A control method for SCR denitration system adaptable to frequent fluctuations in unit load

Abstract

The present invention discloses a control method for an SCR denitration system adapted to frequent fluctuations in unit load. The ammonia injection amount is used to adjust the NOx concentration at the outlet of the SCR denitration system, and the deviation between the NOx concentration at the outlet of the SCR denitration system and the set value of the outlet NOx concentration is obtained through PID calculation to obtain the ammonia injection amount command. The feedforward of the ammonia injection amount command consists of three parts: one is the command obtained based on the NOx concentration at the inlet of the denitration system; the second is obtained based on the deviation between the predicted value and the actual value of the SCR reaction temperature; the third is obtained based on the change in the opening of the flue gas damper of the coal-fired unit. At the same time, the change rate of the SCR reaction temperature acts on the ammonia injection command. When the decrease rate of the SCR reaction temperature is large, the change rate of the ammonia injection amount is restricted from being too large.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired power generation, and particularly to a control method for an SCR denitration system adaptable to frequent fluctuations in unit load. Background Art

[0002] Coal-fired units are the "ballast stones" for the safe and stable supply of China's energy. In the future, coal-fired units will undertake more peak shaving and frequency modulation tasks to accommodate more wind energy and solar energy. Therefore, coal-fired units will frequently be in a large variable load range and a fast variable load rate process, which will inevitably affect the safe and stable operation of the denitration system of coal-fired units. In China, there are strict regulations on the NOx concentration and ammonia slip rate at the outlet of the denitration system of coal-fired units.

[0003] Currently, the SCR denitration technology is the most widely used denitration technology in coal-fired power plants. The principle of this technology is to mix ammonia with NOx in the flue gas and carry out an oxidation-reduction reaction under the action of a catalyst to generate N2 and H2O. The required reaction temperature is generally 320 - 400°C. Frequent load changes cause frequent changes in the SCR reaction temperature, which may result in the problem of exceeding the standard or transient exceeding the standard of the NOx concentration at the outlet of the SCR system. The current SCR denitration control method cannot solve this problem well. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a control method for an SCR denitration system adaptable to frequent fluctuations in unit load, introducing the change of the denitration reaction temperature into the denitration control strategy, so as to solve the problem of exceeding the standard or transient exceeding the standard of the NOx concentration at the denitration outlet caused by the denitration temperature fluctuation during the frequent load change process.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A control method for an SCR denitration system adaptable to frequent fluctuations in unit load, using the ammonia injection amount to adjust the NOx concentration at the outlet of the SCR denitration system. The deviation between the NOx concentration at the outlet of the SCR denitration system and the set value of the outlet NOx concentration is obtained through PID calculation to obtain the ammonia injection amount command;

[0007] The feedforward of the ammonia injection amount command consists of three parts. One is the command obtained based on the NOx concentration at the inlet of the SCR denitration system:

[0008]

[0009] In the formula, Fdd1 is the feedforward 1 of the ammonia injection amount command, mol m -3 ; E NO is the activation energy of the SCR selective reduction reaction, J·mol -1 ; E oxis the activation energy of the redox reaction of the catalyst adsorbed with NH3 itself, J·mol -1 ; R is the ideal gas constant, with the unit J·mol -1 ·K -1 ; T1 is the SCR denitration reaction temperature, K; C NO-in is the NOx concentration at the inlet of the SCR denitration system, mol m -3 ; C NO-out is the NOx concentration at the outlet of the SCR denitration system, mol m -3 ; is the NH3 concentration at the outlet of the SCR denitration system, mol m -3 ; is the pre-exponential factor of the redox reaction of the catalyst adsorbed with NH3 itself, with the unit m 3 ·mol -1 ·s -1 ; is the pre-exponential factor of the SCR selective reduction reaction, with the unit m 3 ·mol -1 ·s -1 ; γ is a correction coefficient and is a constant;

[0010] The second one is obtained based on the deviation between the predicted value and the actual value of the SCR reaction temperature:

[0011] Fdd2 = k1·(AIG(x1, x2, x3, x4, x5) - T)

[0012] In the formula, Fdd2 is the feedforward 2 of the ammonia injection amount instruction, mol m -3 ; x1 is the unit load rate; x2 is the flue gas baffle opening; x3 is the feed water temperature, °C; x4 is the inlet temperature of the low-temperature reheater, °C; x5 is the intermediate point temperature, °C; AIG is an intelligent algorithm that predicts the SCR denitration reaction temperature from x1, x2, x3, x4, x5 according to the historical operation data of the coal-fired unit; T is the actual SCR denitration reaction temperature, °C; k1 is an adjustment coefficient that is adjusted according to the actual operation conditions;

