JPS6388021A - Apparatus for controlling concentration of discharged nox of boiler - Google Patents

Abstract

PURPOSE:To enhance the control performance in the injection quantity of NH3, by a method wherein the load change of a boiler is detected and the future value of the concn. of discharged NOX is outputted from an estimated mathematical model on the basis of the detection value and a NH3 quantity set value is increased and decreased according to the output. CONSTITUTION:The change of discharged NOX accompanying the load change of boiler is calculated as the estimated value X thereof according to formula I [wherein y is a boiler load order, L1 and L2 are a wasted time, G1 and G2 are transfer function excepting the wasted time and W is G1(S).y at the time of L1<L2 and G2(S).Z at the time of L1<L2]. The load order of a boiler load detector 41 is inputted to devices 11, 12, 13, and G1 and G2 as well as third item of the above-mentioned model formula are calculated and the estimated value X of the change of discharged NOX obtained by an adder 14 is multiplied by a constant Kp at a coefficient device 15 to obtain a correction signal Z and a NH3 quantity set value is controlled by said signal Z.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a boiler exhaust NOx concentration control device in a catalytic flue gas denitrification device used in a boiler flue gas system.

[Conventional technology]

FIG. 3 is a diagram schematically showing a catalytic flue gas denitrification device used in a boiler flue gas system. 31 is a boiler, 32 is a furnace, and 33 is a flue. When the fuel A introduced into the furnace 32 together with the combustion air B is combusted in the furnace 32, the combustion gas passes through the flue 33 and is discharged toward the chimney side as shown by the arrow C. An ammonia injection nozzle 34 is located in the middle of the flue 33.
and a denitrification reactor 35 are arranged in this order. For the ammonia injection nozzle 34, the ammonia gas supply source 3
The ammonia gas from 6 is supplied to the ammonia gas control valve 37.
．． It is supplied via a mixer 38.

The ammonia gas control valve 37 has its valve opening degree controlled by receiving a valve opening degree command signal from a NOx concentration control system, which will be described later. Also mixer 3
Reference numeral 8 is configured to mix the dilution air E with the ammonia gas by feeding the ammonia gas dilution air E by a fan 39, thereby diluting the ammonia gas.

FIG. 4 is a block diagram showing the configuration of a conventional exhaust NOx concentration control system. In FIG. 4, reference numeral 41 denotes a load index (index) detector 1 that indicates the state of change in the boiler load, which detects the flow rate of the fuel A or the flow rate of the air B, and outputs a load index signal. 42 is a function generator;
A required ammonia amount signal corresponding to the output signal of the load index detector 41 is generated. 43 is reactor population NOx
This is a concentration detector and outputs a reactor inlet NOx concentration signal. 44 is a corrector consisting of an adder or a multiplier;
The required ammonia amount signal output from the function generator 42 is corrected by the reactor inlet NOx concentration signal from the reactor inlet NOx concentration detector 43.

45 is a boiler load command device, which sends out a boiler load command signal. 46 is a differentiator that multiplies the temporal rate of change (velocity) of the output signal from the boiler load command device 45 by a predetermined coefficient and outputs the result. Reference numeral 47 denotes a signal limiter, which allows only the positive signal of the output of the differentiator 46 to pass through as is, and outputs the negative signal as a "0" signal.

An adder 48 adds the output signal of the signal limiter 47 to the corrected necessary ammonia melon signal output from the corrector 44. Thus, the adder 48 outputs a required ammonia amount signal that increases in accordance with the rising speed only when the boiler load command signal from the boiler load command device 45 is rising.

An ammonia flow rate detector 49 detects the flow rate of ammonia gas supplied through the control valve 37 and outputs an actual ammonia amount signal. A subtracter 50 obtains the difference between the required ammonia amount signal outputted from the adder 48 and the actual ammonia amount signal detected by the ammonia flow rate detector 49. A proportional-integral calculator 51 performs proportional-integral calculations on the difference signal output from the subtracter 50 and outputs the calculated signal as a valve opening command signal for the ammonia control valve 37.

In this way, the conventional exhaust NOxl agricultural elasticity control system shown in FIG. 4 uses the actual ammonia amount signal detected by the ammonia flow rate detector 49 and the required ammonia amount signal ( Ammonia set value signal) is compared with the subtractor 50, and according to the difference, the proportional integral calculator 51 adjusts the ammonia control valve opening command signal so that the actual ammonia amount becomes equal to the set value. be making. Here, the required ammonia amount signal (ammonia set value signal) is determined from the reactor type rotor from the reactor population NOx concentration detector 43 based on the signal output from the function generator 42 as a function for the load index detector 41. It is created by modifying the NOx-a degree signal and the load increase speed signal based on the load command signal from the boiler load command device 45.

[Problem that the invention seeks to solve]

The conventional υ[output NOx concentration control system described above has the following problems. The dynamic characteristics of denitrification chemical reactions generally involve large time delays, making it a difficult process to control.

