JPH08131766A - Method and apparatus for controlling injection amount of reducing agent in denitration facility - Google Patents

Abstract

PURPOSE: To maintain NOx concentration at the outlet of a denitration facility close to a set value by correcting the injection of a reducing agent the basis of the rate of change in load requirement of a combustion apparatus and the rate of change in NOx concentration at the outlet of the denitration facility. CONSTITUTION: The amount of ammonia to be injected is determined from a signal 13 of an ammonia molar ratio necessary to obtain the rate of denitration which is necessary to maintain NOx concentration at the outlet of a denitration facility at a set value, a signal 15 of a feedback correction molar ratio by the output signal of an outlet NOx concent,ration meter 4, a signal 33 of ammonia injection correction by a fuzzy controller 30, and a signal 32 of a dynamic previous value to a signal 5 of load requirement. In this way, the delay of denitration reaction is compensated by dynamic previous control in response to the rate of change in load to the generation of a peak value in NOx concentration at the time of load variation in a coal burning plant, and the shortage of ammonia due to dynamic previous control is compensated by fuzzy control based on the rate of change in load and the rate of change in outlet NOx concentration. Therefore, even at the time of high speed load variation, the outlet NOx concentration is made close to a set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration device, and more particularly to a reducing agent injection amount control device and an inflow amount control method for a denitration device suitable for reducing nitrogen oxides in exhaust gas.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional ammonia injection amount control device for a denitration device multiplies an output signal of a process gas flow meter 1 and an output signal of an inlet NOx concentration meter 2 by a multiplier 7a, The inlet NOx amount signal 21 is used. On the other hand, inlet NOx
From the output signal of the densitometer 2 and the output signal of the outlet NOx concentration setting device 3, the required denitration rate signal 10 is calculated by the subtractor 8a and the divider 9, and the required denitration rate signal 10 is input to the function generator 11. Then, the ammonia molar ratio signal 13 required for the NOx amount is calculated.

A subtracter 8 calculates a deviation signal between the output signal of the outlet NOx concentration setting device 3 and the output signal of the outlet NOx concentration meter 4.
Then, the signal is processed by the controller 12a, and the feedback molar ratio signal 15 is calculated. In the adder 14a, the required molar ratio signal 13 and the feedback molar ratio signal 15 are added to obtain the total molar ratio signal 16, and the multiplier 7b supplies the inlet NO
The required ammonia flow rate signal 22 is multiplied by the x quantity signal 21.
And

Next, the load request signal 5 is processed by the differentiator 17 and the second-order differentiator 18 and the resulting signal is input to the adder 14b. In the adder 14b, these signals and the above-mentioned required ammonia flow rate signal 22 are input. Then, the ammonia flow rate request signal 19 is calculated.

The difference between the ammonia flow rate request signal 19 and the ammonia flow rate detection signal of the ammonia flow meter 6 is obtained by the subtractor 8c, the signal is processed by the controller 12b, and the ammonia flow rate adjusting valve 20 is opened and closed. The NOx concentration at the outlet of the denitration device was maintained near the set value.

This control system is basically based on the inlet NOx.
This is a method for determining the amount of ammonia injection based on the preceding value for the amount, feedback correction based on the deviation from the outlet concentration set value, and the dynamic preceding value for the load request signal. The dynamic leading value is provided to compensate for the delay of the denitration reaction with respect to the change in the amount of injected ammonia, which is usually ten or more minutes.

In recent years, with the rapid load change rate operation of a thermal power plant, the variation range of the deviation of the NOx concentration at the outlet with respect to the set value of the NOx concentration at the outlet of the denitrification apparatus has been changed, despite the rapid change in the denitrification load. It is required to keep it small. That is, it is essential to improve the controllability of the outlet NOx concentration.

Particularly, in the coal-fired boiler, the operation of starting and stopping the mill is performed when the load changes, but at this time, in order to supply the mill warming air or the air for purging the mill residual coal, a temporary excess air is supplied. A condition occurs. Therefore, a peak value occurs in the NOx concentration at the inlet of the denitration device. When a large amount of ammonia is injected to maintain the NOx concentration at the outlet of the denitrification device in the vicinity of the set value with respect to this peak value, the outlet N corresponding to the peak of the inlet NOx concentration is discharged.
The peak of Ox concentration can be suppressed, but the inlet NOx
When the concentration shows no peak value, the ammonia becomes excessive.

FIG. 3 shows an example of such a situation. The shaded area in FIG. 3 causes excess ammonia and leak ammonia is generated, which makes economical operation difficult.

[0010]

In the above-mentioned conventional technique, even when the denitration load changes abruptly, the denitration device outlet N
No consideration was given to maintaining the Ox concentration in the vicinity of the set value. Even though the upper limit value of the outlet NOx concentration could be cleared by the injection of a large amount of ammonia by the dynamic advance control, the lower limit value was exceeded, and ₃ Increases consumption.

