JP2024121432A - Denitrification control device, denitrification control method, and program - Google Patents

Abstract

The present invention aims to achieve stable control of NOx concentration at the denitration outlet over a long period of time.
[Solution] The denitration control device controls the amount of ammonia injected into a denitration device that decomposes NOx in combustion gas discharged from a boiler. The denitration control device includes a correction unit 60 that corrects a denitration outlet NOx set value, and an ammonia amount calculation unit that calculates the amount of ammonia required for the denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value. The correction unit 60 corrects the denitration outlet NOx set value using the deviation between a smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value.
[Selected figure] Figure 5

Description

This disclosure relates to a denitration control device, a denitration control method, and a program.

In thermal power plants, denitration devices are often installed to remove nitrogen oxides (NOx) from the combustion gas discharged from combustion equipment such as gas turbines or boilers. Denitration control in the denitration device is performed, for example, by determining a set value for the NOx concentration at the outlet of the denitration device so that the NOx concentration in the gas discharged from the chimney does not exceed a regulated value, and by determining the amount of ammonia to be injected based on the NOx concentration contained in the combustion gas at the outlet of the combustion equipment (see, for example, Patent Document 1).

In addition, when the amount of fuel input increases or decreases transiently, such as when the load on the combustion equipment changes or when the burner is ignited or extinguished, the NOx concentration contained in the combustion gas may change suddenly. For this reason, for example, when the load changes or the burner is ignited or extinguished, advance control is performed to correct the amount of ammonia input, thereby maintaining stable control of the NOx concentration at the denitration outlet.

JP 2015-48975 A

In recent years, with the widespread use of renewable energy, thermal power plants have come to play a greater role in adjusting the amount of electricity supplied, and burners are now being ignited and extinguished frequently to adjust output. This has resulted in an increased frequency of sudden changes in the NOx concentration in the combustion gas, raising concerns that if denitration control is not performed properly, ammonia consumption will increase, leading to higher operating costs. Furthermore, if excessive ammonia is added, unreacted ammonia will flow downstream in the denitration device and react with sulfide compounds in the combustion gas, potentially producing acid ammonium sulfate in the air preheater. This could result in the air preheater becoming clogged, making it impossible to continue operating the plant.

In addition, if the denitration performance of the denitration equipment deteriorates due to aging, the NOx concentration at the denitration outlet may be higher than the set value, raising the concern that the NOx concentration in the gas discharged from the chimney may exceed the regulated value.
Thus, while management of the NOx concentration at the denitration outlet is extremely important, it is difficult to maintain stable control over the long term, which is an issue for power plants.

This disclosure has been made in consideration of these circumstances, and aims to provide a denitration control device, a denitration control method, and a program that can achieve stable control of the denitration outlet NOx concentration over the long term.

One aspect of the present disclosure is a denitration control device that controls the amount of reducing agent injected into a denitration device that decomposes NOx in combustion gas discharged from a combustion facility, and includes a correction means for correcting a denitration outlet NOx set value, and a reducing agent amount calculation means for calculating the amount of reducing agent required for the denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value, and the correction means corrects the denitration outlet NOx set value using the deviation between a smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value.

One aspect of the present disclosure is a denitration device equipped with the above-described denitration control device.

One aspect of the present disclosure is a power generation plant equipped with the above-mentioned denitrification device.

One aspect of the present disclosure is a denitration control method for controlling the amount of reducing agent injected into a denitration device that decomposes NOx in combustion gas discharged from a combustion facility, in which a computer executes a correction process for correcting a denitration outlet NOx set value, and a reducing agent amount calculation process for calculating the amount of reducing agent required for the denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value, and the correction process corrects the denitration outlet NOx set value using the deviation between a smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value.

One aspect of the present disclosure is a program for causing a computer to function as the above-mentioned denitration control device.

The denitration control device, method, and program disclosed herein have the effect of realizing stable control of the denitration outlet NOx concentration over a long period of time.

1 is an overall schematic configuration diagram of a power plant according to an embodiment of the present disclosure; FIG. 1 is a schematic configuration diagram of a boiler according to an embodiment of the present disclosure. 1 is a schematic configuration diagram of a denitration device according to an embodiment of the present disclosure. FIG. 2 is a functional configuration diagram illustrating an example of functions provided in a denitration control device according to an embodiment of the present disclosure. 4 is a functional configuration diagram illustrating an example of functions included in a correction unit according to an embodiment of the present disclosure. FIG. 4 is a functional configuration diagram illustrating an example of functions included in a correction permission determination unit and an operation determination unit according to an embodiment of the present disclosure. FIG. 4 is a functional configuration diagram illustrating an example of functions of a correction value setting unit according to an embodiment of the present disclosure. FIG.

A denitration control device, a denitration control method, and a program according to an embodiment of the present disclosure will be described below with reference to the drawings. The denitration control device will be described below as an example of application to a denitration device that removes NOx from combustion gas generated in a boiler (combustion equipment) of a thermal power plant. Other examples of the combustion equipment include gas turbines, industrial furnaces, and waste incinerators.
In the following description, top and upward refer to the upper side in the vertical direction, and bottom and downward refer to the lower side in the vertical direction, and the vertical direction is not precise and may include errors.

