CN109201067B

CN109201067B - Denitration catalyst, preparation method thereof and method for reducing emission of nitrogen oxides of circulating fluidized bed boiler

Info

Publication number: CN109201067B
Application number: CN201811405693.7A
Authority: CN
Inventors: 齐文义; 郝代军; 杨金辉; 李小苗; 左世伟; 陈千惠; 黄延召; 孟学峰
Original assignee: Sinopec Engineering Group Co Ltd
Current assignee: Sinopec Engineering Group Co Ltd; Sinopec Energy Management Co Ltd
Priority date: 2018-11-23
Filing date: 2018-11-23
Publication date: 2021-08-31
Anticipated expiration: 2038-11-23
Also published as: CN109201067A

Abstract

The invention discloses a denitration catalyst, a preparation method thereof and a method for reducing the emission of nitrogen oxides of a circulating fluidized bed boiler, wherein the method for reducing the emission of the nitrogen oxides comprises the following steps: adding a denitration catalyst into a dense bed layer of a boiler of the circulating fluidized bed boiler. The denitration catalyst at least comprises 15-50 parts by weight of activated alumina, 12-45 parts by weight of fly ash of the coal-fired circulating fluidized bed boiler with the carbon content of less than 6.0wt%, 1-7 parts by weight of lanthanide oxide, 2-15 parts by weight of transition metal oxide and 15-25 parts by weight of adhesive. Which makes NO in flue gas be converted in situ in the combustion chamber of the boiler under the action of the denitration catalyst in the combustion process of CFB coal_xRealize the reduction of NO in the flue gas_xThe purpose of (1).

Description

Denitration catalyst, preparation method thereof and method for reducing emission of nitrogen oxides of circulating fluidized bed boiler

Technical Field

The invention relates to the technical field of denitration, and particularly relates to a denitration catalyst, a preparation method of the denitration catalyst and a method for reducing emission of nitrogen oxides in a circulating fluidized bed boiler.

Background

Circulating Fluidized Bed (CFB) boilers, one of the most successful clean coal combustion technologies currently in commercial use, have coal typesGood adaptability, excellent load regulation performance, convenient comprehensive utilization of ash slag and the like. Compared with a pulverized coal fired boiler, the pulverized coal fired boiler has the advantage of natural low NOx emission, and can generally reach 200mg/m³Can meet the national and regional emission standards. However, with the implementation of the emission Standard for atmospheric pollutants for thermal Power plants (GB 13223-2011), the emission concentration of NOx is required to be 100mg/m³(with NO)₂Calculated as dry basis, O₂Volume fraction 6.0%), even further up to 50mg/m³The CFB boiler NOx emission reaching standards faces a great challenge.

In order to meet the emission requirements of the emission standard of atmospheric pollutants of thermal power plants (GB 13223-2011), selective non-catalytic reduction denitration facilities are installed inside most CFB boilers, and the standard emission of NOx is realized by spraying ammonia liquid or urea solution in the boilers. To cope with 50mg/m³The enterprise adds measures such as Selective Catalytic Reduction (SCR), low-temperature oxidation (such as LoTOx and COA) and the like at the rear part, but the SCR catalyst can cause SO₂To SO₃SO that SO in the flue gas₃The content is increased, so that the corrosion and blockage of equipment at the rear part of the SCR are caused, and the blue smoke plume of the discharged smoke is aggravated; the problems of pollutant transfer, high denitration cost and the like exist in low-temperature oxidation; this undoubtedly increases the complexity of the plant operation, but also increases the plant denitration operation cost, so that the advantages of low-cost pollution control of the CFB boiler do not exist.

Disclosure of Invention

One of the objectives of the present invention is to provide a denitration catalyst, a preparation method thereof, and a method for reducing nitrogen oxide emission of a circulating fluidized bed boiler, so as to reduce nitrogen oxide emission of the circulating fluidized bed boiler at a lower cost and in a simple process.

The technical problem to be solved by the invention is realized by adopting the following technical scheme.

The invention provides a method for reducing nitrogen oxide emission of a circulating fluidized bed boiler, which comprises the following steps: adding a denitration catalyst into a dense bed layer of a boiler of the circulating fluidized bed boiler.

The invention also provides a denitration catalyst which is of a porous structure and at least comprises the following components in parts by weight: 15-50 parts of activated alumina, 12-45 parts of fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, 1-7 parts of lanthanide oxide, 2-15 parts of transition metal oxide and 15-25 parts of a binder.

