Gas stream treatment installation

Abstract

The invention relates to an installation for treating a gas stream containing an undesirable component, such as sulfur dioxide or mercury, the gas stream originating from a combustion unit (10) in which at least one mineral material is suitable for calcination and comprising, in particular, a first injection device (162) which is connected to a second gas / particle separation device (140) such that at least a portion of the first particles injected into the gas stream by the first injection device (162) consists at least partially of the second particle stream originating from a second gas / particle separation device (140). Figure 1

Description

Title of the invention: Installation for treating a gas flow

[0001] The invention relates to the field of combustion gas treatment. In particular, the invention relates to the treatment of combustion gases from a combustion unit.

[0002] In the following, we are particularly interested in the manufacture of cement although the invention can be applied to other processes for treating mineral materials.

[0003] The manufacture of cement uses for the most part a cooked material, clinker, which is produced from minerals whose essential constituent is calcium carbonate.

[0004] More precisely, clinker is obtained from a raw material composed of a mixture of minerals, including clay and limestone. These minerals are successively ground, preheated, then fired in a rotary kiln.

[0005] During the formation of clinker, gaseous effluents are produced.

[0006] Due in particular to the increase in gaseous pollution of the local, regional and global atmosphere, the decontamination of gaseous effluents is necessary. Moreover, regional, national and international regulations impose ever lower limits on the quantities of undesirable components, i.e. pollutants, released into the atmosphere.

[0007] There are many processes for decontaminating gaseous effluents, such as wet processes, such as washing, or dry processes. However, decontaminating effluents by washing poses the problem of treating the resulting liquid effluents. This is both a technical and economic problem.

[0008] Similarly, effluent decontamination processes are known in which a reactive agent in powder form, i.e. in the form of solid particles, is injected into the gaseous effluents, for example downstream of the preheater, and configured to become loaded with undesirable components. In this case, the fate of the solid particles loaded with undesirable components must be technically and economically considered.

[0009] However, all the processes currently used, even if they already develop a good capacity to depollute the gaseous effluents resulting from industrial activities, do not achieve a thorough depollution, that is to say a sufficiently complete depollution of said effluents so that the most essential and most dangerous components of these components undesirable for the environment, such as sulphur dioxide or mercury, are completely eliminated from the gaseous effluents before their release into the atmosphere.

[0010] There is therefore a need to provide an installation which makes it possible to reduce the concentration of undesirable component contained in such gaseous effluents, in particular from a cement manufacturing process, and a corresponding process overcoming in particular the aforementioned drawbacks.

[0011] Thus, a first object of the invention is to propose a reduction in the concentration of undesirable component contained in gaseous flows from a combustion unit in order to effectively limit the release of the undesirable component into the atmosphere.

[0012] A second object of the invention is to propose a reduction in the concentration of undesirable component contained in gaseous flows from a combustion unit in which the use of the reactive agent is optimized, so as to reduce the consumption of the fresh reactive agent, that is to say of the reactive agent which has not yet been in contact with the undesirable component to be treated, and also so as to reduce the cost of treatment of the reactive agent partially loaded with undesirable compound.

[0013] A third object of the invention is to propose a reduction in the concentration of undesirable component contained in gaseous flows from a combustion unit without increasing the manufacturing costs of the installations currently implemented.

[0014] A fourth object of the invention is to propose a reduction in the concentration of undesirable component contained in gaseous flows from a combustion unit which can easily be integrated into a pre-existing process and installation for treating gaseous effluents.

