A method for using a powdered scr catalyst in a cement kiln

Abstract

The present application belongs to the field of flue gas denitrification in cement industry, and particularly relates to a method for using powdered SCR catalyst in a cement kiln, comprising the following steps: when the concentration of nitrogen oxide emission increases to a certain value and remains stable, powdered SCR catalyst with a particle size of 0.5-1 mu m is mixed into the C2-C1 air pipe at a certain speed, and the SCR catalyst circulates in the C2-C1 air pipe, C1 cyclone drum, dust collector inlet pipe, high-temperature bag-type dust collector, and between the C2-C1 air pipes; after the addition of the SCR catalyst is started, the concentration of nitrogen oxide emission decreases, and when the SCR catalyst spreads throughout the circulation system, the denitrification efficiency and the concentration of nitrogen oxide emission tend to be stable, at which time the addition of the SCR catalyst is stopped; or the addition of the SCR catalyst is continuously made, but the addition amount is reduced compared with before. The present application can adjust the addition amount of the catalyst according to the change in the concentration of nitrogen oxide emission. In addition, the SCR catalyst is used in a circulating manner, and the operation cost is low.

Description

Technical Field

[0001] This invention belongs to the field of flue gas denitrification in the cement industry, specifically relating to a method for using a powdered SCR catalyst in a cement kiln. Background Technology

[0002] Nitrogen oxides (NOx) are harmful pollutants that can easily cause acid rain and other damage. To strengthen environmental protection, cement plants currently widely use selective non-catalytic reduction (SNCR) technology for NOx removal. my country has established relevant standards to control NOx emissions, but with increasingly stringent environmental requirements, the converted NOx emission concentration must be below 50 mg / m³. 3 However, selective non-catalytic reduction (SNCR) technology has difficulty guaranteeing levels below 50 mg / m³. 3 Therefore, many cement companies have begun to use selective catalytic reduction (SCR) technology.

[0003] By the end of 2022, nearly 50 cement production lines in my country had adopted SCR technology for denitrification, ensuring that the equivalent nitrogen oxide emission concentration was below 50 mg / m³. 3 However, the application of SCR in the cement industry has brought about a series of problems:

[0004] First, spent SCR catalysts are classified as hazardous waste. After a period of use and subsequent deactivation, they must be disposed of by a qualified treatment facility, which incurs high costs.

[0005] Secondly, if discarded SCRs are recycled, their denitrification effect will be poor because their surfaces are covered with multiple layers of inert substances such as dust.

[0006] Third, due to the technological characteristics of the cement industry, the dust concentration in the flue gas that SCR catalysts need to treat is often as high as 100-200 g / Nm³. 3 High dust concentrations can abrade and damage the formed catalyst.

[0007] Fourth, SCR towers currently commonly use honeycomb or plate-shaped catalysts. Over time, the pores of these catalysts are easily clogged by dust, resulting in decreased activity and reduced denitrification efficiency.

[0008] Fifth, when the pores of SCR catalysts such as honeycomb and plate-shaped catalysts are blocked by dust, they need to be cleaned with compressed air using a rake soot blower. The rake soot blower is in operation for a long time and consumes a lot of electricity.

[0009] Sixth, SCR towers are fixed installations and cannot be adjusted according to changes in nitrogen oxides in flue gas after they are put into operation. Therefore, when the initial nitrogen oxide concentration in a cement plant increases significantly for some reason, the calculated emission concentration of nitrogen oxides is still likely to exceed the standard.

[0010] Seventh, ordinary additive catalysts are added only once and are quickly depleted. To maintain the denitrification effect, they need to be added continuously. They cannot be reused, and the amount of catalyst used is large, resulting in high operating costs.

[0011] Eighth, ammonium bisulfate and ammonium bisulfite can deposit on SCR catalysts, leading to a decrease in catalyst activity. Summary of the Invention

[0012] In order to solve the above-mentioned technical problems existing in the prior art

[0013] The present invention adopts the following technical solution:

[0014] First, the present invention provides a method for using powdered SCR catalyst in a cement kiln. The cement kiln involved in the method includes a C2 cyclone separator, a C1 cyclone separator, a high-temperature bag filter, and a preheating power generation boiler connected in sequence. A C2-C1 duct is connected between the C1 and C2 cyclone separators, and a dust collector inlet pipe is provided between the high-temperature bag filter and the C1 cyclone separator.

