Flue gas denitrification ammonia injection mixing system and ammonia injection control method

Abstract

This invention discloses a flue gas denitrification ammonia injection mixing system, comprising: an ammonia injection assembly, which includes: a main pipe with a main flow regulating valve and an auxiliary flow regulating valve connected in parallel thereon, the maximum flow rate of the auxiliary flow regulating valve being less than or equal to 30% of the maximum flow rate of the main flow regulating valve; multiple branch pipes connected to the main pipe, each branch pipe being equipped with a branch pipe flow regulating valve; multiple nozzles, each connected to one of the branch pipes; and a static mixing assembly located downstream of the ammonia injection assembly. This invention also discloses an ammonia injection control method. This invention uses a fixed outlet NO... x The total ammonia usage in the SCR denitrification reaction is controlled by a content control method. When the outlet NO x Concentration exceeding export NO x When the concentration reaches the upper limit, the main flow control valve remains stationary, while the auxiliary flow control valve is used to increase the ammonia flow rate. The ammonia flow rate of the auxiliary flow control valve is much lower than that of the main flow control valve. When the limit is exceeded, the ammonia flow rate is gradually increased in small amounts to prevent ammonia escape from increasing significantly and to improve the accuracy of ammonia injection control.

Description

Technical Field

[0001] This invention relates to the field of flue gas denitrification technology, and in particular to a flue gas denitrification ammonia injection mixing system and ammonia injection control method thereof. Background Technology

[0002] Currently, the most widely used flue gas denitrification method is selective catalytic reduction (SCR) denitrification technology. The main principle of SCR denitrification technology is to inject ammonia (NH3) as a reducing agent into flue gas at 280℃~420℃ and mix it evenly. Under the action of the denitrification catalyst, the ammonia removes nitrogen oxides (NOx) from the flue gas. x The mixture is reduced to non-toxic and non-polluting nitrogen and water, thereby achieving the removal of NO from the mixed gas. x The purpose is to achieve the following main reactions in SCR denitrification technology:

[0003] NO + NO₂ + 2NH₃ → 2N₂ + 3H₂O

[0004] 4NO + 4NH3 + O2 → 4N2 + 6H2O

[0005] For flue gas SCR denitrification technology, denitrification efficiency and ammonia slip are two core performance indicators. Controlling the ammonia injection flow rate is crucial for achieving high-efficiency denitrification. If the ammonia injection rate is lower than the denitrification requirement, the denitrification reaction will be incomplete, leading to NO2 buildup. x Emissions exceed standards; if the amount of ammonia injected exceeds the denitrification requirement, the excess ammonia that does not participate in the denitrification reaction will enter the flue gas and cause ammonia escape. Ammonia will react with sulfur trioxide (SO3) in the flue gas to form adhesive ammonium bisulfate (NH4HSO4), which will cause severe blockage or corrosion leakage of equipment such as air preheater or economizer at the downstream of the SCR reactor. If a sodium alkali wet desulfurization device is subsequently used, the ammonia nitrogen content in the desulfurization wastewater will also exceed the standard significantly. If limestone (lime)-gypsum wet flue gas desulfurization is used, the gypsum products produced will have an irritating odor, resulting in the gypsum products being unqualified.

[0006] To meet relevant environmental protection requirements, companies typically discharge NO into their flue gas. x The concentration is monitored dynamically in real time, but ammonia slip values ​​are not yet included in the monitoring scope. This method is used to control NO in the exhaust gas. x Concentration, when flue gas NO x The emission standard is 100 mg / m³ 3 When the ammonia-to-nitrogen ratio in the flue gas is less than 1, the ammonia slip problem is not significant; however, when ultra-low flue gas emission standards (NOx-to-nitrogen ratio) are implemented... x ≤50mg / m 3 When ), to ensure the export of NO x To meet the standards, the NO in the exhaust gas is generally... x Content controlled at 35mg / m 3To ensure compliance with environmental standards, companies generally increase ammonia injection to reduce NO emissions from flue gas. x When the ammonia is controlled at a low level, the amount of ammonia injected into the flue far exceeds the amount of ammonia required for denitrification, resulting in severe ammonia escape.

[0007] Currently, ammonia injection control in SCR denitrification technology mainly focuses on two aspects: controlling the ammonia injection flow rate and controlling the uniformity of ammonia injection.

[0008] SCR denitrification systems typically control ammonia flow rate using a fixed ammonia-nitrogen molar ratio and a fixed outlet NO. x Content control methods. The fixed ammonia nitrogen molar ratio control method is based on NH3 and NO... x The reaction molar ratio of NO and NO2 is 1. Under this control mode, the system removes NO from the flue gas according to a fixed ammonia-nitrogen molar ratio. x The fixed ammonia-nitrogen molar ratio control method is a single-loop ammonia injection control with an adjustable ammonia-nitrogen molar ratio setpoint. Its advantages are simplicity and ease of operation, but its disadvantages include limitations when implementing ultra-low emission standards (NOx). x ≤50mg / m 3 When emission standards are set at even lower levels, excessive ammonia injection is common to ensure denitrification efficiency, leading to a significant increase in ammonia slip from the denitrification system. The formula for calculating the amount of reducing agent NH3 (ammonia injection) is as follows:

[0009]

[0010] in, Ammonia usage, kg / h; Q 烟气 The inlet flue gas flow rate of the SCR reactor is Nm³. 3 / h;C NOx NO in the inlet flue gas of the SCR reactor x Concentration (as NO2), mg / Nm 3 ; Here is the molar mass of NO2, in g / mol; NH3 is the molar mass of NH3, in g / mol; n is the ammonia-to-nitrogen molar ratio (NH3 / NO3). x ).

