Method and device for treating gas by injecting a powdered compound and an aqueous phase

Abstract

A method for treating a gas is shown which includes the steps of: injecting a powdered compound into the gas line, injecting an aqueous phase in droplet form into the line, capturing pollutants from the gases, and recovering the powdered compound separately. The step for injecting an aqueous phase in droplet form is done so as to moisten those particles of powdered compound in the gas line, when they are injected.

Claims

1. A method for treating gas having a predetermined flow direction in a gas conduit comprising the steps of a) injecting a powdery compound into the gas conduit at an injection point of a powdery compound, via a powdery compound injection piping, said injection piping having an internal face being in contact with said powdery compound and an external face, and so forming a cloud or flow of particles of powdery compound in said gas conduit at said injection point, b) injecting a monophasic liquid aqueous phase as droplets into said gas conduit, c) capturing pollutants of the gases with said powdery compound, and d) separately recovering said powdery compound enriched in pollutants and the gases depleted in pollutants, wherein said step for injecting a monophasic liquid aqueous phase as droplets is carried out inside said gas conduit in the injected cloud or flow of powdery compound particles, so as to humidify these powdery compound particles inside the gas conduit, during their injection, according to a weight ratio between the monophasic liquid aqueous phase injected as droplets and the injected powdery compound of greater than or equal to 0.05 and less than or equal to 1.2, said step for injecting a monophasic liquid aqueous phase being carried out via at least one monophasic liquid aqueous phase injection piping located within a peripheral space localized around said external face and having an external cover, the method further comprising isolation of said external face by at least one insulating layer positioned in said peripheral space between said external face and said external cover.

2. The method according to claim 1, wherein said powdery compound injection step is carried out in the gas conduit following an injection direction forming an angle from 90 to 150 degrees, relatively to the flow direction of the gases.

3. The method according to claim 1, wherein said powdery compound has an average particle size d.sub.50 of less than 80 m.

4. The method according to claim 1, wherein said powdery compound, before injection into said gas conduit, has a humidity (water mass content) comprised between 0.2 and 10%.

5. The method according to claim 1, wherein the weight ratio between the aqueous phase injected as droplets and the injected powdery compound is greater than or equal to 0.1, and less than or equal to 1.

6. The method according to claim 1, wherein said gases before injection of said powdery compound, have a temperature comprised between 10 C. and 100 C.

7. The method according to claim 1, wherein said gases before injection of said powdery compound, have a temperature comprised between 100 C. and 300 C.

8. The method according to claim 1, wherein said gases, before injection of said powdery compound, have a temperature comprised between 300 C. and 500 C.

9. The method according to claim 1, wherein said gases before injection of said powdery compound, have a temperature comprised between 850 C. and 1,100 C.

10. The method according to claim 1, wherein said gases, after injection of said powdery compound and of the aqueous phase as droplets, have a temperature comprised between n and n10 C., n being the temperature of the gases before injection of the powdery compound and of the aqueous phase.

11. The method according to claim 1, wherein said injection of the aqueous phase is carried out at a pressure comprised between 2 and 150 bars.

12. The method according to claim 1, characterized in that the powdery compound is a mineral compound selected from the group consisting of hydrated lime, sodium carbonate or bicarbonate, halloysite and sepiolite, a carbonaceous organic compound selected from active coal and lignite coke, or a mixture of these compounds.

13. The method according to claim 1, characterized in that the aqueous phase consists of water or of an aqueous solution of an alkaline or ammonia-based compound or based on halides, or on acids.

14. A device for injection of a powdery compound, to be introduced into a flue gas conduit comprising a source of powdery compound, a powdery compound injection piping supplied by the source of powdery compound and laid out in order to open into said gas conduit, said powdery compound injection piping having an internal face being in contact with said powdery compound and an external face, said powdery compound injection device further comprising a source of monophasic liquid aqueous phase and at least one piping for injecting an aqueous phase as droplets supplied by this monophasic liquid aqueous phase source, said at least one monophasic liquid aqueous phase injection piping being located within a peripheral space localized around said external face of the powdery compound injection piping and having an external cover, at least one insulating layer being positioned in said peripheral space between said external face of said powdery compound injection piping and the external cover.