Figure 1 is an overall schematic diagram of a power plant 1 according to an embodiment of the present disclosure. As shown in Figure 1, the power plant 1 of this embodiment mainly comprises a boiler 10, a steam turbine 2 that is rotationally driven by steam generated in the boiler 10, and a generator 3 that is connected to the steam turbine 2 and generates electricity using the rotational force of the steam turbine 2. The steam after driving the steam turbine 2 is condensed in a condenser 4 and returned to the boiler 10.

The boiler 10 is a boiler that can generate superheated steam by burning pulverized fuel, for example, pulverized solid fuel, with a burner and exchanging the heat generated by the combustion with feed water or steam. As the solid fuel, coal, biomass fuel, petroleum coke (PC) fuel, petroleum residue, etc. can be used. Note that the fuel of the boiler 10 is not limited to solid fuel, and can also be petroleum such as heavy oil, light oil, and heavy oil, industrial wastewater, and liquid fuel such as liquefied ammonia. In addition, gaseous fuels such as natural gas, various petroleum gases, by-product gases generated in the steelmaking process, hydrogen gas, and ammonia gas can also be used. Furthermore, it is possible to use a combination of these various fuels.

Figure 2 is a schematic diagram of a boiler 10 according to this embodiment. As shown in Figure 2, the boiler 10 has, for example, a furnace 11, a combustion gas passage 12, and a flue 13.

The furnace 11 is, for example, a hollow rectangular cylinder installed vertically. A plurality of burners 14 are provided in the lower region of the furnace 11 as a combustion device. The burners 14 are connected to a plurality of mills (pulverizers) 15 via a plurality of pulverized fuel supply pipes 19. The mills 15 pulverize solid fuel to generate pulverized fuel. The pulverized fuel is mixed with primary air and supplied to the burners 14 as a pulverized fuel mixture. The pulverized fuel mixture fed from the burners 14 to the furnace 11 is ignited and reacts with the secondary air separately fed from the burners 14 to form a flame. This causes high-temperature combustion gas to rise inside the furnace 11 and flow into the combustion gas passage 12.

The combustion gas passage 12 is connected to the vertical upper part of the furnace 11. The combustion gas passage 12 is provided with a heat exchanger (not shown) for recovering heat from the combustion gas. Examples of heat exchangers include a superheater, a reheater, and a coal economizer. Steam is generated by exchanging heat with the combustion gas in these heat exchangers, and is supplied to the steam turbine 2 (see FIG. 1) described above.

A flue 13 is connected downstream of the combustion gas passage 12, through which the combustion gas whose heat has been recovered by the heat exchanger is discharged. An air preheater (air heater) 17 is provided between the flue 13 and the wind duct 16, and heat is exchanged between the air flowing through the wind duct 16 and the combustion gas flowing through the flue 13, heating the primary air supplied to the mill 15 and the secondary air supplied to the burner 14, thereby recovering further heat from the combustion gas after heat exchange with water and steam.

The flue 13 is provided with a denitration device 20 at a position upstream of the air preheater 17. The denitration device 20 supplies a reducing agent, such as ammonia or urea water, which has the effect of reducing nitrogen oxides, to the combustion gas flowing through the flue 13, and promotes the reaction between the nitrogen oxides (NOx) in the combustion gas to which the reducing agent has been supplied and the reducing agent through the catalytic action of a denitration catalyst installed in the denitration device 20, thereby removing and reducing the nitrogen oxides in the combustion gas. Details of the denitration device 20 will be described later.

A gas duct 18 is connected downstream of the air preheater 17 of the flue 13. The gas duct 18 is provided with a dust collector 21 such as an electric dust collector for removing ash from the combustion gas, an environmental device 22 such as a desulfurization device for removing sulfur oxides, and an induced draft fan (IDF) 23 for directing the combustion gas to these environmental devices. The downstream end of the gas duct 18 is connected to a chimney 24, and the combustion gas treated by the environmental device 22 is discharged outside the system as exhaust gas. In addition, for example, a chimney inlet NOx analyzer 36 is provided between the chimney 24 and the environmental device 22 for measuring the NOx concentration in the combustion gas G discharged from the chimney 24 (hereinafter referred to as the "chimney inlet NOx concentration").

Figure 3 is a schematic diagram of the denitration device 20 according to this embodiment. The denitration device 20 decomposes NOx in the combustion gas G discharged from the boiler 10. The denitration device 20 includes, for example, an inlet duct 32, a reaction section 31, and an outlet duct 33 from the upstream side in the flow direction of the combustion gas G. In the denitration device 20, ammonia, which is a reducing agent, is injected into the combustion gas G introduced from the inlet duct 32, and the gas is denitrified in the reaction section 31 and discharged to the outlet duct 33.

