SCR denitration control method based on ammonia injection amount and flue gas temperature collaborative regulation

Abstract

The application discloses a kind of based on ammonia injection quantity and flue gas temperature synergic control's SCR denitration control method, using ammonia injection quantity adjustment SCR denitration system export NOx concentration and using control SCR denitration system entrance flue gas temperature adjustment ammonia escape rate.Specifically include: by controlling ammonia escape rate through regulating SCR denitration reaction temperature, the feedforward of SCR denitration reaction temperature instruction is obtained based on SCR system entrance NOx concentration and SCR entrance flue gas flow rate.The deviation of SCR entrance flue gas temperature and SCR denitration reaction temperature instruction obtains the opening degree instruction of economizer feedwater bypass valve or flue gas bypass baffle by PID calculation, and the feedforward of opening degree instruction is obtained by load instruction and SCR denitration reaction temperature instruction.SCR system export NOx concentration uses the control of adjusting ammonia injection quantity, and the feedforward of ammonia injection instruction is composed of three parts, one is obtained by the deviation of SCR entrance flue gas temperature and SCR denitration reaction temperature instruction;Second is obtained based on SCR system entrance NOx concentration, and third is the ammonia storage variation of SCR catalyst layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coal-fired power generation, in particular to a SCR denitration control method based on ammonia injection amount and flue gas temperature coordinated regulation. BACKGROUND

[0002] With the rapid increase of the use of renewable energy such as solar energy and wind energy, the fluctuation, intermittence and unpredictability of renewable energy have brought great challenges to the stable and safe operation of power grid. Coal-fired generating units are an important source of electric energy supply, so frequent load variation adjustment is required to ensure the safe and efficient operation of the power grid. Frequent load variation will inevitably affect the operation of the unit denitration system. In China, there are strict regulations on the outlet NOx concentration and ammonia escape rate of the coal-fired unit denitration system.

[0003] The current SCR denitration technology is the most widely used denitration technology in coal-fired power plants. The principle of this technology is to mix ammonia and NOx in flue gas, and generate N2 and H2O through oxidation-reduction reaction under the action of catalyst, which requires a reaction temperature of 320-400℃. However, with coal-fired units taking on more peak-shaving and frequency-regulating tasks, the SCR reaction temperature changes frequently, which may cause the outlet NOx concentration and ammonia escape rate of the SCR system to exceed the standard or be instantaneously over-standard. In view of this problem, many coal-fired units are equipped with economizer feedwater bypass or economizer flue gas bypass to increase the SCR denitration reaction temperature at low load. However, the current research on SCR control strategy does not include the regulation of SCR denitration reaction temperature in the control strategy. In this case, the main problems to be solved are as follows:

[0004] 1) When the unit is in a low load variation range, the SCR reaction temperature is very low, making it difficult for the outlet NOx concentration and ammonia escape rate of the SCR system to meet the requirements of coal-fired power plants at the same time.

[0005] 2) When the unit is in a fast load variation rate, the SCR reaction temperature will fluctuate, causing the outlet NOx concentration and ammonia escape rate of the SCR system to be instantaneously over-standard. SUMMARY

[0006] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a SCR denitration control method based on ammonia injection amount and flue gas temperature coordinated regulation, which uses ammonia injection amount and flue gas temperature to coordinate the adjustment of the outlet NOx concentration and ammonia escape rate of the SCR denitration system, thereby ensuring the safe and efficient operation of the SCR denitration system.

[0007] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0008] The application discloses an SCR denitration control method based on ammonia injection amount and flue gas temperature coordination regulation.

