JPH08117553A - Method and device for controlling injection amount of ammonia of denitration apparatus - Google Patents

Abstract

PURPOSE: To suppress a momentary discharge amt. of NOx to a prescribed value or less while holding a time average discharge amt. of NOx to a prescribed value or less in the control of the injection amt. of NH3 of a denitration apparatus. CONSTITUTION: An NH3 injection amt. signal 14 is calculated on the basis of the flow rate 22 of exhaust gas to be treated, the NOx concn. at the inlet of a denitration apparatus, the NOx concn. 3a at the outlet thereof and an outlet NOx concn. set value 6a while an NH3 injection amt. correction signal 23a is calculated on the basis of the deviation of the moving average operation value 5a over a predetermined time of the outlet NOx concn. and the outlet NOx concn. set value 6a and an NH3 injection amt. setting signal 14a is calculated on the basis of both signals 14, 23a and an NH3 flow rate adjusting valve is controlled on the basis of the signal 14a and an actually measured NH3 injection amt. signal 4a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling the amount of ammonia injection in a denitration device, and more particularly to injecting ammonia (NH ₃ ) into a dry denitration device that removes nitrogen oxides (NO _x ) in exhaust gas. The present invention relates to a method and a device for controlling the injection amount of ammonia.

[0002]

2. Description of the Related Art In recent years, in Japan, fuel oil is being converted from conventional heavy oil burning to coal burning and LNG (liquefied natural gas) burning in order to correct the dependence on oil due to the tight supply of heavy oil. Yes, especially in commercial boilers, large-capacity thermal power plants exclusively burning coal and LNG are being constructed.

However, since coal fuel has a poorer fuel property than petroleum fuel and gas fuel, NO _x and unburned components contained in the exhaust gas are likely to be generated, and especially flames are divided to reduce NO _x , It is also practiced to recycle exhaust gas, carry out two-stage combustion, denitration in a furnace, etc. to perform slow combustion to reduce NO _x . In the coal-fired combustion power and the LNG-dedicated combustion power, there are few boiler loads that are always operated at full load, and the load is 75% load, 50
The so-called high-frequency start and stop (Daily S / S, etc.)
tart Stop (hereinafter simply referred to as DSS) is being operated and the plant is moving to a thermal power plant that bears an intermediate load.

On the other hand, in addition to this thermal power generation boiler, a so-called combined plant, which is a combination of a gas turbine with good starting characteristics and an exhaust heat recovery boiler, is also used for this intermediate load thermal power, and DSS operation is performed to obtain the power demand. It is about to be constructed in such a way that only the middle of the road, which has a lot of traffic, operates, and the operation stops at night. However, this coal-, LNG mono-fuel combustion of the intermediate load boiler, not accompanied the tighter regulation of the NO _x emission concentrations in a gas turbine, in addition to the conventional combustion improvement, NH
_An increasing number of plants are installing dry catalytic reduction NOx removal equipment that performs NOx removal in the presence of a catalyst using ₃ as a reducing agent.

[0005] In a coal-fired boiler, since the combustibility of the fuel is poor, the amount of NO _x increases, and the LNG-fired boiler,
Since the gas turbine plant has a large amount of oxygen and performs high-temperature combustion, a large amount of NO _x is contained in the exhaust gas as in the case of the coal-only boiler, so a denitration device as shown in FIG. 3 is installed. . FIG. 3 shows a typical flue air duct system of a boiler in which a denitration device is installed.

The combustion air in the air duct 31 is pressurized by the forced draft fan 32 and heated by the exhaust gas in the exhaust gas duct 34 in the air preheater 33, and then the wind box 3 is opened.
5 is supplied to the boiler 36. On the other hand, the exhaust gas burned in the boiler 36 is fed into the exhaust gas duct 34 through the NH ₃ injection pipe 37.
With the denitration by NH ₃ from, promote denitrification in the catalyst 39 in the denitration apparatus 38 disposed downstream, NO _x in the exhaust gas is removed the air preheater 33, a dust collector 4
0, the pressure is increased by the induction fan 41 and released to the atmosphere.

However, in the denitration apparatus 38, although the reaction temperature range is somewhat different depending on the type of the catalyst 39, the temperature range having the highest denitration efficiency is 300 to 400 ° C.
The temperature is relatively high and the temperature range is narrow. Therefore, in a boiler for intermediate load thermal power or a combined cycle that is always operated by DSS, there is a drawback that the exhaust gas temperature constantly fluctuates due to load fluctuations, and the catalyst 39 deviates from the usable range.