15. The device according to claim 14, comprising a plurality of pipings for injecting an aqueous phase as droplets, each connected to a distributor connected to said aqueous phase source, each piping of said plurality of aqueous phase injection pipings being located in said peripheral space and further being provided with a stop valve.

16. The device according to claim 14, wherein each aqueous phase injection piping is laid out in a concentric tube out of which the aqueous phase injection piping is retractable.

17. The device according to claim 14, wherein each aqueous phase injection piping includes an outlet orifice formed as a slot.

18. The device according to claim 15, wherein the distributor is connected to a pressurization means for imparting to the aqueous phase a pressure comprised between 2 and 150 bars.

19. The device according to claim 14, further comprising a device for dosing said peripheral space provided with a series of orifices, among which a mineral compound orifice and at least one aqueous phase orifice, said mineral compound orifice being laid out for housing an outlet of said powdery compound injection piping, each aqueous phase orifice being laid out for housing an outlet of each aqueous phase injection piping.

20. The device according to claim 14, wherein said external cover has a diameter comprised between 100 and 250 mm.

21. The device according to claim 14, wherein said powdery compound injection piping has a diameter comprised between 75 and 150 mm.

22. The device according to claim 14, wherein each aqueous phase injection piping has a diameter comprised between 5 and 30 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a schematic side view of a first embodiment of the device for treating gases according to the present invention. FIG. 1B is a sectional view along the line I-I of FIG. 1A.

(2) FIG. 2A is a schematic side view of a second embodiment of the device for treating gases according to the present invention. FIG. 2B is a sectional view along the line II-II of FIG. 2A.

(3) FIG. 3 is a schematic side view of the embodiment according to FIG. 1 of the device for treating gases according to the present invention, for example used in a flue gas conduit, the direction of Injection of the powdery compound here being perpendicular to the flow direction of the flue gases.

(4) FIG. 4 is a schematic side view of the second embodiment according to FIG. 2 of the device for treating flue gases according to the present invention, used in a flue gas conduit, the direction of injection of the powdery compound here being also perpendicular to the flow direction of the flue gases.

(5) FIG. 5 is a schematic side view of the embodiment according to FIG. 2 of the device for treating flue gases according to the present invention, used in a flue gas conduit. Here, the direction of injection of the powdery compound is located obliquely with respect to the flow direction of the flue gases.

(6) FIGS. 3 to 5 illustrate methods, inter alia, for coupling devices according to the invention to a flue gas conduit.

DETAILED DESCRIPTION OF THE INVENTION

(7) In the Figures, identical or similar elements bear the same references. The injected powdery compound is in the illustrated cases of a mineral nature and the treated gases are flue gases.

(8) As this may be ascertained in FIGS. 1A and 1B, the device according to the present invention is a device for injecting a powdery mineral compound 1 to be introduced into a flue gas conduit, comprising a piping for injecting the powdery mineral compound 2 connected to a source of powdery mineral compound (not shown). The piping for injecting the mineral compound is laid out so as to open into said flue gas conduit 3 (see FIG. 3) and for allowing exit of the mineral compound via an outlet orifice for the mineral compound 14. The piping for injecting the mineral compound 2 has an external face 4 and an internal face 5. During operation, the internal face 5 is in contact with said powdery mineral compound during its use in the injection piping 2.

(9) The powdery mineral compound injection device 1 comprises in this illustrated embodiment a plurality of pipings for injecting an aqueous phase 6 as droplets, each connected to a distributor 7 connected to a supply of aqueous phase 8. As this may be seen in FIG. 1A or 1B, each piping 6 of the plurality of injection pipings is located around the mineral compound injection piping 2 in a space outside the latter, called here a peripheral space 9. Each aqueous phase injection piping 6 further comprises a valve 10 located between the distributor 7 and the aqueous phase outlet 11 of each aqueous phase injection piping 6. The exit of an aqueous phase 11 as droplets from each aqueous phase injection piping is practically and advantageously achieved by an aqueous phase outlet orifice in the form of a slot of planar spray, by means of a nozzle (not shown).

