BE1025964B1 - SORBENT COMPOSITION FOR AN ELECTROSTATIC PRECIPITATOR - Google Patents

Abstract

Powdered calcium-magnesium compound, calcium-magnesium-based sober composition for use in treating flue gas, compatible with electrostatic precipitators, and method for reducing the resistivity of a powdery sorbent composition for an installation for treating flue gas comprising an electrostatic precipitator.

Description

SORBENT COMPOSITION FOR AN ELECTROSTATIC PRECIPITATOR

Technical area

The present invention relates to a calcium magnesium compound and a sorbent composition for use in a flue gas installation equipped with an electrostatic precipitator, a method for obtaining such a sorbent composition and a method for treating flue gas using an electrostatic precipitator which comprises a step of injecting such a sorbent composition. In another aspect, the present invention relates to a smoke gas treatment installation using the sorbent composition according to the invention.

State of the art

The combustion of fuel in industrial processes or the production of energy generates fly ash and acid gases which must be minimized in the atmosphere. The removal of fly ash from the flue gas stream can be achieved by an electrostatic precipitator (ESP). Some examples of electrostatic precipitators are described in US Patent 4,502,872, US Patent 8,328,902 or US Patent 6,797,035. An electrostatic precipitator generally includes a shell with a flue gas inlet and a flue gas outlet , the shell containing a plurality of collection electrodes, and discharge electrodes spaced from each other and a plurality of hoppers positioned under the collection plates. A voltage is applied between the discharge electrodes and the collection electrodes so as to create an electrostatic field charging the particulate matter in the flue gases to obtain a charged particulate matter. The charged particulate matter is collected by the collection electrodes. The electrostatic precipitator further includes knockers which provide mechanical shock or vibration to the collection electrodes to remove the particles collected from the collection electrodes. The collected particles fall in

BE2018 / 5534 hoppers arranged at the bottom of the hull and which are emptied periodically or continuously. The collection electrodes can be flat or in the form of a tubular or honeycomb structure and the discharge electrodes are generally in the form of a wire or a rod.

Generally, smoke gas treatment installations comprising electrostatic precipitators are provided with an air preheater, which is sometimes included in a boiler and / or otherwise supplied as an additional element of the gas installation. smoke. The air preheater includes a heat exchanger that transfers heat from the flue gas stream produced by the boiler to heat combustion air to the boiler to increase the thermal efficiency of the boiler. In some embodiments, the treatment of flue gases includes multiple electrostatic precipitators. Electrostatic precipitators on the cold side are located downstream of the air preheater, thus operating at lower temperatures generally below 200 ° C (392 ° F). Electrostatic precipitators on the hot side are located upstream of the air preheater and operate at higher temperatures, usually above 250 ° C (482 ° F).

Sometimes for existing factories, the electrostatic precipitator units are already operating at the limit of their nominal capacity due to more stringent limits on particulate matter emissions that have been introduced over the years and / or changes in operating conditions. factories such as a fuel change.

The Deutsch-Anderson equation describes with some approximations the collection efficiency of an electrostatic precipitator by:

where η is the fractional collection efficiency, A _c is the area of the collection electrode, V _pm is the particle migration speed and Q is the volumetric flow of gas. The properties of the particles which influence the collection yield are above all the distribution of particle size and their

BE2018 / 5534 resistivity. Particle resistivity influences the rate of particle migration as previously described in the Deutsch-Anderson equation.

Various attempts have been made to reduce the resistivity of particles. It is known for example from US Pat. No. 4,439,351 that for an electrostatic precipitator to operate effectively, the electrical resistivity of the fly ash must be between 1E7 (1x10 ⁷ ) and 2E10 (2x10) ohms.cm. Another document, Mastropietro, RA Impact of Hydrated Lime Injection on Electrostatic Percipitator Performance in ASTM Symposium on Lime Utilization; 2012; pages 2 to 10, states that the resistivity of fly ash should be between 1E8 (1x10 ⁸ ) and 1E11 (1x10 ¹¹ ) ohms.cm. However, the electrical resistivity of fly ash is generally higher and chemical additives have been used such as SO ₃ , HCl, NH ₃ , Na ₂ CO ₃ , Na ₂ SO ₄ and NH (CH ₂ CH ₂ OH) to lower the resistivity of fly ash. However, these additives are capable of releasing undesirable compounds. The same document discloses the use of polymers to lower the resistivity of fly ash. However, polymeric additives generally degrade at high temperatures and must be injected into the flue gas stream at low temperatures.

Document US Pat. No. 6,126,910 discloses the removal of acid gases from a smoke gas with an electrostatic precipitator by spraying with a solution of sodium bisulfite, calcium bisulfite, magnesium bisulfite, potassium bisulfite or potassium bisulfite. ammonium or one of their combinations in a gas flow upstream of the electrostatic precipitator unit. Such bisulfite salts selectively remove acid gases such as HCl, HF and SO ₃ but they do not remove sulfur dioxide. The sulfur dioxide in the flue gases must be removed later with a reagent such as hydrated lime. Patent document US 6,803,025 discloses a similar process using a reaction compound selected from the group consisting of sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonium hydroxide, potassium hydroxide , potassium hydroxide, potassium carbonate and potassium bicarbonate for

BE2018 / 5534 remove acid gases such as HCl, HF, SO ₃ and partially SO ₂ from smoke gases. However, the remaining SO ₂ must always be removed by using another reagent such as hydrated lime. For the treatment of smoke gases released by power plants, the quantities of chloride released by the fuel or the coal in combustion are generally very small compared to SO ₂ , therefore the process of treatment of smoke gases can be simplified by using only hydrated lime as sorbent.

Document WO2015 / 119880 relates to the drawbacks of trona or hydrated lime as sorbents for a process for treating flue gas with electrostatic precipitator units. Sorbents based on sodium are known to decrease the resistivity of a particulate material, however a main drawback of using sodium sorbents is that the leaching of heavy metals from fly ash is increased, leading to environmental contamination. potential. Calcium hydroxide sorbents do not have the problem of leaching heavy metals from fly ash, but they are known to increase the resistivity of particulate matter (fly ash) entrained in the flue gas flow if although the efficiency of the electrostatic precipitator unit can be lowered when using calcium-based sorbents. The same document discloses a composition for reducing particulate resistivity in smoke gases and capturing acid gases, wherein the composition comprising a particulate alkali / alkaline earth metal having the formula (Li ^ ap Na _a Kp) _w (Mgi. ₅ Caô) _x (OH) _y (CO ₃ ) _z -nH ₂ O, more specifically the formula Na _w Ca _x (OH) _y (CO ₃ ) _z nH ₂ O, in which a ratio W to x is approximately 1 / 3 to about 3/1. Consequently, the composition still has a large amount of sodium which would not only be capable of leaching, but sodium is also known to increase the leaching of heavy metals contained in the fly ash.

Document US 6,797,035 discloses a process for reducing the resistivity of fly ash by spraying an aqueous solution of potassium nitrate or potassium nitrite on the flue gas stream or by

BE2018 / 5534 injection of potassium nitrate or potassium nitrite powder into the duct through which the flue gases pass. A disadvantage of using these nitrate or nitrite salt powders is that they react with other species than fly ash and result in a less reactive chemical reaching the collecting plates of the electrostatic precipitator. Therefore, it is suggested to inject these nitrate salts as finely divided powders to reduce the reactive area exposed and inhibit reactions with nitrous oxides and sulfur oxides.