In this case, if the temperature of the used gas of the catalyst 39 is too high, the structure of the catalyst 39 is changed and the function as the catalyst 39 is impaired, and if the temperature of the used gas is too low, the anhydrous sulfuric acid present in the exhaust gas is present. After reacting with (SO ₃ ), the catalyst 3
The function of 9 deteriorates. On the other hand, in a thermal power generation boiler and a combined cycle that are always operated by DSS, there is a drawback that the exhaust gas amount and the NO _x concentration fluctuate, which deteriorates the followability of the denitration performance.

When the amount of exhaust gas and the NO _x concentration due to the reaction mechanism of NO _x and NH ₃ on the catalyst 39 fluctuates, such as when the engine is started and when the load is changed, NH ₃ is adjusted according to the load change. This is because the denitration performance cannot follow the load fluctuation even if the injection amount is changed. FIG. 2 shows a typical example of a conventional NH ₃ injection amount control device proposed in order to avoid these problems.

In FIG. 2, the inlet NO _x signal 1a detected by the inlet NO _x concentration detector 1 and the exhaust gas flow rate signal 22 are detected.
Is calculated by the calculator 11 to calculate the total NO _x amount signal 12.
On the other hand, a required molar ratio setting unit 8 calculates a required molar ratio (ratio of NO _x amount and NH ₃ amount) signal 8a from the inlet NO _x signal 1a and the set NO _x signal 6a set by the outlet NO _x setting device 6, It performs correction by the deviation between the outlet concentration of NO _x detector 3 and the measured outlet NO _x signal 3a detected by the set NO _x signal 6a in the adder 7a, described in this corrected required molar ratio signal 8b and above The total NO _x amount signal 12 and the calculator 1
3 to calculate the necessary NH ₃ flow rate signal 14.

This required NH₃Flow rate signal 14 and measured NH₃
Measured NH detected by the flow rate detector 4 ₃Compare the flow rate signal 4a
The deviation signal 15 is calculated by comparing with the comparator 9b,
The proportional integrator 16 converts the valve opening signal 17 into an electro-pneumatic converter.
Converted to control signal 19 by 18, NH₃N of piping 20
H₃The flow control valve 2 is opened and closed.

[0012]

The above-mentioned prior art has the function of keeping the concentration of nitrogen oxides at the outlet of the denitration device at a certain value or less at an instant, but the nitrogen oxidation at an average value for a certain period of time. It did not have the function of suppressing the substance concentration below a certain value. Therefore, when the emission concentration of nitrogen oxides temporarily exceeds the specified value due to load fluctuations or the like, there is a problem that the time average value also exceeds the regulation value.

An object of the present invention is to provide a method and apparatus for controlling the amount of ammonia injection in a denitration device, which has a function of keeping an instantaneous NO _x emission amount below a prescribed value, and also keeping a time average NO _x emission amount below a regulation value. To provide.

[0014]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The invention claimed in this application is as follows. (1) NO of inlet of denitration device_xConcentration and outlet NO_xConcentration and
The required ammonia molar ratio signal
Therefore, this signal and exhaust gas total NO_xAmmo based on quantity and
Obtain the near injection amount setting signal and inject the ammonia with the setting signal.
Ammonia to denitration equipment based on deviation from measured input
In the method of controlling the injection amount, the outlet NO _xPredetermined concentration
Moving average calculation value over time and the exit NO_xConcentration setting
The ammonia injection amount setting signal based on the deviation from the value
Ammonia injection of denitration device characterized by correcting the
Quantity control method. (2) Total NO of exhaust gas to be treated by denitration equipment_xAccording to quantity
Ammonia injection of denitration equipment that controls ammonia injection amount
In the amount control device, the exhaust gas flow rate to be treated and the inlet N
O_xConcentration and outlet NO_xBased on density and density setpoint
Means for calculating the ammonia injection amount signal and the outlet NO_x
Moving to calculate the moving average of concentration over a specified time
Average calculator, calculated value and exit NO_xDeviation from concentration setting
Compensation for calculating the ammonia injection amount correction signal based on the difference value
Positive means, said ammonia injection amount signal and ammonia injection
Calculate the ammonia injection amount set value with the amount correction signal
Means, this ammonia injection amount set value and ammonia injection
Means for controlling the ammonia flow control valve based on the measured quantity
Ammonia injection into denitration equipment characterized by
Quantity control device.

[0015]

According to the present invention, the moving average calculation of the nitrogen oxide concentration at the outlet of the denitration apparatus is performed. As a result, when the time-averaged emission amount exceeds the regulation value, excessive ammonia is injected and nitrogen oxidation is performed. Since the substance concentration is kept low, the time-averaged regulation value will not be exceeded.

