High-efficiency SNCR control methods

Abstract

This invention discloses a high-efficiency SNCR control method, relating to the field of SNCR denitrification technology. The high-efficiency SNCR control method is used in an SNCR denitrification system for a boiler. The boiler furnace is divided into several zones horizontally, and multiple layers of spray guns are arranged along the height of the furnace in each zone. The method includes: acquiring the boiler load during operation, the moisture content of the boiler outlet flue gas, and the flue gas temperature of each zone in the layer where the temperature measuring device is located; calculating the flue gas temperature at each spray gun in real time using a pre-established three-dimensional temperature field calculation model based on the boiler load, the moisture content of the boiler outlet flue gas, and the flue gas temperature of each zone in the layer where the temperature measuring device is located; selecting spray guns in the optimal denitrification reaction temperature range in each zone based on the flue gas temperature at each spray gun; and controlling the selected spray guns in each zone to put them into operation. This invention can solve the problems of low NOx removal efficiency or high NH3 escape in different furnace areas.

Description

Technical Field

[0001] This invention relates to the field of SNCR denitrification technology, and in particular to a highly efficient SNCR control method. Background Technology

[0002] With increasing global energy consumption, NOx is produced in the flue gas from the combustion of fuels such as coal, biomass, waste, natural gas, and oil. NOx released into the atmosphere causes problems such as acid rain, acid fog, photochemical smog, ozone depletion, soil acidification, and eutrophication of surface water. Flue gas denitrification (NOx removal) reactions inevitably result in the escape of ammonia into the atmosphere. Ammonia (NH3) is an important alkaline gas in the atmosphere and can react with acidic gases such as sulfuric acid and nitric acid to form ammonium salts, which are important precursors to secondary inorganic aerosol particles. Excessive ammonia in the atmosphere is harmful to human health and the environment. Therefore, controlling NOx emissions and NH3 escape is imperative.

[0003] Selective non-catalytic reduction (SNCR) technology is a widely used flue gas denitrification technology in the boiler and waste incineration industries, primarily for reducing NOx emissions. Its core principle involves injecting a reducing agent (such as ammonia or urea) into the flue gas at high temperatures (900–1050°C) to reduce NOx to nitrogen (N2) and water (H2O) without the need for a catalyst.

[0004] For denitrification in waste-to-energy plants, SNCR has the following advantages compared to selective catalytic reduction (SCR) technology:

[0005] Low investment cost: No catalyst is required, the equipment structure is simple, and the installation and maintenance costs are low.

[0006] Flexible operation: It is suitable for the high-temperature environment of waste incineration boilers and can carry out denitrification reaction directly in the furnace.

[0007] Highly adaptable: It can be adjusted to suit the combustion characteristics of different fuels (such as municipal solid waste and industrial waste).

[0008] SNCR systems in waste incineration plants typically include the following key components:

[0009] Reducing agent storage and preparation module: Ammonia or urea solution is used as the reducing agent.

[0010] Reducing agent mixing and dispensing module: Mixes the reducing agent and dilution water (usually softened water or demineralized water) in a suitable ratio and supplies it to the spray gun that needs to be used.

[0011] Injection system: Usually uses compressed air atomization, and the reducing agent is atomized and sprayed into the appropriate position in the furnace through a dual-fluid spray gun, so that the reducing agent and flue gas are mixed.

[0012] Measurement and Control System: The furnace temperature is monitored using infrared thermography or thermocouples, while NOx emissions and NH3 escape in the flue gas are measured simultaneously. The measurement results are used by the control system to adjust the reducing agent and dilution water levels.

[0013] However, SNCR technology also has some inherent drawbacks. The optimal reaction temperature range for SNCR denitrification is relatively narrow (typically 900–1050°C). If the temperature is too high, some NH3 will be oxidized, causing a significant decrease in denitrification efficiency. If the temperature is too low, the amount of NH3 escaped will increase significantly while denitrification efficiency decreases. Furthermore, the combustion process often involves uneven distribution of flue gas temperature and composition across the flue gas flow cross-section, and fluctuations in flue gas temperature and composition due to changes in the calorific value and composition of waste. In addition, the inaccuracy and reaction lag of thermocouple temperature measurement make it very difficult to add the appropriate amount of reducing agent within the suitable temperature range and achieve good mixing between the flue gas and the reducing agent. This results in situations where NOx removal efficiency is low or NH3 escape is high in different furnace regions. Summary of the Invention

[0014] In view of this, embodiments of the present invention provide an efficient SNCR control method to solve the problems of low NOx removal efficiency or high NH3 escape in different furnace regions.

[0015] A high-efficiency SNCR control method is provided for an SNCR denitrification system in a boiler. The boiler furnace is equipped with a temperature measuring device. The boiler furnace is divided into several horizontal zones, and multiple layers of spray guns are arranged along the height of the furnace in each zone. The spray guns in each zone and the layers of spray guns in each zone are connected in parallel. The method includes:

[0016] Step S101: Obtain the boiler load during operation, the moisture content of the flue gas at the boiler outlet, and the flue gas temperature of each zone on the floor where the temperature measuring device is located.

[0017] Step S102: Based on the boiler load, the moisture content of the flue gas at the boiler outlet, and the flue gas temperature of each zone in the layer where the temperature measuring device is located, the flue gas temperature at each spray gun is calculated in real time using a pre-established three-dimensional temperature field calculation model.

[0018] Step S103: Based on the flue gas temperature at each spray gun, select a spray gun in the optimal denitrification reaction temperature range for each zone;

[0019] Step S104: Calculate the flow rate of the high-concentration reducing agent and dilution water, and control the selected spray guns for each zone to put them into operation.

[0020] Furthermore, step S102 includes:

[0021] Step S1021: Calculate the flue gas temperature gradient that has been corrected for load but not for flue gas moisture content based on the current boiler evaporation rate;

[0022] Step S1022: Calculate the flue gas temperature gradient after moisture content correction based on the boiler outlet flue gas moisture content and the flue gas temperature gradient after load correction but without flue gas moisture content correction.

