Efficient SNCR control method

Abstract

The embodiment of the invention discloses an efficient SNCR control method, and relates to the technical field of SNCR denitration. The efficient SNCR control method is used for the SNCR denitration system of the boiler, a hearth of the boiler is divided into a plurality of subareas in the horizontal direction, multiple layers of spray guns are arranged in each subarea in the height direction of the hearth, and the method comprises the steps that the boiler load during operation, the boiler outlet smoke water content and the smoke temperature of each subarea of the layer where a temperature measuring device is located are obtained; according to the boiler load, the boiler outlet flue gas moisture content and the flue gas temperature of each subarea of the layer where the temperature measuring device is located, the flue gas temperature of each spray gun is calculated in real time through a pre-established three-dimensional temperature field calculation model; according to the flue gas temperature of each spray gun, the spray gun in the optimal denitration reaction temperature interval is selected in each subarea; and the spray gun selected in each zone is controlled to be put into operation. According to the invention, the problem of low NOx removal efficiency or high NH3 escape in different hearth areas can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of SNCR denitration technology, in particular to a high-efficiency SNCR control method. BACKGROUND

[0002] With the increasing global energy consumption, the flue gas from the combustion of fuels such as coal, biomass, garbage, natural gas, and oil will produce NOx, which will cause problems such as acid rain, acid fog, photochemical smog, ozone depletion, soil acidification, and eutrophication of surface water. The reactions of flue gas denitration (NOx removal) will cause some ammonia to escape into the atmosphere. Ammonia (NH3) is an important alkaline gas in the atmosphere, which can react with acidic gases such as sulfuric acid and nitric acid in the atmosphere to form ammonium salt, which is an important precursor of secondary inorganic aerosol particles. Excessive ammonia in the atmosphere can harm the human body and the environment. Therefore, it is imperative to control NOx emissions and NH3 escape.

[0003] Selective Non-Catalytic Reduction (SNCR) technology is a widely used flue gas denitration technology in the boiler industry and the waste incineration industry, mainly used for reducing NOx emissions. Its core principle is to inject a reducing agent (such as ammonia water or urea) into the flue gas at high temperature (900-1050°C) without the participation of a catalyst, reducing NOx to nitrogen (N2) and water (H2O).

[0004] For the denitration of waste incineration power plants, compared with Selective Catalytic Reduction (SCR) technology, SNCR has the following advantages:

[0005] Low investment cost: no catalyst is needed, the equipment structure is simple, and the installation and maintenance costs are lower.

[0006] Flexible operation: suitable for the high-temperature environment of waste incineration boilers, and can directly perform denitration reactions in the furnace.

[0007] Strong adaptability: can be adjusted to the combustion characteristics of different fuels (such as household garbage and industrial waste).

[0008] The SNCR system of a waste incineration plant usually includes the following key components:

[0009] Reducing agent storage and preparation module: using ammonia water or urea solution as the reducing agent.

[0010] Reducing agent mixing and distribution module: mixing the reducing agent and dilution water (usually softened water or desalted water) in the appropriate proportion and providing it to the injection lances that need to be injected.

[0011] Injection system: usually using compressed air atomization, through the double fluid spray gun to atomize and spray the reducing agent into the appropriate position of the furnace, so that the reducing agent and the flue gas are mixed.

[0012] Measurement and control system: using infrared temperature measurement or thermocouple to monitor the furnace temperature, while measuring the NOx emission and NH3 escape indicators in the flue gas. The measurement results are used for the control system to adjust the amount of reducing agent and dilution water.

[0013] However, the SNCR technology also has some inherent defects. The optimal reaction temperature range of SNCR denitration reaction is relatively narrow (usually 900-1050°C). If the temperature is too high, part of the NH3 will be oxidized, causing a significant decrease in denitration efficiency. If the temperature is too low, the amount of NH3 escape will increase significantly while the denitration efficiency decreases. In addition, due to the uneven distribution of flue gas temperature and composition on the flue gas flow cross section, and the fluctuation of flue gas temperature and composition caused by the change of garbage heat value and composition, combined with the inaccuracy and reaction lag of thermocouple temperature measurement, it is difficult to inject the appropriate amount of reducing agent in the appropriate temperature range and achieve good mixing of flue gas and reducing agent. This leads to low NOx removal efficiency or high NH3 escape in different furnace areas. SUMMARY

[0014] Therefore, the embodiments of the present application provide an efficient SNCR control method to solve the problem of low NOx removal efficiency or high NH3 escape in different furnace areas.

[0015] An efficient SNCR control method for a SNCR denitration system of a boiler, wherein a temperature measuring device is arranged in the furnace of the boiler, the furnace of the boiler is divided into several zones along the horizontal direction, and multiple layers of spray guns are arranged in each zone along the height direction of the furnace. The spray guns of each zone and the spray guns of each layer in each zone are connected in parallel. The method comprises the following steps:

[0016] Step S101: acquiring the boiler load, the water content of flue gas at the outlet of the boiler, and the flue gas temperature of each zone at the layer of the temperature measuring device;

[0017] Step S102: using a pre-established three-dimensional temperature field calculation model to calculate the flue gas temperature at each spray gun in real time according to the boiler load, the water content of flue gas at the outlet of the boiler, and the flue gas temperature of each zone at the layer of the temperature measuring device;

[0018] Step S103: selecting the spray gun in the optimal denitration reaction temperature range in each zone according to the flue gas temperature at each spray gun;

[0019] Step S104: calculating the flow of high-concentration reducing agent and dilution water, and controlling the selected spray gun in each zone to operate.