[0013] The third one is obtained based on the change in the flue gas baffle opening of the coal-fired unit:

[0014] Fdd3 = k2·Δv

[0015] In the formula, Fdd3 is the feedforward 3 of the ammonia injection amount instruction, mol m -3 ; Δv is the change rate of the flue gas baffle opening of the coal-fired unit; k2 is an adjustment coefficient that is adjusted according to the actual operation conditions.

[0016] Preferably, the rate of change of the SCR reaction temperature acts on the ammonia injection command. When the rate of change of the SCR denitration reaction temperature v1 < N, the rate of change of the ammonia injection amount command v2 < M is set: where N ranges from -0.1 to -0.2; M ranges from 0.05 to 0.1.

[0017] Preferably, in the expression of Fdd1, the SCR denitration reaction temperature T1 takes a fixed value, and the value range is 603.15 - 633.15K.

[0018] Preferably, in the expression of Fdd1, C NO-out takes a fixed value, and the value range is 0.0014 - 0.0018molm -3 .

[0019] Preferably, in the expression of Fdd1, takes a fixed value, and the value range is 0.0001 - 0.0002molm -3 .

[0020] Preferably, in the expression of Fdd1, the value range of γ is 1.4 - 1.8.

[0021] Preferably, in the expression of Fdd2, during the process of predicting the SCR denitration reaction temperature using the intelligent algorithm AIG, the hysteresis time Δt of each parameter on the change of the SCR denitration reaction temperature is considered, and the specific calculation is as follows:

[0022]

[0023] In the formula, Δt is the hysteresis time of each parameter on the change of the SCR denitration reaction temperature, s; k3, k4, k5 are calculation coefficients, which are obtained from the historical operation data of the coal-fired power plant.

[0024] Preferably, in the expression of Fdd2, during the process of predicting the SCR denitration reaction temperature using the intelligent algorithm AIG, the intelligent algorithm AIG adopts the BP neural network algorithm, the LSTM neural network algorithm, the convolutional neural network algorithm or the random forest algorithm.

[0025] Preferably, in the expression of Fdd2, during the process of load change of the coal-fired unit, when the load of the coal-fired unit changes to the target command, k1 = 0; that is, the feedforward 2 of the ammonia injection amount command exits the control logic.

[0026] Compared with the prior art, the present invention introduces the SCR denitration reaction temperature into the denitration control method, solves the problem of difficult control of the NOx concentration at the outlet of the denitration system caused by the fluctuation of the SCR denitration reaction temperature during the frequent load change process, and can effectively solve the problem of transient over-standard of the NOx outlet of the unit denitration system during the load change process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the control method diagram of the present invention.

[0028] Figure 2 It shows the change of the NOx concentration at the outlet of the SCR system when the load is reduced from 75% THA to 50% THA under the denitration control method of the present invention, and is compared with the conventional SCR denitration control method. Specific embodiments

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] As Figure 1 shown, the present invention proposes a control method for an SCR denitration system adapted to frequent fluctuations in unit load.

[0031] The control target is the NOx concentration at the outlet of the SCR denitration system: the deviation (Δ1) between the NOx concentration at the outlet of the SCR denitration system and the set value of the outlet NOx concentration is obtained through PID calculation to obtain the ammonia injection amount command. The feedforward of the ammonia injection amount command consists of three parts. One is the command obtained based on the NOx concentration at the inlet of the SCR denitration system:

[0032]

[0033] In the formula, Fdd1 is the feedforward 1 of the ammonia injection amount command, mol m -3 ; E NO is the activation energy of the SCR selective reduction reaction, J·mol -1 ; E ox is the activation energy of the redox reaction of the catalyst-adsorbed NH3 itself, J·mol -1 ; R is the ideal gas constant, with the unit J·mol -1 ·K -1 ; T1 is the SCR denitration reaction temperature, K; C NO-in is the NOx concentration at the inlet of the SCR denitration system, mol m -3 ; C NO-out is the NOx concentration at the outlet of the SCR denitration system, mol m -3 ; is the NH3 concentration at the outlet of the SCR denitration system, mol m -3 ; is the pre-exponential factor of the redox reaction of the catalyst-adsorbed NH3 itself, with the unit m 3 ·mol -1 ·s -1 ; is the pre-exponential factor of the SCR selective reduction reaction, with the unit m 3 ·mol -1 ·s -1 ; γ is a correction coefficient and is a constant;

