WO1998025693A1 - Composition for treating fumes and uses - Google Patents

Abstract

The invention concerns a composition for treating fumes comprising: a base constituent containing bicarbonate and optionally a source of NH3; and catalytic quantities of one or several denitrification catalysts, obtained at least partly by recycling of all or part of the slag and/or the final residues of the treatment of the fumes.

Description

 FUME TREATMENT COMPOSITION AND USES

The subject of the present invention is a new composition and its uses, in particular in the treatment of fumes, in particular industrial fumes.

The treatment of fumes comprising all kinds of pollutants, such as mineral acids, such as the acids of formula HX in which X represents a halogen, compounds of the SOx, NOx type, organic derivatives, such as dioxins, furans, for example, as well as metals considered toxic, is experiencing a particular boom due to the increasing pressure of environmental regulations exerted on companies emitting such gaseous emissions.

Among the processes generating such gases, we can, among others, mention household waste incinerators, hospital waste and special industrial waste incinerators, thermal power stations, certain products of the chemical industry and glass-type ovens .

Conventional gas treatment installations use so-called dry treatments, or semi-wet treatments. In the first case, the smoke neutralizing agent is introduced in the form of a solid, and in the second case, the said agent is used in the form of a suspension or an aqueous solution, the amount of water is calculated so that the product resulting from the treatment is a solid, as in the first case.

One of the oldest dry type processes uses lime as reactant, which imposes a significant stoichiometric ratio because of the low reactivity of lime.

These methods also have the disadvantage of creating solid residues which are very difficult to recover and which must be placed in a special landfill, due to the presence of metals considered to be toxic. The quantities of solids in this case are relatively large and cause high additional costs for the process.

A more interesting method is to use sodium bicarbonate. The use of this neutralizing agent provides a solid residue which is easily recyclable. Furthermore, the stoichiometric ratio (quantity introduced in moles / quantity theoretically necessary in moles) of sodium bicarbonate relative to the compounds to be neutralized present in the gases to be treated is much lower than in the case of lime. This last type of process constitutes a technological advance in the field. However, it has limitations, in particular, an insufficient nitrogen oxide smoke treatment function.

The object of the invention is to overcome this drawback and to make it possible to treat the fumes in order to neutralize both the nitrogen oxides (NOx, with x = 1 or 2) and the sulfur oxides (SOx with x ≈ 2 or 3). ).

In addition, it is known that the fumes, in particular the fumes from glass furnaces, are rich in metals considered to be toxic, more particularly heavy metals and / or polyvalent metals, for example, mercury, cadmium, lead, l , selenium, silver, antimony, zinc, silicon, calcium, titanium, chromium, manganese, iron, nickel, copper, molybdenum, tin, bismuth , vanadium and cobalt.

It would therefore be interesting to be able to recycle these metals in the treatment of smoke for obvious reasons of a complete environmental cycle. This object is achieved thanks to the composition of the invention intended for the treatment of fumes comprising:

- a basic component comprising bicarbonate and optionally a source of NH3; and

- catalytic quantities of one or more denitrification catalysts, obtained at least in part by recycling all or part of the dross and / or the ultimate residues from the treatment of the fumes.

The subject of the invention is also a process for the treatment of fumes, in which fumes comprising NOx and SOx are treated with a composition as described above, in the presence of ammonia, when the basic component does not contain any. not.

The basic component can be commercial sodium hydrogencarbonate. It can also consist of a mixture of sodium bicarbonate and sodium carbonate, in particular obtained either by gentle drying of sodium bicarbonate, or by mechanical mixing of sodium bicarbonate and sodium carbonate. The sesqui form (enthroned: NaHCθ3. Na2Cθ3-2H2θ) is also suitable.

Advantageously, the basic component comprises a mixture of sodium bicarbonate, sodium carbonate and ammonia in the form of ammonium salts. Advantageously, the sodium bicarbonate content is at least

70% by weight, preferably at least 80%, and more particularly between 80 and 95% by weight. The amount of sodium carbonate present is advantageously less than 30% by weight, preferably less than 20%, and more particularly between 5 and 15% by weight. The amount of ammonia expressed in the form of ammonium ion present is preferably less than 1% by weight and more particularly varies between 0.2 and 0.7% by weight.

This composition may further comprise salts of carbamate and water. The content of ammonium carbamate is preferably less than 0.1% by weight and more preferably between 0.01 and 0.06% by weight. The water is preferably present in an amount less than 10% by weight and more particularly from 0.2 to 6% by weight.