[0009] The control target 1 is the ammonia escape rate of the SCR denitration system: firstly, the deviation of the ammonia escape rate and the ammonia escape rate set value is subjected to PID calculation to obtain an SCR denitration reaction temperature instruction, the feedforward of the SCR denitration reaction temperature instruction is obtained from the SCR denitration system inlet NOx concentration and the SCR denitration system inlet flue gas flow rate; the calculation expression is as follows, wherein the SCR system outlet NH3 concentration and NOx concentration value are taken as the maximum values required by the coal-fired power station:

[0010]

[0011] In the formula, Fdd1 is the feedforward of the SCR denitration reaction temperature instruction, K; E NO is the activation energy of the SCR reduction reaction, J·mol -1 ; R is the ideal gas constant, unit J·mol -1 ·K -1 ; C NO-in is the SCR denitration system inlet NOx concentration, mol m -3 ; u is the SCR denitration system inlet flue gas flow rate, unit m·s -1 ; C NO-out is the SCR denitration system outlet NOx concentration, mol m -3 ; is the SCR denitration system outlet NH3 concentration, mol m -3 ; L is the SCR denitration catalyst thickness, m; is the pre-exponential factor of the NH3 adsorption reaction on the SCR denitration catalyst surface, unit m 3 ·mol -1 ·s -1 ; is the SCR catalyst surface NH3 adsorption amount, mol NH3 m -3 , γ is a correction coefficient, which is a constant;

[0012] Secondly, the deviation of the SCR denitration system inlet flue gas temperature and the SCR denitration reaction temperature instruction is subjected to PID calculation to obtain an economizer feed water bypass valve opening degree instruction or a flue gas bypass damper opening degree instruction, and the feedforward of the economizer feed water bypass valve opening degree instruction or the flue gas bypass damper opening degree instruction is specifically calculated as follows:

[0013] Fdd2=(k1·Load+k2-T_s) / ΔT1

[0014] In the formula, Fdd2 is the feedforward of the economizer feedwater bypass valve opening degree command or the flue gas bypass damper opening degree command; Load is the unit load command; T_s is the SCR denitration reaction temperature command, K; ΔT1 is the change amount of the economizer feedwater bypass valve or flue gas bypass damper opening degree by 1%, the change amount of the SCR system inlet flue gas temperature, K; k1 and k2 are calculation coefficients, which are calculated by fitting the SCR inlet flue gas temperature and the load command at 75% THA and 50% THA loads of the coal-fired unit.

[0015] The control target 2 is the SCR denitration system outlet NOx concentration: the deviation of the SCR denitration system outlet NOx concentration and the outlet NOx concentration set value is calculated by PID to obtain the ammonia injection amount command, which is composed of three parts: the first part is the command obtained based on the NOx inlet concentration; the second part is the change amount of the ammonia storage in the SCR catalyst layer; and the third part is calculated from the deviation of the SCR denitration system inlet flue gas temperature, and the expression is:

[0016] Fdd3=k3·C NO-in

[0017] Fdd4=k4·NH3_c

[0018] Fdd5=k5·ΔT2

[0019] In the formula, Fdd3 is the feedforward 1 of the ammonia injection amount command, mol m -3 ; Fdd4 is the feedforward 2 of the ammonia injection amount command, mol m -3 ; NH3_c is the total ammonia storage amount in the SCR denitration catalyst layer, mol m -3 ; Fdd5 is the feedforward 3 of the ammonia injection amount command, mol m -3 ; ΔT2 is the deviation of the SCR denitration system inlet flue gas temperature and the SCR denitration reaction temperature command, K; k3 is the ratio of the ammonia injection amount to the SCR system inlet NOx concentration, generally taken as 0.8-1.0. k4 and k5 can be given according to the actual operation of the coal-fired unit.

[0020] The upper limit and the lower limit of the ammonia injection amount are set, which are obtained based on the SCR denitration system inlet NOx concentration; at the same time, the ammonia slip rate of the SCR denitration system acts on the ammonia injection command to prevent the ammonia slip rate from being too large to affect the safe operation of the coal-fired unit; the upper limit NH3_H and the lower limit NH3_L of the ammonia injection amount are calculated as follows:

[0021] NH3_H=min(k6·C NO-in , k7·NH3_slip)

[0022] NH3_L=k8·C NO-in

[0023] NH3_H is the upper limit of ammonia injection amount, mol m -3 min is the minimum value function; NH3_slip is the ammonia slip rate of the SCR denitration system, ppm; NH3_L is the lower limit of ammonia injection amount, mol m -3 k6 and k8 are the maximum and minimum values of the ratio of ammonia injection amount to the inlet NOx concentration of the SCR denitration system, k6 is generally 1.2-1.8, k8 is generally 0.5-0.8, and k7 is given according to the maximum ammonia slip rate allowed by the coal-fired power plant.