[0034] In the above formula, the value range of T1 is 603.15 - 633.15K; C NO-out The value range is 0.0014 - 0.0018 mol m -3 ; The value range is 0.0001 - 0.0002 mol m -3 ; The value range of γ is 1.4 - 1.8;

[0035] The second is obtained based on the deviation (Δ2) between the predicted value and the actual value of the SCR reaction temperature:

[0036] Fdd2 = k1·(AIG(x1, x2, x3, x4, x5) - T)

[0037] In the formula, Fdd2 is the feedforward 2 of the ammonia injection amount instruction, mol m -3 ; x1 is the unit load rate; x2 is the flue gas baffle opening; x3 is the feed water temperature, °C; x4 is the inlet temperature of the low-temperature reheater, °C; x5 is the intermediate point temperature, °C; The intelligent algorithm AIG includes deep learning algorithms such as BP neural network, LSTM neural network, convolutional neural network, and random forest algorithm. According to the historical operation data of the coal-fired unit, the SCR denitration reaction temperature is predicted by x1, x2, x3, x4, and x5; T is the actual SCR denitration reaction temperature, °C; k1 is an adjustment coefficient, which can be adjusted according to the actual operation conditions;

[0038] In the above formula, during the process of predicting the SCR reaction temperature using the intelligent algorithm AIG, the hysteresis time Δt of each parameter on the change of the SCR denitration reaction temperature is considered, and the specific calculation is as follows:

[0039]

[0040] In the formula, Δt is the hysteresis time of each parameter on the change of the SCR denitration reaction temperature, s; k3, k4, and k5 are calculation coefficients, which can be obtained according to the historical operation data of the coal-fired power station.

[0041] In the above formula, during the process of load change of the coal-fired unit, when the unit load changes to the target instruction, k1 = 0; that is, the feedforward 2 of the ammonia injection amount instruction exits the control logic.

[0042] The third is obtained based on the change of the flue gas baffle opening of the coal-fired unit:

[0043] Fdd3 = k2·Δv

[0044] In the formula, Fdd3 is the feedforward 3 of the ammonia injection amount instruction, mol m -3 ; Δv is the change rate of the flue gas baffle opening of the coal-fired unit; k2 is an adjustment coefficient, which can be adjusted according to the actual operation conditions;

[0045] The change rate of the SCR reaction temperature acts on the ammonia injection command. When the change rate v1 of the SCR reaction temperature < N, the change rate v2 of the ammonia injection amount command is set < M: where N is generally taken as -0.1 to -0.2; M is generally taken as 0.05 to 0.1;

[0046] The SCR denitration control strategy that uses the ammonia injection amount to adjust the NOx concentration at the outlet of the SCR denitration system and the feedforward command is only obtained from the NOx concentration at the inlet of the denitration system is called the original control strategy. The denitration control strategy of the present invention is called the optimized control strategy. Under these two control strategies, during the process of the coal-fired unit reducing from 75% THA operating condition to 50% THA operating condition, the change of the NOx concentration at the outlet of the SCR system is as Figure 2 shown. It can be found that after adopting the optimized control strategy, the problem of transient over-standard of the NOx concentration at the outlet of the SCR system has been better solved.

