A control method for ammonia water injection in an SCR denitration system of a waste incinerator

Abstract

The application discloses a control method for ammonia water injection in SCR denitration of a waste incinerator, and relates to the technical field of environmental protection engineering. The method comprises the following steps: detecting the flue gas flow, flue gas temperature, flue gas pressure and nitrogen oxide concentration at the inlet of a flue gas reactor; detecting the absolute temperature distribution image of the ammonia water injection layer of the reactor in the transverse section and converting the same into the absolute temperature distribution contour map of the transverse section; detecting the nitrogen oxide concentration distribution image of the ammonia water injection layer of the reactor in the transverse section and converting the same into the concentration distribution contour map of the transverse section; determining the optimal denitration reduction temperature line, wherein the neighborhood of the line is the optimal denitration interval of ammonia water; adjusting the number of core positions and the injection amount of the corresponding temperature of the nozzle according to the nitrogen oxide concentration distribution contour map; fitting the ammonia removal efficiency under different working conditions by means of a random forest algorithm, and optimizing the parameters of the trained model; and optimizing the use of ammonia water under different working conditions by means of a genetic algorithm, and finding the optimal ammonia injection amount under the corresponding working condition.

Description

Technical Field

[0001] This application relates to the field of environmental engineering technology, and in particular to a method for controlling ammonia water injection in SCR denitrification of a waste incinerator. Background Technology

[0002] Nitrogen oxides produced during waste incineration are a significant contributor to air pollution. Nitrogen oxides mainly include nitrogen oxides such as NO, NO2, N2O, N2O3, N2O4, and N2O5, with NO and NO2 being the primary components.

[0003] According to the denitrification process, there are two types of denitrification in waste incinerators: non-incineration denitrification (SNCR) and flue gas denitrification (SCR). SCR has high reliability and high denitrification efficiency, but its operation and maintenance are complex and its operating cost is high; SNCR has simple operation and maintenance and low operating cost, but its denitrification efficiency is low.

[0004] The reducing agent in SCR denitrification systems is ammonia, which typically comes from three sources: liquid ammonia, urea, and ammonia water. Liquid ammonia is relatively inexpensive to transport and use, but it is toxic and requires high-pressure storage; ammonia water is more expensive to transport and use, but it is harmless and can be stored at normal atmospheric pressure; urea is the most expensive to use, but inexpensive to transport, harmless, and can be stored at normal atmospheric pressure. Currently, liquid ammonia is the most commonly used reducing agent in SCR denitrification systems in my country.

[0005] SCR denitrification technology calculates the amount of reducing agent required under corresponding operating conditions by measuring the content of nitrogen oxides in flue gas, flue gas flow rate and temperature, and carries out the denitrification reaction in the denitrification reactor. The reducing agent is injected to reduce the flue gas.

[0006] SCR denitrification systems have high denitrification reduction reaction efficiency at 300-400℃. The amount of reducing agent needs to be adjusted promptly according to different operating conditions; otherwise, insufficient reducing agent will lead to incomplete reaction, or excessive reducing agent will reduce efficiency and waste the reducing agent. Therefore, controlling the SCR reducing agent is crucial to directly affecting denitrification efficiency. Summary of the Invention

[0007] To address the issue of controlling the amount of liquid ammonia injected, and to enable timely adjustments based on the required amount of reducing agent under different conditions, thereby improving denitrification efficiency, this application provides a method for controlling ammonia injection in SCR denitrification of a waste incinerator.

[0008] The present application provides a method for controlling ammonia water injection in SCR denitrification of a waste incinerator, which adopts the following technical solution.

[0009] A method for controlling ammonia injection in SCR denitrification of a waste incinerator includes the following steps:

[0010] Step (1): Detect the flue gas flow rate, flue gas temperature, flue gas pressure, and nitrogen oxide concentration at the reactor inlet to obtain the initial detection parameters;

[0011] Step (2): Based on the detected initial parameters, obtain the absolute temperature distribution image of the cross section of the ammonia water injection layer in the reactor according to the initial parameters of the flue gas temperature, and convert it into an isopleth map of the absolute temperature distribution of the cross section.

