EP3700660A1 - Method for removal of mercury from gaseous effluents - Google Patents

Method for removal of mercury from gaseous effluents

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Publication number
EP3700660A1
EP3700660A1 EP18792939.3A EP18792939A EP3700660A1 EP 3700660 A1 EP3700660 A1 EP 3700660A1 EP 18792939 A EP18792939 A EP 18792939A EP 3700660 A1 EP3700660 A1 EP 3700660A1
Authority
EP
European Patent Office
Prior art keywords
mercury
solution
bicarbonate
reagent
gas stream
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP18792939.3A
Other languages
German (de)
French (fr)
Inventor
Bernard Siret
Frank Tabaries
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LAB SAS
Original Assignee
LAB SAS
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Filing date
Publication date
Application filed by LAB SAS filed Critical LAB SAS
Publication of EP3700660A1 publication Critical patent/EP3700660A1/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/64—Heavy metals or compounds thereof, e.g. mercury
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/30—Alkali metal compounds
    • B01D2251/304—Alkali metal compounds of sodium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/30—Alkali metal compounds
    • B01D2251/306—Alkali metal compounds of potassium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/40—Alkaline earth metal or magnesium compounds
    • B01D2251/404—Alkaline earth metal or magnesium compounds of calcium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/60—Inorganic bases or salts
    • B01D2251/606—Carbonates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/20—Halogens or halogen compounds
    • B01D2257/204—Inorganic halogen compounds
    • B01D2257/2045—Hydrochloric acid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/30—Sulfur compounds
    • B01D2257/302—Sulfur oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/60—Heavy metals or heavy metal compounds
    • B01D2257/602—Mercury or mercury compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/02—Other waste gases
    • B01D2258/0283—Flue gases

Definitions

  • the present invention relates to a process for the demercurization of gaseous effluents.
  • mercury is found in the gaseous effluents of power plants that burn coal, coal naturally containing a little mercury which, during combustion, will end up in combustion fumes in the form of mercury metal or oxidized mercury.
  • Mercury is also found in flue gases from waste-to-energy plants and waste incineration plants because the waste contains some mercury.
  • the most common way to proceed is to bring the gaseous effluents into contact with powdery or granular adsorbents.
  • the most used of these adsorbents is activated carbon because it is inexpensive and effective for other pollutants, such as volatile organic compounds, dioxins and furans.
  • This activated carbon can be doped with compounds such as halogens, such as chlorine, bromine or iodine, sulfur or selenium.
  • halogens such as chlorine, bromine or iodine, sulfur or selenium.
  • the adsorption isotherms become very unfavorable: it is then necessary to use significant amounts of coal, which adversely affects the operating cost, as well as the quality of the products. solid residues generated.
  • activated charcoal dosages may not be sufficient and peaks, beyond allowable limits, occur.
  • the use of doped coals improves this situation a little, but the cost of these products is high and secondary problems, for example due to the corrosivity of the halogenated coals, occur.
  • the use of brominated coals can also, by association with ammonium chloride present in the gaseous effluents, generate corrosive mixtures for exchangers operating at low relative temperatures, such as economizers.
  • US 2016/279568 discloses a gaseous effluent demineralization process, in which carbon particles, activated by hydrobromic acid, are injected into a hot gas stream to oxidize and adsorb mercury present therein. gas flow. D1 plans to inject into the hot gas stream, in addition to the above-mentioned carbon particles, a solution of sodium hydroxide and sodium carbonate. calcium: this solution does not capture mercury present in the gas stream, but reacts with carbon dioxide and sulfur oxides, present in this gas stream. In particular, by reaction with carbon dioxide, sodium bicarbonate is produced, however, it is noted that the formation of this bicarbonate is limited because of the low transfer of carbon dioxide to the drops of the solution given the low value. the gas-liquid transfer coefficient of carbon dioxide, compared with that of hydrochloric acid or sulfur dioxide.
  • US 2014/0050640 discloses a gaseous effluent demercurization process, wherein a solution containing an active mercury capture compound is injected into a gas stream to be treated.
  • This active compound is based on silica and may in particular result from the reaction between a precursor containing silica and a sulphide, it being noted that this sulphide is no longer available as such in the injected solution since it has been consumed by reaction with the precursor containing silica.
  • This solution can be mixed with an alkaline reagent that does not capture mercury, but that captures sulfur oxides, this alkaline reagent may be trona.
  • clays or mixtures of clays and lime. But, as a rule, at equivalent dosage and at equivalent temperature, these clay products are less capacitive and less effective than activated carbons.
  • wet processes are also used, in which the solubility of the mercury salts is used, or in which an oxidation of the mercury metal to ionic mercury is carried out before or during its transfer in the liquid phase.
  • These wet processes are effective, but not always usable: this is for example the case when the gaseous effluents to be treated are located in an area with no water or at which a significant wet discharge is problematic.
  • the object of the present invention is to propose a new method of demercurization, which is effective, economical and simple to implement.
  • the subject of the invention is a process for the demercurisation of gaseous effluents, as defined in claim 1.
  • the idea underlying the invention is to create, in situ, that is to say in the gaseous stream to be demercurized, powdery solid grains, formed of a carbonate compound and a suitable sulfur compound. to retain mercury.
  • the invention provides for injecting into the gaseous flow to demercurise a reagent in liquid form, consisting of a solution of a bicarbonate, preferably sodium bicarbonate, and a sulphide, preferably a polysulfide. .
  • a polysulfide is considered to be a form of sulfide.
  • sodium bicarbonate is a solid compound conventionally used for purifying fumes of their acidic pollutants such as hydrochloric acid (HCl), sulfur dioxide (S0 2 ) and sulfur trioxide (S0). 3 ).
  • acidic pollutants such as hydrochloric acid (HCl), sulfur dioxide (S0 2 ) and sulfur trioxide (S0). 3 ).
  • HCl hydrochloric acid
  • S0 2 sulfur dioxide
  • S0 sulfur trioxide
  • One of the factors that contributes to the high efficiency of sodium bicarbonate for the purification of acid pollutants is that, when the sodium bicarbonate is placed in a sufficiently hot stream, the reaction occurs 2 NaHCO 3 ⁇ Na 2 CO 3 + C0 2 + H 2 0.
  • the release of gases C0 2 and H 2 0 causes the bicarbonate grain NaHC0 3 , initially quite compact, to burst and cavities and cavities at the microscopic scale are created, which increases considerably the active surface of the grain. This effect is often called the "popcorn" effect in the technical literature on sodium
  • the invention takes advantage of this "popcorn" effect, in the sense that by injecting the aforementioned solution, forming the mercury capture reagent, into a gaseous stream to be demercurized having a temperature greater than 140 ° C., preferably between 170 ° C and 220 ° C, the water of this solution evaporates on contact with the hot gas stream, then the bicarbonate of the solution decomposes according to the "popcorn” effect to give the resulting dry grains a large surface area , of cavernous type, which distributes the sulfur compound initially present in the solution: this large sulfur surface forms a large specific surface, active for the capture of mercury present in the gas stream.
  • FIG. 2 is a view similar to FIG. 1, illustrating a second embodiment of the method according to the invention.
  • FIG. 1 and 2 is shown a sheath 1 in which a gas stream 2 flows, and from left to right in the figure.
  • the embodiment of the sheath 1 is not limiting.
  • the gas stream 2 contains mercury.
  • a mercury capture reagent 3 is injected into the gas stream, at one or more injection points in the sheath 1, where appropriate distributed along the latter.
