A denitration precise ammonia injection system based on bus communication and a control method thereof

Abstract

This invention discloses a bus-communication-based precision ammonia injection system for denitrification and its control method, comprising: a bus communication control box, which is sequentially equipped with PA cards, DP cards, and Modbus cards; the PA cards are sequentially connected in series with the urea main pipe inlet flow rate, the urea total flow rate regulating valve, and the urea spray gun regulating valve; a DCS cabinet, located on one side of the bus communication control box; a denitrification island, which is respectively equipped with an AB-side ammonia-air mixture main valve, an AB-side inlet rapid testing device, an AB-side ammonia injection zone regulating valve, an AB-side outlet rapid testing device, and an AB-side ammonia escape valve, which are sequentially connected to the DCS cabinet via the bus communication control box; a denitrification electric heating control cabinet, which is electrically connected to the DCS cabinet via a DP card; and a pyrolysis furnace. This invention enables unified management of precision ammonia injection equipment after decentralized installation, features an open system access point, reserves access for future upgrades and modifications to the precision ammonia injection system, shortens equipment installation and commissioning time, has a simple structure, is modularly easy to install, and has low maintenance costs.

Description

Technical Field

[0001] This invention relates to the field of ammonia injection technology, and in particular to a bus-communication-based precision ammonia injection system for denitrification and its control method. Background Technology

[0002] NOx emissions from coal-fired power plants account for more than 40% of NOx emissions from coal combustion. It is one of the main pollutants causing acid rain, the greenhouse effect, and smog. Precision ammonia injection technology for denitrification has high denitrification efficiency, no secondary pollution, and is a mature technology that is widely used in large coal-fired units.

[0003] The original thermal power unit's denitrification system was designed with DCS control and hard-wired data acquisition. The number of data points required varied depending on the installed capacity. With increasing environmental protection requirements, the following shortcomings also exist: the existing CEMS control method of the denitrification system cannot meet environmental protection requirements, and the denitrification system needs to be upgraded and transformed to add a precision ammonia injection system. The hard-wired signal transmission method requires the addition of a DCS cabinet. The equipment installation locations are scattered, requiring a large amount of cable laying, which increases the workload of the transformation and makes the later linkage commissioning and upgrade of the system more difficult. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings mentioned above by providing a bus-communication-based precision ammonia injection system for denitrification and its control method. This system enables unified management of precision ammonia injection equipment after it has been installed in a distributed manner. It features an open system interface, reserves access for future upgrades and modifications to the precision ammonia injection system, shortens equipment installation and commissioning time, has a simple structure, is modular and easy to install, and has low maintenance costs.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a bus communication-based precision ammonia injection system for denitrification, comprising: The bus communication control box is equipped with PA card, DP card and Modbus card in sequence; The PA card is connected in series with the urea main pipe inlet flow rate, the urea total volume regulating valve, and the urea spray gun regulating valve. The DCS cabinet is located on one side of the bus communication control box; The denitrification island is equipped with an A / B side ammonia-air mixture main valve, an A / B side inlet rapid testing device, an A / B side ammonia injection zone regulating valve, an A / B side outlet rapid testing device, and an A / B side ammonia escape valve, which are connected to the DCS cabinet in sequence through a bus communication control box. The denitrification electric heating control cabinet is electrically connected to the DCS cabinet via a DP card. The pyrolysis furnace is connected to the urea main pipe inlet flow, urea total volume regulating valve, and urea spray gun regulating valve in sequence through the denitrification electric heating control cabinet. The denitrification electric heating control cabinet 4 and the pyrolysis furnace outlet temperature are aggregated by the industrial data acquisition module and connected to the DCS cabinet through the Modbus communication protocol.