[0023] Step S1023: Calculate the flue gas temperature at each spray gun based on the flue gas temperature gradient corrected for flue gas moisture content and the flue gas temperature of each zone in the layer where the temperature measuring device is located.

[0024] Furthermore, in step S1021, the flue gas temperature gradient is corrected by load but not by flue gas moisture content. The calculation formula is:

[0025] ;

[0026] Where A1, B1, and C1 are fitting constants, and D is the current boiler evaporation rate. MCR The boiler evaporation rate at the MCR point. The flue gas temperature gradient is the MCR point.

[0027] Furthermore, in step S1022, the flue gas temperature gradient after correction for flue gas moisture content... The calculation formula is:

[0028] ;

[0029] Where A2, B2, and C2 are fitting constants, and H2O is the moisture content of the flue gas at the boiler outlet. MCR The moisture content of the boiler outlet flue gas is the MCR point.

[0030] Furthermore, in step S1023, the formula for calculating the flue gas temperature at each spray gun is as follows:

[0031] ;

[0032] Among them, t ij The flue gas temperature at the spray gun in zone i, layer j, t i The average temperature of the temperature measuring device layer in zone i. The height difference between the spray gun and the temperature measuring device is j.

[0033] Furthermore, step S103 further comprises:

[0034] Based on the flue gas temperature at each spray gun, select the spray gun in each zone that is closest to the denitrification reaction set temperature.

[0035] Furthermore, step S104 includes:

[0036] Step S1041: The high-concentration reducing agent consumption of the SNCR denitrification system is calculated based on the boiler evaporation rate measurement, boiler outlet flue gas moisture content measurement, NOx emission concentration and NH3 escape concentration set values, and then corrected by the measured values ​​of NOx emission concentration and NH3 escape concentration.

[0037] Step S1042: The diluted reducing agent flow rate for each partition is obtained from CFD simulation and debugging experience;

[0038] Step S1043: The high-concentration reducing agent consumption of each reducing agent mixing and distribution module of the SNCR denitrification system is determined by the proportion of the diluted reducing agent flow rate set value of the corresponding zone of each reducing agent mixing and distribution module to the total amount; the dilution water consumption of this module is obtained by the difference between the sum of the diluted reducing agent flow rate set values ​​of each branch / zone corresponding to this module and the high-concentration reducing agent consumption of this module.

[0039] Furthermore, in step S1041, the calculation formula for the high-concentration reducing agent consumption of the SNCR denitrification system is as follows:

[0040] ;

[0041] Where, q hsd For high-concentration reducing agent consumption setpoints, k1 is the evaporation rate correction factor, k2 is the boiler outlet flue gas moisture content correction factor, k3 is the NOx emission concentration setpoint correction factor, k4 is the NH3 escape concentration setpoint correction factor, and q MCR High-concentration reducing agent consumption calculated for MCR conditions;

[0042] ;

[0043] Where, q h The SNCR denitrification system has a high-concentration reducing agent consumption, u(t)1 is the correction value of the NOx emission concentration setpoint and measured value after passing through the PID controller, u(t)2 is the correction value of the NH3 escape concentration setpoint and measured value after passing through the PID controller, and q hsd Set the consumption value for high-concentration reducing agent;

[0044] And / or, in step S1043, the calculation formula for the high-concentration reducing agent consumption of each reducing agent mixing and distribution module of the SNCR denitrification system is as follows:

[0045] ;

[0046] Where, q hx q represents the high-concentration reducing agent consumption of the x-th reducing agent mixing and dispensing module. h For the high-concentration reducing agent consumption of the SNCR denitrification system, q m1 q m2 The diluted reducing agent flow rates, q, are for the branches / zones corresponding to the first and second reducing agent mixing and distribution modules, respectively. mx The diluted reducing agent flow rate is the branch / zone corresponding to the x-th reducing agent mixing and distribution module, where x is 1 or 2;

[0047] The formula for calculating the dilution water consumption of each reducing agent mixing and dispensing module is as follows:

[0048] ;

[0049] Where, q sx Let q1, q2, q3, and q be the dilution water consumption of the xth reducing agent mixing and distribution module. n These represent the diluted reducing agent flow rates (q) for zones 1 through n corresponding to the reducing agent mixing and distribution module. hx This represents the high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module.

[0050] Furthermore, the temperature measuring device adopts an infrared temperature measuring device or an acoustic temperature measuring device;

[0051] And / or, the arrangement of multiple spray guns ensures that the position of the lowest spray gun is the optimal denitrification reaction temperature range when the flue gas temperature is the lowest during boiler operation, and the position of the highest spray gun is the optimal denitrification reaction temperature range when the flue gas temperature is the highest during boiler operation.

[0052] Furthermore, the SNCR denitrification system includes a softened water supply module and a reducing agent supply module. The softened water supply module consists of a softened water tank and a softened water delivery pump, and the reducing agent supply module consists of a reducing agent tank and a reducing agent delivery pump.

[0053] And / or, the SNCR denitrification system includes a reducing agent mixing and dispensing module, and the number of the reducing agent mixing and dispensing module is one or two;

[0054] And / or, the SNCR denitrification system includes a reducing agent injection system, which atomizes the reducing agent under the action of compressed air;

[0055] And / or, for waste heat boilers with a depth of less than 5 meters and a width of less than 10 meters, spray guns are only installed on the front wall or side wall, and fan-shaped or conical spray guns are selected; for waste heat boilers with a depth of more than 5 meters and a width of more than 10 meters, spray guns are installed on both the front wall and the side wall. The spray guns on the front wall are used to remove NOx from the area close to the front wall in 1 / 2 to 2 / 3, and the spray guns on the side wall are used to remove NOx from the area close to the rear wall. Fan-shaped spray guns are selected for the front wall, and conical spray guns are selected for the side wall.

