SCR catalyst specification design method for coal-fired power plants considering uneven fly ash distribution

Abstract

The present invention discloses a method for designing the specifications of SCR catalysts for coal-fired power plants that takes into account the uneven distribution of fly ash. The method first calculates the concentration distribution of fly ash of different particle sizes in the SCR denitrification device, then calculates the converted concentration distribution of the full-particle fly ash at the upstream section of the top catalyst, and designs the specifications of the SCR catalysts row by row or column by column. The specifications of the lower catalyst layer are consistent with those of the top catalyst layer, so that the anti-clogging and wear resistance of the catalysts at different positions match the fly ash concentration. The method for designing the specifications of SCR catalysts for coal-fired power plants that takes into account the uneven distribution of fly ash provided by the present invention addresses the objective condition of the uneven distribution of fly ash in the SCR reactor and proposes a method for designing the wall thickness and pore size of the SCR catalysts row by row or column by column based on the actual distribution of the converted concentration of the full-particle fly ash at the upstream section of the top catalyst layer. This ensures that the anti-clogging and wear resistance of the catalysts at different positions match the fly ash concentration, and the catalysts on the entire cross section have the same service life.

Description

Technical Field

[0001] The invention belongs to the technical field of flue gas treatment, and in particular relates to a method for designing specifications of an SCR catalyst in a coal-fired power plant taking into account uneven distribution of fly ash. Background Art

[0002] Most SCR systems in thermal power plants utilize high-dust installations, making catalysts susceptible to clogging and wear. Due to the characteristics of coal types in my country and cost constraints, power plants often burn high-calcium and low-quality coal. These coals produce fly ash with high content, large particle size, and high hardness, further exacerbating catalyst wear. In recent years, catalyst wear and ash accumulation in domestic coal-fired power plants has become an increasingly prominent issue, following ABS contamination and clogging as another key issue impacting SCR denitrification and the safe and stable operation of units.

[0003] On-site investigations found that the degree of dust wear in different areas of the catalyst layer cross-section varies greatly. For example, in the SCR denitrification device of a π-type boiler, the catalyst in the direction of the furnace is severely worn by dust accumulation, while it is lighter in the direction of the furnace. Studies have shown that uneven distribution of fly ash concentration is an important cause of severe wear and blockage of local catalysts. However, when designing an SCR denitrification device, the catalyst specifications are designed according to the average fly ash concentration. Among them, the selection of honeycomb catalysts is based on the average fly ash content in the flue gas. As shown in the honeycomb catalyst design table in Table 1 below, if the ash content is low, a catalyst with a large number of holes and a small pitch is selected. If the ash content is high, a catalyst with a small number of holes and a large pitch is selected. Each layer of catalyst uses a uniform specification and model, and the difference in fly ash concentration distribution is not taken into account.

[0004] Table 1

[0005] Summary of the Invention

[0006] In order to solve the technical problems existing in the prior art, the purpose of the present invention is to provide a method for designing the specifications of SCR catalysts for coal-fired power plants taking into account the uneven distribution of fly ash.

[0007] In order to achieve the above-mentioned purpose and the above-mentioned technical effect, the technical solution adopted by the present invention is:

[0008] The SCR catalyst specification design method for coal-fired power plants takes into account the uneven distribution of fly ash. First, the concentration distribution of fly ash of different particle sizes in the SCR denitrification device is calculated. Then, the converted concentration distribution of full-particle fly ash in the upstream section of the top catalyst is calculated. The specifications of the SCR catalyst are designed row by row or column by column. The specifications of the lower catalyst are consistent with those of the top catalyst, so that the anti-clogging and wear resistance of the catalysts at different positions match the fly ash concentration.

[0009] The SCR catalyst specification design method for coal-fired power plants considering uneven fly ash distribution includes the following steps:

[0010] (1) Based on the structure and size of the SCR denitrification device, a 3D full-scale geometric model of the SCR denitrification device was constructed using 3D modeling software at a 1:1 ratio. The modeling range was from the boiler economizer outlet to the SCR reactor outlet. The model included at least the guide and rectifier device, static mixer, and SCR catalyst in the SCR reactor. The obtained model was imported into the adaptation software for meshing.