[0006] Furthermore, the AB-side ammonia-air mixture main valve includes an A-side ammonia-air mixture main valve located on one side of the denitrification island, and a B-side ammonia-air mixture main valve located on one side of the denitrification island. The AB side entrance rapid testing device includes an A side entrance rapid testing device installed on one side of the desinking island and a B side entrance rapid testing device installed on one side of the desinking island. The AB-side ammonia injection zone control gate includes the A-side ammonia injection zone control gate located on one side of the denitrification island, and the B-side ammonia injection zone control gate located on one side of the denitrification island. The AB side outlet rapid testing device includes an A side outlet rapid testing device installed on one side of the descaling island and a B side outlet rapid testing device installed on one side of the descaling island. Ammonia escape on the AB side includes ammonia escape on the A side located on one side of the denitrification island and ammonia escape on the B side located on one side of the denitrification island.

[0007] Furthermore, the number of the A-side inlet rapid testing device and the B-side inlet rapid testing device is at least two, the number of the A-side outlet rapid testing device and the B-side outlet rapid testing device is at least six, and the number of the AB-side ammonia-air mixture main valve and the AB-side ammonia injection zone regulating valve is at least six.

[0008] Furthermore, the main valve for the ammonia-air mixture on the AB side and the ammonia injection zone control valve on the AB side are respectively fixedly connected to the vertical flue.

[0009] Furthermore, the AB side inlet rapid testing device, the AB side outlet rapid testing device, and the AB side ammonia escape device are used to measure real-time ammonia data and predict boiler load and coal type changes, and are controlled by DCS logic, as well as to control the opening and closing degree of the AB side ammonia injection zone regulating valve, urea total regulating valve, and AB side ammonia-air mixture main valve.

[0010] Furthermore, the vertical flue is divided into 6 ammonia injection zones, each zone is equipped with an in-situ analyzer to measure NOx and O2 in real time, and the opening of the zone regulating valve is limited to 35% to 100%.

[0011] Furthermore, two NOx measuring points are arranged at the inlet on one side and six NOx measuring points are arranged at the outlet. When the oxygen content of a zone is greater than 10% and the measuring point is a bad point, the data of that measuring point is excluded and is not included in the average calculation.

[0012] The control method for a bus-communication-based precision ammonia injection system for denitrification includes the following steps: S1, Urea pyrolysis mixing section, PA bus is connected in series with urea main pipe inlet flow, urea total volume regulating valve, urea spray gun regulating valve and connected to local bus control box PA card. The electrical control section of the denitrification electric heating control cabinet 4 uses the DP bus method to send signals and controls to the DCS control. The temperature of the denitrification electric heating and the outlet temperature of the pyrolysis furnace are collected by the industrial data acquisition module and connected to the DCS through the Modbus communication protocol. S2. For the rapid measurement of denitrification flue gas data, taking side A as an example, two rapid measurement devices at the inlet of side A and six rapid measurement devices at the outlet of side A are connected in series using Modbus RTU communication. One ammonia escape device is also connected on side A. The same applies to side B. In the future, it will be necessary to further expand the inlet and outlet rapid measurement devices for direct connection. S3, Ammonia-air mixing regulation section, taking side A as an example, PA bus is connected in series with the main valve of ammonia-air mixing gas on side A and 6 zoning valves of ammonia injection zone on side A. The same applies to side B. S4. Set up a bus communication control box, and reserve expansion serial interfaces for S1, S2 and S3 above. Add devices that can be connected in series as needed. This system combination can adapt to boilers with larger capacity.

[0013] Furthermore, the actual denitrification efficiency is calculated as follows: (NOx inlet average (converted) - NOx outlet average (converted)) / NOx inlet average (converted) = actual denitrification efficiency; Calculation of denitrification setpoint efficiency: (NOx inlet average (converted) - NOx setpoint) / NOx inlet average (converted) = denitrification setpoint efficiency.

[0014] Furthermore, the changes in boiler load, sudden changes in inlet NOx, and widening of outlet NOx deviation directly affect the auxiliary control circuit. When the coal mill starts, the ammonia injection rate is increased for a short period, and the output of the main control circuit is limited to ±0.35. Both the main and auxiliary control PID circuits are counteracting. When the inlet / outlet NOx or oxygen level is abnormal, the valve command and feedback deviation is greater than 10%, or the NOx setpoint and actual value deviation is greater than 30 mg / Nm³, the system will automatically switch to manual mode and trigger an alarm.