An object of the present invention is to provide a reducing agent injection amount control device and an injection amount control method for a denitration device that can maintain the NOx concentration at the outlet of the denitration device near a set value even when the load changes rapidly.

[0012]

The above object is to control a reducing agent injection amount of a denitration device for injecting a reducing agent into exhaust gas generated from a combustion device and reducing nitrogen oxides in the exhaust gas by a dry catalytic reduction method. In the first aspect, the first correction means is provided to correct the injection amount of the reducing agent based on both the change rate of the load demand of the combustion apparatus and the change rate of the nitrogen oxide concentration change rate at the outlet of the denitration apparatus. It is achieved by means of.

In addition to the first correcting means, the first means is provided with a second correcting means for correcting the injection amount of the reducing agent based on the load demand change rate of the combustion device. It is achieved by the second means.

In the first or second means, based on the deviation between the nitrogen oxide concentration at the outlet of the denitration device and the nitrogen oxide concentration set value at the outlet of the denitration device, in addition to the first correction means. This is achieved by a third means that is provided with a third correction means for correcting the injection amount of the reducing agent.

In any one of the first to third means, in addition to the first correcting means, based on the nitrogen oxide amount at the denitration device inlet and the nitrogen oxide concentration set value at the denitration device outlet. This is achieved by the fourth means which is provided with a computing means for computing the required reducing agent.

Further, in any one of the first to fourth means, the first correcting means is achieved by a fifth means composed of a calculation section using fuzzy inference.

[0017]

The dynamic advance signal corresponding to the rate of change of the load request signal operates to compensate for the delay of the denitration reaction. In addition,
This dynamic lead signal, along with the mill start / stop signal,
Operates at any timing.

Since the injection amount of ammonia due to this signal is inevitably excessive, the injection amount of ammonia is reduced immediately after the excessive injection. This is when the load is increasing, and the reverse operation when the load is decreasing.

The control device for correcting the ammonia injection amount using the fuzzy inference corrects the ammonia injection amount based on the change rate of the load request signal and the NOx concentration change rate of the denitration device. Considering the time, the supply amount of ammonia increases as the load increases, but when the outlet NOx concentration starts to decrease, the ammonia injection amount is reduced.

In short, a dynamic advance control responds to a large state change such as a high-speed load change, and the excess / deficiency of the ammonia injection amount due to this is controlled by fuzzy control.

As a result, the NOx concentration at the outlet of the denitration device is maintained near the set value, so that stable outlet NOx concentration characteristics can be obtained.

[0022]

EXAMPLE A concrete example of the ammonia injection amount control device of the denitration apparatus according to the present invention is shown in FIG. Incidentally, the same parts as those of the conventional example shown in FIG.

The present control apparatus uses the necessary ammonia molar ratio signal 13 (output signal of the function generator 11) for obtaining the NOx removal rate necessary to maintain the NOx concentration at the outlet of the NOx removal apparatus at a set value.
The amount of ammonia injection is determined by the feedback correction molar ratio signal 15 by the output signal of the outlet NOx concentration meter 4, the ammonia injection correction signal 33 by the fuzzy controller 30 and the dynamic lead value signal 32 for the load request signal 5.

Of these, the ammonia molar ratio signal 13 and the feedback correction molar ratio signal 15 are the same as in the conventional control system. Incidentally, 31 is a coefficient unit, and 34 is a dynamic preceding signal calculator.

The fuzzy controller 30 receives the load request signal 5 and the output signal of the outlet NOx concentration meter 4 and performs the following arithmetic processing.

The load request signal at the time point n is x
(N), where y (n) is the output signal of the outlet NOx concentration meter, the change rate signals Δx (n) and Δy (n) are given by the following equations. Δx (n) = [x (n) −x (n−1)] · s (x) (1) Δy (n) = [y (n) −y (n−1)] · s (y ) (2) Here, an example of the membership function of s (x), s (y): scaling factors Δx (n), Δy (n) is shown in FIG. The meanings of the symbols in the figure are shown below.

NB: Negative and large, NM: Negative and slightly large, NS: Negative and small, ZO: Almost zero. PS: Positive and small, PM: Positive and slightly large, PB: Positive and large.

FIG. 5 shows an example of a control rule for determining the increment Hn of the ammonia injection amount to be corrected depending on the conditions of Δx (n) and Δy (n). In the figure, for example, if Δ
If x (n) = PS and Δy (n) = NM, Hn = NM
And read this as a control rule.

FIG. 6 shows a method for specifically determining the basic increment of the manipulated variable.

