A method for optimizing and adjusting ammonia injection in a W-type boiler SCR denitrification system

Abstract

The present invention relates to a W-type boiler SCR denitrification system ammonia injection optimization adjustment method, which can effectively solve the problem that conventional ammonia injection optimization adjustment test cannot adapt to the denitrification system NO under different load conditions of the W-type boiler. x The problem of distribution change is solved, which makes up for the defect that the conventional ammonia injection optimization adjustment method cannot take into account the different load conditions of W-type flame boilers, and can achieve full-load ammonia injection optimization effect, which can effectively reduce the NH3 / NO x The relative deviation of molar ratio can significantly reduce the amount of ammonia slip in the system, solve or alleviate the air preheater blockage problem of coal-fired units caused by high ammonia slip at the reactor outlet. x The combination of coal mills with similar distribution provides power generation company operators with a NOx removal system. x Improve the W-type flame boiler SCR denitrification outlet DCS about NO x The representativeness of the measuring points ensures the economical and stable operation of the unit.

Description

Technical Field

[0001] The invention belongs to the technical field of atmospheric pollutant control emitted by coal-fired boilers, and in particular to a method for optimizing and adjusting ammonia injection of a W-type boiler SCR denitration system. Background Art

[0002] Selective catalytic reduction (SCR) flue gas denitrification technology is currently the main process for removing nitrogen oxides in large power plants. The SCR system is a multi-nozzle adjustable flow ammonia injection grid system (AIG). The denitrification AIG grid is arranged as follows: there are several ammonia injection branch pipes in the single-side SCR inlet flue, each branch pipe is equipped with a manual regulating valve, which can independently control the ammonia injection amount of a region. Ammonia injection zone leveling valves and ammonia injection zone small main pipes are installed between the ammonia injection main pipe and the ammonia injection branch pipes. By real-time measurement of NO at the outlet of each zone, the ammonia injection zone leveling valves and ammonia injection zone small main pipes are installed. x The ammonia injection leveling valve of each zone is automatically adjusted to distribute the ammonia injection amount of each zone, thereby achieving ammonia injection in each zone. The optimization of ammonia injection of each ammonia injection branch pipe is mainly based on the SCR outlet NO x This is achieved by adjusting the opening of the manual regulating valve on each ammonia supply branch pipe according to the distribution situation.

[0003] Denitrification AIG layout Figure 1 In actual operation, the blockage of some nozzles or the displacement of the butterfly valve opening will change the ammonia flow distribution, and the air flow in the tail flue is complex, and the secondary separation of large fly ash particles is serious. The flow velocity distribution of the flue gas at the reactor catalyst inlet interface, the fly ash concentration and the cross-section of the ammonia injection device have great deviations, resulting in a large difference between the actual ammonia injection amount and the NO in the flue gas. x There is a serious mismatch between the amount of ammonia sprayed and the amount of removal required. x Ultra-low emissions require regular high-quality AIG ammonia injection flow distribution optimization adjustment tests, that is, according to the NO x The actual ammonia injection amount of each ammonia injection branch pipe of the SCR system is adjusted accordingly.

[0004] At present, the conventional ammonia injection optimization adjustment test first selects the most commonly used load condition of the unit as the "priority load adjustment condition" to test the flue gas flow rate, NO x concentration, NH3 / NO x Mole ratio and other flue gas parameter distribution characteristics, reactor inlet, outlet, NO x Based on the concentration distribution characteristics, the flow rate of each ammonia injection branch is continuously adjusted until the SCR outlet NO x The concentration distribution is relatively uniform. The adjustment results are then verified under other load conditions, and fine-tuned according to the situation to determine the optimal adjustment plan that can take into account all load conditions.