[0015] To this end, according to a first aspect, the invention proposes an installation for treating a gas flow containing an undesirable component, such as sulfur dioxide or mercury, the gas flow coming from a combustion unit, the installation comprising, in the direction of circulation of the gas flow:

[0016] a first device for injecting, into the gas flow, first particles of an agent reactive with the undesirable component to obtain a gas flow loaded with first particles;

[0017] a first gas / particle separation device configured to receive the gas flow loaded with first particles, and to obtain: - a gas flow separated from the first particles, and - a flow of first particles;

[0018] a second device for injecting, into the gas flow separated from the first particles, second particles of an agent reactive with the undesirable component, called fresh reactive agent, to obtain a gas flow separated from the first particles and loaded with second particles,

[0019] a second gas / particle separation device, fluidically connected to the first gas / particle separation device, configured to receive the gas flow separated from the first particles and loaded with second particles, and to obtain: - a gas flow separated from the second particles, and - a flow of second particles,

[0020] the installation being characterized in that the first injection device is connected to the second gas / particle separation device so that at least part of the first particles injected by the first injection device consists at least partially of the flow of second particles coming from the second gas / particle separation device.

[0021] This method advantageously makes it possible to improve the efficiency of the decontamination treatment of the gas flow while optimizing the quantity of fresh reactive agent injected.

[0022] Various additional features may be provided alone or in combination: - the installation further comprises a first distribution device configured to distribute the first flow of first particles from the first gas / particle separation device between a flow of particles to be extracted from the installation and a flow of particles to be reinjected into the gas flow, - the installation further comprises a third injection device placed upstream of the first gas / particle separation device and configured to reinject, into the gas flow, the flow of particles to be reinjected, - the first injection device is further configured to inject, into the gas flow upstream of the first gas / particle separation device, the flow of particles to be reinjected, - the first gas / particle separation device is of the cyclone type, - the second gas / particle separation device is of the bag filter type, - the installation further comprises a second distribution device configured to distribute the second flow of particles from the second gas / particle separation device between a flow of particles to be sent into the first injection device, and a flow of particles to be reinjected, via a fourth injection device, into the gas flow separated from the first portion of particles of an agent reactive with the undesirable component, - the installation further comprises one or more devices for reconditioning the flow of particles to be reinjected placed upstream of the first injection device and / or the third injection device and / or the fourth injection device, - the combustion unit is a mineral material calcination unit, - the combustion unit includes a preheater and / or a cooking oven cement clinker.

[0023] Secondly, a method is proposed for treating a gas stream containing an undesirable component, such as sulfur dioxide or mercury, the gas stream coming from a combustion unit, the method being capable of implementing the installation described above, and comprising the following steps:

[0024] a) injecting first particles of an agent reactive with the undesirable component into the gas flow to obtain a gas flow loaded with first particles,

[0025] b) separation of the gas flow loaded with first particles to obtain: a separate gas flow of the first particles, and a flow of first particles;

[0026] c) injecting second particles of an agent reactive with the undesirable component, called fresh reactive agent, into the gas flow separated from the first particles to obtain a gas flow separated from the first particles and loaded with second particles,

[0027] d) separation of the gas flow separated from the first particles and loaded with second particles to obtain: a separate gas flow of the second particles, and a flow of second particles,

[0028] the method being characterized in that the injection step a) comprises an operation 01) of re-injecting at least part of the flow of second particles into the gas flow so that at least part of the first particles injected during the injection step a) consists at least in part of the flow of second particles obtained at the end of the separation step d).

[0029] Various additional features may be provided alone or in combination: the method further comprises a step e) of distributing the flow of first particles resulting from the separation step b), between a flow of particles to be extracted and a flow of particles to be reinjected into the gas flow during the reinjection operation 01), so that at least part of the first particles injected during the injection step a) is furthermore constituted at least in part by the flow of first particles obtained at the end of the separation step b),

[0030] - the method further comprises a step f) of distributing the flow of second particles resulting from separation step d), between a flow of particles to be reinjected into the gas flow during reinjection operation 01) and a flow of particles to be reinjected into the gas flow separated from the first particles resulting from separation step b),

[0031] - the method further comprises a step of reconditioning one or more particle flows to be reinjected into the gas flow.

[0032] Thirdly, a cement manufacturing process is proposed comprising the aforementioned treatment process, according to which the gas flow comes from a calcination of at least one mineral material used during a clinker firing step.

[0033] Other effects and advantages will appear in the light of the description of embodiments of the invention accompanied by figures 1 and 2 schematically illustrating two examples of embodiment of an installation for treating a gas flow from a combustion unit, each of these two examples operating according to an operating mode of the installation.