Document US Pat. No. 7,744,678 B2 discloses a method in which the addition of an alkali metal species, comprising sodium, between 0.2 and 3.5% by weight, to calcium hydroxide sorbents confers improved reactivity vis-à-vis the capture of SO2. The addition of the alkali metal species is carried out in such a way that the BET specific area (SSA) by nitrogen adsorption remains high at 30 <SSA <40 (m ² / g).

The combination of sodium salts and hydrated lime above concentrations mentioned in US 7,744,678 B2 is undesirable due to three detrimental effects: (1) an increase in the sodium content will lead to increased leaching of heavy metals to from the fly ash residue, (2) in hydrated lime, mixtures of sodium salts lead to a reaction which takes place in the presence of water to form sodium hydroxide thus increasing the pH of said mixture to values beyond pH = 12.5 thus raising safety issues, (3) adding sodium in aqueous form to hydrated lime reduces the BET specific area of hydrated lime thus reducing the reactivity towards acid gases.

In article N ° 49 presented at the MEGA symposium on the regulation of pollutants from power plants and carbon management, August 16 to 19, 2016, Baltimore, MD, Foo et al. present a successful industrial application of the removal of SO ₂ with a reinforced hydrated lime sorbent used in an electrostatic precipitator on the cold side. Laboratory resistivity measurements of mixtures of fly ash with hydrated lime and reinforced hydrated lime were performed with CaSCU, where CaSCU was added to typically simulate residues of

BE2018 / 5534 fly ash. The reinforced hydrated lime of this article has an area of more than 40 m ² / g, a pore volume of more than 0.2 cm ³ / g and a median particle size d ₅₀ of between 6 and 12 micrometers and s' is found to have a maximum acceptable resistivity of 1E11 (1x10 ¹¹ ) Ohms.cm.

However, there is still a need to provide a calcium-magnesium compound which can be advantageously used in flue gas treatment plants highly compatible with electrostatic precipitators.

The object of the present invention is to provide a calcium-magnesium compound and a sorbent composition comprising said calcium-magnesium compound eliminating the intrinsic disadvantage of these sorbents when applied to electrostatic precipitator units.

Summary of the invention

According to a first aspect, the present invention relates to a powdered calcium-magnesium compound comprising at least one calcium-magnesium carbonate content greater than or equal to 80% by weight or a calcium-magnesium hydroxide content greater than or equal to 80% by weight, relative to the total weight of the powdered calcium-magnesium compound, further having a resistivity at 300 ° C (372 ° F) R ₃₀₀ lower than 1E11 (1x10 ¹¹ ) Ohms.cm and higher than 1E7 ( 1x10 ⁷ ) Ohms.cm, advantageously lower than 1E10 (1x10 ¹⁰ ) Ohms.cm and higher than 5E7 (5x10 ⁷ ) Ohms.cm, preferably lower than 5E9 (5x10 ⁹ ) Ohms.cm, more preferably lower than 1E9 (1x10 ⁹ ) Ohms.cm, even more preferably lower than 5E8 (5x10 ⁸ ) Ohms.cm.

Indeed, it has surprisingly been observed that a powdered calcium magnesium compound can be successfully used in the treatment of flue gases using electrostatic precipitators when the resistivity at 300 ° C (372 ° F) is even higher low than 1E11 (1x10 ¹¹ ) Ohms.cm, preferably lower than 1E10 (1x10 ¹⁰ ) Ohms.cm, meaning that the calcium-magnesium compound

BE2018 / 5534 powder is robust and does not decompose at relatively high temperature. Consequently, this powdery calcium-magnesium compound is capable of positively modifying the resistivity of fly ash without negatively impacting the operation of the electrostatic precipitator.

In fact, if the powdered calcium-magnesium is a calcium-magnesium compound comprising at least one calcium-magnesium carbonate content greater than or equal to 80% by weight, preferably greater than or equal to 82% by weight, more preferred greater than or equal to 85% by weight, advantageously greater than or equal to 88% by weight relative to the total weight of the powdery calcium-magnesium compound, it will preferably be injected at a location near the boiler or even in the boiler because at this location of the flue gas stream inside which the calcium-magnesium compound must be injected, the temperature is favorable for an adequate capture of pollutants of flue gas by the high carbonate content. In this case, as the product does not decompose, the resistivity at a temperature of 300 ° C (372 ° F) is still low enough to modify the resistivity of the mixture of fly ash present in the flue gases and the calcium compound -magnesium injected.

By the expression calcium-magnesium compound with a calcium-magnesium carbonate content greater than or equal to 80% by weight, preferably greater than or equal to 82% by weight, more preferably greater than or equal to 85% by weight , advantageously greater than or equal to 88% by weight, relative to the total weight of the powdery calcium-magnesium compound, is meant within the meaning of the present invention calcium carbonate and / or natural magnesium such as dolomite, limestone, or even precipitated calcium and / or magnesium carbonate.

The molar proportion of calcium to magnesium in dolomite can vary from 0.8 to 1.2. In the calcium-magnesium compound, the proportion calcium to magnesium can also be higher or lower going up to 0,01 to 10 or even to 100. Indeed, the natural limestone includes magnesium carbonate at a rate which can vary from 1 to 10% by weight per

BE2018 / 5534 compared to the total weight of the powdered calcium-magnesium compound. If the compound in question is a magnesium carbonate, its calcium carbonate content can also vary from 1 to 10% by weight.

The calcium-magnesium compound may also contain impurities. The impurities include in particular all those that are found in natural limestones and dolomites, such as clays of the silicoaluminate type, silica, impurities based on iron or manganese.

In fact, if the powdery calcium-magnesium compound is a calcium-magnesium compound comprising at least one calcium-magnesium hydroxide content greater than or equal to 80% by weight, preferably greater than or equal to 82% by weight, more preferably greater than or equal to 85% by weight, advantageously greater than or equal to 88% by weight, relative to the total weight of the powdered calcium magnesium compound, it will preferably be injected at a location close to the upstream of the preheater, given that at this location in the flue gas stream inside which the calcium-magnesium compound is to be injected, the temperature is favorable for an adequate capture of pollutant compounds from the flue gases by the high hydroxide content. In this case, as the product does not decompose, the resistivity at a temperature of 300 ° C (372 ° F) is still low enough to modify the resistivity of the mixture of fly ash present in the flue gases and the calcium compound -magnesium injected.

By the expression calcium-magnesium compound with a calcium-magnesium hydroxide content greater than or equal to 80% by weight, preferably greater than or equal to 82% by weight, more preferably greater than or equal to 85% by weight , advantageously greater than or equal to 88% by weight, relative to the total weight of the powdered calcium-magnesium compound, it is meant in the sense of the present invention that said at least one calcium-magnesium compound according to the present invention is therefore at less formed with slaked lime (calcitic), slaked dolomitic lime (or dolime), slaked lime of magnesium.