[0011] (2) The gas-solid two-phase flow numerical simulation method was used to obtain the particle sizes d i The concentration of fly ash in the SCR reactor is m i The distribution pattern of

[0012] (3) After the simulation converges, the reduced ash concentration is defined as w in the CFD simulation software. i =d i 0.5 *m i Calculate the reduced ash concentration w of each representative particle size fly ash in the upstream section of the top catalyst i distribution of

[0013] (4) According to the conversion concentration w of fly ash of different particle sizes i The distribution of fly ash particles is used to calculate the reduced concentration ∑w of fly ash in the upstream section of the top catalyst. i distributed;

[0014] (5) According to the converted concentration of full-size fly ash in the upstream section of the top catalyst, ∑w i Distribution: Design the specifications of SCR catalysts row by row or column by column, including wall thickness and pore size. The specifications of the lower catalyst layer are consistent with those of the top catalyst layer, so that the anti-clogging and wear resistance of catalysts at different positions match the fly ash concentration, thereby improving the consistency of catalyst service life across the entire cross-section.

[0015] Furthermore, in step (2), boundary conditions are set according to the design parameters of the SCR denitrification device, and CFD simulation software is used to perform gas-solid two-phase flow simulation calculations in the SCR denitrification device. During the simulation calculation, several groups of representative particle sizes are selected to perform full-particle size simulation calculations to obtain the concentration distribution law of fly ash with different particle sizes in the SCR reactor. The representative particle size is set according to the fly ash particle size distribution measurement results.

[0016] Furthermore, the boundary conditions are set according to the flue gas volume, composition, temperature, fly ash concentration and particle size distribution in the SCR denitrification device design parameters.

[0017] Furthermore, in step (5), the converted concentration of full-size fly ash at the upstream section of the top catalyst is ∑w i The larger it is, the larger the pore size, pitch and wall thickness of the honeycomb catalyst.

[0018] Furthermore, according to the converted concentration of full-size fly ash in the upstream section of the top catalyst, ∑w i Distribution, design the pitch, pore size and wall thickness of the honeycomb catalyst according to the table below to obtain the catalyst specifications in different areas:

[0019]

[0020]

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention discloses a method for designing the specifications of SCR catalysts for coal-fired power plants that takes into account the uneven distribution of fly ash, comprising the following steps: first calculating the concentration distribution of fly ash of different particle sizes in the SCR denitrification device, then calculating the converted concentration distribution of the full-particle fly ash at the upstream section of the top catalyst, and designing the specifications of the SCR catalyst row by row or column by column, with the specifications of the lower catalyst layer being consistent with those of the top catalyst layer. The method for designing the specifications of SCR catalysts for coal-fired power plants that takes into account the uneven distribution of fly ash provided by the present invention, in view of the objective condition of the uneven distribution of fly ash in the SCR reactor, proposes a method for designing the wall thickness and pore size of the SCR catalysts row by row or column by column, based on the actual distribution of the converted concentration of the full-particle fly ash at the upstream section of the top catalyst layer, so that the anti-clogging and wear resistance of the catalysts at different positions match the fly ash concentration, and the catalysts on the entire cross section achieve the same service life; the present invention not only takes into account the fly ash concentration (obtained through numerical simulation calculations), but also takes into account the influence of the fly ash particle size, resulting in more accurate results. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the present invention;

[0024] Figure 2 This is the full particle size concentration distribution diagram of the upstream 500 mm section of the top catalyst of Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0026] The following is a brief summary of one or more aspects to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceivable aspects and is neither intended to identify key or critical elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that will be provided later.

[0027] like Figure 1 As shown, the SCR catalyst specification design method for coal-fired power plants considering uneven fly ash distribution includes the following steps:

[0028] (1) Based on the structure and size of the SCR denitrification device, a 3D full-scale geometric model of the SCR denitrification device was constructed using 3D modeling software at a 1:1 ratio. The modeling range was from the boiler economizer outlet to the SCR reactor outlet. The model included at least the flow guide and rectification device, static mixer, and SCR catalyst in the SCR reactor. The obtained model was imported into an adaptation software such as ICEM to divide the mesh.