The reason why the above-mentioned conventional control system does not directly feedback control the exhaust NOx concentration but mainly controls the feedforward signal based on the load index detection signal is because of the above-mentioned time delay, after the exhaust NOx concentration has increased. This is because even if the amount of ammonia is increased, it will not be enough.

On the other hand, concentrated NOx emissions are strictly regulated by law from an environmental perspective. Therefore, in the conventional control system, the exhaust NO.
Systems 45 to 48 in FIG. 4 are added in order to inject a large amount of ammonia gas when the load increases and the x concentration increases. However, if the action of this system is sufficiently strengthened so that the exhaust NOx concentration is well below the legal regulation value, ammonia gas will be injected excessively, and excess ammonia gas that did not participate in the reaction will be released into the atmosphere. It becomes a new source of pollution and is economically wasteful.

By the way, if we can predict how the exhaust NOx concentration will change in the future, we can adjust the ammonia injection amount from now on so that the predicted value is appropriate, and as a result, the NOx value and It should be possible to use ammonia in an appropriate manner, avoid wasting ammonia, and pass legal regulations.

Therefore, by using the pre-11111 method, the present invention can perform control that always anticipates the results of the denitrification process, which has a large time delay, and improves control performance.
It is an object of the present invention to provide a NOx concentration control device for a boiler that can make the NOx value and the amount of ammonia appropriate and can clear the regulations of the law without causing any harmful effects due to excessive injection of ammonia.

[Means for solving problems]

The present invention solves the above problems [in order to achieve the first objective,
The following measures were taken: In other words, a boiler load change is detected, and the emission NO is adjusted according to the detected boiler load change.
The future value of the x concentration is output from the predictive formula model, and a correction signal is obtained for increasing or decreasing the ammonia amount set value according to the increase or decrease in the future value of the emitted NOx concentration, and this hli positive signal is used as the ammonia amount set value. The correction is now performed by adding the

The above model is constructed for a combination of a denitrification process and a conventional control system, and is expressed as a transfer function using Laplace transform in the following form.

z-e″″L1°5-01 (s)ay+6-L*°S
・G2 (S) ・Z ... (1) However, χ is the amount of change in exhaust NOx, y is the boiler load command,
Z is a correction signal for the ammonia injection amount set value, and both are Laplace transforms. Ll.

L is a dead time, and G2 is a transfer function excluding the dead time. A plurality of parameters are included inside C and G2. The parameters included in G, are expressed as plt (+-,,2°...), and G2
The parameters included in 1) 2 j (j−1
, 2, ...). L, L2゜1)i, and p2j are all defined as a function of the load command y, and the value of the function is determined from the boiler operation performance data.

Equation (1) indicates the dynamic characteristics of NOx, and in order to put it into practical use, it is necessary to derive a mathematical expression for subtracting 1'8111 from equation (1). In this case, only the larger of the wasted time and L2 is predicted first.

741. The preliminary A11j value is represented by X, and L
-max (L, L2) e-Σ a K/lcl, then X-eL゛S・z=G1 (s)・'1+62
(S) QZ+W - L21 to -8K)...(2) However, W is w-01(s) ・y in the case of Ll less L2, and in the case of Ll, ≧L2, w = 02 ( s) ・Z. Note that the third term on the right side of equation (2) is calculated by cutting off the value of k at an appropriate point in actual calculation.

There are various ways to create the correction signal Z for the ammonia amount setting value, but here, as an example, Z-Kp-X
, ... shall be created using the formula (3). Kp is a constant or a positive value set as a function of the negative 411 command y.

[Effect]

By combining the above means, the following effects are achieved. That is, according to equation (3), if the predicted discharge NOx concentration value X increases, the ammonia amount setting value increases by the proportionally increasing correction value Z.

Therefore, the NOx value, which is likely to increase in the future, can be reduced by preemptively punching the ammonia gas. Furthermore, since the correction signal Z is pre-Al11 calculated as Z in equation (2), the effect of adding the correction signal Z is pre-ap+ as the pre-7I-1 value X of NOx becomes smaller. , the correction signal Z also becomes smaller. As a result, excessive injection of ammonia gas is prevented.

〔Example〕

The solid line portion in FIG. 1 is a block diagram showing the configuration of a control system according to a first embodiment of the present invention. In the figure, the same parts as in FIG. 4 are designated by the same reference numerals (41, 44, 49.degree. 50).

As shown in FIG. 1, in this embodiment, a new adder 10 is inserted between a corrector 44 and a subtracter 50 of the conventional control system, and a correction signal Z is added to the output of the corrector 44. The signal is supplied to a subtracter 50. In addition, corrector 4
4 or subtraction 2'A 50 is iIJ with 3 manpower calculation processing
If it is possible, the 1-2 adder 10 is replaced by the corrector 4.
4 or may be included in the subtracter 50.

In FIG. 1, 11 and 12 are Gl in formula (2), respectively.

It is a 1,000M1 mathematical model that calculates G2, and 13 is (2)
This is a predictive mathematical model that calculates the third term on the right side of the equation.