The inlet duct 32 is provided with an ammonia injector 34 for injecting ammonia. The ammonia injector 34 is connected to an ammonia supply pipe 35. The ammonia supply pipe 35 is provided with an ammonia flowmeter 39 for measuring the flow rate of ammonia, and an ammonia flow control valve 40 for adjusting the flow rate of ammonia. The valve opening of the ammonia flow control valve 40 is controlled by a denitration control device 50 (described later), so that an amount of ammonia appropriate for the NOx concentration in the combustion gas G flowing through the inlet duct 32 is injected from the ammonia injector 34.

The reaction section 31 is filled with a denitrification catalyst. The NOx in the combustion gas G introduced into the reaction section 31 is decomposed into harmless water vapor and nitrogen gas by the action of ammonia supplied from the ammonia injector 34 and the denitrification catalyst filled in the reaction section 31, and is removed.

Normally, the operation of the denitration device 20 is controlled so that the NOx concentration in the combustion gas G at the outlet duct 33 (hereinafter referred to as the "denitration outlet NOx concentration") is below a specified value even when the NOx concentration in the combustion gas G at the inlet duct 32 (hereinafter referred to as the "denitration inlet NOx concentration") fluctuates, such as when the load of the combustion gas G source (e.g., boiler 10, etc.) changes. Here, the denitration inlet NOx concentration is measured by the denitration inlet NOx analyzer 37, and the denitration outlet NOx concentration is measured by the denitration outlet NOx analyzer 38.

Next, the denitration control device 50 according to this embodiment will be described with reference to the drawings. Fig. 4 is a functional configuration diagram showing an example of functions provided in the denitration control device 50 according to this embodiment.
The denitration control device 50 is, for example, a computer, and includes a CPU (Central Processing Unit: processor), a main memory, a secondary storage, and the like.

As an example, a series of processes for realizing the functions of the denitration control device 50 is stored in a secondary storage device or the like in the form of a program, and the CPU (processor) reads this program into the main storage device and executes information processing and arithmetic processing to realize various functions. The program may be pre-installed in the secondary storage device, provided in a state stored in other non-transient computer-readable storage media, or distributed via wired or wireless communication means. Examples of non-transient computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

As described above, the denitration control device 50 controls the amount of ammonia injected into the denitration device 20. As shown in FIG. 4, for example, the denitration control device 50 includes a correction unit (correction means) 60, an ammonia amount calculation unit (reducing agent amount calculation means) 51, a subtractor 52, and a controller 53.

The correction unit 60 corrects the denitration outlet NOx set value. The correction unit 60 will be described in detail later.
The ammonia amount calculation unit 51 calculates the amount of ammonia required for the denitration reaction using the denitration outlet NOx set value, the denitration outlet NOx concentration, and the denitration inlet NOx concentration corrected by the correction unit 60, and converts the calculated ammonia amount into an ammonia flow rate target value (NH3 flow rate target value) and outputs it. Note that many known methods have been proposed for calculating the required ammonia amount by the ammonia amount calculation unit 51, and these methods may be appropriately adopted. Therefore, detailed explanations will be omitted here. Note that, as an example, the method disclosed in JP 2003-10645 A can be used.
The denitration outlet NOx set value is set, for example, based on a value stipulated by laws and regulations such as the Air Pollution Control Act or a value conforming to an agreement concluded between the operator of the power plant and the local government where the plant is located.

The subtractor 52 calculates a control deviation, which is the difference between the ammonia flow rate (NH3 flow rate) measured by the ammonia flow meter 39 (see FIG. 3) and the ammonia flow rate target value (NH3 flow rate target value).
The controller 53 performs a feedback calculation, for example, PI (Proportional-Integral) control (proportional-integral calculation), on the control deviation to calculate a valve opening command. Note that the feedback calculation executed by the controller 53 is not limited to this example. For example, the controller 53 may perform PID (Proportional-Integral-Differential) control, or may perform other known calculations related to feedback.
The valve opening command is given to the ammonia flow rate control valve 40 (see FIG. 3), and the amount of ammonia injected is controlled to an appropriate value.

Fig. 5 is a functional configuration diagram showing an example of the functions of the correction unit 60 according to this embodiment. As shown in Fig. 5, the correction unit 60 includes, for example, a smoothing processing unit 61, a subtractor 62, a correction permission determination unit (correction permission determination means) 63, an operation determination unit (operation determination means) 64, a correction value setting unit (correction value setting means) 65, and an adder 66.

The smoothing processing unit 61 performs a smoothing process on the time series data of the stack inlet NOx concentration acquired during a predetermined period, and outputs the stack inlet NOx concentration after the smoothing process (hereinafter referred to as the "smoothed NOx concentration"). One example of the smoothing process is a moving average process. The period for which the averaging is performed is determined, for example, by an agreement with the local government in which the power plant is installed, and one example is a one-hour average value.
The subtractor 62 calculates the difference between the smoothed NOx concentration and the denitration outlet NOx set value. In this embodiment, the subtractor 62 subtracts the denitration outlet NOx set value from the smoothed NOx concentration.

