SCR denitration ammonia injection grid cold state debugging method

Abstract

The application discloses a kind of SCR denitration ammonia injection grid cold-state debugging methods, comprising the following steps: in the entrance flue of SCR denitration device arrangement ammonia injection branch pipe array, each ammonia injection branch pipe is equipped with a regulating valve, each regulating valve downstream is equipped with throttle orifice plate differential pressure measuring device;Calculate the flow velocity distribution of ammonia injection grid upstream section, the proportion of each area flue gas flow in total flow is counted;In the unit shutdown state, the corresponding flow characteristic curve of each regulating valve is calculated;The theoretical orifice plate differential pressure value of different area regulating valve is calculated;The initial opening of each regulating valve is calculated.The SCR denitration ammonia injection grid cold-state debugging method provided by the application is to optimize and adjust the opening of the regulating valve of ammonia injection grid in the unit shutdown state, which can improve the uniformity of NOx concentration distribution at the outlet of SCR denitration device after the unit starts, reduce the local ammonia escape concentration and reduce the risk of ammonium bisulfate plugging of denitration downstream equipment.

Description

Technical Field

[0001] This invention belongs to the field of SCR denitrification technology, specifically relating to a cold-state commissioning method for an SCR denitrification ammonia injection grid. Background Technology

[0002] Selective catalytic reduction (SCR) flue gas denitrification technology is currently the main process for removing nitrogen oxides in large power plants. During generator unit operation, fly ash blockage, erosion, or ammonium bisulfate blockage can affect the local catalyst activity at the cross-section of the SCR reactor. Blockage of some nozzles in the ammonia injection grille (AIG) or displacement of the butterfly valve opening can change the ammonia flow distribution. Changes in boiler combustion or deformation of the guide plate can cause changes in the flue gas velocity and NOx distribution upstream of the AIG. These factors combined affect the uniformity of the NH3 / NO molar ratio distribution in the flue gas at the denitrification inlet, which will increase the local ammonia slip concentration at the reactor outlet and reduce the overall performance of the denitrification unit. Therefore, it is necessary to conduct regular optimization and adjustment tests on the AIG ammonia injection flow distribution.

[0003] Currently, ammonia injection grid AIGs generally adopt a layout in which grid branches are arranged along the width and depth of the flue. The conventional method for optimizing and adjusting ammonia injection is to test the NOx concentration at the SCR inlet and outlet point by point during unit operation, adjust the flow rate of each branch according to the test data, and repeat the above process until the NOx concentration at the SCR outlet and ammonia slip are relatively uniform.

[0004] Chinese invention patent, publication number CN112705046A, discloses a method and device for fine adjustment of ammonia injection in denitrification. The method involves dividing the SCR flue into several virtual zones along its width and adjusting the valve opening of each zone according to the inlet NOx concentration and ammonia-nitrogen molar ratio of each zone.

[0005] Chinese invention patent, publication number CN105126616A, discloses an optimization method for ammonia injection in an SCR denitrification system based on weighted valve control. The method involves first measuring the flue gas flow field characteristics at the transverse section of the flue gas duct before the ammonia injection grid in the SCR denitrification system under constant load conditions; then, combining the nozzle distribution of the ammonia injection grid, analyzing the continuous flow distribution characteristics of the flue gas flow field region that matches the ammonia injection nozzle distribution; obtaining the weights of the ammonia injection valves based on the regional flow characteristics of the flue gas flow field under various load conditions; and finally, adjusting the opening degree of each valve according to the differences in valve weights.

[0006] However, the currently publicly available optimization and adjustment of SCR denitrification ammonia injection needs to be carried out under the hot and stable operating conditions of the unit. The optimization process lasts for 3 to 5 days and requires prior application for operating conditions such as test load and test coal type. Therefore, it cannot be carried out for a period of time before and after the unit starts up and is connected to the grid.