The invention also provides a preparation method of the denitration catalyst, which comprises the following steps: roasting green pellets prepared from activated alumina, fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, lanthanide element salts, transition metal salts and an adhesive.

By adding the denitration catalyst into the dense bed layer of the boiler of the circulating fluidized bed boiler, a large amount of reducing substances existing in the boiler are utilized in the combustion process of CFB (circulating fluid bed) coal, and NO (nitric oxide) in the flue gas is generated under the action of the denitration catalyst_xWith the carbon particles in the furnace, CO and NH in the flue gas₃Reacts with HCN to generate NO in the flue gas in situ in the combustion chamber of the boiler_xConversion to N₂Realize the reduction of NO in the flue gas_xThe purpose of (1).

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a scanning electron micrograph of a denitration catalyst according to example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Those whose specific conditions are not specified in the embodiment or examples are carried out according to the conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The following is a detailed description of a denitration catalyst, a preparation method thereof and a method for reducing nitrogen oxide emission of a circulating fluidized bed boiler according to embodiments of the present invention.

Some embodiments of the present invention provide a denitration catalyst, which can be used in a dense bed layer of a boiler of a circulating fluidized bed boiler, wherein the denitration catalyst has a porous structure and at least comprises the following components in parts by weight: 15-50 parts of activated alumina, 12-45 parts of fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, 1-7 parts of lanthanide oxide, 2-15 parts of transition metal oxide and 15-25 parts of a binder.

The inventor finds in research that the combustion temperature of the circulating fluidized bed boiler is low, and a large amount of carbonaceous solid particles, CO and NH exist in the boiler₃And HCN and the like, and when the denitration catalyst is added into a dense-phase bed layer of a boiler of a circulating fluidized bed boiler, nitrogen oxide generated by the combustion can be reduced and converted into N by the reductive material under the catalysis of the catalyst₂Further realizing the purpose of reducing the nitrogen oxides in the flue gas. And because the in-situ reduction is carried out in the furnace, no additional process step and reduction equipment are needed, thereby reducing the cost. The component proportion of the catalyst can fully adapt to the reduction of the reduction raw materials in the circulating fluidized bed boiler so as to achieve better catalytic reduction efficiency.

The active alumina in the denitration catalyst is mainly used as a framework material carrier of the catalyst, and the active alumina is selected as the carrier of the denitration catalyst in the embodiment of the invention, and the main reason is that the active alumina has stronger activity and good high temperature resistance, so that the denitration catalyst can keep a temperature structure at a high temperature of a circulating fluidized bed, and the reduction of catalytic reduction efficiency or the deactivation of the denitration catalyst caused by the structural damage of the denitration catalyst under the long-term action of the high temperature can be avoided. Fly ash of coal-fired circulating fluidized bed boiler with carbon content less than 6.0wt%, oxide of lanthanide and oxide of transition metal areThe effective active components playing a catalytic role as the denitration catalyst are mixed according to the proportion, so that the denitration catalyst can play an excellent catalytic effect, and the reason probably lies in that the selection and the proportion configuration of the three components can be fully matched with the carbon solid particles, CO and NH in the circulating fluidized bed₃And reducing atmosphere of various reducing substances HCN. Further, the inventor researches and discovers that when the fly ash of the coal-fired circulating fluidized bed boiler with high carbon content is selected, the formed denitration catalyst can be burnt due to the fly ash of the coal-fired circulating fluidized bed boiler under the action of high temperature, so that the structure of the denitration catalyst is damaged, and the catalytic reduction efficiency is reduced. Therefore, the fly ash of the coal-fired circulating fluidized bed boiler with the carbon content lower than 6.0wt% is selected in the denitration catalyst, so that the fly ash of the coal-fired circulating fluidized bed boiler can not generate combustion reaction or change at high temperature in the circulating fluidized bed boiler, and the stability and the catalytic performance of the denitration catalyst structure are further ensured.

In some embodiments, the amount of activated alumina in the components of the denitration catalyst may be 15 to 50 parts by weight, or 20 to 47 parts by weight, or 22 to 40 parts by weight; the fly ash of the coal-fired circulating fluidized bed boiler with the carbon content of less than 6.0wt% can be 12-45 parts, or 15-42 parts, or 20-38 parts; the lanthanide oxide can be 1-7 parts, or 1.5-6 parts, or 2-5 parts; the transition metal oxide can be 2-15 parts, or 3-12 parts, or 4-10 parts; the binder may be 15-25 parts, or 17-22 parts, or 18-21 parts.