[0056] The present invention has the following beneficial effects:

[0057] (1) Use precise infrared or acoustic temperature measurement devices, and establish a three-dimensional temperature field calculation model based on the results of CFD and thermodynamic calculations. Calculate the flue gas temperature at each spray gun in real time based on the boiler load (evaporation rate) and the moisture content of the flue gas at the boiler outlet, so as to provide parameter basis for the selection of spray guns.

[0058] (2) The reducing agent mixing and distribution module adjusts and measures the reducing agent flow rate in each zone according to the zone, and automatically selects the appropriate spray guns in each zone to be put into operation according to the optimal reaction temperature range requirements and the real-time calculated flue gas temperature results. That is, when the temperature field distribution is uneven, the height position of the spray guns in each zone is different, but they are all within the appropriate temperature range.

[0059] (3) Based on the results of the spray gun atomization performance test and the CFD report, different types of spray guns are selected in each area. Under the premise of manually setting the atomization compressed air pressure of each spray gun, combined with the automatic reduction agent flow rate adjustment, the reduction agent is sprayed into the furnace and the droplets evaporate to achieve good coverage of the reduction agent and good mixing with the flue gas.

[0060] (4) A multivariate collaborative control algorithm (temperature + boiler evaporation rate + boiler outlet flue gas moisture content + NOx emission concentration + NH3 escape concentration) was developed, which can achieve a denitrification efficiency of over 75%, and usually maintains 80%. 85%, and meets the requirement of ammonia slip below 2.5 mg / Nm³. 3 The indicators show that, while maintaining the same denitrification efficiency, the consumption of reducing agent is reduced by more than 20% compared to similar technologies. Attached Figure Description

[0061] 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.

[0062] Figure 1This is a flowchart illustrating the efficient SNCR control method of the present invention;

[0063] Figure 2 This is a flowchart of the mixing and distribution module for the 4-zone, 5-layer spray gun configuration in this invention;

[0064] Figure 3 This is a schematic diagram of the 5-zone, 5-layer spray gun arrangement in this invention;

[0065] Figure 4 A diagram showing the atomized droplet trajectory of different spray guns installed on the front and side walls in this invention.

[0066] Figure 5 This is a block diagram showing the control logic for the consumption of reducing agent and dilution water in this invention. Detailed Implementation

[0067] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0068] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0069] Traditional SNCR denitrification solutions mainly employ:

[0070] Layered fixed spray guns: 2-3 layers of spray guns are arranged at a preset height, and the reducing agent is supplied to one of the spray guns by the reducing agent mixing module;

[0071] Temperature feedback control: Adjust the total injection volume through a limited number of temperature measuring points.

[0072] Traditional SNCR systems have the following drawbacks:

[0073] The temperature measuring device has too large a deviation in its measurement results: The thermocouple is used as the measuring device, but the temperature measured by the thermocouple is lower than the actual flue gas temperature due to the cold radiation from the water-cooled wall, and the response is lagging.

[0074] Inaccurate temperature matching: During boiler operation, uneven distribution of flue gas temperature field in the furnace often occurs. The method of using the whole layer of spray guns to inject the reducing agent cannot be accurately injected into the optimal reaction temperature window (900-1050℃). In areas where the flue gas temperature is too high, the reducing agent will be oxidized and the NOx removal rate will be too low. In areas where the flue gas temperature is too low, a large amount of ammonia will escape and the NOx removal rate will be too low.

[0075] The selection of spray guns is limited: only one type of spray gun is selected for each boiler. Under the same process parameters, the atomization effect of each spray gun is the same. Moreover, due to the limited penetration of the spray gun, it is impossible to achieve the coverage of reducing agent and good mixing with flue gas on large-scale boilers, resulting in excessive reducing agent in some areas and insufficient reducing agent in others.

[0076] Dynamic response lag: The existing system relies on manual experience to adjust the position of the spray gun (i.e., the spray gun layer) and the spray volume, which cannot track the temperature gradient caused by changes in flue gas composition (mainly moisture content) due to changes in boiler load and flue gas composition (mainly moisture content) caused by changes in waste composition in real time, resulting in unreasonable spray gun position for a long time.

[0077] The closest prior art is invention patent application CN116610170A, which discloses a highly efficient SNCR intelligent three-dimensional temperature zoning control method, wherein:

[0078] The method involves sequentially connecting adjacent spray guns vertically within the boiler furnace to form several vertical spray gun groups, which are then connected in parallel. However, this sequential connection of adjacent spray guns within the vertical plane of the boiler furnace cannot achieve the function of activating a specific layer in each zone, and it still cannot accurately match the appropriate reaction temperature range according to the optimal reaction temperature.

[0079] Based on the aforementioned three-dimensional temperature field dataset, the three-dimensional temperature difference relationship of the boiler furnace temperature measurement area under different evaporation rates, flue gas volumes, and outlet oxygen contents under each operating condition is obtained. Based on the boiler's measured evaporation rate, flue gas volume, outlet oxygen content, and the aforementioned three-dimensional temperature distribution dataset and three-dimensional temperature difference relationship, a real-time three-dimensional temperature distribution dataset covering the area where each spray gun is located is synthesized, and the real-time temperature dataset of the three-dimensional atomization zone coordinate subdomain corresponding to each spray gun is detected. This calculation method uses flue gas volume and outlet oxygen content parameters. In actual engineering, due to space constraints, flue gas flow meters cannot be installed at the boiler outlet. In actual operation, the oxygen content in the outlet flue gas can be controlled relatively stably. However, since the raw material processed by the waste incineration system is waste, changes in its moisture content will cause changes in calorific value. During combustion, the flue gas moisture content and the flue gas volume corresponding to each ton of evaporation will also change accordingly. These two parameters have a significant impact on the flue gas temperature drop gradient within the furnace. Ignoring the influence of the flue gas moisture content parameter will result in unreasonable spray gun placement for extended periods. This application uses a method that is easy to implement in engineering, namely measuring the moisture content of boiler outlet flue gas, to participate in the temperature gradient calculation.