[0020] Further, the step S102 comprises:

[0021] Step S1021: calculating the flue gas temperature gradient which is corrected by load but not corrected by flue gas moisture content according to the current boiler evaporation capacity;

[0022] Step S1022: calculating the flue gas temperature gradient which is corrected by flue gas moisture content according to the flue gas moisture content at the boiler outlet and the flue gas temperature gradient which is corrected by load but not corrected by flue gas moisture content;

[0023] Step S1023: calculating the flue gas temperature at each lance according to the flue gas temperature gradient which is corrected by flue gas moisture content and the flue gas temperature of each sub-zone at the layer where the temperature measuring device is located.

[0024] Further, in the step S1021, the flue gas temperature gradient which is corrected by load but not corrected by flue gas moisture content is calculated according to the following formula:

[0025]

[0026] Wherein, A, B and C are fitting constants, D is the current boiler evaporation capacity, D MCR is the boiler evaporation capacity at the MCR point, is the flue gas temperature gradient at the MCR point.

[0027] Further, in the step S1022, the flue gas temperature gradient which is corrected by flue gas moisture content is calculated according to the following formula:

[0028]

[0029] Wherein, A, B and C are fitting constants, H2O is the flue gas moisture content at the boiler outlet, H2O MCR is the flue gas moisture content at the boiler outlet at the MCR point.

[0030] Further, in the step S1023, the flue gas temperature at each lance is calculated according to the following formula:

[0031]

[0032] Wherein, t ij is the flue gas temperature at the lance in the i-th sub-zone and the j-th layer, t i is the average temperature of the i-th sub-zone at the layer where the temperature measuring device is located, is the height difference between the lance and the temperature measuring device in the j-th layer.

[0033] Further, the step S103 further comprises:

[0034] ​​​​​According to the flue gas temperature at each lance, the lance closest to the set temperature of the denitration reaction is selected in each subzone.

[0035] Further, the step S104 includes:

[0036] Step S1041: The high-concentration reducing agent consumption of the SNCR denitration system is calculated based on the set values of the boiler evaporation capacity measurement, the boiler outlet flue gas moisture content measurement, the NOx emission concentration, and the NH3 escape concentration, and is corrected by the measured values of the NOx emission concentration and the NH3 escape concentration to obtain a basic flow rate;

[0037] Step S1042: The diluted reducing agent flow rate of each subzone 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 denitration system is determined by the proportion of the diluted reducing agent flow rate set value of the subzone corresponding to each reducing agent mixing and distribution module in the total amount; the diluted water consumption of the module is obtained from the difference between the sum of the diluted reducing agent flow rate set values of each branch / subzone corresponding to the module and the high-concentration reducing agent consumption of the module.

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

[0040] ;

[0041] wherein q hsd is the high-concentration reducing agent consumption set value, k1 is the evaporation capacity correction coefficient, k2 is the boiler outlet flue gas moisture content correction coefficient, k3 is the NOx emission concentration set value correction coefficient, k4 is the NH3 escape concentration set value correction coefficient, q MCR is the high-concentration reducing agent consumption calculated under the MCR condition;

[0042] ;

[0043] wherein q h is the high-concentration reducing agent consumption of the SNCR denitration system, u(t)1 is the correction value of the NOx emission concentration set value and measured value after the PID controller, u(t)2 is the correction value of the NH3 escape concentration set value and measured value after the PID controller, q hsd is the high-concentration reducing agent consumption set value;

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

[0045] ;

[0046] wherein q hx is the high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module, q h is the high-concentration reducing agent consumption of the SNCR denitration system, q m1 , q m2 are the diluted reducing agent flows of the branch / zone corresponding to the 1st and 2nd reducing agent mixing and distribution modules, respectively, q mx is the diluted reducing agent flow of the branch / zone corresponding to the xth reducing agent mixing and distribution module, x being 1 or 2;

[0047] The calculation formula of the diluted water consumption of each reducing agent mixing and distribution module is:

[0048]

[0049] wherein q sx is the diluted water consumption of the xth reducing agent mixing and distribution module, q1, q2, q3, q n are the diluted reducing agent flows of the 1st to n th zones corresponding to the reducing agent mixing and distribution module, respectively, q hx is the high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module.

[0050] Further, the temperature measuring device adopts an infrared temperature measuring device or an acoustic wave temperature measuring device.

[0051] And / or, the arrangement of the multi-layer spray guns is such that the position of the lowest layer of spray guns can ensure that it is in the optimal denitration reaction temperature range when the flue gas temperature of the boiler is at its lowest, and the position of the highest layer of spray guns can ensure that it is in the optimal denitration reaction temperature range when the flue gas temperature of the boiler is at its highest.

[0052] Further, the SNCR denitration system comprises a softened water supply module and a reducing agent supply module, the softened water supply module being composed of a softened water tank and a softened water delivery pump, and the reducing agent supply module being composed of a reducing agent tank and a reducing agent delivery pump.

[0053] And / or, the SNCR denitration system comprises one or two reducing agent mixing and distribution modules.

[0054] And / or, the SNCR denitration system comprises a reducing agent injection system which realizes the atomization of the reducing agent under the action of compressed air.

