JP3544716B2 - Method and apparatus for controlling ammonia injection amount in denitration apparatus - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method and an apparatus for controlling the injection amount of ammonia in a denitration apparatus, and more particularly to a method and apparatus for controlling the injection amount of ammonia to inject ammonia (NH ₃ ) into a dry denitration apparatus for removing nitrogen oxides (NO _x ) in exhaust gas. And devices.
[0002]
[Prior art]
In recent years, Japan has been converting fuel from conventional heavy oil burning to coal burning and LNG (liquefied natural gas) burning in order to correct the dependence on petroleum due to the tight supply of heavy oil. In the boiler, large-capacity thermal power plants have been constructed that are exclusively used for coal and LNG.
[0003]
However, coal petroleum fuels, NO _x and unburned prone included because poor fuel resistance in the exhaust gas as compared with the gas fuel, in particular split flames for measures to reduce the NO _x, re exhaust gas circulation is also performed to employ such two-stage combustion and furnace denitration to perform a slow combustion to reduce the NO _x to.
Of the coal-fired power and LNG-fired power, there are few boiler loads that are always operated at full load. The boiler load is increased to 75% load, 50% load, and 25% load, and the boiler load is reduced. There is a shift to a thermal power plant that carries an intermediate load by performing a so-called high-frequency start-stop (hereinafter simply referred to as DSS) operation such as stopping the operation.
[0004]
On the other hand, for this intermediate-load thermal power plant, in addition to this thermal power generation boiler, a so-called combined plant combining a gas turbine with good startup characteristics and an exhaust heat recovery boiler is also used. Only driving and shutting down at night are being built.
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, the denitration in the presence of a catalyst and NH ₃ as a reducing agent The number of plants equipped with dry catalytic reduction denitration equipment for performing the process is increasing.
[0005]
It increases _the amount of NO _x since poor combustion of the fuel in coal-boiler, LNG-fired boiler, in order to perform the amount of oxygen are many high-temperature combustion in a gas turbine plant, like the coal-boiler, the flue gas since contains a large amount of NO _x, NO x removal apparatus is installed as shown in FIG.
FIG. 3 shows a typical flue duct system of a boiler provided with a denitration device.
[0006]
The air for combustion in the air duct 31 is pressurized by a forced draft fan 32, heated by exhaust gas from an exhaust gas duct 34 by an air preheater 33, and then supplied from a wind box 35 to a boiler 36.
On the other hand, the exhaust gas burned in the boiler 36 is denitrified by the NH ₃ from the NH ₃ injection pipe 37 in the exhaust gas duct 34, and promotes the denitration in the catalyst 39 in the denitration device 38 arranged downstream, so that the NO in the exhaust gas is reduced. _{The x} is removed, and the pressure is increased by the air preheater 33, the dust collector 40, and the induction ventilator 41 and released to the atmosphere.
[0007]
However, in such a denitration device 38, the reaction temperature range slightly varies depending on the type of the catalyst 39, but the temperature range in which the denitration efficiency is highest is a relatively high temperature of 300 to 400 ° C, and the temperature range is extremely narrow. Therefore, in the case of a boiler or a combined cycle for an intermediate-load thermal power plant that is always operated in the DSS, there is a drawback that the exhaust gas temperature always fluctuates due to the load fluctuation and deviates from the usable area of the catalyst 39.
[0008]
In this case, if the working gas temperature of the catalyst 39 is too high, the structure of the catalyst 39 changes and the function as the catalyst 39 is impaired. If the working gas temperature is too low, the sulfuric anhydride (SO ₃₎ present in the exhaust gas is present. ), The function of the catalyst 39 also deteriorates.
On the other hand, always thermal power boiler being DSS operation, the combined cycle, exhaust gas volume and concentration of NO _x is varied, whereby there is a disadvantage that followability of the NOx removal performance is deteriorated.
[0009]
It startup exhaust gas amount and concentration of NO _x due to the reaction mechanism of the NO _x and NH ₃ in the above catalyst 39, in the case of variation such as during load changes, the NH ₃ injection rate according to the load variation This is because the denitration performance cannot follow the load fluctuation even if it is changed.