[0011] Fixed Export NO x The method of content control is to reduce the NO content in the flue gas outlet of the SCR reactor. x The concentration is set to a fixed value lower than the maximum allowable emission concentration. The formula for calculating the ammonia injection rate is as follows:

[0012]

[0013] Among them, C NOx入口 NO in the inlet flue gas of the SCR reactorx Concentration (as NO2), mg / Nm 3 C NOx出口 NO in the flue gas at the outlet of the SCR reactor x Concentration (as NO2), mg / Nm 3 .

[0014] Currently NO x The online analyzer is an extraction-type online analyzer, housed in an analysis cabin. Typically, the flue gas sampling point is tens of meters above the ground, while the analysis cabin is located on the ground. Flue gas is drawn from the inlet and outlet flues of the SCR reactor into the analysis cabin, where it undergoes cooling and filtration before entering the instrument's analysis module to analyze NO. x The concentration of NO₂ at the outlet is affected by the inherent delay in the denitrification reaction system and sampling measurement system, resulting in a 2-5 minute response delay in the automatic ammonia injection control system. This means that after the ammonia injection regulating valve activates, the outlet NO₂ concentration will be significantly reduced. x It takes time for changes to occur, resulting in a significant lag in ammonia injection rate adjustment. This is especially true when the NO inlet temperature of the SCR reactor is high. x When the concentration fluctuates drastically, delayed ammonia injection can lead to insufficient or excessive ammonia gas required for the SCR denitrification reaction. Insufficient ammonia gas will result in insufficient NO at the outlet. x Concentration exceeded the standard; in order to reduce NO export x When the concentration is too high, operators will usually switch the automatic control system to manual mode and increase the amount of ammonia injected. At this time, the amount of ammonia injected will increase significantly, even reaching twice the calculated value of the required amount of ammonia injected, causing a large amount of ammonia to escape. Similarly, when the ammonia injection is delayed and the amount of ammonia required for the SCR denitrification reaction is excessive, a large amount of ammonia will also escape.

[0015] Adjustments to the uniformity of ammonia injection are generally made during unit startup, based on on-site measurements of NO levels at the SCR reactor inlet or outlet flue. x The concentration distribution was adjusted one by one according to the ammonia injection valve, NO x In areas with high concentrations, the corresponding ammonia injection valve opening is increased, and vice versa. This repeated adjustment ensures uniformity of ammonia injection (ammonia-nitrogen molar ratio), aiming to make the ammonia-nitrogen molar ratio in different areas as consistent as possible. Because adjusting the ammonia injection uniformity at startup is time-consuming and technically demanding, SCR denitrification systems are generally adjusted only at startup, and the ammonia injection valve opening is no longer adjusted afterward. When the load, combustion method, or type of coal in the boiler, coal-fired unit, or equipment changes, the flue gas flow field distribution in the flue changes under different operating conditions, affecting the NO content in the flue gas. x The concentration distribution has also changed. The opening of the manual ammonia injection regulating valve set at the start of the unit can no longer meet the requirements of other operating conditions. The uniformity of ammonia injection has deteriorated, and the deviation between the ammonia-nitrogen molar ratio and the average value has increased in some areas. Areas with an excessively small ammonia-nitrogen molar ratio have low denitrification efficiency, and the outlet NO... xAreas where the ammonia nitrogen molar ratio is too high cannot meet the standards and ammonia escape exceeds the limit.

[0016] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0017] One of the objectives of this invention is to provide a flue gas denitrification ammonia injection mixing system and its ammonia injection control method, thereby improving the problems of inaccurate ammonia injection quantity control and serious ammonia escape in the prior art.

[0018] Another objective of this invention is to provide a flue gas denitrification ammonia injection mixing system and ammonia injection control method thereof, thereby improving denitrification efficiency and reducing ammonia escape while achieving ultra-low flue gas emission targets.

[0019] To achieve the above objectives, according to a first aspect of the present invention, the present invention provides a flue gas denitrification ammonia injection mixing system, comprising: an ammonia injection assembly, which includes: a main pipe on which a main flow regulating valve and an auxiliary flow regulating valve are connected in parallel, wherein the maximum flow rate of the auxiliary flow regulating valve is less than or equal to 30% of the maximum flow rate of the main flow regulating valve; a plurality of branch pipes connected to the main pipe, wherein branch pipes are provided with branch pipe flow regulating valves; and a plurality of nozzles respectively connected to the plurality of branch pipes; a static mixing assembly disposed downstream of the ammonia injection assembly; and a denitrification unit disposed downstream of the static mixing assembly.

[0020] Furthermore, in the above technical solution, the flue upstream of the static mixing component is divided into multiple first ammonia injection zones, each first ammonia injection zone corresponding to a branch pipe, and the flue downstream of the static mixing component is divided into multiple second ammonia injection zones, each second ammonia injection zone corresponding to one or more first ammonia injection zones.

[0021] Furthermore, in the above technical solution, the flue gas denitrification ammonia injection mixing system also includes: a flue gas flow meter, which is used to monitor the flue gas flow rate; multiple NO... x Online analyzer, used to monitor NO in each of the first ammonia injection zones. x Concentration and export NO x Concentration; and multiple online ammonia detectors, which are used to monitor the ammonia concentration in each second ammonia injection zone.

