JP3537100B2 - Method and apparatus for controlling ammonia injection amount in denitration apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling the amount of injected ammonia in a denitration apparatus, and more particularly to a method and apparatus for controlling the amount of nitrogen oxides in exhaust gas efficiently even at a rapid load change. The present invention relates to a method and apparatus for controlling an amount of injected ammonia.

[0002]

Conventional denitration apparatus for ammonia injection control system, as shown in FIG. 2, by multiplying the processing gas flowmeter 1 of the output signal and the inlet NO _X concentration meter 2 of the output signal at the multiplier 7a, The inlet NO _X amount signal 21 is used. On the other hand, the output signal of the inlet NO _X concentration meter 2 and the output signal from the outlet NO _X concentration setting device 3, and calculates the required denitrification rate signal 10 from subtractor 8a and divider 9, the function generator of this signal 11 enter the ammonia necessary for _the amount of NO _X molar ratio signal 13
Is calculated.

A difference signal between the output signal of the outlet NO _X concentration setting device 3 and the output signal of the outlet NO _X concentration meter 4 is subtracted by a subtractor 8.
b, and the signal is processed by the controller 12a to calculate the feedback molar ratio signal 15. The adder 14a adds the required molar ratio signal 13 and the feedback molar ratio signal 15 to obtain a total molar ratio signal 16, and the multiplier 7b uses the input NO.
_The required ammonia flow signal 22 is multiplied by the _X amount signal 21.
And Next, a signal obtained by subjecting the load request signal 5 to arithmetic processing by the differentiator 17 and the second-order differentiator 18 is input to an adder 14b, and the adder 14b adds these signals to the necessary ammonia flow signal 22 described above. Then, the ammonia flow request signal 19 is calculated. This ammonia flow request signal 19
And the deviation of the ammonia flow meter 6 output signal determined by the subtractor 8c, by opening and closing the ammonia flow control valve 20 to the signal processing by the controllers 12b, maintaining the denitration apparatus outlet NO _X concentration near the set value I was

[0004] This control method basically includes an inlet NO _X
In this method, the ammonia injection amount is determined from a preceding value for the amount, feedback correction based on a deviation from the outlet concentration set value, and a dynamic preceding value for the load request signal. The dynamic leading value is provided to compensate for the denitration reaction (usually several tens of minutes) caused by a change in the ammonia injection amount.

Recently, high-speed load change of a plant
Fluctuations in the denitration load have become more rapid with the operation of the rate
On the other hand, exit NO_XDensity setting is smaller than before
With the conventional control method, high-speed load
At the time of load change, exit NO _XConcentration maintained near set value
If you try, a large amount of ammonia will be injected,
The value of the ammonia concentration leaking from the denitration device
O_XThe density setting value will be exceeded. Normal,
The leak ammonia concentration is measured at the outlet NO_XBelow the density setting
This must be maintained, but with conventional control methods
Although there is consideration for ammonia concentration,
Load change and exit NO_XFor a decrease in the density setting,
Consideration has not been given to ensure sufficient controllability
Was.

[0006]

[0007] The above prior art, even when the denitration load changes rapidly, the consideration for the points of maintaining the outlet NO _X concentration and the leak ammonia concentration to a low value (about 1 ppm) Not exit N
When the O _X concentration when you suppress below the set value, will leak ammonia concentration exceeds the set value, and you suppress leakage of ammonia concentration below the set value in the opposite, outlet NO _X
There is a problem that the density exceeds the set value.

An object of the present invention, even during fast load variations, can maintain a NO _X concentration and the leak ammonia concentration of the denitration device outlet to a low concentration to provide an ammonia injection amount control method and apparatus for denitration system .

[0008]

The invention claimed in the present application to achieve the above object is as follows. (1) An exhaust gas containing nitrogen oxides (NO _x ) is introduced from the inlet of the device, ammonia is injected into the exhaust gas, and the NO _x is catalytically reduced by a denitration catalyst provided in the device, and then discharged from the outlet of the device. In the method for controlling the amount of ammonia injected into a denitration apparatus, a step of obtaining an inlet NO _X amount from an introduced exhaust gas flow rate and an inlet NO _X concentration, and a step of calculating a required ammonia for the NO _X amount based on the inlet NO _X concentration and the outlet NO _X concentration. A step of determining a molar ratio;
A step of calculating the required ammonia flow rate from the _X amount and the required ammonia molar ratio, a step of calculating the current amount of catalyst-adsorbed ammonia using the current processing gas flow rate and the denitration rate, and a processing gas flow rate expected after n minutes Calculating the amount of catalyst-adsorbed ammonia required n minutes after the denitration rate, correcting the required ammonia flow based on the difference between the amounts of the adsorbed ammonia, and obtaining an ammonia flow request signal; A step of operating the ammonia flow control device based on a deviation between the request signal and the current ammonia injection amount. (2) After the catalytic reduction of the NO _X by the denitration catalyst disposed in the injection to the equipment ammonia in the exhaust gas is introduced to the exhaust gas containing NO _X from the device inlet to the denitration apparatus for discharging from the apparatus outlet In the ammonia injection amount control device, a multiplier for calculating the inlet NO _X amount from the introduced treated exhaust gas flow rate and the inlet NO _X concentration, and a required ammonia mole ratio for the NO _X amount based on the inlet NO _X concentration and the outlet NO _X concentration set value. means for calculating a ratio, and means for calculating the total molar ratio signal based on the deviation value and the required ammonia molar ratio of the actual outlet NO _X concentration and the outlet NO _X concentration setting, the inlet amount of NO _X and the total mole A means for calculating a required ammonia flow rate signal from the ratio signal, a calculator for calculating the current amount of catalyst-adsorbed ammonia from the current processing gas flow rate and the denitration rate, and a prediction after n minutes A calculator for calculating the amount of catalyst-adsorbed ammonia required after n minutes from the processing gas flow rate and the required denitration rate, based on the deviation value of the adsorbed ammonia quantity of both, the required ammonia flow rate signal, and the current injected ammonia flow rate Means for controlling the amount of injected ammonia to the denitration apparatus.