(10) By means of the valves 10, it is possible to not supply some of the pipings 6 and for example only supply those located immediately downstream from the injection point of the mineral compound relatively to the flow direction G of the flue gases in the flue gas conduit 3.

(11) The distributor 7 is connected to a pressurized aqueous phase supply 8. In an alternative of the device, a pressurizing means 12 gives the possibility of imparting the intended pressure to the water entering via the water supply 8. The pressure of the aqueous phase supply 8 is typically comprised between 2 and 150 bars. In one alternative, this pressure will rather be comprised between 2 and 20 bars, preferably between 3 and 15 bars and still more preferentially of about 8 bars. In another alternative, the pressure will be comprised between 20 and 150 bars, in particular between 30 and 100 bars. These high pressures give the possibility of avoiding fouling of the spraying piping.

(12) The mineral compound injection device further comprises a flange 13 provided with through-orifices 18 in order to be able to bolt or attach by any other means the device for treating flue gases through a flue gas conduit.

(13) Indeed, as this may be seen in FIG. 3, the flue gas conduit 3 to be treated includes an orifice for introducing the device 1. The latter is introduced into this orifice and attached on the conduit in a common way, by the flange 13 and attachment means 15. Tightening the flange 13 gives the possibility of maintaining pressure on the external face 16 of the flue gas conduit 3, but also ensures the seal of the connection of the device according to the present invention.

(14) In the embodiment illustrated in FIGS. 1A and 1B, a second flange 17 is present on the flue gas treatment device. This flange 17 is provided with a series of through-orifices 19 laid out for receiving attachment means. The flange 17 is laid out so as to be connected to a current mineral compound source (not illustrated).

(15) Advantageously, an external cover 20 is present around said peripheral space 9. The external cover 20 preferably has a diameter comprised between 100 and 250 mm, preferably less than 200 mm and more preferentially between 110 and 170 mm, in particular between 125 and 150 mm.

(16) In the peripheral space 9, an insulator layer may be provided between the external face 4 of said mineral compound injection piping and the external cover 20. The insulator may be simply air or any other insulating material known to one skilled in the art. It gives the possibility of avoiding cooling of the external face 4 which is isolated from the piping 6 which reduces the risks of agglomeration against the internal face 5 of the mineral compound circulating in the mineral compound injection piping.

(17) The device according to the present invention further comprises preferably a cap or a device 21 for closing said peripheral space. This cap is provided with a series of orifices among which the outlet orifice for the mineral compound 14 and as many outlet orifices for the aqueous phase 11 as aqueous phase piping 6 which are present.

(18) For injecting a mineral compound, a cylindrical tube 2 with a diameter of about 125 mm in stainless steel is typically used, which is mounted on a flange 13. The stainless steel is a source of agglomeration and clogging of the mineral compound and accordingly, the tube 2 in stainless steel (mineral compound injection piping 2) should be as short as possible and as direct as possible (without any obstacle) for reducing the dead areas. Consequently, the substantially cylindrical tube 2 (a bend may notably be used as illustrated in FIG. 2A) should take into account these considerations. Briefly, the device according to the present invention includes such a cylindrical mineral compound injection tube 2 which was modified in such a way that at least one aqueous phase injection piping 6 may be inserted along the substantially cylindrical mineral compound injection tube 2 without generating any obstacle in the flow of particles of the mineral compound in the substantially cylindrical piping/tube 2. In the embodiment illustrated in FIGS. 1A, 1B and 3, eight pipings for injecting an aqueous phase 6 as droplets, have been placed around the mineral compound injection piping 2, and the diameters of these piping 6 were selected so that the piping 6 may be integrated into the flange 13.

(19) Typically, the powdery mineral compound injection piping 2 has a diameter comprised between 75 and 150 mm, preferably between 80 and 125 mm and in particular of about 100 mm. Generally, each water injection piping 6 has a diameter comprised between 5 and 30 mm, preferably between 6 and 20 mm and more preferentially between 8 and 16 mm.