A particularly advantageous basic component of this type is the product obtained by heat treatment of an ammoniacal bicarbonate at a temperature of between 20 and 150 ° C., the heat treatment preferably being carried out under a controlled atmosphere which may comprise water and / or carbon dioxide.

It should be noted that the ammoniacal bicarbonate used is the intermediate product obtained by implementing the process for the preparation of sodium carbonate by the technique of sodium hydroxide with ammonia, known under the name of "Solvay process".

More precisely, the product obtained after dissolving gaseous ammonia in an aqueous solution of sodium chloride so as to produce an ammoniacal brine is called ammoniacal bicarbonate for the purposes of the present invention. This is then treated with a gas containing carbon dioxide to give ammoniacal bicarbonate crystals.

Ammoniacal bicarbonate in fact designates a composition mainly comprising sodium bicarbonate, sodium carbonate, and to a lesser extent, ammonia in the form of ammonium salts such as bicarbonate, carbonate and / or carbamate, and water. .

As an indication, a composition of this type can comprise: 70 to 90

% by weight of sodium bicarbonate (NaHC03), 2 to 20% by weight of sodium carbonate (Na2C03>, 0.2 to 1.0% by weight of ammonia expressed in the form of ammonium ion, 0.3 to 2.0% by weight of ammonium carbamate (NH4O2CNH2) and 5 to

20% by weight of water.

The treatment of ammoniacal bicarbonate in the specified temperature range, and more particularly at high temperature, and under a controlled atmosphere of water and / or carbon dioxide, makes it possible to selectively dry and decompose the ammonium salts present such as bicarbonate , carbonate and / or carbamate, into ammonia and carbon dioxide, without substantial decomposition of the sodium bicarbonate present in the mixture into sodium carbonate. The heat treatment can take place at a temperature between 20 and 150 ° C, advantageously between 20 and 130 ° C, under a controlled atmosphere which can include water and / or carbon dioxide, preferably with stirring. More particularly, the heat treatment is carried out in the presence of an atmosphere whose water vapor content is between 0 and 10 mol%.

As regards carbon dioxide, the heat treatment is carried out in the presence of an atmosphere whose carbon dioxide content is between 0 and 100 mol%.

Furthermore, the heat treatment is carried out under an atmosphere which may include air, or any other inert gas such as rare gases, nitrogen. The content of this type of gas, if used, ensures the balance to reach the desired total pressure. The treatment temperature of the ammoniacal bicarbonate can be adapted as a function of the quantity of water vapor and carbon dioxide present.

Thus, in the case where the atmosphere is a nitrogen / oxygen or air mixture, the temperature range for the heat treatment will preferably be less than 80 ° C.

Furthermore, if the treatment is carried out under an atmosphere comprising a mixture of carbon dioxide and water vapor, and possibly air or an inert gas, it is then possible to carry out the latter at a temperature close to 120 ° C-130 ° C, although lower temperatures are still possible.

For the above, the temperature values are expressed at atmospheric pressure. A person skilled in the art is able to adapt the temperature values as a function of the pressure under which the treatment is carried out, the preparation of the basic component according to the invention being able to be carried out under any pressure.

The heat treatment is preferably carried out under a gas flow.

One reason for this is that it is highly desirable not to maintain a partial ammonia pressure above the ammoniacal bicarbonate, in order to promote the decomposition of ammonium salts such as bicarbonate, carbonate and / or carbamate.

Usually the duration of the operation and at most a few hours. At the end of this treatment, a mixture of bicarbonate and carbonate comprising ammonia is obtained, as described above. This mixture is used for the basic component of the present invention. The advantage of a basic component of this type is that it contains ammonia and therefore allows the introduction of the ammonia source at the same time as the bicarbonate during the smoke treatment process. The catalytic denitrification component is advantageously based on vanadium, titanium, zirconium, copper, manganese and / or tungsten.

Other elements present in the ultimate smoke treatment residues may also be suitable.

Advantageously, all or part of the metallic elements present in the ultimate residues and / or dross from the treatment of smoke are used as catalytic components.

The term "ultimate residues" denotes the cakes obtained after leaching of the solid residues resulting from the treatment of smoke. These cakes contain the metals listed above, especially in the form of hydrates or oxyhydrates. By dross, the solid residues resulting from the treatment of fumes and recovered by filtration essentially comprising sodium sulphate and heavy metals as listed above are called.