[0016]

FIG. 1 shows an embodiment of an ammonia injection amount control circuit according to the present invention. 1, the same symbols as those in FIG. 2 indicate the same components as those in FIG. The combustion exhaust gas from the boiler or the gas turbine is injected with ammonia through an ammonia injection pipe 37 immediately before the denitration device 38, the nitrogen oxide in the exhaust gas is reduced by the denitration device, and the exhaust gas is discharged from the chimney. In such a denitration device, the entrance N of the denitration device
The inlet NO _x signal 1a from the O _x concentration detector 1 and the set NO _x signal 6a set by the outlet NO _x setter 6 of the denitration device
Based on the above, the required molar ratio 8a is calculated by the molar ratio setter 8. If there is a deviation between the measured outlet NO _x signal 3a according to this and the denitrator outlet concentration of NO _x detector 3 to correct the molar ratio by the adder 7a.

The required molar ratio signal 8b thus obtained is
Exhaust gas amount signal 22 and denitration device inlet NO _x concentration detector 1
Total NO calculated by multiplication with the inlet NO _x signal 1a by
By multiplying the _x amount signal 12, the required ammonia injection amount signal 14 is obtained. Furthermore, in the present invention, the moving average calculator 5 calculates the moving average of the measured outlet NO _x signal 3a by the NOx concentration outlet NO _x concentration detector 3. The moving average value 5a of the measured outlet NO _x obtained by this and the set NO _x set by the outlet NO _x setting device 6
The subtractor 9c calculates the difference between the signals 6a.

[0018] Consequently, the moving average value 5a of the NO _x is to inject an excess of ammonia if it exceeds the setting NO _x signal 6a, necessary ammonia the output value 23a of the function generator 23 based on the excess amount It is added to the value of the injection amount signal 14. The added final required ammonia injection amount signal 14a is given as a set value of a circuit constituted by the ammonia flow rate 4 and the ammonia flow rate control valve 2.

[0019]

The prior art has only the function of suppressing the instantaneous value of the NO _x amount at the outlet of the denitration device to be below a certain specified value. Therefore, if the outlet NO _x amount temporarily exceeds the specified value due to load changes, etc., the time-averaged emission amount becomes
As a result, it was supposed to exceed the regulation value,
According to the present invention, even if the amount of NO _x temporarily exceeds the specified value, the catalyst is impregnated by injecting ammonia excessively thereafter to suppress the NO _x emission amount below the specified value. You can As a result, the time average value satisfies the regulation value.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an ammonia injection amount control circuit of a conventional denitration device.

FIG. 3 is a smoke flue system diagram of a boiler in which a denitration device is installed.

[Explanation of symbols]

 1 ... Entrance NO_xConcentration detector, 2 ... Ammonia flow rate adjustment
Valve, 3 ... Exit NO_xConcentration detector, 4 ... NH₃Flow rate detection
Unit, 5 ... Moving average calculator, 6 ... Exit NO_xSetting device, 7 ...
Adder, 8 ... Required molar ratio setter, 9 ... Subtractor, 11 ...
Calculator, 12 ... Total NO _xQuantity signal, 13 ... Multiplier, 14 ... Required
NH required₃Flow rate signal, 14a ... NH₃Flow rate setting signal, 15
… NH₃Flow rate deviation signal, 19 ... Control signal, 20 ... NH₃
Piping, 22 ... Exhaust gas flow rate signal, 23 ... Function generator, 37
… NH₃Injection pipe, 38 ... Denitration device.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01D 53/86 ZAB 53/94 B01D 53/36 ZAB 101 Z

Claims (2)

[Claims] 1. A inlet concentration of NO _x denitration unit and the outlet NO _x
The required ammonia molar ratio signal is obtained from the concentration and the same concentration set value, the ammonia injection amount setting signal is obtained based on this signal and the total NO _x amount of the exhaust gas, and the deviation between the setting signal and the ammonia injection amount measured value is calculated. In the method of controlling the amount of ammonia injection into the denitration device based on the above, a moving average calculated value of the outlet NO _x concentration over a predetermined time and the outlet NO _x
A method for controlling an ammonia injection amount of a denitration device, characterized in that the ammonia injection amount setting signal is corrected based on a deviation from a concentration set value. 2. Total NO _{x of} exhaust gas to be treated by a denitration device
In the ammonia injection amount control device of the denitration device that controls the ammonia injection amount according to the amount, the ammonia injection amount signal is calculated based on the exhaust gas flow rate to be processed, the inlet NO _x concentration, the outlet NO _x concentration, and the concentration set value. means a correction calculating a moving average calculator for calculating a moving average operation value over a predetermined time of the outlet concentration of NO _x, the ammonia injection amount correction signal based on the deviation between the calculated value and the outlet concentration of NO _x set value Means, means for calculating an ammonia injection amount set value by the ammonia injection amount signal and the ammonia injection amount correction signal, and means for controlling the ammonia flow rate control valve by the ammonia injection amount set value and the ammonia injection amount measured value. A device for controlling the amount of ammonia injected into a denitration device, characterized by being provided with.