[0012] Step (3): Based on step (2), determine the optimal denitrification reduction temperature line, and the neighborhood of this line is the optimal denitrification range for ammonia water;

[0013] Step (4): Based on the initial parameters detected in step (1), obtain the nitrogen oxide concentration distribution map of the cross section of the ammonia water spray layer in the reactor according to the nitrogen oxide concentration and convert it into a cross section concentration distribution contour map.

[0014] Step (5): Based on the isopleth map of nitrogen oxide concentration distribution, adjust the number of core positions of the nozzle corresponding to the temperature and the spray volume;

[0015] Step (6): Fit the ammonia removal efficiency under different working conditions using the random forest algorithm, and fine-tune the parameters of the trained model;

[0016] Step (7): Optimize the use of ammonia water under different working conditions using a genetic algorithm to find the optimal amount of ammonia to be injected under the corresponding working conditions.

[0017] Optionally, the cross-sectional absolute temperature distribution contour map obtained in step (2) and the optimal denitrification reduction temperature line determined in step (3) are located in the neighborhood of the optimal denitrification range of ammonia water.

[0018] Based on the chemical reactions occurring during SCR denitrification (such as Equations 1 and 2), the reaction proceeds more fully and the utilization rate of ammonia water in the reaction is higher when the reaction temperature is between 350-390℃. Therefore, it is necessary to distinguish the temperatures in the cross-sectional absolute temperature isopleth diagram.

[0019] Optionally, the cross-sectional nitrogen oxide concentration distribution contour map obtained in step (4) and the number and spray volume of the core positions corresponding to the temperature of the nozzle in step (5) are adjusted.

[0020] Based on the isopleth map of nitrogen oxide concentration distribution, different concentration zones can be divided. According to the actual situation, the zones can be divided into three areas: high concentration zone, medium concentration zone, and low concentration zone. Different data volumes of nozzles are adjusted for the three different zones. The zones can be divided in a ratio of 5:4:3 for high, medium, and low concentration zones. The valve opening of the nozzles is adjusted according to the high, medium, and low opening of the high, medium, and low zones.

[0021] Optionally, steps (6) and (7) control the ammonia injection amount according to different working conditions. Therefore, it is necessary to collect data corresponding to various working conditions, conduct data analysis and cleaning, obtain a model through fitting and learning, and optimize the ammonia injection amount to obtain the optimal ammonia injection amount under the corresponding working conditions.

[0022] In summary, this application includes at least the following beneficial effects:

[0023] 1. By using the absolute temperature distribution contour map of the cross section, determine the optimal denitrification reduction temperature line. The neighborhood of this line is the optimal denitrification range for ammonia water, thereby improving the utilization rate of ammonia water.

[0024] 2. Based on the cross-sectional nitrogen oxide concentration distribution contour map, adjust the number and spray volume of the core positions corresponding to the temperature of the nozzles, and adjust the supply of ammonia water to avoid waste due to too much or reduced denitrification efficiency due to too little.

[0025] 3. The ammonia removal efficiency under different operating conditions is fitted by random forest algorithm, and the ammonia water usage under different operating conditions is optimized by genetic algorithm. The ammonia injection amount is optimized to obtain the optimal ammonia injection amount under the corresponding operating conditions, thereby improving the denitrification efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Fig. 1 It is a control flow diagram.

[0028] Fig. 2 It is a contour map of the absolute temperature distribution across a cross section.

[0029] Fig. 3 It is a contour map of nitrogen oxide concentration distribution in a cross section. Detailed Implementation

[0030] 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 some embodiments of the present invention, and not all embodiments. 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.

[0031] The following is in conjunction with the appendix Figs. 1 to 3 This application will be described in further detail.

[0032] This application discloses a method for controlling ammonia water injection in SCR denitrification of a waste incinerator.

[0033] This invention achieves ammonia injection control through a waste incinerator detection and an ammonia injection device, including a flue gas detection device and an ammonia injection device.

[0034] The flue gas detection device is connected to the host computer software and can be used to detect flue gas flow rate, flue gas temperature, flue gas pressure, and nitrogen oxide concentration in real time. It also injects ammonia water through an ammonia water injection device.

[0035] The flow rate of flue gas is detected by a Pitot tube flow meter. The Pitot tube flow meter is a double-layered hollow composite tube bent at a right angle with multiple pressure taps. It can simultaneously measure the total pressure and static pressure of the fluid. It is used in conjunction with a differential pressure transmitter and a flow display instrument. The flow velocity is calculated by measuring the difference between the total pressure and the static pressure of the fluid, and the flue gas pressure is also detected at the same time.