[0034] The combustion unit 10 shown in Figures 1 and 2 contains a plant for combustion or calcination of mineral materials.

[0035] In this combustion unit 10 a combustion reaction takes place, generally with the appearance of a flame, so that combustion gases in the form of fumes, including in particular undesirable components, are generated.

[0036] More specifically, in the following, in a non-limiting manner for the invention, it is considered that the combustion unit 10 is contained in a cement manufacturing installation, in particular in a cement plant cooking line.

[0037] In an exemplary embodiment, the combustion unit 10 is a unit for calcining mineral materials. The calcination unit preferably comprises a rotary kiln and a cyclone preheater, and may further comprise any other equipment for thermal treatment of mineral materials.

[0038] Preferably, mineral materials, for example a mixture of raw material, are fed to the cyclone preheater from a homogenization and dosing system. The cyclone preheater makes it possible to increase the temperature of the mineral materials before they enter the rotary kiln. This kiln typically comprises at least one burner capable of creating the flame, placed in the kiln at an end opposite that through which the preheated mineral materials enter. The mineral materials move in the kiln towards the burner, and emerge calcined from the kiln, forming the clinker.

[0039] The combustion gases are extracted at the outlet of the preheater and include in particular mineral dust and one or more undesirable components. Among the undesirable components contained in the combustion gases, mention may be made, for example, of sulfur dioxide, nitrogen oxides, carbon monoxide, volatile organic compounds and mercury.

[0040] The combustion gases then extracted form a gaseous flow to be treated F1 which is conveyed into a treatment installation according to an exemplary embodiment of the invention. The treatment installation comprises a circulation circuit into which the gaseous flow to be treated F1 is introduced, then circulates, so as to be treated before being extracted from the treatment plant.

[0041] A pretreatment device (not shown in the figures) for the combustion gases is preferably arranged between the combustion unit 10, in particular the preheater, and the treatment installation. For example, the pretreatment device may be configured to filter all or part of the mineral dust contained in the combustion gases. The pretreatment device is then connected both to the combustion unit 10 and also to the treatment installation.

[0042] In the embodiment described below, the treatment installation is capable of separating sulfur dioxide from the combustion gases.

[0043] To do this, an agent reactive with the sulfur dioxide contained in the combustion gases will be injected into the gas flow to be treated to reduce its sulfur dioxide concentration.

[0044] The reactive agent is preferably powdery when it is injected into the gas flow to be treated, that is to say it comprises particles such as will be explained later. The reactive agent may however be injected into the gas flow to be treated in liquid form and, upon contact with it, transform into powdery material after changes brought about by different physicochemical reactions, for example by evaporation of the water contained in the liquid reactive agent.

[0045] Preferably, when it is desired to reduce the sulfur dioxide concentration of the gas stream to be treated F1, the reactive agent typically used is hydrated lime (Ca(OH)2), which is advantageously in dry form, and which is in powder form. In another embodiment, the reactive agent may be in wet form, for example in the form of milk of lime which is in liquid form and which will then transform into particles in the gas stream to be treated. Hydrated lime has the advantage of combining naturally with the sulfur contained in the sulfur dioxide with which it is in contact in order to form gypsum.

[0046] In an alternative embodiment, the reactive agent is activated carbon which may optionally be added.

[0047] According to the embodiment illustrated in [Fig.l], the circulation circuit comprises the devices presented below, and listed in the direction of circulation of the gas flow to be treated. As will be seen below, to facilitate reading, the gas flow to be treated will be designated, according to its position and its movement in the circulation circuit, by:

[0048] - gas flow loaded with hydrated lime particles partially combined with sulfur dioxide Fl',

[0049] - gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide F2,

[0050] - gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2', or

[0051] - gas flow separated from the hydrated lime particles F3.

[0052] The devices contained in the circulation circuit are as follows: a first injection device 162, a first gas / particle separation device 120, a second injection device 164, and a second gas / particle separation device 140.