The correction permission determination unit 63 determines whether or not a preset correction permission condition is satisfied, for example, when the NOx deviation obtained by subtracting the denitration outlet NOx set value from the smoothed NOx concentration is outside a predetermined upper and lower limit range, the smoothed NOx concentration has been maintained within the predetermined range for a predetermined period of time, the burner 14 provided in the boiler 10 is not in ignition operation or extinguishing operation, the boiler 10 is not undergoing a load change, the process value related to the denitration control does not indicate an abnormal value, and the boiler 10 is operating, the correction permission determination unit 63 determines that the correction permission condition is satisfied.
Then, the correction permission judgment unit 63 outputs a correction permission judgment signal of "0 (off)" if, for example, a state in which the correction permission condition is satisfied is maintained for a predetermined period of time, and outputs a correction permission judgment signal of "1 (on)" otherwise.

The operation determination unit 64, for example, determines whether the operation conditions for determining whether the denitration control by the denitration device 20 can be continued are satisfied. The operation determination unit 64 determines that the operation conditions are satisfied, for example, when the process values related to the denitration control (e.g., the chimney inlet NOx concentration, the denitration outlet NOx concentration, the denitration inlet NOx concentration, the ammonia flow rate, etc.) do not indicate abnormal values and the boiler 10 is operating, in other words, when combustion is occurring in the boiler 10. The operation determination unit 64 outputs an operation determination signal of "0 (off)" when the operation conditions are satisfied, and outputs an operation determination signal of "1 (on)" when the operation conditions are not satisfied.

FIG. 6 is a functional configuration diagram showing an example of functions provided in the correction permission determination unit 63 and the operation determination unit 64.
As shown in Fig. 6, the operation determination unit 64 receives a process value abnormality signal and a fuel cutoff signal. The process value abnormality signal is, for example, "1 (on signal)" when the process value related to the denitration control does not indicate an abnormal value, in other words, when the sensor that detects these process values does not have an abnormality, and is "0 (off signal)" when the process value related to the denitration control indicates an abnormal value, in other words, when the sensor that detects these process values has an abnormality. The combustion cutoff signal is a signal that indicates whether the boiler 10 is operating or stopped, and is "1" when the boiler 10 is operating and is "0" when the boiler is stopped. For example, a Master Fuel Trip (MFT) signal can be used as the combustion cutoff signal.

The process value abnormality signal and the combustion cutoff signal are input to an AND circuit (logical product circuit) 81, and if both signals are on signals, a "1" is output, and then the signal is inverted by a NOT circuit 82 to become a "0". Also, if either of the above two signals is a "0", the AND circuit 81 outputs a "0", and then the signal is inverted by a NOT circuit 82 to become a "1". The output of the NOT circuit 82 is output to the correction value setting unit 65 as an operation determination signal.

The smoothed NOx concentration, the denitration outlet NOx set value, the burner ignition extinguishing signal, and the load signal are input to the correction permission determination unit 63. In addition, the output of the AND circuit 81 of the operation determination unit 64 is input to the correction permission determination unit 63.

In the correction permission determination unit 63, the smoothed NOx concentration and the denitration outlet NOx concentration are input to a difference comparator 71, which outputs "1" if the NOx deviation, which is the difference between the smoothed NOx concentration and the denitration outlet NOx concentration, is outside the specified upper and lower limit range, and outputs "0" if it is within the specified range.

The smoothed NOx concentration is also input to a comparator 72, which outputs "0" if the smoothed NOx concentration is within a predetermined range, then the signal is inverted by a NOT circuit (negation circuit) 73 to become "1", and furthermore, if the signal is maintained at "1" for a predetermined period by an on-delay timer 74, "1" (on signal) is output. On the other hand, if the smoothed NOx concentration is outside the predetermined range, the comparator 72 outputs "1", then the signal is inverted by a NOT circuit 73 to become "0". As a result, the on-delay timer 74 outputs "0".

The burner ignition/extinction signal is set to "1" when the extinguishing operation to extinguish an ignited burner 14 is not in progress, or when the ignition operation to ignite an extinguished burner 14 is not in progress, and is set to "0" when the extinguishing operation or ignition operation is in progress.

The load signal is input as "1" when the load is not changing and as "0" when the load is changing.

The output of the difference comparator 71, the output of the on-delay timer 74, the burner ignition/extinguishing signal, the load signal, and the output of the AND circuit 81 are output to the AND circuit 76. When all of these signals are "1", the AND circuit 76 outputs "1". This output "1" is then inverted by the NOT circuit 77 to become "0", and when "0" is maintained for a predetermined period, a signal of "0" is output from the off-delay timer 78.
On the other hand, if any of the above signals is "0", the AND circuit 76 outputs "0". This output "0" is inverted to "1" by the subsequent NOT circuit 77. As a result, the off-delay timer 78 outputs "1".
The output of the off-delay timer 78 is outputted to the correction value setting section 65 as a correction permission determination signal.

