JP2015075277A - Ammonia injection quantity control device and ammonia injection quantity control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ammonia injection quantity control device and an ammonia injection quantity control method for a denitrification plant, capable of detecting an abnormality that an ammonia flow transmitter malfunctions, and preventing continuation of operation in an excessive ammonia injection state.SOLUTION: An ammonia injection quantity control device for injecting ammonia into a denitrification plant includes circuits that calculate a denitrification ratio from a deviation between a value obtained by converting a NOx concentration at an inlet of the denitrification plant to a NOx concentration at a predetermined oxygen concentration and a set value of a NOx concentration at an outlet of the nitrification plant to convert the denitrification ratio to a molar ratio, that correct the molar ratio in view of the NOx concentration at the outlet, that determine an ammonia required quantity from the corrected molar ratio and a total NOx quantity, control an ammonia injection quantity based on the ammonia required quantity and an ammonia flow indication value, and detect an abnormality if a deviation between an ammonia required quantity determined from the total NOx quantity and the uncorrected molar ratio and the ammonia flow indication value is not smaller than a predetermined value. By providing the circuits, it is possible to notify surroundings of the abnormality. Therefore, it is possible to prevent continuation of operation in an abnormal state such as an excessive ammonia injection state.

Description

  TECHNICAL FIELD The present invention relates to an ammonia injection amount control device and an ammonia injection amount control method for injecting ammonia as a nitrogen oxide reducing agent into a denitration device in which a denitration catalyst is installed. The present invention relates to an ammonia injection amount control device and an ammonia injection amount control method that are suitable for removal by an ammonia catalytic reduction method using ammonia.

Exhaust gas generated from combustion devices such as boilers and gas turbines in a thermal power plant is led to a denitration device equipped with a denitration catalyst layer to remove nitrogen oxides (NOx), etc. in the exhaust gas, and then discharged outside the system. However, ammonia (NH ₃ ) is injected as a reducing agent into the exhaust gas at the inlet of the denitration apparatus.

  FIG. 2 shows a control system diagram of a method for controlling the NOx concentration at the outlet of the denitration device to be constant, showing a method for controlling the ammonia injection amount of the denitration device for exhaust gas of a conventional gas turbine exhaust gas boiler. The ammonia injection amount control device 50 includes the following circuit.

In FIG. 2, first, an exhaust gas flow rate signal 9a from the exhaust gas flow meter 9 and an inlet NOx concentration signal 10a (actually measured NOx concentration) which is an actual measurement value from the NOx concentration meter 10 installed at the inlet of the denitration apparatus. Based on this, the multiplier 3 calculates the total amount of NOx in the exhaust gas. Further, from the NOx concentration meter 11 at the inlet of the denitration apparatus (which may be the same as the NOx concentration meter 10), the NOx concentration inlet NOx concentration signal 11a when the actually measured NOx concentration is converted into the oxygen concentration 16%. Is output. The NOx concentration (16% O ₂ ) when converted to an oxygen concentration of 16% is obtained by the following formula from the actually measured NOx concentration (actual O ₂ ) and the actual oxygen concentration (O ₂ concentration). In the following numerical value, “21” is the O ₂ concentration (%) of normal air.
NOx concentration (16% O ₂ ) = NOx concentration (actual O ₂ ) × (21−16) / (21−O ₂ concentration)

Since the NOx concentration (actual O ₂ ) in the exhaust gas varies depending on the O ₂ concentration even with the same NOx amount, the NOx concentration when converted to an oxygen concentration of 16% is used in order to evaluate on the basis of a constant oxygen concentration. In the Air Pollution Control Law, the NOx concentration is determined by correcting the oxygen concentration, and the emission standard is determined. The corrected oxygen concentration varies depending on the facility where the smoke is generated. For example, the exhaust gas of a gas turbine exhaust gas boiler has a 16% O ₂ concentration, and the NOx concentration when corrected to this O ₂ concentration is used as a reference. In addition, in the exhaust gas from another combustion apparatus, it converts into each predetermined oxygen concentration. For example, the exhaust gas from a coal-fired boiler has a 6% O ₂ concentration.