[0022] Furthermore, in the above technical solution, the distance from the first ammonia injection zone and the main flow regulating valve to the nozzle is set such that the time for the flue gas to travel from the first ammonia injection zone to the nozzle is equal to the time for the ammonia gas to travel from the main flow regulating valve to the nozzle, wherein the flow rates of both the flue gas and the ammonia gas are designed values.

[0023] Furthermore, in the above technical solution, the flue gas flow meter is located on the cross-section of the flue where the first ammonia injection zone is located.

[0024] Furthermore, in the above technical solutions, multiple NOs x The online analyzer is a direct-access analyzer.

[0025] Furthermore, in the above technical solution, the flue gas denitrification ammonia injection mixing system also includes: an ammonia injection control unit, which, based on the flue gas flow rate and the NO content of multiple first ammonia injection zones... x Average concentration and outlet NO x The concentration setpoint controls the opening of the main flow regulating valve; based on the ammonia concentration of each second ammonia injection zone and the corresponding NO concentration of all first ammonia injection zones... x The average concentration is used to control the opening of the branch flow regulating valve; based on the outlet NO... x Concentration and export NO x The upper limit of concentration controls the opening degree of the auxiliary flow regulating valve.

[0026] Furthermore, in the above technical solution, an ammonia-air mixer is installed on the main pipe or branch pipe, and the ammonia-air mixer is connected to the dilution air duct.

[0027] Furthermore, in the above technical solution, the denitrification unit includes at least one layer of denitrification catalyst, and a rectifier grid is provided at the top of the denitrification unit; a flow guiding component is provided between the static mixing component and the denitrification unit, and the flow guiding component turns the upward flue gas into the downward entry of the denitrification unit.

[0028] According to a second aspect of the present invention, an ammonia injection control method is provided for a flue gas denitrification ammonia injection mixing system as described above. The ammonia injection control method includes the following steps: obtaining flue gas flow rate, inlet NO... x Concentration, export NO x Concentration and ammonia concentration in each second ammonia injection zone; setting outlet NO x Concentration setpoint and outlet NO x Upper limit of concentration; based on flue gas flow rate and inlet NO x Concentration and export NO x Calculate the required total ammonia injection flow rate based on the concentration setpoint; according to the inlet NO... x Calculate the ammonia concentration and the ammonia concentration in each second ammonia injection zone, and calculate the ammonia-nitrogen molar ratio for each second ammonia injection zone and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones; adjust the flow rate of the main flow control valve to the required total ammonia injection flow rate; adjust the branch flow control valve so that the ammonia-nitrogen molar ratio for each second ammonia injection zone is equal to the average ammonia-nitrogen molar ratio; when the outlet NO x Concentration exceeding export NO x When the concentration reaches the upper limit, open the auxiliary flow regulating valve.

[0029] Furthermore, in the above technical solution, the entry NO x Concentrations include NO in each of the first ammonia injection zones. x Concentration, based on flue gas flow rate and NO in the first ammonia injection zone. x Average concentration and outlet NO x Calculate the required total ammonia injection flow rate based on the concentration setpoint; and based on the ammonia concentration of each second ammonia injection zone and the corresponding NO concentration of the first ammonia injection zone. x The average concentration is used to calculate the ammonia-nitrogen molar ratio for each second ammonia injection zone and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones.

[0030] According to a third aspect of the present invention, an ammonia injection control method is provided for a flue gas denitrification ammonia injection mixing system as described above. The ammonia injection control method includes the following steps: obtaining the flue gas flow range and the inlet NO... x Concentration ranges were defined and gridded accordingly; outlet NO was set. x Concentration setpoint; based on flue gas flow rate and inlet NO at each grid point. x Concentration and export NO x The concentration setpoint is used to calculate the required total ammonia injection flow rate for each grid point, and a model for the opening degree of the main flow control valve is constructed; the outlet NO is set. x Upper limit of concentration; real-time acquisition of flue gas flow rate and inlet NO x Concentration, export NO x Concentration and ammonia concentration in each second ammonia injection zone; real-time flue gas flow rate and inlet NO... x The concentration input model of the main flow control valve is used to obtain the required opening degree of the main flow control valve; the main flow control valve is adjusted to the required opening degree; based on the real-time acquired inlet NO... x Calculate the ammonia concentration and the ammonia concentration in each of the second ammonia injection zones, and calculate the ammonia-nitrogen molar ratio for each of the second ammonia injection zones and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones; adjust the branch flow regulating valve so that the ammonia-nitrogen molar ratio for each of the second ammonia injection zones is equal to the average ammonia-nitrogen molar ratio; when the real-time acquired outlet NO x Concentration exceeding export NO x When the concentration reaches the upper limit, open the auxiliary flow regulating valve.

[0031] Furthermore, in the above technical solution, obtaining the required opening degree of the main flow regulating valve includes: determining the opening degree model of the main flow regulating valve in relation to the real-time acquired flue gas flow rate and inlet NO. x The maximum or minimum value among the openings of the main flow control valves corresponding to all adjacent grid points is used to determine the required opening of the main flow control valve.

[0032] Furthermore, in the above technical solution, the entry point NO is obtained in real time. x Concentration includes real-time acquisition of NO in each of the first ammonia injection zones. x concentration.

[0033] Furthermore, in the above technical solution, the interval of the gridded flue gas flow range is 0.5% to 5% of the flue gas volume, and the inlet NO... x The concentration range gridding interval is 5–50 mg / Nm 3 .