In a first embodiment according to the invention, all or part of the above-mentioned ultimate or foul residues are used as such after addition to a basic component as described above.

In a second embodiment, the ultimate or grime residues described above are treated to recover the metallic elements, in particular in the form of hydrates or oxyhydrates which are doped, if necessary, with additional metallic elements. The effectiveness of the composition according to the invention can also be adapted by the introduction of other transition metals, whether or not included in cakes or dross, or even rare earths, such as cerium.

ou {CuO.K₂Sθ4}/AI₂O₃.The catalytic components can be introduced in the solid state, in particular when the basic component is in solid form. One type of solid catalysts obtained from ultimate or foul residues which can be used in the context of the present invention consists of solid reagents of formulas {V2O5. V2O5. Wθ3} Tiθ2,

or {CuO.K ₂ Sθ4} / AI ₂ O ₃ .

Vanadium can also be replaced by manganese. Preferred manganese-based catalytic components are of the Mnθ2 or Mnθ3 type, optionally added with rare earths. The catalytic components can also be introduced in the form of their precursors when the basic component is in the form of an aqueous suspension or solution.

The catalytic elements are present in a proportion of between 0.0001 and 0.2, preferably 0.001 and 0.1, these figures expressing the molar ratio of the metallic species of the catalytic component to sodium of the basic component.

The composition according to the invention is obtained by mixing, in a suitable reactor, the bicarbonate-based component with a catalytic composition, described above.

When the bicarbonate component and the catalytic component are in solid form, the mixing is carried out using a known solid / solid mixing technique, in a reactor such as a kneader or a granulator. When the bicarbonate-based component is in liquid form, in aqueous solution or suspension, the catalytic component will be introduced in the form of a precursor of the various metals and the mixture will be produced, for example, in a granulator.

When using neutralization dross, the quantity of Na2Sθ4 should be adjusted so as to obtain an adequate ratio of metallic elements to sodium, before mixing with the basic component.

The water content of the final composition can be between 2 and 15% by weight, relative to the bicarbonate-based component, preferably between 5 and 10%.

It is preferable to use a reagent, which is in solid form, of fine and controlled particle size so as to improve the kinetics of the neutralization treatment.

For example, we prefer to use a reagent whose average particle size is less than 50 μm.

According to a more particular embodiment, a reagent is used whose average particle size is between 5 and 30 μm.

If a reagent with a greater particle size or of the order of 50 μm is used, it may be advantageous to carry out, prior to the treatment of the fumes, a step of grinding said reagent to achieve a particle size of the order of 5 at 30 μm. Such a step can be implemented by any conventional means known to those skilled in the art. If the variant is implemented with an extemporaneous supply of water, the latter can be provided before the treatment of the fumes or alternatively, during the treatment of these fumes.

Thus, it is possible to bring the water in spray form into contact with the composition according to the invention, in a humidifying drum, if the supply of water takes place before the treatment of the fumes itself.

In the case where water is brought in when the reactant is brought into contact with the fumes, the latter is injected in the required quantities, directly into the gas stream. The subject of the invention is also a process for the treatment of fumes, comprising bringing a composition as defined above into contact with the fumes to be treated at a temperature between 200 and 700 ° C., advantageously 300 and 500 °. C, a preferred temperature being around 350 ° C. The composition according to the invention is particularly useful for the treatment of fumes containing mainly SOx, in particular SO2 and SO3, and NOx, in particular NO and NO2.

These may also contain acids of formula HX, X being a halogen atom, in particular chlorine as well as metals considered to be toxic.

The functions of the composition and of the method according to the invention in the treatment of fumes, in particular from glass furnaces are the following:

- continuously create a micron dispersion of Na2C03 according to the equation:

2 aHCθ3 → Na2Cθ3 + H2O + CO2 (1)

- neutralize the sulfur oxides (mainly SO2) according to equation (2):

SO2 + (1 + x) Na ₂ -xHxC03 + 1/2 O → Na2SO ₄ + xH O + CO2 (2)

- favor the partial neutralization of nitrogen oxides by SO2 by the "contact" effect on the surface of Na2Cθ3, according to equations (3) and (4):

2 NO + 2SO → N + 2 SO3 (3)

2 NO ₂ + 4SO ₂ → N + 4 SO3 (4) - release a partial localized water pressure which is very favorable for the capture of pollutants, such as SOx and NOx.