[0036] The flue gas temperature is measured by an infrared temperature sensor. The infrared temperature sensor is a non-contact infrared temperature measurement device, which can be used for flue gas temperature detection in high-temperature scenarios such as waste incinerators. The infrared temperature sensor uses infrared light to measure temperature. It does not contact the object being measured during temperature measurement and has the advantages of short response time, no interference with the measured temperature field, long service life, and convenient operation.

[0037] The concentration of nitrogen oxides is detected by using a nitrogen oxide analyzer based on chemiluminescence detection technology.

[0038] The ammonia injection device includes multiple nozzles for spraying ammonia water branched from a main pipeline. A main valve is installed on the main pipeline, and an electronically controlled valve is installed on each nozzle, which facilitates the adjustment and control of the nozzle flow rate.

[0039] Reference Figs. 1 to 3 The method for controlling ammonia injection in SCR denitrification of a waste incinerator according to the present invention includes the following steps:

[0040] Step (1): Using the flue gas detection device, detect the flue gas flow rate, flue gas temperature, flue gas pressure, and nitrogen oxide concentration at the reactor inlet to obtain the initial detection parameters;

[0041] Step (2): Based on the initial parameters obtained in step (1), the absolute temperature distribution image of the cross section of the ammonia water injection layer in the reactor is obtained according to the initial parameters of the flue gas temperature, and then converted into an isopleth map of the absolute temperature distribution of the cross section.

[0042] Step (3): Based on the data, obtain the average temperature of the upper, middle and bottom of the reactor, the ammonia injection rate and the nitrogen oxide concentration at the reactor outlet, confirm the effect of temperature on the denitrification rate under ammonia saturation conditions, draw the denitrification efficiency curves at different temperatures, and confirm the optimal denitrification temperature. Through the cross-sectional absolute temperature distribution contour map obtained in step (2), determine the optimal denitrification reduction temperature line. The neighborhood of this line is the optimal denitrification range for ammonia water.

[0043] Based on the chemical reactions occurring during SCR denitrification (such as Equations 1 and 2), the reaction proceeds more fully and the utilization rate of ammonia water in the reaction is higher when the reaction temperature is between 350-390℃. Therefore, it is necessary to distinguish the temperatures in the cross-sectional absolute temperature isopleth diagram.

[0044] 4NO + 4NH3 + O2 → 4N2 + 6H2O (Equation 1)

[0045] 4NO₂ + 8NH₃ + O₂ → 7N₂ + 12H₂O (Equation 2)

[0046] Step (4): Based on the initial parameters detected in step (1), obtain the nitrogen oxide concentration distribution map of the cross section of the ammonia water spray layer in the reactor according to the nitrogen oxide concentration and convert it into a cross section concentration distribution contour map.

[0047] Step (5): Using the cross-sectional nitrogen oxide concentration distribution contour map obtained in step (4), adjust the number of core positions and spray volume of the nozzle corresponding to the temperature.

[0048] Based on the nitrogen oxide concentration distribution isopleth map, different concentration zones are defined. These zones can be divided into high-concentration, medium-concentration, and low-concentration areas, depending on the actual situation. Specifically, the data is first processed using a box plot to remove outliers. Then, the data is divided into three levels (high, medium, and low) based on the highest and lowest values. For ammonia injection pipelines where the nozzle valve opening cannot be freely controlled, the nozzles in the three different zones can be adjusted. The high-concentration zone is defined as 100% ammonia injection under saturated ammonia conditions. Line graphs of ammonia injection volume and temperature are created for the medium and low-concentration zones based on data analysis under saturated ammonia conditions. This determines the optimal ammonia injection volume for each zone, and the number of nozzles to be adjusted accordingly.

[0049] Step (6): Fit the ammonia removal efficiency under different working conditions using the random forest algorithm, and fine-tune the parameters of the trained model;

[0050] Fitting the denitrification efficiency requires confirming the nitrogen oxide concentrations at the reactor inlet and outlet, the ammonia content at the reactor outlet, the flue gas temperature, flow rate, and pressure at the reactor inlet, and the oxygen content at the reactor outlet. The outlet nitrogen oxide concentration is then used as a label for fitting.

