A method and system for controlling nitrogen oxide emissions

Abstract

The present application discloses a nitrogen oxide emission control method and system, which includes obtaining nitrogen oxide concentrations at an SCR inlet and outlet and a current ammonia volume flow rate; dividing the current ammonia volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet to obtain a current calculated molar ratio; obtaining a current adaptive molar ratio, performing a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate a target adaptive molar ratio, and taking the current adaptive molar ratio as the target adaptive molar ratio; obtaining a target nitrogen oxide emission concentration value, subtracting the nitrogen oxide emission concentration target value from the nitrogen oxide concentration at the SCR inlet, and then multiplying the result by the target adaptive molar ratio to obtain a calculated target ammonia volume flow rate; taking the current ammonia volume flow rate as the calculated target ammonia volume flow rate, thereby being able to adapt to changes in operating conditions, more accurately control the amount of ammonia added, and accurately control nitrogen oxide emissions.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas emission control, and in particular relates to a nitrogen oxide emission control method and system. Background Art

[0002] Coal-fired boilers usually use post-combustion denitrification technology to control nitrogen oxide emissions, including selective non-catalytic reduction denitrification (SNCR) and selective catalytic reduction denitrification (SCR). Taking SCR as an example, SCR technology is currently the most mature flue gas post-combustion denitrification technology. It is a process in which the reducing agent NH3 (liquid ammonia, ammonia water, urea, etc.) reacts with NO in the flue gas under the action of a metal catalyst TiO2. X reaction, converting NO in the flue gas X The SCR reactor is a major challenge in controlling the ammonia injection process. Evenly mixing the injected ammonia with the flue gas is crucial for ensuring denitrification rates and reducing ammonia escape.

[0003] In the prior art, the amount of ammonia water (ammonia gas) added is usually fixed in molar ratio, which refers to the ratio of ammonia nitrogen involved in the denitrification reaction, i.e. NH3 / NO X It is an important technical indicator of the SCR denitrification system. According to the denitrification reaction equation, 1 mole of NH3 and 1 mole of NO x Theoretically, assuming all ammonia participates in the reaction, NH3 / NO X When the molar ratio of nitrate is 0.8, the denitration efficiency can reach 80%. According to this theory, the conventional automatic control scheme of nitrogen oxides is based on the outlet NO of the denitration device. X Target and denitrification device import NO X The measured value can be used to calculate the NH3 flow rate that needs to be added through the molar ratio. The NH3 flow rate can be closed-loop controlled by adjusting the opening of the ammonia inlet regulating valve. However, the adaptability of this control method is relatively poor because the molar ratio is calculated based on the original design parameters of the boiler and is a fixed number. Therefore, when the combustion conditions change, such as changes in coal quality or load, if the molar ratio is not suitable, under-adjustment or over-adjustment will occur, resulting in NO X If the control index fluctuates greatly, NO will appear. X The problem of excessive emissions, or NO X If the emission parameters are controlled too low, it will lead to other hazards caused by excessive ammonia escape. When the air volume or coal volume changes significantly, the nitrogen oxide emission control is prone to untimely problems. Summary of the Invention

[0004] To solve the above problems, the present invention provides a nitrogen oxide emission control method and system, which can automatically adapt to changes in operating conditions, more accurately control the amount of ammonia added, and more accurately control the emission of nitrogen oxides.

[0005] The present invention provides a method for controlling nitrogen oxide emissions, comprising:

[0006] Obtain the SCR inlet nitrogen oxide concentration, SCR outlet nitrogen oxide concentration and current ammonia volume flow rate;

[0007] The current calculated molar ratio is obtained by dividing the current ammonia volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet;

[0008] Obtaining a current adaptive molar ratio, performing a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate a target adaptive molar ratio, and setting the current adaptive molar ratio as the target adaptive molar ratio;

[0009] Obtaining a target nitrogen oxide emission concentration value, subtracting the target nitrogen oxide emission concentration value from the SCR inlet nitrogen oxide concentration, and multiplying the result by the target adaptive molar ratio to obtain a target ammonia aqueous solution volume flow calculation value;

[0010] The current ammonia water volume flow rate is taken as the ammonia water volume flow rate calculation target value.