[0024] In the control process of the ammonia slip rate: when the coal-fired unit adopts the economizer feedwater bypass valve to adjust the inlet flue gas temperature of the SCR denitration system, the maximum value of the economizer feedwater bypass flow rate fw_bs is set to ensure the safe operation of the coal-fired unit, specifically:

[0025] fw_bs≤M1

[0026] M1=k9·Load+k 10 -N

[0027] wherein fw_bs is the bypass flow rate of the economizer feedwater bypass, kg s -1 M1 is the maximum allowed flow rate of the economizer feedwater bypass, kg s -1 N is the safety margin of the economizer feedwater bypass, kg s -1 k9 and k 10 are calculation coefficients, the maximum allowed bypass flow rate of the coal-fired unit is calculated at 75% THA and 50% THA loads, and then k9 and k 10 are fitted with the load command.

[0028] When the coal-fired unit adopts the flue gas bypass to adjust the inlet flue gas temperature of the SCR denitration system, the maximum value of the bypass flow rate proportion fg-bs of the flue gas bypass is set as a constant value to meet the safe and efficient operation of the SCR denitration system at 30% THA load of the unit, and the maximum value of the bypass damper opening rate fg-v of the flue gas bypass is set, specifically:

[0029] fg_bs≤M2

[0030] fg_v≤M3

[0031] wherein fg-bs is the bypass flow rate proportion of the flue gas bypass, kg s -1 M2 is the maximum allowed value of the bypass flow rate proportion of the flue gas bypass, kg s -1Generally, 20%-30% can be taken; fg-v is the opening change rate of the bypass damper of the flue gas bypass; M3 is a set value of the maximum flue gas bypass damper change rate, which can be given according to the flue gas damper characteristics used by the coal-fired generating unit.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] 1) Compared with the control strategy of only using the ammonia injection amount to control the NOx concentration at the outlet of the SCR denitration system, the SCR denitration control strategy of the present application uses the ammonia injection amount to adjust the NOx concentration at the outlet of the SCR denitration system and uses the regulation of the flue gas temperature at the inlet of the SCR denitration system to adjust the ammonia escape rate.

[0034] 2) The control strategy of the present application can solve the problem of transient over-standard of the NOx concentration at the outlet of the SCR denitration system of the coal-fired generating unit in the process of frequent load variation.

[0035] 3) The control strategy of the present application can make the SCR denitration system of the coal-fired generating unit in the process of frequent load variation

[0036] The ammonia escape rate is always kept within a reasonable range. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a schematic diagram of the feedwater bypass and the flue gas bypass of the coal economizer of the coal-fired generating unit.

[0038] Figure 2 It is an SCR denitration control strategy based on the collaborative regulation of the ammonia injection amount and the flue gas temperature of the present application.

[0039] Figure 3a and Figure 3b It is the change of the NOx concentration at the outlet of the SCR system and the ammonia escape rate when the load is reduced from 75%THA to 50%THA, under the SCR denitration control strategy based on the collaborative regulation of the ammonia injection amount and the flue gas temperature of the present application, and compared with the SCR denitration control strategy of only using the ammonia injection amount adjustment. DETAILED DESCRIPTION

[0040] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0041] As shown in the drawings, Figure 1 The coal-fired generating unit is provided with a feedwater bypass and a flue gas bypass of the coal economizer, and the bypass valve of the coal economizer can be controlled to change the bypass flow of the feedwater of the coal economizer, so as to change the flue gas temperature at the inlet of the SCR denitration system. Similarly, the opening of the flue gas damper of the flue gas bypass of the coal economizer can be changed to control the bypass flow of the flue gas of the coal economizer, so as to change the flue gas temperature at the inlet of the SCR denitration system.

