JPH11530A - Ammonia injection controller for denitration reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress the NOx concn. in the outlet of a denitration reactor to an already set value or below by providing the apparatus with means for detecting a frequency in precedence to a rapid change in the NOx concn. in the gas to be treated by a frequency fluctuation and correcting the injection rate of ammonia by increasing or decreasing this rate. SOLUTION: This ammonia injection controller has the injection rate correcting means 59 for correcting the necessary ammonia flow rate signal 35 by increasing or decreasing the same in correspondence to the fluctuation rate of the frequency in precedence to the rapid change in the NOx concn. in the gas to be treated by the fluctuation in the frequency. This means previously calculates the corresponding load fluctuation rate in accordance with the fluctuation rate of the frequency fluctuation by a differentiator 62 from the AFC signal 61 transmitted by an AFC command 60 and the upper and lower limit values of the load fluctuation rate is limitted by an upper and lower limiter 63. A load command signal 52 based on a DPC command or ALR command with respect to this signal 64 is multiplied by a multiplier 65 to form an increase/decrease correction signal 66 for the ammonia injection rate, by which the bias correction of the necessary ammonia flow rate signal 35 is executed. As a result, the correction of the ammonia injection rate is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the decomposition by the injection of nitrogen oxides to be treated gas (hereinafter referred to as "NOx") with ammonia gas (hereinafter referred to as "NH _3"), of the denitration reactor to remove The present invention relates to an ammonia injection control device.

[0002]

2. Description of the Related Art FIG. 3 is a schematic diagram showing a nitrogen oxide measurement position and an ammonia injection position of a denitration reactor. The denitration reactor 2 introduces a source of the gas to be treated G, for example, exhaust gas from a boiler, from an inlet duct 3, performs denitration treatment by injecting ammonia, and discharges it to an outlet duct 4. To be discharged. At this time, the NOx in the gas to be treated G is passed through the ammonia injection pipe 5 provided in the inlet duct 3 so that the NH ₃ amount corresponding to (corresponding to) the NOx amount in the gas to be treated G is adjusted by the ammonia flow meter 40 and the ammonia flow rate. It is injected through the flow control valve 12 and decomposed into harmless water vapor and nitrogen gas by a denitration catalyst (not shown) filled in the denitration reactor 2 and removed.

Normally, the operation of the denitration reactor 2 is controlled such that the NOx concentration at the outlet of the denitration reactor 2 becomes lower than a specified value even when the load of a boiler or the like generating the gas to be treated G changes. Control is performed such that an injection amount of ammonia corresponding to the NOx amount is injected. Here, the inlet NOx concentration in the gas to be treated G is determined by the inlet NOx analyzer 14 to determine the outlet NOx.
The x concentration is measured by the outlet NOx analyzer 24.

FIG. 2 is a control circuit diagram showing an example of an ammonia injection control device for a denitration reactor according to the prior art. The conventional ammonia injection control device 9 includes an injection amount calculation unit 11 that calculates an injection amount of ammonia necessary for decomposing and removing nitrogen oxides in the gas to be processed, and a change rate of the load only when the load changes. And an ammonia adding means 50 for adding ammonia to the injection amount of ammonia in advance.

[0005] The injection amount calculating means 11 calculates the injection amount of ammonia from the NOx concentration at the inlet, the set value of NOx at the outlet, the NOx concentration at the outlet, the amount of gas to be treated, and the like. That is, the inlet NOx signal 15 measured by the inlet NOx analyzer 14 of the denitration reactor is multiplied by the to-be-processed gas flow signal 31 of the to-be-processed gas amount 30 by the multiplier 33 to calculate the total NOx amount signal 32.

On the other hand, a (necessary) molar ratio calculation unit 20 calculates a required injection molar ratio signal 22 of ammonia from the inlet NOx signal 15 and the set NOx signal 18 set by the deNOx reactor outlet NOx setting device 17. Outlet NOx analyzer 24
The required injection molar ratio signal 22 is corrected based on the deviation between the actually measured outlet NOx signal 25 and the set NOx signal 18 measured in step (1).