The NOx removal rate is calculated based on the inlet NOx concentration signal 11a and the outlet NOx concentration setting value signal 2a of the outlet NOx concentration setting device 2. The relationship between the denitration rate and the molar ratio of the NH ₃ amount to the NOx amount for satisfying the denitration rate (hereinafter referred to as the molar ratio (NH ₃ / NOx)) is set in advance as a function and stored in the control device 50. . The molar ratio substantially corresponds to (denitration rate / 100). In the signal generator 19, the denitration rate is converted into a molar ratio (NH ₃ / NOx) and input to the switch 115.

  Then, the ammonia demand signal 21 is obtained from the NOx total amount from the NOx total amount signal 13 and the molar ratio. This ammonia demand amount signal 21 is obtained based on the outlet NOx concentration (set value) of the outlet NOx concentration setting device 2 with respect to the NOx concentration at the outlet of the NOx removal apparatus, and takes into account the outlet NOx concentration actually measured. This is a signal of the ammonia demand in the absence.

  Further, the outlet NOx concentration set value signal 2a of the outlet NOx concentration setting device 2 and the outlet NOx concentration signal from the NOx concentration meter 1 installed at the outlet of the denitration device (the actually measured NOx concentration is converted into an oxygen concentration of 16%). The deviation of the NOx concentration at the outlet NOx concentration signal) 1a is supplied as a feedback signal to the adder 23 via the proportional-plus-integral calculator 17, and after correcting the input signal of the molar ratio from the signal generator 19 , Input to the switch 15. Then, the ammonia demand signal 14 is obtained from the NOx total amount from the NOx total amount signal 13 and the corrected molar ratio.

  This ammonia demand amount signal 14 is a signal of the ammonia demand amount in consideration of the actual measurement value from the NOx concentration meter 1 at the denitration apparatus outlet. In the present specification, a method of controlling the NOx concentration at the outlet of the denitration apparatus (a value converted from an actual measurement value into a NOx concentration at a predetermined oxygen concentration) to be constant is referred to as outlet NOx constant control.

  On the other hand, the ammonia demand amount signal 21 is an ammonia demand amount signal calculated from the outlet NOx concentration set value (not an actual value or a value converted from the actual value), and therefore, when the NOx constant control is not included. It is a signal of ammonia demand.

  Then, the degree of opening of the ammonia flow rate control valve 6 is calculated by the proportional-plus-integral calculator 17 from the deviation between the ammonia demand signal 14 including the outlet NOx constant control and the ammonia flow rate instruction value signal 12a of the ammonia flow rate transmitter 12. The adjustment opening degree command 41 is made, and the amount of ammonia injected from the pipe 5 into the denitration apparatus inlet duct is controlled.

  When the outlet NOx concentration meter 1 is calibrated or abnormal, the ammonia injection amount control is switched to the control of the inlet NOx concentration meter 11 and the molar ratio manual setting device 25, and the ammonia when the outlet NOx constant control is not included. The demand quantity signal 21 is used instead of the ammonia demand quantity signal 14 including the outlet NOx constant control. The signal route in this case is as follows. A signal 25a from the molar ratio manual setting device 25 is input to the switch 115, and this molar ratio and the total NOx amount from the NOx total amount signal 13 are input to the multiplier 3, whereby the ammonia demand signal 21 is obtained. .

  Patent Document 1 discloses an ammonia injection amount control method by constant control of outlet NOx, and in order to prevent hunting of NOx concentration at the outlet of the denitration device that occurs when a load fluctuation of the boiler occurs, ammonia is detected with respect to the boiler load signal. When the molar ratio bias increases, an increase bias is instantaneously applied to prevent a delay in response, and when the ammonia molar ratio bias decreases, a decrease bias is gradually applied to suppress fluctuations in the ammonia flow rate.

JP 2001-104755 A JP 2010-133354 A

Recent thermal power plant plants often do not have an NH ₃ meter installed at the exit of the denitration unit to reduce costs. In that case, abnormalities in ammonia flow due to excessive ammonia injection cannot be detected, which is a problem. ing.

  Patent Document 2 discloses an injection that compares the sensor value of a sensor that is sensitive to NOx and ammonia provided on the exhaust gas downstream side of a reduction catalyst with a predetermined threshold value to determine an abnormality in the injection amount of a reducing agent injection device such as ammonia. A reducing agent injection control device provided with a quantity abnormality determination unit is disclosed. Specifically, NOx and ammonia are detected by a NOx sensor.

  According to the configuration of Patent Literature 2, if NOx is detected by the NOx sensor, it means that the reducing agent is insufficient, and if ammonia is detected by the NOx sensor, it means that the reducing agent is excessive. This is determined by comparison with a threshold value.