[0080] This invention addresses the technical pain points through the following methods:

[0081] Based on the arrangement of the spray guns, the furnace is divided into several zones along the horizontal direction. The accurate flue gas temperature of each zone in the layer where the temperature measuring device is located is measured by infrared thermometry or acoustic thermometry. Based on the flue gas temperature distribution in the furnace under different operating conditions (including different boiler evaporation rates and different waste moisture contents) calculated by CFD (Computational Fluid Dynamics) and thermodynamic calculations, as well as the actual operating parameters such as boiler load (evaporation rate) and boiler outlet flue gas moisture content, the temperature drop gradient along the flue gas flow direction (vertical direction) of the furnace is determined. The flue gas temperature of each zone at different heights can be calculated in real time during actual operation.

[0082] Multiple layers of spray guns are arranged along the height of the furnace (direction of flue gas flow) within each zone. The position of the lowest layer of spray guns ensures that the optimal denitrification reaction temperature range is reached when the flue gas temperature is lowest during boiler operation, while the position of the highest layer of spray guns ensures that the optimal denitrification reaction temperature range is reached when the flue gas temperature is highest during boiler operation. This arrangement ensures that there is always one layer of spray guns in the optimal denitrification reaction range within the load adjustment range of boiler operation. The zones are connected in parallel, and the reductant flow rate can be controlled and measured by regulating valves and flow meters on the reductant pipelines of each zone. The spray guns in each zone are also connected in parallel. During operation, the spray gun in the optimal denitrification reaction temperature range of each zone is selected for operation. The method of operation is to open the solenoid valve in front of the spray gun in that zone, while the solenoid valves in front of the other spray guns in that zone are closed.

[0083] By selecting different types of spray guns and manually setting the atomizing compressed air pressure of each spray gun, and adjusting the reducing agent flow rate during operation, good atomization and coverage of the reducing agent can be achieved. After the atomized droplets evaporate, the distribution of the reducing agent ensures that the reducing agent in each zone can be well mixed with the flue gas, avoiding the occurrence of excessive or insufficient reducing agent in any place.

[0084] The advanced automatic control system calculates the flue gas temperature at each spray gun in real time and automatically selects the spray guns to be used in each zone. It also automatically adjusts the concentration of reducing agent according to the NOx emission concentration and NH3 escape concentration in the flue gas.

[0085] This invention provides an efficient SNCR control method, such as... Figure 1-3 As shown, an SNCR denitrification system for boilers (various types of boilers, especially municipal solid waste incineration waste heat boilers) is described. The boiler furnace is equipped with a temperature measuring device (not shown). The boiler furnace is divided into several horizontal zones, and each zone has multiple layers of spray guns arranged along the furnace height (at least two layers, which can be flexibly set as needed). The spray guns in each zone and the spray guns between layers within each zone are connected in parallel. Figure 2 As an example of the present invention, a system configuration of 4 zones and 5 layers is shown. Figure 3 In another example of the invention, a spray gun arrangement with 5 zones and 5 layers is shown;

[0086] like Figure 1 As shown, the method includes:

[0087] Step S101: Obtain the boiler load (i.e., evaporation rate), boiler outlet flue gas moisture content, and flue gas temperature of each zone on the floor where the temperature measuring device is located during operation.

[0088] In the specific implementation of this step, the boiler load (i.e., evaporation rate), boiler outlet flue gas moisture content, and flue gas temperature in each zone of the floor where the temperature measuring device is located can be obtained through instruments. These instruments may include separately installed infrared or acoustic temperature measuring devices for precise temperature measurement, pollutant measuring instruments for NOx emission concentration and NH3 escape concentration, flue gas moisture content measuring instruments, boiler main steam flow measuring instruments, and... Figure 3 The flow meter and pressure sensor are shown in the diagram. The temperature measuring device can be a single-layer, double-layer, or multi-layer setup to facilitate subsequent automatic calculation of the temperature field. Its installation is common knowledge in the field and will not be described in detail here.

[0089] Step S102: Based on the boiler load, the moisture content of the flue gas at the boiler outlet, and the flue gas temperature of each zone in the layer where the temperature measuring device is located, the flue gas temperature at each spray gun is calculated in real time using a pre-established three-dimensional temperature field calculation model.

[0090] This step corresponds to temperature field calculation: the temperature measuring device can measure the temperature field of this layer and the average temperature of each zone, and the control system calculates the furnace temperature gradient under the current operating conditions based on the boiler evaporation rate and flue gas moisture content.

[0091] As an optional embodiment, step S102 includes:

[0092] Step S1021: Calculate the flue gas temperature gradient that has been corrected for load but not for flue gas moisture content based on the current boiler evaporation rate;

[0093] Preferably, in step S1021, the flue gas temperature gradient is corrected by load but not by flue gas moisture content. The calculation formula is:

[0094] ;

[0095] in:

[0096] : Flue gas temperature gradient corrected for load but not for flue gas moisture content, in °C / m;

[0097] A1, B1, and C1 are all constants for fitting, which can be constants of the piecewise function and are dimensionless.

[0098] D: Current boiler evaporation rate, in t / h or kg / s;

[0099] D MCR MCR (Maximum Continuous Rating) refers to the boiler evaporation rate at the maximum continuous evaporation rate point, expressed in t / h or kg / s.

[0100] : Flue gas temperature gradient at MCR point, in °C / m.

[0101] Step S1022: Calculate the flue gas temperature gradient after moisture content correction based on the boiler outlet flue gas moisture content and the flue gas temperature gradient after load correction but without flue gas moisture content correction.