[0007] It is important to note that SCR denitrification flow field optimization will alter the flue gas velocity distribution upstream of the AIG. Maintenance or replacement of the ammonia injection grid regulating valve, as well as unclogging and clearing blockages in the ammonia injection grid pipeline, will change the ammonia flow distribution pattern. If the opening of the ammonia injection grid regulating valve is not adjusted accordingly before startup, poor AIG ammonia flow distribution after startup and before the start of hot-state commissioning will lead to uneven NOx concentration distribution at the SCR outlet. This will cause downstream denitrification equipment, such as the air preheater, to operate in an environment with high local ammonia escape concentrations for extended periods, increasing the risk of ammonium bisulfate blockage. Therefore, after SCR denitrification flow field optimization or ammonia injection grid maintenance, cold-state commissioning of the ammonia injection grid based on the flue gas flow field characteristics and the flow characteristics of the ammonia injection grid branch pipes is essential. However, currently, there is no method for cold-state commissioning of the ammonia injection grid valves during shutdown after SCR denitrification flow field optimization or ammonia injection grid maintenance. Summary of the Invention

[0008] To address the technical problems existing in the prior art, the present invention aims to provide a cold-state commissioning method for SCR denitrification ammonia injection grid, which aims to enable cold-state commissioning of the SCR denitrification ammonia injection grid while the unit is shut down, thus providing a good foundation for hot-state ammonia injection adjustment tests.

[0009] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0010] A cold commissioning method for an SCR denitrification ammonia injection grid includes the following steps:

[0011] 1) Arrange an array of ammonia injection branch pipes in the inlet flue of the SCR denitrification unit. Each ammonia injection branch pipe is equipped with a regulating valve, and a differential pressure measuring device with a throttling orifice plate is installed downstream of each regulating valve.

[0012] 2) Calculate the velocity distribution of the upstream section of the ammonia injection grid and statistically analyze the proportion of flue gas flow rate in each region of the section to the total flow rate;

[0013] 3) With the unit shut down, the flow characteristic curves corresponding to each regulating valve are calculated;

[0014] 4) Calculate the theoretical orifice plate differential pressure values ​​of the regulating valves in different zones;

[0015] 5) Calculate the initial opening degree of each regulating valve.

[0016] Furthermore, in step 1), m ammonia injection branch pipes are arranged along the width direction and n ammonia injection branch pipes are arranged along the depth direction in the inlet flue of the SCR denitrification unit to form an m×n ammonia injection branch pipe array. The partition numbering of the ammonia injection branch pipes is shown in the table below.

[0017] Table 1

[0018]

[0019] Furthermore, in step 2), the SCR denitrification flue is modeled based on the SCR denitrification flue and its internal flow guidance and mixing diagrams. By inputting the corresponding process parameters through CFD numerical simulation software, the velocity distribution of the upstream section of the ammonia injection grid is calculated, and the proportion of flue gas flow in each region of the section to the total flow is statistically analyzed.

[0020] Furthermore, in step 3), the step of calculating the flow characteristic curves corresponding to each regulating valve while the unit is shut down includes:

[0021] With the unit shut down, start the dilution fan, and open each regulating valve from 0 to 90° to the same initial opening value.

[0022] Close the opening of the first regulating valve from its initial value to a certain value, record the orifice plate differential pressure, then increase the opening gradually, recording the corresponding orifice plate differential pressure each time the opening is adjusted, until the opening reaches 90°, then restore the opening of the first regulating valve to its initial value; repeat the above operation for the remaining regulating valves in sequence.

[0023] Finally, the orifice differential pressure data corresponding to each opening degree of each regulating valve are summarized to obtain the flow characteristic curve and fitting formula for each regulating valve.

[0024] Furthermore, the flow characteristic curve is based on the valve opening degree. x The differential pressure between the shaft and the orifice plate is y Axis established x - y The coordinate system, the flow characteristic curves and fitting formulas of different regulating valves are all different, and the flow characteristic curves of different regulating valves are all power function curves.

