JP7358405B2 - Adsorbent composition for electrostatic precipitators - Google Patents

Description

The present invention provides a calcium-magnesium compound, an adsorbent composition for use in an exhaust gas stream comprising an electrostatic precipitator, a method for obtaining such an adsorbent composition, and a process for treating exhaust gas using an electrostatic precipitator. The present invention relates to a method comprising the step of dispensing with such an adsorbent composition. In another aspect, the invention relates to an exhaust gas treatment installation using an adsorbent composition according to the invention.

The combustion of fuels in industrial processes or energy production generates particulate matter (eg fly ash) and acid gases, whose release to the atmosphere needs to be minimized. Removing fly ash from the exhaust gas stream can be performed by an electrostatic precipitator (ESP). Some examples of electrostatic precipitators are described in US Pat. No. 4,502,872, US Pat. No. 8,328,902, or US Pat. No. 6,797,035. Generally, an electrostatic precipitator includes a shell with a flue gas inlet and a flue gas outlet, a plurality of collection electrodes and a discharge electrode spaced apart from each other, and a plurality of hoppers arranged below the dust collection plate. surround. A voltage is applied between the discharge electrode and the collection electrode to create an electrostatic field that charges the particulate matter in the exhaust gas, resulting in charged particulate matter. Charged particulate matter is collected by a collection electrode. The electrostatic precipitator further includes a trumpet that provides a mechanical shock or vibration to the collection electrode to remove the collected particles from the collection electrode. The collected particles fall into hoppers located at the bottom of the shell, and these hoppers are emptied periodically or continuously. The collection electrode can be flat, tubular in form or honeycomb structured, and the discharge electrode is generally in the form of a wire or rod.

Generally, exhaust gas treatment equipment including an electrostatic precipitator is provided with a preheater. This preheater may be included in the boiler and/or may instead be provided as an additional element of the exhaust gas installation. The air preheater includes a heat exchanger that transfers heat from the exhaust gas stream produced from the boiler, thereby heating the combustion air to the boiler and improving the thermal efficiency of the boiler. In some examples, exhaust gas treatment includes multiple electrostatic precipitators. The cold side electrostatic precipitator is located downstream of the air preheater and therefore operates at low temperatures, typically less than 200°C (392°F). The hot side electrostatic precipitator is located upstream of the air preheater and typically operates at temperatures above 250°C (482°F).

Current plants may find that electrostatic precipitator units are already operating at the limits of their design capabilities due to more stringent particulate emission limits introduced in recent years and/or changes in plant operating conditions such as fuel changeovers. There is also.

The Deutsch-Anderson equation roughly represents the dust collection rate of an electrostatic precipitator as follows.

Here, η is the partial collection rate, A _c is the area of the collection electrode, V _pm is the moving velocity of the particles, and Q is the volume flow rate of the gas. The properties of particles that affect the dust collection rate are mainly particle size distribution and their resistivity. Particle resistivity affects particle migration speed, as shown in the Deutsch-Anderson equation discussed above.

Various attempts have been tried to reduce the resistivity of particles. For example, from U.S. Pat. No. 4,439,351, for an electrostatic precipitator to work efficiently, the electrical resistivity of fly ash must be between 1E7 (1×10 ⁷ ) and 2E10 (2×10 ¹⁰ ) ohms. It is known that it should be within cm. In a separate document, Mastropietro, R. A. Impact of Hydrated Lime Injection on Electrostatic Percipitator Performance in ASTM Symposium on Lime Utilization; 201 2; On pages 2 to 10, the resistivity of fly ash is within 1E8 (1×10 ⁸ ) to 1E11 (1×10 ¹¹ ) ohms cm. It states that this should be done. However, the electrical resistivity of fly ash is generally higher, and SO ₃ , HCl, NH ₃ , Na ₂ CO ₃ , Na ₂ SO ₄ , and NH(CH ₂ CH ₂ Chemical additives such as OH) were used. However, these additives tend to release undesirable compounds. The same document discloses the use of polymers to reduce the resistivity of fly ash. However, polymer additives typically degrade at high temperatures and must be injected into the exhaust gas stream at low temperatures.

U.S. Pat. No. 6,126,910 discloses a solution of sodium bisulfite, calcium bisulfite, magnesium bisulfite, potassium bisulfite, or ammonium bisulfite, or a combination thereof, in a gas stream upstream of an electrostatic precipitator unit. discloses the use of an electrostatic precipitator to remove acid gases from exhaust gases by spraying them into the exhaust gas. Such bisulfites selectively remove acid gases such as HCl, HF, and _SO3 , but not sulfur dioxide gas. Sulfur dioxide gas in the exhaust gas must be removed later using a reagent such as slaked lime. U.S. Pat. No. 6,803,025 discloses a reactive compound selected from the group consisting of sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonium hydroxide, potassium hydroxide, potassium hydroxide, potassium carbonate, and potassium bicarbonate. discloses a similar method for removing acid gases such as HCl, HF, SO ₃ and some SO ₂ from exhaust gases using . However, the remaining _SO2 needs to be removed using another reagent such as slaked lime. For the treatment of flue gas emitted by power plants, the amount of chloride released from the combustion fuel or coal is generally very low compared to _SO2 , so the flue gas treatment method uses only slaked lime as an adsorbent. It may be simplified by using

WO2015/119880 relates to the drawbacks of trona or slaked lime as adsorbents in exhaust gas treatment methods using electrostatic precipitator units. Although sodium-based adsorbents are known to reduce the resistivity of particulate matter, the main drawback of using sodium adsorbents is that they encourage leaching of heavy metals from the fly ash, leading to possible environmental pollution. It is to bring about sex. Calcium hydroxide-based adsorbents do not pose the problem of heavy metal leaching from fly ash, but they do increase the resistivity of particulate matter (fly ash) that is introduced into the flue gas stream, which is why calcium-based adsorbents It is known that when used, it can reduce the efficiency of an electrostatic precipitator unit. The same document discloses compositions for reducing the resistivity of particles in exhaust gases and for scavenging acid gases. This composition has the chemical formula (Li _1-α-β Na _α K _β ) _W (Mg _1-δ Ca _δ ) _x (OH) _y (CO ₃ ) _z ·nH ₂ O, more specifically the chemical formula Na _w Contains alkali metal/alkaline earth particles that are Ca _x (OH) _y (CO ₃ ) _z ·nH ₂ O. Here, the ratio of W to x is about 1/3 to about 3/1. Therefore, this composition also provides a high sodium content, which can not only be leached itself, but is also known to increase the leaching of heavy metals contained in the fly ash.