[0015] The method of use includes the following steps: When the concentration of nitrogen oxide emissions in the chimney rises to a certain value and remains stable, powdered SCR catalyst with a particle size of 0.5-1μm is mixed into the C2-C1 duct at a certain rate. The SCR catalyst circulates between the C2-C1 duct, the C1 cyclone separator, the dust collector inlet pipe, the high-temperature bag filter, and the C2-C1 duct. After the SCR catalyst is added, the denitrification efficiency gradually increases and the nitrogen oxide emission concentration gradually decreases. When the SCR catalyst is distributed throughout the entire circulation system, the denitrification efficiency and nitrogen oxide emission concentration tend to stabilize. At this point, the addition of the SCR catalyst is stopped; or the SCR catalyst can be added continuously, but the amount added is reduced compared to before.

[0016] Furthermore, the SCR catalyst operates in the cement kiln at a temperature range of 260-400 degrees Celsius.

[0017] Furthermore, the SCR catalyst is entirely fresh SCR catalyst, or a mixture of fresh SCR catalyst and waste SCR catalyst at a mass ratio of no more than 30%.

[0018] Furthermore, when the concentration of nitrogen oxides emitted from the chimney is 300 mg / m³ 3 At that time, the SCR catalyst dosage was 50 kg / hour.

[0019] Furthermore, when the concentration of nitrogen oxides emitted from the chimney is 50 mg / m³ 3 At that time, the SCR catalyst dosage was 5 kg / hour.

[0020] Furthermore, when the concentration of nitrogen oxide emissions from the chimney stabilizes at 30 mg / m³ 3 Stop adding SCR catalyst.

[0021] Furthermore, when the concentration of nitrogen oxide emissions from the chimney stabilizes at 30 mg / m³ 3 The SCR catalyst dosage is 1 kg / hour.

[0022] The advantages and positive effects of this invention are:

[0023] First, in the method of using the powdered SCR catalyst of the present invention in a cement kiln, after long-term use, the particle size will gradually increase and be collected by the cyclone separator, and finally enter the cement rotary kiln, where it will be solidified into the cement raw material for harmless treatment. Therefore, no hazardous waste is generated, and it does not need to be handed over to a specialized qualified institution for disposal, and there are no disposal costs.

[0024] Secondly, when utilizing waste SCR catalyst, the waste SCR catalyst has been ground to 0.5-1μm, and other dust covering the surface has been separated from the SCR catalyst, resulting in good denitrification effect after regeneration.

[0025] Third, although the dust concentration is high during the SCR catalyst of the present invention, the SCR catalyst is also in a dust state and will not be damaged by dust abrasion.

[0026] Fourth, the SCR catalyst of the present invention is in a dust state during the circulation process, without pores, and therefore cannot be blocked by dust.

[0027] Fifth, the SCR catalyst of the present invention is in a dust state during the circulation process, so there is no need for a rake-type soot blower, nor is it necessary to consume this part of the electrical energy.

[0028] Sixth, in the method of using the powdered SCR catalyst of the present invention in a cement kiln, the amount of catalyst added can be adjusted according to the change in the nitrogen oxide emission concentration to change the nitrogen oxide emission concentration.

[0029] Seventh, in the method of using the powdered SCR catalyst of the present invention in a cement kiln, the SCR catalyst is recycled, unlike the high operating cost of one-time addition.

[0030] Eighth, in the method of using the powdered SCR catalyst of the present invention in a cement kiln, even if ammonium bisulfate, ammonium sulfate, etc. are deposited on the surface of the SCR catalyst, when the SCR catalyst is circulated to the preheater C2-C1 air duct, the temperature there is as high as 400°C or more, which is higher than the decomposition temperature of ammonium bisulfate and ammonium sulfate, so ammonium bisulfate and ammonium sulfate will decompose. Attached Figure Description

[0031] Figure 1 This is a schematic diagram showing the circulation of the SCR catalyst of the present invention between the preheater C2-C1 duct, the C1 cyclone separator, the C1 cyclone separator-high-temperature bag filter duct, and the high-temperature bag filter.