[0055] ​And / or, for the waste heat boiler with the depth less than 5 meters and the width less than 10 meters, only arranging the lance on the front wall or the side wall, selecting the sector-shaped lance or the conical lance; for the waste heat boiler with the depth more than 5 meters and the width more than 10 meters, arranging the lance on the front wall and the side wall simultaneously, the lance on the front wall is used for removing the NOx near the area of 1 / 2-2 / 3 of the front wall, the lance on the side wall is used for removing the NOx near the area of the back wall, the lance on the front wall selects the sector-shaped lance, and the lance on the side wall selects the conical lance.

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

[0057] (1) Precise infrared temperature measurement or sound wave temperature measurement device is adopted, and a three-dimensional temperature field calculation model is established according to the results of CFD and thermal calculation, the flue gas temperature at each lance is calculated in real time according to the boiler load (evaporation capacity) and the flue gas moisture content at the boiler outlet during operation, and the parameter basis for the selection of lance investment is provided.

[0058] (2) The reducing agent mixing and distribution module adjusts and measures the reducing agent flow of each zone according to the partition, and selects the lance at the appropriate position of each zone to operate according to the best reaction temperature interval requirement and the real-time calculation result of the flue gas temperature. That is, when the temperature field distribution is uneven, the height position of the lance invested in each zone is different, but they are all in the appropriate temperature interval.

[0059] (3) According to the results of the lance atomization performance test and the CFD report, different types of lances are selected in each zone, and under the premise of manually setting the atomizing compressed air pressure of each lance, combined with automatic reducing agent flow adjustment, the reducing agent is sprayed into the furnace to achieve good coverage of the reducing agent after the droplets evaporate and good mixing with the flue gas.

[0060] (4) A multivariable collaborative control algorithm (temperature + boiler evaporation capacity + flue gas moisture content at the boiler outlet + NOx emission concentration + NH3 escape concentration) is developed, which can realize the denitration efficiency of more than 75%, usually maintained at 80%-85%, and meet the index of ammonia escape less than 2.5mg / Nm 3 Under the premise of maintaining the same denitration efficiency, the reducing agent consumption is reduced by more than 20% compared with similar technologies. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, without creative labor, other drawings can also be obtained from these drawings.

[0062] Figure 1 It is a flowchart of the high-efficiency SNCR control method of the present application;

[0063] Figure 2 The mixing and distribution module flow chart for the 4-zone 5-layer lance in the present application;

[0064] Figure 3 The schematic diagram for the 5-zone 5-layer lance arrangement in the present application;

[0065] Figure 4 The atomized droplet trajectory diagram for the different lances arranged for the front wall and the side wall in the present application;

[0066] Figure 5 The control logic block diagram for the consumption of the reducing agent and the dilution water in the present application. DETAILED DESCRIPTION

[0067] The embodiments of the present application will be described in detail below with reference to the drawings.

[0068] It should be noted that the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0069] The traditional SNCR denitration scheme mainly adopts:

[0070] Layered fixed lance arrangement: 2-3 layers of lances are arranged at preset heights, and one layer of lances is provided with reducing agent by a reducing agent mixing module;

[0071] Temperature feedback control: the total injection amount is adjusted by limited temperature measurement points.

[0072] The traditional SNCR system has the following disadvantages:

[0073] The measurement result of the temperature measurement device deviates too much: a thermocouple is used as the measurement device, and the thermocouple measures a temperature lower than the actual flue gas temperature due to the cold radiation of the water-cooled wall and has a reaction lag;

[0074] Inaccurate temperature matching: during the operation of the boiler, the flue gas temperature field distribution in the furnace is often uneven, and the use of the whole layer lance injection method causes the reducing agent to be unable to be accurately injected into the best reaction temperature window (900-1050℃), the area with too high flue gas temperature will have too low NOx removal rate of the reducing agent, and the area with too low flue gas temperature will have too much ammonia escape and too low NOx removal rate;

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

[0076] Dynamic response lag: the existing system relies on manual experience to adjust the spray gun injection position (i.e. spray gun layer) and the amount of injection, and cannot track in real time the changes in temperature gradient caused by changes in boiler load and changes in flue gas composition (mainly water content) due to changes in garbage composition, resulting in unreasonable long-term spray gun injection position.

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

[0078] The method of the present application is to connect the upper and lower adjacent spray guns in the vertical plane of the boiler furnace in series, thereby forming a plurality of vertical plane spray gun groups, and finally connecting the vertical plane spray gun groups in parallel. The method of connecting the upper and lower adjacent spray guns in the vertical plane of the boiler furnace in series cannot realize the function of injecting a certain layer in each zone, and still cannot accurately match the appropriate reaction temperature interval according to the best reaction temperature.

[0079] According to the three-dimensional temperature field data set, the three-dimensional temperature difference relationship of the boiler furnace temperature measurement region space under different evaporation amounts, flue gas amounts, and outlet oxygen amounts in each working condition is obtained; according to the evaporation amount, flue gas amount, outlet oxygen amount, three-dimensional temperature distribution data set, and three-dimensional temperature difference relationship measured and fed back by the boiler, a real-time temperature three-dimensional distribution data set covering the region space of each spray gun is synthesized, and the temperature real-time data set of the three-dimensional atomization partition coordinate sub-domain corresponding to each spray gun is detected. The calculation method uses the flue gas amount and outlet oxygen amount parameters. In actual engineering, due to the arrangement space, it is not possible to arrange a flue gas flow meter instrument at the outlet of the boiler. In actual operation, the oxygen content in the outlet flue gas can be controlled relatively stably. The garbage incineration system processes garbage as raw material, and the change in water content will cause the change in heat value. The water content of the flue gas and the flue gas amount corresponding to each ton of evaporation amount will also change accordingly. These two parameters have a significant impact on the flue gas temperature drop gradient in the furnace. If the influence of the water content of the flue gas is not considered, the spray gun injection position will be unreasonable for a long time. The present application uses the method of measuring the water content of the flue gas at the outlet of the boiler to participate in the calculation of the temperature gradient.