[0102] Preferably, in step S1022, the flue gas temperature gradient after correction for flue gas moisture content... The calculation formula is:

[0103] ;

[0104] in:

[0105] : Flue gas temperature gradient after correction for flue gas moisture content, in °C / m;

[0106] A2, B2, and C2 are all constants for fitting, which can be constants of the piecewise function and are dimensionless;

[0107] H2O: Moisture content of flue gas at boiler outlet, in % .

[0108] H2O MCR Moisture content of boiler outlet flue gas at MCR point, in %

[0109] Flue gas temperature gradient corrected for load but not for flue gas moisture content, in °C / m.

[0110] Step S1023: Calculate the flue gas temperature at each spray gun based on the flue gas temperature gradient corrected for flue gas moisture content and the flue gas temperature of each zone in the layer where the temperature measuring device is located.

[0111] Preferably, in step S1023, the formula for calculating the flue gas temperature at each spray gun is as follows:

[0112] ;

[0113] in:

[0114] t ij : Flue gas temperature at the spray gun in zone i, layer j, in °C;

[0115] t i The average temperature of the i-zone temperature measurement device layer, in °C;

[0116] : Flue gas temperature gradient after correction for flue gas moisture content, in °C / m;

[0117] : The height difference between the spray gun and the temperature measuring device at layer j, in meters.

[0118] Thus, based on the above steps S1021-S1023, the flue gas temperature at each spray gun can be calculated in real time, as described above in this invention. Figure 3 The measured temperatures (the row of temperature measuring devices in the table below) and the calculated temperatures at the spray guns in each zone and layer of the example shown are shown in Table 1.

[0119] Table 1

[0120]

[0121] Step S103: Based on the flue gas temperature at each spray gun, select a spray gun in the optimal denitrification reaction temperature range for each zone;

[0122] This step corresponds to the selection of spray gun positions in each area. As an optional embodiment, step S103 further includes:

[0123] Based on the flue gas temperature at each spray gun, select the spray gun in each zone that is closest to the denitrification reaction set temperature.

[0124] In practical implementation, the selection of spray gun layers in each zone is as follows: Based on the real-time calculated temperature shown in Table 1, the spray gun layer closest to the denitrification reaction set temperature can be selected as the preferred spray gun layer. The calculation method is to calculate the absolute value of the difference between the calculated temperature and the set temperature at each spray gun in each zone and automatically select the data with the smallest absolute value as the preferred data. The formula is as follows:

[0125] ;

[0126] in:

[0127] : Deviation between the flue gas temperature at the spray gun in zone i, layer j and the set temperature, in °C;

[0128] t ij : Flue gas temperature at the spray gun in zone i, layer j, in °C;

[0129] T: Set temperature;

[0130] The foregoing Figure 3In the example shown, the set temperature is 920℃. The temperature deviation of the spray guns in each zone and layer is shown in Table 2. The system will automatically select the spray guns in Zone 1, Layer 2, Zone 2, Zone 3, Zone 4, and Zone 5, Layer 3, as the preferred spray guns and put them into operation. The method of operation is to open the solenoid valve in front of the spray gun in that zone and layer, while the solenoid valves in front of the spray guns in other layers of that zone are in the closed state.

[0131] Table 2

[0132]

[0133] Step S104: Calculate the flow rate of the high-concentration reducing agent (i.e., the original reducing agent solution) and dilution water, and control the selected spray guns for each zone to put them into operation.

[0134] In this step, the calculation and control of the dilute reducing agent flow rate in each zone can be achieved by: programming the optimal reducing agent flow rate for each zone, determined by CFD, into a program as the base value. For spray guns with different spray gun types and parameters, the base flow rate data for each zone will be different. The optimal atomization effect and droplet trajectory are ensured by manually setting the compressed air pressure. In this invention, high-concentration reducing agent and diluted reducing agent are distinguished. High-concentration reducing agent corresponds to the reducing agent mixing and distribution module, while diluted reducing agent corresponds to each branch / zone. The control of the high-concentration reducing agent regulating valve and the dilution water regulating valve can employ conventional techniques in the field. For example, the control of the high-concentration reducing agent regulating valve is implemented using a PID controller. The input of the PID controller is the set value and measured value of the flow rate, and the output is the opening degree of the high-concentration reducing agent regulating valve. The control of the dilution water regulating valve is also implemented using a PID controller. The input of the PID controller is the set value and measured value of the mixer outlet pressure, and the output is the opening degree of the dilution water regulating valve.

[0135] As an optional embodiment, step S104 includes:

[0136] Step S1041: The high-concentration reducing agent consumption of the SNCR denitrification system is calculated based on the boiler evaporation rate measurement, boiler outlet flue gas moisture content measurement, NOx emission concentration and NH3 escape concentration set values, and then corrected by the measured values ​​of NOx emission concentration and NH3 escape concentration.

[0137] In this step, the calculation and flow control of the high-concentration reducing agent consumption in the high-efficiency SNCR system can be as follows: The reducing agent consumption control is based on the measured values ​​of the waste heat boiler evaporation rate, the measured value of the boiler outlet flue gas moisture content, and the set values ​​of NOx emission concentration and NH3 slip concentration. The base flow rate is then calculated and corrected using the measured values ​​of NOx emission concentration and NH3 slip concentration. The base value is obtained from CFD calculations and preliminary debugging, and corrected using the measured values ​​of NOx emission concentration and NH3 slip concentration. The control logic block diagram is shown below. Figure 5As shown.

