A method and system for precise ammonia injection control in a circulating fluidized bed boiler

Abstract

This invention relates to a method and system for precise ammonia injection control in a circulating fluidized bed boiler, comprising the following steps: S1, acquiring the flue gas temperature, flue gas velocity, and NOx concentration at each measuring point at the cyclone outlet, and calculating the average NOx concentration, average flue gas velocity, and average flue gas temperature; S2, based on the calculation results of S1, calculating the total amount of ammonia injected as a reducing agent, forming pre-feedback, and adjusting the total amount of reducing agent passing through the ammonia injection main valve; S3, acquiring the NOx concentration, flue gas temperature, and flue gas velocity at each spray gun, calculating the reducing agent dosage at each measuring point, forming post-feedback, and adjusting the reducing agent dosage passing through the ammonia injection branch valve on the branch where the spray gun is located at each measuring point; this method, by measuring the flue gas temperature, flue gas velocity, and NOx concentration at each measuring point at the cyclone outlet and at each spray gun, calculates the total amount of ammonia injected as a reducing agent and the amount of reducing agent used in each branch in real time, thereby adjusting the reducing agent dosage of the ammonia injection main valve and the ammonia injection branch valves of each branch, and achieving precise ammonia injection adjustment in real time.

Description

Technical Field

[0001] This invention relates to the field of SNCR denitrification technology, and in particular to a method and system for precise ammonia injection control in a circulating fluidized bed boiler. Background Technology

[0002] The existing ammonia injection control in the SNCR denitrification system of a circulating fluidized bed boiler adjusts the ammonia injection main valve based on the NOx concentration at the furnace outlet. Specifically, if the NOx concentration at the furnace outlet is too high, the opening of the main valve is increased, increasing the injection rate; conversely, if the NOx concentration is too low, the valve opening is decreased, reducing the injection rate. This control method uses the furnace outlet NOx concentration as the ultimate basis for control, adjusting only the main valve while keeping the opening of each individual spray nozzle valve fixed (the nozzle valve opening remains fixed after initial commissioning and does not change with temperature, flow rate, or NOx concentration). This means that increasing the main valve opening leads to a uniform increase in the injection rate of each nozzle, resulting in reductant waste; conversely, decreasing the main valve opening leads to a uniform decrease in the injection rate of each nozzle, increasing environmental risks. Therefore, the existing ammonia injection control method does not effectively control reductant consumption, leading to problems such as inefficient SNCR operation under varying load conditions and ineffective control of ammonia escape concentration, which need to be addressed. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the defects in the existing ammonia injection control technology, such as the inability to effectively control the consumption of reducing agent, resulting in the inefficient operation of SNCR under variable load conditions and the inability to effectively control the ammonia escape concentration. The present invention provides a method and system for precise ammonia injection control of circulating fluidized bed boilers.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for precise ammonia injection control in a circulating fluidized bed boiler includes the following steps:

[0006] S1, obtain the flue gas temperature, flue gas velocity and NOx concentration at each measuring point at the cyclone outlet, and calculate the average NOx concentration, average flue gas velocity and average flue gas temperature;

[0007] S2, based on the calculation results of S1, calculates the total amount of ammonia injected as reducing agent, forms pre-feedback, and controls the total amount of reducing agent passing through the ammonia injection main valve;

[0008] S3, obtain the NOx concentration, flue gas temperature and flue gas velocity at each spray gun, calculate the reduction dose at each measuring point, generate feedback, and adjust the reduction dose passed through the ammonia injection branch valve on the branch where the spray gun is located at each measuring point.

[0009] Preferably, the formula for calculating the average NOx concentration in S1 is:

[0010]

[0011]

[0012]

[0013] in: ν0 represents the average NOx concentration, mg / m3; ν0 represents the average flue gas velocity, m / s; T0 represents the average flue gas temperature, K. v represents the NOx concentration at the nth measuring point, in mg / m3; n T represents the flue gas velocity at the nth measuring point, in m / s. n Let n be the smoke temperature at the nth measuring point, in K; n is the nth measuring point.

[0014] The formula for calculating the total amount of ammonia injected as the reducing agent in S2 is:

[0015]

[0016] Among them: Q 总 Total amount of reducing agent sprayed, kg; S 总 Let be the total cross-sectional area of ​​the flue, in m2.