[0080] The present application solves the technical problems by the following methods:

[0081] According to the arrangement scheme of the lance, the furnace is divided into several zones along the horizontal direction, the accurate flue gas temperature of each zone of the layer where the temperature measuring device is located is measured by using infrared temperature measurement or acoustic wave temperature measurement, and the temperature drop gradient along the flue gas flow direction (vertical direction) is determined according to the flue gas temperature distribution in the furnace under different operating conditions (including different boiler evaporation capacities, different waste moisture contents) of CFD (Computational Fluid Dynamics) and thermal calculation and parameters such as the boiler load (evaporation capacity), the flue gas moisture content at the outlet of the boiler and the like during actual operation, so that the flue gas temperature at different heights in each zone during actual operation can be calculated in real time.

[0082] The multiple layers of lances are arranged along the height direction of the furnace (the flue gas flow direction) in each zone, wherein the position of the lowest layer of lances can ensure that, when the flue gas temperature during the operation of the boiler is the lowest, the position is in the optimal denitration reaction temperature range, and the position of the highest layer of lances can ensure that, when the flue gas temperature during the operation of the boiler is the highest, the position is in the optimal denitration reaction temperature range, so that it is ensured that, within the load adjustment range of the boiler, there is always a layer of lances in the optimal denitration reaction temperature range, and each zone is in a parallel structure, the reducing agent flow of each zone can be controlled and measured through the adjusting valve and the flow meter on the reducing agent pipeline of each zone, and each layer of lances in each zone is also in a parallel manner, during operation, the lances in the optimal denitration reaction temperature range are selected for each zone and put into operation, and the method for putting into operation is to open the electromagnetic valve in front of the lances in the layer in the zone, and the electromagnetic valves in front of the lances in other layers in the zone are in a closed state.

[0083] Different types of lances are selected, under the premise that the atomizing compressed air pressure of each lance is manually set, and the reducing agent flow is adjusted during operation to achieve good atomization and coverage of the reducing agent, and the distribution of the reducing agent after evaporation of the atomized droplets ensures that the reducing agent in each zone can be well mixed with the flue gas, so that the occurrence of excessive or insufficient reducing agent in a certain place is avoided.

[0084] An advanced automatic control system is used to calculate the flue gas temperature at each lance in real time, automatically select the lances put into each zone, and automatically adjust the concentration of the reducing agent according to the NOx emission concentration and the NH3 escape concentration in the flue gas.

[0085] The embodiment of the present application provides a kind of high-efficiency SNCR control method, as Figures 1-3 As shown in the figure, the SNCR denitration system of the boiler (all kinds of boilers, especially waste incineration waste heat boiler), the furnace of the boiler is equipped with temperature measuring device (not shown), the furnace of the boiler is divided into several zones along the horizontal direction, multiple layers of lances (at least two layers, can be flexibly set according to needs) are arranged along the height direction of the furnace in each zone, the lances of each zone and each layer of lances in each zone are in parallel, Figure 2 It is an example of the present application, wherein a 4-zone 5-layer system configuration is shown,Figure 3 Another example of the present application is shown, wherein a 5-zone 5-layer lance arrangement is shown;

[0086] As Figure 1 shown, the method comprises:

[0087] Step S101: obtaining the boiler load (i.e. evaporation amount), the boiler outlet flue gas moisture content, and the flue gas temperature of each zone of the layer where the temperature measuring device is located at the runtime;

[0088] In the implementation of this step, the boiler load (i.e. evaporation amount), the boiler outlet flue gas moisture content, and the flue gas temperature of each zone of the layer where the temperature measuring device is located can be obtained by instruments, which can include separately arranged infrared or acoustic temperature measuring devices for accurate 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 flow meters, pressure sensors as shown in Figure 3 . The temperature measuring device can be single-layer, double-layer or multi-layer arranged to facilitate subsequent self-computation of the temperature field, and its installation is well known in the art, which will not be described here.

[0089] Step S102: according to the boiler load, the boiler outlet flue gas moisture content, and the flue gas temperature of each zone of the layer where the temperature measuring device is located, using a pre-established three-dimensional temperature field calculation model, real-time calculation of the flue gas temperature at each lance;

[0090] This step corresponds to temperature field calculation: the temperature measuring device can measure the temperature field of the layer and the average temperature of each zone, and the control system calculates the furnace temperature gradient under the current working condition according to the boiler evaporation amount and the flue gas moisture content.

[0091] As an optional embodiment, the step S102 comprises:

[0092] Step S1021: according to the current boiler evaporation amount, calculating the flue gas temperature gradient corrected by the load but not by the flue gas moisture content;

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

[0094] ;

[0095] Wherein:

[0096] : the flue gas temperature gradient corrected by the load but not by the flue gas moisture content, unit: ℃ / m;

[0097] A, B, C are all fitting constants, which can be constants of piecewise functions, dimensionless;

[0098] D: current boiler evaporation capacity, unit t / h or kg / s;

[0099] D MCR : boiler evaporation capacity at MCR (Maximum Continuous Rating) point, unit t / h or kg / s;

[0100] : flue gas temperature gradient at MCR point, unit ℃ / m.