[0053] The first injection device 162 is capable of injecting, into the gas flow to be treated F1, particles of hydrated lime partially combined with sulfur dioxide to obtain the gas flow loaded with particles of hydrated lime partially combined with sulfur dioxide F1'.

[0054] The first gas / particle separation device 120 is configured to carry out a first separation in order to separate the hydrated lime particles at least partially combined with sulfur dioxide from the gas stream to be treated F1 and obtain the gas stream separated from the hydrated lime particles at least partially combined with sulfur dioxide F2.

[0055] The second injection device 164 is capable of injecting, into the gas flow separated from the hydrated lime particles partially combined with sulfur dioxide F2, fresh hydrated lime particles and obtaining the gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2'.

[0056] The second gas / particle separation device 140, fluidly connected to the first gas / particle separation device 120, is configured to carry out a second separation in order to separate the hydrated lime particles from the gas stream separated from the hydrated lime particles partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2' and obtain the gas stream separated from the hydrated lime particles F3, in other words a treated gas stream.

[0057] The first injection device 162 is arranged upstream of the first gas / particle separation device 120. This first injection device 162 is configured to implement a step a) of injecting, into the gas flow to be treated F1, particles of hydrated lime partially combined with sulfur dioxide. In particular, the first injection device 162 makes it possible to bring into contact, in a first reaction zone, the gas flow to be treated F1 with particles of hydrated lime partially combined with sulfur dioxide. In this first reaction zone, following the implementation of this injection step a), the gas flow to be treated F1 comes into intimate contact with the particles of hydrated lime partially combined with sulfur dioxide, these then capture sulfur contained in the gas flow to be treated F1 by combining with more sulfur dioxide. The gas flow to treat Fl then becomes depleted in sulfur dioxide to become a gaseous stream loaded with hydrated lime particles partially combined with sulfur dioxide Fl'.

[0058] The gas flow loaded with hydrated lime particles partially combined with sulfur dioxide F1' is then conveyed, via a fluid conduit, from the first reaction zone to the first gas / particle separation device 120 contained in a first separation zone and in which a step b) of separating the gas flow loaded with hydrated lime particles partially combined with sulfur dioxide F1' will take place. Carrying out such a step b) makes it possible to obtain, on the one hand, for example at an upper outlet of the first gas / particle separation device 120, the gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide F2, and on the other hand, for example at a lower outlet of the first gas / particle separation device 120, a flow of hydrated lime particles at least partially combined with sulfur dioxide F10.

[0059] Depending on the residence time and the capacity of the hydrated lime particles to combine with sulfur dioxide, the latter may be, at the inlet of the first gas / particle separation device 120, either still partially combined with sulfur dioxide, or completely combined with sulfur dioxide.

[0060] By capacity of hydrated lime particles to combine with sulfur dioxide, within the meaning of the present invention, is meant the capacity of a hydrated lime particle to capture sulfur dioxide, by chemical combination to form gypsum.

[0061] By particle of hydrated lime totally combined with sulfur dioxide, within the meaning of the present invention, is meant a particle of hydrated lime which has mainly combined with sulfur dioxide and which is therefore tending towards its maximum capture capacity.

[0062] In the exemplary embodiment illustrated in Figures 1 and 2, the first gas / particle separation device 120 is of the cyclone type.

[0063] Advantageously, before being injected into the gas flow to be treated F1 via the first 162 and / or third 166 and / or fourth 168 injection devices, the hydrated lime particles partially combined with sulfur dioxide are reconditioned, for example rehumidified via at least one rehumidification device (not shown in the figures). This has the effect of improving the capacity of the hydrated lime particles to combine with sulfur dioxide.

[0064] The gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide F2, emerging from the first gas / particle separation device 120, for example via its upper outlet, can then be transported to the second gas / particle separation device 140 to which it is fluidically connected. by a pipe.