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The molar proportion of calcium to magnesium in dolimitic lime (also called dolime) can vary from 0.8 to 1.2. In the calcium-magnesium compound, the calcium to magnesium proportion can also be higher or lower up to 0.01 per 10 or even per 100. Indeed, natural limestone which is cooked to form quicklime, which is further quenched to form hydrated lime comprises magnesium carbonate at a rate which can vary from 1 to 10% by weight relative to the total weight of the powdered calcium magnesium compound. If the compound in question is a magnesium carbonate which is cooked to form magnesium oxide, the latter being also quenched to form magnesium hydroxide, its calcium carbonate content can also vary from 1 to 10 % in weight. It should be noted that part of the magnesium oxide could remain un-extinguished.

The calcium-magnesium compound may also contain impurities. The impurities include in particular all those found in natural limestones and dolomites, such as clays of the silicoaluminate type, silica, impurities based on iron or manganese.

The contents of CaCOß, MgCOß, Ca (OH) ₂ and Mg (OH) ₂ in calcium-magnesium compounds can be easily determined by conventional methods. For example, they can be determined by X-ray fluorescence analysis, the procedure of which is described in standard EN 15309, coupled with a measurement of loss on ignition and a measurement of the volume of CO ₂ according to standard EN 459-2: 2010. E.

Preferably, the calcium-magnesium compound according to the present invention has a maximum resistivity R _ma x lower than 5E11 (5x10 ¹¹ ) Ohms.cm, preferably lower than 1E11 (1x10 ¹¹ ) Ohms.cm and more preferably more lower than 5E10 (5x10 ¹⁰ ) Ohms.cm.

Advantageously, the calcium-magnesium compound is doped with at least one metal ion Μ chosen from the group of metal ion having an atomic number less than or equal to 74 and belonging to the group consisting of a transition metal ion or an ion post-transition metal

BE2018 / 5534 in an amount greater than or equal to 0.05% by weight and less than or equal to 5% by weight relative to the total weight of the powdered calcium-magnesium compound.

In a particular embodiment, the calcium magnesium compound according to the present invention is further doped with at least one counterion X chosen from the group consisting of nitrates, nitrites, and their mixture in an amount greater than or equal to 0 0.05% by weight and less than or equal to 5% by weight relative to the total weight of the powdered calcium-magnesium compound.

In a preferred embodiment of the calcium magnesium compound according to the present invention, the total weight of said metal ion and of said counter ion is greater than or equal to 0.1% by weight and less than or equal to 5% by weight, preferably included between 0.3 and 3% by weight, relative to the total weight of the powdered calcium-magnesium compound.

In yet another preferred embodiment, the calcium-magnesium compound of the invention further comprises sodium in an amount of up to 3.5% by weight relative to the total weight of the powdery calcium-magnesium compound, expressed in sodium equivalent. Preferably, the sodium is in a minimum quantity of 0.2% by weight relative to the total weight of the powdery calcium-magnesium compound and expressed in sodium equivalent.

Sodium in the form of sodium additive in such amounts is known to have a slight effect on the decrease in the resistivity of the sorbent, as presented by the document by Foo et al. (2016) previously mentioned. The applicant has found that the sodium additive in such amounts in combination with the presence as described below of at least one metal ion and / or a counterion additionally confers an additional effect on the reduction of the resistivity of the composition of sorbent. The use of sodium additive in combination with the presence as described below of at least one metal ion and / or a counterion decreases the resistivity of the sorbent composition more than when the presence as described below below at least one metal ion and / or a counterion is used

BE2018 / 5534 alone in the calcium-magnesium compound and more than when sodium is used alone in the calcium-magnesium compound.

In an advantageous embodiment of the calcium magnesium compound, said metal ion M is one of the ions from Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , Mn ²⁺ , Co ²⁺ , Mo ²⁺ , Ni ²⁺ , Zn ²⁺ .

Preferably, said metal ion M is one of the ions from Cu ²⁺ , Fe ²⁺ , Fe ³⁺ .

Preferably, said counterion X is a nitrate.

It has been found that the presence of a metal ion as disclosed above and / or a counterion as described above in the calcium-magnesium compound, decreases the resistivity of the calcium-magnesium compound.

In a preferred embodiment, the powdered calcium magnesium comprises particles having a d ₅₀ value of between 5 and 25 μm, preferably between 5 and 20 μm, more preferably between 5 and 16 μm.

The notation d _x represents a diameter expressed in μm, as measured by laser granulometry in methanol optionally after sonication, with respect to which X% by mass of the particles measured are less than or equal.

Preferably, in particular if the powdered calcium magnesium compound is a calcium magnesium compound comprising at least one calcium magnesium hydroxide content greater than or equal to 80% by weight, the calcium magnesium compound according to the invention has a BET specific area of at least 20 m ² / g, preferably at least 25 m ² / g, preferably at least 30 m ² / g, more preferably at least 35 m ² / g . The BET specific area is determined by manometry with nitrogen adsorption after degassing under vacuum at 190 ° C (374 ° F) for at least 2 hours and calculated according to the BET multipoint method as described in standard ISO 9277 / 2010E.

Preferably, in particular if the powdered calcium magnesium compound is a calcium magnesium compound comprising at least

BE2018 / 5534 minus a calcium-magnesium hydroxide content greater than or equal to 80% by weight, the sorbent composition according to the invention has a BJH pore volume of at least 0.1 cm ³ / g, preferably d at least 0.15 cm ³ / g, preferably at least 0.17 cm ³ / g, more preferably at least 0.2 cm ³ / g. The BJH pore volume is determined by manometry with nitrogen desorption after degassing under vacuum at 190 ° C (374 ° F) for at least 2 hours and calculated according to the BJH method as described in standard ISO 9277 / 2010E.

Other embodiments of the calcium magnesium compound according to the present invention are mentioned in the appended claims.

According to a second aspect, the present invention also relates to a sorbent composition for a smoke gas treatment installation including an electrostatic precipitator comprising said calcium-magnesium compound according to the present invention.

Preferably, the sorbent composition according to the invention further comprises activated carbon, lignite coke, halloysite, sepiolite, clays such as bentonite, kaolin, vermiculite or any other sorbent such as refractory clay, air-entrained cement dust, perlite, expanded clay, lime sandstone dust, trass dust, Yali rock dust, trass lime, fuller's earth, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfide, calcium sulfate, open hearth coke, lignite dust, fly ash, or water glass.

In a preferred embodiment, the sorbent composition according to the present invention comprises a sodium additive comprising sodium in an amount of up to 3.5% by weight relative to the total weight of the powdered calcium-magnesium compound expressed in sodium equivalent. In particular, the amount of sodium in the composition would be greater than 0.2% by weight relative to the total weight of the powdery sorbent composition.

BE2018 / 5534

In a preferred embodiment, the sorbent composition according to the present invention comprises said metal ion M and / or said counterion X which are present in an amount greater than or equal to 0.05% by weight and less than or equal to 5% in weight relative to the total weight of the powdered calcium magnesium compound and in which preferably the total weight of said metal ion and of said counterion is greater than or equal to 0.1% by weight and less than or equal to 5% by weight, preferably between 0.3 and 3% by weight, relative to the total weight of the dry sorbent composition.