[0017] Preferably, the formula for calculating the reduction dose of the branch where the spray gun is located at each measuring point in S3 is as follows:

[0018]

[0019] Among them: Q n The amount of reducing agent injected at the nth measuring point is in kg.

[0020] A precision ammonia injection system for a circulating fluidized bed boiler includes a boiler, a cyclone separator, a urea solution storage tank, a urea solution buffer tank, a NOx zoned rotation measurement subsystem, and a flue gas temperature and velocity measurement subsystem. The urea solution storage tank is connected to the urea solution buffer tank, and the urea solution buffer tank is connected to an ammonia injection main pipe. An ammonia injection main valve and a main pipe flow meter are connected to the ammonia injection main pipe. Multiple branch pipes are connected to the ammonia injection main pipe, and each branch pipe is connected to an ammonia injection branch valve and a branch flow meter. A spray gun is connected to the end of each branch pipe, and the multiple spray guns are evenly distributed circumferentially at the outlet of the cyclone separator. Each measurement point of the flue gas temperature and velocity measurement subsystem and each measurement point of the NOx zoned rotation measurement subsystem are correspondingly located below each spray gun. The NOx zoned rotation measurement subsystem, the flue gas temperature and velocity measurement subsystem, the ammonia injection main valve, the main pipe flow meter, the ammonia injection branch valve, and the branch flow meter are all electrically connected to the power plant's main control system.

[0021] Preferably, multiple spray guns constitute a spray gun arrangement layer, the measuring points of the flue gas temperature and flue gas velocity measuring subsystem are arranged 0.5-1.5m below the spray gun arrangement layer, and the measuring points of the NOx zoning and rotation measuring subsystem are located 1.0-2.0m below the spray gun arrangement layer.

[0022] Preferably, the measurement point of the NOx zone rotation measurement subsystem is located 0.5-1.0m below the measurement point of the flue gas temperature and flue gas velocity measurement subsystem.

[0023] Preferably, the NOx zoned rotation measurement subsystem includes a simultaneous sampling system, a sample gas storage system, a time-sharing rotation measurement system, and a flue gas analyzer. The simultaneous sampling system, the sample gas storage system, the time-sharing rotation measurement system, and the flue gas analyzer are connected in sequence, and the flue gas analyzer is electrically connected to the power plant's main control system.

[0024] Preferably, the above-mentioned flue gas temperature and flue gas velocity measurement subsystem includes a flue gas temperature measuring device and a flue gas velocity measuring device, both of which are electrically connected to the power plant's main control system.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention measures the flue gas temperature, flue gas velocity, and NOx concentration at each measuring point at the cyclone outlet and at each spray gun, thereby calculating the total amount of ammonia injected as reducing agent and the amount of reducing agent used in each branch in real time. This allows for the adjustment of the reducing agent dosage through the main ammonia injection valve and the branch ammonia injection valves in each branch, ensuring that the reducing agent dosage from each spray gun is adapted to the NOx concentration in the flue gas at each location. This achieves precise real-time ammonia injection adjustment, effectively ensuring the efficient operation of SNCR under variable load conditions, further reducing the operating cost of the SNCR denitrification system, effectively controlling reducing agent consumption, reducing ammonia escape concentration, reducing the risk of tail-end facility blockage, and achieving efficient, stable, and precise NOx control of circulating fluidized bed boilers under wide loads, ensuring ultra-low NOx emissions and avoiding environmental risks caused by excessive pollutant emissions. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart of a method for precise ammonia injection control in a circulating fluidized bed boiler according to Embodiment 1 of the present invention.

[0029] Figure 2 This is a schematic diagram of the overall structure of a precision ammonia injection system for a circulating fluidized bed boiler according to Embodiment 2 of the present invention;

[0030] Figure 3 This is a schematic diagram of the spray gun setup in a precision ammonia injection system for a circulating fluidized bed boiler according to Embodiment 2 of the present invention.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1. Boiler; 2. Cyclone separator; 3. Urea solution storage tank; 4. Urea solution buffer tank; 5. NOx zoned rotation measurement subsystem; 6. Flue gas temperature and flow rate measurement subsystem; 7. Ammonia injection main pipe; 8. Ammonia injection main valve; 9. Main pipe flow meter; 10. Branch pipes; 11. Ammonia injection branch valve; 12. Branch flow meter; 13. Spray gun. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] Example 1

[0037] like Figure 1 As shown in the figure, this invention provides a method for precise ammonia injection in a circulating fluidized bed boiler, comprising the following steps:

[0038] S1 acquires the flue gas temperature, flue gas velocity, and NOx concentration at each measuring point at the cyclone outlet. The power plant control system calculates the average NOx concentration, average flue gas velocity, and average flue gas temperature using internal formulas. Specifically, the formula for calculating the average NOx concentration is:

[0039]

[0040]

[0041]

[0042] in: ν0 represents the average NOx concentration, mg / m3; ν0 represents the average flue gas velocity, m / s; T0 represents the average flue gas temperature, K. v represents the NOx concentration at the nth measuring point, in mg / m3; n T represents the flue gas velocity at the nth measuring point, in m / s. n Let be the smoke temperature at the nth measuring point, in K; n is the nth measuring point.

[0043] Specifically, first calculate the average flue gas velocity v0 and the average flue gas temperature T0, and then calculate the average NOx concentration based on the average flue gas velocity v0 and the average flue gas temperature T0.

[0044] S2, based on the calculated average flue gas velocity v0, average flue gas temperature T0, and average NOx concentration. The power plant's main control system calculates the total ammonia injection amount as reducing agent, establishing feedback. The main control system then adjusts the opening of the main ammonia injection valve, thereby regulating the total amount of reducing agent passing through the valve to match the calculated amount, achieving real-time control of the total reducing agent flow. Specifically, the formula for calculating the total ammonia injection amount is:

[0045]

[0046] Among them: Q 总 Total amount of reducing agent sprayed, kg; S 总 Let be the total cross-sectional area of ​​the flue, in m2.

[0047] In step S3, the NOx concentration, flue gas temperature, and flue gas velocity at each spray gun are acquired. These values ​​are identical to those acquired in step S1. The power plant's main control system then calculates the reduction dose at each measuring point, generates a feedback loop, and adjusts the reduction dose passing through the ammonia injection branch valve on each branch's spray gun to match the calculated reduction dose. This allows for precise real-time control of the reduction dose sprayed by each branch's nozzles. Specifically, the formula for calculating the reduction dose in step S3 for each branch's spray gun is as follows:

[0048]

[0049] Among them: Q n The amount of reducing agent injected at the nth measuring point is in kg.

[0050] This control method acquires the flue gas temperature, flue gas velocity, and NOx concentration at each measuring point at the cyclone outlet, calculates the average NOx concentration, average flue gas velocity, and average flue gas temperature, and then calculates the required total amount of reducing agent. This allows control of the reducing agent flow through the main ammonia injection valve. Furthermore, this data is used to calculate the required reducing agent injection amount at each spray gun, and then precisely controls the reducing agent flow through the ammonia injection branch valves of each branch pipeline. Ultimately, this enables each spray gun to spray the corresponding flow rate of reducing agent in real time based on its respective NOx concentration environment, achieving precise real-time ammonia injection adjustment. This effectively ensures the efficient operation of SNCR under variable load conditions, further reduces the operating cost of the SNCR denitrification system, effectively controls reducing agent consumption, reduces ammonia escape concentration, reduces the risk of tail-end facility blockage, and achieves efficient, stable, and precise NOx control over a wide load range in circulating fluidized bed boilers, ensuring ultra-low NOx emissions and avoiding environmental risks caused by excessive pollutant emissions.

[0051] Example 2

[0052] like Figure 2-3 As shown, a precise ammonia injection control system for a circulating fluidized bed boiler is proposed corresponding to Embodiment 1. It includes a boiler 1, a cyclone separator 2, a urea solution storage tank 3, a urea solution buffer tank 4, a NOx zoned rotation measurement subsystem 5, and a flue gas temperature and flow rate measurement subsystem 6. The urea solution storage tank 3 and the urea solution buffer tank 4 are connected by an inlet pipe, which is equipped with an inlet valve and an inlet pump (not shown in the figure). The urea solution buffer tank 4 is connected to an ammonia injection main pipe 7, which is connected to an ammonia injection main valve 8 and a main pipe flow meter 9. Multiple branch pipes 10 are connected to the ammonia injection main pipe 7. Specifically, there are four branch pipes 10, each connected to an ammonia injection branch valve 11 and a branch flow meter 12. Each branch pipe 10 has a spray gun 13 connected to its end. Figure 3As shown, the four spray guns 13 are evenly distributed around the outlet of the cyclone separator 2. Each measurement point of the flue gas temperature and flue gas velocity measurement subsystem 6 and each measurement point of the NOx zone rotation measurement subsystem 5 are also four, and are correspondingly set below the four spray guns 13. The NOx zone rotation measurement subsystem 5, the flue gas temperature and flue gas velocity measurement subsystem 6, the ammonia injection main valve 8, the main pipe flow meter 9, the ammonia injection branch pipe valve 11 and the branch pipe flow meter 12 are all electrically connected to the power plant's main control system.