[0005] With the rapid growth of installed capacity of renewable energy power generation, it is a general trend for thermal power units to frequently participate in load peak regulation. Power station boilers have a variety of mill combination operation modes under different loads. Actual tests show that the above adjustment method is suitable for most four-corner tangential circle and front and rear wall counter-fired boilers. However, due to the different furnace structures and combustion organization modes of W-type flame boilers, different mill combination operation modes are used. x The concentration distribution is very different, and even the distribution pattern is completely opposite. The use of conventional adjustment methods may cause low NO under partial load after adjustment. x The phenomenon of lower ammonia slip is higher. Higher ammonia slip rates will significantly increase the risk of corrosion and blockage in subsequent air preheaters and dust collectors, reducing the safety of system operation. Therefore, improvement and innovation are imperative. Summary of the Invention

[0006] In view of the above situation, in order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a W-type boiler SCR denitrification system ammonia injection optimization adjustment method, which can effectively solve the problem that the conventional ammonia injection optimization adjustment test cannot adapt to the denitrification system NO under different load conditions of the W-type boiler. x The problem of distribution change.

[0007] The technical solution provided by the present invention is:

[0008] A method for optimizing and adjusting ammonia injection in a W-type boiler SCR denitrification system comprises the following steps:

[0009] Step S1: Under high, medium and low loads of the boiler, various coal mill combinations are respectively used to operate, and points are arranged in the SCR inlet and outlet flues according to the grid method to test different coal mill combinations, SCR denitrification device flue gas flow rates at the inlet and outlet of the denitrification reactor under different working conditions, NO x mass concentration;

[0010] Step S2: Find the NO inlet of denitrification under different load sections x The coal mill combination with similar concentration distribution along the flue width is used as the recommended coal mill combination under different loads. After adjustment, the unit operates according to the recommended coal mill combination under different loads to achieve a set of branch valve opening optimization results that adapts to different load conditions.

[0011] Step S3: Calculate the optimal flow rate of each ammonia injection branch pipe under different loads:

[0012] Combined with the NO in the corresponding area of ​​the denitrification inlet x The optimal flow rate of each ammonia injection branch pipe under different loads is calculated based on the change in flow rate. The optimal flow rate calculation formula is as follows:

[0013]

[0014] q i =3600ω i A n

[0015] Where: q′ g，i is the optimal flow rate of a certain ammonia injection branch pipe, q i is the flue gas flow corresponding to a single ammonia injection branch pipe, NO at the corresponding measuring point x Mass concentration measurements, NO x Emission limit values, is the concentration of ammonia in the mixed gas, α is the denitrification reaction coefficient, ω i is the flue gas velocity at the corresponding measuring point, A n is the average flue flow cross-sectional area corresponding to each ammonia injection branch pipe, and β is the reaction margin coefficient;

[0016] Step S4: By adjusting the flow rate of each ammonia injection branch pipe to match the optimal flow rate, the ammonia flow rate injected into each ammonia injection port is consistent with the NO content of the original flue gas in the coverage area. x The concentration is matched to achieve the NO x The purpose of uniform distribution;

[0017] Step S5: Test the NO at each measuring point of the SCR outlet under each load after adjustment. x Concentration, calculate NO x The relative standard deviation (RSD) of the mass concentration distribution is calculated as follows:

[0018]

[0019]

[0020] Where: SCR outlet plane NO x The average mass concentration of n is the total number of measurement points distributed according to the grid method, x i NO is the measuring point location x mass concentration;

[0021] If the relative standard deviation (RSD) is less than 20%, proceed to the next step;

[0022] If the relative standard deviation RSD is greater than 20%, then according to the current denitrification outlet flue cross section NO x The distribution law of the ammonia injection branch pipe is locally adjusted. The specific method is as follows:

[0023] Select the local NO at the denitrification outlet x Adjust the manual valve of the ammonia injection branch pipe corresponding to the position where the concentration value deviates the most from the average concentration value.x When the mass concentration value is greater than the average mass concentration value, increase the valve opening; when the local NO x When the mass concentration value is less than the average mass concentration value, reduce the valve opening, adjust the valve opening by 5% each time, and re-measure the NO at each measuring point of the SCR outlet. x Concentration distribution, recalculation of NO x Relative standard deviation of mass concentration distribution, until the relative standard deviation is less than 20%;

[0024] Step S6: Observe the NO at the CEMS measuring points at the SCR outlet and the desulfurization outlet. x Check whether there is a positive or negative fluctuation between mass concentrations. If the deviation is less than 10%, the optimization adjustment of ammonia injection of the denitrification system is completed;