In a particular embodiment according to the present invention, the sorbent composition comprises water in an amount such that the sorbent composition is in the form of a suspension. Examples of amounts can be 40 to 90% by weight of water, where the sorbent is included in an amount of 10 to 60% by weight relative to the total weight of the sorbent composition in the form of a suspension.

The sorbent composition in the form of a suspension can be used for example in a dry spray absorber, which can be followed by an electrostatic precipitator.

In a particularly preferred embodiment, said calcium-magnesium compound is hydrated lime. In this case, if the sorbent composition is in the form of a suspension, it will be in the form of a lime milk where the solids content will be from 10 to 50% by weight relative to the total weight of the whitewash.

Other embodiments of the sorbent composition according to the present invention are mentioned in the appended claims.

According to a third aspect, the present invention relates to a method of manufacturing a sorbent composition for a smoke gas treatment installation including an electrostatic precipitator, comprising the steps of:

a) supply of a calcium-magnesium compound to a reactor

b) addition of an additive or a mixture of additives, comprising at least one metal ion M and / or a counterion X, M being a metal ion having an atomic number less than or equal to 74 and is an ion of metal of

BE2018 / 5534 transition or a post-transition metal ion, and X being one of the counterions among nitrates, nitrites, oxides (O ² '), hydroxides (OH'), and their mixture in an amount calculated to obtain between 0.1% by weight and 5% by weight, preferably between 0.3% by weight and 3% by weight of said metal ion Μ and / or of said counterion X by weight of the composition of dry sorbent.

As a variant, the present invention relates to a method of manufacturing a sorbent composition for a smoke gas treatment installation including an electrostatic precipitator, comprising the steps of:

a) supply of a calcium-magnesium compound to a reactor

b) addition of an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X, Μ being a metal ion having an atomic number less than or equal to 74 and being an ion of transition metal or a post-transition metal ion, and X being one of the counterions among nitrates, nitrites, oxides (O ² '), hydroxides (OH'), and their mixture in an amount calculated to obtain between 0.1% by weight and 5% by weight, preferably between 0.3% by weight and 3% by weight of said metal ion Μ and / or of said counterion X by weight of the calcium magnesium compound .

In a preferred embodiment, the sorbent composition comprises particles having a d ₅₀ value of between 5 and 25 μm, preferably between 5 and 20 μm, more preferably between 5 and 16 μm.

In a preferred embodiment of the method according to the present invention, said calcium-magnesium compound comprises at least one calcium-magnesium carbonate content greater than or equal to 80% by weight relative to the total weight of the dry calcium-magnesium compound .

In another preferred embodiment of the process according to the present invention, said calcium-magnesium compound comprises a calcium-magnesium hydroxide content greater than or equal to 80% by weight, relative to the total weight of the dry calcium-magnesium compound .

BE2018 / 5534

Preferably, in the process for manufacturing said sorbent composition, said metal ion Μ is one of the ions from Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , Mn ²⁺ , Co ²⁺ , Mo ²⁺ , Ni ²⁺ , Zn ²⁺ . More preferably, in the process for manufacturing said sorbent composition, said metal ion Μ is one of the ions from Cu ²⁺ , Fe ²⁺ , Fe ³⁺ .

Preferably, in the process for manufacturing said sorbent composition, said counterion X is a nitrate.

Preferably, the method for manufacturing said sorbent composition comprises a step of adding another additive comprising sodium expressed as sodium equivalent in an amount calculated to obtain up to 3.5% sodium equivalent by weight of the composition of dry sorbent.

In one embodiment of the manufacturing method according to the invention, the step of supplying a calcium-magnesium compound to a reactor comprises the step of supplying quicklime to said reactor, quenching said lime living with a predetermined amount of water to obtain said calcium-magnesium compound comprising at least one calcium hydroxide content greater than or equal to 80% by weight, relative to the total weight of the dry calcium-magnesium compound with an amount of predetermined humidity.

More advantageously, said quenching step is carried out under conditions so as to obtain hydrated lime with a specific BET area by nitrogen adsorption of at least 20 m ² / g, preferably at least 25 m ² / g, preferably at least 30 m ² / g, more preferably at least 35 m ² / g.

In a further preferred embodiment, said quenching step is carried out under conditions so as to obtain hydrated lime with a volume of pore BJH for pores having a diameter less than or equal to 1000 A by nitrogen desorption at least 0.1 cm ³ / g, 0.15 cm ³ / g, preferably at least 0.17 cm ³ / g, more preferably at least 0.2 cm ³ / g.

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Preferably, said extinction step is carried out under the same conditions as those described in US Pat. No. 6,322,769 and incorporated by reference.

In an alternative embodiment of the manufacturing method according to the invention, said extinguishing step is carried out under the same conditions as those described in US patent 7,744,678 of the applicant and incorporated by reference.

In one embodiment of the method for manufacturing said sorbent according to the invention, the step of adding an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X is performed before said quicklime quenching step.

In another embodiment of the method for manufacturing said sorbent composition, said step of adding an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X is performed during said quicklime quenching step.

As a variant, in the method for manufacturing said sorbent composition, said step of adding an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X is carried out after said step of slaking quicklime.

It has been found by the applicant that the step of adding an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X is carried out during or after said step d extinction does not substantially change the specific area or the pore volume of the calcium-magnesium compound, for example as a sorbent. In particular, the specific area and the pore volume of the sorbent composition according to the present invention are substantially the same as for a calcium hydroxide sorbent prepared by known methods such as that described in US Patents 6,322,769 and 7,744,678 incorporated by reference. Consequently, the properties of the sorbent ensuring the SO2 removal yield are preserved.

Preferably, said manufacturing process is characterized in that it further comprises a step of adding activated carbon, lignite coke,

BE2018 / 5534 halloysite, sepiolite, clays, bentonite, kaolin, vermiculite, refractory clay, air-entrained cement dust, perlite, expanded clay , lime sandstone dust, trass dust, Yali rock dust, trass lime, fuller's earth, cement, calcium aluminate, aluminate of sodium, calcium sulfide, organic sulfide, calcium sulfate, open hearth coke, lignite dust, fly ash, or water glass, preferably made after said quenching step.

Other embodiments of the process for manufacturing a sorbent composition according to the present invention are mentioned in the appended claims.

In a fourth aspect, the present invention relates to a method for treating smoke gases using an installation comprising an injection zone arranged upstream of an electrostatic precipitator, characterized in that it comprises an injection step in said zone for injecting a sorbent composition according to the present invention.

More particularly, the smoke gas treatment method using an installation including an electrostatic precipitator, and an injection zone arranged upstream of said electrostatic precipitator and crossed by smoke gases towards said electrostatic precipitator is characterized in that said method comprises a step of injecting a sorbent composition into said injection zone, said sorbent composition comprising a calcium-magnesium sorbent, at least one metal ion Μ having an atomic number less than or equal to 74 and which is an ion of transition metal or a post-transition metal ion, and optionally at least one counterion X chosen from nitrates, nitrites, and their mixture, the total amount of said at least one metal ion Μ and of said optionally at least a counterion X being between 0.1% and 5%, preferably between 0.3 and 3.5% by weight of the dry composition.