Claims

1. A control method for an SCR denitration system adapted to frequent fluctuations in unit load, characterized in that: The ammonia injection rate is used to adjust the NOx concentration at the outlet of the SCR denitration system. The deviation between the NOx concentration at the outlet of the SCR denitration system and the set value of the NOx concentration at the outlet is obtained through PID calculation to obtain the ammonia injection rate command. The feedforward of the ammonia injection rate command consists of three parts. One is the command obtained based on the NOx concentration at the inlet of the SCR denitration system: In the formula, Fdd1 is the feedforward 1 of the ammonia injection amount command, with the unit of mol·m -3 ; E NO is the activation energy of the selective catalytic reduction (SCR) reaction, with the unit of J·mol -1 ; E ox is the activation energy of the oxidation-reduction reaction of the catalyst-adsorbed NH3 itself, with the unit of J·mol -1 ; R is the ideal gas constant, with the unit of J·mol -1 ·K -1 ; T1 is the SCR denitration reaction temperature, with the unit of K; C NO-in is the NOx concentration at the inlet of the SCR denitration system, with the unit of mol·m -3 ; C NO-out is the NOx concentration at the outlet of the SCR denitration system, with the unit of mol·m -3 ; is the NH3 concentration at the outlet of the SCR denitration system, with the unit of mol·m -3 ; is the pre-exponential factor of the oxidation-reduction reaction of the catalyst-adsorbed NH3 itself, with the unit of m 3 ·mol -1 ·s -1 ; is the pre-exponential factor of the SCR selective reduction reaction, with the unit of m 3 ·mol -1 ·s -1 ; γ is a correction coefficient and is a constant; The second is obtained based on the deviation between the predicted value and the actual value of the SCR reaction temperature: Fdd2 = k1·(AIG(x1,x2,x3,x4,x5)-T) Wherein, Fdd2 is the feedforward 2 of the ammonia injection amount command, with the unit of mol·m -3 ; x1 is the unit load rate; x2 is the flue gas damper opening; x3 is the feed water temperature, with the unit of °C; x4 is the inlet temperature of the low-temperature reheater, with the unit of °C; x5 is the intermediate point temperature, with the unit of °C; AIG is an intelligent algorithm that predicts the SCR denitration reaction temperature by x1, x2, x3, x4, and x5 based on the historical operation data of the coal-fired unit; T is the actual SCR denitration reaction temperature, with the unit of °C; k1 is an adjustment coefficient that is adjusted according to the actual operation conditions; The third is obtained based on the change in the opening of the flue gas damper of the coal-fired unit: Fdd3 = k2·Δν where Fdd3 is the feedforward 3 of the ammonia injection rate command, with the unit of mol·m -3 ; Δv is the change rate of the flue gas damper opening of the coal-fired unit; k2 is the adjustment coefficient, which is adjusted according to the actual operating conditions.

2. The SCR denitration system control method for adapting to frequent fluctuations in unit load according to claim 1, wherein, The change rate of the SCR reaction temperature acts on the ammonia injection command. When the change rate v1 of the SCR denitration reaction temperature < N, the change rate v2 of the ammonia injection rate command is set < M: where N ranges from -0.1 to -0.2; M ranges from 0.05 to 0.

1.

3. The control method of the SCR denitration system adapted to frequent fluctuations in unit load according to claim 1, characterized in that, In the expression of Fdd1, the SCR denitration reaction temperature T1 takes a fixed value, and the value range is 603.15 - 633.15K.

4. The control method of the SCR denitration system adapted to frequent fluctuations in unit load according to claim 1, wherein, In the expression of Fdd1, C NO-out takes a fixed value, and the value range is 0.0014 to 0.0018 mol·m -3 .

5. The control method of the SCR denitration system adapted to frequent fluctuations in unit load according to claim 1, characterized in that, In the expression of Fdd1, takes a fixed value, and the value range is 0.0001 to 0.0002 mol·m -3 .

6. The control method of the SCR denitration system adapted to frequent fluctuations in unit load according to claim 1, characterized in that, In the expression of Fdd1, the value range of γ is 1.4 - 1.

8.

7. The SCR denitration system control method for adapting to frequent fluctuations in unit load according to claim 1, characterized in that, In the expression of Fdd2, during the process of predicting the SCR denitration reaction temperature using the intelligent algorithm AIG, the hysteresis time Δt of each parameter on the change of the SCR denitration reaction temperature is considered. The specific calculation is as follows: In the formula, Δt is the hysteresis time of each parameter on the change of the SCR denitration reaction temperature, s; k3, k4, k5 are calculation coefficients obtained according to the historical operation data of the coal-fired power station.

8. The control method of the SCR denitration system adapted to frequent fluctuations in unit load according to claim 1, wherein, In the expression of Fdd2, during the process of predicting the SCR denitration reaction temperature using the intelligent algorithm AIG, the intelligent algorithm AIG uses the BP neural network algorithm, the LSTM neural network algorithm, the convolutional neural network algorithm or the random forest algorithm.

9. The control method of the SCR denitration system adapted to frequent fluctuations in unit load according to claim 1, characterized in that, In the expression of Fdd2, during the process of the coal-fired unit changing load, when the load of the coal-fired unit changes to the target command, k1 = 0; that is, the feedforward 2 of the ammonia injection rate command exits the control logic.

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