[0009]

There is a fixed causal relationship between the amount of treated gas, the denitration rate and the amount of ammonia adsorbed on the catalyst. Therefore, the current amount of ammonia adsorbed on the catalyst can be obtained from the amount of the processing gas and the denitration rate that can be measured online. Next, since there is a large response delay in the change in the amount of the catalyst-adsorbed ammonia with respect to the amount of the injected ammonia, the operating conditions are predicted and the amount of the catalyst-adsorbed ammonia necessary after n minutes is obtained. If the amount of injected ammonia is increased or decreased as soon as possible in response to the difference between the two amounts of ammonia adsorbed on the catalyst, the amount of ammonia adsorbed on the catalyst can be maintained at a value close to the required value after n minutes. the NO _X concentration can be maintained in the vicinity of the target value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a specific embodiment of an ammonia injection amount control method for a denitration apparatus according to the present invention. This control method
Required molar ratio signal 13 to obtain required denitration rate, outlet N
O _X densitometer third output signal by the feedback molar ratio signal 15 and the adsorbed ammonia density difference by the correction signal 28
Is used to determine the amount of injected ammonia.

The method of obtaining the required molar ratio signal 13 and the feedback molar ratio signal 15 is the same as that of the conventional control method already described with reference to FIG. 2, and calculates the present and n minutes after the catalyst adsorption ammonia concentration. The feature of the present invention lies in that the amount of injected ammonia is corrected in accordance with the difference between the two concentrations. The adsorbed ammonia concentration calculator 23 calculates the adsorbed ammonia concentration using the following relationship.

[0012]

Q = k · G _g · f (η) (1) where, Q: adsorbed amount of ammonia, k: constant, G _g : treated gas amount, η: denitration rate, f (η) : Dimensionless number determined by the denitration rate. Therefore, the adsorption ammonia concentration calculator 2
In step 3a, the adsorbed ammonia concentration signal 26 is obtained from the denitration rate signal 29 that can be measured online and the output signal of the processing gas flow meter 1 using equation (1).

Next, based on the load request signal 5, the differentiator 17,
The load request signal 31 after n minutes is obtained by using the coefficient unit 24 and the adder 14c. From this signal 31, an inlet NO _X concentration signal 32 after n minutes is obtained using the function generator 11b, and an output signal of the outlet NO _X concentration setter 3, a subtracter 8e and a divider 9b are used. Required denitration rate signal 30 after n minutes
Is found.

Further, in the processing gas amount predicting calculator 25,
The processing gas amount signal 33 after n minutes is obtained by using the load request signal 31 after n minutes and the output signal of the coefficient unit 24. Note that n
Although the prediction of the load request signal after minutes is linear prediction based on the differential value of the load request signal, the processing gas amount prediction calculator 25 calculates the processing gas amount signal 3 after n minutes by the following operation.
Ask for 3.

[0015]

(Equation 2)

Here, MWD: load request signal, t: current time, n: n minutes. In the equation (2), the first term on the right side is
This is a processing gas amount based on static characteristics, and is determined from a load request signal. The second term on the right side corresponds to over / under firing, and is determined by the load change rate. In this way, the adsorption ammonia concentration calculator 23a
And 23b, a current adsorption ammonia concentration signal 26 and an adsorption ammonia concentration prediction signal 27 after n minutes are obtained, and this concentration difference is obtained by the subtractor 8d, and the controller 12c
, And a correction signal 2 based on the difference in the concentration of adsorbed ammonia
As 8 is input to the adder 14b. The adder 14b adds the required ammonia flow signal 22 obtained from the required molar ratio signal 13 and the feedback molar ratio signal 15 and the correction signal 28 based on the difference in the concentration of adsorbed ammonia to obtain an ammonia flow request signal 19, and outputs the ammonia flow request signal 19. The deviation from the signal is obtained by the subtractor 8c, the signal is processed by the controller 12b, and the ammonia flow control valve 20 is opened and closed to adjust the amount of ammonia injected into the denitration apparatus.