[0101] Step S1022: calculating flue gas temperature gradient after flue gas moisture content correction according to boiler outlet flue gas moisture content and flue gas temperature gradient after load correction but before flue gas moisture content correction;

[0102] Preferably, in the step S1022, the flue gas temperature gradient after flue gas moisture content correction is calculated according to the following formula:

[0103] ;

[0104] Wherein:

[0105] : flue gas temperature gradient after flue gas moisture content correction, unit ℃ / m;

[0106] A, B, C are all fitting constants, which can be constants of piecewise function, dimensionless;

[0107] H2O: boiler outlet flue gas moisture content, unit %;

[0108] H2O MCR : boiler outlet flue gas moisture content at MCR point, unit %;

[0109] : flue gas temperature gradient after load correction but before flue gas moisture content correction, unit ℃ / m.

[0110] Step S1023: calculating flue gas temperature at each lance according to flue gas temperature gradient after flue gas moisture content correction and flue gas temperature of each sub-zone of the layer where the temperature measuring device is located.

[0111] Preferably, in the step S1023, the calculation formula of flue gas temperature at each lance is as follows:

[0112] ;

[0113] Wherein:

[0114] t ij : flue gas temperature at i-zone j-layer lance, unit ℃; ​

[0115] t i : Zone average temperature of the temperature measuring device layer in the i-th zone, unit: ℃;

[0116] : Flue gas temperature gradient after correction of the flue gas moisture content, unit: ℃ / m;

[0117] : Height difference between the j-th layer of the spray gun and the temperature measuring device, unit: m.

[0118] Thus, the flue gas temperature at each spray gun can be calculated in real time according to the above steps S1021-S1023, and the foregoing Figure 3 The measured temperature (the temperature measuring device row in the table below) and the calculated temperature at each spray gun in each zone and each layer in the example shown in the table 1.

[0119] Table 1

[0120]

[0121] Step S103: According to the flue gas temperature at each spray gun, select the spray gun in the optimal denitration reaction temperature range in each subzone;

[0122] This step corresponds to the selection of the spray gun position in each zone. As an optional embodiment, the step S103 is further provided as:

[0123] According to the flue gas temperature at each spray gun, select the spray gun closest to the denitration reaction set temperature in each subzone.

[0124] In specific implementation, the selection of the spray gun layer in each zone: according to the real-time calculated temperature shown in the table 1, the spray gun closest to the denitration reaction set temperature is selected as the preferred spray gun layer, the calculation method is to calculate the absolute value of the difference between the calculated temperature at each spray gun in each zone and each layer and the set temperature, and automatically select the data with the smallest absolute value as the preferred data, the formula is as follows:

[0125] ;

[0126] Wherein:

[0127] : Deviation of the flue gas temperature at the j-th layer of the spray gun in the i-th zone from the set temperature, unit: ℃;

[0128] t ij : Flue gas temperature at the j-th layer of the spray gun in the i-th zone, unit: ℃;

[0129] T: Set temperature;

[0130] the foregoing Figure 3In the shown example, the temperature is set to 920℃, and the temperature deviation of each layer of each zone is as shown in Table 2. The system automatically selects the preferred spray guns of zone 2 layer 2, zone 2 layer 2, zone 3 layer 3, zone 4 layer 2 and zone 5 layer 3, and puts them into operation. The method of putting into operation is to open the electromagnetic valve in front of the spray gun, and the electromagnetic valves in front of the spray guns of other layers in the zone are in the closed state.

[0131] Table 2

[0132]

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

[0134] In this step, the calculation and flow control of the reducing agent flow after dilution in each zone can be: the optimal reducing agent flow of each zone determined by CFD is programmed as a basic value. For spray guns with different types and parameters, the basic flow data of each zone is different, and the pressure of compressed air is manually set to ensure the best atomization effect and droplet trajectory. In the present application, high-concentration reducing agent and reducing agent after dilution are distinguished. High-concentration reducing agent corresponds to the reducing agent mixing and distribution module, and reducing agent after dilution corresponds to each branch / sub-zone. The control of high-concentration reducing agent regulating valve and dilution water regulating valve can adopt conventional techniques in the art, for example, the control of high-concentration reducing agent regulating valve is realized by PID, the input of PID is the set value and measured value of flow, and the output is the opening of high-concentration reducing agent regulating valve; the control of dilution water regulating valve is realized by PID, the input of PID is the set value and measured value of mixer outlet pressure, and the output is the opening of dilution water regulating valve.

[0135] As an optional embodiment, the step S104 comprises:

[0136] Step S1041: The consumption of high-concentration reducing agent of the SNCR denitration system is calculated based on the measured value of the evaporation capacity of the boiler, the measured value of the water content of the flue gas at the outlet of the boiler, the set value of NOx emission concentration and NH3 escape concentration, and is corrected by the measured values of NOx emission concentration and NH3 escape concentration to obtain the basic flow.

[0137] In this step, the calculation and flow control of the high-concentration reducing agent consumption of the high-efficiency SNCR system can be: the reducing agent consumption control is calculated based on the measured value of the evaporation capacity of the boiler, the measured value of the water content of the flue gas at the outlet of the boiler, the set value of NOx emission concentration and NH3 escape concentration, and is corrected by the measured values of NOx emission concentration and NH3 escape concentration. The basic value is obtained from the CFD calculation results and preliminary debugging, and is corrected by the measured values of NOx emission concentration and NH3 escape concentration. The control logic diagram is as shown in Figure 5as shown.