In some embodiments, the denitration catalyst comprises at least the following components in parts by weight: 20-47 parts of activated alumina, 15-42 parts of fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, 1.5-6 parts of lanthanide oxide, 3-12 parts of transition metal oxide and 17-22 parts of a binder.

Further, in some embodiments, the lanthanide corresponding to the lanthanide oxide includes one or a combination of two or more of lanthanum, cerium, praseodymium, and neodymium. For example, the lanthanoid oxide may be lanthanum oxide, cerium oxide, praseodymium oxide or neodymium oxide alone, may be a mixture obtained by mixing one or more of lanthanum oxide, cerium oxide, praseodymium oxide or neodymium oxide, and may be an oxide obtained by oxidizing a salt containing one or more of lanthanum, cerium, praseodymium and neodymium elements.

In some embodiments, the transition metal corresponding to the transition metal oxide includes one or a combination of two or more of Cu, Zn, W, Co, Fe, and Mn. For example, the transition metal oxide may be copper oxide, zinc oxide, tungsten oxide, cobalt oxide, iron oxide, or manganese oxide alone, or may be a mixture of one or more of copper oxide, zinc oxide, tungsten oxide, cobalt oxide, iron oxide, or manganese oxide, or may be an oxide obtained by mixing one or more salts including Cu, Zn, W, Co, Fe, and Mn and then oxidizing the mixture.

Further, in order to form a stable porous structure of the denitration catalyst, the components need to be structured with each other, and in an embodiment of the present invention, a binder capable of making some adhesive bonding between the components is further added, wherein the binder includes one or a combination of two of aluminum sol and silica sol, for example, the binder may be aluminum sol or silica sol, or a mixture of the aluminum sol and the silica sol, and the mixing ratio may be 1: 1.

further, in order to enable the denitration catalyst to have a better catalytic effect in the dense-phase bed layer in the circulating fluidized bed boiler, the denitration catalyst needs to have a better specific surface area, and the inventor finds that the specific surface area of the denitration catalyst is 50m²When the specific surface area is more than 60m, the denitration catalyst prepared from the components can fully react nitrogen oxides in flue gas, and the specific surface area is preferably 60m²/g～200m²G, e.g. 70m²/g，80m²/g，90m²/g，100m²/g，110m²/g，120m²/g，130m²/g，140m²/g，150m²/g，160m²/g，170m²/g，180m²(iv)/g or 190m²/g。

Further, in some embodiments of the present invention, the denitration catalyst is spherical and has a particle size of 1.0 to 10.0mm, preferably 2.0 to 8.0mm, and more preferably 2 to 4 mm. The shape and the size of the catalyst can influence the contact between the catalyst and the flue gas, and the spherical catalyst and the size range of the particle size of the spherical catalyst enable the catalyst to have better fluidity and fully contact the flue gas, so that the catalytic reduction reaction is facilitated.

According to some embodiments, the denitration catalyst further comprises 0.5-5 parts of a pore-expanding agent, preferably 1-4 parts of a pore-expanding agent, and preferably the pore-expanding agent is urotropin or activated carbon. The pore-expanding agent is added into the components of the denitration catalyst, so that the denitration catalyst prepared by roasting can form a better pore structure, a larger specific surface area can be achieved, the flue gas in the boiler can fully act with the denitration catalyst, and a better catalytic effect is achieved.

Some embodiments of the present invention also provide a method for preparing the above denitration catalyst, which includes: roasting green pellets prepared from activated alumina, fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, lanthanide element salts, transition metal salts and an adhesive.

Further, in some embodiments, the preparation method of the denitration catalyst specifically includes:

s1, preparing raw pellets from activated alumina, fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, lanthanide element salts, transition metal salts and a binder.

Specifically, a solid mixture obtained by mixing activated alumina and fly ash of a coal-fired circulating fluidized bed boiler with the carbon content of less than 6.0wt% is placed in a rotary table rolling machine, and the solid mixture is sprayed by a sprayer under the condition that the rotary table rolling machine rotates, so that the solid mixture of the rotary table rolling machine gradually forms green balls, wherein the spraying material of the sprayer is a mixed solution of dilute hydrochloric acid, an aqueous solution of salts of lanthanide elements, an aqueous solution of salts of transition metals and a binder. It should be noted that pore-expanding agents may also be added to the solid mixture.