[0025] Furthermore, in step 3), the formulas for calculating the orifice plate differential pressure and flow rate are as follows:

[0026]

[0027] in, q m This is the instantaneous mass flow rate, expressed in kg / s. The outflow coefficient is dimensionless. β It is the diameter ratio. β = d / D ; D This is the inner diameter of the pipe, in mm. d The diameter of the opening is in mm; ε The coefficient of expansion; △p The measured value of the orifice plate differential pressure is expressed in Pa. ρThe fluid density on the plane of the pressure tap at the positive end of the throttling device, in kg / m³. 3 This formula shows that the differential pressure of a flow-throttling orifice plate of the same type is proportional to the square of the flow rate.

[0028] Furthermore, in step 4), the formula for calculating the theoretical orifice plate differential pressure value of the regulating valves in different zones is as follows:

[0029]

[0030] in, Differential pressure is calculated in Pa. △p The measured value of the orifice plate differential pressure is expressed in Pa. k This represents the proportion of traffic in each partition to the total traffic, calculated based on CFD.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention discloses a cold-state commissioning method for an SCR denitrification ammonia injection grid, comprising the following steps: While the unit is shut down, the flow characteristic curves of the regulating valves corresponding to each ammonia injection branch are obtained by testing the differential pressure data of orifice plates with different openings. The flow field of the denitrification process is simulated using CFD to obtain the velocity distribution characteristics of the flue gas upstream of the ammonia injection grid, thereby calculating the initial opening of the regulating valves corresponding to each ammonia injection branch. This invention optimizes and adjusts the opening of the regulating valves of the ammonia injection grid before startup, which can improve the uniformity of NOx concentration distribution at the outlet of the SCR denitrification unit after unit startup, reduce local ammonia escape concentration, and reduce the risk of ammonium bisulfate blockage in downstream denitrification equipment. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the ammonia injection grid arrangement in Embodiment 1 of the present invention;

[0034] Figure 2 This is a simulation diagram of the flow velocity distribution at the upstream section of the ammonia injection grid in Embodiment 1 of the present invention;

[0035] Figure 3 The flow characteristic curve of regulating valve 1-a in Embodiment 1 of the present invention;

[0036] Figure 4 The flow characteristic curve of the regulating valve 2-a in Embodiment 1 of the present invention;

[0037] Figure 5 The flow characteristic curve of the regulating valve 3-a in Embodiment 1 of the present invention;

[0038] Figure 6 The flow characteristic curve of the regulating valve 4-a in Embodiment 1 of the present invention;

[0039] Figure 7The flow characteristic curve of the regulating valve 5-a in Embodiment 1 of the present invention;

[0040] Figure 8 The flow characteristic curve of the regulating valve 6-a in Embodiment 1 of the present invention;

[0041] Figure 9 The flow characteristic curve of the regulating valve 7-a in Embodiment 1 of the present invention;

[0042] Figure 10 The flow characteristic curve of regulating valve 1-b in Embodiment 1 of the present invention;

[0043] Figure 11 The flow characteristic curve of the regulating valve 2-b in Embodiment 1 of the present invention;

[0044] Figure 12 The flow characteristic curve of the regulating valve 3-b in Embodiment 1 of the present invention;

[0045] Figure 13 The flow characteristic curve of the regulating valve 4-b in Embodiment 1 of the present invention;

[0046] Figure 14 The flow characteristic curve of the regulating valve 5-b in Embodiment 1 of the present invention;

[0047] Figure 15 The flow characteristic curve of the regulating valve 6-b in Embodiment 1 of the present invention;

[0048] Figure 16 The flow characteristic curve of the regulating valve 5-b in Embodiment 1 of the present invention;

[0049] Figure 17 The flow characteristic curve of the regulating valve 1-c in Embodiment 1 of the present invention;

[0050] Figure 18 The flow characteristic curve of the regulating valve 2-c in Embodiment 1 of the present invention;

[0051] Figure 19 The flow characteristic curve of the regulating valve 3-c in Embodiment 1 of the present invention;

[0052] Figure 20 The flow characteristic curve of the regulating valve 4-c in Embodiment 1 of the present invention;