  • This reagent for capturing mercury 3 is injected into the gas stream 2 in liquid form, consisting, before injection, of a solution of a bicarbonate and a sulphide.
  • the bicarbonate may be any inorganic bicarbonate, for example sodium bicarbonate, potassium or ammonium.
  • the bicarbonate of reagent 3 contains, or even consists of, sodium bicarbonate. In all cases, the bicarbonate of the reagent solution 3 is intended, when the solution is injected into the gas stream 2, to trigger the activation of bicarbonate grains by the effect "popcorn" described above.
  • the cation associated with the sulfide of the reagent 3 is of no real importance, being able to be, but not limited to, sodium or potassium or any other chemical element forming an alkaline sulfide. It will be appreciated that although a simple sulfide, such as an alkali metal sulfide such as Na 2 S, gives satisfactory results, it is preferred that the sulfide of the reagent 3 solution be a polysulfide because the molecule is heavier and less subject to heat release of hydrogen sulphide.
  • the polysulfide of reagent 3 contains, or even consists of, an alkali polysulfide, in particular sodium polysulfide having a molar ratio (S / Na) between sulfur and sodium of between 1 and 4: in practice, the sodium polysulfide can be prepared, in a manner known per se, by incorporation of yellow sulfur in an alkaline sulphide or caustic soda solution.
  • alkali polysulfide in particular sodium polysulfide having a molar ratio (S / Na) between sulfur and sodium of between 1 and 4:
  • the sodium polysulfide can be prepared, in a manner known per se, by incorporation of yellow sulfur in an alkaline sulphide or caustic soda solution.
  • Other polysulfides, for example potassium polysulfide are also suitable.
  • the sulphide, in particular the polysulphide, of the solution of the reagent 3 is intended, when the solution is injected into the gas stream 2, to form, on the free surface or in the pore volume of the carbonate grains, a solid sulfur compound that captures the mercury present in the gas stream.
  • the reagent 3 solution may contain other components than the carbonate and sulphide described above, especially halogenated salts.
  • the solution of the reagent 3 is advantageously prepared by dissolving bicarbonate, for example sodium bicarbonate, ammonium or potassium, in a solution of sulphide, especially polysulphide, or by mixing a solution of bicarbonate and a sulphide solution, in particular polysulfide.
  • the polysulfides have a composition which, in essence, is of variable sulfur content, it may be useful to characterize the reagent 3, not in terms of the sulphide concentration, but in terms of the molar ratio (S / HC0 3 ) between the sulfur and bicarbonate which are respectively brought at the time of the preparation of the reagent 3, since it is the bicarbonate which triggers the activation of the carbonate grains and it is the sulfur which is the active element for the capture of the mercury: this molar ratio S / HC0 3 may advantageously be between 0.2 and 5.
  • the overall concentration expressed in grams per liter of dry matter, is of little importance. It is also not necessary that all the bicarbonate contained in the reagent solution 3 is dissolved: a heterogeneous suspension of bicarbonate in a sulfur solution, for example sodium polysulfide, is usable.
  • an installation comprising, for example, one or more stirred tanks and means for introducing, on the one hand, bicarbonate and, on the other hand, the sulfur.
  • the injection of the reagent solution 3 into the sheath 1 is carried out by any appropriate means.
  • this injection consists of a spraying or atomization, carried out by nozzles or by two-fluid air nozzles or, more generally, by any material making it possible to finely disperse the solution in the gas stream 2, typically in fine droplets.
  • the water of each of the droplets of the injected reagent solution 3 evaporates in contact with the gas stream 2; then, in a second step, the bicarbonate present in each droplet decomposes thermally, according to the "popcorn" effect, which creates dry grains of carbonate having, on the microscopic scale, cavities and caves, which induce large specific surfaces for each grain.
  • the sulphide initially present in the solution of the reagent 3 is distributed over this large specific surface, which gives each grain a large active surface for the demercurization of the gas stream 2: in contact with the active sulfur sites, the mercury is transferred from the gas phase of the gas stream 2 to the solid phase of the grains, to which the mercury is strongly bound.
  • the solid grains, having captured the mercury, are carried by the gas stream 2, until they are then separated by means known per se, such as bag filters or electrostatic precipitators. It is particularly important that the gas stream 2 in which the solution of the reagent 3 is injected is at a temperature of at least 140 ° C, and preferably between 170 and 220 ° C. At a lower temperature, the thermal decomposition reaction of the bicarbonate is too slow. The characteristic time required for the process of this decomposition depends of course on the temperature and is well known to those skilled in the art: it is characteristic of bicarbonate, typically being between 0.3 and 1.5 seconds.
  • the injection point of this reagent 3 is not critical.
  • the reagent 3 can be injected downstream of a heat saver, or upstream of such an economizer, where the temperature is warmer.
  • the solution of the reagent 3 is injected into the gas stream 2 by being atomized therein in the presence of solid particles, as explained in more detail below.
  • the solid particles in the presence of which the atomization of the reagent solution 3 is carried out are referenced 4 and result from the injection of a dedicated flow 4 'into the gas stream 2 upstream of the injection of the reagent 3, the injection of this stream 4 'being operated at one or more injection points in the sheath, which, where appropriate, are distributed along the latter and which are all located before the injection point (s) of the reagent 3.
  • the flow 4 ' is introduced inside the sheath 1 by any suitable material, for example canes, nozzles, straight or beveled pipes. .
  • the solid particles 4 from the stream 4' are dispersed and gradually form a cloud 5 which, along the sheath 1 from of the injection point (s) of the flow 4 ', extends downstream, to cover the entire section of the sheath 1.
  • the solid particles 4 are intended to capture acidic pollutants present in the gas stream 2, such as hydrogen chloride (HCl) and sulfur dioxide (S0 2 ): for this purpose, the 4 'stream then contains sodium bicarbonate or sodium sesquicarbonate as the trona, which is a natural mineral. Bicarbonate or sodium sesquicarbonate are injected into the gaseous stream 2 in pulverulent form, typically obtained by grinding, and, in contact with the gas stream 2, produce the solid particles 4 by partial decomposition.
  • the stream 4 ' may contain, in addition or alternatively to sodium bicarbonate and sesquicarbonate, other reactive products, such as lime, which, in particular after decomposition in contact with the gas stream 2, form in this process. last solid particles 4 able to capture the acid pollutants present in the gas stream 2.
  • the mercury uptake reagent 3 is atomized within the cloud 5 of the particles 4.
  • the reagent 3 will undergo both the thermal decomposition described above, which generates the active surface to demercurise the gas stream 2, but also be dispersed and carried by the surface of all the particles 4 of the cloud 5: the active sulfur sites are thus dispersed and deposited on an even larger surface, further enhancing the demercurization performance.
  • the injection of the reagent 3 is not located too far downstream of the injection of the flow 4 '. Indeed, this arrangement makes it possible to deposit the reagent 3, on the one hand, on the solid particles 4 still fresh, in particular still developing their surface when these particles 4 contain bicarbonate, and on the other hand, in a zone where the mass concentration, for example in grams per cubic meter, of the particles 4 is high, these particles 4 being still in dispersion phase in the sheath 1 to form the cloud 5, as illustrated in FIG.
  • the transit time of the gas stream 2 in the sheath 1 between the injection zone of the flow 4 'and the injection zone of the reagent 3 is advantageously less than 0.5 seconds.
  • the solid particles in the presence of which the atomization of the solution of the reagent 3 is produced are pre-existing in the gas stream 2, without requiring a specific additional injection by a separate dedicated stream such as that the flow 4 'of Figure 1.