(20) When it is desirable to treat flue gases in a conduit with hydrated lime for lowering inter alia acid pollutants, the device according to the present invention is positioned as illustrated for example in FIG. 3. Hydrated lime is then injected into the hydrated lime injection piping 2 and leaves the piping via the outlet orifice 14. At this moment, a hydrated lime cloud, the particles of which typically have an average particle size d.sub.50 of less than 80 m, advantageously less than 50 m, preferably less than 35 m, preferably less than 25 m and more particularly less than or equal to 10 m, in particular less than or equal to 8 m, is formed in the conduit of flue gases to be treated 3. Advantageously, before injection into the flue gases, the hydrated lime has a humidity comprised between 0.2 and 10% by weight, in particular between 0.5 and 4% by weight, preferably less than 2%, in particular less than 1.5%.

(21) The pressurized aqueous phase enters the distributor 7 via said supply 8 and then penetrates into the water injection piping 6 for which the valves 10 or some of them are in an open position.

(22) According to an enhanced embodiment of the method according to the present invention, the step for injecting the aqueous phase as droplets is carried out in said cloud or flow of mineral compound in said flue gas conduit 3, in a close vicinity downstream from said injection point of the mineral compound relatively to the flow direction of the flue gases (indicated by a dual arrow G in FIG. 3), in said flue gas conduit 3. In this way, the injected powdery mineral compound is humidified and not or very few flue gases to be treated. The injection of aqueous solution droplets in a close vicinity downstream from the injected particles of mineral compound, relatively to the flow direction of the flue gases to be treated, is carried out in this embodiment by closing the valves 10 present on the aqueous phase injection piping 6 located upstream and opening those of the pipings located downstream.

(23) In the device, illustrated in FIG. 3, only the aqueous phase droplet injection pipings under pressure located in the portion S of the flue gas treatment device according to the present invention (downstream relatively to the gas flow) may have their valves in the open position while the other pressurized droplet injection pipings have valves in a closed position. In this way, the Injected pressurized aqueous phase droplets are introduced into a close vicinity downstream from the injection point of mineral compound particles, and the mineral compound particles are advantageously humidified.

(24) The pollutants of the flue gases are then captured by said mineral compound and this in an improved way by the presence of the aqueous phase particles surrounding the mineral compound particles. Next, the mineral compound enriched with pollutant compound and flue gases depleted in pollutants are recovered separately in a common way, notably by filtration.

(25) The mixed device for injection of a mineral compound/aqueous phase according to the present invention is therefore a simple, easy and inexpensive concept which gives the possibility of improving the capture of acid gases from flue gases.

(26) The temperature of the flue gases is typically comprised between 100 and 1,100 C. In certain facilities, this temperature varies from 110 C. to 350 C., preferably between 130 C. and 250 C. and even more preferentially between 150 C. and 230 C., in particular 180 C. and 220 C. In other cases, notably the activities generating SO.sub.2 as a main pollutant, the temperature of the flue gases is typically comprised between 250 C. and 500 C. or between 850 C. and 1,100 C. in a more upstream position (closer to the combustion area), preferably between 300 C. and 450 C. or between 900 C. and 1,100 C. in a more upstream position and preferentially between 330 C. and 400 C. or between 950 C. and 1,050 C. in a more upstream position. The effect of humidification of the mineral compound is of a relatively short period of time since the aqueous phase droplets evaporate very quickly in hot gases. Therefore, the contact between the mineral compound particles injected into the flue gases and the water droplets has to be obtained as rapidly as possible.

(27) The size of the aqueous phase droplets is on average comprised between 500 and 5,000 m, preferably between 500 and 1,000 m or between 1,000 and 5,000 m depending on the injection conditions, and is in particular obtained by using pipings with flat outlet orifices (as slots) through which the aqueous phase droplets are formed. The size of the obtained droplets also promotes contact between the aqueous phase droplets injected into the cloud of particles of mineral compound and the mineral compound particles as soon as they are injected into the flue gas conduit.