[0065] The second injection device 164 is, for its part, arranged upstream of the second gas / particle separation device 140, arranged in particular in a second reaction zone. The second injection device 164 is configured to carry out a step c) of injecting, into the gas flow separated from the hydrated lime particles partially combined with sulfur dioxide F2, fresh hydrated lime particles, i.e. hydrated lime particles which have not yet been in contact with sulfur dioxide, in particular with the gas flow to be treated FL. Such an injection makes it possible to obtain a gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2'.Fresh hydrated lime particles are injected to capture residual sulfur oxides contained in the gas stream separated from the hydrated lime particles at least partially combined with sulfur dioxide F2. In this way, at least part of the injected fresh hydrated lime particles combine with these residual sulfur oxides.

[0066] For example, the second injection device 164 is connected to a silo 1642 of fresh hydrated lime particles.

[0067] The circulation circuit of the gas flow to be treated is configured so that the gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2' is then conveyed, via a fluid conduit, from the second reaction zone to the second gas / particle separation device 140 contained in a second separation zone. A separation step d) takes place and makes it possible to obtain on the one hand, for example at an upper outlet of the second gas / particle separation device 140, a gas flow separated from the hydrated lime particles F3, and on the other hand, for example at a lower outlet of the second gas / particle separation device 140, a flow of hydrated lime particles partially combined with sulfur dioxide F20.

[0068] Advantageously, the second gas / particle separation device 140 is of the bag filter type. The gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2' then passes through the filter bags. During this passage, the hydrated lime particles are retained.

[0069] Then, the gas flow separated from the hydrated lime particles F3, i.e. the decontaminated gas flow which has been treated, can then be released into the atmosphere via a first chimney 18, possibly using an extraction fan 182.

[0070] According to the invention, the first injection device 162 is connected to the second gas / particle separation device 140, in particular at its lower outlet, so that at least part of the flow of hydrated lime particles F20 is injected by the first injection device 162 into the gas flow to be treated F1 introduced into the treatment installation. In this way, an operation 01) of re-injecting at least part of the flow of hydrated lime particles partially combined with sulfur dioxide F20 into the gas flow to be treated F1 takes place.

[0071] Advantageously, the installation further comprises a first distribution device 122 configured to distribute the flow of hydrated lime particles partially combined with sulfur dioxide F10 from the first gas / particle separation device 120 between a flow of particles to be extracted F12 from the installation, and a flow of hydrated lime particles partially combined with sulfur dioxide F10 to be reinjected F1 into the gas flow to be treated F1. The first distribution device 122 is then capable of carrying out a step e) of distribution of the flow of hydrated lime particles partially combined with sulfur dioxide F10 from the separation step b). Thus, using this first distribution device 122, all or part of the flow of hydrated lime particles partially combined with sulfur dioxide F10 can be recycled (i.e.reinjected) into the gas stream to be treated F1 or into the gas stream loaded with hydrated lime particles partially combined with sulfur dioxide F1' entering the first gas / particle separation device 120, either immediately or after transfer to an intermediate storage means (not shown in the figures). This recycling is made possible by sending the part of the stream of hydrated lime particles partially combined with sulfur dioxide to be reinjected F1, either into a third injection device 166 as illustrated in [Fig.l], or into the first injection device 162 as illustrated in [Fig.2]. This makes it possible to reuse the hydrated lime particles which have not yet completely combined with sulfur dioxide. Preferably, the stream of particles to be extracted F12 from the installation then consists of hydrated lime particles which have completely combined with sulfur dioxide.The stream of particles to be extracted F12 is then not recycled into the first reaction zone and can be introduced into a temporary storage means such as a recovery silo (not shown in the figures). Preferably, the third injection device 166 is placed upstream of the first injection device 162 so as to guarantee an optimal residence time of the hydrated lime particles partially combined with sulfur dioxide from the stream Fl 1 to be reinjected into the gas stream to be treated FL .

[0072] Preferably, the first distribution device 122 is capable of continuously extracting a fraction of the flow of hydrated lime particles partially combined with sulfur dioxide F10. The fraction of the flow of particles to be extracted F12 actually extracted is for example weighed to obtain its weight and a fraction of fresh hydrated lime of equivalent weight is injected by the injection device 164. For example, the first distribution device 122 may be a distribution valve or any other distribution system known to those skilled in the art.