In some embodiments, the green pellets are baked at a temperature of 120 to 140 ℃ for 2 to 6 hours before the green pellets are baked. Further, in some embodiments, the green pellets are dried before being baked, for example, the green pellets are placed in a ventilated and cool place and spread open for 48-96 hours. In some preferred embodiments, the green pellets are screened to select 2-4 mm pellets for calcination.

And S2, roasting the green pellets at high temperature.

Specifically, the green pellets are placed in a muffle furnace for roasting, and in some embodiments, the roasting temperature is 600-650 ℃, for example, the roasting temperature can be 610 ℃, 615 ℃, 620 ℃, 625 ℃, 630 ℃, 635 ℃, 640 ℃ or 645 ℃. The calcination time is 4 to 10 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or 9 hours.

The green pellets prepared from various compositions are roasted at high temperature, lanthanide element salts and transition metal salts can be converted into lanthanide element oxides and transition metal oxides at high temperature, and a catalyst with a porous structure is formed by the binder together with activated alumina and fly ash of a coal-fired circulating fluidized bed boiler with the carbon content of less than 6.0wt% in the roasting process, so that a good catalytic effect can be achieved under the condition that various reducing materials in the circulating fluidized bed boiler exist, the catalytic reduction efficiency is improved, and the discharge of nitrogen oxides is reduced.

In some embodiments, the lanthanide salt is a lanthanide nitrate or a lanthanide chloride, and the transition metal salt is a transition metal nitrate or a transition metal chloride.

The amounts of the raw material components are selected so that the quality of the product obtained by calcination can meet the catalyst component ratio.

Some embodiments of the present invention further provide a specific preparation method of the above denitration catalyst, which comprises:

(1) weighing activated alumina, fly ash of a coal-fired CFB boiler with carbon content lower than 6.0wt% and a pore-expanding agent, and putting the fly ash and the pore-expanding agent into a turntable ball machine; (2) mechanically mixing the three components uniformly; (3) weighing lanthanide salts, such as nitrates or chlorides of lanthanum, cerium, praseodymium and neodymium, putting the lanthanide salts into a first beaker, and adding distilled water to completely dissolve the salts; (4) weighing transition metal nitrate or chloride selected from Cu, Zn, Co, Fe and Mn, putting into a second beaker, and adding distilled water to completely dissolve the salts; (5) the lanthanide salt water solution, transition metal nitrate or chloride, alumina sol or silica sol and dilute hydrochloric acid are sprayed slowly while the ball rolling machine is rotating to make the material grow into balls gradually. (6) And screening to select small balls with the diameter of 2-4 mm, ventilating in a shade place, spreading out, cooling for 48-96 hours, and airing. (7) And baking the dried pellets in an oven at 120-140 ℃ for 2-6 hours, then baking the pellets in a muffle furnace at 600-650 ℃ for 4-10 hours, and sieving to obtain the denitration catalyst.

It should be noted that the catalyst of the above embodiment of the present invention is suitable for the existing coal-fired, coal-fired and petroleum coke, biomass steam or power generation boiler.

Some embodiments of the present invention also provide a method of reducing nitrogen oxide emissions from a circulating fluidized bed boiler, comprising: adding a denitration catalyst into a dense bed layer of a boiler of the circulating fluidized bed boiler. The denitration catalyst of the above embodiment is preferable, and it is needless to say that the existing denitration catalyst can be selected to reduce the emission of nitrogen oxides in the circulating fluidized bed boiler to some extent. In some embodiments, the denitration catalyst can be added into the boiler dense bed layer through the existing coal feeding port, the secondary air port or the limestone feeding port.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