In the figure, two control rules (rule 1 and rule 2) are shown as an example, and a representative amount of change rate of the load request signal is X and a representative amount of change rate of the outlet NOx concentration is Y.
The fuzzy sets for the values of X = X ′ and Y = Y ′ are A ₁ and B ₁ for rule _1, and A ₂ and B for rule 2.
_{Assume 2} . Let C _{1 be} the fuzzy set of the increment of the operation amount determined from rule 1, C ₂ be the one corresponding to rule 2, and the membership functions of them be μC ₁ and μC ₂ , respectively. At this time, from rule 1, w ₁ = Min {μA ₁ (X ′), μB ₁ (Y ′)} (3) From rule 2, w ₂ = Min {μA ₂ (X ′), μB ₂ ( Y ′)} (4) Using w ₁ and w ₂ , the membership function μC ^* of the basic increment of the manipulated variable that satisfies Rule 1 and Rule 2 is μC ^* = Max {w ₁ μC ₁ , w ₂ μC ₂ } (5) The barycentric coordinate Z ^* of this μC ^* is calculated by the following formula with reference to FIG.

Z ^* = ∫ZμC ^* (Z) dZ / ∫μC ^* (Z) dZ (6) This value Z ^* is the basic increment H of the manipulated variable. actually,
Four control rules are involved for the values of X'and Y ', but H is determined by a similar procedure. This H is multiplied by the control gain K, and K · H becomes the output signal of the fuzzy controller 30.

In this way, the fuzzy controller 30 carries out the calculations shown in the equations (1) to (6) at every sample time to obtain the ammonia injection amount control signal 33.

Next, for the dynamic preceding value signal 32, the load request signal 5 is differentiated by the differentiator 17, scaled by the coefficient unit 31, and input to the multiplier 7c. The dynamic preceding signal calculator 34 performs the following calculations. Taking load rise as an example,
If the load before the start of load increase is L ₀ , the load at any time during load increase is L, and the output signal of the dynamic lead signal calculator 34 is y (dynamic lead signal adjustment signal 35): When 0 + C ≦ L / L ₀ ≦ α, y = a (7) When α ≦ L / L ₀ and dL / dt> 0, y = −b (8) where 1 <α < 1.5,0 <a ≦ 1,0 <b ≦ 1,0
<C <1 Expression (7) is a dynamic pre-injection of ammonia, which compensates for the delay of the denitration reaction with respect to the injection of ammonia, and Expression (8) compensates for the excess of ammonia due to the dynamic pre-injection. To do.

When the load changes, by controlling the number of mills,
The mill is started and stopped while the load changes, but in this control method, for example, when the load rises, the dynamic pre-injection of ammonia is started in accordance with the coal feed start command of the first mill to be charged, and the second mill is started. A large amount of ammonia is injected at an arbitrary time such as stopping the dynamic pre-injection of ammonia on the basis of the coal supply start command of the mill.

Thus, in the adder 14a, the preceding value molar ratio signal (output signal of the function generator 11a), the feedback molar ratio signal, the ammonia injection amount correction signal by the fuzzy controller 30 and the dynamic preceding value signal 32 are added. Is added and multiplied by the inlet NOx amount signal 21 by the multiplier 7b to obtain the ammonia flow rate request signal 19, the deviation from the output signal of the ammonia flow meter 6 is obtained by the subtractor 8c, and the signal is processed by the controller 12b. By opening and closing the ammonia flow rate adjusting valve 20, the amount of ammonia injected into the denitration device is adjusted.

In the present control device, the dynamic lead value signal is applied in order to compensate for the large delay of the denitration reaction with respect to the injection of ammonia. However, since this signal alone causes excess and deficiency of ammonia, the load change rate and This excess and deficiency is solved by fuzzy inference based on the outlet NOx concentration change rate. That is, the dynamic pre-injection of ammonia is performed at an arbitrary load, and corresponding to the peak value of the inlet NOx concentration,
The subsequent fine adjustment is performed by fuzzy control.

Therefore, according to the present invention, the outlet NOx concentration can be maintained in the vicinity of the set value and the leakage ammonia can be reduced even with respect to the peak of the NOx value at the inlet of the denitration device when the load changes in the coal burning plant.

The effect of the present invention will be specifically described with reference to FIG. In the conventional control method shown in FIG. 3, when the load rises, the dynamic pre-injection of ammonia is started at the same time as the start of the load change. Therefore, from the behavior of the inlet NOx concentration, the large amount of this ammonia injection causes the outlet NOx concentration to reach the lower limit , And this effect appears as an increase in the denitration performance after the peak of the NOx concentration at the inlet has passed, and the NOx concentration at the outlet again appears.
The x concentration is below the lower limit. Here, in the conventional proportional-plus-integral controller, since the ammonia injection amount is increased or decreased after the control deviation occurs, it is not possible to cope with a large delay of the denitration reaction.