As described above, the correction permission determination unit 63 outputs a correction permission determination signal of "0" when the correction permission conditions are satisfied, and outputs a correction permission determination signal of "1" when the correction permission conditions are not satisfied.
Moreover, the operation determination unit 64 outputs an operation determination signal of "0" if the operation condition is satisfied, and outputs an operation determination signal of "1" if the operation condition is not satisfied.

When the correction permission condition is satisfied, the correction value setting unit 65 sets a correction value for correcting the denitration outlet NOx set value using a NOx deviation obtained by subtracting the denitration outlet NOx set value from the smoothed NOx.
Furthermore, when the correction permission condition is not satisfied, the correction value setting unit 65 maintains the previous value of the correction value.
Furthermore, the correction value setting unit 65 sets the correction value to zero when the operating conditions are not satisfied.

Figure 7 is a functional configuration diagram showing an example of the functions of the correction value setting unit 65 according to this embodiment. As shown in Figure 7, the correction value setting unit 65 includes, for example, a first correction value calculation unit 90, a second correction value calculation unit 100, a setting unit 110, and a signal switcher 115.

The first correction value calculation unit 90 includes, for example, a PI controller 91 and a signal switch 92 .
The PI controller 91 calculates a first correction value by performing proportional-integral control on the NOx deviation obtained by subtracting the denitration outlet NOx concentration from the smoothed NOx concentration. Specifically, the PI controller 91 performs proportional-integral calculation on the NOx deviation when the correction permission signal is "0", and stops the proportional-integral calculation when the correction permission signal is "1". A limiter is provided at the output of the PI controller 91. Therefore, the first correction value output from the PI controller 91 is adjusted so as not to exceed a predetermined upper and lower limit range.

Furthermore, the output of the signal switch 92 is input to the PI controller 91. When the operation determination signal is "1", the signal switch 92 outputs "0%" to the PI controller 91, and when the operation determination signal is "0", the signal switch 92 feeds back the output (previous value) of the PI controller 91 to the PI controller 91.

The second correction value calculation section 100 includes, for example, a function generator 101 and a signal switch 102 .
The function generator 101 calculates the second correction value so that the second correction value increases in the positive direction as the NOx deviation increases in the positive direction, and increases in the negative direction as the NOx deviation increases in the negative direction. For example, the function generator 101 calculates and outputs the second correction value from the NOx deviation using a preset bias function. The function generator 101 outputs, for example, the second correction value for effectively mitigating fluctuations in the stack inlet NOx concentration.

In order to improve the controllability of the denitration outlet NOx concentration, the bias function may be provided with a dead band for setting the second correction value to zero when the absolute value of the NOx deviation is equal to or less than a predetermined value. In addition, the bias function may be set to a proportional gain greater than the proportional gain of the PI controller 91 in the range where the absolute value of the NOx deviation exceeds a predetermined value. By configuring in this way, when the absolute value of the NOx deviation exceeds a certain value and is large, it becomes possible to set a second correction value for controlling the NOx deviation in a direction that quickly reduces the NOx deviation.

A signal switch 102 is provided on the output side of the function generator 101. When the correction permission determination signal is "0", the signal switch 102 outputs the second correction value input from the function generator 101, and when the correction permission determination signal is "1", the signal switch 102 holds the output (previous value) of the function generator 101.

The setting unit 110 calculates a correction value for correcting the denitration outlet NOx setting value by adding the first correction value output from the first correction value calculation unit 90 and the second correction value output from the second correction value calculation unit 100.

A signal switch 115 is provided on the output side of the setting unit 110. When the operation determination signal is "0", the signal switch 115 outputs the output of the setting unit 110 as a correction value, and when the operation determination signal is an on signal "1", the signal switch 115 outputs "0%" as a correction value.

With this correction value setting unit 65, the following correction values are calculated and output:

[State A: When the correction permission determination signal is "0" and the operation determination signal is "0"]
In this case, proportional-integral control based on the NOx deviation is performed in the PI controller 91, and the output is output to the setting unit 110 as a first correction value. Also, a bias value according to the NOx deviation is calculated in the function generator 101 as a second correction value, and this second correction value is output to the setting unit 110 via the signal switch 102. The setting unit 110 outputs a value obtained by adding the first correction value and the second correction value as a correction value. This correction value is output as a correction value via the signal switch 115. This correction value is added to the denitration outlet NOx set value in the adder 66, and the corrected denitration outlet NOx set value is output to the ammonia amount calculation unit 51.

[State B: When the correction permission determination signal is "1" and the operation determination signal is "0"]
In this case, the PI controller 91 of the first correction value calculation unit 90 stops the proportional action control. As a result, the previous value of the PI controller 91 is held by the signal switch 92. Also, in the second correction value calculation unit 100, the previous value of the second correction value is held by the signal switch 102.
As a result, the correction value output from the setting unit 110 becomes a value obtained by adding the previous value of the first correction value and the previous value of the second correction value, and this correction value is held.
Therefore, the same correction value is maintained in state B. In the adder 66, the same correction value is added to the denitration outlet NOx set value, and the corrected denitration outlet NOx set value is output to the ammonia amount calculation unit 51.