[0032] In the diagram: 1. C1 cyclone separator; 2. C2 cyclone separator; 3. C2-C1 duct; 4. High-temperature baghouse dust collector; 5. Preheating power generation boiler; 6. Dust collector inlet pipe. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below; obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, this invention discloses a method for using a powdered SCR catalyst in a cement kiln. The catalyst is in powder form with a particle size of 0.5-1 μm. The cement kiln involved in this method includes a C2 cyclone separator 2, a C1 cyclone separator 1, a high-temperature bag filter 4, and a preheating power generation boiler 5 connected in sequence. A C2-C1 duct 3 connects the C1 and C2 cyclones, and a dust collector inlet pipe 6 is provided between the high-temperature bag filter 4 and the C1 cyclone separator 1. The method includes the following steps: when the nitrogen oxide emission concentration in the chimney rises to a certain value and remains stable, the SCR catalyst with a particle size of 0.5-1 μm is mixed into the C2-C1 duct at a certain rate. The SCR catalyst... The system circulates between C2-C1 duct 3, C1 cyclone separator 1, dust collector inlet pipe 6, high-temperature bag filter 4, and C2-C1 duct 3. After the SCR catalyst is initially added, the denitrification efficiency gradually increases, and the nitrogen oxide emission concentration gradually decreases. When the SCR catalyst is distributed throughout the entire circulation system, the denitrification efficiency and nitrogen oxide emission concentration tend to stabilize, at which point the addition of the SCR catalyst is stopped. In subsequent use, if the nitrogen oxide emission concentration increases, the SCR catalyst can be added again. Alternatively, small amounts of SCR catalyst can be added continuously during use.

[0035] The SCR catalyst operates in the cement kiln at a temperature range of 260-400 degrees Celsius.

[0036] The SCR catalyst can be a fresh SCR catalyst or a mixture of up to 30% by mass of waste SCR catalyst that has been ground to 0.5-1μm.

[0037] Working principle:

[0038] 1. The catalyst powder will not be collected by the cyclone separator, but will be discharged from the preheater with the flue gas.

[0039] According to public knowledge [1,2,3] Particle size distribution significantly affects the dust collection efficiency of cyclone dust collectors. Typically, high separation efficiency is maintained only for particles larger than 10 μm, while the classification efficiency for fine particles with a diameter less than 6 μm is relatively low. The separation efficiency of cyclone dust collectors decreases sharply with decreasing median particle size of the inlet raw material. Cyclone dust collectors are relatively sensitive to the size of small particles but have a high separation capacity for large particles. When the inlet particle size is less than 1.9 μm, the separation efficiency drops to 65%. [2] When the inlet particle size is less than 1 μm, the separation efficiency drops to below 10%. [3] .

[0040] [1] Zhang Changle, Relationship between dust collection efficiency of cyclone dust collector and particle size distribution of raw material, Cement Engineering, 2018.3: 15-17;

[0041] [2] Meng Kehan, Separation characteristics of a high-efficiency cyclone separator, Journal of Harbin University of Science and Technology, 2020.3(25):116-121;

[0042] [3] Ma Qinglei, Influence of particle size distribution at the inlet of guide vane cyclone separator on separation efficiency, China Powder Technology, 2007.2: 21-23;

[0043] Therefore, by taking advantage of the fact that the cyclone separator in the cement kiln preheater system can hardly separate dust particles smaller than 1μm, catalyst particles can be prevented from being collected by the cyclone separator after entering the preheater and can be discharged with the flue gas.

[0044] 2. The catalyst particles are collected by a high-temperature bag filter and will not be emitted through a chimney in subsequent processes.

[0045] The dust collection efficiency of baghouse dust collectors is also affected by particle size. (Based on publicly available information) [4] For particles larger than 1μm, the dust removal efficiency can reach 99.5%, and even for particles of 0.2-0.4μm, the dust removal efficiency can reach over 90%. The actual dust removal efficiency in modern cement processes is generally above 99.9%. This application uses 0.5-1μm SCR catalyst particles, ensuring collection in a high-temperature baghouse dust collector and preventing them from entering the raw material mill and ultimately being emitted through the chimney as pollutants, thus avoiding waste.

[0046] [4] Secretariat of the National Registered Engineers in Surveying and Design Public Utility Equipment Professional Management Committee, 2020 edition of the National Registered Engineers in Surveying and Design Public Utility Equipment Professional Examination Review Textbook for HVAC Professional, p. 215.

[0047] 3. Mechanism of SCR catalyst circulation in the system

[0048] Since the SCR catalyst in this scheme will not be collected by the preheater cyclone or pass through the bag filter to enter the chimney after being added, it will continuously circulate between the C2-C1 duct, the C1 cyclone, the dust collector inlet pipe, and the high-temperature bag filter, catalyzing the reaction between ammonia and nitrogen oxides and reducing nitrogen oxide emissions.