[0053] Figure 21 The flow characteristic curve of the regulating valve 5-c in Embodiment 1 of the present invention;

[0054] Figure 22 The flow characteristic curve of the regulating valve 6-c in Embodiment 1 of the present invention;

[0055] Figure 23 The flow characteristic curve of the regulating valve 7-c in Embodiment 1 of the present invention;

[0056] Figure 24 The flow characteristic curve of regulating valve 1-d in Embodiment 1 of the present invention;

[0057] Figure 25 The flow characteristic curve of regulating valve 2-d in Embodiment 1 of the present invention;

[0058] Figure 26 The flow characteristic curve of the regulating valve 3-d in Embodiment 1 of the present invention;

[0059] Figure 27 The flow characteristic curve of the regulating valve 4-d in Embodiment 1 of the present invention;

[0060] Figure 28 The flow characteristic curve of the regulating valve 5-d in Embodiment 1 of the present invention;

[0061] Figure 29 The flow characteristic curve of the regulating valve 6-d in Embodiment 1 of the present invention;

[0062] Figure 30 This is the flow characteristic curve of the regulating valve 7-d in Embodiment 1 of the present invention. Detailed Implementation

[0063] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0064] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive 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 to prepare for the more detailed descriptions that follow.

[0065] A cold commissioning method for an SCR denitrification ammonia injection grid includes the following steps:

[0066] 1) Several ammonia injection branch pipes are arranged along the width and depth directions in the inlet flue of the SCR denitrification unit. Each ammonia injection branch pipe is equipped with a regulating valve. The flow rate of the ammonia injection branch pipe is controlled by changing the opening of the regulating valve. A differential pressure measuring device (mainly a differential pressure orifice plate flow meter) is installed downstream of each regulating valve. Specifically, an m×n ammonia injection branch pipe array is arranged in the inlet flue of the SCR denitrification unit, with m ammonia injection branch pipes arranged along the width direction and n ammonia injection branch pipes arranged along the depth direction. The upstream section of the ammonia injection grid is divided into m×n regions along the width and depth, and the region numbering is shown in Table 1.

[0067] Table 1

[0068]

[0069] 2) Model the SCR denitrification flue based on the SCR denitrification flue and its internal flow guidance and mixing drawings. Using CFD numerical simulation software, input parameters such as design flue gas volume and flue gas temperature to calculate the velocity distribution of the upstream section of the ammonia injection grid and statistically analyze the proportion of flue gas flow in each region of the section to the total flow.

[0070] 3) With the unit shut down, start the dilution fan to ensure fluid flow through the ammonia injection grille, facilitating differential pressure measurement of each branch pipe once flow is established. The manual control valves for the ammonia injection grille have an opening range of 0~90° (0° is closed, 90° is fully open). All valves should be opened to a uniform initial opening value, which can be 70° or 60°, allowing for some adjustment space. Assuming there are N control valves in the ammonia injection grille (N=m×n), sort all valves according to a certain pattern. Close the first control valve to a certain opening, such as 20°, and record the orifice differential pressure using an orifice differential pressure measuring device. Then increase the opening in 10° increments, recording the corresponding orifice differential pressure each time, until the opening reaches 90°. Then restore the first control valve to its initial opening value. Repeat the above operation for the remaining control valves. By summarizing the orifice differential pressure data corresponding to each opening degree of each control valve, the flow characteristic curve and fitting formula corresponding to the control valve are obtained.

[0071] The flow rate calculation formula for a differential pressure orifice plate flow meter is as follows:

[0072]

[0073] in, q m This is the instantaneous mass flow rate, expressed in kg / s. The outflow coefficient is dimensionless. β It is the diameter ratio. β = d / D ; D This is the inner diameter of the pipe, in mm.d The diameter of the opening is in mm; ε The coefficient of expansion; △p The measured value of the orifice plate differential pressure is expressed in Pa. ρ The fluid density on the plane of the pressure tap at the positive end of the throttling device, in kg / m³. 3 This formula shows that the differential pressure of a flow-throttling orifice plate of the same type is proportional to the square of the flow rate;

[0074] 4) Calculate the theoretical orifice plate differential pressure value for each zone. The calculation formula is as follows:

[0075]

[0076] in, Differential pressure is calculated in Pa. △p The measured differential pressure of the orifice plate is expressed in Pa. k This represents the proportion of traffic in each partition to the total traffic, calculated based on CFD.