[0034] Compared with the prior art, the present invention has one or more of the following beneficial effects:

[0035] 1. The flue gas denitrification ammonia injection mixing system and its ammonia injection control method of the present invention adopt a fixed outlet NO x The total ammonia usage in the SCR denitrification reaction is controlled by a content control method. When the NO content in the flue gas at the SCR reactor outlet is... x Concentration exceeding export NO x When the concentration exceeds the upper limit (e.g., environmental control limits), the main flow control valve of the ammonia main pipe remains stationary, while an auxiliary flow control valve is used to increase the ammonia flow. The ammonia flow through the auxiliary flow control valve is much lower than the ammonia flow through the main flow control valve. Therefore, when the limit is exceeded, the ammonia flow entering the system is gradually increased in small amounts to avoid a significant increase in ammonia escape caused by a large increase in the ammonia injection volume, thus improving the accuracy of ammonia injection control.

[0036] 2. By constructing a gridded opening model of the main flow control valve, the main flow control valve can be quickly adjusted to the required flow rate, significantly reducing the time required for ammonia flow regulation, improving the response lag of existing ammonia injection control methods, and avoiding excessive or insufficient ammonia injection, as well as SCR outlet NO. x Phenomena such as excessively high or low concentrations of ammonia, and severe ammonia slippage are observed, especially in the flue gas flow rate and / or the inlet flue gas of the SCR denitrification reactor. x Even when the concentration fluctuates significantly, this invention can still achieve precise control of the amount of ammonia injected, greatly reducing the amount of ammonia escape.

[0037] 3. This invention sets the relevant pipeline lengths based on the design values ​​of flue gas and ammonia flow rates, ensuring that the time for flue gas to travel from the first ammonia injection zone to the nozzle is approximately equal to the time for ammonia to travel from the main flow regulating valve to the nozzle. Therefore, the amount of ammonia injected into the flue gas is proportional to the amount of NO in the flue gas. x Synchronized ammonia injection control ensures more precise control, preventing ammonia escape due to excessive injection and NO2 buildup due to insufficient injection. x Phenomena such as exceeding standards.

[0038] 4. This invention uses the average ammonia-nitrogen molar ratio of the second ammonia injection zone as the basis for adjusting the ammonia flow rate of the first ammonia injection zone, which is more conducive to accurately controlling the ammonia flow rate, improving the uniformity of ammonia-nitrogen distribution, thereby improving ammonia utilization, reducing ammonia escape, and avoiding excessive ammonia injection that could lead to corrosion, leakage or blockage of downstream air preheaters or economizers, as well as excessive ammonia-nitrogen content in the desulfurization wastewater of subsequent wet desulfurization units.

[0039] 5. This invention uses NO from the first ammonia injection zone. x The average concentration is used as the basis for adjusting the required total ammonia injection flow rate, in conjunction with the method of measuring NO in flue gas at a single point. x Compared to the concentration, the NO concentration controlled by the ammonia injection method of this invention is significantly lower. x The concentration measurement is more accurate, and therefore the flow rate of the injected ammonia gas is also more precise.

[0040] 6. The NO used in this invention x The online analyzer is a direct-insertion analyzer with a short response time, avoiding the large amount of ammonia escape caused by response delay and ammonia injection lag in existing extraction-type online analyzers.

[0041] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other objects, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0042] Figure 1 This is a partial structural schematic diagram of a flue gas denitrification ammonia injection mixing system according to an embodiment of the present invention.

[0043] Figure 2 yes Figure 1 A schematic diagram of the first ammonia injection zone.

[0044] Figure 3 yes Figure 1 A schematic diagram of the second ammonia injection zone.

[0045] Figure 4 This is a schematic diagram of a flue gas denitrification ammonia injection mixing system according to an embodiment of the present invention.

[0046] Explanation of key figure labels:

[0047] 10-Flue duct, 11-First ammonia injection zone, 12-Second ammonia injection zone, 13-Flue gas flow meter, 14-First NO x Online analyzer, 15-Second NO xOnline analyzer, 16-Ammonia online detector, 20-Ammonia injection assembly, 21-Main pipe, 211-Main flow regulating valve, 212-Auxiliary flow regulating valve, 22-Branch pipe, 221-Branch pipe flow regulating valve, 23-Nozzle, 24-Dilution air duct, 241-Ammonia-air mixer, 30-Static mixing assembly, 41-Guide plate, 42-Baffle plate, 50-Rectifying grid, 60-Denitrification unit, 61-Denitrification catalyst. Detailed Implementation

[0048] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0049] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0050] In this document, for ease of description, spatial relative terms such as “below,” “under,” “down,” “above,” “above,” “upper,” etc., are used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that spatial relative terms are intended to encompass different orientations of an object in use or operation, in addition to those depicted in the figures. For example, if an object in the figure is flipped, an element described as “below” or “under” other elements or features will be oriented “above” the element or feature. Thus, the exemplary term “below” can encompass both the downward and upward orientations. Objects may also have other orientations (rotated 90 degrees or other orientations), and the spatial relative terms used herein should be interpreted accordingly.