Then, the corrected corrected injection molar ratio signal 2
8 and the total NOx amount signal 32 described above are multiplied to calculate a required ammonia flow rate signal 35 (amount of injected ammonia). An ammonia addition signal 5 transmitted by the following ammonia addition means 50 to the necessary ammonia flow signal 35
A corrected ammonia flow signal 38 obtained by adding 7a and 57b;
The measured NH ₃ flow signal 41 measured by the ammonia flow meter 40 is subtracted from the actual measured NH ₃ flow signal 41, and given as a set value of a circuit composed of an ammonia flow meter (not shown in FIG. 3) and the ammonia flow control valve 12. . That is, the NH ₃ flow deviation signal 43 is calculated, and the NH ₃ flow deviation signal 43 is converted into a valve opening signal 45 by a proportional integrator 44.
7 and opens and closes the ammonia flow control valve 12 provided in the NH ₃ pipe 6.

The ammonia adding means 50 provides a load command, for example, an economic load distribution (hereinafter referred to as "DPC") command or an automatic load adjustment (hereinafter referred to as "A") as a boiler load command 51.
LR "), when the load is changed by the command, the load command signal 52 prompts the change in the state of the boiler load to operate only when the load changes based on the DPC and ALR.
The stage differentiating circuit 53 (the bias is corrected at a constant value from when the load of the DPC or ALR command changes until it reaches) and the two-stage differentiating circuit 54 (the bias is temporarily corrected when the load changes and when the load changes. ) Preliminarily corrects the required ammonia flow signal 35 for bias. The corrected ammonia flow signal 38 thus obtained is input to the subtractor 42. Thereby, the injection amount of ammonia is controlled so as to keep the NOx concentration at the outlet of the denitration reactor at a specified value or less.

In FIG. 2, reference numerals 55a and 55b denote upper and lower limiters, and reference numerals 56a and 56b denote switches that change a → c during a load change.

[0010]

However, when the frequency fluctuates, when the boiler load rises and changes due to a frequency fluctuation correction (hereinafter referred to as "AFC") command for correcting the fluctuation of the frequency, the load is matched. As a result, the fuel amount and the air flow rate increase, so that the NOx concentration flowing into the denitration reactor increases. The necessary ammonia flow signal 35 cannot be corrected by the first-stage differentiating circuit 53 and the second-stage differentiating circuit 54 in response to the rapid rise in the NOx concentration at the denitration reactor inlet.

Similarly, when the boiler load drops due to the AFC command, the above-described one-stage and two-stage differentiation circuits 53, 5
No. 4 cannot correct the required ammonia flow signal 35 by cutting the amount of injected ammonia due to the decrease in the NOx concentration during the load change by the AFC command.

The above-described conventional ammonia injection control device 9 comprises:
Denitration reactor inlet NO with excess air due to air-rich during boiler load rise change due to DPC and ALR
There is a function to suppress the nitrogen oxide concentration in the denitration reactor to a specified value or less against a sudden decrease in NOx concentration at the exit of the denitration reactor due to a decrease in air flow rate during a rapid change in the boiler load based on the DPC and ALR commands. A
During a load drop change according to the FC command, a sudden decrease in NOx concentration occurs due to a decrease in fuel and air flow rates, and NOx due to an increase in fuel and air flow rates during a load rise change according to the AFC command.
With respect to the occurrence of the rapid rise, no consideration is given to increasing or decreasing the amount of injected ammonia in advance to keep it below the specified value and to reduce the deviation from the NOx set value at the denitration reactor outlet. There was a fear of exceeding the specified value.

An object of the present invention is to suppress the nitrogen oxide concentration at the outlet of a denitration reactor to a specified value or less and suppress the deviation from the set value in response to a sudden change in the nitrogen oxide concentration in the gas to be treated due to a frequency change. Is to reduce the

[0014]

In order to achieve the above object, the present invention provides a denitration reactor for decomposing and removing nitrogen oxides in a gas to be treated by injecting ammonia. The injection molar ratio of the ammonia (= the molar amount of ammonia injected / the molar amount of nitrogen oxides in the gas to be treated) is calculated from the measured value and the set value of the substance concentration, and the molar ratio of the injection and the total nitrogen in the gas to be treated are calculated. An injection amount calculating means for calculating an injection amount of ammonia based on the amount of oxide, and an ammonia adding means for adding ammonia to the injection amount of ammonia in advance according to the change rate of the load only when the load changes. In the ammonia injection control device for the denitration reactor, the change in frequency is detected prior to the rapid change in the nitrogen oxide concentration in the gas to be treated due to the change in frequency, and the amount of ammonia injected is determined. Is that having an injection amount correction means for increasing or decreasing correction.