[0011] Preferably, in the above-mentioned nitrogen oxide emission control method, the target adaptive molar ratio is calculated by taking a weighted average of the current calculated molar ratio and the current adaptive molar ratio:

[0012] Using the formula:

[0013] (IN*X+OUT 当前 *Y) / (X+Y)=OUT 目标

[0014] Perform weighted average, where IN is the current calculated molar ratio, OUT 当前 is the current adaptive molar ratio, OUT 目标 is the target adaptive molar ratio, X is the weight of the currently calculated molar ratio, which is between 1 and 5, and Y is the weight of the current adaptive molar ratio, which is between 2000 and 5000.

[0015] Preferably, in the above-mentioned nitrogen oxide emission control method, the method further comprises:

[0016] Get the current fuel level;

[0017] The current fuel amount is multiplied by a coefficient as a feedforward of the ammonia solution volume flow calculation target value, so as to correct the ammonia solution volume flow calculation target value.

[0018] Preferably, in the above-mentioned nitrogen oxide emission control method, the method further comprises:

[0019] Get the current oxygen content;

[0020] The current oxygen amount is multiplied by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

[0021] Preferably, in the above-mentioned nitrogen oxide emission control method, the method further comprises:

[0022] Get the current nitrogen oxide concentration at the chimney outlet;

[0023] The current chimney outlet nitrogen oxide concentration is multiplied by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

[0024] Preferably, in the above-mentioned nitrogen oxide emission control method, the current ammonia volume flow rate is taken as the ammonia volume flow rate calculation target value:

[0025] Utilize PID, based on the current ammonia volume flow rate and the ammonia volume flow rate calculation target value, output the ammonia volume flow rate regulating valve control instruction, and adjust the opening of the ammonia volume flow rate regulating valve until the ammonia volume flow rate calculation target value is reached.

[0026] The present invention provides a nitrogen oxide emission control system comprising:

[0027] The first acquisition device is used to obtain the nitrogen oxide concentration at the SCR inlet, the nitrogen oxide concentration at the SCR outlet and the current ammonia volume flow rate;

[0028] a current molar ratio calculating device for obtaining a current calculated molar ratio by dividing the current ammonia aqueous solution volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet;

[0029] a target adaptive molar ratio calculation device for obtaining a current adaptive molar ratio, performing a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate a target adaptive molar ratio, and setting the current adaptive molar ratio as the target adaptive molar ratio;

[0030] an ammonia volume flow target value calculation device, configured to obtain a nitrogen oxide emission concentration target value by subtracting the nitrogen oxide emission concentration target value from the SCR inlet nitrogen oxide concentration and multiplying the result by the target adaptive molar ratio to obtain the ammonia volume flow target value;

[0031] The current ammonia water volume flow regulating device is used to take the current ammonia water volume flow as the ammonia water volume flow calculation target value.

[0032] Preferably, in the above nitrogen oxide emission control system, it further includes:

[0033] a second obtaining means for obtaining a current fuel quantity;

[0034] The first correction device is used to multiply the current fuel amount by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

[0035] Preferably, in the above nitrogen oxide emission control system, it further includes:

[0036] A third obtaining device is used to obtain the current oxygen content;

[0037] The second correction device is used to multiply the current oxygen amount by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

[0038] Preferably, in the above nitrogen oxide emission control system, it further includes:

[0039] The fourth obtaining means is used to obtain the current nitrogen oxide concentration at the chimney outlet;

[0040] The third correction device is used to multiply the current chimney outlet nitrogen oxide concentration by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

[0041] From the above description, it can be seen that the above-mentioned nitrogen oxide emission control method provided by the present invention includes obtaining the nitrogen oxide concentration at the SCR inlet, the nitrogen oxide concentration at the SCR outlet, and the current ammonia volume flow rate; using the current ammonia volume flow rate to divide the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet to obtain the current calculated molar ratio; obtaining the current adaptive molar ratio, performing a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate the target adaptive molar ratio, and taking the current adaptive molar ratio as the target adaptive molar ratio; obtaining the nitrogen oxide emission concentration target value, using the nitrogen oxide concentration at the SCR inlet minus the nitrogen oxide emission concentration target value, and then multiplying it by the target adaptive molar ratio to obtain the ammonia volume flow calculation target value; taking the current ammonia volume flow rate as the ammonia volume flow calculation target value, so it can automatically adapt to changes in operating conditions, more accurately control the amount of ammonia added, and more accurately control nitrogen oxide emissions. The above-mentioned nitrogen oxide emission control system provided by the present invention has the same advantages as the above-mentioned method. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0043] Figure 1 A schematic diagram of an embodiment of a method for controlling nitrogen oxide emissions provided by the present invention;