According to the present invention, said sorbent composition has a lower resistivity compared to prior art calcium magnesium sorbents, especially at a temperature of 300 ° C (372 ° F). A

BE2018 / 5534 injection of the sorbent composition according to the invention into an injection zone for mixing with smoke gases is effective for the removal of SO2 and other gaseous acids and the lower resistivity of such a composition of sorbent improves the collection of particulate matter from the electrodes of the electrostatic precipitator.

In a preferred embodiment of the process according to the present invention, the sorbent composition comprises as calcium magnesium compound at least one calcium magnesium carbonate, and said sorbent composition is injected into said injection zone, said smoke gases having a temperature greater than or equal to 850 ° C (1,562 ° F).

In another preferred embodiment of the process according to the present invention, the sorbent composition comprises a calcium-magnesium compound at least one calcium-magnesium hydroxide, and said sorbent composition is injected into said injection zone, said gases smoke having a temperature greater than or equal to 180 ° C (356 ° F), preferably greater than 200 ° C (392 ° F), more preferably between 300 ° C (372 ° F) and 425 ° C ( 797 ° F).

Preferably, in the smoke gas treatment method according to the invention, said calcium-magnesium compound in the sorbent composition is mixed with an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X before said injection step.

Alternatively, in the smoke gas treatment process according to the invention, the calcium-magnesium compound and an additive or a mixture of additives, comprising at least one metal ion Μ and / or a counterion X are injected separately and mixed with said smoke gases in said injection zone.

Said sorbent composition can be used in the flue gas treatment process according to the present invention in a wide temperature range, for example between 100 ° C (212 ° F) and 425 ° C (797 ° F) or even more when the sorbent composition mainly comprises a carbonate sorbent (typically a temperature higher than 850 ° C (1,562 ° F)).

BE2018 / 5534

Advantageously, said additives of the sorbent composition according to the present invention do not experience degradation at temperatures higher than 180 ° C (356 ° F) so that said sorbent composition can be injected into said injection zone where the temperature is greater than or equal to 180 ° C (356 ° F), preferably greater than or equal to 300 ° C (372 ° F). As the injection zone is located upstream of the air preheater, temperatures in the injection zone can vary between 300 ° C (372 ° F) and 425 ° C (797 ° F), preferably 350 ° C (662 ° F) and 380 ° C (716 ° F).

Preferably, in the smoke gas treatment process according to the invention, said injection zone is located upstream of an air preheater itself located upstream of said electrostatic precipitator.

Preferably, in the smoke gas treatment method according to the invention, said ion ion is one of the ions from Cu ²⁺ , Fe ²⁺ , Fe ³⁺ , Mn ²⁺ , Co ²⁺ , Mo ²⁺ , Nî ²⁺ , Zn ²⁺ .

More preferably, in the flue gas treatment method of the invention, said Μ ion is one of the ions from Cu ²⁺ , Fe ²⁺ , Fe ³⁺ .

Preferably, in the smoke gas treatment process of the invention, said counterion X is a nitrate.

Preferably, in the smoke gas treatment process of the invention, said sorbent composition comprises another additive comprising sodium in an amount up to 3.5% by weight of the dry composition and expressed in sodium equivalent .

Preferably, in the smoke gas treatment process of the invention, said sorbent composition has a BET specific area of at least 20 m ² / g.

Preferably, in the smoke gas treatment process of the invention, said sorbent composition has a BJH pore volume obtained from nitrogen desorption of at least 0.1 cm ³ / g.

Preferably, in the smoke gas treatment process of the invention, said sorbent composition has a BJH pore volume obtained at

BE2018 / 5534 from nitrogen desorption at least 0.15 cm ³ / g, preferably at least 0.17 cm ³ / g, more preferably at least 0.2 cm ³ / g .

Preferably, in the smoke gas treatment process of the invention, said sorbent composition further comprises activated carbon, lignite coke, halloysite, sepiolite, clays, bentonite, kaolin, vermiculite, refractory clay, air entrained cement dust, perlite, expanded clay, lime sandstone dust, trass dust, rock dust Yali, trass lime, fuller's earth, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfide, calcium sulfate, hot coke open, lignite dust, fly ash, or water glass.

Other embodiments of the flue gas treatment method according to the present invention are mentioned in the appended claims.

In a fifth aspect, the present invention relates to a flue gas treatment device comprising an electrostatic precipitator downstream of an air preheater, said air preheater being connected to said electrostatic precipitator by a conduit, characterized in that it further comprises an injection zone intended to inject a sorbent composition according to the present invention arranged upstream of said air preheater.

Other embodiments of the flue gas treatment device according to the present invention are mentioned in the appended claims.

Preferably, said smoke gas treatment device or installation is used to treat smoke gases from a factory, in particular from a power plant, using coal or fuel containing sulfur species or other precursors. of acid gases.

Preferably, said smoke gas treatment installation further comprises a reservoir comprising said sorbent composition for supplying said sorbent composition to said injection zone through a sorbent inlet.

BE2018 / 5534

The present invention can also be described as a method of reducing the resistivity of a powdery sorbent composition for a smoke gas treatment installation including an electrostatic precipitator below 1E11 Ohms.cm and above 1E07 Ohm.cm at 300 ° C, wherein said resistivity of said powdery sorbent composition is measured in a resistivity cell in an oven under an air flow comprising 10% humidity, said powdery sorbent composition comprising a powdery calcium-magnesium compound comprising at least one calcium magnesium carbonate content greater than or equal to 80% by weight or a calcium magnesium hydroxide content greater than or equal to 80% by weight, relative to the total weight of the powdered calcium magnesium content, the process comprising the steps of:

a) supplying said powdery sorbent composition to a reactor and;

b) adding to said pulverulent sorbent composition an additive or a mixture of additives, comprising at least one metal ion M and / or a counterion X, M being a metal ion having an atomic number less than or equal at 74 and being Mg ²⁺ or Na ⁺ or Li ⁺ and X being a nitrate in an amount calculated to obtain between 0.1% by weight and 5% by weight, preferably between 0.3% by weight and 3% by weight of said metal ion M and / or of said counterion X by weight relative to the total weight of the dry sorbent composition.

Preferably, said powdery calcium magnesium compound has a specific BET area by nitrogen adsorption of at least 20 m ² / g, preferably at least 25 m ² / g, preferably at least 30 m ² / g, more preferably at least 35 m ² / g.

Preferably, said powdery calcium magnesium compound has a BJH pore volume for pores having a diameter less than or equal to 1000 A by nitrogen desorption of at least 0.1 cm ³ / g preferably at least minus 0.17 cm ³ / g, more preferably at least 0.2 cm ³ / g.

Preferably, said pulverulent sorbent composition further comprises activated carbon, lignite coke, halloysite,

BE2018 / 5534 sepiolite, clays, bentonite, kaolin, vermiculite, refractory clay, air-entrained cement dust, perlite, expanded clay, sandstone dust from lime, trass dust, Yali rock dust, trass lime, fuller's earth, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfide, calcium sulfate, open hearth coke, lignite dust, fly ash, or water glass.