[0042] As shown in the drawings, Figure 2As shown, the application proposes a SCR denitration control method based on ammonia injection amount and flue gas temperature coordinated control.

[0043] The control target 1 is the ammonia escape rate of the SCR denitration system: first, the deviation (Δ2) of the ammonia escape rate and the ammonia escape rate set value is calculated by PID to obtain the SCR denitration reaction temperature instruction, and the feedforward (Fdd1) of the SCR denitration reaction temperature instruction is obtained from the SCR denitration system inlet NOx concentration and the SCR denitration system inlet flue gas flow rate; the calculation expression is as follows, wherein the SCR system outlet NH3 concentration and NOx concentration value are taken as the maximum value required by the coal-fired power plant:

[0044]

[0045] In the formula, Fdd1 is the feedforward of the SCR denitration reaction temperature instruction, K; E NO is the activation energy of the SCR reduction reaction, J·mol -1 ; R is the ideal gas constant, unit J·mol -1 ·K -1 ; C NO-in is the SCR denitration system inlet NOx concentration, mol m -3 ; u is the SCR denitration system inlet flue gas flow rate, unit m·s -1 ; C NO-out is the SCR denitration system outlet NOx concentration, mol m -3 ; is the SCR denitration system outlet NH3 concentration, mol m -3 ; L is the SCR denitration catalyst thickness, m; is the pre-exponential factor of the adsorption reaction of NH3 on the surface of the SCR denitration catalyst, unit m 3 ·mol -1 ·s -1 ; is the NH3 adsorption amount on the surface of the SCR catalyst, mol NH3 m -3 , γ is a correction coefficient, which is a constant;

[0046] Secondly, the deviation (Δ3) of the SCR denitration system inlet flue gas temperature and the SCR denitration reaction temperature instruction is calculated by PID to obtain the economizer feed water bypass valve opening degree instruction or the flue gas bypass damper opening degree instruction, and the feedforward (Fdd2) of the economizer feed water bypass valve opening degree instruction or the flue gas bypass damper opening degree instruction is specifically calculated as follows:

[0047] Fdd2=(k1·Load+k2-T_s) / ΔT1

[0048] In the formula, Fdd2 is the feedforward of the economizer feedwater bypass valve opening degree command or the flue gas bypass damper opening degree command; Load is the unit load command; T_s is the SCR denitration reaction temperature command, K; ΔT1 is the change of 1% of the economizer feedwater bypass valve or flue gas bypass damper opening degree, the change of the SCR system inlet flue gas temperature, K; k1 and k2 are calculation coefficients, which are fitted with the SCR inlet flue gas temperature and the load command at 75% THA and 50% THA loads of the coal-fired unit respectively, that is, k1 and k2 can be calculated.

[0049] The control target 2 is the SCR denitration system outlet NOx concentration: the deviation (Δ1) of the SCR denitration system outlet NOx concentration and the outlet NOx concentration set value is subjected to PID calculation to obtain the ammonia injection amount command, the feedforward of which is composed of three parts, one of which is the command (Fdd3) obtained based on the NOx inlet concentration; the second is the change of the ammonia storage in the SCR catalyst layer (Fdd4); and the third is calculated from the deviation of the SCR denitration system inlet flue gas temperature (Fdd5), and the expression is:

[0050] Fdd3=k3·C NO-in

[0051] Fdd4=k4·NH3_c

[0052] Fdd5=k5·ΔT2

[0053] In the formula, Fdd3 is the feedforward 1 of the ammonia injection amount command, mol m -3 ; Fdd4 is the feedforward 2 of the ammonia injection amount command, mol m -3 ; NH3_c is the total ammonia storage in the SCR denitration catalyst layer, mol m -3 ; Fdd5 is the feedforward 3 of the ammonia injection amount command, mol m -3 ; ΔT2 is the deviation of the SCR denitration system inlet flue gas temperature and the SCR denitration reaction temperature command, K; k3 is the ratio of the ammonia injection amount to the SCR system inlet NOx concentration, generally taken as 0.8-1.0. k4 and k5 can be given according to the actual operation of the coal-fired unit.