[0025] If the deviation is greater than 10%, adjust the ammonia injection branch flow corresponding to the SCR outlet CEMS measuring point. The specific method is as follows:

[0026] The SCR outlet CEMS measuring point should be set to NO x The mass concentration is as close as possible to the average concentration value of the outlet section to improve the representativeness of the CEMS measuring point. The ammonia injection branch valve corresponding to the CEMS measuring point is selected and the valve opening amplitude is adjusted by 5% each time. When the CEMS measuring point NO x When the mass concentration value is greater than the average mass concentration value, increase the valve opening of the corresponding ammonia injection branch pipe; when the local NO x When the mass concentration value is less than the average mass concentration value, reduce the valve opening until the deviation is less than 10%.

[0027] Preferably, the step S2 finds the denitrification inlet NO under different load sections. x The specific method of combining pulverizers with similar concentration distribution along the flue width is as follows:

[0028] Due to the different load sections, the denitrification inlet NO x The mass concentration levels vary greatly. In specific implementation, the number of each measuring hole and the NO x The slope of the linear regression equation of mass concentration data is determined. When the slopes of the linear regression equations on both sides of A and B are the same in positive and negative directions under different working conditions, it is determined that NO x The concentration distribution is similar, and the calculation and judgment are made by substituting it into the following formula:

[0029]

[0030]

[0031]

[0032] Where: m is the number of measuring holes, b is the number of each measuring hole and NO x The slope of the linear regression equation of mass concentration data, i is the number of the measuring well, The NO of the measuring hole position number i x mass concentration;

[0033] The definition of the linear regression equation slopes on both sides A and B being the same under different working conditions is: Under the same working conditions of the coal mill combination, the data of the linear regression equation slopes on both sides A and B are compared. If both are positive or negative, it is judged that NO x The concentration distribution is similar, otherwise it is judged to be dissimilar; for example, under low load, if the slope of the coal mill combination mode A side is positive and the slope of the coal mill combination mode B side is also positive, then the coal mill combination mode NO x The concentration distribution is similar; if the slope of the coal mill combination mode A is positive and the slope of the coal mill combination mode B is negative, then the coal mill combination mode NO x The concentration distributions are not similar.

[0034] Preferably, the specific method of adjusting the flow rate of each ammonia injection branch pipe to match the optimal flow item in step S2 is:

[0035] Record the valve opening of each ammonia injection branch pipe, and adjust the valve opening of each ammonia injection branch pipe to the valve opening corresponding to the optimal flow rate according to the ammonia injection flow rate corresponding to each opening in the valve flow characteristic curve. To avoid excessive valve adjustment resulting in low branch flow rate, causing problems such as urea crystallization blockage in the branch pipe and dust accumulation blockage at the nozzle, if the valve opening corresponding to the optimal flow rate is less than 25%, adjust it to 25%.

[0036] Preferably, the denitration reaction coefficient α in step S3 is 3.53.

[0037] Preferably, the reaction margin coefficient β in step S3 takes a value of 1.15.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) The patent of this invention makes up for the defect that the conventional ammonia injection optimization adjustment method cannot take into account the different load conditions of W-type flame boilers, and can achieve the full load ammonia injection optimization effect, which can effectively reduce the NH3 / NO3 ratio at the reactor inlet. x The relative deviation of the molar ratio significantly reduces the amount of ammonia slip in the system, solving or alleviating the air preheater blockage problem caused by high ammonia slip at the reactor outlet in current coal-fired units;

[0040] (2) This method can obtain the NO inlet and outlet of denitrification under each load section. x The combination of coal mills with similar distribution provides power generation company operators with a NOx removal system. xIt provides a basis for operational adjustments.

[0041] (3) After optimization and adjustment using this method, the DCS of the SCR denitrification outlet of the W-type flame boiler can be improved. x The representativeness of the measuring point partially eliminates the DCS's NO x The positive and inverted problems between the measuring points and the CMES measuring points are solved to ensure the economic and stable operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the layout of a multi-nozzle adjustable flow ammonia spray grid system.

[0043] Figure 2 This is a flowchart of the optimization and adjustment method of the present invention.