[0029] (2) The cross-sectional area of ​​the SCR denitrification device of the coal-fired power plant is large (on the order of hundreds of square meters), and it is very difficult to directly measure the fly ash concentration distribution. Therefore, the present invention adopts the gas-solid two-phase flow numerical simulation method to obtain the distribution of fly ash with different particle sizes d i The concentration of fly ash in the SCR reactor is m i Specifically, based on the flue gas volume, composition, temperature, fly ash concentration, particle size distribution and other data in the SCR denitrification device design parameters as boundary conditions, CFD simulation software is used to simulate the gas-solid two-phase flow in the SCR denitrification device. The present invention uses the Lagrangian model to simulate the fly ash motion trajectory. During the simulation calculation, several groups of representative particle sizes are selected to perform full particle size simulation calculations to obtain the concentration distribution law of fly ash of different particle sizes in the SCR reactor. Representative particle size d i Set according to the fly ash particle size distribution measurement results, usually 1 to 10 groups, i = 1 to 10;

[0030] (3) According to research by foreign scholars, the empirical formula for fly ash wear on unit mass of catalyst is:

[0031] M=k1*∑ i m i *d i 0.5 *k2*v i 3

[0032] Where k1 is the mass fraction of the blocked catalyst, m i is the mass percentage of fly ash particles within the size interval i, d i is the average particle diameter, k2 is the catalyst wear index, which is related to the fly ash wear characteristics, v iis the linear velocity of the fly ash particles. As can be seen from the above, the larger and coarser the fly ash particle size, the more severe the wear, especially the catalyst wear in the high-concentration and large-particle area will be more severe. In addition, the larger the fly ash particle size, the greater its inertia and the more uneven the distribution. Assuming that the average fly ash concentration remains unchanged, the fly ash concentration in a certain area is high, and the fly ash concentration in other areas must be lower. In areas with high fly ash concentration, the catalyst wears severely, and in areas with low fly ash concentration, the catalyst wears less. Under the condition of the same catalyst specifications, the areas with severe wear are damaged first and have a short lifespan, while the catalyst in areas with light wear has a longer service life, resulting in inconsistent catalyst lifespan. However, the influence of fly ash particle size and the influence of uneven concentration are usually not considered in the selection and design of existing catalysts, resulting in the problem that the catalyst often has severe local dust accumulation and wear and has to be replaced in advance. In order to solve this technical problem, the present invention innovatively proposes to consider both the fly ash concentration and the influence of fly ash particle size when designing catalyst specifications. Therefore, after the simulation calculation converges, the converted ash concentration is defined as w in the CFD simulation software. i =d i 0.5 *m i , calculate the fly ash concentration m at the upstream section of the top catalyst i Distribution, calculate the reduced ash concentration w of the upstream section of the top catalyst for each representative particle size i distribution of

[0033] (4) According to the conversion concentration w of fly ash of different particle sizes i The distribution of fly ash particles is used to calculate the reduced concentration ∑w of fly ash in the upstream section of the top catalyst. i distributed;

[0034] (5) According to the converted concentration of full-size fly ash in the upstream section of the top catalyst, ∑w i Distribution: According to the honeycomb catalyst pitch wall thickness design table in Table 2, the specifications of the SCR catalyst are designed row by row or column by column, including pitch, wall thickness and pore size. The specifications of the lower catalyst are consistent with those of the top catalyst, so that the anti-clogging and wear resistance of the catalysts at different positions match the fly ash concentration, thereby improving the consistency of the catalyst service life on the entire cross section and reducing the complexity of the design.

[0035] Table 2

[0036]

[0037] The reduced ash concentration proposed in the present invention takes both fly ash concentration and particle size into consideration. High ash concentration and large particle size will increase the reduced ash concentration. This is more reasonable than the prior art method of designing catalyst specifications based solely on fly ash concentration.

[0038] Example 1

[0039] The wet flue gas volume at the economizer outlet of a 350MW coal-fired power generation unit is 1030290m 3 / h, oxygen content is 3.2%, flue gas humidity is 8.7%, and smoke concentration is about 35g / m 3 The average particle size of fly ash is 54 μm. The total particle size fly ash conversion concentration ∑w i The distribution simulation results are as follows Figure 2 As shown, the fly ash concentration in the front-to-back direction deviates significantly. Therefore, the SCR catalyst pitch, wall thickness, and pore diameter were designed based on the calculated ash concentration row by row in the front-to-back direction. The design results are shown in Table 3, which shows the calculated ash concentration and catalyst specification design. In the high ash concentration area in front of the furnace, a catalyst with a large pore diameter and thick wall was used.