  • These pre-existing solid particles, referenced 6 in FIG. 2 form a pre-existing cloud 7 all along the sheath 1, in particular upstream of the injection of the reagent 3.
  • These solid particles 6 comprise, in particular, fly ash which is carried in combustion fumes constituting the gas stream 2, these fly ash being present from the production of such combustion fumes.
  • the grains resulting from the atomization and the thermal decomposition of the reagent solution 3 are deposited and are dispersed over the large surface that the solid particles 6 of the cloud 7 present, as illustrated in FIG. Figure 2.
  • FIG. 1 and FIG. 2 can be combined, so that the reagent 3 is atomized within a cloud which contains, at the same time, solid particles resulting from the injection of a dedicated stream which is added to the gas stream 2, such as the solid particles 4 resulting from the injection of the stream 4 'into the FIG. 1, and pre-existing solid particles in the gas stream 2, such as solid particles 6 in Figure 2.
  • the atomization of the reagent 3 in a cloud of solid particles increases the effective surface of demercurization because the solid particles form a support for the deposition and dispersion of mercury capture grains;
  • the implementation of the method of the invention is simple, since it suffices to inject, in particular to atomize, a reactive solution into a flow duct of the gas stream

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Biomedical Technology (AREA)
  • Environmental & Geological Engineering (AREA)
  • Analytical Chemistry (AREA)
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Abstract

In order to effectively, inexpensively and easily remove mercury from gaseous effluents, the invention proposes a method for removal of mercury, wherein a reagent for capturing mercury (3), which is made up of a solution of a bicarbonate and a sulfide, is injected in liquid form into a gaseous stream (2) having a temperature greater than 140°C, preferably between 170ºC and 220ºC, so that dry grains, resulting from evaporation of the water of the solution followed by thermal decomposition of the bicarbonate of the solution into carbonate, have a large specific surface area on which the sulfide initially present in the solution is distributed in order to bond with and thus capture the mercury present in the gaseous stream.

Description

Procédé de démercurisation d'effluents gazeux  Process for the demercurization of gaseous effluents
La présente invention concerne un procédé de démercurisation d'effluents gazeux.The present invention relates to a process for the demercurization of gaseous effluents.
Beaucoup d'industries génèrent des effluents gazeux contenant du mercure, qui est un composé hautement toxique et qu'il faut retirer de ces effluents gazeux. En particulier, du mercure se retrouve dans les effluents gazeux des usines de production d'énergie qui brûlent du charbon, le charbon contenant naturellement un peu de mercure qui, lors de la combustion, va se retrouver dans les fumées de combustion sous forme de mercure métal ou de mercure oxydé. On retrouve également du mercure dans les fumées de combustion issues des usines de valorisation énergétique des déchets et les usines d'incinération de déchets, parce que les déchets contiennent un peu de mercure. Many industries generate gaseous effluents containing mercury, which is a highly toxic compound and must be removed from these gaseous effluents. In particular, mercury is found in the gaseous effluents of power plants that burn coal, coal naturally containing a little mercury which, during combustion, will end up in combustion fumes in the form of mercury metal or oxidized mercury. Mercury is also found in flue gases from waste-to-energy plants and waste incineration plants because the waste contains some mercury.
Plusieurs procédés sont utilisés pour démercuriser les effluents gazeux, notamment les fumées précitées, c'est-à-dire pour épurer ces effluents gazeux en retenant le mercure.  Several processes are used to demercurise the gaseous effluents, especially the aforementioned fumes, that is to say to purify these gaseous effluents by retaining mercury.
La manière la plus commune de procéder est de mettre en contact les effluents gazeux avec des adsorbants pulvérulents ou en grains. Le plus utilisé de ces adsorbants est le charbon actif car il est peu onéreux et efficace pour d'autres polluants, comme les composés organiques volatils, les dioxines et les furanes. Ce charbon actif peut être dopé avec des composés comme des halogènes, tels que le chlore, le brome ou l'iode, du soufre ou du sélénium. Toutefois, à haute température et tout particulièrement quand la température dépasse 200°C, les isothermes d'adsorption deviennent très défavorables : il faut alors utiliser des quantités importantes de charbon, ce qui impacte défavorablement le coût d'exploitation, ainsi que la qualité des résidus solides générés. De plus, une augmentation des dosages de charbon actif peut ne pas suffire et des pics, au-delà des limites permises, se produisent. Par rapport à l'utilisation de charbon actif simple, l'emploi de charbons dopés améliore un peu cette situation, mais le coût de ces produits est important et des problèmes secondaires, par exemple dus à la corrosivité des charbons halogénés, surviennent. De même, l'utilisation de charbons bromés peut également, par association à du chlorure d'ammonium présent dans les effluents gazeux, générer des mélanges corrosifs pour les échangeurs opérant à des températures relatives basses, tels que des économiseurs.  The most common way to proceed is to bring the gaseous effluents into contact with powdery or granular adsorbents. The most used of these adsorbents is activated carbon because it is inexpensive and effective for other pollutants, such as volatile organic compounds, dioxins and furans. This activated carbon can be doped with compounds such as halogens, such as chlorine, bromine or iodine, sulfur or selenium. However, at high temperature and particularly when the temperature exceeds 200 ° C, the adsorption isotherms become very unfavorable: it is then necessary to use significant amounts of coal, which adversely affects the operating cost, as well as the quality of the products. solid residues generated. In addition, an increase in activated charcoal dosages may not be sufficient and peaks, beyond allowable limits, occur. Compared with the use of simple activated charcoal, the use of doped coals improves this situation a little, but the cost of these products is high and secondary problems, for example due to the corrosivity of the halogenated coals, occur. Likewise, the use of brominated coals can also, by association with ammonium chloride present in the gaseous effluents, generate corrosive mixtures for exchangers operating at low relative temperatures, such as economizers.
Par exemple, US 2016/279568 divulgue un procédé de démercurisation d'effluents gazeux, procédé dans lequel des particules de carbone, activées par de l'acide bromhydrique, sont injectées dans un flux gazeux chaud pour y oxyder et adsorber du mercure présent dans ce flux gazeux. D1 envisage d'injecter dans le flux gazeux chaud, en plus des particules de carbone précitées, une solution de soude et de carbonate de calcium : cette solution ne permet pas de capter du mercure présent dans le flux gazeux, mais réagit avec le dioxyde de carbone et les oxydes de soufre, présents dans ce flux gazeux. En particulier, par réaction avec le dioxyde de carbone, du bicarbonate de sodium est produit, étant toutefois noté que la formation de ce bicarbonate reste limitée du fait du faible transfert du dioxyde de carbone vers les gouttes de la solution compte tenu de la valeur faible du coefficient de transfert gaz-liquide du dioxyde de carbone, comparé à celui de l'acide chlorhydrique ou du dioxyde de soufre. For example, US 2016/279568 discloses a gaseous effluent demineralization process, in which carbon particles, activated by hydrobromic acid, are injected into a hot gas stream to oxidize and adsorb mercury present therein. gas flow. D1 plans to inject into the hot gas stream, in addition to the above-mentioned carbon particles, a solution of sodium hydroxide and sodium carbonate. calcium: this solution does not capture mercury present in the gas stream, but reacts with carbon dioxide and sulfur oxides, present in this gas stream. In particular, by reaction with carbon dioxide, sodium bicarbonate is produced, however, it is noted that the formation of this bicarbonate is limited because of the low transfer of carbon dioxide to the drops of the solution given the low value. the gas-liquid transfer coefficient of carbon dioxide, compared with that of hydrochloric acid or sulfur dioxide.