- constitute a releasable NH3 reservoir for the non-catalytic or catalytic reduction of NOx according to equations (5) and (6):

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6 H2O (5)

2NO ₂ + 4NH ₃ + O ₂ → 3N ₂ + 6 H ₂ O (6)

- provide catalytic principles releasable by fluidization in the gas stream, for catalytic reductive denitrification.

The fumes can be treated, advantageously, by the semi-wet route or by the dry route.

By semi-wet route, a process is defined in which the composition resulting from the process according to the invention (also called hereinafter reactive) is introduced in the presence of water in an amount such that the products obtained after the treatment are found under a solid form. In this case, the reagent is used in the form of a suspension or a solution.

The water content necessary to obtain a solution or a suspension of the reagent can be determined by a person skilled in the art depending on the technological constraints of the process. More particularly, this content depends on the smoke treatment temperature, on the evaporation capacity of the equipment and on the fact that it is desired to obtain, after said treatment, a solid product.

In this case, two types of implementation can be distinguished, the first variant is carried out without additional water supply, and the second variant is carried out by supplying water but with an amount such that the reagent retains its appearance of powder.

In the latter case, the water content is between 2 and 15% by weight relative to the weight of the reagent. Preferably, the amount of water is between 5 and 10%.

Fumes of this type are more particularly due to the incineration of household waste, hospital waste or even special industrial waste.

The fumes comprising mainly SOx are more particularly encountered with the operation of thermal power stations, ovens glassmakers, for example, which also include dust and / or fly ash, as well as other pollutants, in particular compounds of the NOx type, or organic compounds, such as dioxins or furans.

The fumes comprising significant quantities of NOx are in particular those from glass furnaces. These fumes can be treated, advantageously, dry.

Advantageously, the smoke treatment is carried out so that the stoichiometric ratio between the reagent and the compounds of the SOx type which it is sought to eliminate is between 1.02 and 2. Preferably, said stoichiometric ratio is between 1, 02 and

1, 5. According to an advantageous embodiment, the stoichiometric ratio is between 1.05 and 1.3.

When the basic component does not contain a source of NH3, this is injected into the gas stream at the same time as the composition of the invention.

The method of injection by dry or semi-wet route into the gas stream is carried out according to a technique well known to those skilled in the art.

If the fumes to be treated include organic pollutants, it may be advantageous to also inject an adsorbent into the gas stream, with the reagent and possibly the water. The adsorbent comprising the organic pollutants can then be recovered with the solids from the smoke treatment.

It should be noted that this treatment also makes it possible to increase the quantity of mercury recovered if it is present in the fumes.

The adsorbent is generally activated carbon and / or lignite coke. In addition, if the fumes include dust or fly ash, these can be recovered with the solids produced during neutralization, or else prior to treatment according to the invention, by conventional methods.

The contacting of said fumes with the reagent, optionally water and the adsorbent, is carried out in a known manner.

Thus, it can take place co-current or counter-current.

The treatment can likewise be carried out in any type of reactor favoring the dispersion of the solid, the suspension or the solution in the flue gases, such as reactors comprising Venturi type systems, or fluidized bed reactors.

The solids produced by the smoke treatment process are then separated using conventional techniques such as electrostatic precipitators or bag filters. According to an advantageous embodiment of the present invention, at least part of the solids resulting from the treatment of the fumes is recycled to a new stage of treatment of the fumes.

In the case where a dry treatment is carried out in the presence of water supplied extemporaneously, said solids can be recycled in the zone for preparing the reactive / water mixture.

If water is brought into contact in the neutralization zone, the solids are introduced into this zone, separately or with the introduction of fresh reagent.

This embodiment with recycling is advantageous for further increasing the efficiency of the process, in particular in the event of a short residence time in the neutralization zone. This mode also makes it possible to lower the smoke purification thresholds.

The solids resulting from the process according to the invention have the advantage of being valorized. Thus, the solids from the smoke treatment are purified by implementing a first step of dissolution in water, followed by a step of separation of the metals considered to be toxic that they contain.

In the more particular case where the fumes mainly comprise acids of formula HX, and more particularly hydrochloric acid, the solids resulting from the process according to the invention contain sodium halides such as sodium chloride, in addition to the metals considered as toxic.