Preferably, said method for reducing the resistivity of said pulverulent sorbent composition further comprises a step of adding to said pulverulent sorbent composition a sodium additive comprising sodium in an amount of up to 3.5% by weight relative to the total weight of the powder sorbent composition and expressed in sodium equivalent.

Preferably, said powdered calcium magnesium compound is hydrated lime.

The invention also relates to the use of a pulverulent sorbent composition as described here in a smoke gas treatment process using an installation comprising an electrostatic precipitator.

Brief description of the drawings

Figure 1 shows a schematic embodiment of a smoke gas treatment installation carrying out the smoke gas treatment process with the sorbent composition according to the present invention.

Detailed description of the invention

According to a first aspect, the present invention relates to a sorbent composition for a smoke gas treatment installation including an electrostatic precipitator, said sorbent composition comprising a calcium-magnesium compound, characterized in that it further comprises an additive or a mixture of additives in an amount between 0.1% and 5%, preferably from 0.3% to 3% by weight of the dry composition, said additive or said additives containing at least one ion

BE2018 / 5534 metallic Μ having an atomic number less than or equal to 74 and being a transition metal ion or a post-transition metal ion, and at least one counterion X chosen from nitrates, nitrites, and their mixed.

In a preferred embodiment, the calcium magnesium compound is based on hydrated lime.

Calcium hydroxide sorbents are made by reacting (or quenching) calcium oxide, CaO or quicklime, with water in a so-called hydrator, also called a unit extinction. Alternatively, calcium magnesium hydroxide sorbents are made by reacting dolimitic lime (also called dolime) or magnesium lime with water in a hydrator. Alternatively, quicklime and dolimitic lime can be mixed together and quenched with water in a hydrator to provide a mixture of calcium hydroxide and calcium magnesium hydroxide. In the following, the method of manufacturing the sorbent composition will refer to quicklime but the manufacturing method is not limited to quicklime as starting material and dolimitic lime or a combination of dolimitic lime and / or magnesium lime and quicklime can also be used as the starting material.

The method for manufacturing said sorbent composition according to the invention comprises a step of quenching quicklime with a predetermined amount of water to obtain hydrated lime with a predetermined amount of moisture, and is characterized in that it comprises a step of adding an additive or a mixture of additives in an amount calculated to obtain between 0.1% and 5%, preferably between 0.3 and 3.5% of said additive or mixture of additives by weight of the dry sorbent composition, said additive or additives containing at least one metal ion Μ having an atomic number less than or equal to 74 and being a transition metal ion or a post-transition metal ion, and at least one counterion X chosen from nitrates, nitrites, O ² ', and OH' and their mixture.

BE2018 / 5534

In one embodiment of the process for manufacturing said sorbent composition, the predetermined amount of water in said quenching step is in a water to lime ratio of 2: 1 by weight or more.

In one embodiment of the process for manufacturing said sorbent composition, the amount of water in the quenching step can be adapted to obtain hydrated lime with a humidity less than or equal to 10% by weight, preferably less or equal to 5% by weight, preferably less than or equal to 2% by weight, more preferably less than or equal to 1% by weight relative to the total weight of the sorbent composition in a pulverulent state.

In another embodiment, the amount of water in the quenching step can be adapted to obtain hydrated lime with a moisture content of between 5% by weight and 20% by weight. The amount of water in the quenching step can also be higher so as to obtain hydrated lime with a moisture content above 20% by weight, all the% being expressed relative to the total weight of the sorbent composition in a powdery state.

In one embodiment, the hydrated lime obtained after the quenching step is dried in an additional step.

In one embodiment of the process for manufacturing the sorbent composition according to the invention, said additive containing at least one metal ion M and at least one counterion X is added in the form of an aqueous solution or of suspension or powder before or during said step of quenching calcium oxide or calcium magnesium oxide or one of their combinations.

In another embodiment of the process for manufacturing the sorbent composition according to the invention, said additive or mixture of additives containing at least one metal ion M and at least one counterion X is added in the form of an aqueous solution or suspension or powder after said extinction step. Said additive or mixture of additives containing at least one metal ion M and at least one counterion X is preferably added to calcium hydroxide or calcium magnesium hydroxide before

BE2018 / 5534 injection into an injection area of the smoke gas treatment installation. As a variant, said additive or mixture of additives containing at least one metal ion Μ and at least one counterion X can be added during an injection into an injection zone of the smoke gas treatment installation, separately from calcium hydroxide or calcium magnesium hydroxide and upstream of the electrostatic precipitator.

In a preferred embodiment of the process for manufacturing the sorbent composition, said quicklime quenching step is carried out under the conditions so as to obtain hydrated lime with a specific BET area from nitrogen adsorption at least 20 m ² / g and a volume of BJH pore obtained from nitrogen desorption of at least 0.1 cm ³ / g. Various methods are available to those skilled in the art for obtaining hydrated lime having such properties, and are disclosed, for example, in documents US Pat. No. 6,322,769 and US Pat. No. 7,744,678 of the applicant and incorporated by reference.

In the manufacturing process, of the sorbent composition according to the invention, quicklime particles are advantageously used, which have a particle size distribution of less than 5 mm, in particular quicklime particles having a distribution of particle size from 0 to 2 mm.

Other methods for obtaining hydrated lime with a high specific area and / or high pore volume have been found for example in US Pat. No. 5,492,685 in which an amount of alcohol such as methanol or ethanol is added before and / or during the quicklime quenching step and is removed after drying, in patent DE 3 620 024 in which sugar is added in the quenching step to increase the specific area and in which glycols or amines are added to increase the fluidity, in US patent 5,277,837 and US patent 5,705,141 in which additives such as ethylene glycol, diethylene glycol, triethylene glycol, monoethanolamine, diethanolamine, triethanolamine or one of their combinations is added in the quenching step to increase the area of hydrated lime.

BE2018 / 5534

In the process for manufacturing the sorbent composition, said additive or mixture of additives containing at least one metal ion Μ and at least one counterion X can be added before said quenching step, during the quenching step or after the quenching step without substantially changing the BET specific area or the BJH pore volume for pores having a diameter less than or equal to 1000 A of the sorbent composition. Furthermore, the BET specific area and the BJH pore volume of the sorbent composition according to the present invention are substantially the same as for a calcium hydroxide sorbent prepared by known methods such as that described in US Pat. 322,769 and 7,744,678 incorporated by reference. Consequently, the properties of the sorbent ensuring the removal efficiency of SO ₂ are preserved.

In said method for manufacturing the sorbent composition according to the invention, if a hydrated lime composition is prepared according to the method described in US Pat. No. 7,744,678, such a method comprises a step of adding an amount of metal alkaline, preferably sodium in an amount using quicklime or quenching water or hydrated lime, sufficient to obtain in the hydrated lime an alkali metal content which is greater than or equal to 0.2% and less than or equal to 3.5% by weight relative to the total weight of the dry sorbent composition. According to this embodiment, said additive or said mixture of additives containing at least one metal ion Μ and at least one counterion X is also added to quicklime or to quenching water or hydrated lime with an amount such that an additive or additive mixture content containing at least one metal ion Μ and at least one counterion X is obtained between 0.1% and 5%, preferably 0.3% and 3 % by weight of the dry sorbent composition.