[0044] Figure 2 A schematic diagram of an embodiment of a nitrogen oxide emission control system provided by the present invention. DETAILED DESCRIPTION

[0045] The core of the present invention is to provide a nitrogen oxide emission control method and system that can automatically adapt to changes in operating conditions, more accurately control the amount of ammonia added, and more accurately control the emission of nitrogen oxides.

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] The present invention provides a method for controlling nitrogen oxide emissions. Figure 1 As shown, Figure 1 This is a schematic diagram of an embodiment of a method for controlling nitrogen oxide emissions provided by the present invention. The method may include the following steps:

[0048] S1: Obtain the SCR inlet nitrogen oxide concentration, SCR outlet nitrogen oxide concentration and current ammonia volume flow rate;

[0049] It should be noted that SCR stands for Selective Catalytic Reduction, a technology that uses a catalyst (such as V2O5 / TiO2 and V2O5-WO3 / TiO2) to reduce NO and NO2 to N2 using the reducing agent NH3 at temperatures between 290 and 400°C, with virtually no NH3 oxidation. This improves N2 selectivity and reduces NH3 consumption. Because ammonia may not completely reduce all nitrogen oxides, a certain concentration of nitrogen oxides will remain at the SCR outlet. Obtaining the nitrogen oxide concentrations at both the SCR inlet and outlet provides a basis for subsequent calculations.

[0050] S2: Divide the current ammonia volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet to obtain the current calculated molar ratio;

[0051] Specifically, it can be calculated using the following formula: M1 = FT_V / (NOX_IN-NOX_OUT), where M1 is the current calculated molar ratio, FT_V is the measured value of the ammonia volume flow rate, NOX_IN is the nitrogen oxide concentration at the SCR inlet, and NOX_OUT is the nitrogen oxide concentration at the SCR outlet.

[0052] S3: Obtain the current adaptive molar ratio, perform weighted average of the current calculated molar ratio and the current adaptive molar ratio, calculate the target adaptive molar ratio, and set the current adaptive molar ratio as the target adaptive molar ratio;

[0053] Specifically, the formula can be used:

[0054] (IN*X+OUT 当前 *Y) / (X+Y)=OUT 目标

[0055] Perform weighted averaging, where IN is the current calculated molar ratio, which is the M1 mentioned above, and OUT 当前 is the current adaptive molar ratio, OUT 目标is the target adaptive molar ratio, X is the weight of the currently calculated molar ratio, which can range from 1 to 5, and Y is the weight of the current adaptive molar ratio, which can range from 2000 to 5000. In this case, a change in the outlet NOx concentration will not immediately significantly affect the adaptive molar ratio. Instead, only after a period of time, when the changed concentration is maintained, will the adaptive molar ratio change significantly. This allows adaptive adjustment of the ammonia volume flow rate based on the current NOx treatment situation, ensuring more targeted treatment and achieving better NOx treatment results.

[0056] S4: Obtain the target value of nitrogen oxide emission concentration, subtract the target value of nitrogen oxide emission concentration from the nitrogen oxide concentration at the SCR inlet, and multiply the result by the target adaptive molar ratio to obtain the target value of ammonia volume flow rate calculation;

[0057] It should be noted that the following formula can be used for calculation:

[0058] FT_S=(NOX_IN-NOX_S)*M2,

[0059] Where: M2 is the target adaptive molar ratio OUT in the previous formula 目标 , FT_S is the target value for calculating the volume flow of ammonia water, NOX_IN is the nitrogen oxide concentration at the SCR inlet, and NOX_S is the target value for the nitrogen oxide emission concentration.

[0060] S5: The current ammonia volume flow rate is taken as the target value for ammonia volume flow rate calculation.

[0061] That is to say, the target value of the ammonia volume flow calculated in the previous step is used as the new value of the current ammonia volume flow, thereby achieving the purpose of adaptively adjusting the ammonia volume flow according to the on-site reaction situation.