357.1g of activated alumina (70 wt% on a dry basis), 444.4g of fly ash of a coal-fired CFB boiler (90 wt% on a dry basis) with the carbon content lower than 6.0wt% and 40g of pore-enlarging agent are weighed and put into a ball roller machine to be uniformly stirred; weighing 137.5g of lanthanum nitrate, putting the lanthanum nitrate into a beaker 1 with the volume of 500ml, adding 150g of distilled water, and stirring to completely dissolve the lanthanum nitrate; weighing 161.3g of copper nitrate, putting the copper nitrate into a beaker 2 with the volume of 500ml, adding 200g of distilled water, and stirring to completely dissolve the copper nitrate; 975g of alumina sol is weighed and put into a beaker 3; weighing 210g of 15% strengthPlacing the dilute hydrochloric acid solution into a beaker 4; and starting the ball rolling machine, and spraying the lanthanum nitrate solution in the beaker 1, the copper nitrate solution in the beaker 2, the alumina sol in the beaker 3 and the dilute hydrochloric acid solution in the beaker 4 into the ball rolling machine in turn by using a sprayer in batches, so that the materials in the ball rolling machine gradually grow into balls. And screening the material pellets into pellets of 2-4 mm, ventilating in a shade, spreading out, cooling for 76 hours, and airing. And (3) baking the aired pellets in an oven at 120 ℃ for 5 hours, and then baking the aired pellets in a muffle furnace at 620 ℃ for 8 hours to obtain the denitration catalyst. Wherein, lanthanum nitrate reacts to form oxide La₂O₃The amount of (b) was 40% by mass of lanthanum nitrate, and the amount of CuO, an oxide formed by the reaction of copper nitrate, was 62% by mass of copper nitrate.

Example 2

Weighing 500.0g of activated alumina (dry basis is 70 wt%), 333.3g of fly ash of a coal-fired CFB boiler (dry basis is 90 wt%) with carbon content lower than 6.0wt% and 30g of pore-expanding agent, putting into a ball roller, and uniformly stirring; weighing 125.0g of cerium nitrate, putting the cerium nitrate into a beaker 1 with the volume of 500ml, adding 150g of distilled water, and stirring to completely dissolve the cerium nitrate; 320.0g of zinc nitrate is weighed and put into a beaker 2 with the volume of 1000ml, 400g of distilled water is added, and the mixture is stirred to be completely dissolved; weighing 1100.0g of alumina sol and putting the alumina sol into a beaker 3; weighing 70g of 15% dilute hydrochloric acid solution and putting the solution into a beaker 4; and starting the ball rolling machine, and spraying the lanthanum nitrate solution in the beaker 1, the copper nitrate solution in the beaker 2, the alumina sol in the beaker 3 and the dilute hydrochloric acid solution in the beaker 4 into the ball rolling machine in turn by using a sprayer in batches, so that the materials in the ball rolling machine gradually grow into balls. And screening the material pellets into pellets of 2-4 mm, ventilating in a shade, spreading out, cooling for 90 hours, and airing. And (3) baking the aired pellets in an oven at 130 ℃ for 5 hours, and then baking the aired pellets in a muffle furnace at 650 ℃ for 7 hours to obtain the denitration catalyst. Wherein, cerium nitrate reacts to form oxide CeO₂The mass of (b) is 40% of that of cerium nitrate, and the mass of ZnO oxide formed by the reaction of zinc nitrate is 25% of that of zinc nitrate.

Example 3

671.4g of activated alumina (dry basis is 70 wt%), 277.8g of fly ash of coal-fired CFB boiler (dry basis is 90 wt%) with carbon content lower than 6.0wt% and 40g of pore-expanding agent are weighed and put into the fly ashStirring uniformly in a ball rolling machine; weighing 150.0g of praseodymium nitrate, putting the praseodymium nitrate into a beaker 1 with the volume of 500ml, adding 150g of distilled water, and stirring to completely dissolve the praseodymium nitrate; 240g of cobalt nitrate (with 25 wt% of CoO content) is weighed and placed into a beaker 2 with the volume of 500ml, 250g of distilled water is added, and the mixture is stirred to be completely dissolved; weighing 850g of alumina sol and putting into a beaker 3; weighing 150g of a 15% dilute hydrochloric acid solution, and putting the solution into a beaker 4; and starting the ball rolling machine, and spraying the lanthanum nitrate solution in the beaker 1, the copper nitrate solution in the beaker 2, the alumina sol in the beaker 3 and the dilute hydrochloric acid solution in the beaker 4 into the ball rolling machine in turn by using a sprayer in batches, so that the materials in the ball rolling machine gradually grow into balls. And screening the material pellets into pellets of 2-4 mm, ventilating in a shade, spreading out, cooling and standing for 65 hours, and drying in the air. And (3) baking the aired pellets in an oven at 140 ℃ for 2 hours, and then baking the aired pellets in a muffle furnace at 640 ℃ for 6 hours to obtain the denitration catalyst. Wherein, oxide Pr formed by praseodymium nitrate reaction₂O₃The mass of (b) is 40% of that of praseodymium nitrate, and the mass of an oxide CoO formed by the cobalt nitrate reaction is 25% of that of cobalt nitrate.