U.S. Pat. No. 6,797,035 teaches fly ashing by spraying an aqueous solution of potassium nitrate or potassium nitrite into the exhaust gas stream or by introducing a powder of potassium nitrate or potassium nitrite into a duct through which the exhaust gas flows. Discloses a method for reducing the resistivity of. The disadvantage of using these nitrate or nitrite powders is that they react with other species other than fly ash, reducing the amount of reactive chemicals that reach the collection plate of the electrostatic precipitator. It is therefore proposed that these nitrates be introduced as finely divided powders to reduce the exposed reactive surface area and inhibit the reaction with nitrous oxide and sulfur oxides.

U.S. Pat. No. 7,744,678 (B2) discloses that adding an alkali metal species containing between 0.2 and 3.5% by weight of sodium to a calcium hydroxide adsorbent is effective for capturing _SO2. A method is disclosed that provides an improved response of. The addition of the alkali metal species is performed such that the BET specific surface area (SSA) due to nitrogen adsorption remains as high as 30<SSA<40 (m ² /g).

Combinations of sodium salts and slaked lime in concentrations exceeding those described in US Pat. No. 7,744,678 (B2) are undesirable due to two adverse effects. (1) Increased sodium content results in increased leaching of heavy metals from the fly ash residue. (2) Adding aqueous sodium to slaked lime reduces the BET specific surface area of slaked lime and thus reduces its response to acid gases.

The paper #49 presented at the power plant pollutant control and carbon management “MEGA” symposium, August 16-19, 2016, Bal Timore, MD, Foo et al. present successful industrial applications in SO ₂ removal using improved slaked lime adsorbents used in low-temperature electrostatic precipitators. Laboratory resistivity measurements of mixtures of fly ash and slaked lime and enhanced slaked lime were performed using _CaSO4 . _CaSO4 was added to mimic typical fly ash residue. The improved slaked lime in this document has a surface area greater than 40 m ² /g, a pore volume greater than 0.2 cm ³ /g, and a median particle size d ₅₀ between 6 and 12 micrometers and has a surface area of 1E11 ( It was found to exhibit an acceptable maximum resistivity of 1×10 ¹¹ ) Ohms·cm.

U.S. Patent No. 4,502,872 U.S. Patent No. 8,328,902 U.S. Patent No. 6,797,035 U.S. Patent No. 4,439,351 U.S. Patent No. 6,126,910 U.S. Patent No. 6,803,025 WO2015/119880 U.S. Patent No. 7,744,678 (B2) U.S. Patent No. 6,322,769 U.S. Patent No. 7,744,678 U.S. Patent No. 5,492,685 DE3620024 U.S. Patent No. 5,277,837 U.S. Patent No. 5,705,141 U.S. Patent No. 6,322,769 (B1)

Mastropietro, R. A. Impact of Hydrated Lime Injection on Electrostatic Percipitator Performance in ASTM Symposium on Lime Utilization; 201 2; pages 2-10 The paper #49 presented at the power plant pollutant control and carbon management “MEGA” symposium, August 16-19, 2016, Bal Timore, MD, Foo et al.

However, there remains a need to provide calcium-magnesium compounds that are highly compatible with electrostatic precipitators and can be advantageously used in exhaust gas treatment equipment.

It is an object of the present invention to provide a calcium-magnesium compound and an adsorbent composition comprising this calcium-magnesium compound, obviating the essential drawbacks of these adsorbents in the application of electrostatic precipitator units.

According to a first aspect, the present invention has a calcium-magnesium hydroxide content of at least 80% by weight, based on the total weight of the powdered calcium-magnesium compound, and in which the resistivity R ₃₀₀ is less than 1E11 (1×10 ¹¹ ) Ohms·cm and higher than 1E7 (1×10 ⁷ ) Ohms·cm, advantageously less than 1E10 (1×10 ¹⁰ ) Ohms·cm and 5E7 (5×10 ⁷ ) Ohms·cm, preferably less than 5E9 (5×10 ⁹ ) Ohms·cm, more preferably less than 1E9 (1×10 ⁹ ) Ohms·cm, even more preferably 5E8 (5×10 ⁸ ) Concerning a powdered calcium-magnesium compound with less than Ohms·cm. This calcium-magnesium compound is doped with calcium nitrate in an amount of 0.05% by weight or more and 5% by weight or less based on the total weight of the powdered calcium-magnesium compound.

Surprisingly, the powdered calcium-magnesium compound has a resistivity at 300° C. (372° F.) that is even lower than 1E11 (1×10 ¹¹ ) Ohms·cm, preferably 1E10 (1×10 ¹⁰ ) Ohms·cm. It has been confirmed that electrostatic precipitators can be successfully used in exhaust gas treatment when the This means that the powdered calcium-magnesium compound is robust and does not decompose even at relatively high temperatures. Therefore, this powdered calcium-magnesium compound can reliably modify the resistivity of air pollution control residues without adversely affecting the operation of the electrostatic precipitator.