[0138] Preferably, in the step S1041, the high-concentration reducing agent consumption of the SNCR denitration system is calculated according to the following formula:

[0139] ;

[0140] wherein:

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

[0142] k1: evaporation amount correction coefficient;

[0143] k2: boiler outlet flue gas moisture content correction coefficient;

[0144] k3: NOx emission (concentration) set value correction coefficient;

[0145] k4: NH3 escape (concentration) set value correction coefficient;

[0146] q MCR : high-concentration reducing agent consumption calculated under MCR working condition, unit l / min;

[0147] ;

[0148] wherein:

[0149] q h : high-concentration reducing agent consumption of the SNCR denitration system, unit l / min;

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

[0151] u(t)2: correction value of NH3 escape concentration set value and measured value after PID controller (i.e. NH3 escape concentration correction value);

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

[0153] In specific implementation, both u(t)1 and u(t)2 can be obtained by using PID controller, and the calculation formula is as follows:

[0154] ;

[0155] wherein:

[0156] u(t): controller output;

[0157] : error (difference between set value r(t) and actual value y(t));

[0158] K p : proportional coefficient;

[0159] K i : integral coefficient.

[0160] Step S1042: The diluted reductant flow rate of each zone is obtained by CFD simulation and commissioning experience;

[0161] In this step, the diluted reductant flow rate of each zone is obtained by CFD, and each reductant mixing and mixing module corresponds to several zones. Herein, only the diluted water flow rate of the module is calculated for control.

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

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

[0164] ;

[0165] Wherein, q hx is the high-concentration reductant consumption of the xth reductant mixing and distribution module, q h is the high-concentration reductant consumption of the SNCR denitration system, q m1 , q m2 are the diluted reductant flow rates of the 1st and 2nd reductant mixing and distribution modules, respectively, and q mx is the diluted reductant flow rate of the xth reductant mixing and distribution module, and x is 1 or 2.

[0166] The calculation formula of the diluted water consumption of each reductant mixing and distribution module is as follows:

[0167] ;

[0168] Wherein, q sx is the diluted water consumption of the xth reductant mixing and distribution module, q n , q hxThe high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module.

[0169] As another alternative embodiment, the system (SNCR denitration system of the boiler) in the present application 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) for the reducing agent mixing and distribution module, which is composed of a softened water tank, a softened water delivery pump, and a reducing agent tank and a 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 zones of the waste heat boiler, one or two modules can be set. Generally, one module can be set when the number of zones is not higher than 4, and two modules can be set when the number of zones is higher than 4. In the case of one module, the reducing agent (high-concentration) and the dilution water are respectively metered and adjusted and mixed, and then the flow of the diluted reducing agent is adjusted by the regulating valve of each branch (one branch corresponds to each zone), and the flow is measured by the flow meter. Each layer of the spray gun of each branch is provided with an electromagnetic valve, and the electromagnetic valve in front of the spray gun to be put into operation is opened according to the instruction of the control system, and the electromagnetic valves of the remaining spray gun layers are in the closed state. For the system with two modules, when the number of zones is even, each module corresponds to 50% of the zones, and when the number of zones is odd, the number of zones corresponding to the first module is: zone number / 2+0.5, and the number of zones corresponding to the second module is: zone number / 2-0.5. Figure 2 System diagram of a reducing agent mixing and distribution module for a 4-zone 5-layer spray gun system, which mixing function is composed of switch valve 1, flow meter 1 and regulating valve 1 and switch valve 2, flow meter 2 and regulating valve 2 and mixer, wherein switch valve 1 and switch valve 2 are used for isolating the reducing agent and the dilution water, regulating valve 1 and regulating valve 2 are used for adjusting the flow of the reducing agent and the dilution water, flow meter 1 and flow meter 2 are used for measuring the flow of the reducing agent and the dilution water, and the mixer is used for mixing the reducing agent and the dilution water. A pressure sensor is arranged after the mixer for measuring the pressure of the diluted reducing agent for adjusting the control system. A flow meter, a regulating valve, a pressure gauge (1-4 for the first to fourth zones) and an electromagnetic valve corresponding to each layer of the spray gun (11-51 for the first zone, 21-25 for the second zone, and so on) are arranged in sequence on the branch of each zone, wherein the flow meter is used for measuring the flow of each zone, the regulating valve is used for adjusting the flow of each zone, the pressure gauge is used for pressure measurement, and the opening and closing of each electromagnetic valve corresponds to the operation and stop of the corresponding spray gun.

