JP2002018234A - Method and apparatus for controlling amount of injection of ammonia into denitrification apparatus for treating exhaust combustion gas of pulverized coal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for controlling the amount of injection of ammonia into a denitrification apparatus for treating exhaust combustion gas of pulverized coal by which the amount and time of injection of ammonia into the denitrificaion apparatus can be controlled in cope with the peak of NOx and the amount of injection of ammonia can be prevented from becoming in improper quantities. SOLUTION: In the method in which the total amount of NOx is obtained by output signals of an exhaust gas flowmeter 2 and an inlet NOx concentration meter 3, and a molar fraction signal 16 on ammonia is obtained based on the inlet NOx concentration meter 3 and an outlet NOx concentration setting instrument 4 and a molar fraction correction signal 18 is obtained by deviation of an output signal of an outlet NOx concentration meter 5 from that of the setting instrument 4 and, based on these signals, the amount of injection of ammonia into the denitrification apparatus is controlled, necessary ammonia flow rate signal 21 is corrected by a correction signal 45 on the amount of injection of ammonia calculated based on a signal 7 on the number of operating mills showing how many operating mills the mill to be started or stopped is and a signal 50 on time passage after the mill is started or stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a control device for controlling the amount of ammonia injected into a denitration system for treating pulverized coal combustion exhaust gas. Appropriately deal with temporary increase in concentration and amount, NOx (NOx)
The present invention relates to a method and a control device for controlling the amount of ammonia injected into a denitration apparatus suitable for reducing leakage ammonia and suppressing leak ammonia.

[0002]

2. Description of the Related Art FIG. 4 shows an outline of a boiler furnace equipped with a pulverized coal combustion burner. In the figure, 26 is a boiler, 27
Denotes a furnace, 28 denotes a pulverized coal burner, 29 denotes a fuel pipe for feeding pulverized coal pulverized by a coal pulverizing mill to the burner 28, and 30 to 35 denote mills.

[0003] FIG. 3 is a schematic diagram of a denitration apparatus for introducing combustion exhaust gas from the boiler of FIG. 4 and removing NOx in the exhaust gas. In the figure, reference numeral 37 denotes a denitration device, 38 denotes an electric precipitator for collecting fine powder in exhaust gas, and 39 denotes an air preheater for preheating combustion air of a burner by thermal energy of the exhaust gas. 41 is a forced air blower, 3 is an inlet NOx meter for measuring the NOx concentration in the exhaust gas at the denitration device, and 5 is an outlet NOx for measuring the NOx concentration in the exhaust gas at the outlet of the denitration device.
Reference numeral 24 denotes a flow control valve for ammonia sprayed on the exhaust gas at the denitration apparatus, and reference numeral 43 denotes an ammonia spray nozzle.

A conventional ammonia injection amount control device for a denitration apparatus uses a multiplier 10a to output an output signal of a flow meter 2 of an exhaust gas to be treated and an output signal of a concentration meter 3 of NOx at the denitration apparatus as shown in FIG. The result is multiplied to obtain an inlet NOx amount signal 11. On the other hand, a subtractor 12 is obtained from the output signal of the NOx concentration meter 3 at the inlet of the denitration device and the output signal of the NOx concentration setter 4 at the outlet.
a and a divider 13a to calculate a required denitration rate signal 14, and input this signal to a function generator 15 to calculate an ammonia molar ratio signal (preceding value molar ratio signal) 16 necessary for the NOx amount. .

On the other hand, a difference signal between the output signal of the outlet NOx concentration setting device 4 and the output signal of the outlet NOx concentration meter 5 is obtained by a subtractor 12b, processed by a controller 17a and processed by a feedback molar ratio signal 18 Is calculated. The adder 19a adds the required molar ratio signal 16 and the feedback molar ratio signal 18 to obtain a total molar ratio signal 20, and the multiplier 10b inputs the N signal.
Required ammonia flow signal 21 by multiplying by Ox amount signal 11
And Next, a signal obtained by subjecting the load request signal 6 to arithmetic processing by the differentiator 25 and the second-order differentiator 23 is input to the adder 19b, and the adder 19b adds these signals to the necessary ammonia flow signal 21 described above. An ammonia flow rate request signal 22 is calculated. The difference between the ammonia flow request signal 22 and the output signal of the ammonia flow meter 1 is obtained by the subtractor 12c, the signal is processed by the controller 17b, and the ammonia flow control valve 24 is opened and closed to set the NOx concentration at the outlet of the denitration apparatus. It was kept near the value. This control method basically determines the ammonia injection amount based on a preceding value for the inlet NOx 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 a delay (usually more than ten minutes) in the denitration reaction due to a change in the amount of injected ammonia.