At least a calcium-magnesium hydroxide content of at least 80% by weight, preferably at least 82% by weight, more preferably at least 85% by weight, advantageously at least 88% by weight, based on the total weight of the powdered calcium-magnesium compound. If it is a calcium-magnesium compound, it is preferably dosed at a point close to upstream of the preheater, such as where the exhaust gas flows, inside where the calcium-magnesium compound will be dosed. That temperature is favorable for trapping pollutant compounds in the exhaust gas with high hydroxide content. In this case, the resistivity of the calcium-magnesium compound after exposure at a normal temperature of 370°C (700°F), for example, is ESP because the product does not decompose upstream or near upstream of the air preheater at normal temperatures. At normal temperatures on the cold side of the installation or on the hot side of the ESP installation, it is still low enough to modify the resistivity of the mixture of fly ash present in the exhaust gas and the calcium-magnesium compound introduced.

with a calcium-magnesium hydroxide content of at least 80% by weight, preferably at least 82% by weight, more preferably at least 85% by weight, advantageously at least 88% by weight, relative to the total weight of the powdered calcium-magnesium compound. Depending on the conditions of the calcium-magnesium compound, within the meaning of the invention, at least one calcium-magnesium compound according to the invention is thus formed using at least (calcite) slaked lime, dolomite slaked lime (or dolime), magnesium slaked lime It means that.

The molar ratio of calcium to magnesium in dolomitic lime (also called dolime) can vary from 0.8 to 1.2. In calcium-magnesium compounds, the ratio of calcium to magnesium can be as high or as low as 0.01 to 10, or even 100. In practice, the natural limestone which is calcined to form quicklime, which is further slaked to give slaked lime, is prepared by calcination of the natural limestone, which is further slaked to give slaked lime, at levels which may vary from 1 to 10% by weight relative to the total weight of the powdered calcium-magnesium compound. Contains magnesium carbonate. If the compound of interest is magnesium carbonate, which is calcined to form magnesium oxide, which is further quenched to yield magnesium hydroxide, its content in calcium carbonate also varies from 1 to 10% by weight. obtain. Note that some of the magnesium oxide remains undissolved.

Calcium-magnesium compounds may also contain impurities. Impurities include, inter alia, all those found in natural limestones and dolomites, such as clays of the silicoaluminate type, silica, impurities based on common transition metals such as iron or manganese. The content of CaCO ₃ , MgCO ₃ , Ca(OH) ₂ , and Mg(OH) ₂ in calcium-magnesium compounds can be easily determined using conventional methods. For example, they may be determined by X-ray fluorescence analysis, the procedure for which is described in the EN 15309 standard, together with the measurement of losses in ignition and the measurement of CO ₂ volume according to the EN 459-2:2010E standard.

Preferably, the calcium-magnesium compound according to the present invention has a crystallinity of less than 5E11 (5×10 ¹¹ ) Ohms·cm, preferably less than 1E11 (1×10 ¹¹ ) Ohms·cm, more preferably less than 5E10 (5×10 ¹⁰ ) Ohms·cm. It exhibits a maximum resistivity R _max of less than cm.

In a preferred embodiment of the calcium-magnesium compound according to the invention, the total weight of calcium nitrate is 0.1% by weight or more and 5% by weight or less, preferably 0.1% by weight or less, based on the total weight of the powdered calcium-magnesium compound. Between 3 and 3% by weight.

In yet another embodiment, the calcium-magnesium compound of the invention contains a sodium-based compound, expressed as sodium equivalent, in an amount of up to 3.5% by weight, relative to the total weight of the powdered calcium-magnesium compound. Including further. Preferably, the sodium is in a minimum amount of 0.2% by weight relative to the total weight of the powdered calcium-magnesium compound, expressed as sodium equivalent.

Such amounts of sodium, in the form of sodium-based additives, are known to have a slight effect of reducing the resistivity of adsorbents, as in the aforementioned 2016 paper by Foo et al. . Applicants have determined that such amounts of sodium-based additives in combination with the presence of calcium nitrate, described below, further provide an additional effect of reducing the resistivity of the adsorbent composition. The use of a sodium additive, in combination with the presence of calcium nitrate described below, is superior to the presence of calcium nitrate described below used alone in calcium-magnesium compounds and the presence of sodium additives in calcium-magnesium compounds. lowers the resistivity of the adsorbent composition than when used alone.

In a preferred embodiment, the powdered calcium-magnesium comprises particles with a d ₅₀ comprised between 5 and 25 μm, preferably between 5 and 20 μm, more preferably between 5 and 16 μm.

The notation d _x represents the diameter in μm, measured by laser particle size analysis in methanol, optionally after sonication, and is smaller than or equal to X volume % of the measured particles.

Preferably, in particular when the powdered calcium-magnesium compound is a calcium-magnesium compound having at least a calcium-magnesium hydroxide content of 80% by weight or more, the calcium-magnesium compound according to the invention has an 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 surface area is determined by the manometry method with nitrogen adsorption after degassing at 190° C. (374° F.) in vacuo for at least 2 hours and is calculated according to the BET multipoint method as described in the ISO 9277/2010E standard.

Preferably, in particular when the powdered calcium-magnesium compound is a calcium-magnesium compound having at least a calcium-magnesium hydroxide content of 80% by weight or more, the adsorbent composition according to the invention ³ /g, preferably at least 0.15 cm ³ /g, preferably at least 0.17 cm ³ /g, more preferably at least 0.2 cm ³ /g. BJH pore volume is determined by manometry with nitrogen desorption after degassing in vacuo at 190° C. (374° F.) for at least 2 hours and is calculated according to the BJH method described in the ISO 9277/2010E standard.

Other embodiments of calcium-magnesium compounds according to the invention are set out in the appended claims.

According to a second aspect, the invention also relates to an adsorbent composition for exhaust gas treatment installations, including electrostatic precipitators, comprising the above calcium-magnesium compound according to the invention.