[0054] The upper limit and the lower limit of the ammonia injection amount are set, which are obtained based on the SCR denitration system inlet NOx concentration; at the same time, the ammonia slip rate of the SCR denitration system acts on the ammonia injection command to prevent the ammonia slip rate from being too large to affect the safe operation of the coal-fired unit; the upper limit NH3_H and the lower limit NH3_L of the ammonia injection amount are calculated as follows:

[0055] NH3_H=min(k6·C NO-in , k7·NH3_slip)

[0056] NH3_L=k8·C NO -in

[0057] NH3_H is the upper limit of ammonia injection amount, mol m -3 ; min is the minimum value function; NH3_slip is the ammonia slip rate of the SCR denitration system, ppm; NH3_L is the lower limit of ammonia injection amount, mol m -3 ; k6 and k8 are the maximum and minimum values of the ratio of ammonia injection amount to the inlet NOx concentration of the SCR denitration system, k6 is generally 1.2-1.8, k8 is generally 0.5-0.8, and k7 is given according to the maximum ammonia slip rate allowed by the coal-fired power plant.

[0058] In the control process of the ammonia slip rate: when the coal-fired unit adopts the economizer feedwater bypass valve to adjust the inlet flue gas temperature of the SCR denitration system, the maximum value of the economizer feedwater bypass flow rate fw_bs is set to ensure the safe operation of the coal-fired unit, and specifically:

[0059] fw__bs≤M1

[0060] M1=k9·Load+k 10 -N

[0061] In the formula, fw_bs is the bypass flow rate of the economizer feedwater bypass, kg s -1 ; M1 is the maximum allowed flow rate of the economizer feedwater bypass, kg s -1 ; N is the safety margin of the economizer feedwater bypass, kg s -1 ; k9 and k 10 are calculation coefficients, the maximum allowed bypass flow rate of the coal-fired unit is calculated at 75% THA and 50% THA loads, and then k9 and k 10 are obtained by fitting with the load command.

[0062] When the coal-fired unit adopts the flue gas bypass to adjust the inlet flue gas temperature of the SCR denitration system, the maximum value of the bypass flow rate proportion fg-bs of the flue gas bypass is set to a constant value to meet the safe and efficient operation of the SCR denitration system at 30% THA load of the unit, and the maximum value of the bypass damper opening rate variation fg-v of the flue gas bypass is set, and specifically:

[0063] fg_bs≤M2

[0064] fg_v≤M3

[0065] In the formula, fg-bs is the bypass flow rate proportion of the flue gas bypass, kg s -1 ; M2 is the maximum allowed value of the bypass flow rate proportion of the flue gas bypass, kg s -1Generally, 20%-30% is enough; fg-v is the opening rate change of the bypass damper of the flue gas bypass; M3 is the set value of the maximum flue gas bypass damper change rate, which can be given according to the flue gas damper characteristics used by the coal-fired generating unit.

[0066] As shown in Figure 3a and Figure 3b , the SCR denitration control strategy that only uses the ammonia injection amount to adjust the NOx concentration at the outlet of the SCR system is referred to as the original control strategy. The SCR denitration control strategy based on the coordinated regulation of the ammonia injection amount and the flue gas temperature according to the present application is referred to as the optimized control strategy. Under the two control strategies, the changes of the NOx concentration at the outlet of the SCR system and the ammonia escape rate during the process in which the coal-fired generating unit is reduced from 75% THA to 50% THA are shown in Figure 3a and Figure 3b . It can be found that, after the optimized control strategy is used, the problem of the transient over-standard of the NOx concentration at the outlet of the SCR system is better solved, and the ammonia escape rate can also be controlled to a lower level, ensuring the safe operation of the coal-fired generating unit.