[0062] From the above description, it can be seen that in the embodiment of the above-mentioned nitrogen oxide emission control method provided by the present invention, since it includes obtaining the nitrogen oxide concentration at the SCR inlet, the nitrogen oxide concentration at the SCR outlet and the current ammonia volume flow rate; dividing the current ammonia volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet to obtain the current calculated molar ratio; obtaining the current adaptive molar ratio, taking a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate the target adaptive molar ratio, and taking the current adaptive molar ratio as the target adaptive molar ratio; obtaining the target value of the nitrogen oxide emission concentration, subtracting the target value of the nitrogen oxide emission concentration from the nitrogen oxide concentration at the SCR inlet, and then multiplying it by the target adaptive molar ratio to obtain the calculated target value of the ammonia volume flow rate; taking the current ammonia volume flow rate as the calculated target value of the ammonia volume flow rate, it can automatically adapt to changes in operating conditions, more accurately control the amount of ammonia added, and more accurately control the emission of nitrogen oxides.

[0063] In addition, the path from adjusting the amount of ammonia to the denitrification device reaction and then to the chimney outlet is relatively long, and the change in nitrogen oxides lags behind by about 10 minutes. When the fuel, air volume, and oxygen content change, without these related feedforward signals, the lag in nitrogen oxide control will be significant, resulting in poor results. Based on this, in a specific embodiment of the above-mentioned nitrogen oxide emission control method, the following steps may also be included:

[0064] Get the current fuel level;

[0065] The current fuel amount is multiplied by a coefficient as a feedforward of the target value for calculating the volume flow rate of ammonia water, so as to correct the target value for calculating the volume flow rate of ammonia water.

[0066] Specifically, the opening of the ammonia volume flow control valve is adjusted in a closed loop based on the deviation between the target value and the actual value calculated based on the ammonia volume flow rate, and the current fuel quantity measurement value is multiplied by a coefficient as the feedforward of the ammonia volume flow rate adjustment. When these signals change, the NH3 flow rate is corrected in advance to achieve the purpose of precise control. Moreover, increasing the fuel correction reduces the target value of the ammonia quantity, and reducing the fuel correction increases the target value of the ammonia quantity.

[0067] In another specific embodiment of the above-mentioned method for controlling nitrogen oxide emissions, the following steps may also be included:

[0068] Get the current oxygen content;

[0069] The current oxygen amount is multiplied by a coefficient as a feedforward of the target value for calculating the volume flow rate of ammonia water, so as to correct the target value for calculating the volume flow rate of ammonia water.

[0070] Specifically, the opening of the ammonia volume flow control valve is adjusted in a closed loop based on the deviation between the target value and the actual value calculated based on the ammonia volume flow rate, and the current oxygen measurement value is multiplied by a coefficient as the feedforward of the ammonia volume flow rate adjustment. When these signals change, the NH3 flow rate is corrected in advance to achieve the purpose of precise control. Moreover, when the oxygen content increases, the target value of the ammonia volume is increased, and when the oxygen content decreases, the target value of the ammonia volume is decreased.

[0071] In a preferred embodiment of the above-mentioned method for controlling nitrogen oxide emissions, the following steps may also be included:

[0072] Get the current nitrogen oxide concentration at the chimney outlet;

[0073] The current chimney outlet nitrogen oxide concentration is multiplied by a coefficient as a feedforward of the ammonia volume flow calculation target value, so as to correct the ammonia volume flow calculation target value.

[0074] Specifically, the opening of the ammonia volume flow control valve is adjusted in a closed loop based on the deviation between the target value and the actual value calculated based on the ammonia volume flow rate, and the current nitrogen oxide concentration at the chimney outlet is multiplied by a coefficient as the feedforward of the ammonia volume flow rate regulation. When these signals change, the NH3 flow rate is corrected in advance to achieve the purpose of precise control. Moreover, the target value of ammonia volume is increased when the nitrogen oxide concentration increases, and the target value of ammonia volume is decreased when the nitrogen oxide concentration decreases.