[0051] In this document, the terms "first," "second," etc., are used to distinguish two different elements or parts, and are not used to define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0052] like Figures 1 to 3As shown, the flue gas denitrification ammonia injection mixing system according to a specific embodiment of the present invention includes an ammonia injection assembly 20 and a static mixing assembly 30. The ammonia injection assembly 20 injects ammonia into the flue duct 10 through a main pipe 21, multiple branch pipes 22, and multiple nozzles 23. A main flow regulating valve 211 and an auxiliary flow regulating valve 212 are connected in parallel on the main pipe 21. The maximum flow rate of the auxiliary flow regulating valve 212 is less than or equal to 30% of the maximum flow rate of the main flow regulating valve 211, and the auxiliary flow regulating valve 212 has higher regulation accuracy. Multiple nozzles 23 are connected to the main pipe 21 through multiple branch pipes 22, and branch pipes 22 are equipped with branch pipe flow regulating valves 221. The static mixing assembly 30 is located downstream of the ammonia injection assembly 20.

[0053] Furthermore, in one or more exemplary embodiments of the present invention, the flue 10 upstream of the static mixing component 30 is divided into a plurality of first ammonia injection zones 11, each first ammonia injection zone 11 corresponding to a branch pipe 221, and the flue 10 downstream of the static mixing component 30 is divided into a plurality of second ammonia injection zones 12, each second ammonia injection zone 12 corresponding to one or more first ammonia injection zones 11. It should be understood that the second ammonia injection zones 12 and the first ammonia injection zones 11 shown in the figure are in one-to-one correspondence, and are merely exemplary, and the present invention is not limited thereto.

[0054] Furthermore, in one or more exemplary embodiments of the present invention, a flue gas flow meter 13 is provided at the inlet of the flue 10 for monitoring the flue gas flow rate. Exemplarily, the flue gas flow meter 13 is disposed on the cross-section of the flue where the first ammonia injection zone 11 is located; each first ammonia injection zone 11 is provided with at least one first NO... x Online analyzer 14, which is used to monitor NO in each of the first ammonia injection zones 11 x Concentration; each second ammonia injection zone 12 is equipped with an online ammonia detector 16, which is used to monitor the ammonia concentration in each second ammonia injection zone 12. For example, the first NO... x All online analyzers 14 use a direct-insertion analyzer to reduce measurement lag.

[0055] Furthermore, in one or more exemplary embodiments of the present invention, the distance from the first ammonia injection zone 11 and the main flow regulating valve 211 to the nozzle 23 is set according to the design values ​​of the flow rates of flue gas and ammonia in the flue gas denitrification ammonia injection mixing system, such that the time for flue gas to travel from the first ammonia injection zone 11 to the nozzle 23 is substantially equal to the time for ammonia to travel from the main flow regulating valve 211 to the nozzle 23.

[0056] Furthermore, in one or more exemplary embodiments of the present invention, an ammonia-air mixer 241 is provided on the main pipe 21, and the ammonia-air mixer 241 is connected to the dilution air duct 24, thereby reducing the ammonia gas to below its explosion limit before it is injected into the flue 10 through the nozzle 23. It should be understood that the present invention is not limited thereto, and the ammonia-air mixer may also be provided on a branch pipe.

[0057] Furthermore, in one or more exemplary embodiments of the present invention, the flue gas denitrification ammonia injection mixing system sequentially includes, along the flue gas flow direction: an ammonia injection assembly 20, a static mixing assembly 30, a flow guiding assembly, a flow rectifying grid 50, and a denitrification unit 60. The denitrification unit 60 includes three layers of denitrification catalyst 61. The flow guiding assembly directs the upward-flowing flue gas downwards into the denitrification unit 60. Exemplarily, the flow guiding assembly may include a flow guide plate 41 and a baffle plate 42. It should be understood that the flow guiding assembly, the flow rectifying grid 50, and the denitrification unit 60 can all employ existing technologies, and the present invention is not limited thereto.

[0058] Furthermore, in one or more exemplary embodiments of the present invention, a second NOx is provided at the outlet of the flue gas denitrification ammonia injection mixing system. x Online analyzer 15, used to monitor NO at the outlet x concentration.

[0059] Furthermore, in one or more exemplary embodiments of the present invention, the flue gas denitrification ammonia injection mixing system may include an ammonia injection control unit (not shown in the figure), which, based on the flue gas flow rate and the NO content of multiple first ammonia injection zones, x Average concentration and outlet NO x The concentration setpoint controls the opening of the main flow regulating valve 211; based on the ammonia concentration of each second ammonia injection zone and the corresponding NO concentration of all first ammonia injection zones... x The average concentration is used to control the opening of the branch flow regulating valve 221; based on the outlet NO... x Concentration and export NO x The upper limit of concentration controls the opening degree of the auxiliary flow regulating valve 212.

[0060] The flue gas denitrification ammonia injection mixing system and ammonia injection control method of the present invention will be described in more detail below with reference to specific embodiments. It should be understood that the present invention is not limited thereto.

[0061] Example 1

[0062] refer to Figures 1-4 As shown, the flue gas denitrification ammonia injection mixing system of this embodiment includes, in sequence along the flue gas flow direction: ammonia injection component 20, static mixing component 30, flow guiding component, rectifier grid 50 and denitrification unit 60.

[0063] The main pipe 21 of the ammonia injection assembly 20 is divided into 10 branch pipes 22, each branch pipe 22 connecting to 8 nozzles 23 to inject ammonia into the flue 10. The flue 10 upstream of the static mixing assembly 30 is divided into 10 first ammonia injection zones 11, each first ammonia injection zone 11 corresponding to one branch pipe 22 and 8 nozzles; the flue 10 downstream of the static mixing assembly 30 is divided into 10 second ammonia injection zones 12, each second ammonia injection zone 12 corresponding to one first ammonia injection zone 11. A main flow regulating valve 211 and an auxiliary flow regulating valve 212 are connected in parallel on the main pipe 21, the maximum flow rate of the auxiliary flow regulating valve 212 being 30% of the maximum flow rate of the main flow regulating valve 211; each branch pipe 22 is equipped with a branch pipe flow regulating valve 221.