14 is the above 3'F jpI vI model 11-1
This is an adder that adds the three outputs and outputs a pre-rule value X of the exhaust NOx concentration. Reference numeral 15 denotes a coefficient unit that multiplies the output of the adder 14 by a constant Kp to obtain a correction signal Z, and executes the calculation of equation (3).

FIG. 2 is a diagram showing temporal changes in each signal in the first embodiment. In FIG. 2, solid lines a and c show the case of this embodiment, and broken lines a and d show the case of the conventional example. As is clear from Fig. 2, in the conventional example, since ammonia was injected into the boiler negative 6 (j command y in proportion to the upper sea speed) through systems 45 to 47, ammonia gas became excessive and the latter half of the exhaust NOx The concentration drops too much,
Moreover, ammonia gas tends to be wasted. On the other hand, in the case of this embodiment, since the prediction includes the effect of the self-generated correction port Z, it is predicted that the NOx concentration will decrease in the future, and Z is decreased in advance. Therefore, the NOx value can be made appropriate, and ammonia gas is not wasted.

Next, a second embodiment will be described. In FIG. 1, a portion indicated by a broken line indicates a second embodiment of the present invention. In this second embodiment, the constant Kp is set as a function of the signal from the load index detector 41 indicating the load change or the load command y, and the constant Kp is set by the function generator 16.
p is generated.

Generally, the dynamic characteristics of a boiler plant vary greatly depending on the 1'+6:7 band. For this reason, the person in charge
It is desirable to use several kg) which can be adjusted to an appropriate value depending on the load change. Therefore, if the configuration is as in this embodiment, there are many advantages in terms of controllability.

Note that the first thing. In both cases of the second embodiment, the constant K
The value of p may be determined by trial operation of the boiler or denitrification device, simulation (numerical experiment), or the like.

As a third embodiment, an embodiment may be considered in which equation (3) is changed to a proportional-integral form as shown in the following equation, and the coefficient 415 in FIG. 1 is replaced with a proportional integrator.

Z = K pΦ (1+1/TiΦS)・X...(
4) Note that Ti is a parameter (integration time) that determines the effect of the integral operation, and when Ti wa oo, it is the same as in the first embodiment. As a characteristic of integral operation, pre-7l-INO
As long as the amount of change X in x does not become zero, the correction signal Z will continue to change.

As a fourth embodiment, Kp in the equation (4) is generated as a function of y by a function generator 16, and the integral time Ti in the equation (4) is also generated as a function of y in a function generator (not shown). Equation 11 can be considered to improve controllability.

Note that the present invention is not limited to the above embodiments,
Of course, various modifications can be made without departing from the spirit of the invention.

〔Effect of the invention〕

According to the present invention, a boiler load change is detected, and a future value of υ[output NOx concentration according to the detected boiler load change is outputted from a prediction/Ip1 mathematical model, and an increase or decrease in the future value of this emitted NOx concentration is Accordingly, a correction signal is obtained to increase or decrease the ammonia amount set value, and this correction signal is added to the ammonia amount set value to perform correction, so that the results can always be obtained for the denitrification process, which has a large time delay. Anticipatory control can be performed, control performance is improved, and NO
It is possible to provide an NOx concentration control device for a boiler that can set the x value and the amount of ammonia to appropriate values and can meet legal regulations without causing any harm due to excessive injection of ammonia.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing a first embodiment of the present invention,
Figure 1 is a block diagram showing the configuration of the exhaust NOx concentration control system, Figure 2 is a waveform diagram showing temporal changes in each signal, and Figure 3 is a catalytic exhaust gas used in a general boiler υF smoke system. FIG. 4 is a block diagram showing the configuration of a conventional exhaust NOx concentration control system. 10.14.48... Adder, 11.12.13...
・Child al G-type model, 15...Coefficient unit, 16.42
... Function generator, 31 ... Boiler, 32 ... Furnace, 33 ... Flue, 34 ... Ammonia injection nozzle,
35... Denitration reactor, 36... Ammonia gas supply source, 37... Ammonia gas control valve, 38... Mixer, 39... Fan, 41... Load index detector, 43... ...Reactor inlet NOx concentration detector, 44.
... Corrector consisting of an adder or multiplier, 45... Boiler negative 6I command device, 46... Differentiator, 47... Signal limiter, 49... Ammonia flow rate detector, 50...
Subtractor D unit, 51...proportional integral calculator. Applicant Sub-Agent Patent Attorney Takehiko Suzue No. 1 Figure No. 2

Claims (1)

[Claims] A means for detecting a boiler load change, a predictive mathematical model that uses the boiler load change detected by this means as input and outputs a future value of the exhaust NO_x concentration, and ammonia NO_x concentration discharged from a boiler, characterized by comprising means for obtaining a correction signal for increasing or decreasing the ammonia amount setting value, and means for performing correction by adding the correction signal obtained by this means to the ammonia amount setting value. Control device.