JP3410555B2 - Ammonia injection amount control device for denitration equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
Injection volumeControl deviceLow nitrogen oxides in exhaust gas
Suitable ammonia injection volume to reduceControl deviceAbout. [0002] 2. Description of the Related Art Amount of control of ammonia injection in conventional denitration equipment
The apparatus, as shown in FIG.
No. and entrance NO_xMultiplier 7a multiplies output signal of densitometer 2
And the entrance NO_xLet it be an amount signal 21. On the other hand, the entrance NO_x
Output signal and outlet NO of densitometer 2_xOutput of density setting device 3
From the force signal, the required denitration rate from the subtractor 8a and the divider 9
Calculate the signal 10 and input this signal to the function generator 11.
And entrance NO_xAmmonia molar ratio signal required for quantity
13 is calculated. [0003] Exit NO_xOutput signal and outlet of concentration setting device 3
NO_xThe difference signal between the output signal of the densitometer 4 and the subtractor 8 is calculated.
b, signal processed by the controller 12a, and
The cumole ratio signal 15 is calculated. Required by the adder 14a
Add the molar ratio signal 13 and the feedback molar ratio signal 15
Then, a total molar ratio signal 16 is obtained.
_xThe required ammonia flow signal 22 is multiplied by the amount signal 21.
And Next, the load request signal 5 is supplied to the differentiator 17 and the second order.
The signal processed by the differentiator 18 is input to the adder 14b.
Then, the adder 14b compares these signals with the necessary
Add the ammonia flow rate signal 22 and the ammonia flow rate request.
The signal 19 is calculated. This ammonia flow request signal 19
And the deviation of the output signal of the ammonia flow meter 6 by the subtractor 8c.
And process the signal with controller 12b to adjust ammonia flow rate
By opening and closing the valve 20, the NOx removal outlet NO_xconcentration
Was maintained near the set value. This control method is basically based on an inlet NO._x
Leading value for quantity, exit NO_xConcentration and outlet NO_xConcentration setting
Feedback correction and load demand due to deviation from fixed value
The dynamic lead value for the signal determines the amount of ammonia injected.
It is a method to determine. Note that the dynamic leading value is
Delay of denitration reaction to change in input, usually 10 minutes
It is provided for repair. Recently, high-speed load change rates of thermal power plants have been increasing.
De-NOx load fluctuates rapidly with operation
Regardless, NOx outlet NO_xConcentration setting
Exit NO_xImprove controllability of concentration, leak ammonia
It is essential to reduce the concentration. example
For example, when the load rises, for example,
Is the ammonium by dynamic precedence control for the load request signal.
A large amount of a_xConcentration is set
Can be maintained near the value, but after that, the denitration load becomes constant.
In this case, ammonia becomes excessive and the denitration rate rises,
NOx outlet NO_xThe concentration will drop extremely. [0006] Thus, the conventional ammonia injection
In the input control method, when the load changes at high speed,
Exit NO_xKeep the concentration close to the set value, and
Enough to also reduce the concentration of ammonia
Was not considered. [0007] The above prior art is based on denitration.
Even if the load changes suddenly, the denitration device outlet N
O_xConsider keeping the concentration near the set value
Has not been carried out and a large amount of ammonia
Outlet NO by injection_xThe concentration is kept close to the set value
Also, due to the large delay of the denitration reaction, the outlet NO
_xConcentration is much lower than the set value, leak ammonia
There was a problem of increasing. An object of the present invention is to provide a high speed load change
NO at the denitration device outlet_xMaintain the concentration near the set value,
Ammonia injection amount that can reduce leak ammonia concentrationSystem
Control deviceIs to provide. [0009] [MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The invention claimed in the present application is as follows. (1)Total NO of exhaust gas to be processed by denitration equipment _x According to quantity
Injection of denitration equipment that controls the injection amount of ammonia
In the inlet control device, the total exhaust gas NO _x Calculate the amount
Mechanism and exhaust gas inlet NO _x Concentration and outlet NO _x To the concentration
For calculating the preceding value molar ratio signal of ammonia based on
And exit NO _x For correction based on density setting value and measured value
A mechanism for calculating the feedback molar ratio signal of the
Gas flow rate and temperature, inlet and outlet exhaust gas NO _x Concentration, a
N minutes based on the ammonia injection volume and leak ammonia concentration
Exit NO after _x Predict concentration and leaked ammonia concentration
Denitration reaction simulation model and prediction after n minutes
Calculate feedback corrected molar ratio signal based on value
Mechanism and total NO of the inlet exhaust gas _x Amount and leading molar ratio signal
And feedback mole ratio signal and feedback correction mole
Ammonia based on ratio signal and ammonia injection signal
A mechanism for controlling the flow rate adjusting means.