[0015] The beneficial effects of this invention are reflected in: This invention ensures signal accuracy through oxygen content conversion, defect elimination, and inlet / outlet average value calculation. It employs cascaded PID control with multiple feedforwards, side-to-side leveling, and zoned fine-tuning to precisely match the ammonia demand in each zone, maintaining outlet NOx stably below 35 mg / Nm³, significantly reducing ammonia escape and preventing ammonium bisulfate blockage and corrosion. It uses fieldbus instead of traditional hardwiring, reducing DCS cabinets, extensive cable laying, and cable tray construction. Distributed equipment installation and modular access shorten the construction cycle by approximately 30%. New measuring points and zoned control valves can be directly connected in series later, facilitating expansion and maintenance and reducing maintenance costs by approximately 40%. It also addresses load and inlet NOx issues. x. Triple feedforward for outlet deviation ensures early and minimal lag in adjustment. It features short-term ammonia replenishment during pulverizer startup and rapid adaptation to changing operating conditions via load curves. The system response time is less than 10 seconds, effectively addressing coal type changes, load fluctuations, and pulverizer start-up and shutdown. Bus AB network redundancy prevents single-point communication failures. Multiple protection mechanisms, including faulty measurement point removal, abnormal alarms, and automatic / manual switching, prevent erroneous adjustments. Seamless switching between manual and automatic modes ensures flexible operation suitable for long-term continuous operation. It directly upgrades existing denitrification DCS systems, boasting high reuse rates. The control logic is mature, parameters are easy to tune, and it has been successfully applied in similar units. Reserved expansion interfaces allow for adaptation to units of different capacities, making it highly valuable for widespread adoption. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural flowchart of the present invention; Figure 2 This is a diagram showing the total ammonia injection control of the present invention; Figure 3 This is a diagram illustrating the NOx calculation formula for exports according to the present invention. Figure 4 This is a diagram illustrating the NOx (converted) inlet / outlet calculation formula of the present invention; Figure 5 The diagram shows the NOx reaction efficiency calculation formula of this invention. Figure 6 A diagram showing the NOx efficiency calculation formula for this invention; Figure 7 This is a zonal control diagram of the regulating valves for each zone at the outlet of the denitrification system of the present invention.

[0017] In the picture: 1. Urea main pipe inlet flow rate; 11. Bus communication control box; 12. DCS cabinet; 2. Urea total volume regulating valve; 3. Urea spray gun adjustment; 4. Denitrification electric heating control cabinet; 5. Pyrolysis furnace; 61. Ammonia-air mixture main valve on side A; 62. Ammonia-air mixture main valve on side B; 71. Rapid testing device for entrance A; 72. Rapid testing device for entrance B; 81. Ammonia injection zone control valve on side A; 82. Ammonia injection zone control valve on side B; 91. Rapid testing device at outlet A; 92. Rapid testing device at outlet B; 101. Ammonia escape from side A; 102. Ammonia escape from side B. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. 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.