(28) As mentioned earlier, it is generally difficult to inject into the flue gases a mineral composition, in particular humid hydrated lime (containing more than 2% or even 4% of water) or humidified beforehand because of the agglomeration of the particles which occurs and which has the effect of clogging the injection pipings. Further, humid hydrated lime or humidified beforehand is more easily subject to carbonatation (quite fast), which induces a reduction in the capture performances. Finally, the agglomerated particles of mineral compound, in particular humid hydrated lime have reduced capture capacities because of the reduction in the accessibility to their pores. Typically, the fine particles are sought for improving the capture performances. The use of the device according to the present invention allows humidification of the fine mineral compound particles injected into the conduit of flue gases to be treated as such, in situ and they react with notably acid gases in the cloud of aqueous phase droplets directly generated and also dry in situ since evaporation is very fast in the hot flue gases. Therefore, water evaporation occurs before the particles have had the time to agglomerate.

(29) This is also due to the fact that according to the present invention, the amount of injected water is only the amount of water required for humidifying the mineral compound particles and for generating a cloud formed with mineral compound particles and with aqueous phase droplets. The weight ratio between said injected aqueous phase as droplets and said injected powdery mineral compound is less than or equal to 1.2, preferably less than or equal to 1 and in particular less than or equal to 0.8. The aforesaid weight ratio is also greater than or equal to 0.1 and particularly greater than or equal to 0.2. Accordingly, the aqueous phase injected as fine droplets has only little impact on the temperature of the flue gases to be treated and does not perturb the subsequent potential steps for heat recovery. According to the present invention, the flue gases have after injection of the mineral compound and of the aqueous phase as droplets, a temperature comprised between n and n10 C., preferably between n and n8 C., preferably between n and n5 C., in particular between n3 C., n being the temperature of the flue gases before injecting the mineral compound and said aqueous phase.

(30) According to the present invention, even if typically both aqueous phase and mineral compound injection systems are attached on the same device for treating flue gases, it is obvious that they operate independently of each other. Accordingly, it is possible to only operate by injecting aqueous phase droplets or only the mineral compound, if the actual case requires this.

(31) FIG. 2 illustrates an alternative of the device for treating flue gases according to the present invention.

(32) As this may be seen, the device 1 according to the present invention comprises here a piping for injecting a powdery mineral compound 2 connected to a powdery mineral compound source (not shown). The piping for injecting a mineral compound is laid out so as to open into said conduit of flue gases 3 (see FIGS. 4 and 5) and for allowing outflow of the mineral compound via an outlet orifice for the mineral compound 14. The piping for injecting a mineral compound 2 has an external face 4 and an internal face 5. During operation, the internal face 5 is in contact with said powdery mineral compound which is injected into the injection piping 2.

(33) The device for injecting a powdery mineral compound 1 also comprises a piping for injecting an aqueous phase 6 as droplets, which is connected to an aqueous phase supply 8, and which is localized in a concentric tube located in the peripheral space 9. The piping for injecting an aqueous phase, although this is not illustrated here, may further comprise a stop valve 10. The outlet orifice for an aqueous phase 11 as droplets from the aqueous phase of injection piping is in practice achieved as a slot or a planar sprayer.

(34) The pressure of the aqueous phase supply 8 is typically comprised between 2 and 150 bars. In an alternative, this pressure will rather be comprised between 2 and 20 bars, preferably between 3 and 15 bars and still more preferentially of about 8 bars. In another alternative, the pressure will be comprised between 10 and 150 bars, in particular between 20 and 100 bars. These high pressures give the possibility of avoiding fouling of the spraying piping.

(35) The mineral compound injection device further comprises a flange 13 provided with through-orifices 18 in order to bolt or attach through any other means the device for treating flue gases to a flue gas conduit via a flange 23.

(36) Indeed, as this may be seen in FIG. 5, the conduit of flue gases 3 to be treated may include an introduction conduit 22 for the device 1 according to the present invention. The introduction conduit 22 is provided with a flange 23 at its end. The device according to the present invention 1 is introduced into this conduit and attached thereon by means of the flanges 13 and 23.

(37) As this may be seen in these FIGS. 4 and 5, the step for injecting a powdery mineral compound is carried out in the conduit of flue gases 3 according to an angle from 90 to 150 degrees, preferably less than or equal to 145 degrees, preferentially less than or equal to 140 degrees and in particular less than or equal to 135 degrees, relatively to the flow direction G of the flue gases.