[0172] Reductant injection system: The atomization of reductant is realized under the action of compressed air. The number of single-layer spray guns is a multiple of the number of partitions. Each partition can be provided with one spray gun or two parallel spray guns. The number of layers of spray guns should be considered so that the spray guns are in the appropriate denitration reaction interval when the load of the waste heat boiler, the composition of the waste and the fluctuations change. That is, the position of the lowest layer of spray guns can ensure that it is in the optimal denitration reaction temperature interval when the boiler operates at the lowest flue gas temperature, and the position of the highest layer of spray guns can ensure that it is in the optimal denitration reaction temperature interval when the boiler operates at the highest flue gas temperature. The height difference between the positions of adjacent two layers of spray guns needs to ensure that the difference in flue gas temperature is not higher than 50℃. Therefore, generally 5-6 layers of spray guns are needed (see Figure 3 ). The setting of the spray guns also needs to be determined according to the size of the furnace by CFD simulation calculation. For waste heat boilers with a depth of less than 5 meters and a width of less than 10 meters, only the front wall or the side wall can be considered for arranging spray guns, and fan-shaped spray guns or conical spray guns can be selected. For waste heat boilers with a depth of more than 5 meters and a width of more than 10 meters, spray guns need to be arranged on the front wall and the side wall. The spray guns on the front wall are used to remove NOx in the area close to the front wall, and the spray guns on the side wall are used to remove NOx in the area close to the back wall. The front wall spray guns preferentially select fan-shaped spray guns with smaller atomization particle size, and the side wall spray guns preferentially select conical spray guns with larger atomization particle size. The furnace partitioning and atomization effect of the front wall and the side wall with spray guns are shown in Figure 4 . The rear wall has no space for spray guns, the front wall is provided with 6 fan-shaped spray guns, each spray gun has a reductant flow rate of 2 kg / s, and each side wall is provided with 1 solid conical spray gun, each spray gun has a reductant flow rate of 2.7 kg / s. It can be seen that its coverage is obviously better than that of the conventional spray guns.

[0173] Instruments and control system: The instruments include separately arranged 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 flow meters, pressure sensors shown in Figure 2 . The functions of the control system are realized in the PLC or DCS. After receiving the signals of the above instruments, the control system automatically adjusts the flow rates of the reductant and the dilution water and the flow rates of each branch. Its functions include: temperature field calculation and selection of the positions of the spray guns in each zone, calculation and flow control of the reductant flow rate in each zone, calculation and flow control of the high-concentration reductant consumption and the dilution water consumption to control the indicators of pollutant emission.

[0174] The innovation of the present application is that the reduction agent flow rate and the injection position of the lance in each zone are controlled by zoning and layering; each zone has a parallel structure, and each zone has a lance in operation during operation; each layer in each zone has a parallel structure, and only one layer in each zone is in operation according to the selection of the optimal temperature. Different types of lances are used according to the requirement of the reduction agent coverage, such as fan-shaped and solid cone-shaped. The control method for automatically calculating and correcting the consumption of the reduction agent and the dilution water is based on the measured value of the boiler evaporation capacity, the measured value of the boiler outlet flue gas moisture content, the set value and the measured value of the NOx emission concentration and the NH3 escape concentration.

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

[0176] (1) Precise infrared temperature measurement or acoustic wave temperature measurement device is used, and a three-dimensional temperature field calculation model is established according to the results of CFD and thermal calculation, and the flue gas temperature at each lance is calculated in real time according to the boiler load (evaporation capacity) and the boiler outlet flue gas moisture content during operation, thereby providing parameter basis for the selection of lance injection.

[0177] (2) The reduction agent mixing and distribution module adjusts and measures the reduction agent flow rate of each zone, and automatically selects the lances in each zone to be in operation at appropriate positions according to the optimal reaction temperature interval requirement and the real-time calculated flue gas temperature result. That is, when the temperature field distribution is uneven, the height position of the lances in each zone is different, but they are all in the appropriate temperature interval.

[0178] (3) According to the results of the spray performance test of the lance and the CFD report, different types of lances are selected for each zone, and under the premise of manually setting the atomizing compressed air pressure, combined with automatic reduction agent flow rate adjustment, good reduction agent coverage and good mixing with flue gas are achieved after the droplets of the reduction agent sprayed into the furnace evaporate.

[0179] (4) The development of a multivariable collaborative control algorithm (temperature + boiler evaporation capacity + boiler outlet flue gas moisture content + NOx emission concentration + NH3 escape concentration) can achieve a denitration efficiency of more than 75%, usually maintained at 80%-85%, and meet the index of ammonia escape less than 2.5mg / Nm 3 . Under the premise of maintaining the same denitration efficiency, the reduction agent consumption is reduced by more than 20% compared with similar technologies; in the invention application CN116610170A, the denitration efficiency is more than 70%, but the ammonia escape only meets the index of less than 8mg / Nm 3 .

[0180] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A high-efficiency SNCR control method for a boiler's SNCR denitrification system, characterized in that: A temperature measuring device is provided in the furnace of the boiler. The furnace of the boiler is divided into several zones in the horizontal direction. In each zone, multiple layers of spray guns are arranged along the height direction of the furnace. The spray guns in each zone and the spray guns in each layer of each zone 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: Calculate 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 flue gas at the boiler outlet, and the flue gas temperature of each zone on the layer where the temperature measuring device is located; Step S103: selecting a spray gun in the optimal denitrification reaction temperature range in each zone according to the flue gas temperature at each spray gun; Step S104: Calculate the flow rates of the high-concentration reducing agent and the dilution water, and control the spray guns selected in each partition to put them into operation.

2. The high-efficiency SNCR control method according to claim 1, characterized in that: The step S102 includes: Step S1021: Calculate the flue gas temperature gradient after load correction but without correction for flue gas moisture content based on the current boiler evaporation rate; Step S1022: Calculating the flue gas temperature gradient corrected for the flue gas moisture content based on the flue gas moisture content at the boiler outlet and the flue gas temperature gradient corrected for the load but not for the flue gas moisture content; Step S1023: Calculate the flue gas temperature at each spray gun based on the flue gas temperature gradient corrected by the flue gas moisture content and the flue gas temperature of each partition of the layer where the temperature measuring device is located.