[0075] In another preferred embodiment of the above-mentioned nitrogen oxide emission control method, the current ammonia volume flow rate is taken as the ammonia volume flow rate calculation target value, which can be:

[0076] Using PID, based on the current ammonia volume flow rate and the ammonia volume flow rate target value, the ammonia volume flow rate control valve control instruction is output to adjust the opening of the ammonia volume flow rate control valve until the ammonia volume flow rate target value is reached.

[0077] It should be noted that this can realize automatic control of the volume flow of ammonia water on the basis of automated calculation without manual intervention, thereby reducing labor costs.

[0078] The present invention provides a nitrogen oxide emission control system. Figure 2 As shown, Figure 2 This is a schematic diagram of an embodiment of a nitrogen oxide emission control system provided by the present invention, which may include:

[0079] The first acquisition device 201 is used to obtain the nitrogen oxide concentration at the SCR inlet, the nitrogen oxide concentration at the SCR outlet, and the current ammonia volume flow rate. It should be noted that SCR stands for Selective Catalytic Reduction, which is a selective catalytic reduction technology. Under the action of a catalyst (such as V2O5 / TiO2 and V2O5-WO3 / TiO2), the reducing agent NH3 reduces NO and NO2 to N2 at 290-400°C, with almost no NH3 oxidation reaction, thereby improving N2 selectivity and reducing NH3 consumption. Because ammonia may not reduce all nitrogen oxides, there will be a certain nitrogen oxide concentration at the SCR outlet. After obtaining the nitrogen oxide concentrations at the SCR inlet and outlet, it can provide a basis for subsequent calculations;

[0080] The current molar ratio calculation device 202 is used to obtain the current calculated molar ratio by dividing the current ammonia volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet. Specifically, the calculation can be performed using the following formula: M1=FT_V / (NOX_IN-NOX_OUT), where M1 is the current calculated molar ratio, FT_V is the measured ammonia volume flow rate, NOX_IN is the nitrogen oxide concentration at the SCR inlet, and NOX_OUT is the nitrogen oxide concentration at the SCR outlet.

[0081] The target adaptive molar ratio calculation device 203 is used to obtain the current adaptive molar ratio, perform a weighted average of the current calculated molar ratio and the current adaptive molar ratio, calculate the target adaptive molar ratio, and set the current adaptive molar ratio as the target adaptive molar ratio. Specifically, the formula can be used:

[0082] (IN*X+OUT 当前 *Y) / (X+Y)=OUT 目标

[0083] Perform weighted averaging, where IN is the current calculated molar ratio, which is the M1 mentioned above, and OUT 当前 is the current adaptive molar ratio, OUT 目标 is the target adaptive molar ratio, X is the weight of the current calculated molar ratio, which can be between 1 and 5, and Y is the weight of the current adaptive molar ratio, which can be between 2000 and 5000. In this case, after the outlet nitrogen oxide concentration changes, it will not immediately and significantly affect the value of the adaptive molar ratio. Instead, only after a period of time, when the changed concentration is maintained, will the adaptive molar ratio change significantly. It can be seen that in this way, the ammonia volume flow rate can be adaptively adjusted according to the current nitrogen oxide treatment situation, thereby ensuring more targeted treatment and better nitrogen oxide treatment effect.

[0084] The ammonia volume flow target value calculation device 204 is used to obtain the nitrogen oxide emission concentration target value by subtracting the nitrogen oxide emission concentration target value from the nitrogen oxide concentration at the SCR inlet and multiplying the result by the target adaptive molar ratio to obtain the ammonia volume flow target value. It should be noted that the calculation can be performed using the following formula:

[0085] FT_S=(NOX_IN-NOX_S)*M2,

[0086] Where: M2 is the target adaptive molar ratio OUT in the previous formula 目标 , FT_S is the target value for calculating the volume flow rate of ammonia water, NOX_IN is the nitrogen oxide concentration at the SCR inlet, and NOX_S is the target value for the nitrogen oxide emission concentration;

[0087] The current ammonia volume flow regulating device 205 is used to take the current ammonia volume flow as the ammonia volume flow calculation target value, that is, the ammonia volume flow calculation target value calculated in the previous step is used as the new current ammonia volume flow value, thereby achieving the purpose of adaptively adjusting the ammonia volume flow according to the on-site reaction conditions.