[0006] Recently, despite the rapid change in the denitration load accompanying the high-speed load change rate operation of a thermal power plant, the deviation of the exit NOx concentration deviation from the set value of the denitration device exit NOx concentration has been increasing. It is required to keep the change width small. That is, it is indispensable to improve the controllability of the outlet NOx concentration and reduce the leak ammonia.

Particularly in a coal-fired boiler, the mill is started or stopped when the load fluctuates. At this time, in order to supply mill warming air when the mill is started or air for purging the mill residual coal when the mill is stopped, In the combustion zone in the boiler, a state of excessive air temporarily occurs. Therefore, a peak value is generated in the exhaust gas NOx concentration at the denitration device inlet. When a large amount of ammonia is injected to maintain the NOx concentration at the outlet of the denitration apparatus near the set value with respect to this peak value, the peak of the outlet NOx concentration corresponding to the peak of the inlet NOx concentration can be suppressed. If the inlet NOx concentration suddenly decreases after the peak value, the supplied ammonia becomes excessive, the leaked ammonia increases, and the denitration rate rises, causing a problem that the NOx concentration at the outlet of the denitration device drops extremely more than necessary. Was.

[0008]

That is, in the conventional denitration apparatus for treating pulverized coal combustion exhaust gas, when starting or stopping the mill at the time of load change, the warming air of the mill at the time of starting or at the time of stopping the mill is required. In order to supply air for purging residual coal in the mill, a state of excessive air temporarily occurs in the combustion area of the boiler furnace. As a result, a temporary peak value is generated in the exhaust gas NOx concentration at the inlet of the denitration apparatus. When a large amount of ammonia is injected in response to the above, the supply ammonia becomes excessive when the NOx concentration suddenly decreases after the peak value, and the NOx concentration at the outlet of the denitration device decreases more than necessary, and the leak ammonia to the downstream of the denitration device is reduced. There was a problem that occurred.

At the same time, in the conventional denitration apparatus for treating pulverized coal combustion exhaust gas, when starting or stopping the mill when the load changes, the state of fluctuation of the exhaust gas NOx concentration at the entrance of the denitration apparatus depends on the number of operating mills at that time. Turned out different. That is, as shown in FIG. 5, a temporary increase curve A of the NOx concentration at the denitration apparatus inlet when the fifth mill is started for the purpose of increasing the load while the four mills are operating.
The temporary increase curve B of the inlet NOx concentration when the sixth mill is started when the fifth mill is operating is different. In FIG. 5, the peak value of NOx is higher when the sixth mill is started, and The duration is long. Further, the rising peak value C of the NOx concentration at the denitration apparatus inlet when the sixth mill is stopped is higher than that at the time of starting, and the continuation time is longer.

The difference in the mode of temporary increase in the NOx concentration at the exhaust gas at the denitration apparatus due to the start of the fifth and sixth mills is shown in FIG. 4, as shown in FIG. This is considered to be due to the fact that the arrangement position in the furnace differs for each mill. It is considered that the combustion state in the boiler furnace is not uniform and differs depending on the position in the furnace, and also depending on the magnitude of the load (the number of operating mills). However, in the prior art, the ammonia supply amount correction at the time of starting and stopping the mill is the same as shown in FIG. 5, and therefore, there is a problem that the ammonia correction to the denitration device is not always appropriate.