However, if an erroneous flow rate is detected due to an abnormality in the instrument, it may be judged abnormal even though it is actually normal.
In the conventional technology as described above, when the ammonia flow rate transmitter (for example, the reducing agent injection device 40 of Patent Document 2) malfunctions, the reliability of the indicated value is lowered and normal control is performed. I won't break.

  An object of the present invention is to solve the problems of the prior art as described above, in an ammonia injection amount control device and an ammonia injection amount control method for injecting ammonia as a reducing agent for NOx in exhaust gas into a denitration device. It is to provide an ammonia injection amount control device and an ammonia injection amount control method capable of detecting an abnormality and preventing continuation of operation in an over-injected state of ammonia when a malfunction occurs in the vessel.

The object of the present invention can be achieved by adopting the following constitution.
The invention according to claim 1 is an ammonia injection amount control device for injecting ammonia as a reducing agent into a denitration device that removes nitrogen oxides from exhaust gas of a combustion device including a boiler. A circuit for calculating a denitration rate from a deviation between an inlet conversion value obtained by converting a measured value into a nitrogen oxide concentration at a predetermined oxygen concentration and a set value of the nitrogen oxide concentration at the denitration device outlet, and nitrogen oxidation at the denitration device inlet A circuit for obtaining the total amount of nitrogen oxides in the exhaust gas from the measured value of the substance concentration and the amount of exhaust gas, and the denitration rate, the molar ratio of the NH ₃ amount to the NOx amount for satisfying the preset denitration rate and the denitration rate A circuit for converting the molar ratio (M1) from the relationship with (NH ₃ / NOx), and the molar ratio (M1), the measured value of the nitrogen oxide concentration at the outlet of the denitration apparatus is the nitrogen oxide at a predetermined oxygen concentration Change to concentration A circuit for correcting the deviation between the converted outlet value and the set value of the concentration of nitrogen oxides at the outlet of the denitration apparatus, and the reduction of nitrogen oxides from the corrected molar ratio (M2) and the total amount of nitrogen oxides in the exhaust gas. A circuit for determining the required ammonia demand (A), and a circuit for controlling the ammonia injection amount from the deviation between the ammonia demand (A) and the flow rate instruction value of ammonia injected into the denitration device, A circuit for obtaining a required ammonia amount (B) required for the reduction of nitrogen oxides from the molar ratio (M1) and the total amount of nitrogen oxides in the exhaust gas, and the ammonia required amount (B) and an ammonia flow rate indication value When the deviation is equal to or greater than a predetermined value, the ammonia injection amount control device includes a circuit that detects an abnormality in the ammonia flow rate.

The invention according to claim 2 measures the nitrogen oxide concentration at the inlet of the denitration apparatus in the ammonia injection amount control method in which ammonia is injected as a reducing agent into the denitration apparatus that removes nitrogen oxide from the exhaust gas of the combustion apparatus including the boiler. The measured value is converted into a nitrogen oxide concentration at a predetermined oxygen concentration, a denitration rate is calculated based on the converted value at the inlet and the set value of the nitrogen oxide concentration at the outlet of the denitration device, and the denitration rate is calculated. The NOx removal rate is converted into a molar ratio (M1) based on the relationship between a predetermined denitration rate and the molar ratio (NH ₃ / NOx) of the NH ₃ amount to the NOx amount to satisfy the denitration rate. The concentration is measured, the measured value is converted into a nitrogen oxide concentration at a predetermined oxygen concentration, and the molar ratio (M1) is determined by a deviation between the outlet converted value and the set value of the nitrogen oxide concentration at the outlet of the denitration apparatus. And correcting the denitration equipment The total amount of nitrogen oxides in the exhaust gas is obtained from the measured value of the nitrogen oxide concentration at the inlet and the amount of exhaust gas, and the nitrogen oxide is reduced from the corrected molar ratio (M2) and the total amount of nitrogen oxide in the exhaust gas. The required ammonia demand (A) is obtained, and the ammonia injection amount is controlled from the deviation between the ammonia demand (A) and the flow rate instruction value of ammonia injected into the denitration device, and the molar ratio (M1) and the exhaust gas are controlled. The ammonia demand (B) required for the reduction of nitrogen oxides is determined from the total amount of nitrogen oxides contained therein, and when the deviation between the ammonia demand (B) and the ammonia flow rate instruction value is greater than or equal to a predetermined value, the ammonia flow rate This is a method for controlling the amount of ammonia injected to detect an abnormality.