[0044] Figure 3 This is a schematic diagram of the arrangement of denitrification inlet measurement points in an application example of the present invention.

[0045] Figure 4 The denitrification inlet NO of 150MW and 240MW working conditions is adjusted by traditional method in the application example of the present invention. X Mean distribution plot.

[0046] Figure 5 The application example of this invention adopts the traditional method to adjust the 150MW and 240MW working conditions of denitrification outlet NO X Mean distribution plot.

[0047] Figure 6 This is an application example of the present invention. When the AD coal mill is running at low load, the denitrification inlet NO x The denitrification inlet NO of distributed and medium load BCD coal mill is running x Mean distribution plot.

[0048] Figure 7 This is an application example of the present invention. When the AD coal mill is running at low load, the denitrification outlet NO x The NO2 content of the denitrification outlet of the distributed and medium-load BCD coal mill is x Mean distribution plot.

[0049] Figure 8 This is the characteristic curve of the manual valve of the ammonia injection branch pipe in the application example of the present invention.

[0050] Figure 9 For the application example A of the present invention, the denitrification outlet NO before and after adjustment is x Distribution comparison.

[0051] Figure 10 For the application example B of the present invention, the NO2 of the denitrification outlet is adjusted before and after x Distribution comparison. DETAILED DESCRIPTION

[0052] The specific implementation of the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0053] Boiler No. 3 at a power generation company is a subcritical, single-stage reheat, natural circulation boiler manufactured by Dongfang Boiler (Group) Co., Ltd. It features a double-arched single furnace with burners located on the front and rear arches of the lower furnace. It employs a "W" flame combustion method, a double flue at the rear, uses baffles to regulate the reheat steam temperature, and features solid slag removal. The boiler is all-steel, fully suspended, and has balanced ventilation. It is located outdoors. The model number is DG1025 / 18.2-II14. It utilizes a positive pressure, direct-blowing pulverizing system and four BBD3854 series double-inlet, double-outlet coal mills manufactured by Shenyang Heavy Machinery Plant.

[0054] The denitrification system is divided into two flues, A / B, and the denitrification inlet measuring point is on the vertical flue at the inlet. Five measuring holes are arranged on each flue, and the measuring holes are numbered from side A to side B as A1 to A5 on side A; and B1 to B5 on side B. Three measuring points are arranged in each measuring hole, and are numbered 1, 2, and 3 from shallow to deep. The schematic diagram of the denitrification inlet measuring point arrangement is as follows: Figure 3 shown.

[0055] Denitrification outlet measurement points are located on the horizontal flue at the denitrification system outlet and air preheater inlet, divided into two flues, A and B. Seven measurement holes are located on each flue, numbered from side A to side B: A1 to A7 on side A; B1 to B7 on side B. Three measurement points are located in each measurement hole, numbered 1, 2, and 3 from shallow to deep along the depth of the hole.

[0056] During the ammonia injection optimization test, it was found that the denitrification inlet and outlet NO x The distribution pattern is completely opposite (such as Figure 4 、 5 As shown), after optimizing and adjusting the ammonia injection valve according to a certain load, the NO at the denitrification outlet under another load x The distribution will show a phenomenon of lower low points and higher local ammonia escape rate. The traditional ammonia injection optimization adjustment test method cannot simultaneously meet the NO2 content of the denitrification outlet under different loads. x Evenly distributed adjustment targets.

[0057] Adjustment is performed by the method of the present invention:

[0058] (1) Measurement of NO in the denitrification inlet under different coal mill combinations X Distribution, find out the combined operation modes of coal mills with similar NOx distribution at the denitrification inlet under each load section.

[0059] Due to load limitations, only the denitrification inlet NO was tested at different mill combinations under medium and low loads. XThrough the test data, it is found that under the combination of AD, BD, BC coal mills at low load and ACD, BCD coal mills at medium load, the denitrification inlet NO X The distribution is similar. It is recommended that the operation mode of the coal mill should strictly follow these five combinations.

[0060] Since there are many possible combinations of coal mills, the test data will not be listed one by one. X The denitrification inlet NO of distributed and medium load BCD coal mill is running X The distribution is described (e.g. Figure 6 、 7 shown).