Preferably, the adsorbent composition according to the invention comprises activated carbon, lignite coke, halloysite, sepiolite, clays such as bentonite, kaolin, any other adsorbent such as vermiculite or refractory clay, aerated cement dust, perlite, expanded Clay, lime sandstone dust, truss dust, Yali rock dust, truss lime, acid clay, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfide, calcium sulfate, open hearth coke, lignite dust, fly ash, or water glass It further has.

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

In a preferred embodiment, the adsorbent composition according to the invention comprises calcium nitrate as described above in an amount of 0.05% by weight or more and 5% by weight or less, based on the total weight of the powdered calcium-magnesium compound. Preferably, the total weight of said calcium nitrate is greater than or equal to 0.1% 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 adsorbent composition. .

In a preferred embodiment of the adsorbent composition according to the invention, the calcium-magnesium compound mentioned above is slaked lime.

Other embodiments of adsorbent compositions according to the invention are set out in the appended claims.

According to a third aspect, the invention provides a method for producing an adsorbent composition for exhaust gas treatment equipment including an electrostatic precipitator, comprising:
a) providing a calcium-magnesium compound to the reactor;
b) calcium nitrate in an amount calculated to obtain between 0.1% and 5% by weight of calcium nitrate, preferably between 0.3% and 3% by weight of the dry adsorbent composition; or nitric acid, or a combination thereof.

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

In another preferred embodiment of the process according to the invention, the calcium-magnesium compound described above has a calcium-magnesium hydroxide content of 80% by weight or more, based on the total weight of the dry calcium-magnesium compound.

Preferably, the method of making the adsorbent composition comprises adding a sodium-based additive, expressed as sodium equivalent, in an amount calculated to obtain a sodium equivalent of up to 3.5% by weight of the dry adsorbent composition. Includes steps to add.

In an embodiment of the method of production according to the invention, the step of providing the calcium-magnesium compound to the reactor comprises providing quicklime to the reactor and slaking the quicklime with a predetermined amount of water to provide a predetermined amount of water. obtaining a calcium-magnesium compound having at least a calcium hydroxide content of 80% by weight or more based on the total weight of the dry calcium-magnesium compound comprising:

More advantageously, said quenching step has a BET ratio 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. It is carried out under conditions to obtain slaked lime with a surface area.

In a more preferred embodiment, said quenching step comprises 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. , is carried out under conditions to obtain slaked lime with a BJH pore volume of pores with a diameter of 1000 Å or less due to nitrogen desorption.

Preferably, the above-described subduing step is carried out under the same conditions as described in applicant's US Pat. No. 6,322,769, which is incorporated by reference.

In an alternative embodiment of the method of manufacture according to the present invention, the above-described step of dissipating is carried out under the same conditions as described in applicant's U.S. Pat. No. 7,744,678, which is incorporated by reference. be done.

In an embodiment of the method for producing the above-mentioned adsorbent according to the invention, the step of adding an additive or a mixture of additives comprising at least calcium nitrate or nitric acid, or a combination thereof, is performed before the above-mentioned step of slaking the quicklime. Implemented.

In another embodiment of the method of making the above sorbent composition, the above step of adding an additive or mixture of additives comprising at least calcium nitrate or nitric acid, or a combination thereof, comprises the step of adding an additive or a mixture of additives comprising at least calcium nitrate or nitric acid, or a combination thereof. performed during the step.

Alternatively, in embodiments of the method of manufacturing the adsorbent composition described above, the step of adding an additive or mixture of additives comprising at least calcium nitrate or nitric acid, or a combination thereof, comprises is carried out after the step.

The step of adding an additive or mixture of additives comprising at least calcium nitrate or nitric acid, or a combination thereof, in the amount described above, carried out before, during, or after the quenching step above, - The applicant has confirmed that it does not substantially change the pore volume of the magnesium compound. Furthermore, the specific surface area in any case remains greater than 20 m ² /g. In particular, as long as the addition of calcium nitrate or nitric acid or a combination thereof is carried out after the slaked step and preferably before the drying step, the specific surface area of the adsorbent composition according to the invention is incorporated by reference. Calcium hydroxide adsorbents prepared by known methods such as those described in US Pat. No. 6,322,769 and US Pat. No. 7,744,678. Therefore, the properties of the adsorbent that ensure efficiency in removing SO ₂ are preserved.

Preferably, the above manufacturing method includes activated carbon, lignite coke, halloysite, sepiolite, clay, bentonite, kaolin, vermiculite, fireclay, aerated cement dust, perlite, expanded clay, lime sandstone dust, truss dust, Yali rock dust. , truss lime, acid clay, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfides, calcium sulfate, open-hearth coke, lignite dust, fly ash, or water glass, preferably after the above slaked step. The method further includes the step of adding.

Other embodiments of methods for manufacturing adsorbent compositions according to the invention are set out in the appended claims.

In a fourth aspect, the present invention provides a method for treating flue gas using equipment comprising an input zone located upstream of an electrostatic precipitator, the method comprising: 1. An exhaust gas treatment method characterized by including a step of charging the exhaust gas in a charging zone of the exhaust gas.

More specifically, a method for treating waste gas using equipment comprising an electrostatic precipitator and an input zone arranged upstream of the electrostatic precipitator, through which the exhaust gas flows towards the electrostatic precipitator, - charging said adsorbent composition comprising calcium nitrate, a magnesium adsorbent, into said loading zone, the total amount of said calcium nitrate being between 0.1% and 5% by weight of the dry composition; The content is preferably between 0.3 and 3.5% by weight.

According to the present invention, for example, after exposure to a temperature of 300° C. (572° F.), the above-described adsorbent composition has a low resistivity below 200° C. when compared to prior art calcium-magnesium adsorbents. . Dosing the adsorbent composition according to the invention into the input zone for mixing with the exhaust gas is effective in removing _SO2 and other acid gases, and the lower resistivity of such adsorbent compositions improves the accumulation of particulate matter in the collection electrode of an electrostatic precipitator.