Various sorbent compositions were prepared according to the method of the present invention and measurements of the resistivity of the dry powders of said sorbent compositions were carried out in the following procedure underlined by ΙΊΕΕΕ (Esctcourt, 1984). Basically, a resistivity cell of a determined volume is filled with a dry powder of sorbent composition and the powder is then compacted with a weight

BE2018 / 5534 so as to obtain a flat surface. An electrode with a protection is placed on the surface of the powder and the resistivity of the powder is measured in an oven under an air flow comprising 10% humidity at various temperatures between 150 ° C (302 ° F) and 300 ° C (372 ° F). The resistivity of comparative examples was measured under the same conditions. For each measurement, a maximum resistivity Rmax and a resistivity at 300 ° C (372 ° F) were determined. The resistivity measurements are presented below.

Example set A

Example 1 is a comparative example of a calcium hydroxide sorbent designed for the removal of pollutants of acid gas produced according to document US 6 322 769 B1. No sodium or additive with the general formula MX has been added.

Example 2 is a comparative example of a calcium hydroxide sorbent designed for the removal of pollutants of acid gas produced according to document US 7,744,678 B2. This sample comprises 1% by weight of sodium in the form of Na ₂ CO ₃ . No sodium or additional additive of general formula MX has been added.

Example 3 is a calcium hydroxide sorbent made according to the present invention using iron nitrate as a dopant.

Table 1 shows the measured resistivity parameters R _max and

· R300

Table 1: resistivity parameters of calcium hydroxide sorbents doped with sodium and iron salts.

Example Composition Na2OO3 (% by weight Fe (N0 ₃ ) ₃ (% by weight) Cu (N0 ₃ ) ₂ (% by weight) Rmax (Ω cm) R300 (Ω cm) Ex. 1 Ca (OH) ₂ 0 0 0 8 E12 3 E12 Ex. 2 Ca (OH) ₂ + Na2OO3 1 0 0 4E11 1 E11 Ex. 3 Ca (OH) ₂ + Fe (N0 ₃ ) ₃ 0 0.5 0 1 E12 2E10

From Table 1, it can be seen that the value R _ma x and the value R _3O o of Example 1 are both high at and above the range

BE2018 / 5534 preferred resistivity values between 10E7 ohms.cm and 2E10 ohms.cm.

An addition of 1% by weight of sodium in Example 2 reduces the R _max and R ₃₀₀ values by more than an order of magnitude. Surprisingly, the addition of a small amount of iron nitrate to 0.5% by weight reduces the value R _ma x by almost an order of magnitude and by almost two orders of magnitude for R ₃ o- Surprisingly, the addition iron nitrate is more effective than adding sodium.

Example set B

A set of sorbents is prepared by taking the sorbents manufactured according to document US Pat. No. 7,744,678 B2 and by adding iron and copper salts according to the method of the present invention to said sorbents.

Example 4 is a sample of a calcium hydroxide sorbent designed for the removal of acid gas pollutants manufactured according to document US Pat. No. 7,744,678 B2 into which an amount of iron nitrate has been added. According to the manufacturing method presented in document US Pat. No. 7,744,678, an amount of sodium has been added.

Example 5 is a sample of calcium hydroxide sorbent designed for the removal of acid gas pollutants manufactured according to document US Pat. No. 7,744,678 B2 into which an amount of copper nitrate has been added. According to the manufacturing method presented in document US Pat. No. 7,744,678, an amount of sodium has been added.

Table 2: resistivity parameters of calcium hydroxide sorbents doped with sodium, iron and copper salts

Example Composition N3 ₂ CO ₃ (% by weight) Fe (NO ₃ ) ₃ (% by weight) Cu (NO ₃ ) ₂ (% by weight) Rmax (Ω cm) R ₃ oo (Ω cm) Ex. 1 C _a (OH) ₂ 0 0 0 8 E12 3 E12 Ex. 4 C _a (OH) ₂ + N _a2 CO ₃ + Fe (NO ₃ ) ₃ 1 0.5 0 1 E11 1 E10 Ex. 5 C _a (OH) ₂ + Na2CO3 + Cu (NO3) 2 1 0 0.5 2 E10 2E8

Table 2 shows that for these sorbents, the addition of an iron nitrate results in a resistivity value R _ma x of almost two orders of magnitude lower than that of comparative example 1. The addition of copper nitrate resulting

BE2018 / 5534 at a resistivity of almost three orders of magnitude lower for R _max and a resistivity drop of more than three orders of magnitude for R ₃₀₀ .

Example set C

A set of sorbents is prepared by taking the sorbents according to document US Pat. No. 7,744,678 and various iron salts have been added to measure the influence of the counterion on the resistivity of the sorbent.

Example 4 is a sample of a calcium hydroxide sorbent designed for the removal of acid gas pollutants manufactured according to document US Pat. No. 7,744,678 B2 into which an amount of iron nitrate has been added. According to the manufacturing method presented in document US Pat. No. 7,744,678, an amount of sodium has been added.

Example 6 is a comparative example of a calcium hydroxide sorbent designed for the removal of acid gas pollutants manufactured according to document US Pat. No. 7,744,678 B2 in which an amount of iron sulphate has been added. According to the manufacturing method presented in document US Pat. No. 7,744,678, an amount of sodium has been added.

Example 7 is a comparative sample of a calcium hydroxide sorbent designed for the removal of acid gas pollutants manufactured according to document US Pat. No. 7,744,678 B2 in which a quantity of iron acetate has been added. According to the manufacturing method presented in document US Pat. No. 7,744,678, an amount of sodium has been added.

Table 3: resistivity parameters of sorbents of calcium hydroxide using different iron salts.

Example Composition Na ₂ CO ₃ (% by weight) Fe (NO ₃ ) ₃ (% by weight) Fe ₂ (SO4) 3 (% by weight) Fe (C ₂ H ₃ O ₂ ) ₂ (% by weight) Rmax (Ω cm) R300 (Ω cm) Ex. 2 Ca (OH) ₂ + Na2OO3 1 0 0 0 4E11 1 E11 Ex. 4 Ca (OH) ₂ + N32CO3 + Fe (NO ₃ ) s 1 0.5 0 0 1 E11 1 E10 Ex. 6 Ca (OH) ₂ + Na2OO3 + Fe2 (SC> 4) 3 1 0 0.5 0 2E12 2E12 Ex. 7 Ca (OH) ₂ + Na2CC> 3 + iron acetate 1 0 0 0.5 3E12 4E11

Table 3 shows that the use of iron nitrate results in a resistivity value R _ma x four times lower than that of the example.

BE2018 / 5534 comparative 2 and of an order of magnitude smaller for R ₃₀₀ . Surprisingly, the use of iron salts of different composition such as sulphate and acetate leads to an increase in resistivity, both for R _ma x and for R ₃ oo compared to comparative example 2. To note that the use of iron sulphate results in a resistivity which does not present lower values for R300 compared to R _max .

Example set D

A set of sorbents is prepared by taking the sorbents according to document US Pat. No. 7,744,678 and various copper salts have been added to measure the influence of the counterion on the resistivity of the sorbent.