[0138] Preferably, in step S1041, the calculation formula for the high-concentration reducing agent consumption of the SNCR denitrification system is as follows:

[0139] ;

[0140] in:

[0141] q hsd : Setpoint for high-concentration reducing agent consumption, unit: l / min;

[0142] k1: Evaporation correction factor;

[0143] k2: Correction coefficient for moisture content of flue gas at boiler outlet;

[0144] k3: NOx emission (concentration) setpoint correction factor;

[0145] k4: Correction factor for NH3 escape (concentration) setpoint;

[0146] q MCR : High-concentration reducing agent consumption calculated under MCR conditions, in units of l / min;

[0147] ;

[0148] in:

[0149] q h : High-concentration reducing agent consumption in SNCR denitrification system, unit: l / min;

[0150] u(t)1: The correction value of NOx emission concentration setpoint and measured value after passing through the PID controller (i.e. NOx emission concentration correction value);

[0151] u(t)2: The correction value of the NH3 escape concentration setpoint and measured value after passing through the PID controller (i.e., the NH3 escape concentration correction value).

[0152] q hsd : High-concentration reducing agent consumption setting value, unit l / min.

[0153] In practice, both u(t)1 and u(t)2 can be obtained using a PID controller, and their calculation formulas are as follows:

[0154] ;

[0155] in:

[0156] u(t): Controller output;

[0157] Error (the difference between the set value r(t) and the actual value y(t));

[0158] K p : Proportional coefficient;

[0159] K i Integral coefficient.

[0160] Step S1042: The diluted reducing agent flow rate for each partition is obtained from CFD simulation and debugging experience;

[0161] In this step, the diluted reducing agent flow rate of each partition is obtained by CFD. Each reducing agent mixing and mixing module corresponds to several partitions. Here, only the dilution water flow rate of the module is calculated for control.

[0162] Step S1043: The high-concentration reducing agent consumption of each reducing agent mixing and distribution module of the SNCR denitrification system is determined by the proportion of the diluted reducing agent flow rate set value of the corresponding zone of each reducing agent mixing and distribution module to the total amount; the dilution water consumption of this module is obtained by the difference between the sum of the diluted reducing agent flow rate set values ​​of each branch / zone corresponding to this module and the high-concentration reducing agent consumption of this module.

[0163] Preferably, in step S1043, the calculation formula for the high-concentration reducing agent consumption of each reducing agent mixing and distribution module of the SNCR denitrification system is as follows:

[0164] ;

[0165] Where, q hx q represents the high-concentration reducing agent consumption of the x-th reducing agent mixing and dispensing module. h For the high-concentration reducing agent consumption of the SNCR denitrification system, q m1 q m2 The diluted reducing agent flow rates, q, are for the branches / zones corresponding to the first and second reducing agent mixing and distribution modules, respectively. mx The diluted reducing agent flow rate is the branch / zone corresponding to the x-th reducing agent mixing and distribution module, where x is 1 or 2;

[0166] The formula for calculating the dilution water consumption of each reducing agent mixing and dispensing module is as follows:

[0167] ;

[0168] Where, q sx Let q1, q2, q3, and q be the dilution water consumption of the xth reducing agent mixing and distribution module. n These represent the diluted reducing agent flow rates (q) for zones 1 through n corresponding to the reducing agent mixing and distribution module. hxThis represents the high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module.

[0169] As another optional embodiment, the system (SNCR denitrification system for boiler) in this invention is configured as follows:

[0170] Softened water and reducing agent supply module: The function of this module is to provide softened water and reducing agent (high concentration reducing agent) to the reducing agent mixing and distribution module. It consists of a softened water tank, a softened water delivery pump, and a reducing agent tank and reducing agent delivery pump. If the reducing agent is urea, it also contains a urea solution preparation unit.

[0171] Reducing agent mixing and distribution module: Depending on the number of waste heat boiler zones, one or two modules can be set up. Generally, one module can be set up when the number of zones is no more than four, and two modules can be set up when the number of zones is more than four. With one module, the reducing agent (high concentration) and dilution water are metered, regulated, and mixed separately. The flow rate of the diluted reducing agent in each branch (one branch per zone) is regulated by the regulating valve and measured by a flow meter. Each layer of spray guns in each branch is equipped with a solenoid valve. The solenoid valve before the spray gun to be used is opened according to the control system's instructions, while the solenoid valves of the other spray gun layers remain closed. For a system with two modules, when the number of zones is even, each module corresponds to 50% of the zones. When the number of zones is odd, the number of zones corresponding to the first module is: number of zones / 2 + 0.5, and the number of zones corresponding to the second module is: number of zones / 2 - 0.5. Figure 2 This is a system diagram of a reducing agent mixing and distribution module consisting of a 4-zone, 5-layer spray gun system. Its mixing function comprises switch valve 1, flow meter 1, regulating valve 1, switch valve 2, flow meter 2, regulating valve 2, and a mixer. Switch valves 1 and 2 are used to isolate the reducing agent and dilution water, respectively; regulating valves 1 and 2 regulate the flow rates of the reducing agent and dilution water, respectively; flow meters 1 and 2 measure the flow rates of the reducing agent and dilution water, respectively; and the mixer thoroughly mixes the reducing agent and dilution water. A pressure sensor is installed after the mixer to measure the pressure of the diluted reducing agent for adjustment by the automatic control system. Each zone's branch line is equipped with a flow meter, regulating valve, pressure gauge (numbered 10-40 for zones one through four), and a solenoid valve corresponding to each spray gun (numbered 11-51 for zone one, 21-25 for zone two, and so on). The flow meter is used to measure the flow rate in each zone, the regulating valve is used to adjust the flow rate in each zone, the pressure gauge is used to measure the pressure, and the opening and closing of each solenoid valve corresponds to the activation and deactivation of the corresponding spray gun.