[0019] Please see Figure 1-6 This invention discloses a bus-communication-based precision ammonia injection system for denitrification and its control method, comprising: The bus communication control box 11 is equipped with PA card, DP card and Modbus card in sequence. The PA card uses PROFIBUS-PA bus to connect to the flow rate, total volume control valve and spray gun control valve. PA card is connected in series with urea main pipe inlet flow 1, urea total volume regulating valve 2, urea spray gun regulating valve 3; DCS cabinet 12 is located on one side of bus communication control box 11. The DP card adopts PROFIBUS-DP bus. The temperature parameters of the pyrolysis furnace are connected to the DCS via Modbus. The flue gas measurement section uses Modbus RTU to connect the inlet / outlet fast measurement device and the ammonia escape monitoring device. The ammonia air conditioning section uses PROFIBUS-PA bus to connect the ammonia air mixture main valve and the zone control valve. The denitrification island is equipped with an A / B side ammonia-air mixture main valve, an A / B side inlet rapid testing device, an A / B side ammonia injection zone regulating valve, an A / B side outlet rapid testing device, and an A / B side ammonia escape valve. These are connected sequentially to the DCS cabinet 12 via a bus communication control box 11, with redundant A / B network segments. Urea solution enters the pyrolysis furnace via flow monitoring, total volume regulating valve, and spray gun regulating valve, where it mixes with hot primary air to generate an ammonia-air mixture. This mixture then enters the flue gas duct through the ammonia-air mixture main valve and zone regulating valve to participate in the denitrification reaction. The denitrification island is divided into A and B sides. On each side, six rapid testing devices are installed at the outlet of the vertical flue and two rapid testing devices are installed at the inlet. There is also one ammonia escape monitoring device in each side. The flue is divided into six ammonia injection zones along the width direction. Each zone is equipped with two zone control valves and one in-situ analyzer. The urea system includes a urea main pipe inlet flow meter, one urea total volume control valve, five urea spray gun control valves, a pyrolysis furnace, and a denitrification electric heating control cabinet. All field equipment is connected to the local bus control box via a bus and then connected to the DCS system via a redundant AB network. The denitrification electric heating control cabinet 4 is electrically connected to the DCS cabinet 12 via a DP card; The pyrolysis furnace 5 is connected to the urea main pipe inlet flow 1, urea total volume regulating valve 2, and urea spray gun regulating valve 3 via the denitrification electric heating control cabinet 4. The temperature of the denitrification electric heating and the outlet temperature of the pyrolysis furnace 5 are aggregated by the industrial data acquisition module IDAS and connected to the DCS cabinet 12 via the Modbus communication protocol. The urea flow required for precise ammonia injection is to enter the pyrolysis furnace 5 through the urea main pipe inlet flow 1, urea total volume regulating valve 2, and urea spray gun regulating valve 3 for pyrolysis. The boiler hot primary air enters the pyrolysis furnace 5 through the denitrification electric heating and mixes with the urea solution to form an ammonia-air mixture. The ammonia-air mixture enters the vertical flue through the AB side ammonia-air mixture main valve and the AB side ammonia injection zone regulating valve to participate in the flue gas denitrification catalytic reduction reaction.

[0020] Urea pyrolysis mixing section: The PROFIBUS-PA bus is used to connect the urea main pipe inlet flow 1, the urea total volume regulating valve 2, and the 5 spray gun regulating valves 3 in sequence, and is connected to the bus communication control box 11PA card. Denitrification electric heating control cabinet 4 and pyrolysis furnace 5: Denitrification electric heating is controlled by PROFIBUS-DP bus to start / stop and power. The outlet temperature and wall temperature of the pyrolysis furnace are uploaded to DCS via Modbus. Flue gas measurement section: The inlet and outlet rapid testing devices and ammonia slip monitoring devices are connected in series via Modbus RTU bus to upload NOx, O2, temperature and pressure data; Ammonia-air mixture regulating section: The main valve for ammonia-air mixture and 6 zone regulating valves are connected to the bus control box via PROFIBUS-PA bus; The entire network adopts AB dual-network redundancy, so the failure of any one network will not affect the operation of the system.

[0021] In one embodiment, the control of the total urea control valve 2: The automatic control of ammonia injection for denitrification adopts a cascade PID control strategy with feedforward. The setpoint is the outlet NOx content. The set efficiency is used as the SP of the cascade master PID controller, and the actual efficiency is used as the measured value PV of the master PID controller. The set efficiency and the output of the master PID controller are superimposed to generate a correction efficiency value. This value is multiplied by parameters such as the denitrification inlet NOx average, flue gas flow rate (load-based), and ammonia-nitrogen molar ratio to obtain the theoretically calculated ammonia flow rate signal. The theoretically calculated ammonia flow rate signal is divided by the number of spray guns in operation to obtain the average theoretically calculated ammonia flow rate of the spray guns. This average value SP is sent to the secondary PID controller and compared with the measured urea solution flow rate (m3 / h) PV signal. After calculation, the PID controller sends an adjustment signal to control the opening of the urea spray gun flow regulating valve to adjust the flow rate.