Control device for ammonia injection of denitration equipment. [0010] [0011] [0012] [0013] [Operation] Operating conditions of the denitration equipment from the present time to n minutes later
Conditions, ie exhaust gas flow rate, inlet gas temperature and inlet N
O_xFirst, the concentration is predicted using past data.
I do. Next, regarding the amount of ammonia injected,
Using the denitration reaction simulation model
And NO at NOx outlet after n minutes_xConcentration and leakage
Predict Monia concentration. The exit NO at the present time_xConcentration and
And leak ammonia concentration are
Applies to parameter fixing. Thus, at the moment
Outlet when the injection amount of ammonia in n is continued until after n minutes
NO_xN minutes after the concentration and leak ammonia concentration
Predict accurately. Using these predicted values, exit NO
_xSet value and predicted value of concentration and leak ammonia concentration
The ammonia injection amount must be corrected according to the deviation between
With this, it is possible to compensate for the large delay of the denitration reaction,
Exit NO even during high-speed load changes _xConcentration and Lee
The ammonia concentration can be maintained near the set value.
Does not deviate greatly. [0015] DESCRIPTION OF THE PREFERRED EMBODIMENTS Ammonia injection rate control for denitration equipment according to the present invention
FIG. 1 shows a specific embodiment of the control device. The same reference numerals as in FIG.
Since the attached parts have the same configuration and the same function, a detailed explanation
Description is omitted. This control device is a NOx removal NO._xconcentration
Leading value to obtain the denitration rate required to maintain the set value
Molar ratio signal 13 (output signal of function generator 11), exit N
O_xDensitometer 4 and outlet NO_xAccording to the output signal of the density setting device 3
Feedback molar ratio signal 15, concentration predictor after n minutes
35. Exit NO after n minutes_xConcentration prediction
Signal 34 and leak ammonia concentration prediction signal after n minutes
33, the feedback corrected molar ratio signal (controller 12
c and 12d), the amount of ammonia injected
Is determined. Of these, the leading value molar ratio signal 13 and the output
Mouth NO_xFor the feedback molar ratio signal 15 depending on the concentration
This is the same as the conventional control method. concentration after n minutes
In the measuring instrument 35, from the operating conditions of the denitration device,
Ammonia concentration prediction signal 33 and exit N after n minutes
O_xThe density prediction signal 34 is calculated. First, a simulation model of the denitration reaction
Consists of the following causal relationships. Adsorption of denitration catalyst surface
From the mass balance of ammonia, [0018] (Equation 1) Here, C_NH3: Amount of adsorbed ammonia (mol /
m^Two), G_NH3i： Ammonia injection amount (mol / m^Twoh), G_NH3o:
Leak ammonia flow rate (mol / m^Twoh), G_N2: By denitration reaction
N_TwoFlow rate (mol / m^Twoh) and G_g, N
O_xi, Η. The denitration rate η is       η = f (G_g, NO_xi, T_g, C_NH3…… (2) Where G_g: Exhaust gas flow rate (m^ThreeN / h), NO_xi:entrance
NO_xConcentration (ppm), T_g: Inlet gas temperature (℃) Therefore, exit NO_xConcentration NO_xoIs       NO_xo= (1-η) NO_xi                  …… (3) Leak ammonia concentration L_NH3Is   L_NH3= G (G_NH3o) = G (NO_xi, C_NH3, Η, G_g)                                                 …… (4) From the above equations (1) to (4), the operating conditions (exhaust gas flow rate,
Entrance NO_xConcentration, inlet gas temperature and outlet NO_xConcentration
And the causal relationship with the leaked ammonia concentration. What
G in equation (4) represents a function. Here, exit NO_xConcentration and leakage
Based on the deviation between the calculated and measured Monia concentration,
Modify the parameters in equations (2) and (4). next,
The prediction of the operating conditions after n minutes is calculated by the following method.       X_{t + n}= H (X_t, X_t-1, ……, X_tm) …… (5)       X = ｛G_g, T_g, NO_xi｝ …… (6) Here, t: current time point, t + n: time point n minutes later, t−
m: time point m minutes ago In other words, predicting future values from past data
Easily calculated, for example, by applying an autoregressive model
it can. Thus, the concentration predictor 35 after n minutes has elapsed.
Now, the operating conditions after n minutes shown in equations (5) and (6)
That is, exhaust gas flow rate, inlet gas temperature and inlet NO_xDark
Using the degree, the outlet N after n minutes by the formulas (1) to (4)
O_xThe concentration and the leaked ammonia concentration are calculated. What
The ammonia injection amount is the value at the current time point.