Example 4

285.7g of activated alumina (dry basis is 70 wt%), 466.7g of fly ash of a coal-fired CFB boiler (dry basis is 90 wt%) with carbon content lower than 6.0wt% and 20g of pore-expanding agent are weighed and put into a ball roller machine to be uniformly stirred; weighing 100.0g of neodymium nitrate, putting the neodymium nitrate into a beaker 1 with the volume of 500ml, adding 120g of distilled water, and stirring to completely dissolve the neodymium nitrate; weighing 126.3g of ferric trichloride, putting the ferric trichloride into a beaker 2 with the volume of 500ml, adding 150g of distilled water, and stirring to completely dissolve the ferric trichloride; 758.70.0g of silica sol is weighed and put into a beaker 3; weighing 50g of a 15% dilute hydrochloric acid solution and putting the solution into a beaker 4; and starting the ball rolling machine, and spraying the lanthanum nitrate solution in the beaker 1, the copper nitrate solution in the beaker 2, the alumina sol in the beaker 3 and the dilute hydrochloric acid solution in the beaker 4 into the ball rolling machine in turn by using a sprayer in batches, so that the materials in the ball rolling machine gradually grow into balls. And screening the material pellets into pellets of 2-4 mm, ventilating in a shade, spreading out, cooling for 96 hours, and drying. And (3) baking the aired pellets in an oven at 130 ℃ for 3 hours, and then baking the aired pellets in a muffle furnace at 610 ℃ for 10 hours to obtain the denitration catalyst. Wherein, praseodymium nitrate reacts to form oxide Nd₂O₃40% of praseodymium nitrate and an oxide Fe formed by the reaction of ferric trichloride₂O₃The mass of (A) is 25% of that of the ferric trichloride.

Example 5

471.4g of activated alumina (dry basis is 70 wt%), 411.1g of fly ash of a coal-fired CFB boiler (dry basis is 90 wt%) with carbon content lower than 6.0wt% and 25g of pore-expanding agent are weighed and put into a ball roller, and are uniformly stirred; weighing 125.0g of cerium nitrate, putting the cerium nitrate into a beaker 1 with the volume of 500ml, adding 140g of distilled water, and stirring to completely dissolve the cerium nitrate; weighing 72.7g of anhydrous manganese chloride (MnO content is 55 wt.%) and placing the anhydrous manganese chloride into a beaker 2 with the volume of 500ml, adding 100g of distilled water, and stirring to completely dissolve the anhydrous manganese chloride; weighing 1050.0g of alumina sol and putting into a beaker 3; weighing 50g of a 15% dilute hydrochloric acid solution and putting the solution into a beaker 4; and starting the ball rolling machine, and spraying the lanthanum nitrate solution in the beaker 1, the copper nitrate solution in the beaker 2, the alumina sol in the beaker 3 and the dilute hydrochloric acid solution in the beaker 4 into the ball rolling machine in turn by using a sprayer in batches, so that the materials in the ball rolling machine gradually grow into balls. And screening the material pellets into pellets of 2-4 mm, ventilating in a shade, spreading out, cooling and standing for 56 hours, and drying. And (3) baking the aired pellets in an oven at 120 ℃ for 4 hours, and then baking the aired pellets in a muffle furnace at 650 ℃ for 4 hours to obtain the denitration catalyst. Wherein, cerium nitrate reacts to form oxide CeO₂The mass of (b) is 40% of that of cerium nitrate, and the mass of an oxide MnO formed by the reaction of anhydrous manganese chloride is 25% of that of anhydrous manganese chloride.