[0022] In a specific embodiment, the efficiency is set to 95%, and the total urea volume control valve is automatically activated. If the actual efficiency is lower than the set efficiency, the main control output increases and the control loop opens the urea capacity control valve. If the actual efficiency is higher than the set efficiency, the main control output decreases and the control loop closes the urea capacity control valve, thus achieving coarse adjustment of ammonia injection control and keeping the adjustment stable within a certain range. With the NOx value set at 35, the measured NOx value at the outlet shows a continuing trend of increasing compared to the set value. This directly affects the switching of the total control valve in the secondary regulating control loop. A change in power generation (boiler load) also directly affects the switching of the total control valve in the secondary regulating control loop. A change in the measured NOx value at the inlet also directly affects the switching of the total control valve. By incorporating the influence of these three variables into the control, the denitrification system can be controlled earlier, increasing the influence time of the regulating system and achieving precise control of the outlet NOx. When the auxiliary control feedforward coal mill starts up, the ammonia injection rate is increased for a certain period of time to achieve more precise regulation.

[0023] In a specific embodiment, the AB-side ammonia-air mixture main valve includes an A-side ammonia-air mixture main valve 61 located on one side of the denitrification island and a B-side ammonia-air mixture main valve 62 located on one side of the denitrification island. The A / B-side mixture main valves mainly ensure the leveling control of the reactors on both sides. First, manual control is performed based on the NOx values ​​at the outlets on both sides. When the average deviation value at the outlets on both sides is <10mg / Nm³, automatic control is activated for hot adjustment. The control method is as follows (taking the outlet on the A side as an example): the average value of the six measuring points (A1, A2, A3, A4, A5, A6) at the outlet of the flue on the A side is compared with the set value at the outlet on the A side to calculate the deviation value. The deviation value is output to the PID controller for calculation and is applied to the regulating valve on the A side to adjust the opening. The valve opening is adjusted accordingly based on the current valve opening. The valve opening is limited according to the actual adjustment of the ammonia injection grid and the required ammonia amount. The AB side entrance rapid testing device includes an A side entrance rapid testing device 71 installed on one side of the descaling island and a B side entrance rapid testing device 72 installed on one side of the descaling island. The A and B side ammonia injection zone control valves include the A side ammonia injection zone control valve 81 located on one side of the denitrification island and the B side ammonia injection zone control valve 82 located on one side of the denitrification island. To achieve precise ammonia injection, the flue gas duct ammonia injection grid branch pipes are divided into zones, resulting in 6 zones. Each zone is equipped with an in-situ analysis instrument to measure NOx and O2. The control method for each zone is as follows (taking the outlet zone A1 as an example): The measured value at point A1 is compared with the average value of the 6 measuring points (1, 2, 3, 4, 5, 6) on the A side flue gas duct to calculate the deviation. The deviation value is output to the PID controller for calculation, which then adjusts the opening of the two pneumatic regulating valves in zone 1. The valve opening is adjusted based on the existing valve opening, and the valve opening is limited according to the actual adjustment of the ammonia injection grid. Finally, the corresponding parameters are carefully modified during hot commissioning. The AB side outlet rapid testing device includes an A side outlet rapid testing device 91 installed on one side of the descaling island and a B side outlet rapid testing device 92 installed on one side of the descaling island. Ammonia escape on the AB side includes A-side ammonia escape 101 located on one side of the denitrification island and B-side ammonia escape 102 located on one side of the denitrification island. First, manually adjust the ammonia-air mixture main valve on sides A and B to ensure that the average NOx value deviation at both outlets is <10mg / Nm³. Then, switch to automatic mode and use the deviation between the average NOx value at one outlet and the set value as the PID input to adjust the opening of the ammonia-air mixture main valve to avoid over-injection or under-injection on one side. Each zone's in-situ analyzer uploads NOx and O2 in real time. The deviation between the zone's NOx and the side outlet average is calculated and then output as an adjustment command through PID calculation to control the opening of the zone's regulating valve. The opening is limited to 35% to 100% to prevent it from being completely closed or fully open. If the zone's oxygen content is >10% or the valve malfunctions, manual operation is activated after a 3-second delay and an alarm is triggered. If the inlet / outlet oxygen content is >8%, an alarm will be triggered. If the measuring point is faulty, the valve command / feedback deviation is >10%, or the NOx setting / actual deviation is >30mg / Nm³, the system will automatically switch to manual mode and trigger an alarm. In manual mode, the main controller tracks the "ammonia supply flow / C - actual efficiency", while the secondary controller tracks the valve position feedback to achieve seamless switching.