And corrects the excess or deficiency assuming that
And exit NO in FIG._xBasic considerations on concentration control
Show how In the figure, the exit NO until time t_xconcentration
Is maintained near the set value. afterwards,
At time t, the amount of ammonia injected until time t + n
For n minutes, the operating conditions, ie exhaust gas flow, inlet gas
Temperature and inlet NO_xPredict concentration and exit after n minutes
NO_xPredict concentration. Next, this NO_xPredicted concentration and
The ammonia injection amount is compensated based on the deviation from the set value.
To predict the result n minutes later,
Increase or decrease the injection amount of ammonia
Can compensate. The delay in the denitration reaction is shown in equation (1).
Large change in the amount of adsorbed ammonia
It is. In this way, the concentration predictor 35 after n minutes
, The exit NO after n minutes_xConcentration prediction signal 34 and
The leak ammonia concentration prediction signal 33 after n minutes
Compare with setter output signals 3 and 32 and adjust the deviation
The signals are processed by a total of 12c and 12d and input to the adder 14c.
Power. The adder 14c adds the preceding value model to these signals.
Signal 13 and the feedback molar ratio signal 15
To obtain the final molar ratio signal. Next, the total NO is output by the multiplier 7b._xMultiply by the amount
Calculate the ammonia injection demand
The deviation from the output signal of the flow meter 6 is obtained by the subtractor 8c and adjusted.
Signal processing with a total of 12b and opening and closing of ammonia flow control valve
This determines the amount of injected ammonia.
You. Thus, according to the present invention, a suitable ammonia
Injection volume control enables denitration even during high-speed load changes.
Exit NO_xSet concentration and leak ammonia concentration
Can be maintained near. In the embodiment shown in FIG. 1, the entrance NO
_xThe amount signal 21 is changed to the processing gas flow rate and the inlet gas NO._xFrom concentration
An example of the calculation is shown, but the load of the combustion device (for example, boiler)
From the entrance NO_xCalculate the amount and load and inlet gas N
O_xInlet NO from concentration_xThe amount can also be calculated. [0025] According to the present invention, when the load changes at a high speed,
Even after n minutes, according to the denitration reaction simulation model
NOx outlet NO_xConcentration and leak ammonia concentration
To predict the amount of ammonia injected n minutes ago
The initial operation compensates for the large delay in the denitration reaction.
I can compensate. Therefore, exit NO_xConcentration and leak ammo
There is an effect that the near density can be maintained near the set value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a control system diagram showing an embodiment of an ammonia injection amount control device of a denitration device according to the present invention. FIG. 2 is a control system diagram showing a conventional ammonia injection amount control device. FIG. 3 is an explanatory diagram showing the concept of a control device according to the present invention. [Reference Numerals] 1 ... processing gas flow meter, 2 ... inlet concentration of NO _x meter, 3 ... outlet concentration of NO _x setter, 4 ... outlet concentration of NO _x setter, 6 ... ammonia flow meter, 7a, 7b ... multiplier , 8a, 8b, 8
c, 8d, 8e: subtractor, 9: divider, 10: required denitration rate signal, 11: function generator, 12a, 12b, 12c,
12d: controller, 13: preceding value (necessary) molar ratio signal, 1
4a, 14b, 14c: adder, 15: feedback molar ratio signal, 16, 16a: total molar ratio signal, 19: ammonia injection amount request signal, 20: ammonia flow control valve,
21: Inlet NO _x amount signal, 30: Inlet gas thermometer, 31
... leak ammonia densitometer, 32 ... leak ammonia concentration setter, leak ammonia concentration prediction signal after 33 ... n min, the outlet concentration of NO _x prediction signal after 34 ... n min, 35 ... n
Minute concentration estimator, 36a, 36b ... feedback corrected molar ratio signal.

Claims (1)

(57) [Claims] 1. A total NO _x in the exhaust gas to be treated by the denitration unit
In the ammonia injection rate control unit of the denitration device for controlling ammonia injection amount depending on the amount, a mechanism for calculating the inlet flue gas total amount of NO _x, the inlet concentration of NO _x exhaust gas and outlet NO
a mechanism for calculating the preceding value molar ratio signal of ammonia based on the _x concentration, a mechanism for calculating a feedback molar ratio signal for correction based on the set value and the measured value of the outlet NO _x concentration, a process exhaust gas flow rate and temperature, Inlet and outlet exhaust gas NO
_x concentration, ammonia injection amount, and the denitration reaction simulation model to predict the exit concentration of NO _x and leak ammonia concentration after n minutes based on the leakage of ammonia concentration, the n
A mechanism for calculating a feedback correction molar ratio signal based on the predicted value of the minute later, the said inlet exhaust gas total amount of NO _x prior value molar ratio signal and the feedback molar ratio signal and the feedback correction molar ratio signal and ammonia injection amount signal And a mechanism for controlling the ammonia flow rate adjusting means on the basis of the ammonia flow rate control means.