[0051] The parameter optimization of the model mainly considers the size and depth of the tree, and grid search is used for optimization during the adjustment.

[0052] Step (7): Optimize the use of ammonia water under different working conditions using a genetic algorithm to find the optimal amount of ammonia to be injected under the corresponding working conditions.

[0053] According to the SCR denitrification process, the control points include the opening degree of the flue gas inlet valve, the frequency of the reactor fan, and the opening degree of the ammonia injection pipeline valve. These control points are adjusted under different operating conditions (different flue gas temperatures, flow rates, pressures, and nitrogen oxide concentrations). Based on the fitting model obtained in step (6), the controllable points—the opening degree of the flue gas inlet valve, the frequency of the reactor fan, and the opening degree of the ammonia injection pipeline valve—are combined as a single unit. The optimization algorithm will arbitrarily generate a specified number of combinations within the upper and lower limits of each control point. Under each operating condition, the nitrogen oxide concentration of the generated combinations can be predicted. The optimal ammonia injection rate is the combination that results in the lowest ammonia injection rate under each operating condition and meets the nitrogen oxide emission standards.

[0054] The above are merely preferred embodiments of the present invention and are 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 method for controlling ammonia water injection in SCR denitrification of a waste incinerator, characterized in that, Includes the following steps: Step (1): Detect the flue gas flow rate, flue gas temperature, flue gas pressure, and nitrogen oxide concentration at the reactor inlet to obtain the initial detection parameters; Step (2): Based on the initial parameters, obtain the absolute temperature distribution image of the cross section of the ammonia water injection layer in the reactor according to the initial parameters of the flue gas temperature, and convert it into an isopleth map of the absolute temperature distribution of the cross section. Step (3): Based on step (2), determine the optimal denitrification reduction temperature line, and the neighborhood of this line is the optimal denitrification range for ammonia water; Step (4): Based on the initial parameters detected in step (1), obtain the nitrogen oxide concentration distribution map of the cross section of the ammonia water spray layer in the reactor according to the nitrogen oxide concentration and convert it into a cross section concentration distribution contour map. Step (5): Based on the isopleth map of nitrogen oxide concentration distribution, adjust the number of core locations corresponding to the temperature of the nozzles and the spray volume; Step (6): Fit the ammonia removal efficiency under different working conditions using the random forest algorithm, and fine-tune the parameters of the trained model; Step (7): Optimize the use of ammonia water under different working conditions using a genetic algorithm to find the optimal amount of ammonia to be injected under the corresponding working conditions.

2. The method for controlling ammonia water injection in SCR denitrification of a waste incinerator according to claim 1, characterized in that, The cross-sectional absolute temperature distribution contour map obtained in step (2) and the optimal denitrification reduction temperature line determined in step (3) are located in the neighborhood of the optimal denitrification range of ammonia water. Based on the chemical reactions that occur during the SCR denitrification process When the reaction temperature is between 350-390℃, the reaction occurs more fully and the utilization rate of ammonia water in the reaction is higher. Therefore, it is necessary to distinguish the temperatures in the cross-sectional absolute temperature isopleth diagram.

3. The method for controlling ammonia water injection in SCR denitrification of a waste incinerator according to claim 1, characterized in that, The contour map of nitrogen oxide concentration distribution in the cross section obtained in step (4), and the number and spray volume of the core positions corresponding to the temperature of the nozzle in step (5); Based on the isopleth map of nitrogen oxide concentration distribution, different concentration zones were divided into three areas according to the actual situation: high concentration zone, medium concentration zone, and low concentration zone. Different data volumes of nozzles were adjusted for the three different zones, and the zones were divided in a ratio of 5:4:3 for high, medium, and low concentration zones. The valve opening of the nozzles was adjusted according to the high, medium, and low openings of the high, medium, and low zones.

4. The method for controlling ammonia injection in SCR denitrification of a waste incinerator according to claim 1, characterized in that, Steps (6) and (7) control the amount of ammonia injected under different working conditions. Therefore, it is necessary to collect data corresponding to various working conditions, analyze and clean the data, obtain a model through fitting and learning, and optimize the amount of ammonia injected to obtain the optimal amount of ammonia injected under the corresponding working conditions.

Images