BE2018 / 5534

Example 10 Example 9 Example 8 Example 5 Example 2 Example O Q) O I + Q. “Τ’ -Ο ω + Ο ω οΓ Ο 0) Ο I + ζ 0) Ο ο ω + Ο c Ο ο ω Ô οί c ^1x0 ω ⁺ g? - Ο ω + Ο 0) Ο ο3 C Ν> ζ + Ο Ζ ω Q) Μ Ο ω + Ο 0) Ο I + Ζ 0) Ο ο ω Composition - - - - = S Ό Ο 2. Ο <-> ω ω. ο ο ο ο σι Ο X © Ο α> c ²⁵ Ζ ό η 2. ί? Q. rj ω ο ο ο σι ο Ο ? α> Ο Ζ5 C ο Ο CL. * ο ο σι ο ο ο CuCI ₂ (% by weight) ο σι ο ο ο ο Cu citrate (% by weight) 7Ε12 3 Ε12 2Ε12 2 Ε10 4Ε11 Ο 73 there 2Ε12 6 Ε11 3Ε11 2 Ε8 ΓΤΊ P 73 Ο ^ω yog °

BE2018 / 5534

It appears from Table 4 that, surprisingly, all the salts, except copper nitrate, increase the resistivity of the sorbent compared to Comparative Example 2.

It should be mentioned that the examples of sorbent compositions presented above do not constitute a limitation for the present invention, and that other additives in the amounts between 0.1 and 5% by weight of the dry sorbent composition can be used to decrease the resistivity of sorbent compositions for use in smoke gas treatment processes using an electrostatic precipitator.

It should be mentioned that improvements in particulate matter collection on electrodes for collecting an electrostatic precipitator can be observed with the use of the sorbent according to the present invention.

According to another aspect, the present invention relates to a smoke gas treatment installation. FIG. 1 shows a schematic embodiment of a smoke gas treatment installation 100 comprising an electrostatic precipitator 101 arranged downstream of a first portion of duct 102 arranged downstream of an air preheater 103, characterized in that an injection zone 104 is arranged upstream of said air preheater 103 and comprises a sorbent inlet 105. Said smoke gas treatment installation 100 further comprises a tank 106 comprising said sorbent composition S for supplying said sorbent composition at said injection area through said sorbent inlet. The hot smoke gases FG produced by a boiler 10 pass through the injection zone into which the sorbent S according to the invention is injected to react with SO ₂ and other acid gases from the smoke gases, then the combustion gases hot smoke pass through the air preheater through which cold air CA circulates to absorb the heat from the hot smoke gases and to be injected as hot air HA into the boiler. Then, the smoke gases pass through the electrostatic precipitator 101 in which charged collection electrodes collect the particulate matter, the sorbent composition of which according to the invention has reacted with undesirable acid gases.

BE2018 / 5534

The smoke gas treatment installation described here is relatively simple and well suited to the use of the sorbent composition according to the present invention.

Preferably, said smoke gas treatment installation is used to treat smoke gases from a power plant using coal or fuel containing sulfur species or other acid gas precursors.

It should be understood that the present invention is not limited to the embodiments described and that variations can be applied without departing from the scope of the appended claims.

For example, in the preferred embodiment, the installation intended for the treatment of smoke gases has been described with an electrostatic precipitator downstream of an air preheater, said air preheater being connected to said electrostatic precipitator by a conduit. with an injection zone intended for injecting a sorbent composition according to the present invention arranged upstream of said air preheater. An alternative within the scope of the present invention may include a particulate collection device upstream of said preheater.

Another alternative of the smoke gas treatment device according to the present invention comprises in sequence an electrostatic precipitator, a preheater optionally followed by a particulate collection device, before reaching the chimney.

The particulate collection device can be another electrostatic precipitator or any kind of filter, such as a bag filter.

In all these embodiments, the sorbent composition according to the present invention is injected into an injection zone located upstream of said electrostatic precipitator, before or after the preheater, according to the configuration on site.

Claims (8)

claims 1. Method for reducing the resistivity of a pulverulent sorbent composition for a smoke gas treatment installation comprising an electrostatic precipitator below 1E11 Ohms.cm and above 1E07 Ohm.cm at 300 ° C, in which said resistivity of said powdery sorbent composition is measured in a resistivity cell in an oven under an air flow comprising 10% humidity, said powdery sorbent composition comprising a powdery calcium-magnesium compound comprising at least one content of calcium magnesium carbonate greater than or equal to 80% by weight or a calcium magnesium hydroxide content greater than or equal to 80% by weight, relative to the total weight of the powdery calcium magnesium content, the process comprising the steps of: a) supplying said powdery sorbent composition to a reactor and; b) adding to said pulverulent sorbent composition an additive or a mixture of additives, comprising at least one metal ion M and / or a counterion X, M being Mg ²⁺ or Na ⁺ or Li ⁺ and X being a nitrate in an amount calculated to obtain between 0.1% by weight and 5% by weight, of said metal ion M and / or of said counterion X by weight relative to the total weight of the dry sorbent composition. 2. The method of claim 1, wherein said powdered calcium magnesium compound has a BET specific area by nitrogen adsorption of at least 20 m ² / g. 3. Method according to any one of the preceding claims, in which said powdery calcium-magnesium compound has a BJH pore volume for pores having a diameter less than or equal to 1000 A by nitrogen desorption of at least 0 , 1 cm ³ / g. 4. Method according to any one of the preceding claims, in which said pulverulent sorbent composition further comprises activated carbon, lignite coke, halloysite, sepiolite, BE2018 / 5534 35 clays, bentonite, kaolin, vermiculite, refractory clay, air-entrained cement dust, perlite, expanded clay, lime sandstone dust, dust trass, Yali rock dust, trass lime, fuller's earth, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfide, calcium sulphate, open coke, lignite dust, fly ash, or water glass. 5. Method according to any one of the preceding claims, further comprising a step of adding to said pulverulent sorbent composition a sodium additive comprising sodium in an amount of up to 3.5% by weight relative to the weight total of the powdery sorbent composition and expressed in sodium equivalent. 6. Method according to any one of the preceding claims, in which said powdered calcium magnesium compound is hydrated lime. 7. A powder sorbent composition for a smoke gas treatment installation including an electrostatic precipitator, said powder sorbent composition comprising a powdered calcium magnesium compound comprising at least a calcium carbonate magnesium content greater than or equal to 80% by weight or a calcium-magnesium hydroxide content greater than or equal to 80% by weight, relative to the total weight of the powdered calcium-magnesium content, characterized in that said powdery sorbent composition has a reduced resistivity below 1E11 Ohms .cm and above 1E07 Ohms.cm at 300 ° C, wherein said resistivity of said powdery sorbent composition is measured in a resistivity cell in an oven under an air flow comprising 10% humidity, said reduced resistivity being ensured by an additive or a mixture of additives, comprising at least one metal ion M and / or u n counterion X, M being Mg ²⁺ or Na ⁺ or Li ⁺ and X being a nitrate in an amount calculated to obtain between 0.1% by weight and 5% by weight of said metal ion M and / or of said counter ion X by weight relative to the total weight of the dry sorbent composition. BE2018 / 5534 8. Use of a pulverulent sorbent composition according to claim 7 in a process for treating smoke gases using an installation comprising an electrostatic precipitator.