In this control method, as can be seen from equation (1), the denitration rate depends on the concentration of adsorbed ammonia when the amount of processing gas is determined.
It is almost determined by the balance with the amount of ammonia consumed by the reaction with _X , overlaps with the large volume capacity effect, and involves a large time delay. Therefore, the state after n minutes corresponding to the delay is predicted, and the required ammonia concentration is ensured by correcting the ammonia injection amount early.

[0018] Thus, in the present embodiment, since the catalyst adsorbed ammonia concentration can be maintained to the required value, even during fast load changes, it is possible to maintain the concentration of NO _X denitrator exit the vicinity of the target value, the leak The ammonia concentration can be suppressed to a low value.

[0019]

According to the present invention, the touch controlling the denitration performance is obtained.
Can calculate the concentration of adsorbed ammonia on the medium online
It is necessary after the current concentration of adsorbed ammonia and n minutes.
The concentration of adsorbed ammonia, and then denitrate according to this concentration difference.
By increasing or decreasing the amount of ammonia injected into the device, high speed
Even when the load fluctuates, the response of the concentration of adsorbed ammonia
In response to this, the injection amount of ammonia was corrected early.
Therefore, NOx at the denitration device exit _XTo keep the concentration at the target value
To obtain the required concentration of adsorbed ammonia.

[0020] Thus, since always supplied without excess or shortage of ammonia required for denitration reaction, even during fast load change, it is possible to maintain a denitrator outlet NO _X concentration near the target value, the leak of the denitration device outlet There is an effect that the ammonia concentration can be reduced.

[Brief description of the drawings]

FIG. 1 is a control system diagram showing an embodiment of a method for controlling an ammonia injection amount of a denitration apparatus according to the present invention.

FIG. 2 is a control system diagram showing a conventional ammonia injection amount control method.

[Explanation of symbols]

1 ... gas flowmeter, 2 ... inlet NO _X concentration meter, 3 ... outlet NO
_X concentration setting unit, 4 ... outlet NO _X concentration meter, 5 ... load demand signal, 6 ... ammonia flow meter, 10 ... required denitrification rate signal, 1
2: Controller, 13: Required molar ratio signal, 15: Feedback molar ratio signal, 16: Total molar ratio signal, 19: Ammonia flow rate request signal, 21: Inlet NO _X amount signal, 22: Required ammonia flow signal, 23a, 23b: adsorbed ammonia concentration calculator, 25: processing gas amount prediction calculator, 26: current adsorbed ammonia concentration signal, 27 ... adsorbed ammonia concentration prediction signal after n minutes, 28 ... correction signal based on difference in adsorbed ammonia concentration, 29 ... denitration ratio signal, required denitration rate signal after 30 ... n min, a load request signal after 31 ... n min, inlet NO _X concentration signal after 32 ... n min, 33 ... n min after treatment gas amount signal.

Claims (2)

(57) [Claims] [Claim 1, wherein the denitration catalyst disposed in the apparatus by injecting ammonia into the exhaust gas is introduced to the exhaust gas containing nitrogen oxides from the device inlet (NO _X) NO _X
After catalytic reduction, the ammonia injection rate control method for denitration device for discharging from the apparatus outlet, a step of the treated flue gas flow rate and inlet NO _X concentrations introduced Request inlet amount of NO _X, the inlet NO _X concentration and outlet NO NO _X based on _X concentration
A step of determining the necessary ammonia molar ratio to the amount, calculates the current catalyst adsorbed ammonia amount using the step of obtaining the required flow rate of ammonia, the current processing gas flow rate and denitrification rate from the inlet amount of NO _X and the required ammonia mole ratio Process and
calculating a required amount of catalyst-adsorbed ammonia after n minutes from the process gas flow rate expected after n minutes and the required denitration rate; and correcting the required ammonia flow rate based on the difference between the two amounts of adsorbed ammonia. A method for controlling an ammonia injection amount of a denitration apparatus, comprising: a step of obtaining a flow rate request signal; and a step of operating an ammonia flow rate control device based on a deviation between the ammonia flow request signal and a current ammonia injection amount. 2. After catalytic reduction of the NO _X by the denitration catalyst disposed in the apparatus by injecting ammonia into the exhaust gas is introduced to the exhaust gas containing the device inlet NO _X, denitrator for discharging from the apparatus outlet in the ammonia injection rate control device to, for the multiplier and, _the amount of NO _X based on the inlet NO _X concentration and the outlet NO _X concentration setting for calculating the inlet amount of NO _X from the treated flue gas flow rate and inlet NO _X concentrations introduced A means for calculating a required ammonia molar ratio; a means for calculating a total molar ratio signal based on a deviation value between an outlet NO _X concentration set value and an actual outlet NO _X concentration and the required ammonia molar ratio; and an inlet NO _X amount Means for calculating a required ammonia flow rate signal from the total molar ratio signal, a calculator for calculating the current amount of catalyst-adsorbed ammonia from the current processing gas flow rate and the denitration rate, A calculator for calculating the amount of catalyst-adsorbed ammonia required n minutes after the expected processing gas flow rate and the required denitration rate, a deviation value of the adsorbed ammonia amounts of both, the required ammonia flow signal, and the current injected ammonia flow rate Control means for controlling the amount of ammonia injection based on the above conditions.