[0073] Optionally, the particles introduced into the recovery silo can, in a subsequent step, be used as gypsum to be introduced into a cement.

[0074] Rather than reinjecting the entire flow of hydrated lime particles partially combined with sulfur dioxide F20 from the second gas / particle separation device 140 into the gas flow to be treated F1 via the first injection device 162, the installation advantageously comprises a second distribution device 142 configured to distribute the flow of hydrated lime particles partially combined with sulfur dioxide F20 from the second gas / particle separation device 140 between a flow of particles to be sent F22 into the first injection device 162, and a flow of particles to be reinjected F21, via a fourth injection device 168, into the gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide F2, i.e. before the second injection device 164,or in the gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide and loaded with fresh hydrated lime particles F2', i.e. after the second injection device 164. This reinjection takes place in both cases upstream of the second gas / particle separation device 140. The second distribution device 142 is then capable of carrying out an additional step f) of distributing the flow of hydrated lime particles partially combined with sulfur dioxide F20, between a flow of particles to be reinjected F22 into the gas flow to be treated F1 during the reinjection operation 01) and a flow of particles to be reinjected F21 into the gas flow separated from the hydrated lime particles at least partially combined with sulfur dioxide F2 from the separation step b).

[0075] Preferably, the second distribution device 142 is also a distribution valve or any other distribution system known to those skilled in the art.

[0076] In an exemplary embodiment not shown in the figures, the second injection device 164 may also be configured to inject a mixture of fresh hydrated lime particles and hydrated lime particles partially combined with sulfur dioxide. The hydrated lime particles partially combined with sulfur dioxide may come from the second separation zone. In an alternative embodiment not shown, the second injection device 164 and the fourth injection device 168 may be combined and therefore inject a mixture of fresh hydrated lime particles and hydrated lime particles partially combined with sulfur dioxide into the gas stream separated from the hydrated lime particles at least partially combined with sulfur dioxide F2.

[0077] This treatment installation allows the gas flow to be treated to be several times in contact with hydrated lime particles. First with hydrated lime particles partially combined with sulfur dioxide for an initial reduction, then with fresh hydrated lime particles to complete the flue gas desulfurization treatment. The hydrated lime particles can be recirculated as much as necessary in the installation, and they are only extracted from the circulation circuit after having been placed in prolonged contact with the gas flow to be treated so as to tend towards the maximum capture capacity of the hydrated lime.

[0078] In particular, using such a treatment installation, a first treatment is carried out by bringing a gas flow to be treated, defined by a high concentration of sulfur oxides, into contact with hydrated lime particles partially combined with sulfur dioxide. During this first treatment, the hydrated lime particles partially combined with sulfur dioxide, then defined by an average capacity to combine with sulfur dioxide, are brought into contact with the gas flow to be treated, which is highly concentrated in sulfur dioxide; this makes it possible to carry out a so-called "coarse" treatment. Then, a second treatment is carried out by bringing the gas flow resulting from the first treatment, defined by a low concentration of sulfur oxides, into contact with fresh hydrated lime particles.During this second treatment, the fresh hydrated lime particles, defined by a high capacity to combine with sulfur dioxide, are brought into contact with the gas flow with a low concentration of sulfur dioxide; this allows for a so-called "fine" treatment.

[0079] Implementing these two successive treatments makes it possible to effectively use the different levels of reactivity of the hydrated lime particles as a function of the reduction in the sulfur dioxide concentration of the gas flow.

Claims

1.