[0049] The present invention will be described in detail below through two embodiments:

[0050] Example 1

[0051] After SNCR denitrification, the nitrogen oxide emission concentration from the chimney of a factory in Zhejiang Province was 300 mg / m³. 3 To maintain stability, SCR catalyst with a particle size of 0.5-1 μm was mixed into the C2-C1 duct at a dosage of 50 kg / hour. Five minutes after addition, the chimney emission concentration decreased to approximately 110 mg / m³. 3 Ten minutes after addition, the chimney emission concentration stabilized at approximately 30 mg / m³. 3 If the temperature drops further, stop adding SCR catalyst.

[0052] After 14 days of operation, the chimney emission concentration slowly increased to 50 mg / m³. 3 Then, begin adding 0.5-1 μm SCR catalyst at a rate of 5 kg / h until the chimney emission concentration stabilizes at approximately 30 mg / m³. 3 .

[0053] Example 2

[0054] After SNCR denitrification, the nitrogen oxide emission concentration from the chimney of a factory in Zhejiang Province was 300 mg / m³. 3 To maintain stability, SCR catalyst with a particle size of 0.5-1 μm was mixed into the C2-C1 duct at a dosage of 50 kg / hour. Five minutes after addition, the chimney emission concentration decreased to approximately 110 mg / m³. 3 Ten minutes after addition, the chimney emission concentration stabilized at approximately 30 mg / m³. 3 Then, an SCR catalyst was added at a constant rate of 1 kg / hour, and the emission concentration from the chimney remained stable at approximately 30 mg / m³. 3 .

[0055] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for using a powdered SCR catalyst in a cement kiln, characterized in that: The cement kiln involved in this method includes a C2 cyclone separator, a C1 cyclone separator, a high-temperature bag filter, and a preheating power generation boiler connected in sequence; a C2-C1 duct is connected between the C1 and C2 cyclone separators, and a dust collector inlet pipe is provided between the high-temperature bag filter and the C1 cyclone separator. The method of use includes the following steps: When the concentration of nitrogen oxide emissions in the chimney rises to a certain value and remains stable, powdered SCR catalyst with a particle size of 0.5-1μm is mixed into the C2-C1 duct at a certain rate. The SCR catalyst circulates between the C2-C1 duct, the C1 cyclone separator, the dust collector inlet pipe, the high-temperature bag filter, and the C2-C1 duct. After the SCR catalyst is added, the denitrification efficiency gradually increases and the nitrogen oxide emission concentration gradually decreases. When the SCR catalyst is distributed throughout the entire circulation system, the denitrification efficiency and nitrogen oxide emission concentration tend to stabilize. At this point, the addition of the SCR catalyst is stopped; or the SCR catalyst can be added continuously, but the amount added is reduced compared to before.

2. The method of using the powdered SCR catalyst as described in claim 1 in a cement kiln, characterized in that: The SCR catalyst operates in the cement kiln at a temperature range of 260-400 degrees Celsius.

3. The method of using the powdered SCR catalyst as described in claim 1 in a cement kiln, characterized in that: The SCR catalyst is entirely fresh SCR catalyst, or fresh SCR catalyst mixed with up to 30% waste SCR catalyst by mass.

4. The method of using the powdered SCR catalyst as described in claim 3 in a cement kiln, characterized in that: When the concentration of nitrogen oxides emitted from the chimney is 300 mg / m³ 3 At that time, the SCR catalyst dosage was 50 kg / hour.

5. The method of using the powdered SCR catalyst as described in claim 1 in a cement kiln, characterized in that: When the concentration of nitrogen oxides emitted from the chimney is 50 mg / m³ 3 At that time, the SCR catalyst dosage was 5 kg / hour.

6. The method of using the powdered SCR catalyst as described in claim 4 or 5 in a cement kiln, characterized in that: When the concentration of nitrogen oxide emissions from the chimney stabilizes at 30 mg / m³ 3 Stop adding SCR catalyst.

7. The method of using the powdered SCR catalyst as described in claim 4 or 5 in a cement kiln, characterized in that: When the concentration of nitrogen oxide emissions from the chimney stabilizes at 30 mg / m³ 3 The SCR catalyst dosage is 1 kg / hour.

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