An object of the present invention is to appropriately adjust the amount of ammonia injected in response to a change in the NOx amount of exhaust gas at the inlet of a denitrification apparatus even when the load of a pulverized coal combustion apparatus changes at high speed and when the number of operating pulverized coal production mills changes. Control and NOx at NOx outlet
An object of the present invention is to provide a method and a control device for controlling the amount of ammonia injected into a denitration apparatus for treating pulverized coal combustion exhaust gas, which can maintain the concentration below a set value and reduce the amount of leaked ammonia.

[0012]

Means for Solving the Problems The invention claimed in the present application to solve the above problems is as follows. (1) The total NOx amount at the inlet is obtained based on the flow rate of the gas to be treated from the pulverized coal combustion device and the NOx concentration at the inlet gas of the denitration device,
Based on the inlet NOx concentration and the outlet NOx concentration set value, a preceding molar ratio signal of ammonia to exhaust gas is obtained.
A method for obtaining a molar ratio correction signal based on a deviation between a set value and a detected value of the Ox concentration, and controlling the amount of ammonia injected into the denitration apparatus based on the total NOx amount, the preceding molar ratio signal, and the molar ratio correction signal, The ammonia injection amount is corrected based on a signal indicating the number of the operation mill to be started or stopped based on the load command signal of the pulverized coal combustion device and the elapsed time after the start or stop of the mill. A method for controlling the amount of ammonia injected into a denitration apparatus for treating pulverized coal combustion exhaust gas, the method comprising:

(2) The total NOx amount is obtained based on the flow rate of the gas to be treated from the pulverized coal combustion device and the NOx concentration at the denitration device inlet, and the preceding molar ratio of ammonia to exhaust gas based on the inlet NOx concentration and the outlet NOx concentration set value. A signal is obtained, a molar ratio correction signal is obtained based on the deviation between the set value of the outlet NOx concentration and the detected value, a total molar ratio signal is obtained based on the preceding molar ratio signal and the molar ratio correction signal, and the total NOx amount and the total NOx amount are calculated. In the method for controlling the amount of ammonia injected into the denitration apparatus based on the molar ratio signal and the detected value of the amount of injected ammonia, the coal mill that starts or stops on the basis of the load command signal of the pulverized coal combustion apparatus is the number-th operating mill. A denitration apparatus for treating pulverized coal combustion exhaust gas, wherein the ammonia injection amount is corrected based on such a signal and the elapsed time after starting or stopping the mill. Ammonia injection rate control method.

(3) Means for calculating the total NOx amount of the exhaust gas flowing from the pulverized coal combustion device to the denitration device, and a preceding molar ratio signal of ammonia with respect to the exhaust gas based on the set value of the NOx concentration at the inlet and the NOx concentration at the outlet of the denitration device Means for calculating a molar ratio correction signal for ammonia based on the difference between the set value of the outlet NOx concentration and the detected value; and
A means for calculating an ammonia request signal based on the x amount, the preceding mole ratio signal and the mole ratio correction signal, and means for controlling an ammonia flow control valve based on the ammonia request signal and the ammonia flow detection signal. In the ammonia injection amount control device, based on a signal indicating the number of the operating mill to be started or stopped based on the load command signal of the pulverized coal combustion device, and the elapsed time after starting or stopping the mill, An apparatus for controlling the amount of ammonia injected into a denitration apparatus for treating pulverized coal combustion exhaust gas, comprising a fuzzy control means for correcting a control amount of an ammonia flow control valve.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention relating to a control device for controlling the amount of ammonia injected from a pulverized coal combustion device into a denitration device for treating exhaust gas. The output signal of the flow meter 2 of the exhaust gas to be processed and the output signal of the NOx concentration meter 3 at the denitration device are multiplied by a multiplier 10a to obtain an inlet NOx amount signal 11. The difference between the output signal of the NOx concentration meter 3 at the denitration device and the output signal of the NOx concentration setting device 4 at the outlet is obtained by the subtractor 12a, and this value is divided by the output signal of the NOx concentration meter 3 by the divider 13a. The required denitration rate signal 14 is calculated by this, and this signal is input to the function generator 15 to calculate the ammonia molar ratio signal (preceding value molar ratio signal) 16 necessary for the NOx amount.