[0061] (2) Calculate the optimal flow rate of each ammonia injection branch under different loads

[0062] There are 6 valves on one side of the ammonia injection grid of the denitrification system, which control 6 areas in the width direction. Each manual door can only control the NO in the corresponding area in the width direction. X concentration, but cannot control the NO concentration in the corresponding area along the depth direction. X Concentration: the valve groups on the A side are numbered A1 to A6 from A to B, and the valve groups on the B side are numbered B1 to B6 from A to B.

[0063]

[0064] q i =3600ω i A n

[0065] Taking 240MW operating conditions as an example, the optimal ammonia injection rate of the ammonia injection branch pipe controlled by 12 manual valves is calculated according to the formula as follows:

[0066] Table 1 Optimal ammonia injection flow rate of each ammonia injection branch pipe under 240MW operating conditions

[0067]

[0068] (3) Adjust the opening of the manual valve of the ammonia spray grid

[0069] The characteristic curve of the manual valve of the ammonia injection branch is as follows Figure 8 As shown in the table below, the adjustment of the manual ammonia injection door before and after optimization is shown in the table below:

[0070] Table 2 Manual door position data before and after adjustment of ammonia injection branch pipe

[0071]

[0072]

[0073] (4) Measure the NO at the denitrification outlet under various loads x distributed

[0074] The NO at the denitrification outlet under various working conditions before and after optimization adjustment x Compare the distribution field and compare NO x The distribution trend along the width of the flue (single hole average) is as follows Figure 9 、 10 As shown:

[0075] (5) Evaluation of optimization and adjustment results

[0076] The NO2 content of the denitrification outlet cross section under various working conditions before and after optimization adjustment X The relative standard deviation of the distribution is compared, and the SCR outlet NO under each load condition after adjustment is X The relative standard deviation of concentration is less than 20%, and the NO X The concentration deviation was less than 10%, achieving the adjustment target. Furthermore, the ammonia slip rates on both sides A and B decreased significantly after the adjustment, and urea consumption decreased by 24.1% before and after the adjustment (as shown in the table below).

[0077] Table 3 Relative standard deviation values ​​under various working conditions before and after adjustment

[0078] Working conditions unit A-side relative standard deviation B-side relative standard deviation 240MW original operating conditions ％ 107.4 42.8 150MW original working conditions ％ 136.9 48.6 240MW adjusted operating conditions ％ 14.6 16.1 150MW adjusted operating conditions ％ 12.9 17.2

[0079] Table 4 Comparison of 240MW measured SCR outlet and CEMS indication values

[0080]

[0081] Table 5 Ammonia slip rate and urea demand before and after adjustment of 240MW

[0082]

[0083]