In this case, these solids are brought into contact with water, which has the effect of dissolving the sodium halides present as well as some of the metals considered toxic present. A first step is then carried out to separate the materials that remain insoluble, generally by filtration.

The metals considered toxic which have been dissolved are in turn separated from the aqueous sodium chloride solution to be purified. More particularly, one or more precipitation steps are used. The pH value is checked by adding either an acid or a base. For obvious reasons aiming not to pollute the mixture, the acid and the base are chosen according to the ions which they bring. Therefore, it is preferred to use hydrochloric acid as the acid, and sodium hydroxide, carbonate or sodium bicarbonate as bases. The precipitates of metals considered toxic are then removed by filtration in particular.

It is also possible to add a precipitating agent for the compounds based on sulphate, obtained by the neutralization of SOx during the treatment of the fumes, such as calcium chloride. Next, a separation of the gypsum and the calcium fluoride, possibly present, which have precipitated, is carried out. This separation step can take place at the same time as that of the precipitate containing the metals considered to be toxic. If a degree of purity of the aqueous sodium chloride solution is desired, one or more additional purification steps can be carried out.

A first variant consists in bringing said aqueous solution into contact with one or more ion exchange resins. The resins can be in the form of hydrogen or sodium, with however a preference for the second type of resins which allows optimal extraction of the ions of the metals considered to be toxic present in the solution.

Another possible variant relates to the use of agents such as mineral sulfides or organic sulfur compounds. Among the mineral sulfides, mention may be made of sodium, iron or barium sulfides. As examples of organic sulfur compounds, there may be mentioned more particularly the trisodium salt of trimercapto-S-triazine, in 15% solution in water (TMT 15®).

A third variant consists of the combination of these possibilities.

The aqueous solutions of sodium chloride, the degrees of purity of which can be adapted, are used in various industrial processes.

Thus, these solutions can be used in the synthesis of sodium carbonate or bicarbonate (Solvay process), or even in the preparation of sodium hydroxide solutions by electrolysis.

In the case where the fumes are mainly based on compounds of the SOx type, the residues obtained, mainly based on sodium sulphate and likewise comprising metals considered to be toxic, can also advantageously be upgraded optionally after purification, the way described in this document.

A first step may consist in bringing the solid residues into contact with water or a recycled aqueous solution comprising sodium sulphate.

The purpose of this second step is on the one hand to selectively dissolve the sulfates, if necessary the halogenated salts, which are most often chlorides. On the other hand, the objective of this step is to leave in suspension most of the metals considered toxic which will then be recycled in the preparation of the catalyst. Such a selective dissolution operation is carried out by controlling the pH of the medium to be in a minimum solubility range of metals, which are in particular in the form of hydroxide and / or carbonates.

It is clear that the range depends on the nature of the metals present and a compromise between each of them may be necessary.

As a general rule, the dissolution is carried out in a pH range of between 3 and 10, these two limits being included.

According to a first variant, and if aluminum is not present in a high quantity compared to the other metals, a pH range between 7 and 10, the two limits being included, represents a good compromise. More particularly, the dissolution can be carried out in a pH range between 7 and 9, these two limits being included.

According to a second variant and in the case where the amount of aluminum is high, it may be desirable to carry out the dissolution at a pH of between 3 and 7, these two limits being understood.

It would not go beyond the scope of the present invention to implement the two aforementioned variants successively. Thus, the dissolution step can correspond to two successive steps with an intermediate separation step, one carried out at a pH between 7 and 10, the second at a pH between 3 and 7, the order depending on the pH value of the initial solution.

The pH value is checked by adding either an acid or a base, chosen so as not to pollute the mixture. Thus, it is preferred to use sulfuric acid or sodium carbonate or bicarbonate.

The step of selective dissolution of the sulfates is carried out, according to a particular embodiment of the invention, at a temperature between 15 and 80 ° C, more particularly between 20 and 60 ° C. An advantageous embodiment consists in carrying out this dissolution at a temperature in the region of 30 to 40 ° C.

After the dissolution and in the case where the treated fumes contain sulfites or bisulfites, these species can be oxidized to sulfates. This operation is generally carried out by adding at least one oxidizing compound to the mixture, possibly in combination with heating of the latter. By way of example of oxidizing compounds, mention may be made of air, hydrogen peroxide, persulfates or even the salt of Caro acid.

Once the sodium sulfate has dissolved, the solution is separated from the solids it contains by filtration, or any other conventional method.