[0024] In one embodiment, the number of A-side inlet rapid testing devices 71 and B-side inlet rapid testing devices 72 is at least two, the number of A-side outlet rapid testing devices 91 and B-side outlet rapid testing devices 92 is at least six, and the number of AB-side ammonia-air mixture main valve and AB-side ammonia injection zone regulating valve is at least six.

[0025] In a specific embodiment, the main valve for ammonia-air mixture on the AB side and the ammonia injection zone control valve on the AB side are fixedly connected to the vertical flue.

[0026] In one embodiment, the AB-side inlet rapid testing device, the AB-side outlet rapid testing device, and the AB-side ammonia escape device are used to measure real-time ammonia data and predict boiler load and coal type changes. Through DCS logic control, the opening and closing degrees of the AB-side ammonia injection zone regulating valve, urea total regulating valve 2, and AB-side ammonia-air mixture main valve are controlled. By controlling the NOx values ​​at the inlet and outlet of the denitrification device, the opening degree of the zone regulating valve and the opening degree of the spray gun regulating valve are controlled, thereby controlling the NOx value at the outlet of the denitrification device, so that the NOx at the SCR outlet and the chimney inlet meets the emission standards.

[0027] A control logic switching button has been added to the DCS screen and displayed on the screen. Operators can switch between the new control logic and the original control logic. The screen allows manual operation of the NOx setpoint. In manual mode, the NOx setpoint tracks the average NOx output value O2 = 6%.

[0028] Two methods for controlling flue gas flow: ① Directly cite the sum of the newly added flue gas flow rates; ② Calculate the flue gas flow rate using a load piecewise linear function; The two methods can be switched from within the logic. During debugging, the load piecewise linear function is used first, and the switch to the sum of the newly added flue gas flow is determined based on the actual debugging effect.

[0029] In a specific embodiment, the vertical flue is divided into 6 ammonia injection zones, each zone is equipped with an in-situ analyzer to measure NOx and O2 in real time, and the opening of the zone regulating valve is limited to 35% to 100%.

[0030] In one embodiment, two NOx measuring points are arranged at the inlet on one side and six NOx measuring points are arranged at the outlet. When the oxygen content of a zone is greater than 10% and the measuring point is a bad point, the data of that measuring point is discarded and is not included in the mean calculation.

[0031] In a specific embodiment, the determination of the load-flue gas volume piecewise linear function f(L) is as follows: f(L) is a piecewise function, a custom function based on design or test data; Compile the measured or design flue gas flow rates corresponding to 3-5 different load points (e.g., 100%, 75%, 50%, 30% load); Piecewise linear fitting: Plot these points (load rate - flue gas rate) on graph paper and connect adjacent points with straight line segments to obtain the piecewise linear function; Example (data for a typical coal-fired boiler):

[0032] For any load factor, f(L) is calculated using linear interpolation. The formula is as follows: f(L) = y1 + {y2 - y1} / {x2 - x1} (L-x1) (x1,y1) and (x2,y2) are two known endpoints of the interval containing the load factor L.