The injection amount correcting means increases or decreases the injection amount of ammonia in response to a change in the frequency. Therefore, the injection amount correction means appropriately increases or decreases the ammonia in response to a sudden change in the nitrogen oxide concentration in the gas to be treated due to the change in the frequency. The nitrogen oxide concentration at the outlet of the denitration reactor is suppressed to a specified value or less, and the deviation from the set value is reduced.

Further, in the ammonia injection control device for a denitration reactor, the injection amount correction means increases or decreases the ammonia injection amount in accordance with the frequency fluctuation rate. The injection amount correction means increases and decreases the injection amount of ammonia according to the fluctuation rate when the frequency changes, in addition to the operation of the ammonia injection control device of the denitration reactor. The injection amount of ammonia is increased when the load increases when the rate of change of the frequency becomes a positive value, and the injection amount of ammonia decreases when the load decreases when the frequency becomes a negative value. As the correction amount to be increased or decreased, a value determined in advance corresponding to the fluctuation rate is adopted. Thus, even during the frequency fluctuation operation, the nitrogen oxide concentration at the outlet of the denitration reactor does not exceed the specified value, and the deviation from the set value of nitrogen oxide concentration at the outlet of the denitration reactor does not increase.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an ammonia injection control device for a denitration reactor according to the present invention will be described with reference to FIG.

FIG. 1 is a control circuit diagram showing an embodiment of an ammonia injection control device for a denitration reactor according to the present invention. The ammonia injection control device 8 in FIG. 1 is obtained by adding an injection amount correction means 59 to the ammonia injection control device 9 in FIG. 2, and includes an injection amount calculation means 11, an ammonia addition means 50, and an injection amount correction means 59. I have. Injection amount calculation means 11
Since the configuration and operation of the ammonia addition means 50 are the same as those described with reference to FIG. 2, the same structures and operation portions as those in FIG.

In the meantime, the injection amount calculating means 11 determines whether the inlet NOx
From the inlet NOx signal 15 (measured value of nitrogen oxide concentration) actually measured by the analyzer 14 and the set NOx signal 18 (set value) set by the outlet NOx setting device 17, the necessary injection molar ratio signal 2
2 is calculated. Further, the setting NOx signal 18 and the exit NOx
A deviation is calculated by a subtracter 26 from the actually measured outlet NOx signal 25 actually measured by the analyzer 24, and the necessary injection molar ratio signal 22 is corrected by an adder 27 to calculate a corrected injection molar ratio signal 28.

On the other hand, a multiplier 33 multiplies the inlet NOx signal 15 and the gas flow signal 31 based on the gas amount 30 to calculate a total NOx amount signal 32 (total nitrogen oxide amount in the gas to be processed). The total NOx amount signal 32 is multiplied by the corrected injection molar ratio signal 28 by a multiplier 34 to calculate a required ammonia flow rate signal 35 (amount of injected ammonia). Further, the required ammonia flow signal 35 is added with the following ammonia addition signals 57a and 57b of the ammonia addition means 50 and the increase / decrease correction signal 66 of the injection amount correction means 59 to obtain a corrected ammonia flow signal 38.
8 and the measured NH ₃ flow signal 41 measured by the ammonia flow meter 40 are subtracted by a subtractor 42 to calculate an NH ₃ flow deviation signal 43, which is then calculated by a proportional integrator 44 to a valve opening signal 45.
Then, the control signal 47 is converted into a control signal 47 by the electropneumatic converter 46, and the ammonia flow control valve 12 provided in the NH ₃ pipe 6 is opened and closed.

The ammonia adding means 50 adds the necessary ammonia flow signal 35 to the required ammonia flow rate signal 35 in advance according to the load change rate only when the load changes. The boiler load command 51 is based on a DPC command or an ALR command. When the load changes, the load command signal 52 detects that the state of the boiler load has changed, and the one-stage differential circuit 53 (DPC or AL) that operates only when the load changes due to DPC and ALR.
The required ammonia flow rate is preceded by the bias correction of the R command at a constant value from the time the load changes until the R command arrives, and the two-stage differentiating circuit 54 (the bias is temporarily corrected when the load changes and when the load arrives, respectively). The signal (amount of injected ammonia) 35 is bias-corrected. The corrected ammonia flow signal 38 thus obtained is input to the subtracter 42 described above.