[State C: When the correction permission determination signal is "1" and the operation determination signal is "1"]
In this case, 0% is selected in the signal switch 115, and the correction value becomes zero. As a result, in the case of state C, the denitration outlet NOx set value is output to the ammonia amount calculation unit 51 without being corrected.

As described above, the denitration control device 50 and the denitration control method and program according to the present embodiment provide the following advantageous effects.
The denitration control device 50 of this embodiment is equipped with a correction unit 60 that corrects the denitration outlet NOx set value, and an ammonia amount calculation unit 51 that calculates the amount of ammonia required for the denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value, and the correction unit 60 corrects the denitration outlet NOx set value using the NOx deviation between the smoothed NOx value obtained by smoothing the chimney inlet NOx value and the denitration outlet NOx set value.

In this way, according to this embodiment, the amount of ammonia calculated by the ammonia amount calculation unit 51 is not directly corrected, but the denitration outlet NOx setting value, which is one of the parameters used to calculate the amount of ammonia, is corrected. This makes it possible to optimize the amount of ammonia input to the reaction unit 31, and to appropriately suppress the NOx concentration discharged to the environment while suppressing the occurrence of problems due to excessive input of ammonia. As a result, it becomes possible to achieve stable denitration control.

In addition, according to this embodiment, the denitration outlet NOx set value is corrected using the deviation between the smoothed NOx value obtained by smoothing the chimney inlet NOx value and the denitration outlet NOx set value, so that even if it becomes difficult to suppress the denitration outlet NOx concentration due to deterioration of the reaction section 31 over time, it is possible to inject an amount of ammonia that takes into account the deterioration over time.
In addition, since the denitration outlet NOx set value is corrected using the deviation between the smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value, it is possible to reflect the state of the smoothed NOx value at each time in the ammonia amount calculated by the ammonia amount calculation unit 51. As a result, when ammonia is pre-injected, the amount of ammonia to be pre-injected (base bias amount) can be set low, and the shortage or excess can be adjusted by correction by the correction unit 60. As a result, it is possible to suppress the excessive injection of ammonia, and it is possible to suppress the occurrence of problems such as increased costs and clogging of the air preheater that are associated with the excessive injection of ammonia.
From the above, it is possible to realize stable control of the NOx concentration at the denitration outlet for a long period of time.

Although the present disclosure has been described above using embodiments, the technical scope of the present disclosure is not limited to the scope described in the above embodiments. Various modifications or improvements can be made to the above embodiments without departing from the gist of the invention, and forms with such modifications or improvements are also included in the technical scope of the present disclosure. In addition, the above embodiments may be combined as appropriate.

The denitration control device, denitration control method, and program described in each of the above-described embodiments can be understood, for example, as follows.

The denitration control device (50) according to the first aspect of the present disclosure is a denitration control device (50) that controls the amount of reducing agent injected into a denitration device (20) that decomposes NOx in the combustion gas discharged from a combustion facility (10), and includes a correction means (60) that corrects a denitration outlet NOx set value, and a reducing agent amount calculation means (51) that calculates the amount of reducing agent required for the denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value, and the correction means corrects the denitration outlet NOx set value using the deviation between the smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value.

According to this aspect, the denitration outlet NOx set value is corrected using the deviation between the smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value. For example, when correcting the opening command value of the reducing agent flow rate control valve, which is a parameter downstream of the reducing agent amount calculation means, the value output based on the feedback calculation result for the control deviation, which is the difference between the reducing agent flow rate measured by the reducing agent flow meter and the reducing agent flow rate target value, is corrected. For this reason, the influence of the correction value on the opening command value of the reducing agent flow rate control valve may be large, and there is a risk of excessive injection of reducing agent. In contrast, this aspect corrects the denitration outlet NOx set value, which is one of the parameters used to calculate the required reducing agent amount in the reducing agent amount calculation means. This makes it possible to optimize the influence of the correction value on the output value of the final reducing agent amount, and to optimize the injection amount of reducing agent. As a result, it becomes possible to appropriately suppress the NOx concentration discharged to the environment while suppressing the occurrence of problems due to excessive injection of reducing agent. Therefore, it becomes possible to realize stable control of denitration control and cost reduction.
Here, the NOx value is a parameter related to NOx, and examples of the NOx value include NOx concentration, NOx flow rate, etc. In the above-described embodiment, the case where the NOx concentration is used as the NOx value is described as an example.

In the denitration control device (50) according to the second aspect of the present disclosure, in the first aspect described above, the correction means corrects the denitration outlet NOx set value when the deviation between the smoothed NOx value and the denitration outlet NOx set value is outside a predetermined upper or lower limit range.