[0088] By utilizing the above system, it is possible to automatically adapt to changes in operating conditions, more accurately control the amount of ammonia added, and more accurately control the emission of nitrogen oxides.

[0089] In addition, the path from adjusting the amount of ammonia to the denitrification device reaction and then to the chimney outlet is relatively long, and the change in nitrogen oxides lags behind by about 10 minutes. When the fuel, air volume, and oxygen content change, without these related feedforward signals, the lag in nitrogen oxide control will be very large, resulting in poor results. Based on this, in a specific embodiment of the above-mentioned nitrogen oxide emission control system, it also includes:

[0090] a second obtaining means for obtaining a current fuel quantity;

[0091] The first correction device is used to multiply the current fuel amount by a coefficient as a feedforward of the ammonia volume flow calculation target value, so as to correct the ammonia volume flow calculation target value.

[0092] Specifically, the opening of the ammonia volume flow control valve is adjusted in a closed loop based on the deviation between the target value and the actual value calculated based on the ammonia volume flow rate, and the current fuel quantity measurement value is multiplied by a coefficient as the feedforward of the ammonia volume flow rate adjustment. When these signals change, the NH3 flow rate is corrected in advance to achieve the purpose of precise control. Moreover, increasing the fuel correction reduces the target value of the ammonia quantity, and reducing the fuel correction increases the target value of the ammonia quantity.

[0093] In another specific embodiment of the above nitrogen oxide emission control system, the system may further include:

[0094] A third obtaining device is used to obtain the current oxygen content;

[0095] The second correction device is used to multiply the current oxygen amount by a coefficient as a feedforward of the ammonia volume flow calculation target value, so as to correct the ammonia volume flow calculation target value.

[0096] Specifically, the opening of the ammonia volume flow control valve is adjusted in a closed loop based on the deviation between the target value and the actual value calculated based on the ammonia volume flow rate, and the current oxygen measurement value is multiplied by a coefficient as the feedforward of the ammonia volume flow rate adjustment. When these signals change, the NH3 flow rate is corrected in advance to achieve the purpose of precise control. Moreover, when the oxygen content increases, the target value of the ammonia volume is increased, and when the oxygen content decreases, the target value of the ammonia volume is decreased.

[0097] In another specific embodiment of the above nitrogen oxide emission control system, the system may further include:

[0098] The fourth obtaining means is used to obtain the current nitrogen oxide concentration at the chimney outlet;

[0099] The third correction device is used to multiply the current chimney outlet nitrogen oxide concentration by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

[0100] Specifically, the opening of the ammonia volume flow control valve is adjusted in a closed loop based on the deviation between the target value and the actual value calculated based on the ammonia volume flow rate, and the current nitrogen oxide concentration at the chimney outlet is multiplied by a coefficient as the feedforward of the ammonia volume flow rate regulation. When these signals change, the NH3 flow rate is corrected in advance to achieve the purpose of precise control. Moreover, the target value of ammonia volume is increased when the nitrogen oxide concentration increases, and the target value of ammonia volume is decreased when the nitrogen oxide concentration decreases.

[0101] In addition, PID can be used to output the ammonia volume flow regulating valve control instruction based on the current ammonia volume flow rate and the ammonia volume flow rate calculation target value, and adjust the opening of the ammonia volume flow regulating valve until the ammonia volume flow rate calculation target value is reached. In this way, automatic control of the ammonia volume flow rate can be achieved on the basis of automated calculation without manual participation, thereby reducing labor costs.

[0102] In summary, the above-mentioned method and system are used to change the fixed molar ratio in the existing technology into a big data adaptive dynamic molar ratio. The molar ratio can be self-learned and adaptive online, and is a dynamic value. It automatically adapts to the deviation of boiler design parameters and the adjustment accuracy when the operating conditions change significantly, and the control is more precise. Moreover, NH3 flow feedforward signals such as fuel quantity, oxygen quantity, and chimney outlet nitrogen oxide concentration are introduced. When these signals change, the NH3 flow is corrected in advance to achieve the purpose of precise control, avoid control lag, and achieve the purpose of precise control. In addition, it has stronger adaptability, and various coal-fired boilers can be applied to the above-mentioned method and system.