[0077] 5) The initial opening degree of each regulating valve is obtained by fitting the formula of the regulating valve of each zone.

[0078] Example 1

[0079] like Figure 1-30 As shown, a 7×4 ammonia injection branch pipe array is arranged in the inlet flue of the SCR denitrification unit. Specifically, 7 ammonia injection branch pipes are arranged along the width direction of the inlet flue of the SCR denitrification unit, and 4 ammonia injection branch pipes (numbered a, b, c, d) are arranged along the depth direction of each ammonia injection branch pipe in the width direction, for a total of 28 ammonia injection branch pipes. The ammonia injection grid is arranged as follows. Figure 1 As shown, the partition numbers are listed in Table 2.

[0080] Table 2

[0081]

[0082] Based on the SCR denitrification flue gas duct and its internal flow guidance and mixing diagrams, a model of the SCR denitrification flue gas duct was created. Using CFD numerical simulation software, parameters such as the design flue gas volume and temperature were input to calculate the results. Figure 2 The velocity distribution of the upstream section of the ammonia injection grid and the proportion of flue gas flow in each region of the statistical section to the total flow are shown in Table 3.

[0083] Table 3

[0084]

[0085] With the unit shut down, start the dilution fan. The manual control valves of the ammonia injection grille, with an opening range of 0~90°, are all opened to a uniform opening. Taking 70° as an example, assuming there are N control valves in the ammonia injection grille, close the first control valve to 20° and record the orifice plate differential pressure. Then, increase the opening of the first control valve in increments of 10°, recording the corresponding orifice plate differential pressure for each adjustment, until the valve opening reaches 90°. Then, restore the opening of the first control valve to 70°. Repeat the above operation for the second control valve, and so on, until all N control valves have been operated on. Summarize the orifice plate differential pressure data corresponding to each opening of each control valve, and record the results in Table 4. Based on the orifice plate differential pressure corresponding to each opening of each control valve, derive the flow characteristic curve and fitting formula for each control valve. The flow characteristic curves of each control valve and their corresponding fitting formulas are as follows: Figure 3-30 As shown, the flow characteristic curves of different regulating valves are all power function curves, where the horizontal axis... x Valve opening degree, in degrees, ordinate. y The pressure is the orifice differential pressure, expressed in Pa. The fitting formulas for different control valves vary, and the fitting formulas for the same control valve may also differ under different test conditions.

[0086] Table 4

[0087]

[0088] The flow rate calculation formula for a differential pressure orifice plate flow meter is as follows:

[0089]

[0090] in, q m This is the instantaneous mass flow rate, expressed in kg / s. The outflow coefficient is dimensionless. β It is the diameter ratio. β = d / D ; D This is the inner diameter of the pipe, in mm. d The diameter of the opening is in mm; ε The coefficient of expansion; △p The measured value of the orifice plate differential pressure is expressed in Pa. ρ The fluid density on the plane of the pressure tap at the positive end of the throttling device, in kg / m³. 3 This formula shows that the differential pressure of a flow-throttling orifice plate of the same type is proportional to the square of the flow rate.

[0091] The measured values ​​of the orifice plate differential pressure are shown in Table 5 when all 28 regulating valves are open at 70°. The proportion of flow rate in each zone to the total flow rate, obtained from CFD numerical simulation, is shown in Table 3. The theoretical orifice plate differential pressure values ​​for each zone were calculated, and the results are shown in Table 6. The initial opening degree of each regulating valve was obtained using the fitting formula for the regulating valve in each zone, as shown in Table 7.