In another preferred embodiment of the method according to the invention, the adsorbent composition comprises at least a calcium-magnesium compound of calcium-magnesium hydroxide, and this adsorbent composition is dosed in the above-mentioned dosing zone. Here, the above exhaust gas has a temperature of 180°C (356°F) or higher, preferably 200°C (392°F) or higher, more preferably between 300°C (572°F) and 425°C (797°F). have

The adsorbent compositions described above can be used in the exhaust gas treatment method according to the present invention under a wide range of temperatures, for example between 100°C (212°F) and 425°C (797°F).

Advantageously, the above-mentioned additives of the adsorbent composition according to the invention do not undergo degradation at temperatures higher than 180°C (356°F), so that the adsorbent composition can be used at temperatures above 180°C (356°F). F) above, preferably above 300° C. (572° F.). The input zone is located upstream of the air preheater so that the temperature in the input zone is between 300°C (372°F) and 425°C (797°F), preferably between 350°C (662°F) and 380°C. The range can be between 716°F.

Preferably, in the exhaust gas treatment method of the invention, the above-mentioned input zone is located upstream of the air preheater, which is itself located upstream of the electrostatic precipitator.

Preferably, in the exhaust gas treatment method of the invention, the adsorbent composition as described above comprises another sodium-based additive, expressed as sodium equivalent, in an amount up to 3.5% by weight of the dry composition.

Preferably, in the exhaust gas treatment method of the present invention, the above adsorbent composition has a BET specific surface area of at least 20 m ² /g.

Preferably, in the exhaust gas treatment method of the invention, the adsorbent composition has a BJH pore volume resulting from nitrogen desorption of at least 0.1 cm ³ /g.

Preferably, in the exhaust gas treatment method of the present invention, the adsorbent composition has a nitrogen desorption capacity of at least 0.15 cm ³ /g, preferably at least 0.17 cm ³ /g, more preferably 0.2 cm ³ /g. has a BJH pore volume obtained from .

Preferably, in the exhaust gas treatment method of the present invention, the above adsorbent composition includes activated carbon, lignite coke, halloysite, sepiolite, clay, bentonite, kaolin, vermiculite, fireclay, cellular cement dust, perlite, expanded clay, Lime sandstone dust, truss dust, Yali rock dust, truss lime, acid clay, cement, calcium aluminate, sodium aluminate, calcium sulfide, organic sulfide, calcium sulfate, open hearth coke, lignite dust, fly ash, or water glass, It also has.

In an embodiment of the exhaust gas treatment method of the present invention, the adsorbent composition described above is dosed as a dry powder in a dry dosing system or as an atomized slurry in a spray drying absorption device.

Other embodiments of the exhaust gas treatment method according to the invention are described in the appended claims.

In a fifth aspect, the invention relates to an exhaust gas treatment device that includes an electrostatic precipitator downstream of an air preheater. This air preheater is connected by a duct to the electrostatic precipitator and further comprises a dosing zone arranged upstream of the air preheater for dosing the adsorbent composition according to the invention. do.

Other embodiments of the exhaust gas treatment device according to the invention are set out in the appended claims.

Preferably, the exhaust gas treatment device or equipment described above is used for exhaust gas treatment of plants, especially power plants that use coal or fuel containing sulfur species or other acid gas precursors.

Preferably, said exhaust gas treatment equipment further comprises a reservoir containing said adsorbent composition, said adsorbent composition being provided to said input zone via an adsorbent inlet.

1 is a diagram showing a schematic embodiment of an exhaust gas treatment facility for carrying out an exhaust gas treatment method using an adsorbent composition according to the present invention; FIG.

According to a first aspect, the invention provides an adsorbent composition for exhaust gas treatment equipment, including electrostatic precipitators, comprising a calcium-magnesium compound, comprising from 0.1% to 5% by weight of the dry composition. adsorbent composition, characterized in that it further comprises an additive or a mixture of additives in an amount comprised between 0.3% and 3% by weight, and these additives contain at least calcium nitrate. relating to things.

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

Calcium hydroxide adsorbents are produced by reacting (or slaking) calcium oxide CaO or quicklime with water in a so-called hydrator, also called a slaking unit. Alternatively, calcium-magnesium hydroxide adsorbents are produced by reacting dolomitic lime (also called dolime) or magnesium lime with hydrator water. Alternatively, quicklime and dolomitic lime can be mixed together and slaked with hydrator water to yield a mixture of calcium hydroxide and calcium-magnesium hydroxide. In the following, the method for producing an adsorbent composition refers to quicklime, but the method for producing it is not limited to quicklime as a raw material, but also includes dolomite lime, or a combination of dolomite lime and/or magnesium lime and quicklime. , can be used as raw material.

The method for producing the above-mentioned adsorbent composition according to the present invention includes the step of slaking quicklime with a predetermined amount of water to obtain slaked lime containing a predetermined amount of water. This method of manufacturing is calculated to obtain an additive or mixture of additives between 0.1% and 5%, preferably between 0.3 and 3.5% by weight of the dry adsorbent composition. doping the adsorbent composition with the additive or mixture of additives in an amount determined, characterized in that these additives contain at least calcium nitrate or nitric acid, or a combination thereof.

In an embodiment of the method of making the above sorbent composition, the predetermined amount of water in the slaking step is greater than or equal to a 2:1 water to lime weight ratio.

In an embodiment of the method for producing an adsorbent composition as described above, the amount of water in the slaked step is not more than 10% by weight, preferably not more than 5% by weight, preferably not more than 5% by weight, based on the total weight of the adsorbent composition in powder form. It can be adjusted to obtain slaked lime containing water of 2% by weight or less, more preferably 1% by weight or less.

In another example, the amount of water in the slaking step can be adjusted to obtain slaked lime with a water content of between 5 and 20% by weight. The amount of water in the slaking step may be higher to obtain slaked lime with a water content of more than 20% by weight, all % expressed relative to the total weight of the adsorbent composition in powdered form. can.