Example 6

671.4g of activated alumina (dry basis is 70 wt%), 166.7g of fly ash of a coal-fired CFB boiler (dry basis is 90 wt%) with the carbon content lower than 6.0% (weight percentage) and 35g of pore-expanding agent are weighed and put into a ball roller machine to be uniformly stirred; weighing 100.0g of cerium nitrate and 50.0g of lanthanum nitrate, putting the cerium nitrate and the 50.0g of lanthanum nitrate into a beaker 1 with the volume of 500ml, adding 150g of distilled water, and stirring to completely dissolve the cerium nitrate and the lanthanum nitrate; 177.4g of copper nitrate is weighed and put into a beaker 2 with the volume of 500ml, 200g of distilled water is added, and the mixture is stirred to be completely dissolved; weighing 1050.0g of alumina sol and putting into a beaker 3; weighing 50g of a 15% dilute hydrochloric acid solution and putting the solution into a beaker 4; starting a ball rolling machine, and sequentially dissolving the lanthanum nitrate solution in the beaker 1 and the copper nitrate solution in the beaker 2 in batches by using a sprayerThe liquid, the alumina sol in beaker 3 and the dilute hydrochloric acid solution in beaker 4 are sprayed into a ball rolling machine to make the materials in the ball rolling machine grow gradually into balls. And screening the material pellets into pellets of 2-4 mm, ventilating in a shade, spreading out, cooling and standing for 72 hours, and drying. And (3) baking the aired pellets in an oven at 130 ℃ for 3 hours, and then baking the aired pellets in a muffle furnace at 650 ℃ for 6 hours to obtain the denitration catalyst. Wherein, cerium nitrate reacts to form oxide CeO₂Is 40% of cerium nitrate, and lanthanum nitrate reacts to form an oxide La₂O₃The amount of (b) was 40% by mass of lanthanum nitrate, and the amount of CuO, an oxide formed by the reaction of copper nitrate, was 62% by mass of copper nitrate.

The pore-expanding agents in examples 1 to 6 were all activated carbon.

Comparative example 1

This comparative example differs from example 1 in that 137.5g of lanthanum nitrate was replaced by 88.7g of copper nitrate.

Comparative example 2

This comparative example differs from example 1 in that 161.3g of copper nitrate was replaced by 250g of lanthanum nitrate.

Comparative example 3

The comparative example differs in that 444.4g of coal fired CFB boiler fly ash having a carbon content of less than 6.0wt% was replaced with 500g of lanthanum nitrate and 322.5g of copper nitrate.

Comparative example 4

The comparative example was identical to example 1 in the content of each component, except that activated alumina having the same content of component, fly ash of a coal-fired circulating fluidized bed boiler having a carbon content of less than 6.0wt%, a lanthanoid oxide and a transition metal oxide were directly and uniformly mixed to serve as a denitration catalyst.

Comparative example 5

Pure quartz sand

Test example 1

The denitration catalyst of example 1 was observed by a scanning electron microscope as shown in fig. 1, and as can be seen from fig. 1, the denitration catalyst of example 1 had a good pore structure.

Test example 2

The NOx removal performance evaluation conditions and the evaluation results of the denitration catalyst were as follows:

on a miniature quartz reactor, the combustion reaction conditions of a CFB boiler furnace were simulated, and the NOx removal performance of the composition under the set conditions was evaluated. The flue gas is composed of N₂、CO、NO、O₂The standard gas is mixed gas prepared according to a certain proportion. The composition of each standard gas was as follows: NO standard gas NO is 2500mg/m³、N₂Is a balance gas; the standard CO gas was 5.0 (v)%, N₂Is a balance gas; o is₂Standard gas O₂10.0 (v)%, N₂Is the balance gas. When the evaluation is carried out, quartz sand is used as a diluent, and the content of the denitration catalyst in the quartz sand is 3.0%. Weighing 1g of quartz sand and a denitration catalyst mixture, loading the quartz sand and the denitration catalyst mixture into a quartz tube reactor with the diameter of 8 multiplied by 1mm, heating the mixture to 850 ℃ under the nitrogen flow, stopping the nitrogen flow, introducing mixed gas, reacting at a certain gas flow rate, sampling and analyzing the mixture once every 30 minutes for 8 hours, and taking the average value of NO removal rates of 8 hours as the comparison of the performance of the denitration catalyst composition.

The denitration catalyst composition has NO removal performance:

in the formula: DeNO is the NO removal rate of the denitration catalyst composition,%; c₁In terms of NO content in the gas before reaction, mg/m³；C₂Is the content of NO in the gas mixture after reaction, mg/m³。

The denitration catalysts of examples 1 to 6 and comparative examples 1 to 4 and the quartz sand of comparative example 5 were tested by the above-described method, and the denitration rate was calculated, and the results are shown in table 1.

Table 1 denitration catalyst composition denitration performance evaluation results

As can be seen from the results in table 1, the denitration catalyst obtained in each example of the present invention can achieve good catalytic reduction efficiency in the gas in the simulated circulating fluidized bed boiler environment, thereby achieving a higher denitration rate. As can be seen from comparison of the results of comparative examples 1 to 3 with the examples, the components of fly ash of coal-fired circulating fluidized bed boiler, lanthanide oxide and transition metal oxide having carbon content of less than 6.0wt% each have a significant influence on the catalytic performance of the denitration catalyst, and when the denitration catalyst is formed by using a combination of the three, excellent catalytic effect can be produced. By comparing comparative example 4 with example 1, it can be seen that the components of the denitration catalyst can achieve more excellent denitration effect after being sintered to form a porous structure.