FIG. 2 shows a typical example of a conventional NH ₃ injection amount control device proposed to avoid these problems.
[0010]
2, calculates the inlet NO _x signal 1a detected by the inlet concentration of NO _x detector 1 calculates the exhaust gas flow rate signal 22 in arithmetic unit 11 of the total amount of NO _x signal 12. Meanwhile calculates the inlet NO _x signal 1a and the outlet NO _x setter 6 set by the setting NO _x signal 6a required molar ratio than a necessary molar ratio setter 8 (NO _x amount and the amount of NH ₃ ratio) signals 8a, 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 calculated total NO _x amount signal 12 is calculated by the calculator 13 to calculate the required NH ₃ flow rate signal 14.
[0011]
The required NH ₃ flow rate signal 14 and the measured NH ₃ flow rate signal 4 a detected by the measured NH ₃ flow rate detector 4 are compared by a comparator 9 b to calculate a deviation signal 15, which is opened by a proportional integrator 16. The control signal 19 is converted into a control signal 19 by the electropneumatic converter 18, and the NH ₃ flow control valve 2 in the NH ₃ pipe 20 is opened and closed.
[0012]
[Problems to be solved by the invention]
The above prior art has a function to keep the concentration of nitrogen oxides at the outlet of the denitration apparatus at a moment or less at a specified value or less, but suppresses the nitrogen oxide concentration at an average value for a certain period of time to a certain value or less. Had no function. Therefore, when the nitrogen oxide emission concentration temporarily exceeds the specified value due to a load change or the like, there is a problem that the time average value also exceeds the regulated value as it is.
[0013]
An object of the present invention, while maintaining the instantaneous of the NO _x emissions below a specified value, yet provides ammonia injection amount control method and apparatus for denitration device having a function to keep below the regulated value NO _x emissions of the time average It is in.
[0014]
[Means for Solving the Problems]
The invention claimed in this application to achieve the above object is as follows.
(1) determine the required ammonia molar ratio signal by an inlet concentration of NO _x and outlet concentration of NO _x and the concentration setting of the denitration apparatus, obtains the ammonia injection amount setting signal based on the total amount of NO _x of the signal and the exhaust gas a method for controlling ammonia injection amount to the denitrification device based on a deviation between the set signal and the ammonia injection quantity measurement value, moving average calculation value over a predetermined time of the outlet concentration of NO _x and said outlet concentration of NO _x set value Wherein the ammonia injection amount setting signal is corrected based on the deviation of the ammonia injection amount setting signal.
(2) in the ammonia injection rate control unit of the denitration device for controlling ammonia injection amount according to the total amount of NO _x of the exhaust gas to be treated by the denitration apparatus, the exhaust gas flow rate and inlet concentration of NO _x to be processed and an outlet concentration of NO _x and means for calculating the ammonia injection amount signal based on the density setting value, a moving average calculator for calculating a moving average operation value over a predetermined time of the outlet concentration of NO _x, and the calculated value and the outlet concentration of NO _x set value Correction means for calculating an ammonia injection amount correction signal based on the deviation value; means for calculating an ammonia injection amount set value based on the ammonia injection amount signal and the ammonia injection amount correction signal; Means for controlling an ammonia flow control valve based on an amount measurement value, and an ammonia injection amount control apparatus for a denitration apparatus.
[0015]
[Action]
According to the present invention, a moving average calculation of the nitrogen oxide concentration at the outlet of the denitration apparatus is performed, and as a result, when the time-average emission exceeds the regulation value, excessive ammonia is injected to reduce the nitrogen oxide concentration. Since it will be kept low, it will not exceed the hourly average regulation value.
[0016]
【Example】
FIG. 1 shows an embodiment of an ammonia injection amount control circuit according to the present invention. 1, the same reference numerals as those in FIG. 2 indicate the same components as those in FIG. The combustion exhaust gas from the boiler or gas turbine is injected with ammonia by an ammonia injection pipe 37 immediately before the denitration device 38, and the nitrogen oxides in the exhaust gas are reduced by the denitration device and discharged from the chimney. Such, in denitration device, denitrification device inlet concentration of NO _x detector 1 according to the inlet NO _x signal 1a and the denitration apparatus outlet NO _x setter on the basis of the setting NO _x signal 6a which is set in 6 molar ratio setter 8 , The required molar ratio 8a is calculated. 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.