3. The high-efficiency SNCR control method according to claim 2, characterized in that: In step S1021, the flue gas temperature gradient corrected by load but not corrected by flue gas moisture content The calculation formula is: ； Among them, A, B, and C are all fitting constants, D is the current boiler evaporation capacity, and D MCR is the boiler evaporation rate at the MCR point, is the flue gas temperature gradient at the MCR point.

4. The high-efficiency SNCR control method according to claim 3, characterized in that: In step S1022, the flue gas temperature gradient after the flue gas moisture content correction The calculation formula is: ； Among them, A, B, and C are all fitting constants, H2O is the moisture content of the flue gas at the boiler outlet, and H2O MCR is the moisture content of boiler outlet flue gas at the MCR point.

5. The high-efficiency SNCR control method according to claim 4, characterized in that: In step S1023, the calculation formula for the flue gas temperature at each spray gun is: ； Among them, t ij is the flue gas temperature at the spray gun of layer j in zone i, t i is the average temperature of the temperature measuring device layer in zone i, is the height difference between the j-layer spray gun and the temperature measuring device.

6. The high-efficiency SNCR control method according to claim 1, characterized in that: The step S103 is further as follows: According to the flue gas temperature at each spray gun, the spray gun closest to the set temperature of the denitrification reaction is selected in each zone.

7. The high-efficiency SNCR control method according to claim 1, characterized in that: The step S104 includes: Step S1041: The high-concentration reducing agent consumption of the SNCR denitration system is calculated based on the boiler evaporation rate measurement value, the boiler outlet flue gas moisture content measurement value, the NOx emission concentration and the set value of the NH3 slip concentration, and is corrected by the measured values ​​of the NOx emission concentration and the NH3 slip concentration; Step S1042: The diluted reducing agent flow rate of each partition is obtained by 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 setting value of the partition corresponding to each reducing agent mixing and distribution module to the total amount; the dilution water consumption of the module is obtained based on the difference between the sum of the diluted reducing agent flow setting values ​​of each branch / partition corresponding to the module and the high-concentration reducing agent consumption of the module.

8. The high-efficiency SNCR control method according to claim 7, characterized in that: In step S1041, the calculation formula for the high-concentration reducing agent consumption of the SNCR denitration system is as follows: ； Among them, q hsd is the set value of high concentration reducing agent consumption, k1 is the evaporation correction coefficient, k2 is the boiler outlet flue gas moisture content correction coefficient, k3 is the NOx emission concentration set value correction coefficient, k4 is the NH3 escape concentration set value correction coefficient, q MCR High concentration reducing agent consumption calculated for MCR operating conditions; ； Among them, q h is the high concentration reducing agent consumption of the SNCR denitrification system, u(t)1 is the correction value of the NOx emission concentration set value and the measured value after the PID controller is passed, u(t2) is the correction value of the NH3 escape concentration set value and the measured value after the PID controller is passed, q hsd Set the value for high concentration reducing agent consumption; 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 denitration system is: ； Among them, q hx is the high concentration reducing agent consumption of the xth reducing agent mixing and distribution module, q h is the high concentration reducing agent consumption of the SNCR denitrification system, q m1 ,q m2 The diluted reducing agent flow rates of the branches / partitions corresponding to the first and second reducing agent mixing and distribution modules, q mx is the diluted reducing agent flow rate of the branch / partition corresponding to the xth reducing agent mixing and distribution module, where x is 1 or 2; The calculation formula for the dilution water consumption of each reducing agent mixing and distribution module is: ； Among them, q sx is the dilution water consumption of the xth reducing agent mixing and distribution module, q1, q2, q3, q n are the diluted reducing agent flow rates of zones 1 to n corresponding to the reducing agent mixing and distribution modules, q hx The high-concentration reducing agent consumption of the xth reducing agent mixing and distribution module.

9. The high-efficiency SNCR control method according to any one of claims 1 to 8, characterized in that: The temperature measuring device adopts an infrared temperature measuring device or an acoustic temperature measuring device; And / or, the arrangement of multiple layers of spray guns ensures that the position of the spray guns in the lowest layer can ensure that the temperature range is optimal for the denitrification reaction when the flue gas temperature is lowest during boiler operation, and the position of the spray guns in the highest layer can ensure that the temperature range is optimal for the denitrification reaction when the flue gas temperature is highest during boiler operation.

10. The high-efficiency SNCR control method according to claim 9, characterized in that: The SNCR denitrification system includes a softened water supply module and a reducing agent supply module. The softened water supply module is composed of a softened water tank and a softened water delivery pump. The reducing agent supply module is composed of a reducing agent tank and a reducing agent delivery pump. And / or, the SNCR denitration system includes a reducing agent mixing and distribution module, and the number of the reducing agent mixing and distribution modules is one or two; and / or, the SNCR denitration system includes a reducing agent injection system, which realizes atomization of the reducing agent under the action of compressed air; And / or, for a waste heat boiler with a depth of less than 5 meters and a width of less than 10 meters, spray guns are arranged only on the front wall or side wall, and fan-shaped spray guns or conical spray guns are selected; for a waste heat boiler with a depth of more than 5 meters and a width of more than 10 meters, spray guns are set on both the front wall and the side walls. The spray guns on the front wall are used to remove NOx in the area of ​​1 / 2 to 2 / 3 close to the front wall, and the spray guns on the side walls are used to remove NOx close to the rear wall. The spray guns on the front wall can be fan-shaped, and the spray guns on the side walls can be conical.

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