[0172] Reducing agent injection system: The reducing agent is atomized using compressed air. The number of single-layer spray guns is a multiple of the number of zones. Each zone can have one spray gun or two identical spray guns connected in parallel. The number of spray gun layers should ensure that there are spray guns in the appropriate denitrification reaction zone when the waste heat boiler load and waste composition change and fluctuate. Specifically, the lowest layer of spray guns should be positioned to ensure that the optimal denitrification reaction temperature zone is reached when the boiler flue gas temperature is lowest, while the highest layer should be positioned to ensure that the optimal denitrification reaction temperature zone is reached when the boiler flue gas temperature is highest. The height difference between adjacent spray gun layers should ensure that the flue gas temperature difference does not exceed 50℃. Therefore, generally 5-6 layers of spray guns are required (see...). Figure 3 The placement of the spray guns also needs to be determined through CFD simulation calculations based on the furnace dimensions. For waste heat boilers with a depth of less than 5 meters and a width of less than 10 meters, spray guns can be placed only on the front or side walls, and either fan-shaped or conical spray guns can be selected. For waste heat boilers with a depth greater than 5 meters and a width greater than 10 meters, spray guns need to be installed on both the front and side walls. The spray guns on the front wall are used to remove NOx from the area closest to the front wall (1 / 2 to 2 / 3), while the spray guns on the side walls are used to remove NOx from the area closest to the rear wall. For the front wall, fan-shaped spray guns with smaller atomized particle size are preferred, while for the side wall, conical spray guns with larger atomized particle size are preferred. The furnace zoning and atomization effect for installing spray guns on both the front and side walls are detailed in [link to relevant documentation]. Figure 4 There is no space to install spray guns on the back wall, but six fan-shaped spray guns are installed on the front wall, each with a reducing agent flow rate of 2 kg / s. One solid cone spray gun is installed on each of the two side walls, with a reducing agent flow rate of 2.7 kg / s. It can be seen that its coverage is significantly better than that of conventionally installed spray guns.

[0173] Instrumentation and Control System: Instrumentation includes separately installed infrared or acoustic temperature measuring devices for precise temperature measurement, pollutant measuring instruments for NOx emission concentration and NH3 escape concentration, flue gas moisture content measuring instruments, boiler main steam flow measuring instruments, and... Figure 2 The flow meter and pressure sensor shown are illustrated. The control functions are implemented in a PLC or DCS. After receiving the signals from the aforementioned instruments, the control system automatically adjusts the flow rates of the reducing agent and dilution water, as well as the reducing agent flow rate in each branch. Its functions include: temperature field calculation and selection of spray gun positions in each zone, calculation and flow control of the reducing agent flow rate in each zone, and calculation and flow control of high-concentration reducing agent consumption and dilution water consumption, in order to control pollutant emission indicators.

[0174] The innovation of this invention lies in: a method of controlling the reducing agent flow rate and spray gun placement in each zone through a first-zone, then-layer approach; each zone is a parallel structure, with spray guns in operation in each zone; each layer in each zone is a parallel structure, with only one layer in operation per zone, depending on the optimal temperature selection. Different types of spray guns, such as fan-shaped and solid cone-shaped, are used according to the required reducing agent coverage. The invention also includes a method for automatically calculating and correcting the reducing agent and dilution water consumption based on boiler evaporation measurements, boiler outlet flue gas moisture content measurements, and set and measured values ​​of NOx emission concentration and NH3 escape concentration.

[0175] In summary, the present invention has the following beneficial effects:

[0176] (1) Use precise infrared or acoustic temperature measurement devices, and establish a three-dimensional temperature field calculation model based on the results of CFD and thermodynamic calculations. Calculate the flue gas temperature at each spray gun in real time based on the boiler load (evaporation rate) and the moisture content of the flue gas at the boiler outlet, so as to provide parameter basis for the selection of spray guns.

[0177] (2) The reducing agent mixing and distribution module adjusts and measures the reducing agent flow rate in each zone according to the zone, and automatically selects the appropriate spray guns in each zone to be put into operation according to the optimal reaction temperature range requirements and the real-time calculated flue gas temperature results. That is, when the temperature field distribution is uneven, the height position of the spray guns in each zone is different, but they are all within the appropriate temperature range.

[0178] (3) Based on the results of the spray gun atomization performance test and the CFD report, different types of spray guns are selected in each area. Under the premise of manually setting the atomization compressed air pressure, combined with the automatic reduction agent flow rate adjustment, the reduction agent is sprayed into the furnace and the droplets evaporate to achieve good coverage of the reduction agent and good mixing with the flue gas.

[0179] (4) The development of a multivariate collaborative control algorithm (temperature + boiler evaporation rate + boiler outlet flue gas moisture content + NOx emission concentration + NH3 escape concentration) can generally achieve a denitrification efficiency of over 75%, and usually maintains 80%. 85%, and meets the requirement of ammonia slip below 2.5 mg / Nm³. 3 The indicators show that, while maintaining the same denitrification efficiency, the reducing agent consumption is reduced by more than 20% compared to similar technologies; while in invention application CN116610170A, although the denitrification efficiency is above 70%, its ammonia slip only meets the requirement of being below 8 mg / Nm³. 3 The indicators.