Further, prior to the rapid change of the nitrogen oxide concentration in the gas to be treated due to the fluctuation of the frequency, the ammonia injection control device 8 of the above-mentioned denitration reactor performs the necessary ammonia flow rate signal 35 corresponding to the fluctuation rate of the frequency. The injection amount correcting means 59 for increasing and decreasing the correction amount is provided. The injection amount correcting means 59 converts the AFC signal 61 transmitted by the AFC command 60 into a differentiator 62.
, The load change rate corresponding to the change rate of the frequency change is calculated in advance, and the upper and lower limiter 63 limits the upper and lower limit values of the load change rate. DPC command or ALR for this signal 64
The load command signal 52 based on the command is multiplied by a multiplier 65 and the required ammonia flow rate signal 35 is bias-corrected as an ammonia injection amount increase / decrease correction signal 66. As a result, a correction of the injection amount of ammonia is made in accordance with a change in nitrogen oxides caused by a change in boiler load caused by a frequency change.

Ammonia injection control device 8 of the present embodiment
Indicates that the AFC signal 61 is taken into the denitration control, and when the boiler load is changed by the AFC command due to the frequency change, A
A one-stage differentiation circuit that operates only when the FC signal fluctuates is installed.
The required amount of ammonia flow signal 35 is corrected by determining the amount of decrease or increase in the amount of ammonia injection corresponding to the first-stage differential value.

When the AFC signal is differentiated by one stage in response to a change in the boiler load that increases or decreases in accordance with the AFC signal 61, the injection amount of ammonia increases when the load rises to a positive value, and increases when the load decreases to a negative value. Decrease the injection volume. The increase / decrease amount is the AFC signal 6 according to the AFC command which is the load change rate.
The injection is performed according to the numerical value obtained by differentiating 1 by one stage. As a result, even during AFC operation, the nitrogen oxide concentration can be suppressed to a specified value or less, and the deviation from the set value of the nitrogen oxide concentration at the outlet of the denitration reactor can be reduced.

In the prior art, a boiler DPC command or A
There was only a function of suppressing the sudden change of the nitrogen oxide concentration during the load change based on the LR command to a specified value or less by an ammonia advance injection circuit such as one-stage differentiation and two-stage differentiation (FIG. 2). For this reason, there is no circuit corresponding to a sudden change in the nitrogen oxide concentration accompanying a load change based on the AFC signal, and the NOx concentration at the outlet of the denitration reactor would exceed a specified value during AFC operation. However, the ammonia injection control device 8 according to the present embodiment captures the fluctuation rate of the AFC signal largely related to the level of the nitrogen oxide concentration with respect to the rapid change of the nitrogen oxide concentration during the AFC load operation, and Can be corrected.

[0026]

According to the ammonia injection control device for a denitration reactor of the present invention, the nitrogen oxide concentration at the outlet of the denitration reactor is regulated in response to a sudden change in the nitrogen oxide concentration in the gas to be treated due to a frequency change. Value and the deviation from the set value can be reduced.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram showing an embodiment of an ammonia injection control device for a denitration reactor according to the present invention.

FIG. 2 is a control circuit diagram showing an example of an ammonia injection control device of a denitration reactor according to the related art.

FIG. 3 is a schematic diagram showing a nitrogen oxide measurement position and an ammonia injection position of a denitration reactor.

[Explanation of symbols]

 8 Ammonia injection control device 11 Injection amount calculation means 35 Required ammonia flow rate signal 50 Ammonia addition means 52 Load command signal 59 Injection amount correction means 61 AFC signal 66 Increase / decrease correction signal

Claims (2)

[Claims] 1. A denitration reactor for decomposing and removing nitrogen oxides in a gas to be treated by injecting ammonia, wherein the nitrogen injection concentration is determined from a measured value and a set value of a nitrogen oxide concentration in the denitration reactor. Ratio (= mol of ammonia injected /
Injection amount calculating means for calculating the injection amount of ammonia based on the injection molar ratio and the total amount of nitrogen oxides in the target gas. Only the ammonia injection means for adding ammonia to the ammonia injection amount in advance in accordance with the rate of change of the load. An ammonia injection control device for a denitration reactor, comprising an injection amount correction means for detecting a change in frequency prior to a sudden change in substance concentration and increasing and decreasing the injection amount of ammonia to correct the injection amount. 2. The ammonia injection control device for a denitration reactor according to claim 1, wherein said injection amount correction means increases or decreases the ammonia injection amount in accordance with the frequency fluctuation rate.