The difference signal between the output signal of the outlet NOx concentration setting device 4 and the output signal of the outlet NOx concentration meter 5 is subtracted by a subtractor 12b.
The signal is processed by the controller 17a to calculate the feedback molar ratio signal 18. The adder 19a adds the required molar ratio signal 16 and the feedback molar ratio signal 18 to obtain a total molar ratio signal 20, and multiplies the inlet NOx amount signal 11 by a multiplier 10b to obtain a required ammonia flow signal 21.

In the fuzzy controller 44, the load request signal 6,
Mill operating number signal 7, heavy oil burner point fire extinguishing signal 8, output signal of inlet NOx concentration meter 3, output signal of outlet NOx concentration meter 5, elapsed time signal 5 after start / stop command signal of mill
0, input the output signal of the gas concentrator outlet gas O ₂ concentration meter 9,
The following arithmetic processing is performed.

The following five types of combinations of the fuzzy rule antecedent in the fuzzy controller 44 are used. (1) load change rate, economizer outlet gas O ₂ concentration change rate (2) denitrification device inlet NOx concentration change rate, denitration unit inlet N
Ox second order differentiation (3) Number of operating mills, elapsed time after mill start / stop command signal (4) NOx concentration change rate at denitrification device, elapsed time after completion of load change (5) Number of fire extinguishing points at heavy oil burner point, heavy oil burner Elapsed time after point fire extinguishing.

The fuzzy controller 44 performs processing based on the above rules, and determines the number of operating mills, that is, the number of the starting or stopping mill, and the progress after the start or stop command signal of the mill. A time-adjusted ammonia flow correction signal 45 is output.

This signal 45 is added to the required ammonia flow signal 21 by the adder 19b to calculate the ammonia flow request signal 22. The signal 22 is input to the subtractor 12c to calculate a deviation from the output signal of the ammonia flow meter 1, and the deviation signal is input to the controller 17b to control the ammonia flow control valve 24.

FIG. 6 shows a comparison of the ammonia injection amount correction state and the NOx concentration at the outlet of the denitration apparatus according to this embodiment and the prior art. In the figure, in this embodiment, since the ammonia flow rate is appropriately corrected in accordance with the fluctuation of the NOx concentration at the denitration device inlet at the start / stop of the mill, the NOx concentration at the denitration device outlet is below the reference value and largely deviates from the reference value. It turns out that there is nothing.

[0022]

According to the present invention, even when the load of the pulverized coal combustion device (boiler) changes at high speed or the number of operating mills changes, the reaction of the denitration device with respect to the change in the NOx amount of the exhaust gas at the entrance of the denitration device can be improved. The delay can be compensated for, the NOx concentration at the denitration device outlet can be maintained near the set value, and the amount of ammonia consumed can be reduced by reducing leaked ammonia.

[Brief description of the drawings]

FIG. 1 is a system diagram of an ammonia injection amount control device of a denitration device according to an embodiment of the present invention.

FIG. 2 is a system diagram of an ammonia injection amount control device of a denitration device according to the related art.

FIG. 3 is a schematic diagram of a denitration apparatus for treating combustion exhaust gas from a pulverized coal combustion boiler.

FIG. 4 is a schematic view of a boiler furnace provided with a pulverized coal combustion burner.

FIG. 5 is an explanatory diagram of a state of correction of an ammonia injection amount in the related art.