(Function)
According to the present invention, when the deviation between the required ammonia amount required for the reduction of NOx in the exhaust gas and the ammonia flow rate instruction value exceeds a predetermined value, the abnormality is detected and an alarm is issued to notify the surroundings. be able to.
In addition, when an abnormality occurs in an ammonia flow transmitter such as an ammonia flow meter and a flow rate signal exceeding the actual flow rate is generated, ammonia is reduced by the required ammonia amount (A) considering the measured NOx concentration at the denitration device outlet. When injected, the actual NOx concentration at the outlet of the denitration device falls below the set value, the ammonia demand (A) and the ammonia flow rate also fall, and the NOx concentration at the exit of the denitration device becomes close to the set value. Be controlled. In this case, ammonia is in an over-injected state until it is controlled to the set value.

  However, according to the first or second aspect of the invention, even when an erroneous flow rate is detected due to an abnormality in the meter, the measured NOx concentration at the denitration device outlet is not taken into account, and the NOx concentration at the denitration device outlet is not taken into consideration. By using the deviation between the ammonia demand (B) calculated from the set value and the ammonia flow rate instruction value as a criterion for abnormality determination, it is possible to prevent continuation of operation in an abnormal state such as ammonia over-injection.

  If the deviation between the ammonia requirement amount (A) taking into account the actual measured value of the NOx concentration at the outlet of the NOx removal apparatus and the ammonia flow rate instruction value is used as a criterion for abnormality determination, it is controlled to the set value by feedback control as described above. Although it is assumed that an abnormality is not detected, the deviation between the ammonia demand (B) and the ammonia flow rate instruction value is used as a criterion for abnormality determination. Can be detected.

  According to the first or second aspect of the present invention, in the denitration apparatus using ammonia as a reducing agent, even when the ammonia flow rate transmitter is malfunctioning, the abnormality can be detected. Can be prevented.

It is the figure which showed the ammonia flow control circuit of the Example of this invention. It is the figure which showed the ammonia flow control circuit of the prior art.

  Embodiments of the present invention are shown below. In addition, although the case where it applies to the exhaust gas from the boiler for gas turbine exhaust gas (HRSG) is shown in the following Example, it cannot be overemphasized that it applies also to the exhaust gas from a coal-fired boiler and other combustion apparatuses.

  FIG. 1 shows a control system diagram of a method for controlling the ammonia injection amount of the denitration device for exhaust gas according to the first embodiment and controlling the NOx concentration at the exit of the denitration device to be constant. The ammonia injection amount control device 60 includes the following circuit.

In FIG. 1, first, a multiplier based on an exhaust gas flow rate signal 9a from the exhaust gas flow meter 9 and an inlet NOx concentration signal 10a (actual O ₂ ) which is an actual measurement value from a NOx concentration meter 10 installed at the inlet of the denitration device. 3 calculates the total amount of NOx. Further, the denitration rate is calculated based on the inlet NOx concentration signal 11a (16% O ₂ conversion value) from the NOx concentration meter 11 at the inlet of the denitration apparatus and the outlet NOx concentration set value signal 2a. The relationship between the denitration rate and the molar ratio (NH ₃ / NOx) is preset as a function and stored in the control device 60. In the signal generator 19, the denitration rate is converted into a molar ratio (M 1) and input to the switch 115.

  The ammonia demand signal 21 is obtained from the total NOx amount from the total NOx signal 13 and the molar ratio (M1). This ammonia requirement amount signal 21 is an ammonia requirement amount signal calculated from the outlet NOx concentration set value (not an actual value or a value converted from the actual value), and does not include the outlet NOx constant control as described above. This is a signal of the required ammonia amount (B).

Further, the deviation between the outlet NOx concentration set value signal 2a of the outlet NOx concentration setter 2 and the outlet NOx concentration signal 1a (a 16% O ₂ equivalent value) 1a from the NOx concentration meter 1 installed at the outlet of the denitration apparatus is a proportional integral calculation. The signal is supplied as a feedback signal to the adder 23 via the device 17, and the input signal of the molar ratio (M1) from the signal generator 19 is corrected and then input to the switch 15. Then, the ammonia demand amount signal 14 is obtained from the NOx total amount from the NOx total amount signal 13 and the corrected molar ratio (M2). This ammonia demand amount signal 14 is a signal of ammonia demand amount in consideration of the actual measurement value from the NOx concentration meter 1 at the outlet of the denitration device, and is a signal of ammonia demand amount (A) including the outlet NOx constant control as described above. is there.