In the present invention, the injection timing of ammonia can be determined at any time when the load changes, for example, based on the coal feeding start command after the mill is charged. Therefore, the NOx concentration at the outlet decreases due to the increase in the denitration performance immediately after the load changes. Ammonia is injected in advance by the fuzzy controller 30, and the outlet NOx concentration is maintained near the set value and is maintained between the upper limit and the lower limit. Therefore, the injection amount of ammonia becomes appropriate, and the leak ammonia can be reduced.

The first correction means in claim 1 is composed of the fuzzy controller 30 and the like. Also,
The second correcting means in claim 2 is composed of a multiplier 7c, a differentiator 17, a coefficient unit 31, a dynamic preceding signal calculator 34, and the like. The third correction means in claim 3 is composed of a subtractor 8b, a controller 12a, and the like.
The calculating means in claim 4 includes a multiplier 7a, a subtractor 8a, a divider 9, an adder 14 and the like.

[0041]

According to the present invention, with respect to the generation of the peak value of NOx concentration when the load changes in the coal-fired plant, the delay of the denitration reaction is compensated by the dynamic advanced control corresponding to the load change rate, and the load is reduced. The fuzzy control based on the change rate and the outlet NOx concentration change rate can compensate the excess / deficiency of ammonia by the dynamic preceding control, so that the NOx concentration at the outlet of the denitration device can be maintained near the set value even when the load changes at high speed. effective.

Further, since the amount of leaked ammonia can be reduced, there is an effect that economical operation becomes possible.

[Brief description of 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 a problem of a conventional ammonia injection amount control device.

FIG. 4 is an explanatory diagram showing an example of a membership function.

FIG. 5 is an explanatory diagram showing an example of control rules.

FIG. 6 is an explanatory diagram showing the principle of fuzzy inference.

FIG. 7 is an explanatory diagram specifically showing the effect of the present invention.

[Explanation of symbols]

 1 Processed gas flow meter 2 Inlet NOx concentration meter 3 Outlet NOx concentration setter 4 Outlet NOx concentration meter 5 Load request signal 6 Ammonia flow meter 7 Multiplier 8 Subtractor 9 Divider 10 Necessary denitration rate signal 11 Function generator 12 Controller 13 Necessary molar ratio signal 14 Adder 15 Feedback molar ratio signal 16 Total molar ratio signal 17 Differentiator 18 Second stage differentiator 19 Ammonia flow rate request signal 20 Ammonia flow rate adjusting valve 21 Inlet NOx amount signal 22 Necessary ammonia flow rate signal 30 Fuzzy Controller 31 Coefficient device 32 Dynamic leading value signal 33 Ammonia injection amount correction signal 34 Dynamic leading value signal

Claims (6)

[Claims] 1. A reducing agent injection amount control device for a denitration device that injects a reducing agent into exhaust gas generated from a combustion device and reduces nitrogen oxides in the exhaust gas by a dry catalytic reduction method, wherein a load demand of the combustion device is provided. A reducing agent for a denitrification apparatus, comprising first correction means for correcting the injection amount of the reducing agent based on both the rate of change and the rate of change of the nitrogen oxide concentration at the outlet of the denitrification apparatus. Injection volume control device. 2. The second correction means for correcting the injection amount of the reducing agent based on the load demand change rate of the combustion device in addition to the first correction means according to claim 1. A reducing agent injection amount control device for a denitration device, which is characterized in that 3. The method according to claim 1 or 2, wherein, in addition to the first correction means, the difference between the nitrogen oxide concentration at the outlet of the denitration apparatus and the nitrogen oxide concentration set value at the outlet of the denitration apparatus is used. A reducing agent injection amount control device for a denitration device, characterized in that a third correcting means for correcting the reducing agent injection amount is provided. 4. The method according to claim 1, which is required based on the amount of nitrogen oxides at the inlet of the denitration device and the nitrogen oxide concentration set value at the outlet of the denitration device, in addition to the first correction means. A reducing agent injection amount control device for a denitration device, which is provided with a calculating means for calculating a reducing agent. 5. The reducing agent injection amount control device for a denitration device according to claim 1, wherein the first correction means is composed of a calculation unit using fuzzy inference. 6. A method for controlling the injection amount of a reducing agent in a denitration device, which comprises injecting a reducing agent into exhaust gas generated from a combustion apparatus and reducing nitrogen oxides in the exhaust gas by a dry catalytic reduction method, the load demand of the combustion apparatus. A correction value of the reducing agent injection amount is calculated by the first correction means for correcting the injection amount of the reducing agent based on the change rates of both the change rate and the nitrogen oxide concentration change rate at the outlet of the denitration device, A reducing agent injection amount control method for a denitration device, which comprises adjusting the reducing agent injection amount based on the correction value.