(38) This orientation of the piping for the mineral compound relatively to the flow direction of the flue gases is by no means related to the embodiment of the device according to the invention. This means that the embodiment comprising a plurality of aqueous phase injection pipings illustrated in FIGS. 1 and 3 may also be oriented in a tilted way relatively to the wall of the conduit of flue gases.

(39) Further, the device according to the present invention, in the version illustrated in FIGS. 1A, 1B, 2A and 2B, may be more or less inserted into the conduit of flue gases, depending on the desiderata and may typically penetrate into the gas conduit by a length comprised between 0 and 40 cm.

(40) The technical considerations such as the length of the piping, the operating parameters of the device according to the present invention, in this embodiment, vary to the same extent as what was described for FIGS. 1A, 1B and 3.

(41) In the embodiment illustrated in FIGS. 2A and 2B, a second flange 17 is present on the device for treating flue gases. This flange 17 is provided with a series of through-orifices 19 laid out for receiving an attachment means. The flange 17 is laid out so as to be connected to a source of mineral compound (not shown).

(42) Advantageously, an external cover 20 is present around said peripheral space 9. The external cover 20 preferably has a diameter comprised between 100 and 250 mm, preferably less than 200 mm and more preferentially between 110 and 170 mm, in particular between 125 and 150 mm.

(43) In the peripheral space 9, provision may be made for an insulator layer between said external face 4 of said powdery mineral compound injection piping and the external cover 20. The insulator may simply be air or any insulator known to one skilled in the art and gives the possibility of avoiding cooling of the external face 4, thus isolated from the aqueous solution piping 6 which reduces the risks of agglomeration of the particles of the mineral compound, in particular of the hydrated lime, circulating in the injection piping 2.

(44) The device according to the present invention further preferably comprises a cap or a device 21 for closing said peripheral space provided with a series of orifices among which an outlet orifice for the mineral compound 14 and an outlet orifice of the tube concentric with the aqueous phase injection piping 11.

(45) As this may also be seen in this embodiment illustrated in FIGS. 2A, 2B, 4 and 5, the aqueous phase injection piping 6 is laid out in a concentric tube, from which the aqueous phase injection piping 25 is retractable, which gives the possibility of cleaning or changing the aqueous phase injection piping without stopping the injection of mineral compound. In order to facilitate the extraction from the aqueous phase injection piping, the present invention provides a slight curvature in the mineral compound injection piping, which remains as small as possible for avoiding obstacles inside the essentially cylindrical tube for bringing the mineral compound 2 and thereby reducing the agglomeration of mineral compound on the walls.

(46) For the embodiment illustrated in FIGS. 2A, 2B, 4 and 5, the main tubing for injecting a mineral compound typically has a diameter of 100 mm and the tube concentric with the aqueous phase injection piping has a diameter of 25 mm. Both tubes are confined in a cover 20 having a diameter of about 125 mm.

EXAMPLES

Example 1

(47) SO.sub.2 reducing tests were conducted by using the pilot facility described in WO 2007/000433 (FIG. 2, p 10, I.20 to p 12, I.14). In a tubular reactor, calcium hydroxide (hydrated lime) particles are passed as a co-current with a gas containing 1,500 mg/Nm.sup.3 of SO.sub.2, 9% by Vol. of CO.sub.2 and 10% by Vol. of H.sub.2O, and having a total flow rate of 1.132 Nm.sup.3/h and a temperature of 220 C.

(48) Two types of hydrated times were used. The first sample (Sample 1) was hydrated lime obtained according to the teaching of patent application WO 97/14650. The second sample (Sample 2) was hydrated lime obtained according to the teaching of patent application WO 2007/000433.

(49) The table shows the SO.sub.2 reducing levels obtained by varying the humidity of the tested reagents from 0.7% by weight based on the weight of hydrated lime to 4.1% by weight for a stoichiometric factor of 2.5 and an absorbent flow rate of Q.

(50) The Q absorbent flow rate corresponds to the hydrated lime flow rate required for neutralizing the SO.sub.2 flow rate, if the yield of the reaction was 100% (stoichiometric equilibrium), multiplied by a stoichiometric factor, taking into account that a portion of the injected absorbent does not actually participate in the reaction. In the present case, Q has the value of 5.05 g/h.