  Then, the degree of opening of the ammonia flow rate control valve 6 is calculated by the proportional integral calculator 17 from the deviation between the ammonia required amount signal 14 including the outlet NOx constant control and the ammonia flow rate instruction value signal 12a from the ammonia flow rate transmitter 12. A flow rate adjustment opening degree command 41 is made, and the amount of ammonia injected from the pipe 5 into the denitration apparatus inlet duct is controlled.

  Here, when an abnormality occurs in the ammonia flow rate transmitter 12 and an ammonia flow rate instruction value signal 12a exceeding the actual flow rate is generated, the outlet NOx concentration of the denitration device decreases below the set value, and the ammonia including the outlet NOx constant control. The ammonia request amount and the ammonia flow rate from the request amount signal 14 are also reduced, and the NOx concentration at the denitration apparatus outlet is controlled to be close to the set value. In this case, ammonia is in an over-injected state until it is controlled to the set value.

  Therefore, the deviation between the ammonia demand amount signal 21 not including the feedback signal from the NOx concentration meter 1 and the ammonia flow rate instruction value signal 12a is monitored, and if the deviation exceeds a predetermined value, an alarm of large ammonia flow rate deviation is issued. A system that emits light may be used.

  The deviation between the ammonia demand amount signal 21 and the ammonia flow rate instruction value signal 12a is converted into an absolute value by the absolute value calculator 32, and if it is equal to or greater than the predetermined value by the determiner 33, the alarm is transmitted. An alarm signal 34a is output from the device 34 to issue an alarm.

  Here, if the deviation between the ammonia demand amount signal 14 and the ammonia flow rate instruction value signal 12a in consideration of the actual measured value of the NOx concentration at the outlet of the NOx removal apparatus is used as a criterion for abnormality determination, the abnormality is detected because it is controlled to the set value by feedback control. Although the case where it is not detected is also assumed, such a thing can be prevented.

  In consideration of the boiler load change signal 35a from the boiler load change signal generator 35, an alarm may be issued under conditions where the load is not changing. That is, when the load is changing, no alarm is issued even if the deviation is large. When the load is changing, a deviation between the ammonia demand amount signal 21 and the ammonia flow rate instruction value signal 12a occurs due to a follow-up delay. Therefore, the ammonia demand amount signal 21 changes according to the load change. Since the change in the signal 12a is delayed in response, the deviation becomes large.

  Therefore, since a deviation occurs even in such a normal operation, the condition is excluded during a load change. When the load change determining unit 36 is not changing the load, the boiler load change signal 35a is not generated and is not input to the alarm transmitter 34. However, when the load is changing, the boiler change change signal 35a is output from the load change determining unit 36. Input to the alarm transmitter 34.

For example, the operational load zone of the boiler is set to 100 MW to 260 MW, and the ammonia injection amount is changed between 10 to 30 m ³ N / h. In this case, an alarm is issued when the deviation between the ammonia request amount and the ammonia flow rate by the ammonia request amount signal 21 is 6 m ³ N / h or more. Note that the reference value of the alarm generation deviation (in this example, 6 m ³ N / h) is set in consideration of the ammonia flow rate at each load.

  Although not shown, when the outlet NOx concentration meter 1 is calibrated or abnormal, the control is performed to the inlet NOx concentration meter 11 and the molar ratio manual setting device 25 as described above, and the outlet NOx constant control is not included. From the deviation between the ammonia demand signal 21 and the ammonia flow command value signal 12a from the ammonia flow transmitter 12, the proportional integral calculator 17 calculates the opening of the ammonia flow control valve 6, and the ammonia flow control opening command 41 The ammonia injection amount is controlled. Also in this case, when the deviation between the ammonia demand amount signal 21 and the ammonia flow rate instruction value signal 12a when the constant control of the outlet NOx is not included becomes a predetermined value or more, a system that issues an alarm of large ammonia flow rate deviation may be used. .

  In a denitration apparatus that removes nitrogen oxides from exhaust gas from a combustion apparatus such as a boiler, it may be used as an injection amount control technique for ammonia that is a reducing agent for nitrogen oxides.