[0064] A flue gas flow meter 13 is installed at the inlet of flue 10, and it is located within the same cross-section of the flue as the first ammonia injection zone 11; each first ammonia injection zone 11 is equipped with a first NO x Online analyzer 14; each second ammonia injection zone 12 is equipped with an online ammonia detector 16; the outlet of the flue gas denitrification ammonia injection mixing system is equipped with a second NO... x Online Analyzer 15. First NO. x Online Analyzer 14 and Second NO x All online analyzers 15 use a direct-insertion analyzer.

[0065] Example 2

[0066] The ammonia injection control method of this embodiment is used in the flue gas denitrification ammonia injection mixing system of Embodiment 1. The ammonia injection control method of this embodiment includes the following steps: obtaining flue gas flow rate, inlet NO... x Concentration, export NO x Concentration and ammonia concentration in each second ammonia injection zone; setting outlet NO x Concentration setpoint and outlet NO x Upper limit of concentration; based on flue gas flow rate and inlet NO x Concentration and export NO x Calculate the required total ammonia injection flow rate based on the concentration setpoint; according to the inlet NO... x Calculate the ammonia concentration and the ammonia concentration in each of the second ammonia injection zones 12, and calculate the ammonia-nitrogen molar ratio for each of the second ammonia injection zones 12 and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones 12; adjust the flow rate of the main flow regulating valve 211 to the required total ammonia injection flow rate; adjust the branch flow regulating valve 221 so that the ammonia-nitrogen molar ratio of each of the second ammonia injection zones 12 is equal to the average ammonia-nitrogen molar ratio; when the outlet NO x Concentration exceeding export NO x When the concentration reaches the upper limit, open the auxiliary flow regulating valve 212.

[0067] In this embodiment, inlet NO xConcentrations include NO in each of the first ammonia injection zones 11. x Concentration, based on flue gas flow rate and NO in 10 first ammonia injection zones. x Average concentration and outlet NO x Calculate the required total ammonia injection flow rate based on the concentration setpoint; and based on the ammonia concentration in each second ammonia injection zone 12 and the corresponding NO concentration in the first ammonia injection zone 11. x Concentration, calculate the ammonia-nitrogen molar ratio of each second ammonia injection zone 12 and the average ammonia-nitrogen molar ratio of multiple second ammonia injection zones 12.

[0068] After adopting the flue gas denitrification ammonia injection mixing system of Example 1 and the ammonia injection control method of this embodiment, the average outlet ammonia escape concentration of a certain catalytic cracking flue gas SCR denitrification unit was reduced from 5 ppm to 1 ppm.

[0069] Example 3

[0070] The ammonia injection control method of this embodiment is used in the flue gas denitrification ammonia injection mixing system of Embodiment 1. The ammonia injection control method of this embodiment includes the following steps: obtaining the flue gas flow range and inlet NO... x Concentration ranges were defined and gridded accordingly; outlet NO was set. x Concentration setpoint; based on flue gas flow rate and inlet NO at each grid point. x Concentration and export NO x The concentration setpoint is used to calculate the required total ammonia injection flow rate for each grid point, and a model for the opening degree of the main flow control valve is constructed; the outlet NO is set. x Upper limit of concentration; real-time acquisition of flue gas flow rate and inlet NO x Concentration, export NO x Concentration and ammonia concentration in each of the second ammonia injection zones 12; real-time flue gas flow rate and inlet NO x The concentration input model of the main flow regulating valve 211 is used to obtain the required opening degree of the main flow regulating valve 211; the main flow regulating valve 211 is adjusted to the required opening degree; based on the real-time acquired inlet NO... x Calculate the ammonia concentration and the ammonia concentration in each of the second ammonia injection zones 12, and calculate the ammonia-nitrogen molar ratio for each of the second ammonia injection zones 12 and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones 12; adjust the branch pipe flow regulating valve 221 so that the ammonia-nitrogen molar ratio for each of the second ammonia injection zones 12 is equal to the average ammonia-nitrogen molar ratio; when the outlet NO x Concentration exceeding export NO x When the concentration reaches the upper limit, open the auxiliary flow regulating valve 212.

[0071] In this embodiment, the entry point NO is obtained in real time. x Concentration includes real-time acquisition of NO in each of the first ammonia injection zones. x concentration.

[0072] In this embodiment, obtaining the required opening degree of the main flow regulating valve includes: determining the opening degree model of the main flow regulating valve in relation to the real-time obtained flue gas flow rate and inlet NO. x The minimum value among the openings of the main flow control valves corresponding to all adjacent grid points is determined as the required opening of the main flow control valve.

[0073] A flue gas denitrification device for a coal-fired boiler has a designed flue gas volume of 500,000 Nm³. 3 / h, inlet NOx concentration is 600 mg / Nm 3 In actual operation, the flue gas volume of this pulverized coal boiler flue gas volume fluctuates between 350,000 and 650,000 Nm³. 3 / h、Entry NO x Concentration fluctuations ranged from 400 to 700 mg / Nm 3 The average ammonia slip was approximately 6.5 ppm. Using the flue gas denitrification ammonia injection mixing system of Example 1 and the ammonia injection control method of this example, the interval for the flue gas flow range gridding was 5000 Nm. 3 / h, Entry NO x The concentration range gridding interval is 20 mg / Nm 3 Due to local regulations regarding NOx emissions... x The requirements for emission concentration are relatively lenient (NO) x ≤100mg / Nm 3 The minimum value among the openings of the main flow control valves corresponding to all adjacent grid points is determined as the required opening of the main flow control valve. After industrial operation, the ammonia slip value is reduced to <1ppm.