[0017]
The required molar ratio signal 8b thus obtained, an exhaust gas amount signal 22, by multiplying the total amount of NO _x signal 12 is calculated by multiplying the inlet NO _x signal 1a by denitrator inlet concentration of NO _x detector 1, The required ammonia injection amount signal 14 is obtained.
Further, in the present invention, the moving average computing unit 5 performs the calculation of the moving average of the measured outlet NO _x signal 3a according denitrator outlet concentration of NO _x detector 3. This difference in the obtained measured outlet NO _x moving average 5a and outlet NO _x setter 6 set by the setting NO _x signal 6a of the calculated by the subtracter 9c.
[0018]
As a result, the moving average value 5a of the NO _x is set NO _x if it exceeds a signal 6a to inject an excess of ammonia, required ammonia injection amount signal output value 23a of the function generator 23 based on the excess amount above Add to the value of 14. The added final required ammonia injection amount signal 14a is given as a set value of a circuit composed of the ammonia flow rate 4 and the ammonia flow rate control valve 2.
[0019]
【The invention's effect】
In the prior art, only it had no function to suppress below a specified value in the instantaneous value of the denitrator outlet amount of NO _x. Therefore, the load variation or the like, when the amount of the outlet NO _x exceeds the temporary specified value, the discharge amount of the time average value, was supposed to become excess as a result, the regulated value, the present invention According to temporarily amount of NO _x is even exceeded the prescribed value, then the ammonia which is impregnated into the catalyst by excessively injected and NO _x emissions amount can be lowered than the specified value . As a result, the time average value satisfies the regulation value.
[Brief description of the drawings]
FIG. 1 is a diagram showing an ammonia injection amount control circuit of a denitration apparatus according to the present invention.
FIG. 2 is a diagram showing an ammonia injection amount control circuit of a conventional denitration apparatus.
FIG. 3 is a flue system diagram of a boiler provided with a denitration device.
[Explanation of symbols]
1 ... inlet concentration of NO _x detector, 2 ... ammonia flow control valve, 3 ... outlet concentration of NO _x detector, 4 ... NH ₃ flow rate detector, 5 ... moving average calculator, 6 ... outlet NO _x setter, 7 ... adder, 8 ... required molar ratio setter 9 ... subtractor, 11 ... multiplier, 12 ... total amount of NO _x signal, 13 ... multiplier, 14 ... need NH ₃ flow rate signal, 14a ... NH ₃ flow rate setting signal, 15: NH ₃ flow deviation signal, 19: control signal, 20: NH ₃ pipe, 22: exhaust gas flow signal, 23: function generator, 37: NH ₃ injection pipe, 38: denitration device.

Claims (2)

Seeking necessary ammonia molar ratio signal by an inlet concentration of NO _x and outlet concentration of NO _x and the concentration setting of the denitration apparatus, obtains the ammonia injection amount setting signal based on the total amount of NO _x of the signal and the exhaust gas, the setting a method for controlling ammonia injection amount to the denitrification device based on a deviation between the signal and the ammonia injection quantity measurement, the deviation between the outlet concentration of NO _x set value and the moving average operation value over a predetermined time of the outlet concentration of NO _x And correcting the ammonia injection amount setting signal on the basis of the ammonia injection amount setting signal. In the ammonia injection rate control unit of the denitration device for controlling ammonia injection amount according to the total amount of NO _x of the exhaust gas to be treated by the denitration apparatus, the exhaust gas flow to be treated and an inlet concentration of NO _x and outlet concentration of NO _x and concentration setting means for calculating the ammonia injection amount signal based on the bets, and the moving average calculator for calculating a moving average operation value over a predetermined time of the outlet concentration of NO _x, the deviation between the calculated value and the outlet concentration of NO _x set value Correction means for calculating an ammonia injection amount correction signal based on the ammonia injection amount signal and the ammonia injection amount correction signal; and means for calculating an ammonia injection amount set value based on the ammonia injection amount signal and the ammonia injection amount correction signal. And means for controlling the ammonia flow control valve by means of the above.

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