De son côté, US 2014/0050640 divulgue un procédé de démercurisation d'effluents gazeux, dans lequel une solution contenant un composé actif de captation du mercure est injectée dans un flux gazeux à traiter. Ce composé actif est à base de silice et peut notamment résulter de la réaction entre un précurseur contenant de la silice et un sulfure, étant remarqué que ce sulfure n'est plus disponible en tant que tel dans la solution injectée puisqu'il a été consommé par réaction avec le précurseur contenant de la silice. Cette solution peut être mélangée à un réactif alcalin qui ne capte pas le mercure, mais qui capte des oxydes de soufre, ce réactif alcalin pouvant être du trôna.  For its part, US 2014/0050640 discloses a gaseous effluent demercurization process, wherein a solution containing an active mercury capture compound is injected into a gas stream to be treated. This active compound is based on silica and may in particular result from the reaction between a precursor containing silica and a sulphide, it being noted that this sulphide is no longer available as such in the injected solution since it has been consumed by reaction with the precursor containing silica. This solution can be mixed with an alkaline reagent that does not capture mercury, but that captures sulfur oxides, this alkaline reagent may be trona.
Par ailleurs, il a été proposé d'utiliser des argiles, ou bien des mélanges d'argiles et de chaux. Mais, en règle générale, à dosage équivalent et à température équivalente, ces produits argileux sont moins capacitifs et moins efficaces que les charbons actifs.  In addition, it has been proposed to use clays, or mixtures of clays and lime. But, as a rule, at equivalent dosage and at equivalent temperature, these clay products are less capacitive and less effective than activated carbons.
Il a aussi été proposé de faire percoler les effluents gazeux dans des tours remplies de charbon actif en granulés. Toutefois, cette technique est peu attractive en termes d'encombrement volumique et présente des risques potentiels de sécurité au vu des tonnages statiques importants de charbon utilisés, les fumées à démercuriser étant en général chaudes. Les phénomènes d'auto-combustion du charbon aux températures de fonctionnement, c'est-à-dire entre 140 et 200°C, sont courants et leurs conséquences sont importantes sur la perte de disponibilité de l'installation.  It has also been proposed to percolate the gaseous effluents in towers filled with granular activated carbon. However, this technique is unattractive in terms of bulk volume and presents potential safety risks in view of the large static tonnages of coal used, the fumes to be demercurized being generally hot. The phenomena of coal self-combustion at operating temperatures, that is to say between 140 and 200 ° C, are common and their consequences are important for the loss of availability of the installation.
Des procédés humides sont par ailleurs utilisés, dans lesquels on exploite la solubilité des sels de mercure, ou bien dans lesquels on réalise une oxydation du mercure métal en mercure ionique avant ou lors de son transfert en phase liquide. Ces procédés humides sont efficaces, mais pas toujours utilisables : c'est par exemple le cas lorsque les effluents gazeux à traiter sont situés dans une zone ne disposant pas d'eau ou au niveau de laquelle un rejet humide important est problématique.  Wet processes are also used, in which the solubility of the mercury salts is used, or in which an oxidation of the mercury metal to ionic mercury is carried out before or during its transfer in the liquid phase. These wet processes are effective, but not always usable: this is for example the case when the gaseous effluents to be treated are located in an area with no water or at which a significant wet discharge is problematic.
Le but de la présente invention est de proposer un nouveau procédé de démercurisation, qui soit efficace, économique et simple à mettre en œuvre.  The object of the present invention is to propose a new method of demercurization, which is effective, economical and simple to implement.
A cet effet, l'invention a pour objet un procédé de démercurisation d'effluents gazeux, tel que défini à la revendication 1 . L'idée à la base de l'invention est de créer, in situ, c'est-à-dire dans le flux gazeux à démercuriser, des grains solides pulvérulents, formés d'un composé de carbonate et d'un composé soufré apte à retenir le mercure. Pour ce faire, l'invention prévoit d'injecter dans le flux gazeux à démercuriser un réactif sous forme liquide, constitué d'une solution d'un bicarbonate, de préférence du bicarbonate de sodium, et d'un sulfure, de préférence un polysulfure. On notera que dans le présent document, un polysulfure est considéré comme étant une forme de sulfure. For this purpose, the subject of the invention is a process for the demercurisation of gaseous effluents, as defined in claim 1. The idea underlying the invention is to create, in situ, that is to say in the gaseous stream to be demercurized, powdery solid grains, formed of a carbonate compound and a suitable sulfur compound. to retain mercury. To do this, the invention provides for injecting into the gaseous flow to demercurise a reagent in liquid form, consisting of a solution of a bicarbonate, preferably sodium bicarbonate, and a sulphide, preferably a polysulfide. . It will be appreciated that in this document a polysulfide is considered to be a form of sulfide.
On rappelle que le bicarbonate de sodium (NaHC03) est un composé solide, utilisé classiquement pour épurer des fumées de leurs polluants acides comme l'acide chlorhydrique (HCI), le dioxyde de soufre (S02) et le trioxyde de soufre (S03). Un des facteurs qui contribue à la grande efficacité du bicarbonate de sodium pour l'épuration des polluants acides est que, lorsque le bicarbonate de sodium est placé dans un flux suffisamment chaud, il se produit la réaction 2 NaHC03→ Na2C03 + C02 + H20. Le dégagement des gaz C02 et H20 fait que le grain de bicarbonate NaHC03, au départ assez compact, éclate et que des cavités et des cavernes à l'échelle microscopique se créent, ce qui accroît considérablement la surface active du grain. Cet effet est souvent appelé effet « pop corn » dans la littérature technique relative au bicarbonate de sodium. It is recalled that sodium bicarbonate (NaHCO 3 ) is a solid compound conventionally used for purifying fumes of their acidic pollutants such as hydrochloric acid (HCl), sulfur dioxide (S0 2 ) and sulfur trioxide (S0). 3 ). One of the factors that contributes to the high efficiency of sodium bicarbonate for the purification of acid pollutants is that, when the sodium bicarbonate is placed in a sufficiently hot stream, the reaction occurs 2 NaHCO 3 → Na 2 CO 3 + C0 2 + H 2 0. The release of gases C0 2 and H 2 0 causes the bicarbonate grain NaHC0 3 , initially quite compact, to burst and cavities and cavities at the microscopic scale are created, which increases considerably the active surface of the grain. This effect is often called the "popcorn" effect in the technical literature on sodium bicarbonate.