[0053] Specifically, the NOx concentration at each measuring point is measured by the NOx zoned measurement subsystem 5, and the flue gas temperature and flue gas velocity at each measuring point are measured by the flue gas temperature and flue gas velocity measurement subsystem 6. The required data on NOx concentration, flue gas temperature, and flue gas velocity at the outlet of the cyclone separator 2 are the same set of data as the data on NOx concentration, flue gas temperature, and flue gas velocity at each spray gun 13. This data is obtained by measuring each measuring point separately by the NOx zoned measurement subsystem 5 and the flue gas temperature and flue gas velocity measurement subsystem 6. Based on the measured NOx concentration, flue gas temperature, and flue gas velocity, the power plant's main control system calculates the average NOx concentration, average flue gas velocity, and average flue gas temperature according to the formula in Example 1. Then, the total amount of reducing agent used by each spray gun 13 is calculated. Finally, the power plant's main control system controls the opening of the ammonia injection main valve 8 according to the data from the main pipe flow meter 9, so that the flow rate passing through at this time conforms to the calculated value. The total amount of reducing agent is calculated, and then the power plant's main control system calculates the required amount of reducing agent at each of the 13 spray guns. Based on the data from the flow meters 12 of each branch pipe, the main control system controls the opening of the ammonia injection branch valve 11, ensuring that the reducing agent flow through each branch matches the calculated amount of reducing agent used in each branch. This achieves precise control of the reducing agent usage in each branch, enabling real-time and accurate ammonia injection adjustment. This effectively ensures the efficient operation of the SNCR under varying load conditions, further reducing the operating cost of the SNCR denitrification system, effectively controlling reducing agent consumption, reducing ammonia escape concentration, reducing the risk of tail-end facility blockage, and achieving efficient, stable, and precise NOx control of the circulating fluidized bed boiler 1 under wide loads, ensuring ultra-low NOx emissions and avoiding environmental risks caused by excessive pollutant emissions. Specifically, although the control of the main ammonia injection valve 8 and the control of each ammonia injection branch valve 11 occur sequentially, the control time is extremely short and negligible.

[0054] The NOx concentration, flue gas temperature, and flue gas velocity data mentioned above can be obtained from the outlet of cyclone separator 2, or from the data measured at each of the 13 spray guns.

[0055] Specifically, multiple spray guns 13 form a spray gun 13 arrangement layer. The measurement points of the flue gas temperature and flue gas velocity measurement subsystem 6 are arranged 0.5-1.5m below the spray gun 13 arrangement layer. The measurement points of the NOx zone rotation measurement subsystem 5 are set 1.0-2.0m below the spray gun 13 arrangement layer, and the measurement points of the NOx zone rotation measurement subsystem 5 are set 0.5-1.0m below the measurement points of the flue gas temperature and flue gas velocity measurement subsystem 6. This ensures that the spray gun 13 arrangement layer, the measurement points of the flue gas temperature and flue gas velocity measurement subsystem 6, and the measurement points of the NOx zone rotation measurement subsystem 5 are at a certain distance, so that the measurement of the flue gas temperature and flue gas velocity measurement subsystem 6 and the NOx zone rotation measurement subsystem 5 does not affect each other, while the distance between them is not far. This achieves stable flue gas concentration in this space with little variation, so that a set of data can be used universally.

[0056] Specifically, the NOx zoned rotation measurement subsystem 5 includes a simultaneous sampling system, a sample gas storage system, a time-sharing rotation measurement system, and a flue gas analyzer. The simultaneous sampling system, sample gas storage system, time-sharing rotation measurement system, and flue gas analyzer are connected in sequence. The flue gas analyzer is electrically connected to the power plant's main control system. For details on its specific structure and method, please refer to the "Simultaneous Sampling and Time-Sharing Rotation Measurement Device for NOx in an SCR Denitrification System" published in CN213456307U.

