 10, wherein openings are arranged in the bottom and/or the sides of the chute, so as to permit the removal by the gas upflow of a part of the powdery material 15 flowing in the chute.

12. Device according to any one of Claims 1 to 11, wherein the gravity distributors extend in substantially vertical planes perpendicular to the wall of the reactor or in vertical planes inclined to planes 20 perpendicular to the wall of the reactor.

13. Device according to any one of Claims 1 to 12, for a cylindrical reactor with substantially circular cross section, wherein at least one air slide comprises at least two linear sections forming, in 25 succession, a part of a polygon, and each externally tangent to the side wall of the reactor, at the level of a respective feed opening of the reactor.

14. Device according to any one of Claims 1 to 12, for a reactor of four-sided horizontal, and 30 preferably elongated rectangular cross section, wherein it comprises at least one air slide extending along the whole of at least one of the sides, preferably a long side, of the cross section, and supplying feed openings and gravity distributors substantially uniformly spaced 35 along said side of the cross section of the reactor.

15. Device according to Claim 14, wherein it comprises at least two air slides each extending along 2399755_1 (GHMatters) respectively one of the two long opposite sides of the rectangular cross section of the reactor, the two air slides preferably having a common feed via their end located in a same short side of the cross section. 5

16. Device according to either of Claims 14 and 15, wherein the gravity distributors are identical to one another and have their lower end substantially aligned with a mid-axis of the cross section of the reactor, preferably the longitudinal mid-axis of said 10 cross section.

17. Device according to either of Claims 14 and 15, wherein the lengths of the gravity distributors are adapted so that their lower ends are placed alternately in a staggered arrangement with respect to the mid-axis 15 of the cross section, preferably the longitudinal mid axis of the said section.

18. Reactor for stripping at least one pollutant effluent from a gas upflow in the reactor, particularly from a gas flow issuing from aluminium electrolysis 20 cells or furnaces for baking anodes for aluminium electrolysis, and in which reactor a powdery material is introduced and distributed as an agent for chemical and/or physical neutralization of said pollutant effluents, particularly fresh and/or recycled alumina, 25 or coke powder, wherein the reactor is equipped with a device for feeding and distributing powdery material according to any one of Claims 1 to 17, so as to neutralize, by adsorption or by chemical reaction in particular, fluorinated elements, particularly HF, 30 fluorinated gaseous compounds, tars, pitch and other organic elements such as polycyclic aromatic hydrocarbons.

19. A device for feeding and distributing a powdery material in a gas upflow substantially 35 described herein, with reference to the accompanying drawings.

20. A reactor for stripping at least one pollutant effluent from a gas upflow substantially described herein, with reference to the accompanying drawings. 2399755I (GHMatters)