L'invention met à profit cet effet « pop corn », dans le sens où en injectant la solution précitée, formant le réactif de captation du mercure, dans un flux gazeux à démercuriser présentant une température supérieure à 140°C, de préférence comprise entre 170°C et 220°C, l'eau de cette solution s'évapore au contact du flux gazeux chaud, puis le bicarbonate de la solution se décompose selon l'effet « pop corn » pour conférer aux grains secs en résultant une grande surface, de type caverneuse, où se répartit le composé soufré initialement présent dans la solution : cette grande surface soufrée forme une grande surface spécifique, active pour la captation du mercure présent dans le flux gazeux. En d'autres termes, lors de l'évaporation de l'eau de la solution puis de la décomposition du bicarbonate en carbonate, se créent des grains secs qui contiennent à la fois le carbonate et l'agent actif sulfuré et qui présentent une structure caverneuse à grande surface spécifique. La performance de démercurisation est ainsi remarquable. En pratique, la préparation de la solution formant le réactif de captation du mercure, ainsi que l'injection de cette solution dans la gaine où circule le flux gazeux chaud sont simples à mettre en œuvre, comme détaillé par la suite.  The invention takes advantage of this "popcorn" effect, in the sense that by injecting the aforementioned solution, forming the mercury capture reagent, into a gaseous stream to be demercurized having a temperature greater than 140 ° C., preferably between 170 ° C and 220 ° C, the water of this solution evaporates on contact with the hot gas stream, then the bicarbonate of the solution decomposes according to the "popcorn" effect to give the resulting dry grains a large surface area , of cavernous type, which distributes the sulfur compound initially present in the solution: this large sulfur surface forms a large specific surface, active for the capture of mercury present in the gas stream. In other words, during the evaporation of the water from the solution and then the decomposition of the carbonate bicarbonate, dry grains are created which contain both the carbonate and the sulphurised active agent and which have a structure cavernous with large specific surface. The demercurization performance is thus remarkable. In practice, the preparation of the solution forming the mercury capture reagent, as well as the injection of this solution into the sheath where the hot gas flow circulates, are simple to implement, as detailed below.
Des caractéristiques additionnelles avantageuses du procédé conforme à l'invention sont spécifiées aux revendications dépendantes.  Additional advantageous features of the method according to the invention are specified in the dependent claims.
L'invention sera mieux comprise à la lecture de la description qui va suivre, donnée uniquement à titre d'exemple et faite en se référant aux dessins sur lesquels : - la figure 1 est un schéma d'une installation mettant en œuvre un premier mode de réalisation du procédé conforme à l'invention ; et The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the drawings in which: - Figure 1 is a diagram of an installation implementing a first embodiment of the method according to the invention; and
- la figure 2 est une vue similaire à la figure 1 , illustrant un second mode de réalisation du procédé conforme à l'invention.  FIG. 2 is a view similar to FIG. 1, illustrating a second embodiment of the method according to the invention.
Sur les figures 1 et 2 est représentée une gaine 1 dans laquelle un flux gazeux 2 circule, et ce de la gauche vers la droite sur la figure. La forme de réalisation de la gaine 1 n'est pas limitative.  In Figures 1 and 2 is shown a sheath 1 in which a gas stream 2 flows, and from left to right in the figure. The embodiment of the sheath 1 is not limiting.
Le flux gazeux 2 contient du mercure. Afin de démercuriser le flux gazeux 2, un réactif de captation du mercure 3 est injecté dans le flux gazeux, au niveau d'un ou de plusieurs points d'injection dans la gaine 1 , le cas échéant répartis le long de cette dernière.  The gas stream 2 contains mercury. In order to demercurise the gas stream 2, a mercury capture reagent 3 is injected into the gas stream, at one or more injection points in the sheath 1, where appropriate distributed along the latter.
Ce réactif de captation du mercure 3 est injecté dans le flux gazeux 2 sous forme liquide, en étant constitué, avant injection, d'une solution d'un bicarbonate et d'un sulfure.  This reagent for capturing mercury 3 is injected into the gas stream 2 in liquid form, consisting, before injection, of a solution of a bicarbonate and a sulphide.
Le bicarbonate peut être constitué par n'importe quel bicarbonate minéral, par exemple du bicarbonate de sodium, de potassium ou d'ammonium. De manière préférée, le bicarbonate du réactif 3 contient, voire est constitué de bicarbonate de sodium. Dans tous les cas, le bicarbonate de la solution du réactif 3 est destiné, lorsque la solution est injectée dans le flux gazeux 2, à déclencher l'activation de grains de bicarbonate par l'effet « pop corn » décrit plus haut.  The bicarbonate may be any inorganic bicarbonate, for example sodium bicarbonate, potassium or ammonium. Preferably, the bicarbonate of reagent 3 contains, or even consists of, sodium bicarbonate. In all cases, the bicarbonate of the reagent solution 3 is intended, when the solution is injected into the gas stream 2, to trigger the activation of bicarbonate grains by the effect "popcorn" described above.
De manière similaire, le cation associé au sulfure du réactif 3 est sans réelle importance, en pouvant être, de manière non limitative, le sodium ou le potassium ou tout autre élément chimique formant un sulfure alcalin. On notera que, bien qu'un sulfure simple, tel qu'un sulfure alcalin comme Na2S, donne des résultats satisfaisants, il est préféré que le sulfure de la solution du réactif 3 soit un polysulfure car la molécule est plus lourde et moins sujette à relâcher thermiquement le sulfure d'hydrogène. De manière préférée, le polysulfure du réactif 3 contient, voire est constitué d'un polysulfure alcalin, en particulier de polysulfure de sodium ayant un rapport molaire (S/Na) entre le soufre et le sodium compris entre 1 et 4 : en pratique, le polysulfure de sodium peut être préparé, de manière connue en soi, par incorporation de soufre jaune dans une solution de sulfure alcalin ou bien de soude caustique. D'autres polysulfures, par exemple le polysulfure de potassium, conviennent également. Dans tous les cas, le sulfure, notamment le polysulfure, de la solution du réactif 3 est destiné, lorsque la solution est injectée dans le flux gazeux 2, à former, à la surface libre ou dans le volume poreux des grains de carbonate, un composé solide soufré qui capte le mercure présent dans le flux gazeux. Similarly, the cation associated with the sulfide of the reagent 3 is of no real importance, being able to be, but not limited to, sodium or potassium or any other chemical element forming an alkaline sulfide. It will be appreciated that although a simple sulfide, such as an alkali metal sulfide such as Na 2 S, gives satisfactory results, it is preferred that the sulfide of the reagent 3 solution be a polysulfide because the molecule is heavier and less subject to heat release of hydrogen sulphide. Preferably, the polysulfide of reagent 3 contains, or even consists of, an alkali polysulfide, in particular sodium polysulfide having a molar ratio (S / Na) between sulfur and sodium of between 1 and 4: in practice, the sodium polysulfide can be prepared, in a manner known per se, by incorporation of yellow sulfur in an alkaline sulphide or caustic soda solution. Other polysulfides, for example potassium polysulfide, are also suitable. In all cases, the sulphide, in particular the polysulphide, of the solution of the reagent 3 is intended, when the solution is injected into the gas stream 2, to form, on the free surface or in the pore volume of the carbonate grains, a solid sulfur compound that captures the mercury present in the gas stream.
En pratique, la solution du réactif 3 peut contenir d'autres composants que le carbonate et le sulfure décrits ci-dessus, notamment des sels halogénés. La solution du réactif 3 est avantageusement préparée par dissolution de bicarbonate, par exemple de bicarbonate de sodium, d'ammonium ou de potassium, dans une solution de sulfure, notamment de polysulfure, ou bien par mélange d'une solution de bicarbonate et d'une solution de sulfure, notamment de polysulfure. Les polysulfures ayant une composition qui, par essence, est à teneur en soufre variable, il peut être utile de caractériser le réactif 3, non pas en termes de concentration de sulfure, mais en termes de rapport molaire (S/HC03) entre le soufre et le bicarbonate qui sont respectivement apportés au moment de la préparation du réactif 3, puisque c'est le bicarbonate qui déclenche l'activation des grains de carbonate et c'est le soufre qui est l'élément actif pour la captation du mercure : ce rapport molaire S/HC03 peut avantageusement être compris entre 0,2 et 5. Ainsi, la concentration globale, exprimée en gramme par litre de matière sèche, est de peu d'importance. Il n'est d'ailleurs pas nécessaire que tout le bicarbonate contenu dans la solution du réactif 3 soit dissout : une suspension hétérogène de bicarbonate dans une solution soufrée, par exemple de polysulfure de sodium, est utilisable. In practice, the reagent 3 solution may contain other components than the carbonate and sulphide described above, especially halogenated salts. The solution of the reagent 3 is advantageously prepared by dissolving bicarbonate, for example sodium bicarbonate, ammonium or potassium, in a solution of sulphide, especially polysulphide, or by mixing a solution of bicarbonate and a sulphide solution, in particular polysulfide. Since the polysulfides have a composition which, in essence, is of variable sulfur content, it may be useful to characterize the reagent 3, not in terms of the sulphide concentration, but in terms of the molar ratio (S / HC0 3 ) between the sulfur and bicarbonate which are respectively brought at the time of the preparation of the reagent 3, since it is the bicarbonate which triggers the activation of the carbonate grains and it is the sulfur which is the active element for the capture of the mercury: this molar ratio S / HC0 3 may advantageously be between 0.2 and 5. Thus, the overall concentration, expressed in grams per liter of dry matter, is of little importance. It is also not necessary that all the bicarbonate contained in the reagent solution 3 is dissolved: a heterogeneous suspension of bicarbonate in a sulfur solution, for example sodium polysulfide, is usable.