According to this aspect, when the deviation between the smoothed NOx value and the denitration outlet NOx set value is outside a predetermined upper and lower limit range, the denitration outlet NOx set value is corrected. In other words, when the difference between the smoothed NOx value and the denitration outlet NOx set value is equal to or less than a predetermined value, no correction is performed by the correction means, and the amount of reducing agent required for the denitration reaction is calculated using the denitration outlet NOx set value. In this way, when the smoothed NOx value indicates a value close to the specified value, the correction of the denitration outlet NOx set value by the correction means can be stopped, making it possible to realize stable denitration control while appropriately suppressing the NOx concentration discharged to the environment.

In the denitration control device (50) according to the third aspect of the present disclosure, in the first or second aspect described above, the correction means includes a correction permission determination means (63) that determines whether a preset correction permission condition is satisfied, and a correction value setting means (65) that sets a correction value for correcting the denitration outlet NOx set value using the deviation between the smoothed NOx value and the denitration outlet NOx set value when the correction permission condition is satisfied.

This aspect makes it possible to appropriately determine whether or not correction of the denitration outlet NOx setting value is necessary.

In the denitration control device (50) according to the fourth aspect of the present disclosure, in the above third aspect, the correction permission determination means (63) determines that the correction permission condition is satisfied when the deviation between the smoothed NOx value and the denitration outlet NOx set value is outside a predetermined upper and lower limit range, the smoothed NOx value is maintained within the predetermined range for a predetermined period of time, the burner (14) provided in the combustion equipment (10) is not in ignition or extinguishing operation, there is no load change, the process value related to the denitration control does not indicate an abnormal value, and the combustion equipment (10) is operating.

According to this aspect, it becomes possible to appropriately determine whether or not the denitration outlet NOx setting value needs to be corrected depending on the state of the plant and the state of the process values related to denitration control.

In the denitration control device (50) according to the fifth aspect of the present disclosure, in the third or fourth aspect described above, the correction value setting means (65) maintains the previous value of the correction value when the correction permission condition is not satisfied.

According to this aspect, it is possible to set appropriate correction values depending on the state of the plant and the state of the process values related to denitrification control.

In the denitration control device (50) according to the sixth aspect of the present disclosure, in any one of the third to fifth aspects, the correction value setting means (65) includes a first correction value calculation means (90) that calculates a first correction value by performing proportional-integral control on the deviation between the smoothed NOx value and the denitration outlet NOx set value, a second correction value calculation means (100) that calculates a second correction value that increases in the positive direction when the deviation increases in the positive direction and increases in the negative direction when the deviation increases in the negative direction, and a setting means (110) that sets the correction value using the first correction value and the second correction value.

According to this aspect, the correction value is set using a first correction value calculated by proportional-integral control and a second correction value calculated directly according to the deviation. By using the first correction value, stable control of the reducing agent injection according to the deviation can be realized, and by using the second correction value, the responsiveness of the reducing agent injection to the deviation can be improved. In this way, by correcting the denitration outlet NOx set value using the correction value calculated using the first and second correction values, it is possible to improve the responsiveness to the NOx deviation and perform stable NOx suppression control.

The denitration control device (50) according to the seventh aspect of the present disclosure is any one of the third to sixth aspects, in which the second correction value calculation means (100) sets the second correction value to zero when the absolute value of the deviation is equal to or less than a predetermined value.

According to this aspect, it is possible to prevent the denitration outlet NOx setting value from being frequently corrected. This makes it possible to realize stable denitration control while appropriately suppressing the NOx concentration discharged into the environment.

The denitration control device (50) according to the eighth aspect of the present disclosure is any one of the first to seventh aspects, in which the correction means (60) outputs the denitration outlet NOx set value to the reducing agent amount calculation means without correcting it when the operating conditions for corrective calculation of the denitration control are not satisfied.

According to this aspect, it is possible to stop the correction of the denitration outlet NOx set value when the denitration control is unstable. In other words, by stopping the correction calculation in a transitional state when the denitration control is unstable, it is possible to prevent the calculation of an erroneous correction value.

The denitration control device (50) according to the ninth aspect of the present disclosure is the eighth aspect, in which the correction means includes an operation determination means that determines that the operating conditions are not satisfied when a process value related to denitration control indicates an abnormal value or when the combustion equipment is not operating.

According to this aspect, if the process value related to the denitration control indicates an abnormal value or if the combustion equipment is not operating, in other words, if combustion is not occurring, it is determined that the operating conditions are not met and the correction value is reset. In other words, if the state in which denitration control cannot be continued continues, the operating state may change and the previous correction value may become a disturbance. According to this aspect, when denitration control is newly resumed, the correction value is reset to zero, so it is possible to at least return to the normal state with a proven operating history.

The denitration device (20) according to the tenth aspect of the present disclosure includes a denitration control device (50) according to any one of the first to ninth aspects described above.

The power plant (1) according to the eleventh aspect of the present disclosure is equipped with the denitrification device according to the tenth aspect.