In an embodiment, the slaked lime obtained after the slaking step is dried in a separate step.

In an embodiment of the method for producing an adsorbent composition according to the invention, the above-mentioned additive containing calcium nitrate is added to the calcium oxide, or the calcium-magnesium oxide, or a combination thereof, before or after the step of slaked. It is used to dope the adsorbent composition by adding calcium nitrate-containing additives therein, either as an aqueous solution or as a suspension, or as a powder.

In another embodiment of the method for producing an adsorbent composition according to the invention, calcium nitrate is added after the above slaked step, either as an aqueous solution or as a suspension or as a powder. Preferably, the drying step is carried out after the slaked step and after the calcium nitrate addition step. Preferably, the calcium nitrate is added to the calcium hydroxide or calcium-magnesium hydroxide before dosing in the dosing zone of the exhaust gas treatment facility.

In a preferred embodiment of the method for producing an adsorbent composition, the step of slaking the quicklime comprises a BET specific surface area from nitrogen adsorption of at least 20 m ² /g and a nitrogen adsorption of at least 0.1 cm ³ /g. It is carried out under such conditions as to obtain slaked lime with a BJH pore volume obtained from desorption. Those skilled in the art will appreciate that various methods are available for obtaining slaked lime with such properties, such as those described in applicant's U.S. Pat. No. 6,322,769, and U.S. Pat. , 744,678.

In the method for producing the adsorbent composition according to the invention, particles of quicklime are preferably used which have a particle size distribution of less than 5 mm, in particular particles of quicklime with a particle size distribution of from 0 to 2 mm.

Other methods for obtaining slaked lime with high specific area and/or high pore volume can be found, for example, in US Pat. It is added before and/or during the slaking step and removed after drying. In DE 3620024, sugars are added in the saccharification step to increase the specific surface area, and glycols or amines are added to improve the flowability. In U.S. Pat. No. 5,277,837 and U.S. Pat. No. 5,705,141, ethylene glycol, diethylene glycol, triethylene glycol, monoethanolamine, diethanolamine, triethanolamine, or Additives, such as combinations thereof, are added in the attenuating step.

In a method of producing an adsorbent composition, calcium nitrate is quenched before the above quenching step without substantially changing the BJH pore volume of pores having a diameter of 1000 Å or less in the adsorbent composition. During the step of decontaminating or after the step of decontamination, specific amounts according to the invention can be added, as disclosed herein. Additionally, the BJH pore volume of adsorbent compositions according to the present invention can be determined using known BJH pore volumes, such as those described in U.S. Pat. is substantially the same as the calcium hydroxide adsorbent prepared by the method. Furthermore, the BET specific surface area of the adsorbent composition is greater than 20 m ² /g. Therefore, the properties of the adsorbent that ensure the efficiency of SO ₂ removal are preserved. Alternatively, nitric acid or calcium nitrate and nitric acid can be added before, during or after the slaking step. Preferably, a greater BET specific surface area is obtained when calcium nitrate or nitric acid, or a combination thereof, is added after the slaked step and preferably before the drying step.

In the above method of making an adsorbent composition according to the invention, when the slaked lime composition is prepared by the method described in US Pat. No. 7,744,678, this method preferably contains some amount of sodium adding to the quicklime or slaked water, or slaked lime an amount of an alkali metal that is not less than 0.2% and not more than 3.5% by weight, based on the total weight of the dry adsorbent composition. is sufficient to obtain an alkali metal content in slaked lime. Sodium _can be added, for example as _Na2CO3 . According to this example, calcium nitrate or nitric acid, or a combination thereof, is preferably between 0.1% and 5% by weight of the dry adsorbent composition after the slaked step and preferably before the drying step. is further added in such an amount as to obtain a calcium nitrate content of 0.3% to 3% by weight.

Various adsorbent compositions were prepared according to the method of the present invention and measurements of the dry powder resistivity of the adsorbent compositions were carried out with the following procedure outlined by IEEE (Estcourt, 1984). . Basically, a resistivity cell of a predetermined volume is filled with a dry powder of the adsorbent composition, and then this powder is compacted using a weight to obtain a flat surface. An electrode with a guard is placed across the surface of the powder, and the resistivity of the powder is determined by the addition of air containing 10% humidity at various temperatures between 150°C (302°F) and 300°C (372°F). Measured in the oven under the stream. The resistivity of the comparative example was measured under the same conditions. For each measurement, the maximum resistivity R _max and the resistivity at 300° C. (572° F.) were determined. Resistivity measurements are presented below.

"Example set A"
"Example 1"
Example 1 is a comparative sample of a calcium hydroxide adsorbent designed to remove acid gas contamination and manufactured in accordance with US Pat. No. 6,322,769 (B1). This sample was obtained from an industrial facility. No sodium, calcium nitrate, or nitric acid was added.

"Example 2"
Example 2 is a comparative sample of a calcium hydroxide adsorbent designed to remove acid gas contamination and manufactured in accordance with US Pat. No. 7,744,678 (B2). This sample has a content of more than 90% by weight Ca(OH) ₂ , less than 8% by weight CaCO ₃ and about 0.8% by weight Na ₂ CO ₃ , the remainder being impurities. No sodium or calcium nitrate or nitric acid was added. This sample was obtained from an industrial facility.

"Example 3"
Example 3 is another sample of a calcium hydroxide adsorbent designed to remove acid gas contamination and manufactured in accordance with U.S. Pat. No. 7,744,678 (B2), with lime coming from another source. belongs to. This sample has a content of more than 90% by weight Ca(OH) ₂ , less than 7% by weight CaCO ₃ and 2.1% by weight Na ₂ CO ₃ , the rest being impurities. No sodium or calcium nitrate or nitric acid was added. This sample was obtained from an industrial facility.

"Example 4"
Example 4 is a calcium hydroxide adsorbent prepared according to the invention using lime from the same source as Example 3 and using calcium nitrate as a dopant in an amount of 1% based on the dry product. . This sample was obtained from an industrial facility.