DESCRIPTION OF SYMBOLS 1 Outlet NOx concentration meter 2 Outlet NOx concentration setter 3 Multiplier 5 Piping 6 Ammonia flow control valve 9 Exhaust gas flow meter 10, 11 Inlet NOx concentration meter 12 Ammonia flow transmitter 13 NOx total amount signal
14 Ammonia demand amount signal 15, 115 including constant control of outlet NOx 17 Switcher 17 Proportional integral calculator 19 Signal generator
21 Excluded NOx constant control does not include ammonia demand signal 23 Adder 25 Molar ratio manual setter 32 Absolute value calculator 33 Determinator 34 Alarm transmitter 35 Boiler load change signal generator 36 Load change determiner 50, 60 Controller 41 Ammonia flow rate adjustment opening command

Claims (2)

In an ammonia injection amount control device that injects ammonia as a reducing agent into a denitration device that removes nitrogen oxides from exhaust gas of a combustion device including a boiler,
The denitration rate is calculated from the deviation between the converted value of the nitrogen oxide concentration measured at the inlet of the denitration device into the nitrogen oxide concentration at a predetermined oxygen concentration and the set value of the nitrogen oxide concentration at the denitration device outlet. Circuit,
A circuit for obtaining the total amount of nitrogen oxides in the exhaust gas from the measured value of the nitrogen oxide concentration at the inlet of the denitration device and the amount of exhaust gas;
A circuit for converting the denitration rate into a molar ratio (M1) from a relationship between a preset denitration rate and a molar ratio of NH ₃ amount to NHx amount (NH ₃ / NOx) for satisfying the denitration rate;
For the molar ratio (M1), an outlet converted value obtained by converting a measured value of the nitrogen oxide concentration at the outlet of the denitration apparatus into a nitrogen oxide concentration at a predetermined oxygen concentration and a set value of the nitrogen oxide concentration at the outlet of the denitration apparatus A circuit to correct by deviation,
A circuit for obtaining an ammonia requirement amount (A) required for reduction of nitrogen oxides from the corrected molar ratio (M2) and the total amount of nitrogen oxides in the exhaust gas;
A circuit for controlling the ammonia injection amount from the deviation between the ammonia demand (A) and the flow rate instruction value of ammonia injected into the denitration device,
Furthermore, a circuit for obtaining an ammonia requirement amount (B) required for reduction of nitrogen oxides from the molar ratio (M1) and the total amount of nitrogen oxides in the exhaust gas;
An ammonia injection amount control device comprising: a circuit for detecting an abnormality in the ammonia flow rate when a deviation between the ammonia demand amount (B) and an ammonia flow rate instruction value is a predetermined value or more. In an ammonia injection amount control method for injecting ammonia as a reducing agent into a denitration device that removes nitrogen oxides from exhaust gas of a combustion device including a boiler,
Measure the nitrogen oxide concentration at the inlet of the denitration device, convert the measured value to the nitrogen oxide concentration at the predetermined oxygen concentration,
Calculate the denitration rate based on the inlet conversion value and the set value of the nitrogen oxide concentration at the denitration device outlet,
The denitration rate is converted into a molar ratio (M1) from a relationship between a preset denitration rate and a molar ratio of NH ₃ amount to NHx amount (NH ₃ / NOx) to satisfy the denitration rate,
Measure the nitrogen oxide concentration at the outlet of the denitration device, convert the measured value to the nitrogen oxide concentration at the predetermined oxygen concentration,
The molar ratio (M1) is corrected by the deviation between the outlet conversion value and the set value of the nitrogen oxide concentration at the outlet of the denitration device, and the measured value of the nitrogen oxide concentration at the denitration device inlet and the amount of exhaust gas Find the total amount of nitrogen oxides,
From the corrected molar ratio (M2) and the total amount of nitrogen oxides in the exhaust gas, the ammonia requirement amount (A) required for the reduction of nitrogen oxides is determined,
While controlling the ammonia injection amount from the deviation between the ammonia demand (A) and the flow rate instruction value of ammonia injected into the denitration device,
From the molar ratio (M1) and the total amount of nitrogen oxides in the exhaust gas, the ammonia requirement amount (B) required for the reduction of nitrogen oxides is determined,
An ammonia injection amount control method, wherein an abnormality in ammonia flow rate is detected when a deviation between the ammonia demand amount (B) and an ammonia flow rate instruction value is a predetermined value or more.

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