[0103] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling nitrogen oxide emissions, characterized in that: include: Obtain the SCR inlet nitrogen oxide concentration, SCR outlet nitrogen oxide concentration and current ammonia volume flow rate; The current calculated molar ratio is obtained by dividing the current ammonia volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet; Obtaining a current adaptive molar ratio, performing a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate a target adaptive molar ratio, and setting the current adaptive molar ratio as the target adaptive molar ratio; Obtaining a target nitrogen oxide emission concentration value, subtracting the target nitrogen oxide emission concentration value from the SCR inlet nitrogen oxide concentration, and multiplying the result by the target adaptive molar ratio to obtain a target ammonia aqueous solution volume flow calculation value; The current ammonia water volume flow rate is taken as the ammonia water volume flow rate calculation target value.

2. The method for controlling nitrogen oxide emissions according to claim 1, wherein: The target adaptive molar ratio is calculated by weighted averaging the current calculated molar ratio and the current adaptive molar ratio: Using the formula: (IN*X+OUT 当前 *Y) / (X+Y)=OUT 目标 Perform weighted averaging, where IN is the current calculated molar ratio, OUT 当前 is the current adaptive molar ratio, OUT 目标 is the target adaptive molar ratio, X is the weight of the currently calculated molar ratio, which is between 1 and 5, and Y is the weight of the current adaptive molar ratio, which is between 2000 and 5000.

3. The method for controlling nitrogen oxide emissions according to claim 1, wherein: Also includes: Get the current fuel level; The current fuel amount is multiplied by a coefficient as a feedforward of the ammonia solution volume flow calculation target value, so as to correct the ammonia solution volume flow calculation target value.

4. The method for controlling nitrogen oxide emissions according to claim 1, wherein: Also includes: Get the current oxygen content; The current oxygen amount is multiplied by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

5. The method for controlling nitrogen oxide emissions according to claim 1, wherein: Also includes: Get the current nitrogen oxide concentration at the chimney outlet; The current chimney outlet nitrogen oxide concentration is multiplied by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

6. The method for controlling nitrogen oxide emissions according to claim 1, wherein: The current ammonia volume flow rate is taken as the ammonia volume flow rate calculation target value: Utilize PID, based on the current ammonia volume flow rate and the ammonia volume flow rate calculation target value, output the ammonia volume flow rate regulating valve control instruction, and adjust the opening of the ammonia volume flow rate regulating valve until the ammonia volume flow rate calculation target value is reached.

7. A nitrogen oxide emission control system, characterized in that: include: The first acquisition device is used to obtain the nitrogen oxide concentration at the SCR inlet, the nitrogen oxide concentration at the SCR outlet and the current ammonia volume flow rate; a current molar ratio calculating device for obtaining a current calculated molar ratio by dividing the current ammonia aqueous solution volume flow rate by the difference between the nitrogen oxide concentration at the SCR inlet and the nitrogen oxide concentration at the SCR outlet; a target adaptive molar ratio calculation device for obtaining a current adaptive molar ratio, performing a weighted average of the current calculated molar ratio and the current adaptive molar ratio to calculate a target adaptive molar ratio, and setting the current adaptive molar ratio as the target adaptive molar ratio; an ammonia volume flow target value calculation device, configured to obtain a nitrogen oxide emission concentration target value by subtracting the nitrogen oxide emission concentration target value from the SCR inlet nitrogen oxide concentration and multiplying the result by the target adaptive molar ratio to obtain the ammonia volume flow target value; The current ammonia water volume flow regulating device is used to take the current ammonia water volume flow as the ammonia water volume flow calculation target value.

8. The nitrogen oxide emission control system according to claim 7, characterized in that: Also includes: a second obtaining means for obtaining a current fuel quantity; The first correction device is used to multiply the current fuel amount by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

9. The nitrogen oxide emission control system according to claim 7, characterized in that: Also includes: A third obtaining device is used to obtain the current oxygen content; The second correction device is used to multiply the current oxygen amount by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

10. The nitrogen oxide emission control system according to claim 7, characterized in that: Also includes: The fourth obtaining means is used to obtain the current nitrogen oxide concentration at the chimney outlet; The third correction device is used to multiply the current chimney outlet nitrogen oxide concentration by a coefficient as a feedforward of the ammonia water volume flow calculation target value, so as to correct the ammonia water volume flow calculation target value.

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