En pratique, pour préparer en ligne la solution du réactif 3, on utilise une installation comprenant, par exemple, un ou plusieurs bacs agités et des moyens permettant d'introduire, d'une part, le bicarbonate et, d'autre part, le soufre.  In practice, in order to prepare the reagent 3 solution online, an installation comprising, for example, one or more stirred tanks and means for introducing, on the one hand, bicarbonate and, on the other hand, the sulfur.
L'injection de la solution du réactif 3 dans la gaine 1 est réalisée par tout moyen approprié. Avantageusement, cette injection consiste en une pulvérisation ou une atomisation, opérée par des buses ou par des buses à air bi-fluides ou, plus généralement, par tout matériel permettant de disperser finement la solution dans le flux gazeux 2, typiquement en fines gouttelettes. Dans tous les cas, dans un premier temps, l'eau de chacune des gouttelettes de la solution du réactif 3 injecté s'évapore au contact du flux gazeux 2 ; puis, dans un second temps, le bicarbonate présent dans chaque gouttelette se décompose thermiquement, selon l'effet « pop corn », ce qui crée des grains secs de carbonate présentant, à l'échelle microscopique, des cavités et des cavernes, qui induisent de grandes surfaces spécifiques pour chaque grain. Le sulfure initialement présent dans la solution du réactif 3 se retrouve réparti sur cette grande surface spécifique, ce qui confère à chaque grain une grande surface active pour la démercurisation du flux gazeux 2 : au contact des sites actifs soufrés, le mercure est transféré de la phase gaz du flux gazeux 2 à la phase solide des grains, à laquelle le mercure se retrouve fortement lié.  The injection of the reagent solution 3 into the sheath 1 is carried out by any appropriate means. Advantageously, this injection consists of a spraying or atomization, carried out by nozzles or by two-fluid air nozzles or, more generally, by any material making it possible to finely disperse the solution in the gas stream 2, typically in fine droplets. In all cases, initially, the water of each of the droplets of the injected reagent solution 3 evaporates in contact with the gas stream 2; then, in a second step, the bicarbonate present in each droplet decomposes thermally, according to the "popcorn" effect, which creates dry grains of carbonate having, on the microscopic scale, cavities and caves, which induce large specific surfaces for each grain. The sulphide initially present in the solution of the reagent 3 is distributed over this large specific surface, which gives each grain a large active surface for the demercurization of the gas stream 2: in contact with the active sulfur sites, the mercury is transferred from the gas phase of the gas stream 2 to the solid phase of the grains, to which the mercury is strongly bound.
Les grains solides, ayant captés le mercure, sont charriés par le flux gazeux 2, jusqu'à en être ensuite séparés par des moyens connus en soi, comme des filtres à manches ou des électrofiltres. Il est particulièrement important que le flux gazeux 2 dans lequel la solution du réactif 3 est injecté soit à une température d'au moins 140°C, et de manière préférée comprise entre 170 et 220°C. A une température moindre, la réaction de décomposition thermique du bicarbonate est trop lente. Le temps caractéristique nécessaire au processus de cette décomposition dépend bien entendu de la température et est bien connu de l'homme de l'art : il est caractéristique du bicarbonate, en étant typiquement compris entre 0,3 et 1 ,5 secondes. The solid grains, having captured the mercury, are carried by the gas stream 2, until they are then separated by means known per se, such as bag filters or electrostatic precipitators. It is particularly important that the gas stream 2 in which the solution of the reagent 3 is injected is at a temperature of at least 140 ° C, and preferably between 170 and 220 ° C. At a lower temperature, the thermal decomposition reaction of the bicarbonate is too slow. The characteristic time required for the process of this decomposition depends of course on the temperature and is well known to those skilled in the art: it is characteristic of bicarbonate, typically being between 0.3 and 1.5 seconds.
On comprend que, aussi longtemps que le réactif 3 est injecté dans une zone suffisamment chaude du flux gazeux 2, le point d'injection de ce réactif 3 n'est pas critique. Par exemple, le réactif 3 peut être injecté en aval d'un économiseur de chaleur, ou bien en amont d'un tel économiseur, là où la température est plus chaude.  It is understood that, as long as the reagent 3 is injected into a sufficiently hot zone of the gas stream 2, the injection point of this reagent 3 is not critical. For example, the reagent 3 can be injected downstream of a heat saver, or upstream of such an economizer, where the temperature is warmer.
Suivant une disposition optionnelle particulièrement avantageuse, la solution du réactif 3 est injectée dans le flux gazeux 2 en y étant atomisée en présence de particules solides, comme expliqué plus en détail ci-après.  According to a particularly advantageous optional arrangement, the solution of the reagent 3 is injected into the gas stream 2 by being atomized therein in the presence of solid particles, as explained in more detail below.
Dans le mode de réalisation préféré de la figure 1 , les particules solides en présence desquelles l'atomisation de la solution du réactif 3 est réalisée sont référencées 4 et résultent de l'injection d'un flux dédié 4' dans le flux gazeux 2 en amont de l'injection du réactif 3, l'injection de ce flux 4' étant opérée au niveau d'un ou de plusieurs points d'injection dans la gaine, qui, le cas échéant, sont répartis le long de cette dernière et qui sont tous situés avant le ou les points d'injection du réactif 3. En pratique, le flux 4' est introduit à l'intérieur de la gaine 1 par tout matériel approprié, par exemple des cannes, des buses, des tuyaux droits ou biseautés. Une fois que le flux 4' est injecté dans le flux gazeux 2 à l'intérieur de la gaine 1 , les particules solides 4 provenant du flux 4' se dispersent et forment progressivement un nuage 5 qui, le long de la gaine 1 à partir du ou des points d'injection du flux 4', s'étend vers l'aval, jusqu'à couvrir toute la section de la gaine 1 .  In the preferred embodiment of FIG. 1, the solid particles in the presence of which the atomization of the reagent solution 3 is carried out are referenced 4 and result from the injection of a dedicated flow 4 'into the gas stream 2 upstream of the injection of the reagent 3, the injection of this stream 4 'being operated at one or more injection points in the sheath, which, where appropriate, are distributed along the latter and which are all located before the injection point (s) of the reagent 3. In practice, the flow 4 'is introduced inside the sheath 1 by any suitable material, for example canes, nozzles, straight or beveled pipes. . Once the stream 4 'is injected into the gas stream 2 inside the sheath 1, the solid particles 4 from the stream 4' are dispersed and gradually form a cloud 5 which, along the sheath 1 from of the injection point (s) of the flow 4 ', extends downstream, to cover the entire section of the sheath 1.