[0074] Example 4

[0075] The ammonia injection control method of this embodiment is used in the flue gas denitrification ammonia injection mixing system of Embodiment 1. The ammonia injection control method of this embodiment includes the following steps: obtaining the flue gas flow range and inlet NO... x Concentration ranges were defined and gridded accordingly; outlet NO was set. x Concentration setpoint; based on flue gas flow rate and inlet NO at each grid point. x Concentration and export NO x The concentration setpoint is used to calculate the required total ammonia injection flow rate for each grid point, and a model for the opening degree of the main flow control valve is constructed; the outlet NO is set. x Upper limit of concentration; real-time acquisition of flue gas flow rate and inlet NO x Concentration, export NO x Concentration and ammonia concentration in each second ammonia injection zone; real-time flue gas flow rate and inlet NO... xThe concentration input model of the main flow control valve is used to obtain the required opening degree of the main flow control valve; the main flow control valve 211 is adjusted to the required opening degree; based on the real-time acquired inlet NO... x Calculate the ammonia concentration and the ammonia concentration in each second ammonia injection zone, and calculate the ammonia-nitrogen molar ratio for each second ammonia injection zone and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones; adjust the branch pipe flow regulating valve 221 so that the ammonia-nitrogen molar ratio for each second ammonia injection zone is equal to the average ammonia-nitrogen molar ratio; when the outlet NO x Concentration exceeding export NO x When the concentration reaches the upper limit, open the auxiliary flow regulating valve 212.

[0076] In this embodiment, the entry point NO is obtained in real time. x Concentration includes real-time acquisition of NO in each of the first ammonia injection zones. x concentration.

[0077] In this embodiment, obtaining the required opening degree of the main flow regulating valve includes: determining the opening degree model of the main flow regulating valve in relation to the real-time obtained flue gas flow rate and inlet NO. x The maximum value among the openings of the main flow control valves corresponding to all adjacent grid points is determined as the required opening of the main flow control valve.

[0078] A pulverized coal boiler flue gas denitrification device has a designed flue gas volume of 250,000 Nm³. 3 / h、Entry NO x Concentration of 800 mg / Nm 3 In actual operation, the flue gas volume of this pulverized coal boiler flues between 150,000 and 270,000 Nm³. 3 / h、Entry NO x Concentration fluctuations ranged from 450 to 850 mg / Nm 3 Ammonia slip was essentially at full scale (10 ppm). Using the flue gas denitrification ammonia injection mixing system of Example 1 and the ammonia injection control method of this example, due to local requirements for ultra-low emission standards (NOx emission concentration) in flue gas... x ≤50mg / Nm 3 The requirements are even more stringent during periods of heavy pollution (NO). x ≤30mg / Nm 3 Therefore, the maximum value among the openings of the main flow control valves corresponding to all adjacent grid points is determined as the required opening of the main flow control valve, and the grid interval for the flue gas flow range is 2000 Nm. 3 / h, the gridded interval for the inlet NOx concentration range is 10 mg / Nm 3 After industrial operation, the ammonia slip value decreased to <1.5ppm.

[0079] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. Any simple modifications, equivalent changes, and alterations made to the foregoing exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. A flue gas denitrification ammonia injection mixing system, characterized in that, include: Ammonia injection assembly, comprising: The main pipe is equipped with a main flow regulating valve and an auxiliary flow regulating valve connected in parallel. The maximum flow rate of the auxiliary flow regulating valve is less than or equal to 30% of the maximum flow rate of the main flow regulating valve. Multiple branch pipes, connected to the main pipe, are equipped with branch pipe flow regulating valves; and Multiple nozzles, each connected to one of the multiple branch pipes; A static mixing assembly, disposed downstream of the ammonia injection assembly; and A denitrification unit is located downstream of the static mixing assembly; The flue upstream of the static mixing component is divided into multiple first ammonia injection zones, each first ammonia injection zone corresponding to one of the branch pipes; the flue downstream of the static mixing component is divided into multiple second ammonia injection zones, each second ammonia injection zone corresponding to one or more first ammonia injection zones. The system also includes: The ammonia injection control unit can determine the ammonia concentration in each second ammonia injection zone and the corresponding NO concentration in all first ammonia injection zones. x The average concentration is calculated, the ammonia-nitrogen molar ratio of each of the second ammonia injection zones and the average ammonia-nitrogen molar ratio of the plurality of second ammonia injection zones are calculated, the branch flow regulating valve is adjusted so that the ammonia-nitrogen molar ratio of each of the second ammonia injection zones is equal to the average ammonia-nitrogen molar ratio, and the opening degree of the branch flow regulating valve is controlled.

2. The flue gas denitrification ammonia injection mixing system according to claim 1, characterized in that, Also includes: A flue gas flow meter is used to monitor the flow rate of flue gas. Multiple NOs x Online analyzer, used to monitor NO in each of the first ammonia injection zones. x Concentration, export NO x Concentration; and Multiple online ammonia detectors are used to monitor the ammonia concentration in each of the second ammonia injection zones.