[0067] The SCR denitration control method based on the coordinated regulation of the ammonia injection amount and the flue gas temperature can better solve the problems of the over-standard or transient over-standard of the NOx concentration at the outlet of the SCR system and the ammonia escape rate that may exist during the variable load process of the coal-fired generating unit, and has important significance for reducing the pollutant emissions of the coal-fired generating unit. Reducing the ammonia escape rate can reduce the formation of ammonium bisulfate, ensuring the safe and efficient operation of the coal-fired generating unit.

Claims

1. A SCR denitration control method based on synergistic regulation of ammonia injection amount and flue gas temperature, characterized in that: The ammonia injection amount is adjusted to regulate the NOx concentration at the outlet of the SCR denitration system, and the inlet flue gas temperature of the SCR denitration system is adjusted to regulate the ammonia escape rate; the specific control method is as follows: Control target 1 is the ammonia escape rate of the SCR denitration system: first, the deviation of the ammonia escape rate from the ammonia escape rate set value is calculated by PID to obtain the SCR denitration reaction temperature instruction, the feedforward of which is obtained from the SCR denitration system inlet NOx concentration and the SCR denitration system inlet flue gas flow rate; the calculation expression is as follows, wherein the SCR system outlet NH3 concentration and NOx concentration values are taken as the maximum values required by the coal-fired power plant: In the formula, Fdd1 is the feedforward of the SCR denitrification reaction temperature command, in K; E NO Select the activation energy for the reduction reaction of SCR, in J·mol⁻¹. -1 R is the ideal gas constant, with units of J·mol⁻¹. -1 ·K -1 C NO-in NOx concentration at the inlet of the SCR denitrification system, in mol / m³ -3 u represents the inlet flue gas velocity of the SCR denitrification system, in m·s. -1 C NO-out NOx concentration at the outlet of the SCR denitrification system, in mol / m³. -3 ; The NH3 concentration at the outlet of the SCR denitrification system is expressed in mol / m³. -3 L represents the thickness of the SCR denitrification catalyst, in meters (m). The pre-exponential factor for the adsorption reaction of NH3 on the surface of the SCR denitrification catalyst is given, in units of m. 3 ·mol -1 ·s -1 ; The amount of NH3 adsorbed on the surface of the SCR catalyst is expressed in mol. NH3 m -3 , γ is the correction factor, which is a constant; Secondly, the deviation of the SCR denitration system inlet flue gas temperature and the SCR denitration reaction temperature instruction is calculated by PID to obtain the economizer feed water bypass valve opening degree instruction or the flue gas bypass damper opening degree instruction, the feedforward of which is calculated as follows: Fdd2=(k1·Load+k2-T_s) / ΔT1 In the formula, Fdd2 is the feedforward of the economizer feed water bypass valve opening degree instruction or the flue gas bypass damper opening degree instruction; Load is the unit load instruction; T_s is the SCR denitration reaction temperature instruction, in K; ΔT1 is the change amount of the economizer feed water bypass valve or the flue gas bypass damper opening degree by 1%, and the change amount of the SCR system inlet flue gas temperature, in K; k1 and k2 are calculation coefficients, which are fitted by the SCR inlet flue gas temperature and the load instruction at 75% THA and 50% THA loads of the coal-fired unit respectively, that is, k1 and k2 can be calculated; Control target 2 is the SCR denitration system outlet NOx concentration: the deviation of the SCR denitration system outlet NOx concentration and the outlet NOx concentration set value is calculated by PID to obtain the ammonia injection amount instruction, the feedforward of which is composed of three parts, one of which is the instruction obtained based on the NOx inlet concentration; the second is the change amount of ammonia storage in the SCR catalyst layer; and the third is calculated from the deviation of the SCR denitration system inlet flue gas temperature, and the expression is as follows: Fdd3 = k3 - C NO-in Fdd4=k4·NH3_c Fdd5=k5·ΔT2 In the formula, Fdd3 is feedforward 1 of ammonia injection amount instruction, with unit of mol m -3 ; Fdd4 is feedforward 2 of ammonia injection amount instruction, with unit of mol m -3 ; NH3_c is total ammonia storage amount in the SCR denitration catalyst layer, with unit of mol m -3 ; Fdd5 is feedforward 3 of ammonia injection amount instruction, with unit of mol m -3 ; ΔT2 is the deviation of the SCR denitration system inlet flue gas temperature and the SCR denitration reaction temperature instruction, with unit of K; k3 is the ratio of ammonia injection amount and the SCR system inlet NOx concentration, taking 0.8-1.0; k4, k5 are given according to the actual operation of the coal-fired unit.