FIG. 6 is a diagram showing proportionally the correction state of the amount of ammonia injected into the denitration device and the NOx concentration at the denitration device outlet in the present invention and the prior art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ammonia flow meter, 2 ... Process gas flow meter, 3 ... NOx concentration meter at the denitration device outlet, 4 ... NOx concentration setting device at the denitration device outlet, 5 ... NOx concentration meter at the denitration device outlet, 6 ... Load request signal, 7 ... Mil the number of operating units signal, 8 ... heavy-diesel burner ignition extinguishing signal, 9 ... economizer exit gas O ₂ meter, 10 ... multiplier, 1
1 ... NOx amount signal at inlet, 12 ... subtractor, 13 ... divider,
14 required denitration rate signal, 15 function generator, 16 ammonia molar ratio signal, 17 controller, 18 feedback molar ratio signal, 19 adder, 20 total molar ratio signal, 2
DESCRIPTION OF SYMBOLS 1 ... necessary ammonia molar ratio signal, 22 ... ammonia flow request signal, 23 ... second-order differentiator, 24 ... ammonia flow control valve, 25 ... differentiator, 26 ... boiler, 27 ... furnace, 28
... pulverized coal burner, 29 ... fuel pipe, 30-35 ... mill, 3
6: gas flow, 37: denitration device, 38: electric dust collector, 3
9: Air preheater, 41: Push-in ventilator, 43: Ammonia injection nozzle, 44: Fuzzy controller, 45: Ammonia injection amount correction signal, 50: Elapsed time signal after start / stop command signal of mill.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G05B 13/02 F term (Reference) 3K070 DA02 DA14 DA22 DA30 DA60 4D002 AA12 AC01 BA06 DA07 GA02 GA03 GA04 GB01 GB02 GB06 HA02 HA10 5H004 GA07 GA16 GA34 GB04 HA04 HB02 HB04 JB07 JB08 KB33 KB39 KD02 KD25 MA02 MA19 MA60

Claims (3)

[Claims] 1. An inlet total NOx amount is determined based on a flow rate of a gas to be treated from a pulverized coal combustion device and a NOx concentration at an inlet of a denitration device, and a preceding mole of ammonia with respect to exhaust gas is determined based on a set value of an inlet NOx concentration and an outlet NOx concentration. A ratio signal is obtained, a molar ratio correction signal is obtained based on a deviation between the set value of the outlet NOx concentration and the detected value, and the amount of ammonia injected into the denitration apparatus based on the total NOx amount, the preceding molar ratio signal, and the molar ratio correction signal. In the method of controlling the pulverized coal combustion device, based on the load command signal of the pulverized coal combustion device, the signal of the number of the operation mill is a coal mill to start or stop, and the elapsed time after the start or stop of the mill, A method of controlling the amount of ammonia injected into a denitration apparatus for treating pulverized coal combustion exhaust gas, the method comprising correcting the amount of ammonia injected. 2. A total NOx amount is determined based on a flow rate of a gas to be treated from a pulverized coal combustion device and a NOx concentration at a denitration device inlet.
Based on the inlet NOx concentration and the outlet NOx concentration set value, a preceding molar ratio signal of ammonia to exhaust gas is obtained.
A mole ratio correction signal is obtained based on the deviation between the set value of the Ox concentration and the detected value, a total mole ratio signal is obtained based on the preceding mole ratio signal and the mole ratio correction signal, and the total NOx amount, the total mole ratio signal, and ammonia are obtained. In the method of controlling the ammonia injection amount to the denitration device based on the injection amount detection value, a signal of the number of the operation mill is a coal mill to start or stop based on a load command signal of the pulverized coal combustion device, A method for controlling an amount of ammonia injected into a denitration apparatus for treating pulverized coal combustion exhaust gas, wherein the amount of ammonia injected is corrected based on an elapsed time after starting or stopping the mill. 3. A means for calculating a total NOx amount of exhaust gas flowing from a pulverized coal combustion device to a denitration device, and a preceding molar ratio signal of ammonia to exhaust gas based on a set value of an inlet NOx concentration and an outlet NOx concentration of the denitration device. Means for calculating, a means for calculating a molar ratio correction signal for ammonia based on a deviation between a set value of the outlet NOx concentration and a detected value, and a ammonia request signal based on the total NOx amount, the preceding molar ratio signal, and the molar ratio correction signal. A means for controlling the amount of ammonia injected into the denitration apparatus, comprising means for controlling the ammonia flow rate control valve based on the ammonia request signal and the ammonia flow rate detection signal. Based on a signal indicating the number of the operating mill to be stopped and the elapsed time since the start or stop of the mill, the amm. An ammonia injection amount control device for a pulverized coal combustion exhaust gas treatment denitration device, comprising fuzzy control means for correcting a control amount of a near flow control valve.