[0180] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-efficiency SNCR control method for use in an SNCR denitrification system of a boiler, characterized in that, The boiler furnace is equipped with a temperature measuring device. The boiler furnace is divided into several sections horizontally. Multiple layers of spray guns are arranged along the height of the furnace in each section. The spray guns in each section and the layers of spray guns in each section are connected in parallel. The method includes: Step S101: Obtain the boiler load during operation, the moisture content of the flue gas at the boiler outlet, and the flue gas temperature of each zone on the floor where the temperature measuring device is located. Step S102: Based on the boiler load, the moisture content of the flue gas at the boiler outlet, and the flue gas temperature of each zone in the layer where the temperature measuring device is located, the flue gas temperature at each spray gun is calculated in real time using a pre-established three-dimensional temperature field calculation model. Step S103: Based on the flue gas temperature at each spray gun, select a spray gun in the optimal denitrification reaction temperature range for each zone; Step S104: Calculate the flow rate of the high-concentration reducing agent and dilution water, and control the selected spray guns for each zone to put them into operation; Step S102 includes: Step S1021: Calculate the flue gas temperature gradient that has been corrected for load but not for flue gas moisture content based on the current boiler evaporation rate; Step S1022: Calculate the flue gas temperature gradient after moisture content correction based on the boiler outlet flue gas moisture content and the flue gas temperature gradient after load correction but without flue gas moisture content correction. Step S1023: Calculate the flue gas temperature at each spray gun based on the flue gas temperature gradient corrected for flue gas moisture content and the flue gas temperature of each zone in the layer where the temperature measuring device is located. In step S1021, the flue gas temperature gradient is corrected by load but not by flue gas moisture content. The calculation formula is: ； Where A1, B1, and C1 are fitting constants, and D is the current boiler evaporation rate. MCR The boiler evaporation rate at the MCR point. The flue gas temperature gradient at the MCR point; In step S1022, the flue gas temperature gradient after correction for flue gas moisture content The calculation formula is: ； Where A2, B2, and C2 are fitting constants, and H2O is the moisture content of the flue gas at the boiler outlet. MCR The moisture content of the boiler outlet flue gas at the MCR point; In step S1023, the formula for calculating the flue gas temperature at each spray gun is as follows: ； Among them, t ij The flue gas temperature at the spray gun in zone i, layer j, t i The average temperature of the temperature measuring device layer in zone i. The height difference between the spray gun and the temperature measuring device is j.

2. The high-efficiency SNCR control method according to claim 1, characterized in that, Step S103 further comprises: Based on the flue gas temperature at each spray gun, select the spray gun in each zone that is closest to the denitrification reaction set temperature.

3. The high-efficiency SNCR control method according to claim 1, characterized in that, Step S104 includes: Step S1041: The high-concentration reducing agent consumption of the SNCR denitrification system is calculated based on the boiler evaporation rate measurement, boiler outlet flue gas moisture content measurement, NOx emission concentration and NH3 escape concentration set values, and then corrected by the measured values ​​of NOx emission concentration and NH3 escape concentration. Step S1042: The diluted reducing agent flow rate for each partition is obtained from CFD simulation and debugging experience; Step S1043: The high-concentration reducing agent consumption of each reducing agent mixing and distribution module of the SNCR denitrification system is determined by the proportion of the diluted reducing agent flow rate set value of the corresponding zone of each reducing agent mixing and distribution module to the total amount; the dilution water consumption of this module is obtained by the difference between the sum of the diluted reducing agent flow rate set values ​​of each branch / zone corresponding to this module and the high-concentration reducing agent consumption of this module.

4. The high-efficiency SNCR control method according to claim 3, characterized in that, In step S1041, the calculation formula for the high-concentration reducing agent consumption of the SNCR denitrification system is as follows: ； Where, q hsd For high-concentration reducing agent consumption setpoints, k1 is the evaporation rate correction factor, k2 is the boiler outlet flue gas moisture content correction factor, k3 is the NOx emission concentration setpoint correction factor, k4 is the NH3 escape concentration setpoint correction factor, and q MCR High-concentration reducing agent consumption calculated for MCR conditions; ； Where, q h The SNCR denitrification system has a high-concentration reducing agent consumption, u(t)1 is the correction value of the NOx emission concentration setpoint and measured value after passing through the PID controller, u(t)2 is the correction value of the NH3 escape concentration setpoint and measured value after passing through the PID controller, and q hsd Set the consumption value for high-concentration reducing agent; And / or, in step S1043, the calculation formula for the high-concentration reducing agent consumption of each reducing agent mixing and distribution module of the SNCR denitrification system is as follows: ； Where, q hx q represents the high-concentration reducing agent consumption of the x-th reducing agent mixing and dispensing module. h For the high-concentration reducing agent consumption of the SNCR denitrification system, q m1 q m2 The diluted reducing agent flow rates, q, are for the branches / zones corresponding to the first and second reducing agent mixing and distribution modules, respectively. mx The diluted reducing agent flow rate is the branch / zone corresponding to the x-th reducing agent mixing and distribution module, where x is 1 or 2; The formula for calculating the dilution water consumption of each reducing agent mixing and dispensing module is as follows: ； Where, q sx Let q1, q2, q3, and q be the dilution water consumption of the xth reducing agent mixing and distribution module. n These represent the diluted reducing agent flow rates (q) for zones 1 through n corresponding to the reducing agent mixing and distribution module. hx This represents the high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module.

5. The efficient SNCR control method according to any one of claims 1-4, characterized in that, The temperature measuring device is an infrared temperature measuring device or an acoustic temperature measuring device. And / or, the arrangement of multiple spray guns ensures that the position of the lowest spray gun is the optimal denitrification reaction temperature range when the flue gas temperature is the lowest during boiler operation, and the position of the highest spray gun is the optimal denitrification reaction temperature range when the flue gas temperature is the highest during boiler operation.

6. The high-efficiency SNCR control method according to claim 5, characterized in that, The SNCR denitrification system includes a softened water supply module and a reducing agent supply module. The softened water supply module consists of a softened water tank and a softened water delivery pump, and the reducing agent supply module consists of a reducing agent tank and a reducing agent delivery pump. And / or, the SNCR denitrification system includes a reducing agent mixing and dispensing module, and the number of the reducing agent mixing and dispensing module is one or two; And / or, the SNCR denitrification system includes a reducing agent injection system, which atomizes the reducing agent under the action of compressed air; And / or, for waste heat boilers with a depth of less than 5 meters and a width of less than 10 meters, spray guns are only installed on the front wall or side wall, and fan-shaped or conical spray guns are selected; for waste heat boilers with a depth of more than 5 meters and a width of more than 10 meters, spray guns are installed on both the front wall and the side wall. The spray guns on the front wall are used to remove NOx from the area close to the front wall in 1 / 2 to 2 / 3, and the spray guns on the side wall are used to remove NOx from the area close to the rear wall. Fan-shaped spray guns are selected for the front wall, and conical spray guns are selected for the side wall.

Images