"Example 5"
Example 5 is a calcium hydroxide adsorbent prepared according to the invention using lime from the same source as Example 3 and using calcium nitrate as a dopant in an amount of 2% based on the dry product. . This sample was obtained from an industrial facility.

"Example 6"
Example 6 shows how, on a laboratory scale, quicklime was prepared in a paddle with a stoichiometric amount of water and an amount of _NaCO3 to obtain a sodium content of 2% by weight, relative to the total weight of the resulting dry powder composition. Calcium hydroxide adsorbent prepared according to the present invention by mixing (slaking) in a fixed mixer. This quicklime was obtained by calcining lime from the same locality as in Example 3. After the reaction in the mixer, the slaked lime (calcium hydroxide) was discharged, dried and subjected to post-treatment with HNO ₃ at 1% by weight of the dry product.

Table 1 shows the resistivity parameters R _max and R ₃₀₀ measured for those examples. All measurements of resistivity parameters were performed by measuring the resistivity of the samples under increasing temperature.

From Table 1, both the R _max and R ₃₀₀ values in Example 1 are above the preferred range of resistivity values consisting of between 10E7 ohms·cm and 2E10 ohms·cm.

The presence of 0.8% by weight Na ₂ CO ₃ in the adsorbent composition of Example 2 increases the R _max and R ₃₀₀ values by more than an order of magnitude relative to the R _max and R ₃₀₀ values in the composition of Example 1. decrease. The presence of 2.1% by weight Na ₂ CO ₃ in the adsorbent composition of Example 3 increases the R _max and R ₃₀₀ values by more than two orders of magnitude relative to the R _max and R ₃₀₀ values in the composition of Example 1. decrease. Surprisingly, the presence of a small amount of calcium nitrate in an amount of 1% by weight in the composition of Example 4 increases the R _max value by almost three orders of magnitude, compared to the R _max and R ₃₀₀ values of the composition of Example 1. _{The 300} value is reduced by almost 4 orders of magnitude. The presence of 2% by weight of calcium nitrate in the composition of Example 5 reduces the R _max and R ₃₀₀ values even more relative to the composition of Example 1. Therefore, surprisingly the addition of calcium nitrate or nitric acid is more effective in reducing resistivity than the addition of sodium. Regardless of some _differences due to different process conditions (industrial scale and laboratory scale), the presence of calcium nitrate in the composition of Example 6 was reduced by adding _HNO3 instead of adding calcium nitrate. ) has the same tendency to reduce the resistivity of the adsorbent by the addition of ₂ .

"Example set B"
"Example 7"
Example 7 is a sample of fly ash obtained from a coal-fired power plant.

"Example 8"
Example 8 is a blend of 80% by weight fly ash from Example 7 and 20% by weight adsorbent from Example 3.

"Example 9"
Example 9 is a blend of 80% by weight fly ash from Example 7 and 20% by weight adsorbent from Example 4.

"Example 10"
Example 10 is a blend of 80% by weight fly ash from Example 7 and 20% by weight adsorbent from Example 5.

Table 2 shows the measured values of the resistivity parameters R _max and R ₃₀₀ for Examples 7 to 10. One set of measurements for R _max and R ₃₀₀ is performed by measuring the resistivity of the sample under increasing temperature, and one set of measurements for R _max is performed by measuring the resistivity of the sample under decreasing temperature. It was carried out by measuring.

The results presented in Table 2 show that blends of fly ash and calcium-based adsorbents without calcium nitrate additives, where fly ash and calcium-based adsorbents are in the same ratio, It presents higher resistivity parameters R _max and R ₃₀₀ than fly ash without, while the presence of only 1% by weight, preferably 2% by weight, of _CaNO3 in the calcium-based adsorbent reduces the It has a good influence on the resistivity parameters R _max and R ₃₀₀ .

The illustrative adsorbent compositions presented hereinabove do not limit the invention, and the addition of other additives in amounts comprised between 0.1 and 5% by weight of the dry adsorbent composition. It should be noted that materials can be used to reduce the resistivity of adsorbent compositions to be used in exhaust gas treatment methods using electrostatic precipitators.

It is noteworthy that an improvement in the accumulation of particulate matter in the collection electrode of an electrostatic precipitator can be observed with the use of the adsorbent according to the invention.

According to another aspect, the invention relates to an exhaust gas treatment installation. FIG. 1 shows a schematic example of an exhaust gas treatment installation 100 including an electrostatic precipitator 101 arranged downstream of a first duct section 102 arranged downstream of an air preheater 103, in which an input zone 104 is used for air preheating. It is located upstream of the vessel 103 and is characterized by including an adsorbent inlet 105. The exhaust gas treatment facility 100 further includes a reservoir 106 containing the above-described adsorbent composition S, and provides the above-described adsorbent composition to the above-mentioned input zone via the above-mentioned adsorbent inlet. The hot exhaust gas FG produced by the boiler 10 is flowed through the input zone, the adsorbent S according to the invention is input and reacts with SO ₂ and other acid gases from the exhaust gas, and then the hot exhaust gas is transferred to the air Cross the preheater. Low-temperature air (cold air) CA is flowed through the air preheater, absorbs the heat of high-temperature exhaust gas, and is input into the boiler as high-temperature air (hot air) HA. The exhaust gas then flows through an electrostatic precipitator 101 where charged collection electrodes collect particulate matter containing the sorbent composition according to the invention that has reacted with the undesired acid gas. The exhaust gas treatment equipment described herein is relatively simple and well adapted for use with adsorbent compositions according to the invention.

Preferably, the exhaust gas treatment equipment described above is used for exhaust gas treatment in power plants that use coal or fuel containing sulfur species or other acid gas precursors.

It is to be understood that the invention is not limited to the embodiments described and that modifications may be applied without departing from the scope of the appended claims.