Claims

1. A W-type boiler SCR denitrification system ammonia injection optimization adjustment method, characterized in that: The following steps are involved: Step S1: Under high, medium and low loads of the boiler, various coal mill combinations are respectively used to operate, and points are arranged in the SCR inlet and outlet flues according to the grid method to test different coal mill combinations, SCR denitrification device flue gas flow rates at the inlet and outlet of the denitrification reactor under different working conditions, NO x mass concentration; Step S2: Find the NO inlet of denitrification under different load sections x The coal mill combination with similar concentration distribution along the flue width is used as the recommended coal mill combination under different loads. After adjustment, the unit operates according to the recommended coal mill combination under different loads to achieve a set of branch valve opening optimization results that adapts to different load conditions. Step S3: Calculate the optimal flow rate of each ammonia injection branch pipe under different loads: Combined with the NO in the corresponding area of ​​the denitrification inlet x The optimal flow rate of each ammonia injection branch pipe under different loads is calculated based on the change in flow rate. The optimal flow rate calculation formula is as follows: in: is the optimal flow rate of a certain ammonia injection branch pipe, is the flue gas flow corresponding to a single ammonia injection branch pipe, The corresponding measuring point is NO x Mass concentration measurements, NO x Emission limit values, is the concentration of ammonia in the mixed gas, is the denitrification reaction coefficient, is the flue gas velocity at the corresponding measuring point, is the average flue flow cross-sectional area corresponding to each ammonia injection branch pipe, is the reaction margin coefficient; Step S4: By adjusting the flow rate of each ammonia injection branch pipe to match the optimal flow rate, the ammonia flow rate injected into each ammonia injection port is consistent with the NO content of the original flue gas in the coverage area. x The concentration is matched to achieve the NO x The purpose of uniform distribution; Step S5: Test the NO at each measuring point of the SCR outlet under each load after adjustment. x Concentration, calculate NO x The relative standard deviation (RSD) of the mass concentration distribution is calculated as follows: Where: SCR outlet plane NO x The average mass concentration of n is the total number of measurement points distributed by the grid method, x i NO is the measuring point location x mass concentration; If the relative standard deviation RSD is less than 20%, proceed to the next step; If the relative standard deviation RSD is greater than 20%, then according to the current denitrification outlet flue cross section NO x The distribution law of the ammonia injection branch pipe is locally adjusted. The specific method is as follows: Select the local NO at the denitrification outlet x Adjust the manual valve of the ammonia injection branch pipe corresponding to the position where the concentration value deviates the most from the average concentration value. x When the mass concentration value is greater than the average mass concentration value, increase the valve opening; when the local NO x When the mass concentration value is less than the average mass concentration value, reduce the valve opening, adjust the valve opening by 5% each time, and re-measure the NO at each measuring point of the SCR outlet. x Concentration distribution, recalculation of NO x Relative standard deviation of mass concentration distribution, until the relative standard deviation is less than 20%; Step S6: Observe the NO at the CEMS measuring points at the SCR outlet and the desulfurization outlet. x Check whether there is a positive or negative fluctuation between mass concentrations. If the deviation is less than 10%, the optimization adjustment of ammonia injection in the denitrification system is completed. If the deviation is greater than 10%, adjust the ammonia injection branch flow corresponding to the SCR outlet CEMS measuring point. The specific method is as follows: The SCR outlet CEMS measuring point should be set to NO x The mass concentration is as close as possible to the average concentration value of the outlet section to improve the representativeness of the CEMS measuring point. The ammonia injection branch valve corresponding to the CEMS measuring point is selected and the valve opening amplitude is adjusted by 5% each time. When the CEMS measuring point NO x When the mass concentration value is greater than the average mass concentration value, increase the valve opening of the corresponding ammonia injection branch pipe; when the local NO x When the mass concentration value is less than the average mass concentration value, reduce the valve opening until the deviation is less than 10%.

2. The W-type boiler SCR denitrification system ammonia injection optimization adjustment method according to claim 1 is characterized in that: The step S2 finds the denitrification inlet NO under different load sections. x The specific method of combining pulverizers with similar concentration distribution along the flue width is as follows: The number of each measuring hole and NO in different coal mill combinations under this working condition x The slope of the linear regression equation of mass concentration data is determined. When the slopes of the linear regression equations on both sides of A and B are the same in positive and negative directions under different working conditions, it is determined that NO x The concentration distribution is similar, and the calculation and judgment are made by substituting it into the following formula: Where: m is the number of measuring holes, b Number each measuring hole with NO x The slope of the linear regression equation for mass concentration data, i is the number of the measuring hole, Number i NO of hole position x Mass concentration.

3. The W-type boiler SCR denitrification system ammonia injection optimization adjustment method according to claim 1 is characterized in that: The specific method of adjusting the flow rate of each ammonia injection branch pipe to match the optimal flow rate in step S2 is: Record the valve opening of each ammonia injection branch pipe, and adjust the valve opening of each ammonia injection branch pipe to the valve opening corresponding to the optimal flow rate according to the ammonia injection flow rate corresponding to each opening in the valve flow characteristic curve.

4. The W-type boiler SCR denitrification system ammonia injection optimization adjustment method according to claim 1 is characterized in that: The denitrification reaction coefficient in step S3 The value is 3.

53.

5. The W-type boiler SCR denitrification system ammonia injection optimization adjustment method according to claim 1, characterized in that: The reaction margin coefficient in step S3 The value is 1.15.

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