3. The flue gas denitrification ammonia injection mixing system according to claim 2, characterized in that, The distances from the flue gas flow meter and the main flow regulating valve to the nozzle are set such that the time it takes for the flue gas to travel from the flue gas flow meter to the nozzle is equal to the time it takes for the ammonia to travel from the main flow regulating valve to the nozzle, wherein the flow velocities of both the flue gas and the ammonia are designed values.

4. The flue gas denitrification ammonia injection mixing system according to claim 3, characterized in that, The flue gas flow meter is installed on the cross-section of the flue where the first ammonia injection zone is located.

5. The flue gas denitrification ammonia injection mixing system according to claim 2, characterized in that, The multiple NO x The online analyzer is a direct-access analyzer.

6. The flue gas denitrification ammonia injection mixing system according to claim 2, characterized in that, The ammonia injection control unit can also adjust the flue gas flow rate and the NO content of multiple first ammonia injection zones based on the flue gas flow rate. x Average concentration and outlet NO x The concentration setpoint controls the opening degree of the main flow regulating valve; based on the outlet NO... x Concentration and export NO x The upper limit of the concentration controls the opening degree of the auxiliary flow regulating valve.

7. The flue gas denitrification ammonia injection mixing system according to claim 1, characterized in that, An ammonia-air mixer is installed on the main pipe or the branch pipe, and the ammonia-air mixer is connected to the dilution air duct.

8. The flue gas denitrification ammonia injection mixing system according to claim 1, characterized in that, The denitrification unit includes at least one layer of denitrification catalyst, and a flow-rectifying grid is provided on the upper part of the denitrification unit; a flow-guiding component is provided between the static mixing component and the denitrification unit, and the flow-guiding component turns the upward flue gas into the downward entry of the denitrification unit.

9. A method for controlling ammonia injection, characterized in that, It is used in the flue gas denitrification ammonia injection mixing system as described in claim 1, and the ammonia injection control method includes the following steps: Obtain flue gas flow rate and inlet NO x Concentration, export NO x Concentration and ammonia concentration in each second ammonia injection zone; Set export NO x Concentration setpoint and outlet NO x Upper limit of concentration; Based on flue gas flow rate and inlet NO x Concentration and export NO x Calculate the required total ammonia injection flow rate based on the concentration setpoint. According to entry NO x The concentration and the ammonia concentration of each second ammonia injection zone are used to calculate the ammonia-nitrogen molar ratio of each second ammonia injection zone and the average ammonia-nitrogen molar ratio of the plurality of second ammonia injection zones; Adjust the flow rate of the main flow regulating valve to the required total ammonia injection flow rate; Adjust the branch flow regulating valve so that the ammonia-nitrogen molar ratio of each second ammonia injection zone is equal to the average value of the ammonia-nitrogen molar ratio; When the export NO x Concentration exceeding the outlet NO x When the concentration reaches the upper limit, the auxiliary flow regulating valve is opened; The entry NO x Concentrations include NO in each of the first ammonia injection zones. x Concentration, based on flue gas flow rate and NO in the first ammonia injection zone. x Average concentration and outlet NO x Calculate the required total ammonia injection flow rate based on the concentration setpoint; and based on the ammonia concentration of each second ammonia injection zone and the corresponding NO concentration of the first ammonia injection zone. x The average concentration is used to calculate the ammonia-nitrogen molar ratio for each second ammonia injection zone and the average ammonia-nitrogen molar ratio for multiple second ammonia injection zones.

10. A method for controlling ammonia injection, characterized in that, It is used in the flue gas denitrification ammonia injection mixing system as described in claim 1, and the ammonia injection control method includes the following steps: Obtain flue gas flow range and inlet NO x Concentration range, and then gridded; Set export NO x Concentration setpoint; Based on the flue gas flow rate and inlet NO at each grid point x Concentration and export NO x The concentration setpoint is used to calculate the required total ammonia injection flow rate for each grid point and construct the opening model of the main flow control valve. Set export NO x Upper limit of concentration; Real-time acquisition of flue gas flow rate and inlet NO x Concentration, export NO x Concentration and ammonia concentration in each second ammonia injection zone; real-time acquisition of inlet NO. x Concentration includes real-time acquisition of NO in each of the first ammonia injection zones. x concentration; The real-time acquired flue gas flow rate and inlet NO x The concentration input model of the main flow control valve is used to obtain the required opening degree of the main flow control valve. Adjust the main flow regulating valve to the required opening degree; According to the real-time obtained entry point NO x The concentration and the ammonia concentration of each second ammonia injection zone are calculated, and the ammonia-nitrogen molar ratio of each second ammonia injection zone and the average ammonia-nitrogen molar ratio of multiple second ammonia injection zones are calculated. Adjust the branch flow regulating valve so that the ammonia-nitrogen molar ratio of each second ammonia injection zone is equal to the average value of the ammonia-nitrogen molar ratio; When the real-time acquired export NO x Concentration exceeding the outlet NO x When the concentration reaches the upper limit, the auxiliary flow regulating valve is opened.

11. The ammonia injection control method according to claim 10, characterized in that, The required opening degree of the main flow regulating valve includes: The opening model of the main flow control valve is determined in conjunction with the real-time flue gas flow rate and inlet NO. x Grid points with adjacent concentrations; The maximum or minimum value among the openings of the main flow control valves corresponding to all adjacent grid points is determined as the required opening of the main flow control valve.

12. The ammonia injection control method according to claim 10, characterized in that, The interval for the gridding of flue gas flow rate is 0.5%~5% of the flue gas volume, and the inlet NO... x The concentration range gridding interval is 5~50 mg / m 3 .

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