[0033] The control method for a bus-communication-based precision ammonia injection system for denitrification includes the following steps: S1, Urea pyrolysis mixing section, PA bus is connected in series with urea main pipe inlet flow 1, urea total volume regulating valve 2, urea spray gun regulating valve 3 and connected to local bus control box PA card. The electrical control section of the denitrification electric heating control cabinet 4 uses the DP bus method to send signals and controls to the DCS for control. The temperature of the denitrification electric heating and the outlet temperature of the pyrolysis furnace 5 are collected by the Industrial Data Acquisition Module (IDAS) and connected to the DCS through the Modbus communication protocol. S2. For the rapid measurement of denitrification flue gas data, taking side A as an example, two rapid measurement devices at the inlet of side A and six rapid measurement devices at the outlet of side A are connected in series using Modbus RTU communication. One ammonia escape device is also connected on side A. The same applies to side B. In the future, it will be necessary to further expand the inlet and outlet rapid measurement devices for direct connection. S3, Ammonia-air mixing regulation section, taking side A as an example, PA bus is connected in series with the main valve of ammonia-air mixing gas on side A and 6 zoning valves of ammonia injection zone on side A. The same applies to side B. S4. Set up a bus communication control box 11, and reserve expansion serial interfaces for S1, S2 and S3 above. Add devices that can be connected in series as needed. This system combination can adapt to boilers with larger capacity.

[0034] In a specific embodiment, the actual denitrification efficiency is calculated as follows: (NOx inlet average value (converted) - NOx outlet average value (converted)) / NOx inlet average value (converted) = actual denitrification efficiency; Calculation of denitrification setpoint efficiency: (NOx inlet average (converted) - NOx setpoint) / NOx inlet average (converted) = denitrification setpoint efficiency.

[0035] In one embodiment, changes in boiler load, sudden changes in inlet NOx, and increased deviations in outlet NOx directly affect the secondary control circuit. When the coal mill starts, the ammonia injection rate is increased briefly, and the main control output is limited to ±0.35. Both the main and secondary control PID controllers are counteracting. When the inlet / outlet NOx or oxygen level is abnormal, the valve command and feedback deviation is greater than 10%, or the NOx setpoint and actual value deviation is greater than 30 mg / Nm³, the system will automatically switch to manual mode and trigger an alarm.

[0036] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0037] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0038] Additionally, "multiple" refers to two or more.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A bus-communication-based precision ammonia injection system for denitrification, characterized in that, include: The bus communication control box (11) is equipped with PA card, DP card and Modbus card in sequence; The PA card is connected in series with the urea main pipe inlet flow (1), the urea total volume regulating valve (2), and the urea spray gun regulating valve (3). DCS cabinet (12) is located on one side of bus communication control box (11); The denitrification island is equipped with an AB side ammonia-air mixture main valve, an AB side inlet rapid testing device, an AB side ammonia injection zone regulating valve, an AB side outlet rapid testing device, and an AB side ammonia escape device, which are connected to the DCS cabinet (12) in sequence through the bus communication control box (11). The denitrification electric heating control cabinet (4) is electrically connected to the DCS cabinet (12) via a DP card; The pyrolysis furnace (5) is connected to the urea main pipe inlet flow (1), urea total volume regulating valve (2), and urea spray gun regulating valve (3) in sequence through the denitrification electric heating control cabinet (4). The outlet temperatures of the denitrification electric heating control cabinet (4) and the pyrolysis furnace (5) are aggregated by the Industrial Data Acquisition Module (IDAS) and connected to the DCS cabinet (12) through the Modbus communication protocol.

2. The bus-communication-based precision ammonia injection system for denitrification as described in claim 1, characterized in that: The AB-side ammonia-air mixture main valve includes an A-side ammonia-air mixture main valve (61) located on one side of the denitrification island, and a B-side ammonia-air mixture main valve (62) located on one side of the denitrification island. The AB side entrance rapid testing device includes an A side entrance rapid testing device (71) installed on one side of the descaling island and a B side entrance rapid testing device (72) installed on one side of the descaling island. The AB side ammonia injection zone control valve includes the A side ammonia injection zone control valve (81) located on one side of the denitrification island, and the B side ammonia injection zone control valve (82) located on one side of the denitrification island. The AB side outlet fast testing device includes an A side outlet fast testing device (91) installed on one side of the descaling island, and a B side outlet fast testing device (92) installed on one side of the descaling island. Ammonia escape on the AB side includes ammonia escape on the A side (101) located on one side of the denitrification island, and ammonia escape on the B side (102) located on one side of the denitrification island.