The denitration control method according to the twelfth aspect of the present disclosure is a denitration control method for controlling the amount of reducing agent injected into a denitration device (20) that decomposes NOx in the combustion gas discharged from a combustion facility (10), in which a computer executes a correction process for correcting a denitration outlet NOx set value, and a reducing agent amount calculation process for calculating the amount of reducing agent required for the denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value, and the correction process corrects the denitration outlet NOx set value using the deviation between the smoothed NOx value obtained by smoothing the stack inlet NOx value and the denitration outlet NOx set value.

The program according to the thirteenth aspect of the present disclosure causes a computer to function as the denitration control device (50) described in any one of the first to ninth aspects above.

1: Power plant 10: Boiler 14: Burner 17: Air preheater 20: Denitrification device 24: Chimney 31: Reaction section 32: Inlet duct 33: Outlet duct 34: Ammonia injector 35: Ammonia supply piping 36: Chimney inlet NOx analyzer 37: Denitrification inlet NOx analyzer 38: Denitrification outlet NOx analyzer 39: Ammonia flow meter 40: Ammonia flow control valve 50: Denitrification control device 51: Ammonia amount calculation section (reducing agent amount calculation means)
52: Subtractor 53: Controller 60: Correction section (correction means)
61: Smoothing processing unit 62: Subtractor 63: Correction permission determination unit (correction permission determination means)
64: Operation determination unit 65: Correction value setting unit (correction value setting means)
66: Adder 71: Difference comparator 72: Comparator 73: NOT circuit 74: On-delay timer 76: AND circuit 77: NOT circuit 78: Off-delay timer 81: AND circuit 82: NOT circuit 90: First correction value calculation unit (first correction value calculation means)
91: PI controller 92: signal switch 100: second correction value calculation unit (second correction value calculation means)
101: Function generator 102: Signal switch 110: Setting section (setting means)
115: Signal switch

Claims (13)

A denitration control device that controls an amount of a reducing agent injected into a denitration device that decomposes NOx in a combustion gas discharged from a combustion facility,
A correction means for correcting a denitration outlet NOx set value;
a reducing agent amount calculation means for calculating an amount of reducing agent required for a denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value;
The correction means is a denitration control device that corrects the denitration outlet NOx set value using a deviation between a smoothed NOx value obtained by smoothing a stack inlet NOx value and a denitration outlet NOx set value. The denitration control device according to claim 1, wherein the correction means corrects the denitration outlet NOx set value when the deviation between the smoothed NOx value and the denitration outlet NOx set value is outside a predetermined upper or lower limit range. The correction means is
a correction permission determination means for determining whether a preset correction permission condition is satisfied;
2. The denitration control device according to claim 1, further comprising a correction value setting means for setting a correction value for correcting the denitration outlet NOx set value using a deviation between the smoothed NOx value and the denitration outlet NOx set value when the correction permission condition is satisfied. The denitration control device according to claim 3, wherein the correction permission determination means determines that the correction permission condition is satisfied when the deviation between the smoothed NOx value and the denitration outlet NOx set value is outside a predetermined upper and lower limit range, the smoothed NOx value is maintained within the predetermined range for a predetermined period of time, the burner installed in the combustion equipment is not in ignition or extinguishing operation, there is no load change, the process value related to denitration control does not indicate an abnormal value, and the combustion equipment is operating. The denitration control device according to claim 3, wherein the correction value setting means maintains the previous value of the correction value when the correction permission condition is not satisfied. The correction value setting means
a first correction value calculation means for calculating a first correction value by performing proportional-integral control on a deviation between the smoothed NOx value and the denitration outlet NOx set value;
a second correction value calculation means for calculating a second correction value which increases in a positive direction when the deviation increases in a positive direction and which increases in a negative direction when the deviation increases in a negative direction;
The denitration control device according to claim 3 , further comprising: a setting unit that sets the correction value using the first correction value and the second correction value. The denitration control device according to claim 6, wherein the second correction value calculation means sets the second correction value to zero when the absolute value of the deviation is equal to or less than a predetermined value. The denitration control device according to claim 1, wherein the correction means outputs the denitration outlet NOx set value to the reducing agent amount calculation means without correction when the operating conditions for corrective calculation of the denitration control are not satisfied. The denitration control device according to claim 8, wherein the correction means includes an operation determination means for determining that the operating conditions are not satisfied when a process value related to denitration control indicates an abnormal value or when the combustion equipment is not operating. A denitration device equipped with a denitration control device according to any one of claims 1 to 9. A power plant equipped with the denitrification device according to claim 10. A denitration control method for controlling an amount of a reducing agent injected into a denitration device that decomposes NOx in a combustion gas discharged from a combustion facility, comprising:
The computer
A correction step of correcting a denitration outlet NOx set value;
a reducing agent amount calculation step of calculating an amount of reducing agent required for a denitration reaction using the corrected denitration outlet NOx set value, the denitration outlet NOx value, and the denitration inlet NOx value;
The correction step corrects the denitration outlet NOx set value using a deviation between a smoothed NOx value obtained by smoothing a stack inlet NOx value and the denitration outlet NOx set value. A program for causing a computer to function as the denitration control device according to any one of claims 1 to 9.