2. Claims Installation for treating a gas flow containing an undesirable component, such as sulfur dioxide or mercury, the gas flow coming from a combustion unit (10), the installation comprising, in the direction of circulation of the gas flow: • a first device (162) for injecting, into the gas flow, first particles of an agent reactive with the undesirable component to obtain a gas flow loaded with first particles; • a first gas / particle separation device (120) configured to receive the gas flow loaded with first particles, and to obtain: • a gas flow separated from the first particles, and • a flow of first particles; • a second injection device (164), into the gas flow separated from the first particles, of second particles of an agent reactive with the undesirable component, called fresh reactive agent, to obtain a gas flow separated from the first particles and loaded with second particles, • a second gas / particle separation device (140), fluidly connected to the first gas / particle separation device (120), configured to receive the gas flow separated from the first particles and loaded with second particles, and to obtain: • a gas flow separated from the second particles, and • a flow of second particles, the installation being characterized in that the first injection device (162) is connected to the second gas / particle separation device (140) so that at least part of the first particles injected by the first injection device (162) consists at least partially of the flow of second particles from the second gas / particle separation device (140). Installation according to claim 1, further comprising a first distribution device (122) configured to distribute the first flow of first particles from the first gas / separation device particles (120) between a flow of particles to be extracted from the installation and a flow of particles to be reinjected into the gas flow.

3. Installation according to claim 2, further comprising a third injection device (166) placed upstream of the first gas / particle separation device (120) and configured to reinject, into the gas flow, the flow of particles to be reinjected.

4. Installation according to claim 2, in which the first injection device (162) is further configured to inject, into the gas flow upstream of the first gas / particle separation device (120), the flow of particles to be reinjected.

5. Installation according to one of claims 1 to 4, in which the first gas / particle separation device (120) is of the cyclone type.

6. Installation according to one of claims 1 to 5, in which the second gas / particle separation device (140) is of the bag filter type.

7. Installation according to one of claims 1 to 6, further comprising a second distribution device (142) configured to distribute the second flow of particles from the second gas / particle separation device (140) between a flow of particles to be sent into the first injection device (162), and a flow of particles to be reinjected, via a fourth injection device (168), into the gas flow separated from the first portion of particles of an agent reactive with the undesirable component.

8. Installation according to one of claims 1 to 7, further comprising one or more devices for reconditioning the flow of particles to be reinjected placed upstream of the first injection device (162) and / or the third injection device (166) and / or the fourth injection device (168).

9. Installation according to one of claims 1 to 8, in which the combustion unit (10) is a unit for calcining mineral materials.

10. Installation according to claim 9, in which the combustion unit (10) comprises a preheater and / or a cement clinker cooking kiln.

11. A method of treating a gas stream containing an undesirable component, such as sulfur dioxide or mercury, the gas stream coming from a combustion unit (10), the method being carried out using the installation according to one of claims 1 to 10 and comprising the following steps: a) injecting first particles of an agent reactive with the undesirable component into the gas flow to obtain a gas flow loaded with first particles, b) separating the gas flow loaded with first particles to obtain: • a gas flow separated from the first particles, and • a flow of first particles;c) injection of second particles of an agent reactive with the undesirable component, called fresh reactive agent, into the gas flow separated from the first particles to obtain a gas flow separated from the first particles and loaded with second particles, d) separation of the gas flow separated from the first particles and loaded with second particles to obtain: • a gas flow separated from the second particles, and • a flow of second particles, the method being characterized in that step a) of injection comprises an operation 01) of reinjection of at least part of the flow of second particles into the gas flow so that at least part of the first particles injected during step a) of injection consists at least in part of the flow of second particles obtained at the end of step d) of separation.;

12. Method according to claim 11, further comprising a step e) of distributing the flow of first particles resulting from the separation step b), between a flow of particles to be extracted and a flow of particles to be reinjected into the gas flow during the reinjection operation 01), so that at least part of the first particles injected during the injection step a) is furthermore constituted at least in part by the flow of first particles obtained at the end of the separation step b).

13. Method according to one of claims 11 or 12, further comprising a step f) of distributing the flow of second particles resulting from step d) of separation, between a flow of particles to be reinjected into the gas flow during the reinjection operation 01) and a flow of particles to be reinjected into the gas flow separated from the first particles. particles from separation step b).

14. Method according to one of claims 11 to 13, further comprising a step of reconditioning one or more of the particle streams to be reinjected into the gas stream.

15. A method of manufacturing cement comprising a method according to one of claims 11 to 14, according to which the gas flow comes from a calcination of at least one mineral material implemented during a clinker firing step.

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