(51) TABLE-US-00001 TABLE Humidity at 150 C. in % Reduction of SO.sub.2 to a Sample by mass stoichiometric factor of 2.5 (%) Sample 1 0.7% 18 2.0% 27 2.6% 28 3.0% 29 3.7% 29 4.0% 29 Sample 2 0.9% 27 1.9% 36 2.6% 38 2.7% 39 3.8% 36 4.1% 35

Example 2

Industrial Test

(52) The parameters of the flue gases are the following:

(53) Total flow rate: 20,000 Nm.sup.3/h

(54) Temperature: 180 C.

(55) Water content: 4-5% by volume

(56) O.sub.2 content: 15-18% by volume

(57) Hydrated lime prepared according to the teaching of patent application WO 2007/000433 was injected upstream from a sleeve filter for reducing SO.sub.2. For an SO.sub.2 content of 1,800 mg/Nm.sup.3 upstream from the sleeve filter and of 700 mg/Nm.sup.3 at the outlet, a reduction by 15 to 20% of the lime consumption was observed when the lime was humidified as compared with the situation when the lime was not humidified (17 dm.sup.3/h of water or a water/time mass ratio of 0.25). Indeed, a transformation rate of the lime of 35% is observed when the lime is not humidified and of 40% when it is humidified. The device of FIG. 1 according to the present invention was used; it had a tilt of about 120 relatively to the direction of flow of the gases.

Example 3

Industrial Test

(58) The parameters of the flue gases are the following:

(59) Total flow rate: 250,000 Nm.sup.3/h

(60) Temperature: 150 C.

(61) Water content 10% by volume

(62) O.sub.2 content: 16% by volume

(63) A hydrated lime prepared according to the teaching of patent application WO 2007/000433 was injected upstream from a sleeve filter in order to study the effects of its humidification level on the SO.sub.2 reducing levels.

(64) Thus, for an SO.sub.2 content of 224 mg/Nm.sup.3 upstream from the sleeve filter and for a same lime consumption (flow rate of 50 kg/h), an SO.sub.2 content at the outlet of the filter is obtained of respectively 134 mg/Nm.sup.3 (which is equivalent to a transformation rate of the lime of 53%) when the lime is not humidified and of 112 mg/Nm.sup.3 (transformation rate of the lime of 67%) when the lime is humidified in an amount of 30 dm.sup.3/h of water (water/lime mass ratio of 0.6). Therefore it is observed that humidified lime allows a gain in SO.sub.2 reduction of 25% as compared with the same non-humidified lime.

Example 4

Industrial Test

(65) A standard hydrated lime was injected into the same facility and with the same parameters of the flue gases as in Example 3 in order to study the effects of its humidification level on the SO.sub.2 reduction levels.

(66) Thus, for an SO.sub.2 level of 420 mg/Nm.sup.3 upstream from the sleeve filter and for a same lime consumption (flow rate of 120 kg/h), an SO.sub.2 content is obtained at the outlet of the filter of respectively 336 mg/Nm.sup.3 (which is equivalent to a transformation rate of the lime of 20%) when the lime is not humidified, of 266 mg/Nm.sup.3 (transformation rate of the lime of 37%) when the lime is humidified in an amount of 30 dm.sup.3/h of water (water/lime mass ratio of 0.25) and of 241 mg/Nm.sup.3 (transformation rate of the lime of 43%) when the lime is humidified in an amount of 120 dm.sup.3/h of water (water/lime mass ratio of 1). It is therefore observed that humidified lime in an amount of 30 and 120 dm.sup.3/h of water allows a SO.sub.2 reduction gain of respectively 85% and 110% as compared with the same non-humidified lime.

(67) It is quite understood that the present invention is by no means limited to the embodiments described above and that many modifications may be brought thereto without departing from the scope of the appended claims. For example, it is possible to combine the presence of the distributor 7 with a single water injection piping 6 or with any other desired number in the device for treating flue gases according to the present invention. It is also possible that the assemblies of FIGS. 3 and 4 include, like in FIG. 5, an introduction conduit 22 provided with a flange 23 at its end.