3. The bus-communication-based precision ammonia injection system for denitrification as described in claim 2, characterized in that: The number of the A-side inlet fast testing device (71) and the B-side inlet fast testing device (72) is at least two, the number of the A-side outlet fast testing device (91) and the B-side outlet fast testing device (92) is at least six, and the number of the AB-side ammonia-air mixture main valve and the AB-side ammonia injection zone regulating valve is at least six.

4. The bus-communication-based precision ammonia injection system for denitrification as described in claim 1, characterized in that: The main valve for ammonia-air mixture on the AB side and the zoned valve for ammonia injection on the AB side are fixedly connected to the vertical flue.

5. The bus-communication-based precision ammonia injection system for denitrification as described in claim 1, characterized in that: The AB side inlet fast test device, AB side outlet fast test device and AB side ammonia escape are used to measure real-time data of ammonia and predict boiler load and coal type changes, and are controlled by DCS logic, as well as control the opening and closing degree of AB side ammonia injection zone regulating valve, urea total regulating valve (2) and AB side ammonia-air mixture main valve.

6. The bus-communication-based precision ammonia injection system for denitrification as described in claim 4, characterized in that: The vertical flue is divided into 6 ammonia injection zones, each zone is equipped with an in-situ analyzer to measure NOx and O2 in real time, and the opening of the zone regulating valve is limited to 35% to 100%.

7. The bus-communication-based precision ammonia injection system for denitrification as described in claim 1, characterized in that: Two NOx measuring points are arranged at the inlet on one side and six NOx measuring points are arranged at the outlet. When the oxygen content of a zone is greater than 10% and the measuring point is a bad point, the data of that measuring point is excluded and is not included in the mean calculation.

8. The control method for a bus-communication-based precision ammonia injection system for denitrification according to any one of claims 1-7, characterized in that: Includes the following steps: S1, Urea pyrolysis mixing section, PA bus is connected in series with urea main pipe inlet flow (1), urea total volume regulating valve (2), urea spray gun regulating valve (3) and connected to local bus control box PA card. The electrical control part of the denitrification electric heating control cabinet (4) uses the DP bus method to send signals and control to the DCS for control. The temperature of the denitrification electric heating and the outlet temperature of the pyrolysis furnace (5) are collected by the Industrial Data Acquisition Module (IDAS) and connected to the DCS through the Modbus communication protocol. S2. For the rapid measurement of denitrification flue gas data, taking side A as an example, two rapid measurement devices at the inlet of side A and six rapid measurement devices at the outlet of side A are connected in series using Modbus RTU communication. One ammonia escape device is also connected on side A. The same applies to side B. In the future, it will be necessary to further expand the inlet and outlet rapid measurement devices for direct connection. S3, Ammonia-air mixing regulation section, taking side A as an example, PA bus is connected in series with the main valve of ammonia-air mixing gas on side A and 6 zoning valves of ammonia injection zone on side A. The same applies to side B. S4. Set up a bus communication control box (11), and reserve an expansion serial interface for the above S1, S2 and S3. Add devices that can be connected in series as needed. This system combination can adapt to boilers with larger capacity.

9. The control method for a bus-communication-based precision ammonia injection system for denitrification, as described in claim 8, is characterized in that: Calculation of actual denitrification efficiency: (NOx inlet average (converted) - NOx outlet average (converted)) / NOx inlet average (converted) = actual denitrification efficiency; Calculation of denitrification setpoint efficiency: (NOx inlet average (converted) - NOx setpoint) / NOx inlet average (converted) = denitrification setpoint efficiency.

10. The control method for a bus-communication-based precision ammonia injection system for denitrification, as described in claim 9, is characterized in that: The changes in boiler load, sudden changes in inlet NOx, and widening of outlet NOx deviation directly affect the auxiliary control circuit. When the coal mill starts, the ammonia injection rate is increased for a short period of time, and the output of the main control circuit is limited to ±0.

35. Both the main and auxiliary control PID circuits are counteracting. When the inlet / outlet NOx or oxygen content is bad, the valve command and feedback deviation is greater than 10%, or the NOx set value and actual value deviation is greater than 30 mg / Nm³, the system will automatically switch to manual mode and trigger an alarm.

Images