Suivant une disposition optionnelle particulièrement avantageuse, les particules solides 4 sont prévues pour capter des polluants acides présents dans le flux gazeux 2, tels que le chlorure d'hydrogène (HCI) et le dioxyde de soufre (S02) : à cet effet, le flux 4' contient alors du bicarbonate de sodium ou du sesquicarbonate de sodium comme le trôna, qui est un minéral naturel. Le bicarbonate ou le sesquicarbonate de sodium sont injectés dans le flux gazeux 2 sous forme pulvérulente, typiquement obtenue par broyage, et, au contact du flux gazeux 2, produisent les particules solides 4 par décomposition partielle. Bien entendu, le flux 4' peut contenir, en complément ou en alternative au bicarbonate et sesquicarbonate de sodium, d'autres produits réactifs, tels que la chaux, qui, notamment après décomposition au contact du flux gazeux 2, forment dans ce dernier les particules solides 4 à même de capter les polluants acides présents dans le flux gazeux 2. According to a particularly advantageous optional arrangement, the solid particles 4 are intended to capture acidic pollutants present in the gas stream 2, such as hydrogen chloride (HCl) and sulfur dioxide (S0 2 ): for this purpose, the 4 'stream then contains sodium bicarbonate or sodium sesquicarbonate as the trona, which is a natural mineral. Bicarbonate or sodium sesquicarbonate are injected into the gaseous stream 2 in pulverulent form, typically obtained by grinding, and, in contact with the gas stream 2, produce the solid particles 4 by partial decomposition. Of course, the stream 4 'may contain, in addition or alternatively to sodium bicarbonate and sesquicarbonate, other reactive products, such as lime, which, in particular after decomposition in contact with the gas stream 2, form in this process. last solid particles 4 able to capture the acid pollutants present in the gas stream 2.
Le réactif de captation du mercure 3 est atomisé au sein du nuage 5 des particules 4. Ainsi, le réactif 3 va à la fois subir la décomposition thermique, décrite plus haut, qui génère de la surface active pour démercuriser le flux gazeux 2, mais aussi être dispersé et porté par la surface de toutes les particules 4 du nuage 5 : les sites actifs soufrés se retrouvent ainsi dispersés et déposés sur une surface encore plus grande, accentuant encore la performance de démercurisation.  The mercury uptake reagent 3 is atomized within the cloud 5 of the particles 4. Thus, the reagent 3 will undergo both the thermal decomposition described above, which generates the active surface to demercurise the gas stream 2, but also be dispersed and carried by the surface of all the particles 4 of the cloud 5: the active sulfur sites are thus dispersed and deposited on an even larger surface, further enhancing the demercurization performance.
En aval de l'injection du réactif 3, tous les solides charriés par le flux gazeux 2 sont séparés de ce dernier.  Downstream of the injection of the reagent 3, all the solids carried by the gas stream 2 are separated from the latter.
En pratique, il est avantageux que l'injection du réactif 3 ne soit pas située trop en aval de l'injection du flux 4'. En effet, cette disposition permet de déposer le réactif 3, d'une part, sur les particules solides 4 encore fraîches, notamment encore en train de développer leur surface quand ces particules 4 contiennent du bicarbonate, et d'autre part, dans une zone où la concentration massique, par exemple en gramme par mètre cube, des particules 4 est élevée, ces particules 4 étant encore en phase de dispersion dans la gaine 1 pour former le nuage 5, comme illustré à la figure 1 . A cet effet, le temps de transit du flux gazeux 2 dans la gaine 1 entre la zone d'injection du flux 4' et la zone d'injection du réactif 3 est avantageusement inférieur à 0,5 seconde.  In practice, it is advantageous that the injection of the reagent 3 is not located too far downstream of the injection of the flow 4 '. Indeed, this arrangement makes it possible to deposit the reagent 3, on the one hand, on the solid particles 4 still fresh, in particular still developing their surface when these particles 4 contain bicarbonate, and on the other hand, in a zone where the mass concentration, for example in grams per cubic meter, of the particles 4 is high, these particles 4 being still in dispersion phase in the sheath 1 to form the cloud 5, as illustrated in FIG. For this purpose, the transit time of the gas stream 2 in the sheath 1 between the injection zone of the flow 4 'and the injection zone of the reagent 3 is advantageously less than 0.5 seconds.
Dans un mode de réalisation alternatif, montré à la figure 2, les particules solides en présence desquelles l'atomisation de la solution du réactif 3 est réalisée sont préexistantes dans le flux gazeux 2, sans nécessiter une injection additionnelle spécifique par un flux dédié distinct tel que le flux 4' de la figure 1 . Ces particules solides préexistantes, référencées 6 sur la figure 2, forment un nuage 7 préexistant tout le long de la gaine 1 , notamment en amont de l'injection du réactif 3. Ces particules solides 6 comprennent notamment des cendres volantes qui sont charriées dans des fumées de combustion constituant le flux gazeux 2, ces cendres volantes étant présentes dès la production de telles fumées de combustion.  In an alternative embodiment, shown in FIG. 2, the solid particles in the presence of which the atomization of the solution of the reagent 3 is produced are pre-existing in the gas stream 2, without requiring a specific additional injection by a separate dedicated stream such as that the flow 4 'of Figure 1. These pre-existing solid particles, referenced 6 in FIG. 2, form a pre-existing cloud 7 all along the sheath 1, in particular upstream of the injection of the reagent 3. These solid particles 6 comprise, in particular, fly ash which is carried in combustion fumes constituting the gas stream 2, these fly ash being present from the production of such combustion fumes.
Comme expliqué précédemment en lien avec la figure 1 , les grains résultant de l'atomisation et de la décomposition thermique de la solution du réactif 3 se déposent et se dispersent sur la grande surface que présentent les particules solides 6 du nuage 7, comme illustré à la figure 2.  As explained above with reference to FIG. 1, the grains resulting from the atomization and the thermal decomposition of the reagent solution 3 are deposited and are dispersed over the large surface that the solid particles 6 of the cloud 7 present, as illustrated in FIG. Figure 2.
Bien entendu, en variante, les modes de réalisation de la figure 1 et de la figure 2 peuvent être combinés, de sorte que le réactif 3 est atomisé au sein d'un nuage qui contient, à la fois, des particules solides résultant de l'injection d'un flux dédié qui ajouté au flux gazeux 2, telles les particules solides 4 résultant de l'injection du flux 4' à la figure 1 , et des particules solides préexistantes dans le flux gazeux 2, telles que les particules solides 6 à la figure 2. Of course, in a variant, the embodiments of FIG. 1 and FIG. 2 can be combined, so that the reagent 3 is atomized within a cloud which contains, at the same time, solid particles resulting from the injection of a dedicated stream which is added to the gas stream 2, such as the solid particles 4 resulting from the injection of the stream 4 'into the FIG. 1, and pre-existing solid particles in the gas stream 2, such as solid particles 6 in Figure 2.