2. The SCR deNOx control method based on synergistic regulation of ammonia injection amount and flue gas temperature according to claim 1, characterized in that, The SCR denitration control method further comprises: The upper limit and the lower limit of the ammonia injection amount are set, which are obtained based on the SCR denitration system inlet NOx concentration; at the same time, the ammonia escape rate of the SCR denitration system acts on the ammonia injection instruction to prevent the ammonia escape rate from being too large to affect the safe operation of the coal-fired unit; the upper limit NH3_H and the lower limit NH3_L of the ammonia injection amount are calculated as follows: NH3_H = min(k6 · C NO-in ,k7 · NH3_slip) NH3_L = k8 - C NO-in NH3_H is the upper limit of ammonia injection, with the unit of mol m -3 ; min is the minimum function; NH3_slip is the ammonia slip rate of the SCR denitration system, with the unit of ppm; NH3_L is the lower limit of ammonia injection, with the unit of mol m -3 ; k6 and k8 are the maximum and minimum values of the ratio of ammonia injection to the inlet NOx concentration of the SCR denitration system, k6 is taken as 1.2-1.8, k8 is taken as 0.5-0.8, and k7 is given according to the maximum ammonia slip rate allowed by the coal-fired power plant.

3. The SCR deNOx control method based on synergistic regulation of ammonia injection amount and flue gas temperature according to claim 1, characterized in that, In the control process of the ammonia escape rate: When the coal-fired unit adjusts the SCR denitration system inlet flue gas temperature by using the economizer feed water bypass valve, the maximum value of the economizer feed water bypass flow rate fw_bs is set to ensure the safe operation of the coal-fired unit, and specifically: fw_bs≤M1 M1 = k9-Load + k 10 -N wherein fw_bs is the bypass flow of the economizer feedwater bypass, in kg s -1 ; M1 is the maximum allowed flow of the economizer feedwater bypass, in kg s -1 ; N is the safety margin of the economizer feedwater bypass, in kg s -1 ; k9, k 10 are calculation coefficients, the maximum allowed bypass flow of the coal-fired unit is calculated at 75% THA and 50% THA loads, and then fitted with the load command, i.e., k9, k 10 are calculated.

4. The SCR deNOx control method based on synergistic regulation of ammonia injection amount and flue gas temperature according to claim 1, characterized in that, In the control process of the ammonia escape rate: When the coal-fired unit adopts the flue gas bypass to regulate the inlet flue gas temperature of the SCR denitration system, the maximum value of the bypass flow rate ratio fg-bs of the flue gas bypass is a constant, which meets the safe and efficient operation of the SCR denitration system at 30% THA load of the unit; meanwhile, the maximum value of the bypass damper opening change rate fg-v of the flue gas bypass is set, which is specifically: fg_bs≤M2 fg_v≤M3 wherein fg-bs is the bypass flow rate ratio of the flue gas bypass, in kg s -1 ; M2 is the maximum allowable value of the bypass flow rate ratio of the flue gas bypass, in kg s -1 ; fg-v is the opening rate change rate of the bypass damper of the flue gas bypass; and M3 is the set value of the maximum flue gas bypass damper change rate, which is given according to the flue gas damper characteristics used by the coal-fired generating unit.

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