In conclusion, the catalyst is added into a dense-phase bed layer of a boiler through the existing coal feeding port, the secondary air port or the limestone feeding port, and NOx in flue gas, carbonaceous particles in the boiler and CO and NH in the flue gas are catalyzed by utilizing a large amount of reducing substances in the boiler in the combustion process of CFB (circulating fluidized bed) coal₃Reacts with HCN to improve the catalytic reduction efficiency of NOx in dense phase and dilute phase beds, and converts the NOx in the flue gas into N in situ in the combustion chamber of the boiler₂And the aim of reducing NOx in the smoke is fulfilled. The denitration catalyst provided by the embodiment of the invention can effectively remove the content of NOx in the flue gas, and has the characteristics of small dosage, simple use, low denitration cost, no negative influence on combustion efficiency and other pollutant emissions and the like.

The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims

1. A method of reducing nitrogen oxide emissions from a circulating fluidized bed boiler, comprising: adding a denitration catalyst into a dense bed layer of the boiler of the circulating fluidized bed boiler, wherein the denitration catalyst is of a porous structure and at least comprises the following components in parts by weight: 15-50 parts of activated alumina, 12-45 parts of fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, 1-7 parts of lanthanide oxide, 2-15 parts of transition metal oxide and 15-25 parts of a binder; the lanthanide corresponding to the lanthanide oxide is selected from one or a combination of more than two of lanthanum, cerium, praseodymium and neodymium, the transition metal corresponding to the transition metal oxide is selected from one or a combination of more than two of Cu, Zn, W, Co, Fe and Mn, and the binder is selected from one or a combination of two of aluminum sol and silica sol;

the preparation method of the denitration catalyst comprises the following steps: roasting green pellets prepared from activated alumina, fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, lanthanide element salts, transition metal salts and an adhesive.

2. The method of claim 1, wherein the denitration catalyst comprises at least the following components in parts by weight: 20-47 parts of activated alumina, 15-42 parts of fly ash of a coal-fired circulating fluidized bed boiler with carbon content lower than 6.0wt%, 1.5-6 parts of lanthanide oxide, 3-12 parts of transition metal oxide and 17-22 parts of a binder.

3. The method according to claim 1, wherein the denitration catalyst has a specific surface area of 60m²/g~200m²/g。

4. The method according to claim 1, wherein the denitration catalyst is spherical and has a particle size of 1.0 to 10.0 mm.

5. The method according to claim 1, wherein the denitration catalyst has a particle size of 2.0 to 8.0 mm.

6. The method according to any one of claims 1 to 5, wherein the denitration catalyst further comprises 0.5 to 5 parts of a pore-expanding agent.

7. The method of claim 6, wherein the pore-expanding agent is urotropin or activated carbon.

8. The method according to claim 1, wherein the calcination temperature is 600 to 650 ℃ and the calcination time is 4 to 10 hours.

9. The method according to claim 8, wherein the green pellets are baked at a temperature of 120 to 140 ℃ for 2 to 6 hours before the green pellets are baked.

10. The method of claim 9, wherein the green pellets are air dried prior to baking the green pellets.

11. The method according to claim 10, wherein the preparation of green pellets comprises: and putting a solid mixture obtained by mixing the activated alumina and the fly ash of the coal-fired circulating fluidized bed boiler with the carbon content of less than 6.0wt% into a rotary table ball rolling machine, and spraying the solid mixture through a sprayer under the condition that the rotary table ball rolling machine rotates so that the solid mixture of the rotary table ball rolling machine gradually forms green balls, wherein the spraying material of the sprayer is a mixed solution of dilute hydrochloric acid, a lanthanide salt aqueous solution, a transition metal salt aqueous solution and an adhesive.

12. The method according to claim 11, wherein a pore-expanding agent is further added to the solid mixture, and the obtained green pellets are screened to select pellets of 2-4 mm for roasting.

13. The method of claim 1, wherein the lanthanide salt is a lanthanide nitrate or a lanthanide chloride, and the transition metal salt is a transition metal nitrate or a transition metal chloride.