The solid residues are then recycled at least in part for the preparation of the catalyst, as described in this document. The filtrate corresponding to an aqueous solution of purified sodium sulfate is then treated so as to crystallize said sulfate.

This operation can be carried out by any means known to those skilled in the art. According to a first variant, the filtrate is cooled until a temperature difference of 15 to 20 ° C. is obtained between the dissolution and crystallization temperatures.

In this case, the crystals obtained are in decahydrate form.

According to a second variant, the sodium sulfate is crystallized by evaporation of at least part of the water from the solution.

The resulting crystals are in anhydrous form.

The liquid resulting from crystallization can advantageously be recycled to the step of dissolving the solids from the step of treating the fumes.

Before recycling, it may be advantageous to take a part of this liquid in order to avoid enriching liquids with metals considered to be toxic, or possibly to treat this liquid.

Although such a step is only optional, it is again possible to proceed, before crystallization of the sodium sulfate, to an additional purification of the solution, so as to remove the metals considered as toxic possibly remaining in solution which will then be recycled in the preparation of the catalyst.

A first method consists in adding to the solution at least one suitable precipitating agent, chosen in particular from alkali metal hydroxides, sodium carbonate, sodium carbonate, or else silicates, these precipitating agents being able to be used alone or as a mixture .

As agents of this type, mention may also be made of the products sold under the name Profix®, Max Flow®, Low Ash®.

A second method consists in bringing the solution into contact with at least one mineral sulphide, at least one organic sulfur compound, or a mixture thereof. What has been indicated for the variant where the fumes to be treated more particularly contain acids of formula HX remains valid and will therefore not be repeated here.

A third suitable method is to contact the solution with an ion exchange resin. Reference may be made, as previously, to what has been described for the additional purification of the solutions resulting from the treatment of fumes comprising mainly acids of formula

HX. The purity of these crystals is such that they may be my _â valoris directly or after drying or granulation.

Sodium sulphate can in particular be revalued in glass furnaces for example.

Catalytic or non-catalytic denitrification produces molecular nitrogen which is released into the atmosphere.

An exemplary embodiment of the method according to the invention will be given below.

Example 1: Preparation of the component based on bicarbonate, carbonate and ammonia.

The treatment is carried out in air at 30 ° C., of 50 g of ammoniacal bicarbonate comprising 74.1% by weight of sodium bicarbonate, 9% by weight of sodium carbonate, 1% by weight of ammonium carbamate, 1 to 2% by weight of bicarbonate and ammonium carbonate, the rest being water, with a negligible amount of sodium chloride. The table below summarizes the results obtained.

Total NH3 (% by weight) expressed as ammonium ion

The value relative to the total ammonia present, expressed in the form of an ammonium ion content, corresponds to the totality of the ammoniacal compounds capable of releasing ammonia.

After two hours, it is found that the value of total ammonia no longer varies substantially, even after a treatment of ten hours. The final product, that is to say after two hours of treatment, comprises 83.7% by weight of sodium bicarbonate, 10% by weight of sodium carbonate, the complement to 100% consisting of water , with a negligible amount of sodium chloride. Example 2;

Preparation of a reagent according to the invention

We start with dross having the following composition, the percentages being given by weight:

Na2Sθ4 95.00% Na2C03 4.50% K SO 0.11%

CaS04 0.31%

NaHSO ₄ 0.08%

V ₂ O ₅ 0.04%

Σ M _x O _y (OH) _z 0.05% (approximately)

M = Cu, Pb, Zr, Fe.

On these drosses, a leaching treatment is carried out until the soluble salts are used up. Mixing by the solid / solid mixing method, in a granulator

99% by weight of basic component obtained in Example 1, and

1% by weight of ultimate residue obtained after leaching of dross.

Example 3 to 5:

Implementation

The effectiveness of gas treatment formulations was tested comparatively using a laboratory setup under conditions representative of industrial smoke treatment.

A reactor of approximately 35 mm in diameter comprising a bed of product to be tested is traversed for a period of 15 to 30 minutes by the gas to be treated.

The bed height is kept almost constant for the different products. The composition of the gas in the feed is as follows (the proportions are indicated relative to the dry gas composition):

CO2: 9% mol

SO ₂ (1060 vpm): 0.1060% mol 98/25693

16

NOx (550 vpm) 0.0550% mol of which NO (525 vpm) 0.0525% mol

O ₂ 7% mol

H ₂ O 8.6% mol

Supplement with nitrogen.