Quel que soit le mode de réalisation de l'invention, les avantages conférés par cette dernière sont nombreux :  Whatever the embodiment of the invention, the advantages conferred by the latter are numerous:
- l'utilisation conjointe d'un bicarbonate et d'un sulfure, notamment d'un polysulfure, permet, par effet « pop corn », la génération de grains soufrés à grande surface spécifique, étant souligné que les surfaces soufrées des grains sont fraîches et très réactives puisque l'activation par effet « pop corn » a lieu in situ, c'est-à-dire directement au sein du flux gazeux 2 ;  the joint use of a bicarbonate and a sulphide, in particular a polysulphide, makes it possible, by the "popcorn" effect, to generate sulfur grains with a large specific surface area, underlining that the sulfur surfaces of the grains are fresh; and very reactive since activation by "popcorn" effect takes place in situ, that is to say directly within the gas stream 2;
- l'atomisation du réactif 3 au sein d'un nuage de particules solides, tel que le nuage 5 de particules 4 ou le nuage 7 de particules 6, démultiplie la surface effective de démercurisation du fait que les particules solides forment un support pour la déposition et la dispersion des grains de captation du mercure ; et  the atomization of the reagent 3 in a cloud of solid particles, such as the cloud of particles 4 or the cloud 7 of particles 6, increases the effective surface of demercurization because the solid particles form a support for the deposition and dispersion of mercury capture grains; and
- la mise en œuvre du procédé de l'invention est simple, puisqu'il suffit d'injecter, notamment d'atomiser, une solution réactive dans une gaine de circulation du flux gazeux the implementation of the method of the invention is simple, since it suffices to inject, in particular to atomize, a reactive solution into a flow duct of the gas stream
2, en une zone suffisamment chaude de ce flux gazeux. 2, in a sufficiently hot zone of this gas flow.

Claims

REVENDICATIONS
1 .- Procédé de démercurisation d'effluents gazeux, 1 .- Process of demercurization of gaseous effluents,
dans lequel un réactif de captation du mercure (3), qui est constitué d'une solution d'un bicarbonate et d'un sulfure, est injecté sous forme liquide dans un flux gazeux (2) ayant une température supérieure à 140°C, de préférence comprise entre 170°C et 220°C, de manière que des grains secs, résultant de l'évaporation de l'eau de la solution puis de la décomposition thermique du bicarbonate de la solution en carbonate, présentent une grande surface spécifique sur laquelle le sulfure initialement présent dans la solution se retrouve réparti pour se lier à et ainsi capter du mercure présent dans le flux gazeux.  wherein a mercury uptake reagent (3), which consists of a solution of a bicarbonate and a sulfide, is injected in liquid form into a gas stream (2) having a temperature greater than 140 ° C, preferably between 170 ° C and 220 ° C, so that dry grains, resulting from the evaporation of water from the solution and then thermal decomposition of the bicarbonate from the carbonate solution, have a large specific surface area. which sulphide initially present in the solution is distributed to bind to and thus capture mercury present in the gas stream.
2. - Procédé suivant la revendication 1 , dans lequel le sulfure du réactif de captation du mercure (3) est un polysulfure. The process of claim 1, wherein the sulfide of the mercury capture reagent (3) is a polysulfide.
3. - Procédé suivant la revendication 2, dans lequel le polysulfure du réactif de captation du mercure (3) contient du polysulfure de sodium, avec un rapport molaire (S/Na) entre le soufre et le sodium compris entre 1 et 4. 3. - Process according to claim 2, wherein the polysulfide of the mercury capture reagent (3) contains sodium polysulfide, with a molar ratio (S / Na) between sulfur and sodium of between 1 and 4.
4.- Procédé suivant l'une quelconque des revendications précédentes, 4. A process according to any one of the preceding claims,
dans lequel, avant d'être injecté dans le flux gazeux (2), le réactif de captation du mercure (3) est préparé par dissolution de bicarbonate dans une solution de sulfure, notamment de polysulfure, ou bien par mélange d'une solution de bicarbonate et d'une solution de sulfure, notamment de polysulfure,  in which, before being injected into the gas stream (2), the mercury-uptake reagent (3) is prepared by dissolving bicarbonate in a solution of sulphide, in particular polysulphide, or by mixing a solution of bicarbonate and a solution of sulphide, in particular polysulfide,
et dans lequel le rapport molaire (S/HC03) entre le soufre et le bicarbonate qui sont respectivement apportés au moment de la préparation du réactif de captation du mercure (3) est compris entre 0,2 et 5. and wherein the molar ratio (S / HC0 3 ) between sulfur and bicarbonate which are respectively provided at the time of preparation of the mercury capture reagent (3) is between 0.2 and 5.
5. - Procédé suivant l'une quelconque des revendications précédentes, dans lequel le bicarbonate du réactif de captation du mercure (3) contient du bicarbonate de sodium. The process of any of the preceding claims, wherein the bicarbonate of the mercury capture reagent (3) contains sodium bicarbonate.
6. - Procédé suivant l'une quelconque des revendications précédentes, dans lequel le réactif de captation du mercure (3) est injecté dans le flux gazeux (2) en y étant atomisé en présence de particules solides (4 ; 6). 6. - Process according to any one of the preceding claims, wherein the mercury capture reagent (3) is injected into the gas stream (2) by being atomized therein in the presence of solid particles (4; 6).
7.- Procédé selon la revendication 6, dans lequel au moins une partie des particules solides (4) résulte de l'injection d'un flux dédié (4') dans le flux gazeux (2) en amont de l'injection du réactif de captation du mercure (3). 7. A process according to claim 6, wherein at least a portion of the solid particles (4) results from the injection of a dedicated stream (4 ') into the gas stream (2) upstream of the injection of the reagent. mercury uptake (3).
8.- Procédé selon la revendication 7, dans lequel ledit flux dédié (4') contient un réactif de captation de polluants acides contenus dans le flux gazeux (2), tel que du bicarbonate de sodium et/ou du sesquicarbonate de sodium et/ou de la chaux. 8. A process according to claim 7, wherein said dedicated stream (4 ') contains a reagent for capturing acid pollutants contained in the gas stream (2), such as sodium bicarbonate and / or sodium sesquicarbonate and / or lime.
9. - Procédé selon l'une quelconque des revendications 7 ou 8, dans lequel le temps de transit du flux gazeux (2) entre la zone d'injection dudit flux dédié (4') et la zone d'injection du réactif de captation du mercure (3) est inférieur à 0,5 seconde. 9. - Process according to any one of claims 7 or 8, wherein the transit time of the gas stream (2) between the injection zone of said dedicated flow (4 ') and the injection zone of the capture reagent mercury (3) is less than 0.5 seconds.
10. - Procédé selon l'une quelconque des revendications 6 à 9, dans lequel le flux gazeux à démercuriser (2) consiste en des fumées de combustion, et dans lequel au moins une partie des particules solides (6) est constituée de cendres volantes présentes dans lesdites fumées de combustion. 10. - Process according to any one of claims 6 to 9, wherein the gaseous gas to be demercurized (2) consists of combustion fumes, and wherein at least a portion of the solid particles (6) is composed of fly ash present in said combustion fumes.
EP18792939.3A 2017-10-26 2018-10-25 Method for removal of mercury from gaseous effluents Withdrawn EP3700660A1 (en)

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FR1760086A FR3072887B1 (en) 2017-10-26 2017-10-26 GAS EFFLUENT DEMERCURIZATION PROCESS
PCT/EP2018/079271 WO2019081635A1 (en) 2017-10-26 2018-10-25 Method for removal of mercury from gaseous effluents

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WO2014062438A2 (en) * 2012-10-16 2014-04-24 Novinda Corporation Solution-based mercury capture
US9566551B2 (en) * 2013-07-16 2017-02-14 S&S Lime, Inc. Flue gas treatment using kraft mill waste products
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