[0092] Table 5

[0093]

[0094] Table 6

[0095]

[0096] Table 7

[0097]

[0098] All fitted curves R 2 A value greater than 0.99 generally indicates an R-value. 2 The closer the value is to 1, the better the fit.

[0099] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0100] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A cold-state commissioning method for an SCR denitrification ammonia injection grid, characterized in that, Includes the following steps: 1) Arrange an array of ammonia injection branch pipes in the inlet flue of the SCR denitrification unit. Each ammonia injection branch pipe is equipped with a regulating valve, and a differential pressure measuring device with a throttling orifice plate is installed downstream of each regulating valve. 2) Calculate the velocity distribution of the upstream section of the ammonia injection grid and statistically analyze the proportion of flue gas flow rate to the total flow rate in each region of the section; 3) With the unit shut down, the flow characteristic curves corresponding to each regulating valve are calculated; 4) Calculate the theoretical orifice plate differential pressure values ​​of the regulating valves in different zones; 5) Calculate the initial opening degree of each regulating valve; Step 3), in which the flow characteristic curves corresponding to each regulating valve are calculated while the unit is shut down, includes the following steps: With the unit shut down, start the dilution fan, and open each regulating valve from 0 to 90° to the same initial opening value. Close the opening of the first regulating valve from its initial value to a certain value, record the orifice plate differential pressure, then increase the opening gradually, recording the corresponding orifice plate differential pressure each time the opening is adjusted, until the opening reaches 90°, then restore the opening of the first regulating valve to its initial value; repeat the above operation for the remaining regulating valves in sequence. Finally, the orifice differential pressure data corresponding to each opening degree of each regulating valve are summarized to obtain the flow characteristic curve and fitting formula for each regulating valve.

2. The cold commissioning method for an SCR denitrification ammonia injection grid according to claim 1, characterized in that, In step 1), m ammonia injection branch pipes are arranged along the width direction and n ammonia injection branch pipes are arranged along the depth direction in the inlet flue of the SCR denitrification unit to form an m×n ammonia injection branch pipe array.

3. The cold commissioning method for an SCR denitrification ammonia injection grid according to claim 1, characterized in that, In step 2), the SCR denitrification flue is modeled according to the SCR denitrification flue and its internal flow guidance and mixing drawings. The corresponding process parameters are input through CFD numerical simulation software to calculate the velocity distribution of the upstream section of the ammonia injection grid and to calculate the proportion of flue gas flow in each area of ​​the section to the total flow.

4. The cold commissioning method for an SCR denitrification ammonia injection grid according to claim 1, characterized in that, In step 3), the flow characteristic curve is based on the valve opening degree. x The differential pressure between the shaft and the orifice plate is y Axis established x - y The coordinate system, the flow characteristic curves and fitting formulas of different regulating valves are all different, and the flow characteristic curves of different regulating valves are all power function curves.

5. The cold commissioning method for an SCR denitrification ammonia injection grid according to claim 1, characterized in that, In step 3), the formulas for calculating the orifice plate differential pressure and flow rate are as follows: ； in, q m This is the instantaneous mass flow rate, expressed in kg / s. The outflow coefficient is dimensionless. β It is the diameter ratio. β = d / D ; D This is the inner diameter of the pipe, in mm. d This refers to the opening diameter, in mm. ε The coefficient of expansion; △p The measured value of the orifice plate differential pressure is expressed in Pa. ρ The fluid density on the plane of the pressure tap at the positive end of the throttling device, in kg / m³. 3 This formula shows that the differential pressure of the same type of orifice plate is proportional to the square of the flow rate.

6. The cold commissioning method for an SCR denitrification ammonia injection grid according to claim 1, characterized in that, In step 4), the formula for calculating the theoretical orifice plate differential pressure value of the regulating valves in different zones is as follows: ； in, Differential pressure is calculated in Pa. △p The measured value of the orifice plate differential pressure is expressed in Pa. k This represents the proportion of traffic in each partition to the total traffic, calculated based on CFD.

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