The reagent is introduced at a stoichiometric ratio RS defined below for the lime-based reagents

moles Ca (OH) 2

RS = SO2 moles at the input

- for reagents based on sodium bicarbonate moles equivalent NaHC03 RS =

2 x SO ₂ moles at the entrance

To compare the reagents, we placed ourselves in similar conditions of DeSOx yield by adjusting the RS. The bed height having to be constant, we played on the gas flow taking into account the density of the different products.

The reagents for the test are as follows: lime, 100% NaHCO 3 and the reagent obtained in Example 2.

The results are reported in the table below:

(mole SO2)E ^_ (mole Sθ2)s

(mole SO2) E ^_ (mole Sθ2) s

(1) DeSOx yield: x 100

(mole SO2) E

(mole NO) E - (mole NO) s

(2) YND yield: x 100

(mole NO) E

(mole (NO + NO)) £ - (mole (NO + NO ₂ )) s

(3) DeNOx yield: x 100

(mole (NO + NO ₂ )) E

E: entry

S: outlet

Claims

1. Smoke treatment composition comprising: - a basic component comprising bicarbonate and optionally a source of NH3; and - catalytic quantities of one or more denitrification catalysts, obtained at least in part by recycling all or part of the dross and / or the ultimate residues from the treatment of the fumes. 2. Composition according to claim 1, characterized in that the basic component also comprises at least sodium carbonate and at least ammonia in the form of ammonium salts. 3. Composition according to claim 2, characterized in that it comprises at least 70% by weight of sodium bicarbonate, preferably at least 80% by weight, and more preferably between 80 and 95% by weight. 4. Composition according to claim 3, characterized in that it comprises less than 30% by weight of sodium carbonate, preferably less than 20% by weight, and more preferably between 5 and 15% by weight. 5. Composition according to claim 3, characterized in that the basic component comprises from 0.2 to 0.7% by weight of ammonia, expressed as ammonium ion. 6. Composition according to claim 1, characterized in that it comprises sodium bicarbonate, sodium carbonate, ammonia in the form of ammonium salts such as bicarbonate, carbonate and / or carbamate, and water. 7. Composition according to claim 6, characterized in that it comprises less than 0.1% by weight of ammonium carbamate and preferably between 0.01 and 0.06% by weight. 8. Composition according to claim 6, characterized in that it comprises less than 10% by weight of water and preferably between 0.2 and 6% by weight. 9. Composition according to claim 1, characterized in that it is in the form of an easily manipulated powder. 10. Composition according to any one of the preceding claims, characterized in that the basic component is obtained by heat treatment at a temperature between 20 and 150 ° C of ammoniacal bicarbonate. 1 1. Composition according to any one of the preceding claims, characterized in that the catalytic denitrification component is based on vanadium, titanium, manganese, copper, zirconium and / or tungsten. 12. Composition according to any one of the preceding claims, characterized in that the denitrification catalyst is based on vanadium or manganese, dispersed on titanium. 13. Composition according to claim 1 1 or claim 12, characterized in that the catalyst further comprises another transition metal, or a rare earth. 14. Composition according to claim 11, characterized in that the catalyst is obtained by recycling all or part of the ultimate residues from the treatment of smoke from glass furnaces. 15. Process for the preparation of a composition according to any one of the preceding claims, characterized in that it consists in mixing the base component with the catalyst (s) or a precursor of the catalyst (s) ), in solid or liquid medium. 16. Method according to claim 15, characterized in that the preparation of a solid composition is carried out by a solid / solid mixing technique. 17. The method of claim 15, characterized in that a solution or dispersion of the base component is mixed with a solution of a (of) precursor (s) of the catalyst. 18. Use of the composition according to any one of claims 1 to 13 in the treatment of fumes. 19. Use of the composition according to any one of claims 1 to 14 for the treatment of fumes containing compounds of the type SOx and / or NOx. 20. Use of the composition according to any one of claims 1 to 14 in the treatment of fumes, characterized in that said fumes are treated dry. 21. Use according to any one of claims 18 to 20, characterized in that the composition is injected into the gas stream, optionally in the presence of NH3. 22. Use according to any one of claims 18 to 21, characterized in that the treatment is carried out at a temperature between 200 and 700 ° C, advantageously 300 and 500 ° C. 23. Use according to any one of claims 18 to 22 for the treatment of smoke from glass furnaces.