[0057] Specifically, the flue gas temperature and flue gas velocity measurement subsystem 6 includes a flue gas temperature measuring device and a flue gas velocity measuring device. Both the flue gas temperature measuring device and the flue gas velocity measuring device are electrically connected to the power plant's main control system. Specifically, the flue gas temperature measuring device can be a commonly used thermocouple or an infrared thermometer, and the flue gas velocity measuring device can be a commonly used flow meter or a back tube.

[0058] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for precise ammonia injection control in a circulating fluidized bed boiler, characterized by Includes the following steps: S1: Obtain the flue gas temperature, flue gas velocity, and NOx concentration at each measuring point at the cyclone outlet, and calculate the average NOx concentration, average flue gas velocity, and average flue gas temperature. The formula for calculating the average NOx concentration in S1 is: wherein: is the average NOx concentration, mg / m 3 is the average flue gas flow rate, m / s; is the average flue gas temperature, K; is the NOx concentration at the nth measurement point, mg / m 3 ; is the flue gas flow rate at the nth measurement point, m / s; is the flue gas temperature at the nth measurement point, K; n is the nth measurement point; S2, based on the calculation results of S1, calculates the total amount of ammonia injected as the reducing agent, forming a pre-feedback mechanism to control the total amount of reducing agent passing through the main ammonia injection valve. The formula for calculating the total amount of ammonia injected as the reducing agent in S2 is: wherein: is the total amount of reducing agent injected, kg; is the total cross-sectional area of the flue, m 2 ; S3: Obtain the NOx concentration, flue gas temperature, and flue gas velocity at each spray gun, calculate the reduction dose at each measuring point, generate feedback, and adjust the reduction dose at the ammonia injection branch valve on the branch where the spray gun is located. The calculation formula for the reduction dose of the branch where the spray gun is located at each measuring point in S3 is as follows: wherein: is the injection amount of the reducing agent at the nth measuring point, kg.

2. A precise ammonia injection system for a circulating fluidized bed boiler for implementing the precise ammonia injection control method for a circulating fluidized bed boiler as claimed in claim 1, characterized by, The system includes a boiler, a cyclone separator, a urea solution storage tank, a urea solution buffer tank, a NOx zoned rotation measurement subsystem, and a flue gas temperature and velocity measurement subsystem. The urea solution storage tank is connected to the urea solution buffer tank, which is connected to an ammonia injection main pipe. The ammonia injection main pipe is connected to an ammonia injection main valve and a main pipe flow meter. The ammonia injection main pipe is connected to multiple branch pipes, each of which is connected to an ammonia injection branch valve and a branch flow meter. Each branch pipe has a spray gun at its end, and the multiple spray guns are evenly distributed circumferentially at the outlet of the cyclone separator. The measurement points of the flue gas temperature and velocity measurement subsystem and the measurement points of the NOx zoned rotation measurement subsystem are located one-to-one below each spray gun. The NOx zoned rotation measurement subsystem, the flue gas temperature and velocity measurement subsystem, the ammonia injection main valve, the main pipe flow meter, the ammonia injection branch valve, and the branch flow meter are all electrically connected to the power plant's overall control system.

3. The precision ammonia injection system of claim 2, wherein, Multiple spray guns form a spray gun arrangement layer. The measurement points of the flue gas temperature and flue gas velocity measurement subsystem are arranged 0.5-1.5m below the spray gun arrangement layer, and the measurement points of the NOx zone rotation measurement subsystem are located 1.0-2.0m below the spray gun arrangement layer.

4. The precision ammonia injection system of claim 3, wherein, Furthermore, the measurement point of the NOx zone rotation measurement subsystem is located 0.5-1.0m below the measurement point of the flue gas temperature and flue gas velocity measurement subsystem.

5. The precision ammonia injection system of claim 2, wherein, The NOx zoned rotation measurement subsystem includes a simultaneous sampling system, a sample gas storage system, a time-sharing rotation measurement system, and a flue gas analyzer. The simultaneous sampling system, the sample gas storage system, the time-sharing rotation measurement system, and the flue gas analyzer are connected in sequence, and the flue gas analyzer is electrically connected to the power plant's main control system.

6. The precision ammonia injection system of claim 2, wherein, The flue gas temperature and flue gas velocity measurement subsystem includes a flue gas temperature measuring device and a flue gas velocity measuring device, both of which are electrically connected to the power plant's main control system.

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