For example, in a preferred embodiment, the equipment for exhaust gas treatment comprises an electrostatic precipitator downstream of an air preheater, which air preheater is connected to said electrostatic precipitator by a duct; It has been described as having a dosing zone for dosing the adsorbent composition according to the invention located upstream. Alternatives within the scope of the invention may include a particle collection device upstream of the preheater described above.

Another alternative to the exhaust gas treatment device according to the invention is, before reaching the chimney, followed in sequence by an electrostatic precipitator, a preheater and optionally a particle accumulation device.

The particle collection device can be another electrostatic precipitator or any type of filter, such as a baghouse filter.

In all these examples, the adsorbent composition according to the invention is dosed upstream of the electrostatic precipitator described above, in a dosing zone located before or after the preheater, depending on the site configuration.

Claims (18)

An adsorbent composition containing at least one hydroxide selected from the group consisting of calcium hydroxide and magnesium hydroxide in a content of 80% by weight or more based on the total weight,
the adsorbent composition exhibits a resistivity of less than 1E11 Ohms·cm and greater than 1E7 Ohms·cm at 300°C; An adsorbent composition characterized in that it is doped with calcium nitrate in an amount of 0.5% by weight or more and 5% by weight or less. The adsorbent composition of claim 1 exhibiting a maximum resistivity R _max of less than 1E11 Ohms·cm. Adsorbent composition according to claim 1 or 2, further comprising a sodium-based additive in an amount of up to 3.5% by weight, expressed as sodium equivalent, relative to the total weight of the adsorbent composition. Adsorbent composition according to any one of claims 1 to 3, exhibiting a BET specific surface area due to nitrogen adsorption of at least 20 ^m2 / g . Adsorbent composition according to any one of claims 1 to 4, exhibiting a BJH pore volume of pores with a diameter of 1000 Å or less due to nitrogen desorption of at least 0.1 cm ³ /g. Adsorbent composition according to any one of claims 1 to 5 for an exhaust gas treatment installation having an electrostatic precipitator. Activated carbon, lignite coke, halloysite, sepiolite, clay, bentonite, kaolin, vermiculite, fireclay, aerated cement dust, perlite, expanded clay, lime sandstone dust, truss dust , truss lime, acid clay, cement, calcium aluminate, Any one of claims 1 to 6 further comprising an additive selected from the group consisting of sodium aluminate, calcium sulfide, organic sulfides, calcium sulfate, open hearth coke, lignite dust, fly ash, and water glass. The adsorbent composition described in . A method for producing an adsorbent composition for an exhaust gas treatment facility having an electrostatic precipitator, the method comprising:
a) providing the reactor with at least one first compound selected from the group consisting of slaked lime, dolomite slaked lime and magnesium slaked lime ;
b) a second compound selected from the group consisting of calcium nitrate and nitric acid, and combinations thereof, so as to obtain between 0.1% and 5% calcium nitrate by weight of the adsorbent composition; and adding the calculated amount . The first compound contains at least one hydroxide selected from the group consisting of calcium hydroxide and magnesium hydroxide in a content of 80% by weight or more based on the total weight of the dried first compound. 9. The method according to claim 8 , comprising: The step of providing a first compound to a reactor comprises a step of providing quicklime to the reactor, and a slaking step of slaking the quicklime with a predetermined amount of water, thereby providing a predetermined amount of water. and a slaking step of obtaining the first compound having at least a calcium hydroxide content of 80% by weight or more based on the total weight of the dry first compound containing water. Method. From claim 8 , characterized in that it comprises the step of adding a sodium-based additive, expressed as sodium equivalent, in an amount calculated to obtain a sodium equivalent of up to 3.5% by weight of the dry adsorbent composition. 11. A method for producing an adsorbent composition according to any one of claims 1 to 10 . Claim 10, or reference to claim 10, characterized in that the slaked step is carried out under conditions such as to obtain slaked lime with a BET specific surface area determined by nitrogen adsorption of at least 20 m ² /g. A method of manufacturing an adsorbent composition according to claim 11 . Claim 10 , wherein the slaked step is carried out under conditions such as to obtain a BJH pore volume of slaked lime of at least 0.1 cm ³ /g of pores with a diameter of 1000 Å or less, as measured by nitrogen desorption. A method for producing an adsorbent composition according to claim 11 or claim 12, which refers to claim 10 . Activated carbon, lignite coke, halloysite, sepiolite, clay, bentonite, kaolin, vermiculite, fireclay, aerated cement dust, perlite, expanded clay, lime sandstone dust, truss dust , truss lime, acid clay, cement, calcium aluminate, Claim further comprising the step of adding an additional additive selected from the group consisting of sodium aluminate, calcium sulfide, organic sulfides, calcium sulfate, open hearth coke, lignite dust, fly ash, and water glass. A method for producing the adsorbent composition according to any one of items 8 to 13 . 8. A method for treating exhaust gas using equipment having a charging zone arranged upstream of an electrostatic precipitator, the step of charging the adsorbent composition according to any one of claims 1 to 7 into the charging zone. An exhaust gas treatment method characterized by comprising: The adsorbent composition includes a first compound selected from the group consisting of slaked lime, dolomite slaked lime, and magnesium slaked lime, and the adsorbent composition is charged into the input zone, where the exhaust gas is at a temperature of 180° C. or higher. The exhaust gas treatment method according to claim 15 , comprising: 17. The exhaust gas treatment method according to claim 15 or 16 , wherein the adsorbent composition is dosed as a dry powder in a dry adsorbent dosing system or as an atomized slurry in a spray dry absorber system. An exhaust gas treatment device having an electrostatic precipitator downstream of an air preheater, the air preheater being connected to the electrostatic precipitator by a duct, the exhaust gas treatment device being arranged upstream of the air preheater. An exhaust gas treatment device further comprising an input zone for inputting the adsorbent composition according to any one of claims 1 to 7 .

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