[0040] Table 3

[0041]

[0042] The present invention provides a method for designing the wall thickness and pore size of SCR catalysts row by row or column by column based on the actual distribution of fly ash concentration converted from the catalyst inlet, so that the anti-clogging and wear resistance of the catalysts at different positions match the fly ash concentration, which can significantly improve the consistency of the catalyst service life across the entire cross-section.

[0043] Parts or structures not specifically described in the present invention may adopt existing technologies or existing products and will not be described in detail here.

[0044] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for designing SCR catalyst specifications for coal-fired power plants considering uneven fly ash distribution, characterized in that: First, the concentration distribution of fly ash of different particle sizes within the SCR denitrification device is calculated. Then, the equivalent concentration distribution of fly ash of all particle sizes in the upstream section of the top catalyst is calculated. The specifications of the SCR catalysts are designed row by row or column by column. The specifications of the lower catalyst layer are kept consistent with those of the top catalyst layer, so that the anti-clogging and wear resistance of the catalysts at different locations match the fly ash concentration. The method specifically comprises the following steps: (1) Based on the structure and size of the SCR denitrification device, a 3D full-scale geometric model of the SCR denitrification device was constructed using 3D modeling software at a 1:1 ratio. The modeling range was from the boiler economizer outlet to the SCR reactor outlet. The model obtained included at least the guide and rectifier device, static mixer, and SCR catalyst in the SCR reactor. The obtained model was imported into the adaptation software for meshing. (2) The gas-solid two-phase flow numerical simulation method was used to obtain the particle sizes d i The concentration of fly ash in the SCR reactor is m i The distribution pattern of (3) After the simulation converges, the reduced ash concentration is defined as w in the CFD simulation software. i =d i 0.5 *m i Calculate the reduced ash concentration w of each representative particle size fly ash in the upstream section of the top catalyst i distribution of (4) According to the conversion concentration w of fly ash of different particle sizes i The distribution of fly ash particles is used to calculate the reduced concentration ∑w of fly ash in the upstream section of the top catalyst. i distributed; (5) According to the converted concentration of full-size fly ash in the upstream section of the top catalyst, ∑w i Distribution: Design the specifications of the SCR catalysts, including wall thickness and pore size, row by row or column by column. The specifications of the lower catalyst layer are consistent with those of the top catalyst layer. This ensures that the anti-clogging and wear resistance of the catalysts at different locations match the fly ash concentration, thereby improving the consistency of the catalyst service life across the entire cross-section. According to the converted concentration of full-size fly ash in the upstream section of the top catalyst ∑w i Distribution, design the pitch, pore size and wall thickness of the honeycomb catalyst according to the table below to obtain the catalyst specifications in different areas:

2. The method for designing SCR catalyst specifications for coal-fired power plants considering uneven fly ash distribution according to claim 1, characterized in that: In step (2), boundary conditions are set according to the design parameters of the SCR denitrification device, and CFD simulation software is used to perform gas-solid two-phase flow simulation calculations in the SCR denitrification device. During the simulation calculation, several groups of representative particle sizes are selected to perform full-particle size simulation calculations to obtain the concentration distribution law of fly ash with different particle sizes in the SCR reactor. The representative particle size is set according to the fly ash particle size distribution measurement results.

3. The method for designing SCR catalyst specifications for coal-fired power plants considering uneven fly ash distribution according to claim 2, characterized in that: The boundary conditions are set according to the flue gas volume, composition, temperature, fly ash concentration and particle size distribution in the SCR denitrification device design parameters.

4. The method for designing SCR catalyst specifications for a coal-fired power plant considering uneven fly ash distribution according to claim 1, characterized in that: In step (5), the converted concentration of full-size fly ash at the upstream section of the top catalyst is ∑w i The larger it is, the larger the pore size, pitch and wall thickness of the honeycomb catalyst.

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